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Molecular weight-based fractionation of lignin oils by membrane separation technology
Holzforschung
Abstract
Lignin is a renewable and abundant source for production of bio-based chemicals and is a valuable alternative to crude oil to obtain aromatic building blocks. It is built from aromatic units with strong chemical linkages, which need to be cleaved to enable the use of the aromatic compounds in industrial applications. In addition to depolymerizing lignin, efficient fractionation and conversion of the resulting complex mixtures is an essential step in the valorization of lignin derivatives for different applications. In this work, we studied the separation of a lignin oil obtained by catalytic cleavage in supercritical ethanol (scEtOH) of technical lignin produced by means of soda pulping of wheat straw. The use of six commercial polymeric nanofiltration (NF) membranes and one in-house developed Grignard-functionalized ceramic membrane was investigated for the fractionation of a mixture of lignin derivatives. Separation by molecular weight (MW) was observed with the polymeric NP030 membrane but not with the other membranes tested. The development of a protocol using this membrane in the diafiltration mode for fractionation of crude lignin oils (CLOs) is discussed.
... Only a small number of studies have covered nanofiltration-based fractionation of lignin oil. Of particular importance are the studies by Sultan et al. [41], Polizzi et al. [42], Servaes et al. [43], Konscag et al. [44] and Saboe et al. [45], who have all screened commercial nanofiltration membranes for their fractionation capabilities. However, since their lignin oils had higher average MW and molecular complexity, their fractionation processes focused less on the purification of monomers, showed lower yields of monomers, and used higher MW cutoffs. ...
... This leaves reviewers with few other options than to merely compare the fluxes and target MW's of each study [28]. The papers that quantitatively assess fractionation performance calculate peak areas by vertical cut-offs, (not taking substantial attributions from larger peaks into smaller peaks into account), and report a rejection value or contribution at an arbitrary molecular weight [41,42,46]. Only the article by Aminzadeh et al. [24] and the recent paper by Saboe et al. [45] contain more rigorous quantitative analyses, such as 2D NMR, GC-MS and LC-MS. ...
... Thus, the desired fractions can be acquired at the right time, and diafiltration can be halted when the feed only has oligomers left. Similar research was carried out by Polizzi et al [42], though with heavier lignin oil, largely different membranes, ethanol as solvent and higher MW cutoffs. In their trials, NP030 was shown to be the most suitable to fractionate their lignin oil. ...
Organic solvent nanofiltration membranes were employed to fractionate birch derived reductive catalytic fractionated (RCF) lignin oil. This lignin oil is highly depolymerized, with most, if not all chemical compounds lighter than 3 kDa. Sixteen commercially available membranes were investigated for the fractionation, in combination with methanol and ethyl acetate as solvents. Membrane performances were quantified using Gaussian fits of gel permeation chromatograms and separation factor calculations. The separation factor was found to be primarily based on affinities instead of size-exclusion. The silicon-based membranes from Borsig (Germany) and PuraMem S600 from Evonik (UK) proved best at separating lignin into different functional fractions, showing monomer separation factors up to 7.4 and providing a permeate fraction with 88% phenolic monomer purity. These membranes were further examined in batch diafiltration and two-stage filtration. This increased the separation factor from 7.4 to 25.4, and the monomer purity of the permeate to 95%, proving that membrane purification of the lignin-derived monophenols is technically feasible.
... Only a small number of studies have covered nanofiltration-based fractionation of lignin oil. Of particular importance are the studies by Sultan et al. [41], Polizzi et al. [42], Servaes et al. [43], Konscag et al. [44] and Saboe et al. [45], who have all screened commercial nanofiltration membranes for their fractionation capabilities. However, since their lignin oils had higher average MW and molecular complexity, their fractionation processes focused less on the purification of monomers, showed lower yields of monomers, and used higher MW cutoffs. ...
... This leaves reviewers with few other options than to merely compare the fluxes and target MW's of each study [28]. The papers that quantitatively assess fractionation performance calculate peak areas by vertical cut-offs, (not taking substantial attributions from larger peaks into smaller peaks into account), and report a rejection value or contribution at an arbitrary molecular weight [41,42,46]. Only the article by Aminzadeh et al. [24] and the recent paper by Saboe et al. [45] contain more rigorous quantitative analyses, such as 2D NMR, GC-MS and LC-MS. ...
... Thus, the desired fractions can be acquired at the right time, and diafiltration can be halted when the feed only has oligomers left. Similar research was carried out by Polizzi et al [42], though with heavier lignin oil, largely different membranes, ethanol as solvent and higher MW cutoffs. In their trials, NP030 was shown to be the most suitable to fractionate their lignin oil. ...
... In general, membranes are classified according to their pore sizes, which determine their ability to effectively exclude certain contaminants, including organic matter, AOX, lignin, and ions. 57,58 Polymeric and ceramic membranes are the two main types of membranes, each of which has its advantages and disadvantages. As opposed to polymer membranes, ceramic membranes can be cleaned with a variety of harsh cleaning agents when fouling or scaling occurs. ...
The pulp and paper industry generates vast amounts of wastewater, and its character heavily depends on various factors (raw material, the undertaken process, the final product, etc.). The wastewater from this sector, which originates from several sources in each mill and are mostly combined, is polluting and hazardous. This paper presents a state-of-the-art review of the physical, chemical, biological, and advanced hybrid treatment techniques, concerning their effectiveness in removing specific pollutants, namely, chemical oxygen demand, lignin, color, and adsorbable organo-halogens. Throughout the manuscript, at the end of each section, a conclusive comparison has been presented and the proper method is introduced. Furthermore, numeric data regarding the effectiveness of each technique toward each pollutant are gathered from the literature and are available in the Supporting Information of the paper. Biological treatment processes using anaerobic–aerobic treatment mostly cure organic biodegradable contaminants (75–90% COD removal). Moreover, biological treatment using a consortium of microorganisms can potentially increase color removal efficiency (from 65 to 97%). Hybrid treatment is also among the candidates for color removal. To treat complex matters (lignin and AOX), physical and chemical treatments have shown promising performance, but they are generally expensive and impractical to treat huge amounts of wastewater. For the treatment of high molecular weight contaminants (lignin) advanced oxidation processes (AOPs), including ozonation and Fenton-based treatment, have shown great performance (90–99%); however, they are limited due to their maintenance and operation costs. To overcome these challenges, source separation of the wastewater streams in the pulp and paper industry is recommended. AOPs or membrane technologies or hybrid processes are suggested for the bleaching effluent (80% AOX removal), which is relatively low in amount, and a combination of conventional treatment processes would be preferred to treat wastewater streams that are more biodegradable. The biological performance can also be enhanced using granular activated carbon on the sequence. Finally, for treating black liquor, adsorption processes have proven to be the prime candidate.
... Cross-analysis was made between the majors of the interviewed students and the ideological and political education carried out by their schools through the teaching of specialized courses and general courses (as shown in Figure 4). More students receive ideological and political education in the teaching of knowledge courses, and fewer students who are partial to science and engineering majors in economics, science, and engineering receive ideological and political education in the teaching of specialized courses and general courses [10,11]. e proportion of college students who have received ideological and political education in professional and general courses is much lower than the proportion of students who have not received ideological and political education. ...
The construction of green campus in colleges and universities in the new era is an important part of the construction of socialist modern ecological civilization. Therefore, in the process of building a green campus, we should not simply pay attention to “green”, but integrate the ecological civilization into it. In order to further enhance the role of implicit education function in the process of green campus construction, with the help of actual case analysis, this study focuses on how to actively integrate implicit education into the process of building a green campus, and truly give full play to the role of implicit education in building morality, cultivating people and cultural inheritance, starting from three aspects: the realization of the implicit education function, the construction mechanism of green campus environment, and the realization path of implicit ideological and political education in Colleges and universities in the new era.
... In this regard, when analyzing lignin by GPC, separation is not only due to size exclusion but also to other interactions given by the heteropolymeric nature and functional groups of lignin. However, despite these limitations, the method of determining the distribution of molecular weights of lignin by CPG using polystyrene standards remains valid and widely used by the scientific community [38,[52][53][54][55][56][57][58][59][60] since it can facilitate the comparison of chromatograms obtained in different laboratories and using different combinations of columns. ...
The elucidation of lignin structural features is necessary for the efficient application of this polymer. Fractionation is an effective technique to achieve homogeneous lignin fractions, helping to better understand its composition and structure, and improving its use as source of phenolic compounds. This work develops a new and simple fractionation method of organosolv extracts obtained from lignocellulosic materials that enables the selective separation of lignin (from complex macromolecules to low molecular weight aromatic compounds originated from their degradation) from saccharides derived from hemicelluloses and cellulose. For this purpose, the non-catalytic organosolv extraction of lignin from almond shells was performed with dioxane/water mixtures and then the successful fractionation of the organosolv extracts with anhydrous tetrahydrofuran was achieved, resulting in the selective separation of lignin (lignin fraction) from saccharides (saccharide fraction). Gel permeation chromatography (GPC), thioacidolysis, and GC-MS were used as analytical methods to qualitatively determine the purity of both fractions. In addition, GPC was also used to quantify the content of lignin monomers and furfural in the organosolv extracts, thus allowing valuable information on the state of degradation of the lignin and hemicelluloses extracted to be obtained, respectively. The application of the GPC method also enabled the determination of the molecular weight distribution of the extracted lignin in the same analysis.
Graphical abstract
Reductive catalytic fractionation (RCF) is a lignin-first biorefining technique that produces a polysaccharide-rich pulp and a lignin oil that is rich in aromatic monomers from aryl-ether bond cleavage and carbon–carbon...
Lignin is a polyaromatic polymer contained in plant cell walls, and it is considered the most abundant noncarbohydrate polymer on Earth. The aromaticity and richness of its functional groups render lignin an attractive starting biomacromolecule for conversion into a variety of value‐added products. The development of successful strategies for lignin valorization infers the design of effective depolymerization protocols. Most research on lignin depolymerization has focused on batch‐mode processing, whereas only a few studies have investigated such lignin transformations in continuous reactor systems. In this Concept, emerging developments within the concept of continuous lignin processing and the challenges remaining in realizing the efficient valorization of lignin by using this technology are highlighted. A special focus is set on the hydrothermal conversion of technical lignin under continuous‐flow conditions, together with suggestions for future research and technology development.
Much scientific research has been carried to convert lignin into valuable biobased chemicals or fuels. Most of these studies had the objective to develop active and selective catalysts for effective lignin depolymerization; this with little regard for the parameters that are necessary for later commercialization of these technologies. In this work, we have chosen as a case study a process that has been extensively studied and reported on earlier by our group. This process converts (technical) lignin into mainly aromatic compounds, using supercritical ethanol and a Cu–Mg–Al mixed oxide catalyst. Here, we investigate the impact of scaling up this process from lab to bench scale. More specifically, we study the influence of higher lignin loadings than previously reported on, amongst other parameters, monomer yield, solvent losses and catalyst fouling; all of which being critical performance parameters for industrial operation. After we examined the technical feasibility of our process at 4 L scale, we further looked into the economic viability of this technology, by introducing two performance criteria, both of which being a function of lignin monomer yield. The ratios (g/g) of yield over total feed, and yield over ethanol losses are presented as qualitative indicators for capital expenditure (CAPEX) and operational expenditure (OPEX), respectively. This exercise sheds some much needed light on the trade-off between yield optimization and cost minimization.
Lignin represents a considerable source of renewable and bio-based carbon. Pulping processes enable lignin, together with all components of the lignocellulosic biomass, to enter valorizable streams. A current key objective is to further valorize this versatile aromatic biopolymer, and for that, to go beyond its mere energy use. Despite the emergence of numerous proposals for value-added products coming from lignin, most of them remain at the research stage. The main challenges arise from the complexity and heterogeneity of the lignin structure and resulting molecular properties, the variability of biomass source, pre-treatment processes, growing environment. Keeping in mind that future integrated biorefineries must take into account environmental concerns, lignin processing in accordance with green chemistry principles should first be favoured. From this very perspective, this work proposes to review the most promising current routes towards fractionation and/or depolymerization of lignin. Those should represent sustainable treatment technologies potentially leading to a broad spectrum of marketable lignin-based molecules and products. First, lignin fractionation by selective precipitation using pH as well as green solvents, or by using membrane technologies will be addressed. Then lignin depolymerization will be discussed at length, notably from a catalytic point of view and by hydrogenolysis; the knowledge about the fundamental chemistry stemming from the use of model compounds will be described. Substitution of organic solvents with environmentally harmless supercritical fluids or with negligible vapour pressure ionic liquids is of great interest to modify lignin, and is finally reviewed. Lastly, challenges for integrated biorefineries and for launching new lignin-based compounds and products will be discussed.
Utilization of renewable resources is becoming increasingly important, and only sustainable processes that convert such resources into useful products can achieve environmentally beneficial economic growth. Wastewater from the pulp and paper industry is an unutilized resource offering the potential to recover valuable products such as lignin, pigments, and water [1]. The recovery of lignin is particularly important because it has many applications, and membrane technology has been investigated as the basis of innovative recovery solutions. The concentration of lignin can be increased from 62 to 285 g∙L−1 using membranes and the recovered lignin is extremely pure. Membrane technology is also scalable and adaptable to different waste liquors from the pulp and paper industry.
Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine-tuning of multiple “upstream” (i.e., lignin bioengineering, lignin isolation and “early-stage catalytic conversion of lignin”) and “downstream” (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a “beginning-to-end” analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignin's biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.
The present invention relates to a method for the modification of metal hydroxide and/or metal oxide surfaces of an inorganic matrix with an organometallic reagent for obtaining an organic functionalized matrix suitable for filtration processes. The method involves the direct covalent binding of organic functional groups by allowing a pre-treated matrix to react with organometallic reagents in the present of a suitable solvent. The present invention further relates to an organic functionalized matrix obtainable or obtained by carrying out a method according to the invention. The invention also provides various uses of a surface-modified matrices as described herein in various industrial applications, including for instance in filtration and/or adsorption and/or separation processes, or as support, e.g. for catalyst systems or for enzyme systems.
Obtaining renewable fuels and chemicals from lignin presents an important challenge to the use of lignocellulosic biomass in order to meet sustainability and energy goals. We report on a thermocatalytic process for the depolymerization of lignin in supercritical ethanol over a CuMgAlOx catalyst. Ethanol as solvent results in much higher monomer yields than methanol, because ethanol effectively scavenges formaldehyde derived from lignin. Experiments with phenol and alkylated phenols point out the critical role of phenolic –OH groups and formaldehyde in undesired repolymerization reactions. O-alkylation and C-alkylation capping reactions with ethanol hinder repolymerization of the phenolic monomers formed during lignin disassembly. After reaction in ethanol at 380 °C for 8 h, this process delivers high yield of mainly alkylated mono-aromatics (60–86 wt%, depending on the lignin used) with a significant degree of deoxygenation. The oxygen-free aromatics can be used to replace reformate or serve as base aromatic chemicals; the oxygenated aromatics can be used as low-sooting diesel fuel additives and as building blocks for polymers.
The demand for petroleum dependent chemicals and materials has been increasing despite the dwindling of their fossil resources. As the dead-end of petroleum based industry has started to appear, today’s modern society has to implement alternative energy and valuable chemical resources immediately. Owing to the importance of lignocellulosic biomass for being the most abundant and bio-renewable biomass on earth, this critical review provides insights into the potential of lignocellulosic biomass as an alternative platform to fossil resources. In this context, over 200 value-added compounds, which can be derived from lignocellulosic biomass by using various treatment methods, are presented with their references. Lignocellulosic biomass based polymers and their commercial importance are also reported mainly in the frame of these compounds. The review article aims to draw the map of lignocellulosic biomass derived chemicals and their synthetic polymers, and to reveal the scope of this map in today’s modern chemical and polymer industry.
More recently, the concept of integrated forest biorefnery (IFBR) has received much attention as a promising solution for the struggling forest industry in North America and Europe to overcome its difcult fnancial period and competes globally. This new business paradigm offers a broad range of potentially attractive products, from bioenergy to value-added green organic chemicals in addition to traditional pulp and paper products. However, it also implies adoption of different types of appropriate separation technologies. Recent advancements in membrane technologies and their valuable applications have resulted in numerous breakthroughs in IFBR. The review of the implementation of membrane technologies for the separation of the value-added chemicals in the integrated forest biorefnery could contribute to the knowledge required for the large-scale adoption of membrane technologies in the forest industry. This paper aims to present a state-of-the-art review on the applications and the recent advancements of membrane technologies in IFBR, and their capacities to produce value-added chemicals and bioenergy. The emphasis is given to the focus areas of IFBR, particularly: the recovery of value-added chemicals, black liquor concentration, product recovery from Kraft evaporator condensates, tall oil recovery, inorganic and inorganic compounds recovery, fermentation inhibitors removal, enzyme recovery, biobutanol and bioethanol production and recovery. The paper also discusses the challenges and opportunities of this new business paradigm of forest industries.
Lignin, which is the second most abundant biomass component and has carbon-rich phenolic content, is a promising renewable raw material for multiple applications, such as carbon fibers, adhesives, and emulsifiers. To use lignin efficiently, it is important to ensure its purity and homogeneity. As a result, the separation of lignin into fractions with high purity and narrow molecular-weight distributions is likely a prerequisite for several applications. Ultrafiltration using ceramic membranes has many advantages, including enabling direct lignin extraction from Kraft pulp cooking liquors without pH and temperature adjustment. One challenge with membrane filtration using such a system is the potential for reduced membrane performance over time, which is associated with fouling.
In this study, LignoBoost Kraft lignin was fractionated using a ceramic membrane with a molecular weight cut-off of 1 kDa. The separation behavior during ultrafiltration fractionation was investigated and the antioxidant properties of the recovered low-molecular-weight (low-MW) lignin samples were evaluated.
Using this model system, the permeate fluxes were unstable during the 100 h of membrane operation. However, a decrease in the average MW in the permeate over time was observed. The shift in MW was most pronounced for virgin membranes, while a more stable MW distribution was evident for membranes subjected to multiple cleaning cycles. According to 2D NMR analysis, low-MW lignin that was recovered after 100 h of operation, consisted of smaller lignin fragments, such as dimers and oligomers, with a high content of methoxy-groups. This was confirmed using the size exclusion chromatography method, which indicated an weigh average molecular weight in the range of 450-500 Da. 31P NMR spectroscopy showed that, despite the lower total content of phenolic OH groups, the low-MW sample had a higher proportion of non-condensed phenolic OH groups. The results of the antioxidant tests demonstrated the strong potential of lignin and its low-MW fraction as a natural antioxidant, particularly for lipid-containing systems. The low-MW lignin fraction showed better antioxidant activity than the non-fractionated LignoBoost lignin in the kinetic oxygen radical absorbance capacity (ORAC) test and demonstrated three-fold stronger inhibition of the substrate (fluorescein) than the reference antioxidant Trolox (a water-soluble derivative of vitamin E).
Valorization of biomass calls for development of new and/or optimized process technologies. Cost-effective separation processes are of utmost importance to separate biomass components on an industrial scale. Also the complexity of biomass depolymerization/hydrolysis processes increases even further the need for efficient separation processes. Within this study, the use of commercial nanofiltration membranes and in-house developed Grignard-functionalized ceramic membranes has been investigated for the fractionation of a mixture of lignin derivatives, obtained from the depolymerization of Organosolv lignin according to the derivatization followed by reductive cleavage (DFRC) approach. Gas chromatography coupled with mass spectrometry, liquid chromatography-high resolution -mass spectrometry and gel permeation chromatography have been intensively used for the characterization of the depolymerization mixture before and after membrane separation. Higher permeation fluxes are observed with the modified ceramic membranes (25-30 L/m².h) exhibiting amphiphilic surface properties. Separation of lignin derivatives by molecular weight based on size-exclusion has been observed with the polyamide Desal-5DK membrane, while a separation governed by solute-membrane interactions appears to be possible with the functionalized ceramic membranes, where retentions for individual solutes are highly dependent on the chemistry of the grafted groups. For instance, it has been observed that aromatics such as 2,6-dimethoxy-4-propenylphenol are either rejected by or preferentially transported across the membrane, depending on the chosen membrane functionalization. This offers perspectives towards the development of membrane processes for fine separation of small lignols and to enable the use of these molecules in chemical and materials applications.
Different value-added products can be produced from lignin. To produce lignin based products, lignin derivatives need to be isolated from pulping spent liquors, as pulping spent liquors are dilute in lignin and impure. In this chapter, methods for isolating lignin derivatives from pulping spent liquors are reviewed. The main challenges and perspectives in the development of viable lignin production processes are described. LignoBoost and LignoForce were designed based on the acidification concept to isolate Kraft lignin from black liquor on the commercial scale, both of which produce pure lignin. To extract lignosulfonate from sulfite spent liquors, ultrafiltration seemed to be an industrially viable method, but the extracted lignin will likely contain impurities. Laboratory studies on adsorption and flocculation techniques for isolating lignin from other spent liquors with a low lignin content, e.g. prehydrolysis liquor of Kraft based processes, or the spent liquor of the neutral sulfite semichemical processes, are also discussed. Although these techniques seem to be industrially attractive, the purity of lignin that is produced in these processes are not high.
Membranes playa central role in our daily life, or as indicated by one of my foreign colleagues, Richard Bowen, 'If you are tired of membranes, you are tired of life' . Biological membranes are hardly used in industrial applications, but separations with synthetic membranes have become increasingly important. Today, membrane processes are used in a wide range of applications and their numbers will certainly increase. Therefore, there is a need for well educated and qualified engineers, chemists, scientists and technicians who have been taught the basic principles of membrane technology. However, despite the growing importance of membrane processes, there are only a few universities that include membrane technology in their regular curricula. One of the reasons for this may be the lack of a comprehensive textbook. For me, this was one of the driving forces for writing a textbook on the basic principles of membrane technology which provides a broad view on the various aspects of membrane technology. I realise that membrane technology covers a broad field but nevertheless I have tried to describe the basic principles of the various disciplines. Although the book was written with the student in mind it can also serve as a first introduction for engineers, chemists, and technicians in all kind of industries who wish to learn the basics of membrane technology.
Recovery of dilignols–trilignols fraction was studied in this work. Solvent resistant ultrafiltration and nanofiltration membranes were used to fractionate ethanol and ethanol/dichloromethane extracts obtained from straw degraded by Pleurotus ostreatus. It was shown that ultrafiltration is very effective in removing solid suspensions. Permeates from ultrafiltration were processed by nanofiltration membranes with MWCO = 1000, 350, 250, and 200 Da, in a screening study aimed to find the best option for the separation and concentration of the dilignols–trilignols fraction. It was demonstrated that it is possible to separate and concentrate the lignin degradation products with molecular mass of 200–390 Da in an integrated UF/NF process with good yields (60–85%) and concentrating the product tenfold.
The 1st generation of biofuels stemming from sugar cane, rape or corn is commercially established today and holds a considerable market share as a drop-in fuel. However, due to interference with the food chain, the ethical discussion on ‘fuel or food’ has originated. Therefore, current research focuses on the utilization of lignocellulosic materials as a bio-renewable feedstock. Simultaneously several biomass-based processes were developed over the past decade suggesting scenarios from a classic biofuel plant to a new biorefinery concept which produces for instance polymers which were previous fossil resources based. The growth of bio resource based chemicals, functional monomers as well as fuels leads to an increased demand for new separation processes. This review highlights the role of membrane separations within current and future biofuel and biorefinery scenarios. Membrane processes reviewed are for instance pervaporation for alcohol recovery and ultrafiltration of canola oil, as well as new developments such as the ultrafiltration/nanofiltration of lignin in a solvent-based lignocellulose conversion process or the recovery of amino acids via electrodialysis. The membrane processes are classically categorized as concentration-driven membrane processes, pressure-driven membrane processes, electrical-driven membrane processes and prospective membrane processes. It follows the transition of a classic biofuel production plant to a new sophisticated biorefinery. The review closes with a reflection of membrane-based downstream processes required in a biorefinery transforming cellulose into an itaconic acid.
The emerging field of organic solvent nanofiltration (OSN) opened up novel opportunities in fractionation and purification of polydisperse mixtures during the last decade. In this work we report about the application of OSN for the valorization of lignin as a renewable source of chemicals. Oxidation of lignin yields high-value monomeric chemicals including vanillin and methyl vanillate which have to be separated from the remaining mixture of high molecular weight reaction products. Five membranes from the DuraMemTMDuraMemTM, PuraMemTMPuraMemTM and SelRo®SelRo® series with a molecular weight cut-off (MWCO) in the range of 250–900 g mol−1 were characterized concerning solvent flux of ethyl acetate and rejection of four model compounds. Afterwards, four of the membranes were employed in the separation of the lignin product mixture which has a weight average molecular weight of approximately 1150 g mol−1. Retentate samples were analyzed concerning monomer content and remaining molecular weight distribution by gas chromatography/mass spectrometry (GC/MS) and size-exclusion chromatography (SEC). All four studied membranes proved to be very effective in separating monomeric products from the reaction mixture. The best results in terms of permeate flux and rejection of high molecular weight compounds were obtained with PuraMemTMPuraMemTM S380, which therefore turned out to be the most appropriate membrane for the desired separation step.
The basic principles of the various aspects of membrane technology are reviewed. Polymers used as membrane material are surveyed and factors determining material properties described. Various preparation techniques are overviewed and the phase-inversion process is discussed in detail. Characterization techniques are included, both for porous and nonporous membranes. Types of driving forces, transport processes and concentration polarization are described together with membrane fouling. Aspects of module and process design are given together with some process calculations. (P.M.T.)
The structure of lignin suggests that it can be a valuable source of chemicals, particularly phenolics. However, lignin depolymerization with selective bond cleavage is the major challenge for converting it into value-added chemicals. Pyrolysis (thermolysis), gasification, hydrogenolysis, chemical oxidation, and hydrolysis under supercritical conditions are the major thermochemical methods studied with regard to lignin depolymerization. Pyrolytic oil and syngases are the primary products obtained from pyrolysis and gasification. A significant amount of char is also produced during pyrolysis. Thermal treatment in a hydrogen environment seems very promising for converting lignin to liquid fuel and chemicals like phenols, while oxidation can produce phenolic aldehydes. Reaction severity, solvents, and catalysts are the factors of prime importance that control yield and composition of the product.
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Lignin: Technology, Applications and Markets - Special Market Analysis Study
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