Abstract:

The CFD simulation of the egg-shell Co-based catalyst Fischer-Tropsch synthesis reaction system was carried out by Comsol-Multiphysics software. The effects of catalyst active component thickness on product and temperature distribution, conversion of F-T synthesis were studied by establishing a reasonable three-dimensional model of catalyst. The results show that the CO concentration has obvious difference between the outside and inside of catalyst due to strong diffusion limitation. And because the diffusion rate of H₂ is much larger than the diffusion rate of CO, the internal hydrogen-carbon ratio of the catalyst particles is very high, which is not conducive to the formation of oils and waxes. As the thickness of catalyst active components increases, the conversion of CO and the selectivity of methane and low hydrocarbons increases, while the selectivity of C₁₀H₂₂ and C₂₂H₄₆ decreases. The peak temperature inside the catalyst moves towards the inside of the catalyst, which isn’t conducive to the transfer of reaction heat. For the shell-type spherical catalyst with the size of 2.5mm, the optimum catalyst thickness of the active component is 0.125 mm.

Key words: F-T synthesis, computational fluid dynamics, diffusion, catalyst, thickness of active components

摘要：

采用Comsol-Multiphysics软件对蛋壳型Co基催化剂费托合成反应体系进行了CFD模拟计算。通过建立合理的费托合成催化剂颗粒三维模型进行计算，重点研究了催化剂活性组分厚度对费托合成反应产物分布、温度分布以及转化率的影响。结果表明：费托合成反应内扩散阻力较大，CO在催化剂表面和内部存在明显的浓度差。且由于H₂的扩散速率远大于CO的扩散速率，导致催化剂颗粒内部氢碳比很高，不利于油类和蜡类物质的生成；随着催化剂活性组分厚度的增加，CO转化率逐渐提高，甲烷和低碳烃的选择性逐渐增大，而C₁₀H₂₂和C₂₂H₄₆的选择性逐渐减小；催化剂颗粒内部的温度峰值逐渐向催化剂内部移动，不利于反应热的转移。对于尺寸为?2.5 mm的蛋壳型球形催化剂，较佳的催化剂活性组分厚度为0.125 mm。

关键词: 费托合成, 计算流体力学, 扩散, 催化剂, 活性组分厚度