Molecular Dynamics Simulations of the Stability and Dissociation of Structure-H Clathrate Hydrates in the Presence of Different Amino Acids, Gas Species, and sH Hydrate Formers

Hydrate-based technologies for CO2 captureand storageor utilization (CCSU) have been perceived as a novel and effectiveoption to arrest increasing concentrations of CO2 in theatmosphere. In this regard, structure-H (sH) of the clathrate hydratesin terms of the operating conditions and storage capacity would bea proper alternative. In addition, the utilization of organic aminoacids is able to improve the features of CO2 hydrate-basedapproaches. However, the microscopic influences of such componentson CO2 sH hydrates are mostly unexplored, and the effectsof associated gas species as well as sH large guests at the molecularlevel still need to be studied. This work investigates the stabilityand dissociation of CO2 sH hydrates in the existence ofCH(4), N-2, H-2, amino acids, and variouslarge molecular guest substances via classical molecular dynamics(MD) simulations. Results reveal that the hydroxyl of amino acids,by attaching to the surrounding water molecules of the sH hydrate,weakens the hydrogen bonds of the water molecules in the sH clathrate.Also, the effects of such a physical approach are relevant to theoperating conditions. Unlike CH4 and N-2, thepresence of H-2 molecules significantly induces the mobilityof molecules in the clathrate network, which was even intensifiedwhen double cage occupancy for H-2 molecules was considered.This may be due to the significantly lower molecular weight of thismolecule in comparison with either CH4 or N-2. Moreover, in comparison to full occupation, the partial occupancyof small cages can contribute to the distribution of water moleculesin the sH clathrate hydrate. Among investigated sH hydrate formers,adamantane and 1,1-dimethyl cyclohexane were identified as the moststable sH hydrates, which suggests that the cyclic hydrocarbons withlarger carbon numbers may help large cages remain integrated.