Portable Micro Gas Chromatography – Fast and Accurate Analysis of Biogas and Related Streams

Importance of the Topic

Rapid and reliable determination of biogas composition is essential for optimizing its use as a renewable energy source. Biogas typically contains methane, carbon dioxide, minor permanent gases and trace contaminants such as hydrogen sulfide. Fast field analysis supports real-time process control in wastewater treatment, agricultural digesters and landfill gas recovery. A compact, portable analytical platform that delivers lab-quality results within minutes improves operational efficiency and safety.

Scope and Objectives

This study presents the performance of a portable micro gas chromatograph (Micro GC) configured as a biogas analyzer. The goals are to achieve:

• Complete separation of permanent gases (H₂, O₂, N₂, CH₄, CO)
• Baseline resolution of CO₂ and H₂S
• Extended analysis for higher hydrocarbons in mixed streams
• Analysis time of roughly two minutes per sample

This work evaluates two system variants: a standard two-channel biogas analyzer and an extended three-channel version for biogas blends with natural gas or LPG.

Methods and Instrumentation

The core instrument is the Agilent 490 Micro GC Biogas Analyzer. Key features include:

• Independent micro-GC channels with electronic carrier-gas control and μTCD detectors
• Molecular sieve column (CP-MolSieve 5Å) for permanent gases
• Porous polymer column (PoraPLOT U) for CO₂ and H₂S
• Optional dimethylpolysiloxane column (CP-Sil 5 CB) for higher hydrocarbons
• UltiMetal deactivation on stainless steel flow paths to sharpen H₂S peaks
• Built-in rechargeable batteries and carrier-gas canisters for field mobility

Carrier gases used include helium and argon at 150–200 kPa. Typical column temperatures are 60–80 °C, injector at 110 °C, with injection times near 40 ms and back-flush intervals of 11–14 s.

Main Results and Discussion

The standard analyzer resolves H₂, O₂, N₂, CH₄ and CO within two minutes. The second channel achieves baseline separation of CO₂ and H₂S at trace levels. In extended mode, the third channel separates C₃–C₇ hydrocarbons in blended samples; late-eluting compounds are back-flushed to shorten cycle time and protect the analytical column. Field case trials confirm consistent performance under diverse environmental conditions.

Benefits and Practical Applications

The portable Micro GC system offers:

• On-site, real-time monitoring without external lab support
• High analytical precision for process optimization and emissions control
• Rapid return on investment through reduced downtime and improved safety
• Flexibility to analyze pure biogas and hydrocarbon blends with a single instrument

This platform meets needs in biogas plants, quality control labs, landfill monitoring and emergency response.

Future Trends and Potential Uses

Advances in micro-fabrication and data analytics may enable:

• Integration with wireless networks and IoT for continuous monitoring
• Expanded detection of trace contaminants (e.g., siloxanes, ammonia)
• Further miniaturization for handheld deployment
• Automated calibration and self-diagnostics for unattended operation

Adapting the system for other renewable gas streams and process gases will broaden its industrial impact.

Conclusion

The Agilent 490 Micro GC Biogas Analyzer delivers fast, accurate and portable analysis of biogas and related hydrocarbon mixtures. Its modular channel design, robust detector and inert flow paths achieve baseline separations in under two minutes, supporting real-time field decisions. The extended configuration handles LPG and natural gas blends, ensuring versatile application across the renewable energy sector.

References

Agilent Technologies. Application Note 5990-9508EN: Analysis of Biogas Using the Agilent Biogas Analyzer. November 2011.
Agilent Technologies. Data Sheet 5990-9517EN: Agilent 490 Micro GC Biogas Analyzers. November 2011.
Agilent Technologies. Brochure 5991-1093EN: Agilent Analyzers and Application Kits. October 2012.