Until now, the oil shale kukersite has been used mainly for energy and oil production. To broaden the possible applications of oil shales, the wet air oxidation of kukersite (an organic-rich sedimentary rock from Estonia) was studied. Kukersite was oxidized with an oxygen-rich gas in water at temperatures up to 200 °C and pressures up to 60 bar. The efficiency of this batch process was evaluated from organic matter conversion, from the amount of solubilized organics obtained, and from the rate of dicarboxylic acid (DCA) formation. The effect of several reaction parameters—pressure, temperature, time, acid/base additives, substrate concentration, the origin of a substrate and its organic matter content, and so forth—was measured. A conversion of 91% in total organic carbon was achieved at 175 °C with 40 bar of the 1:1 oxygen/nitrogen mixture in 3 h without the presence of any additives. Under basic conditions, high yields (up to 50%) of dissolved organic matter were obtained with 8% of DCA; the best results are obtained with K 2 CO 3 and KOH. The highest DCA outcome (12%) within the 3 h reaction time was obtained in the presence of acetic acid. It was found that temperatures higher than 185 °C, pressures over 30 bar of pO 2 , and long reaction times in the acidic media caused a considerable decrease in the DCA outcome. It was also found that the same process can be applied to shales of different origins, although with lower DCA yields.

The reactivity of the aliphatic dicarboxylic acids (DCAs) mixtures in conditions similar to industrial wet air oxidation (WAO) process conditions has been investigated. DCAs have potential to be separated during WAO of highly polymerized organic matter (e.g., organic waste, biomass, kerogen in oil shale) before transforming to final oxidation products (CO 2 and water). However, a shortage of information about the DCAs stability in such processes restricts this application. The influence of oxygen pressure, temperature, pH, various metal salts, and radical generating organic compounds on DCAs possible transformation was established. High stability of DCAs (C4−C10) was shown at 175 °C with 40 bar of oxygen mixture in wide pH range. The increase in the DCA decomposition with the formation of lower chain DCAs was found to be inevitable in the presence of alkali and homogeneous iron or copper salts in nonbuffered solutions. The relationship between organic co-oxidants, such as malonic acid and resorcinols, and the stability of DCAs was studied. Of them, 5-methylresorcinol was the most efficacious in increasing oxidation of DCAs, and retention values of less than 10% were observed.

Society's growing demands on everyday products and materials are increasingly difficult to meet in an environment that seeks to avoid petroleumbased processes. Instead of abandoning fossil materials altogether, more research should be done on their efficient and clean conversion. One option for this is the oxidative dissolution of kerogen in water under conditions that satisfy the subcritical range (T = 150-200 °C, pO 2 = 0.5-4 MPa). The resulting mixture contains a substantial amount of various aliphatic carboxylic and dicarboxylic acids. Both batch and semi-continuous processes were set up to find the main factors and optimal conditions for the kerogen dissolution process. The rate of transformation of organic carbon to dissolved organic compounds was mainly influenced by elevated temperature and oxygen partial pressure. To obtain high yields of organic carbon dissolution and to avoid the formation of excess CO 2 , the oxidation of kerogen should be carried out fast (< 1 h) and under high oxygen pressure. By employing a temperature of 175 °C and O 2 pressure of 2 MPa, over 65% of the initial organic carbon dissolves in about one hour. Prolonged reaction times or harsher oxidation conditions resulted in a rapid degradation of dissolved matter and also of the valuable products formed. The organic matter content of the initial oil shale had a direct effect on the further degradation of dicarboxylic acid and consequently on the overall yield. The suitability of using a trickle-bed reactor for kerogen dissolution is discussed in detail on the basis of experimental results.

Oxidation has been a long sought-after alternative to classical thermal processing of oil shale, in order to obtain valuable raw materials for the chemical industry. A number of different methods have been applied, but thus far, one of the most effective ways to transform oil shale to value added products, such as aliphatic terminal dicarboxylic acids, is oxidation with nitric acid. In order to obtain insight into the reactivity of oil shale in nitric acid, a study focusing on the kinetics and behavior of oil shale particles during oxidative leaching was performed. To that end, the particle size distribution, surface area, and carbon content were measured during the leaching process in addition to the amount of total residual solids. Determining the carbon content of the solid residue was proposed as a simple measure of the reaction progress, based on the hypothesis that all carbon measured by elemental analysis correspond to organic carbon since inorganic carbon is present as carbonate in the starting material and would have dissolved under the acidic conditions. To our surprise, the solid residue had a significant amount of organic carbon in the form of calcium oxalate mineral. Thus, measuring carbon content in the solid residue could provide only an indirect measure of the overall oxidation degree provided that the amount of oxalates was known. In general, the results revealed that the total solid residue amounts to between 20% and 34% of the initial values after 24 h of the reaction, while the total carbon content ranges from 4% to 14% of the starting values. These results show that we were able to extract around 90% of the organic carbon present in the solid phase.