Pyrolysis of four waste biomasses and elucidation of reaction kinetics and pyrolytic products

Abstract

With the increase of bioenergy crops and the rapid development of agriculture, the total amount of solid waste is increasing rapidly. This study quantified the pyrolytic performance and gaseous products of spent coffee grounds (SCG), Chinese medicine residue (CMR), vinasse (VI) and camellia oil shell (COS) by using (derivative) thermogravimetric ((D)TG), Fourier transform infrared spectrometry (FTIR) and mass spectrometry (MS) analyses. There are two main stages of mass loss: volatilisation of volatiles and continuous decomposition of macromolecules. At a heating rate of 20°C/min, COS has the slowest pyrolysis rate compared to the other three. Model-free methods: Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) were used to calculate the activation energy (E) of samples with different conversion rates (α). SCG and VI have the highest average activation energy (about 240kJ/mol), followed by CMR (200kJ/mol), and COS the lowest (175kJ/mol). FTIR was mainly used to detect functional group types (including hydroxyl, carbonyl, aldehyde and ester groups, etc.), while MS co-detected the characteristics of condensable/non-condensable gases (including H2O, CO2, NOx, SOx, C6H6, C7H8, C9H8 and other major gas emissions, pollutants and hydrocarbons). Nitrogen oxides are produced in the range of 500–800°C. SCG and VI emit more gas pollutants than CMR and COS.