Assuring Ethylene Purity: Reliable Ppm and Ppb Measurement of Acetylene with Online TDL Analyzers

Real-time measurement of certain trace gas species during ethylene production is critically important for optimized production and quality control. Trace gas species such as ammonia (NH₃), moisture (H₂O) and acetylene (C₂H₂) need to be maintained at appropriate concentration levels to achieve optimum catalytic efficiency, catalyst life time and reactor throughput without compromising product purity for polymerization processes. This requires accurate monitoring of these trace gases at various stages of the ethylene production process.

Conventional detection of acetylene primarily relies upon gas chromatograph (GC), which comes with a high cost of ownership, high requirements for operator expertise, intensive maintenance and slow (several minutes) measurement response times. This paper will introduce TDL analyzers SpectraSensors developed for C₂H₂ measurements in various stages of the ethylene production process. This paper will describe system design and present both lab experiment and field operation data for C₂H₂ measurements in the range of 0-10 ppm­_v, 0-100 ppm_v and 0-5000 ppm_v.  Employing 2^nd-harmonic (2f) spectroscopy, multipass Herriott cells, advanced spectroscopy analysis algorithms, a fast Reduced Instruction Set Computer (RISC) and compact modular sample handling systems, these analyzers have demonstrated fast response time (in seconds), superior detection sensitivity and reading repeatability. The analyzers achieved 3σ repeatability of better than ±50ppb_v for 0-10 ppm­_v measurement range, better than +/- 2% of full scale for 0-100 ppm_v and 0-5000 ppm_v ranges.