Quantitative acquisition of differential absorption cross sections of chlorobenzenes at different temperatures

Abstract

Chlorobenzene is considered an essential organic synthesis intermediate and a precursor for the generation of persistent organic compounds in the waste disposal process, for which accurate detection of gaseous chlorobenzene can further help understand and control various chemical processes and effectively reduce pollution. Differential optical absorption spectroscopy is a reliable online method for detecting gaseous chlorobenzenes. It is crucial to investigate the effect of temperature on the optical absorption of the chlorobenzenes to quantify chlorobenzenes more precisely at various temperatures. A method to fix the effect of temperature variation on absorption spectra of chlorobenzene is initially proposed in this study, and it gave accurate concentrations. The proposed method can effectively improve the accuracy of chlorobenzene concentration measurements with an inverse concentration deviation of 3.2 % or less. The differential absorption cross sections at various temperatures are studied to understand how chlorobenzene absorption cross sections vary with temperature. Such a study is also helpful in reducing the concentration inversion errors induced by the variation of absorption cross sections of chlorobenzene with temperature. A novel method of introducing the binary function of the differential absorption cross sections with respect to wavelength and temperature is also proposed. The fitting of the binary function is done by downscaling functions at fixed wavelength and fixed temperature,respectively. Both fitting approaches obtained continuous differential absorption cross sections in the 201-220 nm wavelength band and 288-473 K temperature range, along with less than 2.74 % deviation in the concentration inversion measurements. Finally,based on the temperature specificity of the shape of the differential absorption cross sections,we developed another method using differential absorption spectroscopy for the simultaneous measurement of temperature and concentration, with a temperature prediction error of less than 1.89 %. This method is favorable to the applications of differential absorption spectroscopy in simultaneous measurement of temperature and concentration.

Keywords: Concentration inversion; Differential absorption cross section; Simultaneous measurements; Temperature dependence; UV differential optical absorption spectroscopy.