Kinetics of xylose dehydration into furfural in acetic acid

Model-Assisted Optimization of Xylose, Arabinose, Glucose, Mannose, Galactose and Real Hemicellulose Streams Dehydration To (Hydroxymethyl)Furfural and Levulinic Acid

Conversion of hemicellulose streams and the constituent monosaccharides, xylose, arabinose, glucose, mannose, and galactose, was conducted to produce value-added chemicals, including furfural, hydroxymethylfurfural (HMF), levulinic acid and anhydrosugars. The study aimed at developing a kinetic model relevant for direct post-Organosolv hemicellulose conversion. Monosaccharides served as a tool to in detail describe the kinetic behavior and segregate contribution of hydrothermal decomposition and acid catalyzed dehydration at the temperature range of 120-190 °C. Catalyst free aqueous media demonstrated enhanced formation of furanics, while elevated temperatures led to significant saccharide isomerization. The introduction of sulfuric and formic acids maximized furfural yield and significantly reduced HMF concentration by facilitating its rehydration into levulinic acid (46 mol%). Formic acid additionally substantially enhanced formation of anhydrosaccharides. An excellent correlation between modeled and experimental data enabled process optimization to maximize furanic yield in two distinct hemicellulose streams. Sulfuric acid-containing hemicellulose stream achieved the highest furfural yield after 30 minutes at 238 °C, primarily due to the high Ea for pentose dehydration (150-160 kJ mol-1). Contrarily, formic acid-containing hemicellulose stream enabled maximal furfural yield at more moderate temperature and extended reaction time due to its lower Ea for the same reaction step (115-125 kJ mol-1).

Delignification of poplar for xylo-oligosaccharides production using lactic acid catalysis

Recently, xylo-oligosaccharides (XOS) production from lignocelluloses by organic acid catalysis has been widely reported. However, the effect of delignification of lignocelluloses on XOS production by organic acid catalysis was unclear, and lactic acid (LA) catalysis in XOS production from lignocelluloses has not been reported. In this work, the effect of delignification on XOS production from poplar by LA catalysis was investigated. Results demonstrated that hydrogen peroxide-acetic acid (HPAA) pretreatment removed 83.2% of lignin and retained 95.4% of xylan. After 2% LA catalysis (170 °C, 30 min), a high XOS yield of 42.7% was obtained from HPAA₁-LA-pretreated poplar. Lignin removal from poplar was positively correlated with XOS yield. Glucose yield of HPAA₁-LA-pretreated poplar by cellulase was 88.9%. Compared with LA-catalyzed poplar, the XOS and glucose production from HPAA₁-LA-pretreated poplar by cellulase increased by 1.4-fold and 6.8-fold, respectively. This work presents a novel strategy for efficient producing XOS and monosaccharides from poplar.

Catalytic Conversion of Xylose to Furfural by p-Toluenesulfonic Acid (pTSA) and Chlorides: Process Optimization and Kinetic Modeling

Furfural is one of the most promising precursor chemicals with an extended range of downstream derivatives. In this work, conversion of xylose to produce furfural was performed by employing p-toluenesulfonic acid (pTSA) as a catalyst in DMSO medium at moderate temperature and atmospheric pressure. The production process was optimized based on kinetic modeling of xylose conversion to furfural alongwith simultaneous formation of humin from xylose and furfural. The synergetic effects of organic acids and Lewis acids were investigated. Results showed that the catalyst pTSA-CrCl₃·6H₂O was a promising combined catalyst due to the high furfural yield (53.10%) at a moderate temperature of 120 °C. Observed kinetic modeling illustrated that the condensation of furfural in the DMSO solvent medium actually could be neglected. The established model was found to be satisfactory and could be well applied for process simulation and optimization with adequate accuracy. The estimated values of activation energies for xylose dehydration, condensation of xylose, and furfural to humin were 81.80, 66.50, and 93.02 kJ/mol, respectively.

Xylan and xylose decomposition during hot water pre-extraction: A pH-regulated hydrolysis

One of the key issues in the development of biofuels using lignocellulosic feedstocks is to increase the yield of fermented sugar, and simultaneously decrease the generation of fermentation inhibitors. Therefore, it is essential to understand the degradation mechanism of xylan during hot-water pretreatment. We analyzed the hydrothermal degradation products of xylan and xylose under different conditions. Results showed that furfural and formic acid formed from xylose reached a maximum value of 32.56 % and 35.14 %, respectively. By increasing the initial pH of the xylan solution, the furfural concentration can be reduced effectively to 2% and the formation of formic acid was preferred under alkaline conditions. On this basis, we proposed a new hydrothermal degradation pathway of xylan in alkaline solution. The in-depth understanding of xlyan degradation during hot water pre-treatment will be beneficial for improving the efficiency of biofuel production.

Chemical-enzymatic conversion of corncob-derived xylose to furfuralcohol by the tandem catalysis with SO42-/SnO2-kaoline and E. coli CCZU-T15 cells in toluene-water media

One-pot synthesis of furfuralcohol from corncob-derived xylose was attempted by the tandem catalysis with solid acid SO₄^2-/SnO₂-kaoline and recombination Escherichia coli CCZU-T15 whole-cells in the toluene-water media. Using SO₄^2-/SnO₂-kaoline (3.5wt%) as catalyst, the furfural yield of 74.3% was obtained from corncob-derived xylose in the toluene-water (1:2, v:v) containing 10mM OP-10 at 170°C for 30min. After furfural liquor was mixed with corncob-hydrolysate from the enzymatic hydrolysis of oxalic acid-pretreated corncob residue, furfural (50.5mM) could be completely biotransformed to furfuralcohol with Escherichia coli CCZU-T15 whole-cells harboring an NADH-dependent reductase (ClCR) in the toluene-water (1:3, v:v) containing 12.5mM OP-10 and 1.6mM glucose/mM furfural at 30°C and pH 6.5. Furfuralcohol was obtained at 13.0% yield based on starting material corncob (100% furfuralcohol yield for bioreduction of furfural step). Clearly, this one-pot synthesis of furfuralcohol strategy shows high potential application for the effective utilization of corncob.

Effective Utilization of Carbohydrate in Corncob to Synthesize Furfuralcohol by Chemical-Enzymatic Catalysis in Toluene-Water Media

In this study, carbohydrates (cellulose plus hemicellulose) in corncob were effectively converted furfuralcohol (FOL) via chemical-enzymatic catalysis in a one-pot manner. After corncob (2.5 g, dry weight) was pretreated with 0.5 wt% oxalic acid, the obtained corncob-derived xylose (19.8 g/L xylose) could be converted to furfural at 60.1% yield with solid acid catalyst SO₄^2-/SnO₂-attapulgite (3.6 wt% catalyst loading) in the water-toluene (3:1, v/v) at 170 °C for 20 min. Moreover, the oxalic acid-pretreated corncob residue (1.152 g, dry weight) was enzymatically hydrolyzed to 0.902 g glucose and 0.202 g arabinose. Using the corncob-derived glucose (1.0 mM glucose/mM furfural) as cosubstrate, the furfural liquor (48.3 mM furfural) was successfully biotransformed to FOL by recombinant Escherichia coli CCZU-A13 cells harboring an NADH-dependent reductase (SsCR) in the water-toluene (4:1, v/v) under the optimum conditions (50 mM PEG-6000, 0.2 mM Zn²⁺, 0.1 g wet cells/mL, 30 °C, pH 6.5). After the bioreduction for 2 h, FAL was completely converted to FOL. The FOL yield was obtained at 0.11 g FOL/g corncob. Clearly, this one-pot synthesis strategy shows high potential application for the effective synthesis of FOL.