水性炭质中间体的制备及热解动力学模型

Preparation and pyrolysis kinetic model of water-soluble carbonaceous intermediate

为了给水性炭质中间体作为前驱体制备各种炭材料的加热过程提供基础研究,本文以中温煤焦油沥青、中间相炭微球、墙外体保温残料炭为原料,混酸氧化-碱溶酸沉净化制备水性炭质中间体。采用热重法研究原料和纯化的pH值对所得水性炭质中间体热稳定性及热解机理的影响,利用机理函数法建立水性炭质中间体热解动力学方程,并利用Achar-Brindley-Wendworth方程拟合直线计算动力学参数。结果表明:原料和纯化的pH值对制备水性炭质中间体的热解行为皆有影响,但以制备条件pH更显著。中温沥青、碳微球、墙外体保温残料炭三种原料,pH为4沉淀得到的水性炭质中间体,在135～370℃之间热解机理均符合三维扩散模型;在440～660℃的温度范围内,热解机理分别为二级、一级化学反应模型和三维扩散模型。pH为2时,在135～370℃之间热解机理分别符合一级、二级、三级化学反应模型;在440～660℃的温度范围内,热解机理分别为一级、一级、三级化学反应模型;中温沥青、墙外体保温材料炭两种原料,pH为6沉淀得到的水性炭质中间体,在135～370℃之间以及440～660℃之间,均符合三级化学反应模型。

In order to provide references for fundamental researches on the heating process of water-based carbonaceous intermediates as precursors for the preparation of various carbon materials, using medium-temperature coal tar pitch, mesocarbon microbeads and the exterior wall insulation boards, respectively, as the raw materials, water-soluble carbonaceous intermediates were prepared by means of mixed acid oxidation, alkali-solution and acid-isolation purification. Influences of the types of raw materials and the values of purification pH on the thermal stability and pyrolysis mechanism of the prepared water-soluble carbonaceous intermediates were studied by using thermogravimetry（TG/DTG） method. The pyrolysis kinetic equations of water-soluble carbonaceous intermediates were established with mechanism function method, and the Achar-Brindley-Wendworth equation was used for linear curve fitting to calculate the kinetic parameters. The results suggest that both the raw material type and the purification pH have effects on the pyrolysis behavior of aqueous carbonaceous intermediates but with the latter being more significant. For the water-soluble carbonaceous intermediates prepared under pH of 4 from the three raw materials（i.e., medium-temperature coal tar pitch, mesocarbon microbeads and the exterior wall insulation board）, their pyrolysis mechanisms in temperature range of 135-370 ℃ all match the three-dimensional diffusion and spherical symmetry model, while in temperature range of440 -660 ℃ the pyrolysis mechanisms match second, first order chemical reaction and three-dimensional diffusion models, respectively. Changing the pH value to 2, in temperature range of 135 -370 ℃ the pyrolysis mechanisms of the carbonaceous intermediates prepared from the three raw materials exhibit second, first and third order chemical reaction kinetic behaviors, respectively; in temperature range of 440-660 ℃ the pyrolysis mechanisms follow first, first and third order chemical reaction kinetics, respectively. For the water-soluble carbonaceous intermediates prepared at pH = 6 from medium coal tar pitch and the exterior wall insulation board, their pyrolysis mechanisms at temperature in ranges of 135-370 ℃ and 440-660 ℃ both match third order chemical reaction model.