Effect of the experimental conditions on BTX formation from hydrotreated light cycle oil

Abstract

The study of a light cycle oil (LCO) upgrading alternative involving hydrotreating and hydrocracking/transalkylation procedures for obtaining a benzene, toluene and xylene (BTX) enriched fraction is presented. The research work was focused on the effect of the experimental conditions on the hydrocracking of an hydrotreated light cycle oil (HDT LCO) in order to produce the highest amounts of BTX, when the catalysts consisted of a mixture (50/50 in weight) of nickel-molybdenum on alumina (NiMo/Al 2 O 3) and ZSM-5 materials (NiMo/ZSM-5 (50)). It was found that 7.4 MPa, up to 375 °C, LHSV of 1.2 h −1 and a H 2 /Oil value of 442 m 3 /m 3 were the optimal experimental conditions for producing an enriched BTX fraction (31%). In order to facilitate the analysis, the study was carried out considering four types of hydrocarbons as lumps for the feed and HCK products: light hydrocarbons (LHC) composed by C4-C7 non-aromatic compounds, BTX, middle hydrocarbons (MHC) consisting of C7-C10 paraffins and isoparaffins, alkylbenzenes, tetralin and naphthalene derivatives and a small amount of high molecular weight hydrocarbons (HHC). Based on this description, HDT LCO used as feedstock for the hydrocracking (HCK) procedure, presents a 99% of a MHC fraction. The HCK conversion, BTX selectivity and yields were obtained from the chromatographic analysis of the products. A simple kinetic model considering only the MHC conversion was carried out. The obtained activation energy confirmed the endothermic nature of the HCK process. The activity decay of the catalytic mixture was also studied by varying the time on stream.

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

“…Tetralin: 1 mol of tetralin (132.2 g) will produce according to previous experiments [3,4] approximately 0.1, 0.4, 0.18. 0.09 and 0.08 mol of benzene, toluene, p-, m-and o-xylenes, respectively.…”

“…The protonic forms of USY-1 and USY-3 were produced by calcination (500 °C, 3 h). USY-2 and USY-4 were prepared by NH 4 + exchange from a commercial NaY sample, followed by washing until the absence of chlorine, drying at 100 °C overnight, and steamed at 600 and 700 °C for 3 and 5 h, respectively. Finally, the sample USY-4 was further steamed at 760 °C for 8 h. Ammonium exchange treatments were carried out with a 2.5 N aqueous solution of NH 4 Cl at 80 °C for 2 h under agitation.…”

“…However, the major challenge is to convert a real feed like LCO into valuable benzene, toluene, and xylene hydrocarbons, mainly due to the presence of another type of compounds like sulfur, nitrogen, and heavy aromatic hydrocarbons which are going to test the hydrocracking process. Therefore, usually, the real feed requires to be hydrotreated (HDT) before the next HCK step is going to be taken [2,4].…”

“…The production of benzene, toluene, and xylene (BTX) from light cycle oil (LCO) has been our matter of interest in the last years [1][2][3][4]. LCO, a middle distillate from FCC (fluid catalytic cracking), has lost market as a part of the diesel feedstock due to its inherent low quality (high sulfur, nitrogen, and aromatic contents) [5][6][7], which makes the resulting fuel difficult to comply with the stringent worldwide environmental regulations [8,9].…”

“…Among the alternatives for LCO upgrading, the production of BTX after successive hydrotreating (HDT) and hydrocracking (HCK) procedures (Fig. 1) [1,2,10] has been studied either using model mixtures [1,3] or in a lesser extent using real feeds [2,4]. Additionally, it is well known [1,2,10] that catalysts play a key role in the hydrogenation (partial saturation) of naphthalene followed by the selective cracking of naphthenic structures, producing one-ring-aromatic hydrocarbons with alkyl chains.…”