The removal of CO₂ from gaseous streams using solid sorbents

Carbon dioxide (CO2) is one of a number of gases known as green-house gases which are believed to contribute to global climate change. Anthropogenic sources of CO2 emissions have increased significantly in the atmosphere. It is believed that the burning of fossil fuels in electric power generation plants is one of the main contributors as in these plants CO2 is released in the flue gas. This is one of the most serious challenges facing our world. The current liquid amine scrubber used for CO2 capture from flue gas stream is inefficient. This work focused on the synthesis of a more efficient solid amine sorbent to remove CO2 from flue gas streams and also ambient air. Two amines; APTES and TEPA were successfully fixed onto SBA-15, Al-SBA-15 and PE-SBA-15. These solids successfully removed CO2 from a gas stream from the laboratory test rig. 70%TEPA/SBA-15(I) showed a particularly high capacity and proved stable over 5 CO2 adsorption/desorption cycles. This solid also successfully captured CO2 from ambient air with a relative humidity of 89 % and 100 %. This solid is one of the highest capacity solids for CO2 capture from ambient air. Two methods of pelletising were investigated. The first method utilised the use of a binder and plasticiser (kaolin and methylcellulose). This method was used to pelletise SBA-15, resulting in cylindrical pellets 1 mm in diameter and 2 mm in length. 70%TEPA/SBA-15(I) was not successfully pelletised using this method, as TEPA was lost during the calcination stage. Therefore the SBA-15 pellets were modified after pellet formation. The second method involved simply pressing 70%TEPA/SBA-15(I) into a circular pellet. The binder based method produced strong, durable pellets, while the self-supported method produced less durable pellets. It is likely that the binder adds strength to the SBA-15 pellets as it bind the SBA-15 particles together into a cohesive unit. The effect of pressure and temperature were also investigated on 70%APTES/SBA-15(CI) and 70%TEPA/SBA-15(I). Temperature, in particular was found to impact adsorption capacity, while both solids showed high CO2 uptake at low partial pressures. Overall, the solids showed adsorption characteristics similar to the Dual- The removal of gaseous streams using solid sorbents Emma Daniels Site Langmuir isotherm model, which is indicative of chemisorption at two adsorption sites. These may be adsorption sites located near the pore moths and further within the solid.