Thermal conversion potential of tea stems: Experimental investigation, reaction mechanism, and kinetic modeling

Abstract

Recent studies on tea waste pyrolysis have revealed significant gaps, including a lack of experimental data regarding the types of tea waste and a scarcity of comprehensive studies devoted to kinetic models and well-established reaction pathways tailored to this process. This study systematically investigates tea stem pyrolysis, employing comprehensive physicochemical, thermogravimetric, and kinetic analyses. By Identifying the promising characteristics of tea stem, such as its low ash content, high volatile matter, substantial phenolic compounds, and impressive calorific value, this study underscores its potential and delves deep into the complex stages of tea stem pyrolysis. The decomposition process of pseudo-components related to cellulose, hemicellulose, and lignin is an integral part of the comprehensive description of the thermal degradation of tea stems. This description includes the analysis of the contribution factors of its components and their interactions, which significantly influence the reaction rates. These aspects constitute key focal points of our investigation. Furthermore, a comprehensive comparative analysis, incorporating four semi-global reaction mechanisms, was conducted to identify the most optimal reaction mechanism for the thermal decomposition of tea stems. The present study employed a multivariate optimization technique to intricately characterize the kinetics of the process, with a final objective of determining the most appropriate reaction mechanism. Additionally, during the optimization process, it was found that incorporating nucleation-growth reaction model into the reaction mechanism substantially enhances the accuracy. Based on the analysis of kinetic triplets and a comparison of the reaction mechanisms, the mechanism with two independent parallel reactions containing an intermediate consecutive step demonstrates the best agreement with experimental results, with a fit quality of 4.396% and an R-squared (R2) value of 0.997. The findings of this study contribute to a better understanding of the thermal conversion potential of tea stems and provide a deeper understanding of their pyrolysis behavior and kinetic characteristics.