Production of sea mango (Cerbera Odollam) based activated carbon for CO2 adsorption

Abstract

The activated carbon utilization for carbon dioxide (CO2) adsorption process is a promising method to reduce the emission of CO2. The activated carbon was produced from the non-edible sea mango (Cerbera odollam) fruit through sequential chemical and physical processes. There were two methods of activated carbon preparation; i.e. Method 1: the precursor was impregnated with phosphoric acid (H3PO4) and then thermally activated at 500 °C with different activation atmosphere for 2 hours, Method 2: the precursor was heated at 200 °C with nitrogen gas (N2) flow prior to chemical and thermal activation processes as performed in Method 1. Porous structures were developed on the surface of the activated carbon due to the physicochemical activation process and proven by surface morphology study. The best virgin activated carbon prepared by double-stage activation via Method 2 in the absence of any gases (RCIHM2-A) which recorded the highest BET surface area (1475.43 m2/g), iodine adsorption capacity (1040.58 mg/g) and the highest carbon element (79.17 %). The activation process was further confirmed to happen with the unchanged and/or disappearance of C-H and -C≡C-H:C-H of the functional group at peaks 2936.73 cm-1 and 617.76 cm-1 as compared to raw sea mango sample. The prepared mesoporous activated carbon with pore diameter 2.86 nm was then modified with amine-based chemical (AMP, PZ, MEA, and DEA) impregnation to improve its adsorption capability and selectivity to adsorb CO2. Physisorption process which has weak Van der Waals forces interaction between CO2 molecules and pores on virgin activated carbon surface has been transformed to chemisorptions process (covalent bond) via amine impregnation. The performance of the activated carbon on CO2 adsorption was obtained through breakthrough time curve and adsorption capacity. The reduction of BET surface area was approximately 56 % to 62 % after amine impregnation proved that amine molecules successfully attach on the activated carbon surface. The result was further confirmed by SEM images which illustrated that amine molecules filled up most of the activated carbon pores. The best amine functionalized on carbon surface was 2-amino-2-methyl-1-propanol (AMP) with highest CO2 adsorption capacity 23.05 mgCO2/gsorbent and has been able to achieve 94.47 % of regeneration. The nitrogen (N) element measurement via elemental analysis by EDX was enhanced two-fold (from 4.73% to 7.25 %) after impregnated with this AMP amine and confirmed by the existence of N-H bond at 3391.22 cm-1 and C-N bond at 1173.19 and 1047.55 cm-1, respectively. The result indicated that elemental N functionalized activated carbon surface for CO2 adsorption. The effect of other operating parameters such as the lowest inlet flow rate (5.00 mL/min) and sample loading (2.00 g) recorded the highest CO2 adsorption capacity, 23.05 mgCO2/gsorbent, and 28.18 mgCO2/gsorbent, respectively, whilst CO2 adsorption capacity was inversely proportional to inlet flow rate and adsorbent loading increment.