Raman spectroscopy for on-line distillation process control

In order to effectively control distillation processes, it is necessary that the composition of the chemical mixtures within the column be measured directly or estimated from physical measurements. Direct on-line composition measurement has many advantages, but has been difficult in the past to implement with laboratory spectroscopic instrumentation. Raman spectroscopy is a highly selective method for composition determination which shows great promise for plant-wide on-line process measurements and control in these applications. The scientific and economic feasibility of using Raman spectroscopy has been demonstrated based on laboratory experiments utilizing a Fourier transform Raman spectrometer with a 1.06 micron near-infrared YAG laser. The use of near infrared excitation has been successful in minimizing fluorescence problems. A prototype instrument for on-line work is under development. Preliminary studies have employed fiber optics in laser excitation and Raman collection. This will allow the instrument to be placed in a control room. Optical multiplexers will be utilized to allow a single analyzer to determine concentrations at a number of points within the process. 4 figs.