低碳烷烃无氧芳构化热力学分析及平衡产物分布

Thermodynamics analysis of low carbon alkane aromatization and equilibrium product distribution

进行了低碳烷烃的无氧芳构化反应的热力学计算。计算结果表明,在相同温度下,芳构化反应吉布斯自由能(ΔG)随着低碳烷烃含碳数目的增长而减少,以产物为苯进行计算,低碳烷烃热力学上无氧芳构化自发进行的顺序为丁烷>丙烷>乙烷>甲烷。甲烷芳构化生成甲基数依次增加的苯同系物的反应ΔG差别较大,相同反应温度下,ΔG随着甲基数的增加而增加,生成产物自发进行的顺序为苯>甲苯>二甲苯>三甲苯。ΔG随侧链碳数的增加而增加,生成产物倾向于热力学自发进行的顺序为苯>甲苯>乙苯>丙苯。甲烷无氧芳构化反应的副反应主要为积碳反应和生成小分子的乙烯、乙烷、丙烯和丙烷等反应,其中温度变化对副反应的热力学影响较小。以甲烷作为反应物进行无氧芳构化反应,反应达到平衡状态时,系统中会有多种产物。当不考虑积碳反应时,随着温度的升高,在平衡系统中甲烷含量逐渐降低,氢气含量逐渐升高,表明升高温度有利于甲烷芳构化反应的正向进行。

Thermodynamic calculations of anaerobic aromatization of light paraffins were conducted.The results showed that at the same temperature,the Gibbs free energy(ΔG)of the aromatization reaction decreases as the carbon number in light paraffins increases.Calculations using benzene as the product indicate that the thermodynamic spontaneity of anaerobic aromatization follows the order:butane>propane>ethane>methane.For methane aromatization,theΔG values for generating benzene homologues vary significantly.At the same temperature,theΔG for generating benzene homologues increases with the number of methyl groups,and the spontaneous order of product formation is benzene>toluene>xylene>trimethylbenzene.TheΔG increases with the number of side-chain carbons,and the reaction spontaneity order is benzene>toluene>ethylbenzene>propylbenzene.The side reactions of methane anaerobic aromatization mainly include carbon deposition and the formation of small molecules such as ethylene,ethane,propylene,and propane,with minimal thermodynamic impact from temperature changes.When methane is used as the reactant in anaerobic aromatization,equilibrium results in a variety of products in the system.Excluding the carbon deposition reaction,the methane content decreases,and the hydrogen content increases with rising temperature,indicating that higher temperatures favor the forward aromatization reaction.