A review on thermodynamic modeling of pervaporation for organic compounds removal from dilute aqueous solutions

Benzene, toluene, and xylene (BTX) isomers are major components of gasoline. They are also used extensively as solvents and feedstocks by chemical industries.Compared to other hydrocarbons, BTX have relatively high water solubility; accidental gasoline spills and leaky service station tanks are prime sources of aquifer contamination. Because of their water solubility and their acute toxicities and genotoxicities, BTX compo-nents are classified as priority pollutants by the U.S. Environmental Protection Agency.The thermodynamic models of Flory-Huggins, UNIFAC-FV and UNIFAC-ZM for separating mixtures of substances such as water/benzene, toluene/chloro-form and benzene/cyclohexane have been reviewed. A modified solution-diffusion model was established based on Flory-Huggins thermodynamic theory and Fujita's free volume theory. This model was used for description of mass transfer of benzene removal from dilute aqueous solutions through PDMS membranes. A predictive model was proposed based on solution-diffusion mechanism to predict mass transfer during pervaporation process. The solubility of components in the membrane was described by UNIFAC-FV model, and the diffusion coefficients in polymeric membrane were calculated by free volume and Vrentas-Duda theories. It has shown that the proposed model can be applied to select membrane materials and predict the permeation flux and selectivity of components through the polymeric membrane. A modified solution-diffusion model is proposed to account for the mass transport of penetrants in the polymer membrane. In the model, the group contribution method (UNIFAC-ZM model) is introduced to calculate the activity of penetrants in the polymer membrane. This model has advantage over the UNIFAC-FV model that it does not require the knowledge of the molar volumes of the system components

Keywords:

Thermodynamic models , Pervaporation , PDMS membrane , Benzene , Aqueous solution