On-line remote prediction of gasoline properties by combined optical methods

Abstract

On-line prediction of 10 gasoline properties, such as research and motor octane numbers, vapor pressure, API gravity, aromatic contents, etc., are carried out on-line by a remotely operated detector coupled to the main control unit by communication optical fibers. This information is of considerable importance since it is needed for process monitoring and for the preparation of final petrochemical products of well defined properties. The currently available spectroscopic methods for predicting gasoline properties, which are based on near infrared (NIR) (and recently on Fourier transform infrared (FTIR) spectrometry) coupled with chemometric algorithms, provide limited performance (e.g. 0.4 standard error of prediction (SEP), for octane number). We propose an improvement of the performance by applying combined optical methods. In this study we combine on-line information from a short-wave NIR photodiode array spectrometer (700–1000 nm) with laser induced fluorescence (LIF) spectra obtained with a PC-plugged in linear CCD spectrometer. UV excitation is performed by harmonics of a compact and low-cost Nd:YAG laser, and the system is remotely operated through optical fibers. A comparison between the octane number predictions by NIR spectrometry and by LIF from third and fourth harmonics, is provided. It is shown that the addition of the fluorescence information improves octane number prediction (<0.2 SEP). These two setups (NIR and LIF) can be combined into one integrated system, based on common optical fibers and detector.