Selection of elastomeric membranes for the removal of volatile organics from water

Abstract

SYNOPSISA wide range of homogeneous elastomeric membranes has been prepared using dicumylperoxide as a general cross-linking agent. The membranes have been used for both equilibrium sorption measurements and steady-state pervaporation experiments to study solution-diffusion phenomena in the removal of volatile organic components from aqueous solutions. Pervaporation experiments have been performed under identical hydrodynamic conditions in order to fix the boundary layer mass transfer coefficient a t a constant and known value. For comparison of the permeabilities of different pervaporation membrane materials, this is of utmost importance. A wide range of selectivity factors up to a value of 100,000 are obtained, whereas usually the permeabilities for the organic component are in the range of 10-'0-10-9 m'/s and 10-'4-10-'2 m 2 / s for water. The permeation and sorption data obtained for the various elastomers have been related to the chemical and physical nature of the elastomers through the solubility parameter and the glass transition temperature, respectively. Both diffusional and sorption effects seem to be important, determining the water-transport behavior in the elastomeric membranes. The solubility of the organic component appears to be independent of this combined solubility parameter. Differences in the permeabilities of the organic component can primarily be ascribed to structural parameters in the membrane material, like degree of unsaturation and presence of steric side groups. 0 1993 John Wiley & Sons, Inc.

Swelling of medical grade silicones in liquids and calculation of their cross-link densities

“…Two previous studies on silicones [25,57] obtained a value of ı p = 15.3 MPa 1/2 , while three other studies [10,34,53], suggested using ı p = 15.8, 16.2 and 15.1 MPa 1/2 , respectively.…”

“…Eq. (2) arises directly from the definition of , where l is the density of the liquid, and has been published previously [31][32][33][34]. All calculations of from are based on the Flory-Rehner theory [8], which states that the change in the Gibbs function on mixing a liquid with a polymer, of density , is given by…”

Polysiloxaneimide membranes for removal of VOCs from water by pervaporation

“…The degree of sorption for BT-DA-SIDA prepared by the two-pot system tends to increase with the hydrophobicity of organic compounds, and the degree of sorption of TCE is found to be the highest (about 1800 wt %). In Figure 4, the degree of sorption for the crosslinked PDMS membranes [25][26][27][28] is also shown, and compared with that of BTDA-SIDA prepared by the two-pot system. The degree of sorption for the crosslinked PDMS membranes increases gradually with the hydrophobicity of the organic compounds.…”

Removal of trace VOCs from water through PDMS membranes and analysis of their permeation behaviors

“…Elastomeric organophilic membranes that preferentially permeate organic compounds but retain water are widely used to remove organic compounds from water. Nijhuis et al 5 have prepared a wide range of homogeneous elastomeric membranes, such as nitrilbutadiene rubber (NBR), ethylene-propylene terpolymer (EPDM), and poly(dimethylsiloxane) (PDMS), which showed extremely high pervaporation. In selecting membrane material according to the solution diffusion mechanism by which the pervaporation process is most expressed, physicalchemical interactions with permeating molecules should be taken into account in terms of their solubilities and diffusivities in the membrane material.…”