Influence of sulfur dioxide-ethanol-water pretreatment on the physicochemical properties and enzymatic digestibility of bamboo residues

Mild γ-Butyrolactone/Water Pretreatment for Highly Efficient Sugar Production from Corn Stover

In this study, γ-butyrolactone/water (GBL/H2O) was explored as a mild, efficient, and cost-effective binary solvent pretreatment to enhance hydrolyzability of corn stover (CS). Key pretreatment parameters-reaction time, temperature, and H2SO4 concentration-were systematically investigated for their effects on the physicochemical properties of CS. Specifically, increased temperature and acid concentration significantly decreased cellulose crystallinity (from 1.39 for untreated CS to 1.04 for CS pretreated by GBL/H2O with 100 mM H2SO4 at 120 °C for 1 h) and promoted lignin removal (47.3% for CS pretreated by GBL/H2O with 150 mM H2SO4 at 120 °C for 1 h). Acknowledging the cellulase's limited hydrolysis efficiency, a dual-enzyme scheme using a low cellulase dosage (10 FPU/g) supplemented with β-glucosidase or xylanase was tested, enhancing hydrolysis of CS pretreated under low temperature-long duration and high temperature-short duration conditions, respectively. Optimum sugar release was obtained from CS pretreated with GBL/H2O and 150 mM H2SO4 at 120 °C for 1 h, achieving 98% glucan and 82.3% xylan conversion, compared with 53.9% and 17% of glucan and xylan conversion from untreated CS. GBL/H2O pretreatment outperformed other binary systems in literature, achieving the highest sugar conversions with lower enzyme loading. These results highlight the potential of GBL/H2O pretreatment for efficient biomass conversion, contributing to the goals of the green economy.

Enhancing enzymatic digestibility of bamboo residues using a combined low severity steam explosion and green liquor-sulfite pretreatment

In this study, the effect of the green liquor (GL)-sulfite pretreatment on bamboo for enzymatic hydrolysis was investigated. The performance characterization of the pretreated bamboo substrates, including the chemical composition, and the structural characteristics was carried out. The results showed that 91.3% of lignin removal was achieved when the sample was treated with a GL loading of 12.0 mL per g-DS at 120 °C for 1 h. After 120 h hydrolysis with 18 FPU per g-cellulose for cellulase and 27 CBU per g-cellulose for glucosidase, the glucose yield increased from 54.6% to 89.6%. The SE-treated bamboo could bind more easily to cellulase than GL-sulfite treated bamboo could. The structural changes on the surface of the samples were characterized by SEM. The results indicated that the surface lignin could be effectively removed during pretreatment, thereby decreasing the enzyme-lignin binding activity.

Green chemical and hybrid enzymatic pretreatments for lignocellulosic biorefineries: Mechanism and challenges

The greener chemical and enzymatic pretreatments for lignocellulosic biomasses are portraying a crucial role owing to their recalcitrant nature. Traditional pretreatments lead to partial degradation of lignin and hemicellulose moieties from the pretreated biomass. But it still restricts the enzyme accessibility for the digestibility towards the celluloses and the interaction of lignin-enzymes, nonproductively. Moreover, incursion of certain special chemical treatments and other lignin sulfonation techniques to the enzymatic pretreatment (hybrid enzymatic pretreatment) enhances the lignin structural modification, solubilization of the hemicelluloses and both saccharification and fermentation processes (SAF). This article concentrates on recent developments in various chemical and hybrid enzymatic pretreatments on biomass materials with their mode of activities. Furthermore, the issues on strategies of the existing pretreatments towards their industrial applications are highlighted, which could lead to innovative ideas to overcome the challenges and give guideline for the researchers towards the lignocellulosic biorefineries.

Waste bamboo framework decorated with α-FeOOH nanoneedles for effective arsenic (V/III) removal

Arsenic pollution of water is one of the severest environmental challenges for human health, and adsorption is the most often used technique in investigations of selective As removal. However, the development of low-cost and easily recoverable adsorbent for aqueous arsenic adsorption remains a challenge. In this work, the α-FeOOH-decorated monolith bamboo composites (α-FeOOH/MB) were fabricated via directly decorating α-FeOOH nanoneedles on the waste bamboo framework without pre‑carbonization. As expected, the as-prepared α-FeOOH/MB exhibits considerably increased adsorption capacity for aqueous arsenic over pure α-FeOOH nanoneedles, with increases of 1.88 and 1.52 times for As(V) and As(III), respectively. Meanwhile, the α-FeOOH/MB composites exhibit positive reusability (recovering 89.73 % and 80.17 % adsorption capacity for As(V) and As(III) after 5 cycles) and are easy to separate after water treatment. Furthermore, the α-FeOOH/MB composites exhibit high arsenic adsorption selectivity even in the presence of competing anions. Overall, the as-obtained α-FeOOH/MB composites, reuse of waste bamboo, are a kind of favorable candidate for arsenic decontamination in practical application owing to the high adsorption capacity, low-cost and facile separation features.

In-situ lignin sulfonation for enhancing enzymatic hydrolysis of poplar using mild organic solvent pretreatment

Biomass pretreatment is an essential strategy to overcome biomass recalcitrance and promote lignocellulosic bioconversion. Here, a reusable organic solvent system (formic acid-methanesulfonic acid) was explored to pretreat poplar under a mild temperature (below 100 °C). The results showed that the co-solvent system could extract basically complete hemicelluloses and part of lignin with original cellulose retained in the pretreated substrates. Meanwhile, sulfonic acid groups were introduced into lignin structure remained in the substrates. The glucose conversion yield of the substrates with a higher concentration of sulfonic acid groups (13.2 mmol/kg) reached 45.9 % by reducing the hydrophobic interaction between lignin and cellulase, showing 89.3 % improvement compared with that of the substrates treated with single formic acid. This progressive study aimed to develop a new strategy to realize sulfonation and promote enzymatic hydrolysis of substrates by using mild organic solvent pretreatment.

Improve Enzymatic Hydrolysis of Lignocellulosic Biomass by Modifying Lignin Structure via Sulfite Pretreatment and Using Lignin Blockers

Even traditional pretreatments can partially remove or degrade lignin and hemicellulose from lignocellulosic biomass for enhancing its enzymatic digestibility, the remaining lignin in pretreated biomass still restricts its enzymatic hydrolysis by limiting cellulose accessibility and lignin-enzyme nonproductive interaction. Therefore, many pretreatments that can modify lignin structure in a unique way and approaches to block the lignin’s adverse impact have been proposed to directly improve the enzymatic digestibility of pretreated biomass. In this review, recent development in sulfite pretreatment that can transform the native lignin into lignosulfonate and subsequently enhance saccharification of pretreated biomass under certain conditions was summarized. In addition, we also reviewed the approaches of the addition of reactive agents to block the lignin’s reactive sites and limit the cellulase-enzyme adsorption during hydrolysis. It is our hope that this summary can provide a guideline for workers engaged in biorefining for the goal of reaching high enzymatic digestibility of lignocellulose.

Valorization of bamboo shoot shell waste for the coproduction of fermentable sugars and xylooligosaccharides

In this work, hydrothermal pretreatment (autohydrolysis) was coupled with endo-xylanase enzymatic hydrolysis for bamboo shoot shell (BSS) to produce glucose and valuable xylooligosaccharides (XOS) rich in xylobiose (X2) and xylotriose (X3). Results showed that the enzymatic hydrolysis efficiency of pretreated BSS residue reached 88.4% with addition of PEG during the hydrolysis process. To enrich the portions of X2–X3 in XOS, endo-xylanase was used to hydrolyze the XOS in the prehydrolysate, which was obtained at the optimum condition (170°C, 50 min). After enzymatic hydrolysis, the yield of XOS reached 25.6%, which contained 76.7% of X2–X3. Moreover, the prehydrolysate contained a low concentration of fermentation inhibitors (formic acid 0.7 g/L, acetic acid 2.6 g/L, furfural 0.7 g/L). Based on mass balance, 32.1 g of glucose and 6.6 g of XOS (containing 5.1 g of X2-X3) could be produced from 100.0 g of BSS by the coupled technology. These results indicate that BSS could be an economical feedstock for the production of glucose and XOS.

Enhancement of sugar release from sugarcane bagasse through NaOH-catalyzed ethylene glycol pretreatment and water-soluble sulfonated lignin

In this work, five different NaOH-catalyzed ethylene glycol (EG) pretreatments together with water-soluble sulfonated lignin (SL) were used for enhancing sugarcane bagasse (SCB) enzymatic digestion. The results showed that the coupling of NaOH and EG into a one-pot pretreatment (10%NaOH/EG) was more beneficial to improve SCB enzymatic hydrolysis than that of single 10%NaOH or EG pretreatment, or the two-step pretreatment of NaOH and EG in different sequence (10%NaOH+EG and EG + 10%NaOH, respectively). The highest glucose yield of this work was 91.2 %, mainly released from the SCB that pretreated with 10%NaOH/EG at 130 °C for 60 min and 72 h enzymatic hydrolysis. The adding of SL into the enzymatic hydrolysis step could significantly lower the cellulase dosage and hydrolysis time from 20 FPU/g and 72 h to 10 FPU/g and 24 h, respectively, meanwhile keeping a high glucose yield of 90.4 %. The characterization of various pretreated or un-pretreated SCB confirmed that the improvement of hydrolysis efficiency of SCB after 10%NaOH/EG pretreatment was closely related to the removal of various components barriers in SCB and the fragmentation of pretreated solid. It can be concluded that the developed NaOH-catalyzed ethylene glycol pretreatment was an efficiency way to enhance the sugar release from SCB.

Structural Evolution of Cellulose from Bamboo Fibers and Parenchyma Cells during Ionic Liquid Pretreatment for Enhanced Hydrolysis

Bamboo fibers and parenchyma cells, the two dominant types of cells in bamboo, exhibit some interesting differences in cellulose crystalline structures. In the present investigation, we further demonstrated that these structural differences affect their response during ionic liquid (IL) pretreatment and the sugar conversion yield, by tracking their changes in morphology, chemical, and crystalline structures. All of the results pointed to the fact that the cellulose from bamboo fibers exhibited higher recalcitrance to IL pretreatment, with a significantly lower change in crystallinity index, d spacings from the (110) and (11̅0) planes, crystallite sizes, and easier transformation from cellulose I to cellulose II after pretreatment, as compared to that from parenchyma cells. Furthermore, the crystalline parameters of (110) and (11̅0) lattice planes exhibited more changes compared to the (200) direction. This investigation highlights the significance of parenchyma cell wastes from bamboo processing plants as a competitive candidate for the biorefinery industry.

Enhancing enzymatic digestibility of bamboo residues using a three-constituent deep eutectic solvent pretreatment

A three-constituent deep eutectic solvent (3c-DES) pretreatment with choline chloride-oxalic acid-ethylene glycol was applied to examine its effectiveness on bamboo residues. The 3c-DES pretreatment can remove 91.09% xylan and significantly improved the 72 h hydrolysis yield of D. sinicus by 6.3 and 1.7 times as compared with the liquid hot water and two-constituent deep eutectic solvent (2c-DES) pretreatment. The introduction of ethylene glycol (EG) into choline chloride (ChCl)/ oxalic acid (OA) decreased the content of surface lignin and the condensation of lignin, which contributed to the increase of hydrophilic nature and cellulose accessibility in substrates. Moreover, higher glucose (85.72%) and xylose (91.05%) yields of 3c-DES pretreated bamboo were achieved with the addition of Tween 80. The 3c-DES system provides an alternative approach for the development of efficient bamboo pretreatment, and had broad space for bamboo biorefinery in southern China.

Combination of hydrothermal and chemi-mechanical pretreatments to enhance enzymatic hydrolysis of poplar branches and insights on cellulase adsorption

An integration of different pretreatments is important to overcome recalcitrance and realize efficient bioconversion of lignocellulosic biomass. This study aims at the effects of combination of hydrothermal pretreatment and different chemi-mechanical pretreatments on enzymatic hydrolysis, and understanding the enzymes adsorption mechanism. The combination of hydrothermal and chemi-mechanical pretreatments effectively improved the enzymatic hydrolysis of poplar substrates, in which the enzymatic hydrolysis of substrates pretreated by hydrothermal pretreatment + Fenton pretreatment + mechanical refining (HFM) was the highest (92.39% of glucose conversion yield, and 20.88 g/L of glucose concentration). The substrates' main characteristics were obviously changed after combined pretreatments, such as swelling ability and specific surface area of substrates were increased. The Langmuir adsorption model (R² > 0.98) and pseudo second-order adsorption kinetic model (R²≈1) were well suitable to describe the adsorption of enzymes on substrates, meanwhile the adsorption mechanism was summarized.

Enhancing the enzymatic digestibility of bamboo residues by biphasic phenoxyethanol-acid pretreatment

The high content of lignin in bamboo is considered as the major obstacle for its biorefining. In this work, a green, lignin-selective, and recyclable solvent of phenoxyethanol was coupled with acid solution to deconstruct recalcitrant structure of bamboo residues (BR) to boost its enzymatic digestibility. Results showed phenoxyethanol has excellent lignin-removal ability from 29.4% to 91.6% when phenoxyethanol:acid ratios increased from 0:1 to 4:1 at 120 °C. 82.5%-87.8% of cellulose was preserved in pretreated BR. The enzymatic digestibility of BR significantly improved from 20.0% to 91.3% when it was pretreated under optimized conditions. With lower enzyme dosages (10 FPU/g) and 5 recycled using of pretreatment liquor, pretreated BR still showed a good enzymatic digestibility of 67.4%-93.7% and 67.1-76.8%, respectively. Examination of physicochemical changes revealed that improvements to accessibility, reduction of crystallite size, decrease of surface lignin and hydrophobicity for pretreated BR showed positive correlations (R² > 0.7) with their enzymatic digestibility.

Recyclable deep eutectic solvent coupling sodium hydroxide post-treatment for boosting woody/herbaceous biomass conversion at mild condition

A novel recyclable deep eutectic solvent (DES) consisting of p-toluene sulfonic acid (p-TsOH) and choline chloride (ChCl) was developed for efficient woody poplar sawdust (PL) and herbaceous miscanthus (MC) conversion at mild condition. The extraction of leftover lignin on the surface of DES pretreated residues using NaOH solution at room temperature greatly improved the enzymatic hydrolysis efficiency. Near complete cellulose conversion of PL and MC residues were obtained with a degree of delignification and xylan removal over 90% at 100 °C within 40 min. The strong correlations between xylan (R² = 0.95) and lignin (R² = 0.82) removal with cellulose conversion were observed in MC as well as positive correlations (R² > 0.77) in PL. The results demonstrated that the DES system coupling NaOH post-treatment was a promising method to achieve an economically feasible biomass conversion process, which was effective for both woody PL residues and herbaceous MC.

Falling Leaves Return to Their Roots: A Review on the Preparation of γ-Valerolactone from Lignocellulose and Its Application in the Conversion of Lignocellulose

γ-Valerolactone (GVL), derived from renewable lignocellulosic biomass, has been considered as a cost-competitive and green platform chemical. With the increasingly prominent environmental problems, a deep understanding of the preparation and transformation of GVL is highly needed. Based on the latest progress made with GVL, preparation and applications of GVL are summarized and discussed in this Review. In particular, the state-of-the-art in catalytic production of GVL is described based on the use of noble-metal and non-noble-metal catalysts. The application of GVL for the valorization of lignocellulose would improve the yield of target products such as sugar monomers and furfural. Thus, GVL can be produced from lignocellulose and simultaneously it can also be used for the valorization of lignocellulose, just as in the sustainable and renewable cycle, "the falling leaves returns to their roots". This Review is expected to provide valuable reference and new proposal for the further development and better utilization of GVL.

Enhanced Enzymatic Hydrolysis and Structure Properties of Bamboo by Moderate Two-Step Pretreatment

A moderate two-step pretreatment method was investigated to improve the enzymatic saccharification of bamboo residues. SEM and FTIR were employed to characterize the structure changes. Fed-batch enzymatic saccharification was performed to obtain high concentration of fermentable sugar. Bamboo was impregnated at low severity of conditions (room temperature, 2% H₂SO₄ or 2% NaOH, 48 h) to initially alter the structure of bamboo, and then further pretreated by steam explosion at 1.0 MPa for 6 min. The highest delignification of 51% and the highest enzymatic hydrolysis of 47.1% were reached at 2% NaOH impregnation followed by steam explosion. The changes in the structural characteristics showed beneficial effects on the enzymatic hydrolysis. When a mixer of cellulase (30 FPU) and β-glucosidase (10 CBU) was further used, the maximum enzymatic hydrolysis of 78.9% and total glucose yield of 68.2% were obtained. The maximum sugar release from the holocellulose was 500 mg/g bamboo, approximately 83.3% conversion efficiency based on monomeric sugar recovery. With fed-batch saccharification, a final substrate loading of 30% brought 107.7 g/L glucose, 35.81 g/L xylose, and 7.82 g/L arabinose release, respectively. This study provided an effective strategy for potential utilization of bamboo residues.

Gelatin as green adhesive for the preparation of a multifunctional biobased cryogel derived from bamboo industrial waste

The effective utilization of bamboo industrial waste to produce value-added products is an important subject. In this paper, a multifunctional biobased cryogel derived from bamboo industrial waste was successfully developed. Bamboo fibres were first extracted from bamboo industrial waste and then dispersed in the gelatin solution to produce bamboo fibres/gelatin cryogels (BFs/G cryogels) by a freeze-drying process. The hydrophobicities of BFs/G cryogels were further improved by modification with methyltrichlorosilane. The prepared BFs/G cryogels possessed low density (23.9-29.5 mg/cm³), high porosity (90.41-95.85%), low thermal conductivity (0.031‒0.047 W/m·K) and excellent sound-insulating performance. The presence of rigid bamboo fibres improved the mechanical performance of the BFs/G cryogel. Furthermore, the BFs/G cryogels exhibited high oil absorption capacities of 23-66 times that of their dry weights. The successful development of this cryogel provides a path for the efficient utilization of bamboo industrial waste as a renewable biomass resource.

Greener and sustainable production of bioethylene from bioethanol: current status, opportunities and perspectives

The economic value of bioethylene produced from bioethanol dehydration is remarkable due to its extensive usage in the petrochemical industry. Bioethylene is produced through several routes, such as steam cracking of hydrocarbons from fossil fuel and dehydration of bioethanol, which can be produced through fermentation processes using renewable substrates such as glucose and starch. The rise in oil prices, environmental issues due to toxic emissions caused by the combustion of fossil fuel and depletion of fossil fuel resources have led a demand for an alternative pathway to produce green ethylene. One of the abundant alternative renewable sources for bioethanol production is biomass. Bioethanol produced from biomass is alleged to be a competitive alternative to bioethylene production as it is environmentally friendly and economical. In recent years, many studies have investigated catalysts and new reaction engineering pathways to enhance the bioethylene yield and to lower reaction temperature to drive the technology toward economic feasibility and practicality. This paper critically reviews bioethylene production from bioethanol in the presence of different catalysts, reaction conditions and reactor technologies to achieve a higher yield and selectivity of ethylene. Techno-economic and environmental assessments are performed to further development and commercialization. Finally, key issues and perspectives that require utmost attention to facilitate global penetration of technology are highlighted.

Non-productive celluase binding onto deep eutectic solvent (DES) extracted lignin from willow and corn stover with inhibitory effects on enzymatic hydrolysis of cellulose

In this work, deep eutectic solvent (DES) was prepared by mixing choline chloride (ChCl) with lactic acid (LA), and effects of cellulase non-productive binding onto DES-extracted lignin from willow and corn stover on enzymatic hydrolysis of cellulose was investigated. The correlation between hydrolysis yield of cellulose and chemical features of lignin was evaluated, and a potential inhibitory mechanism was proposed. Condensation of lignin was observed during DES treatment, and these condensed aromatic structures had an increased tendency to adsorb enzymes through hydrophobic interactions. As well as hydrophobic interactions mediated by lignin condensation, an increase in phenolic hydroxyl groups resulted in a greater amount of hydrogen bonds between cellulases and lignin that appeared to inhibit enzymatic hydrolysis yields of cellulose (39.96-42.86 % to 31.96-32.68 %). Although large amounts of COOHs were generated, the elevated electrostatic repulsion as a result of ionic groups was insufficient to decrease non-productive adsorption.

Study of supercritical carbon dioxide pretreatment processes on green coconut fiber to enhance enzymatic hydrolysis of cellulose

Green coconut fiber was treated by supercritical CO₂ with the aim to enhance hydrolysis of its enzymatic cellulose. To this end, different static conditions of CO₂ contact times (3 and 5 h) and polarity modifiers (NaOH, NaHSO₄, ethanol) were evaluated at 20 MPa, 70 °C and 1 h of dynamic extraction followed by fast depressurization. After supercritical CO₂ exposition, SEM images showed fiber damage and FTIR spectra showed decreases of phenolic and wax contents, including a reduction in the degree of the hydrogen bond established between lignin and cellulose. Despite the apparent delignification, supercritical CO₂ did not enhance cellulose enzymatic hydrolyses. Fiber exposed to supercritical CO₂ (5 h) demonstrated that the highest sugar content (540.9 μmol glucose likely limited supercritical CO₂ delignification; however, green coconut in natura can be an innovative substrate for fermentation in alcohol production.

Insight into understanding the performance of deep eutectic solvent pretreatment on improving enzymatic digestibility of bamboo residues

Deep eutectic solvent (DES) is a promising pretreatment for improving enzymatic digestibility of lignocellulosic material by altering the physicochemical properties. However, few work has been done to quantitatively analysis the physicochemical properties changes of lignocellulosic material with enzymatic digestibility. In this work, DES pretreatment with different molar ratios of choline chloride/lactic acid was carried out on bamboo residues and respective enzymatic digestibility was investigated and linearly fitted with corresponding physicochemical features changes of the pretreated bamboo residues. Results showed that enzymatic digestibility of DES-pretreated bamboo residues was enhanced with the increasing molar ratio of choline chloride/lactic acid, which was due to DES pretreatment's ability to remove lignin and xylan, reduce the degree of polymerization of cellulose, enhance the crystallite size of cellulose, and improve cellulose accessibility. Several compelling linear correlations (R2 = 0.6-0.9) were observable between enzymatic digestibility and these changes of physicochemical properties, demonstrating how DES pretreatment improve the enzymatic digestibility.

Using highly recyclable sodium caseinate to enhance lignocellulosic hydrolysis and cellulase recovery

Most additives that capable of enhancing enzymatic hydrolysis of lignocellulose are petroleum-based, which are not easy to recycle with poor biodegradability. In this work, highly recyclable and biodegradable sodium caseinate (SC) was used to enhance lignocellulosic hydrolysis with improved cellulase recyclability. When the pH decreased from 5.5 to 4.8, more than 96% SC could be precipitated from the solution and recovered. Adding SC increased enzymatic digestibility of dilute acid pretreated eucalyptus (Eu-DA) from 39.5% to 78.2% under Eu-DA loading of 10 wt% and pH = 5.5, and increase cellulase content in 72 h hydrolysate from only 15.2% of the original to 60.0%, which facilitated the recovery of cellulases through re-adsorption by fresh substrates. With multiple cycles of re-adsorption, application of SC not only increased the sugar yield of Eu-DA by 95.5%, but also reduced cellulase loading by 40%.

Real-Time QCM-D Monitoring of the Adsorption-Desorption of Expansin on Lignin

Expansin has nonhydrolytic disruptive activity and synergistically acts with cellulases to enhance the hydrolysis of cellulose. The adsorption-desorption of expansin on noncellulosic lignin can greatly affect the action of expansin on lignocellulose. In this study, three lignins with different sources (kraft lignin (KL), sodium lignin sulfonate (SLS), and enzymatic hydrolysis lignin (EHL)) were selected as the substrates. The real-time adsorption-desorption of Bacillus subtilis expansin (BsEXLX1) on lignins was monitored using quartz crystal microgravimetry with dissipation (QCM-D). The effects of temperature and Tween 80 on the adsorption-desorption behaviors were also investigated. The results show that BsEXLX1 exhibited high binding ability on lignin and achieved maximum adsorption of 283.2, 273.8, and 266.9 ng cm^-2 at 25 °C on KL, SLS, and EHL, respectively. The maximum adsorption decreased to 148.2-192.8 ng cm^-2 when the temperature increased from 25 to 45 °C. Moreover, Tween 80 competitively bound to lignin and significantly prevented expansin adsorption. After irreversible adsorption of Tween 80, the maximum adsorption of BsEXLX1 greatly decreased to 33.3, 37.2, and 10.3 ng cm^-2 at 25 °C on KL, SLS, and EHL, respectively. Finally, a kinetic model was developed to analyze the adsorption-desorption process of BsEXLX1. BsEXLX1 has a higher adsorption rate constant (k_A) and a lower desorption rate constant (k_D) on KL than on SLS and EHL. The findings of this study provide useful insights into the adsorption-desorption of expansin on lignin.

Integrating bran starch hydrolysates with alkaline pretreated soft wheat bran to boost sugar concentration

Soft wheat bran (SWB), one of the most abundant byproducts from the wheat milling industry, is a potential candidate for biofuel production. In this study, bran starch hydrolysates were separately integrated with dilute acid pretreated SWB and alkaline pretreated SWB to boost fermentable sugar concentration. Alkaline pretreatment showed higher sugar recoveries than acid pretreatment. Significant sugar degradation for acid pretreatment was observed when pretreatment temperature higher than 170 ℃. The optimal pretreatment condition was 15% solid loading with 0.08 mol/L NaOH at 150 ℃ for 20 min. The neutralization reaction between dilute alkaline and released acids reduced sugar decomposition and inhibitors formation. Integrating bran starch hydrolysates with alkaline pretreated SWB yielded the highest glucose concentration of 50.91 g/L and a total sugar concentration of 101.29 g/L.

Corn stover valorization by one-step formic acid fractionation and formylation for 5-hydroxymethylfurfural and high guaiacyl lignin production

One-step fractionation with concentrated formic acid at elevated temperatures with short retention time was investigated for corn stover valorization. Crude pulp (CP) with high purity of cellulose and FA-lignin (FAL) with high guaiacyl content were fractionated through one-step mild pretreatment. Formylation reaction on both CP and FAL fractions occurred during the pretreatment and improved the hydrophobicity and thermal stability of CPs and FALs. The presence of formyl group on CPs significantly inhibited the enzymatic hydrolysis efficiency for sugar production, however, the formylated cellulose showed super high reactivity and selectivity for HMF production through catalysis by maleic acid and aluminum chloride in acetonitrile-water co-solvent system. In addition, the fractionated FAL fraction exhibited a loose structure which is prominent for its further catalytic conversion into chemicals and energy.

Sulfur dioxide-ethanol-water fractionation platform for conversion of recycled wood to sugars, lignin and lignosulfonates

Recycled wood of two grades (A and B) and spruce were converted on bench (100 o.d. g) and pilot (100 o.d. kg) scales to monosugars, lignin and lignosulfonates using SO₂-Ethanol-Water (AVAP®) technology. After digestion, C6 and C5 sugars were recovered at 98-100% and 87-99% for Wood A and Spruce, respectively, while the values for Wood B were 92% and 74-87%. Cellulose was hydrolysed to glucose at 90% or higher using enzyme charge of 7.1 FPU/g glucan. Hemicellulosic sugars were autohydrolyzed to 95-100% monosugars. At bench scale, monosaccharide yield was 609, 561 and 688 kg (hydrous) per BDT biomass for Wood A, Wood B and Spruce, respectively. Corresponding water insoluble lignin yield was 157, 148 and 189 kg per BDT biomass. The preliminary techno-economic evaluation revealed that conversion of recycled wood to sugars using AVAP® fractionation platform results in higher profitability in comparison to virgin wood.

Ultralight Industrial Bamboo Residue-Derived Holocellulose Thermal Insulation Aerogels with Hydrophobic and Fire Resistant Properties

In this study, water-soluble ammonium polyphosphate- (APP) and methyl trimethoxysilane (MTMS)-modified industrial bamboo residue (IBR)-derived holocellulose nanofibrils (HCNF/APP/MTMS) were used as the raw materials to prepare aerogels in a freeze-drying process. Synthetically modified aerogels were confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, and thermal stability measurements. As-prepared HCNF/APP/MTMS aerogels showed themselves to be soft and flexible. The scanning electron microscopy (SEM) analysis showed that the foam-like structure translates into a 3D network structure from HCNF aerogels to HCNF/APP/MTMS aerogels. The compressive modules of the HCNF/APP/MTMS aerogels were decreased from 38 kPa to 8.9 kPa with a density in the range of 12.04-28.54 kg/m³, which was due to the structural change caused by the addition of APP and MTMS. Compared with HCNF aerogels, HCNF/APP/MTMS aerogels showed a high hydrophobicity, in which the water contact angle was 130°, and great flame retardant properties. The peak of heat release rate (pHRR) and total smoke production (TSP) decreased from 466.6 to 219.1 kW/m² and 0.18 to 0.04 m², respectively, meanwhile, the fire growth rate (FIGRA) decreased to 8.76 kW/s·m². The thermal conductivity of the HCNF/APP/MTMS aerogels was 0.039 W/m·K. All results indicated the prepared aerogels should be expected to show great potential for thermally insulative materials.

Comparative study on different pretreatment on enzymatic hydrolysis of corncob residues

Under the situation of increasingly severe challenge of energy consumption, it is of great importance to make full use of bioresources such as forestry and agricultural residues. Herein, the corncob residues generated after processing corncob were enzymatically hydrolyzed to yield fermentable sugars. To overcome the recalcitrance of corncob residues, three kinds of pretreatment methods, i.e., sulfonation, PFI refining, and wet grinding, were applied; their effects on enzymatic hydrolysis and main characteristics of corncob residues substrate were investigated. The results showed that the enzymatic digestibility of the substrate was greatly enhanced by employing each method. The wet grinding exhibited obvious advantages, e.g., the conversion yield of cellulose to glucose and glucose concentration reached 96.7% and 32.2 g/L after 59 h of enzymatic hydrolysis, respectively. The improvement in enzymatic hydrolysis was mainly attributed to the altered characteristics of the substrate such as swelling ability, specific surface area, and particle size and distribution.

The Microstructure and Mechanical Properties of Poplar Catkin Fibers Evaluated by Atomic Force Microscope (AFM) and Nanoindentation

In this study, the microstructure and mechanical properties of poplar (Populus tomentosa) catkin fibers (PCFs) were investigated using field emission scanning electron microscope, atomic force microscopy (AFM), X-ray diffraction, and nanoindentation methods. Experimental results indicated that PCFs had a thin-wall cell structure with a large cell lumen and the hollow part of the cell wall took up 80 percent of the whole cell wall. The average diameters of the fiber and cell lumen, and the cell wall thickness were 5.2, 4.2, and 0.5 µm, respectively. The crystallinity of fibers was 32%. The AFM images showed that the orientation of microfibrils in cell walls was irregular and their average diameters were almost between 20.6–20.8 nm after being treated with 2 and 5 wt.% potassium hydroxide (KOH), respectively. According to the test of nanoindentation, the average longitudinal-reduced elastic modulus of the PCF S2 layer was 5.28 GPa and the hardness was 0.25 GPa.

How Pseudo-lignin Is Generated during Dilute Sulfuric Acid Pretreatment

Pseudo-lignin is generated from lignocellulose biomass during pretreatment with dilute sulfuric acid and has a significant inhibitory effect on cellulase. However, the mechanism of pseudo-lignin generation remains unclear. The following main points have been addressed to help elucidate the pseudo-lignin generation pathway. Cellulose and xylan were pretreated with sulfuric acid at different concentrations; aliquots were periodically collected; and the changes in the byproducts of the prehydrolysate were quantified. Milled wood lignin (MWL) mixed with cellulose and xylan was pretreated to evaluate the impact of lignin on pseudo-lignin generation. Furfural, 5-hydroxymethylfurfural, and MWL were pretreated as model compounds to investigate pseudo-lignin generation. The result indicated that the increasing acid concentration significantly promoted the generation of pseudo-lignin. When the acid concentration was increased from 0 to 1.00 wt %, pseudo-lignin was increased from 1.36 to 4.05 g. In addition, lignin promoted the pseudo-lignin generation through the condensation between lignin and the generated intermediates.

Improving the enzymatic hydrolysis of larch by coupling water pre-extraction with alkaline hydrogen peroxide post-treatment and adding enzyme cocktail

Soluble arabinogalactan (AG) in larch leads to reagent waste during its biorefining using oxidative pretreatment strategies. A two-stage pretreatment of water pre-extraction followed by alkaline hydrogen peroxide (AHP) pretreatment was investigated to more efficiently convert larch cellulose into glucose, while also obtaining a value-added AG product stream. The results showed that water pre-extraction increases the lignin selectivity of both NaOH and H₂O₂ reagents, translating to improved lignin removal and enzymatic hydrolysis yields. This was found to be related to cellulose accessibility alongside the effective consumption of the reagents. Moreover, the addition of mannanase also significantly enhanced enzymatic digestibility of pretreated solid from 81.0% to 97.7% (4% H₂O₂ charge and 180 °C) when 40 U/g mannanase was supplemented with 20 FPU/g cellulase. In all, it was demonstrated that coupling mannanase with cellulase could improve larch's enzymatic digestibility and overall viability for biorefining processes.

Coupling the post-extraction process to remove residual lignin and alter the recalcitrant structures for improving the enzymatic digestibility of acid-pretreated bamboo residues

In this work, a mild and facile post-extraction using different reagents was evaluated to overcome these recalcitrance for improving the enzymatic digestibility of acid-pretreated bamboo residues by removing the lignin and disrupting its inhibitory properties. Results showed that the enzymatic digestibility of acid-pretreated bamboo residues can be improved from 15.4% to 61.4%, 59.7%, and 42.8% by room temperature post-extraction with phosphoric acid, urea, and ethanol, respectively. Several compelling correlations (R² > 0.5) were observable between enzymatic digestibility and structural changes, including delignification, reducing of substrate hydrophobicity, altering cellulose crystallinity, and elevations to the residual lignin syringyl-to-guaiacyl (S/G) ratio and functional groups. The results serve as a demonstration of the downstream value that can be gained when coupling a post-extraction process with acid pretreatment of bamboo residues, resulting in greater fermentable sugar production.

Deep Eutectic Solvent-Assisted In Situ Wood Delignification: A Promising Strategy To Enhance the Efficiency of Wood-Based Solar Steam Generation Devices

Wood-based solar steam generation devices (W-SSGDs) show great promise for desalination and wastewater treatment because they are inexpensive and sustainable. Technical methods for enhancing the efficiency of W-SSGDs have, so far, mainly focused on the optimization of solar-to-thermal conversion efficiency, whereas the properties of the wood matrix have been ignored. Here, we have designed a strategy using deep eutectic solvents to remove lignin from bulk wood in situ for the fabrication of a high-performance W-SSGD (DW-SSGD). Wood delignification increases the water transportation capacity while reducing thermal conductivity and conductive heat loss in the wood matrix. The improved properties of delignified wood allowed us to construct a high-performance DW-SSGD with a steam generation efficiency of 89% and an evaporation rate as high as 1.3 kg m^-2 h^-1 at 1 sun (100 mW cm^-2). To the best of our knowledge, the performance reported here is the highest for a W-SSGD under one solar irradiation.

Valorization of Alkaline Peroxide Mechanical Pulp by Metal Chloride-Assisted Hydrotropic Pretreatment for Enzymatic Saccharification and Cellulose Nanofibrillation

Developing economical and sustainable fractionation technology of lignocellulose cell walls is the key to reaping the full benefits of lignocellulosic biomass. This study evaluated the potential of metal chloride-assisted p-toluenesulfonic acid (p-TsOH) hydrolysis at low temperatures and under acid concentration for the co-production of sugars and lignocellulosic nanofibrils (LCNF). The results indicated that three metal chlorides obviously facilitated lignin solubilization, thereby enhancing the enzymatic hydrolysis efficiency and subsequent cellulose nanofibrillation. The CuCl₂-assisted hydrotropic pretreatment was most suitable for delignification, resulting in a relatively higher enzymatic hydrolysis efficiency of 53.2%. It was observed that the higher residual lignin absorbed on the fiber surface, which exerted inhibitory effects on the enzymatic hydrolysis, while the lower lignin content substrates resulted in less entangled LCNF with thinner diameters. The metal chloride-assisted rapid and low-temperature fractionation process has a significant potential in achieving the energy-efficient and cost-effective valorization of lignocellulosic biomass.

Enhancing enzymatic digestibility of waste wheat straw by presoaking to reduce the ash-influencing effect on autohydrolysis

BACKGROUND

The acid buffering capacity of high free ash in waste wheat straw (WWS) has been revealed to be a significant hindrance on the efficiency of autohydrolysis pretreatment. Previous researches have mainly relied on washing to eliminate the influence of ash, and the underlying mechanism of the ash influencing was not extensively investigated. Presently, studies have found that cations can destroy the acid buffering capacity of ash through cation exchange. Herein, different cations were applied to presoak WWS with the aim to overcome the negative effects of ash on autohydrolysis efficiency, further improving its enzymatic digestibility.

RESULTS

Results showed that cations can be adsorbed on the surface of the material by electrostatic adsorption to change the acid buffering capacity of WWS. The acid buffering capacity of 120 mM Fe²⁺ presoaked WWS is reduced from 226.3 mmol/pH-kg of original WWS to 79.3 mmol/pH-kg. This reduced the autohydrolysis pretreatment medium pH from 5.7 to 3.8 and promoted the removal of xylan from 61.7 to 83.7%. In addition, the enzymatic digestibility of WWS was enhanced from 49.7 to 86.3% by presoaking with 120 mM Fe²⁺ solution. The relationship between enzymatic accessibility and hydrophobicity with enzymatic digestibility of the autohydrolyzed WWS was analyzed.

CONCLUSIONS

The results showed that the acid buffering capacity of the high free ash was detrimental for the autohydrolysis efficiency of WWS. After WWS was presoaked with different cations, the acid buffering capacity of ash was weakened by cation exchange and electrostatic adsorption, which improved the autohydrolysis efficiency. The results expound that the enzymatic digestibility of WWS can be enhanced through presoaking to reduce the ash-influencing effect on autohydrolysis.

Impact of lignin content on alkaline-sulfite pretreatment of Hybrid Pennisetum

This work focuses to investigate the impact of lignin content on chemical compositions, crystallinity, surface characterizations, cellulase adsorption profiles and hydrolysability of Hybrid Pennisetum (HP) after alkaline sulfite pretreatment (ASP). For the HP with lower lignin content, the increase of the cellulose content by ASP was more obvious than raw HP. ASP decreased total lignin content and surface lignin content of HP substrates. HP with lower lignin content (e.g., ∼15%) is suitable for ASP, because a pretty perfect glucose yield (91%) was obtained using a low dosage of enzyme loadings (5 FPU of cellulases/g dry matter). The study provides a potential strategy to efficiently produce platform sugars from HP with reduced lignin content, indicating the importance of reduction HP lignin content properly by breeding or transgenesis programs. The work could also help elucidate the mechanism of alkaline sulfite pretreatment for efficient production of fermentable sugars from lignocelluloses.