Prediction of Gas and Refrigerant Hydrate Equilibrium Conditions With and Without Thermodynamic Inhibitors Using Simple Empirical Correlations

Abstract

Clathrate hydrates (gas hydrates) are solid crystalline compounds formed from water molecules as host molecules and gas molecules as guest molecules. Due to the hydrogen bonds, water constructs a framework that entraps some small nonpolar molecules (typically gases) and in suitable conditions (i. e. low temperature and high pressure) gas hydrate forms. The objective of this research is to estimate the gas and refrigerant hydrate dissociation conditions with and without alcohols and sodium chloride aqueous solutions using simple empirical correlations. Generally, the empirical suggested correlations to estimate the equilibrium clathrate hydrate pressure of CH4, C2H6, C3H8, CO2, N2, H2S, R22, R23, R134a, R116, R125a, R152a, R141b, R410a, R407c, R507c, CH4 + methanol, CH4 + ethylene glycol, CH4 + triethylene glycol, CH4 + ethanol, CH4 + sodium chloride, CO2 + methanol, CO2 + glycerol, CO2 + sodium chloride, R134a + sodium chloride, R507c + sodium chloride and R410a + sodium chloride systems are a function of equilibrium hydrate temperature and concentration. A genetic algorithm was employed as an optimization method to determine correlation coefficients, and the mean squared error was selected as its fitness function. Due to the low values of the calculated absolute average deviations (between 0.00 and 7.65), except for H2S + pure water with the highest amount of the absolute average deviation percent (AAD% equal to 11.51), these correlations are capable of predicting the studied hydrate dissociation conditions.