Amines in scrubber solution of refineries with direct conductivity detection

Significance of the Topic

Monitoring amines and common cations in natural gas sweetening is critical for maintaining process efficiency, ensuring regulatory compliance and protecting downstream equipment from corrosion. A reliable analytical approach enables operators to track reagent degradation, optimize amine reclamation and prevent environmental release of contaminants.

Objectives and Study Overview

The primary goal of this study was to establish a single ion chromatographic method capable of separating and quantifying a suite of alkanolamines together with standard cations in gas sweetening solutions. Target analytes included Li+, Na+, NH4+, K+, Mg2+, Ca2+ and a series of amines: monoethanolamine (MEA), diethanolamine (DEA), diglycolamine (DGA), triethanolamine (TEA), methyldiethanolamine (MDEA), 3-methoxypropylamine (MOPA) and cyclohexylamine.

Methodology

The method employed direct injection of aqueous samples onto a Metrosep C6 – 250/4.0 separation column with a Metrosep C4 guard column. The eluent consisted of 1.0 mmol/L nitric acid, 1.5 mmol/L oxalic acid, 0.75 mmol/L dipicolinic acid and 1 % acetone. Chromatographic conditions included a flow rate of 0.9 mL/min, injection volume of 10 µL, column temperature of 40 °C and a total run time of 75 min. Direct conductivity detection was used to monitor eluting species.

Used Instrumentation

• 940 Professional IC Vario ONE system
• IC Conductivity Detector
• 858 Professional Sample Processor
• Metrosep C6 – 250/4.0 column with Metrosep C4 Guard/4.0

Main Results and Discussion

The method achieved baseline separation of 13 analytes, with retention times well distributed over a 75-minute timeframe. Calibration at 50 mg/L for each species showed recoveries between 49.3 and 50.1 mg/L, indicating excellent accuracy and precision. No significant co-elutions were observed, demonstrating the selectivity of the Metrosep C6 column under the chosen eluent composition.

Benefits and Practical Applications

This robust ion chromatographic procedure offers:

• Simultaneous quantification of amines and inorganic cations.
• Minimal sample preparation via direct injection.
• High analytical throughput and reproducibility suitable for routine QA/QC.
• Flexible adaptation to online or at-line monitoring in gas processing plants.

Future Trends and Opportunities

Potential developments include coupling ion chromatography with mass spectrometry for enhanced sensitivity and structural confirmation, miniaturized or portable systems for on-site analysis, and integration with process control software for real-time monitoring. Method adaptation to shorter columns or higher flow rates may further reduce analysis time.

Conclusion

The presented IC method provides an effective and reliable tool for comprehensive monitoring of amine contaminants and cationic species in natural gas sweetening streams. Its simplicity, accuracy and broad applicability make it a valuable asset for industrial and environmental laboratories.