Effects of Hydrothermal Treatment on the Properties of Jordanian Oil Shale

Oil shale is an important unconventional energy resource, and enhancing its thermal conversion processes can significantly improve the oil yield and quality. However, the complex structure and high sulfur content of marine-origin oil shales, such as Jordanian El-Lajjun oil shale, pose challenges to efficient conversion. This study aims to investigate the influence of hydrothermal treatment (HT) on the structure and thermal behavior of El-Lajjun oil shale to optimize oil production and improve product quality. HT was conducted at different temperatures (150, 200, and 250 °C), and the resulting structural changes were analyzed by using elemental analysis, Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Subsequently, pyrolysis experiments at 520 °C using an alumina bed reactor were performed, and the oils generated from raw and HT samples were characterized by FTIR, 1H NMR, and gas chromatography-mass spectrometry. The results showed that HT led to an increase in the carbon content and a reduction in the sulfur content. TGA results indicated a greater weight loss during the combustion of volatile matter for treated samples, highlighting notable changes in chemical structure. Pyrolysis of HT samples produced higher oil yields with improved quality, demonstrated by increased hydrocarbon content, reduced heteroatom and oxygenated compounds (such as esters and phenols), and an enhanced aromatic yield. Notably, HT at 150 °C was particularly effective in maximizing the oil yield and improving quality. These findings suggest that carefully controlled HT conditions can significantly benefit the thermal conversion of marine high-sulfur oil shales.