Research Note pubs.acs.org/IECR
Pervaporation Dehydration of Ethyl Acetate via PBI/PEI Hollow Fiber Membranes Yan Wang* Key Laboratory for Large-Format Battery Materials and System, Ministry of Education, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, 430074, China S Supporting Information *
ABSTRACT: The dewatering of ethyl acetate (EA) holds a significant role in the production and application of this important chemical material. In this study, pervaporation dehydration of EA is investigated using polybenzimidazole/poly(ether imide) (PBI/PEI) dual-layer hollow fiber membranes. The spinning parameters during the membrane fabrication, including the take-up speed and air gap distance, are varied and found to have a marked influence on the resultant separation performance. Besides, cross-linking modification and post-thermal treatment are applied on the PBI/PEI hollow fiber membranes and their effects on the membrane performance are also investigated. A benchmarking shows that the pervaporation performance of the dual-layer PBI/PEI hollow fiber membranes is superior to most other polymeric membranes for EA dehydration. absorb 15 wt % water at equilibrium.23 Nevertheless, PBI membranes made from solvent-induced phase-inversion technique are very brittle after drying, which makes it difficult to be fabricated into self-standing membranes; its hydrophilicity may also cause its swelling in aqueous solutions and therefore result in an unstable performance; the high cost of PBI is another issue. To overcome the above issues and produce effective PBI membranes for pervaporation applications, various modification methods, including cross-linking, surface modification, blending, thermal treatment, etc., have been proposed.24−27 Among them, the composite membrane morphology with a thin active layer upon a microporous substrate may be a good solution, where synergistic separation performance can be achieved without the aid of intensive thermal or chemical treatments, if inner- and outer-layer materials are properly selected.16−19,28−33 Previous works using dual-layer hollow fiber membranes with PBI outer layer have been reported for pervaporation dehydration of other organics,16−19 and demonstrated superior separation performance to PBI single-layer hollow fiber membranes and most other polymeric membranes. Clearly, there is a great perspective to develop PBI dual-layer hollow fibers membranes for pervaporation separation by using other materials as substrates. Not only can it reduce the usage of the expensive PBI material, but it also can enhance the overall separation performance. In this work, pervaproation dehydration of EA is studied through polybenzimidazole/poly(ether imide) (PBI/PEI) duallayer hollow fiber membranes, with PBI as the selective outerlayer material and PEI as the supporting layer material. With the variation of the air-gap distance and the take-up speed, effects of the spinning parameters on the resultant pervaporation performance are investigated. Cross-linking modification and postthermal treatment on the PBI/PEI hollow fiber membranes are
1. INTRODUCTION Ethyl acetate (EA) is a widely used solvent in chemical industry. It is also an important raw material for the production of perfumes, plasticizers, varnishes, thinners, and drugs, because of its low toxicity, favorable volatility (heat of vaporization is 31.9 kJ/mol), and excellent miscibility with almost all common organic liquids.1 The synthesis of EA is commonly through the conventional esterification of acetic acid with ethanol.2 The resultant product consists of water and residual ethanol, which form a binary or ternary azeotrope mixture with the produced EA. Therefore, further separation to remove water and ethanol is necessary in order to achieve EA product with high purity. The separation process by the classical distillation technology is typically characterized by low separation efficiency and high energy consumption. Alternatively, pervaporation, as a promising membrane-based separation technology, is energy efficient and environmentally friendly. It is particularly suitable for the separation of azeotropic mixtures or those with close boiling points, since the separation is based on the difference in physicochemical properties of components to be separated. Pervaporation separation for aqueous EA azeotrope is thus of great commercial value. Many works have been reported on the recovery of EA from aqueous solution for wastewater treatment.3−6 Relatively, there are fewer studies on pervaporation dehydration for EA/water system. Among them, poly(vinyl alcohol) (PVA)-based membranes are the mostly studied polymeric membranes,7−10 followed by those based on polyacrylonitrile (PAN) and chitosan (CS) materials.11−13 However, these membranes generally lack mechanical strength and performance stability in aqueous solutions due to the excessive swelling, which may lead to a drastic decrease in the separation performance. Polybenzimidazole (PBI), which is an aromatic heterocyclic polymer, with excellent mechanical properties, thermal stability, and chemical resistance,14,15 has emerged as a promising membrane material for pervaporation dehydration in recent years.16−22 This polymer also has good hydrophilicity and could © XXXX American Chemical Society
Received: November 28, 2014 Revised: March 5, 2015 Accepted: March 9, 2015
A
DOI: 10.1021/ie504681v Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Research Note
Industrial & Engineering Chemistry Research
previously.34 A 2-L liquid mixture with the composition of 98/2 wt % EA/water was used as the feed solution and circulated from the feed tank to pass through the shell side of the membrane. The recirculation flow rate was controlled at 0.5 L/min for each hollow fiber module by a flow meter. Since the feed concentration varies by
