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     

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.     

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.     

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     

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.     

POLARITIES OF SHRP ASPHALTS CALCULATED FROM ION EXCHANGE CHROMATOGRAPHY SEPARATION DATA

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.     

CHARACTERIZATION OF VANADIUM COMPOUNDS IN SELECTED CRUDES I. PORPHYRIN AND NON-PORPHYRIN SEPARATION

ABSTRACT

We have applied size-exclusion chromatography (SEC-HPLC) and reversed-phase chromatography (RP-HPLC), with element specific detection, [Inductively coupled and direct current plasma atomic emission spectroscopy (ICP and DCP)], to selected crude oils –– Boscan, Beta, Morichal, Arabian Heavy, and Maya –– and their separated fractions. By these procedures, we have further characterized both the V porphyrin and the V non-porphyrin compounds.

From the SEC-HPLC-ICP profiles of the heavy crude oils we found the V compounds generally have a bimodal distribution, with maxima at approx. 800 and 9000 polystyrene equivalent (PS) molecular weight (MW). Arabian Heavy, though, had relatively few of the small V compounds.

The crude oils were separated into porphyrin and non-porphyrin fractions by methanol extraction. From the SEC-HPLC-ICP profiles of the porphyrin fraction, we Identified and quantitated the maximum at approx. MW 800 (PS) as being V porphyrins. The remaining V compounds are non-porphyrin.     

VARIATION OF FREE RADICAL CONCENTRATION WITH MOLECULAR WEIGHT IN PETROLEUM FEEDSTOCKS

ABSTRACT

Two petroleum residua were studied, one of Mid-Eastern original and the other of Chinese origin. These residua were separated into fractions using preparative size-exclusion chromatography (SEC). Room temperature electron spin resonance (ESR) experiments of SEC separated petroleum-derived fractions are described. A variation of free radical concentration with different molecular weight fractions was observed. Significant increase in free radical concentration was observed in the 1000-2500 amu range. This is in the molecular weight range postulated to be necessary for formation of the mesophase state observed in carbonaceous pitches during conversion to coke and carbon by thermal treatment.     

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.     

EFFECTS OF ASPHALTENE PRECIPITATION AND REPRECIPTION ON THE METAL-CONTAINING COMPOUNDS IN HEAVY RESIDUA

ABSTRACT

Boscan vacuum residuum (VR) has been separated into isooctane insoluble asphaltenes and isooctane soluble maltenes. The asphaltenes were dissolved in a minimum of toluene and were further separated by two additional reprecipitations using isooctane as the precipitating solvent. We examined the fractions, including the recovered isooctane soluble material, by size exclusion chromatography (SEC) with inductively coupled plasma (ICP) emission spectroscopy to determine the effects, if any, the reprecipitations have on the size distribution of the metal-containing compounds.

The asphaltene fractions show little change in size upon reprecipitation, but removal of a small amount of the metal components does occur. The first reprecipitation produces isooctane soluble material which is very similar in size to the original maltene fraction. However, the second reprecipitation removes small amounts of material in the size range of the asphaltenes. When the amounts were weight balanced, the resulting separation did little to effect the overall maltene and asphaltene size profiles.     

NMR Characterization of Size Exclusion Chromatographic Fractions from Asphalt

Abstract

Size exclusion chromatography was used to separate an asphalt into nine fractions, and these fractions were then investigated by ¹H and ¹³C NMR. From the integration of the spectra, various molecular structural parameters were calculated. The aromatic carbon to nitrogen and the aromatic carbon to sulfur ratios were determined for six of the fractions. The catenation (linear and circular) of the aromatic ring structure was determined for six fractions. It appears that circular catenation is more probable for the high molecular weight fraction. For the lower molecular weight fraction, both linear and circular catenation are equally probable.     

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.     

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

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.     

EFFECTS OF ASPHALTENE PRECIPITATION AND A MODIFIED D 2007 SEPARATION ON THE MOLECULAR SIZE OF VANADIUM-AND NICKEL-CONTAINING COMPOUNDS IN HEAVY RESIDUA

ABSTRACT

Boscan vacuum residuum (VR), and Maya atmospheric residuum (AR), were separated into operationally defined components by an isooctane asphaltene precipitation followed by a modified D 2007-80 separation of the isooctane soluble material. These collected fractions were examined by size exclusion chromatography (SEC) with element specific detection employing inductively coupled plasma emission spectroscopy (ICP) to investigate the effect the separation has on the the V and Ni compounds. The V and Ni SEC-ICP profiles of the asphaltene fractions indicated some of the metal-containing molecules are substantially larger in size than those observed in the residua. The asphaltene precipitation appears to cause an increase in molecular size through agglomeration of smaller constituents, and accomplishes only limited size separation of the metal-containing compounds.

The resin fraction, the polar fraction obtained by modified D 2007-80 chromatography of the isooctane soluble portion, contained much of the smaller size molecules of the feeds. The agglomeration seen in the SEC-ICP profiles of the asphaltene fraction was not apparent in any of the resin fraction profiles.     

CHROMATOGRAPHIC ISOLATION OF NITROGEN-CONTAINING COMPOUNDS IN LIQUID FUELS 1 Ti(IV) OXIDE GRAFTED ONTO SILICA AS STATIONARY PHASE

Abstract

The present work describes a novel method for the isolation of the neutral N-containing fraction from crude oil using column liquid chromatography on silica gel chemically modified with Ti(IV) oxide using a grafting method. The crude oil sample is introduced onto the column and eluted with a proper sequence of eluents. The first eluted fraction contains only hydrocarbons. The N-containing compounds are eluted in a isolated fraction. Both fractions are collected, concentrated and analyzed using HRGC with NPD detection. The method is shown to be very selective for the isolation of the neutral N-containing fractions from crude oil.     

CHROMATOGRAPHIC ISOLATION OF NITROGEN - CONTAINING COMPOUNDS IN LIQUID FUELS 2. THERMALLY TREATED SILICA GEL AS STATIONARY PHASE

Abstract

In the present work we describe a novel method for the isolation of the neutral N-containing fraction from crude oil by preparative liquid chromatography using thermally treated silica gel as stationary phase. The hydrocarbons are eluted in the first two fractions and the nitrogen compounds in the third fraction. The collected fractions are analyzed by HRGC-NPD. The method is shown to be very selective for the isolation of nitrogen compounds from the neutral fractions of crude oil.     

Characterization of Thermally Degraded Asphaltene Fractions Using Gel Permeation Chromatography

Abstract

Petroleum asphaltene goes through three stages of mass reduction under thermogravimetric analysis from 25°C to 1,000°C at a heating rate of 1°C/min. The products from thermal degradation of asphaltene at three different temperature intervals are collected. Two residual fractions left in the sample cup are also obtained at two specific temperatures. The collected fractions and the residual fractions are characterized using gel permeation chromatography. The fraction collected between 25°C and 350°C demonstrates similar molecular weight distribution to that collected between 350°C and 450°C, with both fractions showing a typical molecular weight distribution for polymeric material. The fraction collected between 450°C and 650°C illustrates three different molecular weight distributions. The chromatogram of the residual fraction obtained at 350°C resembles that of the undegraded asphaltene. The residual fraction obtained at 450°C also demonstrates three different molecular weight distributions. The experimental data indicate that the mass reduction of asphaltene heated from 25°C to 350°C is mainly due to the evaporation of low boiling point and/or low molecular weight substances in asphaltene. Thermal decomposition and coke production occur significantly in the 350°C–450°C temperature interval. Thermal degradation continues to finish until 650°C.     

LIQUEFACTION AND THE CHARACTERIZATION OF COAL DERIVED LIQUIDS OF MENGEN LIGNITE

ABSTRACT

The liquefaction characteristics of Mengen lignite has been investigated in the presence of cobalt-molybdenum on alumina catalyst in a 1 lt batch autoclave system with anthracene oil used as solvent. The experiments were carried out in the range of 15–60 atm for initial hydrogen pressure, 360–440°C for reaction temperature, 1–5 for solvent to coal ratio and 0–20% of coal for catalyst loading which were chosen as process variables. Coal particle size and reaction time were kept constant as below 200 mesh and 30 minutes respectively, (Erdem 1987)

The product was analyzed in terms of total conversion, liquid yield and liquid product distribution determined as preasphaltenes, asphaltenes and oils. The oil fraction was further separated by column chromatography while the asphaltenes were separated into basic and acid/neutral fractions. The preasphaltenes were divided into two fractions as carbene (CS₂ solubles) and carboid (CS₂ insolubles). (Inanç 1989)

The oil yield is mostly affected by the catalyst loading which shows to a certain extent that the conversion of asphaltenes to oils is a catalytic step. The selected process variables showed a positive trend with respect to the yield of hexane eluted oil which is the desired product of liquefaction.     

COMPOSITIONAL ANALYSIS OF A VACUUM RESIDUE

ABSTRACT

A sample of vacuum residue (VR) was evaluated for its physical and chemical properties. The VR was separated into sixteen fractions according to molecular size distribution on preparative gel permeation chromatography (GPC) columns. Elemental analysis including heteroatoms (N, S) and metal (Ni, V) was carried out on fractions 1 through 9. Molecular weight distribution and number average molecular weight (M¯n) were obtained by analytical GPC for fractions 1 through 11. Forty percent of the VR contains high molecular weight materials (i.e., materials with molecular weights ranging from 1170 to 3920) and 64.3% total vanadium, 62.5% total nickel, 34.1% total sulphur, and 41.6% total nitrogen.