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The gas hydrate equilibrium curves for systems containing methane and nitrogen have been obtained in the temperature interval 32°F. to 72°F. and between pressures of 350 and 5100 Ib./sq.in.abs. The composition of the equilibrium gas and hydrate phases was determined experimentally at 32°F. and 44°F. This information was used to calculate vapor‐solid equilibrium ratios for both nitrogen and methane. A comparison is made between the equilibrium ratios in this system which crystallizes in Structure I and the ratios in systems reported earlier which crystallize in Structure II.

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This paper shows how the rigorous critical state criterion enunciated by Willard Gibbs can be used with a recently formulated two-parameter equation of state to obtain an analytical solution to the problem of predicting the critical properties of defined multicomponent mixtures. Comparisons SCOPEThe critical state of multicomponent mixtures is important from both a theoretical and practical point of view, and an ability to predict this condition is highly desirable. Even though the rigorous thermodynamic criterion for the critical state was enunciated by J. Willard Gibbs (1928) one hundred years ago, no satisfactory analytical method for predicting the critical condition in multicomponent systems based on this criterion has ever been formulated. The object of the work undertaken in this study was to develop a solution to the problem of predicting the critical properties of defined multicomponent mixtures from the rigorous thermodynamic method together with a recently developed two-parameter equation of state.The significance of the work is that it has the potential of replacing the more cumbersome, often unreliable, and sometimes inapplicable methods based on semiempirical or empirical procedures or on conformal solution theory with a method that is thermodynamically rigorous, generally applicable, and simple to use. Furthermore, the proposed method for handling critical property calculations is internally consistent with calculations of all other thermodynamic properties using the same equation of state.Although the majority of the comparisons reported in this work are limited to systems containing three or more components, the method works equally well for binary systems. Only one detailed comparison for a binary system is included, because several previous workers have used the thermodynamic criteria for binary cases (Joffe and Zudlievitch, 1967; Spear et al., 1969; Hissong and Kay, 1970). CONCLUSIONS AND SIGNIFICANCEAlthough previous workers (Spencer et al., 1973) have stated recently that it is not practical to extend the methods for predicting the critical state using the minimum Gibbs free energy criterion to multicomponent systems, it has been concluded from the work undertaken in this study that this is not the case. Use of the thermodynamic criterion together with a simple two-parameter equation of state has yielded results which are remarkably reliable and relatively easy to obtain. One of the key factors in the success of the method has been the use of an equation of state (Peng and Robinson, 1976) that predicts the critical density of pure materials better than any earlier models.Extensive testing of the program on ternary and all available multicomponent mixtures has shown that the method predicts critical temperatures with an absolute error of about 1,3170 and an arithmetic average error of +1.1470. It predicts critical pressures with an absolute error of 2.33% and an arithmetic average error of +0.1370,. The thirty-two systems studied included those containing from three to twelve components co...