块状菱镁矿热分解机理及动力学方程的建立

Thermal Decomposition Mechanism and Establishment of Kinetic Equations of Block Magnesite

采用TG法对块度为20 mm、30 mm、40 mm和50 mm的立方体状菱镁矿的热分解进行了研究。结果表明:在相同转化率条件下,块状菱镁矿的分解活化能随块度增加而增大,块度(L=20～50 mm)与活化能的关系为:E=4.795×L+34.070(kJ·mol-1)。块状菱镁矿在不同的分解阶段,受不同的机理函数控制:分解前期,Anti-Jander方程控制的n=2的3D模型为最概然机理函数,动力学方程为:dα/dT=6.111×1010×β-1exp[(4.098-0.577×L)×T-1](1+α)2/3[(1+α)1/3-1]-1;分解中期,Avrami-Erofeev方程控制的n=3(Code:AE3)的随机成核和随后长大模型为最概然机理函数,动力学方程为:dα/dT=1.422×109×β-1exp[(4.098-0.577×L)×T-1](1-α)[-ln(1-α)]-2;分解后期,Avrami-Erofeev方程控制的n=3/2的随机成核和随后长大模型为最概然机理函数,动力学方程为:dα/dT=2.477×109×β-1exp[(4.098-0.577L)×T-1](1-α)[-ln(1-α)]-2。本项研究为制定块状菱镁矿生产MgO工艺提供了理论依据。

Thermal decomposition of cubic magnesite blocks with the side length of 20 mm,30 mm,40 mm and 50 mm were investigated by TG. The results indicate that under the same conversation ratio,decomposition activation energy increases with size of block magnesite increasing. The relation between block size（L = 20-50 mm） and activation energy meets the formula： E = 4. 795 × L ＋ 34. 070（kJ /mol）.Thermal decomposition of magnesite block is controlled by different mechanism functions at different decomposing stages： At earlier stage,3D mould with n = 2 controlled by Anti-Jander’s formula is the most probable mechanism function. Decomposition equation is dα /dT = 6. 111 × 1010× β- 1exp [（4. 098- 0.577 × L） × T- 1]（1 ＋α）2 /3[（1 ＋α）1 /3- 1]- 1; In the middle stage,random nucleation and subsequent growth models with n = 3（Code： AE3） controlled by Avrami-Erofeev formula is the most probablemechanism function. Decomposition equation is dα /dT = 1. 422 × 109× β- 1exp[（4. 098- 0. 577 × L） ×T- 1]（1-α） [-ln（1-α） ]- 2; in the later stage,random nucleation and subsequent growth models with n = 3 /2 controlled by Avrami-Erofeev formula is the most probable mechanism function. Decomposition equation is dα /dT = 2. 477 × 109× β- 1exp[（4. 098- 0. 577L） × T- 1]（1- α） [- ln（1- α） ]- 2. The study provides a theoretical basis for the planning of block magnesite production MgO process.