Propylene - propane separation using mixed matrix films made of functionalized polymers and zeolitic-imidazolate frameworks

The work presented in this thesis investigates the use of membrane technology in lieu of the energy-intensive distillation process for propylene - propane separation. The polymeric membranes lack the selectivity necessary for efficient separation. A recent breakthrough occurred when the metal-organic framework filler “ZIF-8” was mixed with Polymers of Intrinsic Microporosity (PIMs) to synthesize mixed-matrix films with high propylene selectivity. At high ZIF-8 loadings, the compatibility between the organic PIM and the semi-organic ZIF-8 deteriorates. This work was the first to propose functionalizing the PIM with a “carboxyl” (-COOH) group to enhance the compatibility with ZIF-8. Due to the carboxyl’s higher electronegativity, stronger H-bonding is induced between the mixed-matrix components compared to the hydroxyl (-OH) functionalization proposed in previous studies; the -COOH functionalized polymer “6FDA-TrMCA” was selected for this purpose. In this work, material development activities were limited to the pristine “6FDA-TrMCA” films preparation. The performance of the mixed-matrix membrane was approximated using the Maxwell model, meeting the targeted measures. Since membrane simulation software tools are exclusive to the commercial membrane suppliers, the “quantitative” impact of the selectivity boost on the process performance measures (e.g., purity, recovery, recycle) is not measurable. As part of this work, a novel HYSYS extension “MemCal” was matured in collaboration with a partner to support the simulation of membranes in Aspen HYSYS. The pure polymeric and the mixed-matrix membranes were simulated for their performance in single- and in two-stage designs meant for propylene’s commercial grades production; factors such as feed the propylene content and trans-membrane pressure ratio were accounted for in the analyses. The polymeric membranes were found incapable of producing neither the chemical nor the polymer grades of propylene, even in a two-stage process. Alternatively, the mixed-matrix membranes with the recommended selectivity of 35 (i.e., feasible using 6FDA-TrMCA and ZIF-8) were found capable of producing the chemical and the polymer grades at practical recovery when utilized in the single- and two-stage designs, respectively. The future research should grant more attention to the mixed-matrix high-pressure operation subject, as the latter is a prerequisite for technology’s success.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat