Study On The Deaggregation And Reaggregation Behavior Of Asphaltene Aggregates

Asphaltenes can precipitate from the heavy oil during the oil processing,which in turn causes coking.And the production of cokes will bring lots of problems to industry.The fundamental reason for the production of coke is the generation of asphaltene supramolecular aggregates.Although the current understanding of asphaltene supramolecular chemistry has formed,the study of formation mechanism and deaggregation methods of asphaltene aggregates still have great reseach potential.In this paper,two representative asphaltenes separated from Qingdao Petrochemical Company cacuum residue and Venezuelan vacuum residue respectively were studied.Then the influence on deaggregation and reaggregation of asphaltenes aggregates were investigated after some proper physical and chemical treatments.The research could provide a further theoretical basis for the efficient processing of inferior heavy oil.Aggregation phenomena of asphaltenes from different cacuum residue in different solvents were investigated at a series of concenteations by spectroscopy.The results showed that the solvents had a good deaggregation effect on the asphaltene supramolecular aggregates in dilute solutions.With the increase of asphaltene concentration,asphaltene molecules were reaggregated.And there was a “critical aggregation concentration(CAC)” in the asphaltenes aggregates.The “CAC” of asphaltenes in toluene,tetrahydrofuran(THF)and chloroform decreased successively.It ranged from 15?g/g to 40?g/g at 410 nm excitation wavelength.And the "CAC" of QDAs in the three solvents were lower than that of VNAs.Therefore the "CAC" was closely related to the type of asphaltenes and the nature of the solvents.The effects on deaggregation and reaggregation on asphaltenes of ultrasound were studied.And the results illustrated that the height of crystallite of QDAs aggregates and VNAs aggregates decreased by 0.93? and 0.76? respectively after the ultrasound treatment,and the average number of sheet per crystallite reduced by 0.26 and 0.2 respectively.However,there was no significant change in the "CAC" of two asphaltenes in toluene after ultrasound treatment,which indicated that the effect of ultrasound on asphaltene was mainly physical dispersion.In addition,the UV-Vis absorption spectroscopy study found that the additives with polar functional groups had a good stability effect on the asphaltenes.Oleic acid and sodium dodecyl benzene sulfonate could prevent the asphaltene from precipitating and increase the stability of asphaltenes in solutions.The effects of hydrogen bonding on the aggregation of asphaltenes were studied by sulfonation and methylation of functional groups.The results demonstrated that the sulfonation reaction could enhance the polarity of the asphaltene molecules and strengthen the hydrogen bonding,which together made the forces of aggregation become larger,so that the sulfonated asphaltenes could not be dissolved in toluene and other solvents.The hydrogen bonding between asphaltene molecules was weakened after methylation of functional groups,so that the asphaltene supramolecular aggregates were deaggregated.The "CAC" of VNAs after methylation in toluene was increased by about 10?g/g,which indicated that the methylated asphaltenes were not easy to reaggregate.The effects of alkylation of different chain length groups on aggregation were studied.It was found that the asphaltene supramolecular aggregates were deaggregated after the alkylation reaction.After n-butyl alkylation,the average number of sheet per crystallite reduced from 6~8 to below 3.The introduction of n-butyl or n-octyl groups in asphaltenes made the molecular weight of alkylated asphaltenes significantly lower than that of unalkylated asphaltenes.The alkylated asphaltene aggregates in solutions had a loose laminar morphology,while asphaltenes aggregates before alkylation showed a dense spherical shapes.And the asphaltenes after alkylation were not easy to reaggregate,so that the "CAC" in the three solvents significantly increased.The "CAC" of n-butyl and n-octyl alkylated QDAs in toluene were increased to 100~120?g/g and 120~140?g/g respectively,while that of VNAs were increased to 120~160?g/g and 140~160?g/g respectively.In other two solvents,the "CAC" of alkylated asphaltenes were also significantly improved.The possible mechanism of deaggregation and reaggregation of asphaltene aggregates by alkylation reaction was proposed.