Food waste, despite its great potential as an energy source, is underutilized by salt and has difficulty to complete disposal. In this study, the pyrolysis was used to produce biochar, which is a carbon negative, as a part of the food waste recycling alternative, and characteristics of biochar chang...
Food waste, despite its great potential as an energy source, is underutilized by salt and has difficulty to complete disposal. In this study, the pyrolysis was used to produce biochar, which is a carbon negative, as a part of the food waste recycling alternative, and characteristics of biochar changes and demineralization effects were determined according to the pyrolysis temperature, reaction time, and NaCl concentration difference to remove salts that deteriorate quality as solid fuel. In addition, CO2 gas purged into the demineralization process to prevent ash fusion and harmful substances generation caused by alkali and alkaline earth metal ions during the fuel combustion, and whole experiments were performed on a lab-scale.
According to the results of the pyrolysis of food waste, the higher heating value increased as a pyrolysis temperature increased, and it was considered desirable to maintain the temperature of pyrolysis above 300 °C in consideration of reducing the pollution of effluent from demineralization. As a result of surface chemical analysis of biochar according to the pyrolysis temperature, it was confirmed the functional groups (carbonyl and carboxyl, etc.) are formed, and these groups induce the cation exchange capacity (CEC) of the biochar. As the temperature of pyrolysis increases, some functional groups are decomposed, but the formation of aromatic carbon groups increases, and the CEC increases due to the π-electron resonance of the aromatic ring structure. During the demineralization, the salt crystals were ionized and chlorine ion removed of about 90%, while sodium ions were resorbed to the biochar due to the CEC, and the resorption amount increased as the pyrolysis temperature increased. In the experiments on the salt concentration difference, the demineralization efficiency and the structural change of biochar were analyzed. The salt remaining in food waste biochar with crystalline form may serve as a template for generating the pores of the hexahedron in the form of NaCl crystals when demineralization. The pore formation and pore size could be controlled according to the salt concentration. Above all, the Cl ion removal performance increased through partial molten between KCl and NaCl at higher NaCl concentration.
CO2 purging demineralization was applied to remove resorbed alkali and alkaline earth metal ions. Through this method, the alkali metal ions were exchanged with hydrogen ions, and the removal efficiency was improved by up to 76%. On the other hand, when CO2 purging demineralization, the chlorine ion removal efficiency was reduced under specific pyrolysis temperature because the formation of oxonium structure leads to the anion exchange capacity (AEC), thereby resorbing chlorine ions. This phenomenon occurs only when CO2 purging demineralization because it occurs due to a deficiency of hydroxyl ions (OH-) that reduce re-adsorption of chlorine ions (Cl-) by competing with chlorine ions (Cl-).
In conclusion, the pyrolysis and demineralization experiment were conducted to determine the possibility of using food waste, which consists of organic matter and salt, as a renewable energy source. The pyrolysis and demineralization not only removed chlorine ion, which is the most difficult managed substance of food waste, but also produce biochar having an ion exchange capacity. Also, the ash fusion in the fuel combustion process could be improved by CO2 purging demineralization using the ion exchange capacity of biochar.
Food waste, despite its great potential as an energy source, is underutilized by salt and has difficulty to complete disposal. In this study, the pyrolysis was used to produce biochar, which is a carbon negative, as a part of the food waste recycling alternative, and characteristics of biochar changes and demineralization effects were determined according to the pyrolysis temperature, reaction time, and NaCl concentration difference to remove salts that deteriorate quality as solid fuel. In addition, CO2 gas purged into the demineralization process to prevent ash fusion and harmful substances generation caused by alkali and alkaline earth metal ions during the fuel combustion, and whole experiments were performed on a lab-scale.
According to the results of the pyrolysis of food waste, the higher heating value increased as a pyrolysis temperature increased, and it was considered desirable to maintain the temperature of pyrolysis above 300 °C in consideration of reducing the pollution of effluent from demineralization. As a result of surface chemical analysis of biochar according to the pyrolysis temperature, it was confirmed the functional groups (carbonyl and carboxyl, etc.) are formed, and these groups induce the cation exchange capacity (CEC) of the biochar. As the temperature of pyrolysis increases, some functional groups are decomposed, but the formation of aromatic carbon groups increases, and the CEC increases due to the π-electron resonance of the aromatic ring structure. During the demineralization, the salt crystals were ionized and chlorine ion removed of about 90%, while sodium ions were resorbed to the biochar due to the CEC, and the resorption amount increased as the pyrolysis temperature increased. In the experiments on the salt concentration difference, the demineralization efficiency and the structural change of biochar were analyzed. The salt remaining in food waste biochar with crystalline form may serve as a template for generating the pores of the hexahedron in the form of NaCl crystals when demineralization. The pore formation and pore size could be controlled according to the salt concentration. Above all, the Cl ion removal performance increased through partial molten between KCl and NaCl at higher NaCl concentration.
CO2 purging demineralization was applied to remove resorbed alkali and alkaline earth metal ions. Through this method, the alkali metal ions were exchanged with hydrogen ions, and the removal efficiency was improved by up to 76%. On the other hand, when CO2 purging demineralization, the chlorine ion removal efficiency was reduced under specific pyrolysis temperature because the formation of oxonium structure leads to the anion exchange capacity (AEC), thereby resorbing chlorine ions. This phenomenon occurs only when CO2 purging demineralization because it occurs due to a deficiency of hydroxyl ions (OH-) that reduce re-adsorption of chlorine ions (Cl-) by competing with chlorine ions (Cl-).
In conclusion, the pyrolysis and demineralization experiment were conducted to determine the possibility of using food waste, which consists of organic matter and salt, as a renewable energy source. The pyrolysis and demineralization not only removed chlorine ion, which is the most difficult managed substance of food waste, but also produce biochar having an ion exchange capacity. Also, the ash fusion in the fuel combustion process could be improved by CO2 purging demineralization using the ion exchange capacity of biochar.
주제어
#Food waste Pyrolysis Biochar Demineralization Ion exchange
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