Effect of the catalyst in the BTX production by hydrocracking of light cycle oil

Abstract

Catalysts to produce the important petrochemicals like benzene, toluene, and xylene (BTX) from refinery feedstocks, like light cycle oil (LCO) are reviewed here by covering published papers using model mixtures and real feeds. Model compounds experiments like tetralin and naphthalene derivatives provided a 53–55% total BTX yield. Higher yields were never attained due to the inevitable gas formation and other C9+-alkylbenzenes formed. For tetralin, the best catalysts are those conformed by Ni, CoMo, NiMo, or NiSn over zeolite H-Beta. For naphthalene derivatives, the best catalysts were those conformed by W and NiW over zeolite H-Beta silylated. Real feeds produced a total BTX yield of up to 35% at the best experimental conditions. Higher yields were never reached due to the presence of other types of hydrocarbons in the feed which can compete for the catalytic sites. The best catalysts were those conformed by Mo, CoMo, or NiMo over zeolite H-Beta. Some improvements were obtained by adding ZSM-5 to the support or in mixtures with other catalysts.

Effect of the chemical composition of six hydrotreated light cycle oils for benzene, toluene, ethylbenzene, and xylene production by a hydrocracking process

“…The BTEX formation values ranged from 25.2 to 29.2 wt.%. An unexpected result contrary to the assumptions made in previous reports [4,13,14] that the higher the amounts of monoaromatic compounds, the higher the BTEX formation was obtained. It is noteworthy to mention from Figs.…”

“…The presence of the metallic function (NiMo) in adequate amounts is necessary to reduce the catalyst deactivation by coke formation [3,4]. Nevertheless, as a study carried out before by Laredo et al [13], when departing from real feedstocks like the HDT LCO, a total BTX yield higher than 35% was never attained by using a HCK catalyst of any type. In real feedstocks, this can be due to the presence of another type of competing hydrocarbons [7], the inevitable gas formation and the formation of other C 9+ -AlkylBzs.…”

“…2). Bi-functional catalysts containing acidic supports and hydro/dehydrogenating metals are often used [1,2,[11][12][13]. The group VI and VIII metal sulfide hydrocracking catalysts generally perform well the required hydro-dehydrogenation function [11].…”

“…On the other hand, low catalytic acidity resulted in high hydrogenation activity (high hydrogenation reaction rates) with minimal selective-hydrogenation activity, which means that the consecutive hydrogenation of the first and second aromatic rings, i.e., from naphthalene to tetrahydronaphthalene (tetralin), and finally to decahydronaphthalene (decalin) type compounds, can occur without giving place to the hydrocracking of intermediate mono-aromatic (tetralin) type hydrocarbons for BTEX production. Therefore, moderate acidity showed the best balance between hydrogenation and cracking activity to achieve the highest BTX yields [13]. Another important point was the metal types on the catalysts.…”

“…In a recent review, Laredo et al [13] studied the effect of the catalyst and experimental conditions on the total BTX yields when departing from model molecules, like tetralin and naphthalene derivatives, and from real feedstocks. It was observed that BTX yields higher than 53-55% of the total were never achieved by the hydrocracking of tetralin and naphthalene derivatives, neither by changing the catalyst nor the experimental conditions.…”