Measuring water in glycol during glycol dehydration with a ...
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Measuring water in glycol during glycol dehydration with a solid-state FTIR sensor Author: Dr. Jonathon D. Speed FTIR Spectrometer Abstract The Keit IRmadillo TM was used to monitor levels of water present in monoethylene glycol (MEG) and triethylene glycol (TEG). Quantitative analysis of water content is possible with limits of detection (LoDs) below the practical drying level of glycols. This is an effective method of monitoring water levels in glycols during glycolic dehydration. Introduction Glycol dehydration of liquified natural gas and liquified petroleum gas is a common method of purifying raw materials in the petrochemical industries. A key step in the process is the drying and recycling of glycols for re-use. To maintain effective dehydration, the glycol must be dry before being re-introduced. But how do you monitor the level of water in the glycol? Common water quantifying techniques n Karl Fischer titration – this is a common technique for quantifying water levels in liquids. It is highly accurate and precise but requires taking a sample extract, is slow, and expensive. n Mass loss calculations –a straightforward technique but is affected by all volatile compounds present and can be very inaccurate. It still requires a sample extraction and can be very slow. n On-line spectroscopic techniques – these are real-time measurements with good levels of precision and accuracy. Until recently they haven’t been truly suitable for online analysis, but the development of the IRmadillo enables real-time, online measurements. Key Words n Glycol dehydration n MEG / TEG / PEG n Oil & Gas n Petrochemicals n Water analysis n Online process monitoring www.keit.co.uk The need for a robust solution Spectroscopic measurements typically fall into three main types for process analysis: near infrared (NIR), mid-infrared Fourier transform (i.e., FTIR) and Raman spectroscopy. Both Raman and NIR instruments can be used in industrial processes, but they lack any real sensitivity for water. Conventional FTIR spectrometers are more sensitive to water but necessitate the use of fragile fibre probes, which are wholly unsuited for the industrial environment. Here we present a robust and rugged FTIR- based sensor that is inherently vibration resistant and reliable. This is achieved by the avoidance of all moving parts and fibre probes, offering a tough and resilient method of process monitoring. Suitable insertion points for the IRmadillo into a typical glycol dehydration process are shown in Figure 1. Application Note
Transcript of Measuring water in glycol during glycol dehydration with a ...
Measuring water in glycol during glycol dehydration with a solid-state FTIR sensor
Author: Dr. Jonathon D. Speed
FTIR Spectrometer
AbstractThe Keit IRmadilloTM was used to monitor levels of water present in monoethylene glycol (MEG) and triethylene glycol (TEG). Quantitative analysis of water content is possible with limits of detection (LoDs) below the practical drying level of glycols. This is an effective method of monitoring water levels in glycols during glycolic dehydration.
IntroductionGlycol dehydration of liquified natural gas and liquified petroleum gas is a common method of purifying raw materials in the petrochemical industries. A key step in the process is the drying and recycling of glycols for re-use. To maintain effective dehydration, the glycol must be dry before being re-introduced. But how do you monitor the level of water in the glycol?
Common water quantifying techniques
n Karl Fischer titration – this is a common technique for quantifying water levels in liquids. It is highly accurate and precise but requires taking a sample extract, is slow, and expensive.
n Mass loss calculations –a straightforward technique but is affected by all volatile compounds present and can be very inaccurate. It still requires a sample extraction and can be very slow.
n On-line spectroscopic techniques – these are real-time measurements with good levels of precision and accuracy. Until recently they haven’t been truly suitable for online analysis, but the development of the IRmadillo enables real-time, online measurements.
Key Words
n Glycol dehydrationn MEG / TEG / PEGn Oil & Gasn Petrochemicalsn Water analysisn Online process monitoring
www.keit.co.uk
The need for a robust solutionSpectroscopic measurements typically fall into three main types for process analysis: near infrared (NIR), mid-infrared Fourier transform (i.e., FTIR) and Raman spectroscopy. Both Raman and NIR instruments can be used in industrial processes, but they lack any real sensitivity for water. Conventional FTIR spectrometers are more sensitive to water but necessitate the use of fragile fibre probes, which are wholly unsuited for the industrial environment.
Here we present a robust and rugged FTIR-based sensor that is inherently vibration resistant and reliable. This is achieved by the avoidance of all moving parts and fibre probes, offering a tough and resilient method of process monitoring. Suitable insertion points for the IRmadillo into a typical glycol dehydration process are shown in Figure 1.
Application Note
Figure 1: A simplified schematic showing the glycol dehydration process and possible insertion points.
ExperimentalThe IRmadillo was used to analyse individual samples of monoethylene glycol (MEG) and triethylene glycol (TEG) with known concentrations of water. These ranged from nominally dry (50 and 800 ppm water for MEG and TEG respectively) to ~10,000 ppm. This is the equivalent of 99 – 100 % glycols. The samples were made in anhydrous conditions under a nitrogen atmosphere to prevent any wetting from water in the air.
Samples were acquired for 120 s in batches of six. Five of these spectra were used to build chemometric models and the remaining one spectrum per batch was used to test the model. The data were analysed using orthogonal signal correction (OSC) and partial least squares (PLS) models to predict the concentrations in real time.
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Figure 2: Plots of measured values vs reference values for water in MEG (top) and TEG (bottom).
Results and discussionThe IRmadillo measures how much infrared light the sample absorbs. Water absorbs light a specific frequency, but the change in absorbance is extremely small. This means that it is necessary to use chemometrics to correlate the change in light with the concentration of water. (Once a model has been built this can be performed automatically by the software in real time.)
The results from the chemometric models are shown in Figure 2. These plots show the measured value from the IRmadillo on the y-axis vs the reference value (known from making up stock solutions) on the x-axis. A perfect correlation would be a straight line with a slope of 1. The grey spots show the samples that were used to build
the model, while the red spots show the results from samples that were not used in the model — these are true predictions.
It is immediately apparent from the graphs that there is excellent correlation between the measured and reference samples. This means that the IRmadillo can accurately measure the water concentration. The fact that the samples are closely packed along the line also shows that the IRmadillo is very precise.
The limit of detection (LoD) for water in MEG and TEG is 139 and 96 ppm respectively. This means it is possible to monitor drying of MEG and TEG to >99.985 and 99.990 % respectively.
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ConclusionsThe IRmadilloTM is an effective, accurate and precise sensor for measuring water in glycols. It has been demonstrated directly for monoethylene glycol and triethylene glycol, but the technique is applicable to any glycol dehydration mix. It is possible to monitor water contents to 139 ppm in MEG and 96 ppm in TEG. It should be noted that the practical drying levels for MEG and TEG are 50 and 800 ppm respectively. This means that in the case of TEG it would be possible to monitor the dryness to a level lower than be currently achieved on a practical scale.
©2018 Keit Ltd. trading as Keit Spectrometers4 Zephyr Building, Eighth Street, Harwell Campus, Didcot, Oxfordshire, OX11 0RL, United Kingdom+44 (0) 1235 431260 n [email protected] n www.keit.co.ukIRmadillo is a Registered Trade Mark in the UK under 3185204, in the US under 5389749, and at the EUIPO under 016222408. KEIT is a Registered Trade Mark at the EUIPO under 012140414.
Figure 3: FTIR spectra of water in MEG and TEG as recorded by the IRmadillo spectrometer. The area shown in the red box illustrates the region where water shows a signal.
FTIR Spectrometer
Keep in mindThere may also be other compounds present during the dehydration process, which may be of interest to you (i.e., small organic acids).
The IRmadillo always observes all the compounds of a mixture, and can track multiple compounds simultaneously. It can provide a full picture of your process, with monitoring tailored to your needs.
9 November 2018 10:28 am
