大黄酸和大黄素的热分析及其动力学研究

本文采用热重法(TG)和差热分析法(DTA)测定了大黄酸和大黄素的DTA,TG-DTG曲线。两者的DTA曲线中皆有两个较为明显的吸热峰,第一个在熔化过程中出现,第二个发生在热分解过程中并伴随有明显的失重现象。TG曲线均有一个失重平台,失重率在90%以上。用TG-DTG法对两者在非等温条件下进行热分解动力学研究,把从TG-DTG曲线中取得的数据和31个不同的方程采用Achar微分法和Madhusudanan-Krishnan-Ni-nan(MKN)积分法对其进行非等温分解动力学研究,得到动力学参数活化能(E和指前因子A)和分解动力学机理及方程。得出结论:大黄酸和大黄素的动力学方程为dα/dt=Aexp(-E/RT)3/2(1-α)4/31/(1-α)1/3-1]-1和dα/dt=Aexp(-E/RT)3/2(1-α)2/31/(1-α)1/3]-1,其分解等合3D抗理。二者的活化能E(kJ/mol)分别为117.6和86.79,lnA/s-1分别是36.72和27.44。

Thermal Characterization and Decomposition Kinetics of Rhein and Emodin

The thermal behavior of Rhein and Emodin and their kinetics have been investigated under non-isothermal conditions by means of differential thermal analysis (DTA) and thermogravimetry (TG).The thermal characteristics have been determined using the DTA and TG-DTG curves.The non-isothermal kinetics of the samples was studied by use of non-isothermal TG and DTG curves.The non-isothermal kinetics data were analyzed by Achar differential and Madhusudanan-Krishnan-Ninan (MKN) methods.The possible reaction mechanisms have been investigated by comparing the kinetics parameters.The kinetic equations for the Rhein and Emodin can be expressed as dα/dt= Aexp(-E/RT)3/2(1-α)4/31/(1-α)1/3-1]-1 and dα/dt= Aexp(-E/RT)3/2(1-α)4/31/(1-α)1/3-1]-1 respectively.The activation energy E/(kJ/mol) of the two free anthraquinones from Rheum are 117.6 and 86.79 and their lnA/(1/s) are 36.72 and 27.44,respectively.