Hydrocracking Of Vacuum Gas Oil Research Articles

Hydrocracking of vacuum gas oil in the presence of catalysts NiMo/Al2O3–amorphous aluminosilicates and NiW/Al2O3–amorphous aluminosilicates

Supported nickel–molybdenum and nickel–tungsten hydrocracking catalysts prepared using a support that consists of 70% Al2O3 and 30% amorphous aluminosilicate were characterized by nitrogen and mercury porosimetry, IR spectroscopy of adsorbed CO, and high-resolution electron microscopy. The catalytic tests in hydrocracking of vacuum gas oil containing 3.39% sulfur showed that the nature of the hydrogenating component (NiMo or NiW) only slightly influences the vacuum gas oil conversion and the diesel fraction yield, but noticeable influences the properties of the diesel fraction obtained. The catalyst NiMo/Al2O3–amorphous aluminosilicates, compared to NiW/Al2O3–amorphous aluminosilicates, ensures lower sulfur content in the diesel fraction obtained, whereas the catalyst NiW/Al2O3–amorphous aluminosilicates allows obtaining a diesel fraction with lower content of polyaromatic compounds.

Detailed kinetic modelling of vacuum gas oil hydrocracking using bifunctional catalyst: A distribution approach

A kinetic model for hydrocracking a real vacuum gas oil at 120bar and 400°C in a semi-batch reactor has been constructed based on analysis results from two dimensional gas chromatography (GC×GC). The model has 217 pseudo-component lumps classified by carbon number and hydrocarbon family. Hydrogenation and cracking reactions are included separately and product distributions are generated using a probabilistic approach. Mass transfer resistances and vapour–liquid equilibrium are also accounted for. 17 parameters were estimated and the resulting model is able to fit the experimental data quite well. It was found that it is important to consider the average molecular structure within each lump. To this end, the non-reactivity of components within the paraffin lumps is taken into account in the probability matrix. A parameter has been included for the number of branches removed from the aromatics and naphthenes and it was also necessary to separate the aromatics and naphthenes into mono-ringed and multi-ringed lumps. This many lumped model allows us to approach the results found in studies with model molecules.

Influence of steam-calcination and acid leaching treatment on the VGO hydrocracking performance of faujasite zeolite

The effect of hydrothermal treatment and mild acid leaching on the physico-chemical properties of zeolite Y and its vacuum gas oil hydrocracking performance was investigated. Ultra-stabilized Y (USY) zeolites were obtained by steam-calcination at 500, 600 and 700°C. Steam-treated zeolites were further subjected to a mild acid leaching treatment. The zeolite samples were characterized by XRD, elemental analysis, XPS, N2 adsorption, 29Si and 27Al NMR and FTIR spectroscopy of adsorbed pyridine. Steam-calcination resulted in dealumination and with increasing severity the micropore surface area and the framework Al content decreased. At the same time, the Al content at the zeolite crystal surface increased. Acid leaching improved the pore accessibility and acid properties due to the extraction of extraframework Al species (EFAl). NiMoP-based hydrocracking catalysts were prepared from the modified USY zeolites with alumina as binder. Hydrocracking activities correlated with the acidity of the zeolites. Too severe steam treatment led to depopulation of acid sites and lowered the hydrocracking performance. Hydrocracking catalysts based on the acid leached zeolites were more active than the ones based on the corresponding steam-treated zeolites. It is based on the removal of agglomerated extraframework Al species that block the access to some of the micro- and mesopores. This study points out that, aside from the acidity, also other parameters such as pore accessibility and the presence of EFAl have considerable influence on the hydrocracking of the heavy molecules in a gas oil feed.

Vacuum Gas Oil Hydrocracking on NiMo/USY Zeolite Catalysts. Experimental Study and Kinetic Modeling

A bench-scale experimental unit based on a Robinson–Mahoney reactor with completely mixed gas and liquid phases was used to study the hydrocracking of a light vacuum gas oil on two base metal sulfide containing acid catalysts, characterized by their textural properties, NH3-TPD and pyridine-adsorbed Fourier-transformed infrared (Py-FTIR) acidity. The reactor effluent was analyzed in great detail by means of online gas chromatography and gas chromatography–mass spectrometry which evidenced the role of the catalyst acidity. The detailed analysis allowed the reaction scheme to be expressed at the level required by the kinetic analysis in terms of the fundamental Single Event Kinetics approach and thus drastically reduce the number of independent kinetic parameters to be determined from the experimental data. Reactor simulations illustrate the detailed predictions made possible by this approach.

On the effect of EDTA treatment on the acidic properties of USY zeolite and its performance in vacuum gas oil hydrocracking

USY zeolite catalysts were chemically modified by treatment with aqueous solutions of sodium ethylenediaminetetraacetic acid (EDTA) to study the effect of removal of extraframework aluminum species (EFAl) on hydrocracking performance. The textural, structural and acidic properties were characterized by XRD, elemental analysis, XPS, N2 physisorption, HRTEM, 29Si and 27Al solid-state NMR, ammonia TPD and IR spectroscopy of adsorbed pyridine. The acid catalytic activity of the zeolites was measured by the conversion of propane and 1,3,5-tri-isopropylbenzene. EDTA is a selective agent for the extraction of EFAl from USY preserving the framework Al content. Concomitant with EFAl removal, EDTA enhances the textural properties and changes bulk and surface properties, in particular the Al speciation. Hydrocracking catalysts were prepared from the modified USY zeolites and alumina loaded with a P-promoted NiMo-sulfide phase. Their performance was evaluated in the hydrocracking of a heavy vacuum gas oil under conditions close to the industrial practice. The most active hydrocracking catalyst is obtained by removal of a relatively small amount of EFAl from the USY zeolite. The mild EDTA treatment to achieve this selectively extracts amorphous EFAl species from the mesopore system, resulting in better access to acid sites and an increase of the concentration of strong Brønsted acid sites. Severe EDTA treatment resulted in lower hydrocracking activity which was ascribed to progressive leaching of EFAl synergistically involved in the cracking catalysis. The present study therefore points out the importance of the presence of some EFAl species for the hydrocracking of real feedstocks. This work also shows that even with supports with increased mesoporosity and stronger acid character, higher hydrocracking activity of a real feedstock is not guaranteed.

Vacuum gasoil hydrocracking over three-layered packages consisting of supported sulfide NiMo and NiW catalysts

A method for vacuum gas oil hydrocracking using a three-layered package of catalysts is proposed, in which the top layer is NiMo/Al2O3, the middle is NiM/AAS-Al2O3 and the bottom is NiM/Y-Al2O3, where M is molybdenum or tungsten, AAS-Al2O3 is a support with 70% amorphous aluminosilicate (AAS) and 30% aluminum oxide, and Y is an Al2O3 support with 30% zeolite Y and 70% alumina. The acidic properties of the catalysts are studied via the IR spectroscopy of adsorbed CO. The morphology of sulfide particles on a catalyst’s surface is studied by means of transmission electron microscopy. Textural characteristics of the supports and catalysts are studied via nitrogen porosimetry. Packages containing NiMo and NiW catalysts in different combinations are tested in the hydrocracking of vacuum gas oil. It is shown that replacing NiMo/AAS-Al2O3 with NiW/AAS-Al2O3 in a catalyst package containing only NiMo considerably raises the yield of the diesel fraction.

Maximizing Diesel Production From Vacuum Gas Oil Using a Two Stage Hydrocracker

In this study, a six-lump model was sufficient to describe the kinetics of vacuum gas oil (VGO) hydrocracking in order to maximize the production of middle distillate diesel. The kinetic lump model target was to obtain the reaction rate constants that represent all the hydrocracking reactions in the process. The operating conditions such as temperature, pressure, and hydrogen severity were tested to find the optimum parameters that maximize diesel yields. Mild hydrocracking operating conditions of temperature and pressure were used in a commercial hydrocracker with hydrogen severity similar to hydrotreating processes. The main reaction was the VGO conversion to diesel based on its high reaction rate constant compared with other reactions. In addition, the main reaction had the highest effect on catalyst deactivation based on the resulted deactivation factor. A multi-linear regression correlation was obtained for maximizing diesel production as a function of operating pressure, temperature, and hydrogen amount, keeping the diesel specifications within the market demand.

Application of a Continuous Kinetic Model for the Hydrocracking of Vacuum Gas Oil

Hydrocracking is one of the most versatile petroleum refining processes for production of valuable products including gasoline, gas oil, and jet fuel. In this paper, a five-parameter continuous lumping model was used for kinetic modeling of hydrocracking of vacuum gas oil (VGO). The model parameters were estimated from industrial data obtained from a fixed bed reactor operating at an average temperature of 400°C and residence time of 0.3 h. Product distributions were obtained in terms of the weight fraction of various boiling point cuts. The model parameters were estimated using the Nelder-Mead optimization procedure and were correlated with temperature. Comparison of experimental and predicted product distributions indicated that the model was successful in predicting the products from hydrocracking reactions.

Silica-alumina based nickel-molybdenum catalysts for vacuum gas oil hydrocracking aimed at a higher diesel fraction yield

Nickel-molybdenum hydrocracking catalysts based on amorphous silica-aluminas (ASAs) with Si/Al = 0.3–1.5 have been prepared using chemicals and methods available for catalyst plants. The acidic properties of the ASA surface have been investigated by IR spectroscopy of adsorbed CO, and it has been demonstrated that the Si/Al ratio has an effect on the concentration and strength of Bronsted and Lewis acid sites in the ASA. The catalysts have been characterized by low-temperature nitrogen adsorption and transmission electron microscopy, and it was found that the Si/Al ratio in the ASA has a considerable effect on the textural properties of the catalysts and only a slight effect on the particle size of the sulfide active component. The catalysts have been tested in vacuum gas oil hydrocracking in a laboratory-scale high-pressure flow reactor under typical industrial hydrocracking conditions. The highest diesel fraction yield (>60 wt % at 400°C) has been obtained with the catalyst based on the Si/Al = 0.9 ASA, which has the strongest Bronsted acid sites. With the catalysts based on the Si/Al = 0.3 and 1.5 ASAs, the diesel fraction yield is much lower. This may be due to the lower concentration and strength of acid sites in these catalysts and their smaller specific surface area. The NiMo catalyst based on Si/Al ≈ 0.9 ASA is recommended for industrial use in refineries aimed at obtaining the maximum possible yield of low-sulfur, high-cetane, diesel fuels.

Comparison of Kinetic-based and Artificial Neural Network Modeling Methods for a Pilot Scale Vacuum Gas Oil Hydrocracking Reactor

An artificial neural network (ANN) and kinetic-based models for a pilot scale vacuum gas oil (VGO) hydrocracking plant are presented in this paper. Reported experimental data in the literature were used to develop, train, and check these models. The proposed models are capable of predicting the yield of all main hydrocracking products including dry gas, light naphtha, heavy naphtha, kerosene, diesel, and unconverted VGO (residue). Results showed that kinetic-based and artificial neural models have specific capabilities to predict yield of hydrocracking products. The former is able to accurately predict the yield of lighter products, i.e. light naphtha, heavy naphtha and kerosene. However, ANN model is capable of predicting yields of diesel and residue with higher precision. The comparison shows that the ANN model is superior to the kinetic-base models. © 2013 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Vacuum gas oil hydrocracking performance of bifunctional Mo/Y zeolite catalysts in a semi-batch reactor

A new approach has been developed to characterize bifunctional catalysts in a complex matrix of hydrotreated vacuum gas oil using a batch reactor test. Triphasic reactions were carried out in a reactor equipped with a stationary basket, hydrogen injection and products sampling systems. Bifunctional catalysts containing different relative amounts of alumina-supported NiMo sulfide and zeolite were tested at 400°C under 120 bars over different reaction times. The repeatability of the test conditions was validated and the lack of mass transfer limitations at phase interfaces was confirmed. Gas and liquid samples were analyzed by one and two-dimensional gas chromatography (GC×GC) respectively to obtain quantitative distributions of linear and branched paraffins, naphthenes and aromatics. The details of the products distribution provided by chromatography were explained using mechanisms of bifunctional catalysis. It has been established that the limiting step defining the total conversion is the scission of the hydrocarbon chains on acid sites of the zeolite. The increase of the molybdenum to zeolite ratio provided an improvement of middle distillate selectivity.

Composition of stacked bed for VGO hydrocracking with maximum diesel yield

Hydrocracking catalysts prepared by co-impregnation of three different supports with solutions containing Ni, Mo and citric acid were studied. Pure γ-Al2O3, 30% of zeolite Y/γ-Al2O3 and 70% of amorphous aluminosilicate ASA (Si/Al=0.9)/γ-Al2O3 were used as supports. All the catalysts were shown to contain the particles of Ni-Mo-S phase with similar morphology after liquid phase sulfidation by DMDS. The active component is uniformly distributed on γ-Al2O3 and ASA surface in NiMo/Al2O3 and NiMo/ASA-Al2O3 catalysts. The main amount of Ni and Mo is localized on γ-Al2O3 surface in NiMo/Y-Al2O3 catalyst while the main part of zeolite Y surface is free of supported metals. Testing of stacked beds, which comprise different prepared catalysts, in hydrocracking of vacuum gasoil showed that the NiMo/Al2O3 catalyst had the maximum selectivity to diesel fuel, but its activity was insufficient. Diesel fuel yield did not exceed 50wt.% for the stacked beds comprising NiMo/Y-Al2O3 independent on the process temperature. NiMo/ASA-Al2O3 had an optimal ratio of activity to selectivity for the production of diesel fuel and provided the diesel fuel yield by over 60wt.% at 400°C.

Hydrocracking of Vacuum Gas Oil: Conversion, Product Yields, and Product Quality over an Industrial Hydrocracking Catalyst System

Pilot plant experiments were conducted over an industrial hydrotreating/hydrocracking catalyst system using vacuum gas oil fraction obtained from a refinery crude distillation unit. Extensive pilot plant data were generated on the performance of industrial hydrocracking catalyst system with respect to conversion, product yields, and product quality at various operating conditions. The pilot plant experiments were carried out in a dual-reactor hydrotreating pilot plant system with downflow mode of operation. The temperature varied from 360 to 400°C and liquid hourly space velocity varied from 0.8 to 2.4 hr−1, keeping a constant pressure of 170 kg/cm2 and H2/HC feed ratio of 845 L/L. The hydrocracked total liquid product was distilled in a true boiling point distillation unit to obtain yields and qualities of different fractions such as naphtha, kerosene, diesel, and unconverted oil. The effect of operating conditions on the performance of the hydrocracking catalyst system was discussed in detail. The kinetics of hydrocracking reaction was studied using a simple first-order reaction and a complex four-lump reaction system and the kinetic parameters were reported.

Fundamental kinetic modeling of catalytic hydrocarbon conversion processes

This review discusses a fundamental kinetic approach for the modeling of the conversion of complex hydrocarbon mixtures, called single-event approach. Based upon the transition state theory and statistical thermodynamics and combined with the linear free energy relationship of Evans and Polanyi, it significantly reduces the number of independent kinetic parameters. It is applied to the hydrocracking of vacuum gas oil and the methanol-to-olefin process, which is subject to rapid catalyst deactivation by coke formation. The approach considers a detailed composition of the complex feedstocks, made possible by modern analytical techniques and also by recently introduced computerized methods for the molecular reconstruction of oil fractions. The very large reaction networks should be generated by computer and this aspect is also reviewed. Finally, the application of the method of structural contributions in the reduction of the number of independent kinetic parameters of the hydrodesulfurization of oil fractions is also dealt with.

Performance of Zr- and P-modified USY-based catalyst in hydrocracking of vacuum gas oil

USY zeolites were modified by zirconium, phosphorus and both zirconium and phosphorus, and the corresponding catalysts were prepared for hydrocracking of vacuum gas oil. The results showed that Zr-modified USY enhanced W species dispersion on catalyst surface, weakened interaction of W species with support and improved W species reducibility, leading to formation of highly stacked WS2 slabs and higher sulfidation degree of W species, which was favorable for the enhancement of hydrogenation activity. The influence of the modification with zirconium and phosphorus on these properties of catalyst was more pronounced than that of zirconium or phosphorus modification because of the synergistic action of phosphorus and zirconium. The catalyst containing Zr-USY had slightly lower hydrocracking activity than that containing USY owing to a diminution of acid sites, but presented obviously greater middle distillate selectivity arising from the improvement of hydrogenation activity. The middle distillate selectivity on catalyst containing Zr-P-USY was higher than that on catalysts containing Zr-USY or P-USY, corresponding to its more effective catalyst properties.

Methodology for the Study of Vacuum Gas Oil Hydrocracking Catalysts in a Batch Reactor – Coupling of GC-2D Data with Vapour-Liquid Equilibrium

A new approach for studying complex feedstock conversion with a hydrocracking catalyst is proposed in this work. The reaction was carried out in a batch reactor. Vapor and liquid samples were taken at different reaction times, both at operating conditions and after cooling to room temperature. Two-dimensional gas chromatography was used to characterize in detail the composition of condensed vapor and of liquid phases, while gas samples were analyzed by conventional gas chromatography. From room temperature conditions data, vapor fraction of the hydrocarbon mixture and compositions of each phase at reaction condition were calculated and validated. Following this methodology then allows a simple tracking technique for the study of complex hydrocarbon mixture reactions in liquid and vapor phases.

An optimisation approach for increasing the profit of a commercial VGO hydrocracking process

In this paper, an optimisation approach is proposed to increase the profit of a commercial hydrocracking unit called Isomax. To represent the system, a full-lump kinetic model incorporating the flow rate of fresh vacuum gas oil (VGO), bed temperatures, recycle flow rate and the catalyst life is developed. This model is capable of predicting the yield of all products, and it improves with respect to the previous works by considering LPG and light gases, fresh VGO and recycle streams as separate lumps. After developing and validating the model, the profit function of the plant, including the value of the products, fresh feed and hydrogen, as well as energy expenses, is optimised by manipulating the bed temperatures, flow rate of fresh VGO and combined feed ratio (CFR) whilst all process limitations and operating constraints are taken into account. During two years of study and considering all mechanical and operational constraints, the results confirm that the decision variables, generated by the optimisation package, can increase the gross profit of the Isomax process to about 8.17%, which is equal to $5.6 million of net profit annually. © 2012 Canadian Society for Chemical Engineering

Role of the Zeolite Crystallite Size on Hydrocracking of Vacuum Gas Oil over NiW/Y-ASA Catalysts

The effects of the Y zeolite crystallite size on the hydrocracking activity and middle distillate selectivity in hydrocracking of vacuum gas oil have been investigated using Ni–W catalysts with zeo...

Dynamic Simulation of a Pilot Scale Vacuum Gas Oil Hydrocracking Unit by the Space‐Time CE/SE Method

AbstractThis work introduces a modified space‐time conservation element/solution element (CE/SE) method for the simulation of the dynamic behavior of a pilot‐scale hydrocracking reactor. With this approach, a four‐lump dynamic model including vacuum gas oil (VGO), middle distillate, naphtha and gas is solved. The proposed method is capable of handling the stiffness of the partial differential equations resulting from the hydrocracking reactions. To have a better judgment, the model is also solved by the finite difference method (FDM), and the results from both approaches are compared. Initially, the absolute average deviation of the cold dynamic simulation using the CE/SE approach is 8.98 %, which is better than that obtained using the FDM. Then, the stability analysis proves that for achieving an appropriate response from the dynamic model, the Courant number, which is a function of the time step size, mesh size and volume flow rate through the catalytic bed, should be less than 1. Finally, it is found that, following a careful selection of these parameters, the CE/SE solutions to the hydrocracking model can produce higher accuracy than the FDM results.

Effect of Lump Partitioning on the Accuracy of a Commercial Vacuum Gas Oil Hydrocracking Model

In an industrial hydrocracking plant, except to the reactor, the separation section can affect the accuracy of the developed mathematical model. In this study, two combined-bed six and seven-lump kinetic models for the hydrocracking of vacuum gas oil in a real refinery are developed and their accuracies for the prediction of product yields are compared. In the six-lump model, the engaged components are selected according to the actual products of the plant, but the seven-lump one is included of lumps which are partitioned based on the specified initial and final boiling points.For both approaches, a complete kinetic network with the catalyst-decay functions is considered. It is found that over a 17-month period of operation from the start of run, the average absolute deviation (AAD%) of the six-lump and the seven-lump models for the yield prediction are 20.51% and 5.21%, respectively for all products. Additionally, the sum of residuals for the seven-lump model has been appreciably decreased in comparison to the six-lump one. Therefore, it is confirmed that partitioning of the products to the lumps with specific boiling points can acceptably decrease the deviation of the prediction. So it is conclusive that including the operation of the separation section in commercial models can effectively increase the accuracy of the model and smooth the prediction error.