Total Cellulose Conversion Research Articles

Low-Cost Ni-W Catalysts Supported on Glucose/Carbon Nanotube Hybrid Carbons for Sustainable Ethylene Glycol Synthesis.

The production of ethylene glycol (EG) from cellulose has garnered significant attention in recent years as an attractive alternative to fossil fuels due to the potential of cellulose as a renewable and sustainable feedstock. In this work, to the best of our knowledge, a series of low-cost Ni-W bimetallic catalysts supported on glucose/carbon nanotube hybrid carbons were synthesised for the first time and employed to transform cellulose into EG. Two different strategies were combined for the preparation of the carbons: the activation and addition of carbon nanotubes (CNTs) to obtain a hybrid material (AG-CNT). The catalytic conversion process proceeded through cellulose hydrolysis to glucose, followed by glucose retro-aldol condensation to glycolaldehyde and its subsequent hydrogenation to EG. Through the optimisation of the catalyst's properties, particularly the metals' content, a good synergistic effect of C-C bond cleavage and hydrogenation capabilities was assured, resulting in the highly selective production of EG. The balance between Ni and W active sites was confirmed to be a crucial parameter. Thus, total cellulose conversion (100%) was achieved with EG yields of 60-62%, which are amongst the best yields ever reported for the catalytic conversion of cellulose into EG via carbon-supported catalysts.

Catalytic conversion of cellulose to sorbitol over Ru supported on biomass-derived carbon-based materials

The direct conversion of cellulose into sorbitol, one of the platform molecules of highest potential, by using a low-cost catalyst that yields higher productivity is a current challenge. Ruthenium/glucose-derived carbons with tailored textural and chemical properties were prepared by combining two different strategies: activation and addition of carbon nanotubes (CNT) to obtain a hybrid carbon material (AG-CNT). The appropriate combination of both strategies results in materials with high microporosity and low acidity that favors the dispersion of the metal and, hence, improves the yield of sorbitol. The total conversion of cellulose (100%) and the highest yield of sorbitol (64.1%) were achieved over a hybrid catalyst with high specific surface area of 1200 m2 g−1 (Ru/AG-CNT1200) within 3 h of reaction, at 205 °C and 50 bar of H2. In addition, the catalyst was successfully recycled in four runs. These results are better than those reported over Ru/CNT (the highest yield reported to date over carbon supports) under the same reaction conditions, indicating that CNT can be successfully replaced by a low-cost support derived from biomass. As a result, not only the highest yield of sorbitol is obtained, but cellulose, one of the most important fractions of biomass, is valorized through two pathways: the cellulose itself as the main raw material of the reaction and its monomer, glucose, for the preparation of the catalyst.

Selective fractionation and enzymatic hydrolysis of Eucalyptus nitens wood

Eucalyptus nitens, a fast growing species with remarkable resistance to plagues and ability to grow in frosting zones, was employed as a raw material for chemical fractionation following a selected biorefinery scheme. E. nitens wood samples were assayed for composition, and subjected to consecutive stages of hydrothermal processing (to solubilize the hemicellulosic fraction), organosolv delignification (for obtaining sulfur-free, soluble lignin fragments and a cellulose-enriched solid phase) and swelling. The various fractions from the processing stages were assayed for yield and composition. Operating under selected conditions, the hydrothermal stage allowed the recovery of 80.7% of the initial xylan as soluble hydrolysis or hydrolysis–dehydration products. The solid leaving the swelling stage contained 88.3% cellulose, and accumulated 90.2% of the cellulose present in the native wood. Near total cellulose conversion into glucose was achieved when the swelled solid was employed as a substrate in enzymatic hydrolysis experiments performed under selected operational conditions.

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.

Multifunctional Cellulolytic Enzymes Outperform Processive Fungal Cellulases for Coproduction of Nanocellulose and Biofuels.

Producing fuels, chemicals, and materials from renewable resources to meet societal demands remains an important step in the transition to a sustainable, clean energy economy. The use of cellulolytic enzymes for the production of nanocellulose enables the coproduction of sugars for biofuels production in a format that is largely compatible with the process design employed by modern lignocellulosic (second generation) biorefineries. However, yields of enzymatically produced nanocellulose are typically much lower than those achieved by mineral acid production methods. In this study, we compare the capacity for coproduction of nanocellulose and fermentable sugars using two vastly different cellulase systems: the classical "free enzyme" system of the saprophytic fungus, Trichoderma reesei (T. reesei) and the complexed, multifunctional enzymes produced by the hot springs resident, Caldicellulosiruptor bescii (C. bescii). We demonstrate by comparative digestions that the C. bescii system outperforms the fungal enzyme system in terms of total cellulose conversion, sugar production, and nanocellulose production. In addition, we show by multimodal imaging and dynamic light scattering that the nanocellulose produced by the C. bescii cellulase system is substantially more uniform than that produced by the T. reesei system. These disparities in the yields and characteristics of the nanocellulose produced by these disparate systems can be attributed to the dramatic differences in the mechanisms of action of the dominant enzymes in each system.

Enhancement of high-solids enzymatic hydrolysis and fermentation of furfural residues by addition of Gleditsia saponin

Gleditsia saponin (GS) assisted high-solids enzymatic hydrolysis and fermentation for alkaline peroxide (AP)-pretreated furfural residues (FRs) was investigated. The addition of GS increased the glucose yield of untreated FRs to 74.8% in high-solids-loading enzymatic hydrolysis. AP pretreatment before enzymatic hydrolysis resulted in a high sugar concentration (115.4g/L) and a glucose yield of 57.5% by the end of hydrolysis at 20% solids loading. It was suggested that GS could improve significantly the glucose yields of FRs with high lignin content. After simultaneous saccharification and fermentation (SSF), the total cellulose conversion of FRs with 14.3% lignin content reached 82.2% and the highest ethanol concentration (69.1g/L) was achieved, which was 121% higher than that of untreated FRs (30.1g/L). The results indicated that the main reason behind the decreased glucose yield at high-solids loadings was product inhibition. Moreover, the lignin content plays an important role in the enhancement of GS-assisted high-solids enzymatic hydrolysis of AP-treated FRs.

Thermochemical Decomposition of Microcrystalline Cellulose Using Sub- and Supercritical Tetralin and Decalin with Fe3O4

Direct thermochemical liquefaction of microcrystalline cellulose was investigated in sub- and supercritical solvents in a batch reactor. The liquefaction efficiency of hydrogen donor solvents (tetralin and decalin) was compared to that of m-xylene. Tetralin was the most effective solvent with respect to the conversion at every tested condition starting from 350 °C. At 400 °C, the total conversion of cellulose in tetralin approached 96.8–98.3% with a negligible amount of char formation. The pressure of hydrogen had little effect on conversion for any solvent, while the addition of iron oxide catalyst (Fe3O4) led to improved conversion and liquid yield from the reaction compared to reactions without the catalyst at temperatures higher than 350 °C. Hydrogen pressure in the presence of iron oxide catalyst significantly suppressed the char formation and improved liquid production. The thermal-treated chars collected after liquefaction reactions showed a fair adsorption capacity of CO2 compared to activated carbon.

Efficient Conversion of Cellulose to Levulinic Acid by Hydrothermal Treatment Using Zirconium Dioxide as a Recyclable Solid Acid Catalyst

Conversion of cellulose into platform chemicals is essential for sustainable development of the chemical industry. With this aim, single step hydrothermal conversion of cellulose to industrially important levulinic acid using zirconium dioxide as a catalyst has been investigated. A remarkably high yield (53.9 mol %) of levulinic acid with excellent accountability and total conversion of cellulose has been achieved at 180 °C reaction temperature and reaction time of 3 h with 2 wt % of catalyst and 2 g of cellulose. The major products identified were levulinic acid (LA), formic acid (FA), 5-hydroxymethylfurfural (5-HMF), furfural, and humins. Formation of humins during cellulose hydrolysis and dehydration was observed and is also confirmed by NMR and FTIR analysis. The effect of various reaction parameters such as temperature, time, substrate concentration, and catalyst loading on conversion and selectivity has been studied. The catalyst has been regenerated and recycled several times without any loss of activity and selectivity.

Effects of pretreatment on morphology, chemical composition and enzymatic digestibility of eucalyptus bark: a potentially valuable source of fermentable sugars for biofuel production – part 1

BackgroundIn recent years, the growing demand for biofuels has encouraged the search for different sources of underutilized lignocellulosic feedstocks that are available in sufficient abundance to be used for sustainable biofuel production. Much attention has been focused on biomass from grass. However, large amounts of timber residues such as eucalyptus bark are available and represent a potential source for conversion to bioethanol. In the present paper, we investigate the effects of a delignification process with increasing sodium hydroxide concentrations, preceded or not by diluted acid, on the bark of two eucalyptus clones: Eucalyptus grandis (EG) and the hybrid, E. grandis x urophylla (HGU). The enzymatic digestibility and total cellulose conversion were measured, along with the effect on the composition of the solid and the liquor fractions. Barks were also assessed using Fourier-transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR), X-Ray diffraction, and scanning electron microscopy (SEM).ResultsCompositional analysis revealed an increase in the cellulose content, reaching around 81% and 76% of glucose for HGU and EG, respectively, using a two-step treatment with HCl 1%, followed by 4% NaOH. Lignin removal was 84% (HGU) and 79% (EG), while the hemicellulose removal was 95% and 97% for HGU and EG, respectively. However, when we applied a one-step treatment, with 4% NaOH, higher hydrolysis efficiencies were found after 48 h for both clones, reaching almost 100% for HGU and 80% for EG, in spite of the lower lignin and hemicellulose removal. Total cellulose conversion increased from 5% and 7% to around 65% for HGU and 59% for EG. NMR and FTIR provided important insight into the lignin and hemicellulose removal and SEM studies shed light on the cell-wall unstructuring after pretreatment and lignin migration and precipitation on the fibers surface, which explain the different hydrolysis rates found for the clones.ConclusionOur results show that the single step alkaline pretreatment improves the enzymatic digestibility of Eucalyptus bark. Furthermore, the chemical and physical methods combined in this study provide a better comprehension of the pretreatment effects on cell-wall and the factors that influence enzymatic digestibility of this forest residue.

High glucose selectivity in pressurized water hydrolysis of cellulose using ultra-fast reactors

A new reactor was developed for the selective hydrolysis of cellulose. In this study, the glucose selectivity obtained from cellulose was improved by using ultra-fast reactions in which a selective medium was combined with an effective residence time control. A selective production of glucose, fructose and cellobiose (50%) or total mono-oligo saccharides (>96%) was obtained from the cellulose in a reaction time of 0.03s. Total cellulose conversion was achieved with a 5-hydroxymethylfural concentration lower than 5ppm in a novel micro-reactor. Reducing the residence time from minutes to milliseconds opens the possibility of moving from the conventional m3 to cm3 reactor volumes.

Chemical and morphological characterization of sugarcane bagasse submitted to a delignification process for enhanced enzymatic digestibility

BackgroundIn recent years, biorefining of lignocellulosic biomass to produce multi-products such as ethanol and other biomaterials has become a dynamic research area. Pretreatment technologies that fractionate sugarcane bagasse are essential for the successful use of this feedstock in ethanol production. In this paper, we investigate modifications in the morphology and chemical composition of sugarcane bagasse submitted to a two-step treatment, using diluted acid followed by a delignification process with increasing sodium hydroxide concentrations. Detailed chemical and morphological characterization of the samples after each pretreatment condition, studied by high performance liquid chromatography, solid-state nuclear magnetic resonance, diffuse reflectance Fourier transformed infrared spectroscopy and scanning electron microscopy, is reported, together with sample crystallinity and enzymatic digestibility.ResultsChemical composition analysis performed on samples obtained after different pretreatment conditions showed that up to 96% and 85% of hemicellulose and lignin fractions, respectively, were removed by this two-step method when sodium hydroxide concentrations of 1% (m/v) or higher were used. The efficient lignin removal resulted in an enhanced hydrolysis yield reaching values around 100%. Considering the cellulose loss due to the pretreatment (maximum of 30%, depending on the process), the total cellulose conversion increases significantly from 22.0% (value for the untreated bagasse) to 72.4%. The delignification process, with consequent increase in the cellulose to lignin ratio, is also clearly observed by nuclear magnetic resonance and diffuse reflectance Fourier transformed infrared spectroscopy experiments. We also demonstrated that the morphological changes contributing to this remarkable improvement occur as a consequence of lignin removal from the sample. Bagasse unstructuring is favored by the loss of cohesion between neighboring cell walls, as well as by changes in the inner cell wall structure, such as damaging, hole formation and loss of mechanical resistance, facilitating liquid and enzyme access to crystalline cellulose.ConclusionsThe results presented herewith show the efficiency of the proposed method for improving the enzymatic digestibility of sugarcane bagasse and provide understanding of the pretreatment action mechanism. Combining the different techniques applied in this work warranted thorough information about the undergoing morphological and chemical changes and was an efficient approach to understand the morphological effects resulting from sample delignification and its influence on the enhanced hydrolysis results.

Dilute acid pretreatment of rapeseed straw for fermentable sugar generation

The influence of the main pretreatment variables on fermentable sugar generation from rapeseed straw is studied using an experimental design approach. Low and high levels for pretreatment temperature (140-200 °C), process time (0-20 min) and concentration of sulfuric acid (0.5-2% w/v) were selected according to previous results. Glucose and xylose composition, as well as sugar degradation, were monitored and adjusted to a quadratic model. Non-sugar components of the hydrolysates were also determined. Enzymatic hydrolysis yields were used for assessing pretreatment performance. Optimization based on the mathematical model show that total conversion of cellulose from pretreated solids can be achieved at pretreatment conditions of 200 °C for 27 min and 0.40% free acid concentration. If optimization criteria were based on maximization of hemicellulosic sugars recovery in the hydrolysate along with cellulose preservation in the pretreated solids, milder pretreatment conditions of 144 °C, 6 min and 2% free acid concentration should be used.

Pretreatment of spruce and oak by N-methylmorpholine-N-oxide (NMMO) for efficient conversion of their cellulose to ethanol

Pretreatment of softwood spruce and hardwood oak with an industrial cellulose solvent, N-methylmorpholine-N-oxide (NMMO), was investigated prior to enzymatic hydrolysis and fermentation to ethanol. The pretreatments were carried out at 90, 110 and 130°C for 1–3h with 85% NMMO solution, followed by non-isothermal simultaneous saccharification and fermentation (NSSF). This NSSF included hydrolysis with cellulase and β-glucosidase for 24h at 45°C, followed by continuous saccharification and fermentation with Saccharomyces cerevisiae at 37°C for 3days. The NSSF of untreated oak and spruce resulted in 18.6% and 6.8% ethanol compared to the maximum theoretical yield. However, the pretreatment of oak and spruce at 130°C resulted in almost total conversion of cellulose to ethanol and improved ethanol yield up to 85.4% and 89%, respectively. These numbers are comparable with ethanol from pure glucose with the same strain, which yielded between 84% and 90% of the theoretical ethanol yield.

Synergism between corn stover protein and cellulase

A cellulase synergistic protein named Zea h was purified from fresh postharvest corn stover through sequential treatments. The purified Zea h was homogeneous by PAGE and SDS-PAGE examination, indicating its purity and molecular weight ( M w) of approximately 55.78 kDa. Comparing with cellulase (0.042 FPU) was applied alone in hydrolysis of filter paper, when Zea h (6 μg) and cellulase were applied together, the hydrolysis rate was increased by a factor of 2 within 1 h, and the total cellulose conversion was increased by a factor of 3 during the 24 h's hydrolysis. Thermal stability analysis revealed that 50.2% of the synergetic activity was recovered when Zea h was incubated in water for 30 min at 100 °C, yet the protein was deactivated in high pressure steam (160 °C) for 5 min. Studies on the mechanisms of the synergism between Zea h and cellulase showed that, Zea h could increase the adsorption of cellulase onto substrate, and decrease the hydrogen-bond intensity and CrI of substrate. Yet Zea h has no cellulase activity, and has little effect on cellulase stability under the conditions of hydrolysis. It could be concluded that Zea h may modify the structure of filter paper through weakening or rupturing hydrogen bonds, and more it more accessible to cellulase. The unique property of Zea h provides an opportunity for decreasing enzyme loading while retaining the same degree of hydrolysis.