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Conditioning the volatile stream from biomass fast pyrolysis for the attenuation of steam reforming catalyst deactivation
Abstract
The fast deactivation of the reforming catalyst greatly conditions H2 production from biomass. In order to alleviate this problem, use of conditioning catalysts in a previous conditioning step has been proposed to modify the pyrolysis volatile stream reaching the reforming catalyst. The experimental runs have been conducted in a two-step reactor system, which includes a conical spouted bed reactor for the continuous pinewood sawdust pyrolysis and an in-line fixed bed reactor made up of two sections: the conditioning and the reforming steps. Biomass fast pyrolysis was conducted at 500 °C and the reforming step at 600 °C. Different conditioning beds (inert sand, γ-Al2O3, spent fluid catalytic cracking (FCC) catalyst and olivine) were used for the conditioning of biomass pyrolysis volatiles and the influence their composition has on the performance and deactivation of a commercial Ni/Al2O3 reforming catalyst has been analyzed.
Considerable differences were noticed between the conditioning catalysts, with the reforming catalyst stability decreasing as follows depending on the type of material used: γ-Al2O3 > olivine > inert sand ≈ no guard bed > spent FCC catalyst.
The high acidity of γ-Al2O3 (with a high density of weak acid centers) is suitable for the selective cracking of phenolic compounds (mainly guaiacol and catechol), which are the main precursors of the coke deposited on the Ni active sites. Although H2 production is initially lower, the reforming catalyst stability is enhanced. These results are of uttermost significance in order to step further in the scaling up of the in-line pyrolysis-reforming strategy for the direct production of H2 from biomass.
... [33][34][35] The other main challenge in the biomass pyrolysis and in line steam reforming process, i. e., the fast catalyst deactivation by coke deposition, is greatly conditioned by the composition of the volatile stream entering the reforming reactor. [36] Thus, the identification of the main coke precursor compounds has been of great interest in the literature. [37] However, due to the high heterogeneity of bio-oil derived compounds, made up of water and a wide range of oxygenated compounds, major research efforts have been focused on the evaluation of deactivation mechanisms using different model compounds such as phenol, acetic acid, glycerol, furfural, among others. ...
... It is to note that this catalyst showed a suitable performance for the steam reforming of biomass pyrolysis volatiles. [36,50] It has a NiO content of 14 wt %, is supported on Al 2 O 3 , and is also doped with Ca. The catalyst was supplied in the form of perforated rings, which were ground and sieved to obtain a suitable particle size for the fluidized bed reactor, i. e., 0.4-0.8 ...
... In the case of the microalgae, conversion only reached 50.9 %, which can be partly attributed to the presence of highly refractory compounds in the volatile stream, such as the hydrocarbon fraction (2.78 wt %), which led to a lower initial catalyst activity. [36] However, the results obtained in the OSR of the microalgae pyrolysis cannot be related solely to the lower reactivity of the pyrolysis-derived volatiles, but a very fast deactivation also occurs in the reforming process. Thus, the presence of N-containing compounds in the volatile stream led to a fast catalyst poisoning of Ni 0 active sites and so fast catalyst activity decay. ...
This study evaluates the potential of several biomasses differing in nature and composition for their valorization by pyrolysis and in line oxidative steam reforming. The first task involved the fast pyrolysis of the biomasses in a conical spouted bed reactor (CSBR) at 500 °C, in which product yields were analyzed in detail. Then, the oxidative steam reforming (OSR) of pyrolysis volatiles (gases and bio‐oil) was approached in a fluidized bed reactor (FBR). The reforming experiments were performed at 600 °C, with a steam/biomass (S/B) ratio of 3 and catalyst (Ni/Al2O3) space times of 7.5 and 20 gcat min gvol⁻¹. Concerning equivalence ratio (ER), a value of 0.12 was selected to ensure autothermal operation. Remarkable differences were observed in H2 production depending on the type of biomass. Thus, pine wood led to a H2 production of 9.3 wt %. The lower productions obtained with rice husk (7.7 wt %) and orange peel (5.5 wt %) are associated with their higher ash and fixed carbon content, respectively, which limit the efficiency of biomass conversion to bio‐oil. However, in the case of the microalgae, the poor performance observed is because of the lower conversion in the reforming step toward gases due to the composition of its pyrolysis volatile stream.
... Hydrogen (H 2 ) energy is a renewable green energy carrier with a high energy density value per unit mass (120-142 MJ kg −1 ), 1,2 which is the best alternative to conventional fossil fuels. Currently, the main methods for H 2 production include steam reforming, 3,4 coal gasification, 5,6 the natural gas method, 7,8 industrial by-products for H 2 production, 9,10 electrocatalytic [11][12][13] and photocatalytic water splitting 14,15 and so on. Among these H 2 production methods, electrolysis of water utilizes renewable energy to produce H 2 , with low energy consumption, less greenhouse gas release during the whole preparation process, and the obtained H 2 is of high purity and low impurity content. ...
... 79 In addition to monometallic Cu clusters, Mo-Cu bimetallic clusters have also been reported for photocatalytic H 2 production. Zang's group introduced MoOS 3 2− unit into Cu cluster and prepared a series of atomically precise Cu 6 (MoOS 3 ) 2 (C 7 H 7 S) 2 (PPh 3 ) 4 ·xCH 3 CN (Cu 6 Mo 2 , C 7 H 7 S = benzyl mercaptan). 80 It is well known that gold bulk is chemically inert. ...
Atomically precise metal clusters that possess the exact atom number, definitive composition, and tunable geometric and electronic structures have emerged as ideal model catalysts for many important chemical processes. Recently, metal clusters have been widely used as excellent catalysts for hydrogen production to explore the relationship between the structure and catalytic properties at the atomic level. In this review, we systematically summarize the significant developments concerning metal clusters as electrocatalysts and photocatalysts for hydrogen generation. This review also puts forward the challenges and perspectives of atomically precise metal clusters in electrocatalysis and photocatalysis in the hope of providing a valuable reference for the rational design of high-performance catalysts for hydrogen production.
... He observed that the use of both zeolites resulted in an increased generation of condensable gas during the pyrolysis of LDPE [20]. Fernandez et al., have conducted an experimental study to analyze the catalytic bed material effect of olivine on the pyrolysis yield of biomass and found out that using olivine as the bed material has a minimal effect on pyrolysis yield as the pyrolysis percentages are very similar to non-catalytic silica sand [23]. ...
... Moreover, Primary pyrolysis and secondary pyrolysis were taken into consideration for the pyrolysis of LDPE fuel conversion. Gas, char, tar, and wax percentages vary according to the bed material for both the Beechwood and LDPE pyrolysis process and this variation is accounted for in the present study to model the catalytic effect of bed materials [20,22,23]. Various scalars from existing literature were used in this study to model the solid fuel conversion process [29,35]. ...
In this work, a simplified comprehensive three-dimensional numerical model is developed to study the effect of hydrogen production on co-gasification of biomass and low-density polyethylene (LDPE). CFD software AVL Fire 2020 inbuilt algorithms were employed to develop the gas phase while the solid phase was developed by user-defined FORTRAN subroutines. Solid hydrodynamics, fuel conversion, homogenous and non-homogenous chemical reactions, and heat transfer, including radiation, subroutines were defined and incorporated into AVL FIRE explicitly. Species concentrations of the syngas were analyzed for co-gasification of Beechwood and LDPE for three distinct types of bed materials (silica sand, Na-Y zeolite, and ZSM-5 zeolite). Then, the model is validated with experiment results available in the literature for a lab-scale fluidized bed reactor. The highest hydrogen production was observed in Na-Y zeolite followed by ZSM-5 zeolite and silica in both numerical and experimental analysis for the co-gasification of Beechwood and LDPE, providing a reasonable agreement between the numerical and the experimental results. Therefore, the current model predicts the enhancement of the quality of hydrogen-rich syngas through the application of co-pyrolysis within a fluidized bed reactor, incorporating a catalytic bed material.
... In this case, 0.4-0.8 mm particle size was selected, as previous studies in the group proved the suitability of this fraction to achieve a proper fluidization regime [58,59]. The characterization of the fresh catalyst was carried out by means of BET surface area and TPR analyses. ...
... The main dimensions of both reactors can be found elsewhere [63]. It is to note that, unlike previous biomass pyrolysis and inline steam reforming studies [58,59,64,65], a non-porous draft tube was inserted in the CSBR to improve its performance, i.e., improve stability and reduce minimum spouting velocity [66]. The dimensions of this draft tube, selected according to a previous hydrodynamic study [67], are as follows: 8 mm in diameter, 5.5 mm in gas inlet diameter, 15 mm in the height of the entrainment zone and 89 mm in total height. ...
... Fernandez et al. [28] described the taming of the volatile flow by biomass fast pyrolysis to diminish the steam improving catalyst deactivation. It was revealed that the establishment of small price taming catalysts such as γ-Al 2 O 3 , disbursed FCC and olivine preceding to the reforming reactor permits softening the volatile stream, which results in altered oxygenate configuration that permits the reduction of the wild defusing of the reforming catalyst (G90). ...
... It was concluded that the elevated acidity of γ-Al 2 O 3 is appropriate for the careful splitting of the volatile segment, which is accountable for coke development. It was also concluded that in the early stage H 2 creation diminishes on taking γ-Al 2 O 3 as conditioning catalyst while the constancy of the reforming G90 catalyst is improved, which leads to a feasible retentive interval of the reaction stage [28]. Gao et al. [29] described the improvement and usage of Ni-M/ sepiolite catalysts in biomass pyrolysis to create the syngas. ...
Energy demand is increasing day by day alongside the increased level of pollution due to combustion of conventional energy sources available. This increasing energy demand led us to find some alternate energy resources such as Biomass, Solar energy, Wind energy. Biomass is one of the most abundant sources of energy, which is easily available. During this review, firstly the biomass (mainly lignocellulosic biomasses) and its availability are being studied by taking into the consideration of pre-processing requirements to produce useful energy. Afterwards, the methods to convert biomass into useful energy were studied. Lastly, the tar elimination approaches were studied by using catalysts.KeywordsBiomassThermochemical conversionTar formationCatalytic conversion
... Various reactor configurations have been introduced for in-situ or ex-situ steam reforming of tar, including two-stage fixed bed systems (Cao et al., 2014;Chen et al., 2016;Dharma et al., 2016;Gao et al., 2021b) and fluidized bed-fixed bed systems (Xiao et al., 2011). These configurations can be coupled with other reactor types, such as continuous screw kiln reactors (Efika et al., 2012), spouted bed-fluidized bed reactors (Arregi et al., 2018;Santamaria et al., 2020), and conical spouted bed reactors (Fernandez et al., 2022), to reform the volatile matter produced during biomass pyrolysis or gasification. However, the process faces technical challenges such as catalyst deactivation (Liu et al., 2017) and low mechanical strength and instability of the catalyst within reactors (e.g., fixed bed reactors) (Guan et al., 2016). ...
Chemical and biomass processing systems release volatile matter compounds into the environment daily. Catalytic reforming can convert these compounds into valuable fuels, but developing stable and efficient catalysts is challenging. Machine learning can handle complex relationships in big data and optimize reaction conditions, making it an effective solution for addressing the mentioned issues. This study is the first to develop a machine-learning-based research framework for modeling, understanding, and optimizing the catalytic steam reforming of volatile matter compounds. Toluene catalytic steam reforming is used as a case study to show how chemical/textural analyses (e.g., X-ray diffraction analysis) can be used to obtain input features for machine learning models. Literature is used to compile a database covering a variety of catalyst characteristics and reaction conditions. The process is thoroughly analyzed, mechanistically discussed, modeled by six machine learning models, and optimized using the particle swarm optimization algorithm. Ensemble machine learning provides the best prediction performance (R2 > 0.976) for toluene conversion and product distribution. The optimal tar conversion (higher than 77.2%) is obtained at temperatures between 637.44 and 725.62 {\deg}C, with a steam-to-carbon molar ratio of 5.81-7.15 and a catalyst BET surface area 476.03-638.55 m2/g. The feature importance analysis satisfactorily reveals the effects of input descriptors on model prediction. Operating conditions (50.9%) and catalyst properties (49.1%) are equally important in modeling. The developed framework can expedite the search for optimal catalyst characteristics and reaction conditions, not only for catalytic chemical processing but also for related research areas.
... Various reactor configurations have been introduced for in-situ or ex-situ steam reforming of tar, including two-stage fixed bed systems (Cao et al., 2014;Chen et al., 2016;Dharma et al., 2016;Gao et al., 2021b) and fluidized bed-fixed bed systems (Xiao et al., 2011). These configurations can be coupled with other reactor types, such as continuous screw kiln reactors (Efika et al., 2012), spouted bed-fluidized bed reactors (Arregi et al., 2018;Santamaria et al., 2020), and conical spouted bed reactors (Fernandez et al., 2022), to reform the volatile matter produced during biomass pyrolysis or gasification. However, the process faces technical challenges such as catalyst deactivation (Liu et al., 2017) and low mechanical strength and instability of the catalyst within reactors (e.g., fixed bed reactors) (Guan et al., 2016). ...
Hydrothermal carbonization (HTC) is a process that converts biomass into versatile hydrochar without the need for prior drying. The physicochemical properties of hydrochar are influenced by biomass properties and processing parameters, making it challenging to optimize for specific applications through trial-and-error experiments. To save time and money, machine learning can be used to develop a model that characterizes hydrochar produced from different biomass sources under varying reaction processing parameters. Thus, this study aims to develop an inclusive model to characterize hydrochar using a database covering a range of biomass types and reaction processing parameters. The quality and quantity of hydrochar are predicted using two models (decision tree regression and support vector regression). The decision tree regression model outperforms the support vector regression model in terms of forecast accuracy (R 2 > 0.88, RMSE < 6.848, and MAE < 4.718). Using an evolutionary algorithm, optimum inputs are identified based on cost functions provided by the selected model to optimize hydrochar for energy production, soil amendment, and pollutant adsorption, resulting in hydrochar yields of 84.31%, 84.91%, and 80.40%, respectively. The feature importance analysis reveals that biomass ash/ carbon content and operating temperature are the primary factors affecting hydrochar production in the HTC process.
... In this regard, Santamaria et al. [24] have used the both conical spouted bed reactor and fluidized bed reactor to study the catalytic performance of Ni/Al 2 O 3 modified with CeO 2 and MgO promoters during the steam reforming of biomass. Likewise, Fernandez et al. [25] have developed an integrated reaction system for H 2 production from biomass pyrolysis combined with inline the steam reforming by using a conical spouted bed reactor and an in-line fixed bed reactor. Furthermore, Efika et al. [26] investigated a two-stage continuous screw-kiln reactor-fixed bed reactor for the production of syngas from the pyrolysis of waste wood and subsequent catalytic steam reforming. ...
Biomass to green H2 is a promising strategy to achieve clean energy. This study proposed a novel concept of enhancing H 2 production and tar removal via biomass gasification coupled with inline co-steam reforming (BGCSR) process. Varying gasification/pyrolysis biochar materials (G/PCMs) were applied assisted-reforming agents and co-reactants at the steam reforming stage in the BGCSR process. First, four representative biomass categories (wheat straw, microalgae, sewage sludge, and cow manure) were subjected to BGCSR process. Microalgae presented the more positive synergistic effect on H2 production and tar reduction. It was noticed that microalgae subjected to BGCSR in the presence of G/PCMs showed the comparable H 2 concentration (over 56 vol %). The highest cumulative gas yield (104.17 mmol/g) and H2 yield (59.55 mmol/g) were manifested in the presence of C[F900], with the highest synergistic effect of 16.02% and 19.74%, respectively. C[F900] also presented the most significant synergistic effect (13.81%) on tar elimination. There outcomes were in relation to the properties of G/PCMs, e.g., elemental compositions, inherent alkali and alkaline earth metals (AAEMs), and surface functional groups. In addition, reaction mechanism regarding BGCSR was elucidated. Overall, this study provided a novel and effective way to valorize biomass into H2-enriched gas whilst minimizing tar formation.
... A wide variety of reactor configurations has been used in the literature for biomass pyrolysis and in-line reforming such as a combination of two fixed beds [347,348], fluidized and fixed bed [349], screw kiln and fixed bed [350], spouted and fluidized bed [351,352] and spouted and fixed bed [353]. Fig. 22 shows the combination of conical spouted bed and fluidized bed reactors for the pyrolysis-reforming strategy. ...
In the current energy scenario, the production of heat, power and biofuels from biomass has become of major interest. Amongst diverse thermochemical routes, gasification has stood out as a key technology for the large-scale application of biomass. However, the development of biomass gasification is subjected to the efficient conversion of the biochar and the mitigation of troublesome by-products, such as tar. Syngas with high tar content can cause pipeline fouling, downstream corrosion, catalyst deactivation, as well as adverse impact on health and environment, which obstruct the commercialization of biomass gasification technologies. Since the reduction of tar formation is a key challenge in biomass gasification, a comprehensive overview is provided on the following aspects, which particularly include the definition and complementary classifications of tar, as well as possible tar formation and transformation mechanisms. Moreover, the adverse effects of tar on downstream applications, human health or environment, and tar analyzing techniques (online and off-line) are discussed. Finally, the primary tar removal strategies are summarized. In this respect, the effect of key operation parameters (temperature, ER and S/B), catalysts utilization (natural and supported metal catalysts) and the improvement of reactor design on tar formation and elimination was thoroughly analyzed.
... However, the main challenge in syngas production from biomass catalytic fast pyrolysis is the fast deactivation of catalyst by coke formation [31,32]. To overcome this problem, most efforts have been focused on the development of suitable catalysts, which entails selection of optimum supports, promoters and metal active sites. ...
A novel pyrolysis followed by in-line cascaded catalytic reforming process without additional steam was developed to produce high-purity syngas from woody biomass. The key to the proposed process is the construction of a cascaded biochar + NiAl2O4 catalytic reforming process in which biochar acts as a pre-reforming catalyst, and NiAl2O4 acts as a primary reforming catalyst. The large oxygenates in the pyro-vapors are deeply cracked in the biochar layer due to the increased residence time in the hot-biochar bed. The remaining small molecules are then reformed with the autogenerated steam from pyrolysis catalyzed by the reduced Ni⁰ species in the NiAl2O4 catalyst (NiAlO). The results showed that the yield of syngas for the optimized process was 71.28 wt% (including 44.44 mg-H2/g-biomass and 536.48 mg-CO/g-biomass), and the CO2 yield of the process was only 3 kg-CO2/kg-hydrogen. High-purity syngas with 89.47 vol% of (H2 + CO) was obtained, and the gas energy conversion efficiency (GECE) of the process reached 75.65%. The study shows that in the cascaded catalytic reforming process, cracking of the large oxygenates and reforming of the small molecules are promoted sequentially in separated biochar + NiAlO catalyst layers, which maximizes the syngas production and improves the activity and stability of the Ni-based catalyst.
... Biomass is a kind of renewable feedstock that can realise carbon-neutrality by consuming nearly the same amount of CO 2 during growth compared to the CO 2 released during energy production [17,41]. It has been developed as a worldwide trend to investigate technologies using biomass for energy production with higher efficiency and economic benefit. ...
Excessive utilisation of fossil fuels to meet increasing energy demand results in increasing global CO2 emissions. It is a promising solution to apply carbon capture and utilisation (CCU) for pyrolysis/gasification of biomass and waste plastics, which recycles captured CO2 from pyrolysis/gasification to the reforming stage to serve as the second gasification agent. This paper aims to analyse the potential of combining the pyrolysis/gasification process with CCU and to investigate how to improve this process through process simulation using Aspen Plus®. Process analysis is carried out based on the validated model to investigate the impact of recycling captured CO2 on the product gas production and CO2 conversion when changing various operating conditions (i.e. the amount of recycled CO2, reforming temperature and steam-to-feed ratio). The target is to ensure high H2 production and to promote CO2 conversion. Simulation results indicated that: (i) Applying CCU for pyrolysis/gasification can inhibit the production of H2 andCO2, but it can promote the production of CO; (ii) The H2/CO ratio of gas products can be adjusted flexibly after recycling CO2 to the reforming stage; (iii) Increase of CO2 recycle amount and steam-to-feed ratio results in lower CO2 conversion while the increase of reforming temperature improves the CO2 conversion; (iv) It is suggested to add solid carbon (e.g. bio-char or carbon-based catalyst) in the reforming stage together with adjusting the operating conditions (i.e. relatively high reforming temperature (e.g. 600 ∼ 700 °C) and low steam-to-feed ratio (e.g. 3 ∼ 4)) simultaneously to protect H2 production and achieve high CO2 conversion. The findings in this paper will be very useful for future large-scale commercial deployment of applying CCU for pyrolysis/gasification.
... Although attrition and elutriation create problems in the fluidized bed, they have been documented by various researchers, using a spouted bed reactor was able to solve elutriation (Cortazar et al., 2019;Fernandez et al., 2022). According to their findings, the reactor's dust output was kept to a minimum, and dolomite loss was also kept to a minimum. ...
Fossil fuels are currently the dominant source of electricity and energy production around the world. Biomass is one of the most referred renewable carbonaceous resource(s) that can be employed for the waste-to-energy concept. Syngas obtained from biomass gasification can be utilized for a variety of key industrial purposes, including internal gasification engine operation, power generation, and hydrocarbon compound production using the Fisher-Tropsch technique. However, the existence of impurities such as hydrogen sulfide, tar, and particulate matter along with other undesirable chemicals present in syngas are major disadvantages of biomass gasification. Tar is the most difficult among all the pollutants to be removed from syngas; it also causes serious problems in downstream syngas applications. For decades, studies have been done with various catalysts to remove the tar. Dolomite has shown positive response for tar elimination and hydrogen-enriched gas production. Several studies have been carried out on dolomite for eliminating the tar from syngas. This review encompasses sources of solid waste, the mechanism of catalysis, and in-situ and ex-situ usage of dolomite in the gasification process. It addresses the key issues such as fragmentation and attrition, elutriation, and coke formation along with dolomite's usefulness in amalgamation with other catalysts, environmental consequences, and economic viability of dolomite applications. It also discusses the challenges and opportunities for tar removal using catalysts, with a specific focus on dolomite along with economic and environmental sustainability considerations.
... There are many studies concerning the thermal process mentioned with respect to different experimental conditions such as temperature, residence time, particle size of materials, type of reactor, presence of catalyst, etc. One of the most interesting investigations is solar pyrolysis [10], catalyst applications [11,12], and subcritical and supercritical water gasification [13]. The management of biomass waste using the pyrolysis process has been widely studied by Poskart et al. [14]. ...
This study presents the results of the biomass pyrolysis process focusing on biochar production and its potential energetic (as solid fuel) and material (as adsorbent) applications. Three kinds of biomass waste were investigated: wheat straw, spent coffee grounds, and brewery grains. The pyrolysis process was carried out under nitrogen atmosphere at 400 and 500 °C (residence time of 20 min). A significant increase in the carbon content was observed in the biochars, e.g., from 45% to 73% (at 400 °C) and 77% (at 500 °C) for spent coffee grounds. In addition, the structure and morphology were investigated using scanning electron microscopy. Thermal properties were studied using a simultaneous thermal analysis under an oxidising atmosphere. The chemical activation was completed using KOH. The sorption properties of the obtained biochars were tested using chromium ion (Cr3+) adsorption from liquid solution. The specific surface area and average pore diameter of each sample were determined using the BET method. Finally, it was found that selected biochars can be applied as adsorbent or a fuel. In detail, brewery grains-activated carbon had the highest surface area, wheat straw-activated carbon adsorbed the highest amount of Cr3+, and wheat straw chars presented the best combustion properties.
Catalytic fast pyrolysis of cassava stalks has been intriguing as a promising, feasible chemical refinery method in terms of waste-to-energy conversion from cassava cultivation. This study aims to determine the synergetic influence of Mo and Co on Ni catalysts (Ni, Ni–Mo, and Ni–Co) prepared via ultrasonic-assisted incipient wetness impregnation method for catalytic pyrolysis vapor upgrading. The results indicated that Co and Mo enhance the reducibility of NiO and promote weak-to-medium acidity, thereby enhancing Ni's performance. Mono-Ni favors cracking deoxygenation, whereas oxophilicity promoters particularly enhance the oxygen absorbability efficiency to selective deoxygenated production. A fine Ni dispersion on CoNi/SiO2 catalyst was observed to positively affect the production of monoaromatic hydrocarbons (46.10 %), in contrast to those without promoters (21.63 %). This is attributed to an optimal Ni-metallic distribution with a small crystal size of 7.01 nm and a high surface area of 342.6 m2 g−1, highlighting the effectiveness of the promoter-assisted Ni catalyst. Additionally, a high yield of H2 (66.9 %) in non-condensable gas was recorded at 550 °C. The study suggests that a simplified approach to developing Ni-based catalysts could enhance the eco-friendliness of commercial catalysts, thereby facilitating the scale-up of biomass pyrolysis applications.
The performance of TCC for nominally flat metallic contacts has been predicted using an artificial neural network (ANN) model. Experimental inputs and outputs from a previous work of one of the authors, Tariq and Asif (2019) are employed in the ANN model to predict the results. Therefore, inputs to the model include effective thermal conductivity, Vickers hardness, reduced modulus of elasticity, RMS roughness, Average asperity slope, and contact pressure, while Solid spot conductance, drop in temperature across the border, and percentage thermal loss are the model's outputs. Experiments on the performance of thermal contact conductance are carried out, with the test results serving as target data for training the ANN model. ANN results forecasts are shown to be in good agreement with the experimental test results.KeywordsArtificial Neural NetworkPerformance PredictionThermal Contact Conductance
Chemical and biomass processing systems release volatile matter compounds into the environment daily. Catalytic reforming can convert these compounds into valuable fuels, but developing stable and efficient catalysts is challenging. Machine learning can handle complex relationships in big data and optimize reaction conditions, making it an effective solution for addressing the mentioned issues. This study is the first to develop a machine-learning-based research framework for modeling, understanding, and optimizing the catalytic steam reforming of volatile matter compounds. Toluene catalytic steam reforming is used as a case study to show how chemical/textural analyses (e.g., X-ray diffraction analysis) can be used to obtain input features for machine learning models. Literature is used to compile a database covering a variety of catalyst characteristics and reaction conditions. The process is thoroughly analyzed, mechanistically discussed, modeled by six machine learning models, and optimized using the particle swarm optimization algorithm. Ensemble machine learning provides the best prediction performance (R2 > 0.976) for toluene conversion and product distribution. The optimal tar conversion (higher than 77.2%) is obtained at temperatures between 637.44 and 725.62 °C, with a steam-to-carbon molar ratio of 5.81–7.15 and a catalyst BET surface area of 476.03–638.55 m2/g. The feature importance analysis satisfactorily reveals the effects of input descriptors on model prediction. Operating conditions (50.9%) and catalyst properties (49.1%) are equally important in modeling. The developed framework can expedite the search for optimal catalyst characteristics and reaction conditions, not only for catalytic chemical processing but also for related research areas.
In steam reforming of organics in a fixed-bed reactor, catalyst particles in varied location of catalyst bed will experience different history of contacting with reactants/products. This may affect accumulation of coke in varied section of catalyst bed, which are investigated in steam reforming of some typical oxygen-containing organics (acetic acid, acetone and ethanol) and hydrocarbons (n-hexane and toluene) in a fixed-bed reactor with double layers of catalyst bed for investigating coking depth at 650 °C over Ni/KIT-6 catalyst in this study. The results indicated that the intermediates derived from the oxygen-containing organics in steam reforming could hardly penetrate the upper-layer catalyst to form coke in the lower-layer catalyst. In converse, they reacted quickly over the upper-layer catalyst via gasification or coking, forming coke almost exclusively in the upper-layer catalyst. The hydrocarbon intermediates from the dissociation of hexane or toluene could easily penetrate and reach the lower-layer catalyst to form even more coke therein than the upper-layer catalyst. The characterization showed that the insufficient gasification of *CxHy species led to their aggregation/integration to form more aromatic coke, especially from n-hexane. The aromatic-ring containing intermediates from toluene tended to integrate with *OH species to form ketones that further involved in coking, forming coke of less aromatic nature than that from n-hexane. Steam reforming of oxygen-containing organics also produced oxygen-containing intermediates and coke of higher aliphatic nature, lower carbon to hydrogen (C/H) ratio, lower crystallinity and thermal stability.
Recovering beneficial metal ions from industrial effluents by suitable support can be an efficient and environment-friendly way to prepare specific catalysts directly. Herein, modified lignite was developed as an ion exchange material and used to prepare Co-Cu bimetallic catalysts for hydrogen-rich syngas production from steam reforming reactions. For all the catalysts studied, Co75Cu15/600 (carbonization temperature at 600 oC) exhibits the optimal catalytic activity and stability in both steam reforming of toluene and biomass tar under low temperatures. Fresh and spent catalysts were detailedly characterized to investigate the metal interactions and catalyst deactivation. The introduction of Cu contributes to the formation of Co-Cu alloy and the lower particle size of Co (4.17 nm), thereby suppressing the carbon deposition, the oxidation of metals and the change of catalyst structure after reaction. Therefore, the inexpensive and readily-available Co-Cu/C has the potential to serve as a promising catalyst for large-scale biomass gasification technology.
The rise of consumption of traditional fossil fuels has caused emissions of greenhouse gas and deterioration of air quality. Biomass is a promising substitute for fossil fuels because biomass provides biofuels and chemicals by thermochemical conversion such as pyrolysis. In particular, fast pyrolysis of biomass cellulose into chemicals and biofuels has recently drawn attention. Issues of commercialization of fast pyrolysis products include low heating value, low stability, and high oxygen content and acidity. Consequently, new catalysts for enhanced cellulose conversion are sought for. Here, we review the production of biofuel and renewable chemicals from cellulose pyrolysis using acidic and basic catalysts. Acidic catalysts are more suitable to produce biofuels containing about 50% aromatic hydrocarbons, compared to basic catalysts which give biofuels containing 15% aromatic hydrocarbons. Basic catalysts are preferred to produce renewables chemicals, particularly ketone compounds. We explain the mechanism of cellulose pyrolysis with acidic and basic catalysts. The strong acid sites on the catalyst facilitate high selectivity for aromatic compounds in the pyrolysis oil, whereas basic active sites induce double-bond migration, increase carbon-coupling reactions, and ketone production.
Thermo‐catalytic reforming (TCR®) is a promising conversion technology for the production of liquid bio‐fuels. The process is a proven opportunity to convert biological wastes and residues into hydrogen‐rich syngas, high‐quality oil, and char without volatiles. Bio‐oil produced from TCR® has a high carbon content, low water content, low oxygen content, and a high heating value; it is therefore directly applicable as feed in boilers or as blend in dual fuel engines. A feasible opportunity for using bio‐oil in automotive combustion engines is a further upgrade step to bio‐fuel by hydrogenation. During this hydrotreatment, heterogeneous atoms like sulfur, nitrogen, and oxygen are removed or substituted with hydrogen. Fraunhofer UMSICHT already produces gasoline and diesel that comply with European fuel standards EN 228 and EN 590, using different catalysts like NiMo/Al2O3, CoMo/Al2O3, and Ru/C for hydrogenation at 643 K and a constant hydrogen pressure of 14 MPa. Various hydrocarbons and benzene derivatives are verified after hydrotreating. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.
Hydrogen production from the thermochemical conversion has been considered as a key and the most promising technology for the use of biomass, and some novel methods are also being developed to low cost and high efficiency. This review presents the recent progress on the studies for hydrogen production from different kinds of biomass by pyrolysis, gasification and steam reforming without and/or with chemical-looping technologies. Considering potential applications, the Ni-based catalysts made of cheap and earth abundant elements are especially important for economically viable hydrogen production from biomass by the thermochemical conversion, and also can effectively be compensated and modified to some extent by using extremely low noble metals loading for retaining high catalytic activity, high coke resistance and long terms ability. The catalyst modification strategies by adding other metals, minimizing Ni particles sizes and improving the supports are highlighted. The sorption-enhanced steam reforming (SESR) and chemical looping steam reforming (SE-CLSR) processes with in-situ CO2 removal using different reactors has been considered to change the normal equilibrium limits of water gas shift (WGS) reaction, and thus increase feedstock conversion and processes performances. The auto-thermal operating condition and CO2 capture during hydrogen production can be achieved by chemical looping processes with cyclic oxidation-reduction of oxygen carriers (OCs). The paper discusses the related issues, challenges and prospects, along with the possible solutions in order to help in the development of efficient hydrogen production from thermochemical conversion of biomass.
The pyrolysis-catalytic steam reforming of six agricultural biomass waste samples as well as the three main components of biomass was investigated in a two stage fixed bed reactor. Pyrolysis of the biomass took place in the first stage followed by catalytic steam reforming of the evolved pyrolysis gases in the second stage catalytic reactor. The waste biomass samples were, rice husk, coconut shell, sugarcane bagasse, palm kernel shell, cotton stalk and wheat straw and the biomass components were, cellulose, hemicellulose (xylan) and lignin. The catalyst used for steam reforming was a 10 wt.% nickel-based alumina catalyst (NiAl2O3). In addition, the thermal decomposition characteristics of the biomass wastes and biomass components were also determined using thermogravimetric analysis (TGA). The TGA results showed distinct peaks for the individual biomass components, which were also evident in the biomass waste samples reflecting the existence of the main biomass components in the biomass wastes. The results for the two-stage pyrolysis-catalytic steam reforming showed that introduction of steam and catalyst into the pyrolysis-catalytic steam reforming process significantly increased gas yield and syngas production notably hydrogen. For instance, hydrogen composition increased from 6.62 to 25.35 mmol g-1 by introducing steam and catalyst into the pyrolysis-catalytic steam reforming of palm kernel shell. Lignin produced the most hydrogen compared to cellulose and hemicellulose at 25.25 mmol g-1. The highest residual char production was observed with lignin which produced about 45 wt.% char, more than twice that of cellulose and hemicellulose.
Recent advances in lignocellulosic biomass valorization for producing fuels and commodities (olefins and BTX aromatics) are gathered in this paper, with a focus on the conversion of bio‐oil (produced by fast pyrolysis of biomass). The main valorization routes are: (i) conditioning of bio‐oil (by esterification, aldol condensation, ketonization, in situ cracking, and mild hydrodeoxygenation) for its use as a fuel or stable raw material for further catalytic processing; (ii) production of fuels by deep hydrodeoxygenation; (iii) ex situ catalytic cracking (in line) of the volatiles produced in biomass pyrolysis, aimed at the selective production of olefins and aromatics; (iv) cracking of raw bio‐oil in units designed with specific objectives concerning selectivity; and (v) processing in fluidized bed catalytic cracking (FCC) units. This review deals with the technological evolution of these routes, in terms of catalysts, reaction conditions, reactors, and product yields. A study has been carried out on the current state‐of‐knowledge of the technological capacity, advantages and disadvantages of the different routes, as well as on the prospects for the implementation of each route within the scope of the Sustainable Refinery. © 2018 Society of Chemical Industry
Biomass pyrolysis is a promising renewable sustainable source of fuels and petrochemical substitutes. It may help in compensating the progressive consumption of fossil-fuel reserves. The present article outlines biomass pyrolysis. Various types of biomass used for pyrolysis are encompassed, e.g., wood, agricultural residues, sewage. Categories of pyrolysis are outlined, e.g., flash, fast, and slow. Emphasis is laid on current and future trends in biomass pyrolysis, e.g., microwave pyrolysis, solar pyrolysis, plasma pyrolysis, hydrogen production via biomass pyrolysis, co-pyrolysis of biomass with synthetic polymers and sewage, selective preparation of high-valued chemicals, pyrolysis of exotic biomass (coffee grounds and cotton shells), comparison between algal and terrestrial biomass pyrolysis. Specific future prospects are investigated, e.g., preparation of supercapacitor biochar materials by one-pot one-step pyrolysis of biomass with other ingredients, and fabricating metallic catalysts embedded on biochar for removal of environmental contaminants. The authors predict that combining solar pyrolysis with hydrogen production would be the eco-friendliest and most energetically feasible process in the future. Since hydrogen is an ideal clean fuel, this process may share in limiting climate changes due to CO2 emissions.
Keywords: Sustainable and renewable energy sources; Fossil-fuel alternatives; Biomass
pyrolysis; Biofuel (bio-oil, biogas, biochar); Charcoal (activated carbon); Hydrogen fuel
The characterization of coke, and its types, deposited on a Ni/La2O3-αAl2O3 catalyst used in the steam reforming of bio-oil has been studied by temperature programmed oxidation (TPO) coupled with different in-situ techniques: thermogravimetry (TG), modulated thermogravimetry (MTG), FTIR spectroscopy with mass spectrometry (MS), Raman spectroscopy, and differential scanning calorimetry (DSC). The steam reforming of bio-oil was carried out in a reactor equipment with two steps in series, comprising the bio-oil is thermal treatment (500 ºC) and subsequent reforming in a fluidized bed reactor (550-700 ºC; and steam-to-carbon ratio, 1.5-6). TG/MS-TPO experiments identify encapsulating and filamentous coke, and a more detailed analysis using other in-situ techniques enable to characterize the nature and location of 4 types of coke: (i) an encapsulating coke with aliphatic nature placed in the most superficial layers; (ii) an encapsulating coke with higher aromatic nature in inner layers; (iii) the most superficial layers of a filamentous coke, further from active sites and with a more carbonized structure compared to encapsulating coke; (iv) an innermost and mainly polyaromatic filamentous coke with a low oxygenates content.
The steam pyrolysis of pinewood sawdust has been conducted in a bench scale plant provided with a conical spouted bed reactor (CSBR). This process is of uttermost relevance for the in-line valorisation of pyrolysis volatiles, specifically for their catalytic steam reforming for hydrogen production. The influence of temperature on he product yields has been analysed in the 500-800 ºC range. A detailed analysis of the gaseous stream (condensable and non-condensable components) has been carried out by chromatographic techniques, and the char samples have been characterized by ultimate and proximate analyses, N2 adsorption-desorption, and Scanning Electron Microscopy.
A high bio-oil yield was obtained at 500 ºC (75.4 wt.%), which is evidence of the suitable features of the conical spouted bed reactor for this process. As temperature was increased, higher gas and lower liquid and char yields were obtained. Steam was fully inert at low pyrolysis temperatures (500-600ºC), and only had a little influence at 700ºC due to the low gas residence time in the conical spouted bed reactor. At 800 ºC, the reaction mechanism was controlled by gasification reactions.
The composition of the liquid fraction was considerably influenced by pyrolysis temperature, with a less oxygenated stream as temperature was increased. Thus, phenolic compounds accounted for the major fraction at low pyrolysis temperatures, whereas hydrocarbons prevailed at 800 ºC. The char obtained in the whole temperature range can be further used as active carbon or energy source.
The performance of Fe/olivine catalysts was tested in the continuous steam gasification of sawdust in a bench scale plant provided with a fountain confined conical spouted bed reactor at 850 °C. Olivine was used as catalyst support and loaded with 5 wt% Fe. The activity and stability of the catalyst was monitored by nitrogen adsorption-desorption, X-ray fluorescence spectroscopy (XRF), temperature programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques, which were conducted before and after the runs. The fountain confined conical spouted bed performs well in the biomass steam gasification with primary catalysts. In fact, this reactor allows enhancing the gas-solid contact, and therefore the catalytic activity by avoiding the elutriation of fine catalyst particles. The uncatalysed efficiency of the gasification process, assessed based on the gas production and composition, H2 production, tar concentration and composition, and carbon conversion efficiency, was consideraby improved on the Fe/olivine catalyst, with tar reduction being especially remarkable (to 10.4 g Nm⁻³). After 140 min on stream, catalyst deactivation was particularly evident, as tar concentration increased to 19.84 g Nm⁻³ (90% of that without catalyst). However, Fe/olivine catalyst was still active for WGS and CH4 steam reforming reactions, with gas and H2 productions being 1.35 Nm³ kg⁻¹ and 5.44 wt%, respectively. Metal iron oxidation to Fe3O4 caused catalyst deactivation, as the reaction environment shifted from oxidizing to reducing conditions due to operational limitations.
Biomass pyrolysis and the in-line catalytic cracking of the pyrolysis volatile stream has been approached in this study. The pyrolysis step was carried out in a conical spouted bed reactor at 500 °C, whereas the inert sand or the cracking catalysts (γ-Al2O3, spent FCC and olivine) were placed in a fixed bed reactor at 600 °C. Product analysis was carried out on-line by means of chromatographic methods, and the distribution and composition of the main products obtained have been related to the features characterizing each catalyst (physical properties, chemical composition and acidity).
Decarbonylation reactions were favoured over decarboxylation ones when acid catalysts (spent FCC and γ-Al2O3) were used, whereas olivine promoted ketonization and aldol condensation reactions. The Fe species in the olivine structure enhanced reforming and WGS reactions. Bio-oil cracking was more severe as catalyst acidity was increased, leading to an increase in the hydrocarbon fraction. The Al2O3 derived bio-oil was substantially deoxygenated, with a considerable reduction in the phenolic fraction, which accounted mainly for alkyl-phenols. The three materials tested led to a significant decrease in acid and phenolic compounds in the volatile stream, making it suitable for further catalytic valorization for the production of H2, fuels and chemicals.
In the last few decades, the production of value-added chemicals from biomass has become a key research focus. Biomass gasification into syngas and further for methane, methanol, and C2+ alcohols production has already proved to be promising for utilization of renewable energy. Therefore, heterogeneous catalyst design and optimization are extremely significant for solving the issues of tar formation during biomass gasification. Apart from alkali metals, natural minerals, and synthetic catalysts, char and char supported catalysts prepared from residual biomass or coal have been already proved to be effective for tar reforming due to their relative chemical inertness, cheap price, excellent pore structures, etc. Advantageously, bio−/coal char could be modified and/or functionalized with heteroatoms doping and metal addition to improve activity in tar reforming. In this review, we systematically discussed the preparation, modification, and application of char catalysts in the reforming of biomass tar and tar model compounds. After that, we reviewed and compared the activity of char catalysts in tar reforming, and then we gave corresponding reactions and deactivation mechanisms over char catalysts in biomass tar reforming. Finally, we proposed existed challenges and shared our perspectives regarding future needs in char catalysts design for accelerating fuel sustainability and green development.
Biomass gasification has been a widely explored research area due to world energy security and environmental concerns. It is also found to be commercially viable process for synthetic gas (syngas) production. Different types of gasifiers based on fluid dynamics, modes of heat transfer to the gasification process, gasification agents, and temperature have been studied. Dual fluidized bed gasifiers are one of the recent technologies which can produce syngas of medium heating value (12–20 MJ/Nm³), thereby proving to be industrially more feasible. This review presents analysis of different designs and configurations of dual fluidized bed gasifiers. The impact of different operating conditions, the effect of tar formation, tar abatement techniques and different modeling approaches have been critically evaluated. The present review gives a holistic view on the current research and developments of dual fluidized bed gasification systems for syngas production.
The influence of the metal selected as catalytic active phase in the two-step biomass pyrolysis-catalytic reforming strategy has been analyzed. The pyrolysis step was carried out in a conical spouted bed reactor at 500 °C, whereas steam reforming was performed in a fluidized bed reactor at 600 °C. Ni/Al2O3, Co/Al2O3 and two bimetallic Ni-Co/Al2O3 catalysts with different metal loadings were synthesized by wet impregnation method, and fresh and deactivated catalysts were characterized by N2 adsorption/desorption, X-ray Fluorescence (XRF), Temperature Programmed Reduction (TPR), X-Ray powder Diffraction (XRD), Temperature Programmed Oxidation (TPO), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Although Ni/Al2O3 and both bimetallic catalysts had similar initial activity in terms of oxygenate conversion, (higher than 98%), the poorer metal dispersion observed in both bimetallic catalysts led to a fast decrease in conversion due to the promotion of coke formation on large particles. This occurred even though Ni–Co alloy formation has a positive influence by hindering the oxidation of Co⁰ species. The main cause for the deactivation of these catalysts is the formation of a coke with amorphous structure. The poor initial performance of Co/Al2O3 catalyst is related to changes in the Co⁰ oxidation state induced by the presence of steam, which led to a fast deactivation of this catalyst.
The performance of fixed and fluidized bed reactors in the steam reforming of biomass fast pyrolysis volatiles was compared, with especial attention paying to the differences observed in catalysts deactivation. The experiments were carried out in continuous regime in a bench scale unit provided with a conical spouted bed for the pyrolysis step. They were carried out on a Ni-Ca/Al2O3 commercial catalyst and under optimum conditions determined in previous studies, i.e., pyrolysis temperature 500 °C, reforming temperature 600 °C and a steam/biomass ratio of 4. Moreover, the influence of space time was analysed in both reforming reactors. The fixed bed reactor showed higher initial conversion and H2 yield, as it allowed attaining a H2 yield higher than 90 % with a space time of 10 gcat min g vol⁻¹. However, a space time of 15 gcat min g vol⁻¹ was required in the fluidized bed to obtain a similar H2 yield. Moreover, the fixed bed also led to lower catalyst deactivation. Catalyst deactivation was mainly related to coke deposition, and higher coke contents were observed in the catalysts used in the fluidized bed reactor (1.2 mgCOKE gcat⁻¹ gbiomass⁻¹) than those in the fixed bed one (0.6 mgCOKE gcat⁻¹ gbiomass⁻¹). Therefore, the differences in the performance of the two reactors were analysed and their practical interest was discussed.
This paper investigated the performance of HF modified HZSM-5 supported nickel catalysts (Ni/FZ5) in steam reforming of toluene (TSR) and biomass pyrolysis tar (BSR). The mesopores volume of support increased from 0.021 to 0.061 cm³/g with decreasing acid amount from 2.27 to 0.41 mmol/g after HF treatment. Catalysts with different Ni loadings were prepared and characterized. The Ni/FZ5 with Ni loading of 9 wt.% possesses relatively large specific surface area (337 m²/g) and average pore size (2.91 nm), as well as small Ni particle size (23 nm) and high dispersion. In the process of TSR, 9Ni/FZ5 was kept above 70% for 7h. Owing to the calculated lower apparent activation energy (30.76 KJ/mol), 9Ni/FZ5 exhibited the best performance in BSR at 650 oC, achieving the largest H2 yield of 52.8 mmol/g and the highest selectivity of H2 at 72.8%. Additionally, only 1.6 mg/gcatalyst of coke deposition was detected. Moreover, its high activity was still identified with excellent hydrothermal stability even after 7 times of regeneration. All findings suggest that 9Ni/FZ5 is a promising catalyst for biomass tar cracking.
Sugars and the derivatives of sugars are important fractions in bio-oil, understanding coking behaviors of which are important for development of the robust coking–resistant catalyst for steam reforming of bio-oil. In this study, steam reforming of glucose, xylose, acetic acid and furfuryl alcohol (FA) was carried out, aiming to correlate coking behaviors with molecular structure of these organics. Acetic acid, as a small aliphatic molecule, could be effectively reformed and produced the lowest amount of coke deposit. The carbonyl functionality, the multiple hydroxyl groups in the sugars and the furan ring in FA made polymerisation/cracking to form coke as the dominant reaction route in their steam reforming, diminished hydrogen production while led to rapid catalyst deactivation. The coke formed from acetic acid and FA was more aromatic, containing more CC species, while that from glucose and xylose was more aliphatic, containing more carbonyl functionalities, which projected structural characteristics of the feedstock. In addition, morphologies of the coke formed from acetic acid was mainly carbon nanotube. In comparison, the coke from the sugars and FA was mainly the amorphous coke with cobalt particles wrapped inside, which was more thermally stable, especially for that from FA, relating to the aromatic ring in FA.
A Ni/Al2O3 catalyst has been modified incorporating CeO2 and MgO promoters in order to improve its performance in the steam reforming of biomass pyrolysis volatiles. Ni/Al2O3, Ni/CeO2-Al2O3 and Ni/MgO-Al2O3 catalysts have been prepared and fresh and deactivated catalysts have been characterized by N2 adsorption/desorption, X-ray Fluorescence (XRF), Temperature Programmed Reduction (TPR), X-ray powder diffraction (XRD), Temperature Programmed Oxidation (TPO), Transmission Electron Microscopy (TEM) and a technique based on Fourier Transform Infrared Spectroscopy-Temperature Programmed Oxidation (FTIR-TPO). The results obtained revealed a similar initial activity for the three catalysts tested (conversion higher than 98%), whereas stability has been greatly improved by incorporating CeO2 as promoter, as it enhances the gasification of coke precursors. However, Ni/MgO-Al2O3 catalyst is slightly less stable than Ni/Al2O3, presumably as a result of its lower reducibility due to the formation of MgAl2O4 spinel phase. Catalysts deactivation has been associated with coke deposition, although sintering phenomenon became also evident when the Ni/CeO2-Al2O3 catalyst was tested. The coke deposited on the catalysts does not present any specific morphology, which is evidence of its amorphous structure in the three catalysts studied.
In the future, hydrogen will be an important energy carrier and industrial raw materials. Catalytic steam reforming of bio‐oils is a promising and economically viable technology for hydrogen production. However, during the reforming process, the catalysts are usually deactivated rapidly due to the coke formation and sintering. Thus, maintaining the activity and stability of catalysts is the key issue in this process. Elemental compositions, structure and interaction of catalytic active species and supports are the dominant factors of catalyst design. In addition, operation conditions could extend the lifetime of catalysts by affecting the coke morphology or promoting the coke gasification. This article critically summarizes the recent development of catalytic steam reforming of bio‐oils, in which the operation conditions, the properties of catalysts and the effects of the supports of catalysts are mainly focused. It is expected to get insight understandings on the catalytic steam reforming of bio‐oils and provide a guidance for hydrogen production from bio‐oils.
Undoubtedly, hydrogen (H2) is a clean feedstock and energy carrier whose sustainable production should be anticipated. The pyrolysis of biomass or waste plastics and the subsequent reforming over base (transition) or noble metals supported catalysts allows reaching elevated H2 yields. However, the catalyst used in the reforming step undergoes a rapid and severe deactivation by means of a series of physicochemical phenomena, including metal sintering, metallic phase oxidation, thermal degradation of the support and, more notoriously, coke deposition. This review deals with the currently existing alternatives at the catalyst and reactor level to cope with catalyst deactivation and increase process stability, and then delves with the fundamental phenomena occurring during this catalyst deactivation. An emphasis is placed on coke deposition and its influence on deactivation, which depends on its location, chemical nature, morphology, precursors or formation mechanism, among others. We also discuss the challenges for increasing the value of the carbon materials formed and therefore, enhance process viability.
The effect of La2O3 addition on a Ni/Al2O3 catalyst has been studied in the biomass pyrolysis and in-line catalytic steam reforming process. The results obtained using homemade catalysts (Ni/Al2O3 and Ni/La2O3-Al2O3) have been compared with those obtained using a commercial Ni reforming catalyst (G90LDP). The pyrolysis step has been performed in a conical spouted bed reactor at 500 °C and the reforming one in a fluidized bed reactor placed in-line at 600 °C, using a space time of 20 gcatalyst min gvolatiles⁻¹ and a steam/biomass ratio of 4. The Ni/La2O3-Al2O3 catalyst had a better performance and higher stability than G90LDP and Ni/Al2O3 catalysts, with conversion and H2 yield being higher than 97 and 90%, respectively, for more than 90 min on stream. Nevertheless, conversion and H2 yield decreased significantly with time on stream due to catalyst deactivation. Thus, the deactivated catalysts have been characterized by N2 adsorption-desorption, X-ray diffraction (XRD), temperature programmed oxidation (TPO), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Coke deposition has been determined to be the main cause of catalyst deactivation, with the structure of the coke being fully amorphous in the three catalysts studied.
Biomass gasification converts into syngas, then into other chemicals via Fischer-Tropsch (F-T) synthesis is promising for renewable energy utilization. Although gasification is a sustainable and environmental-friendly technology for value-added utilization of biomass, tar formation is the major problem during the biomass gasification. Tar could condense on the reactor then block and foul equipment. An optimized gasifier and highly active catalyst were proved to be effective for biomass tar elimination. Furthermore, tar formation mechanism and the decomposition pathway were also important to advance the optimization of gasification reactors and catalyst design. This paper summarized the fundamentals, such as gasifier types, Ni-based catalyst, and reaction and deactivation mechanism. This review also sheds light on other excellent catalysts, effective gasifiers and mathematical models of biomass catalytic gasification, and catalyst reaction mechanisms and mathematical models are also discussed in detail. At last, the paper ends with a conclusion and prospective discussion to the latter lab and industrial-scale research.
The study aims to evaluate the catalytic potential of a Ni-based catalyst supported by magnesium slag (MS) for catalytic reforming of pyrolysis volatiles from pine sawdust. The catalysts were prepared by a wet impregnation method. The effects of different parameters (Ni loading content, calcination/catalytic bed temperature and steam to carbon (S/C) ratio) on the catalytic performance were investigated. In addition, tar cracking capability and coke deposition resistance of Ni/MS catalyst and Ni/γ-Al2O3 catalyst were explored under different calcination/catalytic bed temperatures. The catalysts were characterized by BET, XRD, SEM, TEM, TPO and Raman spectroscopy. The Ni/MS catalyst exhibited excellent catalytic reactivity as well as thermal stability. The best tar conversion (95.69%) and the highest hydrogen yield of 38.9 mmol/g biomass were obtained over Ni/MS catalyst under the conditions of Ni loading content = 3%, calcination/catalytic bed temperature = 800 °C, and S/C = 0.5. The interactions among Ni, Fe, Ca, and Mg formed multiple active centers (e.g., Ca2Fe2O5, (Ni, Mg) O solid solution and NiFe2O4) in the catalyst to show synergistic catalysis effects, thereby jointly improving catalyst activity and coke deposition resistance. Furthermore, both amorphous carbon and graphitic carbon were formed on the used catalysts and the D/G ratio (the relative intensity ratio between the D and G bands) was positively correlated with the catalytic activity.
The performances of the primary catalysts olivine, dolomite, γ-alumina and FCC spent catalyst were evaluated in the continuous steam gasification of sawdust in a bench-scale plant equipped with a fountain confined conical spouted bed reactor. The experiments were carried out at 850 °C, and the efficiency of the gasification process was defined by gas yield, H2 production, tar concentration and composition, and carbon conversion efficiency. The benefits of the fountain confiner not only helped to improve the gas-solid contact, and therefore favoured the primary catalysts’ reforming and cracking activity, but also enhanced H2 production and reduce tar formation. Thus, dolomite and γ-alumina recorded the lowest values of tar, 5.0 and 6.7 g Nm⁻³, respectively, which corresponded to 79% and 72% tar reduction compared to the inert sand, whereas olivine and the FCC spent catalyst recorded higher tar contents, 20.6 and 16.2 g Nm⁻³, respectively. It is noteworthy that light PAHs were the most abundant species in the tar (60 wt% of the whole tar content).
The present work comprehensively covers the literature that describes the thermochemical techniques of hydrogen production from biomass. This survey highlights the current approaches, relevant methods, technologies and resources adopted for high yield hydrogen production. Prominent thermochemical methods i.e. pyrolysis, gasification, supercritical water gasification, hydrothermal upgrading followed by steam gasification, bio-oil reforming, and pyrolysis inline reforming have been discussed thoroughly in view of the current research trend and latest emerging technologies. Influences of important factors and parameters on hydrogen yield, such as biomass type, temperature, steam to biomass ratio, retention time, biomass particle size, heating rate, etc. have also been extensively studied. Catalyst is a vital integrant that has received enough attention due to its encouraging influence on hydrogen production. Literature confirms that hydrogen obtained from biomass has high-energy efficiency and potential To reduce greenhouse gases hence, it deserves versatile applications in the coming future. The study also reveals that hydrogen production through steam reforming, pyrolysis, and inline reforming deliver a considerable amount of hydrogen from biomass with higher process efficiency. It has been identified that higher temperature, suitable steam to biomass ratio and catalyst type favor useful hydrogen yield. Nevertheless, hydrogen is not readily available in the sufficient amount and production cost is still high. Tar generation during thermochemical processing of biomass is also a concern and requires consistent efforts to minimize it.
© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Catalytic fast pyrolysis (CFP) is an attractive approach to convert biomass to high-quality bio-oil through the deoxygenation of pyrolysis vapors in the form of H 2 O, CO, and CO 2. However, the deoxygenation process comes at the expense of bio-oil yield. This review begins with recent progress on lignocellulosic biomass pyrolysis chemistry and techniques, and then focuses on the latest improvements to the design of advanced catalysts and novel CFP processes. It was found that basic metal oxides (e.g., MgO and CaO) are promising alternative catalysts to zeolites (such as ZSM-5) with respect to the preferred decarboxylation reaction, which merits additional investigation on their structure-function relationships in the future. Additionally, catalytic co-pyrolysis of bio-mass with waste plastics or waste tires over zeolites is an attractive approach from the viewpoint of preferred dehydration reactions and the high-value utilization of solid wastes. However, the physicochemical properties of the catalysts should be further adjusted. Furthermore, in spite of many interesting results reported in the literature , quantitatively analysis and uniform data presentation format is necessary for the further development of CFP techniques.
A study has been carried out of the influence calcination conditions of a Ni/MgO-Al2O3 catalyst have on its performance and stability in the reforming of biomass fast pyrolysis volatiles. Accordingly, the first calcination temperature subsequent to promoter impregnation on the Al2O3 has been modified from 900 to 700 °C. Subsequently, Ni was incorporated by impregnation and a second calcination was carried out at three temperatures (500, 600 and 700 °C). The performance of the different Ni/MgO-Al2O3 catalysts was evaluated in a bench scale plant operating in continuous regime, which consists of a conical spouted bed reactor for pyrolysis step and a fluidized bed reactor for the in-line catalytic steam reforming. The fresh catalyst has also been characterized in order to establish the relationship between catalyst properties and calcination temperatures in the synthesis step. Moreover, the deactivated catalysts have characterized in detail in order ascertain the main causes of activity decay in the catalysts. Thus, the catalyst calcined at the lowest temperature subsequent to both impregnation steps (Ni500/MgO700Al2O3) showed the best performance in the reforming step, as the amount of the spinel phase formed is lower, and therefore catalyst reducibility is increased, leading to a higher reforming activity and stability with time on stream.
In response to the awareness of limited fossil resources and environmental concerns, catalytic conversion of renewable lignocellulose biomass to value-added chemicals and fuels is of great significance and attractive for sustainable chemistry. Division of Biomass Conversion and Bio-Energy attached to Dalian National Laboratory for Clean Energy has devoted themselves to valorization of lignocellulose biomass since launched in 2011. Our research interests focus on breeding of biomass resources (inulin and microalgae), exploration of catalytic and biological technologies, and production of energy chemicals and fuels. Although lignocellulose biomass is renewable and abundant, the way of utilization should be reasonable according to its structural characteristics in view of efficiency and economy. In this review, to celebrate the DICP's 70th anniversary, we will highlight the major fundamental advances in DICP about the conversion of lignocellulose to value-added chemicals and liquid fuels. Particular attention will be paid to the transformation of cellulose and its derivatives to glycols, acids and nitrogen-containing chemicals, hemicellulose-derived platform molecule furfural to jet fuels and lignin to aromatics using catalytic technologies. © 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences
In this study, innovative Ni-based catalysts supported by five typical slag carriers (magnesium slag (MS), steel slag (SS), blast furnace slag (BFS), pyrite cinder (PyC) and calcium silicate slag (CSS)) were prepared by wet impregnation. With the prepared catalysts and Ni/γ-Al 2 O 3 catalyst, catalytic reforming of pyrolysis volatiles from pine sawdust for syngas production and tar removal was investigated. The catalysts were characterized by BET, XRD, SEM, TEM and Raman. The catalytic performances of the six catalysts were decreasing in the following order: Ni/MS > Ni/γ-Al 2 O 3 > Ni/SS > Ni/BFS > Ni/CSS > Ni/PyC. Ni/MS catalyst exhibited excellent catalytic reactivity as well as thermal stability in terms of tar conversion (95.19%), gas yield (1.46 Nm ³ /kg) and CO 2 capture ability (CO 2 yield of 0.5%). Both amorphous carbon and graphite-type carbon were formed on the catalysts after catalytic reforming and the D/G ratio (the relative intensity ratio of the D-band to the G-band) was positively correlated to the catalytic activity.
Pinewood sawdust and the waste rubber from truck tyres have been co-pyrolysed in order to improve the properties of bio-oil for its integration in oil refineries. In addition, an analysis has been conducted of the effect the interactions between these two materials’ pyrolysis reactions have on product yields and properties. Biomass/tyre mixing ratios of 100/0, 75/25, 50/50, 25/75 and 0/100 by weight percentage have been pyrolysed in continuous mode at 500 °C in a conical spouted bed reactor, obtaining oil yields in the 55.2–71.6 wt% range. Gaseous, oil and solid fractions have been characterised for the 50/50 biomass/tyre mixture, paying special attention to the oil fraction by determining its detailed composition, elemental analysis and calorific value. Co-processing enables the stabilization of the liquid, as the co-pyrolysis oil has a stable single phase, being composed mainly of water, aromatic hydrocarbons and phenols in concentrations of 14.5, 11.1 and 9.7 wt%, respectively. Adding tyre rubber to the biomass in the pyrolysis feed improves the oil's properties, as a liquid with higher carbon content and lower oxygen and water is obtained, even if sulphur content is also increased.
Alkyl-phenols and hydroxy- or methoxy-phenols (e.g., catechols, guaiacols and syringols) tend to polymerize into carbonaceous structures, causing clogging of reaction equipment and high coke deposition during bio-oil steam reforming (SR). In this work, removal of these phenolic compounds from raw bio-oil was addressed by accelerated aging and liquid-liquid extraction methods. The solvent-anti-solvent extraction with dichloromethane and water was suitable for obtaining a treated bio-oil appropriate for SR. The effect that phenols extraction has on the stability and regenerability of a NiAl2O4 spinel catalyst was studied by conducting reaction-regeneration cycles. Operating conditions were: 700 °C; S/C, 6; space-time, 0.15 gcatalysth/gbio-oil (reaction step), and in situ coke combustion at 850 °C for 4 h (regeneration step). Fresh, deactivated and regenerated catalyst samples were analyzed by temperature programmed oxidation (TPO), temperature programmed reduction (TPR) and X-ray diffraction (XRD). Stability of the Ni-spinel derived catalyst was significantly improved by removing phenols due to attenuation of both coke deposition and Ni sintering. Regenerability of this catalyst was also slightly improved when reforming the treated bio-oil.
Indirect or allothermal gasification of biomass in dual fluidized bed (DFB) gasifiers such as the Güssing gasifier or the biomass heatpipe reformer becomes particularly attractive for the conversion of biomass into hydrogen or any second generation fuel such as substitute natural gas (SNG), methanol or Fischer-Tropsch diesel fuel. Interconnected and indirectly heated DFB gasifiers produce syngas with H2/CO ratios of 2–3 and hydrogen concentrations even above 50 vol%(dry basis). Fluidized bed particles, the operating pressure, solids circulation rate and heat transfer coefficients determine the layout of these gasifiers. This article summarizes the state of the art with respect to layout and dimensioning of DFB gasifiers and reviews the impact of the steam equivalence ratio, fuel and bed material properties, char conversion, and combustion efficiency on cold gas efficiency and syngas quality of DFB gasifiers.
Biomass has been recognised as a promising resource for future energy and fuels. The biomass, originated from plants, is renewable and application of its derived energy and fuels is close to carbon-neutral by considering that the growing plants absorb CO2 for photosynthesis. However, the complex physical structure and chemical composition of the biomass significantly hinder its conversion to gaseous and liquid fuels.
This paper reviews recent advances in biomass thermochemical conversion technologies for energy, liquid fuels and chemicals. Combustion process produces heat or heat and power from the biomass through oxidation reactions; however, this is a mature technology and has been successfully applied in industry. Therefore, this review will focus on the remaining three thermochemical processes, namely biomass pyrolysis, biomass thermal liquefaction and biomass gasification. For biomass pyrolysis, biomass pretreatment and application of catalysts can simplify the bio-oil composition and retain high yield. In biomass liquefaction, application of appropriate solvents and catalysts improves the liquid product quality and yield. Gaseous product from biomass gasification is relatively simple and can be further processed for useful products. Dual fluidised bed (DFB) gasification technology using steam as gasification agent provides an opportunity for achieving high hydrogen content and CO2 capture with application of appropriate catalytic bed materials. In addition, multi-staged gasification technology, and integrated biomass pyrolysis and gasification as well as gasification for poly-generation have attracted increasing attention.
The performance and stability of different Ni supported catalysts have been studied in a continuous bench scale plant fitted with a conical spouted bed reactor for biomass pyrolysis at 500 °C and a fluidized bed reactor for the in line catalytic steam reforming of pyrolysis volatiles at 600 °C. The metal oxides selected as Ni supports have been Al2O3, SiO2, MgO, TiO2 and ZrO2, and all the catalysts have been prepared by the wet impregnation method. Significant differences have been observed in the performance and stability of the catalysts, with the most suitable ones concerning the evolution of bio-oil oxygenate conversion and H2 yield with time on stream being as follows: Ni/Al2O3 > Ni/ZrO2 > Ni/MgO > Ni/TiO2 > Ni/SiO2. The activity and stability are explained based on the properties of the catalysts, which have been measured prior and after their use, by means of different techniques: N2 adsorption/ desorption, X-ray fluorescence (XRF), X-ray powder diffraction (XRD), temperature programmed oxidation (TPO), in-line monitoring by Fourier-transform infrared spectroscopy-temperature programmed oxidation (FTIR-TPO), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
A study has been carried out of the regenerability of a commercial Ni catalyst used in the steam reforming of the volatiles from biomass pyrolysis (gases and bio-oil), determining the evolution of the reaction indices (conversion, product yields and H2 production) in successive reaction–regeneration cycles. The causes of catalyst deactivation (coke deposition and Ni sintering) have been ascertained characterizing the deactivated and regenerated catalysts by TPO, TEM, TPR and XRD. Catalyst activity is not fully recovered by coke combustion in the first cycles due to the irreversible deactivation by Ni sintering, but the catalyst reaches a pseudo-stable state beyond the fourth cycle, reproducing its behaviour in subsequent cycles. © 2018 The Korean Society of Industrial and Engineering Chemistry
The steam gasification of sawdust was carried out in a bench scale plant fitted with a fountain confined conical spouted bed reactor and a nonporous draft tube, and using olivine as primary catalyst. The effect temperature (in the 800–900 °C range) had on product distribution (gas, tar and char) and composition was studied. Not only did temperature have a positive effect on the gas yield and carbon conversion, but it also played a crucial role in tar removal, as its concentration fell from 49.2 g Nm⁻³ (on a dry basis) at 800 °C to 6.7 g Nm⁻³ operating at 900 °C. Moreover, temperature also enhanced the hydrogen yield of the gas, recording a value of 7.28 wt% at 900 °C. Regarding tar formation and its evolution pathway, as gasification temperature was increased the tar composition (analyzed by GC/MS, FTIR and simulated distillation techniques) evolved to more stable aromatic compounds (of higher molecular weight), such as naphthalene or fluoranthene, with heterocyclic or light aromatic compounds being almost absent at 900 °C.
The effects of dealumination of BEA zeolite on the formation of nickel active sites and the performance of Ni-containing BEA zeolite catalysts in the steam reforming of ethanol have been studied. Ni-containing BEA zeolite catalysts were prepared by the impregnation of unmodified and dealuminated BEA zeolites with Ni(NO3)2 precursor. The properties of Ni10HAlBEA and Ni10SiBEA zeolite catalysts were studied by means of X-ray diffraction, ¹H, ²⁷Al and ²⁹Si magic-angle spinning nuclear magnetic resonance, Fourier-transform infrared and Raman spectroscopy, transmission electron microscopy, temperature-programmed reduction, temperature-programmed ammonia and hydrogen desorption methods. High initial activity and selectivity of Ni10HAlBEA to hydrogen and carbon dioxide with unmodified BEA zeolite support in the steam reforming of ethanol reaction performed at 500 °C was observed. However, fast deactivation of Ni10HAlBEA catalyst, manifested in the decrease of water conversion, drop of selectivity to H2 and CO2, and increase in the selectivity to ethylene with the time-on-stream, was observed. In contrast, Ni10SiBEA zeolite catalyst showed lower initial activity but higher durability and resistance for carbon deposition. It was stated that dealumination of BEA zeolite led to the slight structural changes and simultaneously pronounced decrease of acidity. Formation of the large nickel crystallites was hindered on Ni10SiBEA zeolite catalyst. TEM and Raman spectroscopy studies indicated that deactivation of Ni10HAlBEA was related to formation of nickel mediated filamentous, graphitic and amorphous carbon deposits. Much smaller amounts of filamentous carbons were observed on the Ni10SiBEA zeolite catalyst prepared by the use of dealuminated zeolite support.
Tar content in gasification products is a serious problem for fuel gas utilization in downstream applications. Catalytic steam reforming of tar to syngas is a promising way for the removal of tar from the gas products. Nickel-based catalysts, dolomite, and olivine have been widely investigated for tar cracking and reforming by various researchers. This paper presents a review of biomass gasification, tar composition, and its elimination process by using the above three catalysts. This paper summarizes the knowledge in the published literature associated with tar elimination during the biomass gasification including discussion on the effects of different support, promoter on the catalytic performance. The aim of this paper is to collect information on the performance of above catalysts to make them accessible to readers within one paper. Comparative studies on these catalysts carried out by some researchers have also been presented here which show that the nickel-based catalyst is much more active than dolomite and olivine, but they are more expensive and can be also deactivated. Compared to olivine, the dolomite shows better catalytic performance with much higher gas yield and H2. Calcination of these catalysts improves the catalytic activities but the amount of coke deposited on the surface of the dolomite is reported higher than that of the olivine, which may be resulted from the different Fe amount of the catalyst.
H2 is regarded as one of the cleanest future energy carrier that can be generated from renewable sources and will give rise to a reduction of CO2 emissions and environmental problems related to the use of petroleum based feedstock. Thus, the thermochemical routes from biomass for sustainable H2 production compared to other biomass treatment routes have a great potential for its industrial implementation. Gasification of biomass and reforming of the bio-oil produced by biomass pyrolysis are the most researched pathways, although some studies dealing with supercritical water gasification and bio-oil gasification can also be found in the literature. Nevertheless, pyrolysis and in-line catalytic steam reforming strategy is gaining great attention due to its advantages compared to gasification and bio-oil reforming, especially those related to the optimization of each step (pyrolysis and catalytic steps) and bio-oil feeding. This review deals with the different reactor configurations, operating conditions and catalysts used in each process and compares the different alternatives in terms of H2 production, with emphasis placing on the advantages of the two-step strategy.
The valorization of biomass (pine wood) for hydrogen production has been studied in a two-step process, comprising pyrolysis and subsequent steam reforming of the volatiles produced in the first step. This work focuses on the deactivation of the Ni commercial catalyst used in the second step. Pyrolysis of biomass has been performed in a conical spouted bed reactor at 500 °C, and the in-line catalytic steam reforming of the pyrolysis volatiles, in a fluidized bed reactor at 600 °C. Deactivated catalyst samples were recovered at different values of time on stream, and analyzed by means of XRD, N2 adsorption-desorption, SEM and TEM microscopies, TPO, Raman and FTIR spectroscopies. The results show that the deactivation is mainly due to the encapsulation of Ni particles by coke, together with Ni sintering, to a lesser extent (from a Ni particle size of 25 nm in the reduced fresh catalyst, to 39 nm at 100 min). The former is ascribed to the condensation of oxygenates (particularly phenols), and the latter is inevitable within the current conditions. As the fraction of uncovered Ni particles decreases with time on stream, the deposition of encapsulating coke is slowed down (from a formation rate of 0.30 mgcoke gcatalyst⁻¹ min⁻¹ to 0.20 mgcoke gcatalyst⁻¹ min⁻¹, at 0–50 min and 50–100 min on stream, respectively), promoting the deposition of coke on the catalyst support (with a formation rate of 1.04 mgcoke gcatalyst⁻¹ min⁻¹ at 50–100 min on stream), with a more carbonized structure and formed through the thermal decomposition of phenols in the reaction medium.
: In order to facilitate the further processing and utilization of biomass pyrolysis oil, the chemical composition and thermal properties of biomass pyrolysis oil from pyrolysis of rice husk were investigated. The chemical composition analysis revealed that the pyrolysis oil contained large amount of oxygenated compounds, i.e., acid, ketones and phenols. Thermal degradation behaviors and kinetics of pyrolysis oil were investigated at different heating rates (5, 20, 35 and 50 oC min-1) under N2 and air atmosphere by TG. Pyrolysis oil decomposition mainly experienced three stages either in N2 or air atmosphere, and the corresponding activation energies vary with the degree of conversion. Py-GC/MS analysis of the pyrolysis oil reveals that ketones and aromatics are the main pyrolysis products of biomass pyrolysis oil. When the temperature increased from 600 to 700 oC during Py-GC/MS analysis, the content of ketones increased while the content of aromatics decreased. Subsequently, the feasibility of catalytic steam reforming of pyrolysis oil to produce renewable hydrogen was performed in a fixed-bed reactor with a NiO/ceramic foam catalyst. The effects of calcination temperature and metal content on the hydrogen yield were investigated. It is indicated that higher calcination temperature and loading content lead to the aggregation and sintering of NiO particles. A maximum hydrogen yield of 105.28 g H2 kg-1 pyrolysis oil (up to 81.1% of the stoichiometric yield) was obtained at reaction temperature of 700 oC, S/C ratio of 1, NiO loading content of 3.54%.
Toluene as a model tar compound was used to study the effect of atmosphere on carbon deposition during biomass tar reforming. A novel Ni-loaded on lignite char (Ni/LC) and commercial Ni/Al2O3 was employed for stability evaluation in a thermogravimetric analyzer. The mechanism of coke formation under N2, H2 and steam with different steam/carbon (S/C) ratio were investigated during 5 h test. Nickel particle growth is the main reasons responsible for the deactivation of Ni-based catalysts for tar reforming. Steam remarkably suppressed the carbon deposition on Ni/Al2O3, especially in a high S/C ratio. Ni/Al2O3 exhibited high activity and stability for 5 h operation in S/C ratio of 2. H2 significantly promoted the carbon deposition on Ni/Al2O3 and caused the catalyst deactivation within 0.5 h. Ni/LC exhibited great resistance to coke deposition under inert and H2 reforming of toluene. The catalysts before and after catalytic cracking were characterized by X-ray diffraction and transmission electron microscopy to investigate the behavior of carbon deposition. Except for H2 reforming, an obvious change of the Ni crystallite size (NCS) can be found after reforming for 5 h under all conditions used in this study. The NCS in Ni/LC was significantly increased with increasing time and S/C ratio, which should be partly responsible for the deactivation of the Ni/LC.
The effect of reforming conditions (temperature, space time and steam/biomass ratio (S/B)) has been studied in the continuous biomass pyrolysis and in-line catalytic steam reforming process in order to establish suitable conditions for attenuating the deactivation of a commercial Ni catalyst by coke deposition. The experiments have been performed in a conical spouted bed and a fluidized bed reactor for the pyrolysis and reforming steps, respectively. Biomass fast pyrolysis was performed at 500 °C and the reforming operating conditions studied are as follows: 550–700 °C; space time, 10–30 gcat min gvolatiles⁻¹, and; S/B ratio, 2–5. The coke deposited on the catalyst has been analyzed by temperature programmed oxidation (TPO), and two types of coke have been identified, i.e., the coke deposited on the Ni active sites and the one separated from these sites, without filamentous coke being observed by transmission electron microscopy (TEM). Coke deposition has been related to the decomposition of the oxygenates derived from biomass pyrolysis and the re-polymerization of phenolic oxygenates. Suitable conditions to achieve almost full conversion with a H2 yield of up to 95% and stability for 160 min on stream, are as follows: 600 °C, space time of 30 gcat min gvolatiles⁻¹ and S/B ratio of 3.
The performance of HZSM-5 and low cost catalysts, such as the spent fluid catalytic cracking (FCC) catalyst, bentonite, dolomite, and olivine, on the production of high-quality bio-oil during the catalytic pyrolysis of empty fruit bunches (EFBs) was compared in a bench scale fixed bed reactor. The spent FCC and HZSM-5 catalysts showed higher cracking performance than bentonite, dolomite, and olivine. The catalytic pyrolysis of EFB over the spent FCC catalyst showed higher selectivity to phenol (31.5%) and alkyl phenols (26.0%) due to the effective dealkoxylation of guaiacols and syringols, whereas HZSM-5 provided the higher selectivity to aromatic hydrocarbons (40.4%). The catalytic pyrolysis of EFB over the spent FCC catalyst and HZSM-5 produced bio-oil with a higher heating value (28.44–31.18 MJ/kg) than other bio-oils obtained over bentonite (27.89 MJ/kg) and olivine (16.83 MJ/kg). The bio-oils obtained from the catalytic pyrolysis of EFB over the spent FCC and HZSM-5 catalysts also had a lower viscosity (7.0–13.5 mm²/s) than those (13.8–22.1 mm²/s) over the other catalysts, even after accelerated aging at 80 °C for 1 day.
The aim of this work is to study the tars conversion in conditions representative of biomass gasification in a fluidized bed reactor. Experiments are conducted at 850 °C and atmospheric pressure in a fluidized bed reactor with toluene as tar model. Influences of the nature of the media (sand and olivine) and of the reactive atmosphere (steam and hydrogen partial pressures) on toluene conversion are particularly studied. The steam and hydrogen partial pressures were varied in the range of 0.05 to 0.4 bars and 0 to 0.2 bars, respectively. Results showed a strong influence of these parameters on toluene conversion. Olivine was found to have a catalytic activity towards steam reforming reactions which depends on the ratio in the reactor. Both thermodynamic equilibrium and surface analyses (EDX and XRD) of olivine particles suggested that this ratio controls the oxidation/reduction of iron at the olivine surface. Besides, iron is more active towards tars removal when its oxidation state is low. At 850 °C and , the iron is reduced to form native iron (Fe⁰) on the olivine surface which favors the steam reforming of toluene.
This work investigates the correlation of the reaction conditions (temperature and steam-to-carbon ratio (S/C)) and the reaction medium composition with the deactivation behavior of a Ni/La2O3-αAl2O3 catalyst used in the steam reforming of bio-oil, aiming the sustainable hydrogen production from lignocellulosic biomass. The reaction was performed in an in-line two-step system, consisting of a thermal treatment of bio-oil at 500 °C for retaining the thermal pyrolytic lignin, and in-line steam reforming of remaining oxygenates in a fluidized bed catalytic reactor. The reforming step was conducted at 550 and 700 °C and S/C ratio of 1.5 and 6. Fresh and deactivated catalyst samples were characterized using XRD, SEM, TEM, TPO, XPS, Raman and FTIR spectroscopies. The catalyst deactivation is mainly due to the amorphous and encapsulating coke deposition, whose formation is attenuated when both temperature and S/C ratio are increased. Although the highest catalyst stability is attained at 700 °C and/or S/C ratio of 6, Ni sintering is noticeable at these conditions. The encapsulating coke is highly oxygenated, in contrast with the more aromatic and condensed nature of filamentous coke. Based on the correlation between the composition of the coke and the reaction medium, it was established that bio-oil oxygenates are the precursors of the encapsulating coke, particularly phenols and alcohols, whereas CO and CH4 are the possible precursors of the coke fraction constituted by filaments, whose contribution to catalyst deactivation is hardly significant.
Catalytic reforming of real biomass pyrolysis oil (BPO) was carried out with a nano-Ni/ceramic foam catalyst using a fixed bed reactor. XRD, TPR, SEM/EDX and BET were used to characterise the synthesized catalysts. The analysis results showed that nickel oxide was in-situ reduced to active nickel metal during the steam reforming process and the size of NiO particles loaded on the surface of ceramic foam was in the range of 30-40 nm. NiO nanoparticles showed a homogeneous multilayer deposition on the surface of the catalyst and the BET surface area of the fresh catalyst was increased with the increase of Ni loading. The effects of calcination temperature, reaction temperature and weight hourly space velocity (WHSV) on hydrogen production were studied. The results showed that the yields of hydrogen and gas were decreased with the calcination temperature increasing from 400 to 700 °C. The yield of H2 were in the range of 44.41-89.17 g H2 kg⁻¹ BPO when the reaction temperatures varied from 500 to 800°C. The hydrogen yield was decreased with the increase of WHSV, and a low activation energy (25.34 kJ mol⁻¹) was obtained from kinetic studies, indicating the effectiveness of the nano-Ni/ceramic foam catalyst.
Tremendous research efforts have been dedicated towards development and utilization of sustainable alternative energy resources. Depletion of fossil fuels and the rising environmental concerns such as global warming are among the reasons that necessitated such. Hydrogen (H2) has been widely considered a clean fuel for the future, with the highest mass based energy density among known fuels. Bio-oil components are the most renewable energy carriers produced from bio-mass which have been selected for hydrogen production. Phenol and acetic acid are among the major liquid waste components of the bio oil. Catalytic steam reforming of these components in a fixed bed reactor provides a promising technique for hydrogen production from renewable sources. Due to the vital interaction that exists between catalyst and supports, Rh and Ni active metals and ZrO2, La2O3 and CeO2 supports were found to be appropriate catalysts with long-term stability for the hydrogen production via steam reforming of phenol and acetic acid. The process is advantageous due to its high hydrocarbon conversion and H2/CO2 product ratio. The present work provides extensive information about the phenol and acetic acid steam reforming process for producing hydrogen as a renewal energy carrier.
The flash pyrolysis of waste truck-tyres was studied in a conical spouted bed reactor (CSBR) operating in continuous regime. The influence of temperature on product distribution was analysed in the 425–575 °C range. A detailed characterization of the pyrolysis products was carried out in order to assess their most feasible application. Moreover, special attention was paid to the sulphur distribution among the products. The analysis of gaseous products was carried out using a micro-GC and the tyre pyrolysis oil (TPO) by means of GC-FID using peak areas for quantification, with GC/MS for identification and elemental analysis. Finally, the char was subjected to elemental analysis and surface characterization. According to the results, 475 °C is an appropriate temperature for the pyrolysis of waste tyres, given that it ensures total devolatilisation of tyre rubber and a high TPO yield, 58.2 wt.%. Moreover, the quality of the oil is optimum at this temperature, especially in terms of high concentrations of valuable chemicals, such as limonene. An increase in temperature to 575 °C reduced the TPO yield to 53.9 wt.% and substantially changed its chemical composition by increasing the aromatic content. However, the quality of the recovered char was improved at high temperatures.
The Ni-loaded chicken droppings (Ni/CD) and chicken dropping ash (Ni/CDA) were prepared by the impregnation method and applied as catalysts for biomass tar decomposition at low temperature (450 °C) under N2 and steam/N2 conditions. The prepared samples and the supports were characterized by N2 adsorption measurements, X-ray diffraction, H2 temperature-programmed reduction, and X-ray photoelectron spectroscopy. The results reveal that Ni/CD and Ni/CDA showed higher catalytic activity for tar decomposition, in terms of producing hydrogen-rich gas, relative to commercial Ni/Al2O3 under N2 conditions. This higher activity was caused by lower interactions of Ni with the support and the presence of additional reduced Ni. In the case of steam reforming, Ni/CDA also showed higher hydrogen yield and a lower amount of carbon deposition than Ni/Al2O3. This result indicates that a hydrophilic hydroxyapatite in the CDA support promoted the water–gas shift reaction to suppress carbon deposition and increase hydrogen yield.