Processing of ethanol fermentation broths by Candida krusei to separate bioethanol by pervaporation using silicone rubber‐coated silicalite membranes

BACKGROUND: Pervaporation employing ethanol‐permselective silicalite membranes as an alternative to distillation is a promising approach for refining low‐concentration bioethanol solutions. However, to make the separation process practicable, it is extremely important to avoid the problems caused by the adsorption of succinate on the membrane during the separation process. In this work, the pervaporation of an ethanol fermentation broth without succinate was investigated, as well as the influence of several fermentation broth nutrient components. RESULTS: Candida krusei IA‐1 produces an extremely low level of succinate. The decrease in permeate ethanol concentration through a silicone rubber‐coated silicalite membrane during the separation of low‐succinate C. krusei IA‐1 fermentation broth was significantly improved when compared with that obtained using Saccharomyces cerevisiae broth. By treating the fermentation broth with activated carbon, bioethanol was concentrated as efficiently as with binary mixtures of ethanol/water. The total flux was improved upto 56% of that obtained from the separation of binary mixtures, compared with 43% before the addition of activated carbon. Nutrients such as peptone, yeast extract and corn steep liquor had a negative effect on pervaporation, but this response was distinct from that caused by succinate. CONCLUSION: For consistent separation of bioethanol from C. krusei IA‐1 fermentation broth by pervaporation, it is useful to treat the low nutrient broth with activated carbon. To further improve pervaporation performance, it will be necessary to suppress the accumulation of glycerol. Copyright © 2009 Society of Chemical Industry     

Selective separation of n‐butanol from aqueous solutions by pervaporation using silicone rubber‐coated silicalite membranes

BACKGROUND: To use butanol as a liquid fuel and feedstock, it is necessary to establish processes for refining low‐concentration butanol solutions. Pervaporation (PV) employing hydrophobic silicalite membranes for selective recovery of butanol is a promising approach. In this study, the adsorption behavior of components present in clostridia fermentation broths on membrane material (silicalite powder) was investigated. The potential of PV using silicone rubber‐coated silicalite membranes for the selective separation of butanol from model acetone–butanol–ethanol (ABE) solutions was investigated. RESULTS: The equilibrium adsorbed amounts of ABE per gram of silicalite from aqueous solutions of binary mixtures at 30 °C increased as follows: ethanol (95 mg) < acetone (100 mg) < n‐butanol (120 mg). The amount of butanol adsorbed is decreased by the adsorption of acetone and butyric acid. In the separation of ternary butanol/water/acetone mixtures, the enrichment factor for acetone decreased, compared with that in binary acetone/water mixtures. In the separation of a model acetone–butanol–ethanol (ABE) fermentation broth containing butyric acid by PV using a silicone rubber‐coated silicalite membrane, the permeate butanol concentration was comparable with that obtained in the separation of a model ABE broth without butyric acid. The total flux decreased with decreasing feed solution pH. CONCLUSION: A silicone rubber‐coated silicalite membrane exhibited highly selective PV performance in the separation of a model ABE solution. It is very important to demonstrate the effectiveness of PV in the separation of actual clostridia fermentation broths, and to identify the factors affecting PV performance. Copyright © 2011 Society of Chemical Industry     

Stabilization of bioethanol recovery with silicone rubber‐coated ethanol‐permselective silicalite membranes by controlling the pH of acidic feed solution

In order to produce highly concentrated bioethanol by pervaporation using an ethanol‐permselective silicalite membrane, techniques to suppress adsorption of succinic acid, which is a chief by‐product of ethanol fermentation and causes the deterioration in pervaporation performance, onto the silicalite crystals was investigated. The amount adsorbed increased as the pH of the aqueous succinic acid solution decreased. The pervaporation performance also decreased with decreasing pH when the ternary mixtures of ethanol/water/succinic acid were separated. Using silicalite membranes individually coated with two types of silicone rubber, pervaporation performance was significantly improved in the pH range of 5 to 7, when compared with that of non‐coated silicalite membranes in ternary mixtures of ethanol/water/succinic acid. Moreover, when using a silicalite membrane double‐coated with the two types of silicone rubber, pervaporation performance was stabilized at lower pH values. In the separation of bioethanol by pervaporation using the double‐coated silicalite membrane, removal of accumulated substances having an ultraviolet absorption maximum at approximately 260 nm from the fermentation broth proved to be vital for efficient pervaporation. Copyright © 2005 Society of Chemical Industry     

Reliable production of highly concentrated bioethanol by a conjunction of pervaporation using a silicone rubber sheet‐covered silicalite membrane with adsorption process

For the production of highly concentrated bioethanol by pervaporation using an ethanol‐permselective silicalite membrane, pervaporation performance was investigated using a silicalite membrane entirely covered with a silicone rubber sheet to prevent direct contact with acidic compounds. By using a resistance model for membrane permeation, the separation factor of the covered silicalite membrane towards ethanol can be estimated from the individual pervaporation performances of the silicalite membrane and the silicone rubber sheet. No decrease in the ethanol concentration through the silicone rubber sheet‐covered membrane was caused when ethanol solutions containing succinic acid were supplied. By directly passing the permeate‐enriched ethanol vapor mixed with water vapor through a dehydration column packed with a molecular sieve of pore size 0.3 nm, highly concentrated bioethanol up to 97% (w/w), greater than the azeotropic point in the ethanol/water binary systems, can be obtained from 9% (w/w) fermentation broth. Copyright © 2004 Society of Chemical Industry     

Separation by pervaporation of ethanol from aqueous solutions and effect of other components present in fermentation broths

BACKGROUND: In this work, the selective extraction of ethanol by pervaporation through a POMS (polyoctylmethyl siloxane) hydrophobic membrane supplied by GKKS (Germany) was investigated. First, binary ethanol aqueous solutions were studied considering the effect of ethanol feed concentration (0–11 wt%) and operating temperature (307.55–326.35 K). The effect of some by‐products of the ethanol fermentation, such as glycerol, succinic acid, butanol and acetone, on the pervaporation performance has been analyzed. RESULTS: For binary ethanol aqueous solutions, it was found that water permeation flux remained more or less constant while ethanol permeation flux increased continuously when increasing ethanol feed concentration. However, water and ethanol permeances did not change much in the concentration and temperature range studied. It was observed that the addition of glycerol and succinic acid sharply decreased the total permeation flux while ethanol concentration in the permeate was hardly affected. The addition of butanol and acetone resulted in a lower separation factor for ethanol through the POMS membrane. CONCLUSIONS: For ethanol aqueous solutions the POMS membrane was found to be selective towards ethanol, although it does not present higher separation factors than distillation in the concentration range covered in this work. The presence of other components of the fermentation broth has a great influence in the pervaporation behavior. Further work must be done on the study of multicomponent and real mixtures. Copyright © 2009 Society of Chemical Industry     

Drastic improvement of bioethanol recovery using a pervaporation separation technique employing a silicone rubber‐coated silicalite membrane

A coupled fermentation/pervaporation process for reliable production of concentrated ethanol was studied using ethanol permselective silicalite membranes coated with two types of silicone rubber, KE‐45 and KE‐108, as a hydrophobic material. Ethanol recovery was greatly improved by using a membrane coated with KE‐45 silicone rubber. The recovered ethanol concentration in the permeate was 67% (w/w), and the amount of recovered ethanol from the broth was more than 10 times higher than that using a non‐coated membrane. Succinic acid and glycerol, by‐products created during fermentation, interfered with the pervaporation performance of the coated membrane when used to separate an ethanol/water solution. Copyright © 2003 Society of Chemical Industry     

Extraction of 1-butanol from aqueous solutions by pervaporation

The extraction of 1-butanol from fermentation broths by pervaporation offers potential for use in biotechnology. Various membrane materials have been screened for their suitability for this process. Polydimethylsiloxane (PDMS) membranes gave the best results in terms of flux and selectivity, with large variations depending on their nature and preparation. Selectivity was further increased by including either organophilic adorbents (cyclodextrins, zeolites), or oleyl alcohol in dense PDMS membranes. The predominance of driving force (i.e. activity gradient) on pervaporation extraction performances was shown by a comparative study on different binary aqueous solutions of alcohols. Water flux remained practically constant while the alcohol flux was linearly related to its feed concentration. The conclusions obtained with binary mixtures were consistent with those obtained with two model ternary solutions; the influence of salt on 1-butanol permeability was negligible, whereas ethanol had a strong effect.     

Clarification of succinic acid fermentation broth by ultrafiltration in succinic acid bio–refinery

BACKGROUND: Succinic acid is an important precursor chemical for the synthesis of high value‐added products. In this work, ultrafiltration was first investigated to clarify succinic acid fermentation broth by integrating fermentation and separation and removal processes of the product in situ. Four different ultrafiltration membranes (PES 100 kDa, PES 30 kDa, PES 10 kDa and RC 10 kDa) were used in this work. RESULTS: Results indicate that ultrafiltration is feasible for clarifying succinic acid fermentation broth. Almost all the microorganism cells (99.6%) were removed from the fermentation broth. Proteins were also removed effectively by all the membranes studied. The removal rate was 79.86% for PES 100 kDa, 86.43% for PES 30 kDa, 86.83% for PES 10 kDa, and 80.06% for the RC 10 kDa. After ultrafiltration, a clearer permeate was obtained compared with that from centrifugation. CONCLUSION: Membranes operating at high flux are always susceptible to rapid fouling. Compared with molecular weight cut‐offs (MWCO), membrane material has a significant influence on the flux. Membrane flux measured in this study shows industrial potential of this technology in treatment of succinic acid fermentation broth. © 2012 Society of Chemical Industry     

渗透汽化法从丙酮-丁醇-乙醇中分离浓缩丁醇

发酵法生产丁醇的产物质量浓度很低,为了实现丁醇的高效分离浓缩,文中采用渗透汽化膜分离技术对模型发酵液(丙酮、丁醇、乙醇混合溶液,ABE)进行浓缩实验。结果表明:随着温度、真空度、错流速度、料液质量浓度的增大,丁醇通量上升;渗透汽化膜对丁醇选择性在温度50℃时最佳,并随真空度的减小而减小,随料液质量浓度的增大而降低。实验证明,渗透汽化法能实现丁醇的高效分离浓缩,并且利用串联阻力溶解扩散模型可较好地预测ABE溶液体系中各组分的传质和分离效果。     

模拟的发酵液组分对聚二甲基硅氧烷/陶瓷复合膜渗透汽化性能的影响

对所制备的聚二甲基硅氧烷（PDMS）/陶瓷复合膜进行了渗透汽化性能表征。通过在乙醇-水混合体系中添加不同的模拟发酵液组分;如葡萄糖（多羟基醛）、甘油（多元醇）、丁二酸（有机酸）、KCl（无机盐）;考察了各组分对复合膜渗透汽化性能的影响。研究发现：在333 K下;在乙醇浓度为65 g·L-1的混合物中添加不同浓度的第三组分;有机添加物对膜的渗透汽化性能没有明显影响;而无机盐的加入使膜的分离因子稍有提高。所制备的PDMS/陶瓷复合膜;在上述渗透汽化过程中表现出良好的稳定性和对乙醇的优先选择性;渗透通量和分离因子（醇/水）分别在4.5～4.7 kg·m^-2·h^-1、8.3～10.3之间。     

Exclusion and Tortuosity Effects for Alcohol/Water Separation by Zeolite-Filled PDMS Membranes

Abstract

A resistance model has been developed to describe the increased pervaporation flux and selectivity for the separation of ethanol/water mixtures with silicalite-filled silicone rubber (SR) membranes as compared to unfilled SR membranes. The model interprets the increased component flux for ethanol in terms of an increasing ethanol permeability of the membrane. Membrane permeability is given as a function of rubber and silicalite permeabilities and of the silicalite content of the membrane. It is shown that silicalite permeability varies with the type of alcohol and the alcohol concentration in the feed mixture. In the series methanol, ethanol, propanol, and butanol, the alcohol permeability of silicalite varies with the length of the alcohol molecule, the lowest permeability being found for butanol. In the presence of propanol and butanol, the silicalite particles are impermeable to water and obstruct water transport through the membrane.     

PDMS复合膜从发酵液中渗透汽化回收乙醇

The pervaporation behavior of fermentation broth was investigated experimentally and compared with those started with ethanol mixtures. Ethanol was produced by Saccharomyces cerevisiae utilizing technical grade glucose and recovered by pervaporation using a composite polydimethylsiloxane (PDMS) membrane prepared in our laboratory. Ethanol concentration in fermentation broth decreased to a relatively low level when pervaporation was coupled with fermentation. The more active cells appeared in the fermentation broth, the better the membrane performance was.     

POMS Membrane for Selective Separation of Ethanol from Dilute Alcohol-Aqueous Solutions by Pervaporation

Lignocellulosic biomass has potential as an alternative to corn as starting material for the production of ethanol for the development of non-fossil fuel energy sources. In this case, low concentration bioethanol is gained by yeast fermentation and it has to be efficiently recovered and concentrated. For this purpose pervaporation separation of dilute alcohol-aqueous solutions was carried out using a poly(octhylmethyl siloxane) [POMS] membrane. The effect of different process parameters (feed composition, feed temperature, feed flow rate, permeate pressure) on pervaporation performance were investigated and discussed in terms of the separation factor and the total flux. The membrane studied was ethanol to water selective at ethanol feed concentrations lower than 2.5% w/w, while the highest permeability was achieved at feed temperature of 95°C.     

Downstream Processing of Lactic Acid by Membrane-Based Solvent Extraction∗

Abstract

Lactic acid has extensive use in the food and chemical industry. About half the lactic acid used in the world is produced by fermentation of carbohydrates using lactic acid bacteria. The recovery of lactic acid from the fermentation broth is more difficult than the fermentation itself. In the present work a study of membrane-based solvent extraction as a separation unit for the continuous downstream processing of lactic acid from fermentation broth was carried out. The experiments were performed using simulated fermentation broths made of lactic acid in acetate buffer or distilled water as the feed solution. The effects of membrane material, organic carrier, and pH of the feed solution on membrane extraction efficiency were investigated. A separation degree of 35% was obtained by using a polyether-etherketone (PEEK-WC 14%) membrane with 5% trioctylamine as the organic carrier in n-heptane. The experimental results obtained with the simulated system encourage the use of membrane-based solvent extraction with a real fermentation broth.

     

Development of Cellulose Acetate Propionate Membrane for Separation of Ethanol and Ethyl tert-Butyl Ether Mixtures

Abstract

For pervaporation separation of ethanol and ethyl tert-butyl ether mixtures, a cellulose acetate propionate membrane was chosen as the experimental membrane because of its high selectivity and good mass fluxes. The properties of the membranes were evaluated by the pervaporation separation of mixtures of ethyl tert-butyl ether/ethanol and the sorption experiments. The experimental results showed that the selectivity and the permeates depend on the ethanol concentration in the feed and the experimental temperature. With increases of the ethanol weight fraction in the feed and the temperature, the total and partial mass fluxes increased. With respect to the temperature, ethanol mass flux obeys the Arrhenius equation. The selectivity of this membrane decreases as the temperature and the ethanol concentration in the feed increase. This membrane shows special characteristics at the azeotropic composition. In the vicinity of the azeotropic point, minimum values of ethanol concentration in the permeate and in sorption solution are obtained. The swelling ratios increase when temperature and the ethanol concentration in the feed are increasing. The ethanol concentration in the sorption solution is also influenced by the temperature and the mixture's composition. When the temperature increases, the sorption selectivity of the membrane decreases.     

Ethanol/water mixture pervaporation performance of b‐oriented silicalite‐1 membranes made by gel‐free secondary growth

b‐oriented silicalite‐1 membranes on porous silica supports were synthesized using gel‐free secondary growth. The porous silica supports were made by pressing crushed quartz fibers followed by sintering and polishing, and further modified by slip‐coating three layers of Stöber silica particles (1000, 350, and 50 nm). The b‐oriented seed layers were prepared by rubbing silicalite‐1 particles (2 μm × 0.8 μm × 3 μm along a‐, b‐, and c‐axis, respectively) after depositing a polymeric layer on the support. After silicalite‐1 seed deposition, a final coating of spherical silica particles was applied. Well‐intergrown, μm‐thick, b‐oriented membranes were obtained, which, after calcination, exhibited ethanol permselectivity in ethanol/water mixture pervaporation. At 60°C and for ～5 wt % ethanol/water mixtures, the best membrane exhibited overall pervaporation separation factor of 85 (corresponding to membrane intrinsic selectivity of 7.7) and total flux of 2.1 kg/(m²·h). This performance is comparable to the best performing MFI membranes reported in the literature. © 2015 American Institute of Chemical Engineers AIChE J, 62: 556–563, 2016     

生物基有机酸提取分离技术研究进展

有机酸如乳酸、琥珀酸、柠檬酸、衣康酸、苹果酸等在工业上有重要应用,随着食品、医药、化学合成等工业的发展,有机酸需求骤增,发酵生产有机酸逐渐成为生物工程领域中一个重要而成熟的分支,但存在产物浓度低、成分复杂、后处理量大等问题. 有机酸亲水性好、不同有机酸物理化学性质相近等特点导致产物分离提纯困难,成为制约生物法生产有机酸的瓶颈. 分离发酵液中有机酸的方法主要有沉淀法、萃取法、吸附法、离子交换法、膜分离法、电渗析法和酯化法等. 通过各种分离方法的对比,发现单一的分离方法很难有效分离有机酸. 集成不同分离方法,可简化分离工艺,分离效果更好. 此外,采用新型分离耦合技术,可实现有机酸的连续或半连续生产,是未来发酵行业的一个重要发展方向.     

Bioprocessing aspects of fuels and chemicals from biomass

This review deals with a recent development of biofuels and chemicals from biomass. Some of the grainbased biofuels and chemicals have already been in commercial operation, including fuel ethanol, biodiesel, 1.3-propanediol, polylactic acid (PLA) and polyhydroxy butyric acid/alkanoates (PHB/PHA). The next generation bioproducts will be based on lignocellulosics due to their abundance and to stabilize rising food prices. However, the technologies of handling biomass are yet in their infancy and suffer from low yield, low product titer, and low productivity. This review focuses on bioprocessing technologies for biofuels production: organic raw biomaterials available in Korea; volatile fatty acids platform, multi-stage continuous high cell density culture (MSC-HCDC), enrichment of fermentation broth by forward osmosis; various purification methods of pervaporation of ethanol, solvent extraction on succinic, lactic acids and reactive separation methods.     

Ethanol-Herstellung mit Bakterien

Ethanol production with bacteria . Strains of Saccharomyces cerevisiae have mostly been used for the production of ethanol from sugar by yeasts. Recently it was shown that the bacterium Zymomonas mobilis has some advantages compared to yeast for the production of industrial alcohol. Compared to traditional yeast fermentation, ethanol yield is about 5% higher than with yeast, since less sugar is incorporated into cell material by this bacterium. Like yeast, Zymomonas mobilis has remarkably high ethanol tolerance which enables the bacterium to produce ethanol concentrations of more than 13 vol.-% from sugar solutions of appropriate concentration. Investigations of the spectrum of lipids present have shown that this bacterium contains large quantities of hopanoids which are presumably of significance for the stabilization of cell membranes in the presence of ethanol. Since the cost of the sugar greatly influences the profitability fraction formed in the production of glucose syrup from wheat flour was investigated. It was shown that after enzymatic saccharification of this waste starch the glucose was efficiently fermented to ethanol by Zymomonas mobilis. It is planned to broaden the substrate spectrum of Zymomonas mobilis by gene cloning techniques so that in future pentoses, e. g. xylose or arabinose, can also be fermented to ethanol by this organism.     

Dehydration of ethanol/water mixtures by pervaporation using soluble polyimide membranes

A series of soluble polyimides derived from 3,3′,4,4′‐benzhydrol tetracarboxylic dianhydride (BHTDA) with various diamines such as 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene (BATB), 1,4‐bis(4‐aminophenoxy)‐2,5‐di‐tert‐butylbenzene (BADTB), and 2,2′‐dimethyl‐4,4′‐ bis(4‐aminophenoxy)biphenyl (DBAPB) were investigated for pervaporation separation of ethanol/water mixtures. Diamine structure effect on the pervaporation of 90 wt% aqueous ethanol solution through the BHTDA‐based polyimide membranes was studied. The separation factor ranked in the following order: BHTDA–DBAPB > BHTDA–BATB > BHTDA–BADTB. The increase in molecular volume for the substituted group in the polymer backbone increased the permeation rate. As the feed ethanol concentration increased, the permeation rate increased, while the water concentration in the permeate decreased for all polyimide membranes. The optimum pervaporation performance was obtained by the BHTDA–DBAPB membrane with a 90 wt% aqueous ethanol solution, giving a separation factor of 141, permeation rate of 255 g m^?2 h^?1 and 36 000 pervaporation separation index (PSI) value. Copyright © 2006 Society of Chemical Industry