Modeling of the Fischer-Tropsch Synthesis in a fixed bed reactor using a new kinetic model based on the Langmuir-Freundlich isotherm

A Gas to Liquid (GTL) process, which consists of the three stages, converts natural gas to wax and useful hydrocarbons such as benzene and gas oil. In the second stage of a GTL process, the syngas via cobalt or iron catalyst is converted to wax that this step is referred to the Fischer-TropschSynthesis (FTS). Using a slurry or fixed bed reactor, in FTS a durable catalyst should be designed to maximize the CO conversion and produce a suitable distribution of hydrocarbons. In this work, a detailed kinetic model for the FTS over a cobalt catalyst is developed. The commonly usedkinetic model of FTS such as Langmuir-Hinshelwood was developed on the basis of Langmuir isotherm. Since the Langmuir-Freundlich isotherm can predict the adsorption of gases on solid adsorbent more accurate than Langmuir isotherm, we employed this isotherm to develop the newLangmuir-Freundlich-Hinshelwood (LFH) kinetic model. As a result, using the new kinetic model the percent of Average Absolute Deviation is reduced for correlation of the experimental COconversion data in a fixed bed reactor. In order to evaluate our new kinetic model, we use the experimental data of Y. W. Li et al. that was relevant to the industrial operational conditions [temperature, 540-600 K; pressure, 1.0-3.0 MPa; H2/CO feed ratio, 1.0-3.0]. The results show a very good agreement with the available experimental data. To have a good accession of the new model, we compare the present results with those are obtained using common Langmuir- Hinshelwood isotherm as well and evaluated the strength of the two models in prediction of theCO conversion for the FTS at a fixed bed reactor. The results of the new kinetic model show theaverage absolute deviation percentage (AAD %) of 5.59% for the CO conversion while this value is about 18.1% using the original equation based on Langmuir isotherm.

کلیدواژه ها:

Fischer Tropsch Synthesis ، New kinetic model ، Langmuir-Freundlich isotherm ، Fixed bed reactor