Quantitative and kinetic TG-FTIR investigation on three kinds of biomass pyrolysis

Abstract

Biomass is applied in power generation or heat production as renewable energy resources. This paper focused on the pyrolysis in thermogravimetric (TG) analyzer of three biomasses, corn cob, tree root and bagasse, which showed different characteristics on their differential thermogravimetric (DTG) curves. In pyrolysis of corn cob, tree root and bagasse, there were three, one and two obvious peaks of DTG curves, respectively. Thermogravimetric Fourier Transform Infrared (TG-FTIR) analysis showed that the maximum mass loss rate at DTG curves was mainly due to cellulose and lignin pyrolysis, and the second mass loss rate peak of corn cob and the first one of bagasse were mainly due to pyrolysis of hemicellulose; while the first mass loss rate peak of corn cob was most likely due to breaking off of OH stretching function groups and H2O generation of sucrose pyrolysis. The main typical gaseous products were CO2, CO, H2O, CH4, NH3 and acid & aldehydes (CH3COOH or furadelhyde). Quantitative FTIR analysis showed that CO produced variation and CO2 produced before 400°C fitted with DTG curves well. IR results also indicated that hemicellulose pyrolysis had higher CH3COOH generation. Distributed activated energy model (DAEM) was applied to analyze kinetics of biomass pyrolysis. Similar to their DTG curves, the activation energy (AE) of corn cob showed four high distributions, in which the distributions of about 174.7kJ/mol and 181.6kJ/mol were highest (more than 20%), followed by that of 161.1kJ/mol (18.91%) and 140.5kJ/mol (9.08%); the AE of tree root had a distinctive distribution, which was as high as 33.9% at 181.6kJ/mol; while that of bagasse had only two distributions more than 6.8%, one is 50.69% at 181.6kJ/mol, and the other is 25.43% at 167.9kJ/mol. The pseudo-reactions fitting curves showed that the pyrolysis of corn cob was more complicated than the other two, because of more obvious pseudo-reactions contributed to the DTG curve and there were more than three main components in corn cob. It indicated that pseudo-reaction at 181.6kJ/mol was mainly contributed to cellulose pyrolysis in DTG curves, and those at 161.1kJ/mol and 167.9kJ/mol were mainly contributed to hemicellulose pyrolysis, while pseudo-reaction at 174.7kJ/mol might relate to the pyrolysis of sucrose.