Efficient Conversion Of Cellulose Research Articles

Efficient conversion of cellulose into 5-hydroxymethylfurfural by inexpensive SO42-/HfO2 catalyst in a green water-tetrahydrofuran monophasic system

Efficient and green catalysis of cellulose to 5-hydroxymethylfurfural (HMF) is currently a challenge that needs a breakthrough. In this study, a series of inexpensive (x)SO42-/HfO2 heterogeneous catalysts were prepared and exhibited superior catalytic performance for conversion of cellulose into HMF in the green water-tetrahydrofuran monophasic system (H2O-THF). An optimal HMF yield of 54% was acquired through detailed evaluation of reaction conditions. Various analyzes including ICP-OES, XRD, SEM, TEM, FTIR, N2 adsorption–desorption isotherm, XPS, TG, NH3-TPD and Py-FTIR were applied to inspected the physicochemical characteristics of the (x)SO42-/HfO2 catalysts. Meanwhile, the recyclability of the catalyst and the by-products generated during the reaction process were studied and captured, respectively. The results presented herein show that the catalytic system of (30%)SO42-/HfO2 catalyst combined with H2O-THF monophasic solvent is advanced, and it can be both green and efficient without the presence of other additives and promoters, and has great potential in the future.

Deciphering the efficient cellulose degradation by the thermophilic fungus Myceliophthora thermophila focused on the synergistic action of glycoside hydrolases and lytic polysaccharide monooxygenases

The thermophilic fungus Myceliophthora thermophila as an efficient decomposer secretes various glycoside hydrolases and auxiliary oxidation enzymes to deconstruct cellulose. However, the core enzymes critical for efficient cellulose degradation and their interactions with other cellulolytic enzymes remain unclear. Herein, the transcriptomic analysis of M. thermophila grown on Avicel exhibited that cellulases from GH5_5, GH6 and GH7, and lytic polysaccharide monooxygenases (LPMOs) from AA9 contributed to cellulose degradation. Moreover, the peptide mass fingerprinting analysis of major extracellular proteins and corresponding gene-knockout strains studies revealed that MtCel7A and MtCel5A were the core cellulolytic enzymes. Furthermore, synergistic experiments found that hydrolytic efficiencies of MtCel7A and MtCel5A were both improved by mixture C1/C4 oxidizing MtLPMO9H, but inhibited by C1 oxidizing MtLPMO9E and C4 oxidizing MtLPMO9J respectively. These results demonstrated the potential application of C1/C4 oxidizing LPMOs for future designing novel cellulolytic enzyme cocktails on the efficient conversion of cellulose into biofuels and biochemicals.

Valorization of Miscanthus × giganteus by γ-Valerolactone/H2O/FeCl3 system toward efficient conversion of cellulose and hemicelluloses

γ-Valerolactone (GVL), a biomass-derived green chemical, offers an environmentally responsible solvent for conversion of lignocellulose to high value-added chemicals. Herein, we report a two-step process for directly producing cellulosic residual, furfural and lignin from Miscanthus × giganteus (M. × giganteus) bypassing the isolation of xylose, which exhibits promising advantage in energy reduction. The optimized pretreatment (100 mM FeCl3 at 160 °C for 60 min) induced significant xylan removal (98.4%), resulting in rugged fibre surface, thus leading to the peak cellulose conversion of 99.3%. Furfural yield in the second step reached to 76.6% after 100 mM FeCl3 catalyzed GVL/H2O treatment at 180 °C for 10 min without addition of any chemical. The extracted lignin showed representative structure (such as β-O-4′, β-β′ linkages) and medium molecular weight (4275.5 g/mol). 79.6% of furfural can be recovered by distillation. This study proposes a systematic and energy efficient approach for maximizing biomass utilization.

Derived high reducing sugar and lignin colloid particles from corn stover

Lignocellulosic biomass is considered as the largest potential candidate to develop alternative energy, such as biofuel, biomaterial. However, the efficient conversion of cellulose and practical utilization of lignin are great challenges for sustainable biorefinery. In this study, high reducing sugar yield and different size of lignin colloid particles (LCPs) were obtained via tetrahydrofuran–water (THF–H2O) pretreatment of corn stover (CS). THF–H2O as a co-solvent, could efficiently dissolve lignin and retain cellulose. After the pretreatment, 640.87 mg/g of reducing sugar was produced, that was 6.66-fold higher than that of the untreated CS. Meanwhile, the pretreatment liquor could form spherical LCPs with different sizes ranged from 202 to 732 nm through self-assembly. We studied the optimal pretreatment condition to simultaneously realize the high reducing sugar yield (588.4 mg/g) and excellent LCPs preparation with average size of 243 nm was under TH22 (THF–H2O pretreatment at 120 °C for 2 h). To further explore the formation of LCPs with different sizes. We studied the lignin structure changes of various conditions, concluded the size of LCPs was related to the lignin concentration and syringyl/guaiacyl (S/G) ratio. As the increase of the lignin concentration and S/G, the sizes of LCPs were increased. G-type lignin was easier to dissolve in the mild pretreatment supernatant, contributing to form smaller LCPs with a good dispersibility. In the severe condition, both of S and G-type lignin were dissolved due to the lignin depolymerization, formed the larger sphere particles. This work provides a novel perspective for the technical design of lignocellulosic biomass conversion.

Totally green cellulose conversion into bio-oil and cellulose citrate using molten citric acid in an open system: synthesis, characterization and computational investigation of reaction mechanisms.

The simultaneous transformation of crystalline or amorphous cellulose into a furan-based bio-oil and cellulose citrate was realized avoiding the use of strong inorganic acids, drastic conditions, enzymatic treatments or microorganism fermentation. This innovative method is very eco-friendly and involves the use of molten citric acid under solvent free conditions at atmospheric pressure. An accurate discussion on chemical composition of the bio-oil enriched in bioprivileged molecules as well as structural and morphological characterization of cellulose citrate was reported. Moreover, mechanistic hypotheses were formulated on the basis of experimental findings and detailed DFT quantum-mechanical simulations were carried out to confirm, step by step, the proposed reaction paths.

Bioconversion of cellulose and simultaneous production of thermoactive exo- and endoglucanases by Fusarium oxysporum

Saccharification of cellulose is a promising method for production of biofuels. However, low bioconversion efficiency of cellulose to soluble sugars is a major challenge. In this study, a cellulolytic strain of Fusarium oxysporum was cultivated on pure cellulosic substrates (avicel, α-cellulose, carboxymethylcellulose and methylcellulose) and conversion efficiency into glucose was investigated. Production of exo- and endoglucanases during the bioconversion process was evaluated. Influence of pH on saccharification of cellulose and enzyme production by F. oxysporum were determined. Highest yield of glucose (1.76 μmol/ml) was obtained from F. oxysporum on methyl cellulose at 192 h under basal conditions. Liberated glucose under optimized condition of pH 6.0 at 96 h of fermentation was 2.12 μmol/ml with maximum production of exo- and endoglucanases (23.70 and 34.72 U/mg protein, respectively). The crude exo- and endoglucanases had optimum activities at pH 8.0, 70 °C and pH 7.0, 50 °C, respectively. The enzymes were stable over pH of 4.0–7.0 with relative residual activity above 60% after 1 h incubation. Exoglucanase activity was enhanced by Ca2+ and Cu2+ at 5 mM and Mg2+ at 10 mM. Endoglucanase activity was greatly enhanced in the presence of Mn2+, Ca2+, Mg2+, Cu2+ and Fe3+ at 5 and 10 mM. Activities of both enzymes were inhibited in the presence of Hg2+ at 5 and 10 mM. Results show that F. oxysporum possessed good cellulolytic enzyme system for efficient conversion of cellulose. Exhibited thermotolerance of exoglucanase with the striking tolerance of endoglucanase to metal ions demonstrate potentials of enzymes for biofuel industry.

Efficient conversion of cellulose into 5-hydroxymethylfurfural over niobia/carbon composites

A series of novel niobia/carbon composites were synthesized by hydrothermal method following by carbonization with niobium tartrate and glucose as precursors, and used in the conversion of glucose and cellulose to 5-hydroxymethylfurfural (HMF). These catalysts were characterized by XRD, SEM, TEM, N2 adsorption/desorption, NH3-TPD and Py-FTIR techniques and the results showed that the Nb/C catalysts were agglomerated particles, with weak to medium acid strength and suitable Brønsted/Lewis acid sites. When used in the hydrolysis and dehydration of cellulose, as high as 53.3% yield of HMF was achieved over Nb/C-50 catalyst at 170°C for 8h, accompanied with 24.5% glucose, with the total conversion of cellulose, indicating the high carbon yield and excellent activity. Furthermore, this catalyst showed excellent recyclability and its catalytic activity still maintained after 8 cycles.

Kinetic insight into the effect of the catalytic functions on selective conversion of cellulose to polyols on carbon-supported WO3 and Ru catalysts

Efficient conversion of cellulose, the most abundant biomass on Earth, to chemicals in high yields remains a formidable challenge. Here, we report the marked change in the distribution of polyol products in the cellulose reaction on Ru/C and WO3/C, strongly depending on the competitive reactions of the glucose intermediate. WO3 crystallites not only promote, as a solid acid, the efficient hydrolysis of cellulose to glucose, but also catalyze the selective cleavage of the C–C bonds in glucose and other C6 sugar intermediates, leading to the formation of ethylene glycol and propylene glycol, in competition with the sugar hydrogenation to the corresponding C6 polyols (e.g. sorbitol) on Ru/C. The basic C support, behaving similar to other solid bases (i.e. MgO), catalyzes the isomerization of glucose into fructose, leading to the favored formation of propylene glycol instead of ethylene glycol. Such strong dependence of the product distribution on the catalytic functions is clarified by the kinetic analysis of the three competitive reactions of glucose, including its hydrogenation, isomerization and C–C bond cleavage. Importantly, such kinetic analysis can predict the maximum selectivity ratio of propylene glycol to ethylene glycol, which is 2.5, for example, at 478K under the reaction conditions in this work, corresponding to a maximum yield of propylene glycol of ∼71%. These understandings shed new insights into the selective conversion of cellulose, which provides guidance for the rational design of catalyst functions and tuning of reaction parameters towards the controllable synthesis of specific products from cellulose.

Engineering Aspergillus oryzae A-4 through the chromosomal insertion of foreign cellulase expression cassette to improve conversion of cellulosic biomass into lipids.

A genetic modification scheme was designed for Aspergillus oryzae A-4, a natural cellulosic lipids producer, to enhance its lipid production from biomass by putting the spotlight on improving cellulase secretion. Four cellulase genes were separately expressed in A-4 under the control of hlyA promoter, with the help of the successful development of a chromosomal genetic manipulation system. Comparison of cellulase activities of PCR-positive transformants showed that these transformants integrated with celA gene and with celC gene had significantly (p<0.05) higher average FPAase activities than those strains integrated with celB gene and with celD gene. Through the assessment of cellulosic lipids accumulating abilities, celA transformant A2-2 and celC transformant D1-B1 were isolated as promising candidates, which could yield 101%–133% and 35.22%–59.57% higher amount of lipids than the reference strain A-4 (WT) under submerged (SmF) conditions and solid-state (SSF) conditions, respectively. Variability in metabolism associated to the introduction of cellulase gene in A2-2 and D1-B1 was subsequently investigated. It was noted that cellulase expression repressed biomass formation but enhanced lipid accumulation; whereas the inhibitory effect on cell growth would be shielded during cellulosic lipids production owing to the essential role of cellulase in substrate utilization. Different metabolic profiles also existed between A2-2 and D1-B1, which could be attributed to not only different transgene but also biological impacts of different integration. Overall, both simultaneous saccharification and lipid accumulation were enhanced in A2-2 and D1-B1, resulting in efficient conversion of cellulose into lipids. A regulation of cellulase secretion in natural cellulosic lipids producers could be a possible strategy to enhance its lipid production from lignocellulosic biomass.

Microwave-assisted catalytic conversion of cellulose into 5-hydroxymethylfurfural in ionic liquids

Microwave-assisted direct conversion of cellulose into HMF in ionic liquids catalyzed by ZrCl4 has been investigated in search of an efficient and environment-friendly process. Firstly, some representative metal chlorides were used to catalyze the conversion of glucose into HMF, and it was demonstrated that ZrCl4 was superior to other catalysts. Then direct conversion of cellulose into HMF was catalyzed by ZrCl4 under microwave irradiation (MI). Under optimal conditions, a high HMF yield up to 51.4% was obtained from cellulose in 3.5min under MI at 400W. Controllable experiments indicated that both ionic liquids, MI and ZrCl4 showed synergetic effects on the efficient conversion of cellulose into HMF. This work provides a meaningful method for the conversion of carbohydrates into fine chemicals.

Efficient conversion of cellulose into furans catalyzed by metal ions in ionic liquids

5-Hydroxymethylfurfural (HMF) and furfural, two of the most important intermediates derived from biomass, were directly produced from the hydrolysis of microcrystalline cellulose (MCC) with metal ions in ionic liquids as catalyst under mild conditions. Various ionic liquids were tested to obtain the most efficient catalyst, 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1) showed the highest catalytic activity than others, and SO3H-functionalized ionic liquids exhibited better activity than non-functionalized ILs. The co-catalysis effect of Cr3+, Mn2+, Fe3+, Fe2+, Co2+ were much better than other metal ions, with a catalytic amount of these metal ions, MCC conversion increased by 10–19%, and the selectivities of products were also improved obviously. The promoting catalysis of metal nitrates were not as expected as that of chlorides and sulfates, we suggested that nitrate anion may have a negative effect on the hydrolysis of MCC. Reaction conditions were optimized and reaction mechanism was proposed to explain the improved catalysis of metal chlorides and sulfates. Also, the recycling of catalyst was put forward in our system for MCC hydrolysis and these catalysts maintained good performances even after five runs. This simple and effective catalytic system may be valuable to facilitate energy-efficient conversion of cellulose into biofuels and platform chemicals.

Cellulose Conversion under Heterogeneous Catalysis

In view of current problems such as global warming, high oil prices, food crisis, stricter environmental laws, and other geopolitical scenarios surrounding the use of fossil feedstocks and edible resources, the efficient conversion of cellulose, a non-food biomass, into energy, fuels, and chemicals has received much attention. The application of heterogeneous catalysis could allow researchers to develop environmentally benign processes that lead to selective formation of value-added products from cellulose under relatively mild conditions. This Minireview gives insight into the importance of biomass utilization, the current status of cellulose conversion, and further transformation of the primary products obtained.