CO2 adsorption on amine-functionalized clays

Carbon capture using amine-modified porous sorbents is one of the main proposed technologies to reduce the CO2 atmospheric concentration. In this work, a wide series of inexpensive clays have been selected to assess their role as supports of amine-containing sorbents for CO2 capture. Montmorillonite, bentonite, saponite, sepiolite and palygorskite have been hydrated and functionalized by three routes: (a) grafting with aminopropyl (AP) and diethylenetriamine (DT) organosilanes; (b) impregnation with polyethyleneimine (PEI); and (c) double functionalization by impregnating previously grafted samples. XRD, FTIR and N-2 adsorption-desorption analyses along with nitrogen content and CO2 adsorption properties (thermogravimetry and fixed bed) have been evaluated for bare and functionalized clays. Under dry conditions (45 degrees C, 1 bar), grafted and impregnated samples yielded CO2 uptakes as high as 61.3 and 67.1 mg CO2/g ads (for Sepi-DT and Paly-PEI, respectively), with the latter being the best-performing sample in terms of CO2 uptake. On the contrary, double-functionalized samples displayed poor CO2 adsorption properties, probably due to pore-blocking problems related to their high organic loading. The presence of 5% H2O in the feed gas resulted in CO2 uptake increments from 17 to 27%. The adsorption performance of AP, DT and PEI-containing samples was maintained after three adsorption-desorption cycles.