CHARACTERIZATION OF ASPHALTENE PARTICLES BY LIGHT SCATTERING AND ELECTROPHORESIS

The solubility of asphaltenes in heptane/toluene mixtures was studied at several temperatures. A significant increment in asphaltene solubility was observed when the temperature increases from 0°C to 20°C and a moderate increase when the temperature rose from 20°C to 50°C. These results indicate that asphaltenes behave as a higher consulate temperature system, similar to nonpolar waxes. Examined by photon correlation spectroscopy, diameters from the particles formed a range between 125 and 400 nm, depending on the amount of non-solvent (n-heptane) used for the precipitation process and the initial concentration of asphaltenes. The particles presented a small positive surface potential that was not altered by the addition of resins.     

EFFECT OF PRECIPITATION TEMPERATURE ON THE COMPOSITION OF N-HEPTANE ASPHALTENES

Petroleum asphaltenes were separated from Boscan and Kuwait crude oils by n-heptane at constant temperatures ranging from -2 to 80 ° C. A decreased yield with increase in temperature was observed. The precipitated material was characterized using infrared spectroscopic functional group analysis, HPLC-size exclusion chromatography, vapor pressure osmometry, and elemental analysis. The change in vanadium porphyrin content was estimated for Boscan using UV-Vis. With elevated temperature the asphaltenes are more aromatic (lower H/C) and have higher apparent molecular weight, whereas the pattern of changes in functional groups and heteroatoms (NSO) are more complex and apparently dependent on the crude oil. Porphyrins and low molecular weight types were seen to stay in solution at increased temperature, and a specific extraction of these takes place above 40 ° C. Asphaltene solubility is seen to approximate the Flory-Huggins theory as small molecules go into solution before large molecules. Several other mechanisms may, however, be involved in the phase separation. The molecular size distribution curves obtained by HPLC-SEC were found to explain the trends found in the molecular weights by VPO.     

LIQUEFACTION OF BEYPAZARI LIGNITE USING NiCl2-KCl-LiCl CATALYSTS. 1. DIFFERENCE IN SOLID AND MOLTEN SALT CATALYSIS

Liquefaction of Beypazan lignite in tetralin using NiCl₂-KCl-LiCl (14:36:50 molar percentages) as catalyst was investigated. Effects of the catalyst/lignite ratio and temperature were determined in experiments done at 275°C, 300°C and 360°C. Liquid products were separated into oils, asphaltenes and asphaltols by a solvent extraction method. Yield of liquefaction increased with temperature in all experiments, the highest yield was observed in experiments performed at the eutectic temperature of the catalyst mixture. The highest yields of oils were 20% and 30% with a catalyst/coal ratio of 0.5 at 275°C and 300°C, respectively. The activity of the catalyst increased in experiments in which the catalyst was molten. The yield of asphaltenes were not affected with increases in the catalyst/coal ratio in the experiments done at 275°C or 300°C in which the catalyst mixtures were in solid state. Asphaltene yields decreased from 25% to less than 5% with increasing values of catalyst/coal ratio and the asphaltol yields remained constant at 10% between catalyst/coal ratios of 0.25 and 1.00 and suddenly increased to 30% and 40% for catalyst/coal ratios of 1.50 and 2.00, respectively, at 360°C. The molecular weights of the oils decreased from 340 to a minimum value of 245 as the catalyst/coal ratio was increased from 0 to 1.00 in experiments done at 360°C where the catalyst was molten. As the catalyst/coal ratio was further increased from 1.00 to 2.00 the molecular weight increased to 310.It seemed that the N1Cl₂-KCl-LiCl catalyst mixture in all catalyst/coal ratios was more efficient in molten phase than it was used as a solid mixture.     

PRODUCTS FROM FLASH PYROLYSIS OF A TURKISH LIGNITE IN A FREE-FALL REACTOR UNDER VACUUM

Flash pyrolysis of a Turkish lignite under vacuum in a free-fall reactor was examined at a temperature range of 400 - 800 °C. Gaseous products were analysed with an on-line GC equipped with a manuel injection valve. Solvent fractionation was applied to the liquid product to separate preasphaltenes, asphaltenes and oils fractions. Two particle distributions of the lignite were used: -0.315+0.2 mm and -0.1 mm. The liquid yield increased with temperature up to 650 °C and, thereafter decreased for the larger particles. The maximum liquid yield, excluding pyroltic water, was found to be 8 % wt (dal) at 650 °C. In the case of the smaller particles the liquid yield increased steadily with temperature and the yield of liquid, excluding pyrolytic water, was 5.9 % wt (da) at 850 °C. The gaseous product yield also increased with temperature for both size fractions, and CO and CO₂ in the gaseous products were present in large amounts.     

VARIATION IN THE CHEMICAL NATURE OF ASPHALTENES WITH THE PROCESS, THE COAL AND THE REACTION CONDITIONS

Average structure data for twelve asphaltenes are reported, based on ¹³C- and H- n.m.r. spectroscopy combined with elemental, molecular weight and functional group analyses. The asphaltenes were from supercritical gas extraction, flash pyrolysis and hydrogenation of a brown and a bituminous coal. The effect of the reaction temperature and, for hydrogenation, the catalyst and solvent on the nature of the asphaltene produced was studied. The asphaltene obtained from supercritical gas extraction of the brown coal at 350°C was the least aromatic (f_a = 0.44) with the highest H/C atomic ratio (1.16) and probably consists mainly of single ring aromatlcs with about half of the aromatic sites substituted. A significant proportion of the carbon in this asphaltene is in long alkyl chains and the hydroxyl content is high. Whereas, the asphaltenes produced by hydrogenatlon of the bituminous coal at 450°C were far more aromatic with more highly condensed but less substituted aromatic ring systems and few, if any, long alkyl chains, together with a lower hydroxyl content. The asphaltenes obtained from the brown coal are less aromatic with less condensed aromatic ring systems but a higher degree of aromatic substitution than those produced from the bituminous coal under the same conditions. The asphaltenes formed at 450°C had lower H/C atomic ratios, molecular weights and degree of aromatic substitution, but higher aromaticities Ohan those produced at 35O°C or 400°C under like processing conditions. The asphaltene produced in the presence of both stannous chloride catalyst and tetralin was less aromatic than when either of these species was absent.     

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%.     

Variation in Composition of Subfractions of Petroleum Asphaltenes

Boscan asphaltenes were precipitated from the crude oil using mixtures of toluene and heptane at temperatures of 24, 50, and 80°C. Another process of extracting solid n-heptane asphaltenes (24°C) using the same solvent systems and temperatures was also investigated. Asphaltene yield is different by the two processes at similar conditions although both increases in temperature or toluene content lead to lower solid yield. This way the asphaltene continuum was investigated from incipient flocculation to total n-heptane precipitated asphaltenes. The asphaltenes were analyzed using elemental analysis, fluorescence spectroscopy, vapor pressure osmometry, and HPLC size exclusion chromatography. The distribution of porphyrins was also measured using absor-bance spectroscopy. The asphaltenes were found to follow a regular trend in elemental ratios, H/C and N/C, indicating increased aromaticity and nitrogen content as the solid yield decreases. Also the molecular weight was seen to increase. Size exclusion chro-matograms and fluorescence spectra were found to be different comparing solids from the two separation processes. This indicates that the asphaltene fractions obtained by extraction of solid asphaltenes are altered relative to asphaltenes obtained by ordinary precipitation. The porphyrin concentration was found to diminish rapidly with solid yield decrease in both precipitation and extraction experiments, the latter fractions, however, containing significantly less asphaltenes indicating an adsorption step in the coprecipitation of porphyrins. Soluble fractions were found to exhibit relatively low molecular weights and an apparent lack of indications of association up to a point of solubles exceeding 50 % of the total asphaltenes. The-latter have implications for the further understanding and experimental investigation. of the associating nature of asphaltenes such as concentration effects during analytical characterization.     

Kinetic Modeling of Hydrocarbon Conversion to Asphaltenes in Sulphur-treated Asphalts

A study was made of the kinetics of the conversion of the hydrocarbon constituents of residual asphalts to asphaltenes at temperatures of 210-250°C. The reactions occurring led to the manifold increases in the composition of asphaltenes. Kinetic rate parameters were determined at different temperatures and the temperature effect was correlated by Arrhenius dependency. The reaction order was found to vary with temperature, increasing from 1.60 and yielding a maximum order of 4.2 at 250°C, thus confirming other results obtained in the literature. An activation energy of 266.0 kJ/mol was also recorded which is quite lower than 373 kJ/mol reported for the noncatalytic reaction. The overall effect of the catalyst employed was the reduction of the temperature at which maximum asphaltene yield could be obtained.     

ELEMENTAL COMPOSITION OF ASPHALTENES FROM COAL LIQUEFACTION

The elemental composition (C, H, N, S, O) of asphaltenes isolated from coal liquefaction experiments carried out at different temperatures and tetralin/coal ratios has been determined. The liquefaction experiments were conducted in a 250 ml autoclave, with 10 g of a Spanish subbituminous A coal, for 1 hour, and at 17 ± 1 MPa operating pressure and 400 rpm stirring speed. The liquefaction products were fractionated into oils, asphaltenes and preasphaltenes using pentane, toluene and THF as extractive solvents. The % S and % O are lower in asphaltenes than in coal, while the % C and % N are higher and % H depends on the temperature and tetralin/coal ratio used. On the other hand asphaltenes % C decreases, and % H and % O increase as the tetralin/coal ratio is raised at every temperature except 475 °C, while % S and % N do not have a clear variation.     

CATALYTIC HYDROTREATMENT OF PETROLEUM RESIDUE

Iraqi reduced crude (350°C+) with a sulfur content of 4.3 wt% and a total metal content (Ni+V) of 141 WPPM was n-heptane deasphalted at specified conditions. The deasphalted oil (97.2 wt% of original residue) contains 4.1 wt% of sulfur and 103 ppm of metal. The original reduced crude and deasphalted oil were hydrotreated on a commercial Ni-Mo-alumina catalyst presulfided at specified conditions in a laboratory trickle-bed reactor. The reaction temperatures varied from 300 to 420°C with the liquid hourly space velocity (LHSV) ranging from 0.37 to 2.6 h^-1. Hydrogen pressure was kept constant throughout the experiments at 6.1 MPa, with a hydrogen/oil ratio of about 300 NLL^-1 (normal liters of hydrogen per liter of feedstock). Analysis for sulfur, nickel, vanadium and n-pentane asphaltenes were carried out for hydrotreated products from both the original residue and the deasphalted oil. The comparison of the results obtained for the hydrotreatment of deasphalted oil and original reduced crude indicates that the removal of sulfur, nickel and vanadium was higher for the deasphalted oil than those obtained for the non-deasphalted residue over the entire range of conversion. The exclusion of extremely high molecular weight asphaltenes by n-heptane deasphalting seems to improve the access of oil into catalyst pores resulting in higher desulfurization and conversion of the lower molecular weight asphaltenes. The sulfur content of n-pentane precipitated asphaltenes remained unchaneed with LHSV for various temperature for hydrotreated products produced from both deasphalted oil and original reduced crude.     

STUDY OF SERIAL REACTION KINETICS AND CHANGES OF GROUP COMPOSITIONS OF PETROLEUM ASPHALTS IN CONTINUOUS HEAT AND AIR AGING

The serial reaction kinetics and the changes of group compositions of Shengli petroleum asphalt(SPA) and Huansanlian petroleum asphalt(HPA) were studied during continuous heat and air aging(CHAA) at 120 ∼ 180°C. The test results show that at given temperature the contents of saturate constituents of two asphalts change very little, aromatic constituents decrease clearly and asphaltenes increase gradually during CHAA. At lower temperatures(120 ∼ 140 °C) the contents of resins increase slowly and no toluene insolubles form obviously, but at higher temperature(180°C) the resins increase at first and then decrease and the toluene insolubles increase much quickly with the CHAA time. The higher the CHAA temperature, the more evidently the change of asphalt group compositions would change. The apparent aging rate constants and the apparent aging activation     

FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. II. CALCULATION OF THE ONSET OF FLOCCULATION

The influence of pressure on the onset of flocculation of asphaltenes was calculated in the region from 1 to 300 bar and from 50 to 100°C. These calculations are the counterpart to our experimental data which, recently, have been reported in part 1 of an equally titled article [9]. As gas component methane and as precipitant i-octane were used. The asphaltene flocculation was considered to be a liquid-liquid equilibrium. For modelling the van der Waals equation of state (vdW-EOS) in the framework of continuous thermodynamics was applied. The composition of the crude oil was described by a continuous distribution function with respect to the solubility parameter δ of the Scatchard-Hildebrand theory. Within the distribution the asphaltenes represent the species with the highest δ-values. For oils with a very low content of asphaltenes the model developed describes the experimental flocculation data reasonably. In accordance to the experimental data the model predicts that, in the considered pressure range, without addition of i-octane asphaltene flocculation does not occur. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltene content of the crude oil. For very high asphaltene contents the model even completely fails. Probably, the reason of this lack is the disregarding of asphaltene association.     

CATALYTIC TREATMENT OF PETROLEUM ASPHALTS

Catalytic Sulphurization of residual asphalts obtained from Nigeria;i crudes has been investigated at 210 - 250 °C for a period of 1 hour. The overall effect of the reaction was the manifold increase in the asphaltene content of the sulphurized asphalt. The growth of asphaltenes however decreases with temperature which is in sharp contrast to the non-catalytic reaction reported in the literature. Kinetic analysis shows that the apparent reaction order varied from 1.75 to 3.60 while the rate constant follows a decreasing trend with temperature. These results indicate that the role of the catalyst in the sulphurization reaction is to lower the temperature of the reaction.     

INFLUENCE OF TEMPERATURE AND SOLVENT ON THE PRECIPITATION OF ASPHALTENES

Asphaltenes has been precipitated from a Kuwait flash residue using different n-alkanes (n-C5 to n-C8) at various temperatures ranging from 4^°C to reflux temperatures of the used precipitants. Structures in the asphaltene fractions has been revealed using U.V. fluorescence spectroscopy, elemental analysis and to some extent 1H-nmr. These analysis shows that asphaltenes precipitated in the same amount but at different temperature and with different solvents have merely the same composition. For all n-alkanes the curves of precipitated amount versus temperature show maxima at about 25^°C, implying a shift in the solubility of the asphaltenes.The impact of alkane chain length on the aggregation of asphaltenes through hydrogen bonds is discussed using the alkane-alcohol system as a model. The asphaltene solubility is discussed with the help of the Scatchard-Hildebrand equation.     

DIRECT HYDROGENATION OF A SPANISH LOW RANK COAL. THE EFFECT OF PROCESS VARIABLES

The effect of operating conditions on the liquefaction behaviour of a Spanish lignite was studied using a 250 ml stirred autoclave, and the following operating conditions (except otherwise specified): 400 °C, 1 hour, 3.5 MPa initial (cold) H₂ pressure, 400 rpm and 40 g/10 g tetralin/coal charge. The liquefaction products were fractionated into oils, asphaltenes, preasphaltenes and solid residue using pentane, toluene and THF as extractive solvents

The influence of temperature was explored in the 300-475 °C range, observing little further improvement in liquefaction yields over 400 °C, and retrogressive reactions over 450 °C. The effect of time was studied from 0 to 180 minutes and was concluded that 1 hour is an appropriate period for liquefying a black lignite, since there is little further conversion for longer times. The influence of pressure and gas type was studied using 0, 3.5 and 7.0 MPa initial (cold) pressure of H₂ and of N₂, and the effect of stirring using 0 and 400 rpm. Little influence of these variables was observed, which is attributed to the strong H-donor solvent, high solvent/coal ratio and long reaction time used.     

EFFECT OF INTER-MOLECULAR ASSOCIATION ON BITUMEN OXIDATION

The hypothesis that inter-molecular associations between species in petroleum bitumens affects the rate of air oxidation of the bitumens was examined using infrared spectroscopy, gel permeation chromatography and viscosity measurements. Experiments were carried out in which the rate of oxidation of two different bitumens and their fractions (maltenes, resins, asphaltenes) were measured in terms of carbonyl group formation. In THF solution at 30°C the rates of reaction of the maltene and asphaltene fractions were the same when oxidised separately or as a mixture. Although the presence of inter-molecular associations were confirmed by gel permeation chromatography, the results indicated that such effects were unimportant to the rate of the reaction. Further experiments were performed in which neat bitumen, resin and maltene (n-heptane) factors and reconstituted mixtures were oxidised under 2069 kPa of oxygen or air at 40°C or 60°C. Again, no evidence for the effect of inter-molecular association on oxidation rate was obtained. Another experiment in which a bitumen, rejuvenating oil (RO), and a mixture of the two was oxidised (2069 kPa air, 60°C) again showed that the reaction rate of the bitumen and RO were the same when oxidised separately or in the mixture. However, in contrast, the rate of increase of viscosity of the bitumen was significantly affected by the RO and was attributed to dispersal of polar oxidation products by the RO.     

THE MEASUREMENT OF OXYGEN TRANSPORT PARAMETERS FOR ASPHALT/AGGREGATE AND ASPHALT/GLASS SYSTEMS USING AN ELECTRODYNAMIC BALANCE

A gravimetric method using an eledrodynamic balance was developed for the measurement of transport properties such as the diffusion coefficient, D, solubility, S, and permeability, P, for oxygen into thin layers of asphalt materials deposited on aggregate and glass particles. Glass spheres and aggregate particles in the 14 to 50 μm size range coated with asphalt materials (AAB1, AAG1, and AAK1) were suspended contactless in the balance to measure D, S, and P in the temperature range 21 to 61° C. Transport parameters were determined from the changes in the particle mass due to the uptake of oxygen by the asphalt coating on glass spheres and nonspherical aggregate particles.     

A STUDY ON CHANGE OF FAMILY COMPOSITION AND PROPERTIES OF LIAOSHU PAVING ASPHALT ON AGING

In this paper the change of family composition of the paving asphalt, which conforms to the standard of Sinopec Q/SHR-004-1998, was studied under continuous heating and atmosphere at three different temperatures (150, 163, 180°C), at the same time, the changes of pavement performance were studied. The results showed that at three different aging temperatures saturated hydrocarbon contents did not obviously change after 20 hours on aging. The change of aromatic contents was different before and after 20 hours while resins and asphaltenes contents have changed noteworthily. After aging, resins decreased noteworthily, asphaltenes increased obviously, the composition and structure of asphalt were destroyed which had the pavement performance go bad.     

FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. I. EXPERIMENTAL DETERMINATION OF THE ONSET OF FLOCCULATION

The influence of pressure on the onset of flocculation of asphaltenes was investigated in the pressure range from 1 to 300 bar and at temperatures of 55, 75, and 100°C. Methane was employed as gas component, and i-octane was used as precipitant. The onset of flocculation was determined with a light intensity meter. Three crude oils of different provenance were chosen for the investigations. The crude oils were stabilized in a rotary evaporator at 50 mbar and 180°C, and a part of stabilized products were mixed with different amounts of n-octane or methylcyclohexane. The dependence of the onset of flocculation on the pressure is analogous for all products. The required volume of i-octane decreases strongly with pressure up to 100 bar. Above 100 bar the influence of the pressure diminishes. This dependence corresponds with the solubility of methane in crude oil products. The amount of light hydrocarbons determines the position of the pressure dependence of the onset of flocculation. Without the addition of i-octane, the onset of flocculation could not be ascertained. The observed kinetics of flocculation depends on the asphaltene content as well as on the pressure. The influence of dispersing agents was also examined.     

STRUCTURAL CHARACTERIZATION OF ARABIAN HEAVY CRUDE OIL RESIDUE

The residue (370°C+) from Arabian Heavy Crude Oil was separated into four fractions, asphaltenes, resins, aromatcis and saturates. The four fractions were found to be free of artifacts and analytically significant in themselves. Each fraction was further characterized by elemental analysis, infrared spectroscopy, n.m.r. spectroscopy and mass spectroscopy. The aromatics are the major constituent of the residue and the ratio of asphaltenes, resins, aromatics and saturates is about 2:3:8:3. The strucutral characterization study led to the conclusion that asphaltene fraction is maximum hydrogen deficient followed by resins, aromatics and saturates thus suggesting larger degree of ring condensation in the structure of asphaltenes than resins and aromatics.