Article pubs.acs.org/IECR
Regulation of Critical Ethanol Response Concentrations of EthanolResponsive Smart Gating Membranes Peng-Fei Li,†,‡ Rui Xie,*,† Heng Fan,† Xiao-Jie Ju,† Yong-Chao Chen,† Tao Meng,† and Liang-Yin Chu*,†,§ †
School of Chemical Engineering, Sichuan University, Chengdu, Sichuan 610065, PR China State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, PR China
§
ABSTRACT: Regulation of the critical ethanol response concentration of ethanol-responsive smart gating membranes has been systematically investigated by preparing a series of gating membranes with grafted poly(N-isopropylacrylamide) (PNIPAM) and PNIPAM-based copolymer gates. A porous Nylon-6 (N6) membrane is used as the substrate membrane, and the surface-initiated atom transfer radical polymerization (ATRP) method is employed to graft polymers onto the substrate membrane. Fourier Transform Infrared Spectrometer (FT-IR) is used to determine chemical compositions of the prepared membranes, and Scanning Electron Microscope (SEM) is used to investigate the microstructures of membranes. The fluxes of ethanol solutions across different membranes are studied systematically by changing the ethanol concentration. The results show that the introduction of hydrophilic monomer N,N-dimethylacrylamide (DMAA) or hydrophobic monomer butyl methacrylate (BMA) into the grafted PNIPAM-based gates can effectively regulate the critical ethanol response concentration of the gating membranes. The quantitative relationships between the critical ethanol response concentration of the grafted membranes and the lower critical solution temperature (LCST) in water of the PNIPAM-based functional gates are summarized in this study for the first time, by which the critical ethanol response concentration of the grafted membranes can be effectively predicted. The results provide valuable guidance for designing and preparing ethanol-responsive gating membranes with adjustable critical ethanol response concentrations by simply regulating the LCST in water of the grafted PNIPAM-based gates and controlling the operation temperature. potential for practical applications.3−6 Polydimethylsiloxane (PDMS) or PDMS composite membranes are usually used in the membrane pervaporation for continuously removing ethanol from fermentation tanks.3−6 However, the membrane permeability of those existed membranes cannot be adjusted self-regulatively responding to the variation of ethanol concentration in the fermentation tank. If ethanol-concentration-responsive permeability across the membrane can be achieved, i.e., higher transmembrane permeability at higher ethanol concentration while lower permeability at lower ethanol concentration, the ethanol concentration in the fermentation tank can be maintained in a relatively stable level, which enables the fermentation process more efficient. Stimuli-responsive smart membranes,7−9 which exhibit selfregulated permeability responding to mild change of environmental chemical and/or physical conditions, show a promising approach to achieve ethanol-concentration-responsive permeability across the membrane. It has been found that poly(Nisopropylacrylamide) (PNIPAM) exhibits significant ethanolresponsive characteristics,2,10−12 although it is a well-known thermoresponsive material. Recently, ethanol-responsive smart gating membranes have been reported by grafting PNIPAMbased copolymers in the pores of porous substrate membranes.2 The grafted membrane pores could turn from “closed” state to
1. INTRODUCTION Ethanol is widely used in the fields of chemical, biomedical, food, beverage, and energy industry and so on. It is a vital industrial chemical in the production of some organic compounds such as acetic acid, acetaldehyde, and ethylene glycol. The ethanol solution with concentration of 70−75 vol.% is widely used for disinfection in the medical field. In addition, the fuel ethanol as a new energy source is receiving more and more interest because of the ever-increasing demand of clean and regenerative energy. The traditional ethanol fermentation from biomass resources is a typical process of product inhibition,1 in which the product of an enzyme reaction binds to the enzyme and inhibits its activity. That is, during the biofermentation process, with increasing the concentration of ethanol product, the activity of yeast will be inhibited to some extent. However, for the product purification, the higher ethanol concentration in the reservoir is better. Therefore, to achieve the most efficient and stable fermentation, there is the optimum ethanol concentration in the fermentation broth, which has been reported to be about 10 vol.%,2,3 although this value is dependent on the process conditions including tolerance of yeast. Therefore, to improve the efficiency of the fermentation process, the ethanol should be simultaneously removed from the fermentation tank during the fermentation process, which is a key point for the continuous ethanol production. Up to now, various combination technologies have been developed to separate ethanol from the fermentation tanks, among which membrane pervaporation shows promising © 2012 American Chemical Society
Received: Revised: Accepted: Published: 9554
February 7, 2012 June 8, 2012 June 25, 2012 June 25, 2012 dx.doi.org/10.1021/ie300333y | Ind. Eng. Chem. Res. 2012, 51, 9554−9563
Industrial & Engineering Chemistry Research
Article
Figure 1. Schematic illustration of preparation and principle of the ethanol-responsive gating membrane. (a) Ethanol-responsive characteristics of PNIPAM polymer, (b, c) preparation of the PNIPAM-grafted membrane, and (d, e, f) ethanol-responsive gating characteristics of the grafted gating membrane, in which the circles and triangles represent water molecules and ethanol molecules respectively. CE is the ethanol concentration, and CE1 and CE2 (CE1
