CHARACTERIZATION OF VACUUM RESIDS, HYDROCRACKED PRODUCTS AND ASPHALTENES BY PYROLYSIS-GAS CHROMATOGRAPHY (FID-FPD)

This paper describes an exploratory study on the characterization of oil heavy-end fractions through pyrolysis coupled with gas chromatography. A pulse heating pyrolyzer with a platinum-strip sample holder, directly coupled with a capillary column gas chromatograph and equipped with a universal detector (FID) and a sulfur-selective detector (FPD), was used for that purpose.

An analysis of vacuum residua, asphaltenes and resins from different crudes was made, as well as analogous fractions from the hydrocracking products of these vacuum residua. Hydrocarbon qualitative profiles (pyrograms) were very much alike for all fractions studied. However, some differences were observed in pyrogram intensity. In general, fractions from untreated samples showed more intense signals than those from the hydrotreated ones. Besides, each of the fractions from vacuum residua generated more intense pyrograms than the combination thereof (entire residue). It was possible to correlate the process-ability of a vacuum residue during hydrocracking and its hydrocarbon yield in analytical pyrolysis.     

Kinetic Study on the Hydrocracking Reaction of Vacuum Residue Using a Lumping Model

Abstract

Based on the experimental hydrocracking of vacuum residue, a kinetic study using a lumping model was carried out to gain insight into the characteristics of catalytic reactions. The lumped species were the saturates, aromatics, resins, and asphaltenes (SARA) constituents in the residue (798 K⁺) fraction and gas, naphtha, kerosene, gas oil, vacuum gas oil, and coke in the products. The pyrite reaction favoring hydrocracking to lighter products was more temperature-dependent than that using a mixture of pyrite and active carbon. The kinetic study showed that the addition of active carbon to pyrite limited the transformation of resins to asphaltenes.     

MILD HYDROCRACKING OF VACUUM GAS OILS TO IMPROVE FCC PERFORMANCE AND MAXIMIZE DISTILLATE YIELDS

ABSTRACT

A pilot plant study was conducted on mild hydrocracking of heavy vacuum gas oils derived from two different crude sources over a commercially available catalyst to determine the possibility of utilizing mild hydrocracker bottoms as fluidized catalytic cracking feedstock along with improved middle distillate yields. The mild hydrocracking experiments were conducted at 390°C, 60 kg/cm², 1.0/h liquid hourly space velocity and H₂/oil ratio of 390 l/l in a pilot plant trickle bed reactor using two catalyst beds for pretreatment and mild hydrocracking reactions. The experimental results showed that mild hydrocracking would result in valuable middle distillates with low sulphur and nitrogen content. With research octane number of 78, the naphtha obtained from mild hydrocracking was found to be a good blending stock for gasoline pool. The middle distillate fraction (140–370°C) obtained from mild hydrocracking product was found to have cetane number in the range of 48–54. The bottom product from mild hydrocracking of heavy vacuum gas oils was found to be a good feedstock for fluidized catalytic cracking unit because of its low sulphur, nitrogen and aromatic contents. The data obtained from pilot plant studies showed that the processing of mild cracker bottom in FCC unit would result in better quality fuels.     

Mild Hydrocracking—A Review of the Process,Catalysts, Reactions,Kinetics, and Advantages

Abstract

The demand for high quality middle distillates is increasing world wide while the demand for residue and fuel oil is decreasing. Hydrocracking is the major conversion process that meets the twin objectives of producing more middle distillates of very high quality. Since hydrocracking is a capital-intensive process, many refiners consider the option of converting their existing vacuum gas oil hydrotreating units into mild hydrocracking units. The use of mild hydrocracker bottom as FCC feedstock can improve the quality of FCC products. In view of the advantages of mild hydrocracking process, it is essential to understand the process, catalysts used, reactions, kinetics, and advantages. This article reviews recent literature on MHC process, various catalysts used, reactions involved and advantages of mild hydrocracking process in terms of improved product qualities and increased distillates. The kinetics of the mild hydrocracking process and kinetic challenges with respect to aromatic saturation have been summarized. The limitations of the process and future scope of work in this area are also discussed briefly.     

A Predictive Kinetic Model for Delayed Coking

Abstract

Lumping of the residue charge stock is based on saturate, light and heavy aromatics, soft and hard resins, as well as asphaltenes, whose concentrations can be obtained by solvent sedimentation and Al₂O₃ column separation. The reaction scheme contains 11 lumped species, including two middle fractions, naphtha, gas, and coke in addition to the above six lumps for residua. It is shown that these kinetic parameters are all invariant with respect to residue compositions and therefore this model is able to predict yields of delayed coking products for a wide variety of ranges of charge stock and operating conditions beyond that of the tests.     

Soil Microbial Degradation of Vacuum Residue

Abstract

The effect of microbial consortia on the alteration of petroleum residual structure and portions was studied, which can propose an alternative or complementary method for stringent upgrading heavy crude oil methods, which consist of heavy and complex hydrocarbons. Biological processing of petroleum heavy fractions and residua may provide an alternative or complementary process in refining heavy crudes—the dominant refinery feed in the future—with less severe process conditions and higher selectivity to upgrade heavy fractions of crude oil. The primary objective was to observe the ability of an indigenous bacterial consortium taken from a soil bellow the vacuum column contaminated with vacuum residue (VR) for several decades from the Tehran refinery distillation unit, in degradation of residua components. Enrichment with VR, as sole source of carbon and energy, is the selected biosurfactant-producing microbial consortium. The biodegradation of net VR using indigenous consortia from this specific ecosystem was studied. The considered period of biodegradation of these heavy hydrocarbons was remarkably shorter than usual studies. Bacterial growth and VR biodegradation ability of this consortium analyzed with SARA test in 20 days. Studying the inoculum size and aeration effect revealed the significance of oxygen for this consortia activity and the similarity of 7% and 5% inoculation on alteration percentage of alkane, aromatic, and asphaltene and resin in VR. Results study revealed a 30.4%, 6.9%, and 9.4% decrease in the asphaltene, aromatics, and saturated aliphatic contents of VR, respectively, in only 20 days in 30°C at 150 rpm.     

REACTIVITY OF SULPHUR SPECIES IN BITUMEN PITCH AND RESIDUA DURING FLUID COKING AND HYDROCRACKING

X-ray photoelectron spectroscopy (XPS) was used to determine sulphur species and their distribution in fractions of fluid coking residue (CK) and hydro-cracking residue (HC) derived from an Athabasca bitumen pitch (ABP). The major sulphur species were sulphides/mercaptans and thiophenes in each case. No sulphoxides and sulphones were detected in any non-oxidised samples. Each residua was separated into between 9 and 15 front-cut samples and a single end-cut fraction by supercritical fluid extraction and fractionation (SFEF). This approach has been used to produce different molecular weight fractions, depending on the severity of separation conditions. In the fractions from the parent Athabasca bitumen pitch about 65-80 wt% of the total sulphur occurs as thiophenes with the remainder being sulphide species. The reactivity of the sulphur species in the parent pitch was determined under mild conditions using a standard technique for selective oxidation. In this procedure sulphides are preferentially oxidized to sulphoxides while thiophenic sulphur remains unchanged; under the same reaction conditions the degree of sulphide conversion generally declined with increasing molecular weight of the fractions. Commercial catalytic hydrocracking completely removed sulphides from the front-cut fractions of the parent pitch. However, the composition of the end-cut fraction from the residua produced by this process was virtually the same as that for the comparable fraction from fluid coking. This observation demonstrates that hydrocracking has little effect on intractable heavy ends. Also, hydrocracking removed only a relatively small proportion of thiophenic sulphur. On the other hand, while commercial fluid coking removed most of the sulphides from the parent pitch the residue was enriched with thiophene compared to the parent feed. This observation demonstrates the partitioning effect occurring during coking reactions.     

TWO-DIMENSIONAL SOLUBILITY PARAMETER MAPPING OF HEAVY OILS

ABSTRACT

The solubility and insolubility of heavy oils and their fractions in dilute mixtures with various solvents were used to characterize heavy oil interactions. A two-dimensional solubility parameter, developed for the selection of solvents for organic polymers, was found to group all the solvents for each heavy oil fraction in polygon areas when the complexing solubility parameter component was plotted against the field force solubility parameter component. All fractions of Cold Lake vacuum residua, except for the saturate fraction, form concentric solubility areas. Therefore, in going in the direction of decreasing aromaticity from coke to asphaltenes to resins to aromatics, all solvents for the previous fraction in the series are also solvents for all subsequent fractions in the series. As a result, asphaltenes can be precipitated, but not extracted, from heavy oils. This is attributed to the interaction among polynuclear aromatics being the dominate interaction in petroleum that causes insolubility in hydrocarbon liquids. However, the paraffinic chains on the same petroleum molecules limit their solubility in highly complexing liquids. In contrast, even vacuum gas oils from the Exxon Donor Solvent coal liquefaction process are insoluble in aromatic liquids but soluble in moderately complexing liquids because of hydrogen bonding, resulting from oxygen functionality. Hydrotreating of these coal derived vacuum. gas oils reduces their oxygen functionality and increases their solubility areas so that they become compatible with petroleum liquids.     

Studies on Coprocessing Vacuum Residue Oil With Plastics Using Thermogravimetric Analysis

Abstract

Synergism and kinetics of plastic/vacuum residue oil blends pyrolysis were investigated in nitrogen and hydrogen atmosphere. From this comprehensive investigation, the results indicated that the higher temperature of initial weight loss of polyethylene plastics was decreased significantly by the addition of vacuum residue oil. Furthermore, the difference in weight loss, calculated as algebraic sums of those from each separate component, is about 10%. These experimental results show a significant synergistic effect during plastics and vacuum residue oil copyrolysis at higher temperatures. Kinetics data from thermogravimetric (TG) analysis fit well the first-order kinetics for both isolated materials and their blends.     

Hydrocracking of Gudao Residual Oil with Dispersed Catalysts Using Supercritical Water-Syngas as a Hydrogen Source. Part II: The Comparison of Residue Hydrocracking in Different Hydrogen Sources

Abstract

Different catalytical hydrogen sources were compared with molecular hydrogen gas in the hydrocracking of Gudao residue in the presence of catalysts (PMA). The results showed that alternative hydrogen sources were effective in catalytic hydroconversion of heavy oil. The hydroconversion of residue in supercritical water-syngas system showed similar results when performed with molecular hydrogen.     

Investigation on the Chemical Composition and Structure of Daqing Vacuum Residue Narrow Fractions

Abstract

The Daqing vacuum residue (DQVR) was separated into 14 narrow fractions by Supercritical Fluid Extraction and Fractionation (SFEF). The contents of element, metal, molecular weight, density, carbon residue of the narrow fractions were measured. Structure parameters were calculated by Densimetric method. Characterization index K _h , and boiling point of narrow fractions were proposed to characterize the fractions and predict their properties. On the basis of the analysis results, the knowledge of Daqing vacuum residue was extended. There will be a big potential use for the DQVR as catalytic stocks.     

EFFECTS OF ASPHALTENE PRECIPITATION AND A MODIFIED D 2007 SEPARATION ON THE MOLECULAR SIZE OF VANADIUM-AND NICKEL-CONTAINING COMPOUNDS IN HEAVY RESIDUA

ABSTRACT

Boscan vacuum residuum (VR), and Maya atmospheric residuum (AR), were separated into operationally defined components by an isooctane asphaltene precipitation followed by a modified D 2007-80 separation of the isooctane soluble material. These collected fractions were examined by size exclusion chromatography (SEC) with element specific detection employing inductively coupled plasma emission spectroscopy (ICP) to investigate the effect the separation has on the the V and Ni compounds. The V and Ni SEC-ICP profiles of the asphaltene fractions indicated some of the metal-containing molecules are substantially larger in size than those observed in the residua. The asphaltene precipitation appears to cause an increase in molecular size through agglomeration of smaller constituents, and accomplishes only limited size separation of the metal-containing compounds.

The resin fraction, the polar fraction obtained by modified D 2007-80 chromatography of the isooctane soluble portion, contained much of the smaller size molecules of the feeds. The agglomeration seen in the SEC-ICP profiles of the asphaltene fraction was not apparent in any of the resin fraction profiles.     

Preliminary Insights on the Crude Oil Maturation Effects on Asphaltene Stability and Processing

Abstract

Geochemical characterization of crude oils is one important classification and exploration tool within the oil business. One maturation parameter is the ratio of cyclic/open demetallized porphyrins (ratio DPEP types/Ethio types). Chromatographic properties of porphyrinic compounds are briefly reviewed. One high-performance liquid chromatography (HPLC) method was selected for measurement of the DPEP/Ethio parameter. This tool is suited for whole crude oils, vacuum residua, and nonvolatile fractions such as asphaltenes.

Exploratory data from heavy, medium, and light crude oils; their vacuum residua; and asphaltenes suggest a correlation between maturity [DPEP/(DPEP + Ethio) parameter] and aspects such as solid deposition and processability during upgrading operations.

Results with the studied set of samples will be discussed by considering “Earth” (time under reservoir conditions) as a reactor that steadily converts hydrocarbon mixtures, disproportioning them into two major types: I. light ends, II. molecules with a set of undesirable properties such as extended condensation, loss of alkyl appendages, higher density, higher intermolecular aggregation tendency, and high coking indexes. Examples with Venezuelan crude oils will illustrate these aspects.     

Solubility of a Russia vacuum residue and group composition of the soluble fractions in different solvents

Abstract

A Russia vacuum residue (RVR) was ultrasonically extracted with 15 organic solvents, respectively. The soluble fractions (SFs) were analyzed with a gas chromatography/mass spectrometer (GC/MS). The results show that the extract yields of RVR largely increased with the decrease in the dielectric constant of solvents, i.e., RVR tends to dissolve in weakly polar and non-polar solvents. Most of GC/MS-detectable components in the SFs are chain alkanes and cyclanes.     

An Active Carbon Catalyst Prevents Coke Formation from Asphaltenes during the Hydrocracking of Vacuum Residue

Abstract

Active carbons were prepared by the steam activation of a brown coal char. The active carbon with mesopores showed greater adsorption selectivity for asphaltenes. The active carbon was effective at suppressing coke formation, even with the high hydrocracking conversion of vacuum residue. The analysis of the change in the composition of saturates, aromatics, resins, and asphaltenes in the cracked residue with conversion demonstrated the ability of active carbon to restrict the transformation of asphaltenes to coke. The active carbon that was richer in mesopores was presumably more effective at providing adsorption sites for the hydrocarbon free-radicals generated initially during thermal cracking to prevent them from coupling and polycondensing.     

Thermal Hydrocracking Kinetics of Chinese Gudao Vacuum Residue

Abstract

The thermal hydrocracking kinetics of Chinese Gudao vacuum residue was studied in a batch autoclave reactor. The temperature ranged in 390–435°C and the initial hydrogen pressure was 7.0 MPa at 20°C. Ammonium phosphomolybdate (APM) in its dispersed phase was the catalyst. The reaction products, gas, naphtha, atmospheric gas oil (AGO), vacuum gas oil (VGO) and coke, were separated during and after experiments, and their yields vs. reaction time were obtained, for four reaction temperatures: 390, 405, 420, and 435°C. The activation energy was calculated from a traditional kinetic model to be 218.6 kJ/mol. A new kinetic model was proposed in this work that allows for the calculation of activation energy with a minimum number of three tests, each at a different temperature. This is comparable to the traditional model which requires a minimum of 12 tests; a minimum of four tests for one temperature and a minimum of three temperatures. The activation energy calculated from the new model with four tests is 229.6 kJ/mol, only 5% greater than that obtained from the traditional model. The reaction rate constants obtained from this model are also consistent with those from the traditional model.     

SEDIMENT FORMATION DURING HEAVY OIL UPGRADING

ABSTRACT

A soft coke-like substance often forms In the liquid product of visbreaking and hydrocracking processes for upgrading vacuum residue of heavy crude oil. This material usually limits the severity, or conversion of the process because it accumulates in downstream equipment. Although the amount of such material produced depends on the crude oil, it has not been possible before to correlate its production rate to chemical characteristics of the vacuum residue in a quantitative manner. In this work we show that the amount of sediment produced per unit weight of vacuum residue feed in laboratory hydrotreating experiments can be correlated with four chemical characteristic of the vacuum residue: the degree of condensed polynuclear aromaticity, the average number of alkyl-groups substituting the polynuclear aromatics, the ratio of heptane insolubles to pentane insoluble-heptane solubles, and the H/C ratio of the latter fraction. The correlation coefficient is 0.95     

Advantages of Mild Hydrocracking FCC Feed—A Pilot Plant Study

Abstract

In view of increasingly stringent environmental regulations with respect to SOx and particulate emissions, the allowable sulphur and nitrogen levels in diesel and gasoline are reducing all over the world. Fluid catalytic cracking (FCC) unit is a major source of fuels produced from a refinery. Any attempt to reduce sulphur and nitrogen content of distillates produced from FCC unit will greatly improve the quality of fuels. In the present work, pilot plant studies were conducted to evaluate the options of hydrotreating and mild hydrocracking (MHC) of FCC feedstock. Experiments were conducted on commercially available catalyst samples using high nitrogenous vacuum gas oil (VGO) as feedstock. MAT experiments were also conducted to compare the conversions and yields of untreated, hydrotreated, and MHC VGO at constant operating conditions. Pilot plant data showed that MHC of VGO would produce additional fuels to the extent of 15% under moderate operating conditions besides improving the quality of FCC feedstock. The mild hydrocracked VGO as feed was found to increase FCC conversion by 2 wt%, increase fuels by 2.5 wt%, reduce residue by 2.8 wt% compared to untreated vacuum gas oil.     

Determination by PIXE of the Metallic Content in Vacuum Residue,Asphaltenes and Maltenes

Abstract

Asphaltenes from Mexican Maya crude oil were precipitated during one agitation hour using n-C₅, n-C₆, n-C₇, and n-C₈ at room temperature. Later the asphaltenes were washed with a soxhlet extraction system during 24 hr to remove the maltenes. The characterization of the vacuum residue, asphaltenes, and maltenes was realized using proton induced x-ray emission (PIXE) for the direct determination of the distributions and abundances of metals in the vacuum residue and their respective fractions. The analysis revealed that vacuum residue contains Fe, Al, V, and Ni, while the asphaltenes and maltenes mainly contain V and Ni.     

CHARACTERIZATION OF HEAVY RESIDUA BY AAPPLICATION OF A MODIFIED D 2007 SEPARATION AND ELECTRON PARAMAGNETIC RESONANCE

ABSTRACT

Seven atmospheric residua (343^°C + [ 65O^°F + ]) were separated into saturate, aromatic, resin, and asphaltene fractions for detailled assessment of feed structure. The weight percent distribution of the fractions revealed two groupings of the residua. One grouping exhibited 20 wt % saturate composition, while the other only 10 wt %. The residua also exhibited high polar content (resin and asphaltene fractions) consisting of over 40% of the total residua. These results are related to the sulfur composition of the residua, and Indicate a fundamental relationship between the aromatic content and sulfur content. Discussion of the accuracy of the separation technique Is also Included.

The vanadium binding sites In the separated fractions were investigated by EPR spectroscopy. The resin and asphaltene fractions all appear to be dominated by 4N and N 0 2S coordination spheres. Discussion of this technique is also included.