Experimental Study on the Hydrate Phase Equilibrium of Synthetic Natural Gas Containing H2S

The natural gas containing H2S easily forms hydrates, thermodynamic inhibitors are usually injected to pipelines in combination with the dissolved salts to ensure flow safety. This study measured the hydrate phase equilibrium data of two synthetic natural gas (SNG) mixtures with H2S in various systems (pure water, NaCl solution in the absence or presence of MeOH) using the isochoric pressure searching method. The results showed that the addition of (3.5 wt % NaCl + 20 wt % MeOH) to pure water decreased the hydrate equilibrium temperature of SNG with a low H2S content 10.93 K. The presence of (3.5 wt % NaCl + 30 wt % MeOH) lowered the hydrate equilibrium temperature of SNG with a high H2S content 14.39 K. The measured results are compared to the predictions of two semiempirical formulas (Hammerschmidt and Najibi) as well as three-hydrate programs (CSMGem, PVTSim, and Multiflash). The predictions of Hammerschmidt and Najibi formulas have good agreement with the measured values for the system containing a low MeOH content, while they slightly deviated the measured values for the system with high MeOH content. It was found that the CSMGem predictions have good agreement with the measurements for pure water and 3.5 wt % NaCl solution systems. However, the measured values are more consistent with PVTSim calculations for the NaCl solution containing MeOH. The hydrate dissociation enthalpy was calculated with the Clausius-Clapeyron equation. The results indicated that the hydrate dissociation enthalpies of two SNG samples are 83.13 and 83.09 kJ.mol(-1), respectively.