Separation of liquid mixtures by using polymer membranes. I. Permeation of binary organic liquid mixtures through polyethylene

Abstract

AbstractThe permeation characteristics and the separation behavior of 25 combinations of binary liquid mixtures through low‐density polyethylene membrane have been investigated. The organic compounds studied were members of the homologous series of liquid aliphatic hydrocarbons between n‐pentane and n‐nonane as well as some aromatic and cyclic compounds. A special permeation cell was designed in order to study permeation rates at different temperatures ranging from 25 to 45°C. The rate of permeation increased with temperature, and it was found that the temperature dependence of the permeation rate for both pure compounds and mixtures could be expressed by Arrheniustype relationships. The efficiency of separation, however, decreased with increasing temperature. Activation energies of permeation rànged from 16–22 kcal/mol for pure compounds and binary mixtures of benzene, n‐hexane, cyclohexane, and 2–2‐dimethylbutane. The effects of chemical nature, molecular size, and molecular shape of the diffusing species on the permeation and separation were studied and qualitative guidelines were suggested. The effect of the composition of the binary mixtures on the permeation rate has been investigated for several systems. Permeation enhancement effects were observed in which the mixtures permeate considerably faster than either of the pure components. Maximum permeation rates occurred at about 50 wt‐% mixtures for the systems benzene–n‐hexane and benzene–cyclohexane. This phenomenon is explained in terms of a combined internal plasticizing and solubility effect.