Development of a Macro Kinetic Expression for the Iron-based Low-Temperature Fischer-Tropsch Synthesis

In this experimental study, a kinetic model has been developed for Fischer-Tropsch synthesis reactions by using Fe/Ni/Al2O3 as the catalyst (40% Fe/60% Ce/40wt%Al2O3) in a fixed-bed micro reactor assuming no internal or external diffusion. Operating conditions of the reactor are as follows: reactor total pressure 1-12 atm ; Temperature 220-260 ºC; H2/CO feed ratio 1-2 and space velocity 4200 hr-1. 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 kinetic data of this study are fitted fairly well by a simple form − r = AP 0.5 P/(1 + k P+ kP ) 2CO H 2 COCO COH 2OH 2Osimilar to that suggested by Botes. The obtained rate expressions for the COhydrogenation 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 toward CO and H2O were calculated as 78.58 kJ /mol and -30.56 kJ /mol and 30.94 respectively.

کلیدواژه ها:

kinetic modelind ، iron catalyst ، LHHW ، fixed -bed micro reactor