Conversion Of Lignocellulose Research Articles

Enhanced enzymatic hydrolysis of cellulose by endoglucanase via expansin pretreatment and the addition of zinc ions

One of the major limitations of lignocellulose conversion is the relatively low efficiency of cellulases. Expansins can act as an accessory protein to loosen the rigid cellulose structure and promote cellulose hydrolysis. However, the synergistic action of expansin is not well understood. In this study, we employed quartz crystal microbalance with dissipation to real-time monitor the adsorption of Bacillus subtilis expansin (BsEXLX1) and endoglucanase I (Cel7B) and the hydrolysis of cellulose. The effects of pH, temperature, and zinc ions on the initial adsorption rate and adsorption capacity of BsEXLX1 were examined. When 36.5 mM of zinc ions was added, the irreversible adsorption ratio of BsEXLX1 further increased to 4.63 times the value in the absence of zinc ions, whereas the initial adsorption rate and the hydrolysis rate constants of Cel7B could reach 2.16 times and 2.05 times the values in the absence of zinc ions, respectively.

Combining Michaelis-Menten theory and enzyme deactivation reactions for the kinetic study of enzymatic hydrolysis by different pretreated sugarcane bagasse

Conversion of lignocellulose to sugar depends on expensive cellulase and xylanase, hence, improvement of enzyme utilization is important. Enzymatic kinetics can guide researchers toward efficient enzymes utilization. Based on Michaelis-Menten theory and enzyme deactivation reactions, the novel kinetic models describing sugar (glucose and xylose) yield are deduced. The model based on second-order reaction is significantly superior compared to first-order reaction, which is verified by initial and maximum hydrolytic rate. Hydrolytic rate displays a linear relationship with enzyme loading. Sugar yield differs in enzymatic hydrolysis of various pretreated substrates, which is explained by the preferred model. Enzyme deactivation based on the model shows that higher enzyme loading results in reduced activity retention percentage, due to feedback inhibition of products and ineffective adsorption of substrate to enzyme during the hydrolytic process. Therefore, the developed model allows more in-depth study of enzymatic kinetics and provides a useful guide for efficient enzyme utilization.

Thermophilic microbial deconstruction and conversion of natural and transgenic lignocellulose.

The potential to convert renewable plant biomasses into fuels and chemicals by microbial processes presents an attractive, less environmentally intense alternative to conventional routes based on fossil fuels. This would best be done with microbes that natively deconstruct lignocellulose and concomitantly form industrially relevant products, but these two physiological and metabolic features are rarely and simultaneously observed in nature. Genetic modification of both plant feedstocks and microbes can be used to increase lignocellulose deconstruction capability and generate industrially relevant products. Separate efforts on plants and microbes are ongoing, but these studies lack a focus on optimal, complementary combinations of these disparate biological systems to obtain a convergent technology. Improving genetic tools for plants have given rise to the generation of low-lignin lines that are more readily solubilized by microorganisms. Most focus on the microbiological front has involved thermophilic bacteria from the genera Caldicellulosiruptor and Clostridium, given their capacity to degrade lignocellulose and to form bio-products through metabolic engineering strategies enabled by ever-improving molecular genetics tools. Bioengineering plant properties to better fit the deconstruction capabilities of candidate consolidated bioprocessing microorganisms has potential to achieve the efficient lignocellulose deconstruction needed for industrial relevance.

Staged biorefinery of Moso bamboo by integrating polysaccharide hydrolysis and lignin reductive catalytic fractionation (RCF) for the sequential production of sugars and aromatics

Towards a waste-free biorefinery was of the lignocellulose valuable and sustainable conversion. In this study a staged biorefinery for lignocellulose conversion to maximum valuable products was proposed and experimentally demonstrated by using Moso bamboo (Phyllostachys heterocycla cv. Pubescens). It is an integrated sequential process including hemicellulose acidolysis with FeCl3 as the catalyst, reductive catalytic fractionation (RCF) of lignin with Pd/C and sulfuric acid as catalysts, and enzymatic hydrolysis of cellulose. The influence of acid FeCl3 catalyzed hemicellulose acidolysis on the subsequent RCF of lignin and enzymatic hydrolysis of cellulose were investigated and the optimized conditions for hemicellulose acidolysis were obtained. The yield of pentose, aromatic monomers, and glucose was respectively 85.8 wt%, 28.5 wt%, and 64.3 wt% relative to the initial hemicellulose, lignin, and cellulose contained in the Moso bamboo. The conversion and the products were analyzed and characterized using gas chromatography mass spectrometry (GCMS), Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and heteronculear single quantum coherence nuclear magnetic resonance (HSQC-NMR) spectrometry. The results indicated that hemicellulose acidolysis with FeCl3 resulted in the dissolution of some low molecular weight lignin and the cleavage of lignin-carbohydrate linkages of 2-O-Ac-β-d-xylopyranoside, while the connections of 3-O-Ac-β-d-xylopyranoside, phenyl glycoside and the β-ether linkages in lignin were remained. However, excessive removal of hemicellulose negatively influenced the stability of the lignin structure and delignification. RCF of lignin resulted to the hydrolysis of lignocellulose, yielded cellulose and aromatic monomers via the cleavage of β-ether bonds.

Advances in Valorization of Lignocellulosic Biomass towards Energy Generation

The booming demand for energy across the world, especially for petroleum-based fuels, has led to the search for a long-term solution as a perfect source of sustainable energy. Lignocellulosic biomass resolves this obstacle as it is a readily available, inexpensive, and renewable fuel source that fulfills the criteria of sustainability. Valorization of lignocellulosic biomass and its components into value-added products maximizes the energy output and promotes the approach of lignocellulosic biorefinery. However, disruption of the recalcitrant structure of lignocellulosic biomass (LCB) via pretreatment technologies is costly and power-/heat-consuming. Therefore, devising an effective pretreatment method is a challenge. Likewise, the thermochemical and biological lignocellulosic conversion poses problems of efficiency, operational costs, and energy consumption. The advent of integrated technologies would probably resolve this problem. However, it is yet to be explored how to make it applicable at a commercial scale. This article will concisely review basic concepts of lignocellulosic composition and the routes opted by them to produce bioenergy. Moreover, it will also discuss the pros and cons of the pretreatment and conversion methods of lignocellulosic biomass. This critical analysis will bring to light the solutions for efficient and cost-effective conversion of lignocellulosic biomass that would pave the way for the development of sustainable energy systems.

MiR396-GRF module associates with switchgrass biomass yield and feedstock quality.

SummaryImproving plant biomass yield and/or feedstock quality for highly efficient lignocellulose conversion has been the main research focus in genetic modification of switchgrass (Panicum virgatum L.), a dedicated model plant for biofuel production. Here, we proved that overexpression of miR396 (OE‐miR396) leads to reduced plant height and lignin content mainly by reducing G‐lignin monomer content. We identified nineteen PvGRFs in switchgrass and proved thirteen of them were cleaved by miR396. MiR396‐targeted PvGRF1, PvGRF9 and PvGRF3 showed significantly higher expression in stem. By separately overexpressing rPvGRF1, 3 and 9, in which synonymous mutations abolished the miR396 target sites, and suppression of PvGRF1/3/9 activity via PvGRF1/3/9‐SRDX overexpression in switchgrass, we confirmed PvGRF1 and PvGRF9 played positive roles in improving plant height and G‐lignin content. Overexpression of PvGRF9 was sufficient to complement the defective phenotype of OE‐miR396 plants. MiR396‐PvGRF9 modulates these traits partly by interfering GA and auxin biosynthesis and signalling transduction and cell wall lignin, glucose and xylan biosynthesis pathways. Moreover, by enzymatic hydrolysis analyses, we found that overexpression of rPvGRF9 significantly enhanced per plant sugar yield. Our results suggest that PvGRF9 can be utilized as a candidate molecular tool in modifying plant biomass yield and feedstock quality.

Adaptive laboratory evolution of Yarrowia lipolytica improves ferulic acid tolerance

Yarrowia lipolytica strain is a promising cell factory for the conversion of lignocellulose to biofuels and bioproducts. Despite the inherent robustness of this strain, further improvements to lignocellulose-derived inhibitors toxicity tolerance of Y. lipolytica are also required to achieve industrial application. Here, adaptive laboratory evolution was employed with increasing concentrations of ferulic acid. The adaptive laboratory evolution experiments led to evolve Y. lipolytica strain yl-XYL + *FA*4 with increased tolerance to ferulic acid as compared to the parental strain. Specifically, the evolved strain could tolerate 1.5 g/L ferulic acid, whereas 0.5 g/L ferulic acid could cause about 90% lethality of the parental strain. Transcriptome analysis of the evolved strain revealed several targets underlying toxicity tolerance enhancements. YALI0_E25201g, YALI0_F05984g, YALI0_B18854g, and YALI0_F16731g were among the highest upregulated genes, and the beneficial contributions of these genes were verified via reverse engineering. Recombinant strains with overexpressing each of these four genes obtained enhanced tolerance to ferulic acid as compared to the control strain. Fortunately, recombinant strains with overexpression of YALI0_E25201g, YALI0_B18854g, and YALI0_F16731g individually also obtained enhanced tolerance to vanillic acid. Overall, this work demonstrated a whole strain improvement cycle by "non-rational" metabolic engineering and presented new targets to modify Y. lipolytica for microbial lignocellulose valorization. KEY POINTS: • Adaptive evolution improved the ferulic acid tolerance of Yarrowia lipolytica • Transcriptome sequence was applied to analyze the ferulic acid tolerate strain • Three genes were demonstrated for both ferulic acid and vanillic acid tolerance.

Hydrothermal liquefaction conversion of lignocelluloses with enhanced fungal pretreatment

Although it is considered to be an environmental-friendly approach to reduce recalcitrance of lignocellulosic biomass, current fungal pretreatment methods suffer from major weaknesses, including inefficient delignification, loss of cellulose, and the need for long processing time. The addition of Mn to white-rot fungal treatment process could facilitate selective removal of lignin. However, the effect of Mn addition on the thermal decomposition and conversion of fungi-pretreated biomass is not clear. In this study, three types of lignocelluloses (poplar, wheat straw, and corn stover) were pretreated with fungi that was cultured with Mn supplements. Results demonstrated that the Mn addition affected thermogravimetric properties, as well as lignin and hemicellulose contents. The poplar samples showed the highest delignification (50.5 %) and lowest loss of cellulose (1.1 %). The initial degradation temperatures were lowered by 11–36 ℃, measured with thermogravimetric analysis. Additionally, fungi-pretreated feedstocks were converted in a two-stage hydrothermal liquefaction process to produce hydrolyzed sugars and value-added derivatives in a stepwise manner. A 163.6 % more hemicellulose sugars were recovered from poplar with the addition of Mn compared with untreated samples, while 75.2 % of hemicellulose sugar production was achieved in the first stage from fungi-treated corn stover with the Mn addition. Pretreating lignocelluloses with fungi that includes Mn supplements significantly improved sugar production. Thus, the combination of fungal pretreatment with the subsequent thermochemical conversion process offers a promising alternative technical route for lignocellulosic biomass valorization.

Improving the enzymatic digestibility of alkaline-pretreated lignocellulosic biomass using polyDADMAC

Using cheap additives to improve the efficiency of enzymatic hydrolysis and lower the enzyme dosage proves to be an effective way to bring down the lignocellulose conversion cost. When poly-diallyl-dimethyl-ammonium chloride (polyDADMAC) was added in alkaline pretreatment of different lignocelluloses, it did not improve the delignification but significantly enhanced the succeeding enzymatic hydrolysis. The corn stover pretreated with polyDADMAC showed an increase of 18.4 % and 21.8 % in glucan and xylan digestibility, respectively. PolyDADMAC addition also increased the glucan and xylan digestibility of alkaline-pretreated switchgrass by 17.7 % and 12.1 %, respectively. For lignin-free cellulose, the glucan digestibility increased by 31 % with polyDADMAC treatment. The boost effect was because of the disruption of cellulose fiber by polyDADMAC, rather than the removal of lignin. SEM images of pretreated samples showed caustic pits on the surface by etching with polyDADMAC, which facilitated the enzyme accessibility. The crystallinity of treated samples decreased while the surface area, pore size, and pore volume increased with polyDADMAC.

Effect of the method for the elimination of inhibitors present in Miscanthus giganteus hydrolysates on ethanol production effectiveness

The pretreatment of lignocellulosic material performed to improve substrate’s susceptibility to enzymatic hydrolysis is usually accompanied by reactions leading to the synthesis of compounds that inhibit the metabolic activity of microorganisms. Their toxicity is the main obstacle to the successful bioconversion of lignocellulosic hydrolysates. The identification of these inhibitors and the choice of the optimal detoxication method are crucial for the improving the efficiency of fermentation processes. Material rinsing with water after processing is a common detoxication practice. However, it generates material losses, thus affecting contents of saccharides in the fermentation medium, which may in turn trigger higher costs of lignocellulose conversion to ethanol and other products with a higher added value. A study was undertaken to determine the effect of selected methods for the detoxication of an enzymatic hydrolysate from Miscanthus giganteus on the fermentation efficiency of saccharide derivatives. The experiment conducted with Mucor rouxii DSM 1191 demonstrated the usability of the detoxication method based on the activated carbon. After 96-h fermentation of Miscanthus hydrolysates, the alcohol content in the post-reaction medium was higher by 14% than in the control experiment wherein the material was rinsed with water after pretreatment. The experiment carried out with Saccharomyces cerevisiae 7, NRRL 978 showed no positive impact of the alternative detoxication methods replacing material rinsing on the efficiency of ethanol synthesis. The highest concentration of this metabolite (2.04% (v/v)) was obtained in the experimental variant in which the mentioned operation was coupled with detoxication of hydrolysates using calcium hydroxide.

Cellulose Gasification with Ca-Fe Oxygen Carrier in Chemical-Looping Process

Biomass-derived chemical looping gasification (BCLG) is a novel technology for lignocellulose energy applications. Ca-Fe oxygen carriers have been proven to be a potential material for efficient lignocellulose conversion and hydrogen-enriched syngas production in process studies. In this study, Thermogravimetry-mass spectrometry (TG-MS), pyrolysis chromatography-mass spectrometry (Py-GC-MS) and fixed-bed experiments were conducted, and the cellulose BCLG product was analyzed to explore the mechanism of reaction between Ca-Fe OCs and biomass char or volatiles. The mechanism of the synergistic effect of Ca-Fe was analyzed to explain the characteristics of the OCs. The results showed the Ca-based materials act as catalysts to promote the decomposition of cellulose monomers at primary reaction and char at secondary reaction. And also promote the reforming and oxidation of volatiles by chemisorption. Ca participates in the construction of inert substances, such as Ca 2 Fe 2 O 5 , to avoid the deep oxidation of CO and H 2 . Fe-based material supplies oxygen and promotes the reforming of volatile. Compared with Fe 2 O 3 and CaO/Fe 2 O 3 , CaFe 2 O 4 showed a better performance on carbon conversion and H 2 production below 850 °C.

Moving from residual lignocellulosic biomass into high‐value products: Outcomes from a long‐term international cooperation

AbstractMajor progress in the bioprocessing of lignocellulose to fuels and value‐added chemicals has created the possibility of a low carbon‐footprint economy. However, the current complexity and associated costs of lignocellulose conversion result in a higher price for ethanol than for fossil fuels. The cost of cellulosic ethanol production will be lowered by further progress in development of biorefinery technology that produces both ethanol and high‐value chemicals with bio‐based products that are beginning to penetrate consumer markets in the USA, Brazil, and worldwide. The cost‐effectiveness of low carbon‐footprint bioproducts will benefit from advances in supplying large amounts of biomass solids to the biorefinery. We describe here outcomes from a successful long‐term international cooperation between the Laboratory of Renewable Resources Engineering (LORRE) at Purdue University in the United States and Brazil's Agricultural Research Corporation (EMBRAPA) and Federal University of São Carlos (UFSCar), which has contributed practical pathways to enhance the biorefinery concept. This paper gives an overview of developments that address fundamental knowledge of lignocellulosic biomass pretreatment hydrolysis under optimized operational conditions and bioreactor configurations, and the science and engineering that contributes to the effective production of fuel and ethanol and value‐added products from biomass. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd

Lignocellulose Fractionation Using Recyclable Phosphoric Acid: Lignin, Cellulose, and Furfural Production.

The conversion of lignocellulose into its building blocks and their further transformation into valuable platform chemicals (e. g., furfural) are key technologies to move towards the use of renewable resources. This paper explored the disentanglement of lignocellulose into hemicellulose‐derived sugars, cellulose, and lignin in a biphasic solvent system (water/2‐methyltetrahydrofuran) using phosphoric acid as recyclable catalyst. Integrated with the biomass fractionation, in a second step hemicellulose‐derived sugars (mainly xylose) were converted to furfural, which was in situ extracted into 2‐methyltetrahydrofuran with high selectivity (70 %) and yield (56 wt %). To further increase the economic feasibility of the process, a downstream and recycling strategy enabled recovery of phosphoric acid without loss of process efficiency over four consecutive cycles. This outlines a more efficient and sustainable use of phosphoric acid as catalyst, as its inherent costs can be significantly lowered.

Derived high reducing sugar and lignin colloid particles from corn stover

Lignocellulosic biomass is considered as the largest potential candidate to develop alternative energy, such as biofuel, biomaterial. However, the efficient conversion of cellulose and practical utilization of lignin are great challenges for sustainable biorefinery. In this study, high reducing sugar yield and different size of lignin colloid particles (LCPs) were obtained via tetrahydrofuran–water (THF–H2O) pretreatment of corn stover (CS). THF–H2O as a co-solvent, could efficiently dissolve lignin and retain cellulose. After the pretreatment, 640.87 mg/g of reducing sugar was produced, that was 6.66-fold higher than that of the untreated CS. Meanwhile, the pretreatment liquor could form spherical LCPs with different sizes ranged from 202 to 732 nm through self-assembly. We studied the optimal pretreatment condition to simultaneously realize the high reducing sugar yield (588.4 mg/g) and excellent LCPs preparation with average size of 243 nm was under TH22 (THF–H2O pretreatment at 120 °C for 2 h). To further explore the formation of LCPs with different sizes. We studied the lignin structure changes of various conditions, concluded the size of LCPs was related to the lignin concentration and syringyl/guaiacyl (S/G) ratio. As the increase of the lignin concentration and S/G, the sizes of LCPs were increased. G-type lignin was easier to dissolve in the mild pretreatment supernatant, contributing to form smaller LCPs with a good dispersibility. In the severe condition, both of S and G-type lignin were dissolved due to the lignin depolymerization, formed the larger sphere particles. This work provides a novel perspective for the technical design of lignocellulosic biomass conversion.

Local lignocellulosic biofuel and biochar co-production in Sub-Saharan Africa: The role of feedstock provision in economic viability

Bioenergy production in developing countries remains a contentious topic. We study feedstock provision costs in the context of a hybrid thermochemical-biochemical (HTB) lignocellulosic conversion process to co-produce ethanol and biochar in rural Sub-Saharan Africa. Using household-level and market data from Kenya, we examine the availability and cost of purchasing agricultural residues from smallholder farmers and transporting residues to a local-scale (10–20 Mg dry biomass per hour) HTB biofuel-biochar plant with integrated syngas-fermentation for ethanol production. We demonstrate that these costs depend significantly on regionally-specific agroecological and socio-economic conditions, such as crop yields, cropland density, and the value of crop residues to farmers. Only under the best-case scenario do we find that this integrated biofuel-biochar plant with 15 Mg of feedstock per hour capacity has positive net present value.

Cover Feature: Falling Leaves Return to Their Roots: A Review on the Preparation of γ‐Valerolactone from Lignocellulose and Its Application in the Conversion of Lignocellulose (ChemSusChem 24/2020)

The Cover Feature shows the circle of γ-valerolactone (GVL), which can be produced from lignocellulose and simultaneously used for the valorization of lignocellulose, just like the sustainable and renewable cycle “the falling leaves return to their roots”. More information can be found in the Review by R. Xu, K. Liu, et al.

Different acid pretreatments at room temperature boost selective saccharification of lignocellulose via fast pyrolysis

Fermentable sugars are a group of pivotal intermediates and platform compounds achieved by the conversion of lignocellulose. Fast pyrolysis, as a little-explored way to liberate levoglucosan from biomass, may have a potential capability to overcome the technical barriers and fundamental limitations for efficient saccharification. Pretreatment prior to fast pyrolysis is essential to improve levoglucosan yield from lignocellulose. Contrary to typical high-temperature acid pretreatments, a pretreatment under mild conditions was evaluated and optimized, where different acid (formic acid, acetic acid, oxalic acid, nitric acid, phosphoric acid, sulphuric acid and hydrochloric acid) were employed at room temperature prior to fast pyrolysis of lignocellulose. Due to the alteration of chemical compositions and physical structures of biomass, especially the elimination of alkali and alkaline earth metals, the levoglucosan yield of dilute acid pretreated biomass was improved remarkably as compared with that of raw material, meanwhile claimed that acid pretreatments at room temperature had an enough capability in efficient utilization of biomass. In sum, this study offered a novel and economical strategy for selective saccharification of lignocellulose for industrialized bio-refinery.

Establishment of a highly efficient and low cost mixed cellulase system for bioconversion of corn stover by Trichoderma reesei and Aspergillus niger

The high cost of cellulase production is one of the main obstacles for the conversion of lignocellulose into high valued products. As a widely existing biomass resource, corn stover can be used to reduce the cost of cellulase production. In this study, Parameters of producing cellulase by Trichoderma reesei were optimized using Response Surface methodology, the optimum conditions were as follows: 3.84% solid acid pretreated corn stover, 1.19% yeast extract, initial pH of 5.01, 0.12% glycerol monostearate, 0.25% Na2HPO4, with 3% inoculum content for 12 days at 30 °C. Filter paper activity (FPA) of Trichoderma reesei was increased by 180% to 13.44 IU/mL. Enzymatic hydrolysis experiments were performed on different pretreated corn stovers with Trichoderma reesei cellulase produced under optimal conditions, and the highest cellulose conversion efficiency reached 62.39%. In addition, a blend of Trichoderma reesei cellulase at a concentration of 30 FPU/g cellulose and Aspergillus niger beta-glucosidase at a concentration of 50 FPU/g cellulose could effectively hydrolyse alkali pretreated corn stover, resulting in an improvement in the enzymatic hydrolysis efficiency by 17.26% compared to Trichoderma reesei cellulase alone. In parallel, the mixed enzymes achieved an equivalent enzymatic effect with that of commercial cellulase (Novozymes, Cellic Ctec2) at the same concentration. These data suggested that solid acid pretreated corn stover was a promising carbon source for fungal cellulase production for effective saccharification of corn stover biomass. Glycerol monostearate was first found to have a strong induction effect on enzyme production. The development of a high efficiency and low-cost mixed enzyme system had a potential application in future industrialization scale.

Evolutionary engineering of Lactobacillus bulgaricus reduces enzyme usage and enhances conversion of lignocellulosics to D-lactic acid by simultaneous saccharification and fermentation

BackgroundSimultaneous saccharification and fermentation (SSF) of pre-treated lignocellulosics to biofuels and other platform chemicals has long been a promising alternative to separate hydrolysis and fermentation processes. However, the disparity between the optimum conditions (temperature, pH) for fermentation and enzyme hydrolysis leads to execution of the SSF process at sub-optimal conditions, which can affect the rate of hydrolysis and cellulose conversion. The fermentation conditions could be synchronized with hydrolysis optima by carrying out the SSF at a higher temperature, but this would require a thermo-tolerant organism. Economically viable production of platform chemicals from lignocellulosic biomass (LCB) has long been stymied because of the significantly higher cost of hydrolytic enzymes. The major objective of this work is to develop an SSF strategy for D-lactic acid (D-LA) production by a thermo-tolerant organism, in which the enzyme loading could significantly be reduced without compromising on the overall conversion.ResultsA thermo-tolerant strain of Lactobacillus bulgaricus was developed by adaptive laboratory evolution (ALE) which enabled the SSF to be performed at 45 °C with reduced enzyme usage. Despite the reduction of enzyme loading from 15 Filter Paper Unit/gLCB (FPU/gLCB) to 5 FPU/gLCB, we could still achieve ~ 8% higher cellulose to D-LA conversion in batch SSF, in comparison to the conversion by separate enzymatic hydrolysis and fermentation processes at 45 °C and pH 5.5. Extending the batch SSF to SSF with pulse-feeding of 5% pre-treated biomass and 5 FPU/gLCB, at 12-h intervals (36th–96th h), resulted in a titer of 108 g/L D-LA and 60% conversion of cellulose to D-LA. This is one among the highest reported D-LA titers achieved from LCB.ConclusionsWe have demonstrated that the SSF strategy, in conjunction with evolutionary engineering, could drastically reduce enzyme requirement and be the way forward for economical production of platform chemicals from lignocellulosics. We have shown that fed-batch SSF processes, designed with multiple pulse-feedings of the pre-treated biomass and enzyme, can be an effective way of enhancing the product concentrations.

Formation of High Added Value Chemicals by Photocatalytic Treatment of Biomass

The depletion of fossil fuel requires the search for alternative renewable feedstock and environmentally friendly methods for the production of high value-added compounds and fuels. In this context, the efficient use of biomass has emerged as a significant research field as it represents an alternative green and renewable carbon source. Various technologies have been explored for this purpose and heterogeneous photocatalysis represents a valid alternative to the catalytic methods since it can be carried out under mild experimental conditions without the addition of harmful oxidizing agents. Different biomass components have been used as the starting materials, and many valuable chemicals have been obtained with different selectivity depending on some experimental conditions as, for instance, type of photocatalyst, solvent, and physico-chemical features of the catalysts. Moreover, by carrying out the reaction in de-aerated systems, in addition to high added value compounds, hydrogen can be obtained in the gaseous phase. In particular, photocatalytic conversion of lignocellulose, carbohydrates, 5-hydroxymethyl-2-furfural and glycerol (considering only the partial oxidation products) is reported.