EFFECT OF PHOTOOXIDATION ON MOLECULAR WEIGHT DISTRIBUTIONS OF CORBETT ASPHALT FRACTIONS BY GEL PERMEATION CHROMATOGRAPHY

Oxidation of asphalt is believed to be one of the major contributing factors to the failure of asphalt pavement. Due to molecular complexity, the oxidation mechanism of asphalt is complicated by interactions among the molecules of different types. To minimize the interactions, the asphalt sample was separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes. These Corbett fractions were then oxidized under ultraviolet irradiation. Gel permeation chromatography was used to analyze the molecular weight changes of the Corbett fractions during photooxidation. All Corbett fractions have shown significant increase in molecular weight. The oxidized saturates have the highest weight average molecular weight and the most complicated molecular size profiles among the oxidized Corbett fractions     

PHOTOOXIDATION OF CORBETT FRACTIONS OF ASPHALT

ABSTRACT

Oxidation of asphalt causes the degradation and failure of asphalt pavement. Due to the molecular complexity and relatively high molecular weight of asphalt, the oxidation mechanism is complicated by the interactions among the molecules of different types. To minimize the interactions, the asphalt sample was chromatographically separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes. These Corbett fractions were then oxidized under ultraviolet irradiation. Fourier-transform infrared spectroscopy was used to analyze the structural changes of the Corbett fractions during photooxidation. All Corbett fractions have shown significant spectral changes in the region of 3500 ? 3100 cm^?1 characterized the stretching vibrations of hydroxyl or nitrogen-hydrogen groups, the peak around 1700 cm^?1 featured carbonyl groups, and in the region of 1320 ? 1000 cm^?1 characterized the formation of sulfur-containing functional groups. Strong evidence has shown that sulfates are produced in the oxidation of asphalt. The formation of sulfates provides an essential explanation for the deterioration of asphalt pavement.     

PHOTOOXIDATION OF CORBETT FRACTIONS OF ASPHALT

Oxidation of asphalt causes the degradation and failure of asphalt pavement. Due to the molecular complexity and relatively high molecular weight of asphalt, the oxidation mechanism is complicated by the interactions among the molecules of different types. To minimize the interactions, the asphalt sample was chromatographically separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes. These Corbett fractions were then oxidized under ultraviolet irradiation. Fourier-transform infrared spectroscopy was used to analyze the structural changes of the Corbett fractions during photooxidation. All Corbett fractions have shown significant spectral changes in the region of 3500 - 3100 cm^-1 characterized the stretching vibrations of hydroxyl or nitrogen-hydrogen groups, the peak around 1700 cm^-1 featured carbonyl groups, and in the region of 1320 - 1000 cm^-1 characterized the formation of sulfur-containing functional groups. Strong evidence has shown that sulfates are produced in the oxidation of asphalt. The formation of sulfates provides an essential explanation for the deterioration of asphalt pavement.     

COMPARISON OF MOLECULAR WEIGHT DISTRIBUTIONS OF CORBETT ASPHALT FRACTIONS BY GEL PERMEATION CHROMATOGRAPHY

Accurate molecular weight distributions are essential to the determination of the molecular structures of asphalt. Due to molecular complexity and interaction among the molecules of asphalt, precise measurement for the molecular weights of asphalt can not be achieved. In order to minimize the interactions of asphaltic materials, a petroleum asphalt sample was separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes. These Corbett fractions were then analyzed by gel permeation chromatography against nondispersive polystyrene standards. The molecular weights and the molecular size profiles were obtained. Among these Corbett fractions, naphthalene aromatics have the lowest number average molecular weight; saturates have the lowest weight average molecular weight and dispersity; and asphaltenes have the highest number and weight average molecular weights and dispersity.     

Characterization of Asphalt Fractions by NMR Spectroscopy

Abstract

Petroleum asphalt was separated into saturates, naphthalene aromatics, polar aromatics, and asphaltenes using the Corbett method. These asphalt fractions were characterized by H-1 and C-13 nuclear magnetic resonance spectroscopy (NMR). The spectra of saturates illustrate only traceable quantities of aromatic hydrogen and aromatic carbon. Naphthalene aromatics, polar aromatics, and asphaltenes all have broad bands in the aromatic regions of both H-1 and C-13 NMR spectra. These broad bands demonstrate the presence of polycondensed aromatic rings present in the structure of naphthalene aromatics, polar aromatics, and asphaltenes. Based on available literature, numerous NMR resonance bands are identified. The quantitative estimations for various kinds of protons and carbons in the asphalt fractions are compared.     

NMR Fingerprinting of Chemical Changes in Asphalt Fractions on Oxidation

Abstract

The composition of asphalt has been the subject of much study because such data are required in determining its performance-related properties. A problem inherent in studying asphalt composition is its chemical complexity; however, the characterization of asphalt can be better achieved by separating into fractions. In this work, the chemical property of commercial-grade asphalt obtained from BAPCO refinery, Bahrain (BH), was carried out. The rolling thin-film oven (RTFO), used for short-term aging, and pressurized aging vessel (PAV), used for long-term aging, ASTM D4124 (1991) method was used to separate fresh and aged asphalt into four generic fractions such as asphaltenes, polar aromatics, naphthene aromatics, and saturates. The Corbett fractionation procedure was used to separate fresh and aged asphalt into four generic fractions such as asphaltenes, polar aromatics, naphthene aromatics, and saturates. Nuclear magnetic resonance (NMR) was employed to fingerprint the chemical changes that occurred in asphalt during the aging processes. NMR measurements of asphalt fractions showed that during aging, isomerization and dehydrogenation types of reactions took place. Significant differences were observed between the structure and composition of fresh and aged fractions of asphalt. Results from NMR spectrometry provided significant information concerning the chemical transformations that occurred during the aging processes.     

THE EFFECT OF ASPHALT COMPOSITION ON THE FORMATION OF ASPHALTENES AND THEIR CONTRIBUTION TO ASPHALT VISCOSITY

ABSTRACT

Interactions among asphalt components have significant effects on the performance of asphalt binder. To understand those interactions, four asphalts, SHRP AAA-I, AAD-I, AAF-I, and AAG-I, were fractionated into three generic fractions according to Corbett's procedure and reblended into asphaltenes/aromatics/saturates ternary mixtures in various ratios. Mixtures were oxidatively aged with atmospheric air at temperatures of 87.7, 93.3, and 98.8°C for 5 to 33 days. The changes in chemical composition and physical properties were monitored using fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical rheometry

The formation of asphaltenes is a major factor in the hardening of asphalt with aging. The data collected in this study indicate that the saturate content in the maltene phase has a profound impact on the contribution that asphaltenes have on the viscosity of aged asphalt. The data also suggest that the aromatics fraction is solely responsible for the formation of asphaltenes as an asphalt oxidizes.     

OXIDATION KINETICS OF ASPHALT CORBETT FRACTIONS AND COMPOSITIONAL DEPENDENCE OF ASPHALT OXIDATION

ABSTRACT

This paper investigates the oxidation kinetics of asphalt generic fractions and the contribution of each individual fraction to the oxidation of the whole asphalt. Polar aromatic (PA) and naphthene aromatic (NA) fractions of five Strategic Highway Research Program (SHRP) core asphalts (AAA-1, AAD-1, AAF-1, AAG-1 and AAM-1) were prepared and aged at multiple conditions to obtain their kinetic parameters. Aromatics/saturates/asphaltenes blends of four of the five asphalts were also aged to deduce the influence of saturates and asphaltenes.

Carbonyl growth in the PA and NA fractions as a result of oxidation follows a similar profile as the whole asphalts. The kinetic parameters of the NA fractions occur in two groups, one with high reaction order and activation energy, and the other with low values of each. The kinetic parameters of the PA fractions all fall into the low-values group. Although the PA fraction is the most reactive portion in an asphalt, its kinetic parameters (reaction order and activation energy) may be much different from those of its parent asphalt. Saturates have only a dilution effect. The data indicate that the addition of asphaltene increases the oxidation rate. The data also indicate that the PA and NA fractions age faster in a separated state than in a mixed state. This study shows that the kinetic characteristics of an asphalt are determined not only by the kinetic characteristics of the fractions but also by the interactions and molecular associations between the fractions.     

APPLICATION OF HIGH PERFORMANCE LIQUID CHROMATOGRAPHY FOR HYDROCARBON GROUP TYPE ANALYSIS OF CRUDE OILS

ABSTRACT

High performance liquid chromatography (HPLC) was applied to four commercial grade Saudi Arabian crude oils having API gravity in the range 28 to 38 for the determination of hydrocarbon group types namely asphaltenes, saturates, aromatics and polars. Each of these crude oils was separated into asphaltenes and maltenes using n-hexane as the precipitating solvent. The maltenes (n-hexane soluble) were fractionated into saturates, aromatics and polars fractions by n-hexane elution on a column packed with amino propylsilane chemically bonded to porous silica particles.

The data obtained shows that the weight percent saturates increase whereas aromatics, polars and asphaltenes decrease from Arab Heavy to Arab Bern through Arab Medium and Arab Light crude oil. The results obtained from HPLC were in comparison with those obtained from ASTM method D2007. This method is easier, faster and offer good repeatability. This method can be applied to other crude oils.     

THE EFFECT OF ASPHALT COMPOSITION ON THE FORMATION OF ASPHALTENES AND THEIR CONTRIBUTION TO ASPHALT VISCOSITY

Interactions among asphalt components have significant effects on the performance of asphalt binder. To understand those interactions, four asphalts, SHRP AAA-I, AAD-I, AAF-I, and AAG-I, were fractionated into three generic fractions according to Corbett's procedure and reblended into asphaltenes/aromatics/saturates ternary mixtures in various ratios. Mixtures were oxidatively aged with atmospheric air at temperatures of 87.7, 93.3, and 98.8°C for 5 to 33 days. The changes in chemical composition and physical properties were monitored using fourier transform infrared spectroscopy (FT-IR) and dynamic mechanical rheometry

The formation of asphaltenes is a major factor in the hardening of asphalt with aging. The data collected in this study indicate that the saturate content in the maltene phase has a profound impact on the contribution that asphaltenes have on the viscosity of aged asphalt. The data also suggest that the aromatics fraction is solely responsible for the formation of asphaltenes as an asphalt oxidizes.     

STRUCTURAL CHARACTERIZATION OF ARABIAN HEAVY CRUDE OIL RESIDUE

ABSTRACT

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.     

STUDY OF SATURATED COMPONENTS IN ASPHALT

ABSTRACT

The saturated fractions separated from blown and straight run asphalts of the same penetration grade have been investigated by using GC, MS and ¹³ The saturated components in asphalt represent complex mixture of polyalkyl structures in which straight chain paraffins prevail. The content of saturates in asphalt and their molecular composition were found to be affected by the chemical nature of crude oil as well as by the method of its processing into asphalt. Saturated fractions from blown asphalt are richer in long chain paraffins than those from straight run asphalts. The structural examination of saturated components separated from the products of asphalt pyrolysis has confirmed die presence of long straight-chain units in the asphalt-forming micelles. The structural differences between the saturated fractions obtained from asphalts of different origin (Uralian and Brent-blend) suggest, that the distribution of straigh-chain hydrocarbons in asphalts is dependent on the aliphatic network already existing in the raw material.     

FRACTIONATION OF ASPHALT MATERIALS BY USING SUPERCRITICAL CYCLOHEXANE AND PENTANE

ABSTRACT

Fractionation of asphalt materials by using supercritical cyclohexane and pentane has been successfully conducted. Each of three asphalts was fractionated into ten fractions. These asphalts and their fractions were then characterized by a variety of analyses including Corbett chromatographic separation, infrared analysis, refractive index- and intrinsic viscosity-size exclusion chromatography (gel permeation chromatography), and elemental analysis by atomic absorption. The fractions were then reblended to produce materials of typical asphalt consistency. These blends were then subjected to oxidative aging in a pressure oxidation vessel and were found, in some cases, to have improved aging characteristics in the sense that they did not harden in response to a given carbonyl formation (oxidation) as much as normal asphalt materials. Hence, the supercritical fractionation technique is considered to have great potential for producing improved asphalt materials.     

A Study of the Compatibility Between Asphalt and SBS

Abstract

In this article, the compatibilities between different components of a base asphalt and styrene butadiene styrene (SBS) have been analyzed from microscopic structures. Specifically, the asphalt was separated into three components: saturates, aromatics, and resins, by Solvent Recycled Absorption Chromatography Separation Technology (SRACST). The compatibilities between these different components and the polymer were compared with the help of Fluorescence Microscope (FM) with which the existing state of the polymer SBS in these different components could be examined obviously. The modified effects indicated that aromatics could cause SBS swollen and, resins dissolved SBS better than saturates, though both the two components could partially dissolve SBS and the two mixtures presented two immiscible phase systems. In order to further investigate the compatibility between aromatics and SBS, from macroscopic properties, an additive rich in aromatics was added to the SBS/asphalt mixture, and the result was satisfactory.     

ANALYSIS AND PHYSICO-CHEMICAL CHARACTERIZATION ON CHINESE OIL SAND BITUMENS

Abstract

The extraction of four Chinese oil sands from Sinjiang and Inner Mongolia Autonomous Regions with Dean-Stark extractor were investigated. The mineral composition and sand grain distribution were determined and the bitumens were separated into saturates, aromatics, resin-I and resin-II, asphaltenes. The structure parameters and molecular model were made for the bitumens. Elemental analysis, molecular weight, FTIR, 1H-NMR were made for the bitumen fractions. The results show that the molecular structure of Mongolia bitumens have more polycyclic aromatics than that of Sinjiang bitumen. It is believed that the extraction of Sinjiang oil sand bitumen by hot alkaline water is much easier than Mongolia oil sand due to the difference of the viscosity of bitumen, the molecular structure and other physico-chemical properties of the bitumens.     

SOLUBILISED WAXES AND THEIR INFLUENCE ON THE FLOW PROPERTIES OF LUBE OIL BASE STOCKS

ABSTRACT

The physico-chemical properties of Lubricating oil base stocks (LOBS) are generally influenced by the type/nature and concentration of solubilised waxes present in them. Detailed composition of the solubilised waxes, saturates and aromatics present in LOBS and its distillate fractions has been sludied. Further the influence of these solubilised waxes and as well of saturates/aromatics on the flow properties particularly pour point, viscosity and viscosity temperature relationship of LOBS sample and its distillate fractions have been investigated. The response of a commercial pour point depressant additive with varying composition of solubilised waxes in lube oil base stock sample has also been studied.     

OF ASPHALT FRACTIONS OBTAINED BY SUPERCRITICAL AND SOLVENT EXTRACTION

ABSTRACT

Supercritical extraction with n-pentane was used to separate asphalt into distinct fractions having different physical and compositional properties. A pilot-scale supercritical unit capable of processing thirty kilograms of asphalt per day was designed and fabricated specifically for asphalt fractionation. The operation and design of the unit is similar to the ROSE (Residuum Oil Supercritical Extraction) process of Keer-McGee. This unit was used to separate asphalt into five different fractions ranging from soft greases to asphaltene-like solids. Supplemental room-temperature solvent fractionation of the hardest of these five using binary pentane/cyclohexane mixtures produces, a total of eight fractions. A variety of analyses provide chemical and physical ctauracterization of the fractions. These include: (1) Corbett Fractionation, (2) FT-IR spectroscopy, (3) size exclusion chromatography, (4) nickel and vanadium atomic absorption, and (5) viscosity     

聚合物SBS和沥青的相容性研究

以胜华100^#沥青为原料,采用溶剂脱青工艺和溶剂再循环吸附色谱分离技术将沥青分成三组分：富饱和烃组分（S）、富芳香烃组分（A）、富胶质组分（R）。根据微观形态结构的不同,考察了聚合物苯乙烯－丁二烯－苯乙烯（SBS）在不同组分中的存在形式,研究了沥青组分与聚合物的相容性。结果发现：饱和分对SBS起溶胀作用;而芳香分和胶质对SBS部分溶解,整个体系呈两相结构。改性沥青要达到最佳性能,其饱和分、芳香分和胶质需达到一定配比。     

Compositional Changes in Hydrotreated Naphthenic Oil under Ultraviolet Radiation

Abstract

Compositional changes of hydrotreated naphthenic oil during ultraviolet (UV) radiation were studied in detail. First, liquid–solid chromatography was used to separate the initial oil and the UV-irradiated oil into three different fractions: saturates, aromatics, and polars. Then, each fraction's compositional changes were evaluated using a series of instrument technologies including gas chromatography-mass spectroscopy (GC-MS), infrared spectroscopy (IR), atmospheric pressure chemical ionization mass spectroscopy (APCI/MS), and X-ray photo electron spectroscopy (XPS), respectively. The results show that after UV radiation, the UV-irradiated sample exhibited a decrease in saturates concomitant with an increase in the aromatic and polar fractions. For saturates and aromatics, the UV-irradiated sample exhibited a decrease in alkanes, diaromatics, and polyaromatics concomitant with an increase in other aromatics. The UV light had no significant effect on the cycloalkanes. For polars, a relatively large amount of oxygen-containing compounds, such as hydroxyl, carbonyl, and carboxyl groups, was formed in the presence of UV light. XPS data show that a type of S 2pa compound in the initial oil disappears and could be converted to SO₄ ^2?. No obvious changes of molecular weight distribution were observed. A part of polar compounds in the UV-irradiated oil might come from aromatic photooxidation in the initial oil.     

Group Type Analysis of Asphalt by Column Liquid Chromatography

An improved analysis method for characterization of asphalt was established. The method is based on column chromatography technique. The asphalts were separated into four groups: saturates, aromatics, resins, and asphaltenes, quantitatively. About 0.1 g of sample was required in each analysis. About 20 mL of n-heptanes was used to separate out saturates first. Then about 35 mL of n-heptanes/dichloromethane (1/2.5, v/v) mixture was used to separate out aromatics. About 30 mL of dichloromethane/tetrahydrofuran (1/3, v/v) mixture was used to separate out resin. The quality of the separation was confirmed by infrared spectra (IR) and ¹H NMR analysis. The model compounds, tetracosan for saturates, dibenz(ah)anthracen for aromatics, and acetanilide for resins were used for verification. The IR and ¹H NMR analysis of the prepared fractions from the column liquid chromatography were in good agreement that of pure reagents.