Rigorous modelling and multi-objective optimization for hybrid absorption-adsorption separation process of CH4/C2H6 using ZIF-8/iso-hexadecane slurry

Efficient separation of CH 4 and C 2 H 6 remains a critical challenge in the recovery of light hydrocarbons from natural gas. We developed a zeolite imidazolate framework-8 (ZIF-8)/iso-hexadecane slurry for CH 4 /C 2 H 6 separation, and conducted solubility measurements for pure components and equilibrium separation experiments for gas mixtures. A rigorous absorption-adsorption coupled phase equilibrium model and a single equilibrium stage mathematical model were established to describe the phase equilibrium performance of gas-slurry system. The results indicate that the model exhibits high predictive accuracy for the solubility of CH 4 and C 2 H 6 in the slurry, with an average relative error of less than 3.053%. Furthermore, the whole process of absorption-adsorption-desorption was designed, and the mathematical model and multi-objective optimization framework were established. The effects of operating pressure and gas-slurry ratio on product purity, recovery ratio and total unit energy consumption were investigated. The results show that the C 2 H 6 purity in the feed gas is enriched from 22 mol% to 94.69 mol%, the C 2 H 6 recovery ratio reaches 95.21%, and the total unit energy consumption is 0.456 kWh Nm -3 (feed gas). In addition, the effects of pressure, temperature and ZIF-8 solid content on slurry separation performance were analyzed using the established equilibrium-stage model. The results showed that the introduction of ZIF-8 enhances the separation performance of the iso-hexadecane solvent for mixed gases. Compared to the pure solvent, the separation factor increased by an average of 75.2%, which theoretically proved the advantages of slurry separation process. • Phase equilibrium models for the slurry sorption of CH 4 /C 2 H 6 are established. • Effects of pressure, temperature, and solid content on the separation factor are analyzed. • Sensitivity analysis and multi-objective optimization are conducted. • High C 2 H 6 recovery ratio is achieved along with low energy consumption.