Enhancing light olefin recovery using eco-friendly MIL-100(Fe) adsorptive processes
摘要
The applicability of the environmentally friendly MIL-100(Fe) metal-organic framework is explored for the recovery of unreacted monomers from nitrogen-rich vent streams generated in the two highest-volume thermoplastics industries: polyethylene and polypropylene. Adsorption equilibrium isotherms for ethylene and propylene were measured at multiple temperatures and fitted using the Langmuir model. Breakthrough experiments were conducted for ethylene/nitrogen and propylene/nitrogen mixtures using a bench-scale fixed-bed unit. Simulations using a dynamic fixed-bed model accurately reproduced the experimental data, validating both the kinetic and multicomponent equilibrium behavior of the system. Industrial-scale Pressure Swing Adsorption (PSA) and Multitubular Temperature and Pressure-Swing Adsorption (MT-TPSA) separation systems were designed, and evaluated. For ethylene recovery, a three-column PSA cycle operating between 0.3 and 9 bar at 343 K is recommended. This system achieved a productivity of 2.23 mol/(kg·h) and a recovery capacity of 21.0 kg C₂H₄/(m³·h) with a total energy consumption of 10.13 MJ/kgC2H4. For propylene recovery, both a PSA cycle (0.3–8 bar, 343 K) and a MT-TPSA cycle (1–5 bar, 303–393 K) are considered. The MT-TPSA process offered higher productivity (6.72 mol/(kg·h)) and recovery capacity (38.9 kg C₃H₆/(m³·h)), though at a higher total energy cost of 7.46 MJ/kg C₃H₆ compared to 4.37 MJ/kg C₃H₆ for PSA, with a productivity of 1.48 mol/(kg·h) and recovery capacity of 21.03 kg C₃H₆/(m³·h).