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Numerous chemical process benefit from accurate monitoring of chlorine gas. In most cases other chlorinated components are present in the stream as well and it is often useful to utilize the same instrument to measure the concentration of chlorine from low levels (ppm range) to the high percent levels. It will be shown that the CLT-360 being a full spectrum high resolution analyzer is an ideal analyzer for these applications.
Low levels of chlorine gas When measuring low levels of chlorine the absorbencies are usually very low and an analyzer with a high signal to noise ratio is essential. The CLT-360, is a UV/VIS diode array spectrophotometer with 1nm resolution and an accuracy of ±0.0002AU . The chlorine concentration in the gas phase is measured down to 10ppm ±1ppm. (in liquids 1ppm ±0.1ppm).
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High and low levels of chlorine using the same analyzer Many applications require a continuous measurement of chlorine from low levels (ppm range) to the high percent levels. A filter based spectrometer can not be used since the signal will either be saturated at high Cl2 concentration or the signal will be too low for detection at the lower concentration range. However when utilizing the CLT-360, a full spectrum analyzer, it is feasible to cover the complete dynamic range since it allows for the low and high level chlorine streams to be measured at various wavelengths with the same analyzer. The spectrum is measured continuously and analyzed to give the chlorine concentration. If the absorbance is above a certain threshold value a new evaluation method is loaded automatically using a new set of standards and wavelengths for analyses. For example in figure 2, three spectra are shown; The 800ppm Cl2 can be measured at the 300-350nm range, the 8% chlorine can be measured at 400-440nm range and so on, covering the entire range. Since the evaluation methods are different for the various concentration ranges the accuracy of measurement is maintained at any stream composition. Measuring chlorine in the presence of interfering components Yet another advantage of the CLT-360 is its ability to handle either gas or liquid mixtures with interfering spectral features due to its full spectrum capabilities. For example figure 3 and 4 shows the absorbance spectra of Cl2 and NCl3. By measuring a complete UV/Vis spectrum and applying a multi components evaluation analysis to the data the concentration of both components can be continuously monitored. |
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Figure 2: Absorbance spectra of Cl2 gas. |
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