Bio-based Chemicals Research Articles

Identification of Enzymes from Pseudogluconobacter saccharoketogenes Producing d-Glucaric Acid from d-Glucose.

In 2004, the US Department of Energy listed d-glucaric acid as one of the top 12 bio-based chemicals and a potential biopolymer building block. In this study, we show that Pseudogluconobacter saccharoketogenes strains can produce d-glucaric acid from d-glucose, although in low yield because of the generation of the byproduct 2-keto-d-gluconic acid in large quantities. To improve d-glucaric acid yield, we generated Rh47-3, a P. saccharoketogenes IFO14464 mutant, which produced d-glucaric acid from d-gluconic acid and d-glucose with 81 and 53 mol% yields, respectively. Furthermore, the key enzymes involved in d-glucaric acid production, alcohol dehydrogenase (Ps-ADH), aldehyde dehydrogenase (Ps-ALDH), and gluconate 2-dehydrogenase (Ps-GADH), were purified and their roles in d-glucaric acid synthesis were evaluated. Ps-ADH and Ps-ALDH catalyzed d-glucaric acid production, which was mediated by d-gluconic acid and d-glucuronic acid pathways. In contrast, Ps-GADH inhibited d-glucaric acid production by promoting the formation of 2-keto-d-gluconic acid from d-glucose.

Prospecting pecan nutshell pyrolysis as a source of bioenergy and bio-based chemicals using multicomponent kinetic modeling, thermodynamic parameters estimation, and Py-GC/MS analysis

This work reports the first detailed investigation of the physicochemical properties of the pecan nutshell waste (PNS) and its suitability for pyrolytic conversion into bioenergy and bio-based chemicals based on the kinetic triplet, thermodynamic parameters, and Py-GC/MS analysis. The pyrolysis behavior of PNS was assessed using a thermogravimetric analyzer at five heating rate programs under an oxygen-free atmosphere. The Asym2Sig deconvolution function showed that pyrolysis of PNS might be successfully modeled as three parallel devolatilization events (R2 > 99%), which are categorized as the devolatilization of hemicellulose (DE-HC), devolatilization of cellulose (DE-CL), and devolatilization of lignin (DE-LG). The activation energy was obtained for each devolatilization event by concurrent use of four isoconversional methods (Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink), with average values in the range of 100.3–109.0 kJ mol−1 for DE-HC, 124.3–135.3 kJ mol−1 for DE-CL, and 357.1–398.9 kJ mol−1 for DE-LG. Calculations using the compensation effect method indicated pre-exponential factor values of 5.50 × 108 min−1 for DE-HC, 1.32 × 109 min−1 for DE-CL, and 4.86 × 1018 min−1 for DE-LG. It is inferred that the DE-CL corresponds to a geometrical contraction reaction model while the DE-HC and DE-LG follow order-based reaction models. Finally, the summative kinetic interpretation was successfully obtained based on multiple kinetic triplets, providing a useful mathematical tool able to describe the pyrolysis behavior of PNS. From the thermodynamic viewpoint, PNS has significant potential for application as raw material for bioenergy production. Also, the condensable fraction of the volatile products derived from pecan nutshell pyrolysis is a potential source of valuable bio-based chemicals.

Influence of Pd and Pt Promotion in Gold Based Bimetallic Catalysts on Selectivity Modulation in Furfural Base-Free Oxidation

Furfural (FF) has a high potential to become a major renewable platform molecule to produce biofuels and bio-based chemicals. The catalytic performances of AuxPty and AuxPdy bimetallic nanoparticulate systems supported on TiO2 were studied in a base-free aerobic oxidation of furfural to furoic acid (FA) and maleic acid (MA) in water. The characterization of the catalysts was performed using standard techniques. The optimum reaction conditions were also investigated, including the reaction time, the reaction temperature, the metal ratio, and the metal loading. The present work shows a synergistic effect existing between Au, Pd, and Pt in the alloy, where the performances of the catalysts were strongly dependent on the metal ratio. The highest selectivity (100%) to FA was obtained using Au3-Pd1 catalysts, with 88% using 0.5% Au3Pt1 with about 30% of FF conversion at 80 °C. Using Au-Pd-based catalysts, the maximum yield of MA (14%) and 5% of 2(5H)-furanone (FAO) were obtained by using a 2%Au1-Pd1/TiO2 catalyst at 110 °C.

Metabolic engineering design to enhance (R,R)-2,3-butanediol production from glycerol in Bacillus subtilis based on flux balance analysis

BackgroundGlycerol is a desirable alternative substrate for 2,3-butanediol (2,3-BD) production for sustainable development in biotechnological industries and non-food competitive feedstock. B. subtilis, a “generally recognized as safe” organism that is highly tolerant to fermentation products, is an ideal platform microorganism to engineer the pathways for the production of valuable bio-based chemicals, but it has never been engineered to improve 2,3-BD production from glycerol. In this study, we aimed to enhance 2,3-BD production from glycerol in B. subtilis through in silico analysis. Genome-scale metabolic model (GSM) simulations was used to design and develop the metabolic pathways of B. subtilis. Flux balance analysis (FBA) simulation was used to evaluate the effects of step-by-step gene knockouts to improve 2,3-BD production from glycerol in B. subtilis.ResultsB. subtilis was bioengineered to enhance 2,3-BD production from glycerol using FBA in a published GSM model of B. subtilis, iYO844. Four genes, ackA, pta, lctE, and mmgA, were knocked out step by step, and the effects thereof on 2,3-BD production were evaluated. While knockout of ackA and pta had no effect on 2,3-BD production, lctE knockout led to a substantial increase in 2,3-BD production. Moreover, 2,3-BD production was improved by mmgA knockout, which had never been investigated. In addition, comparisons between in silico simulations and fermentation profiles of all B. subtilis strains are presented in this study.ConclusionsThe strategy developed in this study, using in silico FBA combined with experimental validation, can be used to optimize metabolic pathways for enhanced 2,3-BD production from glycerol. It is expected to provide a novel platform for the bioengineering of strains to enhance the bioconversion of glycerol into other highly valuable chemical products.

A novel AST2 mutation generated upon whole-genome transformation of Saccharomyces cerevisiae confers high tolerance to 5-Hydroxymethylfurfural (HMF) and other inhibitors.

Development of cell factories for conversion of lignocellulosic biomass hydrolysates into biofuels or bio-based chemicals faces major challenges, including the presence of inhibitory chemicals derived from biomass hydrolysis or pretreatment. Extensive screening of 2526 Saccharomyces cerevisiae strains and 17 non-conventional yeast species identified a Candida glabrata strain as the most 5-hydroxymethylfurfural (HMF) tolerant. Whole-genome (WG) transformation of the second-generation industrial S. cerevisiae strain MD4 with genomic DNA from C. glabrata, but not from non-tolerant strains, allowed selection of stable transformants in the presence of HMF. Transformant GVM0 showed the highest HMF tolerance for growth on plates and in small-scale fermentations. Comparison of the WG sequence of MD4 and GVM1, a diploid segregant of GVM0 with similarly high HMF tolerance, surprisingly revealed only nine non-synonymous SNPs, of which none were present in the C. glabrata genome. Reciprocal hemizygosity analysis in diploid strain GVM1 revealed AST2N406I as the only causative mutation. This novel SNP improved tolerance to HMF, furfural and other inhibitors, when introduced in different yeast genetic backgrounds and both in synthetic media and lignocellulose hydrolysates. It stimulated disappearance of HMF and furfural from the medium and enhanced in vitro furfural NADH-dependent reducing activity. The corresponding mutation present in AST1 (i.e. AST1D405I) the paralog gene of AST2, also improved inhibitor tolerance but only in combination with AST2N406I and in presence of high inhibitor concentrations. Our work provides a powerful genetic tool to improve yeast inhibitor tolerance in lignocellulosic biomass hydrolysates and other inhibitor-rich industrial media, and it has revealed for the first time a clear function for Ast2 and Ast1 in inhibitor tolerance.

Life cycle assessment of biobased chemicals from different agricultural feedstocks

The production of biobased fuels and chemicals using renewable feedstocks is a promising alternative to achieve sustainability. Research has been focused on evaluating the economic, environmental and social performance of different products along their life cycle. Most of the published research on the evaluation of the environmental performance focuses on single products while examining mostly the global warming potential and/or the energy demand. In this work a “cradle to gate” life cycle assessment is performed for the commercial-scale production of nine different biobased chemicals. To have a comprehensive view about their total sustainability, the impact categories examined are the global warming potential, the acidification potential and the eutrophication potential. Detailed description of the processes and their simulation, design and inventories are presented to facilitate future research efforts. The analysis of the results shows that the main drivers are the production of feedstock and the use of utility steam and electricity across each impact category. Significant advantages over the fossil-based production technologies are demonstrated in all cases where reliable data are available in the open literature.

Sustainable Exploitation of Residual Cynara cardunculus L. to Levulinic Acid and n-Butyl Levulinate

Hydrolysis and butanolysis of lignocellulosic biomass are efficient routes to produce two valuable bio-based platform chemicals, levulinic acid and n-butyl levulinate, which find increasing applications in the field of biofuels and for the synthesis of intermediates for chemical and pharmaceutical industries, food additives, surfactants, solvents and polymers. In this research, the acid-catalyzed hydrolysis of the waste residue of Cynara cardunculus L. (cardoon), remaining after seed removal for oil exploitation, was investigated. The cardoon residue was employed as-received and after a steam-explosion treatment which causes an enrichment in cellulose. The effects of the main reaction parameters, such as catalyst type and loading, reaction time, temperature and heating methodology, on the hydrolysis process were assessed. Levulinic acid molar yields up to about 50 mol % with levulinic acid concentrations of 62.1 g/L were reached. Moreover, the one-pot butanolysis of the steam-exploded cardoon with the bio-alcohol n-butanol was investigated, demonstrating the direct production of n-butyl levulinate with good yield, up to 42.5 mol %. These results demonstrate that such residual biomass represent a promising feedstock for the sustainable production of levulinic acid and n-butyl levulinate, opening the way to the complete exploitation of this crop.

Highly Controllable Hydrogenative Ring Rearrangement and Complete Hydrogenation Of Biobased Furfurals over Pd/La2B2O7 (B=Ti, Zr, Ce)

AbstractDeveloping a highly selective catalyst to upgrade furfurals (5‐hydroxymethyl furfural and furfural) to cyclopentanones (3‐hydroxymethyl cyclopentanone and cyclopentanone) and tetrahydrofuran alcohols (2,5‐bishydroxymethyl tetrahydrofuran and tetrahydrofuran alcohol) is highly significant for biobased fine chemical synthesis. Here, a series of La2B2O7 (B=Ti, Zr, Ce) metal oxides, featuring the same chemical formula but different topological structures are fabricated. After Pd loading, the Lewis acidity and metal‐support interaction are well governed by the support type, which further affects the hydrogenation and acid‐catalyzed ability. A greater than 82 % yield of cyclopentanones is obtained via a hydrogenative ring rearrangement route over Pd/La2Ti2O7. However, Pd/La2Ce2O7 shows high catalytic efficiency for tetrahydrofuran alcohols with an approximately 80 % yield via a complete hydrogenation route. Additionally, the catalyst exhibits outstanding recycling performance and structural stability. This study presents an interesting design strategy for the selective preparation of cyclopentanones and tetrahydrofuran alcohols through the regulation of the adsorption mechanism.

Plant-based nanostructured silicon carbide modified with bisphosphonates for metal adsorption

Nanostructured silicon carbide possesses superior properties such as excellent hardness, high chemical stability, large surface area and good sintering ability at relatively low temperatures compared to bulk silicon carbide. However, its synthesis with conventional methods is still challenging. In the present study, we produced nanostructured silicon carbide from barley husks with a simple self-propagating high-temperature synthesis. Barley husks were chosen as the raw material because they are agricultural residues widely available and contain large amount of nanostructured silica suitable as a precursor in the synthesis. We studied the effect of two processes to valorize the barley husks on the extracted silica particles: burning in an industrial scale furnace to produce heat energy and pyrolysis to extract organic compounds as well as controlled calcination as a reference. The processing prior to the extraction affected morphology and composition of the nanostructured silica. The highest purity and surface area of 187 m2/g was obtained for the silica extracted from pristine barley husks through calcination. On the other hand, pyrolysis allows additional valorisation of the biomass by producing bio-based organic chemicals and still the silica particles with relatively high surface area, 105 m2/g, can be extracted. Nanostructured silicon carbide was produced from the extracted nanostructured silica with magnesiothermic reduction via self-propagating high-temperature synthesis. Nanostructured silicon carbide produced from silica particles undergone calcination had the highest surface area of 196 m2/g. Furthermore, it was functionalized with bisphosphonates to be used as a metal adsorbent and examined in adsorption of manganese from landfill water with pH 8. The functionalization of the silicon carbide with bisphosphonates increased the adsorption capacity by 32 % and the material was able to withstand at least 5 adsorption/desorption cycles.

Selective catalytic conversion of tea waste biomass into phenolic-rich bio-oil and subsequent extraction

Fast pyrolysis has appeared as a promising technology for bio-fuels and bio-based chemicals production. This paper reports tea waste (TW) as a promising source of phenolic-rich bio-oil production via catalytic fast pyrolysis in fluidized bed reactor. TG-FTIR analysis is applied to optimize pyrolysis temperature for phenolic-rich bio-oil production and maximum phenols yield (17.3 %) was obtained at 500 °C. Meanwhile, bio-oils are produced at each corresponding temperatures of TG-FTIR analysis and GC–MS analysis is performed to examine consistency and authenticity of TG-FTIR results. Moreover, catalytic effect of activated carbon + KOH (AC-K) with different biomass-to-catalyst ratio was examined to optimize most efficient ratio at 500 °C and maximum phenol contents (39.72 %) were obtained at 1:6 ratio of biomass-to-catalyst as compared to non-catalytic pyrolysis (23.85 %). Moreover, effect of temperature on product distribution was examined and maximum liquid yield (40.7 %) was obtained at 500 °C. Furthermore, switchable hydrophilic solvents (SHS) were used to isolate phenols from bio-oil with 95.02 % yield calculated by GC–MS analysis. The elemental analysis and high heating value (HHV) of the crude and residue bio-oil were determined. The carbon contents and HHV of residue bio-oil were increased to 67.3 % and 13.7 MJ/Kg from 46.2 % and 10.38 MJ/Kg respectively while; oxygen contents were decreased to 19.7 from 45.3 % demonstrating its potential for fuel application.

Production of bio-based chemicals from palmitic acid by catalytic hydrotreating over low-cost Ni/LY char and limonite catalysts

Catalytic hydrotreating of fatty acid is respected to produce bio-based chemicals especially oleochemicals that can be applied as a high valuable raw material or intermediate materials for industries. Low-cost Ni/LY char and limonite catalysts can compensate the expensively commercial catalysts. Palmitic acid (PA) was represented as reactant. Chemical compositions of liquid product were analyzed and presented in compound group, carbon number distribution and product selectivity. Catalyst characteristics and liquid product properties were also investigated. BET surface area, pore volume, and pore size of the prepared Ni/LY char catalyst were 308 m2/g, 0.188 cm3/g and 2.43 nm, respectively, and those of limonite catalyst were 95 m2/g, 0.3 cm3/g and 12.59 nm, respectively. Based on the initial 3 MPa H2 at 300 °C, the obtained oleochemicals depended on catalyst type, reaction time and solvent. In case of Ni/LY char catalyst, ester was found in yield of 58.94% that mainly contained with isopropyl palmitate up to 82% of ester, meanwhile product from limonite was principally distributed in alcohol group with 51.84% in which n-pentadecanol was the major compound with 37.05% yield. The products showed the oxygen removal in range of 19.11–65.15 mol% and HHVs were increased to 32.11–34.13 MJ/kg when compared with PA.

Impact of uncertainty in technological cycle on circular economy: Bio-based jet fuel range alkenes and pentanediols production

In terms of circular economy (CE), the coproduction of biofuels and bio-based chemicals could be a feasible strategy to improve the biorefinery economics. However, this approach is significantly affected by the variation of the techno-economic parameters. Thus, we evaluated the techno-economic feasibility of an integrated strategy through deterministic and stochastic models for the coproduction of biofuels (jet fuel range alkenes (JFA)) and bio-based chemicals (pentanediols and pentane) to identify the impact of uncertainty in technological cycle on the CE action plan. The deterministic analysis estimated the minimum JFA selling price (MJSP) expressed per gasoline gallon equivalents (GGE) and led to the identification of six major techno-economic parameters having a significant impact on the economics. Stochastic analysis was performed based on the Monte Carlo simulation, leading to probabilistic results on the economic feasibility of the integrated strategy, taking into account the uncertainty in the six identified parameters. In five of the six scenarios developed considering each uncertainty, the chances of MJSP being lower than the maximum biofuel price (USD 3.10 GGE−1) in the last three years (2017–2019) were higher than 50% (53.2–88.1%), implying that, despite the uncertainties reflected in the major techno-economic parameters, the integrated strategy could be a risk-averse investment.

Metal-alkali catalytic valorization of lignocellulose towards aromatics and small molecular alcohols and acids in a holistic approach

In this work, we developed an approach of one-pot complete catalytic conversion of woody biomass into two value product streams: lignin-derived aromatics (monomer yield of 68.54% and oligomer yield of 29.65% based on lignin mass) and (semi-)cellulose-derived small molecular alcohols (about 59.60% of biomass mass). These could be afforded by conducting lignocellulose depolymerization over metal-alkaline catalysts in a mixed n-butanol/H2O solvent system at 250 °C and 30 bar H2. In the valorization process, the homogenous mixture of n-butanol-H2O solvents extract and depolymerize both lignin and hemicellulose, while the catalysts and H2 are essential to cleave the inter-/intramolecular linkage of lignocellulose into target products. After the reaction, the phase separation of n-butanol and H2O takes place when system temperature drops below 125 °C, providing a mild and effective strategy to isolate lignin-derived aromatics (n-butanol phase) from small molecular alcohols/acids (aqueous phase). Ru/C and alkali catalysts are collected by filtration from n-butanol phase and H2O phase, respectively. Meanwhile, the effect of metal-alkali coupled catalysts facilitates the cleavage of β-O-4 linkage of lignin and increases the attainability of (semi-)cellulose-derived oligomers and the small molecular alcohols. This catalytic system provides a versatile valorization approach for biomass catalysis to bio-based chemicals.

Selective Production of Bio-Based Linear Alpha-Olefin from Wasted Fatty Alcohol on Al2O3 for Bio-Based Chemicals.

The catalytic dehydration of a bio-based fatty alcohol was performed using Al2O3 prepared by solvothermal synthesis for selective production of long-chain linear-alpha-olefins (LAO). The effect of the synthesis temperature of alumina precursors on the dehydration of 1-octadecanol (C18H38O) was examined based on the textural properties and Lewis acid–base properties of the catalysts. Amorphous alumina synthesized at 325 °C showed the highest surface area (233.07 m2/g) and total pore volume (1.237 cm3/g) among the catalysts and the best dehydration results: 93% conversion, 62% selectivity of 1-octadecene (C18H36), and 89% LAO purity. This was attributed to the increased Al/O ratio and atomic concentration of surface O in alumina, which were important factors in the catalytic dehydration of 1-octadecanol through the synergistic catalysis of acid–base pairs. The produced bio-based LAO can be key intermediates for synthesis of oxo alcohols and poly-alpha-olefins, as alternatives to petroleum-based LAO to achieve carbon neutrality in chemical industry.

Open Culture Ethanol-Based Chain Elongation to Form Medium Chain Branched Carboxylates and Alcohols.

Chain elongation fermentation allows for the synthesis of biobased chemicals from complex organic residue streams. To expand the product spectrum of chain elongation technology and its application range we investigated 1) how to increase selectivity towards branched chain elongation and 2) whether alternative branched carboxylates such as branched valerates can be used as electron acceptors. Elongation of isobutyrate elongation towards 4-methyl-pentanoate was achieved with a selectivity of 27% (of total products, based on carbon atoms) in a continuous system that operated under CO2 and acetate limited conditions. Increasing the CO2 load led to more in situ acetate formation that increased overall chain elongation rate but decreased the selectivity of branched chain elongation. A part of this acetate formation was related to direct ethanol oxidation that seemed to be thermodynamically coupled to hydrogenotrophic carboxylate reduction to corresponding alcohols. Several alcohols including isobutanol and n-hexanol were formed. The microbiome from the continuous reactor was also able to form small amounts of 5-methyl-hexanoate likely from 3-methyl-butanoate and ethanol as substrate in batch experiments. The highest achieved concentration of isoheptanoate was 6.4 ± 0.9 mM Carbon, or 118 ± 17 mg/L, which contributed for 7% to the total amount of products (based on carbon atoms). The formation of isoheptanoate was dependent on the isoform of branched valerate. With 3-methyl-butanoate as substrate 5-methylhexanoate was formed, whereas a racemic mixture of L/D 2-methyl-butanoate did not lead to an elongated product. When isobutyrate and isovalerate were added simultaneously as substrates there was a large preference for elongation of isobutyrate over isovalerate. Overall, this work showed that chain elongation microbiomes can be further adapted with supplement of branched-electron acceptors towards the formation of iso-caproate and iso-heptanoate as well as that longer chain alcohol formation can be stimulated.

Photoelectrochemical Oxidation in Ambient Conditions Using Earth-Abundant Hematite Anode: A Green Route for the Synthesis of Biobased Polymer Building Blocks

This study demonstrates the use of a photoelectrochemical device comprising earth-abundant hematite photoanode for the oxidation of 5-hydroxymethylfurfural (5-HMF), a versatile bio-based platform chemical, under ambient conditions in the presence of an electron mediator. The results obtained in this study showed that the hematite photoanode, upon doping with fluorine, can oxidize water even at lower pH (4.5 and 9.0). For 5-HMF oxidation, three different pH conditions were investigated, and complete oxidation to 2,5-furandicarboxylic acid (FDCA) via 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) was achieved at pH above 12. At lower pH, the oxidation followed another route via 2,5-diformylfuran (DFF), yielding 5-formyl-2-furancarboxylic acid (FFCA) as the main product. Using the oxidized intermediates as substrates showed DFF to be most efficiently oxidized to FDCA. We also show that, at pH 4.5, the addition of the laccase enzyme promoted the oxidation of 5-HMF to FFCA.

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.

Development of morphology engineering for production of bio-based chemicals

Synthetic biology and metabolic engineering have been widely used to construct microbial cell factories for efficient production of bio-based chemicals, which mainly focus on the modification and regulation of metabolic pathways. The characteristics of microorganisms themselves, e.g. morphology, have rarely been taken into consideration in the biotechnological production processes. Morphology engineering aims to control cell shapes and cell division patterns by manipulating the genes related to cell morphology, providing a new strategy for developing efficient microbial cell factories. This review summarized the proteins related to cell morphology, followed by illustrating a few examples of using morphology engineering strategies for improving production of bio-based chemicals. This includes increasing intracellular product accumulation by regulating cell size, enhancing extracellular secretion of target products by improving cell permeability, reducing production cost by achieving high cell density, and improving product performance by controlling the degree of product hydrolysis. Finally, challenges and perspectives for the development of morphology engineering were discussed.

Ethylene glycol co-solvent enhances alkyl levulinate production from concentrated feeds of sugars in monohydric alcohols

Conversion of carbohydrates at concentrated feeds represents highly desirable for the industrial deployment of biobased fuels and chemicals but challenging. One key bottleneck is that the excessive formation of polymeric humins greatly diminishes the utilization rate of feedstocks and the destination product yield. We report that the use of ethylene glycol as co-solvent for acid-catalyzed conversion of concentrated sugars enhances desirable alkyl levulinate (AL) production compared to reactions carried out in single monohydric alcohols (e.g., methanol, ethanol). Ethylene glycol served not only as a solubilizer of sugars in the reaction medium to lessen their tendency to polymerize by protecting reactive hydroxyl groups in sugars with alcohols, but also as a supporter to restrain the condensation of furan intermediates. With 10 vol% ethylene glycol as the co-solvent of ethanol, an improved yield of ethyl levulinate (EL) from 45% to 56% was accomplished from concentrated feeds of glucose (200 g/L). In particular, high space time yield and EL concentration respectively up to 30 kg/m3·h and 90 g/L were obtained in a batch reactor. The solvents and catalyst could be isolated from the products, and showed good reusability. This contribution opens a reliable avenue for converting highly concentrated feeds of biomass-related sugars to oxygenated liquid fuels and versatile chemicals.

Efficient conversion of carbohydrates and biomass into furan compounds by chitin/Ag co-modified H3PW12O40 catalysts

The development of heterogeneously functional catalysts is of great significance in selective catalysis for biomass valorization. Herein, we report for the first time the applicability of chitin/Ag co-modified H3PW12O40 composites (Chx-AgPW) as catalysts for producing valuable furans from carbohydrates and biomass. The as-prepared Ch15-AgPW catalyst exhibited the best catalytic performance, due to the dual Brǿnsted-Lewis acidity and appropriate chitin content. When the amount of Ch15-AgPW catalyst was 0.25 mmol, an excellent 5-hydroxymethylfurfural (HMF) yield of 78.3% could be achieved at 150 °C for 3 h with nearly 100% glucose conversion in the H2O/MIBK (VH2O:MIBK = 4:6) solvent system. Furthermore, high-yield HMF could also be obtained from other carbohydrates such as fructose (85.3%), sucrose (72.3%), cellobiose (65.6%), starch (52.7%) and inulin (43.5%). Additionally, corn stover, rice straw and sugarcane bagasse under typical reaction conditions simultaneously produced furfural and HMF in yields of 64.6%–72.2% and 18.5%–25.6%, respectively. Combined with the characterization, mechanism study demonstrated that the surface functional groups in chitin were conductive to rapid absorption of the substrates; the Brǿnsted acid sites from heteropoly anion (H2[PW12O40]-) promoted the initial depolymerization of biomass and the final dehydration to furans; the introduction of Ag+ favored the isomerization of intermediates. After reaction finished, the Ch15-AgPW catalyst could be easily recovered by filtration and effectively reused at least eight cycles without substantial loss in catalytic activity. This work provides a novel strategy to synthesize stable heterogeneous catalysts with tunable acidity for producing bio-based fuels and chemicals from renewable resources.