Computer Simulation For Adsorption And Separation By Metal Organic Frameworks UMCM

Metal organic frameworks(MOFs) has high surface areas, high free volume and good thermostability that are promising for separation of gas mixtures and has the broad application prospect. Because of their high surface areas, low density and so on, UMCM-1 and UMCM-2 as the typical MOF material are well known representative of MOFs. Computational chemistry, including molecular simulation and quantum chemistry, can not only overcome the limitations of traditional methods, but also provide theoretical guidance for the design of optimal adsorbents and the determinations of optimal adsorbents and the determination of optimal industrial operation conditions, which also saves a lot of time for complicated experimental works. IAST theory can save more time than GCMC and can guide the experimental researchers who plan to study the separation performance of MOF material. So in this study, we first used GCMC simulations to study the adsorption and separation of N2/H2/CH4/CO2 pure and mixtures in UMCM-1 and UMCM-2, and at the same time IAST adsorption theory was used to predict the separation of N2/H2/CH4/CO2 mixtures.It is found that the excess adsorption isotherms from GCMC simulations basically agree with the available experimental data of pure gases, except for H2 adsorption in UMCM-1 at 298 K. Moreover, the GCMC results show that both MOF materials exhibit an excellent storage capacity for pure CH4 and CO2 at room temperature. The excess uptakes of UMCM-1 and UMCM-2 for CH4 at 5000 kPa are 12.53 and 15.06 mmol/g, while those for CO2 at 4500 kPa are 30.13 and 36.04 mmol/g, respectively, which approaches and even exceeds 30.82 mmol/g of MOF-177. They are suitable for gas storage.The selectivities of CH4/H2 and CH4/N2 in both MOF materials are insensitive to the pressure. The selectivities of CH4/H2 in both MOF materials are almost the same with a value of 4, while they are 2 for CH4/N2. By contrast, the selectivities of CO2/H2, CO2/N2 and CO2/CH4 apparently rely on the pressure, showing 16.39 and 26.88,5.41 and 7.78, and 2.88 and 4.69 at 4000 kPa for UMCM-1 and UMCM-2, respectively. But the selectivities of CH4/H2 in MOF-5 is 5.2. We can know that their separation ability is not prominent.When compare with the IAST theory's, for UMCM-1 material, the IAST can almost reproduce the selectivities of gas mixtures obtained by GCMC simulations, while for UMCM-2, it only performs well for the CO2/N2, CH4/H2 and CH4/N2 mixtures. For CO2-H2 and CO2-CH4 mixtures, the selectivities of UMCM-2 predicted by IAST are much less than the GCMC results.