Stuart Farquharson

Applications of Raman spectroscopy to industrial processes

The role of on-line chemical analyzers is vital to process monitoring and control and product quality. Although traditional optical filter methods such as UV-VIS, NIR, and IR have enjoyed considerable success when applied on-line, they often require inconvenient and complex sampling schemes. These restrictions can be largely eliminated by fiber optic probes as evidenced by their growing popularity. Fiber optic technology also allows remote location of full spectrum analyzers which in turn facilitates multicomponent analysis. Recently, we have developed a Raman spectrograph which utilizes fiber optic probes and a CCD detector. We have been most successful with this system when it is applied to processes in a short term, investigative role. Examples of reaction intermediates and products, contaminant identification, and process optimization will be given.

Structural and vibrational characteristics of the tetrasulfatodimolybdenum ions with MoMo bond orders of 3.5 and 4.0

Abstract The compound K 4 [Mo 2 (SO 4 ) 4 ]Br·4H 2 O has been made and its crystal structure determined. Space group P 4/ mnc ; unit cell dimensions, a = 11.903(2), c = 8.021(1) A, V = 1136(1) A 3 . The compound is isomorphous with the analogous chloride whose structure has been reported. The Moue5f8Mo and Moue5f8Br distances are 2.169(2) and 2.926(1) A, respectively and the [Mo 2 (SO 4 ) 4 ] 3− ions reside on crystallographic special positions with 4/ m symmetry. The Raman spectra of both the bromo and chloro compounds have been measured and the Moue5f8Mo stretching frequency is 370 ± 1.5 cm −1 in each, for the compounds containing the natural isotopic distribution of molybdenum. The chloro compound has been prepared containing the pure isotope 92 Mo as well, and the Raman spectra recorded. The v (Moue5f8Mo) band is shifted by 6.8 ± 0.5 cm −1 . The compound K 4 [Mo 2 (SO 4 ) 4 ]·2H 2 O has also been prepared with Mo at natural abundance and with the pure isotope 100 Mo, whereby a shift of 8.5 ± 0.5 cm −1 was found. These and other results will be discussed with regard to the similarity of the Raman spectra of the Mo 2 (S0 4 ) 4 3− and M0 2 (S0 4 ) 4 4− species.

Applications of fiber optic Raman spectroscopy to chemical processes

The role of on-line chemical analyzers is vital to process monitoring and control and product quality. Although traditional optical filter methods such as UV-VIS, NIR, and IR have enjoyed considerable success when applied on-line, they often require inconvenient and complex sampling schemes. These restrictions can be largely eliminated by fiber optic probes as evidenced by their growing popularity. Fiber optic technology also allows remote location of full spectrum analyzers which in turn facilitates multicomponent analysis. Recently, we have developed a Raman spectrograph which utilizes fiber optic probes and a CCD detector. We have been most successful with this system when it is applied to processes in a short term, investigative role. Examples of reaction intermediates and products, contaminant identification, and process optimization are given.

Extruder Mixing Analysis Via A Fiber Optically Coupled Visible Spectrophotometer

An instrument has been designed to measure residence time distribution (RTD) in an extruder in a fast semiautomatic fashion. The instrument is composed of a spectrophotometer fiber optically coupled to the exit port of the extruder. Experiments illustrate the effects of screw design and rotation speed on RTD elution profiles.

Fiber-optic-based pH measurement in a geothermal brine

The measurement of pH in industrial chemical process is well established. Since pH can affect reaction rates, system corrosion, and/or water quality, a number of on-line electrodes have been commercialized. However, these devices necessarily contain a porous membrane (usually glass) to allow the flow of hydrogen ions which provides the electrical potential for measurement. In a recent application to a geothermal brine solution, we were unable to eliminate electrode fouling, even with considerable sample conditioning. As an alternative, we designed and constructed an in-line pH instrument based on the spectroscopic absorption of acid-base indicator dyes. The instrument introduced bromocresol green into the stream via a static mixer and measured the ratio of the characteristic acidic and basic absorption bands using an in-line fiber optic cell. Details of the design and its application are presented.

Kinetic studies of phosgene reduction via in-situ Fourier transform infrared analysis

Phosgene, a common reactant in the production of polyurethanes and polycarbonates, is unfortunately hazardous (threshold limit value equals 0.1 ppm). Consequently, the detection and elimination of atmospheric releases are paramount safety and environmental concerns. Proper design of systems to mitigate phosgene requires knowledge of the reaction kinetics for the chemistry involved. This paper presents our investigation of the reactions for phosgene with steam and ammonia. A Fourier transform infrared spectrometer (FTIR) equipped with a large volume (15 L), temperature controlled (+0.5 degree(s)C), 24.5 cm path length cell was used to measure the reaction kinetics. The reaction of phosgene with steam at 110 degree(s)C followed first order kinetics (t1/2 equals 10.2 min.) producing carbon dioxide and hydrogen chloride. The reaction of phosgene with ammonia at 80 degree(s)C followed second order kinetics (t1/2 equals 1.2 min.) producing ammonium chloride and urea. It was found, however, that at 25 degree(s)C this reaction follows a previously unreported pathway producing ammonium chloride and ammonium isocyanate at a faster rate (t1/2 equals 15 sec.). Based on this reaction, a pilot scale scrubbing tower was built with a manifold to mix ammonia with ppm levels of phosgene. A complete description of the experimental conditions, the reaction pathways as a function of temperature, and the performance of the ammonia scrubbing tower are given.