Sorption and permeation of aqueous alkyl piperazines through hydrophilic and organophilic membranes: A transport analysis

A detailed analysis of separation of N-methyl piperazine (NMP), N-ethyl piperazine (NEP), and water was undertaken by the pervaporation technique. A systematic study of sorption and permeation of the aqueous alkyl piperazines through poly(dimethylsiloxane) (PDMS), styrene-butadiene rubber (SBR), PDMS filled with zeolites NaX and silicalite (SA-5), polyimide (PI), and poly(acrylonitrile-co-acrylic acid) (PAN-co-AA) was carried out at different concentrations and temperatures. Organophilic membranes showed higher selectivity toward alkyl piperazines during sorption, but permeation was in favor of water. Hydrophilic membranes, however, showed higher affinity toward water during both sorption and permeation. PI membrane showed higher selectivity for water than PAN-co-AA. A model was used to estimate the diffusion coefficients of the various permeants. It was found that the transport selectivity for water in organophilic membranes was due to high diffusion selectivity (for water) although sorption selectivity favored the piperazines.