Catalytic hydrolysis of lignocellulosic biomass into 5-hydroxymethylfurfural in ionic liquid

Production of 5-hydroxymethylfurfural (HMF) from cellulose catalyzed by solid acids and metal chlorides was studied in the 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) under microwave irradiation. Among the applied catalysts, the use of CrCl₃/LiCl resulted in the highest yield of HMF. The effects of catalyst dosage (mole ratio of catalyst to glucose units in the feedstock) and reaction temperature on HMF yields were investigated to obtain optimal process conditions. With the 1:1 mol ratio of catalyst to glucose unit, the HMF yield reached 62.3% at 160 °C for 10 min. Untreated wheat straw was also investigated as feedstock to produce HMF for the practical use of raw biomass, in which the HMF yield was comparable to that from pure cellulose. After the extraction of HMF, [BMIM]Cl and CrCl₃/LiCl could be reused and exhibited no activity loss after three successive runs.     

Conversion of biomass into 5-hydroxymethylfurfural using solid acid catalyst

5-Hydroxymethylfurfural (HMF) was produced from monosaccharide (fructose and glucose), polysaccharide (inulin) and the Jerusalem artichoke juice by a simple one-pot reaction including hydrolysis and dehydration using solid acid under mild condition. Hydrated niobium pentoxide (Nb(2)O(5)·nH(2)O(2)) after pretreatment showed high catalytic activities for dehydration of mono- and polysaccharide to HMF at 433 K in water-2-butanol (2:3 v/v) biphasic system, giving high HMF yield of 89% and 54% from fructose and inulin, respectively. The HMF yield was up to 74% and 65% when inulin and Jerusalem artichoke juice were hydrolyzed by exoinulinase. The solid acid made the process environment-friendly and energy-efficient to convert carbohydrates into bio-fuels and platform chemicals.     

Efficient and selective conversion of sucrose to 5-hydroxymethylfurfural promoted by ammonium halides under mild conditions

The highly efficient and selective production of 5-hydroxymethylfurfural (HMF) from sucrose has been achieved in the presence of metal chlorides and ammonium halides under mild conditions. Notably, an 87% yield of HMF from sucrose was obtained with a catalyst system composed of CrCl(3) and NH(4)Br at 100°C for 1.0 h in N,N-dimethylacetamide (DMAc) solvent. The effect of the reaction temperature and time was investigated in detail, and a possible mechanism for this catalytic process has been proposed. In addition, NH(4)Br is an effective promoter in the conversion of glucose and fructose to HMF.     

贮存时间对不同蜜源蜂蜜中羟甲基糠醛含量增速的影响

为了更好控制蜂蜜在贮藏和流通过程中的羟甲基糠醛含量,研究了其在贮存过程中羟甲基糠醛的增长规律。本文对192个不同蜜源的蜂蜜在常温贮存期间的羟甲基糠醛含量进行了检测,统计了贮存时间和蜜源对羟甲基糠醛增长速率的影响,并分析了组分对羟甲基糠醛增率的相关性。结果表明,贮存450d内,蜂蜜的羟甲基糠醛增率与贮存时间呈正相关;椴树蜜、洋槐蜜、紫云英蜜和百花蜜的羟甲基糠醛增率无显著差异,且极显著高于枣花蜜;羟甲基糠醛增率与葡萄糖含量呈显著相关;果葡比极显著相关于酸度。     

Chromium halides mediated production of hydroxymethylfurfural from starch-rich acorn biomass in an acidic ionic liquid

Chromium halides were introduced for the sustainable production of hydroxymethylfurfural (HMF) from raw acorn biomass using an acidic ionic liquid. The free sugars (glucose and maltose) released by the acidic hydrolysis of the biomass were confirmed by the FT-IR absorption bands around 995–1014 cm⁻¹ and HPLC. FESEM analysis showed that the acorn biomass contains various sizes of starch granules and their structures were severely changed by the acidic hydrolysis. An optimal concentration of HCl for the HMF yields was 0.3 M. The highest HMF yield (58.7 + 1.3 dwt %) was achieved in the reaction mixture of 40% [OMIM]Cl + 10% ethyl acetate + 50% 0.3 M HCl extract containing a mix of CrBr₃/CrF₃. The combined addition of two halide catalysts was more effective in the synthesis of HMF (1.2-fold higher on average) than their single addition. The best productivity of HMF was found at 15% concentration of the biomass and at 50%, its relative productivity declined down to ca. 0.4-fold.     

Detoxification of a lignocellulosic biomass slurry by soluble polyelectrolyte adsorption for improved fermentation efficiency

This study investigated the detoxification of a dilute acid pretreated Ponderosa pine slurry using the polyelectrolyte polyethyleneimine (PEI). The addition of polyelectrolyte to remove enzymatic and/or fermentation inhibitory compounds, that is, acetic acid, furfural, and 5-hydroxymethylfurfural (HMF), was performed either before or after enzymatic hydrolysis to determine the optimal process sequence. Negligible acetic acid, glucose, and xylose were removed regardless of where in the process the polymer addition was made. Maximum furfural and HMF separation was achieved with the addition of PEI to a clarified pre-enzymatic hydrolysis liquor, which showed that 88.3% of furfural and 66.4% of HMF could be removed. On the other hand, only 23.1% and 13.4% of furfural and HMF, respectively, were removed from a post-enzymatic hydrolysis sample; thus, the effects of enzymes, glucose, and wood solids on inhibitor removal were also investigated. The presence of solid particles >0.2 μm and unknown soluble components <10 kDa reduced inhibitory compound removal, but the presence of elevated glucose levels and enzymes (cellulases) did not affect the separation. The fermentability of detoxified versus undetoxified hydrolysate was also investigated. An ethanol yield of 92.6% of theoretical was achieved with Saccharomyces cerevisiae fermenting the detoxified hydrolyzate, while no significant ethanol was produced in the undetoxified hydrolyzate. These results indicate that PEI may provide a practical alternative for furan removal and detoxification of lignocellolosic hydrolysates, and that application before enzymatic hydrolysis minimizes separation interferences.     

Effect of surfactants on separate hydrolysis fermentation and simultaneous saccharification fermentation of pretreated lodgepole pine

The effects of surfactants addition on enzymatic hydrolysis and subsequent fermentation of steam exploded lodgepole pine (SELP) and ethanol pretreated lodgepole pine (EPLP) were investigated in this study. Supplementing Tween 80 during cellulase hydrolysis of SELP resulted in a 32% increase in the cellulose‐to‐glucose yield. However, little improvement was obtained from hydrolyzing EPLP in the presence of the same amount of surfactant. The positive effect of surfactants on SELP hydrolysis led to an increase in final ethanol yield after the fermentation. It was found that the addition of surfactant led to a substantial increase in the amount of free enzymes in the 48 h hydrolysates derived from both substrates. The effect of surfactant addition on final ethanol yield of simultaneous saccharification and fermentation (SSF) was also investigated by using SELP in the presence of additional furfural and hydroxymethylfurfural (HMF). The results showed that the surfactants slightly increased the conversion rates of furfural and HMF during SSF process by Saccharomyces cerevisiae. The presence of furfural and HMF at the experimental concentrations did not affect the final ethanol concentration either. The strategy of applying surfactants in cellulase recycling to reduce enzyme cost is presented. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Reaction pathways of glucose during esterification: effects of reaction parameters on the formation of humin type polymers

The formation of humin-type polymers and other products during exposure of glucose to methanol/water mixtures with methanol/water mass ratios from 10 to 0.22 in the presence of the acid catalyst Amberlyst 70 was investigated. In water-rich medium (methanol/water mass ratio: 0.22), dehydration of glucose produced 5-(hydroxymethyl)furfural (HMF), furfural, and substantial amounts of polymer. In methanol-rich medium (methanol/water mass ratio: 10), the hydroxyl and carbonyl groups of glucose, HMF or furfural were protected via etherification and acetalisation. These protections stabilized these reactive compounds and significantly lowered the polymer formation (1.43% of the glucose loaded). The polymerization of glucose and HMF was also favored at high temperatures and long residence times. Conversely, high catalyst dosage mainly accelerated the conversion of glucose to methyl levulinate. Thus, the polymerization of glucose and HMF can be suppressed in methanol/water mixtures with high methanol ratios, at low temperatures and short residence times.     

Acid hydrolysis of sweet potato for ethanol production

Studies were conducted to establish optimal conditions for the acid hydrolysis of sweet potato for maximal ethanol yield. The starch contents of two sweet potato cultivars (Georgia Red and TG-4), based on fresh weight, were 21.1 +/- 0.6% and 27.5 +/- 1.6%, respectively. The results of acid hydrolysis experiments showed the following: (1) both hydrolysis rate and hydroxymethylfurfural (HMF) concentration were a function of HCL concentration, temperature, and time; (2) the reducing sugars were rapidly formed with elevated concentrations of HCl and temperature, but also destroyed quickly; and (3) HMF concentration increased significantly with the concentration of HCl, temperature, and hydrolysis time.Maximum reducing sugar value of 84.2 DE and 0.056% HMF (based on wet weight) was achieved after heating 8% SPS for 15 min in 1N HCl at 110 degrees C. Degraded 8% SPS (1N HCl, 97 degrees C for 20 min or 110 degrees C for 10 min) was utilized as substrate for ethanol fermentation and 3.8% ethanol (v/v) was produced from 1400 mL fermented wort. This is equal to 41.6 g ethanol (200 proof) from 400 g of fresh sweet potato tuber (Georgia Red) or an ethanol yield potential of 431 gal of 200-proof ethanol/acre (from 500 bushel tubers/acre).     

Direct conversion of cellulose to 1-(furan-2-yl)-2-hydroxyethanone in zinc chloride solution under microwave irradiation

Conversion of cellulose to 1-(furan-2-yl)-2-hydroxyethanone has been demonstrated in concentrated zinc chloride solution under microwave irradiation. Compared with the conventional oil-bath heating mode, microwave irradiation significantly reduced the reaction time and increased the yield of 1-(furan-2-yl)-2-hydroxyethanone. A typical degradation reaction with cellulose produced 1-(furan-2-yl)-2-hydroxyethanone in 12.0% molar yield in ZnCl₂ solution (ZnCl₂–H₂O ratio = 2.25:1, w/w) with microwave irradiation at 600 W for 5 minutes at 135 °C.     

Characterization of biotechnological processes and products using high-performance liquid chromatography (HPLC). II. Analyses of potato starch hydrolysis products

Potato starch hydrolysis products were analyzed for glucose, maltose, higher oligomeric carbohydrates (to a degree of polymerization, dp 11) and 5-hydroxymethylfurfural (HMF) using high-performance liquid chromatography. For quick qualitative and quantitative analyses short glass columns [12] of high efficiency were useful. The hydrolyses were carried out by means of enzymes (e.g. α- and β-amylase) or mineral acids. For the acid degradation procedures hydrochloric acid, sulfuric acid and phosphoric acid of different concentrations (0.1…2.0 N) during times ranging from 5 to 60 min at temperatures ranging from 100 to 140°C were used. Maximum glucose contents (163.4 g/l and 169.3 g/l) were found after 40 to 50 min of hydrolysis in 0.1 N hydrochloric acid heated to 120°C. These values are equivalent to 78.9% or 81.7% glucose yield referred to the initial potato starch amount, respectively. The calculated HMF concentrations were 140 and 180 mg/l.     

Comparison of physicochemical properties and effects of heating regimes on stored Apis mellifera and Apis florea honey

Many of the components, which render honey its specific aroma, flavor, and biological activity, are unstable over time and thermolabile. This study was aimed to compare the chemical composition, effect of heating as well as the time of heat exposure, and storage period on the quality of honey samples from Apis mellifera (A.m.) and Apis florea (A.f.). Methods of the Association of the Official Analytical Chemists (AOAC) were used in this study. The mean values for both A.m. and A.f. honeys were, respectively: moisture (18.5, 13.7%); glucose (35.2, 36.3%); fructose (33.7, 33.8%); sucrose (7.3, 2.9%); invert sugar (68.9, 70.4%); ash (0.26, 1.1%); acidity (51.8, 98.4 meq/kg); pH (3.6, 4.4) and Hydroxy methyl furfural (HMF) (3.78, 3.17 mg/100 g). Honey from A. florea contained less moisture, have higher acidity and ash contents than A. mellifera honey. Significant alterations (P < 0.05) in glucose, fructose, sucrose, and acidity were noticed after six months. Honeys exposed to heating for 15 and 30 min at 50 and 80 °C have shown increased thermo-generated HMF after 15, 30, and 45 days. HMF reached 16.30 ± 1.1 in A. mellifera and 7.41 ± 1.4 mg/100 g in A. florea honeys that exposed for 30 min at 80 °C. Honey from A. florea showed more heat tolerance to thermo-generation of HMF than honey from A. mellifera.     

NADH- vs NADPH-coupled reduction of 5-hydroxymethyl furfural (HMF) and its implications on product distribution in Saccharomyces cerevisiae

Saccharomyces cerevisiae alcohol dehydrogenases responsible for NADH-, and NADPH-specific reduction of the furaldehydes 5-hydroxymethyl-furfural (HMF) and furfural have previously been identified. In the present study, strains overexpressing the corresponding genes (mut-ADH1 and ADH6), together with a control strain, were compared in defined medium for anaerobic fermentation of glucose in the presence and absence of HMF. All strains showed a similar fermentation pattern in the absence of HMF. In the presence of HMF, the strain overexpressing ADH6 showed the highest HMF reduction rate and the highest specific ethanol productivity, followed by the strain overexpressing mut-ADH1. This correlated with in vitro HMF reduction capacity observed in the ADH6 overexpressing strain. Acetate and glycerol yields per biomass increased considerably in the ADH6 strain. In the other two strains, only the overall acetate yield per biomass was affected. When compared in batch fermentation of spruce hydrolysate, strains overexpressing ADH6 and mut-ADH1 had five times higher HMF uptake rate than the control strain and improved specific ethanol productivity. Overall, our results demonstrate that (1) the cofactor usage in the HMF reduction affects the product distribution, and (2) increased HMF reduction activity results in increased specific ethanol productivity in defined mineral medium and in spruce hydrolysate.     

Production of 5-hydroxymethylfurfural in ionic liquids under high fructose concentration conditions

Acid-promoted, selective production of 5-hydroxymethylfurfural (HMF) under high fructose concentration conditions was achieved in ionic liquids (ILs) at 80 °C. A HMF yield up to 97% was obtained in 8 min using 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl) catalyzed with 9 mol % hydrochloric acid. More significantly, an HMF yield of 51% was observed when fructose was loaded at a high concentration of 67 wt % in [C₄mim]Cl. Water content below 15.4% in the system had little effect on HMF yield, whereas a higher water content was detrimental to both reaction rate and HMF yield. In situ NMR analysis suggested that the transformation of fructose to HMF was a highly selective reaction that proceeded through the cyclic fructofuranosyl intermediate pathway. This work increased our capacity to produce HMF, and should be valuable to facilitate cost-efficient conversion of biomass into biofuels and bio-based products.     

Isolation and characterization of Cupriavidus basilensis HMF14 for biological removal of inhibitors from lignocellulosic hydrolysate

The formation of toxic fermentation inhibitors such as furfural and 5-hydroxy-2-methylfurfural (HMF) during acid (pre-)treatment of lignocellulose, calls for the efficient removal of these compounds. Lignocellulosic hydrolysates can be efficiently detoxified biologically with microorganisms that specifically metabolize the fermentation inhibitors while preserving the sugars for subsequent use by the fermentation host. The bacterium Cupriavidus basilensis HMF14 was isolated from enrichment cultures with HMF as the sole carbon source and was found to metabolize many of the toxic constituents of lignocellulosic hydrolysate including furfural, HMF, acetate, formate and a host of aromatic compounds. Remarkably, this microorganism does not grow on the most abundant sugars in lignocellulosic hydrolysates: glucose, xylose and arabinose. In addition, C. basilensis HMF14 can produce polyhydroxyalkanoates. Cultivation of C. basilensis HMF14 on wheat straw hydrolysate resulted in the complete removal of furfural, HMF, acetate and formate, leaving the sugar fraction intact. This unique substrate profile makes C. basilensis HMF14 extremely well suited for biological removal of inhibitors from lignocellulosic hydrolysates prior to their use as fermentation feedstock.     

A versatile Pseudomonas putida KT2440 with new ability: selective oxidation of 5-hydroxymethylfurfural to 5-hydroxymethyl-2-furancarboxylic acid

Currently, biotransformation of 5-hydroxymethylfurfural (HMF) into a series of high-value bio-based platform chemicals is massively studied. In this study, selective biooxidation of HMF to 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) by Pseudomonas putida KT2440 with superior titer, yield, and productivity was reported. The biocatalytic performances of P. putida KT2440 were optimized separately. Under optimal conditions, 100% yield of HMFCA was obtained when HMF concentration was less than 150 mM, while the maximum concentration of 155 mM was achieved from 160 mM HMF in 12 h. P. putida KT2440 was highly tolerate to HMF, up to 190 mM. Besides, it was capable of selective oxidation of other furan aldehydes to the corresponding carboxylic acids with good yield of 100%. This study further demonstrates the potential of P. putida KT2440 as a biocatalyst for biomass conversion, as this strain has been proved the capacity to convert and utilize many kinds of biomass-derived sugars and ligin-derived aromatic compounds.

     

The influence of the initial and catalyst concentrations on the dehydration of d-fructose

The dehydration at 95° of d-fructose (0.25m-1.0m) to 5-hydroxymethyl-2-furaldehyde (HMF) and the rehydration of HMF (0.25-1.0m) to levulinic and formic acids in 0.5-2m HCl has been studied. The conversion rate of d-fructose was proportional to the Hammett activity. The acidity had a smaller influence on the conversion rate of HMF, although it was not proportional to the catalyst concentration. The rehydration of HMF was faster in the presence of d-fructose. The yield of levulinic acid was independent of the catalyst concentration, but was lower at higher initial concentrations of d-fructose and HMF, and a kinetic model has been derived. The formation of humin was of an overall order 1.3 in an intermediate between d-fructose and HMF, and of an order 1.7 in an intermediate between HMF and levulinic acid.     

High temperature dilute acid pretreatment of coastal Bermuda grass for enzymatic hydrolysis

Dilute sulfuric acid was used to pretreat coastal Bermuda grass at high temperature prior to enzymatic hydrolysis. After both pretreatment and enzymatic hydrolysis processes, the highest yield of total sugars (combined xylose and glucose) was 97% of the theoretical value. The prehydrolyzate liquor was analyzed for inhibitory compounds (furfural, hydroxymethylfurfural (HMF)) in order to assess potential risk for inhibition during the following fermentation. Accounting for the formation of the inhibitory compounds, a pretreatment with 1.2% acid at 140 °C for 30 min with a total sugar yield of 94% of the theoretical value may be more favorable for fermentation. From this study, it can be concluded that dilute sulfuric acid pretreatment can be successfully applied to coastal Bermuda grass to achieve high yields of monomeric glucose and xylose with acceptable levels of inhibitory compound formation.