Structure And Composition Characterization Of Solid Asphaltenes

Asphaltene is the most complex component of petroleum with low H/C value and high heteroatom content.The average molecular weight is relatively large.As the precursor of coke during the process of residue processing,it is prone to arise condensation reaction and deposited on the catalyst.The deposition will block the catalyst pore,reduce the activity of catalyst,even lead to poisoning deactivation of catalyst,seriously affecting the lightening process of residue.The acid functional groups and sulfides of asphaltene also corrode oil refining equipment and pipeline.Asphaltene is an intermediate type of petroleum from hydrogen-rich hydrocarbons to carbon-rich toluene insolubles.There are two opposite processes of hydrogen enrichment and carbon enrichment in the process of oil formation and processing.Asphaltene is particularly important as an intermediate part.Therefore,in-depth study of the composition,structure and nature of asphaltene is the basis for the full exploitation and utilization of heavy oil resources.In this paper,the structure and composition of solid phase n-heptane asphaltene of different base residue are mainly studied.The structural units of asphaltene molecules were constructed by solid-state ¹³C-NMR.And asphaltene structure was confirmed by XRD,IR and reasonable assumptions.The result was consistent with result obtained from solid ¹³C-NMR spectra,demonstrating that the simulated asphaltene structural units were reasonable.At the same time,the structure of different asphaltenes was compared.The results showed that the structural units of asphaltene were similar.Asphaltene molecules consist of 4 to 6 structural units,each containing 5 to 7 condensed aromatic rings.The calculated values of naphthenic carbon and alkyl carbon by reasonable assumptions are consistent with those obtained from¹³C-NMR spectra.And naphthenic carbon is the main carbon in saturated carbon of asphaltene.The naphthenes are linked by an approximately equal ratio of cata-condensed and peri-condensed condensation.Alkyl side chains are predominant saturated carbon with short side chains.Compared with residual asphaltene,the average relative molecular mass of coal tar pitch is smaller.There is no?002?peak in XRD spectrum.Due to low number of aromatic rings and alkyl chains,short of alkyl chain,weak interaction between unit flakes,it is difficult to form a stacked structure.So that carbon atoms of structural units tend to be irregularly arranged.Decrease in the lattice level leads to weakening or disappearing of?002?peak intensity.There is a gap between results of asphaltene structure parameters obtained by ¹H-NMR and results obtained by ¹³C-NMR,especially in the value of alkyl carbon and naphtenic carbon.Number of alkyl carbon is much larger than number of naphthenic carbon and alkyl side chain is large in the structure parameters calculated by ¹H-NMR spectrum.However,there was no obvious absorption peak between 724 and 722 cm^-1 in IR spectrum of asphaltene,indicating that asphaltene did not have a long alkyl side chain.It can be concluded that asphaltene structure parameters calculated by ¹H-NMR spectrum have some error.The reason is that when structural parameters of asphaltene are calculated by ¹H-NMR spectrum,the basic premise is that H/C value of?,?and?far of aromatic ring system is equal to 2?x=y=2?.However,for different substances,it will bring about large error when it is assumed that x is equal to 2,especially those with high relative molecular mass,few alkyl substituents and short alkyl side chains.