DETAILED ANALYSIS OF C-5 AND C-6 DIENES IN LIGHT PROCESS STREAMS - QUALITATIVE ASSESSMENT OF CYCLIC VS ACYCLIC DIENES IN HEAVIER PROCESS STREAMS

A method has been developed to aid in identifying dienes, an undesirab le component in some process streams and products. For a sample of lig ht FCC gasoline, the combination of Diels-Alder derivatization of dien es with maleic anhydride and C-13 NMR analysis of the resulting adduct s allowed the identification of all but one of the 19 possible C-5 and C-6 dienes and the determination of their relative abundance. A more detailed analysis of dienes offers the possibility of correlating the extent of catalyst poisoning or gum formation with the total amount an d types of dienes present. Such an NMR analysis is possible only under ultrahigh resolution conditions with a high field magnet. To the best of our knowledge, this work at 11.7 T and a digital resolution of 0.7 2 ppb represents the first attempt at using a high field magnet to obt ain an ultrahigh resolution C-13 spectrum covering almost the entire C -13 chemical shift range. Resolving virtually all the signals for the numerous aliphatic, olefinic, and carbonyl carbons was critical for de termining the relative amount of each diene that reacted. Process stre ams with C-7(+) material (e.g., full range FCC gasoline) can also be d erivatized, but the product gives a carbonyl carbon region too complex for as detailed an analysis. Nevertheless, a qualitative assessment o f the relative amounts of cyclic and acyclic dienes appears possible.