Experimental Investigation of Upgrading Heavy Oil with Supercritical

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Experimental investigation of upgrading heavy oil with supercritical methanol Ting Yan, Kang Chen, Litao Wang, Yindong Liu, Yanmei Zhang, Zhao Jiang, and Tao Fang Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 16 May 2017 Downloaded from http://pubs.acs.org on May 17, 2017

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Experimental investigation of upgrading heavy oil with

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supercritical methanol

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Ting Yan 1, Kang Chen 1, Litao Wang 2, Yindong Liu 2, Yanmei Zhang 2, Zhao Jiang 1, Fang Tao1* （1. School of Chemical Engineering, Xi’an Jiaotong University, China 2. Project Office of Heavy to Light Conversion, Petrochemical Research Institute, China *E-mail：[email protected], Telephone：15202977381） Abstract: The upgrading of heavy oil from Karamay using supercritical methanol (SC-MeOH) as a solvent was studied in a batch reaction. Through orthogonal experiments, the effects of the temperature, mass ratio of methanol to oil, reaction time and agitation speed were investigated. The optimal reaction conditions, depending on the boiling range of light products such as maltenes and the yields of by-products such as asphaltenes, were as follows: reaction temperature of 350 °C, reaction time of 60 min, stirring agitation of 900 rpm and mass ratio of methanol to oil of 1:1. A simultaneous increase agitation speed would significant reduce the condensation behavior. Analysis of the simulated distillation of maltenes indicated that the components with boiling points lower than 380 °C increased from 19 wt% in the raw material to 38 wt% in the products maltenes. The viscosity of light products decreased to 24.1 mPa·s. The FT-IR of asphaltene results showed that the temperature has contradictory influence on upgrading of heavy oils. With increasing temperature, the degree of aromatic ring condensation increases and the length of aliphatic side chains decrease. High temperature can promote the breakage of alkyl side chains and condensation of aromatic rings. The TG-FTIR spectrum proves that SC-MeOH can participant in the reaction as a reactant. However, heteroatom O was introduced into the maltene molecules. All these results proved that SC-MeOH is an excellent solvent for oil pyrolysis. However, the quantity of light products should be improved, the secondary generation of asphaltenes needs to be restrained and heteroatoms need more detailed research. Key words: heavy oils, upgrading, supercritical methanol, asphaltenes 1. Introduction Crude oil is the dominant world energy resource and the foundation of societal development. However, with the decrease in crude oil reserves and excessive exploitation, oil with a high density and high sulfur content already accounts for two-thirds of the oil reserves around the world, as shown in Table 1 1. Carbon rejection and hydrogen addition, conventional oil refining technologies, have already shown limitation to the processing crude oil with inferior quality 2-4. To meet the growing requirements for high quality fuels, the upgrading of heavy oils is of great significance to maximize the utilization of finite oils. Heavy oils include bitumen, asphaltenes and residual oil, which have low H/C atomic ratios, high viscosity and high contents of heteroatoms. As a result, it is necessary

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to develop new technologies to convert the heavy oils into light products efficiently and environmentally. The application of supercritical fluids for heavy oil processing has attracted wide attention 2, 5, 6. Table 1. Crude oil data 1

4

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Year

Relative density (20 °C)

Sulfur content (wt%)

2000

0.8628

1.14

2010

0.8633

1.19

2015 0.8639 1.25 When the temperature and pressure are above the critical point of a fluid, the characteristics of the fluid change greatly 7. The fluid is called a supercritical fluid (SCF). An SCF has the physical and chemical properties of both a liquid and a gas: 1) The diffusivity of an SCF is comparable to that of a gas. 2) The mass transfer rate of an SCF is far greater than that of traditional reaction solvents. 3) Regarding the dissolvability, an SCF is similar to a liquid. Supercritical water (SCW) and supercritical methanol (SC-MeOH) can dissolve organic chemicals and gases; thus, the reaction can proceed in a pseudo-homogeneous phase. 4) The density and dissolvability of an SCF are determined by the pressure and temperature. Accordingly, the distribution of the reaction products can be controlled by manipulating the temperature and pressure 8 1.1 Current situation of upgrading of heavy oil with supercritical SCW . Most studies have focused on utilizing SCW as the reaction solvent 9, 10. SCW (Tc=374 °C, Pc=22.1 MPa) is an ideal solvent for light hydrocarbons, and gases. Most likely, SCW also plays a role as a hydrogen donor due to its high activity, promoting the pyrolysis of heavy oils and simultaneously restraining the formation of coke 11-14. Cheng et al has found that the optional conditions for the pyrolysis of residual oil in SCW are 420 °C, a water density of 0.15 g·cm-3, and a mass ratio of water to oil of 2:1. After reaction for 1 hour, the compounds with boiling points below 350 °C increased to 83.3 wt%, with only 3.64 wt% coke formation 15. A similar result was obtained by Zhao et al. After pyrolysis in SCW at 420 °C and 25 MPa for 1 hour, the coke yield was just 8.19 wt%. The asphaltene content decreased of 30.9 wt%, and the saturates increased to 98.6 wt% compared with the raw material 16. Vilcaes et al studied bitumen thermolysis in SCW. At 440 °C and 29 MPa, the interface between the water and bitumen disappeared. The solubility of bitumen in SCW increases with temperature 17. Morimoto et al studied the extraction of asphaltenes at 400-450 °C and 20-30 MPa in SCW. When the temperature and pressure reached 30 MPa and 440 °C, the maximum rate of extraction was achieved. The extraction behavior of SCW is controlled by the dielectric constant (DC) and the Hansen solubility parameter (HSP, includingδp, δh). δp is polar component parameter, which is the measurement of the dipole


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moment, dielectric coefficient and refractive of the molecule. δh is hydrogen bonding component parameter, which is used to characterize the number of hydrogen bonds and hydrogen bonding force18. When DC=2.2, δp=6.4, and δh=9.7, the solubility of asphaltenes in SCW reached a maximum 19. It was found that under the optional conditions for the pyrolysis of residual oil, the DC, δp andδh of SCW are 2.2, 6.3 and 9.9, respectively, which are similar to the values for asphaltene pyrolysis in SCW. The mechanism of heavy oils’ upgrading in SCW and the role of SCW were studied either. Carr et al studied the decomposition of alkylaromatic hydrocarbons in SCW 20. They found the aliphatic hydrocarbon substituents were cleaved through the β-scission in the alkane chains. Because β-scission has lower activation energy of 120 kJ·mol-1 .The main products of toluene and ethylbenzene were mainly prepared through this route. Kida et al studied the desulfurization of alkyl sulfides and thiophenes in heavy oils by SCW treatment 21-23. Cm-1 alkanes and CO+CO2 were formed when Cm alkyl sulfides decomposed in SCW. During the process, SCW was a reactant in hydrolysis of thioaldehyde, an H-donor for desulfurization and catalyst of hydrogen transferring. However，SCW was ineffective to break thiophenes rings to remove S atom completely. The cleavage of long side chains of thinphenes resulted in desulfurization of heavy fractions. However, it takes too much energy to achieve and exceed the critical point of water, with an associated high operational cost. Moreover, in the literature, serious coke formation was found to occur during the SCW process. When the reaction temperature increased from 390 °C to 430 °C, the coke yield increased from 10 wt% to 30 wt% 10. The hydrogen-donating behavior of SCW is still in dispute. Many studies have shown that SCW is an inert solvent without hydrogen donating ability 12, 24. All these problems listed above limit the application of SCW in commercial production. 1.2 The application of supercritical methanol on upgrading of biomass and fossil fuels Supercritical methanol (SC-MeOH) has mild critical conditions (Tc=239 °C, Pc=8.1 MPa). SC-MeOH has been applied in organic synthesis, in the recycling of waste macromolecular material and in biomass resource utilization 25-28. In SC-MeOH, extraction and transesterification of wet algal biomass can be proceeding, simultaneously29-31. SC-MeOH can destroy microalgae hard cell wall31. Sitthithanaboon et al studied single-step conversion of wet nannochloropsis gaditana to biodiesel in subcritical methanol. Because of high reactivity of SC-MeOH, the esterification does not require a catalyst32, 33. With the presence of free fatty acids, the yield of phospholipids conversion to fatty acid methyl ester can reach 93% without catalyst in SC-MeOH34. In SC-MeOH, methyl lactate (ML) and methyl 2-methoxypropionate (MMP) are obtained in yields of 57.8% and 12.8% when cellulose is liquefied35. In this process, methanol is a methylating agent. In the processing of fossil fuels, SC-MeOH has been attracted some attention. Li et al studied the extraction of coal tar in SC-MeOH. The experimental results revealed that the light oil yield increased from 65.10 wt% to 78.19 wt%. The H/C in the obtained light oil


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increased 28.24 wt% more than that before reaction and 109.62 wt% more than that of raw coal tar 36. SC-MeOH has been used to reduce the total acid number (TAN) of crude oil. After reaction for 1 hour at 350 °C and 10 MPa, the TAN decreased by 99.77% 37. Kwek et al studied upgrading of de-oiled asphaltenes in SC-MeOH38. 78.3 wt% maltene with 2.74 wt% S contents was obtained. In the presence of fomic acid, thermal cracking, desulfurization and demetallization of asphaltenes were carried out simultaneously. In summary, SC-MeOH can destroy macromolecules. SC-MeOH is a commonly used methylation and hydroxymethylation reagent, which could increase the H/C atom ratio of heavy oils. As a result, the author utilized SC-MeOH as a reaction solvent to investigate the influence of different reaction conditions on the upgrading of heavy oil. All experiments were designed according to the orthogonal method. The mechanism of action of SC-MeOH was studied either during the reactions. 2. Experimental 2.1 Materials used Raw heavy oil was obtained from the Karamay Oilfield, supplied by the Petrochemical Research Institute. The properties of the heavy oil are displayed in Table 2.

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Table 2. Properties of the heavy oil Density

Viscosity mm2·s

Distillation range

g·m-3

0.9593 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

wt% 80 °C

100 °C

IBP*~275 °C

275~400 °C

400~520 °C

520 °C +

889.7

242.1

2.9

9.6

28.9

58.6

*IBP: initial boiling point. 2.2 Apparatus and reaction runs A 316L stainless steel autoclave with a capacity of 100 ml was used in the research. The temperature was controlled by a temperature control meter. The pressure was measured by a pressure gauge and controlled by the quantity of methanol added into the reactor. After preheating, suitable amounts of methanol and oil (5--10 g) were introduced into the reactor. High-purity N2 was purged into the reactor to replace the air before the experiment to avoid the influence of O2. The autoclave was heated in a heating furnace. The heating time was about 30-40min. When the temperature of autoclave reached 100 °C, the agitation speed was set at 300--900 rpm. After the temperature of autoclave reached the set value, the reaction was maintained at a constant temperature for 30--90 min. The heating time was about 30 min. The pressure was in the range of 8--13.5 MPa at different temperature. For sampling, the reactor was placed in cool water until its temperature decreased to room temperature. Afterwards, the reaction products were collected from the gas and liquid phases. 2.3 Product separation and analysis The gas product was purged into the sampling bag through differential pressure and


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analyzed by GC. The liquid product was collected following the Industrial Standard of Chinese Petrochemical NB/SH/T 0509-2010. The reaction, separation and analysis procedure is shown in Figure 1. The fraction of condensation products (Ycondensation) and the fraction of maltenes with a distillation range below 380 °C (Ylight oil) in this paper were calculated as follows: Ycondensation =

Ylight

oil

=

m asphaltene + m coke m raw oi l

× 100%

Ym < 380 × m maltene × 100% m raw oi l

(1)

(2)

The masphaltene, mmaltene and mcoke were denotes the weight of asphaltene and coke, respectively. Ym Reaction time> Temperature> Mass ratio of methanol to level oil optimal 330 °C 1:2 30 min 900 rpm As range analysis shown in Table 4, the importance of the four factors is different on restraining the yields of asphaltenes and coke. The agitation speed was the dominant factor for asphaltenes and coke yield reduction. The effect of the reaction time was second. The mass ratio had a negligible influence on the formation of condensation products. The value k (k1/k2/k3) refers to the average of the sum of the corresponding test results when the level number is i on any column. The optimal level of each factor can be obtained from the minimum values of k1, k2 and k3. The optimal conditions inhibiting condensation were reacting for 30 min at a temperature of 330 °C, a mass ratio of 1:2 and an agitation speed of 900 rpm. At the optimal conditions, the yield of condensation products was just 24.5 wt % of asphaltenes with 0.2 wt % of coke. The reason that the agitation rate has the most significant effect on the formation of the condensation products is that the content of asphaltenes in the reaction system increases and the content of maltenes that can dissolve asphaltenes are reduced under conventional thermal reaction conditions, when the conversion of aromatics and resins reaches more than 70% 39. Then, the miscibility between the asphaltenes and maltenes decreases, allowing the main asphaltene condensates intermolecularly to form additional coke. In SC-MeOH, increasing the agitation rate allows the mass transfer rate and the solubility of heavy oil in SC-MeOH to be simultaneously improved. The asphaltenes dissolved in the SC-MeOH can avoid further condensation to form coke, which generally occurs in a conventional reaction environment. Furthermore, a phenomenon called the “cage effect” of SCF is advantageous to suppress the condensation behavior40. The light products and unreacted oil can be mixed with methanol as a solvent to dilute the asphaltenes. The solvent molecules surround the macromolecules as cages. Only small radicals as H· and CH3· can pass through the cages to quench polymerization reactions of free radicals. The high agitation rate is helpful to make asphalttene molecules distribution uniformly, which causes solvent molecules to surround a single asphaltene molecule to avoid polymerization of multiple macromolecules in cages. As a result, the condensation reactions are restrained under high speed agitation. Table 5. Factor analysis based on the yield of maltenes with a distillation range below 380 °C Mass ratio of Temperature Reaction time Agitation speed methanol to oil k1 0.237 0.293 0.247 0.283 k2 0.283 0.280 0.280 0.293 k3 0.320 0.267 0.313 0.263


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0.083 0.026 0.066 0.030 Temperature > Reaction time> Agitation speed> Mass ratio of Effect level methanol to oil Optimal 350 °C 1:1 90 min 300 rpm The content of fractions with a distillation range under 380 °C is the measure of the quality of the light products. As Table 5 demonstrates, temperature has a significant effect on decreasing the distillation range. Similar to the condensation products, the mass ratio has a minimal effect. The optimal level of each factor can be obtained from the maximum values of k1, k2 and k3.The optimal conditions to reduce the distillation range were reacting for 60 min at a temperature of 350 °C, a mass ratio of 1:1 and anagitation speed of 300 rpm. The components of heavy oil pyrolyze through a free radical mechanism 9. The initiation of the pyrolysis of heavy oil requires to break C-C bond with an activation energy about 60-80 kcal·mol-1. In the process of propagation ， a β-scission and H-abstraction reactions of alkyl substituents on aromatic rings need an activation energy about 30 kcal·mol-1 and 12-16 kcal·mol-1, respectively 41, 42. Therefore, temperature plays a dominant role to supply enough energy for pyrolysis. Along with the extending reaction time, the cracking products tend to condense further. An excessively long reaction time has a negative influence on the quality and yield of light products. From the viewpoint of the molecules, the number of methanol molecules is far greater than that of heavy oil molecules in the reaction system. Thus, altering the mass ratio has a limited effect on the reaction performance. Considering the yield of the heavy products and the distillation range of the light products, the optimal conditions of heavy oil pyrolysis in SC-MeOH could be determined as follows: a reaction temperature of 350 °C, a reaction time of 60 min, an agitation speed of 900 rpm and s mass ratio of 1:1. Under the optimal conditions, the yield of asphaltenes was 26 wt%, with a negligible coke yield. The yield of maltenes with distillation range lower than 380 °C was 38 wt%. The viscosity of maltene decreased to 24.1 mPa·s at 80 °C, less than 91% of raw materials. 3.3 FT-IR analysis of the asphaltenes FT-IR has been utilized in various fields of the petrochemical industry with excellent results 43-45. FT-IR is used for identifying the structure of an unknown material or determining functional groups. The infrared absorption peak position can reflect the characteristics of the molecular structure. The intensity of the absorption peak is related to the content of the chemical group. FT-IR can be used for quantitative analysis and purity identification. The three sets of samples were analyzed by 3-5 times under true replicate conditions in order to confirm their similarity. However, the spectrum was obtained from averages of multiple spectra of one set of samples. The FT-IR spectra of the asphaltenes in the raw materials and the experimental products are shown in Figure 3. As shown in Figure 3, the structures of asphaltenes obtained under different temperatures were not significantly different. The 630-930 cm-1


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band was caused by bending vibration of C-H groups of aromatic rings46. The broad absorption band at 930-1800 cm-1 appeared to be oxygen-containing groups deformation vibration46. The 2500-3000 cm-1 absorption band was induced by absorption spectrum of stretching vibration of aliphatic C-H groups46. The absorption band at 3000-3750 cm-1 was assigned to stretching vibration of –OH groups of crystal water maintained in KBr44, 46 . In order to quantitatively analyze the asphaltene structure, FTIR spectra was fitted by Gaussian method. The fitted curves were illustrated in Figure 4. In the fitted curve of 630-930 cm-1 band, there were 4 fitted peaks. The peak at 722 cm-1 was caused by out-of-plane deformation vibration of C=H. The peaks at 750, 804 and 863 cm-1 were assigned to out-of-plane deformation vibration of C-H at different positions on aromatic rings46, 47. There were 17 fitted peaks in the 930-1800 cm-1 fitted curve. The peak at 950 cm-1 was due to carboxylic acid out-of-plane deformation vibration. The broad bands at 1000-1350 cm-1 were caused by stretching vibration of C-O in ether, ketone and alcohol46, 48. The peak at 1600 was due to stretching vibration of C=C on aromatic rings, which was coincidence with the overlap result of fitted peaks of 1572, 1603 and 1627 cm-1 46, 47. The broad bands at 1360-1470 cm-1 were assigned to symmetrical and asymmetrical deformation vibration of CH3 and CH246. There were 6 fitted peaks in the 2500-3000 cm-1 absorption bands. The peaks were caused by stretching vibration of CH at 2780 and 2955 cm-1 46. The peaks at 2868 and 2955 cm-1 were assigned to symmetrical and asymmetrical stretching vibration of CH346. The fitted peaks at 2850 and 2924 cm-1 may arise from stretching vibration of CH246, 49. Table 6. Structure parameters derived from FTIR of asphaltene samples Asphaltene I1 I2 I3 CH2 /CH3 Raw asphaltene 3.578 10.317 0.347 2.013 Exp.1 3.276 9.311 0.352 1.800 Exp.2 3.362 9.757 0.382 1.753 Exp.4 4.048 9.488 0.427 1.579 Exp.5 4.257 10.326 0.412 1.429 Exp.8 3.138 5.236 0.599 1.258 Exp.9 3.381 3.912 0.864 1.195 I1: the relative abundance of aliphatic groups. I2: the relative abundance of aromatic groups. I3: the degree of condensation of aromatic rings. CH2 /CH3: the length and degree of aliphatic substituents. The quantitative analysis of the molecular structure can be obtained by the ratio of the integral area of the fitted peaks. Integrated area ratio I1 (2500-3000 cm-1 / 1600 cm-1) and I2 (2500-3000 cm-1 /630-930 cm-1) can be estimated the relative abundance of aliphatic and aromatic groups. I3 (630-930 cm-1 /1600 cm-1) can be used to evaluate the degree of condensation of aromatic rings. The rate of CH2 /CH3 (2924 cm-1 /2955 cm-1) can be used to estimate the length and degree of aliphatic substituents50. The parameters of asphaltene structure were shown in Table. 6.


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As shown in Table 6, the structure parameters of asphaltene obtained under 310 °C (exp. 1/2) is similar with that of raw asphaltene. The pyrolysis of heavy oil under 310 °C is limited. The values of I1 of exp. 4/5 samples were the maximum among that of all samples, which implied that the aliphatic substituents can be cracked at 330 °C. The further decomposition of alkane substituent causes a decrease of I1 at 350 °C, the values of I1 decreased further. With increasing temperature, the degree of aromatic ring condensation increases and the length of aliphatic side chains decrease. Therefore, temperature has contradictory influence on upgrading of heavy oils. The reaction temperature can be selected by reducing the requirement of the light products in order to inhibit the formation of the polymerization product. 3.2.2 TG-FTIR analysis of the maltenes in the raw material and product under optimal conditions The TG-FTIR has been utilized in various research fields44. Under nitrogen atmosphere, the mass loss is caused by the evaporation and pyrolysis of the sample itself. The molecular structure of the volatile products can be observed by FTIR. As a result, TG-FTIR was used to analyze the pyrolysis characteristics and structural differentiation of maltenes in raw oil and obtained under optimal reaction condition. By comparing the differences in structure, the chemical role of SC-MeOH in the reaction can be determined. The analysis was proceeding as 3.2.1 part. The thermogravimetry (TG) and derivative thermogravimetry (DTG) curves of the maltenes in the raw material (HS1) and maltene obtained under the optimal conditions (HS2) are shown in Figure 5 and 6. As shown in Figure 5 and Figure 6, the initial and final pyrolysis temperature of HS1 were 150 and 550 °C, respectively. The final mass loss of HS1 was less than 90%. There was an unobvious peak in DTG curve of HS1 at 280 °C. The peak was caused by pyrolysis of residual n-heptane in HS1. The second peak appeared at about 460 °C. The mass loss rate got to maximum under this temperature. Most of the components started to pyrolysis under 460 °C. of HS2The initial pyrolysis temperature was about 115 °C. The pyrolysis ended in the range of 550 °C. The final mass loss was about 95%. From the DTG curve, the pyrolysis of HS2 can be divided into four stages. The first stage was the evaporation of residue moisture, which accompanied by a slight thermal decomposition reaction. After heating to 150 °C, the TG of HS2 increased rapidly. Two overlapping peaks appeared on the DTG curve. At this stage, the occurrence was the volatilization of residual n-heptane and decomposition of saturates, aromatics and resins. The position of the first peak at 270 °C was caused by the evaporation of n-heptane. The second peak appeared at about 330 °C. The most intense reactions occurred under this temperature. The second peak was due to pyrolysis of light fractions generated in SC-MeOH. The pyrolysis rate of HS2 was recovered at 400 °C, after it declined at 330 °C. The third peak appeared at 440 °C, which was assigned to the pyrolysis of unreacted components in SC-MeOH. At the last stage (>550 °C), the unreacted liquid phase was transformed into solid phase, forming a relatively stable structure of coke. At this stage, the weight loss curve is relatively flat. Comparison with the TG and DTG curves of two samples, the


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mass loss of HS1 increased rapidly at 300 °C. For HS2, the mass loss rate of HS2 increased at 240 °C. After 400 °C, the DTG curve of HS1 shifted to the right side of the HS2 curve, which indicated that the pyrolysis of HS1 required a higher temperature. Because the latent heat of vaporization and the activation energy of pyrolysis of macromolecule are higher. However, the higher energy chemical bond in HS2 has been opened in SC-MeOH. Compared with N2, SC-MeOH was more conducive to pyrolysis of heavy oils. The FT-IR spectra of the volatile products, which were selected every 100 °C from maltene pyrolysis in the raw material and the reaction product, are shown in Figure 7 and Figure 8, respectively. As shown in Figure 7 and Figure 8, when HS1 and HS2 were heated up to 100 °C, there were a few amounts of CO2 (2360 cm-1) and H2O (3500-3750 cm-1) released50. When temperature increased to more than 500 °C, the structure of volatile products was similar. The peaks at 1400 cm-1 was assigned to in-plane deformation vibration of C-H of alkene46. The peaks at 1500 cm-1 was attributed to C=C stretching vibration on aromatic rings46. The characteristic bands at 2750-3000 cm-1 were due to symmetrical and asymmetrical stretching vibration of aliphatic groups46. All three characteristic peaks mentioned above were typical structure of petroleum. As a result, the reactants of HS1 and HS2 above 500 °C had same molecular structure. However, an obvious peak appeared in 400 °C curve at 1600 cm-1 in Figure 8, which was caused by stretching vibration of ketone. As shown in Figure 8, some absorption peaks near 1000 cm-1 were detected below 400 °C, whereas nothing was detected at the same position in Figure 7. The peaks at 1000-1200 cm-1 are attributed to C-O-C stretching vibrations of alkyl and saturated cyclic ether groups46. It can be concluded that the C-O-C bond was generated by the reaction between maltenes and MeOH. SC-MeOH participated in the reactions through the CH3O· and H· radicals. The mixtures of n-dodecane and hexyl sulfide were chosen to simulate the reaction of heavy oil in supercritical methanol. There were C6H12(OCH3)2 and C12H24(OCH3)2 were detected in the products. The mechanism was still unclear. Heteroatom O was introduced into oil molecules by CH3O·, in spite that heavy oils were upgraded in SC-MeOH. Conclusion This study examined the pyrolysis of heavy oil in the environment of SC-MeOH. The operational conditions were optimized using orthogonal experiments. The quality of the light products and the structure of the heavy products were analyzed. 1) Through the orthogonal experiment, considering the yield and quality of the light products, the optimum reaction conditions were a reaction temperature of 350 °C, reaction time of 60 min, and agitation speed of 900 rpm. The mass ratio of methanol to oil was 1:1. Under the optimal conditions, the contents of maltenes with a distillation range between IBP and 380 °C increased to 38 wt%. The yield of asphaltenes was 26 wt%, with negligible coke formation. 2) In SC-MeOH, some interesting changes took place in the structures of the asphaltenes and maltenes. SC-MeOH acts as a reaction solvent but also as a hydrogen


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donor. More importantly, the catalysis of SC-MeOH probably causes the breakage of polycyclic aromatic hydrocarbons. However, heteroatom O was introduced in to maltene molecules. The detailed reaction mechanism is still unclear. Further investigation of mechanism should be proceeded to reduce of reduce fresh heteroatoms. 3）In addition, a number of asphaltene by-products were formed, which caused huge energy and fuel waste. This problem is worthy of future research, either.

Ackonwledgement： The authors would like to acknowledge the following financial supports: PetroChina Innovation Foundation (2014D-5006-0401), National Natural Science Foundation of China (No. 21376186), the Ministry of Education (Doctoral Special Research Foundation No. 20110201110032) China, Fundamental Research Funds for the Central Universities (New Teacher Research Support Plan No. 08141002, International Cooperation Project No. 2011jdhz37 and Integrated Cross Project xjj2014136 in Xi’an Jiaotong University), Natural Science Basic Research Plan in Shaanxi Province of China (No.2012JM2010) and Sci. & Tech. Project for Overseas Scholars (the Ministry of Human Resources and Social Security of China , No.19900001).

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Experimental Investigation of Upgrading Heavy Oil with Supercritical

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