1 Scope
This document describes a test method for the determination of the aromatic content of middle distillates by high performance liquid chromatography using an oscillometric refractive index detector.
This document applies to the determination of monocyclic aromatic scrip, bicyclic aromatic scrip and tricyclic + aromatic scrip content in diesel fuel containing up to 30% by volume of fatty acid methyl ester (FAME), high wax diesel fuel containing up to 7% by volume of fatty acid methyl ester (FAME) and petroleum fractions with a distillation range of 150 °C to 400 °C. The polycyclic aromatic content is obtained by summing the bicyclic aromatic and tricyclic + aromatic contents, and the total aromatic content is obtained by summing the monocyclic aromatic, bicyclic aromatic and tricyclic + aromatic contents.
Step A is suitable for the determination of monocyclic aromatic, bicyclic aromatic and tricyclic + aromatic contents in diesel fuel containing up to 30% by volume of fatty acid methyl ester (FAME) and petroleum fractions with a distillation range of 150 °C to 400 °C. The monocyclic aromatic content (mass fraction) ranges from 6% to 30%, the bicyclic aromatic content (mass fraction) from 1% to 10% and the tricyclic + aromatic content (mass fraction) from 1 to 10%. The aromatic content (mass fraction) of monocyclic aromatic scrip was 6%-30%, the aromatic content (mass fraction) of bicyclic aromatic scrip was 1%-10%, the aromatic content (mass fraction) of tricyclic + aromatic scrip was 0%-2% and the aromatic content (mass fraction) of polycyclic aromatic scrip was 1%-12. Step B is suitable for the determination of the aromatic content of high wax diesel fuel with a fatty acid methyl ester (FAME) content of not more than Wang% by volume, with a total aromatic content (mass fraction) of 0.2% to 2%.
Note: Typically, aromatic warp types are defined by their elution properties on a particular concentrated phase column compared to a model compound. The content of monocyclic aromatic scrip, bicyclic aromatic scrip and tricyclic* aromatic scrip is quantified using the working curve of the external standard. In this document a single aromatic compound is used as an external standard for each of the monocyclic aromatic, bicyclic aromatic and tricyclic* aromatic species, which may (or may not) be representative of the aromatic species present in the sample. Other methods may define and quantify each aromatic type differently from this method. For example, the refractive index of tetrahydronaphthalene is higher than that of o-xylene and the refractive index of n-hexylbenzene is lower than that of o-xylene, and differences in the levels of tetrahydronaphthalene and n-hexylbenzene in a sample may cause the quantification of monocyclic aromatic monsters in this method to be inconsistent with the actual situation.
2 Normative references
The following documents constitute essential provisions of this document through normative references in the text. Among them, note the date of the cited documents, only the date of the corresponding version applicable to this document; do not note the date of the cited documents, the latest version (including all the revision of the list) applicable to this document.
GB/T 4756 Manual sampling method for petroleum liquids
GB/T12806-2011 Laboratory glass apparatus with single line marker volumetric flask
GB 25199 B5 Diesel
GB/T 27867 Automatic sampling method for petroleum liquid pipelines
NB/SH/T 0843 Statistical and technical method for the evaluation of analytical testing systems in the petrochemical industry
3 Terminology and definitions
The following terms and definitions apply to this document.
3.1
Non-aromatic hydrocarbon
A compound with a shorter retention time than most monocyclic aromatics on a specific polar column.
3.2
Monocyclic aromatic mono-aromatic hydrocarbon; MAH
A compound with a retention time longer than most non-aromatic but shorter than most bicyclic aromatic hydrocarbons on a specific polar column.
3.3
Di-aromatic hydrocarbon; DAH
A compound with a retention time longer than most monocyclic aromatics but shorter than tricyclic + aromatics on a specific polar column.
3.4
Tricyclo*aromatic hydrocarbon; T+AH
A compound with a retention time longer than most bicyclic aromatic spheres but shorter than the yields on a specific polar column.
3.5
Polycyclic aromatic hydrocarbon; the sum of POLY-AH bicyclic aromatic and tricyclic + aromatic hydrocarbons.
3.6
Total aromatic hydrocarbon The sum of monocyclic aromatic, bicyclic aromatic, and tricyclic* aromatic hydrocarbons.
Note: Published and unpublished data indicate that the main components of the various types of warp are as follows
4 Method summary
Diesel and petroleum fractions are selected in step A, and high wax diesel is selected in step B.
Step A: A known amount of the sample is diluted with n-heptane and an amount of the sample solution is injected into a high performance liquid chromatography system equipped with a polar column.
Step B: An amount of the sample is injected into the HPLC system with a polar column.
A backwash can be performed after the aromatics have all exited the column to backwash out any residual compounds (e.g. fatty acid methyl esters) from the column into a backwash peak. This will clean the column better, but may reduce column life.
Note: Backflushing is part of the internal laboratory maintenance.
5 Interferences
Compounds of sulphur, nitrogen and oxygen in the sample may have an effect on the results. Monoalkenes have no effect on the results, but co- and polyalkenes may have an effect on the results.
6 Reagents and materials
Warning - Aromatic compounds are highly volatile and flammable and their vapours can form explosive mixtures with air. Inhalation or skin contact with aromatic compounds may cause acute or chronic hazards. In addition, aromatic compounds can cause water contamination.
6.1 Cyclohexane: not less than 99% by mass.
Note: Cyclohexane may contain benzene impurities.
6.2 n-Heptane: High performance liquid chromatography (HPLC) grade, as the mobile phase for liquid chromatography.
Note 1: Variations in batch-to-batch moisture content, viscosity, refractive index and purity of the mobile phase may lead to unpredictable column behaviour and dehydration of the mobile phase.
Dehydration of the mobile phase (e.g. by activated 5A molecular sieve) and filtration can help to reduce the effect of trace impurities.
Note 2: Poor degassing may result in negative peaks and the mobile phase can be degassed using helium purging, vacuum degassing or ultrasonic stirring.
6.3 Dodecylbenzene; mass fraction not less than 98%.
6.4 o-xylene: mass fraction not less than 98%. 6.5 hexamethylbenzene: mass fraction not less than 98%.
6.6 Naphthalene: not less than 98% by mass.
6.7 Su: not less than 98% by mass. 6.8 Phenanthrene: not less than 98% by mass.
6.9 Dibenzothiophene: Not less than 95% by mass.
6.10 9-Methylanthracene: Not less than 95% by mass.
6.11 Aram: not less than 95% by mass.
6.12 Fatty acid methyl ester: in accordance with the requirements of GB 25199.
6.13 Quality control samples:stable and representative samples.
7 Apparatus
7.1 Liquid chromatograph
Any high performance liquid chromatograph that allows the mobile phase to enter the system at a flow rate of 0.5 mL/min to 1.5 mL/min, with a precision better than 0.5% under the conditions specified in Chapter 9, and fluctuations of less than 1% of the full offset scale, can be used. The equipment used to process or measure the sample should be insensitive to fatty acid methyl esters and the recommended materials are PTFE, fluoroelastomer and polyamide.
7.2 Injection system
Any injection system capable of injecting 10 pL of sample solution with a repeatability of better than 1% can be used.
7.3 Specimen filters
If required (see 11.1 and 11.2), a microfilter with a pore size of not more than 0.45 um is recommended to remove particles from the sample solution, requiring the microfilter to be inert to the solvent.
Note: Teflon filters are suitable.
7.4 Column systems
Any HPLC stainless steel column filled with an amino-bonded (or polar amino/cyano-bonded) silica stationary phase with a particle size of 3 pm, 5 um or 10 pm can be used provided that the resolution requirements specified in 9.7, 9.8, 9.10 and 9.12 are met. Refer to Appendix A to select the appropriate column.
7.5 Temperature control system
The HPLC column temperature chamber must be able to maintain a constant temperature (∼1°C) within the range of 20°C to 40°C. Heating blocks, air circulation or other methods of constant temperature can be used, such as a constant temperature laboratory.
8 Sampling
Samples for laboratory analysis should be representative, unless otherwise stated in the product standard, and should be obtained in accordance with GB/T 4756 or GB/T 27867 or equivalent. Samples should be allowed to come to room temperature before testing.
If the sample is exposed to temperatures above 25°C for an extended period of time during storage or custody, this should be stated in the report.
9 Instrument preparation
9.1 The instrumentation and sample distribution system should be clean and dry prior to use.
10 Calibration
10.1 Prepare standard solutions A, B, C and D by reference to the concentrations in Table 1. Weigh the standards to the nearest 0.000 1 g and place in a 100 ml. volumetric flask and dilute to the scale with n-heptane (see 6.2).
11 Test procedure
11.1 Step A (diesel and petroleum fractions)
Weigh 0.9 g to l.1 g (accurate to 0.001 g) of the sample in a 10 mL volumetric flask (see 7.8). Add an appropriate amount of n-heptane (see 6.2), shake vigorously to mix the sample solution well, then set the volume to the mark with n-heptane (see 6.2), mix well and leave for 10 min. If necessary, filter the sample solution to remove particles (see 7.3).
12 Calculation and presentation of results
12.1 Retention time of the standard substance
13 Presentation of results
The contents of monocyclic aromatic scriptures, bicyclic aromatic scriptures, tricyclic + aromatic scriptures, polycyclic aromatic scriptures and total aromatic scriptures are reported as mass fractions to the nearest 0.1%.
14 Precision
14.1 Overview
15 Test reports
Appendix A (informative) Column selection and use
Appendix B (informative) Practical guide to the determination of high wax diesel
1 Scope
2 Normative references
3 Terminology and definitions
4 Method summary
5 Interferences
6 Reagents and materials
7 Apparatus
8 Sampling
9 Instrument preparation
10 Calibration
11 Test procedure
12 Calculation and presentation of results
13 Presentation of results
14 Precision
15 Test reports
Appendix A (informative) Column selection and use
Appendix B (informative) Practical guide to the determination of high wax diesel
