Pervaporation applications

Dehydration The growing use of isopropanol as a clean-rinse fluid in microelectronics produces significant quantities of an 85—90 percent isopropanol waste. Removing the water and trace contaminants is required before the alcohol can be reused. Pervaporation produces a 99.99 percent alcohol product in one step. It is subsequently polished to remove metals and organics. In Europe, dehydration of ethanol is the largest pervaporation application. For the very large ethanol plants typical of the United States, pervaporation is not competitive with thermally integrated distillation. 

Another type of mixed-matrix membranes for alcohol/water pervaporation applications was developed utilizing hydrophiUc poly(vinyl alcohol) (PVA) and ZSM-5. The ZSM-5/PVA mixed-matrix membranes demonstrated increased selectivity and flux, compared to pure PVA, for the water/isopropyl alcohol separation [97]. This type of mixed-matrix membranes, however, may have membrane swelling issue due to the hydrophilic nature of the PVA polymer. Mixed-matrix membranes comprising modifled poly(vinyl chloride) and NaA zeolite have shown both enhanced flux and selectivity for the ethanol/water separation at high NaA loadings [98]. 

Another potential pervaporation application is removing small amounts of VOCs from industrial wastewaters, allowing the water to be discharged to the sewer and concentrating the VOCs in a small-volume stream that can be sent to a hazardous waste treater [13], Without a treatment system such as pervaporation,... 

MFI zeolite membranes (silicalite-1, ZSM-5), on either flat or tubular porous supports, have been the most investigated for gas separation, catalytic reactors, and pervaporation applications. The structural porosity of MFI zeolite consists of channels of about 5.5 A, in diameter, the sihca-rich compositions induce... 

Zeolites are traditionally used in catalysis/purification and separation applications in the petrochemical industry but are rapidly finding new uses. This section discusses membranes for low-dielectric-constant, corrosion-resistant, hydrophilic and antimicrobial, and pervaporation applications. 

Sebastian V, Mallada R, Coronas J, Julbe A, Terpstta RA, Dirrix RWJ. MW-assisted hydrothermal rapid synthesis of capillary MFI-type zeolite-ceramic membranes for pervaporation application. J Membr Sci 2010 355 28-35. 

Sebastian V, Motuzas J, Dirrix RWJ, Terpstra RA, Mallada R, Julbe A. Synthesis of capillary titanosilicalite TS-1 ceramic membranes by MW assisted hydrothermal heating for pervaporation application. Sep Purif Technol 2010 75 249-256. 

The CS-based mixed matrix membranes are also suitable for pervaporation application. Patil and Aminbhavi [96] prepared mixed matrix membranes of CS by incorporating sili-calite zeolite particles in 5 and 10 wt.% for the pervaporation separation of toluene/methanol and toluene/ethanol feeds in compositions of 10-40 wt.% of toluene at 30°C. The membranes were toluene selective than alcohol selective. Flux of toluene/methanol and toluene/ethanol mixtures decreased, but selectivity increased with increasing alcohol content of the feed. Toluene permeated preferentially with a selectivity of 264 and fluxes of 0.019-0.027 kg/m h for toluene/ methanol mixture. Selectivity of 301 with fluxes ranging from 0.019 to 0.026 kg/m h was observed for tolnene/etha-nol mixtures. Flux increased, while selectivity decreased with increasing toluene content of the feeds. An increase in silicalite content of the MMMs gave increased pervaporation performances. 

FIGURE 21.14 Ethanol and water flows according to the stirring rate [water-ethanol feed (19.5% mass of water) at 60°C, membrane PVA-PAA (90-10) of thickness of 25.2 xm], membrane temperature controlled at 60°C (Rollet, V., Transfert de matiere en pervaporation, application a la deshydratation de melanges complexes, Ph.D. Thesis, University of Technology of Compiegne, France, 2000.). 

Rollet, V., Transfer de matiere en pervaporation, application a la deshydratation de melanges complexes, Ph.D. Thesis, University of Technology of Compiegne, France, 2000. 

Li, X., Basko, M., Prez, F.D. and Vankelecom, F.J. 2008a. Multifunctional membranes for solvent resistant nanofiltration and pervaporation application based on segmented polymer networks. 16539-16545. 

Figure 4.31 Polyamides with different substitution patterns for pervaporation application [69].

Nagase et al. have studied the grafting of polyacetylene and its derivative onto poly(dimethylsiloxane) (PDMS) for membrane applications [118-121]. Poly(l-trimethyl-silyl-l-propyne) (PTMSP) is a polymer known to have excellent gas permeability but suffers from relatively low selectivity and a decrease in gas permeability over time. Graft copolymers of poly(l-phenyl-1-propyne) (PPP) onto PDMS were found to have improved gas permeability and selectivity, and the performance was related non-linearly to the PDMS content. A minimum oxygen permeability coefficient was found for a copolymer with 55 mol% PDMS [118]. The same membrane series was also foimd to be permselective for a range or organic liquids, including an ethanol/water mixture, and was used in pervaporation applications... 

Their applications and improved long-term stability for gas separation and pervaporation were further investigated. A maximum in the separation factor and rate was obtained for the PTMSP copolymer with 12 mol% PDMS. The membrane was able to convert a 7 wt% ethanol mixture to over 70 wt% in ethanol [120]. Good oxygen permeability and stability of over a month was also achieved for the PTMSP copolymers with over 60% PDMS [121]. In a separate study, PPP was foimd to have good permselectivity to water while PTMSP is alcohol permselective. These copolymers as well as a series of poly(phenyl acetylene) graft PTMSP copolymers were further studied for pervaporation applications [122]. 

The plate-and-frame module is highly effective in pervaporation applications, but is much less popular than spiral wound and hollow fiber modules for gas... 

---