Pressurized hydrogasification and cobalt-catalyzed hydrogasification behaviors of naphthalene as a coal-based model compound

Abstract

The pressurized hydrogasification/catalytic hydrogasification behaviors of naphthalene as a coal-based model compound were investigated for the first time in a batch reactor. The composition of products was roundly analyzed by gas chromatography (GC), gas chromatography–mass spectrometer (GC-MS) and laser desorption time-of-flight mass spectrometry (TOF-MS). Based on the product analysis results, the detailed reaction pathways for naphthalene hydrogasification and the effects of cobalt on reaction pathways were elucidated. Naphthalene first destabilized during hydrogasification. Subsequently, the destabilized naphthalene either underwent stepwise hydrocracking by active hydrogen atoms to ultimately produce benzene and methane, or formed naphthalene free radicals to initiate condensation. Cobalt can regulate products distribution to boost methane, benzene and toluene yield by facilitating active hydrogen generation, despite it had a limited ability to facilitate the naphthalene destabilization at temperature below 700 °C. Whereas above 750 °C, cobalt can promote naphthalene destabilization, thereby remarkably enhancing the conversion of naphthalene. Furthermore, cobalt intensified condensation leading to a shift of molecular mass distribution of condensation products from 252 ∼ 500 Da to 750 ∼ 2000 Da. These phenomena supported similar findings in coal catalytic hydrogasification. The rise in temperature, initial H2 pressure (P0), and cobalt content all facilitated the cobalt catalyzed naphthalene hydrocracking to gaseous product, with temperature exerting a particularly significant effect. This trend was similar with cobalt catalyzed coal hydrogasification. For example, when temperature increased from 650 ℃ to 750 ℃, naphthalene conversion improved from 21.2 % to 49.6 %, and gas yield rose from 2.6 % to 29.4 % at 1 % Co and 1.3 MPa P₀. The investigation serves to shed light on the molecular-level understanding of the mechanism underpinning coal hydrogasification.