费托合成钴基催化剂颗粒内的传递反应行为分析

Intragranular transfer reaction behavior analysis of cobalt-based catalyst for Fischer-Tropsch synthesis

基于费托合成钴基催化剂反应动力学模型,建立了针对费托合成复杂多重反应体系的多组分扩散-反应的颗粒数学模型,以此为基础,考察了费托合成体系中催化剂颗粒尺寸、操作条件及反应物在颗粒内的传递反应行为等对费托合成反应性和产物选择性的影响。结果表明,对于毫米级钴基催化剂,费托合成反应主要发生在催化剂颗粒的外部壳层,0.2Rp~0.3Rp厚度区域(Rp为催化剂半径),低碳烃较易在催化剂颗粒内部产生,重质烃则易在催化剂颗粒表面产生,催化剂内部温升为0.0534℃,不会造成催化剂烧结。升高温度和增大颗粒尺寸抑制烃类产物的链增长,增大压力则有利于产物碳链的增长和重质烃的生成。工业用固定床钴基催化剂颗粒采用圆柱形Φ2×2~Φ4×4 mm(直径×高)最为适宜,CO内扩散有效因子范围为0.15~0.30。

Based on the Fischer-Tropsch synthesis reaction kinetic model of cobalt-based catalysts, a multicomponent reactiondiffusion particle model for the complex multi-reaction system of Fischer-Tropsch synthesis was established. Based on the model, the effects of catalyst particle size, operating conditions and the intragranular transfer reaction behavior of the reactants on the reactivity and product selectivity of Fischer-Tropsch synthesis were investigated. The results show that the Fischer-Tropsch synthesis reaction mainly occurs in the outer shell of the catalyst particles with a thickness of 0.2Rp-0.3Rp(Rpis the radius of the catalyst) for millimeter-level catalysts. The low-carbon hydrocarbons are more likely to be generated inside the catalyst particles, while heavy-carbon hydrocarbons are easily generated on the surface of the catalyst particles. The rise of temperature inside the catalyst is 0.0534 ℃,which will not cause the sintering of catalyst. Increasing temperature and particle size will inhibit the chain growth of hydrocarbon products, while increasing pressure will favor the growth of product carbon chains and the formation of heavy hydrocarbons. It is suitable for the industrial cobalt-based catalyst particles for fixed-bed to be cylindrical with Φ 2 × 2-Φ 4 × 4 mm(diameter × hight),and the effective factor of CO internal diffusion ranges from 0.15 to 0.30.