The Pyrolysis Of Oil Sand And The Reaction Performace Research Of Tar Sand Bitumen With Ultrasonic Irradiation

The processes of the residue oil up-gradation and utilization had gained tremendous importance for the development of refinery industry in the current years,owing to the progressively heavier nature and poor quality of the crude oil in the world.Tar sand bitumen produced from oil sands,known as unconventional reserves,was part of the world's oil supplement and characterized with high viscosity,high carbon residue and heavy metals content,which influenced the downstream refining process.Therefor the efficient processing of tar san bitumen was one of the major challenges in refining plant.In this paper,the change of chemical structure of oil sands during pyrolysis was studied by means of modern instrumental analysis,which was helpful to understand the nature of pyrolysis.The mechanism of ultrasound thermal cracking for the tar sand bitumen was studied by the introduction of ultrasound irradiation into the traditional thermal cracking process,which was helpful to enhance the conversion rate of thermal cracking,improve the yield of light oil and further expand the processing methods for heavy oil.The pyrolysis experiments on the oil sands from Kazakhstan were carried out in a batch reactor.In order to understand the structural changes of organic functional groups during pyrolysis,the effects of particle size,heating rate and retorting temperature on the yield of oil and gas were analyzed in detail,and the properties of oil,gas and semi-coke were evaluated under different temperatures.For the gas component of pyrolysis products,both the contents of H₂ and CO₂ increased with the rise of temperature,but the contents of CO and CO₂ decreased after 500?.As was shown on the SARA analysis of the liquid product with different retorting temperature,saturates presented a deceasing trend,whereas aromatics and resin presented an increasing trend with the increasing temperature.The results of semicoke analysis under the temperature of 500?showed that the main components was ash and fixed carbon,and it was worth mentioned that the content of fixed carbon was more than 20%.The sand was mainly composed of SiO₂ and Al₂O₃ with the content of 74.1%and 14.6%respectively.The FT-IR spectrum and the¹H-NMR spectrum of pyrolysis oil under different temperatures were carried out to investigate the changes of functional group with temperature.The main reaction for oil sand before 420?was the desorption and volatilization of light hydrocarbon,and the main reaction ranged from 420 to 450?was the rapture of the carbon-heteroatom bond,and the main reaction after 450?was the decomposition of the carboxyl and the rapture of the carbon-carbon bond,such as the?-position of aromatic side chain.In the process of pyrolysis,the cracking reaction was firstly dominated whereas the condensation reaction played a leading role with the increase of reaction temperature.When the temperature reached 500?,the condensation reaction was completely dominated in the pyrolysis process.It was concluded that the thermal cracking reaction was dominant at first in the process of oil sand pyrolysis,but the condensation reaction was dominant with the increase of reaction temperature.The properties of tar sand bitumen from Inner Mongolia were evalued thoroughly,which belonged to a kind of sour naphthenic based oil with the properties of high density,high viscosity,rich resin and asphalt.To investigate the thermal stability of asphaltene and resin in the colloid system,The SARA in the bitumen were separated.There was an obvious difference for DTA curves between asphaltene and resin.The pyrolysis of asphaltene demonstrated a wide temperature range with the feature of two-peak of weight loss,whereas the resin exhibited only one peak of weight loss.The kinetic parameters of asphalt and resin were calculated using the thermogravimetric analysis?TG/DTA?at 3different heating rates with the following 3 methods:Coats—Redfern,Distributed Activation Energy Model?DAEM?and Multi Peak Fitting?MFT?.Comparing with the three methods,the Coats-Redfem method was only to reflect an average of activation energy in the pyrolysis process,and was not very well to describe the whole reaction as a single reaction mechanism.The DEAM was introduced to calculate the pyrolysis kinetics of asphalting and resin.The results of the continuous distribution of activation energy at different conversion level indicated a complex and continuous molecular chain reaction process during the pyrolysis process,which reflected the difficulty of pyrolysis.The Multi Peak Fitting method was introduced to separate the overlapping peak and calculate the kinetic parameters of the asphaltene on the assumption that pyrolysis reaction mechanism was determined by the two-component parallel model.The results showed that the activation energy of each sub-peak has little fluctuation range,so it was considered that the whole asphaltene pyrolysis process followed a single reaction mechanism.The pyrolysis mechanism of each sub-peak was consistent with the whole asphaltene pyrolysis process,which proved that the two-component superposition reaction model was suitable for describing the pyrolysis mechanism of asphaltene.The bitumen–ball was prepared by the vacuum bitumen?greater than 460??,which was used to determine the kinetics of extraction kinetics in Several kinds of organic solvent.An improved kinetic model of asphalt extraction was deduced through the introduction of the mass transfer area on the base of first-order pseudo kinetics,the change of the dissolution rate and the particle size were established,and the mass transfer parameters were calculated.Ultrasonic treatment played an important role in the properties of tar sand bitumen,and there was an obvious change in the viscosity,the composition of SARA,residual carbon,the distribution of liquid fractions distribution,the CSP and the structure parameters of asphaltene with ultrasonic irradiation,which was conducted in a self-developed ultrasonic reactor.The composition of SARA varied significantly at different ultrasonic treatment temperature,and the total content of asphaltenes and resins increased with the temperature,which improved the dispersion state of asphaltene.Therefore,the CSP of bitumen was changed with temperature under the ultrasonic treatment by changing the content and distribution of SARA.On the one hand,ultrasonic irradiation could destroy the hydrogen bond of the molecules in each part and interaction between the asphaltene and resin;on the other hand,ultrasound irradiation could also destroy the association structure of the structural units of the asphaltene,which promoted the mutual transformation between each component,improving the stability of the colloid system.The simulated distillation results of bitumen after ultrasonic treatement showed that ultrasound treatment significantly increased the yield of intermediate heavy fractions,and dramatically reduced the yield of residuum and the FBP of liquid product,which indicated that the supermolecular structure of bitumen was transformed to the intermediate heavy fractions,reducing the difference of molecular weight between each component.The structure parameters of asphaltene was significantly influenced by ultrasound irradiation,such as a decrease in R_T,R_A,R_N,?,C_A and the condensation degree parameter of the aromatic ring system(H_Au/C_A),which proved the complexity of the asphaltene structure was reduced and the molecular structure of asphaltene unit was more compact by ultrasonic treatment.The types and contents of functional groups in the outer layer of the asphaltene from bitumen had been investigated qualitatively and quantitatively by the multi-peaks Gaussian fitting method with the use of the XPS technique,and the results provided a basis for the research on the asphaltene structural changes after ultrasound treatment.From the analysis of FT-IR spectrum for asphaltene,it could be seen that the ultrasound irradiation could destroy the molecular structure of asphaltene,weaken the hydrogen bonding of asphaltene,decrease the association interaction between the sheets of asphaltene units and lower the association number.It was also confirmed by the analysis of ultraviolet spectroscopy that ultrasonic treatment lowered the total number of aromatic rings in asphaltene.In order to explore process technology of ultrasond thermal cracking and understand influence of ultrasonic irradiation on the thermal cracking of tar-sand bitumen,the thermal cracking with ultrasonic irradiation?UTC?and the conventional thermal cracking?CTC?with an inert atmosphere were investigated thoroughly in a selfmade high temperature ultrasonic chemical reactor.The mechanism of ultrasond thermal cracking was proposed.The product distribution and coke characteristic produced by the conventional thermal cracking?CTC?and the thermal cracking with ultrasonic irradiation?UTC?were invested.The result of the liquid products distribution indicated that UTC can significantly increase gasoline yield and diesel yield,and dramatically reduce VGO yield and residuum?greater than 500??yield.The analysis of gas products showed that there was no significant difference for the gas distribution between the two reactions?methods?,indicating that reaction of UTC still conformed to a radical chain mechanism.Therefore,the composite ratio of CH₄/?C₃H₆+C₃H₈?,defined as the depth of the thermal reaction,was increased greatly with ultrasound irradiation,indicating that deeper thermal cracking reaction of bitumen was promoted by ultrasound through the secondary reaction of light hydrocarbons?C2,C3?;the ratio of olefin/paraffin was greatly reduced in the process of UTC,which was attributed to the hydrogen transfer reaction promoted by ultrasound.The result of the coke analysis by SEM,FT-IR,Raman,XRD,Zeta potential and XPS demonstrated that there was a significant difference for the morphology of cokes produced by the two methods.At the same time,the ultrasonic irradiation is beneficial to the charge transfer,which lead to the oxidative transformation of heteroatom functional group in the formation of coke generated by the condensation reactions of resin and asphaltene.Mesocarbon microbeads?MCMB?was discovered in the process of UTC,which was due to the fact that the polymerization of the free macro-radicals produced from PAHs was promoted by ultrasonic cavitation and the viscosity of the second liquid phase was reduced by ultrasonic mechanical function through the breakage of the stack of asphaltene molecules cross-linked by van der Waals force.According to the mesophase theory,the ultrasound irradiation promoted the formation of the second liquid phase,extended its existence time and reduced its viscosity,resulting in the formation of MCMB controlled by the surface tension during the process of UTC.The coke morphology generated by the ultrasonic thermal cracking was significantly changed with the increase of temperature.The MCMB grown,melt and embed into the coke with the increase of temperature,which was directly influenced by the polycondensation reactivity of asphaltenes and the crosslinking function between layer orderly stack of planar PAH molecular.When the temperature reached 440?,the ultrasonic effect was not enough to destroy the crosslinking function between the layers of graphitic sheet,the block coke was eventually formed.The discovery of MCMB in this paper may lay the foundation of the mesophase theory.