Fundamental Study On The Thermochemical Conversion Of Oil Sand Bitumen

As a kind of unconventional petroleum resources with abundant reserves,oil sands have attracted more and more attention from various countries.As an inferior heavy oil,oil sand bitumen is featured by high density,viscosity,asphaltenes content,heteroatom content and carbon residues.Therefore,whether oil sands are directly retorted or re-processed after extraction,it is necessary to conduct molecular-level thermochemical investigation of oil sand bitumen.However,the current researches on the thermal conversion behavior of oil sand bitumen mainly focus on oil sands or oil sand bitumen itself and fail to reflect in-depth the thermal conversion process of oil sand bitumen in the chemical-groups level,which has been a bottleneck for the efficient conversion and utilization of oil sand resources.Aiming to the basic research of thermal conversion of oil sand bitumen that should be strengthened,three oil sand bitumens are selected as research subject in this study.The present work mainly studies the correlation between chemical structures and thermal conversion mechanism of oil sand bitumen and its group-fractions,the role and influence of each group-fraction during the thermal conversion of oil sand bitumen,as well as the fluid thermal conversion behavior of oil sand bitumen.It is significant to provide the important theoretical basis and guidance for the selection of reactors,optimization of reaction technology and regulation of target products during the thermal upgrading of oil sand bitumen.Related research works are as following:According to the characteristics of oil sand bitumen enriched in oxygen and sulfur polar compounds,the group-fractions of oil sand bitumen were effectively separated by modified eight-fractions separation methods.The oil sand bitumen was separated into saturates,aromatics（light aromatic,medium aromatic and heavy aromatic）,resins（light resin,medium resin and heavy resin）and asphaltenes by using this method.Then,the chemical structures of oil sand bitumen and its group-fractions were studied in detail based on the methods of elemental analysis,FTIR,¹H NMR,etc.The results showed that with the group-fractions from saturates to asphaltenes,the content of methyl substituents and alkyl substituents attached to aromatic ring structure,the number of naphthenic rings,the fraction of aromatic carbon,the number of aromatic rings,condensation degree,and the content of monocyclic,bicyclic and polycyclic aromatic structures in the aromatic ring structure all tended to increase,while the average chain length of the alkyl structure featured the opposite variation.Sulfide sulfur,thiophenic sulfur and sulfoxide/sulfone sulfur accounted for 39.31%,53.93%and 6.74%in total sulfur of oil sand bitumen,respectively.Sulfidic sulfur and thiophenic sulfur in the oil sand bitumen had the highest enrichment in the aromatics,followed by in asphaltenes and resins.In views of the structure characteristics of oil sand bitumen and its group-fractions,the thermal cracking characteristics of oil sand bitumen and its group-fractions were investigated in depth by using the TG-FTIR and Py-GC/TOF-MS.It revealed the correlation between chemical structures and thermal cracking behavior of oil sand bitumen and its group-fractions,and effect of various components on thermal-cracking behavior of oil sand bitumen.Firstly,the results obtained from the TG-FTIR study showed that the thermal-cracking processes of oil sand bitumen and its group-fractions were mainly consisted of three stages,i.e.,volatilization stage,main cracking stage and coking stage.Wherein,the weight loss of saturates and light aromatics mainly occurred in volatilization stage,which was mainly originated from the volatilization of compounds with low points.The cleavage of alkyl side chain structures in light aromatics of aromatics and light resins of resins contributed the most to the thermal-cracking of the oil sand bitumen in the main cracking stage.The release rules of CO₂ among group fractions were not obvious,and the release intensity of CO₂ formed from the medium resins and asphaltenes were markedly larger than that formed others.The saturates,asphaltenes,resins and its subfractions contributed the most to the formation of C₂H₄、CH₄ and light aromatics during the thermal cracking of oil sand bitumen.The formation of gaseous C₂₊aliphatic hydrocarbons for oil sand bitumen was mainly originated from asphaltenes and aromatics（especially for medium aromatics）.The differences in the evolution behaviors of the main gaseous products formed from the thermal-cracking of different group-fractions were related to the differences in composition and chemical structure between these group-fractions.The heating rate had an effect on the thermal-cracking characteristic parameters and the group-fraction which palyed an key role in promoting the formation of volatile products formation during the thermal cracking of oil sand bitumen.The thermal-cracking kinetics of oil sand bitumen and its group-fractions were analyzed by three dynamic methods of FWO,DAEM and Friedman based on TG analysis data.On basis of the conversion rate of group-fractions,the interactive dynamics model based on the group-fractions was established.And then,the effects of temperature,heating rates（10-20000 ^oC/s）and reaction time on composition and distribution of volatile products formed from the fast thermal-cracking process of oil sand bitumen,and the fast thermal cracking behaviors of group-fractions in oil sand bitumen were investigated in detail by using the Py-GC/TOF-MS.The results showed that during the fast thermal cracking of oil sand bitumen,the temperature increase could promote the cleavage of alkyl chain structures.However,when the temperature was too high,especially after 700°C,the relative content of alkene products in the volatile products had a significant decrease,and a remarkable increase was featured in the relative content of diolefins and aromatic products.The prolongation of the reaction time caused the secondary reaction of the alkenes,leading to a decrease in the alkenes and an increase in the aromatic products.The high heating rate,especially the flash rate（20000 ^oC/s）,promoted the formation of alkenes,diolefins and aromatic products.Compared to the relative content distribution of the fast thermal-cracking volatile products among group-fractions of oil sand bitumen,the relative content of alkenes formed from saturates was the largest,while that of alkanes was the lowest.The resins（especially heavy resins）generated more aromatic products.The relative content of alkenes resulting from asphaltenes was the lowest,while that of alkanes and diolefins was the largest.In addition,the relative content of aromatic product obtained from asphaltenes was closed to that from medium resins.The volatile products distribution of aromatic fraction was similar with that of oil sand bitumen,wherein the heavy aromatic fraction featured the closest products distribution to that of oil sand bitumen.In order to further link the theoretical study of thermal-cracking process with the actual process,the fluidized thermal conversion behavior of oil sand bitumen was investigated by a small fluidized bed reactor.This mainly focused on the influences of temperature and heat carriers（silica sand,calcium aluminate and FCC catalyst）on the three-phase products,the chemical structure of liquid products,and the composition and transfer behavior of sulfur compounds in liquid products.The results showed that as the temperature increased,the yields of dry gas,liquefied petroleum gas and coke,as well as the yield and selective of C₂-C₄alkenes in gas products obtained from the thermal cracking of oil sand bitumen over the different heat carriers all increased.However,the yields of liquid products had a decrease tendency with the temperature,of which VGO and heavy oil fractions featured an obvious decrease of yield,while the yield variation of light oil fractions（gasoline and diesel fraction obtained）from the thermal-cracking of oil sand bitumen with temperature was different over different heat carriers.At the same temperature,when the heat carrier was calcium aluminate,the yields of C₂-C₄ alkenes and light oil fractions were the largest,while the coke yield was the lowest.Additionally,in the average molecular structure of liquid products,the content of alkenyl structures,alkyl structures and chain alkyl substituents attached to aromatic ring structures was the highest,the content of aromatic structures,methyl substituents attached to aromatic ring structures and naphthenic structures as well as he average length of alkyl chain structures was the lowest.When the heat carrier was FCC,the yields of gas,LPG and coke yields were the highest,while the liquid products yield was the lowest.Furthermore,the content of the aromatic structures and the alkyl substituents attached to aromatic ring structures was the largest,while the content of alkyl structures and alkenyl structures was lowest.Additionly,the relative content of thioether&mercaptan、thiophenes and benzothiophenes,the relative content of naphthothiophenes and four species of hydrothiophenes,and the relative content of dibenzothiophenes,phenalenothiophenes and benzonaphthothiophenes accounting for sulfur compounds in oil sand oil was largest over silica sand,calcium aluminate and FCC catalyst,respectively.