Separation Performance and Stability of PVDF-co-HFP/Alkylphosphonium Dicyanamide Ionic Liquid Gel-Based Membrane in Pervaporative Separation of 1-Butanol

In this study, a membrane prepared by gelling trihexyl(tetradecyl)phosphonium dicyanamide ionic liquid (IL) with poly(vinylidene fluoride-co-hexafluoropropylene) copolymer is tested for performance and stability in pervaporative separation of 1-butanol. Feed concentration and temperature affected separation performance mainly through plasticizing and swelling effects in the membrane which promoted liquid-like transport behavior. Microscale IL-in-polymer networks formed within the gel matrix where the neat IL possibly functioned as conventional liquid membrane. IL gelling has significantly improved the membrane operational lifetime to ～80 h, a significant improvement on the ～10 h shown by a simple supported IL membrane counterpart. The instability was consequent to polymer-IL incompatibility and so further investigations are underway to resolve this issue.     

硅烷分子接枝ASZ陶瓷膜处理水中苯酚的研究

为了提高陶瓷膜的疏水性,本研究选择硅烷分子对氧化铝支撑氧化锆(ASZ)陶瓷膜进行接枝改性。考察接枝硅烷分子结构(反应基团类型)、碳链长度、硅烷分子中含氟和十七氟癸基三乙氧基硅烷(F17C8OEt3)浓度对疏水性的影响。利用SEM-EDS、FTIR、TGA和接触角测量仪对接枝改性ASZ膜或金属氧化物进行表征。研究结果表明,硅烷分子接枝ASZ膜的疏水性能显著提高,接触角从29°增加到136°。FT-IR、TGA结果证明了硅烷分子成功接枝在ASZ膜或金属氧化物上。利用F17C8OEt3硅烷分子接枝改性ASZ管式膜构建渗透蒸发系统处理水溶液中苯酚,实验结果表明,当进料液中苯酚浓度从672.3 mg/L增加至3 844.6 mg/L时,去除的苯酚浓度从29.1 mg/L增加到407.4mg/L;进料液的温度升高到80℃,去除的苯酚是进料液温度为40℃时的5倍。     

ZIF-8 Filled Polydimethylsiloxane Membranes for Pervaporative Separation of n-Butanol from Aqueous Solution

ZIF-8-filled polydimethylsiloxane (PDMS) membranes, PDMS/ZIF-8, were prepared by a two-step polymerization process and were used to recover n-butanol from an aqueous solution by pervaporation (PV). Compared with pure PDMS membrane, PDMS/ZIF-8 membranes demonstrated an obviously higher n-butanol permselectivity. As an increase of ZIF-8 content, n-butanol/water selectivity increased initially and then decreased, while the n-butanol and water permeability decreased monotonously. PDMS/ZIF-8 membrane containing 2 wt% ZIF-8, that is, PDMS/ZIF-8-2 showed the highest selectivity. On the other hand, selectivity and permeability for n-butanol and water of PDMS/ZIF-8-2 membrane decreased with the increase of operating temperature. The selectivity and permeability for n-butanol reached 7.1 and 3.28 × 10⁵ barrer, respectively, at 30°C when the feed concentration of n-butanol was 0.96 wt%.     

HTPB基聚氨酯膜的制备及渗透汽化脱酚性能研究

采用端羟基聚丁二烯(HTPB)、端羟基聚丁二烯–苯乙烯共聚物(HTBS)和端羟基聚丁二烯–丙烯腈共聚物(HTBN)三种软段制备了聚氨酯(PUR)膜,利用红外光谱仪、差示扫描量热分析仪、热重分析仪表征了膜的结构和热性能;并以苯酚水溶液为目标体系,考察了三种膜的溶胀性以及渗透汽化分离性能。结果表明,HTPB–PUR膜具有最大的微相分离程度和耐热性;软段中的氰基会增大膜的溶胀度;HTBS–PUR膜具有最高的渗透性,而HTPB–PUR膜选择性最好;三种膜的总渗透通量、分离因子和渗透汽化分离指数均随进料温度升高而增加。     

Recovery of Hydrazine and Glycerol from Aqueous Solutions by Membrane Separation Techniques

Hydrazine and glycerol are two widely utilized solvents in the chemical industry, which form aqueous solutions during various stages of their production or application. Distillation of these aqueous solutions is either hazardous due to the explosive nature of hydrazine or energy intensive in case of the high boiling glycerol. The focus of this study was to develop and compare alternative safe and economical methods such as Pervaporation (PV) and Membrane Distillation (MD) for separation of water from these solvents. PV experiments using the indigenously developed thin film composite (TFC) Pebax membrane revealed a high selectivity of 107 at a reasonable flux of 0.05 kg/m² h for a typical hydrazine hydrate feed composition of 64 wt.% N₂H₄. For glycerol-water mixtures, MD through a microporous, hydrophobic polytetrafluoroethylene (PTFE) membrane gave better flux (0.1 kg/m² h) than PV through the Pebax membrane. Interestingly, both membrane types exhibited a selectivity of infinity throughout the range of feed composition (10–90% glycerol) studied due to poor volatility of glycerol. The effect of operating parameters such as permeate pressure (0.5–10 mmHg) and feed temperature (37–100°C) on MD performance for glycerol-water separation was evaluated. The membranes were characterized by scanning electron microscopy (SEM) and sorption experiments to explain the observed results.     

Separation of Phenol from Aqueous Streams by a Composite Hollow Fiber Based Pervaporation Process Using Polydimethyl siloxane (PDMS)/Polyether-Block-Amide (PEBA) as Two-Layer Membranes

Abstract

In order to simultaneously achieve both high permselectivity and permeability (flux) for the recovery of aromatic compounds such as phenol from aqueous streams, a composite organophilic hollow fiber based pervaporation process using PDMS/PEBA as two-layer membranes has been developed. The process employed a hydrophobic microporous polypropylene hollow fiber, having thin layers of silicones (PDMS) and PEBA polymers coating on the inside diameter. The composite membrane module is used to investigate the pervaporation behavior of phenol in water in a separate study; and that of a mixture of phenol, methanol, and formaldehyde in an aqueous stream (a typical constituent of wastewater stream of phenol-formaldehyde resin manufacturing process) in another study. The fluxes of phenol and water increase relatively linearly with increasing concentration especially at low feed concentration, and exhibit a near plateau with further increase in concentration. As a result, the phenol/water separation factor decreases as the feed concentration increases. Significant improvement in phenol/water separation factor and phenol flux is achieved for this two-layer (PDMS/PEBA) membranes as compared to that achieved using only PDMS membrane. The phenol and water fluxes and the separation factor are highly sensitive to permeate pressure as all decrease sharply with increase in permeate pressure. For this membrane, an increase in temperature increases the separation factor, and also permeation fluxes of phenol and water. An increase in feed-solution velocity does not have a significant effect on phenol and water fluxes, and also on the separation factor at least within the range of the feed-solution velocity considered. In the study of pervaporation behavior of a typical constituent of wastewater stream of phenol-formaldehyde resin manufacturing process, phenol permeation shows a much higher flux and a higher increase in flux with increase in concentration is also exhibited as compared to that exhibited by methanol permeation. This thus indicates that the membrane is more permeable to phenol than to methanol and formaldehyde.     

聚氨酯膜的制备及渗透汽化分离水中苯酚性能研究

研究通过两步反应法制备端羟基聚丁二烯基聚氨酯（HTPB-PU）渗透汽化膜,采用红外、热分析、扫描电镜等手段对其结构与性能进行了表征,研究了该膜从水中分离苯酚的渗透汽化性能。结果发现,该膜表现出良好的优先透过苯酚的分离性能。以0.5%苯酚水溶液作为料液,随着操作温度从60℃增加到80℃,渗透通量增加而分离因子下降,在60℃时,分离因子与渗透通量可分别达到23.80与2.85 kg.μm.m-2.h-1。     

新型PVA/PA复合膜的运行工艺对渗透汽化性能的影响

研究了聚乙烯醇（PVA）/聚酰胺（PA）复合膜渗透汽化（PV）分离异丙醇（IPA）/水混合物时运行工艺的影响,模拟了渗透通量（J）预测方程。结果表明,PVA/PA复合膜在料液中w（IPA）%在0～95%范围内或在25℃～100℃的操作温度范围获得的渗透液中IPA含量[w′（IPA）]都小于1%,J随料液中w（IPA）%的下降或操作温度的提高而增加。分离性能预测方程的拟合结果与试验数据有良好一致性。在室温条件下,经过90 d的间歇运行或经过120 d的长期贮存后,PVA/PA复合膜的分离性能稳定,在IPA/水混合物的共沸温度80.4℃运行时的J为73.1 g/m^2·h,渗透液中的水含量[w′（H2O）]都大于99.5%,展示了其在食品、生物、制药和化学等工业中将具有良好的应用前景。     

交联壳聚糖膜对各种醇水体系分离特性的研究

壳聚糖（CS）膜对不同醇水混合物的分离性能与醇分子的体积相关,随醇分子体积的增加,膜的分离因子增加,而渗透通量下降。然而经戊二醛交联后的CS膜,在分离丙醇水体系时不但具有高的分离因子,还具有比乙醇水体系同的渗透通量。本文研究了在分离不同醇水体系时交联剂量对交联CS膜分离性能的影响,并就交联前后CS膜对醇水体系的分离性能发生变化的原因进行了探讨。     

渗透气化膜分离技术在乙醇-水体系中的应用

渗透气化是一种新型的膜分离技术,因其具有独特的优势已被广泛应用于乙醇-水的分离.从渗透气化的原理和特点出发,介绍了渗透气化膜材料以及渗透气化与精馏、化学反应耦合等技术,并概述了国内外渗透气化膜分离技术在乙醇-水分离中的应用现状.     

渗透蒸发过程脱除水溶液中挥发性有机物的研究

采用自制的PDMS膜研究了从VOCs (挥发性有机化合物 )稀水溶液中脱除VOCs的渗透蒸发过程。以分离因子和渗透通量为评价指标 ,考察了料液浓度、温度和流动状况以及膜下游压力对膜的渗透蒸发分离性能的影响 ;并研究了针对脱除水溶液中VOCs的渗透蒸发过程的传质模型。     

硅橡胶膜生物反应器在苹果原汁发酵过程中的膜分离性能

利用硅橡胶膜生物反应器进行了苹果原汁发酵-渗透汽化分离实验,研究了苹果发酵液中的主要风味成分及其渗透汽化分离性能。发酵液中的主要芳香成分与传统苹果酒接近,但酯类物质的含量较低。硅橡胶膜对发酵液中的挥发性轻组分表现出良好的选择透过性,高级醇、酯类和醛类的分离率分别达到90%、76%和67%;而乳酸乙酯、β-苯乙醇和乙酸被不同程度地截留。非挥发性有机酸被截留在膜上游发酵液中。草酸、乙酸、柠檬酸和琥珀酸得到不同程度地浓缩;苹果酸、酒石酸和乳酸在分离过程中可能被微生物细胞所消耗,其含量有所降低。硅橡胶复合膜在选择性地分离挥发性轻组分的同时有效地保护了发酵液中的有机酸等非挥发性营养成分,研究结果进一步证明了采用硅橡胶膜生物反应器同时生产苹果白兰地和果汁发酵饮料的可行性。     

乳状液膜分离富集废水中的苯酚

以聚异丁二烯双丁酰亚胺(T-154)为表面活性剂制备乳状液膜,研究其对废水中苯酚的分离富集效果。通过单因素法和正交实验优选了乳状液膜的制备条件,即:V(T-154)∶V(液体石蜡)∶V(煤油)=4∶2∶30,质量分数3%的Na OH溶液为内水相,油内比为1∶2(体积比);将最优条件下制备的乳状液膜用于对废水中苯酚的分离富集条件为:溶液p H=6,乳水比为1∶4(体积比),富集时间为15 min;在该条件下加标回收率为96%~98%,相对标准偏差RSD(n=6)为3.7%~4.8%。     

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.     

苯酚体系支撑液膜不稳定性研究

The instability mechanisms of the supported liquid membrane using Celgard 2500 membranes as support and tributyl phosphate dissolved in kerosene as carrier for phenol transport was studied by electrochemical impedance spectroscopy. Emulsion formation is demonstrated to be one of the main causes for the instability of supported liquid membrane in the present system. The emulsion-facilitated conditions, such as higher membrane liquid concentration, faster stirring speed, lower salt concentration and higher HLB value, would accelerate the degradation of supported liquid membrane. Other mechanisms including solubility and os-motic pressure work together to increase the membrane liquid loss.     

聚丙烯酸-聚乙烯醇共混膜分离甲醇-碳酸二甲酯共沸体系

采用涂敷法制备了聚丙烯酸(PAA)-聚乙烯醇(PVA)共混膜,将其用于渗透汽化法分离甲醇(MeOH)-碳酸二甲酯(DMC)共沸物,考察了共混比例、热处理条件对甲醇分离性能的影响. 渗透汽化实验结果表明,随着热处理时间延长或热处理温度提高,分离因子先升高后降低,而渗透通量则逐渐减小;随着共混膜中PAA/PVA比例增加,分离因子先升高后降低,而渗透通量先减小后增大;当PAA/PVA质量比为7/3、热处理时间为60 min、热处理温度为150℃时,选择性最佳,在料液组成为70%(w) MeOH-30%(w) DMC及70℃的操作温度下,甲醇的分离因子为9.5(透过侧MeOH浓度为95.5%, w),渗透通量为360 g/(m2×h).     

用于TS-1催化苯酚羟基化的一体式催化/膜过滤系统的模型研究

This research is focused on the development of a simple design model of the submerged catalysis/ membrane filtration (catalysis/MF) system for phenol hydroxylation over TS-1 based on the material balance of the phenol under steady state and the reported kinetic studies. Based on the developed model, the theoretical phenol conversions at steady state could be calculated using the kinetic parameters obtained from the previous batch ex-periments. The theoretical conversions are in good agreement with the experimental data obtained in the submerged catalysis/MF system within relative error of ±5%. The model can be used to determine the optimal experimental conditions to carry out the phenol hydroxylation over TS-1 in the submerged catalysis/MF system.     

Pervaporative Dehydration of Binary Ethanol/Water and Ternary Ethanol/Water/Methanol Mixtures Using a Methylated Silica Membrane: A Mechanistic Approach

The pervaporation properties of a methylated-silica membrane were studied on binary ethanol/water and ternary ethanol/water/methanol mixtures. The aim was to acquire a better understanding of the pervaporation mechanisms by studying the effects of feed temperature, permeate pressure, and feed composition on molecular transport. Emphasis was placed on the role of competitive adsorption and dragging and blocking effects between the components in the context of the adsorption-diffusion model. The results show the potential of the membrane for the coupled removal of water and methanol from bioethanol. This attractive application for process intensification was suggested for the first time in this paper.