Amine functionalized ordered mesoporous silicas for the capture of post combustion flue gas CO₂ via adsorption technologies

Ordered mesoporous silicas (HMS, SBA-I5 and MCF) were functionalized by aminoalkylsilylation via treatment with aminopropyltrialkoxysilane, ethyelendiaminepropyltrialkoxysilane and diethylenetriamine-propyltrialkoxysilane, and separately loaded with the amine polymers polyethyleneimine and polyallylamine via "wet impregnation" to prepare solid amine sorbents for the potential application to capture the post combustion flue gas CO2 emitted by air fired fossil fuel power generators towards reducing anthropogenic greenhouse gas emissions. Silylations were initially mediated via traditional conventional stirred reactor and refluxing solvent techniques, then subsequently via the assistance of sonication and acid gases and via treatment with silane vapors towards improving the extent of aminoalklylsilylation and thereby the CO2 capacity of the sorbent. Sonication and acid gas treatments were found to lead to higher capacity sorbents than the more traditional preparative techniques. The CO2 capture potential of the sorbents was characterized via a custom modified thermogravimetric analyser combined differential thermoanalyser and a custom made "adiabatic" rig, the potential of the sorbents for CO2 capture via vacuum swing adsorption process technology was in particular targeted, however the sorbents were also considered in the context of a potential temperature swing adsorption process. The sorbents were found to exhibit useful selective CO2 sorption capacities which were achieved via the reversible chemisorption of CO2 via reaction with the amine groups to form ammonium carbamates. The larger porosity OMS sorbents were found to lead to higher capacity sorbents on account of their ability to contain more of the active sorbent phase. Sorption at relatively higher process temperatures, as possible for flue gas, was preferred to achieve the kinetics required for VSA processing of the higher capacity sorbents on account of the temperature dependence of the diffusion of gases through the amine sorbent phase. The high process temperatures lead to decomposition of the sorbent by urea formation via carbamate dehydration, however the incorporation of water into the feed gases (such as is in combustion flue gases) was found to inhibit this process and so validate the potential of these types of materials for the proposed application. The sorbents were otherwise found to exhibit stability. Pelletized forms of the sorbents, such as it is thought would be required for industry application, were prepared via compression either in amine form, or in carbamate form for otherwise solid in liquid dispersions. Such pelletized sorbents were likewise found to exhibit viable, albeit reduced, CO2 working capacities under the conditions tested. Solid amine sorbents prepared were thus found to be a promising potential option for the post combustion capture of CO2 towards reducing anthropogenic greenhouse gas emissions.