疏水白炭黑填充PDMS-PA复合膜的渗透汽化性能

在聚二甲基硅氧烷(PDMS)层中引入疏水性气相法白炭黑,制成填充的硅橡胶-聚酰胺(PDMS-PA)多层复合膜;通过扫描电镜(SEM)观察了填充复合膜的截面形态,并考察了填充复合膜的渗透蒸发性能。结果发现,以PDMS层的质量为基准,填充少量的疏水性气相法白炭黑就能显著影响复合膜的渗透性能;填充复合膜的渗透通量随着白炭黑用量的增加而增加,而选择性则没有显著降低。在40℃、乙醇质量分数为5%的乙醇水溶液中,白炭黑质量分数为20%的PDMS-PA复合膜的渗透通量达到2 400 g/m2.h,比非填充复合膜的渗透通量高1倍多;而分离因子为7,稍低于非填充复合膜的8.5。此外,填充复合膜和非填充复合膜的分离性能对温度和浓度变化的依赖关系一致。     

不同交联剂对PDMS/PVDF纳滤膜溶剂回收性能的影响

以聚二甲基硅氧烷(PDMS)为分离层材料,聚偏氟乙烯(PVDF)超滤膜为底膜,采用正硅酸乙酯(TEOS)、苯基三甲氧基硅烷(PTMOS)、辛基三甲氧基硅烷(OTMOS)、γ-氨基丙基三乙氧基硅烷(APTEOS)4种不同的交联剂对PDMS进行交联,制备了PDMS/PVDF纳滤膜。采用接触角、红外谱图、扫描电镜等对膜的物理和化学结构进行了分析和表征。以大豆油/己烷混合油为实验体系,考察了压力和料液浓度对纳滤膜分离性能的影响。结果表明,纳滤膜的通量随压力线性增长,截留率初始随压力上升较快,随后增幅减慢而趋于稳定。随料液浓度的增加,纳滤膜的通量和截留率都有较大幅度的下降。相比较而言,以TEOS为交联剂所制得的纳滤膜分离性能最佳。大豆油/己烷混合油体系同水溶液体系的渗透特性类似,其渗透压可用van't Hoff方程计算。     

纳米白炭黑填充硅橡胶复合膜的制备与渗透汽化分离性能

制备以聚酯(PET)为支撑层,白炭黑填充的聚二甲基硅氧烷(PDMS107)为皮层的硅橡胶复合膜,并以乙醇水物系为料液,对比分析白炭黑增强硅橡胶复合膜的渗透蒸发分离性能,分离因子比空白膜有所提高,在乙醇浓度为3%～5%时,分离因子可达16.09,渗透通量为75.39 g/m2·h;测定填充白炭黑硅橡胶复合膜的拉伸强度,结果表明:拉伸强度可达1.828 MPa,相当于空白膜(0.368 MPa)的5倍.     

沸石填充硅橡胶渗透汽化膜的制备及其优先透醇性能研究

由ZSM-5沸石和聚二甲基硅氧烷(PDMS)制备超薄沸石填充PDMS复合膜,考察沸石填充量、沸石结构中硅铝比和操作温度对沸石填充硅橡胶膜渗透汽化性能的影响。结果表明,超薄复合膜的制备可以改善渗透通量小的缺陷。沸石填充量30%时分离因子最大;具有相同填充量的PDMS膜,硅铝比较大的填充膜,其分离因子和渗透通量均较高;随着操作温度的升高,复合膜分离因子先升高后降低,在50℃达到最大值,其渗透通量呈升高趋势。     

填充法改性PDMS膜及其对乙酸/水的渗透汽化分离性能

用CTAB-蒙脱石填充改性PDMS膜,运用XRD, SEM等手段表征了不同填充量的复合膜结构,证明有机柱撑蒙脱石与聚合物形成插层型复合物后,膜的热稳定性明显改善. 研究了填充膜对乙酸/水体系的渗透汽化分离性能,结果表明,随着温度的升高,渗透通量增大而分离因子降低,通量随填充量增加单调上升,分离因子随填充量增加先增大后降低,填充量为7.4(%, w)时达到最大值. 从膜的结构及其与组分的相互作用对填充膜中蒙脱石可能存在的渗透通道作用进行了探讨.     

沸石填充硅橡胶渗透汽化膜的制备及其优先透醇性能研究

由ZSM-5沸石和聚二甲基硅氧烷(PDMS)制备超薄沸石填充PDMS复合膜,考察沸石填充量、沸石结构中硅铝比和操作温度对沸石填充硅橡胶膜渗透汽化性能的影响。结果表明,超薄复合膜的制备可以改善渗透通量小的缺陷。沸石填充量30%时分离因子最大;具有相同填充量的PDMS膜,硅铝比较大的填充膜,其分离因子和渗透通量均较高;随着操作温度的升高,复合膜分离因子先升高后降低,在50℃达到最大值,其渗透通量呈升高趋势。     

SiO_2/PDMS/PVDF复合膜渗透蒸发回收煤化工废水中酚

采用PVDF中空纤维为基膜,以Si O_2填充PDMS溶液为涂覆液,进行动态负压涂覆,制备Si O_2/PDMS/PVDF复合膜材料,回收处理煤化工废水中的酚。通过扫描电镜(SEM)、能量弥散X射线能谱仪(EDS)及接触角测试仪对Si O_2/PDMS/PVDF复合膜材料进行了表征,并研究了Si O_2质量浓度、涂覆时间对Si O_2/PDMS/PVDF复合膜材料渗透蒸发性能的影响。当Si O_2填充质量浓度占PDMS质量浓度的12%,涂覆时间60 min条件下,制得的Si O_2/PDMS/PVDF复合膜具有最佳的渗透蒸发性能。保持进水温度50℃,膜后压力50 k Pa,进水流速10 L/h,酚通量达到7.16 g/(m~2·h),分离因子为4.26。     

4nm孔径陶瓷膜去除水中钙离子研究

采用孔径为4 nm的陶瓷膜去除水中的Ca2+,考察了不同Ca2+含量、跨膜压差、溶液pH和温度对陶瓷膜渗透通量和Ca2+截留率随时间的变化情况。结果表明,溶液中的Ca2+含量越低,膜渗透通量越高,Ca2+截留率也越高;跨膜压差升高,膜渗透通量增大,Ca2+截留率降低;降低溶液pH及升高温度能够提高膜渗透通量及对Ca2+的截留率。对Ca2+的质量浓度为10 mg/L的水溶液,在TMP为0.1 MPa、溶液pH为3、温度为50℃时、孔径为4 nm陶瓷膜渗透通量稳定在80 L/(m2.h),Ca2+截留率为85%左右。研究结果可为金属离子微污染水的净化提供方法。     

正渗透处理模拟印染废水的性能研究

实验以1 mol/L的NaCl溶液为汲取液,以活性染料印染废水、分散染料印染废水为原料液,探究不同染料类型、膜朝向及温度对正渗透性能的影响,以及不同情况下的膜污染情况。正渗透处理两种染料都有很高的水通量;AL-FS模式初始水通量为14.79 L/(m²·h),COD截留率为98.8%,色度为99.2%。AL-DS模式下分别为17.82L/(m²·h)、93.2%和93.9%;温度由15℃升高到35℃,水通量增加了5.6%,COD截留率降低了1.1%,色度截留率降低了1.2%;超声清洗后AL-FS模式下恢复率为94.3%,AL-DS模式下为91.2%。AL-FS模式优于AL-DS,水通量随温度的升高而升高,膜清洗水通量恢复率较高。     

PDMS/ZSM-5膜的制备及渗透汽化分离水中乙酸正丁酯和乙酸乙酯

为探究出适合分离水中的乙酸正丁酯和乙酸乙酯的新型渗透汽化膜材料,选用沸石ZSM-5 对聚二甲基硅氧烷(PDMS)材料进行填充改性,以聚偏氟乙烯(PVDF)为支撑层,采用刮涂法制备PDMS/ZSM-5/PVDF复合膜渗透汽化分离水中的乙酸正丁酯和乙酸乙酯。采用SEM、接触角测量仪、FTIR、TGA和XRD等对膜材料物理化学性能进行表征,考察了膜材料的溶胀行为及渗透汽化性能。结果表明,ZSM-5在 PDMS 膜中分散均匀,且没有发生化学作用,并提高了膜材料的疏水性和热稳定性。随着ZSM-5添加量的增加,膜在乙酸正丁酯和乙酸乙酯的溶胀度和待分离组分在膜材料中的扩散速率不断增加。随着进料浓度和温度的增加,渗透通量不断增大,分离因子先增大后减小。随着ZSM-5在PDMS/ZSM-5/PVDF复合膜中含量的增加,总渗透通量增加,而分离因子呈现先增加后减小的趋势。当添加量为10%（质量）时,分离因子达到最大值。对于乙酸正丁酯/水体系,渗透通量和分离因子最大值分别为319 g·m ^-2·h ^-1和131;而对于乙酸乙酯/水体系,渗透通量和分离因子最大值分别为1385 g·m ^-2·h ^-1和121。     

硅橡胶膜用于植物油/己烷胶团中溶剂回收的研究

Traditional solvent recovery in the extraction step of edible oil processing is distillation, which consumes large amounts of energy. If the distillation is replaced by membrane process, the energy consumption can be reduced greatly. In this work, two kinds of membrane, PDMS (polydimethylsiloxane) composite membrane and Zeolite filled PDMS membrane were prepared, in which asymmetric microporous PVDF (polyvinylidenefluoride) membrane prepared with phase inversion method was functioned as the microporous supporting layer in the flat-plate composite membrane. The different function compositions of the PDMS/PVDF com-posite membranes were characterized by reflection Fourier transform infrared (FTIR) spectroscopy. The surface and section of PDMS/PVDF composite membranes were investigated by scanning electron microscope (SEM). The PDMS NF (nanofiltration) membranes were then applied in the recovery of hexane from soybean oil/hexane miscellas (1︰3, mass ratio). The effects of pres-sure (0.5-1.5 MPa), cross-linking temperature and PDMS layer thickness on membrane performances were investigated. The results indicated that both two kinds of NF membranes were promising for solvent recovery, and zeolite filled in PDMS NF membrane could enhance the separation performance.     

Degumming of crude soybean oil by ultrafiltration using polymeric membranes

In this study, the ability of two ultrafiltration polymeric membranes to perform the degumming of a crude soybean oil/hexane mixture is tested. The performance of both membranes is defined in terms of their permeation flux, permeate color, and rejection of phospholipids. One of the membranes was synthesized in our laboratories from polyvinylidenefluoride (PVDF); the other one is a commercially available membrane made of polyimide. The degumming experiments were done in a stirred dead-end ultrafiltration cell pressurized with N₂. Results show that tested membranes are suitable for removing phospholipids from the crude oil/hexane miscella in the range of temperature and transmembrane pressure utilized in this work. Both membranes have high selectivity regarding phospholipids and produce a moderate reduction in permeate color. The PVDF membrane gives permeate fluxes up to threefold larger than those obtained with polyimide membrane at the same operational conditions, making the former more suitable for use at industrial scale.     

支撑层对硅橡胶复合膜渗透汽化分离性能的影响

引言 为了扩大渗透汽化技术的应用领域,科研工作者需要进一步增强渗透汽化膜的分离性能.从工业化的观点而言,用于实际应用的渗透汽化膜大多是复合膜,它由选择层(或分离层)和支撑层组成.一般认为,选择层决定着复合膜的选择性和通量,支撑层起支撑和机械稳定作用.Nijhuis[1]在从甲苯-水体系中分离甲苯的过程中对均质膜和以聚砜为支撑层的复合膜的分离性能进行了比较;Sturken[2]分别用聚醚酰亚胺和聚偏氟乙烯为支撑层的硅橡胶膜从二氯乙烷-水体系中提取二氯乙烷,他们得到了相同的结论:支撑层的影响可以忽略.然而Scholz[3],Heinzelmann[4],Rautenbach[5],Borges[6],Vankelecom[7],Farooq[8],Lipnizki[9]等均在各自研究中发现,由于基膜和分离层的物理化学性质以及制膜方法等众多因素的存在使得支撑层在一定程度上影响复合膜的分离性能;Feng[10]对均质硅橡胶膜和有微孔支撑层的硅橡胶复合膜的分离性能进行了比较,发现均质硅橡胶膜优先透过异丙醇,而有微孔亲水性支撑层的硅橡胶复合膜则优先透过水,这表明在一定的情况下,支撑层甚至起主导作用并能够决定复合膜的分离性能.因此,通过系统研究以不同多孔材料为支撑层的复合膜对有机物-水溶液的分离性能的影响,能够找到最优的复合膜支撑层,从而能够提高复合膜的分离性能.然而,至今关于支撑层对渗透汽化膜分离性能影响的系统研究仍相当少.     

Modeling of Nanofiltration Process for Solvent Recovery from Aqueous Ethanol Solution of Soybean Isoflavones

Abstract

In this paper, the feasibility of recovering the solvent from the aqueous ethanol solution of soybean isoflavones with nanofiltration (NF) was studied. Five commercially available polymeric NF membranes were employed and STARMEM? 122 showed acceptable flux and high retention. The central composite design (CCD) of the response surface methodology (RSM) was applied to model the effects of temperature, pressure, and feed concentration on the permeate flux and the total soybean isoflavone retention. The results indicate that the developed models were in good agreement with the experimental results and they can be used to predict this NF process.     

Solvent recovery and partial deacidification of vegetable oils by membrane technology

A process is described using nanofiltration membranes for the partial de-solventizing and de-acidification of hexane-extracted vegetable oils. The model miscella (containing 20% soybean oil with 2% free fatty acids) was concentrated to 45% oil at an average flux of 91/m²h at 2.76 MPa and 24°C. The permeate from this stage was re-concentrated 9-fold at an average flux of 201/m²h. The net recovery of oil was more than 99%, with a simultaneous 40% reduction of FFA and over 50% reduction in the energy required for evaporation of hexane.     

Separation of oil constituents in organic solvents using polymeric membranes

Different types of commercial nonporous (reverse osmosis and gas separation) polymeric membranes were screened for their abilities to separate FFA, MG, DG, and TG from a lipase hydrolysate of high-oleic sunflower oil after diluting it with organic solvents (ethanol and hexane). Cellulose acetate (CA) (NIR-1698) membrane gave the largest difference in rejection between FFA and glycerides and high flux in oil/ethanol mixtures. In the hexane system, the values of permeate flux and rejection were generally lower than those in the ethanol system. The silicone-polyimide composite membrane (NTGS-2100) gave the highest flux and rejections of solutes (70.2% for FFA, 94.4% for TG) in oil/hexane mixtures. In the ethanol system with the CA membrane, TG had the highest rejection (98%) followed by DG (90%) and MG and FFA (50–70%) when the oil concentration was varied from 6.3 to 45.8%. A discontinuous diafiltration process (16 batches) using the CA membrane with ethanol changed the composition of the oil from 31∶28∶9∶32 TG/DG/MG/FFA to 65∶30∶1∶4. The results of this study showed that oil constituents can be separated in suitable solvents using appropriate nonporous membranes.     

Vegetable oil degumming with polyimide and polyvinylidenefluoride ultrafiltration membranes

The removal of phospholipids (‘degumming’) is the first step in the process of refining crude vegetable oil. Membrane separation has been often proposed as an alternative to the conventional procedure (water degumming). Until now, the instability of polymeric membranes in organic solvents has been the major obstacle in applying this technique. In this work, a local synthesized polyvinylidenefluoride (PVDF) and a commercial polyimide (PI) membrane were evaluated for their flux and rejection properties during degumming of soybean oil in a laboratory‐scale cross‐flow ultrafiltration cell. Degumming experiments were done at different temperatures and feed flows, keeping constant both the feed concentration and the transmembrane pressure. PVDF and PI membranes gave selectivity values and permeate color that did not differ significantly from each other. Retention coefficients larger than 98% were obtained in all cases. In every experiment, a decline in permeate flux with time occurred at the beginning of the degumming process. By increasing the feed rate, a higher permeate flux was obtained. The results show that the PVDF membrane had a higher productivity than the PI one. Copyright © 2003 Society of Chemical Industry     

Membrane processing of crude vegetable oils: Pilot plant scale remoyal of solvent from oil miscellas

The recovery of solvents used in the extraction step of edible oil processing is required for economical, environmental, and safety considerations. The miscella (mixture of extracted oil and solvent) exits the extractor at 70 to 75 wt% solvent content. Currently, the solvent is recovered by distillation. This paper reports the results of a study on separation of vegetable oils from commercial extraction solvents using various types of Reverse Osmosis (RO) and Ultrafiltration (UF) membranes. Solvent permeation rates and separation performances of various RO and UF membranes were determined by using ethanol, isopropyl alcohol and hexane as the solvents. One membrane exhibited a flux of 200 GFD (ethanol) with 1% oil remaining in the permeate. However, hexane rapidly deteriorated all but one of the membranes tested. The membrane that was compatible with hexane had a low flux and unacceptably low oil retention. Industrial-scale membranes were also evaluated in pilot plant trials. A hexane separation was attempted with a hollow-fiber membrane unit, and it was noted that the pores of the fibers swelled almost closed. Some of the commercially available membranes selectively removed solvent (ethanol or isopropanol) from the edible oil miscellas with reasonable flow rates. The research reported has shown that membranes manufactured from polyamide were the least affected by hexane. Fluxes achieved during solvent-oil separations were increased by increases in either temperature or pressure and decreased by increases in oil concentration in the feed. The processing temperature affected the percentage of oil in solution in either ethanol or isopropanol as well as the viscosity of the feed. Both of these factors in turn influenced the flux achieved. Approximately 2 trillion Btu/yr could be saved using a hybrid membrane system to recover solvents used in the extraction step of crude oil production. Studies to date report marginal success. The development of hexane-resistant membranes may make this application viable.     

Influence of colloidal fouling and feed water recovery on salt rejection of RO and NF membranes

The influence of colloidal fouling and feed water recovery (or concentration factor, CF) on salt rejection of thin-film composite reverse osmosis (RO) and nanofiltration (NF) membranes was investigated. Fouling experiments were carried out using a laboratory-scale crossflow test unit with continuous permeate disposal to simulate the CF and recovery as commonly observed in full-scale RO/NF systems. For feed waters containing only salt (NaCl), permeate flux declined linearly as CF was increased and salt rejection was nearly constant for both RO and NF membranes. On the other hand, a sharp decrease in permeate flux and significant decline in salt rejection with increasing CF were observed under conditions where colloidal fouling takes place. For both RO and NF membranes, the marked permeate flux decline was attributed to the so-called “cake-enhanced osmotic pressure”. The decline in salt rejection when colloidal fouling predominated was much more substantial for NF than for RO membranes. In all cases, the decline in salt rejection was higher under conditions of more severe colloidal fouling, namely at higher ionic strength and initial permeate flux.