Experimental Study on the Separation of CH4 and N2 via Hydrate Formation in TBAB Solution

In order to reduce the emission of coal bed methane mixed with air (can be regarded as a CH4 and N-2 mixture), which will be helpful to adequately utilize the natural resources and protect environment, the separation of CH4 and N-2 Via hydrate formation in tetra-n-butylammonium bromide (TBAB) solution was systematically studied in this work. The CH4-N-2 hydrate formation conditions were determined in TBAB solution first, and then the separation experiments were carried out in TBAB and TBAB-sodium dodecyl sulfate (SDS) solution, respectively. The experimental results show that CH4 and N-2 form a hydrate much easier after adding TBAB to water. The composition of CH4 in the hydrate after single-stage equilibrium separation in TBAB solution can be increased from 46.25 mol % to 67.86 mol %. At the same conditions, the composition of CH4 after separation in TBAB-SDS solution is 68.66 mol % and the reaction time shortens greatly. Besides, the recovery of CH4 is more than 47%, and the gas storage capacity of hydrate is 19-21 m(3)/m(3). Higher composition and recovery of CH4 are expected to be obtained if multistage separation is applied. It indicates that CH4 can be concentrated effectively from CH4 and N-2 via hydrate formation in TBAB solution. Since the hydrate separation technology can substantially avoid the explosion problem caused by CH4 and on the basis of the results obtained in this work, we may say that this technology is quite suitable for the separation of coal bed methane mixed with air and has broad prospects for industrial applications.