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

A direct and fast method based on H-1 NMR spectroscopy for the determinatio n of paraffins (P), olefins (O), naphthenes (N) and aromatics (A), i.e. PON A content of FCC and coker (visbreaker) gasoline containing olefinic hydroc arbons has been developed. This is in continuation of our earlier work wher e a direct method was developed for the determination of naphthenes and aro matics content in straight run gasoline (no olefins). The total naphthenes have been estimated by applying the overlapping factor (F) due to the overl apping of signals of olefinic hydrocarbons with those of saturated cyclic h ydrocarbons in the region of 1.4-2.0 ppm in the H-1 NMR spectrum. The appli cation 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 hydrogen s (H) or carbons (Co) in the olefinic region (4.5-6.6 ppm) together with th e estimation of average alkyl chain length (n) of gasoline samples have fac ilitated the determination of total olefin content in the sample. The overl apping factor is different for FCC and coker gasoline due to the presence o f different types of olefinic structures and heir relative distribution. Th e utilisation of these parameters (F, n, H and Co), and average group molec ular weight concept have helped the derivation of equation enabling the dir ect estimation of PONA content of a sample. The developed H-1 NMR method is direct, fast, and reliable method and offers an alternative to long and te dious GC and MS methods. (C) 2001 Elsevier Science Ltd. All rights reserved .