The effect of a tributylmethylphosphonium methylsulfate ionic liquid (IL) aqueous solution on the equilibrium conditions of carbon dioxide and methane clathrate hydrates was studied. An isochoric pressure-search method was used to measure the hydrate dissociation conditions for the carbon dioxide + tributylmethylphosphonium methylsulfate + water and methane + tributylmethylphosphonium methylsulfate + water systems in the temperature ranges of (273.5 to 282.2) K and (273.3 to 288.5) K, and pressures up to (4.35 and 14.77) MPa, respectively. The concentrations of tributylmethylphosphonium methylsulfate in the aqueous solutions were 0, 0.2611, and 0.5007 mass fractions. The good agreement between our experimental hydrate dissociation data in the absence of tributylmethylphosphonium methylsulfate with selected literature experimental data demonstrates the reliability of the experimental method used in this work. The comparison between the hydrate dissociation conditions in the presence and absence of tributylmethylphosphonium methylsulfate shows that the IL has an inhibition effect on carbon dioxide and methane clathrate hydrate formation. Furthermore, a thermodynamic model, developed based on van der Waals–Platteeuw solid solution theory accompanied with the Peng–Robinson equation of state (PR-EoS) and the nonrandom two-liquid (NRTL) activity model, was successfully applied to represent/predict the obtained experimental data.

Ethene, ethyne, and propene are common and important industrial gases which are known to form hydrates. There exists in the open literature some hydrate dissociation data for simple hydrates of the three hydrocarbons. Unfortunately the data reported in literature are in some instances very limited, and the data sets are not always in agreement with each other. To evaluate the hydrate data for these hydrocarbons, new hydrate dissociation data were measured and are compared to that in the literature. Measurements for ethyne were undertaken in the temperature and pressure ranges of (273.2 to 285.5) K and (0.614 to 2.467) MPa, respectively. The temperature and pressure ranges for the propene measurements were (273.5 to 274.4) K and (0.492 to 0.613) MPa, respectively. The solid solution theory of van der Waals and Platteeuw, together with the Valderama–Patel–Teja equation of state and the non-density-dependent mixing rules were used to model the experimental hydrate dissociation conditions. Model predictions were found to be in satisfactory agreement with the newly reported data, as well as independent measurements for the ethyne + water and ethene + water systems. However, only a fair agreement is observed when the modeled data is compared to propene hydrate dissociation data found in the literature.

The phase diagrams of the ionic liquid (IL) N-butyl-4-methylpyridinium bis{(trifluoromethyl)sulfonyl}imide ([BM(4)Py][NTf(2)]) with water, an alcohol (1-butanol, 1-hexanol, 1-octanol, 1-decanol), an aromatic hydrocarbon (benzene, toluene, ethylbenzene, n-propylbenzene), an alkane (n-hexane, n-heptane, n-octane), or cyclohexane have been measured at atmospheric pressure using a dynamic method. This work includes the characterization of the synthesized compound by water content and also by differential scanning calorimetry. Phase diagrams for the binary systems of [BM(4)Py][NTf(2)] with all solvents reveal eutectic systems with regards to (solid-liquid) phase equilibria and show immiscibility in the liquid phase region with an upper critical solution temperature (UCST) in most of the mixtures. The phase equilibria (solid, or liquid-liquid) for the binary systems containing aliphatic hydrocarbons reported here exhibit the lowest solubility and the highest immiscibility gap, a trend which has been observed for all ILs. The reduction of experimental data has been carried out using the nonrandom two-liquid (NRTL) correlation equation. The phase diagrams reported here have been compared with analogous phase diagrams reported previously for systems containing the IL N-butyl-4-methylpyridinium tosylate and other pyridinium-based ILs. The influence of the anion of the IL on the phase behavior has been discussed.