(657g) Advancing Light Olefin Recovery Via Adsorptive Processes with Environmentally Friendly MIL-100(Fe) MOF

Polyethylene and polypropylene stand as foundational materials in many facets of everyday life, finding extensive use in packing and diverse consumer goods. Together, they represent an estimated global production of 180 million tons as of 2021, establishing them as the top produced thermoplastics in the global market. However, one of the main challenges in their manufacturing arises from the source and associated costs of their respective chemical feedstock. One of the paths to addressing this challenge involves the recovery of monomer losses incurred during the reactor purge and resin degassing stages within the polyolefin industry. These losses are estimated to range from 1% to 2% of the original feedstock, and conventionally, these are indiscriminately flared to adhere to regulatory emission standards. As such, efficient monomer recovery processes are vital for the polyolefin industry, as they reduce operational costs, enhance competitiveness, and mitigate unnecessary contributions to atmospheric CO₂ levels. This development aligns with broader sustainability goals, emphasizing the economic and environmental significance of such initiatives.

Over recent decades, Metal Organic Framework have gained significant interest due to their high porosity, large surface areas, and customizable pore structures and composition. Consequently, they have emerged as compelling materials for various separation processes in the chemical industry. Notably, research on MIL-100(Fe) has shown promise due to its high capacity and tailored selectivity to olefins by increasing activation temperature, achieved through the reduction of Fe³⁺ ions. Moreover, novel methods facilitating sustainable high-capacity production have further increased its appeal in industrial applications.

This work investigates the potential of the MIL-100(Fe) metal-organic framework for the separation and recovery of ethylene and propylene from nitrogen-rich mixtures, aiming at advancing sustainable monomer recovery processes. Pure component adsorption equilibrium isotherms for ethylene and propylene were measured on MIL-100(Fe) granules, using a Rubotherm magnetic suspension microbalance, for a range of 0 to 5 bar, and 303 to 373 K. Langmuir isotherm models were accurately fitted to the measured experimental results.

Single, binary, and pseudo-binary breakthrough curves were performed on a bench-scale single column unit for ethylene/nitrogen and propylene/nitrogen mixtures. The dynamic behavior of the breakthrough experiments was successfully simulated using a 1-dimensional fixed bed mathematical model, and the pure and multicomponent extension of the Langmuir isotherm model were successfully validated using experimental data.

Mathematical models are formulated to simulate the dynamic behavior of each of the three chosen adsorption-based separation processes: Pressure-Swing Adsorption, Multitubular Temperature and Pressure Swing Adsorption, and Dual-Reflux Pressure Swing Adsorption. Furthermore, this research endeavors to design optimized adsorption-based monomer recovery units tailored to each mixture. These units are designed to yield a monomer stream suitable for direct recycling back into the polymerization unit (95 %), thus promoting process efficiency and resource conservation. Simultaneously, a pure nitrogen stream is generated, meeting emission standards for safe release into the atmosphere (20 ppm). A comparative analysis is conducted between the developed processes, evaluating their performance on an industrial scale.

For the ethylene/nitrogen Pressure-Swing Adsorption cycle, a three-column system, designed for an operating range of 0.3 to 9 bar, was capable of producing an ethylene stream with 95.00 %(v/v) purity and a nitrogen stream with ethylene contamination of 1.90 ppm(v/v), using a total adsorbent mass of 10681 kg. An ethylene productivity and recovery capacity of 2.23 mol/(kg_ads.h) and 21.03 kg_C2H4/(m³_unit.h) was achieved for total thermal energy consumption of 10.13 MJ/kg_C2H4.

For the ethylene/nitrogen Multitubular Temperature and Pressure Swing Adsorption cycle, a three multitubular adsorber system, designed for an operating range of 1 to 8 bar and 303 to 393 K, was capable of producing an ethylene stream with 95.15 %(v/v) purity and a nitrogen stream with ethylene contamination of 16.67 ppm(v/v), using a total adsorbent mass of 3777 kg. An ethylene productivity and recovery capacity of 6.30 mol/(kg_ads.h) and 24.83 kg_C2H4/(m³_unit.h) was achieved for total thermal energy consumption of 20.81 MJ/kg_C2H4., of which a thermal energy consumption of 13.02 MJ/kg_C2H4 is required to supply the heating stages and the electrical energy consumption.

For the propylene/nitrogen Pressure-Swing Adsorption cycle, a three-column system, designed for an operating range of 0.3 to 8 bar, was capable of producing a propylene stream with 95.06 %(v/v) purity and a nitrogen stream with propylene contamination of 19.58 ppm(v/v), using a total adsorbent mass of 10681 kg. A propylene productivity and recovery capacity of 1.48 mol/(kg_ads.h) and 21.03 kg_C3H6/(m³_unit.h) was achieved for total thermal energy consumption of 4.37 MJ/kg_C3H6.

For the propylene/nitrogen Multitubular Temperature and Pressure Swing Adsorption cycle, a three multitubular adsorber system, designed for an operating range of 1 to 5 bar and 303 to 393 K, was capable of producing a propylene stream with 95.32 %(v/v) purity and a nitrogen stream with propylene contamination of 11.16 ppm(v/v), using a total adsorbent mass of 2359 kg. A propylene productivity and recovery capacity of 6.72 mol/(kg_ads.h) and 38.91 kg_C3H6/(m³_unit.h) was achieved for total thermal energy consumption of 7.46 MJ/kg_C3H6, of which a thermal energy consumption of 4.65 MJ/kg_C3H6 is required to supply the heating stages and the electrical energy consumption.

By achieving these objectives, this study contributes to the development of environmentally responsible practices within the polymer industry while addressing the imperative for sustainable monomer recovery processes.