Carbon dioxide separation from flue gas by FSC (Fixed-Site-Carrier) membranes: Investigation on effect of polymer casting solution pH and process parameters on carbon dioxide separation at lab scale and pilot set-up scale

Abstract

In this master thesis work, the fixed site carrier (FSC) polyvinylamine (PVAm) composite membranes were studied for their CO2 separation performance with respect to the pH of their casting solution. The study was done at lab set-up scale using a humidified feed gas with different feed pressure values and membranes with the best separation performance were further studied at pilot set-up scale. A relationship was shown between the separation performance of these membranes and pH of their casting solution. Membranes made of casting solution from pH 4 to pH 10 showed an increase in separation performance with increase in pH. The increase in pH increased the amino groups which are crucial for facilitated transport of CO2 in PVAm membrane. The membranes of low pH (below pH 4) and high pH (above pH 10) affected the membrane support and the low separation performance shown by these membranes was related to this effect. The overall results showed a better separation performance by the membranes made from casting solution of medium pH (from pH 4 to pH 10). The study further showed an increase in separation performance with increasing humidity for all membranes. The high feed pressure was found to cause saturation of the carrier sites and compaction of the membrane which led to the decrease of CO2 permeance and selectivity of the membranes. At pilot set-up scale the CO2 permeance and selectivity of 1.92 m3(STP)/m2barh and 522 respectively with 61.5 % purity were obtained with a pH 4 membrane at low feed pressure and without vacuum on the permeate side. However, the permeance and selectivity were found to decrease with increasing vacuum pressure on the permeate side because of compaction of membrane. It was recommended that, pH 4, 5 and 10 membranes to be further investigated for their separation performance at different feed and sweep flow rates with water saturated sweep gas in order to establish the optimal operating conditions for the pilot set-up equipment when using these membranes.