Abstract:[Purposes] The pyrolysis characteristics of spent coffee grounds (SCG) and defatted coffee grounds (DCG) were studied, and their pyrolysis kinetic parameters were calculated. The three-phase products of pyrolysis at different temperatures were analyzed to realize the secondary utilization of waste coffee grounds.[Methods] The distribution and characteristics of pyrolysis products were studied by tube furnace, thermogravimetric (TG) experiment and gas chromatography-mass spectrometry (Py-GC-MS). The kinetic parameters of pyrolysis were calculated by Flynn-Wall-Ozawa (FWO) method. [Findings] The results of thermogravimetric analysis showed that the pyrolysis of SCG and DCG could be divided into four stages. The heating rate can promote the progress of the pyrolysis reaction. As shown in the kinetic calculation results , the activation energy had increased continuously when the conversion ratio is increased from 0.1 to 0.7. And the activation energy haddecreased when the conversion ratio is increased from 0.7 to 0.9, the activation energy decreases. The average activation energy of SCG and DCG are 293.58 kJ/mol and 307.86 kJ/mol,respectively. Py-GC-MS analysis showed that the main pyrolysis products of SCG could be roughly divided into aromatics, phenols, aldehydes and other compounds, and the main pyrolysis products of DCG could be roughly divided into aldehydes, phenols and heterocycles . In the pyrolysis stage, with the increasing of pyrolysis temperature, the relative content of aromatic, phenolic and heterocyclic compounds decreased, and the relative content of aldehyde compounds firstly increased and then decreased. The results of the tube furnace pyrolysis experiments showed that the yield of bio-oil in the pyrolysis product of SCG was higher, and the yield of coke in the pyrolysis product of DCG was higher. [Conclusions] The pyrolysis of SCG and DCG at a suitable temperature is beneficial to the recovery of important industrial raw materials such as phenol and aromatic compounds, and realizes their high-value utilization.
