FT-IR IN THE QUANTITATIVE-ANALYSIS OF GASEOUS HYDROCARBON MIXTURES

FT-IR spectrometer provided with software for multicomponent analysis of IR spectra was used for simultaneous determination of up to 12 hydr ocarbons in a gaseous mixture. The hydrocarbons, ranging from methane to n-butane, were selected to simulate reaction product mixtures obtai ned in the dehydrogenation of n-butane, The concentrations of the hydr ocarbons in the sample were determined by fitting to the sample spectr um a set of pure calibration spectra of the gases present in the sampl e, In principle, the entire wavenumber range of the low-resolution IR spectrum could be utilized in the fit, The reliability of the results was checked from the residual spectrum, obtained by subtracting the fi tted from the measured spectrum, The residual spectrum will be pure no ise when the set of calibration spectra chosen for the analysis fits e xactly with the sample spectrum, Precision of the results, expressed a s average relative standard deviation, was +/-4%. Concentrations of mo st of the hydrocarbons were determined with an error less than +/-10%, The concentrations of isobutane, trans-2-butene, propane, and ethane deviated by more than 10% from the reference concentrations, The sum c oncentration of ethane and propane, however, deviated less than +/-1% from the reference, Difficulties in determining ethane and propane acc urately were due to the broad nature and small number of peaks in thei r IR spectra, IR spectrometry with multicomponent analysis of spectra provides a rapid and powerful method with potential for the study of c atalytic reactions at a time resolution of seconds.