Modelling of the formation conditions of structure-H hydrates

In this paper, the two-step hydrate formation mechanism proposed by the authors (Chen and Guo, 1998) has been extended to structure-H hydrates (sH). It was assumed that the basic sH hydrate can be formed by large molecules only, termed as sH hydrate formers. A hydrate model based on this formation mechanism has been developed, in which the evaluation of both the thermodynamic parameters of an unstable empty hydrate lattice and the potential parameters of a sH hydrate former are not involved. The characterization parameters of 20 basic sH hydrates were determined from experimental data. The proposed model has been tested on the calculation of the hydrate formation pressures of 20 sH hydrates constituted by a single sH hydrate former and methane (help gas). Parallel comparison with the results reported by Mehta and Sloan [4] using the traditional Van der Waals-Platteeuw type model has been made. In addition, the proposed model was adopted to predict the hydrate formation pressures of systems containing methylcyclopentane/(methylcyclohexane + nitrogen)/(nitrogen + methane). Encouraging results were obtained. (C) 2002 Elsevier Science B.V. All rights reserved.