Chromatographic simulated distillation analysis of gasoline boiling range

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[Abstract] An analytical method for the simulated distillation range of gasoline was developed using gas chromatography, with the aim of optimizing the operating conditions for simulated distillation. Correction curves for the boiling point and retention time of n-alkanes were established using C5–C14 n-alkanes; the cumulative areas corresponding to the percentage yields and retention times were obtained. Using the previously derived relationship curve between retention time and boiling point, the percentage yield versus temperature, that is, the boiling range, could be calculated. [Keywords] Gas chromatography ； Simulated distillation ； Enneal distillation range ； 1. Introduction: As a standard product of refining facilities, gasoline requires that laboratories be able to conduct rapid and accurate analyses, providing the facilities with analysis data in a timely manner. This allows the facilities to adjust their operating parameters quickly and effectively, thereby ensuring the quality of gasoline. Conventional Enneberg distillation (ASTM D86) is used to analyze the boiling range of gasoline; analyzing each sample takes at least 1 hour, whereas rapid simulated distillation requires only about 6 minutes for such analysis. This reduces the analysis time and improves accuracy, making it highly suitable for rapid control and analysis in petroleum refining plants. 2. Experimental principle: The basic principle of the gas chromatography simulated distillation method is to use a non-polar chromatographic column with a certain degree of separation to determine the retention times of the components in a known mixture of normal alkanes under linearly increasing temperature conditions. Then, under the same chromatographic conditions, the sample is separated according to boiling point order; the cumulative areas and retention times corresponding to the percentage yields are obtained. By using the previously established relationship between retention time and boiling point along with specialized analysis software, the distillation range data can be calculated. 3. Experimental instruments 3.1 Agilent 6850 gas chromatograph, equipped with an automatic sampler, split/splitless injection port, EPC, FID, and a chromatography workstation. 3.2 Chromatography column: DB-1 10m×100um×0.2um non-polar column 3.3 Carrier gas: high-purity helium at 99.99% purity 3.4 Reagents: n-alkane mixture (C5-C14), AC sample, naphtha, reformed oil, and refined oil sample CS2. 4. Experimental Conditions: Inlet temperature: 250°C; FID temperature: 250°C; EPC constant pressure: 373 kPa; H2 flow rate: 35 mL/min; split ratio: 600:1; Air flow rate: 350 mL/min; injection volume: 0.1 μL; He flow rate: 20 mL/min. Furnace temperature program: Initial temperature (°C), initial time (min), rate (°C/min): First stage: 35, 0.65, 100; Second stage: 45, 0.75, 100; Third stage: 69, 0.75, 50; Fourth stage: 230. 5. Experimental Procedures and Data: 5.1 Using the established experimental method, normal alkanes were analyzed first: The normal alkane mixture (C5–C14) was diluted with CS2 at a ratio of 1:40 before being injected. and ensures correct identification of the n-alkane peaks. The spectrum is as follows: 5.2 AC standard sample analysis is performed, with quantification achieved through the analysis of AC standard oil 512. Analyze other AC samples, check for shunt discrimination, as well as examine peak identification and D86 calculation. 5.3 Sample analysis: The sample is placed in the automatic sampling sequence, the sample type is selected for analysis; once the analysis is complete, the DHA model software is automatically used to calculate D86, and the analysis results are printed out. 6. Accuracy verification: To verify the feasibility and versatility of the method, we selected three representative types of samples (refined oil, reformed oil, and naphtha) and conducted numerous comparative tests using different analysis methods on the same samples. The comparison results are shown in the table below:
I. Refined oil
Method | Data | Items
Chromatography simulation | Manual distillation | Automatic distillation | Reproducibility (°C)
Initial boiling point (°C): 76.6, 77.8, 76.8; 1.2
5% (°C): 91.1, 90.1, 91.6; 1.5
10% (°C): 95.5, 95.9, 96.6; 1.1
50% (°C): 114.0, 114.8, 115.1; 1.1
90% (°C): 140.8, 141.3, 140.3; 1.0
95% (°C): 147.4, 149.0, 147.9; 1.6
Final boiling point (°C): 154.5, 158.3, 155.2; 3.8

II. Reformate oil
Method | Data | Items
Chromatography simulation | Manual distillation | Automatic distillation | Reproducibility (°C)
Initial boiling point (°C): 47.7, 46.2, 47.9; 1.7
5% (°C): 73.1, 73.5, 73.6; 0.5
10% (°C): 81.5, 82.1, 80.9; 1.2
50% (°C): 114.9, 115.8, 114.8; 1.0
90% (°C): 153.6, 155.1, 154.8; 1.5
95% (°C): 164.6, 162.7, 164.9; 2.2
Final boiling point (°C): 185.0, 186.3, 186.0; 1.3

III. Naphtha
Method | Data | Items
Chromatography simulation | Manual distillation | Automatic distillation | Reproducibility (°C)
Initial boiling point (°C): 39.9, 38.8, 38.9; 1.1
5% (°C): 61.3, 60.7, 61.9; 1.2
10% (°C): 73.7, 74.5, 74.3; 0.8
50% (°C): 113.7, 115.6, 112.5; 3.1
90% (°C): 146.4, 146.4, 146.8; 0.4
95% (°C): 155.1, 154.5, 156.1; 1.6
Final boiling point (°C): 165.9, 164.8, 166.9; 2.1

From the above data, it can be seen that the data obtained through simulated distillation fall within the range of reproducibility specified by standards when compared to both manual and automatic distillation data. The deviations from the manual and automatic distillation results also remain within the limits prescribed by standards. 7. Results and Discussion 1. A small amount of sample is required, the analysis time is short, making it accurate and fast. 2. The experimental results are related to the accuracy of the established method model; when developing such methods, different models should be created for different types of samples. The applicability of the method is related to the type of sample, so it is necessary to correctly select the sample type during analysis. 3. It is necessary to ensure that the retention time of n-pentane falls between 0.50 and 0.52 in order to ensure the correct identification of the sample’s chromatographic peaks; if it is not within this range, the pressure before the column should be adjusted. 8. References and standards for citation: 1. GB/6536-1997 Petroleum products; 2. AC8612; 3. ASTM D86