Dissociation behavior of (CH₄ + C₂H₄) hydrate in the presence of sodium dodecyl sulfate

Separation of a mixture of CH4+C2H4 gas by forming hydrate in ethylene production has become of interest, and the dissociation behavior of (CH4+C2H4) hydrate is of great importance for this process. The hydrate formation rate could be increased by adding a small amount of sodium dodecyl sulfate (SDS) into water. In this work, the kinetic data of CH4(18.5 mol%)+C2H4(81.5 mol%) hydrate decomposition in the presence of 1000 mg center dot L-1 SDS at different temperatures and pressures were measured with the depressurizing method using a sapphire cell apparatus. The experimental results show that the dissociation rate of (CH4+C2H4) mixed gas hydrate was large at high temperature and low pressure, and temperature had great influence on the dissociation rate at high pressure. A kinetic model for hydrate dissociation was proposed and the calculated results from the kinetic model were in good agreement with the experimental data. The activation energy for dissociation of the (CH4+C2H4) mixed gas hydrate was determined to be 43.9 kJ center dot mol(-1), which is lower than that of methane (81.0 kJ center dot mol(-1)) and ethane (104.0 kJ center dot mol(-1)) hydrate in water (Clarke and Bishnoi, 2004). As the similar molecular dimensions between ethane and ethylene, the close activation energy need to be provided for ethylene hydrate dissociation. The obtained activation energy of the (CH4+C2H4) mixed gas hydrate dissociation indicates that the dissociation of the (CH4+C2H4) mixed gas hydrate is easier than that of pure CH4 or C2H4 gas hydrate.