Comparative Analysis of Hydrate Nucleation for Methane and Carbon Dioxide.

Research in the field of hydrate formation requires more focus upon its modelling to enable the researchers to predict and assess the hydrate formation and its characteristics. The main focus of the study was to analyze the deviations induced in various parameters related to hydrate nucleation caused by the choice of different measuring correlations or methods of their sub-components. To serve this purpose under a range of operational conditions, parameters of hydrate nucleation such as rates of nucleation and crystal growth, critical radius of the nucleus, and theoretical induction time for carbon dioxide and methane were considered in this study. From these measurements, we have quantitatively compared the ease of hydrate formation in CO2 and CH4 systems in terms of nucleation while analyzing how various correlations for intermediate parameters were affecting the final output. Values of these parameters were produced under the considered bracket of operational conditions and distributed among six cases using both general and guest-gas specific correlations for gas dissolution and fugacity and their combinations. The isotherms and isobars produced from some of the cases differed from each other considerably. The rate of nucleation in one case showed an exponential deviation with a value over 1 × 1028 at 5 MPa, while the rest showed values as multiples of 106. These deviations explain how sensitive hydrate formation is to processing variables and their respective correlations, highlighting the importance of understanding the applicability of semi-empirical correlations. An attempt was made to define the induction time from a theoretical perspective and derive a relevant equation from the existing models. This equation was validated and analyzed within these six cases from the experimental observations.

Study on CO2 Hydrate Formation Kinetics in Saline Water in the Presence of Low Concentrations of CH4.

Gas-hydrate formation has numerous potential applications in the fields of water desalination, capturing greenhouse gases, and energy storage. Hydrogen bonds between water and guest gas are essential for hydrates to form, and their presence in any system is greatly influenced by the presence of either electrolytes or inhibitors in the liquid or impurities in the gas phase. This study considers CH4 as a gaseous impurity in the gas stream employed to form hydrates. In developing gas-hydrate formation processes to serve multiple purposes, CO2 hydrate formation experiments were conducted in the presence of another hydrate-forming gas, CH4, at low concentrations in saline water. These experiments were conducted in both batch and stirred tank reactors in the presence of sodium dodecyl sulfate (SDS) as a kinetic additive at 3.5 MPa and 274.15 K, under isobaric and isothermal conditions. Gas loading was taken as the detection criterion for hydrate formation. It was observed that overall gas loading was hindered by more than 70% with the addition of salts after 2 days. The addition of CH4 to the gas stream led to a further reduction of approximately 30% of gas loading in the batch reactor under quiescent conditions. However, the addition of 100 ppm of SDS improved the gas loading by recovering 34% of the loss observed in volumetric gas loading through the addition of salts and CH4. The introduction of stirring improved the gas loading, and 64% of the loss was recovered through the addition of salts and CH4 after 34 h. The investigation was continued further by substituting CH4 with N2, whereupon accelerated hydrate formation was observed.