Carbon Dioxide Capture by Pressure Swing Adsorption

Abstract

The increasing worldwide demand for energy bound to a strong dependence of fossil fuels has considerably intensified the concentration of greenhouse gases in the atmosphere, reaching alarming levels. Among those gases, carbon dioxide is considered the main responsible for global warming due to its higher concentration. In order to mitigate the negative effects of global warming and to reduce emissions, many technologies have been developed in the last decades to separate and recover carbon dioxide (CO2) at different capture scenarios. Adsorption processes rely on the use of highly porous solids such as activated carbons, which are either commercially. Pressure Swing Adsorption (PSA) is a cyclic adsorption process, which allows continuous separation of gas streams. PSA is performed by periodic changes of pressure aiming the optimization of contaminants removal and is considered viable for separation of CO2 from flue gases containing about 5-15% v/v. To achieve a certain performance, a PSA process may consist of several steps, columns and cycle time. One of the most basic configurations comprises four steps: pressurization, feed, blowdown and purge. The performance of a PSA process is usually evaluated by the purity, recovery and productivity reached. This study presents experimental and simulated data obtained from a bench-scale PSA, with a maximum pressure of 6bar for pressurization and feed steps and minimum of 1bar for blowdown and purge steps. The unit was tested with a mixture containing 85% of N2 and 15% of CO2 (on a molar basis). Carbon dioxide and nitrogen breakthrough curves were obtained under typical conditions of post combustion capture. A mathematical-phenomenological model combining momentum, mass and heat balances and using the Linear Driving Force approach (LDF) for mass transport and Langmuir model for equilibrium was applied in this study to simulate the dynamic behavior of the process. The performance tests presented productivity of 15mol h-1 kg-ads-1 and, according to the changes of step time, N2 purity of 97.7%. The model predicted reasonably the breakthrough curves and temperature profiles, with more precision for the latter. The combination of the simulation tool with and experimental PSA unit is very valuable for a deeper understanding of the involved phenomena and helpful with the design of optimized and efficient CO2 adsorption-based capture processes.