Membrane separation processes pervaporation

Wee SL, Tye CT, Bhatia S. Membrane separation process— Pervaporation through zeolite membrane. Sep Purif Technol 2008 63 500-516. 

Wee, S.-L., Tye, c.-T. and Bhatia, S. (2008) Membrane separation process— pervaporation through zeolite membrane. Separation and Purification Technology, 63, 500-516. 

Pervaporation is a membrane separation process in which a dense, non-porous membrane separates a liquid feed solution from a vapour permeate (Fig. 19.2c). The transport across the membrane barrier is therefore based, generally, on a solution-difliision mechanism with an intense solute-membrane interaction. It... 

Pervaporation is a membrane separation process where the liquid feed mixture is in contact with the membrane in the upstream under atmospheric pressure and permeate is removed from the downstream as vapor by vacuum or a swept inert gas. Most of the research efforts of the pervaporation have concentrated on the separation of alcohol-water system [1-20] but the separation of acetic acid-water mixtures has received relatively little attention [21-34]. Acetic acid is an important basic chemical in the industry ranking among the top 20 organic intermediates. Because of the small differences in the volatility s of water and acetic acid in dilute aqueous solutions, azeotropic distillation is used instead of normal binary distillation so that the process is an energy intensive process. From this point of view, the pervaporation separation of acetic acid-water mixtures can be one of the alternate processes for saving energy. 

Table 1.1 shows two developing industrial membrane separation processes gas separation with polymer membranes (Chapter 8) and pervaporation (Chapter 9). Gas separation with membranes is the more advanced of the two techniques at least 20 companies worldwide offer industrial, membrane-based gas separation systems for a variety of applications. Only a handful of companies currently offer industrial pervaporation systems. In gas separation, a gas mixture at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the feed mixture the membrane permeate is enriched in this species. The basic process is illustrated in Figure 1.4. Major current applications... 

The layer of solution immediately adjacent to the membrane surface becomes depleted in the permeating solute on the feed side of the membrane and enriched in this component on the permeate side. Equivalent gradients also form for the other component. This concentration polarization reduces the permeating component s concentration difference across the membrane, thereby lowering its flux and the membrane selectivity. The importance of concentration polarization depends on the membrane separation process. Concentration polarization can significantly affect membrane performance in reverse osmosis, but it is usually well controlled in industrial systems. On the other hand, membrane performance in ultrafiltration, electrodialysis, and some pervaporation processes is seriously affected by concentration polarization. 

K.W. Boddeker and G. Bengtson, Selective Pervaporation of Organics from Water, in Pervaporation Membrane Separation Processes, R.Y.M. Huang (ed.), Elsevier, Amsterdam, pp. 437-460 (1991). 

Volume 1 Pervaporation Membrane Separation Processes Edited by R.Y.M. Huang (1991)... 

Desorption on the downstream side of the membrane is generally considered to be rapid and nonselective. The gas phase diffusivities in the final step of transport are very high and hence this step offers the least resistance in the overall transport process. As a separation process, pervaporation relies on the difference in membrane permeabilities, which are dependent on the thermodynamics activities of the components to be separated. 

Sourirajan S and Shiyao Y. An approach to membrane separations by pervaporation. In Bakish R. ed.. Proceedings of Second International Conference on Pervaporation Processes in the Chemical Industries. Englewood, NJ Bakish Materials Corporation, 1987 1-10. 

Neel J (1991) In Huang RYM (ed) Pervaporation membrane separation processes. Elsevier, Amsterdam, p 42... 

Sorption and diffusion in polymers are of fundamental and practical concern. However, data acquisition by conventional methods is difficult and time consuming. Again, IGC represents an attractive alternative. Shiyao and co-workers, concerned with pervaporation processes, use IGC to study adsorption phenomena of single gases and binary mixtures of organic vapors on cellulosic and polyethersulfone membrane materials (13). Their work also notes certain limitations to IGC, which currently restrict its breadth of application. Notable is the upper limit to gas inlet pressure, currently in the vicinity of 100 kPa. Raising this limit would be beneficial to the pertinent use of IGC as an indicator of membrane-vapor interactions under conditions realistic for membrane separation processes. 

Koops, G.H. Smolders, C.A. Estimation and evaluation of polymeric materials for pervaporation membranes. In Pervaporation Membrane Separation Processes Huang, R.Y.M., Ed. Elsevier New York, 1991 253-278. 

Pervaporation (PV) is a membrane-separation process in which one or more components of a liquid mixture diffuse through a selective membrane, evaporate under low pressure on the downstream side, and are removed by a... 

Vapor permeation and pervaporation are membrane separation processes that employ dense, non-porous membranes for the selective separation of dilute solutes from a vapor or liquid bulk, respectively, into a solute-enriched vapor phase. The separation concept of vapor permeation and pervaporation is based on the molecular interaction between the feed components and the dense membrane, unlike some pressure-driven membrane processes such as microfiltration, whose general separation mechanism is primarily based on size-exclusion. Hence, the membrane serves as a selective transport barrier during the permeation of solutes from the feed (upstream) phase to the downstream phase and, in this way, possesses an additional selectivity (permselectivity) compared to evaporative techniques, such as distillation (see Chapter 3.1). This is an advantage when, for example, a feed stream consists of an azeotrope that, by definition, caimot be further separated by distillation. Introducing a permselective membrane barrier through which separation is controlled by solute-membrane interactions rather than those dominating the vapor-liquid equilibrium, such an evaporative separation problem can be overcome without the need for external aids such as entrainers. The most common example for such an application is the dehydration of ethanol. 

Vapor permeation (VP) and pervaporation (PV) are membrane separation processes whose only difference lies in the feed fluid being a vapor (VP) or a liquid (PV), respectively. This difference has impHcations for feed fluid handling as well as the nature of the transport phenomena occurring in the feed stream, as in VP the feed fluid is compressible whilst in PV it is effectively not however, this does not in any way affect the transport phenomena across and after the membrane barrier. For this reason, vapor permeation and pervaporation will be discussed simultaneously, with differences being expHcitly emphasized where necessary. 

Pervaporation is a contraction of the terms permeation and evaporation because the feed is a liquid, and vapor exits the membrane on the permeate side. Pervaporation is a membrane process for liquid separation, and today, it is considered as a basic unit operation for the separation of organic-organic liquid mixtures because of its efficiency in separating azeotropic and close-boiling mixtures, isomers, and heat-sensitive compounds. It allows separations of some mixtures that are difficult to separate by distillation, extraction, and sorption. Pervaporation is one such type of membrane separation process with a wide range of uses such as solvent dehydration and separation of organic mixtures. When a membrane is in contact with a liquid mixture, one of the components can be preferentially removed from the mixture due to its higher affinity and quicker diffusivity in the membrane. 

Commercial membrane separation processes include reverse osmosis, gas permeation, dialysis, electrodialysis, pervaporation, ultrafiltration, and microfiltration. Membranes are mainly synthetic or natural polymers in the form of sheets that are spiral wound or hollow fibers that are bundled together. Reverse osmosis, operating at a feed pressure of 1,000 psia, produces water of 99.95% purity from seawater (3.5 wt% dissolved salts) at a 45% recovery, or with a feed pressure of 250 psia from brackish water (less than 0.5 wt% dissolved salts). Bare-module costs of reverse osmosis plants based on purified water rate in gallons per day are included in Table 16.32. Other membrane separation costs in Table 16.32 are f.o.b. purchase costs. 

In creating your design, give special consideration to processes that reduce the energy expenditure of the plant. In one such process, pervaporation membranes are used to dehydrate ethanol. Pervaporation is a membrane separation process in which the feed and residue streams are liquid, but the permeate is a vapor. The combination of permeation and evaporation in the membrane gives rise to separation factors much greater than can be accomplished by distillation and can be used to break azeotropes. 

Pervaporation and membrane distillation (MD) are distinguished from the above membrane separation processes since phase change, from liquid to vapor, takes place in the process. 

Finally, in Chap. 8, attempts are made to correlate the AFM parameters, such as nodule and pore sizes, to the membrane performance data. Membranes used for a variety of membrane processes, including reverse osmosis, nanofiltration, ultrafiltration, microfiltration, gas and vapor separation, pervaporation, and other membrane separation processes, are covered in this chapter. AFM parameters are also correlated to membrane biofouhng. This chapter also includes appUcations of AFM to characterize biomedical materials, including artificial organs cind drug release. 

Huang, R.Y.M. 1991. Pervaporation Membrane Separation Processes. Elsevier Amsterdam. 

Membrane separation processes such as gas permeation, pervaporation, reverse osmosis (RO), and ultrafiltration (UF) are not operated as equilibrium-staged processes. Instead, these separations are based on the rate at which solutes transfer though a semipermeable membrane. The key to understanding these membrane processes is the rate of mass transfer not equilibrium. Yet, despite this difference we will see many similarities in the solution methods for different flow patterns with the solution methods developed for equilibrium-staged separations. Because the analyses of these processes are often analogous to the methods used for equilibrium processes, we can use our understanding of equilibrium processes to help understand membrane separators. These membrane processes are usually either conplementary or conpetitive with distillation, absorption, and extraction. 

This chapter presents an introduction to the four membrane separation methods most commonly used in industry gas permeation, RO, UF, and pervaporation. At the level of this introduction the mathematical sophistication needed to understand the membrane processes is approximately the same as that needed for the equilibrium-staged processes. A background in mass transfer (Chapter 15) will be helpful but is not essential. Detailed descriptions of these membrane separation processes are found in Baker et al. (1990), Eykanp (199Z), Geankoplis (2Q03), Kucera (2010). Noble and Stern (1985), Mohr et al. (1988), Mulder (1996), Osada and Nakagawa (1992), Hagg (1998), Ho and Sirkar (1992). and Wankat (1990). 

Huang, R. Y. M., and J. W. Rhim, Separation Characteristics of Pervaporation Membrane Separation Processes, in R. Y. M. Huang (Ed.), Pervaporation Membrane Separation Processes, Elsevier, Amsterdam, 1991, pp. 111-180. 

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