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6090104 
Journal Article 
Propane, n-butane and i-butane stabilization effects on methane gas hydrates 
Smith, C; Pack, D; Barifcani, A 
2017 
1 
Journal of Chemical Thermodynamics
ISSN: 0021-9614 
Elsevier 
115 
Elsevier 
293-301 
WOS:000413418600033 
The goal of this work is to analyse the hydrate equilibria of methane+propane, i-butane and n-butane gas mixtures. Experimental hydrate equilibrium data was acquired for various compositions of these components in methane, ranging from 0.5 to 6.8mol%. Applying this information with the Clausius-Clapeyron equation, the extent of hydrate promotion was demonstrated quantitatively by calculating the slope of the equation and the dissociation enthalpy (ΔHd). Methane equilibria was found to be most sensitive towards propane and i-butane, where very small concentrations were sufficient to increase the thermodynamic conditions for hydrate equilibrium drastically. The degree of hydrate stabilisation, i.e. transition from sI to sII hydrate, was immediate – there was no detectable composition slightly above 0.0mol% where propane or i-butane did not have a sII hydrate-promoting impact, although one was implied with the aid of Calsep PVTsim calculations. Addition of n-butane to methane was far less sensitive and was deemed inert from 0.0 to 0.5mol%. It was concluded that the sII hydrate was favoured when the n-butane composition exceeded 0.5–0.75mol%. The influence of composition on stability was quantified by determining the gradient of ΔHd versus mol% plots for the initial steep region that represents the increasing occupancy of the sII guests. Average gradients of 11.66, 26.64 and 43.50kJ/mol.mol% were determined for n-butane, propane and i-butane addition to methane respectively. A hydrate-inert range for propane/i-butane (in methane) was suspected according to the perceived inflection point when less 0.5mol%, implying the gradient was very low at some minute concentration range starting at 0.0mol%. Awareness of these sI to sII transition regions is beneficial to natural gas recovery and processing as a small percentage of these components may remain without being detrimental in terms of promoting the hydrate equilibria. 
Enthalpy of dissociation; Gas hydrate; Hydrate structure