Separation of azeotropic mixtures of alcohols and water with FricDiff

FricDiff is an energy efficient separation process based on a difference in transport velocities of the components of a gas or vapor mixture when they diffuse through a sweep gas (‘enhancer’). The separation process takes place inside the pores of a non-selective macro-porous barrier. In this paper the separation of a 2-propanol–water mixture with the FricDiff-principle is studied, using CO2 as the enhancer. A detailed numerical model is developed that describes the separation process that takes place inside a cylindrical FricDiff-unit. In this unit the vapor mixture to be separated and the sweep gas flow at opposite sides of a porous barrier in a counter current mode. Through the porous barrier selective mass transport of components of the feed mixture through the sweep gas takes place resulting in a separation. The model takes into account axial velocity profiles as a result of laminar flow of the gas and vapor mixtures through the flow channels, radial concentration gradients and radial velocities. The transport through the porous barrier is described with the Binary Friction Model. The influences of process conditions and the characteristics of the porous barrier on the separation process are studied.