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/Al2O3) 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 H2/Oil value of 442 m3/m3 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.
Highlights
The continuation of the work regarding the production of benzene, toluene and xylene (BTX) from light cycle oil (LCO) is presented in these papers [1,2,3]
When a catalyst or a process is almost ready for scaling up or commercial applications, experiments with real feedstocks are mandatory [2, 9]. It is well known [1,2,3, 10] that catalysts play a key role in the hydrogenation of naphthalene followed by the selective cracking of naphthenic structures, producing one-ring-aromatic hydrocarbons with alkyl chains
The main objectives of this work are as follows: (1) to find the optimal experimental conditions for a hydrocracking process employed for producing higher amounts of BTX from hydrotreated light cycle oil (HDT LCO) (Fig. 2), using a 50/50 NiMo/Al2O3// ZSM-5 mixture, from this point on known as NiMo/ZSM-5 (50), (2) to develop a method for feedstock and product characterization as lumps to facilitate the interpretation of results, (3) to estimate kinetic parameters based on the mentioned characterization method and pilot plant data and (4) to study the product distribution depending on the catalyst activity during time on stream (TOS) of 192 h
Summary
The continuation of the work regarding the production of benzene, toluene and xylene (BTX) from light cycle oil (LCO) is presented in these papers [1,2,3]. 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) [4, 5], which makes the resulting fuel difficult to comply with. It is well known [1,2,3, 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. The process was carried out at 430 °C, 6.9 MPa, liquid hourly space velocity (LHSV) of 2 h−1 and with a H2/Oil ratio of 3 m3/m3, obtaining 29% of selectivity to monocyclic aromatic hydrocarbons (MAH)
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