Development of Novel Mixed Matrix Asymmetric Membranes for C02 Separation from Natural Gas

• Main Author: RAFIQ, SIKANDER
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: TP Chemical technology
• Online Access: http://utpedia.utp.edu.my/id/eprint/21196/1/2012%20-CHEMICAL%20-%20DEVELOPMENT%20OF%20MIXED%20MATRIX%20MEMBRANES%20FOR%20CO2%20SEPARATION%20FROM%20NATURAL%20GAS%20-%20SIKANDER%20RAFIQ.pdf; http://utpedia.utp.edu.my/id/eprint/21196/

The use of membrane technology for gas separation applications has been successfully employed since the last few decades. For efficient separation of C02 from natural gas, high performance gas separating membranes is desired. For C02/CIL. gas separation, asymmetric flat sheet membranes are preferred because of their high gas permeance as compared to dense films. In this study, various composition of polyimide (PI) ranging from 5 to 20 wt.% were blended with polysulfone (PSF) and used for the formation of asymmetric flat sheet membranes via dry/wet phase inversion technique. The performance of asymmetric membrane was further enhanced by incorporating inorganic silica of tetraethyl orthosilicate (TEOS) at various proportions ranging from 5-20 wt.% into the membrane system containing 20 wt.% PI (PSF/PI-20wt%) to form mixed matrix membranes (MMMs). All the membranes prepared were characterised using scanning electron microscopy (SEM), thermogravimetric (TGA), differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), mechanical analysis and followed by gas permeation analysis. Morphological analysis indicated that the surfaces of the fabricated membrane blends possessed homogenous surfaces and their cross-sections showed a non-porous top and a diminutive porous substructure. DSC analysis showed the existence of single glass transition temperature (T g) for different membrane blends which indicated miscibility among the polymeric blends. Mechanical analysis showed improvement in young's modulus, tensile strength and elongation at break properties with the increase in PI composition in the membrane blends. Solvents with various compositions ofN�methyl-2-pyrrolidone to dichloromethane (NMP/DCM) were used to prepare the membranes and it is found that 80/20 v/v% solvent composition offered maximum C02/CH4 gas separation performance. Heat treatment was carried out on the membranes prepared from the NMP/DCM (80/20) solvent composition which showed improvement in ideal selectivities with a slight decrease in the permeance for all the membranes. Kinetic analysis on the thermal degradation of the developed membranes was also studied using TGA analysis by Friedman's model approach. The thermal analysis showed improvement in the degradation temperature and increase in activation energy values with an increase in the PI contents in the PSF/PI membrane blends. The developed MMMs showed different morphologies of the surfaces and cross�sections of the membrane where agglomeration was observed at 20 wt.% silica loading. The DSC analysis showed the existence of a single T g value and it increased with the increase in the silica loadings in the MMMs. The XRD analysis showed a decrease in the d-spacing with the increase in silica loadings causing restriction in the polymer chain mobility. The kinetic analysis on the thermal degradation showed an improvement in the thermal stability and the activation energy increased with the increase in the silica contents. Mechanical analysis indicated a steady increase in Young's modulus and tensile strength up to 15 wt.% silica loading. Elongation at break decreased with an increase in the silica contents which indicated the rigidity of the MMMs. The gas permeation results showed that the C02 permeance increased from 73.7±0.2 GPU at 5 wt.% silica content to 95.7±0.4 GPU at 20wt.% silica content. However the maximum ideal selectivity, aco,ICH, of 61.0-60.2 at 2-10 bar feed pressure is observed at 15wt.% silica content. The selectivity using mixed gas analysis at various C02/CH4 compositions of 30/70 v/v%, 50/50v/v% and 30/?0v/v% showed consistent results with the ideal gas selectivity. Finally, various theoretical gas permeation models for predicting C02 gas permeance in the MMMs were applied. A closer look revealed that the existing models assumed the spherical shape of the fillers dispersed in the matrix; however, later investigations by SEM indicated the fillers shape to be actually prolate ellipsoids. It was observed that the percentage of average absolute relative error (AARE %) values obtained from the MWS model were found to be in the range of 1.12-2.17 at 2-10 bar. Further investigations from the shape factor in the z-direction (nL) and the estimated shape factor (n,), AAR% deviations obtained were in the order of nr <n, <nz ; this indicated the importance of shape factor parameter for estimating true C02 permeance.