Title: "Conversion of light cycle oil to benzene and alkylated mono-aromatics over various monometallic and bimetallic oxide catalysts in the presence of hydrogen donor".
Date and Time: January 31st, 2025 (Friday) at 11:30 AM
Venue: Chemical Engineering Department Seminar Room
The meeting link (MS Teams) is given below:
Abstract:
Abstract The per capita consumption of polymers is projected to increase, while the demand for conventional fuels like gasoline and diesel is expected to decrease. This shift has prompted a focus on converting crude to chemicals. Light cycle oil (LCO), with high amounts of sulfur and aromatics, has a low cetane number, making it unsuitable for diesel blends. Converting LCO to benzene, toluene, and xylene (BTX) can meet the rising chemical demand and utilize low-quality LCO feedstock. However, LCO conversion under FCC conditions is typically low, necessitating modifications to catalysts and processes for higher BTX yields. Even though various studies have been performed on bifunctional monometallic and bimetallic oxide catalysts at high pressure, their application at atmospheric pressure has not yet been studied. In this study, the selective conversion of diaromatics and triaromatics in LCO into monoaromatics using bifunctional catalysts is studied under FCC conditions. The hydrogen donor source utilized was n-hexadecane (n-HD) at atmospheric pressure instead of H2. Thermodynamic analysis and cracking experiments indicate that the optimal temperature for maximizing BTX yield is 550 °C. n-HD is found to be an effective hydrogen donor when co-fed with LCO, resulting in enhanced BTX yield and reduced coke formation, with a 30 wt. % concentration shown to optimize feed conversion. 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 pore volume, pore diameter, crystallite size, 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 bond angle analysis. Both monometallic (Ni, W, Co, Mo) and bimetallic (NiW, CoMo) oxide catalysts supported on various zeolites (Mordenite, ZSM-5, Beta, Y, and Mix) were investigated. Bimetallic oxide catalysts exhibited superior performance, displaying higher total monoaromatic hydrocarbon (MAH) yield, BTX yield, and feed conversion compared to monometallic oxide catalysts. This improvement was attributed to the formation of bimetallic oxide species along with their strong interactions with the support, as evidenced by XPS, H2-TPR, and UV-DRS analyses. Bimetallic oxide catalysts also demonstrated higher moderate acidity, an optimal balance of Brønsted and Lewis acid sites, and a higher hydrogen transfer index, explaining their higher BTX yield and lower coke formation. Experiments with n-HD as the sole reactant indicated that LCO primarily contributed to MAH formation, with n-HD serving as the hydrogen source. DFT simulations aligned with experimental findings, showing that bimetallic oxide catalyst had the lowest activation barrier for 1MN cracking in the presence of n-HD. The selective cracking of triaromatic compounds to diaromatics was rapid, with the conversion of diaromatics governing total MAH yield and the cracking of monoaromatic-2-ring compounds governing BTX production. An inverse correlation between the selectivity for 2-ring monoaromatics and BTX shows the formation of 2- ring monoaromatics as intermediates. Based on detailed product characterization, reaction pathways for the conversion of diaromatic and triaromatic are proposed. Additionally, a Co/Mo ratio above 0.5 leads to the formation of a dense CoMoO₄ phase, adversely affecting catalytic activity, while the optimal Co/Mo ratio of 0.5 maximizes BTX yields and minimizes coke production. Similar reactivity among alkylated naphthalene compounds suggested grouping them in developing a lumped kinetic model. A 12-lump kinetic model was developed based on the experimental data to elucidate the kinetic characteristics of LCO cracking on the CoMo/Beta catalyst, serving as a foundational tool for optimizing catalytic processes in refinery operations.