The effect of hydrotropes on gas hydrate formation

In the research spectrum of hydrates in petroleum science and engineering, gas storage in hydrates is an area of study aimed at utilising the gas from marginal and small fields. Additives used with water can improve the gas storage capabilities of hydrates. This work discusses hydrate promotion capabilities of hydrotrope para-toluene sulfonic acid (p-TSA) when used as an additive in water for natural gas-hydrate formation. Hydrotropes are a class of compounds though amphiphilic in character, they have short hydrophobic regions and thus differ from classical surfactants, yet they display substantial ability to solubilise non-polar compounds in water [Langmuir 13 (1997) 3235]. The hydrate promotion capability of p-TSA was tested by forming hydrates with different concentration solutions in the presence of natural gas by subjecting it to hydrate formation conditions, and subsequently, after adequate formation, dissociating and measuring the gas to water ratio in hydrates. The experiments were carried out on macro scale levels to warrant more practical relevance for industrial scale hydrate formation operations. Experimental work on hydrotropes is supported with theoretical justification for the use of hydrotropes as hydrate promoters compared to micelle surfactants. The optimum p-TSA concentration and the optimum temperature–pressure conditions for hydrate formation in a batch process experiment were found as 3.5 g/l, and −10 °C at 1500 psig, respectively.