Pervaporation of Water/Ethanol Mixtures by an Aromatic Polyetherimide Membrane

Abstract

The pervaporation of water/ethanol mixtures through an aromatic polyetherimide membrane was attempted. The membrane was laboratory prepared using the solution casting technique. The sorption characteristics in relation to pervaporation were also studied. It was found that the preferential sorption was altered when the liquid composition was changed, whereas the water component permeated through the membrane preferentially over the whole range of feed mixture compositions. The experimental results were analyzed in terms of sorption ratio and permeation ratio to characterize nonideality of sorption and pervaporation. The effects of some operating parameters, including temperature, feed concentration, and permeate pressure, on the pervaporation performance were also investigated.     

NaA型分子筛膜用于医药工业异丙醇溶媒渗透汽化脱水(英文)

NaA zeolite membranes with 80 cm in length and 12.8 mm in outer diameter were prepared by our research group cooperating with Nanjing Jiusi Hi-Tech Co., China. The influence of dissolved inorganic salts and pH value in the feed of isopropanol (IPA) solution on NaA zeolite membranes was investigated. It was found that both factors exhibited strong influence on the stability of NaA zeolite membranes. A set of pretreatment steps such as pH adjustment and distillation of the IPA solution were proposed to improve stability for pervaporation dehydration. An industrial-scale pervaporation facility with 52 m2 membrane area was built to dehydrate IPA solution from industrial cephalosporin production. The facility was continuously operated at 368-378 K to dehydrate IPA solution from water mass content of 15%-20% to less than 2% with a feed flow rate of 400-500 L·h-1 and an average water flux of 1-1.5 kg·m-2·h-1. The successful application of this facility suggested a promising application of NaA zeolite mem-brane for IPA recovery from pharmaceutical production.     

采用渗透汽化膜技术进行有机溶剂脱水的新方法

简述了渗透汽化膜技术的原理和工艺流程;介绍了其应用于有机溶剂脱水领域在节能、环保、提高产品质量、简化操作等方面的比较优势、应用实例和效果评价;展望了该技术的发展前景。     

Novel Hollow Titania Spheres‐Chitosan Hybrid Membranes with High Isopropanol Dehydration Performance

A new kind of hollow titania spheres‐chitosan (hTiO₂‐CS) hybrid membranes was prepared by a physical blending method. hTiO₂ spheres were found to disperse well in the as‐prepared hTiO₂‐CS hybrid membranes. Their incorporation can reduce the chitosan crystallinity and enhance slightly its hydrophilicity and thermal stability. Subsequently, hTiO₂‐CS/PAN composite membranes comprising of the hTiO₂‐CS hybrid membrane as separation layer and a polyacrylonitrile (PAN) membrane as support layer were fabricated. Compared to the CS/PAN membrane, all of them exhibit a much better flux and separation factor for a 90 wt % aqueous solution of isopropanol at 80 °C. This promising kind of composite membranes may find potential application in the dehydration of alcohols.     

Study of the Dehydration of Isopropanol by a Pervaporation‐Based Hybrid Process

The permeation characteristics of the commercial polymeric membrane PERVAP^® 2201 were studied to carry out the dehydration of binary water/isopropanol mixtures. The influence of the composition (2–75 wt % H₂O) and temperature of the feed (311.15–348.15 K) on the membrane performance was studied. The selected membrane showed a high selectivity towards water in the entire concentration range. It was found that the permeation rate increased with the water content and the operating temperature. The influence of the temperature on the flux can be described by an Arrhenius‐type expression. The commercial software Aspen Plus was used to simulate the dehydration of isopropanol by means of a hybrid process combining distillation and pervaporation.     

Chitosan/ZIF‐8 Mixed‐Matrix Membranes for Pervaporation Dehydration of Isopropanol

Zeolitic imidazolate frameworks (ZIF‐8) nanoparticles were successfully synthesized and embedded into a chitosan (CS) polymeric matrix to prepare CS/ZIF‐8 mixed‐matrix membranes (MMMs) in order to investigate the effect of ZIF‐8 addition as novel filler on the dehydration performance of the CS polymeric membrane. MMMs were evaluated using pervaporation (PV) dehydration of isopropanol (IPA). The synthesized ZIF‐8 nanoparticles and MMMs were characterized by X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy, and a swelling study. The PV performance of the prepared MMMs with different ZIF‐8 loadings for IPA dehydration was investigated. For the ZIF‐8/CS MMMs, at the optimum loading the total flux increases significantly with low separation factor reduction. The good PV performance of the ZIF‐8‐incorporated CS membranes for dehydration of IPA is demonstrated.     

渗透汽化回收制药废液中异丙醇

通过渗透汽化脱水浓缩试验降低回收异丙醇的水分量以使回收异丙醇套用于生产。采用HPDA真空渗透汽化膜进行回收异丙醇脱水浓缩生产试验,渗透汽化膜处理后的异丙醇含水量降到0.5%以下,并且没有引入新杂质,结果表明渗透汽化处理后的异丙醇含水量符合生产要求,套用于生产不影响产品质量。     

Poly(vinyl alcohol)/Carboxyl Graphene Membranes for Ethanol Dehydration by Pervaporation

Carboxyl graphene (CG) with two functions of hybridization and crosslinking was incorporated into poly(vinyl alcohol) (PVA) matrix to form PVA/CG mixed-matrix membranes (MMMs). The membranes demonstrated excellent mechanical properties and thermal stability. The improved hydrophilicity and formed crosslinking structure led to moderate swelling. The membrane crystallinity decreased and the free volume was promoted with increasing CG loading amount. The pervaporation (PV) separation performance for ethanol dehydration indicated that both permeation flux and separation factor were enhanced simultaneously at the optimum CG loading. Subsequently, the permeation flux continued to increase while the separation factor declined at higher CG loadings.     

Synthesis of Chemically Modified Polyvinyl Alcohol Membranes for Dehydration of Dioxane by Pervaporation

Abstract

Polyvinyl alcohol (PVOH) has been chemically modified by polymerizing hydroxyethylmethacrylate (HEMA) in aqueous solution of PVOH and finally crosslinking PVOH with glutaraldehyde to produce a semi-interpenetrating network (SIPN) membrane. Accordingly, three such SIPNs i.e., SIPNI, SIPNII, and SIPNIII were synthesized with different weight ratio of PVOH: HEMA i.e., 1:0.25 (SIPNI), 1:0.50 (SIPNII) and 1:0.75 (SIPNIII). These SIPN membranes were used for pervaporative dehydration of dioxane. PVOH without any chemical modification but crosslinked with the same amount of glutaraldehyde has also been used for this study for comparison. All the SIPN membranes were also characterized with various conventional methods like mechanical properties, DSC and TGA. Water permeability and water selectivity of the IPN membranes were found to be much higher than those of the crosslinked PVOH membrane which was not chemically modified. The permeability of the membranes were also found to increase with increase in the HEMA content in PVOH matrix.     

Removal of Volatile Organic Compounds from Water by Pervaporation Using Polyetherimide-Polyethersulfone Blend Hollow Fiber Membranes

Abstract

Removal of volatile organic compounds (VOCs) such as 1,2-dichloroethane, trichloroethylene, chlorobenzene and toluene from water solutions through polyetherimide (PEI)-polyethersulfone (PES) blend hollow fiber membranes was investigated by pervaporation (PV) in this work. The separation performances of the membranes were researched by varying the spinning conditions (such as coagulation temperature and air gap distance) for the preparation of the hollow fibers and the operation conditions (such as velocity, concentration, and temperature of feed liquids). For the PEI-PES blend hollow fiber membrane prepared when the air gap was 7 cm and the temperature of coagulation bath was 45°C, it possessed high selectivity to the aqueous solutions containing 0.04 wt.% of VOCs at 20°C. The separation factors to 1,2-dichloroethane, trichloroethylene, chlorobenzene and toluene were 7069, 5759, 3952, and 3205, respectively. It was found that the pervaporation performance of the blend hollow fiber membrane was strongly related to the molecular size of the VOCs. The order of the selectivities was 1,2-dichloroethane > trichloroethylene > chlorobenzene > toluene.     

硅橡胶复合膜渗透汽化分离硫/汽油混合物

Worldwide environment has resulted in a limit on the sulfur content of gasoline. It is urgent to investigate the desulfurization of gasoline. The polydimethylsiloxane (PDMS)/polyetherimide (PEI) composite membranes were prepared by casting a PDMS solution onto porous PEI substrates and characterized by scanning electron microscope (SEM). The membranes were used for sulfur removal from gasoline by pervaporation. The effects of feed temperature, sulfur content in the feed and PDMS layer thickness on membrane performance were investigated, and an activation energy of permeation was obtained. Experimental results indicated that higher feed temperature yielded higher total flux and lower sulfur enrichment factor. The total flux varied little with the increase of sulfur content in the feed, but the sulfur enrichment factor first increased with the amount of thiophene added into the gasoline, and then the variation was little. The increase of PDMS layer thickness resulted in a smaller flux but a larger sulfur enrichment factor. The result indicates that the PDMS/PEI composite membranes are promising for desulfurization by pervaporation.     

Effect of Deacetylation Degree in Chitosan Composite Membranes on Pervaporation Performance

ABSTRACT

The effect of the degree of deacetylation in chitosan composite membranes on their pervaporation performance for ethanol dehydration was investigated. The degree of deacetylation of chitosans was measured by using an infrared spectroscopic method and elemental analysis. The chitosan composite membranes were prepared by coating a chitosan solution onto a microporous polyethersulfone membrane with 3–7 nm pore sizes. Then the surface of the top layer (chitosan) of well-dried membranes was crosslinked with sulfuric acid, and pervaporation experiments for binary mixtures (water—ethanol) were carried out at various conditions. In the case of a chitosan membrane with a high degree of deacetylation, the flux increases while the separation factor decreases compared with membranes with a low degree of deacetylation.     

Pervaporation dehydration of ethylene glycol by NaA zeolite membranes

Home-made NaA zeolite membranes were used for pervaporation dehydration of ethylene glycol (EG)/water mixtures. Hydrothermal stability of the membranes in pervaporation was investigated for industrial application purpose. The membranes exhibited good stability for water content of less than 20 wt.% at 100 °C. The reduction of operating temperature was effective to improve membrane stability for operating at high feed water content (e.g. 30 wt.%). The influence of feed water content and operating temperature on dehydration of EG was extensively investigated. A permeation flux of 4.03 kg m⁻² h⁻¹ with separation factor of >5000 was achieved at 120 °C for the separation of the solution with 20 wt.% water content. A pilot-scale pervaporation facility with membrane area of 3 m² was built up for dehydration of EG with the water content of 20 wt.%, which showed technical feasibility for industrial application.     

渗透汽化膜技术及其在有机溶剂脱水领域的应用

简述了渗透汽化膜技术的原理和工艺流程;介绍了其应用于有机溶剂脱水领域在节能、环保、提高产品质量、简化操作等方面的比较优势、应用实例和效果评价;展望了该技术的发展前景.     

芳烃/脂肪烃渗透汽化分离膜的研究进展

芳烃/脂肪烃分离是石油化工中重要的分离过程,渗透汽化膜分离技术是现有高能耗芳烃/脂肪烃分离过程的潜在技术。以调整石脑油的芳烃含量,生产“低苯汽油”或低芳烃含量的优质乙烯裂解原料为背景,论述了芳烃/脂肪烃混合物的渗透汽化分离膜的研究进展。     

3A分子筛在异丙醇脱水中的应用研究

异丙醇是一种重要的化工原料和有机溶剂,广泛应用于化工和制药行业中。工业生产过程产生大量异丙醇和水的混合废液,实现异丙醇和水的完全分离有着重要的意义。通过实验证实了3A分子筛的吸水性和可再生性,确定了通过3A分子筛得到高浓度异丙醇的最优工艺流程和方法。     

Pervaporation Separation of Water/Ethanol Mixtures through Polycarbonate/Cobalt(III) Acetylacetonate Membranes

ABSTRACT

In the present work, cobalt(III) acetylacetonate [Co(acac)₃] was added to polycarbonate (PC) to improve its performance on pervaporation separation of water/ethanol mixtures. By adding 3 wt% of Co(acac)₃ the resulting PC/Co(acac)₃ complex membrane possessed a permeation rate similar to a pure polycarbonate membrane, but the separation factor (water/ethanol) was about three times higher. The stability of the complex membrane was tested, and it was found that, after being immersed in an aqueous ethanol solution for 72 hours, the complex membrane was still stable. In addition, the effects of the added amount of Co(acac)₃ and the feed composition on pervaporation performance are presented in this work, and the mechanism of the improvement in pervaporation performance is briefly discussed.     

Dehydration of water/1-1-dimethylhydrazine mixtures by zeolite membranes

In this research, dehydration of water/1-1-dimethylhydrazine (UDMH) mixtures by zeolite NaA and hydroxy sodalite membranes has been investigated. Support of these membranes has been tubular mullites that have been made by extruding a mixture of about 67–75% kaolin clay and 33–25% distilled water using an extruder. Zeolite NaA and hydroxy sodalite membranes have been coated on the external surface of the porous supports by the hydrothermal synthesis.

UDMH/water mixtures have been separated at ambient temperature and pressure by pervaporation (PV) using these zeolite membranes. These membranes showed very high selectivity of water for all UDMH mixtures. For the UDMH/water mixtures, separation factor as high as 10 000 has been obtained for UDMH feed concentration of 2%. Total mass fluxes of 1.05–0.2 kg/(m² h) have been also obtained.     

Fabrication of Aromatic Polyimide Membrane to Study the Pervaporative Separation of Phenanthrene/n-tetradecane Mixtures (Model Diesel) and Process Optimization Using Response Surface Methodology

To meet stringent fuel specifications, separation of aromatics from aliphatics is an everyday challenge for a refiner. In the present investigation, an aromatic polyimide membrane is fabricated and explored for the separation of a polyaromatic hydrocarbon (phenanthrene) from a model diesel composition (n-tetradecane) via pervaporation. The pervaporative membrane is prepared by casting a solution of polyamic acid, N,N-dimethylacetamide (DMAc), and phenanthrene using a simple and low-cost procedure. Scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), and swelling in feed solution of the synthesized membrane have been conducted for its characterization. The membrane allows preferential permeation of phenanthrene. The influence of different physico-chemical parameters, on permeation flux and enrichment factor for n-tetradecane/phenanthrene mixtures, has been studied. Statistical software Design Expert 7.1.4 is used to derive the regression equation, which describes the effect of time, downstream pressure, feed solute concentration, and operating temperature on the Pervaporation Separation Index (PSI). These factors are optimized using response surface methodology (RSM). The highest value of the PSI obtained is 0.623 kg m^?2 h^?1 and the corresponding optimized condition is: operating time is 11.58 h, the feed solute concentration is 162.96 ppm with a downstream pressure of 0.58 mm of Hg and an operating temperature of 449.03 K.     

Development of a Mixed-Matrix Membrane for Pervaporation

Abstract

In the production of pure alcohol, pervaporation is developing into an important technology. In this study, in order to improve the performance of the pervaporation process, a mixed-matrix polymer-zeolite membrane is developed. In the preparation of these membranes, cellulose acetate as base polymer, acetone or DMF as solvent, and 13X or 4A zeolites as fillers were used. To test the performance of homogeneous and mixed-matrix membranes, a laboratory-scale pervaporation setup was constructed. The effect of the following experimental parameters on the selectivity and flux were experimentally studied to determine the optimum values of operating conditions and to understand the separation mechanism in the indicated ranges: feed concentration, 70–90 wt%; feed temperature, 30–70°C; feed flow rate, 32–76 L/h. It was observed that the addition of zeolite to the membrane matrix improves the flux value twofold with respect to its homogeneous membranes with some loss in their selectivity. For example, for a feed concentration of 74 wt% EtOH at 50°C and 1 mmHg, the flux value for the unfilled membrane is 0.6 L/m²·h, and for a 30% zeolite-filled membrane, the flux is increased to 1.33. For these cases, the selectivities are 7.76 and 5.0 for the unfilled and filled membranes, respectively. TEM micrographs of the mixed-matrix membranes show a homogeneous distribution of zeolite particles which produce a cavelike porous structure in the matrix. The combined effect of this modified morphology and zeolite selectivity is the possible reason for the observed pervaporation performances of mixed-matrix membranes.