PONA analyses of cracked gasoline by 1H NMR spectroscopy. Part II

Abstract

A direct and fast method based on 1H NMR spectroscopy for the determination of paraffins (P), olefins (O), naphthenes (N) and aromatics (A), i.e. PONA content of FCC and coker (visbreaker) gasoline containing olefinic hydrocarbons has been developed. This is in continuation of our earlier work where a direct method was developed for the determination of naphthenes and aromatics content in straight run gasoline (no olefins). The total naphthenes have been estimated by applying the overlapping factor ( F) due to the overlapping of signals of olefinic hydrocarbons with those of saturated cyclic hydrocarbons in the region of 1.4–2.0 ppm in the 1H NMR spectrum. The application of F eliminates contribution of substituted olefinic protons in the naphthenic region and allow measurement of integral area exclusively due to naphthenic protons. The estimation of absolute number of olefinic hydrogens ( H) or carbons (Co) in the olefinic region (4.5–6.6 ppm) together with the estimation of average alkyl chain length ( n) of gasoline samples have facilitated the determination of total olefin content in the sample. The overlapping factor is different for FCC and coker gasoline due to the presence of different types of olefinic structures and their relative distribution. The utilisation of these parameters ( F, n, H and Co), and average group molecular weight concept have helped the derivation of equation enabling the direct estimation of PONA content of a sample. The developed 1H NMR method is direct, fast, and reliable method and offers an alternative to long and tedious GC and MS methods.