Pervaporation-assisted Esterification

In industry, esterifications represent an important class of chemical reactions. As esterifications are equilibrium reactions (9), high yields can be obtained by adding an excess of one reactant or by constant removal of the produced water from the reaction mixture in order to shift the reaction to the product side. 

Application of pervaporation processes to selectively separate water from the reacting mixture forms an interesting alternative to conventional distillation, especially in the case of azeotrope formation and low-boiling reactants. 

Both polymer and ceramic membranes are applied in pervaporation-based reactors, for which Fig. 5.9 shows the two basic configurations [108]. Table 5.2 gives an overview of the performance of various pervaporation membranes and Tab. 5.3 shows some examples of membrane-assisted esterification reactions. In addition to these low molecular weight esters, pervaporation can also be used for the production of polycondensation esters (resins) [99, 100]. 

The influence of four different operating parameters on the conversion were evaluated [96], which can be divided into three groups  

Factors that influence directly the esterification reaction (the catalyst concentration and initial molar ratio) 

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Pervaporation forms an interesting alternative to separate water from the reaction mixture instead of distillation, especially in systems with azeotropes or low boiling reactants. Some examples of pervaporation-assisted esterifications are given in Tab. 13.3. Additionally, pervaporation can also be used for the production of polycondensation esters [36, 37]. 

Fig. 13.5 Concentration profiles in the pervaporation-assisted esterification of 1-propanol and propionic acid.

Fig. 13.7 Required reaction time for 95% conversion in the pervaporation-assisted esterification of tartaric acid with ethanol at different membrane area per reactor volume [35].

Table 5.3 Overview of pervaporation-assisted esterifications, adapted from [14].

Nguyen, Q.T., M Bareck, C.O., David, M.O., Metayer, M. and Alexandre, S. 2003. Ion-exchange membranes made of semi-interpenetrating polymer networks, used for pervaporation assisted esterification and ion transport. MMerRes Imov. 7 212—219. 

Benedict D J, Parulekar S J and Tsai S-P (2006), Pervaporation-assisted esterification of lactic and succinic adds with downstream ester recovery , J Membr Sci, 281,435-445. 

Figueiredo K C S, Salim V M M and Borges C P (2008), Synthesis and characterization of a catalytic membrane for pervaporation-assisted esterification reactors , Catal Today, 133-135,809-814. 

Figueiredo K C S, SaUm VMM and Borges C P (2010), Ethyl oleate production by means of pervaporation-assisted esterification using heterogeneous catalysis ,... 

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

More recently, composite polymeric catalytic membranes consisting of a dense layer of a mixed-matrix of tiny particles of Amberlyst-35 dispersed in PVA cross-linked with maleic add cast over a commercial PVA membrane (PERVAP 1000), were effidently used in the pervaporation-assisted esterification of acetic acid and ethanol. After 8 h of reaction, a 60% increase in conversion was observed for the catalytic membrane configuration, compared to an inert membrane/fiuidized-bed configuration. 

In spite of the growing research effort, with the exception of fuel cells, there are only a few examples of industrial applications of non-biocatalytic polymeric membrane reactors, such as the Remedia Catalytic Filter System for the destruction of dioxins and furans from industrial combustion sources or pervaporation-assisted esterification processes. More research is required in order to find long-lasting high-performance and cheap polymeric materials and catalysts that can effectively compete with the traditional processes. On pursuing this quest, mathematical modelling and simulation are fundamental tools for the better understanding of membranes behaviour and optimization. 

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