Hydrocracking of hydrotreated light cycle oil for optimizing BTEX production: a simple kinetic model

Abstract

The effect of the experimental conditions on the hydrocracking (HCK) of a hydrotreated light cycle oil (HDT LCO) was studied in this work. The catalyst tested was a 50/50 weight mixture of nickel-molybdenum-phosphorous on alumina (NiMo/Al2O3) and a commercial ZSM5 zeolite (HCK 50/50). The experimental conditions tested were 340, 350, 360, and 370 °C; 7.5 MPa; 0.9, 1.2, 1.5, and 1.8 h−1 LHSV, and H2/HC of 752 m3/m3. Two phases: gas and liquid, were obtained as HDK products. The gas phase consisted mostly of C1–C5 paraffins, iso-paraffins, and olefins. The liquid phase was characterized by GC-PIONA and was distributed in lumps as follows: NAPA by C11 to C13-naphthalenes; TET by C11 to C13-tetralins; IND by C9 to C13-indanes and indenes; AKB by C9 to C13-alkylbenzenes; BTEX by benzene, toluene, ethylbenzene, and xylenes; NAPE by C9 to C13-naphthenes; and PIP by C3 to C14 paraffin, iso-paraffin, and olefin type hydrocarbons. Using this classification, the results showed that increments in temperature and decrements in LHSV produced increments in the formation of gases, PIP, BTEX, and NAPE. At the same conditions, AKB, TET, NAPA, and IND decreased sharply. TET and NAPA derivatives were no longer present at high temperatures (360–370 °C). It seemed to be a limit of the BTEX formation directly related to the TET and IND presence, and it did not seem to depend on the transalkylation process of AKB hydrocarbons. Instead, AKB hydrocarbons were directly correlated to NAPE hydrocarbon formation by hydrogenation. A kinetic model was prepared. The model presented correlation coefficients higher than 98 %. The kinetic model that was made predicted that neither increasing the temperature nor lowering the LHSV would improve the BTEX formation when departing from this feedstock.