Utilization of alumina-supported K2CO3 as CO2-selective sorbent: A promising strategy to mitigate the carbon footprint of the maritime sector

Abstract

This paper investigates the application of K2CO3 supported onto porous alumina, as sorbent for selective CO2 capture in marine applications. Alumina-functionalized sorbents were prepared by incipient wetness impregnation achieving K2CO3 loadings from 3.6 to 14.1% wt. Carbonation tests were performed in a fixed-bed column at temperatures between 60 and 105 °C, as those typically occurring at the outlet of a scrubber and/or a waste heat recovery unit, with a model diesel engine exhaust (5% vol. CO2, 5% vol. H2O, balance N2). According to the carbonate loading, the sorbents may reach conversion degrees of carbonate up to 90% and overall capture capacity up to 0.66 mol kg−1 sorbent. Experimental data showed higher conversion degree and capture capacity compared with unsupported K2CO3, which is affected by significant intraparticle diffusion limitations. Steam regeneration tests performed in a fixed-bed column on the sorbent with 3.6% wt K2CO3 loading revealed that a temperature of 120 °C assures almost complete recovery of captured CO2 while preserving the sorbent carbonation degree for 10 consecutive carbonation/regeneration cycles. The preliminary design of a temperature swing carbonation/regeneration unit for on-board ship installation was performed for the reference case study of a passenger ship equipped with a 4.35 MW marine engine fueled with marine gas oil and with a commercial seawater scrubber for SO2 removal. The proposed unit appeared able to cut up to 30% carbon dioxide emission by using the sorbent containing 3.6% wt K2CO3 and operating the carbonation and regeneration stage at 60 and 120 °C, respectively.