Effect of temperature, hydrogen donor, and zeolites on light cycle oil cracking: Thermodynamic, experimental, and DFT analyses

Abstract

This study investigates the thermal and catalytic cracking of light cycle oil (LCO) and its model compounds at ambient pressure, focusing on the effect of temperature, hydrogen donors, and the choice of zeolites on the yield of benzene, toluene, and xylene (BTX). Both thermodynamic analysis and cracking experiments show that the optimal temperature for maximizing the BTX yield is 550 °C. n-hexadecane (n-HD) is found to be an effective hydrogen donor when co-fed with LCO, resulting in enhanced BTX yield and reduced coke formation. Catalytic cracking experiments highlight Beta zeolite's superior activity compared to other zeolites (Y, ZSM-5, and Mordenite), and the trends are correlated to the acidity and structural characteristics such as crystallite size, pore volume, pore diameter, and surface area. Additionally, DFT calculations show that amongst various zeolites, Beta zeolite exhibits the lowest activation barrier for 1-methylnaphthalene cracking. The distinct reactivity levels of triaromatic, diaromatic, and condensed polyaromatic compounds are highlighted, with triaromatic compounds exhibiting the highest reactivity. These results are explained by the degree of unsaturation, and further complemented by DFT-calculated energy required for the saturation of one ring of aromatics and C-C bond angle in the partially saturated product.