A comprehensive study of kinetics mechanism of Fischer-Tropsch synthesis over cobalt-based catalyst

- Comprehensive kinetics of FTS over supported cobalt catalyst was investigated.
- Limitation of power-law rate model as compared to LHHW rate theory were highlighted.
- 8 and 7 series of elementary reaction step for FT and WGS reaction were developed.
- The model was calibrated and validated against experimental results satisfactorily.
- Most accurate model was combined alkyl/alkenyl (FT) with formate (WGS) mechanism.

A comprehensive kinetics study of Fischer-Tropsch (FT) synthesis mechanism was investigated over an in-house 37% Co-based catalyst on a SiO2 support. A series of combined FT and water gas shift (WGS) reaction mechanisms were developed in order to calibrate the model at twelve different operating conditions. Two different approaches were used to develop a model for the FT synthesis reaction network. The first was based on an empirical approach; whereas the second approach explained the novel mechanistic details of FT kinetics. In the former, the rate equations were derived by power-law rate expressions, while in the latter the rate equations were derived by the Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate theory. The limitations of power-law rate model were highlighted for the applications that wider range of operating conditions has to be selected. In contrast the advantages of LHHW for predicting a wider range of operating conditions were underlined. A comprehensive plausible mechanism-derived FT kinetics models with eight elementary reaction pathways along with seven WGS kinetics models were developed. Such reaction networks were investigated to fit and validate against the newly obtained experimental results which can be used as a key tool to emphasise the most significant facts of FT synthesis catalysis and chemistry. Model validation was carried out subsequent to completion of the model calibration and the estimation of proper kinetic parameters. The overall purpose of the validation study was to ensure that the model provides a robust and realistic assessment of all the parameters. In order to ensure model is precise to an appropriate level, the model was assessed against experimental data at four different operating conditions. The results obtained from kinetic study were compared to the most recent findings that have been reported in literature. It was shown that the novel developed kinetic model based on a combination of alkyl/alkenyl mechanism for FT reactions (for production of n-paraffins and α-olefins) along with formate mechanism for WGS reaction can provide the most accurate predictions.