Maltenes and Asphaltenes of Petroleum Vacuum Residues: Physico-Chemical Characterization

Abstract

Solvent separation is frequently applied to petroleum vacuum residues to reduce the coke-forming tendencies of these materials. This process is capable of removing all or a substantial amount of asphaltenes from feedstocks that are destined for further processing and thus applied as the first step of refining. Maltenes and asphaltenes obtained from vacuum residues of Heera (HVR) and Jodhpur (JVR) Indian crude oils using n-hexane, n-heptane, and soluble and insoluble fractions obtained using ethyl acetate, were characterized for elemental analysis, molecular weight, conradson carbon residue (CCR), specific gravity, and pour points. The resulting degree of removal of asphaltenes ranged from 10–28 wt% of the HVR and 25–50 wt% of the JVR. The increasing trend of the American Petroleum Institute (API) gravity and the decreasing trend of CCR and pour point are observed with the increase in removal of asphaltenes.     

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.     

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

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.     

Structural Characterization of Asphaltenes and Ethyl Acetate Insoluble Fractions of Petroleum Vacuum Residues

Asphaltenes and insoluble fractions of vacuum residues (VRs) of two Indian crude oils (viz. Heera and Jodhpur) of different specific gravity were obtained by precipitation of VRs in n-hexane, n-heptane, and ethyl acetate, and also by subsequent reprecipitation of n-heptane and ethyl acetate soluble fractions by n-pentane. The effect of various solvents on average molecular structure of asphaltenes and insolubles was studied using nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), and size exclusion chromatography (SEC). The asphaltenes and insolubles of Jodhpur VR have higher amounts of high molecular weight species with a high concentration of condensed and substituted aromatic rings, branched and/or short alkyl side chains, oxygen and nitrogen functionalities, compared to that of Heera VR. Ethyl acetate insolubles comprise a higher number of substituted aromatic structures, branched aliphatic structures, complex average unit structures, nitrogen and oxygen functionalities, and high molecular weight (MW) species as compared to hexane and heptane asphaltenes. Heptane insolubles consist of more naphthenic rings condensed with aromatic rings than C6A and EAI.     

Structural Characterization of Asphaltenes from Raw and Desulfurized Vacuum Residue and Correlation Between Asphaltene Content and the Tendency of Sediment Formation in H-oil Heavy Products

Asphaltenes obtained from raw vacuum residue from Russian (Ural) petroleum have been characterized by means of elemental analysis and ¹H proton nuclear magnetic resonance (NMR) and compared with asphaltenes separated from the residue desulfurized in the H-oil process. The latter have much lower molecular weight and more aromatic character. In high-temperature conditions of fractionation of the whole H-oil product and in the presence of catalyst dust carried away from reactors, asphaltenes tend to condense, dehydrogenate, and separate from the desulfurized oil as a coke-like sediment. Some correlations have been found between the asphaltene contents of raw and desulfurized residue and the tendency of sediment formation in desulfurized residual oil that causes serious operating problems in H-oil units.     

渣油加氢处理后沥青质组成和结构的变化

采用IR、NMR、XPS等分析手段及钌离子催化氧化(RICO)法,考察了不同加氢反应温度下渣油沥青质组成和结构的变化。结果表明,随着加氢反应温度的升高,沥青质结构中硫质量分数降低,而氮质量分数增加,芳碳率提高;沥青质结构中出现较大的芳香核,芳香环上的取代侧链和芳环间的桥链均变短,分别由C₂₉降至C₁₇、C₂₁降至C₇;沥青质RICO产物中的苯多酸由苯甲酸、苯二甲酸为主逐渐变化为以苯四甲酸至苯六甲酸为主,说明沥青质中的群岛型结构有向大陆型结构转化的趋势。加氢温度升至450℃后,沥青质的组成和结构已基本稳定,说明渣油加氢适宜温度为450℃。     

Characterization of Some Local Petroleum Residues by Spectroscopic Techniques

Abstract

Two vacuum residues were delivered from two different petroleum refineries, one from Suez Petroleum Company and the second from Alexandria Petroleum Company. Two heavy residues were subjected to solvent extraction using n-pentane, n-heptane, and ethyl acetate. The studied residues were fractionated into their components. Infrared spectroscopy was applied to study the distribution of functional groups contained in samples and their components. Some ratios calculated from the peak heights of selected infrared bands allow for a better comparison. The UV-Vis spectroscopic technique was applied to the aromatic fraction to determine how much mono-, di-, and polyaromatics are present in the aromatic fraction. The monoaromatics represent the lowest constituent among the aromatics present, whereas the polyaromatics and diaromatics are predominantly present and form the major constituent.     

Evaluation of Atmospheric and Vacuum Residues Using Molecular Distillation and Optimization

The term atmospheric residue describes the material at the bottom of the atmospheric distillation tower having a lower boiling point limit of about 340°C; the term vacuum residue (heavy petroleum fractions) refers to the bottom of the vacuum distillation, which has an atmospheric equivalent boiling point (AEBP) above 540°C. In this work, the objective is to evaluate the behavior of different kinds of Brazilian atmospheric and vacuum residues using molecular distillation. The Falling Film Molecular Distillator was used. For the results obtained through this process, a significant range of temperature can be explored avoiding the thermal decomposition of the material. So these results are very important to the refinery decisions and improvements. The Experimental Factorial Design results showed that the temperature has more influence on the process than the feed flow rate, when a higher percentage of distillate is required.     

Characterization of Functional Groups of Asphaltenes in Vacuum Residues Using Molecular Modelling and FTIR Techniques

Asphaltenes are components of crude oil, and their average chemical structures are characterized with difficulty. This study shows that simple Fourier transform infrared (FTIR) analysis spectroscopy could be adapted to the determination of aromatic hydrogens in asphaltenes and resins and elucidation of their average molecules. The work demonstrates the existence of a linear correlation in the infrared (IR) intensities of the symmetric and asymmetric aromatic hydrogens in methyl substituted arenes, in the 2,900 to 3,100 cm^-1 region and of the out-of-plane deformation in the 700 to 900 cm^-1 region.     

Recovery and Characterization of Petroleum Residues Through the Molecular Distillation Process

Molecular distillation process is an efficient way to separate complex residues to obtain improvement and a more complete characterization of crude oils. It presents advantages such as to generate distillation products that can be experimentally characterized, and the operation conditions of this process generate distillate cuts with an atmospheric equivalent boiling point (AEBP) above 650°C without risks of thermal degradation. The aim of this work is to carry out the separation of two vacuum residues (VR) within the process temperature range from 550 to 670°C, using the Brazilian Molecular Distillation equipment. As a result, five distillate cuts and five residues from molecular distillation processing were generated. The molecular distillation (MD) technique provided a gain in distillate yield of about 10% over the conventional methods. The efficiency of the technique was verified through the vapor pressure osmometry experiments and the extension of true boiling point (TBP) curves of petroleum. The extended TBP curves by the molecular distillation process demonstrated that this alternative method is appropriate to extend the TBP curves to temperatures above those of the conventional methods.     

Kinetic Studies on Cocracking of Petroleum Vacuum Residue with Thermoplastics and Biomass (Petrocrop)

Cracking of petroleum vacuum residue (XVR) and its cocracking with plastics (PP or PS), Calotropis procera (CL) as a binary, ternary, and quaternary mixture of these individual plastics, and CL with XVR was carried out in a Perkin-Elmer thermogravimetric analyzer (TGA) for the purpose of comparing the process of the mixture with those of the individual components. Experiments were conducted at a heating rate of 40 K/min, in the temperature range of 30-900°C. Based on the results obtained, three temperature regimes were selected for studying the nonisothermal kinetics of TGA of individual XVR, plastics, and biomass as well as of the cocracking of these with XVR, i.e., below 400°C, between 400-500°C, and above 500°C. The kinetic studies were performed using the Coats and Redfern kinetic modeling equation. The overall activation energies obtained were 25 kJ/mole for petroleum vacuum residue, 99 kJ/mole for polypropylene, 21 kJ/mole for coal, and 35 kJ/mole for the mixture of all these materials. Thus, it has been found that there exists an overall synergy when three materials were coprocessed together. The overall orders and activation energies change during coprocessing of two or three different macromolecules, including mixed vacuum residue as presently observed. The detailed results that were obtained will be reported.     

Characterization of Petroleum Asphaltenes by Size Exclusion Chromatography, UV-fluorescence and Mass Spectrometry

The molecular weight of petroleum asphaltenes remains the subject of debate. Our previous work using size exclusion chromatography with 1-methyl-2-pyrrolidinone (NMP) as eluent, combined with mass spectrometry and fluorescence spectroscopy has indicated molecular masses up to 40,000 u. The present work investigates the asphaltene fraction of Kuwaiti crude oil. The asphaltene was separated into several NMP-soluble fractions and an insoluble residue. The evidence from size exclusion chromatography (SEC) and UV-fluorescence spectroscopy (UV-F) shows that the molecular size range and the size of the aromatic chromophores increased with increasing insolubility in NMP. A steady increase in the sizes of the range of chromophores was shown by UV-fluorescence in going from the maltene fraction, via the asphaltene sample to the NMP-insoluble residue, using chloroform as solvent. Laser-desorption mass spectra showed very wide mass ranges for the whole asphaltene and the NMP-insoluble residue of asphaltenes, with a signal up to m/z 200,000 and slightly more ion intensity at high masses for the residue compared to that from the asphaltene.     

Behavior and Role of Asphaltenes in a Two-stage Fixed Bed Hydrotreating Process

Residue upgrading processes are very important for the production of distillates and low sulfur fuel oils. Among those, fixed bed technologies are very efficient for deep desulfurization of petroleum residue heavy oils, even for highly asphaltenic feeds. This work analyzes the effects of the operating conditions on the evolution of asphaltenes and on their inhibition effect during the hydrodesulfurization reactions. Residue hydrotreating experiments were performed on a pilot plant and asphaltene fractions were investigated using size exclusion chromatography (SEC), ¹³C nuclear magnetic resonance (NMR), liquid chromatography, and elemental analyses. Besides the overall decrease in asphaltenes yield, significant changes in the average structure of the asphaltenes were also observed.     

The Effect of Solvent Washing on Asphaltenes and Their Characterization

Asphaltenes from an atmospheric residue of heavy crude were precipitated with n-heptane. Part of the isolated asphaltenes was washed under Soxhlet reflux to remove adsorbed maltenes. Comparison among washed and unwashed asphaltenes was carried out and both samples were characterized by atomic absorption, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and differential scanning calorimetry.     

Behavior and Role of Asphaltenes in a Two-stage Fixed Bed Hydrotreating Process

Abstract

Residue upgrading processes are very important for the production of distillates and low sulfur fuel oils. Among those, fixed bed technologies are very efficient for deep desulfurization of petroleum residue heavy oils, even for highly asphaltenic feeds. This work analyzes the effects of the operating conditions on the evolution of asphaltenes and on their inhibition effect during the hydrodesulfurization reactions. Residue hydrotreating experiments were performed on a pilot plant and asphaltene fractions were investigated using size exclusion chromatography (SEC), ¹³C nuclear magnetic resonance (NMR), liquid chromatography, and elemental analyses. Besides the overall decrease in asphaltenes yield, significant changes in the average structure of the asphaltenes were also observed.     

Chemical Reaction Engineering Studies on Cocracking of Petroleum Vacuum Residue with Coal, Plastics, and Biomass (Bagasse and Petrocrop)

In our previous article, Ahmaruzzaman and Sharma (2007), the cracking of petroleum vacuum residue (XVR) and its coprocessing with thermoplastic and biomass (Calotropis procera) has been discussed. This article deals with the studies on cocracking of XVR with thermosetting plastic, i.e., bakelite (BL), Samla coal (SC), biomass, i.e., bagasse (BG) or C. procera (CL) and their binary, ternary, and quaternary mixtures in a thermogravimetric analyzer (TGA). The kinetic studies were performed using the Coats and Redfern kinetic modeling equation. The overall activation energies obtained were 25 kJ/mole for petroleum vacuum residue, 99 kJ/mole for polypropylene, 21 kJ/mole for coal, 23 kJ/mole for Calotropis procera, and 25 kJ/mole for the combination of these four materials. However, other models, such as van Krevelan et al. and Horowitz and Metzger have also been used in some cases to compare the results with those obtained by the Coats and Redfern kinetic models. In the present work, the effect of catalysts on the cracking of Basra vacuum residue (BVR) has also been reported.     

Correlation Between Properties of Asphaltenes and Precipitation Conditions

Asphaltenes from three crude oils were precipitated by using a pressurized system. Different conditions during the precipitation of asphaltenes were studied: pressure was varied between 15 and 45 kg/cm² and temperature between 40°C and 100°C. The effect of contact time and solvent-to-oil ratio was also studied in the range of 0.5-6 hr and 2:1 to 5:1 mL/g, respectively. Asphaltenes properties were analyzed as a function of pressure and temperature. It was found that in a deeper way temperature influences the asphaltenes properties than pressure in the range studied in this work. Asphaltenes properties were highly dependent on the nature of crude oil. Various correlations were developed and experimental and calculated asphaltenes contents and properties were in good agreement with absolute error less than 0.2%.     

Correlation Between Properties of Asphaltenes and Precipitation Conditions

Abstract

Asphaltenes from three crude oils were precipitated by using a pressurized system. Different conditions during the precipitation of asphaltenes were studied: pressure was varied between 15 and 45 kg/cm² and temperature between 40°C and 100°C. The effect of contact time and solvent-to-oil ratio was also studied in the range of 0.5–6 hr and 2:1 to 5:1 mL/g, respectively. Asphaltenes properties were analyzed as a function of pressure and temperature. It was found that in a deeper way temperature influences the asphaltenes properties than pressure in the range studied in this work. Asphaltenes properties were highly dependent on the nature of crude oil. Various correlations were developed and experimental and calculated asphaltenes contents and properties were in good agreement with absolute error less than 0.2%.     

Characterization of Asphaltenes and Resins Separated from Water-in-Oil Emulsions

Knowledge of the properties and behavior of asphaltenes and resins is indispensable for the design of preventive and curative measure for emulsion problems created by the presence of asphaltene, resins, and other organic and inorganic solids. In order to understand the phenomena of water-oil emulsions formed in Kuwaiti oil fields and determine the factors involved in the stabilization of these emulsions, the role of asphaltenes, resins and wax separated from various samples of oil field emulsions formed in Burgan oil field have been evaluated. Physicochemical properties of asphaltenes, resins, wax, and de-asphalted de-resined (DADR) oil samples have been studied via FT-IR, ¹H, and ¹³C NMR, elemental analysis, and differential scanning calorimetry (DSC). These emulsion samples contain different amounts of water ranges from 24 to 35%, asphaltene content ranges from 0.9 to 1.7%, and resin content from 3.7 to 4.6%. IR-FT spectra were performed to identify the various functional groups which have an effect on the stability of water-oil emulsions. The freezing behavior of an emulsion was characterized by differential scanning calorimetry to determine whether the water in the emulsion is free water or emulsified water.