CO2 Separation from CO2-EOR Associated Gas Using Hollower Fiber Membranes: A Process Design and Simulation Study

The application of CO2 enhanced oil recovery (CO2-EOR) requires an appropriate gas separation method to deal with the associated gas, which has variable and a large amount of CO2 and CH4. Membrane separation was the selected method due to its advantages in various aspects over the other commonly used methods. In this work, a single-stage membrane process was designed to treat the associated gas from an oilfield. A mathematical model of the hollow fiber membrane separator was established to evaluate and optimize the membrane separation performance among three widely used membrane materials in the industry, including cellulose acetate (CA), polyimide (PI) and polysulfone (PSF). The model was verified after a comparison with the published result in the literature. In addition, a field test with a pilot plant was performed in an oilfield, the primary test result showed that the designed membrane-based separation process worked well and the established model presented reliable simulation results. Effects of the main parameters (separation coefficient and permeance) of the membrane materials and the operating conditions (CO2 concentration in the feed gas, feed pressure, and membrane effective surface area) on the separation performance were further studied with the developed model. The result showed that despite the trade-off between CO2 purity and CO2 recovery existing for a polymeric membrane, PI performed relatively better than CA and PSF under the conditions studied in this work (i.e., the operating temperature was 45 degrees C, CO2 concentration in the feed gas was 20-80 vol%, the feed pressure was 0.5-1.0 MPa, and the membrane effective surface area was 50-550 m(2)). With PI as the candidate membrane material, CH4 loss rate could maintain below the requirement of 10%, while both CO2 purity and CO2 recovery could always be higher for a broader range of CO2 concentrations in the associated gas and feed pressures, and a smaller effective surface area was required for the separation process.