Pervaporation plants

Fig. 42. Integrated distillation/pervaporation plant for ethanol recovery from fermentors. The distillation columns concentrate the ethanol—water mixture from 5 to 80%. The pervaporation membrane produces a 99.5% ethanol product stream and a 40—50% ethanol stream that is sent back to the distillation...

Morigami, Y., Kondo, M., Abe, J., Kita, H., and Okamoto, K. (2001) The first large-scale pervaporation plant using tubular-type module with zeolite NaA membrane separ. Purif. Tech., 25, 251-260. 

First commercial VOC-from-water pervaporation plant installed -1996... 

GFT constructs the first commercial pervaporation plant for dehydration of ethanol -1982... 

A flow scheme for an integrated distillation-pervaporation plant operating on a 5 % ethanol feed from a fermentation mash is shown in Figure 9.10. The distillation column produces an ethanol stream containing 80-90 % ethanol, which is fed to the pervaporation system. To maximize the vapor pressure difference and the pressure ratio across the membrane, the pervaporation module usually... 

Figure 9.10 Integrated distillation-pervaporation plant for ethanol recovery from fermentors...

G. Ellinghorst, H. Steinhauser and A. Hubner, Improvement of Pervaporation Plant by Choice of PVA or Plasma Polymerized Membranes, in Proceedings of Sixth International Conference on Pervaporation Processes in the Chemical Industry, R. Bakish (ed.), Bakish Materials Corp., Englewood, NJ, pp. 484-493 (1992). 

Sander U and Soukup P. Design and operation of a pervaporation plant for ethanol dehydration, J. Memb. Sci. 1988 36 463 75. 

Asada T. Dehydration of organic solvents. Some acmal results of pervaporation plants in Japan. In Backish R. ed.. Proceedings of the Third International Conference on Pervaporation Processes in Chemical Industry. Nancy, France, September 1988 Englewood, NJ Bakish Materials Corporation, 1988 379-386. 

In spite of all these hurdles, there are already industrial-scale applications of zeolite membranes for solvent dehydration [106] by pervaporation plants using tubular zeolite A membranes with 0.0275 m of permeation area each (see Section 10.2.3). Li et al. [280] have prepared large area (0.0260 m ) ZSM-5 membranes on tubular a-alumina supports. This work is also interesting from the industrial point of view because the authors used inexpensive n-butylamine as template. Indeed, the cost required for industrial modules, on a general basis, is still far from clear. However, it must be noted that most of the costs can be ascribed to the module, and only 10%-20% to the membrane itself [3]. This underlines again the importance of preparation of zeolite membranes on cheaper, alternative supports that can also pack more area per unit volume. 

Fig. 25 A pervaporation plant for methanol removal, f V eH> this art in color at www.dekker.com.)...

Pervaporation is a membrane process in which a liquid is maintained on the feed side of a membrane and permeate is removed as a vapor on the downstream side of the membrane. Pervaporation is used, because of its low energy consumption and low cost, to separate dissolved organics from water, purify waste water or volatile chemicals, and break azeotropes. Pervaporation plants range from processing a few grams per hour up to thousands of tons per year. For waste water treatment flow of less than 76 L min pervaporation is more cost-effective than other treatment options, such as chemical oxidation, ultraviolet destruction, air stripping followed by carbon adsorption, steam stripping, or distillation/incineration [262]. 

Methylethyl ketone Distillation is only possible with an entrainer because the azeotropic composition is nearly identical to the miscibility limit. Pervaporation is far superior. n-Butanol, n-propanol Form azeotropes with high water content so the distillation/phase separation process involves massive recycle streams. Pervaporation plants are less costly to build and easier to operate. 

Cation-exchanged zeolites show a strong tendency to adsorb water compared to organic molecules, as described in Chapter 7. As a consequence, water can be preferentially removed from solvents. By the use of porous tubes coated in zeolite membranes, water can be removed from the solvent on one side of the membrane and evaporated from the other side. The Japanese Mitsui company, for example, have commercialised the first large-scale pervaporation plant that produces over 500 Ih of solvents with less than 0.2 wt% water from simple alcohols containing 10 wt% water. The plant makes use of over 100 individual sections of NaA zeolite membrane operating at 120 °C. 

The membrane is the key component of a pervaporation plant and it must be protected from damage of other sorts. 

Fig. 3.5 Schematic design of two-stage pervaporation plant (Membrane Technology and Research Inc.).

Similar behavior is observed for the diffusion coefficient. Calculation of flux and selectivity for a membrane even for a simple binary mixture from singlecomponent data therefore requires measurements of solubility and diffusion for both components over the whole range of composition and of temperature of the mixture with high accuracy. For any practical application and engineering design of a pervaporation plant such an approach is not realistic. 

Here it and are the permeabilities of the better permeable and the retained component and Ap and Ap differences in the respective partial vapor pressures. Both R values have to be determined experimentally and are assumed to be constants for a given feed mixture and membrane and a narrow concentration range. Otherwise the same equations (12) to (15) as for pervaporation can be used and the respective constants have to be determined by regression analysis. Calculation of any practical installation is performed analogous to the method as described above for pervaporation plants. 

Figure 17.2 Inocermic semi-technical pervaporation plant (UK). Reprinted from J. Caro, M. Noack and P. Kolsch, Zeolite membranes from the laboratory scale to technical applications, Adsorption 11, 215-227, 2005, with permission of SpringerLink.

Zeolite membranes show high thermal stability and chemical resistance compared with those of polymeric membranes. They are able to separate mixtures continuously on the basis of differences in the molecular size and shape [18], and/or on the basis of different adsorption properties [19], since their separation ability depends on the interplay of the mixture adsorption equilibrium and the mixture. Different types of zeolites have been studied (e.g. MFI, LTA, MOR, FAU) for the membrane separation. They are used still at laboratory level, also as catalytic membranes in membrane reactors (e.g. CO clean-up, water gas shift, methane reforming, etc.) [20,21]. The first commercial application is that of LTA zeolite membranes for solvent dehydration by pervaporation [22], Some other pervaporation plants have been installed since 2001, but no industrial applications use zeolite membranes in the GS field [23]. The reason for this limited application in industry might be due to economical feasibility (development of higher flux membranes should reduce both costs of membranes and modules) and poor reproducibility. 

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