Journal of Membrane Science 322 (2008) 139–145 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Characterization, transport and sorption properties of poly(thiol ester amide) thin-ﬁlm composite pervaporation membranes Shu-Hsien Huang a , Wei-Li Lin a , Der-Jang Liaw b , Chi-Lan Li c , Se-Tsung Kao a,d , Da-Ming Wang a,e , Kueir-Rarn Lee a,∗ , Juin-Yih Lai a a R&D Center for Membrane Technology, Department of Chemical Engineering, Chung Yuan University, Chung-Li 32023, Taiwan b Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan c Department of Chemical and Material Engineering, Nanya Institute of Technology, Chung-Li 32034, Taiwan d Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan e Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan article info Article history: Received 25 March 2008 Received in revised form 14 May 2008 Accepted 15 May 2008 Available online 27 May 2008 Keywords: Pervaporation Poly(thiol ester amide) Thin-ﬁlm composite membrane Interfacial polymerization Positron annihilation spectroscopy Slow positron beam abstract The effect of acyl chloride chemical structure on the ethanol aqueous solution dehydration through the poly(thiol ester amide) thin-ﬁlm composite membrane prepared by reacting 2-aminoethanethiol (AETH) with trimesoyl chloride (TMC) or succinyl chloride (SCC) on the surface of the modiﬁed asymmetric polyacrylonitrile (mPAN) membrane was investigated. SEM/EDX, ATR-FTIR and water contact angle were applied to analyze the S element, chemical structure, and hydrophilicity of the poly(thiol ester amide) active layer of the composite membrane. In order to estimate the variation in the free volume of the poly(thiol ester amide) active layer and correlate that with the pervaporation performance, positron anni- hilation spectroscopy (PAS) experiments were conducted, in which a variable monoenergy slow positron beam was used. Doppler broadening S parameters of annihilation radiation energy spectra showed a sig- niﬁcant variation with the acyl chloride chemical structures of the poly(thiol ester amide) active layers. The S parameters of the AETH–TMC/mPAN thin-ﬁlm composite membrane were found to be lower than those of the AETH–SCC/mPAN thin-ﬁlm composite membrane. In the ethanol aqueous solution dehy- dration, the AETH–TMC/mPAN thin-ﬁlm composite membrane exhibited a lower permeation rate and a higher water concentration in the permeate than the AETH–SCC/mPAN. This is in good agreement with the analysis by positron annihilation spectroscopy. The solution effect dominated the pervaporation sep- aration behavior of the poly(thiol ester amide) thin-ﬁlm composite membrane with TMC substituting for SCC in the poly(thiol ester amide) active layer. The AETH–TMC/mPAN membrane was found to exhibit superior performance compared with some membranes discussed in the literature. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Ethanol aqueous solution, a biofuel, comes from the process of fermenting sugar in biomass resources such as the lees and stems of corn. It is one of the new energy sources that would avoid problems concerned with the lack of petroleum resources [1]. Traditional distillation process usually concentrates ethanol aqueous solutions, but the azeotrope restricts further concentra- tion. To obtain ethanol with high purity, excess water needs to be removed using azeotropic distillation with an azeotrope-breaking component (entrainer) or the hybrid system of multi-stage evapo- ∗ Corresponding author at: R&D Center for Membrane Technology, Department of Chemical Engineering, Chung Yuan University, Chung-Li 32023, Taiwan. Tel.: +886 3 2654190; fax: +886 3 2654198. E-mail address: krlee@cycu.edu.tw (K.-R. Lee). ration and distillation, which consumes large energy and, therefore, entails cost. Pervaporation, which can separate azeotropic mixtures and save energy and cost, can be a substitute for traditional sepa- ration processes, and it is utilized for the dehydration of ethanol aqueous solutions. Polyamide is an excellent membrane material because of its high thermal stability, excellent mechanical strength, and high resis- tance to organic solvents. Although dense polyamide membranes show high selectivity in the dehydration of alcohol at wide range of water concentrations, they have low permeation rates [2–4]. In order to promote the permeation rate across polyamide mem- brane without sacriﬁcing selectivity, the membrane morphology must be converted from a dense thick ﬁlm into an asymmetrical or a composite morphology. However, the performance of a single- material asymmetrical membrane is restricted by its characteristic. A composite membrane would be better as it is characterized by a selective toplayer formed onto a chemically different asymmetri- 0376-7388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2008.05.034