Evaluation of the reaction order and kinetic modeling of Domanic oil shale upgrading at supercritical water conditions

Two different kinetic models were developed for the kinetic study of Domanic oil shale conversion in the supercritical water. The oil shale reaction order was evaluated with a three-lump reaction scheme taking into account oil shale, gases, and synthetic oil. Contrary to the commonly reported first-order, it was found that a higher order (2.5) is more suitable for the conversion of oil shale at supercritical water conditions. The main reaction mechanism and predictions were obtained using a more detailed reaction network (five-lump model), which precisely estimates the experimental yield of all compounds contemplated. The statistical analysis suggested that the estimated kinetic parameters were suitably optimized, as well as the sensitivity analysis confirmed that these are the optimal values. The conversion of organic matter into gas and coke through free radical reactions exhibits larger rates using supercritical water. Low temperature (380 °C) and short reaction times favor the yield of synthetic oil because when these conditions are exceeded secondary cracking reactions provoke the generation of gases. Gas production is mainly carried out by the conversion of organic matter for brief reaction times and the transformation of carbonates for extended periods.