Study of Thermooxidation of Oil Shale Samples and Basics of Processes for Utilization of Oil Shale Ashes

A circular economy becomes an object of actual discussions as a real alternative to the existing linear economy system. The problem is actually in Estonia also, first of all in the sector of heat and power production which based mainly on the combustion of local solid fossil fuel—Estonian oil shale (OS) resulting in the formation of ~5–6 million tons of OS ashes annually. The thermooxidative decomposition of OS samples from different deposits and estimation of the possibilities of utilization of OS ashes formed at both—pulverized firing (PF) and circulating fluidized bed combustion (CFBC) of Estonian OS were studied. The thermal analysis combined with evolved gas analysis (EGA) methods like Fourier transform infrared (FTIR) and mass-spectroscopy (MS) was exploited. It was established that the differences in the thermal behaviour of different OS samples are caused by the differences in the chemical matrix of organic matter, chemical and mineralogical composition of the inorganic part of OS, and morphology of samples. It was also found that moderate grinding of OS ashes with simultaneous moderate water treatment notably improved the SO2 binding efficiency of cyclone ash, and that the strength and leachability characteristics of granulated OS ashes strongly depend on the post-granulation treatment conditions allowing to increase the soil neutralizing ability of the granulated products. This overview was based on our investigations carried out during the last fifteen years.

Thermal and Kinetic Characteristics of some Oil Shale Samples

The thermal behaviour of different oil shale samples (Estonia, Jordan, Israel, Morocco) were studied using a Setaram Setsys 1750 thermoanalyzers coupled to a Nicolet 380 FTIR Spectrometer. The experiments were carried out under non-isothermal heating conditions up to 1000 °C at different heating rates in an oxidizing atmosphere. A model-free kinetic analysis approach based on the differential isoconversional method of Friedman was used to calculate the kinetic parameters. The thermooxidative decomposition of oil shale samples proceeded in three steps. Firstly, thermooxidation of volatile organic compounds occurred – depending on the heating rate, up to 460 °C. Secondly, thermooxidation of heavier part of organic matter (kerogen) and fixed carbon as well as thermooxidation of pyrite proceeded up to 580 °C. Finally, carbonates contained in oil shale samples decomposed up to 870 °C. The combined TG-FTIR study of thermooxidative decomposition of samples made it possible to identify in addition to CO2 and H2O as major gases evolved a number of gaseous species like CO, SO2, COS, methane, ethylene, etc. formed and evolved at that. The value of activation energy E in the low-temperature oxidation region was for Estonian and Jordanian oil shale samples lower than that in the high-temperature region which was contrary for Israeli and Moroccan oil shale samples. Therefore, the results obtained indicated the complex multi-step character of the thermooxidative decomposition of the oil shale samples studied.

Thermally stable oligomer—Metal complexes based on oligo-ortho-aminophenol and oligophenylazomethinephenol

The oligo-ortho-aminophenol was synthesized by the oxidative polycondensation of ortho-aminophenol with air oxygen. The oligophenylazomethinephenol was synthesized by the condensation of aniline with oligosalicylaldehyde. Metal complexes of these oligomers with Cu(II), Co(II), Zn(II), and Ni(II) were synthesized and characterized. Based on the results of thermogravimetric analysis, synthesized oligomer—metal complexes were more stable against heat and thermooxidative decomposition than some polymeric Schiff bases and polymer—metal complexes. Additionally, the presence of metal ions increased the thermal stability of oligo-ortho-aminophenol, while the thermal stability of oligophenylazomethinephenol was lowered.