The response mechanism analysis of HMX1 knockout strain to levulinic acid in Saccharomyces cerevisiae

Levulinic acid, a hydrolysis product of lignocellulose, can be metabolized into important compounds in the field of medicine and pesticides by engineered strains of Saccharomyces cerevisiae. Levulinic acid, as an intermediate product widely found in the conversion process of lignocellulosic biomass, has multiple applications. However, its toxicity to Saccharomyces cerevisiae reduces its conversion efficiency, so screening Saccharomyces cerevisiae genes that can tolerate levulinic acid becomes the key. By creating a whole-genome knockout library and bioinformatics analysis, this study used the phenotypic characteristics of cells as the basis for screening and found the HMX1 gene that is highly sensitive to levulinic acid in the oxidative stress pathway. After knocking out HMX1 and treating with levulinic acid, the omics data of the strain revealed that multiple affected pathways, especially the expression of 14 genes related to the cell wall and membrane system, were significantly downregulated. The levels of acetyl-CoA and riboflavin decreased by 1.02-fold and 1.44-fold, respectively, while the content of pantothenic acid increased. These findings indicate that the cell wall-membrane system, as well as the metabolism of acetyl-CoA and riboflavin, are important in improving the resistance of Saccharomyces cerevisiae to levulinic acid. They provide theoretical support for enhancing the tolerance of microorganisms to levulinic acid, which is significant for optimizing the conversion process of lignocellulosic biomass to levulinic acid.

Acetic acid as a protic solvent for reducing sulphuric acid concentrations in the production of cellulose nanocrystals alongside transition metal co-catalysts

Cellulose nanocrystals (CNC) conventionally involve highly concentrated sulphuric acid, which typically resulted in the formation of undesirable by-products. Although less corrosive mineral acids have been explored as alternatives, high concentrations are still required. In this study, CNC was successfully isolated from Leucaena leucocephala wood using mild sulphuric acid with acetic acid as protic solvent, and it was further studied with the addition of Lewis acids in the form of multivalent transition metal salts as co-catalyst. Selected divalent and trivalent transition metal salts including (Cr(NO3)3, Fe(NO3)3, Co(NO3)2, and Ni(NO3)2) were investigated. The morphology, chemical structure, particle size, and physicochemical properties of the CNCs were determined. Controlled depolymerization of cellulose was observed using transmission electron microscopy (TEM). Rod-like morphology for all CNCs was obtained during the hydrolysis process with the smallest CNC particles found at an average length of 278.1 ± 35.1 nm and a diameter of 13.4 ± 3.0 nm. The results showed that higher valence state metal ions resulted in better cellulose hydrolysis efficiency. In addition, the use of transition metal salt as a co-catalyst improved production efficiency and minimised carbonization of CNC while maintaining desired crystallinity and thermal properties.

Enhancing biomass conversion: Efficient hemicellulose removal and cellulose saccharification in poplar with FeCl3 coupled with acidic electrolyzed water pretreatment

Due to the recalcitrant structure of woody biomass such as poplar, the efficient disassembly and separation of hemicellulose component from woody biomass is crucial for green biomass processing and full component utilization. This study presented an environmentally friendly approach to utilize acidic electrolyzed water (AEW) combined with metal salts and investigated its pretreatment effects on hemicellulose removal and cellulose and lignin retention under different conditions. Meanwhile, the structural properties and enzymatic hydrolysis performance of the pretreated residues were also characterized. As a result, under the optimized pretreatment conditions (0.03 mol/L FeCl3 with AEW at 180 °C for 10 min), hemicellulose removal from poplar wood reached 98.64 %, accompanied by xylose recovery rate of 98.46 %, cellulose retention rate of 93.43 % and lignin retention rate of 94.29 %. Enzymatic hydrolysis rate of the pretreated cellulose-enriched substrate reached 97.65 %. Furthermore, comprehensive structural characterizations revealed that FeCl3 coupled with AEW pretreatment resulted in surface damage to the poplar wood, effective removal of the amorphous hemicellulose component, and partial destruction of the cellulose crystallinity. In conclusion, FeCl3 coupled with AEW pretreatment effectively separates hemicellulose, leading to significant alterations in biomass composition and structure, ultimately resulting in improved enzymatic digestion. These results provide theoretical support for targeted dissociation of hemicellulose and full component utilization of woody biomass.

The key role of pretreatment for the one-step and multi-step conversions of European lignocellulosic materials into furan compounds

Nowadays, an increased interest from the chemical industry towards the furanic compounds production, renewable molecules alternatives to fossil molecules, which can be transformed into a wide range of chemicals and biopolymers. These molecules are produced following hexose and pentose dehydration. In this context, lignocellulosic biomass, owing to its richness in carbohydrates, notably cellulose and hemicellulose, can be the starting material for monosaccharide supply to be converted into bio-based products. Nevertheless, processing biomass is essential to overcome the recalcitrance of biomass, cellulose crystallinity, and lignin crosslinked structure. The previous reports describe only the furanic compound production from monosaccharides, without considering the starting raw material from which they would be extracted, and without paying attention to raw material pretreatment for the furan production pathway, nor the mass balance of the whole process. Taking account of these shortcomings, this review focuses, firstly, on the conversion potential of different European abundant lignocellulosic matrices into 5-hydroxymethyl furfural and 2-furfural based on their chemical composition. The second line of discussion is focused on the many technological approaches reported so far for the conversion of feedstocks into furan intermediates for polymer technology but highlighting those adopting the minimum possible steps and with the lowest possible environmental impact. The focus of this review is to providing an updated discussion of the important issues relevant to bringing chemically furan derivatives into a market context within a green European context.

Intensification of sugar production by using Tween 80 to enhance metal-salt catalyzed pretreatment and enzymatic hydrolysis of sugarcane bagasse

In this study, different metal-salt catalyzed pretreatment was presented to disorganize the obstinate structure by eliminating the majority of hemicellulose, fractional of lignin, and improve the enzymatic saccharification of sugarcane bagasse. With the accession of Tween 80 during enzymolysis, all metal-salt pretreated substrates presented higher glucose yields, especially for CuCl₂. Furthermore, Tween 80 was added to the pretreatment, enhancing the elimination of hemicellulose and lignin, decreasing the degradation of sugars to inhibitors, and presenting superior performance on improving glucose yield. In addition, the maximum glucose yield of 88.0% was achieved by using Tween 80 concomitantly with AlCl₃ pretreatment and enzymolysis. It was also found that adding Tween 80 during pretreatment or/and enzymolysis after 24 h could liberate the similar glucose without Tween 80 after 72 h. However, the enhancement of Tween 80 at 6 h was higher than that at 72 h.

Hydrochar derived from municipal sludge through hydrothermal processing: A critical review on its formation, characterization, and valorization

Additional options for the sustainable treatment of municipal sludge are required due to the significant amounts of sludge, high levels of nutrients (e.g., C, N, and P), and trace constituents it contains. Hydrothermal processing of municipal sludge has recently been recognized as a promising technology to efficiently reduce waste volume, recover bioenergy, destroy organic contaminants, and eliminate pathogens. However, a considerable amount of solid residue, called hydrochar, could remain after hydrothermal treatment. This hydrochar can contain abundant amounts of energy (with a higher heating value up to 24 MJ/kg, dry basis), nutrients, and trace elements, as well as surface functional groups. The valorization of sludge-derived hydrochar can facilitate the development and application of hydrothermal technologies. This review summarizes the formation pathways from municipal sludge to hydrochar, specifically, the impact of hydrothermal conditions on reaction mechanisms and product distribution. Moreover, this study comprehensively encapsulates the described characteristics of hydrochar produced under a wide range of conditions: Yield, energy density, physicochemical properties, elemental distribution, contaminants of concern, surface functionality, and morphology. More importantly, this review compares and evaluates the current state of applications of hydrochar: Energy production, agricultural application, adsorption, heterogeneous catalysis, and nutrient recovery. Ultimately, along with the identified challenges and prospects of valorization approaches for sludge-derived hydrochar, conceptual designs of sustainable municipal sludge management are proposed.

Collaborative Conversion of Biomass Carbohydrates into Valuable Chemicals: Catalytic Strategy and Mechanism Research

Levulinate is one of the high added-value biomass-derived chemicals that is primarily produced from hexoses in cellulose and hemicellulose. Producing levulinate from pentoses in hemicellulose that is extensively distributed in biomass is still highly challenging. In this study, biomass materials and carbohydrates (including cellulose, xylan, glucose, fructose, and xylose) were collaboratively converted into levulinates efficiently over various zeolites with ethanol/dimethoxymethane as cosolvents. The key process for converting pentoses into levulinates is the synthesis of intermediates (furfural) into alkoxy methyl furfural via electrophilic substitution or their conversion into furfuryl alcohol via in situ hydrogenation. The substitution was achieved by the synergic effect between bifunctional catalysts and cosolvents, which promotes conversion of furfural into alkoxy methyl furfural via the electrophilic addition of alkoxy methyl radicals. Hydrogenation of furfural into furfuryl alcohol was impelled by the cooperative process between in situ generated H-donor from alcohol solvents and zeolite catalysts. Moreover, a favorable yield of 21.05 mol % of levulinates was achieved by simultaneous and collaborative conversion of cellulose and hemicellulose with the one-pot process using ethanol/dimethoxymethane as a cosolvent and the zeolite with B and L acid sites as a catalyst.