Exploring the cyclic use of potassium carbonate supported on alumina for CO2 capture in waterborne transport

In this work, two sorbents obtained by dispersion of 4 % and 20 % wt. potassium carbonate (K2CO3) onto γ-Al2O3 (namely K4-Al2O3 and K20-Al2O3) are tested in consecutive adsorption/regeneration cycles for CO2 capture from model gases simulating the exhausts of marine diesel engines. The experiments for K4-Al2O3 sorbent show that an increase in H2O concentration in the gas stream results in a 17 % increase in CO2 adsorption capacity per gram of sorbent. Coherently, the K2CO3 conversion degree becomes almost unitary. The presence of higher H2O concentration increases the adsorption rate, suggesting that H2O adsorption is the rate-controlling step of CO2 carbonation. The K20-Al2O3 sorbent shows an increase in CO2 adsorption capacity per gram of sorbent, which becomes almost 3.7 times greater than the figure retrieved for K4-Al2O3. Simultaneously, K20-Al2O3 shows a slower overall kinetics with respect to K4-Al2O3, probably due to the more marked diffusion limitations occurring at higher active phase load. The K4-Al2O3 sorbent is successfully tested during 30 carbonation/regeneration consecutive cycles for a gas stream containing 5 % H2O. A reduction of CO2 adsorption capacity of less than 10 % is observed at the end of the tests, while negligible differences in kinetic parameters are recorded during the cycles. On the contrary, the K20-Al2O3 sorbent presents a 60 % drop in CO2 adsorption capacity after the first cycle.