Studies On CO₂ Adsorption In Flue Gas With Amine Functional Mesoporous Molecular Sieves

CO₂ is an important greenhouse gas. Due to the excessive emission of CO₂, greenhouse effect would lead to negative effects for the global climate. Coal-fired power plant is one of the most important CO₂ emission sources. The development of separation and recovery technology for CO₂ from coal-fired power plants will be of great importance in alleviating global climate change. Adsorption is one of the most promising methods for post-combustion CO₂ capture technologies.Adsorption using the amine functional mesoporous molecular sieves is very popular in the academic community. The amine functional CO₂ adsorbent was prepared by loading organic amine on mesoporous materials in this work. The CO₂ adsorption performance was investigated in a fixed bed adsorption system.1. MCM-41, SBA-15 and CMK-3 were selected as supports. Both MCM-41 and SBA-15 possessed the structures with closed cylinder pore channel, and CMK-3 had a structure with open pore channel. The CO₂ adsorbents were prepared by loading pentaethylenehexamine ?PEHA? on these supports using a wet impregnation method. Results indicated that the lowest CO₂ adsorption capacity was obtained when PEHA functional CMK-3 was used as CO₂ adsorbent. The CO₂ adsorption capacity of PEHA functional SBA-15 with the structure of closed cylinder pore channel and bigger pore size was better than those of PEHA functional MCM-41 and CMK-3 adsorbents. Then the best support SBA-15 was selected as the support to prepare CO₂ adsorbent, and the CO₂ adsorption performance was tested. Results illustrated that the structure of SBA-15 was maintained after PEHA loading. Both surface area and pore volume decreased with the increase of PEHA loading. With the increase of the operation temperature, the adsorption capacity of CO₂ increased.However, the capacity decreased with further increase of the temperature.80? was the best operation temperature. The increase of amine loading amount was positive to the CO₂ adsorption performance; however, the CO₂ adsorption capacity per gram of PEHA increased and then decreased.The CO₂ working adsorption capacity decreased with the increase of the height of adsorbent bed; however, the CO₂ breakthrough adsorption capacity increased and then decreased. The reason was interpreted by analyzing the distribution of CO₂ concentration in the adsorbent bed.Regeneration experiment showed that the CO₂ adsorption capacities of PEHA functional SBA-15 adsorbent in cyclic adsorptions kept stable.2. The characterizations and the structures of PEHA functional SBA-15 adsorbents were tested, and the CO₂ adsorption mechanism was researched. An CO₂ adsorption model was proposed to interpret the CO₂ adsorption performance. This model described the amine distribution in pore channels and surface of adsorbent particle simultaneously. The effects of amine loading amount and operation temperature on CO₂ adsorption performance of PEHA functional SBA-15 adsorbents were interpreted by this model.3. The CO₂ adsorption performances of the adsorbents prepared by loading various organic amine compounds ?PEHA, TEPA, TETA, PEI and TEA? on SBA-15 were investigated. The results indicated that TEA functional SBA-15 adsorbent almost did not adsorb CO₂ in dry condition.The highest CO₂ working and breakthrough adsorption capacities were obtained when TETA functional SBA-15 was used as CO₂ adsorbent;however, its regeneration was not stable. TEPA, PEHA and PEI functional SBA-15 adsorbents had stable adsorption performances. Due to high CO₂ working adsorption capacity, breakthrough adsorption capacity and stable regeneration, TEPA was found to be the best organic amine compound.4. A novel process for integrated two-stage selective removal of SO₂ and CO₂ from a simulated flue gas was developed. Firstly, the simulated flue gas was composed of SO₂ and N2. The SO₂ adsorption performance of TEA functional SBA-15 adsorbent was investigated. Results indicated that the SO₂ breakthrough adsorption capacity decreased with the rise of temperature. The SO₂ breakthrough adsorption capacity increased with the increase of the height of adsorbent bed. However, the SO₂ breakthrough adsorption capacities almost kept stable after the height was higher than 16mm. Regeneration experiment showed that the SO₂ regeneration of TEA functional SBA-15 adsorbent remained stable.Secondly, the simulated flue gas was composed of SO₂, CO₂ and N2. TEA functional SBA-15 was selected as SO₂ adsorbent, and TEPA functional SBA-15 was chosed as CO₂ adsorbent. The integrated two-stage removal experiment of SO₂ and CO₂ was carried out. Results showed that CO₂ and SO₂ in gas mixture were removed in two stages successfully.Regeneration experiment showed that the adsorption performance of integrated two-stage system was stable. This result indicates that integrated two-stage selective removal of SO₂ and CO₂ from a simulated flue gas is an successful attempt.