Recent advances in the development of a fiber-optic-based instrument for on-line Raman analysis

Abstract
The measurement of composition of chemical process streams at multiple points is a critical problem in many industrial environments. We are developing an instrument, based on laboratory Raman spectroscopy, to measure composition of multiple components in a distillation column. A Nd:YAG laser is used to excite the sample and an interferometer is used to detect the Raman spectrum. The light from the laser is routed to the measurement points through a fiber optic probe which also gathers the light generated in the column by the Raman effect. A multiplexer is introduced to allow sharing of the expensive components of the system among several measurement points. The instrunient will initially be applied to distillation columns, but should be applicable to analysis of many liquid mixtures of commercial interest. The response time is approximately three minutes per measurement. The composition measurement range is from approximately 5% to 100% with an average error of less than 2% RMS. Progress in the implementation of the instrument will be discussed, with particular emphasis on losses due to optical fiber lengths up to 35 meters.

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