Performance of Commercial and Laboratory Membranes for Recovering Bioethanol from Fermentation Broth by Thermopervaporation

A poly[1-(trimethylsilyl)-1-propyne] membrane was studied in a thermopervaporation process for ethanol recovery from fermentation media. Four commercial composite membranes based on polysiloxanes (Pervap 4060, Pervatech PDMS, PolyAn, and MDK-3) were studied for comparison. The dependences of the permeate flux, permeate concentration, separation factor, and pervaporation separation index on the temperature of the feed mixture (5 wt % ethanol in water) were obtained. The maximal values of the ethanol concentration in the permeate (35 wt %) and separation factor (10.2) were obtained for the poly[1-(trimethylsilyl)-1-propyne] membrane, whereas the PolyAn membrane provided the highest permeate flux (5.4 kg m^–2 h^–1). The ethanol/ water separation factor for the systems studied has a maximum at 60°С; this temperature of the feed mixture is optimum for recovering ethanol from aqueous media by thermopervaporation. The existing membranes based on polysiloxanes show low ethanol–water selectivity (less than 1). Poly[1-(trimethylsilyl)-1-propyne] membranes are the most promising for recovering bioethanol from fermentation mixtures by thermopervaporation, because they showed the highest selectivity to ethanol.     

Water–alcohol separation by pervaporation through chemically modified poly(amidesulfonamide)s

Five N-alkylated derivatives of a poly(amidesulfonamide) polymerized from N,N′-bis-4-aminophenylsulfonyl 1,3-diaminopropane and isophthaloyl chloride were synthesized. The new polymeric materials were used to prepare nonporous symmetric membranes. The membranes were characterized by IR spectroscopy, sorption measurements and wide-angle X-ray diffraction. During the pervaporation of 10% aqueous solutions of methanol, ethanol, propan-1-ol and propan-2-ol, membranes made from the parent and modified poly(amidesulfonamide)s were preferentially permeable to water and their separation factors were mainly dependent on the molecular weight of the permeant. By introducing an alkyl pending group to the backbone of the polymer, all modified membranes exhibited an enhancement in flux rate and a variation in separation factor in the pervaporation of aqueous alcohols. In the dehydration of ethanol, several modified membranes possessed separation characteristics that appeared to be superior to that of the parent membrane.     

Membrane separations in ethanol recovery: an analysis of two applications of hyperfiltration

With further development, membrane separations have the potential to contribute to process improvements, especially for energy conservation, in ethanol fuel production. Two applications of hyperfiltration (reverse osmosis) in the recovery and purification of ethanol from fermentation beer are defined and analyzed for energy requirements and economics. These analyses are performed for a complete plant, including a recovery subprocess with and without the use of hyperfiltration. The hyperfiltration processes are designed using existing data for available membranes and hypothetical data for advanced membranes. The overall purpose of these analyses is to identify process modifications and membrane-related research that can contribute to decreasing the energy requirements of ethanol fuel production.

In one application, hyperfiltration is used in a lignocellulose-to-ethanol plant to preconcentrate low-proof (2 wt% beer prior to further purification by fractional and azeotropic distillation. This application requires ethanol-rejecting membranes, which are developed. When lignocellulose is used as a feedstock for ethanol production, a low-proof beer is usually produced. The energy requirements of ethanol recovery from low-proof beer by conventional distillation exceed the energy content of ethanol and frequently preclude the feasibility of producing ethanol from lignocellulose. The use of hyperfiltration to preconcentrate ethanol can significantly reduce the energy requirements of ethanol recovery from low-proof beer. The analyses are based upon process designs using existing and hypothetical membranes. This application is found to conserve 19 to 20 GJ/m³ (67,000 to 72,000 Btu/gal) of anhydrous ethanol as compared to only fractional and azeotropic distillation and to be economically competitive (with a 2 to 4% lower price). The analysis indicates that this application of hyperfiltration is promising and that future research should be devoted to increasing flux (while maintaining or improving ethanol rejection) and to assessing and improving membrane life.

In the other application, hyperfiltration is used to dehydrate high-proof (93 to 95 wt%) ethanol in a corn-to-ethanol plant. Ethanol dehydration is an energy-intensive separation, generally requiring 2.0 to 2.8 GJ/m³ (7,000 to 10,000 Btu/gal) of anhydrous ethanol. This application was designed based upon hypothetical, water-rejecting hyperfiltration membranes, which are not pres ently developed. Although the hyperfiltration process is found to conserve 0.8 GJ/m³ (2,900 Btu/gal) of anhydrous ethanol, it is not found to have an economic advantage over a conventional ethanol purification process. Therefore, this application is not found to be promising and little incentive exists for performing research aimed at development of a water-rejecting membrane for the dehydration of ethanol by hyperfiltration.

Finally, thoughts regarding the use of membrane separations in the chemical/fuel industry are presented.     

QPVA/SMPVA自组装聚离子复合物膜对乙醇中水的渗透汽化性能研究

聚乙烯醇-N,N-二甲基-3-氨基-2-羟基丙基醚的季铵化产物(quaternized PVA-N,N-dimethyl-3-amido-2-hydroxy-propyl ether,简称QPVA)与硫酸单酯化聚乙烯醇(sulphate monoesterified polyvinyl alcohol,简称SMPVA)自组装聚离子复合物(self-assembled polyion complex,简称SAPIC),自组装溶液pH=7时,膜在水中的溶胀度最小.SAPIC均质膜在60vol%～90vol%(间隔10%)乙醇中浸泡48h,观察不同浓度乙醇中水在均质膜中的扩散行为.SAPIC均质膜在95%乙醇中浸泡48h,在20～120℃(间隔20℃)下,观察乙醇中水在膜中的汽化行为.应用FTIR技术跟踪两类吸水膜,确认了水和膜内聚离子基的吸收.改变浓度的一维(1D)和二维(2D)FTIR相关分析表明,渗透过程中形成两种状态的水,游离水和缔合水,随乙醇中水的增加游离水优先变化.游离水靠静电作用与膜内聚离子基优先缔合形成缔合水;改变温度的1D-和2D-FTIR显示,汽化过程中也存在两种状态的水,游离水和缔合水,随温度升高游离水优先变化.游离水较缔合水优先挥发,脱离膜与乙醇分离.同时测定了SAPIC复合膜对95%乙醇/水的渗透汽化性能,分离因子870,渗透通量1400g/(m2·h).为SAPIC膜用于乙醇脱水的渗透汽化过程研究提供了一种简便的方法.     

γ-Al2O3柔性纳米纤维膜的制备及机械性能

以氯化铝和异丙醇铝为原料, 水和乙醇为溶剂, 通过溶胶凝胶结合静电纺丝法制备了柔性γ-Al2O3纳米纤维膜.表征了纤维膜的形貌和机械性质, 并研究了纤维膜的形成过程.组成纤维膜的纤维直径均匀, 平均直径188 nm, 纤维由粒径在15~30 nm的纳米颗粒组成且表面光滑.制备的纤维膜具有较好的柔性及抗拉强度(1.01 MPa).     

渗透汽化优先透醇分离膜

20世纪70年代的能源危机促使了人们对可再生能源-发酵法制备乙醇与节能分离工艺的探求。渗透汽化膜分离技术作为一种新兴的膜分离技术,具有分离效率高、低能耗、易于和发酵装置耦合、易于与其它分离方法联用等显著优点,特别适用于乙醇/水等恒沸混合物体系的分离。本文简要介绍了渗透汽化优先透醇膜的研究背景,总结并分析了用于指导膜材料选择的理论,详细介绍了用于制备优先透醇膜的含硅聚合物、含氟聚合物、有机/无机复合膜材料以及其他聚合物等膜材料的的结构特点、改性方法及膜材料分子结构与渗透汽化性能间的关系,并对不同膜材料对乙醇/水的渗透汽化分离性能进行了总结比较,在此基础上总结了目前渗透汽化乙醇/水分离膜存在的问题,并对其未来的研究方向和发展前景进行了展望。     

Isolation and Purification of Fucoxanthin from Brown Seaweed Sargassum horneri Using Open ODS Column Chromatography and Ethanol Precipitation

As an abundant marine xanthophyll, fucoxanthin (FX) exhibits a broad range of biological activities. The preparation of high-purity FX is in great demand, however, most of the available methods require organic solvents which cannot meet the green chemistry standard. In the present study, a simple and efficient purification approach for the purification of FX from the brown seaweed Sargassum horneri was carried out. The FX-rich ethanol extract was isolated by octadecylsilyl (ODS) column chromatography using ethanol–water solvent as a gradient eluent. The overwhelming majority of FX was successfully eluted by the ethanol–water mixture (9:1, v/v), with a recovery rate of 95.36%. A parametric study was performed to optimize the aqueous ethanol precipitation process by investigating the effects on the purity and recovery of FX. Under the optimal conditions, the purity of FX was 91.07%, and the recovery rate was 74.98%. Collectively, the eco-friendly method was cost-efficient for the purification of FX. The developed method provides a potential approach for the large-scale production of fucoxanthin from the brown seaweed Sargassum horneri.     

Evaluation of PTMSP membranes in achieving enhanced ethanol removal from fermentations by pervaporation

The use of membrane processes for the recovery of fermentation products has been gaining increased acceptance in recent years. Pervaporation has been studied in the past as a process for simultaneous fermentation and recovery of volatile products such as ethanol and butanol. However, membrane fouling and low permeate fluxes have imposed limitations on the effectiveness of the process. In this study, we characterize the performance of a substituted polyacetylene membrane, poly[(l-trimethylsilyl)-l-propyne] (PTMSP), in the recovery of ethanol from aqueous mixtures and fermentation broths. Pervaporation using PTMSP membranes shows a distinct advantage over conventional poly(dimethyl siloxane) (PDMS) membranes in ethanol removal. The flux with PTMSP is about threefold higher and the concentration factor is about twofold higher than the corresponding performance achieved with PDMS under similar conditions. The performance of PTMSP with fermentation broths shows a reduction in both flux and concentration factor relative to ethanol-water mixtures. However, the PTMSP membranes indicate initial promise of increased fouling resistance in operation with cell-containing fermentation broths.     

γ-Al2O3柔性纳米纤维膜的制备及机械性能

以氯化铝和异丙醇铝为原料, 水和乙醇为溶剂, 通过溶胶凝胶结合静电纺丝法制备了柔性γ-Al₂O₃纳米纤维膜. 表征了纤维膜的形貌和机械性质, 并研究了纤维膜的形成过程. 组成纤维膜的纤维直径均匀, 平均直径188 nm, 纤维由粒径在15~30 nm的纳米颗粒组成且表面光滑. 制备的纤维膜具有较好的柔性及抗拉强度(1.01 MPa).     

Development of an ethanol-selective optode membrane based on a reversible chemical recognition process

Lipophilic trifluoroacetophenone derivatives incorporated in plasticized PVC membranes are able to selectively extract water and alcohols from the sample solution into the organic membrane phase, reversibly forming hydrates and hemi-acetals, respectively. Since this is accompanied by a change in the absorption spectrum of the acetophenone isologue, the chemical recognition process can directly be translated into an optical signal. With N-acetyl-N-dodecyl-4-trifluoroacetylaniline (ETH 6022) as the electrically neutral, lipophilized carrier ethanol can be determined from 0.5 to 35% (v/v) in aqueous solutions. The calibration curve for different ethanol-water mixtures shows a good correlation with the mathematically derived formalism and thus confirms the theoretically expected behavior. Besides high reproducibility of the optical signals, very short response times of less than 30 s were realized. The optode membrane presented exhibits a preference for ethanol compared to water by a factor greater than 11. The selectivities for several primary alcohols, such as methanol, ethanol, 1-propanol and 1-n-butanol, are comparable, but isopropanol and tert.-butanol are rejected by a factor of about 10. The alcohol concentration in different beverages was determined to evaluate the reliability of the system. The values obtained for wine, beer and different spirits show an excellent correlation with those obtained by a conventional approach involving distillation and density measurements. A residual standard deviation of ± 0.27% (v/v) over the 0.7–40% (v/v) range was found.     

Synthesis,characterization and separation properties of a composite mordenite/ZSM-5/chabazite hydrophilic membrane

Composite mordenite/ZSM5/chabazite membranes were prepared on α-alumina tubular supports by in situ liquid phase hydrothermal synthesis. The membranes obtained were approximately 10 μm thick and were characterized by XRD, SEM and EPMA, as well as permeation of single gases (N₂ and n-butane). The membranes were then used to separate ternary mixtures, containing water, alcohol (methanol, ethanol or propanol), and a permanent gas (O₂). Water permeated faster because of the hydrophilic character of the composite membrane, with water/propanol selectivities as high as 149. The influence of operating conditions (temperature, pressure and feed composition) on the separation performance was analyzed. Also, the behavior of this composite zeolite membrane was compared with that of pure silicalite and ZSM5 membranes, and the differences observed are discussed in terms of relative organophilicity/hydrophilicity of the zeolites involved.     

Studies on polymeric nanofiltration-based water softening and the effect of anion properties on the softening process

The water softening capability of a polymeric NF-based membrane is investigated in a cross-flow mode. Also, the effects of the anion properties binding to the cation in the feed water are investigated. The softening process is monitored using parameters such as apparent rejection, softening factor, relative softened water recovery and the relative softened water purity to assess the effects of the operating conditions on the softening process. Moreover, a combined solution–diffusion/film theory (SDFT) model reduced to Gupta’s model (dilute solutions) is employed to extract three (3) parameters: the hydraulic permeability (L_p), the reflection coefficients (σ) and the solute permeability (ω) which characterizes the membrane. Preliminary, results show the membrane to possess good water softening properties while the charge, size, and the shape of the anions each play a vital role in the water softening process. Thus, the above protocol provides techniques for monitoring, characterizing and selecting potential polymeric membranes for water softening applications.     

Hydrothermal pretreatment conditions to enhance ethanol production from poplar biomass

Pretreatment has been recognized as a key step in enzyme-based conversion processes of lignocellulose biomass to ethanol. The aim of this study is to evaluate two hydrothermal pretreatments (steam explosion and liquid hot water) to enhance ethanol production from poplar (Populus nigra) biomass by a simultaneous saccharification and fermentation (SSF) process. The composition of liquid and solid fractions obtained after pretreatment, enzymatic digestibility, and ethanol production of poplar biomass pretreated at different experimental conditions was analyzed. The best results were obtained in steam explosion pretreatment at 210°C and 4 min, taking into account cellulose recovery above 95%, enzymatic hydrolysis yield of about 60%, SSF yield of 60% of theoretical, and 41% xylose recovery in the liquid fraction. Large particles can be used for poplar biomass in both pretreatments, since no significant effect of particle size on enzymatic hydrolysis and SSF was obtained.     

Separation of ethanol—water mixtures by pervaporation through thin,composite membranes

This paper reports on the separation of ethanol—water mixtures using pervaporation for several membrane types. The FT30 and RC100 membranes pass ethanol selectively at feed concentrations similar to fermentation beers, and the FT30 membrane continues to pass ethanol selectively at higher ethanol feed concentrations. As the ethanol concentration in the feed increases, the ethanol selectivity of both the FT30 and RC100 membranes decreases; near the ethanol—water azeotrope, both membranes pass water selectively. At lower ethanol concentrations, the selectivity of the FT30 membrane increases as the feed temperature increases above 23°C.     

Nanostructured polyelectrolyte-surfactant complex pervaporation membranes for ethanol recovery: the relationship between the membrane structure and separation performance

Polyelectrolyte-surfactant complexes (PESCs) were fabricated through the interaction of poly(acrylic acid) and four different cationic surfactants or their mixtures.PESC membranes were prepared by solution casting method and were applied in ethanol recovery from aqueous solution via pervaporation.Elemental analysis (EA),Fourier transform infrared spectroscopy (FTIR),water contact angle (CA) measurement,differential scanning calorimetry (DSC) and X-ray scattering were employed to characterize the composition,structure and properties of PESCs.The results reveal that the investigated PESCs are similar in hydrophobicity but different in hierarchical nanostructures.In separating 5 wt％ ethanol/water mixture,PESC membranes with high crystallinity will have both low flux and ethanol selectivity because of the high packing density and low permeability of crystalline regions.Meanwhile,the hierarchical nanostructures of PESC membranes change under pervaporation environment as was revealed by in situ synchrotron radiation X-ray scattering measurement.That is,the crystalline region could melt at high temperature in swelling state,thus consequently enhancing the ethanol selectivity.     

Hard elastic polypropylene-nature,internal friction,and surface energy

Tensile tests were performed at low temperatures, both in liquid and gaseous nitrogen and also at room temperature, using a series of polypropylene (PP) samples with various technological parameters. Crystalline morphology was also measured for film samples. The results show that liquid nitrogen or solvents can induce materials to create hard elasticity, which strongly supports the bulk-microfibril composite structure proposed by Baer et al., and suggests that the nature of hard elasticity is essentially a craze phenomenon. Three conditions of forming hard elastic structure are discussed. The results from long-time relaxation of hard elastic polypropylene (HEPP) and the improvement of necking of the PP samples in ethanol and water suggest that elastic recovery is reduced by internal friction. The relation between morphology and elasticity is also discussed. The methods of estimating the contribution of surface energy in the recovery process and the increase of surface energy of HEPP during the stretching process are provided. The contribution of surface energy to recovery is about 43% to 66% in the first cycle and after relaxation for 1 h at a maximum of 50% strain. The increased surface energy during stretching is about twice the recovery work done by surface energy.     

Interrelation between preparation conditions and structure of asymmetric membranes based on poly((diphenyl oxide amido)-N-phenylphthalimide)

Morphology of asymmetric membranes based on poly((diphenyl oxide amido)-N-phenylphthalimide) was studied by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The effect of preparation conditions on the morphology and transport properties of the membranes was investigated. The test membranes were prepared by the phase-inversion method under the conditions of “wet” casting in the polymer-solvent (N-methyl pyrrolidone)-nonsolvent (water, ethanol, 2-propanol, or aqueous alcohol solutions) systems. Feed casting solutions with a concentration of 10–14 wt %, including those containing a weak nonsolvent (ethyl acetate) were used. A comparative analysis of the structural features and water permeability of the test membranes allows the conclusion that some types of membranes can be used in nanofiltration processes.     

Efficient Protocol for Large-Scale Purification of Naringin with High Recovery from Fructus aurantii by Macroporous Resin Column Chromatography and HSCCC

Several kinds of resins were investigated in the first step and D101 macroporous resin was selected for cleaning-up naringin (NAR), a major flavonoid glycoside from Fructus aurantii. In the subsequent column chromatography, 10% aqueous ethanol was first used to elute the column to remove the undesired constituents and 70% aqueous ethanol was used to elute the target. The content of NAR was 57.1% with 95.7% recovery in this process. In the second step, the obtained crude sample was directly isolated by high-speed counter-current chromatography (HSCCC) with a two-phase solvent system composed of ethyl acetate–n-butanol–water at a volume ratio of 2: 0.8: 3.2 (v/v/v), and 331 mg NAR with 98.3% purity was obtained from 600 mg crude extract in only one run. The recovery of the compound in this step was 95.0%. Thus, the total recovery of NAR was 90.9% after the two step purification. The established protocol for large-scale isolation and separation of NAR with high purity and recovery from F. aurantii was simple, efficient, and suitable for pharmace- utical and commercial use.     

Hydrophilic-hydrophobic interpenetrating polymer networks and dicyanate-based semi-ipn materials

Hydrophilic-hydrophobic IPN materials of poly(acrylic acid)-poly(styrene-co-acrylonitrile) were synthesized and the pervaporation characteristics of the IPN membranes were evaluated for the separation of ethanol/water mixture. Hydrophilic-hydrophobic IPN materials of polyurethane-polystyrene were synthesized and the blood compatibility of the IPN's were measured for the biomedical application. Dicyanate-engineering plastics semi-IPN's were prepared and the morphology and mechanical properties were evaluated for the high temperature composite matrix materials.     

Influence of drying method on morphology and properties of asymmetric cellulose hollow fiber membrane

Using a dry/wet spinning process, asymmetric cellulose hollow fiber membranes (CHFM) were prepared from a dope composed of cellulose/N-methylmorpholine-N-oxide/water. The formation mechanism for the finger-like macrovoids at the inner portion of as-spun fibers was explained. Naturally drying and three solvent exchange drying methods were tried to investigate their influence on morphology and properties of CHFM. It was found that the ethanol–hexane exchange drying was an appropriate method to minimize morphology change of the as-spun CHFM, whereas the naturally drying caused the greatest shrinkage of the fibers that made the porous membrane become dense. As a result, CHFM from ethanol–hexane exchange drying performed the highest gas permeation rate but gas permeation of the naturally dried membrane could not be detectable. The resultant CHFM from the ethanol–hexane exchange drying also showed acceptable mechanical properties, thus it was proposed to be an appropriate method for gas separation purpose. The experimental results supported the proposed drying mechanism of CHFM. The free water would evaporate or be replaced by a solvent that subsequently would evaporate but the bonded water would remain in the membrane. What dominated the changes of membrane morphology during drying should be the molecular affinities of cellulose–water, water–solvent and solvent–solvent.