Structural investigation on column-chromatographed vacuum residues of various petroleum crudes by 13C nuclear magnetic resonance spectroscopy

Abstract

Proton and carbon-13 nuclear magnetic resonance spectroscopy of various vacuum residues and their fractionated samples were carried out to investigate average molecular structures. The structural parameters derived from carbon distribution agreed with those derived from p.m.r. within experimental error. In the aliphatic region of the c.m.r. spectra, characteristic peaks assignable to (CH2)n − n ≧ 6 (29.7 ppm) and CH3CH2CH2CH2 (14.1 ppm) etc. can be observed. The relative intensities of these peaks suggest that the methylene chain contained in vacuum residues is much longer ((CH2)n − n ≧ 12) than has been considered previously. Using the information about the aliphatic region of the c.m.r. spectrum and the structural parameters, an average structural model was deduced.