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Construction and Commissioning of a Continuous Reactor for Hydrothermal Liquefaction
Abstract
The purpose of this paper is to give a comprehensive description of the construction and commissioning of a continuous reactor system for hydrothermal liquefaction of biomass. The basis is a newly established facility at Aarhus University. It is capable of handling viscous biomass slurries and features a novel induction-based heating method that facilitates well defined reaction-environments. Carbon balance closure is obtained as all product fractions are recovered and positively quantified. The paper includes a residence time distribution measurement and a 24 hour proof-of-concept experiment conducted at 350 °C, 250 bar, and 15 minutes reaction time. It is based on the biomass dried distillers grains with solubles (DDGS), a waste product of the bio-ethanol industry. The experiment seeks to determine the steady state characteristics of the continuous reactor system for use in future experimental studies. It was found that steady state occurs within 6 hours. Furthermore, data sampling windows of 2.1 hours were found to mask the intrinsic variations of the system while still exposing trends. At steady state the oil mass yield was found to be 38.9 +- 3.2 % and the higher heating value was 35.3 +- 0.28 MJ kg-1.
... After the rinse, the temperature is decreased to 125 C and the pressure in the BPR is released rapidly, leading to formation of turbulence to loosen sediments in dead zones. A similar cleaning method was used by Mørup et al. [34]. The stainless-steel filter elements are cleaned by combustion in a muffle furnace at 545 C for 6 h to remove organics, and soaking in 2.7 L of 1 M nitric acid overnight to remove ash. ...
... The residence time distribution (RTD) in the CFR system was estimated using a method modified from [34]. A steady flow of water through the CFR was established at the desired temperature (25 C and 350 C), pressure, and flow rate conditions. ...
... In this study, a very small discrepancy (0.54 %) in the RTD was observed at room temperature; the higher discrepancy at 350 C (22.2 %) was attributed to the trailing effect observed in other studies. Kruse et al. [28] operated a lab-scale CFR with a lower discrepancy than that of Mørup et al. [34]. Here, the Peclet numbers under room temperature and 350 C conditions, 18.4 and 13.8, respectively, were lower than that presented in Mørup et al. (28.0), indicating a relatively steady flow throughout this CFR system [34]. ...
A pilot-scale continuous flow reactor (CFR) was modified for hydrothermal liquefaction (HTL) of algae slurry under subcritical conditions to investigate the feasibility of scaling up from batch to continuous processing. Modifications included a novel dual filter system that can remove solids at system pressure and temperature, and undergo in-situ cleaning. Commissioning was carried out to address potential particle settling and clogging problems, and to estimate reactor transport characteristics. CFR performance was evaluated by running 31.4 L algae slurry with solids loadings of 3−5 wt.% under 325−350 °C and 18 MPa for 7 h. C and N elemental yields in HTL aqueous phase reached 39.0 wt.% and 61.8 wt.%, respectively. Future improvements to the CFR system will focus on higher solids loading and addition of in-line HTL liquid upgrading capabilities following the filtration system. • A high-temperature, high-pressure filtration system was designed to remove solids from HTL liquid/gaseous products at near reaction conditions to keep heavy oils in the liquid phase. • Uninterrupted reactor operation was achieved by cycling between the dual filter systems and performing in-situ filter cleaning. • Measured reactor residence time distributions were narrow and close to the calculated theoretical mean time. Method name: Pilot-Scale Continuous Flow Hydrothermal Liquefaction of Biomass, Keywords: Hydrothermal liquefaction, Continuous flow reactor, High-pressure filtration, Microalgae
... Bio-oil from DDGS feedstock was produced in a continuous flow reactor as described elsewhere along with the general experimental procedure [22]. Biomass slurry was prepared from 20 % DDGS (approximately 250-μm grain size), 2 % potassium carbonate, and 78 % solvent. ...
... Thereafter, the product was collected in 42.5-min intervals, which define the data windows. This sampling interval was chosen to coincide with the injector shift intervals that were required to pump biomass slurry in the flow reactor [22]. ...
... A baseline experiment, where demineralized water was used as the solvent. The experiment was used as a commissioning experiment and has been described elsewhere [22]. Thirty-three samples were collected, of which samples HTL 2, HTL 4, HTL 6, HTL 8, and HTL 10 were analyzed. ...
Hydrothermal liquefaction is a promising technique for the production of bio-oil. The process produces an oil phase, a gas phase, a solid residue, and an aqueous phase. Gas chromatography coupled with mass spectrometry is used to analyze the complex aqueous phase. Especially small organic acids and nitrogen-containing compounds are of interest. The efficient derivatization reagent methyl chloroformate was used to make analysis of the complex aqueous phase from hydrothermal liquefaction of dried distillers grains with solubles possible. A circumscribed central composite design was used to optimize the responses of both derivatized and nonderivatized analytes, which included small organic acids, pyrazines, phenol, and cyclic ketones. Response surface methodology was used to visualize significant factors and identify optimized derivatization conditions (volumes of methyl chloroformate, NaOH solution, methanol, and pyridine). Twenty-nine analytes of small organic acids, pyrazines, phenol, and cyclic ketones were quantified. An additional three analytes were pseudoquantified with use of standards with similar mass spectra. Calibration curves with high correlation coefficients were obtained, in most cases R
2
> 0.991. Method validation was evaluated with repeatability, and spike recoveries of all 29 analytes were obtained. The 32 analytes were quantified in samples from the commissioning of a continuous flow reactor and in samples from recirculation experiments involving the aqueous phase. The results indicated when the steady-state condition of the flow reactor was obtained and the effects of recirculation. The validated method will be especially useful for investigations of the effect of small organic acids on the hydrothermal liquefaction process.
Graphical Abstract
Schematic illustration of hydrothermal liquefaction of biomass
... Continuous flow systems are considered ideal for pilot and demonstration scale operations [130][131][132][133][134]. Due to the rapid occurrence of hydrothermal reactions under elevated temperatures and pressures, tubular reactors are more suitable for continuous flow systems. ...
... Figure 5 shows a schematic diagram of a typical continuous reactor used for hydrothermal gasification. Despite the promising results obtained using a continuous flow system, researchers have also reported the major concern of reactor plugging due to char or tar formation and non-uniform mixing of biomass and catalyst with water [130]. Char formation may occur due to incomplete gasification and temperature variations during hydrothermal gasification [135]. ...
The current global greenhouse gas emissions have increased by over 90% since 1860 primarily due to our overreliance on fossil fuels, petrochemicals and their derivatives. Production of petrochemical plastics is also reaching 400 million metric tons in 2023. The lack of effective thermochemical processes for converting wet feedstocks and complex residues such as plastics is calling for hydrothermal gasification as an efficient approach to producing syngas. The demand for hydrogen production through greener approaches is also rising to compete with the commercial steam reforming of natural gas. Here, we review the conversion of biomass and plastics by hydrothermal gasification into hydrogen-rich syngas with a focus on the process parameters influencing the conversion of a variety of feedstock types. Parameters influencing hydrothermal gasification of biomass and plastics include temperature, pressure, reaction time, feedstock concentration, catalysts and reactor types. Several synergetic effects also influence product distribution during the co-processing of biomass and plastics during hydrothermal gasification. Processes that impact biomass conversion to syngas are hydrolysis, water–gas shift, methanation, hydrogenation, steam reforming and polymerization.
... Tubular reactors, owing to their scalability and simplicity, as well as other innovative designs such as continuous stirred tank reactors (CSTRs), offer promising solutions for these issues. The motion of impellers for reactor agitation in CSTRs ensures proper mixing, while the hydrodynamic flow patterns-whether turbulent or laminar, influence the outcome [45,[103][104][105][106][107]. ...
... Predictive models have also been developed to assess yield, thus helping identify optimal feedstock combinations and providing insights into the complex interactions involved in hydrothermal co-liquefaction. As the field of biotechnology continues to advance, HTL holds great promise in shaping a sustainable and efficient future for bioenergy production, waste management, and resource utilization [10,23,31,35,41,[44][45][46]71,94,100,[102][103][104][105]107,108,112,121,123,[127][128][129][130][132][133][134]138,[150][151][152][153][154]156,159,[162][163][164][165][166][167][168]. ...
Hydrothermal liquefaction (HTL) represents a beacon of scientific innovation, which unlocks nature's alchemical wonders while reshaping the waste-to-energy platform. This transformative technology offers sustainable solutions for converting a variety of waste materials to valuable energy products and chemicals-thus addressing environmental concerns, inefficiencies, and high costs associated with conventional waste-management practices. By operating under high temperature and pressure conditions, HTL efficiently reduces waste volume, mitigates harmful pollutant release, and extracts valuable energy from organic waste materials. This comprehensive review delves into the intricacies of the HTL process and explores its applications. Key process parameters, diverse feedstocks, various reactor designs, and recent advancements in HTL technology are thoroughly discussed. Diverse applications of HTL products are examined, and their economic viability toward integration in the market is assessed. Knowledge gaps and opportunities for further exploration are accordingly identified, with a focus on optimizing and scaling up the HTL process for commercial applications. In conclusion, HTL holds great promise as a sustainable technology for waste management , chemical synthesis, and energy production, thus making a significant contribution to a more sustainable future. Its potential to foster a circular economy and its versatility in producing valuable products underscore its transformative role in shaping a more sustainable world.
... The CRS was controlled by a central computer running a customized LabVIEW platform that offered additional safety measures and graphical user interface. More details of commissioning and maintenance of the CRS are provided in (Mørup et al., 2015). ...
... 16 Components of the bench-scale CRS at Aarhus University including (A) dual injector system, (B) induction heating coil and biomass tube encased in a polycarbonate box (the red laser dot marks the focal point of the pyrometer), (C) let-down system with coolers, filter, and back-pressure regulator, and (D) separator vessel and valve. Reproduced with permission from Mørup, A.J., Becker, J., Christensen, P.S., Houlberg, K., Lappa, E.,Klemmer, M., et al., 2015. Construction and commissioning of a continuous reactor for hydrothermal liquefaction. ...
Hydrothermal liquefaction (HTL) is a promising thermochemical conversion technique for producing third-generation biofuels from feedstocks like wet algal biomass and sewage sludge. Commercialization of HTL requires a transition from lab-scale batch research systems to large-scale continuous flow reactor systems and then integration of HTL into complete biorefinery systems. To date, scale-up of continuous flow reactors has been limited by high equipment costs, high operational energy consumption, and technical challenges due to complex feedstocks and products. This chapter presents the state of HTL scale-up, with case studies on the design and commissioning of pilot-scale continuous flow reactor systems around the world. Recommendations are given for overcoming barriers in terms of process modification, energy integration, and economical feasibility. To improve the economic competitiveness of the biomass-to-fuel industry, essential criteria for manufacturing next-generation reactor systems are equipment and operation costs, energy efficiency, value-added uses for co-products, and adaptability toward upstream algal cultivation and downstream biofuel refining.
... However, building a lab-scale continuous-flow system is challenging due to the complexity of system, safety concerns, and scaling down limitations, such as acquiring a lab-scale high-pressure pump. 346 Therefore, most of the studies on continuous-flow HTL systems have been conducted with reactors between lab-and pilot-scale. In their study, Wagner et al. 344 described the design of an inexpensive labscale continuous-flow HTL system by using high-pressure N 2 for feeding. ...
... In their study, Wagner et al. 344 described the design of an inexpensive labscale continuous-flow HTL system by using high-pressure N 2 for feeding. Mørup et al. 346 also published a very detailed study that describes the design and construction of a continuous-flow HTL reactor used in Aarhus University. This study includes the mechanical properties of selected units and acquisition of reactor with LabVIEW software. ...
An increase in environmental awareness has resulted in a significant shift in research towards more renewable and sustainable energy sources and better waste valorization technologies. Within this vast field, biomass conversion technologies and biofuels have attracted much attention due to their adaptability potential to pre-existing infrastructure. Hydrothermal liquefaction is one of the most efficient biomass processing methods and has become a promising technology for future applications. Although many studies have been performed on this process, there is still much to discover about the technology; notably, there are critical gaps in substrate-specific reaction optimization, reactor design, and the effect of catalysts. In order to facilitate future studies reporting on these research gaps, this review summarizes the science and engineering applications of hydrothermal liquefaction of biomass. The effects of reaction temperature, retention time, biomass solid content, biomass type, solvent, and catalyst type on bio-crude yield and quality are discussed. In addition, reaction pathways, reactor types, and process economy are reviewed. In particular, due to their value for future full-scale applications, the emphasis is given to continuous-flow reactor systems. The secondary goal of this review is to serve as a reference point for the new researchers in the field.
... The gas yield of 20.27 wt.% (percentage of kg-gas/kgdry digestate) was also estimated. This gas product is typically composed of CO2 gas [77,78]. The low concentrations of soluble solids in the post-HTL water and the typically high concentration of CO2 in the gas product imply that the post-HTL water and the gas product may not present immediate secondary application opportunities. ...
... The gas yield of 20.27 wt.% (percentage of kg-gas/kg-dry digestate) was also estimated. This gas product is typically composed of CO 2 gas [77,78]. The low concentrations of soluble solids in the post-HTL water and the typically high concentration of CO 2 in the gas product imply that the post-HTL water and the gas product may not present immediate secondary application opportunities. ...
In line with global efforts at encouraging paradigm transitions from waste disposal to resource recovery, the anaerobic co-digestion of substrates of wet hydrolyzed meat processing dissolved air flotation sludge and meat processing stock yard waste was investigated in the present study. It was demonstrated that the co-digestion of these substrates leads to the introduction of co-digestion synergizing effects. This study assessed biomethane potentials of the co-digestion of different substrate mixtures, with the preferred substrate mixture composed of stockyard waste and wet hydrolyzed meat processing dissolved air flotation sludge, present in a 4:1 ratio on a volatile solid mass basis. This co-digestion substrate mix ratio presented an experimentally determined cumulative biomethane potential of 264.13 mL/gVSadded (volatile solid). The experimentally determined cumulative biomethane potential was greater than the predicted maximum cumulative biomethane potential of 148.4 mL/gVSadded, anticipated from a similar substrate mixture if synergizing effects were non-existent. The viability of integrating a downstream hydrothermal liquefaction processing of the digestate residue from the co-digestion process, for enhanced resource recovery, was also initially assessed. Assessments were undertaken via the theoretical based estimation of the yields of useful products of biocrude and biochar obtainable from the hydrothermal liquefaction processing of the digestate residue. The environmental sustainability of the proposed integrated system of anaerobic digestion and hydrothermal liquefaction technologies was also initially assessed. The opportunity for secondary resource recovery from the digestate, via the employment of the hydrothermal liquefaction process and the dependence of the environmental sustainability of the integrated system on the moisture content of the digestate, were established. It is anticipated that the results of this study will constitute an invaluable basis for the future large-scale implementation of the proposed integrated system for enhanced value extraction from organic waste streams.
... Despite stable performance at high pressures and temperatures, successful operation requires uniform feedstock size and careful attention to the feedstock-to-solvent ratio. Progressive cavity, piston, and plunger pumps have also been employed to feed biomass slurries into high pressure reactors (Elliott et al., 2015;1989;Zöhrer et al., 2014;Mørup et al., 2015;Zhang et al., 2015). Generally, these pumps have limited scalability and can be very expensive. ...
Sugars are precursors to the majority of the world’s biofuels. Most of these come from sugar and starch crops, such as sugarcane and corn grain. Lignocellulosic sugars, although more challenging to extract from biomass, represent a large, untapped, opportunity. In response to the increasing attention to renewable energy, fuels, and chemicals, we review and compare two strategies for extracting sugars from lignocellulosic biomass: biochemical and thermochemical processing. Biochemical processing based on enzymatic hydrolysis has high sugar yield but is relatively slow. Thermochemical processing, which includes fast pyrolysis and solvent liquefaction, offers increased throughput and operability at the expense of low sugar yields.
... Continuous-flow HTL system research can be pursued using both labscale continuous-flow reactors and fast-heating batch reactors. However, establishing a lab-scale continuous-flow system presents various challenges stemming from its complexity, safety considerations, and the limitations of scaling it down, including the acquisition of a lab-scale high-pressure pump [200]. As a result, the majority of continuousflow HTL system studies are carried out using reactors that fall between the lab and pilot scale, offering a practical compromise. ...
It is crucial to find sustainable and renewable fuel sources because traditional fossil fuels are running out and pollution levels are rising. In this context, biocrude derived from biomass emerges as a promising alternative, with hydrothermal liquefaction (HTL) playing a pivotal role in this transformation. HTL's versatility in converting a wide range of biomass or waste materials into biocrude is especially notable. Therefore, this comprehensive review focused on the latest advancements in HTL technology, including its potential to process various biomass and waste materials, resulting in high biocrude yields (up to 60-86% from different biomass types). The study explored the latest advancements in HTL such as effects of catalysts in HTL processes, the scalability of the technology, and the potential for commercializing continuous HTL with aqueous phase recycling. It also explored the integration of machine learning for HTL optimization, offering insights into how these advanced computational techniques can enhance process efficiency and output quality. HTL and subsequent hydrotreatment emerge as key technologies for utilizing biomass as a renewable fuel source. This review not only highlights the current state of biocrude refining and upgrading technologies but also stresses the need for ongoing development in these domains. It presented HTL as a transformative solution in the energy sector, offering a sustainable fossil fuel alternative while tackling biocrude impurities and heteroatoms management challenges. The review concluded by underscoring the practical implications of HTL advancements, suggesting a roadmap for future research and development in this field.
... HTL of biosolids, therefore, could be a promising technology to convert biosolids into renewable crude oil by precluding the drying pre-treatment step, which exceeds the energy requirement for the HTL of biosolids with a 30% w/w water content [10][11][12]. HTL is a thermo-chemical process that converts biosolids under moderate temperatures, from 250 to 350 • C, and high pressure, from 50 to 200 bar, into renewable crude oil [13][14][15][16]. The products from the HTL process include renewable crude oil, an aqueous phase, solid residue, and a gaseous product [17]. ...
... 13 However, challenges such as plugging and charring within the system, pressure control and safety, and complex component design have hindered pilot-and full-scale development. 14,15 Products derived from pilot-scale HTL of wet biomass have numerous potentials, including transportation fuels, biobased chemicals, biogas production, and biobinders for applications such as asphalt. 16,17 For example, polyurethane, 18 resin, 19 and adhesive 20 from HTL biocrude have been formulated. ...
... Even though the viscosity is an important process parameter, the rheological study of these biomass slurries is nascent [11,12] and enhancing our knowledge of high solids slurry rheology would improve biochemical [13,14] and thermochemical [8,15,16] conversion processes. Currently, industry often uses capillary rheology (extrusion) tests for viscous shear thinning mixtures because capillary rheology characterizes important physical phenomena, such as liquid phase migration (LPM), which occurs when a suspending fluid flows between stationary particles in a solid/liquid mixture [17][18][19]. ...
Sustainable fuels for industries that cannot be easily electrified, like aviation and marine, will be crucial to achieving a carbon neutral economy. Processing wet solids through a process like hydrothermal liquifaction to produce upgradeable bio-oil is one pathway that could transform high moisture waste into a fuel. This work pioneers two green processing pathways to produce a biomass feedstock for liquefaction that is far less viscous at higher solids loadings than traditional slurries. This decrease in viscosity could significantly improve the profitability of producing fuels through slurry-based conversion processes. Natural biological degradation of corn stover before grinding has been shown to lower slurry viscosity by a factor of three and torrefaction has been shown to produce slurries that are 150x less viscous than the original material. Additionally, new insight has been gained into the critical physical and chemical parameters that impact slurry viscosity. Common parameters in slurry processing, like the average particle size, shear rate, and solids loadings clearly control viscosity, and these results are confirmed for biomass. Additionally, new physical parameters like aspect ratio and sphericity, as well as chemical parameters like extractives content, non-structural sugars, and zeta potential have been shown to impact and be good predictors of slurry viscosity and processability.
... Other RTD curves from literature that employ similar operation conditions use a significantly different reactor setup, where no mixing happens or the fluid is already fully mixed before any heating takes place. Also, the biomass stream considered are relatively diluted algae suspensions (Mørup et al., 2015;Cheng et al., 2019). This work considers lignin solutions, which may not behave in the same manner. ...
A thermophysical model is developed that can predict the properties of two lignin mixtures, black liquor and lignosulfonates, up to 50% mass fractions, at hydrothermal conditions. An uncertainty quantification framework linked with classic thermodynamical modelling was included to account for the extreme variability of the raw material. An idealised flow simulation verified the model, where hot compressed water mixes with a cold, aqueous lignin stream in a T-piece reactor configuration. The uncertainty quantification procedure determined that density and heat capacity uncertainty significantly influence residence time, and viscosity uncertainty mainly affects mixing. Micromixing time is five-fold and ten-fold higher for black liquor and lignosulfonates mixtures, respectively, compared to pure water mixing. The uncertainty in all simulated quantities of interest caused by the thermophysical model is reduced by increasing flow rates. This study predicted chemical reactor behaviour under varying thermophysical conditions and their final effect in terms of confidence intervals.
... L'évolution des groupes fonctionnels par infrarouge [67], l'évolution de sa cristallinité, ou le taux de lignine extractible peuvent également être des indicateurs du taux de conversion. [60], [85]- [87], [92], [94], [95], bien que la présence de valves en amont puisse générer des blocages en présence d'impuretés [60]. Des prospections sont nécessaires dans le cadre du déploiement de la technologie à l'échelle industrielle [96]. ...
L’urgence climatique impose aujourd’hui de développer de nouveaux vecteurs énergétiques, à partir de ressources renouvelables et neutre en carbone. Les résidus agroalimentaires constituent une source de biomasse stable dans le temps. Cependant, en raison de leur humidité importante, ils sont souvent valorisés en produit à faible valeur ajoutée. On s’est ici intéressé à la production d’un carburant, à partir de résidus agroalimentaires par le procédé de liquéfaction hydrothermale. Cette technologie permet la conversion de la biomasse sous l’effet de la température [250 °C – 350 °C] dans une eau pressurisée et gardée liquide. Bien que le procédé soit connu, son développement est freiné par manque d’applications commerciales en raison de la compétitivité des ressources pétrolières, des difficultés technologiques et scientifiques. Peu de pilotes continus existent et les principaux résultats proviennent d’études principalement réalisées en batch. Ce travail étudie le potentiel du passage à l’échelle du procédé de liquéfaction hydrothermale pour la valorisation énergétique de résidus agroalimentaires. Les essais ont été réalisés sur des drêches de cassis (DC) et des drêches de brasserie (DB). Une première étude réalisée sur un pilote batch a permis de mettre en évidence le potentiel des résidus agroalimentaires pour la production de biocrude, mélange d’une fraction solide appelée biochar et une fraction légère la biohuile dont les rendements dépendent des conditions opératoires. On peut ainsi espérer jusqu’à 33 % de biohuile à partir des DC (300 °C) et 24 % à partir des DB (315 °C) pour 15 minutes de temps de palier. Les biocrudes obtenus présentent un pouvoir calorifique proche de 33 MJ/kg et des concentrations en hétéroatomes et biochar élevées. Des étapes de raffinage sont à envisager avant toute valorisation sous forme de carburant. Sur la base de ces résultats, Un modèle prédictif a été construit comme un ensemble de réactions en parallèle et en série, aux cinétiques différentes. Le modèle permet de prédire environ 70 % des résultats expérimentaux dans un intervalle de confiance de 10 % à partir de la composition des biomasses, de la température et du temps de réaction. L’analyse statistique menée sur les coefficients ainsi que la comparaison avec la littérature a permis d’identifier certains chemins réactionnels à retravailler. Des méthodes inspirées des travaux menées de carbonisation hydrothermale ont été développées et ont permis d’observer que la liquéfaction des résidus agroalimentaires était exothermique, avec des enthalpies de réaction estimées entre -3,0 et -1,2 MJ/kg pour les DC et -1,97 et -0,9 MJ/kg pour les DB. Les difficultés techniques ont conduit à adapter le pilote de liquéfaction continu, cependant des essais longue durée ont pu valider le calcul des enthalpies de réaction obtenues sur le batch, validant à l’échelle du pilote la possibilité de réaliser des économies d’énergie. En comparaison avec les rendements obtenus sur le batch, le passage en continu évite la formation de biochar au profit d’une solubilisation accrue de la matière, et de la production de gaz. Enfin, les données expérimentales ont été intégrées dans un outil de simulation (PROSIMPLUS®) et ont servi de base à une évaluation technico économique permettant d’estimer le prix minimum de vente du biocrude. Selon les hypothèses économiques retenues, les prix de vente sont respectivement de 2,28 et 2,97 €/L pour les biocrudes issus des DC et des DB. Ces prix restent élevés en comparaison avec celui du pétrole. La sensibilité de ces prix a été estimée en fonction de la taille de l’installation, du coût initial investi, des rendements en biocrude ainsi que du coût de traitement des résidus (gate fee). Il doit cependant être possible de diminuer le coût du biocrude en considérant des tailles d’installation plus grande.
... Plug flow reactors (PFR) are the most common continuous HTL reactor implemented at the bench scale. Dried distillers grain from the bioethanol industry was successfully converted into bio crude oil with a PFR in a preceding study, leading to a mass yield of 38.9% ± 3.2% [35] . Microalgae were also studied with two different PFRs that had different reactor sizes (0.098 L and 1 L) using the same reaction temperature. ...
Hydrothermal liquefaction (HTL) is a thermochemical conversion technology that shows promising commercial potential for the production of biocrude oil from wet biomass. However, the inevitable production of the hydrothermal liquefaction aqueous phase (HTL-AP) acts as a double-edged sword: it is considered a waste stream that without additional treatment clouds the future scale-up prospects of HTL technology; on the other hand, it also offers potential as an untapped nutrient and energy resource that could be valorized. As more researchers turn to liquefaction as a means of producing renewable fuel, there is a growing need to better understand HTL-AP from a variety of vantage points. Specifically, the HTL-AP chemical composition, conversion pathways, energy valorization potential, and the interconnection of HTL-AP conversion with biofuel production technology are particularly worthy of investigation. This paper extensively reviews the impact of HTL conditions and the feedstock composition on the energy and elemental distribution of process outputs with specific emphasis on the HTL-AP. Moreover, this paper also compares and contrasts the current state of value-added products separation along with biological (biomass cultivation, anaerobic fermentation, and bioelectrochemical systems) and thermochemical (gasification and HTL) pathways to valorize HTL-AP. Furthermore, life cycle analysis (LCA) and techno-economic assessments (TEA) are performed to appraise the environmental sustainability and economic implications of these different valorization techniques. Finally, perspectives and challenges are presented and the integration approaches of HTL-AP valorization pathways with HTL and biorefining are explored.
... Even though work on continuous reactors has been ongoing since the 1980s (Lindemuth, 1981), there are only a few lab-scale continuous reactors, most of which were built recently (Ocfemia et al., 2006). With advances in pumping, filtration and oil-aqueous phase separation systems, the newest continuous reactors can handle biomass slurries with higher solids loadings , and can effectively remove HTL solids, enabling continuous bio-crude oil production for longer time periods between shut downs (Mørup et al., 2015). ...
To explore the feasibility of scaling up hydrothermal liquefaction (HTL) of algal biomass, a pilot-scale continuous flow reactor (CFR) was operated to produce bio-crude oil from algal biomass cultivated in urban wastewater. The CFR system ran algal slurry (5 wt.% solids loading) at 350 °C and 17 MPa for 4 h without any clogging issues. Bio-crude oil chemistry was characterized by high-resolution Fourier transform mass spectroscopy (FT-MS), proton nuclear magnetic resonance spectroscopy (1H NMR), bomb calorimetry, and elemental analysis. Bio-crude oil yield of 28.1 wt% was obtained with higher heating values of 38-39 MJ/kg. The quality of light bio-crude oil produced from the CFR system was comparable in terms of molecular structures to bio-crude oil produced in a batch reactor.
... Post-HTL water and biochar containing mainly water (99.4 wt.%) and mainly ash (75.5 wt.%) [7], were modelled as water and ash respectively. For simplicity the gas product was modelled as a mixture of CO 2 and N 2 gases [31][32][33]. The biocrude has been modelled as a liquid fuel, heavy fraction of petroleum, in the ASPEN plus to limit possible convergence issues. ...
While exports from the meat industry in New Zealand constitute a valuable source of foreign exchange, the meat industry is also responsible for the generation of large masses of waste streams. These meat processing waste streams are largely biologically unstable and are capable of leading to unfavourable environmental outcomes if not properly managed. To enable the effective management of the meat processing waste streams, a value-recovery based strategy, for the complete valorisation of the meat processing waste biomass, is proposed. In the present study therefore, a biorefinery system that integrates the biomass conversion technologies of hydrolysis, esterification, anaerobic digestion and hydrothermal liquefaction has been modelled, simulated and optimized for enhanced environmental performance and economic performance. It was determined that an initial positive correlation between the mass feed rate of the waste to the biorefinery system and its environmental performance exists. However, beyond an optimal total mass feed rate of the waste stream there is a deterioration of the environmental performance of the biorefinery system. It was also determined that economies of scale ensure that any improvement in the economic performance of the biorefinery system with increasing total mass feed rate of the waste stream, is sustained. The present study established that the optimized meat waste biorefinery system facilitated a reduction in the unit production costs of the value-added products of biodiesel, biochar and biocrude compared the literature-obtained unit production costs of the respective aforementioned products when generated from stand-alone systems. The unit production cost of biogas was however shown to be comparable to the literature-obtained unit production cost of biogas. Finally, the present study showed that the optimized meat processing waste biorefinery could achieve enhanced economic performance while simultaneously maintaining favourable environmental sustainability.
... A very detailed and comprehensive description of a bench-scale setup for HTL can be found in the work by Mørup et al. [62], from Aarhus University, Denmark. Also, in this case, the system is based on a tubular reactor, with different sizes that can be adjusted to the actual aim of the experiment. ...
Hydrothermal liquefaction (HTL) of biomass is emerging as an effective technology to efficiently valorize different types of (wet) biomass feedstocks, ranging from lignocellulosics to algae and organic wastes. Significant research into HTL has been conducted in batch systems, which has provided a fundamental understanding of the different process conditions and the behavior of different biomass. The next step towards continuous plants, which are prerequisites for an industrial implementation of the process, has been significantly less explored. In order to facilitate a more focused future development, this review-based on the sources available in the open literature-intends to present the state of the art in the field of continuous HTL as well as to suggest means of interpretation of data from such plants. This contributes to a more holistic understanding of causes and effects, aiding next generation designs as well as pinpointing research focus. Additionally, the documented experiences in upgrading by catalytic hydrotreating are reported. The study reveals some interesting features in terms of energy densification versus the yield of different classes of feedstocks, indicating that some global limitations exist irrespective of processing implementations. Finally, techno-economic considerations, observations and remarks for future studies are presented.E
... The lab scale reactor has been presented in detail elsewhere and only the biomass and their processing parameters and workup procedures are presented. 18 The pilot scale reactor was operated at 350°C with a flow rate of ∼1 L min −1 (± 0.2 L min −1 ). Residence time at 350°C was approximately 10 min with a heat up time from ambient to 350°C of 5 min and a cooling to 70°C of 5.5 min. ...
This paper investigates the use of Fourier-transform infrared spectroscopy (FT-IR) for quantitative analysis of bio-crudes from hydrothermal liquefaction (HTL) of biomass. HTL is a versatile process rendering virtually all biomasses suitable for conversion into bio-crude and side-streams. However, continuous processes require rapid analytical methods applicable to highly diverse bio-crudes. Bio-crudes were obtained from two different continuous HTL reactors (lab scale and pilot scale) and in some cases recirculation of water. The bio-crudes originated from a diverse range of feedstocks including lignocellulosics (pine, Miscanthus), microalgae (Spirulina, Chlorella vulgaris), and residues (sludge, dried distillers grains with solubles). Quantitative analysis of water content, total acid number, and total content of phenolics was performed using FT-IR. Principal component analysis indicated a potential correlation between quantitative measurements and FT-IR. Partial least squares regression was used to develop predictive models that performed well considering the high diversity of the bio-crudes. The content of phenolics was 83.1 - 254.6 mg g-1(gallic acid equivalent) and model calibration was good (RMSE = 19.7, slope = 0.81, y-exp = 81.2%). A diverse set of test samples were subjected to the models. The relative difference for measured and predicted phenolic content was generally < 15%. Total acid numbers (TAN) were 7 - 98 mgKOH g-1 and model calibration was found to be satisfactory considering the titration method used (RMSE = 18.5, slope = 0.53, y-exp = 52.6%). The relative difference for measured and predicted TAN was generally < 20%. The water content (Karl Fischer titration) was 1 - 24 % and model calibration was very good (RMSE = 2.0, slope = 0.93, y-exp = 92.6%). The water content was generally predicted within 1.5% and the relative difference for measured and predicted water content was large (2.7 - 16.6%) due to the small values. All models included samples that deviated and could be considered outliers, however, their deviations were explained from their composition and retained in the models. Overall, the results show the potential of FT-IR as a universal technique to obtain rapid quantitative results from a variety of bio-crudes processed using different reactors.
... Minamisoma sometimes faces clogging problems in the HTL process. In the future, they must adopt a method that can resolve the clogging issue, which will successfully prolong the process time [16]. Other problems, for example, nitrogen content in the oil [17], can be resolved using two-stage HTL. ...
This study investigates the potential of microalgae oil production as an alternative renewable energy source, in a pilot project located at Minamisoma City in the Fukushima Prefecture of Japan. The algal communities used in this research were the locally mixed species, which were mainly composed of Desmodesmus collected from the Minamisoma pilot project. The microalgae oil-production processes in Minamisoma consisted of three stages: cultivation, dewatering, and extraction. The estimated theoretical input-energy requirement for extracting oil was 137.25 MJ to process 50 m3 of microalgae, which was divided into cultivation 15.40 MJ, centrifuge 13.39 MJ, drum filter 14.17 MJ, and hydrothermal liquefaction (HTL) 94.29 MJ. The energy profit ratio (EPR) was 1.41. The total energy requirement was highest in the HTL process (68%) followed by cultivation (11%) and the drum filter (10%). The EPR value increased along with the yield in the cultivation process. Using HTL, the microalgae biomass could be converted to bio-crude oil to increase the oil yield in the extraction process. Therefore, in the long run, the HTL process could help lower production costs, due to the lack of chemical additions, for extracting oil in the downstream estimation of the energy requirements for microalgae oil production.
... Minamisoma sometimes faces clogging problems in the HTL process. In the future, they must adopt a method that can resolve the clogging issue, which will successfully prolong the process time [16]. Other problems, for example, nitrogen content in the oil [17], can be resolved using two-stage HTL. ...
The objective of this study is to use a life-cycle assessment (LCA) to compare and evaluate the environmental impact of combinations of open lagoon technology (COLT) with composting and COLT-Biogas for palm oil mill effluent (POME) treatment in North Sumatera, Indonesia. COLT-Biogas technology consists of three major types: composting, land application, and membrane technology. The environmental impact was evaluated by focusing on global warming potential (GWP), acidification potential, eutrophication potential, human toxicity potential, energy consumption (EC), and net energy ratio (NER). The results presented herein indicate that the GWP was the most significant criteria in the POME environmental impact assessment. With respect to GWP, COLT-Biogas A integrated with composting was observed more environmentally friendly than the other combinations. Approximately 357.18 kg CO2-eq of GWP reduction could be achieved with this technology without considering the utilization potential of its products. With respect to NER, COLT-Biogas B with land application and COLT-Biogas C with membrane technology achieved better results since they do not require fossil fuel input. In terms of EC, COLT Biogas C with membrane technology required the lowest amount of energy among the alternative technologies. A novel approach of comparing POME treatment technologies is presented herein, and the findings could help decision makers and planners to adopt the more environmentally friendly policies, resulting in more sustainable palm oil products.
... Minamisoma sometimes faces clogging problems in the HTL process. In the future, they must adopt a method that can resolve the clogging issue, which will successfully prolong the process time [16]. Other problems, for example, nitrogen content in the oil [17], can be resolved using two-stage HTL. ...
This study investigates the potential of microalgae oil production as an alternative renewable energy source, in a pilot project located at Minamisoma City in the Fukushima Prefecture of Japan. The algal communities used in this research were the locally mixed species, which were mainly composed of Desmodesmus collected from the Minamisoma pilot project. The microalgae oil-production processes in Minamisoma consisted of three stages: cultivation, dewatering, and extraction. The estimated theoretical input-energy requirement for extracting oil was 137.25 MJ to process 50 m3 of microalgae, which was divided into cultivation 15.40 MJ, centrifuge 13.39 MJ, drum filter 14.17 MJ, and hydrothermal liquefaction (HTL) 94.29 MJ. The energy profit ratio (EPR) was 1.41. The total energy requirement was highest in the HTL process (68%) followed by cultivation (11%) and the drum filter (10%). The EPR value increased along with the yield in the cultivation process. Using HTL, the microalgae biomass could be converted to bio-crude oil to increase the oil yield in the extraction process. Therefore, in the long run, the HTL process could help lower production costs, due to the lack of chemical additions, for extracting oil in the downstream estimation of the energy requirements for microalgae oil production.
... Almost all the reported work on algal biomass conversion has been carried out in small volume batch reactors where the slurry feed is introduced and maintained until the optimum product distribution is obtained. In recent times, few studies have been reported for carrying out HTL process in bench/pilot-scale continuous reactors like stirred reactors (Barreiro et al., 2015) and plug-flow (tubular) reactors (Jazrawi et al., 2013;Elliott et al. 2013Elliott et al. , 2015Biller et al., 2015;Mørup et al.,2015;Suesse et al., 2016). But it has been observed that the liquefaction at low Residence Time (RT) reactors could be a better option to produce algal biocrude (Patel and Hellgardt, 2015;Faeth et al., 2013). ...
Computational Fluid Dynamics (CFD) technique is used in this work to simulate the hydrothermal liquefaction of Nannochloropsis sp. microalgae in a lab-scale continuous plug-flow reactor to understand the fluid dynamics, heat transfer, and reaction kinetics in a HTL reactor under hydrothermal condition. The temperature profile in the reactor and the yield of HTL products from the present simulation are obtained and they are validated with the experimental data available in the literature. Furthermore, the parametric study is carried out to study the effect of slurry flow rate, reactor temperature, and external heat transfer coefficient on the yield of products. Though the model predictions are satisfactory in comparison with the experimental results, it still needs to be improved for better prediction of the product yields. This improved model will be considered as a baseline for design and scale-up of large-scale HTL reactor.
... Here, a continuous stirred tank in combination with a plug-flow reactor has been operational at a flow rate of 1-2 L/h [6]. Other examples from laboratory-validated continuous HTL systems include Leeds University (2-3 L/h), Aarhus University (0.5 L/h and 50L/h) andAalborg University (DK) in collaboration with Steeper Energy (14 L/h)[12,24,26,53]. All of the small laboratory systems equate to TRL 4 while Aalborg/Steeper and the Aarhus pilot plant equate to TRL 5. ...
Conversion of wet biomass and waste products via hydrothermal liquefaction (HTL) has been evolving as an alternative thermochemical technology for the production of liquid biofuels. Processing of biomass slurries with approximately 20 % solids content under high temperature and pressure mimics the natural formation of fossil crude on earth. With reaction times of around 10 to 30 minutes, temperatures of 350 °C and pressures of around 200 bar, HTL converts any biomass feedstock to a liquid bio-crude. This raw product roughly resembles petroleum, but exhibits higher oxygen contents (~10 %) and has a higher viscosity. Therefore, development of the hydrothermal liquefaction technology has concentrated on the upgrading of bio-crude via hydrotreatment to reduce its heteroatom content, viscosity, boiling point and density. Upgraded bio-crude can then be further refined via distillation or other established processes into renewable gasoline, diesel and jet fuel. The upgraded fuel’s chemical composition, with a high concentration of aliphatic hydrocarbons showing carbon numbers in the range of C8 to C18, appears promising for application as renewable jet fuel. The specific composition of the refined fuel products (as well as of the bio-crude) is, however, affected to a significant extent by the type of feedstock applied. For example, using lignocellulosic feedstock results in increased concentrations of aromatic hydrocarbons in the final product. The versatility of the HTL technology in terms of feedstocks and products represents a major advantage over other thermochemical conversion processes. Future developments should address tailoring the process to meet specific fuel requirements, e.g. those of renewable aviation fuels. Recent HTL reactor developments have led to proven continuous operation on a variety of feedstocks, but current reactor capacities of about ~1 bbl/d of bio-crude are still limited. Initial environmental and economic assessments of the hydrothermal liquefaction technology are promising, but in-depth studies covering a representative range of feedstock have not yet been published, rendering estimations of minimum fuel selling prices and greenhouse gas (GHG) balances of HTL derived liquid fuels difficult. To advance the technological maturity of hydrothermal liquefaction towards industrial implementation, development efforts should focus on process integration along the entire production chain encompassing pre-treatment, HTL processing, hydrotreatment, distillation and utilization of process water.
... The consensus in most literature is that the reactive liquefaction temperature, residence times, rate of biomass heating, size of biomass particles and the recycle of aqueous residue streams have the largest influence, although with varying impact [1e3, 5,7,9,15]. As of today several continuous and proof-of concept pilot systems are in place independently around the globe [1,16,17], and also, a commercial solution by Steeper Energy, ApS titled Hydrofaction™ Oil is reportedly offered [18]. It is worth to mention that the directly produced Biocrude is not considered an analogue of petroleum crude [19e21]. ...
Hydrothermal liquefaction of biomass continues to show promise in experimental and pilot scale tests for carbon partitioning toward desirable multi-phase organic products. Results from a techno-economic investigation are presented for a commercial scale stand-alone plant with primary production of renewable liquid fuels compatible with current transportation infrastructure. The plant feedstock was forest residues and the non-catalytic hydrothermal conditions were set to 330 °C and 210 bar. A sequential flowsheet was developed and simulated on Aspen Plus® that includes pre-treatment, hydrothermal liquefaction, fuel upgrading and residue recovery functional blocks. Different scenarios for the valorization of the liquefaction residue streams are examined to maximize organic recovery and eliminate process waste streams. The highest plant thermal efficiency on lower heating value basis was recorded for the polygeneration of renewable liquid fuels, Bio-char and hydrogen gas at 85.2%. The plant recorded a minimum selling price of 66 € per MWh of co-products. The break-even prices of the co-products under existing market conditions was found to be 1.03 € per kg of gasoline or 2.46 € per kg of hydrogen gas or 51.4 € per MWh of Bio-char.
... Secondly, the biochemical processes which mainly involve anaerobic digestion, alcoholic fermentation and biodiesel production. 1 Due to the tendency of HTL to achieve high biomass conversion yields and bio-crudes with favorable higher-heating-values (HHVs, typically 30-36 MJ kg À1 ), low oxygen contents (10-20 wt%), reduced presence of corrosive carboxylic acids and a manageable water content (0-5 wt%), 2 the process has attracted signicant attention. [3][4][5] Particularly its capacity to treat biomasses with high water contents is a clear advantage. These combined properties have led to an estimate of superior performance in technoeconomic and lifecycle assessments. ...
Lignocellulosic plant matter, as a second generation biomass, has potential as a feedstock for the production of liquid bio-fuels providing an alternative to fossil fuels. Herein, we report detailed catalyst screening and parameter optimization for catalytic hydrotreatment of bio-crude produced from the continuous hydrothermal liquefaction (HTL) of aspen wood. Three different commercial metal oxide catalysts, NiW/Al2O3 and NiMo/Al2O3 with a high and low NiMo loading, were examined. Elemental analysis showed significant oxygen expulsion from 10.7 wt% in the bio-crude down to a minimum of 0.7 wt% in the hydrotreated bio-oil. Considering the degrees of hydrodeoxygenation (HDO) along with yields, NiMo/Al2O3 with a high NiMo loading showed the best performance with a yield of 71.9 wt% and an oxygen content of 2.4 wt% for the final bio-oil, followed by low loaded NiMo/Al2O3 (yield 67.4 wt%, oxygen content 3.8 wt%) and NiW/Al2O3 (yield 58.7 wt%, oxygen content 6.9 wt%) under relatively mild conditions. Characterization by gas chromatography coupled with mass spectrometry pointed towards possible conversion pathways of the main bio-crude components during hydrotreatment. These included the conversion of substituted cyclopentenones to cycloalkanes, and oxygen-containing substituted polycyclic aromatic hydrocarbons (PAHs) to polycyclic aromatic hydrocarbons (e.g. anthracene, phenanthrene and naphthalene) and cracking of fatty acids to aliphatic hydrocarbons. The effects of initial hydrogen pressure and reaction time were investigated. The results demonstrate the potential of upgrading the bio-crude produced from the HTL of aspen wood to a hydrocarbon product with properties similar to petroleum derived transportation fuels.
Oxygenated biocrude produced from hydrothermal liquefaction is of great interest as it originated from renewable feedstocks. However, they cannot be processed immediately in internal combustion engines due to high oxygen, high acidity, viscosity, and instability. Thus, there is a need for upgradation before its direct consumption. This review demonstrated the advancement in hydrothermal liquefaction of agricultural biomass to produce biocrude and catalytic hydrodeoxygenation for obtaining upgraded transportation fuels. Critical research and development on the hydrothermal liquefaction process have been reviewed for over a decade with an increasing magnitude over the last five years. This study summarized the global agricultural feedstocks and focused on Canadian agricultural biomass based on its location and availability. Further, different upgradation technologies were discussed with the main emphasis on hydrodeoxygenation, upgradation catalysts, and affecting parameters to produce deoxygenated renewable fuels. Co-processing, blending with conventional fuels, techno-economic feasibility, and life cycle studies were also elaborated with future perspectives.
The goal of this work was to study the effect of pH on the extraction yield of phenolic compounds from liquid phases recovered after the hydrothermal treatment of black liquor in the batch and continuous reactors at 280 and 350 °C. The pH values of the recovered liquid phases under investigation were adjusted to 9, 8, and 7. The liquid-liquid extraction was subsequently performed using ethyl acetate for 4 h at room temperature. The identification and quantification of phenolic products were conducted using GC-Mass analysis. The main monomeric compounds identified in the aqueous phase were phenol, guaiacol, and syringol. The results indicated that reducing the pH slightly improved the phenol and guaiacol extraction from the various recovered liquid phases after hydrothermal treatment. However, reducing the pH of liquid phases greatly increased the extraction yield of syringol. This was very noticeable in the recovered liquid phases after treatment at 280 °C, where the quantity of syringol was initially high. Additionally, a lower pH hindered the ethyl acetate hydrolysis during liquid-liquid extraction. The extraction experiments with various pH also confirmed the superior performance of the continuous reactor over the batch reactor to obtain the phenolic compounds. In addition, the phenolic products degraded as the treatment temperature increased from 280 to 350 °C.
The review paper embodies the current trends and advancements involved in the transformation of biomass to enhanced products, bioenergy, and chemicals. Some selected chemical process like the slow-fast pyrolysis, catalytic fast pyrolysis, hydrothermal liquefaction, transesterification and lignin valorization by depolymerization are aptly suited for biorefinery processing, and were discussed in this review. The (catalytic) fast pyrolysis and hydrothermal liquefaction are quite similar, but differ in their feedstock preparations, reactor configuration and thermal or energy optimization. The review covers the biomass selection, chemical conversion techniques and most importantly the required heterogeneous catalysts (where applicable). The work further suggests the superiority of dedicated chemicals over drop-in and smart drop-in chemicals, due the complete usage of biomass. Relative to the oil refinery process, biorefining is quite novel and accompanied by its drawbacks. These challenges range from catalyst poisoning and deactivation to energy intensiveness and eventually as being cost-ineffective. The challenge encountered in biorefinery is in the economic feasibility, as it is inferred from this review that the pre-treatment process takes up to about 20% of the conversion cost. Although the biorefinery plant employ lignocellulosic biomass, but study shows that the use of biomass is largely under-utilized. The solid products/ wastes from pyrolysis for example, can be utilized as source of energy for the process. In the pursuit for sustainability, it is essential to ensure a balance-energy-mix, where every other type of energy will have a role to play to avoid dependence on only one solution for the future. Therefore, in contrast to the dwindling fossil fuels, it can be generally speculated that the future for biorefining is bright. It was concluded that with vast knowledge on the suitable heterogeneous catalysts and proper optimization of process parameters (temperatures, pressure, and reactant species); some of the biorefining processes will result into a significant increase in industrial fuels and bio-based drop-in chemicals leading towards commercialization.
The purpose of the present work is to investigate the feasibility of hydrothermal liquefaction (HTL) on food waste using a mobile pilot scale reactor and assess its techno-economic potential as a renewable energy technology that can be commercialized in the future. A 35 L pilot scale reactor (0.15 gal·min⁻¹, 300°C, and 60 min retention time) resulted in a higher biocrude oil yield than lab scale reactors (29.5 wt.% vs 21.9 wt.%). Biocrude oil qualities from pilot scale and lab scale HTL showed similar characteristics when comparing the elemental distribution, oil composition, and heating values. Further, techno-economic assessment (TEA) showed that the minimum selling price of the biocrude oil from a base case scenario was $3.48 per gallon gasoline equivalent (GGE). The transportation cost of the feedstock and oil product was compared between onsite and mobile scenarios of HTL reactor operation. The results demonstrated that the mobile HTL reactor was more profitable when the sources of food waste were widely distributed (more than 106 miles). Combined pilot reactor results and assessments in different scenarios could be used to assess the sustainability of the HTL process for future large-scale implementation.
With the rapid growth of energy demand and environmental concerns associated with traditional fossil fuels, renewable and sustainable energy sources have attracted intensive research attention in recent years. Biomass is considered as one of the most promising alternative energy resources due to its many advantages including abundance, renewability, carbon neutrality and worldwide distribution. Liquefaction is an efficient thermochemical conversion route for the production of bio-derived fuels and chemicals under mild reaction conditions. In addition, this process does not require energy-intensive drying as a pre-processing step of the wet biomass feedstocks. Nevertheless, subsequent hydrogenation and upgrading treatment of the bio-oil with high oxygen content are imperative for practical applications mainly for improving the calorific value of the bio-oil. The cost and safety issues of external hydrogen are main obstacles for the liquefaction-upgrading route, which can be somewhat offset by the use of in-situ hydrogen. The research on in-situ hydrogen generation and use for biomass liquefaction is nascent. Therefore, the latest research developments on hydro-liquefaction of biomass feedstocks in presence of various in-situ hydrogen donors are reviewed in this article. Several commonly applied in-situ hydrogen donors including formic acid, alcohols (isopropanol, methanol and ethanol) and zero-valent metals (zinc, aluminum, iron, etc.) are discussed in details focusing mainly on their influence on the distribution of liquefied products and the mechanisms of hydrogen-donation/hydrogenation reactions. Moreover, future research directions towards the commercial applications of biomass liquefaction technology with in-situ hydrogenation strategies are presented.
The US annually produces 79 million dry tons of liquid organic waste including sewage sludge. Anaerobic digestion can only reduce the sludge volume by 50% in mass, leaving the other half as a growing waste management and hygienic problem. Hydrothermal Processing (HTP), a set of several chemical digestion processes, could be employed to convert sewage sludge into valuable products and minimize potential environmental pollution risks. Specifically, hydrothermal carbonization and hydrothermal liquefaction have been extensively studied to sustainably manage sludge. Two of the main reasons for this are the high upscaleability of HTP for public waste management and that it is estimated that HTP can recover eleven times more energy from waste products than landfilling. An integration of HTP with anaerobic digestion or recycling the soluble organics (in the HTP aqueous products) into the HTP process could lead to a higher overall rate of energy recovery for municipal sewage sludge.
Continuous hydrothermal liquefaction and further upgrading of the algal biocrude are of great importance for algae biofuel process scale-up and improvement of fuel properties. In this study, two strains of microalgae were used for processing in a continuous stirred tank reactor at 350 °C and 24 MPa for 15 min residence time. An average of 36.2 wt% and 31.5 wt% biocrude yields were achieved for Chlorella vulgaris and Nannochloropsis gaditana, respectively. The obtained biocrude was further upgraded by hydrotreating using commercial NiMo/Al 2 O 3 and NiW/Al 2 O 3 catalysts at two temperatures (250 °C and 400 °C) in a batch autoclave reactor for 4 h. Products distribution, analysis by elemental content, gas chromatography (GC), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and nuclear magnetic resonance spectroscopy ( ¹ H NMR) on upgrading products indicate that upgrading by both catalysts lead to improved physicochemical fuel properties, during 250 °C upgrading step, decarbonylation, decarboxylation and repolymerization are the dominant reactions while hydrodeoxygenation and cracking reaction are more promoted at 400 °C. The gasoline, kerosene and diesel oil components in the algal biocrude were increased from 18 wt% to >30 wt% after catalytic upgrading.
Hydrothermal liquefaction (HTL) of spruce wood was performed without and with the use of a potassium fluoride doped alumina catalyst (KF/Al2O3) in a bench-top reactor. HTL runs were performed at 250, 300 and 350 °C with residence times of 15, 30 and 60 min. The effects of the catalyst at different catalyst loadings (in concentrations from 10 to 40 wt% of the lignocellulose) on the bio-oil and solid residue yields as well as their properties were investigated. The use of the catalyst increased the bio-oil yields over two-fold and reduced char yields. GC-MS analysis revealed that the bio-oil from the non-catalytic and catalytic runs consisted of aldehydes, ketones, phenols, acids and esters. Among these components, phenolic compounds were dominant in both the non-catalytic and catalytic runs. The relative yields of phenolic compounds increased with catalyst use. The highest heating value was estimated to be approximately 29 MJ kg-1. The boiling point distributions of the bio-oils from both runs revealed that the total naphtha fraction (light and heavy) was comparable with that of crude oil.
Hydrothermal liquefaction (HTL) is a promising technology for conversion of wet biomasses to liquid fuels, but considerable amounts of oxygen and nitrogen remain in the bio-crude, while large amounts of water-soluble organics are displaced to the aqueous phase (AqP). In this study the bio-crude and AqP from HTL of 11 different feedstocks of lignocellulosics, residues, macroalgae, microalgae, and their mixtures were analyzed for elemental composition, total acid number, total organic carbon (TOC), total nitrogen, and pH. Quantitative analysis of major compound classes present in both bio-crudes and AqPs was achieved using gas chromatography coupled to mass spectrometry employing prior derivatization of authentic standards. A wide range of biochemical content was obtained through mixing of biomasses and quantitative analysis showed particular interaction between carbohydrates and proteins with extended effect on lipids. The ability of ammonia and amines to form Schiff bases was the key factor affecting elemental distribution and the direction of reaction pathways involved in the formation of cyclic oxygenates, hydroxypyridines, oxygenated aromatics, diols, and fatty acids in bio-crudes. Similarly, Schiff base formation accounts for increased formation of nitrogen-containing compounds in the AqP, leading to a decrease in TOC and total nitrogen in products from HTL of mixed biomasses. This work highlights the quantitative differences in bio-crude and AqP composition from HTL of varying biomasses and provides new knowledge of the effect of mixing biomasses on elemental distribution and composition of product fractions. The results provide valuable information for optimizing the feedstocks used for HTL based on biochemical composition.
Hydrothermal liquefaction (HTL) produces a side-product of solid residue (SR) with an organic fraction of char highly dependent on the feedstock. In this work the char from batch HTL of poplar, spirulina, and their 1:1 mixture was characterized for the first time using stepwise thermal desorption and pyrolysis-gas-chromatography-mass spectrometry (py-GC-MS) along with thermochemolysis. Three distinct compound fractions were identified in the form of trapped or strongly adsorbed compounds, residual lignin, and repolymerized phenolics. The trapped or adsorbed fraction resembled the compounds in bio-crude and aqueous phase from both poplar and spirulina. Residual lignin was only found from poplar while repolymerized phenolics were predominantly observed from poplar through ortho and para-directed polymerization. Multiple alkylated aliphatics and some pyrroles were observed from spirulina. Co-liquefaction of biomasses led to a markedly different SR from the individual biomasses with multiple alkylated pyrroles and indoles, both volatile and non-volatile, while repolymerized phenolics diminished due to Schiff base formation. This work demonstrates that potential bio-crude is present in SR from both poplar and spirulina while co-liquefaction hinders repolymerization of phenolics but also produces a vast number of volatile and non-volatile pyrroles. The work shows that additional information for the reaction pathways of HTL may be found from characterization of the SR and provides researchers within biomass conversion with a method to evaluate effects on SR formation.
Protein hydrolysates from animal by-products have good bioavailability and high nutritional value; thus, they could be used for value added foods, cosmetics and pharmaceutical products. This study investigated the potential of hydrothermal treatment for protein hydrolysis of porcine skin by-product at high temperature (150–250 °C) and pressure (350–3900 kPa). The control showed free amino acid content of 1.4 mg/ml and then increased to 9.4 mg/ml after hydrothermal treatment at 250 °C & 3900 kPa which was named porcine skin hydrolysate PSH-VI. In empirical model fitting, the linear combination coefficient of pressure and temperature (β5) showed the positive values with statistical significance (P < 0.05). Those results suggest that both elevated temperature and pressure are required for protein hydrolysis as compared to single use of elevated temperature or pressure only. The synergistic effect of temperature and pressure on protein hydrolysis was confirmed in the hydrothermal treatment. On protein gel electrophoresis, no obvious peptide band of >15 kDa was observed after treatment above 190 °C & 1100 kPa treatment. This study showed the potential of hydrothermal processing to produce protein hydrolysates used for food ingredients, cosmetics or pharmaceutical products from animal by-products as a green and sustainable technology.
Hydrothermal liquefaction (HTL) is in a closed oxygen-free reactor by pressurizing inert gases (e.g., N2 or He) or reducing gases (e.g., H2 or CO), at a certain temperature (250–380°C) and pressure (5–28 MPa). During HTL, the hot compressed water is used as both solvent and reaction medium. HTL using hot compressed water as the solvent has the advantages of being abundant, non-toxic and non-flammable, inexpensive, and naturally stored in biomass. This chapter aims to provide a review of HTL technology from a perspective of algal biorefinery.
Hydrothermal liquefaction (HTL) is a viable thermochemical process for converting wet solid wastes into biocrude which can be hydroprocessed to liquid transportation fuel blendstocks and specialty chemicals. The aqueous byproduct from HTL contains significant amounts (20 to 50%) of the biogenic feed carbon, which must be valorized to enhance economic sustainability of the process on an industrial scale. In this study, aqueous fractions produced from HTL of food industry wastes, municipal wastes and biomass cultivated on wastewater were characterized using a wide variety of analytical approaches. Organic species present in these aqueous fractions were identified using two-dimensional gas chromatography equipped with time-of-flight mass spectrometry. Identified compounds include organic acids, nitrogen compounds, alcohols, aldehydes, and ketones. Conventional gas chromatography coupled with flame ionization detection and liquid chromatography utilizing refractive index detection were employed to quantify the identified compounds. Inorganic species in the aqueous streams were also were quantified using ion chromatography and inductively coupled plasma optical emission spectroscopy. The concentrations of organic compounds and inorganic species are reported, and the significance of these results are discussed in detail.
The effect of recycling the aqueous phase in a continuous hydrothermal liquefaction process was investigated in terms of product yield distribution, carbon balance, and composition of all main fractions. Using a custom-built continuous reactor system, a long-term experiment was conducted at 350°C and 250 bar with a feedstock of dried distiller’s grains with solubles. In two consecutive recycle experiments, the aqueous phase of the preceding experiment was used as dispersion medium for the feedstock preparation. In these recycle-experiments a significant increase in bio-crude yields was observed with a maximum increase in the first recycle experiment. However, the recycling of the aqueous phase also resulted in lower heating values and higher water contents in the oil fraction. Based on these findings, recycling the aqueous phase is a trade-off between improved yields and reduced burn qualities of the bio-crude. That said, recycling also lowers carbon discharge to the aqueous fraction, which may contribute significantly to reducing the environmental footprint of an industrial HTL-plant.
Bio-crude from hydrothermal liquefaction (HTL) of lignocellulosic biomass is a potential alternative to conventional fossil fuels. Continuous HTL of lignocellulosic biomass requires feedstock pretreatment to obtain pumpable slurries. This work extends upon previous evaluations of pretreatment methods for obtaining stable slurries of Miscanthus х giganteus. In the current study, extensive characterization of the bio-crude and aqueous phase from HTL of thermally and chemically pretreated M. х giganteus is reported and molecular differences of these samples are evaluated. The bio-crude and aqueous phase is characterized with gas chromatography coupled to mass spectrometry using pre-derivatization with silylating reagent and methyl chloroformate, respectively. Principal component analysis shows that bio-crudes of untreated and slurry stabilized samples have higher concentrations of small organic acids and fatty acids, samples pretreated at mild alkali conditions have higher concentrations of alcohols, polyaromatics, and methylated phenolics, and samples pretreated with strong alkali conditions have higher concentrations of cyclic oxygenates and ketonized aromatics. Aqueous phases are separated based on the addition of slurry stabilizer which has higher concentrations of dicarboxylic acids and phenol. The detailed exploration of both bio-crude and aqueous phase will be of interest for other investigations of the pretreatment effects on biomass for hydrothermal liquefaction.
Hydrothermal liquefaction (HTL) is a promising thermo-chemical processing technology for the production of biofuels but produces large amounts of process water. Therefore recirculation of process water from HTL of dried distillers grains with solubles (DDGS) is investigated. Two sets of recirculation on a continuous reactor system using K2CO3 as catalyst were carried out. Following this, the process water was recirculated in batch experiments for a total of 10 rounds. To assess the effect of alkali catalyst, non-catalytic HTL process water recycling was performed with 9 recycle rounds. Both sets of experiments showed a large increase in bio-crude yields from approximately 35 to 55 wt%. The water phase and bio-crude samples from all experiments were analysed via quantitative gas chromatography–mass spectrometry (GC–MS) to investigate their composition and build-up of organic compounds. Overall the results show an increase in HTL conversion efficiency and a lower volume, more concentrated aqueous by-product following recycling.
Hydrothermal processing has evolved as an alternative processing technology for wet biomass and waste materials in recent years. Using hot-compressed water as a reaction medium at temperatures of 200–500°C, materials with increased energy density can be obtained. The technology is particularly suited for wet and waste materials as drying of the feedstock is not required. Hydrothermal processing is divided into three separate areas depending on reaction severity: hydrothermal carbonization (HTC, 180–280°C), hydrothermal liquefaction (HTL, 280–375°C), and hydrothermal gasification (HTG, >350°C). Each of these hydrothermal routes results in energy densification by removal of oxygen to produce hydrochar (HTC), biocrude (HTL), or syngas (HTG). The process chemistry and reactions in hydrothermal media are described for each process. Suitable feedstocks and their considerations are reviewed as the quality of targeted biofuel is a function of feedstock and operating conditions. The quality of hydrochar influences its uses as a solid fuel while biocrude quality affects its use as a liquid fuel and feedstock for upgrading to drop-in replacement fuels, while HTG produces a syngas rich in either H2 or CH4. Hydrothermal processing results in a process water at all temperatures, typical decomposition products, treatments, and uses of the water byproduct are discussed. Advances in reactor design and scale-up efforts to demonstration and industrial scales are reviewed for each technology. An assessment is made of the current state of technology and further areas of research are discussed.
Hydrothermal Liquefaction (HTL) is a versatile thermochemical pathway that converts wet or moist biomass into a bio-oil with promising properties as a future replacement of fossil oil. Lignocellulosic biomasses are of particular interest as they are representative of almost all terrestrial plant material. The fibrous nature of lignocellulosic biomass may however induce clogging and damage in continuous HTL reactors systems. This study investigates the pretreatment of Miscanthus × Giganteus (a perennial grass) in order to achieve stable feedstock slurries. To this end, the stabilizing effects of homogeneous catalysts are studied as well as the use of carboxymethyl cellulose as additive to prevent sedimentation. Finally, the impact of the applied pretreatment methodologies on the HTL process was evaluated with particular emphasis on product distribution and carbon balances.
Bio-oils obtained from hydrothermal liquefaction of biomass are black viscous fuels with good heating values. This paper presents results of physical and chemical characterization of bio-oils produced by hydrothermal liquefaction of blackcurrant pomace. The oils are analyzed with standard normalized tests and compared to specifications required by commercialized biofuels and conventional fuels. Iodine value and total acid number are determined, showing relatively high values. GC/MS analysis demonstrates that bio-oil recovery by solvent extraction followed by subsequent evaporation of the solvent leads to the loss of some volatile compounds in the bio-oil. Thermogravimetric analysis are performed to study the volatility of HTL bio-oils, as well as to evaluate the carbon residue after evaporation. The viscosity of a bio-oil recovered by ethyl-acetate extraction was measured with a rotational viscometer at 25 °C, leading to a viscosity of 1.7 Pa·s. The results show furthermore that adding sodium hydroxide to the reaction medium has a limited influence on the properties of bio-oils. The choice of extraction solvent has conversely a significant influence on the quality of the produced oil. We demonstrate in this paper how standardized tests can be applied to hydrothermal bio-oils, to compare them with commercial fuels and evaluate the need for upgrading.
This review describes the recent results in hydrothermal liquefaction (HTL) of biomass in continuous-flow processing systems. Although much has been published about batch reactor tests of biomass HTL, there is only limited information yet available on continuous-flow tests, which can provide a more reasonable basis for process design and scale-up for commercialization. High-moisture biomass feedstocks are the most likely to be used in HTL. These materials are described and results of their processing are discussed. Engineered systems for HTL are described; however, they are of limited size and do not yet approach a demonstration scale of operation. With the results available, process models have been developed, and mass and energy balances determined. From these models, process costs have been calculated and provide some optimism as to the commercial likelihood of the technology.
Bio-oil and hydrochar were produced through the hydrothermal
liquefaction (HTL) of Salix psammophila (SP) branch residues with
recycled processing water, in order to address the lack of water in
deserts or sandy lands and the difficulty of water treatment in a batch
reactor. The results indicated that the recycling of the HTL processing
water could significantly improve the yield of bio-oil from 30.3% to 46.9%.
The gas chromatography and mass spectrometry analyses of the
obtained bio-oil confirmed the presence of value-added chemicals, such
as phenolics, acetic acid, and furans. The acetic acid in the processing
water played a key role in the HTL. The heavy oil had a high content
(maximum of 42.7 wt%) of the low boiling point fraction (<300 °C),
indicating its potential for further applications. The higher heating value
of the hydrochar was about 27 MJ/kg, equivalent to the heating value of
medium-rank and high-rank coals. These results show that HTL using
recycled processing water has great potential for utilization of desert
biomass wastes.
Preliminary process studies on the conversion of various biomass types into liquid fuels have indicated that HydroThermal Upgrading (HTU) is more attractive than pyrolysis or gasification. In HTU the biomass is treated at temperatures of 300–350 °C in the presence of liquid water for 5–15 min. A large proportion of the oxygen is removed as carbon dioxide.In a case study a process for the production of 3600 t/d hydrocarbons starting from wood is evaluated. Six HTU units convert wood into “biocrude” containing 10 %w oxygen. The biocrude is upgraded by catalytic hydrodeoxygenation in a central facility. The final products are kerosine and gas oil which may be expected to have excellent properties. The manufacturing cost is 400–450 $/t.
Batch pressure vessels commonly used for hydrothermal liquefaction have typical heating times in the range of 30 to 60 min. Thermodynamically, the complex set of reactions are path dependent, so that the heating rate can possibly affect yields and the composition of the resultant liquid products. It is postulated that the mode of heat transfer becomes an uncontrolled variable in kinetic studies and can seriously impact scale-up. To confirm this hypothesis and minimize these heat-transfer-related artifacts, we designed a batch pressure vessel equipped with an induction heating system, which allows the reduction of heat-up times by about two orders of magnitude to several seconds, compared to tens of minutes with standard pressure reactors. This system was used to study the direct liquefaction of corn stover and aspen wood with a pretreatment. The heating rate was found to have no significant effect on the composition of the liquid products. However, the liquid yields are dependent on the heating rate. Varying the cooling rate does not show obvious effects. The results confirm that the heating rate, as governed by the mode of heat transfer, is an important factor that needs to be considered during scale-up.
Biomass liquefaction or carboxylolysis is essentially the production of a liquid fuel by the reaction of pulverized biomass in a slurry medium with carbon monoxide in the presence of an alkaline catalyst. Reaction conditions require high pressure (150–250 atm), moderately high temperature (300–350°C), and residence time of 10–30 min.
The microalgae Phaeodactylum tricornutum was processed by hydrothermal liquefaction in order to assess the influence of reaction temperature and reaction time on the product and elemental distribution. The experiments were carried out at different reaction times (5 and 15 min) and over a wide range of temperatures (275−420 °C) using a batch reactor system. All fractions were quantified and analyzed in terms of specific elemental concentrations. The highest bio-oil yield (39%) was obtained at 350 °C when using a reaction time of 15 min. Under these conditions, 82% of the algal calorific value was recovered in the bio-oil fraction. The higher heating value of the bio-oil increased with reaction temperature and reaction time. The elemental analysis was used to map the distribution of elements in the obtained fractions with increasing temperature. Generally, most of the potassium, sodium, nitrogen, phosphorus, and sulfur were recovered in the aqueous fraction. The solid residue was found to primarily consist of a calcium phosphate compound.
Hydrothermal liquefaction (HTL) of barley straw with K2CO3 at different temperatures (280-400 degrees C) was conducted and compared to optimize its process conditions; the aqueous phase as a co-product from this process was recycled to explore the feasibility of implementing wastewater reuse for bio-crude oil production. Results showed that low temperature favored the formation of bio-crude oil, with a maximum yield of 34.9 wt% at 300 degrees C. Contrarily, at high temperature, the bio-crude oil had better qualities in terms of less oxygen content and higher heating values (HHVs). The compounds identified in bio-crude oil were mainly phenolics, carboxylic acids, aldehydes and alcohols, among which the relative contents of phenolics and carboxylic acids decreased with increasing temperature. In the recirculation studies, bio-crude yield was enhanced gradually with aqueous phase addition at 300 degrees C, and reached 38.4 wt% after three cycles. The HHVs of bio-crude oil from HTL with aqueous phase were 28.4-29.4 MJ/kg, slightly higher than those from HTL with fresh water. While no obvious differences in elemental distribution can be found after aqueous phase recirculation. In conclusion, this study gives a detailed insight into the HTL behavior of barley straw, and offers potential opportunities and benefits for bio-crude oil production through the reuse of aqueous phase.
The effect of the reaction temperature on hydrothermal liquefaction of dried distillers grains with solubles (DDGS) was investigated using a novel stop-flow reactor system at varying temperatures (300–400 °C), fixed pressure (250 bar), and fixed reaction time (15 min). The stop-flow reactor provides rapid heating of biomass feeds and the option of performing multiple sequential repetitions. This bypasses long, uncontrollable temperature gradients and unintended changes in the reaction chemistry. The product, a crude bio-oil, was characterized in terms of yield, elemental composition, and chemical composition. Higher reaction temperatures resulted in improved bio-oil yields, less char formation, and higher heating values of the bio-oil. A supercritical reaction temperature of 400 °C was found to produce bio-oil in the highest yields and of the best quality.
We investigated the fast hydrothermal liquefaction of green marine alga Nannochloropsis sp. at batch reaction times of 1, 3, and 5 min and set-point temperatures of 300–600 °C. We also performed conventional liquefaction for 60 min at the same temperatures. These experiments cover the broadest range of reaction conditions yet reported for algae liquefaction. The biocrude yield obtained for 1 min reaction times, which was only long enough to heat the reactor from room temperature to about half of the set-point temperature (in °C), increased with an increasing set-point temperature to 66 ± 11 wt % (dry and ash-free basis) at a set-point temperature of 600 °C. The biocrude obtained at this condition contains 84% of the carbon and 91 ± 14% of the heating value present in the dry algae feedstock. This biocrude yield and corresponding energy recovery are the highest reported for liquefaction of this alga. For a reaction time of 1 min, as the set-point temperature increases, light biocrude (e.g., hexane solubles) makes up less of the total biocrude. The biocrudes produced by fast liquefaction have carbon contents and higher heating values similar to biocrudes from the traditional isothermal liquefaction process, which involves treatment for tens of minutes. These results indicate that biocrudes of similar quality may be produced in higher yields and in a fraction of the time previously thought necessary. Such a decrease in the reaction time would greatly reduce the reactor volume required for continuous biocrude production, subsequently reducing the capital costs of such a process. We also show that the reaction ordinate is a useful parameter for interpreting results from algae liquefaction performed at different temperatures and reaction times.
Wet macroalgal slurries have been converted into a biocrude by hydrothermal liquefaction (HTL) in a bench-scale continuous-flow reactor system. Carbon conversion to a gravity-separable oil product of 58.8% was accomplished at relatively low temperature (350 °C) in a pressurized (subcritical liquid water) environment (20 MPa) when using feedstock slurries with a 21.7% concentration of dry solids. As opposed to earlier work in batch reactors reported by others, direct oil recovery was achieved without the use of a solvent, and biomass trace mineral components were removed by processing steps so that they did not cause processing difficulties. In addition, catalytic hydrothermal gasification (CHG) was effectively applied for HTL byproduct water cleanup and fuel gas production from water-soluble organics. Conversion of 99.2% of the carbon left in the aqueous phase was demonstrated. As a result, high conversion of macroalgae to liquid and gas fuel products was found with low levels of residual organic contamination in byproduct water. Both process steps were accomplished in continuous-flow reactor systems such that design data for process scale-up was generated.
Fermentation residues are a waste stream of biomethane production containing substantial amounts of organic matter, and thus representing a primary energy source which is mostly unused. For the first time this feedstock was tested for catalytic gasification in supercritical water (T ≥ 374 °C, p ≥ 22 MPa) for methane production. The processing steps include hydrothermal liquefaction, salt separation, as well as catalytic gasification over a ruthenium catalyst in supercritical water.
In continuous experiments at a feed rate of 1 kg h−1 a partial liquefaction and carbonization of some of the solids was observed. Significant amounts of heavy tars were formed. Around 50% of the feed carbon remained in the rig. Furthermore, a homogeneous coke was formed, presumably originating from condensed tars. The mineralization of sulfur and its separation in the salt separator was insufficient, because most of the sulfur was still organically bound after liquefaction.
Desalination was observed at a salt separator set point temperature of 450 °C and 28 MPa; however, some of the salts could not be withdrawn as a concentrated brine. At 430 °C no salt separation took place. Higher temperatures in the salt separator were found to promote tar and coke formation, resulting in conflicting process requirements for efficient biomass liquefaction and desalination. In the salt separator effluent, solid crystals identified as struvite (magnesium ammonium phosphate) were found. This is the first report of struvite formation from a supercritical water biomass conversion process and represents an important finding for producing a fertilizer from the separated salt brine.
This study investigates the influence of heating and cooling rate on liquefaction of lignocellulosic biomass in subH2O (subcritical water) or in scEtOH (supercritical ethanol), in dependency of final reaction temperatures (250–350 °C) and residence times (1–40 min). The heating rate has been identified as a crucial parameter in the subH2O-based liquefaction, whereas it has marginal influence in the scEtOH-based liquefaction. Detailed characterization of gas, liquid and solid products enables to identify the individual reaction steps, which results in a new insight into the reaction mechanisms, depending on the liquefaction solvents and conditions. Similar to fast pyrolysis, hydrothermal liquefaction consists of beneficial primary reactions (pyrolytic & hydrolytic degradation) and non-beneficial secondary reactions i.e. recombination and secondary cracking. In scEtOH, biomass was decomposed by pyrolysis and alcoholysis at relatively high reaction temperatures while the recombination of reaction intermediates are retarded by the unique reactions of scEtOH such as hydrogen donation and hydroxylalkylation.
Supercritical water desulfurization (SCWDS) has potential as a technique for removing sulfur from feedstocks such as heavy oil and bitumen. However, a fundamental understanding of SCWDS (such as the underlying chemical mechanisms, relative rates of desulfurization, and the role of SCW and hydrocarbons) is limited. In the present work, we have gained molecular-level insights into this process by measuring the kinetics of decomposition of a variety of organic sulfides in the presence of hydrocarbons and supercritical water in a continuously fed stirred-tank reactor (CSTR). The results are consistent with a free-radical mechanism, with hydrogen abstraction from the sulfide as the rate-determining step. The decomposition rates of the aliphatic and aromatic sulfides varied depending on their molecular structure, with conversions after 31 min at 400 degrees C ranging from less than 3% (our detection limits) to more than 90%. These differences in the reactivity correlate with the estimated heats of reaction for the critical hydrogen abstraction. The decomposition rates of the sulfides were affected by the presence of hydrocarbon carriers, with the rates being higher in the presence of alkanes than in the presence of toluene, as expected for a free-radical process. Product distributions and rates of radical-induced alkane cracking during this process were likewise affected by the presence of different sulfides. The decomposition of several different sulfides is consistent with 3/2 power kinetics, providing further evidence that the reaction proceeds via a radical mechanism. The knowledge developed in the current work provides a fundamental basis for further improvements in SCWDS.
Wet algae slurries can be converted into an upgradeable biocrude by hydrothermal liquefaction (HTL). High levels of carbon conversion to gravity separable biocrude product were accomplished at relatively low temperature (350 °C) in a continuous-flow, pressurized (sub-critical liquid water) environment (20 MPa). As opposed to earlier work in batch reactors reported by others, direct oil recovery was achieved without the use of a solvent and biomass trace components were removed by processing steps so that they did not cause process difficulties. High conversions were obtained even with high slurry concentrations of up to 35 wt.% of dry solids. Catalytic hydrotreating was effectively applied for hydrodeoxygenation, hydrodenitrogenation, and hydrodesulfurization of the biocrude to form liquid hydrocarbon fuel. Catalytic hydrothermal gasification was effectively applied for HTL byproduct water cleanup and fuel gas production from water soluble organics, allowing the water to be considered for recycle of nutrients to the algae growth ponds. As a result, high conversion of algae to liquid hydrocarbon and gas products was found with low levels of organic contamination in the byproduct water. All three process steps were accomplished in bench-scale, continuous-flow reactor systems such that design data for process scale-up was generated.
We describe a pilot plant for continuous hydrothermal processing of biomass. Results were obtained for two microalgae strains, Chlorella and Spirulina, across a range of biomass loadings (1–10 wt.%), temperatures (250–350 °C), residence times (3–5 min) and pressures (150–200 bar). Overall, the bio-crude yields were found to increase with higher biomass loading, higher temperature and longer residence time. More severe reaction conditions also reduced the oxygen content of the bio-crude, while the nitrogen content was found to increase with higher temperatures, indicating an increase in the bio-crude production from the protein fraction of the algae. The maximum bio-crude yield obtained was 41.7 wt.% for processing Chlorella with a solid loading of 10 wt.% at 350 °C and 3 min residence time. The present results suggest that maximal yields may be obtained in much shorter residence times under continuous flow hydrothermal processing than batch studies have suggested. The maximal yield, however, may not be optimal in terms of properties.A substantial fraction of the feedstock carbon reported to the aqueous phase — this was up to 60% but decreased to 30% at the highest biomass loadings. Gas production (> 90 mol% CO2) increased with severity of processing, reaching up to 5% of the feedstock carbon. Finally, the solid yields consistently decreased with increasing temperatures and residence times.
This report describes the results of the work performed by PNNL using feedstock materials provided by the National Renewable Energy Laboratory, KL Energy and Lignol lignocellulosic ethanol pilot plants. Test results with algae feedstocks provided by Genifuel, which provided in-kind cost share to the project, are also included. The work conducted during this project involved developing and demonstrating on the bench-scale process technology at PNNL for catalytic hydrothermal gasification of lignin-rich biorefinery residues and algae. A technoeconomic assessment evaluated the use of the technology for energy recovery in a lignocellulosic ethanol plant.
Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.
Residence time distribution (RTD) measurements are carried out in a flow-through tubular supercritical water oxidation (SCWO) reactor using ex situ pulse response experiments. The experiments are performed from ambient to supercritical water conditions with a volumetric flow rate fixed at 1ml/min. The transfer function concept is used to interpret tracer information and to elucidate hydrodynamic flow patterns inside the “hot zone” of the reactor vessel. The experimental RTD curves are modeled by an axially dispersed plug flow. At supercritical conditions, the studied tubular SCWO reactor can be characterized as a mixed flow system (with Péclet numbers of 1.4–2). The results also indicate the presence of fast preferential fluid flow in the reactor below 573K and 10MPa.
Use of supercritical water (SCW) as a medium for oxidation reactions, conversion of organic materials to gaseous or liquid products, and for organic and inorganic synthesis processes, has been the subject of extensive research, development, and some commercial activity for over 25 years. A key aspect of the technology concerns the identification of materials, component designs, and operating techniques suitable for handling the moderately high temperatures and pressures and aggressive environments present in many SCW processes. Depending upon the particular application, or upon the particular location within a single process, the SCW process environment may be oxidizing, reducing, acidic, basic, nonionic, or highly ionic. Thus, it is difficult to find any one material or design that can withstand the effects of all feed types under all conditions. Nevertheless, several approaches have been developed to allow successful continuous processing with sufficient corrosion resistance for an acceptable period of time. The present paper reviews the experience to date for methods of corrosion control in the two most prevalent SCW processing applications: supercritical water oxidation (SCWO) and supercritical water gasification (SCWG).
Hydrothermal processing of swine manure is a novel technology that has shown very promising results in treating waste and producing oil. A batch hydrothermal process system that was previously developed at the University of Illinois at Urbana-Champaign successfully converted up to 70% of swine manure volatile solids into oil and reduced manure chemical oxygen demand by up to 75%. Since a continuous system is more applicable for scale-up operations, a small-scale continuous hydrothermal process (CHTP) reactor system was developed to evaluate the technical feasibility of the continuous-mode process. The CHTP reactor system was composed of a high-pressure slurry feeder, a process gas feeder, a continuous stirred tank reactor, a product separation vessel, and process controllers. It had a capacity to process up to 48 kg of manure slurry per day. The CHTP reactor system was successfully operated continuously for up to 16 h per test. Oil yields ranging from 62.0% to 70.4% were achieved. The heating value of the oil product ranged from 25,176 kJ/kg to 31,095 kJ/kg with the highest value at T = 305°C, P = 10.3 MPa, and RT = 80 min. © 2006 American Society of Agricultural and Biological Engineers.
A continuous liquefaction unit for the production of wood oil from aqueous slurries of prehydrolyzed Douglas fir at 330-360/sup 0/C in the presence of reducing gas has been successfully operated since July, 1981. Significant differences in yields and product distribution between this process and an oil-based, recycle process are noted, the former making less wood oil and more water-soluble organics. Higher temperatures lead to a lower molecular-weight oil of lower oxygen content. Carbon monoxide and hydrogen are equally effective reducing gases. Progress in characterizing oil and water-soluble organics is described.
In this paper, we report on the construction of a novel test facility for evaluating catalytic processes at high temperature and high pressure. The design features make the facility well-suited for highly controlled studies of hydrothermal conversion of real biomasses with complex composition. The proof of concept is provided by bio-oil production from (i) Dried Distiller’s Grains with Solubles (DDGS), the results serving to illustrate catalyst performance, and (ii) spent coffee grounds, which exemplify constituent analysis of the as-produced bio-oil. Both studies were carried out under near-critical conditions using both homogeneous and heterogeneous catalysts.
Subcritical water is an environmentally attractive solvent for organic matters and can be used to liquefy biomass to biocrude, which is a mixture of oxygenated hydrocarbons of varying molecular weights. Liquefaction of switchgrass in subcritical water is studied using a semicontinuous reactor in the temperature range of 235−260 °C. Subcritical water is pumped through a tubular reactor packed with switchgrass particles of 40−60 mesh size. The effects of reaction temperature and catalysis by K2CO3 are examined. Potassium carbonate significantly enhances the hydrolysis of macromoleculer components of switchgrass into water-soluble products. More than 50 wt % of the organic carbon available in switchgrass was converted to biocrude after 20 min of steady operation at 235 °C in the presence of 0.15 wt % of K2CO3. At the high temperature (260 °C), dehydration of biomass was favored over hydrolysis reactions. On the basis of chromatography and mass spectrometry analyses, biocrude contains lignin derived products, sugars, and its decomposition products. On the basis of the infrared spectroscopy and electron microscopy of residue solid, the subcritical water treatment causes complete breakdown of lignocellulosic structure of switchgrass. In fact, the residue solid mainly contained lignin fractions.
We collected and analyzed the gas, crude bio-oil, dissolved aqueous solids, and insoluble residual solids product fractions arising from hydrothermal liquefaction of Nannochloropsis sp. at 350 °C for 60 min. Most of the carbon and hydrogen in the algal biomass appears in the crude bio-oil product, as desired. A majority of the original nitrogen appears as ammonia in the aqueous phase. We also determined how the solvent used to recover the crude bio-oil affected the yields and compositions of the product fractions. We used both nonpolar solvents (hexadecane, decane, hexane, and cyclohexane) and polar solvents (methoxycyclopentane, dichloromethane, and chloroform). Hexadecane and decane provided the highest gravimetric yields of bio-oil (39 ± 3 and 39 ± 1 wt %, respectively), but these crude bio-oils had a lower carbon content (69 wt % for decane) than did those recovered with polar solvents such as chloroform (74 wt %) and dichloromethane (76 wt %). We quantified the amount of 19 different individual molecular components in the crude bio-oil for the first time. Fatty acids were the most abundant components, but some aromatic and sulfur- and nitrogen-containing compounds were also quantified. The amount of free fatty acids in the crude bio-oil significantly depended on the solvent used, with polar solvents recovering more fatty acids than nonpolar solvents. The bio-oil recovered with chloroform, for example, had a fatty acid content equal to 9.0 wt % of the initial dry algal biomass.
Over the past years, superheated, close‐to‐critical and supercritical water (hot compressed water) have met with an increasing interest as reaction medium. In this work, a method for determining the residence time distribution of reactors with hot compressed water has been developed. In experiments performed in a testing plant residence time distribution was measured directly downstream of the reactor at high pressure and high temperature and by using a view cell together with an UV‐active tracer substance.
The purpose of the work presented here is the production of liquid biofuels from wet organic waste matter in a continuous one-step catalytic process under hydrothermal conditions. The catalytic reaction of wet organic matter at near-critical water conditions (T > 300 °C, p > 22.1 MPa) is used to produce a mixture of combustible organics which can be used as liquid biofuel. In order to achieve a good product quality in a continuous one-step process, two catalysts were applied, a homogeneous potassium carbonate catalyst and a heterogeneous ZrO2 catalyst. In addition, the reaction mixture was recirculated. The continuous flow of concentrated waste biomass feed at low flow rates and recirculation of the hot reaction mixture were the most challenging obstacles to overcome. The scale of the plant (0.1 l reactor volume) allowed for a variation of the feed, reaction temperature, and recirculation rate in order to optimise the process conditions. Still, the product quantity obtained was sufficient to perform a analytical characterisation. The experimental results confirmed the feasibility of the process. Hydrothermal treatment of waste biomass, after dewatering, resulted in a biocrude oil of high calorific value.
A unified correlation for computation of higher heating value (HHV) from elemental analysis of fuels is proposed in this paper. This correlation has been derived using 225 data points and validated for additional 50 data points. The entire spectrum of fuels ranging from gaseous, liquid, coals, biomass material, char to residue-derived fuels has been considered in derivation of present correlation. The validity of this correlation has been established for fuels having wide range of elemental composition, i.e. C — 0.00–92.25%, H — 0.43–25.15%, O — 0.00–50.00%, N — 0.00–5.60%, S — 0.00–94.08% and Ash — 0.00–71.4%. The correlation offers an average absolute error of 1.45% and bias error as 0.00% and thereby establishes its versatility. Complete details of few salient data points, the methodology used for derivation of the correlation and the base assumptions made for derivation are the important constituents of this work. A summary of published correlations along with their basis also forms an important component of present work.
Diss. no. 14911 techn. sc. SFIT Zurich. Literaturverz.
The semi-pilot scale of continuous flow type hydrothermal reactor has been investigated to separate hemicellulose fraction from corncob. We obtained the effective recovery of hemicellulose using tubular type reactor at 200 degrees C for 10 min. From constituent sugar analysis of corncob, 82.2% of xylan fraction was recovered as mixture of xylose, xylooligosaccharides and higher-xylooligosaccharide which has more than DP 10. During purification of solubilized fraction by hydrothermal reaction such as ultrafiltration and ion exchange resin, higher-xylooligosaccharide was recovered as the precipitate. This precipitate was identified as non-blanched xylan fraction which has from DP 11 to DP 21 mainly. In this system, only a small amount of furfural has been generated. This tubular reactor has a characteristic controllability of thermal history, and seems to be effective for sugar recovery from soft biomass like corncob.
Turning low value commodities into high value syncrude
- L A Rosendahl