Keywords:CO2, hydrogenation, Ni nanocatalyst, supercritical state, CCS technology
Carbon dioxide (CO2) capture and storage (CCS) technology is a promising tool for reducing anthropogenic CO2 emissions from fossil fuel combustion or other industrial sources to the atmosphere. The collected CO2 can then be injected into geological formation reservoirs beneath low-permeability caprocks (shale or mudstone) at depths below 800 m. Within the geological environment, the injected CO2 becomes in a supercritical state beyond its critical point (approximately 304K and 7.4 MPa) and migrates upward and eventually reaches at the bottom of caprock in the course of CO2 injection due to the buoyancy effect of less-dense supercritical CO2 (scCO2). Also, considering natural structure of geological barriers such as caprocks, numerous pre-existing fractures are present, which may allow stored CO2 to escape through them during CO2 injection period, albeit extremely slowly, i.e. CO2 leakage risk. Most notably, long-term stabilization of the injected CO2 plays a critical role in the safe implementation of this technology, In fact, within geological reservoirs, majority of the stored CO2 still remained as an immiscible phase of CO2 in a supercritical state after 20 years of post-CO2 injection. Owing to such challenges, we propose a novel CCS technology involving the direct conversion of CO2 into hydrocarbon compounds without acting buoyancy force in a geological environment, by co-injecting a nanocatalyst with CO2 into the CO2 geological reservoir.
Our purpose of this study is to examine the catalytic activity for CO2 conversion in the scCO2 state using a nickel (Ni) nanocatalyst, which is widely used for a noble metal related to CO2 capture and utilization and Fischer-Tropsch Synthesis technologies, on a laboratory scale.
Our results demonstrate that under CO2 geological storage conditions, Ni nanocatalyst tested makes it possible to occur CO2 hydrogenation to hydrocarbon compounds affording various wide variation of long-chain n-alkanes from liquid to solid phases, which could lead to reducing the risk of CO2 leakage from storage reservoir through fractures in the caprocks.