Gas Analysis for CO2 Conversion Using a GI-30 Auto Gas Injector

Significance of the topic

Gas-phase catalytic conversion of CO2 to value-added products such as methanol and hydrocarbons is a central pathway toward decarbonized chemical manufacturing. Reliable, quantitative gas analysis is essential for catalyst screening, process optimization, and assessing conversion/selectivity in CO2 hydrogenation and downstream reforming experiments. Practical analytical workflows must resolve permanent gases (CO, CO2), light hydrocarbons (C1–C3), higher hydrocarbons (C4+), and oxygenates (e.g., methanol) in complex matrices while minimizing sample handling artifacts and ensuring reproducible injection and detection.

Objectives and study overview

• Demonstrate analytical strategies for comprehensive quantification of products from CO2 conversion using a compact GC system (Brevis GC-2050) equipped with an automatic gas injector (GI-30).
• Show simultaneous analysis of CO, hydrocarbons and methanol by splitting the injector stream to two parallel column–detector trains using an INJ2-way branch unit.
• Present a simplified single-column approach using a packed MICROPACKED-ST column with a thermal conductivity detector (TCD) for quantification of permanent gases and C3-or-smaller hydrocarbons.

Used instrumentation

• Shimadzu Brevis GC-2050 gas chromatograph.
• GI-30 Auto Gas Injector (automatic sampling, minimizes air ingress and adsorption).
• SPI inlet (gas-tight sample path) and INJ2-way branch unit for injection-port splitting.
• Columns: SH-Q-BOND capillary column (30 m × 0.32 mm × 10 µm) for hydrocarbons and methanol; MICROPACKED-ST packed column (1–2 m × 1.0 mm I.D.) for permanent gases and light hydrocarbons.
• Detectors: Flame ionization detector (FID) with Jetanizer accessory (enables CO/CO2 detection via methanizer-like conversion in FID), and Thermal Conductivity Detector (single-filament TCD) for alternative single-column analyses.
• Gases and flows: typical carrier gases used included helium, nitrogen, and hydrogen depending on detector and application; makeup and detector gas flows specified per configuration.

Methodology and operating conditions

• Two analytical schemes were established: (A) dual-column split injection to quantify CO (via MICROPACKED-ST + Jetanizer-FID) concurrently with methanol and C1–C6 hydrocarbons (via SH-Q-BOND + FID); (B) single-column approach using MICROPACKED-ST coupled to TCD for CO and hydrocarbons up to C3.
• Injection: 1 mL loop volume, SPI inlet at 150 °C, injector split implemented with INJ2-way branch unit; typical split ratios and purge flows applied to balance sensitivity and column loading.
• Column oven programs and detector temperatures were tuned to separate light gases and elute higher-boiling organics; example program ranges were 35–270 °C for packed-column TCD runs and 60–240 °C ramp for capillary FID runs.
• Sample preparation: gas mixtures prepared in a vacuum sampling bottle; liquid methanol and higher hydrocarbons introduced by microsyringe and gaseous components injected with gastight syringes; CO2 from sampling bag used to bring total pressure to 1 atm.

Main results and discussion

• Simultaneous dual-column analysis successfully resolved CO, CO2, methanol and hydrocarbons (C1–C6). The SH-Q-BOND capillary separated methanol and higher hydrocarbons effectively while the MICROPACKED-ST packed column provided rapid separation of permanent gases and light hydrocarbons up to C3.
• Calibration performance: strong linearity across tested concentration ranges — hydrocarbons C1–C5 at ~1–100 ppm (v/v) and methanol at ~6–600 ppm (v/v); reported coefficients of determination were R2 ≥ 0.999 for target analytes.
• TCD single-column approach: MICROPACKED-ST + single-filament TCD delivered adequate separation and sensitivity for CO and C1–C3 hydrocarbons. Signal-to-noise ratios exceeded 10 at 100 ppm for each component, demonstrating suitability for routine quantitative monitoring when analytes are limited to light species.
• Detector considerations: the Jetanizer-FID enabled detection of CO/CO2 species not normally observed by conventional FID. TCD sensitivity for low-thermal-conductivity analytes (hydrocarbons) benefits from using high thermal-conductivity carrier gases (He or H2). The GC-2050 TCD single-filament design produced rapid baseline stabilization (~10 minutes), favorable for routine workflows.
• Limitations and practical notes: methanol and hydrocarbons ≥ C4 may be retained or adsorb on the MICROPACKED-ST packed column, potentially causing underestimation or tailing; periodic column conditioning or use of an alternative capillary path (as in the dual-column setup) mitigates these issues.

Benefits and practical applications

• Comprehensive single-run quantification: the INJ2-way branch unit enables concurrent analysis with two different column–detector combinations within a single chromatographic cycle, saving time and improving comparability of product distributions from CO2 conversion experiments.
• Reproducible automatic sampling: the GI-30 Auto Gas Injector provides automated, repeatable injections while minimizing air ingress and adsorption — important for low-ppm trace quantification and high-throughput catalyst testing.
• Compact system footprint: Brevis GC-2050 supports two conventional columns in a ~35 cm oven width, making it suitable for laboratories with space constraints that require multi-detection workflows.
• Flexible configurations: a streamlined TCD-only approach is adequate for studies focused on permanent gases and light hydrocarbons (C3 or smaller), while the dual-column FID/Jetanizer arrangement supports broader product portfolios including methanol and heavier hydrocarbons.

Future trends and potential applications

• Integration with online catalytic reactors and automated sampling valves to enable real-time or near real-time monitoring of CO2 conversion under dynamic conditions.
• Lower detection limits and enhanced selectivity by combining GC separation with mass spectrometry (GC–MS) or advanced detectors (e.g., barrier ionization discharge) for complex reaction matrices and isotopic studies (13C-labelling).
• Improved adsorption management: development of tailored packed- or capillary-phase coatings to minimize retention of polar oxygenates (methanol) and C4+ hydrocarbons, or the use of guard/trap columns and heated sample lines to reduce losses.
• Automation and data analytics: coupling high-throughput GC data with automated calibration routines and chemometric tools to accelerate catalyst screening and kinetic modeling workflows.
• Application expansion: process monitoring in pilot-scale CO2 hydrogenation, quality control for renewable-fuel production, and environmental monitoring of greenhouse‑gas conversion processes.

Conclusion

The study demonstrates practical, flexible GC strategies for quantitative analysis of products from CO2 conversion. Using a Brevis GC-2050 with a GI-30 auto injector and an INJ2-way branch unit enables simultaneous, reproducible quantification of CO, methanol and hydrocarbons across a broad volatility range. For applications limited to permanent gases and light hydrocarbons (≤ C3), a single MICROPACKED-ST column with a single-filament TCD offers a compact, sensitive solution. Attention to adsorption of methanol and C4+ hydrocarbons on packed columns and appropriate choice of carrier/detector combinations are key to reliable results.

References

• Shimadzu Application News: Gas Analysis for CO2 Conversion Using a GI-30 Auto Gas Injector (Brevis GC-2050), First Edition Apr. 2026, Application No. 01-00964-EN.
• Shimadzu Application News No. 01-00661-EN: Simultaneous Analysis of Greenhouse Gases Using Nitrogen Carrier Gas.
• Shimadzu Application News No. 01-00858-EN: Gas Analysis Using a Brevis GC-2050 with GI-30 Auto Gas Injector and TCD/BID Detectors.