Cold sintered geopolymer and geopolymer-zeolite composite sorbents for CO2 capture

Geopolymer and geopolymer-zeolite composite monoliths were produced by cold sintering process (CSP) at 40°C and 56MPa or 168MPa, as solid adsorbents for CO2 capture. Structural integrity, surface area and adsorption capacity are achieved along with reducing the energy penalty, resulting in more efficient, durable and sustainable CO2 adsorbents. KOH or NaOH 4M were used as alkaline solutions (to wet the powders, namely a geopolymer with SiAl = 2.0 and KAl = 1.0, a geopolymer containing 81vol% of in situ formed zeolite NaA and commercial zeolite Na13X, and activate the near room temperature sintering process under pressure. This process resulted in relative densities approaching 60%. Pore size distributions, microstructures, specific surface areas up to 310m2 g-1 for geopolymer-Na13X based monoliths, and compressive strengths from 4 to 27MPa area found to be mainly dependent on the material composition. Adsorption isotherms for CO2 and N2 were also obtained to assess the performances of the adsorbents. The CO2 capacity of zeolite Na13X is basically preserved, reaching 1.9mmolg-1 (at 35°C and pCO2=0.1bar). The great CO2 capacity and CO2/N2 selectivity, especially at low CO2 partial pressure, makes these materials great candidates for post combustion carbon capture adsorbents.