Facilitated Transport of Propylene Through Composite Polymer-Ionic Liquid Membranes. Mass Transfer Analysis

Abstract

Separation of light gaseous olefins from paraffin's of the refinery process off-gasses has been traditionally performed by cryogenic distillation, which is a highly capital and energy intensive operation. This handicap creates an incentive for the investigation of alternative olefin/paraffin separation technologies. In this regard, membrane technology supposes a potential solution for process intensification. Previous works of our research group reported the use of facilitated transport composite membranes integrating the use of PVDF-HFP polymer, BMImBF 4 ionic liquid and AgBF 4 silver salt. In this type of membranes, the silver cations react selectively and reversibly with the olefin, allowing the separation via mobile and fixed carrier mechanisms. Ionic liquids were selected as membrane additives because in addition to their negligible vapor pressure that avoids solvent losses by evaporation, they provide stability to the metallic cation dissolved inside, and modify the structure improving the facilitated transport. This technology offers a commercial attractive separation alternative thanks to their modular form of operation, high values of selectivity and permeability and low operational costs. In the present work, propane/propylene permeation experiments involving the use ionic liquids and different membrane compositions were performed. Moreover, basing on the transport and equilibrium parameters previously obtained, a mathematical model description of the system will be proposed fitting the remaining parameters and allowing the design and optimization of the propane/propylene separation process at industrial levels.

A practical approach to fixed-site-carrier facilitated transport modeling for the separation of propylene/propane mixtures through silver-containing polymeric membranes

“…Comparing Figures 4 (a) and (b) it can be observed that the temperature has a strong influence on the permeation process, increasing the flux of propylene. This increase of the olefin flux is due to the enhancement in the gas diffusivity, as reported before [35].…”

“…The resulting selectivity ranges from 100 to 300. Given that previous studies involving pure gases report lower values of propane permeability in PVDF-HFP [35], a dragging effect caused by the high propylene fluxes is probably happening in membrane 3, resulting in a propane permeability increase. Figure 5 shows the difference between the experimental fluxes of propylene and propane.…”

“…Additionally, our research group has developed composite membranes incorporating ionic liquids to the matrix polymer in order to improve the separation performance and stabilizing the silver cations in the membrane [28,35].…”

“…effective permeability or "hopping constant" for the olefin through the reactive pathway. The values of diffusivity (D) and solubility (S) of propylene in the PVDF-HFP matrix have been calculated in previous works[35];…”

A Perspective of Solutions for Membrane Instabilities in Olefin/Paraffin Separations: A Review

“…This Ag + distribution through the membrane promotes the fixed and mobile carrier facilitated transport mechanisms, leading to higher permeabilities and selectivities. 133 In this line, Ortiz et al 22,134 developed a material with promising characteristics for the separation of light olefin/paraffin mixtures. Previous to the material choice, a thorough investigation on the most suitable IL to form the IL/silver salt pair was carried out 135,136 .…”