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Review ArticleReview on Pervaporation: Theory, Membrane Performance,and Application to Intensification of Esterification Reaction
Ghoshna Jyoti, Amit Keshav, and J. Anandkumar
Department of Chemical Engineering, National Institute of Technology, Raipur 492010, India
Correspondence should be addressed to Amit Keshav; email@example.com
Received 11 September 2015; Revised 17 November 2015; Accepted 26 November 2015
Academic Editor: Georgiy B. Shulpin
Copyright 2015 Ghoshna Jyoti et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The esterification reaction is reversible and has low yield. In order to increase the yield of reaction, it is required to simultaneouslyremove the product of reaction. For this membranes are the viable approach. Pervaporation membranes have success in removalof components in dilute forms. Membrane performance is represented in terms of flux, sorption coefficient, separation factor, andpermeance.These factors are related to the thickness of membrane, temperature, and feed concentration. Higher flux is observed atlower membrane thickness and higher feed concentration of water and lower selectivity is observed at higher temperatures due toincreased free volume, lower viscosity, and higher feed side pressure. Different factors affect the pervaporation aided esterificationreactor setup such as effect of initial molar ratios of the reactants, effect of catalyst concentration, effect ofmembrane area, and effectof temperature. Large membrane size could provide higher surface for the transfer of acid, though the challenges of membranerupture do surround the studies. In the present review work, we tried to collaborate the works in totality of the pervaporationdesign starting from the membrane behavior to the process behavior. Different prospective fields are also explored which needinvestigation.
1. Introduction to Pervaporation
Separation of liquidmixtures by partial vaporization througha membrane (nonporous or porous) is the separation princi-ple in pervaporation. This results in collection of permeatingcomponent in vapor form, which may be either removed byflowing an inert medium or applying low pressure on thepermeant side. The driving force for pervaporation processis the difference in chemical potential, corresponding to theconcentration gradient between phases on the opposite sidesof the interfacial barrier. Sorption diffusion model is usedto describe the transport on the basis of difference in themolecular size instead of volatility as in the case of distillation.Thus, it could be effectively utilized as economical substituteazeotropic separations. In addition to this the no use of thirdcomponent and requirement of low energy consumption (dueto energy integration) are the add-on benefits [1, 2]. In thelast two decades, pervaporation is finding wide range of areasfor its application such as liquid hydrocarbons separations(petrochemical application, alcohol/ether separations) ,
removal of volatile organic compounds (VOCs) from water[6, 7], removal of water from glycerin , and dehydration tointensify esterification reaction [9, 10].
Pervaporation can be integrated with either distillationor a chemical production step to provide intensification andenergy integration. Pervaporation-distillation hybrid systemleads to a clean technology and offer potential savings inenergy because of reduced thermal and pressure require-ments. When integrated with reactions such as esterificationprocess, it offers the opportunity to shift the chemical equi-librium by removing the product of the reaction. Reactor-pervaporation hybrid method overcomes the inhibition ofthe chemical equilibriumof the process and therefore leads toan increased productivity. This process also allows one to useheat of the chemical reaction to increase the efficiency of thepervaporation process and leads consequently to potentialsavings in energy costs.
Membranes are successfully used in separation industriesas selective barriers to prevent unwanted solutes from perme-ating through.Thus the impurity is separated from the target.
Hindawi Publishing CorporationJournal of EngineeringVolume 2015, Article ID 927068, 24 pageshttp://dx.doi.org/10.1155/2015/927068
2 Journal of Engineering
Reverse osmosis Ultrafiltration Particle filtration
Sorption diffusion Hydrodynamic sieving control
0.000 0.001 0.01 0.1 1.0 10 100 1000(m)
Figure 1: The choice of membrane with respect to the size of particles encountered.
Separation is based on pore sizes and hence the membranesgot their characteristic names as microfiltration, ultrafiltra-tion, and nanofiltration membranes (Figure 1). Membranesare either porous or nonporous and in the separation basedon sizes, usually porous membranes are used. Pervaporationis the distinction class among above membranes as theseparation criteria are different. Pervaporation membranesare nonporous and have been widely employed for sepa-rating liquid mixtures. The separation feature is based onaffinity with membrane materials and hence the moleculehaving higher affinity is adsorbed and diffuses through themembranewhile themembrane retainsmolecules having lowaffinity.
2. Membrane Materials for Pervaporation
For pervaporation, the hydrophilic membranes were the firstone to achieve the industrial applications and were usedfor the organic solvent dehydration. The main industrialapplications in pervaporation even today are almost the sameas before, which is the dehydration of organic liquids. Bymodifying the active layer of these membranes with differentchemical compositions and structures, these membranesare enabled to extract water with broad ranges of fluxand selectivity [11, 12]. Commercially available hydrophilicmembranes are made of polymeric membranematerials suchas polyvinyl alcohol (PVA), polyimides, polymaleimides,Nafion, and polyacrylonitrile (PAN).
Presently there have been a number of investigatorsconcerning R&D of the hydrophilic membrane, which canbe cataloged into organic, inorganic, and organic-inorganichybridmembranes. Inorganicmembranes such as zeolite andsilica are generally used [13, 14]. Inorganic membranes arevery suited for high temperature applications (harsh envi-ronments) and generally these membranes are prepared bysol-gel method, which was appropriate to elaborate thin andporous layers with controllable porosity on a wide range ofchemically resistantmacroporous substrates .While theseinorganic membranes showed high dehydration efficiency,their industrialization process may be slow-paced due to thecomplicated large-scale preparation and high manufacturingcost. In addition to this, several kinds of commercial organic
membranes including PERVAP 2201 [16, 17], PERVAP 1005(GFT) , and GFT-1005  have been introduced to thepervaporation-esterification coupling process. Few studies oncross-linked poly(vinyl alcohol) membranes have also beeninvestigated, such as PVA with catalyst Zr(SO
Amberlyst [20, 21], cast on polyethersulfone [22, 23] and onpoly(acrylonitrile) . However, the inherent instabilities ofthese organic membranes severely limit their applications.
Organic-inorganic hybrid materials have been proposedto be the best choice for having both the functionality of theorganic moiety and the stability of inorganic moiety. Buddet al.  employed zeolite/polyelectrolyte (chitosan/poly(4-styrene sulfonate)) multilayer pervaporation membranes toenhance the yield of ethyl lactate. Adoor et al.  pre-pared aluminum-rich zeolite beta incorporated sodium algi-nate pervaporation membranes. Organic-inorganic hybridmembranes showed improved performance of pervaporativedehydration of solution, with better flux and retention.
Hydrophobic membranes used as pervaporation mem-branes are used to separate volatile organic compoundsfrom the body of water. Hydrophobic membrane systemsutilize molecules made from proprietary polymeric hollowfiber membranes. The membrane only permits the volatileorganic compound and rejects water molecule due to itshydrophobic nature. Hence, pervaporation integrated withmembrane separation technology serves as an interestingsubject for the separation of organic compounds such aspollutants and high-value products like aroma compounds.Here the membranes employed are polymeric in nature. Rarely, ceramic membranes  can also beused. However, when it comes to recovering volatile polarorganics from their very dilute solutions in water , theselectivity exhibited by polymeric membranes, as well asceramic membranes, is not high .
One of the most applied polymeric materials for organicseparation is polydimethylsiloxane (PDMS). PDMS exhibitshigh selectivity and permeability towards organic substancesbecause of the flexible structure and therefore is preferredfor the removal of organic compounds from water .Organic liquid membranes of oleyl alcohol (OA) were foundto demonstrate high selectivity for recovering species liken-butanol and acetone  from simulated fermentation
Journal of Engineering 3
Vacuum pumpFeed pump
Figure 2: Schematic diagram of pervaporation-chemical reactor integrated system.
broths. Employing tri-n-octylamine (TOA) as a supportedliquid membrane (SLM), Thongsukmak and Sirkar prepared liquid membrane of trioctylamine (TOA) in thecoated hollow fibers and demonstrated high selectivity of asmuch as 275, 220, and 80 for n-butanol, acetone, and et