Hydroconversion Of Vacuum Residue Research Articles

Comparison of Moving-Bed Catalytic Tar Hydrocracking Processes

In recent years, there has been a trend in the global oil industry to improve the proportion of heavy high-sulfur crude oils in the total volume of extracted and processed resources, reserves of which are estimated at over 800 billion metric tons. Therefore, the main line of oil refining is processing of heavy crudes and residua to allow maximum use of the hydrocarbon potential and yield of high-margin products. Hydrogenation processes of heavy raw materials are most attractive in terms of product quality. This article analyzes tar hydrocracking processes that are either in operation or at the stage of full-scale testing. These include Veba Combi-Cracker (VCC), Uniflex, suspended-bed catalyst hydrocracking (ENI), and vacuum residue hydroconversion (TIPS RAS). These technologies use heterogeneous catalysts and are designed to obtain the largest possible amount of liquid products. This article discusses the features of each technology, highlights their advantages and disadvantages, shows the main approaches to process management, and speculates about the development of these technologies. Tar refining is a major process in heavy oil upgrading, and the development of efficient tar-processing methods will influence refinery configurations and management.

Kinetic modeling of deep vacuum residue hydroconversion in a pilot scale continuous slurry reactor with recycle

Slurry phase hydroconversion is a developing technology with the potential to completely upgrade Vacuum Residues (VR). In this work we use data from a continuous pilot plant with recycle to test and extend an existing distributed lumped kinetic model. The new data includes results from 134 steady state experiments with a Heavy Iran VR, including some at very high conversion, and allows sediment production rates to be quantified as well as sulphur removal in the form of H2S. The purpose of the work is to study the impact of the deep conversion reaction conditions and feedstock on the reaction kinetics. The model uses nineteen distributed lumps to represent the heavy hydrocarbons undergoing hydroconversion and hydrodesulphurisation with VR defined as the boiling range > 525°C. Reaction rates are based on molar concentrations. Hydrogen consumption and sediment production are taken into account in the model, as well as vapour liquid mass transfer resistances and vapour-liquid equilibrium. Parameter estimation has been carried out and the model provides a good fit with the experimental data. The modelling exercise found that, at very high conversions, thermal reactions give way to a cascade of catalytic reactions. The model gave a moderate fit for hydrogen consumption rates, which are strongly dependent on feedstock. Accumulation of sediment at high conversions was identified and well represented and the description of hydrodesulfurisation rates as proportional to cracking rates was validated.

Hydroconversion of Vacuum Residue of a Blend of Western Siberian Oils in the Presence of Ex Situ Synthesized Suspensions of Nanosized Catalysts

Concentrated suspensions of nanosized МоS2, МоS2+Ni7S6, Ni7S6, Fe1– xS, and (NH4)0.25 · WO3 particles with an average size of 273–364 nm have been synthesized from reverse emulsions of aqueous solutions of molybdenum, nickel, iron, and tungsten salts in the presence of a sulfiding agent and hydrogen in oil vacuum distillation residues and tested in oil vacuum distillation residue hydroconversion running in an autoclave and a pilot flow system. The test results have shown that the highest activity in hydrogenolysis reactions is exhibited by Mo-containing catalysts. The kinetic characteristics have been determined; the heat of the hydroconversion process has been calculated.

Distributed lump kinetic modeling for slurry phase vacuum residue hydroconversion

A detailed distributed lumped kinetic model for slurry phase Vacuum Residue hydroconversion process (boiling range 525 + °C) has been constructed. Simulated distillation and Gel Permeation Chromatography analysis results were combined to estimate feedstock and product compositions over the whole boiling range. The model uses 21 distributed lumps to represent the hydrocarbons, takes hydrogen consumption into account and calculates reaction rates using molar concentrations. Vapour liquid mass transfer resistances and vapour-liquid equilibrium are also accounted for. The resulting model represents the evolution of the reaction mixture physical properties well and provides a good fit with the experimental data. From estimated parameters, it is deduced that thermally activated and catalytic reactions in cascade occur simultaneously and also that material boiling above 750 °C is converted in a different manner to lighter material.

Activity of a Molybdenum-Containing Composite Nanocatalyst in Vacuum Residue Hydroconversion

A Мо-containing composite nanocatalyst is synthesized in a hydrocarbon medium containing dissolved low-density polyethylene and is sulfided by dimethyl disulfide. The phase and structural compositions of the catalyst are determined. The activity of the composite nanocatalyst in the hydroconversion of West Siberian vacuum residue is investigated. It is shown that the catalyst performance depends on the way of its distribution in the feedstock. The efficiency of composite nanocatalyst Мо-containing particles in hydroconversion is considerably improved when it is combined with the catalyst synthesized in situ.

Structural transformations of asphaltenes during hydroconversion of vacuum residue with recycling the hydroconversion product distillation residue

The hydroconversion of vacuum residue (VR) with the recycle of the unconverted vacuum residue in the presence of nanosized MoS2 catalyst particles synthesized “in situ” in the hydrocarbon medium has been studied. Changes in the molecular structure of asphaltenes from VR and the products of VR hydroconversion in a mixture with the vacuum residue (recycle), depending on the residence time of asphaltenes in the reaction zone, have been described. The main features of structural transformations of asphaltenes during the hydroconversion with recycle have been established. Trends in the structural properties of the asphaltenes with varying different process parameters, such as the residence time and temperature in the reaction medium, have been compared.

Dependence of onset time for mesophase formation on operating parameters during catalytic hydroconversion of Athabasca vacuum residue

During the catalytic hydroconversion of vacuum residue fractions of bitumen or petroleum, the formation of mesophase can lead to fouling of reactor internals. In this study we examine the dependence of the onset of mesophase in a batch microreactor designed to enable in situ microscopic observation of the reacting liquid. The following process variables were investigated: temperature, partial pressure of hydrogen, catalyst concentration, agitation speed, and their interactions. Athabasca vacuum residue was converted in the presence of an iron sulfide particulate catalyst, and a statistical model was developed to describe the effects of the process variables on the onset time for mesophase formation. The temperature and catalyst concentration, respectively, had the most effect on mesophase onset time. The time for mesophase formation dropped by 12.1min when the operating temperature increased from 440°C to 450°C. The mesophase onset time increased by 7.4min when 3wt.% of catalyst was added at 440°C, compared to no catalyst addition. Partial pressure of hydrogen was not significant as an independent process variable for the range studied, from 2.4 to 5.2MPa. The combined effects of hydrogen partial pressure and catalyst concentration were significant, as were the combined effects of temperature and catalyst concentration.

Development of a General Modelling Methodology for Vacuum Residue Hydroconversion

This work concerns the development of a methodology for kinetic modelling of refining processes, and more specifically for vacuum residue conversion. The proposed approach allows to overcome the lack of molecular detail of the petroleum fractions and to simulate the transformation of the feedstock molecules into effluent molecules by means of a two-step procedure. In the first step, a synthetic mixture of molecules representing the feedstock for the process is generated via a molecular reconstruction method, termed SR-REM molecular reconstruction. In the second step, a kinetic Monte-Carlo method (kMC) is used to simulate the conversion reactions on this mixture of molecules. The molecular reconstruction was applied to several petroleum residues and is illustrated for an Athabasca (Canada) vacuum residue. The kinetic Monte-Carlo method is then described in detail. In order to validate this stochastic approach, a lumped deterministic model for vacuum residue conversion was simulated using Gillespie’s Stochastic Simulation Algorithm. Despite the fact that both approaches are based on very different hypotheses, the stochastic simulation algorithm simulates the conversion reactions with the same accuracy as the deterministic approach. The full-scale stochastic simulation approach using molecular-level reaction pathways provides high amounts of detail on the effluent composition and is briefly illustrated for Athabasca VR hydrocracking.

Simulating vacuum residue hydroconversion by means of Monte-Carlo techniques

The present work focuses on the development of a novel methodology for the kinetic modeling of heavy oil conversion processes. The methodology models both the feedstock composition and the process reactions at a molecular level. The composition modeling consists of generating a set of molecules whose properties are close to those of the process feedstock analyses. This synthetic mixture of molecules is generated by a two-step molecular reconstruction algorithm. In its first step, an equimolar set of molecules is built by assembling structural blocks in a stochastic manner. In the second step, the mole fractions of the molecules are adjusted by maximizing an information entropy criterion. Once the composition of the feedstock is represented, the conversion process is simulated by applying, event by event, its main reactions to the set of molecules by means of a kinetic Monte Carlo (kMC) method. The methodology has been applied to hydroconversion of Ural vacuum residue and both the feed and the predicted effluents were favorably compared to the experimental yield pattern.

A study of structural transformations of asphaltene molecules during hydroconversion of vacuum residue at various temperatures in the presence of nanosized molybdenum disulfide particles

Elemental analysis, molecular mass, and 1H NMR data are presented for vacuum residue asphaltenes and the products of vacuum residue hydroconversion in the presence of nanosized MoS2 catalyst particles obtained “in situ” in the hydrocarbon medium. Structural group analysis of average asphaltene molecules has been performed and their structural units have been described. The main trends of change in the structural parameters of the molecules under the hydroconversion conditions and the effect of temperature on the character of these changes have been revealed.

In Situ Observation of Mesophase Formation and Coalescence in Catalytic Hydroconversion of Vacuum Residue Using a Stirred Hot-Stage Reactor

A microreactor equipped with a view window and a stirrer was used to observe mesophase formation in Athabasca vacuum residue with and without catalyst. The effect of stirring on mesophase formation and its growth and coalescence was studied during the cracking of vacuum residue under hydrogen at 4.8 MPa and 440 °C. Stirring can result in a bimodal distribution of size of mesophase domains. The forced coalescence of mesophase droplets by the stirrer led to the formation of very large mesophase regions (bulk mesophase), which coexisted with a large number of small micrometer-sized mesophase domains. The addition of catalyst likely had both chemical and physical effects on the formation and growth of mesophase. The catalyst gave a delay in the onset of mesophase formation as a chemical effect and a decrease in the amount of bulk mesophase regions by suppressing the coalescence of smaller mesophase domains as a physical effect. The analysis of the resulting cokes by scanning electron microscopy (SEM) showed that catalyst particles agglomerated and stuck to the outer surface of the mesophase domains and suppressed their coalescence. The agglomeration of catalyst particles likely decreased their ability to suppress the formation of small mesophase domains, in the range of a few micrometers in size. However, catalyst was effective in suppressing the formation of bulk mesophase domains with areas over 2000 μm2. The results showed that the onset of observable mesophase initially increased with the addition of catalyst, but then decreased at higher catalyst concentrations. SEM observation confirmed that the significant agglomeration of catalyst particles at higher concentrations was likely responsible for the decreased effectiveness of the catalyst in suppressing mesophase formation.

Study of the role of the catalyst and operating conditions on the sediments formation during deep hydroconversion of vacuum residue

The aim of this work is to investigate the influence of the catalyst and the operating temperature on the sediments formation occurring during vacuum residue hydroconversion. At high conversion, instability phenomena occurring due to carbonaceous sediments formation is a tricky issue to address and has detrimental effects on the operability of industrial units. The impact of the catalyst properties on this phenomenon has been scarcely studied. Therefore, a doped F doped NiMo/Al 2O 3 catalyst has been prepared and catalytic tests performed at two temperature levels (430 and 390 °C) in order to study the effect of catalytic hydrocracking or thermal conversion on the sediment formation. For both temperature regimes, it has been observed that the amount of sediments is strongly reduced with the F-NiMo catalyst compared to the undoped one and attributed to the improvement of the conversion of the sediment precursors (asphaltenes). This improvement is mostly due to the promotion of the acidic and hydrogenation functions by F addition. At 390 °C, coke deposition on F-NiMo catalyst is reduced which limits the plugging of the porous volume and preserve the intragranular diffusion of large molecules in the porosity. It has been shown that deep asphaltenes conversion can be achieved using an improved hydrogenation catalyst by reducing their polarity through the removal of heteroatoms and the saturation of some aromatic rings by hydrogen addition. The residual molecules exhibit lower interactions and self association ability resulting in a lower sediment formation. The temperature has also a great impact on the sediment formation in the effluents since the decrease of the temperature favors hydrogenation and catalytic hydrocracking route which is more appropriated to produce stable effluents compared to radical chemistry predominant at high temperature.

A study of Cold Lake Vacuum Residue hydroconversion in batch and semi-batch reactors using unsupported MoS 2 catalysts

Hydroconversion of Cold Lake Vacuum Residue (CLVR) in both batch and semi-batch slurry reactors using unsupported MoS 2 catalysts is reported. The MoS 2 catalyst precursors were added to the CLVR either as an aqueous solution of ammonium heptamolybdate (AHM) or as molybdenum chloride dispersed in reversed micelles that were stabilized in n-hexane using a surfactant. At the reaction conditions studied in both the batch and semi-batch reactors, the MoS 2 catalyst prepared in the reversed micelles had lower coke yield (toluene-insoluble material), lower gas yield, higher liquid yield and higher H 2 consumption, compared to the AHM-derived MoS 2 catalyst. The coke–catalyst mixture recovered after reaction, characterized by chemical and energy dispersive X-ray analysis, confirmed that most of the added catalyst was captured by the coke. Analysis of the coke by X-ray diffraction and transmission electron microscopy confirmed the presence of highly dispersed MoS 2 that suggests the possibility of catalyst–coke recycle.