On-Line Monitoring of Chlorosilane Streams by Raman Spectroscopy

Abstract

On-line Raman spectroscopy was used to monitor the composition of methylchlorosilane streams from distillation columns. A spectrometer was assembled that used 532 nm laser light and a fiberoptic probe that could be inserted into corrosive liquid streams. The spectral regions below 800 cm−1 and near 2250 cm−1 contained strong, distinctive bands that were used to identify and quantitate the species of interest. On-line spectra were recorded at 5 min sampling intervals. Several instances were found where large changes in the composition of the columns were observed. Detection limits of 1000 ppm were generally achievable, and, in favorable circumstances, compositional changes of 100 ppm could be detected. Raman spectroscopy gave much better time resolution than current gas chromatography (GC) monitoring and is also projected to have lower capital and maintenance costs.

Process Measurements by Raman Spectroscopy

“…Speciation is achieved using optical filters, and (presumably) PMT detection. Concentration strip charts for CO, CO 2 , N 2 , O 2 , H 2 , H 2 O, NH 3 and hydrocarbons were presented which agreed well with GC (gas chromatography) results, although it was not possible to assess detection limits from these data. The Raman method was preferred over either GC or mass spectrometry, owing to superior speed of analysis, lower cost (than mass spectrometry) and simpler maintenance (it was claimed to require only 20 min per 6 months!).…”

“…Real-time feedback can allow action to be taken under unstable operating conditions such as start-up or short-term "glitches", which might be beyond the response speed of an off-line technique. 3 In turn, this can yield higher throughput or better product consistency. This implementation often has the highest commercial benefits of any on-line analyzer system.…”

“…Raman may have operational advantages, such as lower consumables and maintenance costs, and/or ease of interfacing, when compared with alternatives such as chromatography. 3 For these reasons, Raman spectroscopy has actually been used to great advantage for the analysis of process gases (see Section 7.1).…”

“…One of the best known examples of the analysis of a reacting liquid is due to Freeman and coworkers, 99 who developed an on-line Raman method to control the manufacture of PCl 3 . In this reaction elemental phosphorus is combined with chlorine in a boiling solution of PCl 3 . If the chlorine level is too high, PCl 5 is produced as an unwanted by-product, so more phosphorus must be added to prevent this.…”

Raman Spectroscopy

“…Dow Corning monitors the concentration of a chlorosilane distillation stream with Raman spectroscopy [269] . Dow Corning monitors the concentration of a chlorosilane distillation stream with Raman spectroscopy [269] .…”