Effect of cellulosic sugar degradation products (furfural and hydroxymethyl furfural) on acetone–butanol–ethanol (ABE) fermentation using Clostridium beijerinckii P260

Studies were performed to identify chemical compounds present in wheat straw hydrolysate (WSH) that enhance acetone butanol ethanol (ABE) productivity. These compounds were identified as furfural and hydroxymethyl furfural (HMF). Control experiment resulted in the production of 21.38 g L^?1 ABE with a productivity of 0.30 g L^?1 h^?1. WSH contained 0.04–0.34 g L^?1 furfural and 0.12–0.88 g L^?1 HMF. Addition of furfural to the fermentation medium at a concentration of 0.50 g L^?1 resulted in a productivity of 0.88 g L^?1 h^?1 which is 293% of the productivity obtained in control experiments. Supplementation with 1.00 g L^?1 HMF into the fermentation medium produced 25.27 g L^?1 ABE with a productivity of 0.68 g L^?1 h^?1. A combination of furfural (0.50 g L^?1) and HMF (0.50 g L^?1) also enhanced ABE production and productivity when added to the fermentation medium. Both furfural and HMF enhanced specific productivity (233–308%) of ABE. In brief, WSH contained an adequate concentration of furfural and HMF that enhanced ABE productivity, specific productivity, and product concentration.     

Restructuring the processes for furfural and xylose production from sugarcane bagasse in a biorefinery concept for ethanol production

This study consisted in restructuring the processes for furfural and xylose production from sugarcane bagasse in a biorefinery concept for the residues utilization on ethanol production.The dilute acid hydrolysis conditions for furfural or xylose production were firstly established on laboratory scale and then reproduced on a 10-L bench reactor fed with direct steam. The furfural production was maximum when using a 1.25% (w/w on dry fiber) H₂SO₄ solution at 175 °C during 40 min; whereas the xylose production attained the best results when using a 1% (w/v) H₂SO₄ solution in a solid/liquid ratio of 1/4 (g/mL), and the sugarcane bagasse impregnated with the acid solution during 24 h prior to the hydrolysis reaction. Enzymatic hydrolysis of the residual solid material obtained from furfural or xylose production was performed with yields of 17.4 and 9.3 g glucose/100 g initial raw material, respectively. Subsequently, ethanol was produced from the residual solid materials obtained from furfural and xylose production with yields of 87.4% and 89.3% respectively, based on the maximum theoretical value (0.51 g ethanol per g glucose in hydrolysate). Such results demonstrated the possibility of restructuring the processes for furfural or xylose production to obtain solid residues able to be used as substrate for ethanol production by fermentation.     

Bioconversion of corn stover hydrolysate to ethanol by a recombinant yeast strain

Three corn stover hydrolysates, enzymatic hydrolysates prepared from acid and alkaline pretreatments separately and hemicellulosic hydrolysate prepared from acid pretreatment, were evaluated in composition and fermentability. For enzymatic hydrolysate from alkaline pretreatment, ethanol yield on fermentable sugars and fermentation efficiency reached highest among the three hydrolysates; meanwhile, ethanol yield on dry corn stover reached 0.175 g/g, higher than the sum of those of two hydrolysates from acid pretreatment. Fermentation process of the enzymatic hydrolysate from alkaline pretreatment was further investigated using free and immobilized cells of recombinant Saccharomyces cerevisiae ZU-10. Concentrated hydrolysate containing 66.9 g/L glucose and 32.1 g/L xylose was utilized. In the fermentation with free cells, 41.2 g/L ethanol was obtained within 72 h with an ethanol yield on fermentable sugars of 0.416 g/g. Immobilized cells greatly enhanced the ethanol productivity, while the ethanol yield on fermentable sugars of 0.411 g/g could still be reached. Repeated batch fermentation with immobilized cells was further attempted up to six batches. The ethanol yield on fermentable sugars maintained above 0.403 g/g with all glucose and more than 92.83% xylose utilized in each batch. These results demonstrate the feasibility and efficiency of ethanol production from corn stover hydrolysates.     

Catalytic conversion of fructose into furans using FeCl3 as catalyst

Conversion of fructose into furan derivates 5-hydroxymethylfurfural (HMF) and 5-ethoxymethylfurfural (EMF) was performed in ethanol-[Bmim]Cl solvent systems, catalyzed by FeCl₃. HMF was obtained in a high yield of 90.8% for 4 h at 100 °C in 1-butyl-3-methylimidazole chloride ([Bmim]Cl). The ratio of [Bmim]Cl to ethanol showed a remarkable effect on the yields of HMF and EMF. The maximum EMF yield of 30.1% was obtained in a mixed solvent of [Bmim]Cl (0.5 g) and ethanol (4.5 g). On the meanwhile, HMF was obtained in a yield of 60.3%.     

Production of bioethanol from corn meal hydrolyzates

The two-step enzymatic hydrolysis of corn meal by commercially available α-amylase and glucoamylase and further ethanol fermentation of the obtained hydrolyzates by Saccharomyces cerevisiae yeast was studied. The conditions of starch hydrolysis such as substrate and enzyme concentration and the time required for enzymatic action were optimized taking into account both the effects of hydrolysis and ethanol fermentation. The corn meal hydrolyzates obtained were good substrates for ethanol fermentation by S. cerevisiae. The yield of ethanol of more than 80% (w/w) of the theoretical was achieved with a satisfactory volumetric productivity P (g/l h). No shortage of fermentable sugars was observed during simultaneous hydrolysis and fermentation. In this process, the savings in energy by carrying out the saccharification step at lower temperature (32 °C) could be realized, as well as a reduction of the process time for 4 h.     

Integrated supercritical fluid extraction and subcritical water hydrolysis for the recovery of bioactive compounds from pressed palm fiber

Pressed palm fiber (PPF), a residue obtained from palm oil industry, is a source of bioactive compounds, such as carotenoids, which are used as food additives. It also has cellulose and hemicellulose that can be used to yield fermentable sugars for the production of second generation ethanol. Supercritical fluid extraction (SFE) of pressed palm fiber provides an oil rich in carotenoids while subcritical water hydrolysis (SubWH) produces hydrolysates with high amounts of fermentable sugars. In this work, the effects of pressure (15–30 MPa) and temperature (318 and 328 K) on SFE of carotenoids were investigated. The SFE extract with highest carotenoid content was obtained at 318 K and 15 MPa (2.3% d.b., 0.81 mg β-carotene/g extract). After the extraction, the influence of process temperature (423–633 K), pressure (15 and 25 MPa), solvent:feed ratio (120 and 240), and residence time (1.25–5 min) on SubWH of the extraction residue was studied. At the temperature of 523 K, the highest total reducing sugar yield (11–23 g glucose/100 g carbohydrate) and the highest biomass conversion (40–97%) were obtained for any pressure and solvent:feed ratio. The highest selectivity for saccharide formation was found at 423 K (20–59 mol glucose/mol furfural equivalent). Optimal conditions for high saccharide formation and low sugar degradation product in subcritical hydrolysis were obtained at 523 K, 15 MPa, solvent:feed ratio of 120, residence time of 2.5 min with a total reducing sugar yield of 22.9 g glucose/100 g carbohydrate and a conversion of 84.9%.     

Preparation of ferulic acid from corn bran: Its improved extraction and purification by membrane separation

Corn bran contains a high amount of ferulic acid. However, the separation and purification of ferulic acid from corn bran still encounter technical problems. In this research, ferulic acid was obtained from corn bran via membrane separation from hydrolysate treated with an alkaline-ethanol aqueous solution. The technology was optimised as follows. One weight of corn bran was extracted using 0.25 mol/L NaOH in 50% ethanol aqueous solution at 75 °C for 2 h. Filtrates were ultrafiltrated at room temperature using a membrane with 5000 Da molecular cut-off. Permeates with 91.8% recovery of ferulic acid were concentrated by nanofiltration using a membrane with 150 Da molecular cut-off. Ferulic acid crystal (8.47 g/kg corn bran) with 84.45% purity was obtained after the pH of the concentrate was adjusted to 2.0. The reducing sugars released from the alkaline-hydrolysed residue increased by 54.5% compared with the untreated corn bran after xylanase hydrolysis for 8 h.     

Study on the possibility of waste mushroom medium as a biomass resource for biorefinery

In order to investigate the possibility of waste mushroom medium as a biomass resource for biorefinery, characteristics of hydrolysate and pretreated biomass obtained from oxalic acid pretreatment were examined. The hydrolysate contained high glucose and low concentrations of inhibitors. The glucose concentration in the hydrolysate particularly increased when temperature gradient was used during pretreatment, compared with that of isocratic condition. The highest increase rate of glucose was 63.16% when pretreatment was performed at 140 °C for 25 min with 0.032 oxalic acid (g/g), and increased temperature to 170 °C. At the same time, ethanol production of Scheffersomyces stipitis using hydrolysate was 15.72 g/L after 48 h, which correspond to an ethanol volumetric productivity of 0.33 g L^?1 h^?1. Most of the lignin and some of the cellulose remained in the pretreated biomass. The total lignin content of the pretreated biomass, represent between 31.81 and 45.05%, compared to 28.8% of the raw material. The calorific value of the pretreated biomass ranged from 4940 to 5111 kcal/kg which represent increase of 3–6% compared to the raw material, due to higher contents of lignin in the pretreated biomass.     

Direct conversion of citrus peel waste into hydroxymethylfurfural in ionic liquid by mediation of fluorinated metal catalysts

A new green technology was developed using citrus peel waste to produce hydroxymethylfurfual (HMF). FT-IR analysis of the waste showed 4 characteristic vibration modes (CH, CO, COH, and CO/COO^?), contributing to sugars. XRD and FESEM elucidated that the waste and its hydrolysate consist of highly amorphous clusters. HCl increased HMF yield by 1.4-fold. CrF₃ increased its yield by 1.7-fold. At 0.2 of the stoichiometric ratio value, HMF yield was highest. The highest HMF yield was achieved in the reaction mixture of 4 g [OMIM]Cl, 1 mL ethyl acetate, 0.1 g CrF₃, 5 mL 0.3 M HCl, and 0.5 g biomass.     

发酵抑制物对葡萄糖发酵产乙醇的影响

在纤维素乙醇研究中,木质纤维原料在酸性预处理过程中会产生甲酸、乙酸、乙酰丙酸、糠醛和5-羟甲基糠醛等发酵抑制物,这些发酵抑制物会影响葡萄糖发酵生产乙醇的收率。本文考察了发酵液中各种发酵抑制物含量对高温超级酿酒酵母发酵乙醇收率的影响。研究结果表明,多种发酵抑制物的协同作用对乙醇发酵的影响要高于单一种类发酵抑制物对乙醇发酵的影响。发酵液中发酵抑制物总量一般控制在3.0g/L以内时,对葡萄糖发酵生产乙醇的抑制作用不明显。     

Production of fermentable sugars from enzymatic hydrolysis of pretreated municipal solid waste after autoclave process

A ligno-cellulosic concentrate from municipal solid waste (MSW) obtained after an autoclave separation process was investigated for its potential as a feedstock to produce fermentable sugars for ethanol production. A maximum enzymatic hydrolysis conversion of 53% of the cellulose and hemi-cellulose was found using a particle size range of 150–300 μm hydrolyzed in a 100 ml buffer solution containing 6 wt% lingo-cellulosic MSW concentrate with 90 mg cellulase at pH 4.8 held at 40 °C for 12 h. The hydrolysis rate leveled off at longer hydrolysis time and with increased substrate concentration and was related to enzymatic access to substrate. Lower hydrolysis rate at smaller particle size indicates that the grinding process may change the surface chemistry or morphology of the fibers making them less available for enzyme access. A drop in the hydrolysis rate was observed for the particles above 300 μm associate with the longer diffusion time for the enzyme into the fiber particles. The findings indicate that 152 L of ethanol could be obtained from a ton of lingo-cellulosic concentrate from MSW.     

Microwave-enhanced formation of glucose from cellulosic waste

The conversion of cellulose and cellulosic waste to fermentable sugars has been successfully demonstrated. Using a novel microwave intensified hydrothermal depolymerisation of cellulosic materials in liquid hot water, at pressures below 300 psi, conversions of up to 40% of fermentable sugars were obtained with limited by-product formation. A high selectivity for glucose over other sugars has been observed. Temperature is the crucial parameter as limited conversion is observed below 180 °C and optimum conversion is attained around 220 °C.     

Bioconversion of barley straw and corn stover to butanol (a biofuel) in integrated fermentation and simultaneous product recovery bioreactors

In these studies concentrated sugar solutions of barley straw and corn stover hydrolysates were fermented using Clostridium beijerinckii P260 with simultaneous product recovery and compared with the performance of a control glucose batch fermentation process. The control glucose batch fermentation resulted in the production of 23.25 g L⁻¹ ABE from 55.7 g L⁻¹ glucose solution resulting in an ABE productivity and yield of 0.33 g L⁻¹ h⁻¹ and 0.42, respectively. The control reactor (I) was started with 62.5 g L⁻¹ initial glucose and the culture left 6.8 g L⁻¹ unused sugar due to butanol toxicity resulting in incomplete sugar utilization. Barley straw (BS) hydrolysate sugars (90.3 g L⁻¹) resulted in the production of 47.20 g L⁻¹ ABE with a productivity of 0.60 g L⁻¹ h⁻¹ and a yield of 0.42. Fermentation of corn stover (CS) hydrolysate sugars (93.1 g L⁻¹) produced 50.14 g L⁻¹ ABE with a yield of 0.43 and a productivity of 0.70 g L⁻¹ h⁻¹. These productivities are 182–212% higher than the control run. The culture was able to use 99.4–100% sugars (CS & BS respectively) present in these hydrolysates and improve productivities which were possible due to simultaneous product removal. Use of >100 g L⁻¹ hydrolysate sugars was not considered as it would have been toxic to the culture in the integrated (simultaneous fermentation and recovery) process.     

Study on the conditions to brew rice vinegar with high content of γ-amino butyric acid by response surface methodology

In this study, rice vinegar with high content of γ-amino butyric acid (GABA) was prepared by using sprouted rice as raw material, supplemented with red yeast rice, glucoamylase preparation and raw starter complex during saccharification and alcohol fermentation, and the brewing conditions of the rice vinegar with high GABA content were studied. Through Plackett–Burman design, three factors (adding amounts of raw starter complex, red yeast rice and glucoamylase preparation) were identified as significant factors, which were subsequently optimized using Box–Benhnken center-united experiment design. At the optimal conditions, which were 500 g smashed sprouted rice, 4 g red yeast rice, 1.5 g raw starter complex, 1.6 mL glucoamylase preparation, 5 g sodium glutamate, 335 mL water, fermented at pH 6, 28 °C for 5 days, the estimated value of GABA was reached at 147.09 mg/100 mL fermenting mash, and the average experimental GABA value was 145.18 mg/100 mL. After that, the acetic acid fermentation in solid-state through adding wheat bran and chaff into the fermenting mash was carried on for 7 d before maturing for 8 d. In the end, the rice vinegar containing 100 mg/L GABA was prepared.     

Comparison of different procedures for the detoxification of eucalyptus hemicellulosic hydrolysate for use in fermentative processes

Eucalyptus (Eucalyptus grandis) shavings were submitted to an acid hydrolysis process with the aim of obtaining a hemicellulosic hydrolysate rich in fermentable sugars. However, the hydrolysate obtained contained, in addition to sugars, several compounds that are toxic to microorganisms, namely furfural, hydroxymethylfurfural, acetic acid and phenolics. In order to produce a hydrolysate suitable for use in fermentative processes, several procedures were evaluated for hydrolysate detoxification, including concentration by vacuum evaporation and adsorption on activated charcoal, diatomaceous earths, ion‐exchange resin or adsorbent resin. Hydrolysate concentration was especially effective for furfural removal, whereas the adsorbent resin was efficient in removing hydroxymethylfurfural, phenolics and acetic acid. Combination of this resin with activated charcoal was better than with diatomaceous earths for removal of acetic acid and phenolics. The best detoxification procedure evaluated was based on hydrolysate concentration followed by adsorption on activated charcoal and adsorbent resin. By this treatment, removal rates of 82.5, 100, 100 and 94% were attained for acetic acid, furfural, hydroxymethylfurfural and phenolics, respectively. Copyright © 2005 Society of Chemical Industry     

Design and optimization of a semi-continuous high pressure carbon dioxide extraction system for acetic acid

Supercritical fluid extraction with carbon dioxide was performed to extract acetic acid from real and model solutions of cow rumen fluid. Extractions were performed at varying temperature, pressure, solvent flow rate and extraction times for determining the extraction efficiency using a response surface statistical design. Within the range of variables studied, maximum acetic acid recovery of 93% was predicted at 2.0 g CO₂/min solvent flow rate, 2150 psi (14.8 MPa), 45 °C, and a 5 h extraction time using an initial acetic acid concentration of 92.4 g/L. A volumetric mass transfer coefficient of 2.848 h⁻¹ at 35 °C and 1500 psi (10.3 MPa) was calculated using a two-film linear driving force mass transfer model. The developed statistical model was tested for applicability on an acetic acid-spiked cow rumen fluid giving comparable results to the developed model. Results further showed that higher molecular weight volatile fatty acids such as propionic and butyric acid present in the fluid were preferentially removed before acetic acid extraction.     

Simulation and economic analysis of 5-hydroxymethylfurfural conversion to 2,5-furandicarboxylic acid

Two processes for converting 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) were designed using literature data together with simplified process simulation models. The main reaction step is HMF catalytic oxidation using aqueous acetic acid as solvent, Pt/ZrO₂ as catalyst and air as oxidant. The first process investigated involves a mixed-suspension, mixed-product-removal crystallizer and a filter for separating solid FDCA from the solvent. The calculated minimum sale price of FDCA is 3157 $/t, whereas, if pure oxygen is used as oxidant the FDCA price reduces to 2458 $/t. Due to the high melting point of FDCA, the second alternative considered introduces trioctylamine as solvent to facilitate separation of FDCA from the solvent using distillation. The estimated FDCA price using this process is 3885 $/t. Sensitivity analysis shows that selectivity and conversion have small impact on FDCA price, whereas plant capacity, catalyst and HMF costs have large effects on the price of FDCA.     

Obtaining sugars from coconut husk,defatted grape seed,and pressed palm fiber by hydrolysis with subcritical water

In this work, three residues from the food industry (coconut husk, defatted grape seed and pressed palm fiber) were subjected to subcritical water hydrolysis with the aim of producing fermentable sugars. Hydrolysis kinetics were determined using a semi-batch unit equipped with a 50 mL reactor. The process was conducted at 208 °C and 257 °C for 30 min, with water flow rate of 33 mL/min and under 20 MPa. The liquefaction degree of the raw materials increased with temperature. The total reducing sugars recovered also increased with temperature. Maximum total reducing sugars recovered for coconut husk, defatted grape seed and pressed palm fiber using SWH were 11.7%, 6.4% and 11.9% from total raw material, respectively. Coconut husk presented the highest amount of monosaccharides (3.4%), followed by pressed palm fiber (2.4%) and defatted grape seeds (0.7%). On the other hand, the degradation products that are also fermentation inhibitors increased with temperature as well. Each raw material presented a different monosaccharides and inhibitors profile, which indicates that SWH should be evaluated and optimized individually for each case.     

Hydrolysis of sugarcane bagasse in subcritical water

In this work, a subcritical water process was used for the hydrolysis of sugarcane bagasse with the aim of producing fermentable sugars. Hydrolysis kinetics was determined using a semi-batch unit equipped with a 50 mL reactor. Different sample loads (2 and 11 g), flow-rates (11, 22, 33, 44 and 55 mL/min) and temperatures (213, 251 and 290 °C) were evaluated, while maintaining constant pressure (20 MPa). The liquefaction degree of the sugarcane bagasse was not affected by water flow rate and increased with temperature; the maximum liquefaction degree was 95% for hydrolysis at 251 °C and 33 mL/min. The total reducing sugars recovered increased with flow rate up to 23%. The hydrolysis process was completed faster at higher temperatures, requiring 16 min. Maximum monosaccharides + cellobiose + cellotriose yield was 5.6% at 213 °C and 33 mL/min. Approximately 60% of the sugars recovered were in the oligomeric form.     

Effect of impurities in the recovery of 1-(5-bromo-fur-2-il)-2-bromo-2-nitroethane using nanofiltration

The recovery of the active pharmaceutical ingredient 1-(5-bromo-fur-2-il)-2-bromo-2-nitroethane (denoted as G-1) from residual ethanol produced during the purification of G-1 was studied by using solvent resistant nanofiltration. The effect of the impurities pyridine, acetic anhydride and bromine on the process performance was studied.Four commercial nanofiltration membranes were studied in a stirred dead-end filtration module, i.e. NF 90, NF 270, Duramem 150 and BW30XLE, supplied by Evonik Industries and Filmtec (Dow). The membranes Duramem 150 and NF 90 showed the best performance, allowing a recovery of G-1 of above 60% in one stage. The separation factor of pyridine/G-1 for Duramem 150 and NF 90 was found to be higher than 2 for synthetic mixtures containing 26.75 g/L of G-1, 5.35 g/L of pyridine, 0.149 g/L of bromine and 0.105 g/L of acetic anhydride in ethanol. It was found that when using dead-end filtration, the recovery of G-1 is low when a high purity is required; both parameters cannot be optimized together. However, it is shown that with a sequence of filtrations, the recovery can be significantly improved at a given purity of G-1. These results indicate that the application of organic solvent nanofiltration for the recycling of valuable pharmaceutical compounds is feasible in realistic conditions.