ASTM psg. BS Determination of asphaltenes ( heptane insolublesl) in crude petroleum and petroleum products._ __-_- — -_~ ASTM D Standard Test Method for Determination of Asphaltenes (Heptane Insolubles) in Crude Petroleum and Petroleum Products. There are two methods of ASTM D and ASTM. D (equivalent to IP ) in the Asphaltene. Testing Methods for crude oil and petroleum oil. Both.

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Chemical characterization of the asphaltenes from Colombian Colorado light crude oil. Finally, the crystallite parameters of nanoaggregates of CCO asphaltenes in solid phase were calculated using X-ray powder diffraction data. The average diameters of aromatic layers L 0 calculated from XRD and Raman were compared together and proved to be in good agreement. Asphaltenes, Chemical characterization, Average molecular parameters.

Asphaltenes are defined as the fraction of oil that precipitates with n-heptane and which is soluble in toluene.

Studies dealing with the molecular weight of asphaltene are more controversial. D65560 analysis of asphaltenes from different crude oils reveals that some of its elements may vary over a wide range.

The elucidation of the chemical structure of all their molecules is a very complex and yet unfinished task. These results have been interpreted according to the analytical method used and there are basically two options: Based on the AMPs, two types of architecture of these ast, have been proposed: The first model proposal consists of a unique condensed aromatic system and saturated rings substituted with alkyl chains; whereas the second model proposal consists of several and small aromatic rings forming a structure like a group of islands linked by bridges of aliphatic chains.

Characterization methods according to structural groups may sum up the molecular characteristics of complex mixtures in terms of a few parameters. New fragmentation studies by two-step laser desorption laser ionization mass spectrometry L2MS and FTICR-MS support the contention that the dominant structural character of asphaltenes is island-like Hsu et al, ; Sabbah et al, A single molecular model is not sufficient to represent all the d65600 present in d660 sample of asphaltenes.

By using computational methods with molecular dynamics models, it is possible to study asphaltene-asphaltene and asphaltene-resin interactions, and the way they interact with solvents. Using the Monte Carlo method, a molecular representation of Athabasca oil asphaltenes has been reported Sheremata et al, With this technique, a group of one hundred molecules was proposed and MW, and 1 H- and 13 C-NMR were selected through a nonlinear algorithm for sequential optimization, within a subset of six molecules consistent with the data obtained from elemental analysis.

Based on the previous studies, a new asphaltene model has been codified in the “modified Yen model” and stipulates the dominant structure of asphaltene molecules, nanoaggregates and their clusters Mullins, The Yen model has been very useful, particularly for considering bulk properties of phase-separated asphaltenes. Nevertheless, at the time the Yen model was proposed, there were many uncertainties in asphaltene molecular weight, architecture, and colloidal structure. The continental architecture exhibits attractive forces in the molecule interior and steric repulsion from alkane peripheral groups.

These structures were also observed in oil reservoirs with an extensive vertical offset, v6560 gravitational effects are evident Mullins et al. Asphaltenes obtained from light crudes have proven to differ from those obtained from heavy crude oils. Normally, paraffinic crude oils have small amounts of asphaltenes exceeding in one or two percent in a few cases.

However, despite the low content of asphaltenes severe obstruction problems take place, including the plugging of pipelines associated with asphalteneparaffins co-precipitation.

In Colombia, problems have arisen in producing fields whose content of asphaltenes in crude oil reaches one percent.


In most cases it is observed that plugging problems on the deposits formed contain both asphaltenes d65660 paraffins. In laboratory, conventional separation techniques are not sufficient to obtain asphaltene samples free of paraffins. It is therefore important not only getting samples free of paraffin, but also their molecular characterization in order to understand the phenomena associated with asphaltene-paraffins interaction and co-precipitation thereof.


In this work, we present the results of the chemical characterization of the asphaltenes obtained from the Colorado Colombian light crude oil. The spectroscopic characterization includes the results obtained asfm elemental analysis, infrared and Raman spectroscopies, mass spectrometry in the MALDI mode, 1 H- and 13 C-nuclear magnetic resonance spectroscopy; and finally, x-ray diffractometry to calculate the parameters of asphaltenes crystallites.

This d65600 provides a brief description of the procedure. A Colorado crude oil sample was mixed with n-heptane at a mass ratio of 1: Once the single sample was stored in the dark, it was filtered using a filter funnel with Whatman paper grade 42 and mm diameter.

The liquid was decanted into satm filter paper, and the residue in the flask was then transferred as completely as possible with successive quantities of hot heptane, using the stirring rod as necessary. The filter paper containing the asphaltene residue was transferred and placed asmt a reflux extractor and refluxed with heptane for an extraction period of min.

However, saturated compounds as paraffins were trapped in asphaltenes. Therefore the sample was subject to extensive washing with heptane up to one hundred hours.


The asphaltenes were transferred to a flask by refluxing with toluene until all the asphaltenes dissolved from the paper. Finally, the toluene from the asphaltenes dissolved in toluene was evaporated in a rotary evaporator. Only the spectral range from to cm -1 mid-IR was used in this study. Spectra were obtained by adding 64 scans with a spectral sstm of 1 cm 1. The asphaltene sample was reduced to a d65600 powder and then pressed to obtain a pellet of 4 mm in diameter.

The Raman spectrum was acquired in a backscattering configuration with a x long work distance objective used to focus the laser and collect scattered light. A solid-state laser at nm was used as the excitation source, and the typical laser power at the sample position was The Raman spectrum was measured in the range from satm cm 1 at room temperature; this range covers the first-order region.

For data analysis, we used Gaussian functions to fit the best number of peaks. Thirty-degree pulses Bruker zg30 pulse sequence were used, obtaining a delay time of 2 s sweep width Hz data points. Sixteen scans were averaged for the axtm. Thirty-degree pulses Bruker zgig30 pulse sequence were used again and a delay time ofs sweep width D65560 spectrum was recorded using 5mm and 10mm probes for 1 H- and 13 C-NMR, respectively, with a spinning rate of 10 Hz and temperature of The spectrum was acquired using MAS conditions with a rotation rate of Hz and using one-pulse sequence without cross polarization to obtain a quantitative spectrum.

YAG laser emitting at the third harmonic nm, operating aatm a pulse rate of Hz, with a pulse width of 3. Spectra from shots of the laser were added to obtain the final TOF spectrum. The best experimental conditions were selected by comparing satm spectra at different laser intensities and ionization regions in the sample. The mass spectrometer was operated in the reflectrom mode, scale was calibrated prior to measurement with a standard of appropriate molecular mass.

The average number and weighted average of the molecular weights M n and M w of Colorado asphaltenes were calculated using Equations 1 and 2 Qian et al. Finally, the sum was extended over all peaks found in the spectrum using the peak picking procedure implemented in the mMass software Strohalm et al, ; Strohalm et al, X-ray diffraction measurements were made from finely ground powders of asphaltenes using a Bruker D8 Advance automated diffractometer.

The peak profile analysis was performed assuming that single peaks have Gaussian profiles to fit the diffraction pattern, allowing for an accurate determination of peak positions, widths FWHMintensities, and peak areas. This result indicates that the nature of asphaltenes changes according to the molecular characteristics of crude oil.

The CCO is a paraffinic crude oil with a lower content of asphaltenes, approximately 0. The FTIR analysis usually considers two alternatives: The most commonly observed absorption bands in crude oils and their fractions are reported in Table 2.

Some reports using FTIR data intend to obtain quantitative information about the structure of samples. Partial deconvolution can be applied to facilitate the determination of intensities of signals from asphaltene FTIR spectra where signals cannot be differentiated.


The ratio of H Me number of hydrogen atoms present in methyl groups in the sample to H sat number of hydrogen atoms attached to saturated carbon atoms in the sample can be calculated using Equation 4 Coelho et al, The hydrogen ratio for methyl and methylene groups can be calculated directly from signals at and cm -1 assigned to hydrogen atoms on CH 2 and CH 3 groups, respectively.

To calculate the ratio of methyl to methylene groups, we employ Equations 3 to 6. The integrated areas of signals at the frequencies Results are reported in Table 3. In contrast, values calculated using Equations 4 and 5are different. This can be attributed to the number and type of reference compounds used to predict the relationship between signal intensities and the theoretical values of the methylene to methyl ratio.

Additional data from a larger data set from a wider group of model compounds proposes a general rule. In infrared spectra at cm -1a splitting of the methylene “wag” peak is observed in asphaltene samples, indicating formation of ordered crystals with long alkyl chains. The intensity of this infrared peak indicates that this type of contribution is small, assuming that the intensity and contribution of the physical effect are proportional.

A simple yet quantitative description linking the observed modes and the molecular structure was proposed using the intensity ratio between the g mode and the Dl mode.

Given that this paper is focused on evaluating the molecular or the aggregate structure of asphaltene, equation 8 was the sole equation used for estimating L a. However, the parameter L a so evaluated would be jeopardized if the integrated G and D1 intensities are not accurately determined, or if the G is not in the right range i. Accurate determination of G and D intensities is therefore required.

The L a value is close to that obtained by X-Ray diffraction as shown below. Curve fitting of the Raman spectra is often used to extract more reliable G and D band intensities, as shown in Figure 2.

Most commercial data analysis software provides such an option.

Asphaltenes Apparatus | ASTM D | IP

There are several models and functions commonly used for curve fitting. Due to the shoulder incompatibility in the three-peak fitting, we also attempted a nine-peak fitting. Although the nine-peak fitting provides a much more satisfactory fitting quality and to some extent, provides supporting information for the overall structural argument, the nine-peak fitting may pose the risk of ambiguity.

The three peak data were used for our analysis, Figure 2. Because asphaltenes are a complex mixture, the NMR spectra of asphaltenes do not show a pattern like the pattern obtained for pure samples. NMR spectra are divided into regions, with each region being assigned to a chemical group in the sample. Integrated areas are proportional to the relative amount of the chemical groups in the sample.

The main chemical groups present in asphaltenes and the spectral ranges where they appear in 1 H- and 13 C-NMR spectra are shown in Tables 5 and 6respectively. The 1H-NMR spectrum satm characterized by a weak signal of aromatic hydrogens, 6. In this region the solvent signal appears, namely, CDC1 3 7. The region where the alkyl hydrogens appear 0.

Using the Dickinson’s equation Equation 9the average number of carbons per alkyl side chain n can be calculated from the integrated regions in the 1H-NMR spectrum Dickinson, In the regions from 6. The n calculated value was 5.

The spectrum of 1H-NMR shows the paraffinic nature of the sample, and astk signals should be analyzed on the basis of the composition of paraffinic and naphthenic saturated groups in the sample of Colorado asphaltenes. The analysis of the average molecular parameters should be asfm in conjunction with 1 H- and 13 C-NMR, given the fact that the integrated area is quantitative.