| Coal-bed methane?C BM? is an important natural energy source. It is abundant in reserves, but low utilization in our country. Big challenge is the efficient use for low concentration of CMB. Compared with both low temperature distillation and membrane separation, PSA do have the advantages of energy efficient, flexible operation and low cost. Besides, the product obtained from PSA has a high purity, and the related technology has been already developed so far. Thus, PSA is supposed to be a suitable choice for the separation of CMB, especially for low methane content. One of the main problems we are facing in PSA technology is to find more effective adsorbents.Coal-bed methane is composed of N2, CH4 and small amount of CO2. MIL-101 is a chromium-based MOF with unique porous structure and good stability. It was used to evaluate the adsorption characteristics for N2, CH4 and CO2 in this work. MIL-101 was synthesized via a hydrothermal method. The BET specific surface area is about 2560 m2/g and the pore volume is 1.287 cm3/g. The pore size of MIL-101 sample distributes in a narrow range of 1-3 nm, and it shows an average pore width of 1.99 nm. The N2, CH4 and CO2 adsorption isotherms on MIL-101 were collected using volumetric method from 263 to 273 K. It showed that the adsorption capacities for gases decreased in the order CO2>CH4>N2 in both low pressure?0-0.8 MPa? and high pressure?0-5 MPa? experiment. Experimental data agrees well with Langmuir equation, L-F equation and VSMT separately. The fitting results indicated that the L-F model is a more suitable model than the other two models. The isosteric heat of adsorption was calculated using the Gibbs-Helmholtz equation. It decreased in the same order with adsorption amount. The storage capacity of CH4 and CO2 gas on MIL-101 was heavily influenced by temperature. For example, as the adsorption temperature increased from 283 to 313 K, the storage capacity of CH4 and N2 dropped by 35.6% and 50.0% separately.The adsorption equilibrium of N2/CH4/CO2 mixture on MIL-101 was measured with a dynamic method from 273 to 313 K and at pressures up to 2.0 MPa. Then, the adsorption amount was predicted by E-L model, LRC model and IAST model. It found that all the models made poor predictions for N2 adsorption. LRC model had a better performance than the other two models. The CO2/CH4 separation factor on MIL-101 ranged from 5 to 7. In contrast, the CH4/N2 had a low separation factor being about 2 to 2.5. |
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