Publication: Development and modification of leucaena wood-derived adsorbent for carbon dioxide capture
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Date
2024-09-01
Authors
Nuradibah, Mohd Amer
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Abstract
The persistent increase in carbon dioxide (CO2) concentration in the atmosphere, which is the main anthropogenic greenhouse gas causing tremendous impacts on global warming, highlights the necessity for research focused on carbon capture and storage (CCS). The unique properties of biochar prove its ability as a promising carbon-based material as CO2 capturing medium at low adsorption temperature. This work aims to highlight the development of biochar from woody biomass feedstock, specifically Leucaena wood (LW) and its subsequent modification for post combustion CO2 capture. Accordingly, slow pyrolysis was performed to develop biochar at different temperatures of 500, 700 and 900 ℃. Biochar produced at 900 ℃ showed the highest CO2 capture capacity of 52.18 mg/g compared to the ones pyrolyzed at 500 and 700 ℃. Subsequently, different vanadium oxide loadings (1, 3, 4, 5, and 8 %) were introduced to biochar’s structure via impregnation method to increase its surface basicity which is favourable to interact with acidic CO2 molecules. The finding revealed that an increment of 38.3 % in adsorption capacity (72.14 mg/g) to the pristine biochar when impregnated with 4 % of vanadium. Considering that high pyrolysis temperature is necessary to develop biochar, another potential method, namely hydrothermal carbonization using water as a heating medium at low temperature could be implemented. Hydrochar was synthesized at 170 ℃ for 90 min. Further, urea-functionalized hydrochar was prepared at different ratios of urea to hydrochar (1:1, 2:1 and 3:1 w/w), activation temperatures (400-800 ℃) and heating rates (5-15 ℃/min). Urea-functionalized hydrochar possessed the highest adsorption capacity of 76.20 mg/g when activated at 600 ℃ for 60 min with urea to hydrochar ratio of (2:1). Here, the introduction of N-functional group from the incorporation of urea to hydrochar helps to increase the surface basicity which beneficial for CO2 adsorption. of Both modified adsorbent via metallization and urea functionalization showed consistent performance in 11 cycles of CO2 adsorption-desorption and exhibited high affinity towards CO2 compared to other gases such as nitrogen (N2), methane (CH4) and air. Several adsorption kinetic models were used to represent the experimental data which Avrami fitted the data better at any adsorption temperatures. Physisorption was chief governing mechanism of adsorption for pristine biochar, metallized-biochar and urea-functionalized hydrochar implied from their low activation energy, indicating weak interaction of adsorbent and CO2 molecules. In the
next phase, the pristine biochar, metallized-biochar and urea-functionalized hydrochar were subjected to CO2 adsorption in a fixed-bed column. The effects of different total gas flowrates (30, 40, 50 and 60 ml/min), initial CO2 concentrations (5, 10, 15 %) and adsorption temperatures (30, 40, 50 and 70 ℃) on CO2 adsorption capacity were investigated. Correspondingly, the optimized process variables for pristine biochar, metallized-biochar and urea-functionalized hydrochar were at 30 ml/min of total gas flowrate, 15 % of initial CO2 concentration and 30 ℃ of adsorption temperature with maximum CO2 adsorption capacity of 165.67 mg/g, 176.24 mg/g and 195.54 mg/g, respectively. Overall, LW is a potential woody biomass in developing adsorbent to capture CO2.