A Comparison of Porous Layer Open Tubular (PLOT) Columns for the Separation of Refinery Gases

Importance of the Topic

The analysis of refinery gases, composed of light hydrocarbons, is critical for process control, safety and product quality in petrochemical industries. Porous Layer Open Tubular (PLOT) columns offer high selectivity enabling separation of isomeric and unsaturated compounds that are challenging to resolve by standard GC phases.

Aims and Study Overview

This study compares the performance of various Thermo Scientific TracePLOT PLOT columns for the separation of refinery gas components. Two deactivated alumina columns (Na2SO4 and KCl) are evaluated alongside three porous polymer columns (TG-BOND Q+, TG-BOND S and TG-BOND Q) to assess differences in selectivity and elution order.

Methodology and Instrumentation

All analyses were conducted on a TRACE GC Ultra system with FID detection at 250°C. Columns used are 30 m × 0.53 mm ID × 20 µm film thickness. Injection parameters: 10 µL manual split injection (13:1), injector at 200°C, helium carrier gas at 4.0 mL/min, oven program from 50°C (2 min) to 200°C (3 min) at 10°C/min. The alumina stationary phases were deactivated with sodium sulfate or potassium chloride. Polymer columns differ in 4-vinyl pyridine content and overall polarity.

Main Results and Discussion

Alumina Na2SO4 and KCl columns display distinct elution sequences: Na2SO4 elutes propadiene and acetylene after butane, while KCl inverts this order by eluting acetylene before propadiene. Polymer columns maintain consistent elution order among themselves but diverge significantly from alumina, offering alternative separation factors for branched and unsaturated isomers. These differences are attributed to surface chemistry and phase polarity affecting retention behavior.

Benefits and Practical Applications

Deactivated alumina PLOT columns deliver baseline resolution of saturated, unsaturated and branched hydrocarbons, making them ideal for comprehensive refinery gas profiling. Porous polymer columns enable targeted purity assays where trace impurities elute apart from dominant peaks, improving quantitation accuracy for specific hydrocarbons.

Future Trends and Potential Applications

Emerging developments may focus on novel polymer chemistries and hybrid PLOT phases to further tailor selectivity. Coupling PLOT columns with mass spectrometry and automated sampling will enhance real-time monitoring and impurity identification. Portable GC systems using PLOT columns could support on-site analysis for rapid process control in refinery operations.

Conclusion

Thermo Scientific TracePLOT columns exhibit diverse selectivity profiles for refinery gas analysis. Alumina phases remain the standard for broad-spectrum separation, while polymer PLOT phases offer complementary elution characteristics for targeted impurity resolution. Optimal column choice depends on analytical objectives—comprehensive profiling or focused purity assessment.