Optical Absorption Measurements of Hydrogen Chloride at High Temperature and High Concentration in the Presence of Water Using a Tunable Diode Laser System for Application in Pyrohydrolysis Non-Ferrous Industrial Process Control

• Published in: Applied spectroscopy 2015-06, Vol.69 (6), p.705-713
• Main Authors: Tzanetakis, Tommy, Susilo, Robin, Wang, Zhenyou, Padmanabhan, Arathi, Davis, Boyd R., Thomson, Murray J.
• Format: Article
• Language: English
• ISSN: 0003-7028; 1943-3530
• DOI: 10.1366/14-07509

A tunable diode laser (TDL) was used to measure hydrogen chloride (HCl) spectra at 5747 cm−1 (1.74 μm) and temperatures of 25–950 °C in a quartz cell. The purpose was to evaluate the capability of monitoring HCl concentration under pyrohydrolysis conditions using a near-infrared (NIR) laser. These conditions are characterized by 20–40% HCl, 2–40% H2O, and the presence of metal chloride vapors at temperatures of 600–1000 °C. Spectral peak area measurements of HCl–N2 mixtures at atmospheric pressure and a path length of 8.1 cm showed linear absorption behavior between concentrations of 5–95% and temperatures of 25–950 °C. Results from the addition of 2–40% water (H2O) indicate that the HCl peak area relationships are not affected for temperatures of 350–950 °C. Evaporating NiCl2 within the cell did not show spectral interference effects with HCl between 650 and 850 °C. The results from this work indicate that a near-infrared optical sensor is capable of measuring high HCl concentrations at high temperatures in the presence of high H2O content during pyrohydrolysis process conditions.