Synthesis, characterization and CO2 adsorption performance analysis of MgO functionalized activated carbon from palm kernel Shell / Jayaprina Gopalan

Jayaprina , Gopalan (2024) Synthesis, characterization and CO2 adsorption performance analysis of MgO functionalized activated carbon from palm kernel Shell / Jayaprina Gopalan. Masters thesis, Universiti Malaya.

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Abstract

In recent years, there has been a growing interest in solid adsorbents derived from biomass for CO2 adsorption due to their carbonaceous properties which allow for modifications to enhance selectivity towards CO2 in flue gas. Therefore, this study aimed to use innovative and sustainable approach to develop activated carbon (AC) for CO2 adsorption using palm kernel shells (PKS) as the precursor. The PKS were subjected to pyrolysis, and then activated with potassium hydroxide to enhance the porosity and surface area of the material. The properties of raw PKS adsorbents were further modified using magnesium oxide (MgO) to enhance the adsorption capacity, selectivity, and the potential for regeneration. The physicochemical analysis shows that the chemical activation has increased the surface area of the AC where the PKS-AC had a surface area of 1086 m2/g which was significantly higher compared to PKS-Char (435 m2/g) and PKS-AC-MgO (418 m2/g). Although the binding of MgO in PKS-AC-MgO led to a decrease in the surface area affected by pore blockages, this material demonstrated the most significant micropore volume (0.29 cm²/g) and pore diameter (2.8 nm) compared to raw PKS. The functional group analysis confirmed the impregnation of MgO in PKS-AC, as the transmittance band at 861 cm-1 and 617 cm-1 were assigned to metal oxygen bonding of Mg-O. Additionally, thermogravimetric analysis showed that all the PKS-adsorbent have a good thermal and mechanical stability at higher temperatures, up to 500℃. The CO2 adsorption performance analysis revealed that PKS-AC-MgO has highest adsorption capacity of 155.35 mg/g at the lowest temperature of 25°C and 5 bars, compared to PKS-AC (149.63 mg/g) and PKS-Char (138.19 mg/g). On the other hand, PKS-AC-MgO also shows enhanced performance at 50℃ with 117. 5 mg/g of adsorption capacity. Similarly, at a higher temperature of 75℃, the PKS-AC-MgO adsorbent also achieved 92.4 mg/g of adsorption capacity which is 48 % higher than the PKS-AC. This suggested the greater synergistic effect between the PKS-AC and MgO at elevated temperatures. Isotherm analysis indicated the presence of both physisorption and chemisorption of CO2 for all the PKS- adsorbents developed in this study. Langmuir model was best fitted for PKS-AC-MgO with R2 of 0.9916, which described the reaction due to restriction to monolayer formation. Thermodynamic studies showed a negative value of Gibbs free energy, enthalpy, and entropy indicating that the adsorption process of PKS-AC-MgO was spontaneous and favorable at 25°C. The economic analysis showed also shows that PKS-AC-MgO had a specific cost of $1,977 per tonne, which was 20% less than commercial AC. In summary, this study reveals the effectiveness of a novel approach in CO2 adsorption by utilizing AC impregnated with magnesium oxide developed from palm kernel shells.

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