Lignocellulosic Pretreatment Research Articles

Analysis of detoxification kinetics and end products of furan aldehydes in Acinetobacter baylyi ADP1

The efficient utilization of lignocellulosic hydrolysates in bioprocesses is impeded by their complex composition and the presence of toxic compounds, such as furan aldehydes, formed during lignocellulose pretreatment. Biological detoxification of these furan aldehydes offers a promising solution to enhance the utilization of lignocellulosic hydrolysates. Acinetobacter baylyi ADP1 is known to metabolize furan aldehydes, yet the complete spectrum of reaction products and dynamics remains unclear. Here, we determined the detoxification metabolites of furfural and 5-hydroxymethylfurfural in A. baylyi ADP1 and studied the kinetics of detoxification. The results indicate that detoxification in A. baylyi ADP1 follows a typical alcohol-aldehyde-acid scheme, with furoic acid and 5-hydroxymethyl-2-furancarboxylic acid as the final products for furfural and 5-hydroxymethylfurfural, respectively. Both end products were found to be less toxic for cells than their unmodified forms. These findings underscore the potential of A. baylyi ADP1 in detoxifying lignocellulosic hydrolysates for bioprocess applications.

Revisiting alkali pretreatment to transform lignocellulose fermentation with integration of bioprocessible lignin

This study emphasized the synergistic production of bioprocessible lignin and carbohydrates during a sequential liquid hot water and alkali pretreatment of lignocellulose, facilitating their subsequent individual fermentation. Increasing the dose of alkaline lignin from 0 to 8 g/L inhibited cell growth in anaerobic digestion, with varying levels of inhibition observed in the following order: hydrolytic bacteria < acidogens < acetogens. Alkali pretreatment was adapted to maximize yields of bioprocessible lignin liquor without compromising utilization of the carbohydrates. Increasing the NaOH dose from 50 to 200 mg/g-feedstock monotonically improved lignin yields, but further increases in alkali loading led to a decline in lignin recovery. Volatile fatty acids production from anaerobic digestion of the carbohydrate moiety consistently increased with higher NaOH doses. The optimal conditions for maximizing lignin yields were determined to be 105 °C for 30 min, with NaOH loading in the range of 150–200 mg/g-feedstock, resulting in approximately 80 % lignin recovery, of which 35 % was biologically utilizable. Liquid hot water treatment prior to alkali pretreatment was confirmed as necessary to preserve carbohydrates of 0.1 g/g-feedstock at a low temperature of 70 °C. These findings are crucial for economically producing bioprocessible lignin without carbohydrate loss, a key step towards achieving full lignocellulose valorization.

Promoted lignocellulose fractionation and improved enzymatic hydrolysis of corn stalks through cationic surfactant combined with deep eutectic solvent pretreatment

The efficient conversion of lignocellulose relies on the implementation of an effective pretreatment strategy. Cationic surfactants combined with deep eutectic solvent ([Betaine][LA] was employed as a novel pretreatment strategy for treating corn stalks. Valuable insights were provided on the impact of the surfactant hydrophobic segment length on pretreatment efficacy. The specific pretreatment conditions were optimized by single factor and orthogonal experiment. Octadecyl trimethyl ammonium bromide (OTAB, 1.5 wt%) with the longest hydrophobic part combined with [Betaine][LA] (Betaine-to-LA molar ratio 1:4) achieved the best pretreatment effect (delignification 92.8 %, xylan elimination 91.1 %) when severity factor reached 4.26, meanwhile, 1.7 g/L xylo-oligosaccharides and 4.4 g/L furfural were detected in pretreatment liquid due to the hydrolysis of hemicellulose in corn stalks with acidic deep eutectic solvent [Betaine][LA]. The relative saccharification activity reached 2.7 times of raw material, while the lignin surface area significantly decreased, leading to enhanced cellulose accessibility. Additionally, molecular perspective provided by molecular dynamics showed the elimination of lignin and xylan was facilitated by strong interaction of hydrogen-bond and van der Waals force between lignin and hemicellulose with [Betaine][LA] + OTAB. Overall, the effectiveness and potential of cationic surfactant combined deep eutectic solvent pretreatment strategy for lignocellulose pretreatment was revealed.

Acid-assisted pretreatment for sweet elephant grass in choline chloride/glycerol DES: Experimental and mechanism study

Sweet elephant grass (SEG), a promising bioenergy grass, possesses considerable potential for bioenergy production. However, research on its pretreatment and utilization remains limited. In this study, small quantities of Brønsted acids were introduced to a deep eutectic solvent (DES) comprising choline chloride (ChCl) and glycerol (Gly) for SEG pretreatment. Under mild conditions (110 °C, 2 h), a maximum lignin removal rate of 90.08 % and a complete hemicellulose removal could be accomplished in the presence of Brønsted acid. Cellulose retention rates consistently above 70 % were obtained in all the cases, and a desirable glucose yield up to 94.07 % was achieved from the resulting cellulose after further enzymatic hydrolysis. The pretreatment mechanism was elucidated through a combination of characterizations and theoretical calculations, which demonstrated effective disruption of lignin and lignin-carbohydrate complex occurred by the CH···π, HO···H, and Cl···H bond interactions between lignin and DES. Furthermore, the scission of β-O-4 bond was promoted by Brønsted acids in DES. This systematic investigation paves the way for unraveling the mechanism of the efficient pretreatment of lignocellulose in acidic DES.

A deep eutectic solvent with a lignin stabilization and functionalization for lignocellulosic biomass pretreatment

This study synthesized a functional deep eutectic solvent (DES) using betaine and glyoxylic acid (GA) for lignocellulosic biomass pretreatment. The Betaine/GA DES pretreatment resulted a high delignification efficiency of 81.89% and xylan removal of 83.25% while preserving most of cellulose. During pretreatment, lignin was stabilized by GA, preventing its condensation and introducing carboxyl groups onto its molecular backbone. The GA stabilized lignin (GASL), with a high β-O-4 linkage content of 62.92%, was depolymerized for phenolic monomer production with a bio-oil yield of 55.40%. Additionally, the functional lignin was used as a surfactant for GASL-based O/W emulsion (GA-O/W emulsion) preparation. With 0.5% of lignin addition and an optimal O/W ratio of 6:4, the resulting GA-O/W emulsion exhibited a high cream index value of 100% and excellent storage stability without any phase transition or emulsion aggregation. When using the lignin to prepare curcumin-encapsulated microcapsules, a cumulative curcumin remaining of 74.19% under UV radiation and an extraordinary encapsulation efficiency of 62.86% were achieved. Furthermore, this DES pretreatment promoted enzymatic saccharification of the pretreated cellulose substrate, resulting in a glucose yield of 91.49%. After adding 15 wt% of the fibers in soft wood pulp for papermaking, the tear index, ring crush strength index, and tensile index of the produced paper-sheets reached 112.04%, 98.58%, and 83.55% of those of the pure softwood pulp papers, respectively.

Enhanced enzymatic hydrolysis of corn stover by γ-valerolactone pretreatment and the characteristics of enzymatic residues

Efficient pretreatment methods are crucial for the generation of fermentable sugars from the renewable lignocellulose. In this study, γ-valerolactone (GVL), a biomass-derived green solvent, was used to fractionate corn stover (CS). The impact of different additives on the enzymatic hydrolysis and pretreatment of CS within the GVL/water system was carefully investigated. The results demonstrate that the use of H2SO4-assisted GVL/H2O (80:20, w/w) pretreatment at mild conditions successfully facilitates the depolymerization of CS, thereby improving the cellulase accessibility. Furthermore, by increasing the GVL pretreatment temperature to 160 °C with 100 mM H2SO4 addition, the pretreated CS led to nearly 100 % of hydrolysis yield at 2 % (w/v) solid load. Finally, the thermogravimetric analysis (TGA) was performed to evaluate the thermal decomposition characteristics of untreated CS and enzymatic residues based on the H2SO4-assisted GVL/H2O pretreatment. The results indicate that the enzymatic residues had two depolymerization stages from 200 °C to 500 °C with a final residual mass of 22.73 %, which was higher than that of untreated CS (20.56 %). Overall, this study provides an efficient lignocellulose pretreatment for fermentable sugars production and valorization of enzymatic residues.

Microscopic mechanism investigation of extraction of lignin by benzyltriethylammonium chloride-based deep eutectic solvents

Benzyltriethylammonium chloride (BTEAC)-based deep eutectic solvent (DES) has a high delignification rate in the pretreatment of lignocellulose, and the lignin obtained from the removal has the advantages of high purity and low molecular weight. The interaction mechanism between BTEAC-based DES and lignin at molecular level was investigated by multiscale simulation analytical approach. By analyzing the types of weak interaction, charge distribution, number of hydrogen bonds, energy distribution and density distribution in different systems, the influence of six hydrogen bond donor (HBD) structures on the extraction process was clarified. The interaction between Cl- and lignin is mainly electrostatic interaction, and the interaction between BTEA+ and lignin is mainly van der Waals (vdW) interaction. The original π-π stacking of lignin is replaced by the new π-π stacking between BTEA+ and lignin. The effects of different functional groups and length of carbon chain on the interaction were researched. The acidic HBD with short carbon chain has a larger interaction and can affect the ether bond on the lignin. Among them, due to the smaller volume of formic acid (FA), it provides more space for BTEA+ to contact with lignin, resulting in stronger interaction. The molecular-level theoretical foundation underpinning the efficacy of BTEAC-FA in lignin removal during the pretreatment process is provided.

Pretreatment and fermentation of lignocellulose from oil palm fronds as a potential source of fibre for ruminant feed: a review

AbstractOil palm fronds are plantation waste widely available in large quantities and have great potential as a source of ruminant feed due to their high fibre content. However, the lignocellulose content can inhibit feed digestion. This review examines methods that can reduce the lignocellulose content and improve the nutritional quality of palm fronds. The lignin content of palm fronds ranges from 17% to 20%, while the maximum lignin content in ruminant feed is 7%. Processing processes such as pretreatment are needed to reduce the lignocellulose content. Pretreatment can be done physically, chemically, biologically or in combination with other methods. Physical pretreatment aims to reduce the size of lignocellulose, chemical pretreatment seeks to break the crystallinity structure of lignocellulose with chemical solutions such as acids or alkalis, and biological pretreatment degrades the structure of lignocellulose with the help of enzymes produced by microbes. The protein content of palm fronds also does not meet the feed standard, which is only 5%, while according to Indonesian national standards, ruminant feed, especially cattle, must have a minimum protein content of 14%. Therefore, it is necessary to improve the nutritional quality of palm fronds through fermentation methods. The selection of the right microbes is the main factor in the success of increasing nutrition. The SSF fermentation method is frequently used in feed manufacturing. By synthesizing the current knowledge, this review also highlights the challenges of the pretreatment process as well as solutions that include prospects in the research of palm fronds as ruminant feed, which in turn can contribute to the increased utilization of lignocellulosic waste as animal feed.

Current status and future prospects of pretreatment for tobacco stalk lignocellulose.

With the growing demand for sustainable development, tobacco stalks, as a resource-rich and low-cost renewable resource, hold the potential for producing high-value chemicals and materials within a circular economy. Due to the complex and unique structure of tobacco stalk biomass, traditional methods are ineffective in its utilization, making the pretreatment of tobacco stalk lignocellulose a crucial step in obtaining high-value products. This paper reviews recent advancements in various pretreatment technologies for tobacco stalk lignocellulosic biomass, including hydrothermal, steam explosion, acid, alkaline, organic solvent, ionic liquid, and deep eutectic solvent pretreatment. It emphasizes the impact and efficiency of these pretreatment methods on the conversion of tobacco stalk biomass and discusses the advantages and disadvantages of each technique. Finally, the paper forecasts future research directions in the pretreatment of tobacco stalk lignocellulose, providing new insights and methods for enhancing its efficient utilization.

Enhancing detoxification of inhibitors in lignocellulosic pretreatment wastewater by bacterial Action: A pathway to improved biomass utilization

The process of preprocessing techniques such as acid and alkali pretreatment in lignocellulosic industry generates substantial solid residues and lignocellulosic pretreatment wastewater (LPW) containing glucose, xylose and toxic byproducts. In this study, furfural and vanillin were selected as model toxic byproducts. Kurthia huakuii as potential strain could tolerate to high concentrations of inhibitors. The results indicated that vanillin exhibited a higher inhibitory effect on K. huakuii (3.95 % inhibition rate at 1 g/L than furfural (0.45 %). However, 0.5 g/L vanillin promoted the bacterial growth (−2.35 % inhibition rate). Interestingly, the combination of furfural and vanillin exhibited antagonistic effects on bacterial growth (Q<0.85). Furfural and vanillin could be bio-transformed into less toxic molecules (furfuryl alcohol, furoic acid, vanillyl alcohol, and vanillic acid) by K. huakuii, and inhibitor degradation rate could be promoted by expression of antioxidant enzymes. This study provides important insights into how bacteria detoxify inhibitors in LPW, potentially enhancing resource utilization.

Performance Evaluation of Different Clustering Techniques and Parameters of Hybrid PSO- and GA-ANFIS on Optimization and Prediction of Biomethane Yield of Alkali-Pretreated Groundnut Shells

AbstractThe study focuses on optimizing biomethane yield in the anaerobic digestion of alkali-pretreated groundnut shells, involving varied input parameters. Biomethane optimization will improve the economy of the technology, which will assist in managing the environmental challenges of fossil fuel combustion. Traditional methods prove challenging, inaccurate, and uneconomical, necessitating efficient optimization models. This research hybridizes particle swarm optimization (PSO) and genetic algorithms (GA) with adaptive neuro-fuzzy inference system (ANFIS) models, assessing input parameters’ influence on biomethane yield through renowned performance metrics. Comparing the best model in the hybrid analysis, encompassing pretreatments A-E, the PSO-ANFIS (RMSE = 1.1719, MADE = 0.6525, MAE = 0.9314, Theil’s U = 0.1844, and SD = 0.7737) outperformed the GA-ANFIS (RMSE = 1.9338, MADE = 0.9318, MAE = 1.6557, Theil’s U = 0.2734, SD = 1.0598), using the same cluster radius of 0.50. Furthermore, compared to the GA-ANFIS model, the PSO-ANFIS model demonstrated significant improvements across various metrics: RMSE by 39.40%, MADE by 29.97%, MAE by 43.75%, Theil’s U by 32.56%, and SD by 27.00%. Results indicate that the PSO-ANFIS model outperforms the GA-ANFIS model, emphasizing the importance of suitable clustering algorithms and precise parameter adjustment for optimal performance in predicting biomethane yield from pretreated lignocellulose feedstocks. Graphical Abstract

Effects of Sugar Beet Pulp Pretreatment Methods on Hydrogen Production by Dark Fermentation

Methane and hydrogen generated from waste and biomass are renewable resources, which may successfully replace traditional fossil fuels. This paper investigates the enhancement effect of lignocellulosic biomass pretreatment on dark fermentative hydrogen production from sugar beet pulp (SBP). The results showed that sugar beet pulp after pretreatment contained significant amounts of unfermented sugars (mainly glucose, arabinose, galactose, and raffinose), and, therefore, represented an attractive substrate for methane and hydrogen production. The greatest methane yield (495 dm3 CH4/kg VS) was achieved from sugar beet pulp after alkaline pretreatment. High methane production of up to 445 dm3 CH4/kg VS was also obtained using acidic and enzymatic hydrolysis as a preliminary treatment of the pulp. All the pretreatment methods also resulted in the enhancement of hydrogen yield with the highest value of 229 dm3 H2/kg VS achieved using acid hydrolysis compared with 17 dm3 H2/kg VS for raw material subjected to digestion.

Role of microbial laccases in valorization of lignocellulosic biomass to bioethanol.

The persistent expansion in world energy and synthetic compounds requires the improvement of renewable alternatives in contrast to non-sustainable energy wellsprings. Lignocellulose is an encouraging feedstock to be utilized in biorefineries for its conversion into value-added products, including biomaterials, biofuels and several bio-based synthetic compounds. Aside from all categories, biofuel, particularly bioethanol is the most substantial fuel derived from lignocellulosic biomass and can be obtained through microbial fermentation. Generally, extreme settings are required for lignocellulosic pretreatment which results in the formation of inhibitors during biomassdegradation. Occasionally, lignin polymers also act as inhibitors and are left untreated during the pretreatment, engendering inefficient hydrolysis. The valorization of lignocellulosic biomass by laccases can be viewed as a fundamental trend for improving bioethanol production. However, one of the main obstacles for developing commercially viable biofuel industries is the cost of enzymes, which can be resolved by utilizing laccases derived from microbial sources. Microbial laccases have been considered an exceptionally integral asset for delignification and detoxification of pretreated LCB, which amplify the resultant fermentation and saccharification processes. This review provides a summary of microbial laccases and their role in valorizing LCB to bioethanol, compelling enthralling applications in bio-refining industries all across the globe.

Waste to wealth: A novel low temperature eco-friendly lignocellulose pretreatment strategy for glucose production

Acid pretreatment is considered as one of the most promising pretreatment strategies. However, the operation temperature of acid pretreatment is commonly higher, and acid pretreatment is difficult to remove lignin. Herein, a novel pretreatment strategy (dilute sulfuric acid coupling K2S2O8 (DA-PDS) pretreatment) was proposed to remove lignin at lower temperature. The feasibility of DA-PDS pretreatment was predicted by means of density functional theory (DFT). Then, the optimal operation conditions of DA-PDS pretreatment were studied. Temperature was proved to be the most critical factor affecting the DA-PDS pretreatment. The optimal reaction conditions of DA-PDS pretreatment were 5 % DA and 6 % PDS at 80 °C for 2 h. The operation temperature was 40 °C lower than common acid pretreatment. On this condition, the cellulose content and enzymatic hydrolysis efficiency by DA-PDS pretreatment were about 59 % and 73 %, which were 11 % and 13 % higher than that of DA pretreatment, respectively. In addition, this study revealed the mechanism of DA-PDS pretreatment. DA not only accelerated radical generation rate, but also improved the contact probability between radical and lignin. Radicals generated by PDS destroyed the structure of lignin. This made DA more easily to remove hemicellulose. This work presented a novel and energy-saving strategy for lignocellulose pretreatment.

Ionic liquid pretreatment of lignocellulose for complete hemicellulose removal to produce high-purity cellulose mixed esters

Strategic valorization of agricultural waste can serve as waste management and promote sustainable biorefineries. Sugarcane bagasse is a readily available lignocellulosic biomass and can be converted into valuable cellulose-based thermoplastics. However, the cellulose purity significantly influences the material properties of the resulting thermoplastics, potentially limiting their applications. Therefore, conventional production necessitates harsh pretreatment of lignocellulose to isolate high-purity cellulose, followed by chemical modification. Here, we demonstrate a facile and green pretreatment method for complete removal of hemicellulose by incubating bagasse in a mixed system of an ionic liquid, 1-ethyl-3-methylimidazolium acetate (EmimOAc), and dimethyl sulfoxide (DMSO) at 140 °C, followed by precipitation in water, achieving >99 % hemicellulose removal. The pretreated bagasse, containing 71 % cellulose and 28 % lignin, underwent homogeneous transesterification with vinyl decanoate and isopropenyl acetate, using EmimOAc as both the solvent and catalyst, assisted by a co-solvent of DMSO. The polysaccharide derivative in the resulting acylated bagasse was separated from the lignin derivative by precipitation in methanol. The obtained polysaccharide derivative with high cellulose purity displayed a high weight-average molar mass of 1.5×106 g mol−1 and a polydispersity of 4. It also exhibited superior thermal stability (thermal degradation temperature, Td−5 %: 359 °C; glass transition temperature, Tg: 144 °C) compared to pulp-derived cellulose acetate decanoate (Td−5 %: 349 °C; Tg: 129 °C).

Pretreatment of multiple lignocellulosic batches with recoverable and fermentable deep eutectic solvent (FDES) for co-production of sugar, lignin and lipid

Addressing the high cost of comprehensive utilization of lignocellulose, an efficient and green lignocellulosic biorefinery process was developed in this study, which can achieve the co-production of lignin, sugar and lipid. A series of FDES were prepared using glycerin, choline chloride (ChCl), and H2SO4 for the pretreatment of lignocellulose and ultimately for fermentation. After optimization, the hemicellulose removal reaches 98 %, and enzymatic hydrolysis rate of pretreated solids exceeds 90 %. The FDES was then recovered and reused for pretreatment, in total five batches of lignocellulose were pretreated, only a slight decrease in lignin and hemicellulose removal rate occurred, no significant decrease in lignin yield, and a decrease in solid enzyme hydrolysis from 83.26 % to 78.25 %. Finally, FDES after using five batches was used as a substrate for Rhodotorula glutinis with biomass up to 40.25 g/L and lipid concentration up to 8.33 g/L. In addition, the cellulose was probed with high solid-loading enzymatic hydrolysis, obtaining high concentration of glucose (137.4 g/L) for ethanol fermentation. In conclusion, this study developed a biorefinery technology for the efficient utilization of lignocellulosic fractions and pretreatment solvents, which reduces the cost of DES pretreatments of lignocellulose, and achieves the cogeneration of lignin, sugar and lipids.

Competition between biodetoxification fungus and lactic acid bacterium in the biorefinery processing chain for production of cellulosic L-lactic acid

Biodetoxification fungus selectively degrades toxic inhibitors generated from pretreatment of lignocellulose without consuming fermentable sugars. However, one barrier for practical application is the sustained cell viability in the consequent fermentation step to compete the fermentable sugars with fermenting strains, resulting in sugar loss and reduced target product yield. This study investigated the competitive growth property between the biodetoxification fungus Paecilomyces variotii FN89 and the L-lactic acid bacterium Pediococcus acidilactici ZY271 under varying temperature and lactic acid osmatic stress. The results show that the L-lactic acid bacterium Ped. acidilactici ZY271 showed less thermotolerance to Pae. variotii FN89 at high temperature of 45 °C to 50 °C in both synthetic medium and wheat straw hydrolysate. In the higher temperature environment, the growth of the biodetoxification strian failed to compete with the lactic acid fermentation strain and was quickly eliminated from the fermentation system. The high temperature fermentation facilitated a fast transition from the detoxification stage to the fermentation stage for higher production of L-lactic acid.

A novel additive promoting lignocellulose alkali pretreatment for its “two birds with one stone” role

Alkali pretreatment is one of the most commonly used pretreatment methods in lignocellulose bioprocessing. However, there are still some “pseudo-lignin” that hinder enzymatic hydrolysis and seriously affect the industrialization process of biorefining. Excellent pretreatment additives can effectively cover these shortages. However, most additives have disadvantages like high operating temperature, low effective utilization efficiency, or poor performance. To address this issue, we proposed a novel additive, dicyandiamide (DICY), by means of quantum chemical prediction, and verified its ability on assisting alkali to remove lignin by experiments. The results indicate that the lignin removal by KOH-DICY pretreatment is about 15% higher than KOH pretreatment, thereby increasing the enzymatic efficiency to 97%, while the reaction temperature was lower 20 ℃ than common alkali pretreatment. These are due to the “two birds with one stone” role of DICY on lignocellulose alkali-DICY pretreatment. DICY not only dissolves small amounts of lignin, but also assists alkali to remove lignin by reducing the diffusion resistance of KOH in lignin and blocking the generation of “pseudo-lignin”. Thus, DICY effectively improved the lignin removal and enzymatic hydrolysis efficiency of alkali pretreated lignocellulose, and performed better than urea. Moreover, the waste liquid pretreated by DICY combined with KOH has the potential on preparation of agricultural fertilizers. In summary, DICY is a new, environmentally friendly, and energy conservation additive for lign ocellulose alkali pretreatment

Higher efficiency of vanadate iron in heterogeneous Fenton-like systems to pretreat sugarcane bagasse and its enzymatic saccharification.

Pretreatment is crucial for effective enzymatic saccharification of lignocellulose such as sugarcane bagasse (SCB). In the present study, SCB was pretreated with five kinds of heterogeneous Fenton-like systems (HFSs), respectively, in which α-FeOOH, α-Fe2O3, Fe3O4, and FeS2 worked as four traditional heterogeneous Fenton-like catalysts (HFCs), while FeVO4 worked as a novel HFC. The enzymatic reducing sugar conversion rate was then compared among SCB after different heterogeneous Fenton-like pretreatments (HFPs), and the optimal HFS and pretreatment conditions were determined. The mechanism underlying the difference in saccharification efficiency was elucidated by analyzing the composition and morphology of SCB. Moreover, the ion dissolution characteristics, variation of pH and Eh values, H2O2 and hydroxyl radical (·OH) concentration of FeVO4 and α-Fe2O3 HFSs were compared. The results revealed that the sugar conversion rate of SCB pretreated with FeVO4 HFS reached up to 58.25%, which was obviously higher than that under other HFPs. In addition, the surface morphology and composition of the pretreated SCB with FeVO4 HFS were more conducive to enzymatic saccharification. Compared with α-Fe2O3, FeVO4 could utilize H2O2 more efficiently, since the dissolved Fe3+ and V5+ can both react with H2O2 to produce more ·OH, resulting in a higher hemicellulose and lignin removal rate and a higher enzymatic sugar conversion rate. It can be concluded that FeVO4 HFP is a promising approach for lignocellulose pretreatment.

Study on the mechanism of lignin and lignin-carbohydrate complex hydrolysis under alkaline conditions by density functional theory

Lignin hydrolyzes during alkali-heat pretreatment of lignocellulose, due to the cleavage of covalent linkages between lignin and lignin-carbohydrate complex. Various structure of lignin monomers are responsible of the complicated hydrolysis mechanism of lignin and lignin-carbohydrate complex. This study used density functional theory to reveal the hydrolysis mechanism of lignin with various substituents and lignin-carbohydrates complex with different linkages. The results indicated that the SN2 reaction was observed to take place in the lignin. Methoxy groups and methyl group had an insignificant influence on hydrolysis reaction pathway of lignin, whereas the presence of a methyl group on the α-carbon atom had a hindering effect on the nucleophilic attack during alkaline pretreatment. The lignin-carbohydrate complex with different linkage showed a significant difference in hydrolysis reaction pathway. Additionally, the reaction energy barrier of ester bond hydrolysis was lowest among the hydrolysis of ester bond, phenyl glycosidic bond, benzyl ether bond, γ-ester bond, coumarin ester bond and acetal bond under alkaline condition. This study provides valuable insights into the process control, reactor design, and performance enhancement for lignocellulose pretreatment.