New facile process evaluation for membrane-based CO2 capture: Apparent selectivity model

Membrane-based CO2 capture technology is considered a promising alternative to the conventional aqueous amine-based approach. Herein, we propose a simple and efficient process model, denoted as the apparent selectivity model, for predicting the process variables and energy cost of the hollow fiber membrane-based CO2 capture process. The apparent selectivity, alpha*, is defined as the ratio of the average permeate flow rate of CO2 to that of other gases over the effective length of hollow fiber membranes. The proposed alpha* model can predict the CO2 purity, permeate-to-feed pressure ratio, required membrane area, and energy demand of the membrane process provided that permeance, selectivity, and feed composition are known. The main advantage of the proposed model is the ease of determining the CO2 purity for various membrane process configurations under a fixed CO2 recovery rate without performing complex calculations. Furthermore, the alpha* model can be extended to other separation applications, including natural gas processing (CO2/CH4), air separation (O-2/N-2), and H-2/N-2 separation, validating the universality of the model. The alpha* model-based case study analyses suggest that membranes with a CO2 permeance of over 1900 GPU and a CO2/N-2 selectivity of 40-45 can achieve an energy demand of less than 130 kWh t-CO2-1 for CO2 capture. This work offers a powerful tool for evaluating membrane -based separation processes.