In this experimental study, a kinetic model has been developed for Fischer-Tropsch synthesis reactions by using Fe/Ce/Al2O3 as the catalyst (80% Fe/20% Ce/5wt%Al2O3) in a fixed-bed micro reactor assuming no internal or external diffusion. Operating conditions of the reactor are as follows: reactor total pressure 6-22 atm; Temperature 543-573 K; H2/CO feed ratio 1.5-2 and space velocity 4200 hr-1. Light alkenes were successfully produced due to high activity and selectivity of the catalyst. Considering the mechanism of the process and Langmuir-Hinshelwood- Hogan-Watson (LHHW) approach, four different mechanisms, namely carbide, enol, combined carbide-enol, and parallel carbide-enol were defined for CO consumption rate equations. The rate expressions for the CO hydrogenation reactions are based on elementary reaction corresponding to the carbid-enol mechanism. The obtained rate expressions for the CO hydrogenation reactions from nonlinear regression analysis and Levenberg-Marquardt method demonstrate that the formation of monomer species (HCOs) due to CO hydrogenation reaction has controlled the FTS reaction rate. The activation energy and adsorption enthalpy were calculated as 58.38 kJ/mol and -22.26 kJ/mol, respectively. Also, the effects of temperature and pressure variation on selectivity and production rate of light products are presented.
©2012 Walter de Gruyter GmbH & Co. KG, Berlin/Boston
