Kinetic model, Fischer—Tropsch synthesis

Detailed Kinetic Study and Modeling of the Fischer-Tropsch Synthesis over a State-of-the-Art Cobalt-Based Catalyst... 

In this work, a detailed kinetic model for the Fischer-Tropsch synthesis (FTS) has been developed. Based on the analysis of the literature data concerning the FT reaction mechanism and on the results we obtained from chemical enrichment experiments, we have first defined a detailed FT mechanism for a cobalt-based catalyst, explaining the synthesis of each product through the evolution of adsorbed reaction intermediates. Moreover, appropriate rate laws have been attributed to each reaction step and the resulting kinetic scheme fitted to a comprehensive set of FT data describing the effect of process conditions on catalyst activity and selectivity in the range of process conditions typical of industrial operations. 

Kinetic Study and Modeling of the Fischer-Tropsch Synthesis... 

Visconti, C.G., Tronconi, E., Lietti, L., Zennaro, R., and Forzatti, P. 2007. Development of a complete kinetic model for the Fischer-Tropsch synthesis over Co/A1203 catalysts. Chem. Eng. Sci. 62 5338 -3. 

In 1976 he was appointed to Associate Professor for Technical Chemistry at the University Hannover. His research group experimentally investigated the interrelation of adsorption, transfer processes and chemical reaction in bubble columns by means of various model reactions a) the formation of tertiary-butanol from isobutene in the presence of sulphuric acid as a catalyst b) the absorption and interphase mass transfer of CO2 in the presence and absence of the enzyme carboanhydrase c) chlorination of toluene d) Fischer-Tropsch synthesis. Based on these data, the processes were mathematically modelled Fluid dynamic properties in Fischer-Tropsch Slurry Reactors were evaluated and mass transfer limitation of the process was proved. In addition, the solubiHties of oxygen and CO2 in various aqueous solutions and those of chlorine in benzene and toluene were determined. Within the framework of development of a process for reconditioning of nuclear fuel wastes the kinetics of the denitration of efQuents with formic acid was investigated. 

The catalytically active phase was assumed to be exclusively a-Fe, and Fe304 was assumed not to be active for the Fischer-Tropsch reaction. Kinetic parameters for the simulations were obtained independently in separate oxidation/reduction studies. Balancing the oxidation and reduction rates for the CO/CO2 and the H2/H2O systems independently and describing the rate of synthesis in Fischer-Tropsch reactions by a standard expression, Caldwell could predict the oscillations with a simplified model for a tubular reactor fairly well. 

Another proposal for explaining the two slope distributions is very consistent with the peculiarities of the Fischer Tropsch system The products of Fischer Tropsch synthesis do usually provide a liquid phase and a gaseous phase under reaction conditions.The gaseous compounds leave the reactor normally within a few seconds. The liquid does need a day or more until it elutes from the catalyst bed. Solubility of paraffinic hydrocarbon vapours in a paraffinic hydrocarbon liquid increases by a factor of about 2 for each carbon number of the product (ref. 27). Thus it needs only an increase of a very few carbon numbers of the product molecules to have them leaving the reactor mainly with the gas phase or with the liquid phase. With increasing residence time in the reactor the chance of readsorption increases and correspondingly the probability of chain prolongation increases. The kinetic scheme of this model is shown in Fig. 14. This model is very consistent with the experimental distributions. 

This paper discusses research efforts towards the prediction of hydrocarbon product distribution for the Fischer-Tropsch synthesis (FTS) on a cobalt-based catalyst using a micro-kinetic model taken fiom the literature. In the first part of the study, a MATLAB code has been developed which uses the Genetic Algorithm Toolbox to estimate parameter values for the kinetic model. The second part of the study describes an ongoing experimental campaign to validate the model predictions of the fixed-bed reactor FTS product distribution in both conventional (gas phase) and non-conventional (near-critical and supercritical phase) reaction media. 

Keywords Cobalt catalyst. Kinetics, Modeling, Fischer-Tropsch synthesis. Hydrocarbon Product Distribution, Anderson-Schulz-Flory. 

The kinetic model is build upon generally accepted concepts. The mechanism of the Fischer-Tropsch synthesis has been subject of many investigations, but is never fully agreed upon. 

This study explores the potential of periodic operation for the Fischer-Tropsch synthesis aiming at Diesel range products. The approach followed is modeling the process in a dynamic form using a simple CSTR reactor configuration. The kinetic scheme is based on steady-state data reported in literature. The steady-state behavior is in agreement with experimental observations reported earlier by various research groups. 

Fischer-Tropsch synthesis (FTS), directly converting a mixture of carbon monoxide and hydrogen (syngas) into sulfur-free hydrocarbons, has attracted much attention from academic and industrial community. However, the development of FTS mainly depends on experience, resulting in the inefficient development of catalysts and industrialization design. Recently, a new analysis method, mesoscale analysis, has attracted more attention due to researching on between different scales or crossing several scales, which would contribute to efficient R D process of FTS. This chapter will summarize the multiscale effects on FTS products distribution such as ASF distribution, kinetic model. 

Ma W, Li Y, Zhao Y, Xu Y, Zhou J Kinetics of Fischer-Tropsch synthesis over Fe-Cu-K catalyst-kinetic model on the basis of mechanism (1), J Chem Ind Eng (China) 50(2) 159-166, 1999a. 

On the basis of the assumptions of model <22> and <23> the Fischer-Tropsch synthesis in a slurry phase BCR has been modeled [37, 38]. As this hydrocarbon synthesis from synthesis gas (CO + H2) is accompanied by considerable volume contraction, it is clear that gas flow variations have to be accounted for. The developed models are useful to evaluate experimental data from bench scale units and to simulate the behavior of larger scale Fischer-Tropsch slurry reactors. Though only simplified kinetic laws were applied, the predictions of the model are in reasonable agreement with data reported from 1.5 m diameter demonstration plant. Fig. 12 shows computed space-time-yields (STY) as a function of the inlet gas velocity. As the Fischer-Tropsch reaction on suspended catalyst takes place in the slow reaction regime, it is understood that STY passes through a maximum in dependence of uqo- The predicted maximum is in striking agreement with experimental observations [37]. 

---