The mechanism of gas hydrate formation in the presence of kinetic influencing additives has attracted much interest due to the importance of optimizing hydrate formation in areas such as energy supply and the environment. This paper presents experimental studies into hydrate formation of CO2 gas in the presence of sodium halide salts. Pressure and temperature changes versus time during the hydrate formation process were measured under the isochoric conditions. The effect of anion type and concentration on gas maximum uptake, conversion, storage capacity, induction time, and hydrate growth rate has been examined. Surface potential measurements of the hydrates provided further understanding of how halide anions affect CO2 hydrate formation kinetics. It is shown that sodium halides at an approximately 50 mM (mmol/L) concentration can increase gas consumption and conversion to hydrates, and sodium iodide and sodium bromide in a range of concentrations between 50 and 250 mM can significantly increase the hydrate formation kinetics. It has been concluded that, although salts are known as thermodynamic inhibitors, they can be kinetic promoters at low concentration, which enhances hydrate formation. It is argued that halide ions can significantly influence CO2 hydrate formation due to their strong effect on bulk and surface water structures.

Promoting the kinetics of CO 2 hydrate formation using additives is of great importance in industrial applications of gas hydrates such as capture and storage of carbon dioxide. However, the mechanism of hydrate formation in the presence of solid particles is not well understood. This paper aims to gain a better understanding of the fundamental aspects of CO 2 hydrates formation in the presence of hydrophobic silica nanoparticles. A novel mechanism for gas hydrate formation in the presence of hydrophobic particles was established from a series of well-designed experiments. Two types of particle stabilized systems, made by mixing hydrophobic silica nanoparticles and water, were tested: air-in-water foam and water-in-air powder (dry water). Gas consumption, CO 2 conversion, induction time, and hydrate growth rate have been examined to establish the influence of particle hydrophobicity and concentration on hydrate formation kinetics. The results show that the promoting effect depends on the particle hydrophobicity and concentration. The most hydrophobic silica (dry water) enhances the kinetics of CO 2 hydrate formation effectively. Cryogenic scanning electron microscopy, combined with energy-dispersive spectroscopy, was used to examine the morphology, microstructure, and pore characteristics of CO 2 gas hydrates, as well as elemental composition of the samples. To provide further insight into the adsorption of gas molecules at the water/solid interface, surface potential of the hydrophobic fumed silica particles in aqueous system before and after exposing to N 2 and CO 2 gas was measured. These results, in combination with the result of our recent study on the structure of dry water, successfully provided further detailed information on how hydrophobic fumed silica promotes the formation of gas hydrates.

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Mineral carbonation has the potential to store billions of tonnes of CO 2 safely and permanently. Enhancement of the kinetics of the formation of magnesium carbonate from magnesium-bearing silicate minerals has been the subject of numerous research studies. However, significant progress is yet to be achieved. This is, in part, due to a lack of understanding of the mechanism of the formation of magnesite in the presence of additives and under mineral carbonation conditions. In this work, an indepth study was performed to investigate the precipitation of magnesium carbonate during single step high pressure, high temperature carbonation of thermally activated serpentine in an aqueous bicarbonate solution. Slurry samples were obtained throughout the duration of the carbonation experiments, enabling analysis of both the aqueous and solid compositions over time, providing insight into the reaction mechanism. Additionally, the effect of operating temperature on the formation of various magnesium carbonate species was examined. TGA-MS, in combination with XRD and SEM, confirmed the formation of hydromagnesite in the absence of carbon dioxide (CO 2) during the reactor heat up period, owing to a reaction with the sodium bicarbonate (NaHCO 3) carrier solution. Hydromagnesite was transformed to magnesite over time, with the rate of this phase transformation highly dependent on the reaction temperature. At 185 °C all hydromagnesite converted to magnesite in a few minutes whereas at 120 °C even after 90 minutes hydromagnesite remained in the reactor. 2 PHREEQC thermodynamic software was used to assess the observed formation of carbonate species. The model prediction was consistent with the experimental results obtained in this work.