Development of composite membranes for the separation of miscible liquids by applying pervaporation technique to pressurised feed solutions

For the first time pervaporation separation of miscible liquids have been investigated with
three and five layered composite membranes with layers of Natural Rubber Latex (NRL)
and layers of hydrophilic, hydrophobic or organophilic polymers which are placed on top
of each other.
NRL was used in all different types of the membranes, mixed with hydrophilic polymers
in blend membranes and in a layer shape in the three or five layered composite
membranes. Methyl Cellulose (MC), Carboxymethyl Cellulose (CMC) and
Hydroxypropyl Methyl Cellulose (HMC) were used as hydrophilic polymers to increase
the water selectivity of the membrane and in contrast, Ultra-High Molecular Weight
Polyethylene (UHMWPE) and Polydimethylsilane were used to increase organic
component selectivity in the membranes.
These membranes were used to separate miscible liquid solutions including ethanolwater,
propanol 2-water and acetone-waterT. he composition of organic componenti n the
feed was varied within the range of 20 to 90% w/w. The temperature of operation was
kept constant to 20'C.
Scanning Electron Microscope (SEM) has been used to study the distribution of polymers
within the membranes. Morphological features of the cross section and top surface of the
membranes have been used to develop a probable mechanism of water or organic
component transfer through the membrane.
For the first time ever, DMTA technique has been used to identify the type of membranes
which can be used to increase the water selectivity (by studying the changes in the glass
transition temperatureo f the NRL, blend and compositem embranes).
Both SEM and DMTA techniques have proved that the presence of hydrophilic polymers
as in layer forms in the three or five layered composite membranes was the reason for
good distribution of polymers throughout the membrane. It has been established that a
very strong correlation exists between a good distribution of the polymer bridged clusters
of rubber particles within the membrane and the maximum increase in water selectivity.
The influence of using different types of alcohols (ethanol, propanol 2 and acetone) on the
pervaporation separation performance of the membranes has been thoroughly examined.
Using ethanol, having the lowest molecular weight as compared with the other solutions,
leads to the best performance in pervaporation separation.

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