Cylindrical IR-ATR Sensors for Process Analytics

Infrared attenuated total reflection (ATR) spectroscopy is a common laboratory technique for the analysis of highly absorbing liquids and solids. However, in a process environment, maintaining a sufficient sample exchange and cleaning of the sensitive surface of the element is a crucial issue. An important industrial application is the measurement of isocyanate concentrations. Isocyanates are necessary for the fabrication of polyurethane materials and are among the chemicals with the highest production volume worldwide. For process applications, narrowband photometers or MEMS spectrometers are more appropriate than the use of bulky FTIR instruments frequently encountered in a laboratory environment. Toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI) concentrations are measured with a planar ATR photometer setup. Using a miniature Fabry–Perot interferometer (FPI), trace concentrations below 100 ppm (m/m) are detected. By employing an ATR element of the cylindrical shape, sensors can be realized with a smooth surface ideally suited for an automatic cleaning system in a process environment. A laboratory setup with sapphire tubes as ATR elements for incorporation in a liquid flow system is described. Reflection and transmission configurations were investigated. Measurements with acetonitrile as a less toxic substitute showed that with cylindrical ATR sensors’ detection limits for isocyanate concentrations below 100 ppm (m/m) are feasible.

[1]  Chen Qian,et al.  Determination of Chlorinated Hydrocarbons in Water Using Highly Sensitive Mid-Infrared Sensor Technology , 2013, Scientific Reports.

[2]  Tomas Hirschfeld,et al.  Internal Reflection Spectroscopy , 1967 .

[3]  P. Werle,et al.  The limits of signal averaging in atmospheric trace-gas monitoring by tunable diode-laser absorption spectroscopy (TDLAS) , 1993 .

[4]  C. Wolf,et al.  Mid-Infrared Spectroscopy for Monitoring of Anaerobic Digestion Processes - Prospects and Challenges , 2016 .

[5]  M. Dubé,et al.  In-Line Monitoring of SBR Emulsion Polymerization Using ATR-FTIR Spectroscopy , 2010 .

[6]  N. J. Harrick,et al.  Electric Field Strengths at Totally Reflecting Interfaces , 1965 .

[7]  Wen-Hao Su,et al.  Mid-infrared (MIR) Spectroscopy for Quality Analysis of Liquid Foods , 2019, Food Engineering Reviews.

[8]  H. M. Heise,et al.  Multivariate Calibration for the Determination of Analytes in Urine Using Mid-Infrared Attenuated Total Reflection Spectroscopy , 2001 .

[9]  I. Coddington,et al.  Real-time liquid-phase organic reaction monitoring with mid-infrared attenuated total reflectance dual frequency comb spectroscopy , 2019, Journal of Molecular Spectroscopy.

[10]  Armin Lambrecht,et al.  Broadband spectroscopy with external cavity quantum cascade lasers beyond conventional absorption measurements. , 2014, The Analyst.

[11]  A. Lambrecht,et al.  Continuous Glucose Monitoring by Means of Fiber-Based, Mid-Infrared Laser Spectroscopy , 2006, Applied spectroscopy.

[12]  B. Lendl,et al.  A pocket-sized 3D-printed attenuated total reflection-infrared filtometer combined with functionalized silica films for nitrate sensing in water , 2020, Sensors and Actuators B: Chemical.

[13]  Steffen Hennig,et al.  ATR-Photometer zur Bestimmung der Isocyanatkonzentration in Prozessanwendungen , 2015 .

[14]  H. Siesler,et al.  In situ monitoring of an isocyanate reaction by fiber-optic FT-IR/ATR-spectroscopy , 2007 .

[15]  MIR-ATR sensor for process monitoring , 2015 .

[16]  J. Ulrich,et al.  Application of ATR-MIR spectroscopy in the pilot plant—Scope and limitations using the example of Paracetamol crystallizations , 2013 .

[17]  S. Sim,et al.  Partial Least Squares (PLS) Integrated Fourier Transform Infrared (FTIR) Approach for Prediction of Moisture in Transformer Oil and Lubricating Oil , 2019, Journal of Spectroscopy.

[18]  D. W. Allan,et al.  Statistics of atomic frequency standards , 1966 .