Thermokinetic study of macadamia carpel pyrolysis using thermogravimetric analysis

Abstract

AbstractThe macadamia productive process generates a large amount of waste, such as walnut carpel, that is improperly disposed of in most instances. This residue is a promising feedstock for biofuel production and it can be converted through thermochemical routes. Liquid pyrolysis products obtained contain a bio‐oil with great potential for the production of fuels and fine chemicals. The goal of this study was to characterize the macadamia carpel for the first time by ultimate, proximate, FTIR, and TG analysis, as well as HHV determination, which showed this is a potential candidate for thermochemical conversion processes. Thermodynamic and kinetic pyrolysis behaviours were evaluated using Ozawa, Kissinger, Starink, and KAS isoconversional models (140.12, 137.69, 137.41, and 146.63 kJ mol−1, respectively), which attested to the product favourability and the operational viability. Additionally, the master plot method was applied to complete the kinetic description, which identified diffusion and nucleation mechanisms during the carpel degradation. After 50% conversion, the third‐order reaction mechanism occurred due to a predominant lignin decomposition. The results showed that the macadamia carpel properties are similar to traditional feedstock, that it may be decomposed into bio‐oil, and that it can be used as an alternative energy source or bio‐chemicals precursor.