Experiment and model investigation of D-sorbitol as a thermodynamic hydrate inhibitor for methane and carbon dioxide hydrates

Abstract

Pipe plugging and cracking caused by gas hydrate blockage is the major problem in oil/gas flow assurance, especially in deep subsea pipelines. Thermodynamic inhibitors(THIs) are one of the effective methods to inhibit the formation of gas hydrate. This work evaluates the thermodynamic inhibition effect of D-sorbitol, a polyhydroxy compound, for both methane (CH4) and carbon dioxide (CO2) hydrates. The gas-liquid-hydrate equilibrium (GLHE) conditions for CH4 and CO2 were measured by the isothermal pressure search method in the presence of aqueous D-sorbitol solutions (1.00, 2.00, 3.00 mol%). The equilibrium pressure change (ΔP) and hydrate dissociation enthalpies (ΔHdiss) were used to reflect the thermodynamic effects of D-sorbitol on CH4 and CO2 hydrates. The ΔP data show that D-sorbitol has an obvious inhibition impact on CH4 and CO2 hydrates formation. Compared with deionized water system, CH4 hydrate GLHE pressure increased by 11.6, 25.0, 41.4%, while CO2 hydrate GLHE pressure increased by 10.1, 18.6, 32.7% in 1.00, 2.00, 3.00 mol% D-sorbitol solutions, respectively. The ΔHdiss data demonstrate that D-sorbitol does not participate in the formation of the hydrate crystal structure. Chen-Guo hydrate thermodynamic model and Wilson activity model were applied to predict the GLHE conditions of both CH4 and CO2 hydrates in the presence of D-sorbitol. The calculated results can well match the experimental values. The average relative deviations (ARD) between calculated and experimental data for CH4 and CO2 hydrate are less than 2.39% and 3.76%, respectively. D-sorbitol is a non-toxic and environment-friendly compound. The results in this work indicate that D-sorbitol can be applied to flow assurance strategies for hydrate blockage prevention.