Pervaporative separation has gained increasing attention lately. Due to the nature of its driving force thermodynamic separation limitations may be easily overcome. Close boiling and even azeotropic mixtures can be separated. Pervaporation operates at process temperatures below boiling point temperature of the feed which opens up the chance for integration of low temperature process heat.
Application of pervaporation in combination with reactive separations gives access to a variety of promising process concepts. Reactive separation of low molecular weight carboxylic acids, such as formic acid and acetic acid, from aqueous effluents is a very representative example. The carboxylic acids are esterified via reactive distillation and the low boiling esters along with excess alcohol phase are separated from the reaction broth in the distillate. When methanol is applied, a ternary mixture consisting of methyl formate and methyl acetate and excess methanol is obtained in the distillate phase, in which the binary mixture of methyl acetate and methanol exhibits a low boiling azeotrope. For product recovery and methanol recycle the process is coupled with pervaporative separation of methanol with hydrophilic PVA membranes. These membranes show high selectivity for methanol while allowing for sufficient permeate fluxes. Separation characteristics of methanol strongly depend on the feed composition, whether it is a binary or ternary mixture. The effect of the operation conditions feed temperature, feed composition and permeate pressure on methanol separation was investigated.
The high potential of the integration of reactive distillation and pervaporation for carboxylic acid removal from aqueous feed was confirmed.
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