Enhancement of the Separation Performances of High Free Volume Polymers for CO2 Capture

Abstract

Poly(1-trimethylsilyl-1-propyne) (PTMSP) is a high free volume polymer exhibiting preferable properties such as a very high permeability for application in gas separation. Still, the poor selectivity of PTMSP need to be dealt with before the polymer can be economically and technically viable to utilize. This thesis will focus on creating a mixed matrix membrane by addition of nanoparticles into the polymer phase. The nanoparticles are ZIF-7, ZIF-8 and ZIF-8L which are known to have good properties in relations to gas separation and an affinity for CO2, and the theory is that the nanoparticles can enhance the separation properties of the membrane. Nanoparticles of titanium dioxide (TiO2) were also used as fillers.

Analyzes show that the thermal stability of the mixed matrix membranes is good, and that the particles are evenly distributed throughout the membrane matrix when the membranes are fabricated using a casting knife. The solvent used for membrane preparation has proved to be very important. For a pure PTMSP membrane the permeability was reduced by 40% while the separation factor was increased by 150% when changing from chloroform to cyclohexane.

The addition of nanoparticles into the membrane matrix was done with varying results. Only the addition of ZIF-7 increased the separation factor to an extent compared to the linked pure membrane. Overall, the particles were well embedded in the matrix, but did not enhance the separation properties to a great extent. ZIF-8L also showed instability in contact with water vapour.