A New Spectroscopic Technique for in situ Chemical Reaction Monitoring Using Mid-Range Infrared Optical Fibers

A new versatile spectroscopic technique for chemical reaction monitoring using mid-range infrared optical fibers has recently been developed. Chalcogenide glass optical fibers were used to direct infrared radiation from an FT-IR spectrometer through ZnSe Cylindrical Internal Reflectance (CIR) crystals embedded within laboratory scale reactors. The utility of this technique for studying chemical systems was demonstrated by monitoring various stoichiometric reactions at ambient conditions. A laboratory-scale glass reactor fabricated with the capability to mount a CIR crystal was used as the reaction vessel. The ability of this system to monitor high-pressure and/or high-temperature chemical reactions was also demonstrated by studying the cobalt catalyzed hydroformylation of olefins. A stainless steel CIR reactor, slightly modified to allow for connections with optical fibers, was used for experiments ranging from 50 to 90°C and under 750 to 800 psi synthesis gas (H₂/CO mixture). In all cases sufficient signal strength at the detector and adequate penetration into the bulk reaction medium was achieved, resulting in infrared spectra of high quality and resolution. Spectral scans of the reaction in progress allowed the accurate determination of the concentration of reactants and products as a function of time.