Real-time analysis of light alkenes at elevated temperatures and pressures by fiber-optic near-infrared spectroscopy

The effects of elevated temperature (up to 140 degrees C) and pressure (up to 500 psi) on the Fourier transform near-infrared (FT-NIR) spectra of monoalkylated light alkenes and the feasibility of quantitative determination of these compounds were investigated via fiber-optic FT-NIR spectroscopy, The effects of elevated pressures on spectra were found to be insignificant, However, the temperature effects were critical, especially for the lighter molecules such as ethylene and propylene, Therefore, the determination of these compounds at elevated temperatures requires the incorporation of the temperature effects into the calibration model, An apparatus to collect the spectra of these compounds at elevated temperatures and pressures by fiber-optic FT-NIR spectroscopy was constructed, The determination of ethylene and 1-octene was evaluated, Calibration models were built by using partial least-squares (PLS) regressions, Standard errors of prediction values were <0.5 wt % for both ethylene and 1-octene, and the absolute error of determination for alkenes is expected to be less than +/-0.75 wt %.