Pervaporation membrane reactor process

Pervaporation membrane reactors (PVMR) are an emerging area of membrane-based reactive separations. An excellent review paper of the broader area of pervaporation-based, hybrid processes has been published recently [3.1]. The brief discussion here is an extract of the more comprehensive discussions presented in that paper, as well as in an earlier paper by Zhu et al [3.2]. Mostly non-biological applications are discussed in this chapter. Some pervaporation membrane bioreactor (PVMBR) applications are also discussed additional information on the topic can be found in a recent publication [3.3], and a number of other examples are also discussed in Chapter 4. 

Pervaporation membrane reactors are not a recent discovery. The use of a PVMR was proposed in a U.S. patent dating back to 1960 [3.6]. Though the technical details on membrane preparation and experimental apparatus were rather sketchy, the basic idea was described there, namely, the use of a water permeable polymeric membrane to drive an esterification reaction to completion. A more detailed description of a PVMR can be found in a later European patent [3.7], which described the use of a flat membrane (commercial PVA or Nafion ) placed in the middle of a reactor consisting of two half-cells. The reaction studied was the acetic acid esterification reaction with ethanol. For an ethanol to acetic acid ratio of 2, liquid hourly space velocities (LHSV) in the range of 2-5, and a temperature of 90 °C complete conversion of the acetic acid was reported. The use of PVMR for this reaction shows promise for process simplification, as indicated schematically in Figure 3.2, which shows a side-by-side comparison of a conventional and a proposed PVMR plant for ethyl acetate production. 

Chapter 3 is devoted to the topic of pervaporation membrane reactors. These are unique systems in that they use a liquid feed and a vacuum on the permeate side they also mostly utilize polymeric membranes. Chapter 4 presents a survey of membrane bioreactor processes these couple a biological reactor with a membrane process. Reactions studied in such systems include the broad class of fermentation-type or enzymatic processes, widely used in the biotechnology industry for the production of amino acids, antibiotics, and other fine chemicals. Similar membrane bioreactor systems are also fin-... 

Abstract Pervaporation is a peculiar membrane separation process which is currently being considered for integration with a variety of reactions in promising new applications. Indeed, pervaporation membrane reactors have some specific uses in sustainable chemistry, which is an area currently growing in importance. The fundamentals of this type of membrane reactor are presented in this chapter, along with the advantages and limitations of different processes. A number of applications are reviewed with particular attention given to potential future developments. 

Key words pervaporation, membrane reactors, integrated process, process intensification, catalytic membranes. 

It is worth briefly describing the pervaporation process in order to point out the characteristics that should be taken into account in the choice and the design of a pervaporation membrane reactor. 

Park B-G and Tsotsis T T (2004), Models and experiments with pervaporation membrane reactors integrated with an adsorbent system , Chem Eng Process, 43,1171-1180. 

In the membrane reactor shown in Figure 13.16(c), the chemical reaction and the separation step use the same membrane. However, in some processes it is desirable to separate reaction and separation into two distinct operations. If the net result of the process is to change the products of the chemical reaction, the process is still classified under the broad heading of membrane reactor. Two examples in which chemical reaction and separation are physically separated are shown in Figure 13.17. Figure 13.17(a) shows the use of a pervaporation membrane to shift the equilibrium of the de-esterification reaction [39,40], A portion of the organic solution in the esterification reactor is continuously circulated past the... 

Another area where membrane reactors have now reached the industrial scale is in pervaporation-based hybrid processes using various types of polymer membranes (for an informative review, see Ref. [78]). 

A novel type of membrane reactor, emerging presently, is the pervaporation reactor. Conventional pervaporation processes only involve separation and most pervaporation set-ups are used in combination with distillation to break azeotropes or to remove trace impurities from product streams, but using membranes also products can be removed selectively from the reaction zone. Next to the polymer membranes, microporous silica membranes are currently under investigation, because they are more resistant to chemicals like Methyl Tertair Butyl Ether (MTBE) [23-24], Another application is the use of pervaporation with microporous silica membranes to remove water from polycondensation reactions [25], A general representation of such a reaction is ... 

The efforts and advances during the last 15 years in zeolite membrane and coating research have made it possible to synthesize many zeolitic and related-type materials on a wide variety of supports of different composition, geometry, and structure and also to predict their transport properties. Additionally, the widely exploited adsorption and catalytic properties of zeolites have undoubtedly opened up their scope of application beyond traditional separation and pervaporation processes. As a matter-of-fact, zeolite membranes have already been used in the field of membrane reactors (chemical specialties and commodities) and microchemical systems (microreactors, microseparators, and microsensors). 

Of greatest interest to chemical processing is the rough region, which covers most polymer reactors, vacuum distillation columns, vacuum stripping columns, pervaporation membrane separations, vacuum-swing adsorbers, and vacuum crystallizers, evaporators, filters, and dryers. 

Gas separation (GS) is a relatively young technology and accounted for about US 230 million/year in 1998, but is growing fast with a rate higher than 15% a year. The development of membrane reactors is opening a number of new gas applications. For the electrically driven membrane processes the sales in 1998 were around US 180 million. For pervaporation (PV) in 1996 the market was about US 26 million, with a growth rate of 20%. 

Pervaporation, as a non-integrated process, is typically utilized for dehydration and for the recovery or removal of organics from aqueous solutions and sometimes also for the separation of organic mixtures (Neel, 1995). Also many hybrid processes have been developed where PV is coupled with other processes, such as different membrane processes (e.g., reverse osmosis, or organophilic pervaporation coupled with hydrophilic pervaporation), distillation, reactive distillation and, of course, reaction. With these aspects in mind, PV appears particularly suitable to keep the concentration of a by-product low, or to continuously recover a product while it is formed. Note that these are the main objectives typically pursued in membrane reactors. 

Photocatalytic membrane reactors have been analysed over the years (see e.g., Damodar and You, 2010 Grzechulska-Damszel et al, 2009 Molinari et al, 2002,2008,2009,2010 Mozia et al, 2008,2010), but only more recently has photocatalysis been coupled with pervaporation in an integrated process. 

Waldburger R M and Widmer F (1996), Membrane reactors in chemical production processes and the application to the pervaporation-assisted esterification ,... 

An early model describing the pervaporative reaction of acetic acid with ethanol was presented by Krupiczka and Koszorz (1999). It was a simple, three-parameter model describing the concentration profiles in the process (a kinetic approach was considered) in the form of three differential equations. The activity coefficients were calculated using the UNIFAC property method. A hydrophilic membrane PERVAP 1005 GFT was used. Differently, Tanna and Mayadevi (2007) developed a two-step series model to study the performance of the membrane reactor. In this case, the goal was the assessment of the parameters that drive the process. As a conclusion of this work, the authors suggested using a low-flux membrane with a sufficient surface area when designing a PVMR. 

Membrane Processes in Separation and Purification published in 1993, contains chapters on pervaporation, facilitated transport membrane processes, membrane gas absorption processes, hollow fiber contactors, membrane reactors, and the preparation and application of inorganic membranes. In addition to an introductory chapter by the editors. Polymeric... 

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