Evaluation of Asphalt Aging Using Multivariate Analysis Applied to Saturates, Aromatics, Resins, and Asphaltene Determinator Data.

Asphalt is subjected to aging, leading to physical and chemical modifications reducing its performance. Recently, the Western Research Institute developed the SAR-AD method that allowed the separation of asphalt into eight fractions (saturates, aromatics 1, aromatics 2, aromatics 3, resins, asphaltenes 1, asphaltene 2, and asphaltenes 3). In this work, this analytical method was used to study asphalt aging processes in greater detail. Several asphalts of different origins and reconstituted blends were studied. These products were aged during several durations using a PAV (pressure aging vessel) between 0 and 48 h to collect information on the evolution of each SAR-AD fraction. Different evolutions were observed according to the initial asphalt composition and SAR-AD fraction studied. The saturated subfamily seemed to be slightly impacted by aging. The amount of three aromatic subfamilies decreased with a larger decrease of aromatics 3 than aromatics 2, itself larger than aromatics 1. The content of the resin subfamily increased after 48 h of PAV aging. The asphaltene 1 and asphaltene 2 subfamilies exhibited an increasing trend. Moreover, the quantity of asphaltenes 2 created seemed to correlate to the initial asphaltene content. The evolutions of the asphaltene 3 subfamily were not significant. However, a specific behavior was highlighted for the most asphaltenic sample. For this specific sample, the increase of resin content was weaker, the mass of asphaltenes 1 decreased, and the amount of asphaltenes 3 increased during aging. Given the large amount of data generated, an original approach was developed to statistically identify the most affected SAR-AD subfamily and determine correlations among them. Two PCAs (Principal Component Analysis) were conducted on asphalt SAR-AD data. This statistical analysis indicated two generic asphalt aging pathways. The first aging pathway could be the conversion of aromatics 2 into resins, with no evidence that resins could contribute to asphaltene creation. The second aging pathway showed the conversion of aromatics 3 directly into asphaltenes 2. These two aging pathways highlighted that the conversion of molecules in more polar ones during aging could skip SAR-AD subfamilies, meaning that asphaltenes could be created without involving resins.

Investigation of Oxidation Homogeneity in Asphalt Puck after Simulation of Long-Term Aging (Pressure Aging Vessel).

For decades, it has been known that the creation of oxygenated functional groups, especially carbonyl and sulfoxide, is among the main causes of chemical aging and degradation of asphalt. However, is the oxidation of a bitumen homogeneous? The focus of this paper was to follow the oxidation phenomena through an asphalt puck during a pressure aging vessel (PAV) test. According to the literature, the asphalt oxidation process that leads to the creation of oxygenated functions can be divided into the following successive main steps: the absorption of oxygen in asphalt at the air/asphalt interface, diffusion into the matrix, and reaction with asphalt molecules. To study the PAV oxidation process, the creation of carbonyl and sulfoxide functional groups in three asphalts were investigated after various aging protocols by Fourier transform infrared spectroscopy (FTIR). From these experiments performed on different layers of asphalt puck, it was observed that PAV aging resulted in a nonhomogeneous oxidation level inside the entire matrix. Compared to the upper surface, the lower section exhibited carbonyl and sulfoxide indices 70% and 33% lower, respectively. Moreover, the difference in the oxidation level between the top and bottom surfaces increased when the thickness and viscosity of the asphalt sample increased.

Evaluation of Gas Chromatography Columns with Radially Elongated Pillars as Second-Dimension Columns in Comprehensive Two-Dimensional Gas Chromatography.

The present study investigated the use of a dedicated gas chromatography (GC) column (L = 70 cm, 75 µm deep, and 6.195 mm wide) with radially elongated pillars (REPs) as the second column in a comprehensive two-dimensional gas chromatography (GC × µGC) system. Three stationary phases [apolar polydimethylsiloxane (PDMS), medium polar room-temperature ionic liquid (RTIL) based on monocationic phosphonium, and polar polyethylene glycol (PEG-1000)] have been coated using the static method at constant pressure or using an original vacuum pressure program (VPP) from 400 to 4 mbar. The best efficiency reached up to N = 62,000 theoretical plates for a film thickness of 47 nm at 100 °C for an iso-octane peak (k = 0.16) at an optimal flow rate of 4.8 mL/min. The use of the VPP improved the efficiency by approximately 15%. Efficiencies up to 28,000 and 47,000 were obtained for PEG-1000 and RTIL, respectively. A temperature-programmed separation of a mixture of 11 volatile compounds on a PDMS-coated chip was obtained in less than 36 s. The PDMS-, PEG-1000-, and RTIL-coated chips were tested as the second column using a microfluidic reverse fill/flush flow modulator in a GC × µGC system. The REP columns were highly compatible with the operating conditions in terms of flow rate and with more than 30,000 plates for the iso-octane peak. Moreover, a commercial solvent called white spirit containing alkanes and aromatic compounds was injected in three sets of columns in normal and reverse modes, demonstrating the great potential of the chip as a second-dimension separation column.

Retention modeling and retention time prediction in gas chromatography and flow-modulation comprehensive two-dimensional gas chromatography: The contribution of pressure on solute partition.

This study aims at modelling and predicting solute retention in capillary Gas Chromatography (GC) and Flow Modulation comprehensive GC (FM-GCxGC). A new thermodynamic model, taking into account the effects of temperature and pressure, is proposed to describe the variation of the equilibrium partition constant of a solute during its elution. This retention model was challenged with the classical one, and both were applied to: (i) stationary phase film thickness indirect estimation; (ii) retention time (RT) prediction of a set of 11 model polycyclic aromatic hydrocarbons (PAHs) on the SLB-IL60 and DB-35MS columns, in temperature-programmed mode. Film thickness determination led to values about 2 times lower than those indicated by column nominal dimensions, whatever the employed model. Prediction of retention times in GC led to 0.84 and 0.26% mean errors using the classical and the extended models, respectively. Prediction in GCxGC gave 5.5 and 0.44% mean errors in 1st dimension RTs, and 7.3 and 2.2% mean errors in 2nd dimension RTs, using the classical and the extended models, respectively.

Influence of amino acid moiety accessibility on the chiral recognition of cyclodextrin-amino acid mixed selectors in enantioselective gas chromatography.

Original mixed selectors were synthesized by coupling a single L-valine diamide moiety on permethylated ß-cyclodextrin. The structures of the new selectors were designed to limit the interactions between the L-valine derivative and cyclodextrin by removing the amino acid moiety from the cyclodextrin cavity by means of an amide linkage on mono-6-amino permethylated ß-CD or the insertion of a carboxymethyl group. The accessibility of the amino acid group moiety was thus facilitated. The new mixed selectors exhibited better enantioselectivity than Chirasil-L-Val for half (selector based on mono-6-amino permethylated ß-CD) or more (selector with the carboxymethyl group) of the 41 amino acid derivatives. Molecular modeling confirmed that these results could be attributed to an increase in the distance between the chiral center of the amino acid and the cyclodextrin cavity allowing better access of the amino acid moiety. These new mixed chiral selectors demonstrated a novel enantioselective capability with the successful separation of more than 90 racemic mixtures among the 105 chiral compounds tested. These mixed selectors exhibited enhanced enantioselectivity in comparison to binary selectors previously described with respect to both enantiomer resolution and the number of separated chiral compounds. Moreover, an improvement of the enantioseparation factors compared to the corresponding 'parent phases' for the amino acid derivatives was observed in many cases. These mixed selectors should therefore be considered some of the most versatile selectors for chiral gas chromatography.