Methane clathrate hydrate (MCH) is a promising energy resource, but controllable extraction of CH 4 from MCH remains a challenge. Gradually replacing CH 4 in MCH with CO 2 is an attractive scheme, as it is cost efficient and mitigates the environmentally harmful effects of CO 2 by sequestration. However, the practicable implementation of this method has not yet been achieved. In this study, using in situ neutron diffraction, we confirm that CH 4 in the 5 1262 cages of bulk structure-I (sI) MCH can be substituted by gaseous CO 2 under high pressure and low temperature with a high substitution ratio (∼44%) while conserving the structure of the hydrate framework. First-principles calculations indicate that CO 2 binds more strongly to the 5 1262 cages than methane does, and that the diffusion barrier for CH 4 is significantly lowered by an intermediate state in which one hydrate cage is doubly occupied by CH 4 and CO 2. Therefore, exchange of CO 2 for CH 4 in MCH is not only energetically favorable but also kinetically feasible. Experimental and theoretical studies of CH 4/CO 2 substitution elucidate a method to harness energy from these combustible ice resources.
ASJC Scopus subject areas
- Physics and Astronomy(all)