There are two types of oil shale in Estonia - Kukersite, from which oil shale has been produced since 1924, and graptolite argillite (GA), which has not been used for industrial applications so far. As is known, oil can be obtained from oil shale by using thermochemical destruction methods at the temperature of 350-5000C resulting in disproportion of the organic matter (kerogen) of oil shales into oil, gas and solid residue. Yield and quality of the products obtained depend on the processing method and chemical composition of the initial oil shale.

Until now the only industrial technology used for producing shale oil in Estonia and in other countries has been semi-coking. However, semi-coking of GA is not prospective because of extremely low yield of oil compared with Kukersite (1-2% and 23% respectively). The goal of the defended doctoral thesis was working out physical-chemical and technological fundamentals for more efficient liquefaction of GA.

According to the supervisor of the doctoral thesis, Head of the TUT Laboratory of Oil Shale and Renewables Research, Senior Research Scientist Hans Luik, the GA complex study carried out for the first time indicates that thermochemical dissolution and hydrogenation increase oil yield several times at significantly lower temperatures than in Fischer assay pyrolysis.

"Investigation of the qualitative and quantitative compositions of oils by using modern methods proved that oils formed as a result of pyrolysis, thermal dissolution and hydrogenation of GA are similar to Kukersite semi-coking oil in terms of the group composition of the chemical compounds, but the individual composition of groups and their proportions differ significantly, " Luik added.

The only countries in the world that have oil shale industry are Estonia, China, and Brazil. It was found in the doctoral thesis that semi-coking in various retorts used for liquefaction of Estonian Kukersite, Chinese and Brazilian oil shales or planned to be used for oil shale in the USA and Jordan cannot be considered a universal oil shale liquefaction technology applicable to all types of oil shales in their multitude and variety. It is essential to introduce alternative technologies for efficient liquefaction of GA, as well as other oil shales on planet Earth poor in kerogen and hydrogen content.

The supervisor of the doctoral thesis was Head of the TUT Laboratory of Oil Shale and Renewables Research, Senior Research Scientist Hans Luik.

The opponents were Cristian Torri (University of Bologna, Italy) and Aare Ignat (Estonian Research Council).

The doctoral thesis has been published in the digital collection of TUT library at http://digi.lib.ttu.ee/i/?4862