In-Situ Laser Raman Spectroscopy Adapted to Process Conditions for Studying Cyclohexane Oxidation

Abstract

Cyclohexane oxidation is an economically important process. To maintain high selectivities of 70 to 90%, the reaction is performed at low conversion up to 6%. To improve this process, investigations on the reaction mechanism are of high interest, which requires measurement techniques able to detect chemical species precisely even at very low concentrations. For this purpose, an in-situ measurement technique based on laser Raman spectroscopy with superior detection sensitivity and an optically transparent microchannel to monitor the process of cyclohexane oxidation has been developed. The challenge is now to adapt this system to required conditions. In this article, we show that the influence of pressure is negligible. However, increasing temperatures influence the intensity of the Raman spectra significantly. As the temperature influence on the intensity of the Raman light is specific for each species, a temperature dependent calibration must be done to determine the concentrations of the chemical species precisely. In order to reach low detection limits also at high temperatures, the charge-coupled device (CCD) integration time had to be increased. For temperatures below 486 K, the limits of detection are less than 0.05 m/m %.