UOP 939-96: Basic Nitrogen in LPG by Ion Chromatography

Significance of the topic

Natural liquefied petroleum gas (LPG) often contains corrosive acidic gases such as CO₂ and H₂S. Sweetening with alkaline amine solutions removes these contaminants, but residual amines must be quantified to ensure product quality and prevent downstream impacts.

Objectives and study overview

This application note describes a non-suppressed cation chromatography method based on UOP 936-95 and 939-96 for the determination of four amines (dimethylamine, diethylamine, dipropylamine, dibutylamine) in an acetic acid scrubber solution used during LPG sweetening.

Methodology

Sample preparation follows the UOP 936-95 protocol for scrubbing LPG with acetic acid. Separation is achieved using non-suppressed cation exchange chromatography and direct conductivity detection. Key parameters include:

• Eluent: 1.7 mmol/L HNO₃ with 3% acetone
• Flow rate: 0.9 mL/min
• Injection volume: 50 µL
• Column: Metrosep C 4 – 150/4.0 with Metrosep C 4 Guard/4.0
• Column temperature: 30 °C
• Analysis time: 19 min

Instrumentation used

• 940 Professional IC Vario ONE
• IC Conductivity Detector
• 858 Professional Sample Processor
• 800 Dosino
• IC equipment: MiPT

Main results and discussion

The method yielded amine concentrations between 0.46 and 0.59 mg/L with recoveries ranging from 92% to 118%. Matrix peaks corresponding to inorganic cations were detected but did not interfere with amine quantification, demonstrating good resolution and accuracy.

Benefits and practical applications

• Fast, reliable quantification of basic nitrogen species in scrubber solutions
• Compliance with UOP standards for LPG quality control
• Suitable for routine QA/QC workflows in refining and petrochemical industries

Future trends and potential applications

Advances may include coupling with mass spectrometry for definitive identification, development of inline monitoring systems for real-time analysis, and extension to other amine-based sweetening processes.

Conclusion

The non-suppressed cation chromatography approach reliably quantifies dimethylamine, diethylamine, dipropylamine, and dibutylamine in acetic acid scrubber solutions, fulfilling UOP 936-95 and 939-96 requirements and supporting effective LPG sweetening quality control.

References

No additional literature was cited.