Next Generation Mixed Matrix Membranes for CO2 Separations aimed at Energy & Environmental Issues

Abstract

Next Generation Mixed Matrix Membranes for CO2 Separations aimed at Energy & Environmental Issues

The gas separation process is mainly governed by membrane technology in different industries. Currently, gas separations acquire a membrane market of over four hundred million dollars per year which comprise 24% of the overall membrane market. The components of feed mixture can be efficiently separated via membranes, which exhibit promising potential, based on size, shape and physiochemical properties of the components. Generally, inorganic membranes (e.g. alumina, zeolite, carbon etc.) exhibit high separation efficiency and can withstand under high thermal and chemical exposure than polymeric membranes. However, their commercial application is limited due to some disadvantages such as their brittleness, difficult processing and high cost. In past decades, polymeric membranes have attracted the attention of researchers due to their promising intrinsic advantages of efficient removal of unwanted gases from feed stream economically. Gas separation membranes are efficiently used for natural gas treatment, hydrogen recovery, and oxygen and nitrogen recovery from air. The aim of this research work was to fabricate promising mixed matrix membranes with superior CO2 selectivities and high permeabilities at high temperatures and pressures. In chapter 2 of this thesis, MMMs were synthesized comprising of F-SPEEK polymer and zeolite 4A as filler. Gas separation studies for both pure and mixed gases were examined and results revealed the considerable increase in permeability and selectivity at higher filler loadings. Moreover, the combined effect of sulfonic and fluorine groups in the polymer matrix significantly improved molecular sieving effect, fixed pores and high free volume which resulted in enhanced gas separation performance. The increasing permselectivity of F-SPEEK/4A MMMs proved to be an effective material for CO2 sequestration. Chapter 3 deals with Bio-MOF-11 based PSf MMMs for CO2 separation. BioMOFs are the sub-class of MOFs which have Lewis basic sites in their structures. BioMOF-11 consists of nitrogenous base adenine with five nitrogen in the ring which has a strong affinity towards CO2 gas molecules. The gas separation results showed outstanding. CO2 permeabilities (upto 210%) and selectivities (upto 100%) at higher MOF loadings as compared to pure polymer. These performances were attributed to the cobalt-adeninateacetate paddle wheel clusters. Chapter 4 focusses on the investigation of highly stable zirconium based MOF UiO66. MOF particles first functionalized with the sulfonic group which was grafted by the silane coupling agent MPTMS. Sulfonic group imparted high separation properties to the UiO-66 MOF. PSf was used as a polymer matrix and MMMs were synthesized of nonfunctionalized and functionalized UiO-66 and their results were compared. The ideal and mixed gas performance of the synthesized MMMs was investigated by DSC, SEM and results from density and FFV measurements that proved good MOF‐polymer adhesion. Moreover, the MMMs exhibited high CO2 permeabilities and selectivities and proved this material promising for the CO2 separation. PIM-1 and Cu-MOF based MMMs were studied in chapter 5 of this thesis. PIM-1 is well-known for its high rigid backbone structure, interconnected voids and high free volume, high permeabilities ranging from several hundred to thousands (3000-8000 barrer) and comparable selectivities. Cu-MOF consists of a paddle wheel structure which on incorporation with PIM-1 results in high stability and superior gas separation performance.