Polymerization with Monomeric Amines NS-300 Membrane

INTERFACIAL POLYMERIZATION WITH MONOMERIC AMINES NS-300 MEMBRANE 

The initial studies by Cadotte on interfacially formed composite polyamide membranes indicated that monomeric amines behaved poorly in this membrane fabrication approach. This is illustrated in the data listed in Table 5.2, taken from the first public report on the NS-100 membrane.22 Only the polymeric amine polyethylenimine showed development of high rejection membranes at that time. For several years, it was thought that polymeric amine was required to achieve formation of a film that would span the pores in the surface of the microporous polysulfone sheet and resist blowout under pressure However, in 1976, Cadotte and coworkers reported that a monomeric amiri piperazine, could be interfacially reacted with isophthaloyl chloride to give a polyamide barrier layer with salt rejections of 90 to 98% in simulated seawater tests at 1,500 psi.4s This improved membrane formation was achieved through optimization of the interfacial reaction conditions (reactant concentrations, acid acceptors, surfactants). Improved technique after several years of experience in interfacial membrane formation was probably also a factor. 

A typical formula for membrane fabrication consisted of an aqueous phase containing 1 1 0.5 weight percent piperazine sodium hydroxide dodecyl sodium sulfate, and a hexane phase containing 1.0 percent weight/volume of isophthaloyl chloride. This membrane exhibited up to 26 gfd and 98% seawater rejection (3.5% synthetic seawater, 1,500 psi, 25°C) and up to 4 gfd and 99.2% magnesium sulfate rejection (0.5% magnesium sulfate, 200 psi, 25°C). Unfortunately, seawater salt rejections in excess of 96% could not be produced routinely, and brackish water fluxes were too low to be attractive. 

To increase the flux of this membrane, partial or complete substitution of isophthaloyl chloride with trimesoyl chloride was examined.46 47 Dramatic changes in membrane flux and salt rejection were observed. Table 5.3 lists the results of this approach. As the trimesoyl chloride content of the acyl halide reactant was increased from 0 to 100%, seawater salt rejection dropped while 

Polyaraine Hater Flux ( fd) Salt Rejection (percent) 

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