Separation of Phenol from Aqueous Streams by a Composite Hollow Fiber Based Pervaporation Process Using Polydimethyl siloxane (PDMS)/Polyether-Block-Amide (PEBA) as Two-Layer Membranes

In order to simultaneously achieve both high permselectivity and permeability (flux) for the recovery of aromatic compounds such as phenol from aqueous streams, a composite organophilic hollow fiber based pervaporation process using PDMS/PEBA as two-layer membranes has been developed. The process employed a hydrophobic microporous polypropylene hollow fiber, having thin layers of silicones (PDMS) and PEBA polymers coating on the inside diameter. The composite membrane module is used to investigate the pervaporation behavior of phenol in water in a separate study; and that of a mixture of phenol, methanol, and formaldehyde in an aqueous stream (a typical constituent of waste-water stream of phenol-formaldehyde resin manufacturing process) in another study. The fluxes of phenol and water increase relatively linearly with increasing concentration especially at low feed concentration, and exhibit a near plateau with further increase in concentration. As a result, the phenol/water separation factor decreases as the feed concentration increases. Significant improvement in phenol/water separation factor and phenol flux is achieved for this two-layer (PDMS/PEBA) membranes as compared to that achieved using only PDMS membrane. The phenol and water fluxes and the separation factor are highly sensitive to permeate pressure as all decrease sharply with increase in permeate pressure. For this membrane, an increase in temperature increases the separation factor, and also permeation fluxes of phenol and water. An increase in feed-solution velocity does not have a significant effect on phenol and water fluxes, and also on the separation factor at least within the range of the feed-solution velocity considered. In the study of pervaporation behavior of a typical constituent of wastewater stream of phenol-formaldehyde resin manufacturing process, phenol permeation shows a much higher flux and a higher increase in flux with increase in concentration is also exhibited as compared to that exhibited by methanol permeation. This thus indicates that the membrane is more permeable to phenol than to methanol and formaldehyde.