Fast separation of heat stable salts

Importance of the Topic

Heat stable salts (HSS) accumulate in amine-based gas sweetening loops and promote corrosion and unscheduled plant outages. Routine monitoring of HSS concentration is critical for maintaining process integrity, minimizing maintenance costs, and ensuring environmental and safety compliance.

Objectives and Study Overview

This study aimed to develop and validate a rapid ion chromatography (IC) method for the simultaneous separation and quantification of 14 common inorganic and organic anions associated with heat stable salts in refinery amine solutions. Samples from nine refinery streams were analyzed to demonstrate method performance across diverse matrices.

Instrumentation Used

• Thermo Scientific Dionex ICS-5000+ HPIC system with SP/DP Pump, EG KOH Eluent Generator, DC detector and Chromatography module
• Thermo Scientific Dionex IonPac AS25A analytical column (2×250 mm) with AG25A guard column (2×50 mm)
• Thermo Scientific Dionex AERS 500 electrolytically regenerated suppressor (2 mm, recycle mode)
• Chromeleon Chromatography Data System, Version 7.1

Methodology

Sample and standard solutions were prepared in deionized water using certified reagents. A potassium hydroxide gradient eluent (20–43 mM from 0 to 12 min, 43–70 mM from 12 to 25 min, then 20 mM to 30 min) was generated via the EGC III KOH cartridge at 0.25 mL/min. The column temperature was maintained at 30 °C, injection volume was 2.5 µL, and suppression current varied (23 mA for isocratic, 44 mA for gradient). Calibration ranges were 0.10–10 mg/L for thiosulfate and 0.20–20 mg/L for thiocyanate. LODs and LOQs were determined at S/N of 3 and 10.

Main Results and Discussion

The gradient IC method resolved all 14 anions within a 30 min run, with baseline separation for bromide/nitrate and acceptable resolution for fluoride/acetate. Calibration curves for thiosulfate and thiocyanate showed linearity (r2 > 0.999). Retention time reproducibility was 0.02–0.05% RSD. LODs were 0.016–0.018 mg/L and LOQs 0.053–0.061 mg/L. Nine refinery samples displayed varied anion profiles: common detections included acetate, formate, chloride, nitrite, carbonate, sulfate, and oxalate, while some streams exhibited high thiocyanate or thiosulfate levels. Recovery studies spiked at two levels yielded 85–104% for thiosulfate and 83–91% for thiocyanate, confirming method accuracy.

Benefits and Practical Applications

• Fast, reliable quantification of HSS anions in amine process streams
• Trace-level detection to support preventive maintenance and corrosion control
• Adaptable to various refinery matrices and other industrial wastewater analyses
• Automated gradient eluent generation and suppressor operation reduce reagent consumption and downtime

Future Trends and Potential Applications

Advancements may include coupling IC with mass spectrometry for enhanced selectivity, miniaturized or inline monitoring for real-time process control, and application to emerging amine formulations. Further automation and integration with plant control systems can improve response times and reduce manual sampling.

Conclusion

A robust gradient IC method employing the Dionex IonPac AS25A column and ICS-5000+ system has been validated for rapid determination of 14 heat stable salts in refinery amine solutions. Excellent sensitivity, linearity, precision, and recovery make this approach suitable for routine monitoring to mitigate corrosion and optimize gas sweetening operations.

References

1. Shao J; Lu G; Ye M. Removal of Heat Stable Salts – A Solution to Amine Plant Operational Problems. Chem Eng Pet Nat Gas J, 2002.
2. Hajilary N; Ehsani Nejad A; Sheikhaei S; Foroughipour H. Amine Gas Sweetening System Problems Arising from Amine Replacement. J Pet Sci Technol, 2011;1(1):24–30.
3. Tang F; Wang Y; Luo Q; Tang M; Chen G. Determination of Heat Stable Salt Anions by IC. Chin J Chromatogr, 2012;30(4):378–383.
4. Thermo Scientific Technical Note 122: Separation of Heat Stable Amine Salts in MDEA Solutions Using High-Pressure IC. 2016.
5. Thermo Scientific Application Note 138: Determination of Thiosulfate in Refinery and Other Wastewaters. 2001.
6. Thermo Scientific Dionex IonPac AS25 Column Product Manual, 2012.