Abstract:
Biogas can provide an efficient means of meeting several objectives concerning energy, environment, nutrient recovery, and waste management policy. However, raw biogas has low energy density and an unpleasant odor when used in conventional cooking and lighting process. Thus, the main objective of this thesis was to upgrade water hyacinth biogas by natural adsorbents through adsorption column. Raw materials were collected, prepared, characterized and stored for further use. Then, effects of factors such as adsorbents (Commercial Activated Carbon (CAC), Activated Carbon of Water hyacinth (ACW), Wood Ash (WA), Modified Clay (MC)), bed height (4, 8, and 12 cm) and gas flow rate (50,100,150,200 ml/min) were investigated on biogas upgrading quality. After that, upgraded biogas was characterized in terms of percent of methane and the spent adsorbent (Activated carbon of water hyacinth) was characterized with surface area, FT/IR and SEM analysis. Breakthrough curve was investigated at varying flow rate using optimized adsorbent (ACW). Raw biogas was found with 75±1% CH4, BET surface area of raw adsorbent was found to be (789.8, 624.9, 524.8, 522.5 m2/g) for CAC, ACW, WA, and MC respectively, FT/IR results (O‐H, C-H, C=C or C=O) were found with biomass derived
adsorbents (CAC, ACW, WA), (Al-OH, Si-OH, Al-Mg-OH) were found with modified
clay adsorbent. Upgraded biogas was found with (99±0.36, 97.8±0.51, 96.3±0.56, 94.8±0.67) % CH4 at bed height (12 cm) and flowrate (50 ml/min) using CAC, ACW, WA, and MC respectively. From synthesized adsorbents, the highest removal efficiency (96.11±0.51%) of impurities of biogas and purity of methane (97.8±0.51%) was recorded at flowrate (50 ml/min) and bed height (12 cm) using ACW. Longer breakthrough time and highest adsorption capacity were found to be 16min and 0.82 g impurities/g ACW respectively at 50 ml/min and 12cm. The up-grading process with ACW was fitted by Bohart-Adams model and acceptable correlation was obtained (R2=0.9892). Therefore, upon successful impurity sorption, wood ash, modified clay, and activated carbon from water hyacinth is suggested as a viable adsorbent for upgrading of biogas quality.
Keywords: Biogas, up-grading, Adsorbent, Adsorption Column, Removal-Efficiency, Adsorption Capacity, Bed Height