Improved Performance From Packed GC Columns Used For the Analysis of Natural Gas and Natural Gas Liquids in Reference to GPA and ASTM Methods

Importance of the Topic

Analytical determination of BTU content in natural gas and natural gas liquids underpins economic transactions and safety in the energy industry. High reproducibility and accuracy ensure confidence in pipeline custody transfers and compliance with GPA and ASTM standards.

Objectives and Study Overview

This study evaluates packed column performance in valved-GC configurations for BTU analysis following GPA Methods 2261 and 2177 and ASTM Method 2597. It aims to optimize column packing, assess column-to-column and run-to-run reproducibility, and reduce analysis time and column length without compromising resolution.

Methodology and Instrumentation

The experimental setup employed a multidimensional GC system with valved backflush and reversed flow steps. Packing improvements and screen terminations minimized void spaces. Column sets included:

• 1.5 ft and 24 ft 316 SS columns packed with 30% DC-200/500 on Chromosorb P NAW
• Additional 10 ft Porapak Q and Molecular Sieve 13X columns for air and CO₂ separation

Instrumentation details:

• Helium carrier gas at 30 cc/min
• Thermal Conductivity Detector with 0.5 mL sample loop
• 316 SS screen terminations replacing glass wool

Main Results and Discussion

Run-to-run reproducibility of component peak areas remained within 0.2% variation over ten injections. BTU content varied by ±0.10 units across replicate analyses. Column-to-column reproducibility showed nitrogen peak width averaging 2.73 s (SD 0.12 s). Packing optimization and screen terminations allowed reduction of 30 ft column length to 24 ft without loss of resolution. All performance metrics met or exceeded GPA and ASTM specifications.

Practical Benefits and Applications

• Assured accuracy in BTU measurement enhances fiscal and safety assurance in custody transfer
• Improved column reproducibility reduces calibration frequency and operational costs
• Compressed analysis time and shorter columns lower maintenance requirements and instrument footprint

Future Trends and Potential Applications

Advancements may include novel stationary phase materials for higher selectivity, integration of micro-GC systems for field deployment, and coupling with advanced detectors such as mass spectrometers. Automation and real-time monitoring platforms will further streamline gas quality control in industrial settings.

Conclusion

Optimized packed GC columns deliver highly reproducible, accurate natural gas and natural gas liquid analyses in compliance with GPA and ASTM methods. Column packing improvements and screen terminations facilitate shorter columns without compromising resolution, yielding reliable BTU determinations for industrial, laboratory, and pipeline applications.