Kinetic parameters study for the slow pyrolysis of coffee residues based on thermogravimetric analysis

Thermal decomposition of coffee husks was investigated by thermogravimetric analyses. The proximate, ultimate and composition analyses were performed. Thermogravimetric tests were realized, the material was heated to 1173 K using five heating rates: 5, 10, 15, 20, 25 K min-1. The kinetic parameters were estimated using the methods of Kissinger-Akahira-Sunose and Friedman, the distributed activation energy model and the independent parallel reactions model. The isoconversional models of Kissinger-Akahira-Sunose and Friedman showed the dependence between determined values of activation energy and mass conversion, the activation energy values varied from 1437.39 to 199.22 kJ mol-1 for Kissinger-Akahira-Sunose and from 127.81 to 230.35 kJ mol-1 for Friedman model. The values of activation energy were determined for Miura-Maki method; varying from 137.39 to 199.22 kJ mol-1. The model of parallel and independent reactions showed the presence of six different reactions (with activation energy values varying from 42.0 to 214.2 kJ mol-1) occurring during coffee husks pyrolysis, indicating a complex reaction. Currently, works regarding the determination of kinetic parameters for coffee husks pyrolysis are not common. The present work is the first report using the model of parallel and independent reactions to estimate kinetic parameters for pyrolysis of coffee husks, a residue widely generated worldwide.本研究采用热重分析法（thermogravimetric analyses）对咖啡果壳的热分解过程展开了系统研究。开展了工业分析（proximate analysis）、元素分析（ultimate analysis）及组分分析，并完成了系列热重测试：以5、10、15、20、25 K·min⁻¹的五种升温速率将试样加热至1173 K。本研究采用基辛格-秋山-孙濑法（Kissinger-Akahira-Sunose）、弗里德曼法（Friedman）、分布活化能模型（distributed activation energy model）以及独立平行反应模型（independent parallel reactions model）对热解动力学参数进行了估算。结果表明，基辛格-秋山-孙濑法与弗里德曼法这两种等转化率模型（isoconversional models）所得活化能测定值与质量转化率之间存在显著依赖关系；其中基辛格-秋山-孙濑法得到的活化能值介于1437.39至199.22 kJ·mol⁻¹之间，弗里德曼法则介于127.81至230.35 kJ·mol⁻¹之间。采用三浦-牧法（Miura-Maki）测定得到的活化能值介于137.39至199.22 kJ·mol⁻¹之间。独立平行反应模型结果显示，咖啡果壳热解过程中存在6种不同的反应，其活化能值介于42.0至214.2 kJ·mol⁻¹之间，这表明该热解过程为复杂反应。目前，针对咖啡果壳热解动力学参数测定的相关研究尚较为少见。本研究首次采用独立平行反应模型对全球广泛产生的废弃物——咖啡果壳的热解动力学参数进行估算。