Thermodynamic phase equilibrium of single-guest hydrate and formation data of hydrate in presence of chemical additives: a review

Abstract

The present work deals with a review of single-guest hydrate phase equilibrium data and also hydrate equilibrium in presence of chemical additives, which operate as inhibitors, promoters, or both together. In the recent years, a very limited number of data collections on hydrate equilibrium has been produced; moreover, these data have not been fully reported in these works, making further research necessary to obtain complete information. We provide a detailed collection of the equilibrium data of hydrate containing single guest as CH4, C2H6, C3H8, C4H10, CO2, N2, Xe, Ar and Kr and a brief review of las-scale reactors nowadays used for making research on gas hydrate. These two kinds of information, will be extremely helpful for researchers which are planning to realize a new experimental apparatus for studying gas hydrate. It is well known how, rather than process parameters (i.e. pressure, temperature, presence of a porous medium and its permeability and porosity, presence of impurities, and so on), also specifics of each reactor may strongly intervene on formation results. The second part of this work consists in a collection of the thermodynamic equilibrium data of hydrate in the presence of additives. Some substances are known to be selective inhibitors (promoters); other compounds have greater efficiency when coupled to further chemicals while, in some cases, such coupling can cancel the inhibitory (or promoter) effect. Finally, a state of the art of hydrate equilibrium experiments carried out with methane and carbon dioxide, with a simultaneous presence of inhibitors and promoters, was provided.