Optimization of activated carbon preparation from Sea Mango fibrous shell (cerbera odollam) functionalized with deep eutectic solvent (DES) for carbon dioxide (CO₂) adsorption (Restricted)

In recent years, carbon dioxide (CO2) emission has become a major concern as the amount of the emitted gas significantly increases annually. Consequently, this phenomenon contributes to global warming. Several CO2 capture methods, including chemical adsorption by activated carbon (AC) have been proposed. However, the production cost of commercial AC is relatively high. In this study, the AC was prepared from sea mango (Cerbera odollam) in order to reduce the production cost of AC. The preparation of AC has been optimized by using Response Surface Methodology (Box - Behnken Design). The optimized preparation parameters were found to be 53.75% of acid concentration, 519.75oC of carbonization temperature and 2.28 hours of activation time which resulted in 861.95m2/g of BET surface area. The optimized sea mango AC (OSMAC) has been impregnated with Deep Eutectic Solvent (DES) at 1:2 solid-toliquid ratio in order to increase the efficiency of CO2 capture and on the same time lowering the cost comparing to impregnation of amine and an ionic liquid (IL). DES is composed of choline chloride (ChCl) and urea with ratio 1:2 of ChCl to urea. The BET surface area of DES activated carbon (DESAC) is 585.75 m2/g. The activation process was further confirmed by the presence of new bond of theN-H band and C-Cl stretch at peak 1635.19 cm-1 and 628.24 cm-1 respectively. Both of these bonds are suspected to be contributed by the ChCl and urea from the DES. The reduction of BET surface area was approximately 40% after DES impregnation proved that DES molecule successfully attached to the surface of the AC. The result was further confirmed by SEM images which showed most of the pore of the AC has been occupied by the DES. The EDS test also confirmed that the increasing amount of N element from 6.1% to 18.4% after being impregnated with the DES. The performance of the AC on the CO2 adsorption was obtained through breakthrough time curves and adsorption capacity. Three tests were conducted including different types of adsorbent, difference adsorbent dosage and different inlet flow rate. It was found that the DESAC has better CO2 adsorption capacity compare to the OSMAC which is 39.40 mgco2/gsol and 33.46 mgco2/gsol respectively. This is due to the increment of active side contributed from the DES which allows more CO2 molecule to be attached to the DESAC. The increment of active site has been illustrated in the mechanism interaction of CO2 which suggested that 6 molecules of CO2 able to be captured by 1 molecule of DES. For the adsorbent dosage, the increment weight of the AC has increased the CO2 adsorption capacity as more pores and active sites is available, thus increasing the chance for CO2 attachment. In term of flow rate, the increment of flow rate has reduced the breakthrough time. This is due to the high amount of CO2 molecule supplied per minutes during high inlet flow rate, hence causing the AC to be saturated faster. Throughout this study, it is confirmed that the functionalization of DES on the AC has enhanced the CO2 adsorption compare to the OSMAC.