[H-SC07] 地球温暖化防⽌と地学（CO2地中貯留・有効利⽤、地球⼯学）

[HSC07-09] CO₂地中貯留条件下におけるCO₂の炭化水素化に関連したNiナノ触媒活性に関する研究

*藤井 孝志¹、朝比奈 健太¹、西岡 将輝¹、宮川 正人¹、徂徠 正夫¹ (1.国立研究開発法人　産業技術総合研究所)

キーワード：二酸化炭素、水素化、ニッケルナノ触媒、超臨界状態、CO2回収・貯留技術

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.