(600cm) A Novel Catalyst Molding Method to Remove Intraparticle Diffusion Limitation in Fischer-Tropsch Synthesis

The technology of the Fischer-Tropsch synthesis (FTS) in fixed-bed reactor over cobalt-based catalyst, indirect liquefaction of coal to obtain fuel and chemicals, has a promising application due to its easy industrialization. Noticeably, in order to reduce the pressure drop and make sure the reaction could be carried out smoothly, the catalyst particles size should be larger than 1 mm in industrial fixed-bed reactor. However, the intraparticle diffusion limitation of larger catalyst particles becomes serious, which could increase CH₄ selectivity and decrease C₅₊ selectivity, thus significantly reduce the value of products. Small particles could completely eliminate the effect of intraparticle diffusion limitation for short diffusion length. In that case, we intend to enhance mass-transfer in larger catalyst particles (> 1mm in diameter) via secondary molding of smaller catalyst. Specifically, smaller particles (< 0.1mm in diameter) and pore-forming agent would be combined to form larger particles (>1 mm in diameter) by using binders, such as PCS, clay and PMHS. After removing the pore-forming agent, smaller catalyst particles were bonded together. And larger spaces among them, where the pore-forming agent once occupied, were formed. Then, a honeycomb structure catalyst pellets were brought. In this structure, both reactants and products could pass through the interspace quickly during reaction. The new molding method realized negligible diffusion limitations in the catalyst pellets, which meet the need of the industrialization of FTS in fixed-bed reactor. According to the FTS results, the secondary molded catalyst exhibit excellent performance with lower CH₄ selectivity and higher C₅₊ selectivity comparing with those prepared by traditional molding method, such as extrusion.

Keywords: Fischer-Tropsch synthesis, Intraparticle diffusion, molding method

Supported by：

(1) Strategic Priority Research Program, Chinese Academy of Sciences, Grant No. XDA07070700

(2) National Natural Science Foundation of China, Grant No. 21273265