Opportunities and challenges for flow-through hydrothermal pretreatment in advanced biorefineries

Lignin fractionation and condensation in aromatic-additive-assisted acidic pretreatment and their influence on lignin's effect on the enzymatic hydrolysis

Factors influencing inhibition of lignin on the enzymatic hydrolysis have not been fully elucidated. This study aims to elucidate the effects of lignin fractionation and condensation on its inhibition on enzymatic hydrolysis in aromatic-additive-assisted acidic pretreatment using 2-naphthol (2 N), 2-naphthol-7-sulfonate (NS), and resorcinol (RS). Through simulation reactions of pretreatment and physiochemical analyses of ethanol-extractable lignins (ELs) and cellulolytic enzyme lignins (CELs) from pretreatment, it was observed that 2 N addition in the acidic pretreatment could suppress lignin condensation. This suppression consequently mitigated inhibition of EL-AP-2 N on the enzymatic hydrolysis of Avicel. Simultaneously, addition of NS in the pretreatment can enhance lignin fractionation by facilitating decomposition of lignin into water and ethanol soluble fractions, thereby mitigating inhibition of CEL-AP-NS on the enzymatic hydrolysis. Meanwhile, with RS in the pretreatment, EL-AP-RS and CEL-AP-RS demonstrated the most pronounced inhibition among ELs and CELs. This inhibition may be attributed to the increased phenolic OH groups with the introduction of RS units. A heatmap analysis revealing relationship between lignin characteristics and its inhibition indicated that ELs exhibit reduced inhibition on enzymatic hydrolysis when lignin condensation was suppressed. Conversely, CELs would show diminished inhibitory effects when lignin particle sizes were smaller and lignin fractionation was stronger.

Performance Evaluation of Combined Hydrothermal-Mechanical Pretreatment of Lignocellulosic Biomass for Enzymatic Enhancement

Pretreatment is a crucial process in a lignocellulosic biorefinery. Corncob is typically considered as a natural renewable carbon source to produce various bio-based products. This study aimed to evaluate the performance of the hydrothermal-mechanical pretreatment of corncob for biofuels and biochemical production. Corncob was first pretreated by liquid hot water (LHW) at different temperatures (140–180 °C) and duration (30, 60 min) and then subjected to centrifugal milling to produce bio-powders. To evaluate the performance of this combined pretreatment, the energy efficiency and waste generation were investigated. The results indicated that the maximum fermentable sugars (FS) were 0.488 g/g biomass obtained by LHW at 180 °C, 30 min. In order to evaluate the performance of this combined pretreatment, the energy efficiency and waste generation were 28.3 g of FS/kWh and 7.21 kg of waste/kg FS, respectively. These obtained results indicate that the combined hydrothermal-mechanical pretreatment was an effective pretreatment process to provide high energy efficiency and low waste generation to produce biofuels. In addition, the energy efficiency and waste generation will be useful indicators for process scaling-up into the industrial scale. This combined pretreatment could be a promising pretreatment technology for the production of biofuels and biochemicals from lignocellulosic valorization.

A review on physico-chemical delignification as a pretreatment of lignocellulosic biomass for enhanced bioconversion

Effective pretreatment of lignocellulosic biomass (LCB) is one of the most important steps in biorefinery, ensuring the quality and commercial viability of the overall bioprocess. Lignin recalcitrance in LCB is a major bottleneck in biological conversion as the polymerization of lignin with hemicellulose hinders enzyme accessibility and further bioconversion to fuels and chemicals. Therefore, there is a need to delignify LCB to ease further bioprocessing. The efficiency of delignification, quality and quantity of the desired products, and generation of inhibitors depend upon the type of pretreatment employed. This review summarizes different single and integrated physicochemical pretreatments for delignification. Additionally, conditions required for effective delignification and the advantages and drawbacks of each method were evaluated. Advances in overcoming the recalcitrance of residual lignin to saccharification and the methods to recover lignin after delignification are also discussed. Efficient lignin recovery and valorization strategies provide an avenue for the sustainable lignocellulose biorefinery.

Continuous hydrothermal furfural production from xylose in a microreactor with dual-acid catalysts

An effective continuous furfural production from xylose in a microreactor over dual-acid catalysts was proposed. In this work, furfural was synthesized in an organic solvent-free system using formic acid and aluminum chloride as catalyst. The role of these catalysts in the consecutive reactions was examined and verified. The influence of operating conditions including xylose concentration, reaction temperature, residence time, total catalyst concentration, and catalyst ratio on the yield of furfural was investigated and optimized. The furfural yield of 92.2% was achieved at the reaction temperature of 180 °C, residence time of 15 min, catalyst molar ratio of 1 : 1, xylose concentration of 1 g L⁻¹, and total catalyst concentration of 16 mM. The superior production performance of our process was highlighted in terms of the low catalyst concentration and short residence time compared to those of other systems based on the literature. In addition, a continuous in situ catalyst removal (purification) was demonstrated, providing further insights into the practical development of continuous furfural production.

An effective continuous furfural production from xylose in a microreactor over dual-acid catalysts was proposed. In this work, furfural was synthesized in an organic solvent-free system using formic acid and aluminum chloride as catalyst.