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Comprehending and controlling the stability and dissociation of greenhouse gases hydrates are critical for a variety of hydrate-based industrial applications, such as greenhouse gas separation, sequestration, or utilization. Although the promotion effects of greenhouse F-gases (F-promoters) and new cyclic promoters on CO2 hydrates have been acknowledged, the involved molecular mechanisms are poorly understood. This work was therefore conducted to investigate the intermolecular mechanisms of the properties of CO2 and NF3 hydrates using molecular dynamics (MD) simulation to better understand their stability and dissociation and the effects of thermodynamic conditions as well as cage occupancy. In addition, the stability of CO2/CO2 + CH4 hydrates in the presence of seven thermodynamic hydrate promoters (THPs) from different molecular groups or substituents was evaluated. Results reveal that after the breakup of the hydrate, the propensity of NF3 to form nanobubbles is more than that of CO2 molecules. The relative concentration distribution of partially occupied hydrates was also found to be greater than that of completely filled by guest gases. MD simulation results of CO2 double and mixed hydrates also show that the type of large molecular guests in the large cages plays a major role in the stabilization of the clathrate hydrate network. The structural properties, however, indicate that the resistance against being dissociated for CO2 + promoter can be somewhat increased when half of the CO2 molecules in small cages is replaced by CH4. In addition, the existence of neopentyl alcohol in large cavities was found to facilitate the process of hydrate dissociation by making new hydrogen bonds between hydroxyl groups and water molecules. Among studied systems with THPs, cyclopentane, and cyclohexane in comparison with F-promoters seem to be more susceptible to maintaining the stability of CO2 clathrate hydrate.

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Hydrate-based technologies for CO 2 capture and storage or utilization (CCSU) have been perceived as a novel and effective option to arrest increasing concentrations of CO 2 in the atmosphere. In this regard, structure-H (sH) of the clathrate hydrates in terms of the operating conditions and storage capacity would be a proper alternative. In addition, the utilization of organic amino acids is able to improve the features of CO 2 hydrate-based approaches. However, the microscopic influences of such components on CO 2 sH hydrates are mostly unexplored, and the effects of associated gas species as well as sH large guests at the molecular level still need to be studied. This work investigates the stability and dissociation of CO 2 sH hydrates in the existence of CH 4 , N 2 , H 2 , amino acids, and various large 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 the operating conditions. Unlike CH 4 and N 2 , the presence of H 2 molecules significantly induces the mobility of molecules in the clathrate network, which was even intensified when double cage occupancy for H 2 molecules was considered. This may be due to the significantly lower molecular weight of this molecule in comparison with either CH 4 or N 2 . Moreover, in comparison to full occupation, the partial occupancy of small cages can contribute to the distribution of water molecules in the sH clathrate hydrate. Among investigated sH hydrate formers, adamantane and 1,1-dimethyl cyclohexane were identified as the most stable sH hydrates, which suggests that the cyclic hydrocarbons with larger carbon numbers may help large cages remain integrated.

As the major greenhouse gas emission, releasing CO2 through human activities has already devastating consequences on the planet. In this context, hydrate-based (HB) techniques in favour of CO2 capture, sequestration, or utilization (CCSU) are perceived to be a novel option to arrest increasing concentrations of CO2 in the atmosphere. The end uses of captured CO2 encompass its utilization for different realms of industry such as food and beverage manufacturing plants; water desalination; metal fabrication plants; and secondary refrigeration. To offset the cost of CO2 capture as well as generating revenue, the increasing effectiveness of aforesaid techniques is crucial. Although HB approaches are faced with several limitations, the solution would be the inclusion of organic promoters which are classified as environmentally-friendly substances. However, the microscopic influences of such components on CO2 hydrates are mostly unexplored. This work highlights the CO2 clathrate hydrate stability and decomposition in the existence of organic additives through classical molecular dynamics (MD) simulations. The results can help to understand the molecular mechanisms involved in such CO2 hydrate systems which may also aid to find the more efficient organic promoters for HB applications.