Experiment on the Separation of Air-Mixed Coal Bed Methane in THF Solution by Hydrate Formation

Because of the technology limitation and safety requirement, a large amount of air-mixed coal bed methane is released directly to the atmosphere. It leads to severe waste of resources and exacerbates the greenhouse effect. This work tries to alleviate this problem by separating CH4 from a mixture of CH4 and N-2 via hydrate separation method. Several experiments were systematically carried out in 6 mol % tetrahydrofuran (THF) solution to separate CH4/N-2 gas mixtures containing 4.90 to 71.23 mol % CH4. The results that THF can significantly reduce the formation pressure of CH4-N-2 hydrate materialize the possibility of separating CH4 and N-2 using hydrate separation technology in industrial scale. CH4 can be separated effectively from CH4/N-2 mixture and concentrated in hydrate phase with the presence of THF. The recovery of CH4 ranges from 34.06% to 58.16% and the separation factor is between 2.29 and 5.17. A two-stage separation process of 46.28 mol % CH4/53.72 mol % N-2 with recycle is designed to increase the recovery of CH4. The calculated results indicate that CH4 concentration in hydrate gas could reach 82.61 mol % with a recovery yield of 47.28%. Hydrate separation technology is an effective way to process and utilize the air-mixed coal bed methane. Multistage separation process does have wide application prospects.