Institute of Chemical Engineering, University of Science and Technology Liaoning

煤沥青球主要用于制造机械强度与负载密度高、孔径分布可控的球形活性炭,球形活性炭已在环保、医疗等领域得到广泛应用,因而探索煤沥青球的氧化不熔化特性将对球形活性炭的产品性能产生影响以及指导后续炭化、活化操作,对煤沥青球预氧化的热转化机理及热力学性质研究可为利用煤沥青球制备球形活性炭提供重要的理论依据。在氧气气氛中对不同粒径的煤沥青球进行不熔化处理,采用热重分析检测方法,运用KISSINGER法和Satava-Sastak分析法及其41种机理函数模型对煤沥青球的预氧化过程进行化学动力学参数的计算与反应机理分析,探寻其粒径的大小对各参数以及热转化过程中能量需求的影响。研究结果表明:煤沥青球的预氧化过程主要分为2个阶段,第1个阶段属于预氧化不熔化的热分解过程,粒径的大小影响氧分子在沥青球内的扩散,球体粒径越大则预氧化反应能量需求越高;但不同粒径的沥青球体与氧分子发生交联反应的本质相同,活性位点数目不多,指前因子的大小几乎不受粒径的影响。进入第2阶段的热缩聚过程后,沥青球发生剧烈的氧化反应,受第1个阶段不熔化处理的影响,球径越小则表面氧原子交联官能团越多、沥青球越稳定、高温下热分解反应需求能量越多、活性位点越少,导致第2个阶段的反应活化能随着粒径增大而减小,指前因子随着粒径的增大而减小。煤沥青球整个预氧化反应过程为非自发的吸热反应,粒径对焓变(ΔH)、熵变(ΔS)有较大影响;2个阶段中尽管吉布斯自由能变(ΔG)的变化很大,但同一反应阶段下,粒径对ΔG的影响并不明显。煤沥青球热转化过程的第1个阶段符合第18号机理函数,机理函数模型为随机成核模型,随后生长;第2个阶段符合第2号机理函数,机理函数模型为随机成核模型,随后扩散。

Coal pitch balls play a crucial role in the production of spherical activated carbon, known for its robustmechanical strength, high load density and controllable pore size distribution. This type of activated carbon finds ex⁃tensive applications in environmental protection and medical fields. Understanding the oxidation non⁃melting charac⁃teristics of coal pitch balls is paramount for enhancing the performance of spherical activated carbon and optimizingsubsequent carbonization and activation processes. This study delves into the thermal transformation mechanism andthermodynamic properties of preoxidized coal pitch balls, offering a vital theoretical foundation for the production ofspherical activated carbon from this raw material. Through a series of experiments involving non⁃melting treatment ofcoal pitch balls with varying particle sizes in an oxygen⁃rich environment, chemical dynamics parameters and reactionmechanisms during the preoxidation process were meticulously calculated. Employing techniques such as thermogravi⁃metric analysis, KISSINGER method, Satava⁃Sastak analysis and 41 mechanism function models, the investigationalso assessed the impact of particle size on process parameters and energy requirements during thermal conversion.The findings reveal a two⁃stage preoxidation process for coal asphalt balls. The initial stage involves a non⁃meltingpreoxidation thermal decomposition process, where particle size significantly influences the diffusion of oxygen mole⁃cules within the balls. Larger ball sizes demand higher energy for preoxidation reactions. However, the cross⁃linkingreactions between coal pitch spheres with different particle sizes and oxygen molecules are essentially the same, witha small number of active sites, and the size of the pre exponential factor is almost unaffected by particle size. Uponentering the thermal condensation process of the second stage, the pitch balls undergo a violent oxidation reaction.Affected by the non⁃melting treatment of the first stage, the smaller the ball diameter, the more surface oxygen atomcross⁃linking functional groups, the more stable the asphalt ball, the more energy required for thermal decompositionreaction at high temperature and the fewer active sites. The activation energy of the reaction in the second stage de⁃creases with the increase of particle size, and the pre exponential factor decreases with the increase of particle size.The entire preoxidation process of coal pitch balls emerges as a non⁃spontaneous endothermic reaction, with particlesize exerting substantial influence on enthalpy change (ΔH) and entropy change (ΔS) changes. While Gibbs freeenergy change (ΔG) exhibits significant variation across the two reaction stages, the effect of particle size within thesame stage is less pronounced. The first stage of the thermal transformation is conformed to mechanism function of No.18, which is characterized by a random nucleation model succeeded by growth. The second stage aligns with mecha⁃nism function No. 2, featuring a random nucleation model followed by diffusion.

国家自然科学基金资助项目(22208138);辽宁省自然科学基金资助项目(2021-BS-245,2021-MS-306);辽宁科技大学国家级大学生创新创业项目(2023-23)

满梦瑶, 吴秋萍, 宋帅超, 等. 煤沥青球预氧化的热转化机理及热力学特性研究 [J]. 煤质技术, 2023,38 (5): 1-8.

MAN Mengyao, WU Qiuping, SONG Shuaichao, et al. Study on thermal transformation mechanism and thermody⁃namic characteristics of coal pitch ball preoxidation [J]. Coal Quality Technology, 2023, 38 (5): 1-8.