When measuring the water concentrations in an ethylene glycol sample, NIR spectroscopy is the technology of choice. Ethylene glycol and its derivatives are used across a wide range of industries including automotive, polyester fibers and resins, pharmaceuticals, food and beverage processing, pipeline maintenance, textiles, aviation, medical, and HVAC.
The most important variable affecting the glycol production is properly managing the water-to-oxide ratio. In commercial plants, improvement in yields can occur with a large excess of water under controlled pH levels in the solution. A thirty-five-year veteran in applied process analytical technologies (PAT) states, “The trick is to measure and control the level of water to prevent any uncontrolled exothermic reaction. When this is done, both safety and yields are improved in the process.” He continues, “The Process Insights GUIDED WAVE™ technology was selected by a leading worldwide ethylene glycol producer as the most achievable control technology for measuring this process.”
Many ethylene glycol manufacturers prefer using our NIR instruments, due to the state-of-the-art design, repeatability, stability, and elimination of drift. Both analyzers, the full spectrum NIR-O spectrometer or our GUIDED WAVE ClearView® db photometer make managing this measurement efficient. Either analyzer can be used successfully, the choice depends on the complexity of the application (i.e., number of measurements, varying chemistries, number of sample points and measurements). NIR spectroscopy can be used to determine water content in ethylene glycol without sample temperature control. The GUIDED WAVE NIR-O spectrometer was used to measure the NIR spectra of 0 to 100% water in ethylene glycol in the 18- 43°C temperature range using a 10 mm optical path length SST probe. The resulting data were then used to define the wavelengths for our online process photometer.
DATA ANALYSIS OF WATER IN ETHYLENE GLYCOL
The resulting spectra are shown in Figure 1 for five concentrations ranging from 0-100% water in EG, each at 20, 25, 30, 35, 40 and 45°C. To test the viability of a photometer for the real time monitoring of water in ethylene glycol. A multiple linear regression was performed, see Figure 2. Excellent linearity (R2>.9999) is achieved using 4 wavelengths in the range tested showing data at all temperatures.
Our dual beam ClearView db photometer with four filters can be used to determine water from 0-100% in ethylene glycol using a 10 mm optical pathlength insertion probe, or a flow cell (for a slip stream) on-line. The ClearView db can be configured with 4-20 mA analog outputs (six answers max on a single channel system, and four per channel on a dual channel system) and corresponding contact closure outputs to alert error states. Modbus communication over Ethernet is also standard.