Fabrication of Mixed Matrix Membrane for Hydrogen Separation

Abstract

Processed gas streams from the water gas shift reactor (WGSR) are enriched with CO2 and H2. It is mainly present in order of 18-20 % in processed gas after water gas shift reaction. Therefore, it is imperative to purify H2 from CO2 before it is used for different industrial applications. To upgrade hydrogen, it is necessary that such a process be adopted which gives maximum efficiency at low energy consumptions. Membrane technology has multiple advantages over other conventional technologies. Furthermore, the membrane is an economical, green process and can be easily retrofitted to the existing technologies. Permeability and selectivity are two major parameters that define the separation performance of membranes. High selectivity and permeability are required so that purified hydrogen can be obtained at a low cost. Different gas separation membranes have already been studied. The membranes can be made from a variety of materials such as carbon, metals, ceramics, and polymers. The polymeric membranes have advantages over other membrane materials due to their low cost and optimized separation performance. For this purpose, it has been proposed to use a mixed matrix membrane (MMMs), which comprises ZnO nano rods incorporated in cellulose acetate (CA) matrix, or a polymer blended membrane. The OH groups present on the surface of ZnO rods and Lewis’s acid-base interaction between ZnO and CO2 helps in the capturing of CO2.Blended membranes work in the same way, by including such groups in the matrix which have an affinity towards CO2. In this work, synthesis of series of blended membranes, consisting of CA with varying amounts of Polysulfone in Tetrahydrofuran and mixed matrix membranes consisting of ZnO rods in CA synthesized using Tetrahydrofuran (THF) as solvent. Single gas permeation analysis, SEM, XRD, FTIR, UTM, and DSC were used to study the permeation, morphology, chemical structure, presence of functional groups, mechanical and thermal properties respectively. It was found that ZnO rods-based CA membranes gave much better separation CO2/H2 selectivity of 2.77 containing 0.7 wt.% of ZnO rods in CA matrix with a permeability of 58.98 Barrer. The SEM micrographs of ZnO mixed matrix membranes showed a dense and more compact structure. Furthermore, they had a maximum tensile strength of 27.51 iv Mpa at ZnO loading of 0.1 wt.%. In the case of polymer blended membranes, the separation performance of pure CA membrane was enhanced by the addition of PSF. Gas permeation results show that permeability of CO2 increased with increasing concentration of PSF. Notable permeability (P= 60 Barrer) of CO2 and selectivity of CO2/H2 =1.99 of CA/PSF 2wt% were achieved at 25 0C and 2.5 bar compared to pure CA membrane. Modified Higuchi model was used for prediction of permeability of mixed matrix membrane. A good agreement between experimental and theoretical values was found while using a value of k of 3.99. After detailed studying of these two types of membranes, it was concluded that the separation performance of these membranes did not fulfill the industrial requirements, further research need to be carried out using new advanced materials.