POLARITIES OF SHRP ASPHALTS CALCULATED FROM ION EXCHANGE CHROMATOGRAPHY SEPARATION DATA

Abstract

During the Strategic Highway Research Program, four asphalts were separated into polar and non-polar fractions by means of three different ion exchange chromatography procedures. For each asphalt, the non-polar neutral fractions comprised over 50 mass percent of the total asphalt. These neutral materials are much less viscous than corresponding whole asphalts. Molecular weights of the neutral fractions correlate roughly with viscosities, whereas there is no correlation between these properties for whole asphalts.

The various polar fractions were subdivided into acidic, basic, and amphoteric fractions of differing polarities. Based on dipole moments of typical components, polarity factors were assigned to each of these fractions. Multiplication of mass percentages of each fraction by their polarity factors yields polarity indices. Total polarities of asphalts or mixtures of ion exchange fractions are obtained by summing polarity indices of the unique distribution of components. Polarities of asphalts and mixtures of ion exchange fractions and viscosities of neutral fractions can be used to predict viscosities of whole asphalts and mixtures.

The method allows for prediction of effects on Theological properties of asphalts by materials whose polarities can be estimated. The success of the method supports one model of asphalt structure.     

SIZE EXCLUSION CHROMATOGRAPHY STUDIES OF AGED SHRP ASPHALTS

One of Ihe objectives of the Strategic Highway Research Program is the development of a test procedure that accurately predicts pavement aging. In order to accomplish this goal, the nature and mechanism of oxidative-aging of asphalts must be known.

Eight asphalts were aged in a pressure-oxidation vessel at 60°C (140°F) and 2.07 x 10⁶ Pa (300 psi) for 144 hours (6 days) after a preliminary thin-film oven treatment. The tank asphalts and aged asphalts were separated by preparative size exclusion chromatography into two fractions: one consisting of large molecular size, associated molecules and the other consisting of smaller molecules with less tendency lo associate. The amount of the large molecular size fraction is greater in an aged asphalt compared with its parent tank asphalt. Number-average molecular weights of this large molecular size fraction increase substantially in some aged asphalts but not in others. Viscosities of smaller molecular size fractions (which comprise the bulk of both aged and unaged asphalts) of aged asphalts are not greatly different from viscosities of corresponding fractions of parent tank asphalts. Viscosities of the small molecular size fractions are much lower than viscosities of whole asphalts. Oxygen-containing functional groups were observed in both size exclusion chromatography fractions of all eight aged asphalts.

The above results can be rationalized by invoking a model of asphalt structure in which complex structural units composed of polar and/or aromatic molecules arc dispersed in a less polar solvent phase. The aping process causes buildup of more polar molecules, which increases the relative amounts of asphalt components that engage in associative behavior.     

ION EXCHANGE CHROMATOGRAPHY SEPARATION OF SHRP ASPHALTS

ABSTRACT

Eight asphalts selected for intensive study in the Strategic Highway Research Program have been separated into neutral, basic, and acidic fractions by means of ion exchange chromatography. Each asphalt exhibits a characteristic fractionation pattern into neutral, acidic, and basic components. The separations into chemical types were verified by elemental analysis and infrared methods. Separations were reasonably repeatable, and recoveries were acceptable. Large enough amounts of asphalts could be separated so that properties of interest of the fractions could be studied.

In all cases, neutral fractions comprised at leaBt one-half of the asphalts. These neutral fractions are the least aromatic and contain the lowest percentages of heteroatoms and metals compared with the polar fractions. They also are much lower in molecular weight. The viscosities of the neutral fractions are at least two orders of magnitude lower than parent asphalt viscosities measured at the same temperature and rate of shear. The neutral fractions have properties predicted by a model of asphalt structure, which postulates that polar, aromatic materials are dispersed in a less aromatic, nonpolar solvent phase The polar fractions are friable solids or tacky semisolids. Them polar fractions also have properties predicted for dispersed phases in the above mentioned model of asphalt structure. They are more aromatic, contain larger percentages of heteroatoms, and are of higher molecular weight than neutral fractions. The polar fraction designated as the strong acid fraction is the most abundant an d most aromatic of the ion exchange chromatography polar fractions. and it also contains the largest concentration of polar functional groups     

ANALYSIS OF SHHP ASPHALT NONPOLAR FRACTIONS BY SUPERCRITICAL FLUID CHROMATOGRAPHY

ABSTRACT

Three different fractions derived from each of eight SHRP asphalts were analysed by means of supercritical fluid chromatography. The three fractions were a low molecular weight neutral fraction obtained by ion exchange chromatography, a low molecular weight fraction obtained by size exclusion chromatography, end maltenes obtained by precipitation with hydrocarbon solvents. For a given asphalt, these fractions contain much of the same material and all comprise over one-half of the bulk of the asphalts. The ion exchange chromatography neutral fractions contain minimal amounts of polar materials. Based on the microstructural model of asphalt structure, any one of the three fractions might be considered to represent the solvent phase of an asphalt.

The supercritical fluid chromatograms of the asphalt fractions showed that they comprise materials of widely ranging carbon numbers, from 30 to over 110. Chromatograms of all three fractions of each asphalt are similar, particularly the low molecular weight size exclusion chromatography fractions and the maltenes. Chromatograms of fractions derived from different asphalts can differ greatly. The chromatograms of fractions of sol-type asphalts exhibit peaks corresponding to constituents that are more aromatic and of higher carbon number compared with chromatograms of fractions of gel-type asphalts. Thus supercritical fluid chromatography is a useful tool for the investigation of relatively nonpolar fractions derived from asphalts     

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.     

SIZE EXCLUSION CHROMATOGRAPHY STUDIES OF AGED SHRP ASPHALTS

Abstract

One of Ihe objectives of the Strategic Highway Research Program is the development of a test procedure that accurately predicts pavement aging. In order to accomplish this goal, the nature and mechanism of oxidative-aging of asphalts must be known.

Eight asphalts were aged in a pressure-oxidation vessel at 60°C (140°F) and 2.07 x 10⁶ Pa (300 psi) for 144 hours (6 days) after a preliminary thin-film oven treatment. The tank asphalts and aged asphalts were separated by preparative size exclusion chromatography into two fractions: one consisting of large molecular size, associated molecules and the other consisting of smaller molecules with less tendency lo associate. The amount of the large molecular size fraction is greater in an aged asphalt compared with its parent tank asphalt. Number-average molecular weights of this large molecular size fraction increase substantially in some aged asphalts but not in others. Viscosities of smaller molecular size fractions (which comprise the bulk of both aged and unaged asphalts) of aged asphalts are not greatly different from viscosities of corresponding fractions of parent tank asphalts. Viscosities of the small molecular size fractions are much lower than viscosities of whole asphalts. Oxygen-containing functional groups were observed in both size exclusion chromatography fractions of all eight aged asphalts.

The above results can be rationalized by invoking a model of asphalt structure in which complex structural units composed of polar and/or aromatic molecules arc dispersed in a less polar solvent phase. The aping process causes buildup of more polar molecules, which increases the relative amounts of asphalt components that engage in associative behavior.     

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

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.     

ABSORPTION OF ASPHALT INTO POROUS AGGREGATES: TEST OF A SIMPLE PHYSICOCHEMICAL MODEL

Absorption is the process in which asphalt flows into a porous aggregate, under the driving force of capillary pressure. Asphalt absorption is of interest because it represents an economic loss of effective binder, and because it may change the properties of the resulting asphalt film and lead to premature pavement distress. Incorrect air voids estimation may also result from failure to properly account for asphalt absorption in pavement design. The objective of this research was to determine the temporal dependence of absorption upon asphalt and aggregate properties and to test a rational model for this dependence.

Absorption data were obtained for several model liquids and asphalts with synthetic alumina aggregates and a natural limestone aggregate. The data were used to test a simple absorption model incorporating the effects of asphalt and aggregate properties into a single dimensionless time variable.

While quantitative agreement was not obtained in all aspects of the model, certain predictions of the model were verified. The general shape of the absorption data followed the model prediction for synthetic alumina spheres. The effect of viscosity and surface tension was correlated fairly well by the surface tension/virosity factor in the dimensionless time variable

The use of the dimensionless time variable was able to reduce the time span for absorption from ca. four order of magnitude to only ca. one order of magnitude; although, there remained a significant variation in some of the absorption data, probably caused by differences in the contact angles for the various Liquids.

The absorption behavior with a natural Iowa limestone did not follow the shape of the theoretical curve predicted by the model. This deviation is thought to be c a d by the presence of air in the pores coupled with the large and polydisperse pore size of this aggregate     

PREPARATIVE SIZE-EXCLUSION CHROMATOGRAPHY SEPARATION OF SHRP ASPHALTS: CORRELATION WITH YISCOELASTIC PROPERTIES

ABSTRACT

Eight core asphalts and eleven other asphalts selected for study in the Strategic Highway Research Program have been separated into two or more fractions by means of preparative size-exclusion chromatography. The first fraction obtained by this technique is believed to consist of materials that form associations and correspond roughly to asphalt dispersed phases. This phase is polar, aromatic, and of high apparent molecular weight. Subsequent fractions obtained by size exclusion chromatography of the asphalts are of progressively lower molecular weight. When the asphalts were separated into nine fractions, the weights of each fraction were plotted versus elution volume to give distinctive bimodal chromatograms, with one exception.

The first eluted size exclusion fractions consist of the major viscosity-building components of the asphalts. When these fractions are removed from asphalts, the weight fractions of the residual materials correlate with tan δ (ratio of viscous to elastic moduli)s of the whole asphalts at 26° (77°F). Gel-type asphalts have low values of tan δ and large amounts of material in their initially eluted size-exclusion chromatography fractions. For sol-type asphalts, the reverse is true. For the nineteen asphalts studied size-exclusion chromatography fractionation patterns, which are a fundamental chemical property, correlate with the aforementioned fundamental physical property     

STUDIES ON LARGE CRUDE OIL ALKANES. II. ISOLATION AND CHARACTERIZATION OF AROMATIC WAXES AND WAXY ASPHALTENES.

Isolation of very large alkane components as described in the first paper within this series, fail in some cases. This work describes two non-routine isolation procedures applied to two different non-typical petroleum fractions. The first one comprises a chromatographic approach applied for the separation of alkanes from alkylaromatic compounds derived from paving asphalt waxes. The second separation procedure was developed for the isolation of alkane fractions associated with asphaltenes that precipitated during long crude oil storage periods, resulting in highly insoluble organic composites

In the first case, the isolated fractions were characterized by spectroscopic and chromatographic methods. The evidence showed that long chain naphtheno-aromatic molecules behave like waxy asphalt components, which interact by unusual mechanisms with solid sorbents. Their chromatographic behavior was found to be between typical alkanes and typical aromatics. This behavior is caused by the simultaneous presence of three functionalities

The second sample type was characterized by spectroscopic methods only. The results permitted to assess that the waxy composite from crude oil tank sediments precipitated selectively, including highly aromatic and long alkyl chain asphaltenes as well as very large n-alkanes.     

THE EFFECT OF MATTALOPORHYRINS ON ASPHALT OXIDATION. II. THE EFFECT OF VANADYL CHELATES FOUND IN PETROLEUM

Four selected asphalts were blended with zero to five wt. percent of fractions rich in vamady cheltes prepared from two crude oils. The mixture was -coated in a teflon -support, and the whole was heated in an oven at. 113±2°C for 24 hours. The mixture then was analyzed for increases ketone, acid and anhydride functions.

in general, functions rich in vanady ponphyrims tended to promote asphalt oxidation, particularly as measured by increase in kentones. Corelation of vanadyl ponphyrim concentration with asphalt oxidation is observed to the direct only if asphalts are mixed with varying amounts of the same fraction derived from the same crude Possible reasons for this phenomenon are discussed in terms of oxidation susceptibility of aspha1ts, the importance of molecular associations, and the relative catalytic activities of metallaporphyrins and other metal chelates     

THE SOLVENT EXTRACTION APPROACH TO PETROLEUM DEMETALLATION

Metals are present in petroleum depending on age and conditions of diagenesis, and concentrate during refining in heavy fractions and residua. Nickel and vanadium show particularly deleterious effects on catalysts, such as poisoning, excessive gas and coke formation. Besides, removing vanadium from fuel oils reduces the environmental impact of “acid rain” due to the oxidation of sulphur dioxide in the atmosphere.

In this paper, research and industrial practice literature concerning the removal. of nickel and vanadium from petroleum and its fractions by solvent extraction and related techniques is reviewed and arranged into four groups as follows:

i) Processes employing hydrocarbon solvents, used to modify the oily matrix solubility parameter in such a way that asphalt/enes be separated. Because a fraction of total metals present are associated to asphalt/enes, deasphaltation implies partial demetallation.

ii) Processes using polar solvents, scarcely miscible with petroleum and able to selectively extract from it metallic complexes of heteroatomic ligands (e.g. metalloporphyri ns).

iii) Processes not based on molecular phase equilibria like i) and ii) but on the formation, by contact with aqueous solutions, of a separate, colloidally stabilized phase. Either surface active agents are added or the surface activity of substances naturally occurring in petroleum is promoted.

iv) Processes based on extraction with chemical reaction (oxidation, chelation) orion exchange between organometallic species in petroleum and ligandsin solution of non-miscibile media.     

DEASPHALTING AND CHARACTERIZATION OF A SYNCRUDE OBTAINED BY DIRECT LIQUEFACTION OF A SPANISH SUBBITUMINOUS COAL

A synciude obtained by direct liquefaction of a Spanish subbituminous coal was deasphalted as a previous step of upgrading lo get a better feedstock for further processing.

Deasphalting was carried out by ultrasonic extraction with n-hexane. Raw and deasphalted coal syncmdes have been fractionated into six fractions by an extrographic procedure that utilizes six eluents of increasing polarity. Each fraction has been analyzed by FTIR, gas chromatography. GC-MS and high resolution mass spectrometry.

Deasphalting removed 36 % of nitrogen, 44 % of sulphur and 47 % of oxygen. Nevertheless, the deasphalted liquids would require further removal of hetenatoms by hydroprocessing.

Polynuclear aromatic compounds appeared in all extrografic fractions. Nimgen-containing compounds have been found in the fractions In, IV and V, when polar solvents have been used. Some mixed heterocyclic compounds (N-0, N-S) have been observed in the most polar fractions (V and VI).     

ASPHALT DURABILITY: FROM LABORATORY TEST TO FIELD IMPLEMENTATION

Spray and chip seals are the most important form of road surfacings in Australia. The long term hardening of the asphalt binder (its durability) is of critical importance in determining their life. The Australian Road Research Board (ARRB) Durability Test measures the intrinsic resistance of an asphalt cement to oxidative hardening and has been used in specifications for many years. A model which allows calculation of the rate of asphalt hardening in a sprayed seal has already been presented. It is based on data from road trials monitored for up to 15 years.

A second model now permits calculation of the viscosity level at which seal distress occurs in a particular climatic area. By using the combined models it is possible to predict surfacing life. The parameters required for the calculation are the average temperature at the site and the asphalt Durability Test result.

Application of the models to sites; in the U.S. suggests that, if seal lives comparable to those in Australia are to be achieved, it may be necessary to control asphalt durability in the southern part of the U.S. In temperate climate areas only moderately durable asphalts may be necessary. Climatic conditions in the north of the U.S. and in Canada are outside the range of the model but it is clear that binder hardening proceeds at a very slow rate in these regions. Asphalt durability may not be a critical factor in surfacing life in these areas.

The situation for hot mixed a.c. is much more complex than for sprayed seals but the trends; in seal life indicated by the models may provide a guide to a.c. behaviour     

CHARACTERIZATION OF HEAVY RESIDUA BY APPLICATION OF A MODIFIED D 2007 AND ASPHALTENE SEPARATION: EFFECT OF SOLVENTS ON PHYSICAL AND CHEMICAL PROPERTIES OF FRACTIONS DERIVED FROM HONDO 850°F RESIDOOM

Hondo 850 ^°F residuum was separated into saturate, aromatic, resin, and asphaltene fractions by a modified D 2007 and asphaltene separation. Two different asphaltene precipitation solvents were used — isooctane and heptane — and differences in selected physical and chemical properties of the derived fractions were compared.

The principal difference in the use of the two solvents was weight recovery after the separation. Isooctane yielded good recovery, while heptane exhibited poor recovery. Isooctane precipitated substantially more asphaltenes, as predicted from the solubility parameters of the two solvents.

The metals concentrations in the fractions were comparable for each solvent — no metals in the saturate and aromatic fractions, approximately 300 and 1500 ppm Ni + V in the resin and asphaltene fractions respectively. The relative distribution was also similar for both solvents, with the highest percentage coming from the asphaltenes.     

PYROLYSIS AND LIQUEFACTION OF BRAZILIAN COAL AND COAL-DERIVED ASPHALTENES

The present work describes a study of the liquefaction and pyrolysis of a Southern Brazilian mineral coal and its derived asphaltenes, using conversion systems developed in our laboratory.

The results show that significant quantities of the intermediate polarity fraction named resins is obtained through the pyrolysis of coal, while after the liquefaction process higher quantities of the higher fractions was found. A model is proposed to explain the liquefaction and pyrolysis processes of both coal and coal-derived asphaltenes.     

VISCOSITY AND SOLUBILITY OF MIXTURES OF BITUMEN AND SOLVENT

The solubilities of three bitumen samples (Suncor, Syncrude and Lloydminster) in five solvents were examined and prediction on the various bitumen-solvent mixture viscosities were made with Cragoe equation. By calculating the Cragoe constant 'a' for each mixture and using the average value in the Cragoe equation the prediction accuracy of the equation was improved by over 60%. Bitumen-naphtha mixtures showed the best viscosity prediction characteristics.

The solubility of the asphaltenes in the bitumen was highest in toluene among the five solvents However, naphtha, showed a moderate solvating power, which negligibly varied over the range of composition studied. Therefore naphtha, a solvent derived from bitumen was recommended as the most appropriate solvent for reducing the viscosity bitumen.     

EVALUATION OF AN EASTERN SHALE OIL RESIDUE AS AN ASPHALT ADDITIVE

An evaluation of eastern shale oil (ESO) residue as an asphalt additive to reduce oxidative age-hardening and moisture susceptibility was conducted. The ESO residue, having a viscosity of 23.9 Pa"s at 60°C (140°F) was blended with three different petroleum-derived asphalts, AAD-1, AAK-1, and AAM-1, that are known to be very susceptible to oxidative aging. Rheological and infrared analyses of the unaged and aged asphalts and the blends were then conducted to evaluate oxidative age-hardening. In addition, the petroleum-derived asphalts and the blends were coated onto three different aggregates, Lithonia granite (RA) a low-absorption limestone (RD) and a silicious Gulf Coast gravel (RL) and compacted into briquets. Successive freeze-thaw cycling was then conducted to evaluate the moisture susceptibility of the prepared briquets. The abbreviations used above for the asphalts and the aggregates are part of the Strategic Highway Research Program nomenclature.

The rheological analyses of the unaged petroleum-derived asphalts and their respective blends indicate that the samples satisfy the rutting requirement. However, the aging indexes for the RTFO-aged and RTFO/PAV-aged samples indicate that the blends are stiffer than the petroleum-derived asphalts. This means that when in service the blends will be more prone to pavement embrittlement and fatigue cracking than the petroleum-derived asphalts. Infrared analyses were also conducted on the three petroleum-derived asphalts and the blends before and after RTFO/PAV aging.     

REACTION OF PHOSPHORIC ACID WITH THERMAL RESIDUES AND BITUMENS

The purpose of the work was to study the effect of the addition of small quantities of phosphoric acid (or P₂O₅), on the physical and chemical behaviour of petroleum residues and bitumens.

Phosphoric acid (and P₂O₅) reacts only with thermal products such as visbreaker (VB) residues and bitumens, and do not react with straight run (SR) products.

The unstable constituents of VB residues, i.e. carbonaceous material and part of the asphaltenes, contain significant amounts of free radicals which easily share electrons with phosphorous.

The resulting condensed particles are higher molecular wighht, polar material no longher soluble in the bitumen, and flocculate.

This reaction confirms the presence of stable free radicals in thermal bitumens and residues, suggests a way to neutralize their destabilizing effect.     

SIMULATED DISTILLATION BY TRERMO GRAVIMETRIC MEASUREMENTS APPLIED TO THERMAL CRACKING AND THERMAL HYDROCRACKING

A suitable correlation can be made to represent the simulated distillation of heavy oils starting from thennoaravimetric measurements. This method is applicable to hydrocarbons having an initial boiling point equal or greater than 200°C.

The simulated thermogravimetric distillation fit was obtained from experiments with the standard compounds obtained from ASTM D-2887-83 (Boiling range distribution of petroleum fractions by gas chromatography). This method is simple, fast and without problems when applied to heavy feedstocks

The data were used in the determination of average boiling temperatures of products from thermal cracking and thermal hydrocracking. It was also possible to quantify coke yields

Average relative molecular masses of products from the above processes correlated well with the average boiling point temperatures. It indicates that, with respect to the hydrocarbon types, thermal cracking is not selective in comparison with thermal hydrocracking

The equation applied to find the average boiling temperature is following: T = (1/al) (Ttg-a2). T is the boiling temperature, al and a2 are the correction factors, Ttg is the thermogravimetric temperature.