Pervaporative reactor

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 ... 

If [k j is a diagonal matrix, the attainable products will not be affected by interfacial mass-transfer phenomena. In contrast, if the off-diagonal elements of the [k j matrix are not vanishing, mass transfer can have a strong influence on the products. As a consequence, the attainable product region of a membrane reactor, for instance a pervaporative reactor, can be shifted by tailoring the membrane material and/or its pore structure. 

Fig. 5.24 shows some illustrative results of a fixed-point continuation for the reversible reaction A + B o C carried out in a pervaporative reactor with internal reflux. The Damkohler number Da is used as continuation parameter. The boiling sequence p > was assumed so that the desired product C is obtainable as... 

When k c = kg = 1, the off-diagonal elements of [k ] are equal to zero and the RD process discussed in Section 5.3.2 (case b) is recovered. Then, the location of the attainable product composition only depends on the vapor-liquid equilibria. In Fig. 5.24, singular point curves for the attainable bottom products of the depicted counter-current pervaporative reactor are given as a function of ky c (Fig. 5.24a) and kg (Fig. 5.24b). For each set of membrane permeabilities there is one curve of possible singular points. The ftill circles on the singular point curves indicate stable nodes, that is th mark attainable bottom products. For the system considered, stable nodes are only obtained below the chemical equilibrium line. 

Fig. 5.24. Attainable regions of the bottom products (gray) of a pervaporative reactor (left) at different relative membrane permeabilities (dashed line chemical equilibrium line at K — 5, Damkohler number Da — 0...

Fig. 5.9 Configuration of a pervaporation reactor with an external pervaporation unit (1) and with an internal pervaporation unit (2), respectively [108].

It is not odd that the two most diffuse applications of pervaporation reactors are so dissimilar, since, as previously observed, pervaporation is a very versatile process. 

Much research on this topic is reported in the scientific literature and the obtained results are promising, but the process is not problem-free. For further information on this type of pervaporation reactor, see the following reviews that discuss the subject Lipnizki et al. (2000) Sanchez Marcano and Tsotsis (2002) Vane (2005) and Wasewar and Pangarkar (2006). 

Domingues L, Recasens F and Larrayoz M A (1999), Studies of a pervaporation reactor kinetics and equilibrium shift in benzyl alcohol acetylation , Chem Eng... 

Sanz M T and Gmehling J (2006b), Esterification of acetic add with isopropanol coupled with pervaporation. Part 11. Study of a pervaporation reactor , Chem g/, 123,9-14. 

Wasewar K L (2007), Modeling of pervaporation reactor for benzyl alcohol acetylation , Int J Chem React Eng, 5, article A6. 

Wasewar K L, Patidar S, Agarwal V K, Rathod A, Sonawane S S, Agarwal R V, Usln H and Inci I (2010), Performance study of pervaporation reactor (PVR) for esterification of acetic acid with ethanol , Int J Chem React Eng, 8, article A 57. 

Wasewar, K., Patidar, S., Agarwal, V. K. (2009). Esterification of lactic acid with ethanol in a pervaporation reactor modeUng and performance study. Desalination, 243, 305—313. 

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