Topochemical pretreatment of wood biomass to enhance enzymatic hydrolysis of polysaccharides to sugars

Influence of Pine and Alder Woodchips Storage Method on the Chemical Composition and Sugar Yield in Liquid Biofuel Production

The aim of this study was to investigate the effect of storing methods of woodchips from two species, pine (Pinus sylvestris L.) and alder (Alnus Mill.), on the basic chemical composition and sugar yield in liquid biofuel production. Two methods of storing woody biomass were used in the study—an open pile and a cover pile. The wood was felled at the end of November and was stored as industrial chips for eight months from December onward. After this time, material was collected for chemical composition analyses and enzymatic hydrolysis. The results of the chemical composition analysis of the wood for both studied species showed the influence of the type of storage on the composition of the individual structural components of the wood. Based on the results of the enzymatic hydrolysis of the woody biomass, it can be seen that, irrespective of the hydrolysed material (wood, cellulose, holocellulose), the material from the biomass stored in the open pile gave higher results. The hydrolysis efficiency also increased with time, independent of the type of material that was hydrolysed. The highest sugar yield from the enzymatic hydrolysis of wood was obtained for alder wood stored in an open pile. The highest sugar yield from the enzymatic hydrolysis of cellulose was obtained for cellulose extracted from alder wood—as well—that had been stored in an open pile.

Delignification efficiency of various types of biomass using microwave-assisted hydrotropic pretreatment

The use of a method of an effective delignification of lignocellulosic biomass is a key stage of designing processes of its microbiological conversion e.g. for the purposes of the production of cellulosic ethanol. The study was aimed at evaluating the effectiveness of microwave-assisted hydrotropic pretreatment using sodium cumene sulfonate (NaCS) for the delignification of pine and beech chips and wheat straw. Research results presenting the impact of process parameters of microwave-assisted hydrotropic delignification confirm a high effectiveness of this method of pretreatment of lignocellulosic biomass. The observed effects included changes in the composition of the biomass and an increased susceptibility of cellulose to the subsequent enzymatic hydrolysis. The use of microwave heating combined with an addition of hydrotrope of 40% w/v NaCS and 117 PSI for 60 min enabled a reduction of the absolute concentration of lignins by 36.58% in pine chips, by 57.68% in beech chips, and by 74.08% in wheat straw. After enzymatic hydrolysis was conducted, the highest concentration of glucose: 463.27 ± 11.25 mg glucose/g (hydrolysis yield 46.76 ± 1.14%) was obtained from the wheat straw, while 327.70 ± 22.15 mg glucose/g (hydrolysis yield 35.13 ± 2.37%) was acquired from the beech chips, and only 50.77 ± 0.75 mg glucose/g (hydrolysis yield 6.63 ± 0.10%) was obtained from the pine chips. Microwave-assisted hydrotropic delignification in the optimum process conditions additionally allows a complete removal of hemicellulose from biomass, which improves the effectiveness of enzymatic hydrolysis. Due to a significant reduction of lignin and hemicellulose concentration in biomass, cellulose—which is susceptible to enzymatic hydrolysis and a source of carbon in biosynthesis processes—becomes the main biomass component.

Manufacture of Platform Chemicals from Pine Wood Polysaccharides in Media Containing Acidic Ionic Liquids

Pinus pinaster wood samples were subjected to chemical processing for manufacturing furans and organic acids from the polysaccharide fractions (cellulose and hemicellulose). The operation was performed in a single reaction stage at 180 or 190 °C, using a microwave reactor. The reaction media contained wood, water, methyl isobutyl ketone, and an acidic ionic liquid, which acted as a catalyst. In media catalyzed with 1-butyl-3-methylimidazolium hydrogen sulfate, up to 60.5% pentosan conversion into furfural was achieved, but the conversions of cellulose and (galacto) glucomannan in levulinic acid were low. Improved results were achieved when AILs bearing a sulfonated alkyl chain were employed as catalysts. In media containing 1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate as a catalyst, near quantitative conversion of pentosans into furfural was achieved at a short reaction time (7.5 min), together with 32.8% conversion of hexosans into levulinic acid. Longer reaction times improved the production of organic acids, but resulted in some furfural consumption. A similar reaction pattern was observed in experiments using 1-(3-sulfobutyl)-3-methylimidazolium hydrogen sulfate as a catalyst.

Elucidation of Changes in Cellulose Ultrastructure and Accessibility in Hardwood Fractionation Processes with Carbohydrate Binding Modules

We have recently presented a sequential treatment method, in which steam explosion (STEX) was followed by hydrotropic extraction (HEX), to selectively fractionate cellulose, hemicellulose, and lignin in hardwood into separate process streams. However, above a treatment severity threshold, the structural alterations in the cellulose-enriched fraction appeared to restrict the enzymatic hydrolyzability and delignification efficiency. To better understand the ultrastructural changes in the cellulose, hardwood chips were treated by single (STEX or HEX) and combined treatments (STEX and HEX), and the cellulose accessibility quantified with carbohydrate-binding modules (CBMs) that bind preferentially to crystalline (CBM2a) and paracrystalline cellulose (CBM17). Fluorescent-tagged versions of the CBMs were used to map the spatial distribution of cellulose substructures with confocal laser scanning microscopy. With increasing severities, STEX increased the apparent crystallinity (CBM2a/CBM17-ratio) and overall accessibility (CBM2aH6 + CBM17) of the cellulose, whereas HEX demonstrated the opposite trend. The respective effects could also be discerned in the combined treatments where increasing severities further resulted in higher hemicellulose dissolution and, although initially beneficial, in stagnating accessibility and hydrolyzability. This study suggests that balancing the severities in the two treatments is required to maximize the fractionation and simultaneously achieve a reactive and accessible cellulose that is readily hydrolyzable.

Hydrotropic pretreatment on distillery stillage for efficient cellulosic ethanol production

Effectiveness of hydrotropic delignification using sodium cumene sulfonate for pretreatment of rye, wheat and maize stillage for further use in the production of bioethanol was evaluated. The highest stillage biomass extractives was obtained for a biomass particle size <1.0 mm, when exposed to 131 °C for 1 h at 20% v/v hydrotrope concentration. It has been shown that hydrotropic treatment causes changes in the stillage biomass structure (increase in porosity) and reduces the lignin content in biomass by 7-17%. Delignification with a hydrotrope also increased the concentration of fermentable sugars in the media prepared with stillage biomass, which led to a higher final ethanol concentration (up to ca. 3.5 g/L). Hydrotropic treatment is an effective way of pretreatment of stillage biomass. It provides a high degree of biomass bioconversion and creates the prospect of integrating the 1st and 2nd generation ethanol production process to more fully utilize the raw material.

A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids

Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO2 capture, etc. As solvents, the unlimited combinations of cations and anions have given ionic liquids a remarkably wide range of solvation power covering a variety of organic and inorganic materials. Ionic liquids are also considered "green" solvents due to their negligible vapor pressure, which means no emission of volatile organic compounds. Due to these interesting properties, ionic liquids have been explored as promising solvents for the dissolution and fractionation of wood and cellulose for biofuel production, pulping, extraction of nanocellulose, and for processing all-wood and all-cellulose composites. This review describes, at first, the potential of ionic liquids and the impact of the cation/anion combination on their physiochemical properties and on their solvation power and selectivity to wood polymers. It also elaborates on how the dissolution conditions influence these parameters. It then discusses the different approaches, which are followed for the homogeneous and heterogeneous dissolution and fractionation of wood and cellulose using ionic liquids and categorize them based on the target application. It finally highlights the challenges of using ionic liquids for wood and cellulose dissolution and processing, including side reactions, viscosity, recyclability, and price.

Transparent Cellulose/Technical Lignin Composite Films for Advanced Packaging

Although recent work has shown natural lignin products are promising to fabricate various polymer based functional composites, high-value applications were challenged by their structural complexity and inhomogeneity. This work specially assessed the potential of four technical lignins for cellulose based functional films production. These four technical lignins were obtained by emerging pretreatment systems, i.e., lactic acid-betaine deep eutectic solvent (DES), ethanol organosolv, soda/anthraquinone (Soda/AQ) and the sodium salicylate hydrotrope, and their phenolic substructures were comparatively identified by prevalent ³¹P NMR technique. The influence of lignin chemical structure on the antioxidant potential and UV-shielding performance of the prepared cellulose/technical lignin composite films were assessed. Results showed severe organosolv and soda/AQ pretreatment produced technical lignins with higher total phenolic hydroxyl groups (3.37 and 3.23 mmol g-1 respectively), which also exhibited higher antioxidant activities. The composite films could effectively block the ultraviolet lights especially for UVB region (ultraviolet B, 280–315 nm) at only 5 wt.% lignin content. The contribution of lignin phenolic substructures to both antioxidant activity and UV-shielding property from high to low was syringyl > guaiacyl > p-hydroxyphenyl phenolic hydroxyl groups. This work provided some useful information that could facilitate upstream lignin extraction or downstream value-added applications.

The Effect of Lignin Content in Birch and Beech Kraft Cellulosic Pulps on Simple Sugar Yields from the Enzymatic Hydrolysis of Cellulose

The results of enzymatic hydrolysis of birch and beech kraft cellulosic pulps indicate that they may be promising feedstocks for fermentation processes including biofuel manufacturing. The aim of this study was to investigate whether birch and beech wood require the same degree of delignification by kraft pulping as pine wood. The differences observed in the efficiency of hydrolysis for the raw materials tested suggest that the differences in the anatomical structure of the examined wood in relation to pine wood is essential for the efficiency of the enzymatic hydrolysis process. The yields of glucose and other reducing sugars obtained from the birch and beech cellulosic pulps were similar (up to around 75% and 98.3% dry weight, and 76% and 98.6% dry weight, respectively). The highest glucose yields from cellulose contained in the birch and beech pulp were around 81.2% (at a Kappa number of 28.3) and 83.1% (at a Kappa number of 30.4), respectively. The maximum glucose yields and total reducing sugars of birch wood on a dry weight basis (39.8% and 52.1%, respectively) were derived from the pulp at a Kappa number of 28.3, while the highest yields of glucose and total reducing sugars of beech wood on a dry weight basis (around 36.9% and 48.2%, respectively) were reached from the pulp at a Kappa number of 25.3. To obtain the highest glucose yields and total reducing sugars of a wood on a dry weight basis, total lignin elimination from the birch and beech pulps was not necessary. However more in-depth delignification of birch and beech wood is required than for pine wood.

Enhancement of Hydrotropic Fractionation of Poplar Wood using Autohydrolysis and Disk Refining Pretreatment: Morphology and Overall Chemical Characterization

Solid acids have been proposed as a hydrolytic agent for wood biomass dissolution. In this work, we presented an environmentally friendly physicochemical treatment to leave behind cellulose, dissolve hemicellulose, and remove lignin from poplar wood. Several pretreatments, such as autohydrolysis and disk refining, were compared to optimize and modify the process. The p-toluenesulfonic acid could extract lignin from wood with a small amount of cellulose degradation. Disk refining with subsequent acid hydrolysis (so-called physicochemical treatment) doubled the delignification efficiency. A comprehensive morphology and overall chemical composition were provided. The crystallinity index (CrI) of treated poplar was increased and the chemical structure was changed after physicochemical treatment. Optical microscopy and scanning electron microscopy analysis demonstrated physicochemical treatment affected the morphology of poplar wood by removing lignin and generating fiberization. In general, this work demonstrated this physicochemical method could be a promising fractionation technology for lignocellulosic biomass due to its advantages, such as good selectivity, in removing lignin while preserving cellulose.

Sequential fractionation of the lignocellulosic components in hardwood based on steam explosion and hydrotropic extraction

BACKGROUND

The forest biorefinery plays an important part in the evolving circular bioeconomy due to its capacity to produce a portfolio of bio-based and sustainable fuels, chemicals, and materials. To tap into its true potential, more efficient and environmentally benign methods are needed to fractionate woody biomass into its main components (cellulose, hemicellulose, and lignin) without reducing their potential for valorization. This work presents a sequential fractionation method for hardwood based on steam pretreatment (STEX) and hydrotropic extraction (HEX) with sodium xylene sulfonate. By prehydrolyzing the hemicellulose (STEX) and subsequently extract the lignin from the cellulose fraction (HEX), the major wood components can be recovered in separate process streams and be further valorized.

RESULTS

Using autocatalyzed STEX and HEX, hemicellulose (> 70%) and lignin (~ 50%) were successfully fractionated and recovered in separate liquid streams and cellulose preserved (99%) and enriched (~ twofold) in the retained solids. Investigation of pretreatment conditions during HEX showed only incremental effects of temperature (150-190 °C) and hold-up time (2-8 h) variations on the fractionation efficiency. The hydrolyzability of the cellulose-rich solids was analyzed and showed higher cellulose conversion when treated with the combined process (47%) than with HEX alone (29%), but was inferior to STEX alone (75%). Protein adsorption and surface structure analysis suggested decreased accessibility due to the collapse of the fibrillose cellulose structure and an increasingly hydrophobic lignin as potential reasons.

CONCLUSION

This work shows the potential of sequential STEX and HEX to fractionate and isolate cellulose, hemicellulose, and a sulfur-free lignin in separate product streams, in an efficient, sustainable, and scalable process.

Topochemical Engineering of Cellulose-Based Functional Materials

Topochemical engineering is a method of designing the fractionation (disassembly) and fabrication (assembly) of highly engineered functional materials using a combination of molecular and supramolecular techniques. Cellulose is one of the naturally occurring biopolymers, currently considered to be an important raw material for the design and development of sustainable products and processes. This feature article deals with new insights into how cellulose can be processed and functionalized using topochemical engineering in order to create functional fibers, enhance biopolymer dissolution in water-based solvents, and control the shaping of porous materials. Subsequently, topochemical engineering of cellulose offers a variety of morphological structures such as highly engineered fibers, functional cellulose beads, and reactive powders that find relevant applications in pulp bleaching, enzyme and antimicrobial drug carriers, ion exchange resins, photoluminescent materials, waterproof materials, fluorescent materials, flame retardants, and template materials for inorganic synthesis. The topochemical engineering of biopolymers and biohybrids is an exciting and emerging area of research that can boost the design of new bioproducts with novel functionalities and technological advancements for biobased industries.

Microwave-Assisted Oxalic Acid Pretreatment for the Enhancing of Enzyme Hydrolysis in the Production of Xylose and Arabinose from Bagasse

In this study, highly-efficient hydrolysis of bagasse into xylose and arabinose sugars (C5 sugars) was developed by microwave-assisted oxalic acid pretreatment under mild reaction conditions. The effects of acid and hydrolysis conditions on the C5 sugar yields were discussed. The results showed that oxalic acid performed better than hydrochloric acid and maleic acid, and was a promising alternative to sulfuric acid for xylose production at the same acid concentration. The maximum yields of xylose (95.7%) and arabinose (91.5%) were achieved via the microwave-assisted oxalic acid pretreatment (120 °C, 10 min, 0.4 mol/L, solid–liquid ratio of 1:50 g/mL), indicating that almost all xylan-type hemicelluloses were released from the cell wall and hydrolyzed into C5 sugars. After pretreatment, more than 90% of the cellulose in the residual bagasse was converted to glucose (92.2%) by enzymatic hydrolysis. This approach could realize the highly-efficient hydrolysis of xylan from bagasse into C5 sugars, which would enhance the enzyme hydrolysis of treated bagasse into glucose.

Understanding the Changes to Biomass Surface Characteristics after Ammonia and Organosolv Pretreatments by Using Time-of-Flight Secondary-Ion Mass Spectrometry (TOF-SIMS)

Surface characteristic changes to poplar after ammonia and organosolv pretreatments were investigated by means of time-of-flight secondary-ion mass spectrometry (TOF-SIMS) analysis. Whereas normalized total polysaccharides and lignin contents on the surface differed from bulk chemical compositions, the surface cellulose ions detected by TOF-SIMS showed the same value trend as the cellulose content in the biomass. In addition, the lignin syringyl/guaiacyl ratio according to TOF-SIMS results showed the same trend as the ratio measured by means of NMR spectroscopic analysis, even though the ratio scales for each method were different. A similar correlation was determined between the surface cellulose and glucose release after enzymatic hydrolysis. These results demonstrate that surface characterization using TOF-SIMS can provide important information about the effects of pretreatment on biomass properties and its hydrolysis.

Comparison of organosolv and hydrotropic pretreatments of eucalyptus for enhancing enzymatic saccharification

The objective of this study was to investigate the effects of organosolv and hydrotropic pretreatments on improving enzymatic hydrolysis of eucalyptus. The chemical composition of the fiber surface was analyzed using X-ray photoelectron spectroscopy (XPS) to determine the surface characteristics of pretreated eucalyptus. Other than the significant decrease of surface coverage by lignin, hydrotropic pretreatment was more effective in removing the lignin and xylose from fiber cell walls than organosolv pretreatment. The restriction of acetyl and phenolic groups in pretreated substrates was typically eliminated by hydrotropic pretreatments. Moreover, fiber structure and morphology after pretreatments were more suitable for enzymatic hydrolysis. Cellulase adsorption capacity was notably improved by hydrotropic pretreatment, which indicating the better enzyme accessibility of cellulose in pretreated substrates. Eventually, higher glucose yield was obtained with hydrotropic pretreatment. In addition, the precipitated lignin as an important by-product of pretreatments was characterized by Fourier transforms infrared spectroscopy (FTIR) also.

Evaluation of hydrotropic pretreatment on lignocellulosic biomass

The production of cellulosic ethanol from biomass is considered as a promising alternative to fossil fuels, providing a sustainable option for fuels production in an environmentally compatible manner. The presence of lignin poses a significant challenge for obtaining biofuels and bioproducts from biomass. Part of that problem involves understanding fundamental aspects of lignin structure which can provide a pathway for the development of improved technologies for biomass conversion. Hydrotropic pretreatment has several attractive features that make it an attractive alternative for biofuel production. This review highlights the recent developments on hydrotropic pretreatment processes for lignocellulosic biomass on a molecular structure basis for recalcitrance, with emphasis on lignin concerning chemical structure, transformation and recalcitrance. The review also evaluates the hydrotropic delignification in comparison to alkaline delignification on lignin reduction and surface coverage by lignin. The effect of hydrotrope pretreatment on enzymatic saccharification has also been discussed.

Corncob lignocellulose for the production of furfural by hydrothermal pretreatment and heterogeneous catalytic process

In this paper, an environmentally-friendly two-step process for furfural production was developed by the hydrothermal pretreatment of corncob and the heterogeneous catalysis of the hydrolysate using a solid acid catalyst.

Comparative study of alkaline hydrogen peroxide and organosolv pretreatments of sugarcane bagasse to improve the overall sugar yield

Green liquor (GL) combined with H2O2 (GL-H2O2) and green liquor (GL) combined with ethanol (GL-ethanol) were chosen for treating sugarcane bagasse. Results showed that the glucose yield (calculated from the glucose content as a percentage of the theoretical glucose available in the substrates)of sugarcane bagasse from GL-ethanol pretreatment (97.7%) was higher than that from GL-H2O2 pretreatment (41.7%) after 72h hydrolysis with 18 filter paper unit (FPU)/g-cellulose for cellulase, 27,175 cellobiase units (CBU)/g-cellulose for β-glucosidase. Furthermore, about 94.1% of xylan was converted to xylose after GL-ethanol pretreatment without additional xylanase, while the xylose yield was only 29.2% after GL-H2O2 pretreatment. Scanning electron microscopy showed that GL-ethanol pretreatment could break up the fiber severely. Moreover, GL-ethanol pretreated substrate was more accessible to cellulase and more hydrophilic than that of GL-H2O2 pretreated. Therefore, GL-ethanol pretreatment is a promising method for improving the overall sugar (glucose and xylan) yield of sugarcane bagasse.

Coupled enzymatic hydrolysis and ethanol fermentation: ionic liquid pretreatment for enhanced yields

BACKGROUND

Pretreatment is a vital step upon biochemical conversion of lignocellulose materials into biofuels. An acid catalyzed thermochemical treatment is the most commonly employed method for this purpose. Alternatively, ionic liquids (ILs), a class of neoteric solvents, provide unique opportunities as solvents for the pretreatment of a wide range of lignocellulose materials. In the present study, four ionic liquid solvents (ILs), two switchable ILs (SILs) DBU-MEA-SO2 and DBU-MEA-CO2, as well as two 'classical' ILs [Amim][HCO2] and [AMMorp][OAc], were applied in the pretreatment of five different lignocellulosic materials: Spruce (Picea abies) wood, Pine (Pinus sylvestris) stem wood, Birch (Betula pendula) wood, Reed canary grass (RCG, Phalaris arundinacea), and Pine bark. Pure cellulosic substrate, Avicel, was also included in the study. The investigations were carried out in comparison to acid pretreatments. The efficiency of different pretreatments was then evaluated in terms of sugar release and ethanol fermentation.

RESULTS

Excellent glucan-to-glucose conversion levels (between 75 and 97 %, depending on the biomass and pretreatment process applied) were obtained after the enzymatic hydrolysis of IL-treated substrates. This corresponded between 13 and 77 % for the combined acid treatment and enzymatic hydrolysis. With the exception of 77 % for pine bark, the glucan conversions for the non-treated lignocelluloses were much lower. Upon enzymatic hydrolysis of IL-treated lignocelluloses, a maximum of 92 % hemicelluloses were also released. As expected, the ethanol production upon fermentation of hydrolysates reflected their sugar concentrations, respectively.

CONCLUSIONS

Utilization of various ILs as pretreatment solvents for different lignocelluloses was explored. SIL DBU-MEA-SO2 was found to be superior solvent for the pretreatment of lignocelluloses, especially in case of softwood substrates (i.e., spruce and pine). In case of birch and RCG, the hydrolysis efficiency of the SIL DBU-MEA-CO2 was similar or even better than that of DBU-MEA-SO2. Further, the IL [AMMorp][OAc] was found as comparably efficient as DBU-MEA-CO2. Pine bark was highly amorphous and none of the pretreatments applied resulted in clear benefits to improve the product yields.

Quantitative characterization of the impact of pulp refining on enzymatic saccharification of the alkaline pretreated corn stover

In this work, corn stover was refined by a pulp refining instrument (PFI refiner) after NaOH pretreatment under varied conditions. The quantitative characterization of the influence of PFI refining on enzymatic hydrolysis was studied, and it was proved that the enhancement of enzymatic saccharification by PFI refining of the pretreated corn stover was largely due to the significant increment of porosity of substrates and the reduction of cellulose crystallinity. Furthermore, a linear relationship between beating degree and final total sugar yields was found, and a simple way to predict the final total sugar yields by easily testing the beating degree of PFI refined corn stover was established. Therefore, this paper provided the possibility and feasibility for easily monitoring the fermentable sugar production by the simple test of beating degree, and this will be of significant importance for the monitoring and controlling of industrial production in the future.

Combined deacetylation and PFI refining pretreatment of corn cob for the improvement of a two-stage enzymatic hydrolysis

A combined deacetylation and PFI refining pretreatment was applied to corn cob for the improvement of a two-stage enzymatic hydrolysis. In stage 1, the pretreated corn cob was first hydrolyzed by xylanase to produce xylo-oligosaccharides (XOS). In stage 2, the solid residue isolated from stage 1 was further hydrolyzed by cellulase and β-glucosidase. NaOH, Na2CO3, and Ca(OH)2 were tested to remove acetyl groups in the process of deacetylation, and it was found that Ca(OH)2 could be the most suitable alkali for deacetylation in this work. After deacetylation using 0.8 mmol of Ca(OH)2/g of substrate and PFI refining, 50.5% xylan in the raw material could be hydrolyzed into XOS. The corresponding xylan yield of stage 1, the glucan yield of stage 2, and the total sugar yield (all sugars released in the hydrolyzate) after the two-stage enzymatic hydrolysis were 0.306, 0.305, and 0.661 g/g of corn cob, respectively.

Catalytic hydrothermal pretreatment of corncob into xylose and furfural via solid acid catalyst

Selectively catalytic hydrothermal pretreatment of corncob into xylose and furfural has been developed in this work using solid acid catalyst (SO4(2-)/TiO2-ZrO2/La(3+)). The effects of corncob-to-water ratio, reaction temperature and residence time on the performance of catalytic hydrothermal pretreatment were investigated. Results showed that the solid residues contained mainly lignin and cellulose, which was indicative of the efficient removal of hemicelluloses from corncob by hydrothermal method. The prepared catalyst with high thermal stability and strong acid sites originated from the acid functional groups was confirmed to contribute to the hydrolysis of polysaccharides into monosaccharides followed by dehydration into furfural. Highest furfural yield (6.18 g/100g) could be obtained at 180°C for 120 min with 6.80 g/100g xylose yield when the corncob/water ratio of was 10:100. Therefore, selectively catalytic hydrothermal pretreatment of lignocellulosic biomass into important platform chemicals by solid acids is considered to be a potential treatment for biodiesel and chemical production.

Advancing lignocellulose bioconversion through direct assessment of enzyme action on insoluble substrates

Microbial utilization of lignocellulose from plant cell walls is integral to carbon cycling on Earth. Correspondingly, secreted enzymes that initiate lignocellulose depolymerization serve a crucial step in the bioconversion of lignocellulosic biomass to fuels and chemicals. Genome and metagenome sequencing efforts that span the past decade reveal the diversity of enzymes that have evolved to transform lignocellulose from wood, herbaceous plants and grasses. Nevertheless, there are relatively few examples where 'omic' technologies have identified novel enzyme activities or combinations thereof that dramatically improve the economics of lignocellulose bioprocessing and utilization. A likely factor contributing to the discrepancy between sequence-based enzyme discovery and enzyme application is the common practice to screen enzyme candidates based on activity measurements using soluble model compounds. In this context, the development and application of imaging, physicochemical, and spectromicroscopic techniques that allow direct assessment of enzyme action on relevant lignocellulosic substrates is reviewed.

Understanding changes in cellulose crystalline structure of lignocellulosic biomass during ionic liquid pretreatment by XRD

X-ray diffraction (XRD) was used to understand the interactions of cellulose in lignocellulosic biomass with ionic liquids (ILs). The experiment was designed in such a way that the process of swelling and solubilization of crystalline cellulose in plant cell walls was followed by XRD. Three different feedstocks, switchgrass, corn stover and rice husk, were pretreated using 1-butyl-3-methylimidazolium acetate ([C4mim][OAc]) at temperatures of 50-130°C for 6h. At a 5 wt.% biomass loading, increasing pretreatment temperature led to a drop in biomass crystallinity index (CrI), which was due to swelling of crystalline cellulose. After most of the crystalline cellulose was swollen with IL molecules, a low-order structure was found in the pretreated samples. Upon further increasing temperature, cellulose II structure started to form in the pretreated biomass samples as a result of solubilization of cellulose in [C4mim][OAc] and subsequent regeneration.

Topochemistry of alkaline, alkaline-peroxide and hydrotropic pretreatments of common reed to enhance enzymatic hydrolysis efficiency

Common reed was studied as raw material for sugar bioconversion. The low temperature alkaline, alkaline-peroxide and hydrotropic pretreatments were employed to overcome the recalcitrance of reed before enzymatic hydrolysis. After pretreatments, lignin was efficiently decreased from the fiber cell wall. Xylan was significantly reduced by hydrotropic pretreatment as well. The surface chemical compositions of reed before and after pretreatments were investigated by X-ray spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Reed had a high surface coverage by lignin. Hydrotropic pretreatment was outstanding to decrease the surface coverage by lignin and expose the polysaccharides to fiber surface. The surface lignin reduction was also supported by attenuated total reflectance (ATR)-FTIR results. Furthermore, the topochemical modification of the fiber wall by hydrotropic pretreatment could improve the fiber digestibility, and thus the maximum glucan and xylan yields with the cellulase dosage of 20 FPU/g raised to 93.1% and 25.5%, respectively.