Modelling of carbon dioxide separation on zeolite fixed bed by cyclic pressure swing adsorption
The global climate change caused by the greenhouse effect is currently a crucial environmental problem. Carbon dioxide (CO2) is a greenhouse gas that is emitted in massive amounts, mainly through the burning of fossil fuels. To reduce CO2 emissions to the atmosphere, the concept of carbon capture, utilization, and storage (CCUS) was developed. The main idea of CCUS is to capture CO2 and then utilize or store it. One method for CO2 capture is the cyclic adsorption process.
In this project, pressure swing adsorption (PSA) was employed for capturing CO2 from flue gas. The main element of the PSA apparatus was a stainless steel column with an internal diameter of 26 mm, an external diameter of 30 mm, and a length of 500 mm. The column was filled with commercial zeolite 13X (Hurtgral, Poland). In column three, thermocouples were installed to measure the temperature along the bed axis. The flue gas was created by mixing the streams from CO2 (purity 99.995%) and N2 (purity 99.999%) pressure gas cylinders. The flow rates were regulated by mass flow controllers MFC (Aalbrog, USA). The stream of CO2 flowed through the thermostated saturator filled with distilled water.
The cycle in the PSA process consists of four steps: pressurization, adsorption, blowdown, and regeneration. During the pressurization step, the pure N2 gas stream was fed to the column to increase the pressure from ambient to 3 or 5 bar. Next, during the adsorption step, a gas mixture consisting of CO2 (10–20%), N2, and H2O (relative humidity, RH, 50%) in varying ratios was introduced to the column. This step was carried out until the bed was fully saturated with CO2. During the adsorption step, the concentrations of the compound were measured at the column outlet using the HPR-20 R&D quadrupole mass spectrometer (Hiden Analytical, UK). At the next step (blowdown), the pressure in the column was decreased to ambient. At the last step, a small stream of pure nitrogen was fed into the adsorption column to regenerate the zeolite 13X. MS measured the concentration of compounds at the column outlet. During the measurement, six cycles of the PSA process were conducted.
A mathematical model of the PSA process for CO2 capture on zeolite 13X was developed, consisting of partial differential equations (PDEs) and algebraic equations. The model was solved in MATLAB using the numerical method of lines for defined boundary conditions. To validate the model, the calculated breakthrough curves were compared with the experimental breakthrough curves measured by MS. A good fit of the simulated data to the experimental data was obtained.
Project Summary by: Tomasz Aleksandrzak, Ph.D. West Pomeranian University of Technology, Szczecin, Poland.
Paper Reference: Tomasz Aleksandrzak, Kamila Zabielska and Elzbieta Gabrus (2024) ‘Modelling and experimental studies of carbon dioxide separation on zeolite fixed bed by cyclic pressure swing adsorption.’ Polish Journal of Chemical Technology. De Gruyter Open, 26(1) pp. 8–15. DOI: 10.2478/pjct-2024-0002.
