Farhad Fazlollahi

Preparation of Fe-Mn/K/Al2O3 Fischer-Tropsch Catalyst and Its Catalytic Kinetics for the Hydrogenation of Carbon Monoxide

Abstract A K promoted iron-manganese catalyst was prepared by sol-gel method, and subsequently was tested for hydrogenation of carbon monoxide to light olefins. The kinetic experiments on a well-characterized Fe-Mn/K/Al 2 O 3 catalyst were performed in a fixed-bed micro-reactor in a temperature range of 280-380 °C, pressure range of 0.1-1.2 MPa, H 2 /CO feed molar ratio range of 1-2.1 and a space velocity range of 2000-7200 h −1 . Considering the mechanism of the process and Langmuir-Hinshelwood-Hogan-Watson (LHHW) approach, unassisted CO dissociation and H-assisted CO dissociation mechanisms were defined. The best models were obtained using non-linear regression analysis and Levenberg-Marquardt algorithm. Consequently, 4 models were considered as the preferred models based on the carbide mechanism. Finally, a model was proposed as a best model that assumed the following kinetically relevant steps in the iron-Fischer-Tropsch (FT) synthesis: (1) CO dissociation occurred without hydrogen interaction and was not a rate-limiting step; (2) the first hydrogen addition to surface carbon was the rate-determining steps. The activation energy and adsorption enthalpy were calculated 40.0 and −30.2 kJ·mol −1 , respectively.

Fischer Tropsch Synthesis: The Promoter Effects, Operating Conditions, and Reactor Synthesis

The effects of K, Ce, Zn, Cs, and Rb promoters on the structure and catalytic behavior of precipitated 50%Fe/50%Mn catalyst in Fischer–Tropsch synthesis (FTS) were investigated in a fixed-bed reactor. The effects of promoter on Fischer-Tropsch iron catalysts caused an increased growth probability of hydrocarbon chains from 0.67 to 0.75 for K to Rb promoter, and the olefin/paraffin ratios increased from 0.99 to 1.36 for Rb to K-promoted catalyst. The effect on the olefin selectivity was certainly due to increased adsorption strength of CO causing an enhanced displacement of olefin. The catalysts were assessed in terms of their FTS activity and product selectivity using Anderson–Schulz–Flory (ASF) models. The effects of various reaction conditions such as flow rates, temperatures, and H2/CO feed ratios were studied and process synthesis concepts were used to investigate interactions between the optimum regions for reactor operation and the experimental results.

Kinetic Modeling of Fischer-Tropsch Synthesis over Fe/Ce/Al 2 O 3

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.