Thermo Scientific™ Prima PRO Process Mass Spectrometer - Improving ethylene oxide process control

Significance of the topic

The manufacture of ethylene oxide (EO) is a high-volume, high-value industrial process central to the production of ethylene glycols, glycol ethers, ethanolamines and ethoxylates. Optimizing EO selectivity and catalyst life improves economics and reduces safety risk because the competing complete oxidation reaction is far more exothermic and can create hazardous conditions. Fast, accurate, multicomponent gas analysis is therefore essential both for process optimization and for maintaining safe plant operation.

Objectives and article overview

This application note describes how on-line process mass spectrometry—specifically the Thermo Scientific Prima PRO process mass spectrometer—can improve EO process control. It summarizes analytical requirements for the EO process, the advantages of magnetic-sector mass spectrometry combined with rapid multistream sampling, typical performance characteristics for EO inlet/outlet streams, and the ability to measure trace organic chlorides and perform carbon/oxygen/selectivity balances for reliable process control.

Methodology and analytical approach

The EO process is monitored by measuring reactor inlet and outlet gas compositions and deriving key process metrics: Selectivity (moles EO per 100 moles ethylene converted), Carbon Balance and Oxygen Balance. Requirements include rapid analysis (<30 s per stream), wide dynamic range (ppm to percent), and the ability to analyze streams with two different bulk/balance gases (methane during normal operation and nitrogen during start-up/shutdown). Accurate trace analysis of organic chlorides at ppm levels in a complex, high-background matrix is also required.

Used Instrumentation

The Prima PRO solution described combines:

• A laminated magnetic-sector mass analyzer for high precision, stability, resistance to contamination and extended calibration intervals.
• A Rapid Multistream Sampler (RMS) capable of selecting 1 of 32 or 1 of 64 sample streams, with digital sample flow recording and configurable stream settling times.
• An enclosed high-temperature ion source (operated 140–180 °C) and heated sampling/RMS lines (minimum ~80 °C) to avoid condensation and minimize matrix interferences for trace chloride measurement.
• GasWorks software to configure unlimited components, derived values (selectivity, carbon/oxygen balances), methods per stream and to communicate via standard process protocols.

Main results and discussion

Performance highlights reported for typical EO inlet/outlet streams:

• Analysis time: ~25 seconds per stream for 14 components (≈15 s if chlorides are omitted).
• EO measured range 0–4 %mol with typical reactor outlet ~2.2 %mol and standard deviation ≤0.005 %mol over 8 hours.
• Key gases (methane, nitrogen, ethylene, oxygen, argon, CO2) reported with standard deviations in the ranges of ≤0.005–0.03 %mol or 0.1% relative, depending on level.
• Organic chlorides (methyl, vinyl, ethyl chlorides, 1,2-dichloroethane) measured across 0–5 ppm with SDs typically ≤0.2 ppm; repeatability shown over 8 hours.
• Carbon and oxygen balances computed via derived-value formulas produced averages very close to theoretical 100% (examples: Carbon Balance average 100.25 with SD 0.047; Oxygen Balance average 99.03 with SD 0.132 over 10 hours), demonstrating comprehensive accounting of C and O containing species and strong measurement confidence.
• Linearity/dynamic range: Prima PRO calibrated on methane-balance streams successfully measured nitrogen-balance streams without separate calibration, showing robust linearity across very different bulk-gas matrices.

Important practical considerations highlighted: maintaining elevated and uniform sampling temperatures (≥80 °C along the sampling path, higher at the ion source) avoids cold spots and reduces formation or condensation of by-products that interfere with low-mass traces (e.g., ethylene glycol interfering at mass 62 where vinyl chloride appears). Also, while MS measures oxygen, critical safety monitoring typically employs a dedicated paramagnetic oxygen analyzer in parallel.

Practical benefits and applications

The Prima PRO approach provides several operational advantages:

• Rapid, complete stream analysis supports near real-time control loops for selectivity optimization and catalyst management.
• High precision and long-term stability reduce calibration frequency and increase confidence in derived metrics (selectivity, carbon/oxygen balances).
• Single-instrument measurement of both inorganic gases and organic trace chlorides simplifies plant analytics compared with separate GC and oxygen analysers.
• Capability to handle ppm–100% concentration ranges and different balance gases streamlines startup/shutdown transitions and safety procedures.

Future trends and potential applications

Likely developments and opportunities include:

• Tighter integration of high-precision process MS with advanced process control and machine learning models to proactively optimize selectivity and catalyst life.
• Enhanced sampling and materials of construction to further reduce memory effects and broaden chemical compatibility for even more aggressive matrices.
• Improved detector technologies and ion-source designs to push limits of detection for problematic trace species while maintaining robustness for industrial operation.
• Comprehensive digital twins combining on-line MS data, plant telemetry and kinetic models to simulate and optimize reactor behavior in real time.
• Continued coupling of MS with dedicated safety sensors (paramagnetic O2) to provide redundant, independent measurements for critical safety parameters.

Conclusion

High-precision, magnetic-sector process mass spectrometry combined with rapid multistream sampling and robust, high-temperature sample handling offers a compelling analytical solution for ethylene oxide production. The Prima PRO system demonstrates the speed, dynamic range, trace capability and stability required to accurately compute selectivity and carbon/oxygen balances, support safe operation across different balance gases, and enable tighter process control and catalyst management—delivering both safety and economic benefits.

Reference

• Chemical Economics Handbook – Ethylene Oxide, September 2016.