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The membrane separation process such as pervaporation is the basic unit
operation with wide range of applications such as the dehydration and recovery of
organic compounds from water. This technique consists of permeation of
components into a membrane followed by evaporation on the permeate side and operates
on the principle of selective permeation of a liquid component through a membrane.
Although Poly Vinyl Alcohol (PVA) membranes have some unique
characteristics like: good chemical stability, film forming ability and high hydrophilicity, one
of their limitations is their high solubility in water. So, in order to get a
stable membrane, it must be insolubilized by cross linking. Two types of
crosslinked PVA membranes of hydrophilic nature were
used: one is Maleic acid (MA) crosslinked PVA (PVAMA) and the other is Citric acid (CA) cross-linked
PVA (PVACA). To judge the suitability, these membranes were used for the
removal of water in the esterification of ethanol and acetic acid by pervaporation.
The PVACA membrane showed good separation capability of water.
The most common reaction system studied for the application of
pervaporation reactor is an esterification reaction between an alcohol and an acid in the
presence of a catalyst. Esterification reactions are typically limited by
thermodynamic equilibrium, and face challenges with product purification. Commercially,
they are carried out using either large excess of one of the reactants, or by
removing one of the products through reactive distillation. The former is relatively
inefficient approach because it requires a large reactor volume. As a result, reactive
distillation, which favorably shifts the equilibrium through the removal of one of the products,
is becoming more common in plant scale production. It is, however, an
energy demanding operation and is not recommended when dealing with
temperature sensitive chemicals or biocatalysts. These difficulties motivated the
development of other coupled reactive/separation processes. Pervaporation reactors,
in particular, receive increased attention as a potentially competitive alternative
to reactive distillation. |
