Effect of Temperature and Heating Rate on Pyrolysis Characteristics of Spent Coffee Grounds

Considerable increase in global coffee consumption has resulted in a marked increase in the amount of spent coffee grounds (SCG). To examine the applicability of SCG as a renewable energy source this study evaluated the pyrolysis characteristics of SCG. Elemental and proximate analyses were conducted on SCG, and kinetic analysis was performed using thermogravimetric analysis to identify the activation energy for the pyrolysis reaction. The experiment was performed in a nitrogen atmosphere using a fixed-bed reactor to analyze the gas and liquid products as well as the solid residues produced from the pyrolysis reaction by varying the reaction temperature and heating rate. The activation energy for the pyrolysis reaction of coffee hemicellulose and cellulose was higher than that for the pyrolysis reaction of lignin. With regard to gaseous products, CO and CO2 began to occur at a lower temperature than hydrocarbons, and hydrocarbons began to occur at approximately 330 degrees C. The yield of the liquid products was highest at 500 degrees C, and it increased with the heating rate. Moreover, most of the liquid products were components containing oxygen, and the compound composition of the liquid products depended on the reaction temperature and heating rate. The yield of the solid residues decreased according to the reaction temperature and heating rate, and it was confirmed through infrared and X-ray diffraction spectrum analysis that gradual carbonization occurred according to reaction conditions.