CO₂ Adsorption On Activated Carbon Monolith And Electrothermal Desorption

With Copenhagen conference, Kyoto Protocol and Durban climate conference, the greenhouse effect which caused great environmental problems has become one of the most important issues in the world. The massive emission of CO2 during the combustion of fossil fuels was considered as the important contribution. So the effective measures must be taken to reduce the emission of CO2 from the flue gas. In this paper, activated carbon (AC) monoliths were used as adsorbents to capture CO2 from the flue gas. Based on the good electrothermal behavior of AC monolith, the electrothermal desorption process for the adsorbent regeneration was developed, instead of the traditional vacuum desorption process. The feasibility and efficiency of the process for CO2 capture by AC monolith adsorption with the electrothermal desorption were evaluated.AC monolith had the advantages of high specific surface area, controllable pore structure, high adsorption and desorption rates, low pressure drop as well as excellent mechanical strength. So it was generally considered as a promising adsorbent material to capture CO2. In this paper, two commercially available coal/coconut AC monoliths were used as adsorbents to capture CO2 from flue gas. Moreover, these adsorbent materials were soaked in K2CO3 solution to improve the CO2 adsorption capacity and the CO2/N2 selectivity.Adsorption equilibrium isotherms of CO2 and N2 on coal/coconut AC monoliths (before/after soaking in K.2CO3 solution) were measured using the magnetic suspension balance instrument. The experimental data were fitted with Langmuir,Multi-site Langmuir and Viral models, respectively. The CO2 adsorption capacity, the CO2/N2 selectivity and the adsorption heat on AC monoliths (before/after soaking with K2CO3 solution), were calculated and compared with each other, to get the basic parameters for the design and optimization of the adsorption process.Since the AC monolith had a good electrical conductivity, the electrothermal desorption process was developed for the regeneration of adsorbents. AC monolith was packed in a column with the electricity heating system, and the electrical current /resistance and temperature curves in the packed bed were measured to calculate the energy consumption per kilogram of adsorbents when heating with electricity. The utilization efficiency of the electrical energy was discussed.The CO2 adsorption and electrothermal desorption of adsorbents were investigated. The effects of operation conditions, such as CO2 inlet concentration in feed,desorption temperature,purge gas velocity and heating voltage were investigated. The energy consumption to capture one kilogram CO2 was calculated, and the feasibility and efficiency of the electrothermal desorption process was evaluated.In conclusion, with the development of new adsorbent materials having good electrothermal conductivity and high CO2 adsorption capacity, the optimal design of adsorber with electricity heating system, the optimization of the adsorption/electrothermal desorption process, the energy consumption and cost for CO2 capture could be reduced, that would make the electrothermal desorption process more promising.