Determination of liquefaction mechanisms of Zonguldak, Soma and Beypazarı coals Effectiveness of reversible reaction steps on coal liquefaction mechanisms Investigation of the compatibility of the proposed mechanisms with experimental data using Kalman filter Figure A. Comperison of kinetic Model-4 with experimental data for coals; Zonguldak, Soma and Beypazarı Theory and Methods: Four different liquefaction mechanisms having reversible and irreversible reaction steps have been suggested for the liquefaction of Zonguldak, Soma, and Beypazarı coals in tetralin having a ratio of 8/1 Tetralin(S)/Coal(C) using microwave power. Compliance of the proposed mechanisms have been determined by forming first order linear discrete time models with the experimental data and reaction rate constant have been calculated with a program written in MATLAB with the use of Kalman filter. Purpose: The aim of this study is to identify the liquefaction mechanism of Zonguldak, Soma, and Beypazarı coal using discrete time models. Results: The Model-1 involving the subsequent formation of preasphaltene, asphaltene, and oil from a reactive fraction of the parent coal in reversible steps has not fitted with experimental data and this discrepancy is more prevalent in oils and preasphaltenes. On the contrary of the first model, Model-2 and Model-3 suggesting the formation of preasphaltenes, asphaltenes and oils from directly reactive coals in a group of parallel reactions have a better fitting with experimental data. Model-4 demonstrating reversible liquefaction steps shows the best fit between the experimental data and the model. Moreover, the increase in the production of oils reveals that the oils have continued to produce from coal. The presence of reversible reactions in the liquefaction mechanism can result from the solvent not being able to transfer enough hydrogen to the free radicals. The increase in the yield of the oils during the liquefaction process can be explained by the stabilisation of free radicals by hydrogen shuttling from hydrogen rich hydrocarbons, which are found in coal liquefaction, instead of hydrogen donor solvent. Conclusion: In nutshell, the best fit for these coals was obtained with the model having both reversible; coal ↔ preasphaltene, coal ↔ oil, preasphaltene ↔ oil, and irreversible; coal → asphaltene, asphaltene → preasphaltene, oil → asphaltene reaction steps. Additionally, the reaction rate constants from coal to oils are at least twice time higher than that from coal to asphaltene and from coal to preasphaltene for Zonguldak, Soma, and Beypazarı coals. As a result, it has been determined that not only the irreversible reaction steps but also the reversible reaction steps are important in coal liquefaction studies.