Measurements of partition, diffusion coefficients of solvents in polymer membranes using rectangular thin-channel column inverse gas chromatography (RTCCIGC)

Rectangular thin-channel columns were designed to determine partition and d iffusion coefficients of small molecular weight solvents in polymer membran es based on the inverse gas chromatography (IGC) technique. The advantage o f using this novel column was analyzed in terms of uniform distribution of polymer thickness, ease of preparation of stationary phase (thin polymer la yer), and repeated use of the column. A mathematical model was developed to describe the velocity profile of the carrier gas, and both the time- and l ocation-dependent concentration profiles of solvent in the column. By using the moment analysis method, the partition coefficient and diffusion coeffi cient were related to the dimensionless first moment and dimensionless seco nd central moment of the elution curve of the solvent, respectively. The first dimensionless moment of the elution curve was found to be indepen dent of the carrier gas velocity, while the second central moment increased with the increase of the carrier gas velocity. Both these behaviors suppor t the theoretical predictions. The diffusion and partition coefficients of ethanol were obtained on polymers of cellulose diacetate (CDA) and sulfonat ed poly(ether ether ketone) (SPEEK) with a sulfonation degree of 79% over d ifferent temperature ranges. Based on the Arrhenius formula, the diffusion activation energies and the solvent dissolution enthalpies in both polymers were also obtained. The diffusion coefficients of 1-propanol were also obt ained using two different lengths of columns. (C) 2001 Elsevier Science B.V . All rights reserved.