Chapter 28
Improvement of Selectivities of MicrophaseSeparated Membranes for the Removal of Volatile Organic Compounds
Downloaded by UNIV OF ARIZONA on March 15, 2017 | http://pubs.acs.org Publication Date: April 20, 2004 | doi: 10.1021/bk-2004-0876.ch028
Tadashi Uragami, Hiroshi Yamada, Terumi Meotoiwa, and Takashi Miyafa Unit of Chemistry, Faculty of Engineering and High Technology Research Center, Kansai University, Suita, Osaka 564-8680, Japan
This paper describes the removal of benzenefroman aqueous solution by pervaporation using poly(methyl methacrylate)graft-polydimethylsiloxane (PMMA-g-PDMS) membranes, surface-modified with poly(perfluoro alkyl acrylate-graftpolydimethylsiloxane (PFA-g-PDMS/PMMA-g-PDMS) and tert-butylcalix [4] arene (CA/PMMA-g-PDMS). Membranes based on PFA-g-PDMS/PMMA-g-PDMS and CA/PMMA-gPDMS showed high benzene selectivity using an aqueous feed solution containing 0.05 wt% benzene. Both the permeability and the benzene selectivity of these membranes were enhanced by increasing the PFA-g-PDMS and C A content because the membrane surface became more hydrophobic. Furthermore, the affinity of the CA/PMMA-g-PDMS membranes for benzene increased by introducing C A to the membranes. Contact angle measurements and X-ray photoelectron spectroscopy revealed that the addition of PFAg-PDMS produced a hydrophobic surface at the membrane air-side due to surface localization. Transmission electron microscope observations revealed that the CA/PMMA-gPDMS membranes had a microphase-separated structure consisting of a PMMA phase and a PDMS phase containing CA.
© 2004 American Chemical Society
Pinnau and Freeman; Advanced Materials for Membrane Separations ACS Symposium Series; American Chemical Society: Washington, DC, 2004.
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Downloaded by UNIV OF ARIZONA on March 15, 2017 | http://pubs.acs.org Publication Date: April 20, 2004 | doi: 10.1021/bk-2004-0876.ch028
Introduction Recently, research has been focused on the removal of volatile organic compounds (VOCs) from wastewater or groundwater. In addition, treatment of tap water is very important as it contains various organic contaminants. A variety of separation techniques to remove VOCs from water, such as carbon adsorption, air stripping and steam stripping are available. However, the removal of VOCs from water by membrane separation can offer great advantages in potential energy cost savings. Separation of organic liquid mixtures through a variety of polymer membranes by pervaporation has therefore been the subject of many studies (/-J). In a previous paper ((5), we reported that microphase separation of graft copolymer membranes based on poly(methyl methacrylate) (PMMA) and polydimethylsiloxane (PDMS) can significantly influence their permeability and selectivity for the removal of VOCs from an aqueous solution. Furthermore, we suggested that a continuous PDMS phase in the microphase-separated structure plays an important role in the selective removal of VOCs. Generally, surface properties of multicomponent polymers are quite different from their bulk properties, because of surface localization of a specific component. For example, a fluorine-species in a multicomponent polymer is preferentially concentrated at its surface to minimize the surface free energy. Therefore, a fluorine-containing polymer that is spontaneously localized at the polymer surface might enable a simple surface modification for pervaporation membranes. Our previous studies revealed that adding fluorine-containing polymers to ethanol-selective membranes enhances their selectivity for the separation of aqueous ethanol solutions due to their very hydrophobic surface (7,8). Nakagawa et al. improved a PDMS membrane by graft polymerization of lH,lH,9H-hexadecafluorononyl methacrylate, which resulted in an increase of the selectivity for chlorinated hydrocarbons (2). Calixarene is a cyclic oligomer and is composed of phenol units linked to alkylidene groups. It has a cavity for incorporation of organic compounds, which is similar to cyclodextrins or crown ethers. In particular, terf-butylcalix [4] arene (CA) can selectively sorb benzene and its derivatives. In this study, we prepared hydrophobic, surface-modified membranes by adding a fluorine-containing graft copolymer to a microphase-separated membrane. The goal of this work was to (i) develop a high-performance pervaporation membrane for removing VOCs from water and (ii) introducing C A as a transport carrier for VOCs into multicomponent polymer membranes to improve their selectivity. We also evaluated the relationship between the benzene selectivity and the membrane structure.
Pinnau and Freeman; Advanced Materials for Membrane Separations ACS Symposium Series; American Chemical Society: Washington, DC, 2004.
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Experimental Materials The PDMS macromonomer, which has 25 units of the pendant PDMS, was supplied by Toray Dow Corning Silicone Co., Ltd.; 1H,1H,2H,2Hheptadecafluorodecyl acrylate (perfluoroalkylacrylate: PFA) (Clariant, Japan) was used as received;tert-Butylcalix[4] arene (CA) was obtainedfromAldrich Chem. Co., Ltd. The co-monomer, methyl methacrylate (MMA), was purified by distillation under reduced pressure in a nitrogen atmosphere. The initiator, 2,2-azobisisobutyronitrile (AIBN), was recrystallizedfrombenzene solution. In this study, PMMA-g-PDMS with a DMS content of 74 mol% was used as a matrix polymer because this membrane showed the highest permeability and selectivity for a dilute aqueous solution of benzene in PMMA-g-PDMS membranes with various DMS contents (
