Investigation of the evolution of sulphur during the thermal degradation of different oil shales

This paper presents the results of the pyrolytic decomposition of six different oil shale samples with different sulphur contents from Estonia, USA and China using non-isothermal thermogravimetry coupled with a mass spectrometer (TGA-MS). Mass spectrometry (MS) was used to analyse the evaporating gases. The results showed a major difference in the evolution of sulphur containing substances. The sulphur behaviour was found to be in excellent correlation with the composition of the sample. H2S and SO2, the problematic components forming during the pyrolysis process, both exhibited evaporation in two peaks. The kinetic distribution supported the findings of MS - samples with a higher sulphur content exhibited more parallel reactions that had similar weight percentages. SO2 evolution intensifies above 500 degrees C. H2S is released in the temperature range of 350-500 degrees C, depending on the sample. The samples Kentucky, Green River, Estonia and Chinese 2 also have an additional peak at 500-570 degrees C. This is in good accordance with the aforementioned samples having a relatively high amount of sulphur in the forms of organics and sulphides. Based on the results, an important conclusion is that changing the pyrolysis temperature can reduce the sulphur content of the oil produced. The experimental curves obtained were used to calculate the kinetic parameters using a distributed activation energy model. The obtained activation energy values were in the range of 134-276 kJ/mol with the frequency factors ranging from 1.89E10(12) to 1.20E10(14) s(-1). In order to validate the obtained kinetic parameters, the decomposition curves were compared to modelled ones. The dependence of total conversion on reaction time was calculated at isothermal conditions to show the effect of pyrolysis temperature.