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     

ADSORPTION OF ASPHALTS AND THEIR SIZE EXCLUSION CHROMATOGRAPHY FRACTIONS ON AGGREGATE SURFACES

The adsorption behavior of two asphalts and their size exclusion chromatography (SEC) fractions from toluene solution onto aggregate was investigated. The effect of the differences in chemistry and molecular size of the asphalt samples on their adsorption behavior on silica, granite and greywacke was determined. The adsorption of asphalts and SEC fractions on SI-1000 silica was well-represented by the Toth model, while the Radke-Prausnitz model better described their adsorption behavior on both granite and greywacke. Combining the adsorption models with the Gibbs adsorption equation of state gave the spreading pressure of each adsorbate species adsorbed on the aggregate surfaces. The spreading pressure predicted the competitive adsorptive edge of the asphalt fractions. The SEC I fractions, containing molecules of larger molecular size and higher heteroatom contents, showed higher spreading pressures than the SEC II fractions, which contained molecules of smaller molecular size and fewer heteroatoms. The asphalts yielded intermediate spreading pressures for SI-1000 silica and granite, but they gave the highest spreading pressure values for greywacke.     

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.     

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.     

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     

ANALYSIS OF RESIDUUM DEMETALATION BY SIZE EXCLUSION CHROMATOGRAPHY WITH ELEMENT SPECIFIC DETECTION

ABSTRACT

We analyzed thermally treated heavy residua by element specific size exclusion chromatography (SEC-ICF) to elucidate the fate of the V and Ni compounds. Thermal treatment, in addition to removing metals, significantly reduces the size of the remaining metal-containing compounds.We thermally treated the distillable and nondistillable metals separately. The distilled metals, primarily petroporphyrins, were completely removed under moderate conditions. The non-volatile metal-containing components, which constituted most of the Ni and V, were either removed, or reduced in size.when treating heavy residua over commercial fixed-bed hydroprocessing catalysts, the metal-containing molecules in the size range of the catalyst pore are preferentially removed. Those larger than the pore size appear to demetalate more slowly.The results argue demetalation is a function of the ligand structure and size of the metal-containing species and not necessarily the coordination sphere around the metal center.     

ANALYSIS OF RESIDUUM DEMETALATION BY SIZE EXCLUSION CHROMATOGRAPHY WITH ELEMENT SPECIFIC DETECTION

We analyzed thermally treated heavy residua by element specific size exclusion chromatography (SEC-ICF) to elucidate the fate of the V and Ni compounds. Thermal treatment, in addition to removing metals, significantly reduces the size of the remaining metal-containing compounds.We thermally treated the distillable and nondistillable metals separately. The distilled metals, primarily petroporphyrins, were completely removed under moderate conditions. The non-volatile metal-containing components, which constituted most of the Ni and V, were either removed, or reduced in size.when treating heavy residua over commercial fixed-bed hydroprocessing catalysts, the metal-containing molecules in the size range of the catalyst pore are preferentially removed. Those larger than the pore size appear to demetalate more slowly.The results argue demetalation is a function of the ligand structure and size of the metal-containing species and not necessarily the coordination sphere around the metal center.     

COMPARISON OF OXIDATION OF SHRP ASPHALTS BY TWO DIFFERENT METHODS

An objective of the Strategic Highway Research Program is the development of a test procedure that accurately predicts changes in asphalt pavement properties with aging. Many of the methods now in use do not give reliable results. It is desirable to develop a method that takes into account maximum temperatures to which asphalts are subjected in mix plants (about l60°C or 320°F) and during service (60° C or 140°F), but is not impractically long. Therefore, test conditions must involve increased temperature, pressure, or the addition of a chemical accelerant but yield artificially aged materials that have certain properties similar to those of aged pavement binders.|In this study, rheological and chemical properties of asphalts subjected to thin-film oven followed by pressure vessel oxidation under two sets of conditions were compared with properties of asphalts aged in the thin-film accelerated-aging test at two temperatures. Oxidations of asphalts for 144 hours (6 days) at 60°C (I40°F) and 2.07 × 10⁶ Pa pressure following a standard thin-film oven treatment yielded products having characteristic aging indices and enhanced sulfoxide and carbonyl absorbances in their infrared spectra. Oxidation of asphalts under thin-film accelerated-aging lest conditions at 85°C (185°F) for 144 hours provides aged asphalts with rheological properties similar to those obtained from the 60°C (140°F) pressure oxidations. When the pressure oxidation was run at 80°C (176°F) for 144 hours. materials were obtained that were more extensively aged. The aging indices of these materials were somewhat similar to asphalts oxidized for 72 hours at 113°C (235.4°F) under thin-film accelerated-aging test conditions. The aging lendencies of the eight asphalts tested were ranked by the two latter methods in approxmiately the same order.|The thin-film accelerated-aging test procedures are readily performed in a standard oven. but utilize smaller samples (resulting in less material for subsequent analysis) than the pressure oxidations. It is not certain that the mechanism or kinetics of the asphalt oxidations in the higher temperature oven procedures are identical to the mechanisms of oxidation of asphalts in pressure aging. The procedures used in this study, although not themselves definitive test conditions for asphalt-binder aging. should aid in the selection of conditions for an improved aging lest.     

高效分子排阻色谱法测定化学驱油体系中的部分水解聚丙烯酰胺

介绍了用分子排阻色谱技术定量测定化学驱油体系中的部分水解聚丙烯酰胺（ＰＩＩＰＡ）的方法。该方法以ＳＩ－２００二羟基键合相为固定相，以甲醇／０．０５ｍｏｌ／ｌ的ＮａＩＩ２ＰＯ４（体比４０／６０）为流动相，使用ＵＶ检测器在２１３ｎｍ处检测。表面活性剂／聚合物驱油液中所有组分对ＰＩＩＰＡ的测定均无干扰。吸附试验证明测定可靠性好。最低检测浓度为１μｇ／ｍｌ。回收率为９７．３％－１００．５％。     

ANALYSIS OF RESIDUUM DESULFURIZATION BY SIZE EXCLUSION CHROMATOGRAPHY WITH ELEMENT SPECIFIC DETECTION. PART II

Heavy crude residua are analyzed by size exclusion chromatography with elementspecime aerecua(SECIP), to elucidate structural information about the S-contacining compounds. These compounds appear to fall into two categories those which are 1)moderately samll componetis (probablly thiophenid), and ) large components associated with apparent precursors offaphaltense.The effects of thermal hvdretDrocessine on the S-containine eemoounds were also examined. High and moderate thermal seventy appear to, in addition to removing S: 1) remove the larger S-containing compounds, 2) shift the total S profile to smaller molecular size, and 3) form S-containing compounds not existent in the feed. Low thermal severity appears to only partially remove the larger S-containing compounds. These results indicate the S-containing compounds behave similarly to the metal-containing compounds under the same processing conditions, Possible binding site relationships between some of the S- and metal-containing compounds in heavy crudes and residua are discussed. We observed S and V correlations in both feeds and products, suggesting a relationship between the S and V at the molecular level.     

SIZE EXCLUSION CHROMATOGRAPHY AND VAPOR PRESSURE OSMOMETRY IN THE DETERMINATION OF ASPHALTENE MOLECULAR WEIGHT.

Abstract

The problem concerning the determination of asphaltene molecular weight has been critically investigated. A size exclusion chromatography (SEC) analytical method has been developed using innovative calibration standards. The obtained results have been compared with those derived from vapor pressure osmometry (VPO). All the experimental data indicate that the number-average molecular weights (Mn) determined either by SEC or VPO are always different Nevertheless such discrepancies are less pronounced using the new calibration curve instead of either the conventional polystyrene standards or other polymers such as poly(ethylene glycol). Furthermore it has been observed that VPO measurements, considered to give the most reliable Mn values when performed in a highly dissociating solvent, at high temperature and low concentration, fails when strong interactions among single molecules are present.

SEC and VPO have also been employed to study association phenomena undergone by asphaltenes in solution. A correlation between molecular structure and degree of aggregation has been recognized indicating that aromaticity is primarily responsible for the importance of the observed intermolecular associations.     

SIZE EXCLUSION CHROMATOGRAPHY AND VAPOR PRESSURE OSMOMETRY IN THE DETERMINATION OF ASPHALTENE MOLECULAR WEIGHT.

The problem concerning the determination of asphaltene molecular weight has been critically investigated. A size exclusion chromatography (SEC) analytical method has been developed using innovative calibration standards. The obtained results have been compared with those derived from vapor pressure osmometry (VPO). All the experimental data indicate that the number-average molecular weights (Mn) determined either by SEC or VPO are always different Nevertheless such discrepancies are less pronounced using the new calibration curve instead of either the conventional polystyrene standards or other polymers such as poly(ethylene glycol). Furthermore it has been observed that VPO measurements, considered to give the most reliable Mn values when performed in a highly dissociating solvent, at high temperature and low concentration, fails when strong interactions among single molecules are present.

SEC and VPO have also been employed to study association phenomena undergone by asphaltenes in solution. A correlation between molecular structure and degree of aggregation has been recognized indicating that aromaticity is primarily responsible for the importance of the observed intermolecular associations.     

CHARACTERIZATION OF NICKEL AND VANADIUM COMPOUNDS IN TAR SAND BITUMEN BY UV-VIS SPECTROSCOPY AND SIZE EXCLUSION CHROMATOGRAPHY COUPLED WITH ELEMENT SPECIFIC DETECTION

ABSTRACT

Previously, we have examined the Ni and V in heavy crude oils, residua, and processed products by several metal speciation techniques to ascertain molecular structure and processing behavior. Two classes of metal compounds were found -metallopetroporphyrins and metallo-nonporphyrins - each having unique reactivity during processing. In efforts to better understand the binding of metals in the oil medium, we have now examined Ni and V in tar sand bitumens, the bitumen was solvent extracted from the sand matrix and was separated by column chromatography and the petro-porphyrin content was quantitated by UV-vis spectroscopy. The petroporphyrin contents ranged from virtually none to over 36% of the total metals. Asphalt Ridge (Utah) has primarily Ni petroporphyrins; Big Clifty (Kentucky) and Athabasca (Canada) have primarily V petroporphyrins; Arroyo Grande and McKittrick (California) have roughly equal amounts of both types; and Surmyside (Utah) has virtually none of either.

Size characteristic profiles (SEC-ICP) were generated for the extracted bitumens. The profiles are generally bimodal in shape and resemble several different specific heavy crude oils and residua. For examples, Arroyo Grande and McKittrick appear to be similar to Kern River (California) 650°F+ residuum, while Athabasca resembles Morichal (Venezuela) 650°F+ residuum.     

STUDIES ON NIGERIAN CRUDES 3. ANALYSIS OF SULFURIZED ASPHALTS

The residual asphalts obtained from three Nigerian medium crudes were chemically treated with elemental sulfur at 210 to 250°C. The course of the reaction was followed by monitoring the growth of the asphaltene content of the products. The sulfurization reaction led to 5- to 10-fold increases in the asphaltene content of the products. The asphaltene content of one of the samples initially increased with temperature from 210 to 240°C and then dropped sharply. The results obtained revealed that the optimum temperature of the sulfurization reaction was 240°C. It was also observed that the lower the asphaltene content of the untreated asphalt, the higher the growth of the asphaltene content of the product at the same reaction temperature. The absolute viscosity of the sulfurized asphalts increased rapidly with increasing temperature of reaction.     

STUDIES ON NIGERIAN CRUDES 3. ANALYSIS OF SULFURIZED ASPHALTS

ABSTRACT

The residual asphalts obtained from three Nigerian medium crudes were chemically treated with elemental sulfur at 210 to 250°C. The course of the reaction was followed by monitoring the growth of the asphaltene content of the products. The sulfurization reaction led to 5- to 10-fold increases in the asphaltene content of the products. The asphaltene content of one of the samples initially increased with temperature from 210 to 240°C and then dropped sharply. The results obtained revealed that the optimum temperature of the sulfurization reaction was 240°C. It was also observed that the lower the asphaltene content of the untreated asphalt, the higher the growth of the asphaltene content of the product at the same reaction temperature. The absolute viscosity of the sulfurized asphalts increased rapidly with increasing temperature of reaction.     

13C NMR STUDIES ON ROADWAY ASPHALTS

Roadway asphalt has been characterized by ¹³C NMR and reasonable chemical shift assignments made. An initial analysis of the asphalt samples from the refinery liquid, plant mix. Initial and 18 month cores has been made; however, these roadways have not aged sufficiently to develop correlations with performance.     

13C NMR STUDIES ON ROADWAY ASPHALTS

ABSTRACT

Roadway asphalt has been characterized by ¹³C NMR and reasonable chemical shift assignments made. An initial analysis of the asphalt samples from the refinery liquid, plant mix. Initial and 18 month cores has been made; however, these roadways have not aged sufficiently to develop correlations with performance.     

CARBON-13 MOLECULAR STRUCTURE PARAMETERS OF RTFOT AGED ASPHALTS: THREE PROPOSED MECHANISMS FOR AROMATIZATION.

ABSTRACT

The determination of average molecular structural parameters of asphalts represents an important step in describing their skeleton. Using a new method based only on the analysis of carbon-13 nuclear magnetic resonance measurements, the average molecular parameters were determined for three asphalts before and after Rolling Thin Film Oven Test aging. From the analysis of the changes in the parameters, three mechanisms are proposed to explain the aromatization process in asphalts during oxidation.     

CARBON-13 MOLECULAR STRUCTURE PARAMETERS OF RTFOT AGED ASPHALTS: THREE PROPOSED MECHANISMS FOR AROMATIZATION.

The determination of average molecular structural parameters of asphalts represents an important step in describing their skeleton. Using a new method based only on the analysis of carbon-13 nuclear magnetic resonance measurements, the average molecular parameters were determined for three asphalts before and after Rolling Thin Film Oven Test aging. From the analysis of the changes in the parameters, three mechanisms are proposed to explain the aromatization process in asphalts during oxidation.