Development of thermally stable and moisture responsive CO2- selective carboxymethyl chitosan based membrane
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The primary focus of the thesis is to develop a thermally stable and moisture responsive biopolymer-based membrane for CO2 separation. Among various biopolymers, chitosan possesses CO2 transport site as its structure consists of amine group. Moreover, chitosan has very good film forming ability and thermal stability without crosslinking. However, the limited solubility of chitosan in neutral and basic medium drives towards an alteration. Also, the unmodified chitin present in the chitosan solution may hinder the gas permeation through membrane. Therefore, carboxymethyl chitosan (CMC), a water soluble derivative of chitosan has come into picture. The optimum performance of CO2 separation was obtained for CMC membrane at 80 °C with supplied sweep/feed water flow ratio of 1.67 and feed pressure of 2/1.2 bar (feed/sweep) presenting a significant increase of CO2 permeance (~35 GPU) and CO2/N2 selectivity (~39) as compared to that of chitosan membrane. The membrane showed its thermal stability at the operating temperatures. Hence, CMC membrane was further explored for CO2 separation application by incorporation of different amines and fillers. In order to increase the amine content in the membrane matrix, piperazine (PZ), a small molecule amine was blended with CMC and utilized for CO2/N2 separation. Improved performance of CO2 separation was obtained for 20 wt. % PZ containing membrane at the same operating conditions as CMC membrane and exhibited more than two times increase in CO2 permeance (89 GPU) and CO2/N2 selectivity (103) as compared to that of pure CMC membrane. The membrane performance was found stable up to 3 days. Then poly (amidoamine) (PAMAM), a large molecule amine was blended with CMC which remarkably enhanced the CO2/N2 separation performance than pure CMC membrane.
Supervisor: Bishnupada Mandal