石脑油在芳构化反应中活化途径的热力学分析

Thermodynamic Study on the Activation Pathways of Naphtha Fraction in Aromatization

对石脑油组份芳构化反应中的正碳离子活化途径进行了热力学分析。计算了反应温度为530℃时,烃分子以不同方式活化的反应焓变和平衡常数。结果表明,链烷烃在固体酸催化剂上以裂解方式进行活化在热力学上最有利,其次是以氢转移方式进行活化。与链烷烃不同的是,环烷烃在固体酸催化剂上的裂解活化因涉及到开环反应,因而比较困难。相比之下,环烷烃的氢转移活化方式在热力学上最有利。不论链烷烃还是环烷烃,脱氢活化方式在热力学上都是不利的。石脑油组份在固体酸催化剂上的活化反应总体上是吸热反应,因此在反应器设计时需注意热平衡问题。另外,从热力学上看,石脑油组份在进行裂解和氢转移活化时将不可避免地生成大量干气(甲烷和乙烷)和丙烷,因此干气和丙烷副产物的综合利用可能成为石脑油组份芳构化技术工业应用的重要问题。

The carboncation activation pathways of naphtha fraction over solid acid catalyst under the condition of aromatization was studied thermodynamically. Emphasis was given to the enthalpy change and the equilibrium constant of the different activation paths of the hydrocarbons at 530℃. Results show that, paraffin is activated more favorably via cracking than via hydrogen transfer. In the case of naphthene, however, the activation is more favorably via hydrogen transfer than via cracking. This is due to the difficulty of ring-opening reaction of the naphthene molecules. For both paraffin and naphthene, the dehydrogenation activation is less important when compared to the cracking and hydrogen transfer. Generally, the activation of naphtha fraction over solid acid catalyst is endothermic. Therefore, attention should be paid to the thermal equilibrium during reactor design. Besides, dry gas (methane and ethane) and propane are two kinds of by-products that could be generated in considerable amount during the cracking and hydrogen transfer activation of naphtha, thus the comprehensive utilization of these by-products is very important for the practical use of naphtha aromatization.