A continuous and high-efficiency process to separate coal bed methane with porous ZIF-8 slurry: Experimental study and mathematical modelling

Coal bed methane has been considered as an important energy resource. One major difficulty of purifying coal bed methane comes from the similar physical properties of CH4 and N2. The ZIF-8/water-glycol slurry was used as a medium to separate coal bed methane by fluidifying the solid adsorbent material. The sorption equilibrium experiment of binary mixture (CH4/N2) and slurry was conducted. The selectivity of CH4 to N2 is within the range of 2–6, which proved the feasibility of the slurry separation method. The modified Langmuir equation was used to describe the gas-slurry phase equilibrium behavior, and the calculated results were in good agreement with the experimental data. A continuous absorption–adsorption and desorption process on the separation of CH4/N2 in slurry is proposed and its mathematical model is also developed. Sensitivity analysis is conducted to determine the operation conditions and the energy performance of the proposed process was also evaluated. Feed gas contains 30 mol% of methane and the methane concentration in product gas is 95.46 mol% with the methane recovery ratio of 90.74%. The total energy consumption for per unit volume of product gas is determined as 1.846 kWh Nm−3. Experimental results and process simulation provide basic data for the design and operation of pilot and industrial plant.