Abstract:

The solid residues after pyrolysis of pure urea and urea/TiO₂ at different temperatures were collected and analyzed by using infrared spectroscopy(IR) and gas chromatography mass spectrum(GC-MS). Thermogravimetric-infrared(TG-FTIR) technique was used to analyze the pyrolysis characteristics of urea and cyanuric acid and the transformation mechanism of gaseous compounds in the pyrolysis process with and without TiO₂. The kinetic equations and parameters were obtained from the for non-isothermal weight loss curves according to the Coats-Redfern method. The results showed that urea and biuret were the main pyrolytic residues of urea at 100—250℃, while the nitrogenous heterocyclic organic compounds such as cyanuric acid were the main pyrolytic residues of urea at 300—400℃. Anatase TiO₂ can promote the pyrolysis reaction of urea and cyanuric acid and thus shorten the reaction process, since HNCO and water vapor can react easily on the surface of TiO₂. The reaction order of urea for the pyrolysis alone in the first stage of pyrolysis is 2, the activation energy is 113.25kJ/mol, and the pre-exponential factor A is 2.01×10¹¹min^-1. Under the presence of TiO₂, the activation energy E is 77.42kJ/mol, and the pre-exponential factor A becomes 4.82×10⁷min^-1.

Key words: urea, catalysis, kinetics, selective catalytic reduction, solid residues

摘要：

通过实验的方法收集了不同温度下纯尿素和尿素/TiO₂混合物热解后的固体残留物，使用红外光谱（IR）及气相色谱质谱联机（GC-MS）方法对这些热解残留物进行成分分析；使用热重-红外联机（TG-FTIR）技术研究尿素及三聚氰酸在有无催化剂TiO₂的情况下的热解特性及气体产物的生成规律；根据Coats-Renfern方法对尿素热解第一阶段的非等温热失重率曲线的数据进行动力学研究，建立动力学方程。结果表明，100~250℃的尿素热解残留物中主要为尿素和缩二脲，300~400℃的尿素热解残留物中主要为三聚氰酸等含氮杂环有机化合物；锐钛型TiO₂能促进尿素和三聚氰酸的热解反应，缩短其反应进程，HNCO与水蒸气在TiO₂表面易发生反应；尿素第一阶段热解的反应级数为2，单独热解时活化能为113.25kJ/mol，指前因子A为2.01×10¹¹min^-1，在催化剂TiO₂的作用下，活化能E为77.42kJ/mol，指前因子A为4.82×10⁷min^-1。

关键词: 尿素, 催化, 动力学, 选择催化还原, 固体残留物