Hydrocarbon group (PONA) analysis of reformate by FT-i.r. spectroscopy

Multicolumn valve-switching gas chromatography is commonly used in refineries for determining paraffins, olefins, naphthenes and aromatics (PONA) contents of reformate and naphtha samples. A simplified and fast alternative method, Fourier transform infrared (FT-i.r.) spectroscopy, for the same purpose was successfully used in the present work. In this method, a calibration technique which took both spectral and concentration data into consideration was developed by using the instrument manufacturer's software utilizing partial least-squares (PLS) regression analysis. For this, the mid-i.r. range (4000-400 cm^-1) was subdivided into four regions that are usually attributed to different functional groups. An excellent correlation between the FT-i.r. and g.c. results was found, particularly for paraffins and aromatics (R² = 0.97 and 0.96 respectively). The average absolute differences between the results obtained from FT-i.r. and g.c. were 1.3, 0.5, 0.2 and 0.9 vol.% for paraffins, olefins, naphthenes and aromatics respectively.