Conversion of light cycle oil to benzene and alkylated monoaromatics over monometallic and bimetallic CoMo catalysts in the presence of hydrogen donor

Abstract

The conversion of diaromatics and triaromatics present in light cycle oil (LCO) to monoaromatics such as benzene, toluene, and xylene (BTX) is studied under fluid catalytic cracking conditions over zeolite-based monometallic (Co, Mo) and bimetallic (CoMo) bifunctional catalysts. Instead of H2, n-hexadecane (n-HD) is used as the hydrogen donor source at atmospheric pressure, which results in a high yield of the desired products and low coke formation. Additionally, n-HD undergoes cyclization, dehydroaromatization, and cracking as well. The total monoaromatics and BTX yield for various feed compositions follows the order: CoMo/Beta > CoMo/Y > Mo/Beta > Co/Beta > Mo/Y > Co/Y > Beta > Y, with CoMo/Beta resulting in 1-Methylnaphthalene conversion and monoaromatics yield of 84.3 % and 43.9 %, respectively. The monoaromatics and BTX yield over various catalysts is correlated to the coke formation, which is the least over bimetallic catalysts. The presence of rod-type CoMoO4 particles is detected on the bimetallic catalysts, and is supported by XRD, H2-TPR, and Raman analysis. For various feeds and catalysts, the cracking of triaromatics is fast, and the yield of monoaromatics is primarily dependent on the catalytic activity towards the cracking of diaromatics. An inverse correlation between the selectivity for 2-ring monoaromatics and BTX shows the formation of 2-ring monoaromatics as intermediates. Various diaromatic compounds with similar reactivity are identified, which could be used for the development of a lumped kinetic model. Based on a detailed product characterization, reaction pathways for the conversion of 1-Methylnapthalene and anthracene are proposed.