Vacuum Residue Fractions Research Articles

Detailed characterization of coal-derived liquids from direct coal liquefaction on supported catalysts

Coal liquids from Direct Coal Liquefaction (DCL) are one of the possible substitutes of conventional hydrocarbons resources. However the primary liquids obtained from DCL (i.e. outflow liquids of the first reactor in a two stages liquefaction process) do not meet the product specifications and need to be upgraded via downstream catalytic hydrotreatment processes. The in depth knowledge of the feed of this upgrading step is of key importance to design better catalysts. In this study, we applied new cutting-edge techniques to improve the characterization of a coal derived liquid obtained from a liquefaction step starting from Scottish bituminous coal. For this purpose, bidimensional chromatography (GC×GC), and 13C nuclear magnetic resonance (NMR) were used to analyze four cuts of the coal liquid with the following boiling points intervals: heavy naphtha (initial boiling point: IBP-215°C), gas oil (215–343°C), vacuum gas oil (343–524°C) and vacuum residue (524+°C). The analyses showed high aromaticity of all four cuts. The weight content of aromatics in the gas oil fraction, was 75%, with a majority of two rings aromatics and the remainder consisting mostly of normal paraffins. In the vacuum gas oil cut, which contains mostly four aromatic rings, we found 11wt% of asphaltenes (compounds in n-heptane), an unexpected high amount comparing to petroleum VGO fractions. The amount of heptane-insoluble (asphaltenes, preasphaltenes and sediments) is as high as 80% in the vacuum residue fraction (524+°C). Aromaticity given by 13C NMR in this cut is as high as the level observed in petroleum asphaltenes (Caro=53wt%). High content of heteroelements, which highly increase the polarity of the molecules, in the coal liquid and especially in the vacuum residue can explain the enhanced amount of n-heptane-insoluble compounds.

Suitable Density Determination for Heavy Hydrocarbons by Solution Pycnometry: Virgin and Thermal Cracked Athabasca Vacuum Residue Fractions

Density is an important parameter for understanding molecular packing, stability, and reactivity of petroleum fractions. The determination of density for extremely viscous residual fractions measured at high temperature (reduced viscosity) is difficult and prone to error if results are extrapolated to lower temperature ranges. This problem is addressed in the present study with fractions derived from virgin and visbroken Athabasca vacuum residua. Solution pycnometry (toluene solvent) was studied and demonstrated a feasible, fast, simple, and reliable technique, applicable to a wide variety of petroleum materials, including asphaltenes and vacuum residua. Reported densities were affected to the third decimal position [American Petroleum Institute (API) gravities found reliable to ±0.15° API]. The density for mixtures of residual oil fractions was determined to be an additive property. Athabasca vacuum residue solvent deasphalting and thermal cracked fractions are studied. Thermal cracking was observed to i...

Separation of fractions from vacuum residue by supercritical extraction

The Instituto Colombiano del Petróleo (ICP), has implemented a methodology for separating vacuum residue fractions using the technique of supercritical fluid extraction at the pilot scale. The present study evaluates the efficiency of extraction of fractions of a typical vacuum residue in the Barrancabermeja refinery. The extraction test was carried out with n-hexane under supercritical conditions of temperature and pressure of the 265ºC in the range from 450 to 1250 psi, respectively. Finally, each of the fractions were analyzed for their density, viscosity, sulfur content, Conradson Carbon Residue (CCR) content, SARA com-positional analysis, and metals.

Molecular reconstruction of heavy petroleum residue fractions

Molecular reconstruction techniques are methods that allow to create mixtures of molecules from partial analytical data. In this article, a two-step reconstruction algorithm will be presented. The first step, called “stochastic reconstruction” step, assumes that oil mixtures can be described by distributions of structural blocks. The choice of the blocks and distributions is based on expert knowledge. The transformation from a set of distributions into a mixture of molecules is obtained by Monte–Carlo sampling, while a genetic algorithm adjusts the parametric distributions. The second step, termed “reconstruction by entropy maximization”, improves the representativeness of the set of constructed molecules by adjusting their molar fractions. The estimation of these molar fractions is carried out by maximizing an information entropy criterion under linear constraints. The two-step reconstruction algorithm allows to rebuild mixtures that resemble the petroleum fractions more closely than the approaches used previously. To illustrate the approach, the technique is applied to petroleum vacuum residue fractions.

High Temperature Simulated Distillation of Athabasca Vacuum Residue Fractions. Bimodal Distributions and Evidence for Secondary “On-Column” Cracking of Heavy Hydrocarbons

Decreasing conventional oil reserves and existence of large heavy oil and bitumen reservoirs demand novel and cost-effective production and upgrading schemes. One three sequential steps “visbreaking−adsorption−catalytic steam gasification” upgrading process was recently introduced by the group. Thermal cracked heavy molecules were shown to be key components for improved adsorption over solid sorbents. Characterization of the feedstock and the visbroken products is an important part of the study. In this paper, high temperature simulated distillation (HTSD) characterization is covered. Bimodal and monomodal HTSD chromatographic distributions were observed depending on sample relative abundance of heavy resins and asphaltenes. These polar compounds are responsible for the high temperature chromatographic mode. Secondary “on-column” cracking of heavy petroleum components was observed, however not contributing dramatically to the relative abundance of the chromatographic modes. Changes brought by thermal crac...

Behavior of sulfur species present in atmospheric residue in fluid catalytic cracking

Abstract The selective removal of sulfur species in atmospheric residue (AR) is strongly wanted since the species of the hydrodesulfurized AR (HDS-AR) define the sulfur content of the product gasoline in the subsequent fluid catalytic cracking (FCC). Hence, the correlations between sulfur species in HDS-AR and FCC gasoline were explored in the present study. HDS-AR was fractionated into vacuum gas oil (VGO) and vacuum residue (VR) by distillation. Reactivities of HDS-AR ( S = 3000 mass ppm) and its VGO ( S = 900 mass ppm) were measured by micro activity test to clarify which fractions and sulfur compounds in HDS-AR were converted into gasoline and its sulfur species. The yields and sulfur contents of the product gasoline were 45.0 mass% and 52 mass ppm from HDS-AR and 47.7 mass% and 14 mass ppm from VGO, respectively. The sulfur content of the gasoline from HDS-AR was markedly higher than that from HDS-VGO. The saturate and aromatic fractions in HDS-AR are mainly converted to the gasoline in the FCC process, providing similar gasoline yields from HDS-VGO and HDS-AR. Thiophene, methylthiophenes, and benzothiophenes were major sulfur species in both gasolines from HDS-AR and HDS-VGO. Such sulfur species are concluded to be derived from benzothiophenes in VGO and dibenzothiophenes in VR fractions, respectively through hydrogen transferring ring opening and dealkylation during FCC. Sulfur compounds are also produced from H 2 S and olefins in FCC, increasing the sulfur content in the product gasoline. The larger sulfur content in the gasoline from HDS-AR than that from HDS-VGO is ascribed to more H 2 S being produced during the FCC process as well as dibenzothiophenes being present in the feed.

Measurement of Vacuum Residue and Asphaltene Fluid Properties at Process Conditions

The fluid properties of interfacial tension and viscosity, and the fluid-solid interactions embodied in the contact angle, are important in a wide range of phenomena that affect the processing of the vacuum residue fractions of petroleum and oilsand bitumens. Direct measurements of these fluid properties at representative processing conditions can give important insight into a variety of design and operating challenges, from gas holdup in hydroconversion to fouling of furnace tubes. This review summarizes the efforts to measure fluid properties of vacuum residue materials at high temperature and pressure. Significant progress has been made in measuring surface tension and viscosity of vacuum residues at temperatures to 530°C at low pressures. Further work is needed to develop methods for measurement of contact angle, and for measurements at high pressure.

Use of a novel fluorinated organosulfur compound to isolate bacteria capable of carbon-sulfur bond cleavage.

The vacuum residue fraction of heavy crudes contributes to the viscosity of these oils. Specific microbial cleavage of C-S bonds in alkylsulfide bridges that form linkages in this fraction may result in dramatic viscosity reduction. To date, no bacterial strains have been shown conclusively to cleave C-S bonds within alkyl chains. Screening for microbes that can perform this activity was greatly facilitated by the use of a newly synthesized compound, bis-(3-pentafluorophenylpropyl)-sulfide (PFPS), as a novel sulfur source. The terminal pentafluorinated aromatic rings of PFPS preclude growth of aromatic ring-degrading bacteria but allow for selective enrichment of strains capable of cleaving C-S bonds. A unique bacterial strain, Rhodococcus sp. strain JVH1, that used PFPS as a sole sulfur source was isolated from an oil-contaminated environment. Gas chromatography-mass spectrometry analysis revealed that JVH1 oxidized PFPS to a sulfoxide and then a sulfone prior to cleaving the C-S bond to form an alcohol and, presumably, a sulfinate from which sulfur could be extracted for growth. Four known dibenzothiophene-desulfurizing strains, including Rhodococcus sp. strain IGTS8, were all unable to cleave the C-S bond in PFPS but could oxidize PFPS to the sulfone via the sulfoxide. Conversely, JVH1 was unable to oxidize dibenzothiophene but was able to use a variety of alkyl sulfides, in addition to PFPS, as sole sulfur sources. Overall, PFPS is an excellent tool for isolating bacteria capable of cleaving subterminal C-S bonds within alkyl chains. The type of desulfurization displayed by JVH1 differs significantly from previously described reaction results.

A Geochemical Framework for Understanding Residue Properties

Crude oils, and the residual fractions thereof, vary widely in many relevant properties. Thus, a detailed characterization of a single residue stream or even a number of residue streams from one region may not be very relevant in a different part of the world. We have therefore attempted to develop a framework for understanding residue properties in a generic fashion. A detailed analysis of 11 vacuum residue fractions from a wide variety of crude oils resulted in a general model for understanding the composition and processability of residue streams. This model is based on the geochemical origin (kerogen type) and the maturity of the crude oil. The different origin of kerogen I (paraffinic) residues, compared with the more conventional kerogen II residues, is reflected in a large number of properties and also in a larger variability in these properties. However, upon maturation, the average properties of kerogen I residues and kerogen II residues converge so that mature residues of both kerogen types have much in common (low S content, low metals content, high H/C ratio etc). Maturation is found to have a negative effect on the stability and coking tendency of the residue fraction. NMR data reveal that the asphalthenes become more aromatic upon ageing, whereas the maltenes (non-asphalthenes) become less aromatic, thus causing an increasing gap in aromaticity between these fractions. Significant differences in asphaltene molecular structure between kerogen I and kerogen II residues were observed. The analytical data suggest that the concept of kerogen type and maturity may be a useful tool in describing and understanding residue characteristics and assist in optimizing feedstock selection for residue conversion processes and other residue applications (fuel oils, bitumen), as well as in understanding fouling and coking phenomena. Further research is required to establish the trends shown in this paper.

Coking of Hydroprocessing Catalyst by Residue Fractions of Bitumen

The deposition of organic material, or coke, on hydroprocessing catalyst was studied using Athabasca bitumen vacuum residue (ABVB) and narrow fractions of ABVB, prepared by supercritical fluid extraction (SCFE) with n-pentane. The feed materials were diluted in a low-sulfur gas oil and hydroprocessed over a commercial NiMo/γ-Al2O3 catalyst in a 1 L continuous-stirred tank reactor at 440 °C. The coked catalysts were Soxhlet extracted with methylene chloride; then, carbon content, surface area, pore volume, and pore size were measured. Hydrodesulfurization activity was then measured using bitumen and dibenzothiophene as reactants.The SCFE fractions that contained only saturates, aromatics, and resins gave a low yield of carbon on the catalyst (<7.5 wt %). The asphaltene-rich fraction gave higher coke yields, both on the catalyst and in the reactor, and a lower H/C ratio than the lighter fractions. In the worst case with asphaltene-rich feed, over half of the surface area and pore volume of catalyst was lost due to coke deposition on the catalyst. HDS activity of the spent catalyst decreased monotonically with increasing carbon content on the catalyst. A portion of the carbonaceous material, or coke, on the catalyst was mobile and reactive at the conditions used for hydroprocessing of bitumen. The data suggested that this mobile adsorbed material had a significant impact on the observed activity of the catalyst.

Petroleum Heavy Ends Stability: Evolution of Residues Macrostructure by Aging

Rheological and small-angle scattering techniques were used to investigate the evolution of the colloidal structure of the Safaniya vacuum residue during the age hardening process. Rheological measurements revealed an increase in the molecular weight of the vacuum residue and maltene fraction after the RTFO aging test. Even the molecular-weight distribution became slightly wider, the amount of this variation being greater for aged maltenes than for the whole aged vacuum residue. Small-angle scattering results confirmed the importance of maltene aging on the whole sample viscoelastic properties; the macrostructure of asphaltenes both in solution and in a vacuum residue did not appear to be representative of the age hardening process, in contrast to previous findings.

STRUCTURE, INTERACTION AND PHASE TRANSITION OF VACUUM RESIDUE IN APOLAR SOLVENTS

ABSTRACT Structure, Interaction, and phase transition of a vacuum residue fractions In various apolar solvents were Investigated, using viscosity measurements and small angle neutron scattering. Both light and heavy ended fractions form colloidal particles of spherical shape with average sizes of -40 and -60 A respectively. The size distributions follow a Schultz distribution function approximately. Rheological studies of these fractions indicated significant particle solvation. The solvation mechanism is through association of the solvent molecules with individual VR colloids, instead of through solvent entrapment between agglomerated colloids. The viscosity, as a function of temperature, suggested a glass-like transition at approximately 254 K for the heavy ended fraction at 0.5 volume fraction. The small angle neutron scattering measurements confirmed the colloidal structure determined from rheological study. It also provided the information about the total colloids/solvent Interfacial area, from which we found that VR colloids have a rough surface

Rheological properties of vacuum residue fractions in organic solvents

We report our rheological study on Ratawi vacuum residue fractions in various organic solvents. Both light and heavy ended fractions form colloidal particles in these solvents, and the mixtures exhibit Newtonian behaviour. The viscosity data was analysed using various available theories, to determine their colloidal structure and the degree of solvation. We also studied the viscosity response to temperature for the heavy ended fractions in toluene, where a glass-like phase boundary was observed at low temperature.

Determination of the molecular weights of the Ratawi vacuum residue fractions — a comparison of mass spectrometric and vapour phase osmometry techniques

The molecular weight characteristics of Ratawai vacuum residue fractions are determined using mass spectrometric and vapour phase osmometry approaches. Mass spectrometry involves the controlled sublimation of a thin film of hydrocarbon, from a quartz probe tip, into the instrument. Number average molecular weights and rigorous upper bounds on the number average molecular weights are determined from the mass spectrometry data. The upper bounds are found to be smaller than the values determined by VPO. The mass spectrometry technique is the first step in a direct m.s.-m.s. procedure for evaluation of molecular components in heavy oils.