Analyzing Thiophene in Benzene

High-purity benzene is a vital chemical compound for various chemical manufacturing processes. However, trace amounts of thiophene in benzene can poison catalysts, making it essential to determine trace amounts in the petroleum industry.

ASTM Method D7011 is  uses sulfur-selective detection and gas chromatography to determine thiophene in refined benzene.

This article outlines operating parameters and instrument configuration for the detection and quantitation of trace levels of thiophene in benzene using PFPD and ASTM Method D7011.

Instrumentation

The OI Analytical Model 5383 PFPD, shown in Figure 1, was used in this study. The instrument was mounted on an Agilent 7890A GC system with a split/splitless injection port.

OI Analytical Model 5383 PFPD

Figure 1.

Experiment

Table 1. shows the operating conditions of the instrument.

The PFPD was tuned for optimum sulfur response and configured to simultaneously detect sulfur and hydrocarbon, with sulfur run in the linearized mode, i.e. with the square root on.

Table 1. Instrument Configuration and Operating Conditions

Inlet 220°C
Split mode
Split ratio 5:1 (manual injections)
Sulfinert coated
GC Column Agilent J&W DB - WAX
30-m x 0.25-mm ID x 0.5-µm film
Helium carrier gas, 1.2 mL / min
Oven Program (Agilent 7890A) 50°C for 1 minute
10°C / minute to 100°C
30°C / minute to 200°C
Hold for 1 minute
Total run time 10.33 minutes
Sulfur Detection Pulsed Flame Photometric Detector (PFPD)
2-mm combustor, BG-12 filter, R1924 PMT
Detector base temperature 250°C
H2 /air ratio tuned for optimum sulfur emission
6-24 milliseconds sulfur gate (linear mode; square root on)
1-2 milliseconds hydrocarbon gate

By injecting 1 µl thiophene in benzene at 0.02, 0.2, 0.5, 1, and 2 ppm standards, the instrument was calibrated.

A benzene blank and quality assurance check standard were also examined. All injections were made in duplicate.

Results and Discussion

Calibration

A five-point calibration was analyzed and the Agilent GC ChemStation OpenLab data system was employed to create a calibration curve using average response. Linearity was then established with a residual standard deviation of 14.35 and a correlation coefficient of 0.9995 (Figure 2).

Calibration 0.02 - 2.0ppm

Figure 2. Calibration 0.02 - 2.0ppm

0.02ppm standard

Figure 3. 0.02ppm standard

2.0ppm standard

Figure 4. 2.0ppm standard

Method Detection Limit Study

Seven injections of 0.01 ppm thiophene in benzene were prepared. 4.4 ppb was the calculated MDL.

System Stability

A repeatability study was performed over a period of 10 days with 80 replicates (manual injections) of 0.2 ppm. A relatively low RSD of 9.01% exemplifies the stability of the GC system and PFPD.

Conclusion

Equipped with the Agilent 7890A, the OI Analytical 5383 PFPD is suitable for the analysis of thiophene in benzene using ASTM method D7011.

Using a fast and reliable technique, all QC criteria and method requirements were easily met.

Reference

ASTM D7011, 2015, “Standard Test Method for Determination of Trace Thiophene in Refined Benzene by Gas Chroma¬tography and Sulfur Selective Detection,” ASTM International West Conshohocken, PA.

Acknowledgement

Standards were obtained from and QA check sample was provided by DCG Partnership Ltd. in Pearland, Texas.

This information has been sourced, reviewed and adapted from materials provided by OI Analytical.

For more information on this source, please visit OI Analytical.

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