Low acid hydrothermal fractionation of Giant Miscanthus for production of xylose-rich hydrolysate and furfural

Towards efficient and greener processes for furfural production from biomass: A review of the recent trends

As mentioned in several recent reviews, biomass-based furfural is attracting increasing interest as a feasible alternative for the synthesis of a wide range of non-petroleum-derived compounds. However, the lack of environmentally friendly, cost-effective, and sustainable industrial procedures is still evident. This review describes the chemical and biological routes for furfural production. The mechanisms proposed for the chemical transformation of xylose to furfural are detailed, as are the current advances in the manufacture of furfural from biomass. The main goal is to overview the different ways of improving the furfural synthesis process. A pretreatment process, particularly chemical and physico-chemical, enhances the digestibility of biomass, leading to the production of >70 % of available sugars for the production of valuable products. The combination of heterogeneous (zeolite and polymeric solid) catalyst and biphasic solvent system (water/GVL and water/CPME) is regarded as an attractive approach, affording >75 % furfural yield for over 80 % of selectivity with the possibility of catalyst reuse. Microwave heating as an activation technique reduces reaction time at least tenfold, making the process more sustainable. The state of the art in industrial processes is also discussed. It shows that, when sulfuric acid is used, the furfural yields do not exceed 55 % for temperatures close to 180 °C. However, the MTC process recently achieved an 83 % yield by continuously removing furfural from the liquid phase. Finally, the CIMV process, using a formic acid/acetic acid mixture, has been developed. The economic aspects of furfural production are then addressed. Future research will be needed to investigate scaling-up and biological techniques that produce acceptable yields and productivities to become commercially viable and competitive in furfural production from biomass.

Valorisation of xylose to renewable fuels and chemicals, an essential step in augmenting the commercial viability of lignocellulosic biorefineries

Biologists and engineers are making tremendous efforts in contributing to a sustainable and green society. To that end, there is growing interest in waste management and valorisation. Lignocellulosic biomass (LCB) is the most abundant material on the earth and an inevitable waste predominantly originating from agricultural residues, forest biomass and municipal solid waste streams. LCB serves as the renewable feedstock for clean and sustainable processes and products with low carbon emission. Cellulose and hemicellulose constitute the polymeric structure of LCB, which on depolymerisation liberates oligomeric or monomeric glucose and xylose, respectively. The preferential utilization of glucose and/or absence of the xylose metabolic pathway in microbial systems cause xylose valorization to be alienated and abandoned, a major bottleneck in the commercial viability of LCB-based biorefineries. Xylose is the second most abundant sugar in LCB, but a non-conventional industrial substrate unlike glucose. The current review seeks to summarize the recent developments in the biological conversion of xylose into a myriad of sustainable products and associated challenges. The review discusses the microbiology, genetics, and biochemistry of xylose metabolism with hurdles requiring debottlenecking for efficient xylose assimilation. It further describes the product formation by microbial cell factories which can assimilate xylose naturally and rewiring of metabolic networks to ameliorate xylose-based bioproduction in native as well as non-native strains. The review also includes a case study that provides an argument on a suitable pathway for optimal cell growth and succinic acid (SA) production from xylose through elementary flux mode analysis. Finally, a product portfolio from xylose bioconversion has been evaluated along with significant developments made through enzyme, metabolic and process engineering approaches, to maximize the product titers and yield, eventually empowering LCB-based biorefineries. Towards the end, the review is wrapped up with current challenges, concluding remarks, and prospects with an argument for intense future research into xylose-based biorefineries.

Production of Bio-Based Chemicals, Acetic Acid and Furfural, through Low-Acid Hydrothermal Fractionation of Pine Wood (Pinus densiflora) and Combustion Characteristics of the Residual Solid Fuel

Low-acid hydrothermal (LAH) fractionation conditions were optimized for the effective degradation of hemicellulose from pine wood (Pinus densiflora). The hemicellulosic sugar yield was maximized at 82.5% when the pine wood was fractionated at 190 °C, with 0.5 wt.% of sulfuric acid, and for 10 min. Consecutively, acidified heat treatment with zinc chloride and solvent extraction with ethyl acetate were carried out for the recovery of bio-based platform chemicals, such as furfural and acetic acid, from liquid hydrolysate through liquid–liquid extraction (LLE). Overall, 61.5% of xylose was decomposed into furfural, and the yield of acetic acid was 62.3% and furfural 66.1%. After LAH fractionation, 64.8% of the solid remained and was pelletized. The pellets showed excellent fuel characteristics, i.e., significant ash rejection (74.5%) and high calorific values (4770 kcal/kg), and the precursors of NOx and SOx also decreased by up to 60.0% and 71.4%, respectively.

Catalytic valorization of hardwood for enhanced xylose-hydrolysate recovery and cellulose enzymatic efficiency via synergistic effect of Fe3+ and acetic acid

BACKGROUND

Poplars are considered suitable dedicated energy crops, with abundant cellulose and hemicellulose, and huge surplus biomass potential in China. Xylan, the major hemicellulosic component, contributes to the structural stability of wood and represents a tremendous quantity of biobased chemicals for fuel production. Monomeric xylose conversion to value-added chemicals such as furfural, xylitol, and xylonic acid could greatly improve the economics of pulp-paper industry and biorefinery. Acetic acid (HAc) is used as a friendly and recyclable selective catalyst amenable to xylan degradation and xylooligosaccharides production from lignocellulosic materials. However, HAc catalyst usually works much feebly at inert woods than agricultural straws. In this study, effects of different iron species in HAc media on poplar xylan degradation were systematically compared, and a preferable Fe³⁺-assisted HAc hydrolysis process was proposed for comparable xylose-hydrolysate recovery (XHR) and enzymatic saccharification of cellulose.

RESULTS

In presence of 6.5% HAc with 0.17-0.25 wt% Fe³⁺, xylose yield ranged between 72.5 and 73.9%. Additionally, pretreatment was effective in poplar delignification, with a lignin yield falling between 38.6 and 42.5%. Under similar conditions, saccharification efficiency varied between 60.3 and 65.9%. Starting with 100 g poplar biomass, a total amount of 12.7-12.8 g of xylose and 18.8-22.8 g of glucose were harvested from liquid streams during the whole process of Fe³⁺-HAc hydrolysis coupled with enzymatic saccharification. Furthermore, the enhancement mechanism of Fe³⁺ coupled with HAc was investigated after proof-of-concept experiments. Beechwood xylan and xylose were treated under the same condition as poplar sawdust fractionation, giving understanding of the effect of catalysts on the hydrolysis pathway from wood xylan to xylose and furfural by Fe³⁺-HAc.

CONCLUSIONS

The Fe³⁺-assisted HAc hydrolysis process was demonstrated as an effective approach to the wood xylose and other monosaccharides production. Synergistic effect of Lewis acid site and aqueous acetic acid provided a promising strategy for catalytic valorization of poplar biomass.

Hydrolysis of Hemicellulose and Derivatives-A Review of Recent Advances in the Production of Furfural

Biobased production of furfural has been known for decades. Nevertheless, bioeconomy and circular economy concepts is much more recent and has motivated a regain of interest of dedicated research to improve production modes and expand potential uses. Accordingly, this review paper aims essentially at outlining recent breakthroughs obtained in the field of furfural production from sugars and polysaccharides feedstocks. The review discusses advances obtained in major production pathways recently explored splitting in the following categories: (i) non-catalytic routes like use of critical solvents or hot water pretreatment, (ii) use of various homogeneous catalysts like mineral or organic acids, metal salts or ionic liquids, (iii) feedstock dehydration making use of various solid acid catalysts; (iv) feedstock dehydration making use of supported catalysts, (v) other heterogeneous catalytic routes. The paper also briefly overviews current understanding of furfural chemical synthesis and its underpinning mechanism as well as safety issues pertaining to the substance. Eventually, some remaining research topics are put in perspective for further optimization of biobased furfural production.

Thermo-mechanical fractionation of yellow poplar sawdust with a low reaction severity using continuous twin screw-driven reactor for high hemicellulosic sugar recovery

Yellow poplar sawdust (YPS), a wood waste that can be easily collected from a local furniture factory, was fractionated using continuous twin screw-driven reactor for high hemicellulosic sugar recovery. The highest total sugar yields were attained under the following conditions: a barrel temperature of 127°C, sulfuric acid concentration of 0.8wt%, liquid feeding rate of 25mL/min, solid feeding rate of 2.0g/min, screw rotation speed of 25rpm, and residence time of 14.5min. The glucan and hemicellulose contents of the CTSR-fractionated YPS were 47.8% and 10.4%, respectively, and these results indicated that 44.9% of cellulose and 76.3% of the hemicellulose were extracted into liquid hydrolyzate. Meanwhile, the batch fractionation of YPS at the same reaction conditions showed a little fractionation effect, i.e., only 20.5% of hemicellulosic sugar yield was obtained.