Effect of CO addition on upgrading bitumen in supercritical water

Accepted Manuscript Title: Effect of CO addition on upgrading bitumen in supercritical water Author: Takafumi Sato Toyokazu Sumita Naotsugu Itoh PII: DOI: Reference:

S0896-8446(15)30030-9 http://dx.doi.org/doi:10.1016/j.supflu.2015.06.004 SUPFLU 3352

To appear in:

J. of Supercritical Fluids

Received date: Revised date: Accepted date:

2-4-2015 2-6-2015 3-6-2015

Please cite this article as: Takafumi Sato, Toyokazu Sumita, Naotsugu Itoh, Effect of CO addition on upgrading bitumen in supercritical water, The Journal of Supercritical Fluids http://dx.doi.org/10.1016/j.supflu.2015.06.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Re-revised manuscript to the Journal of Supercritical Fluids (SUPFLU-D-15-00143)

Effect of CO addition onupgrading bitumen in supercritical water

Takafumi Sato,a,* Toyokazu Sumita,a Naotsugu Itoha a

Department of Material and Environmental Chemistry, Utsunomiya University

*Corresponding author: Takafumi Sato 7-1-2 Yoto, Utsunomiya, Tochigi 321-8585, Japan E-mail: [email protected] TEL&FAX +81-28-689-6159 Highlights * Upgrading of bitumen was examined with and without CO in supercritical water (SCW). * CO facilitated extraction of oil. *Coke formation in SCW with CO was suppressed. * Extract oil was lightest at 693 K with CO. *Distribution of oil in the reactor and temperature are important for upgrading. 1

2

Abstract Upgrading of bitumen was performed in a semi-batch type reactor in supercritical water (SCW)and in mixtures of SCW with CO orH2 from 673 to 723 K at 30 MPa. The extracted oil yield wasin the order SCW+ CO>SCW+ H2> SCW at 673 K.CO and H2 facilitated the extraction of the oil from inside the reactor to the outside the reactor. The coke yield in SCW + CO was lower than the yieldsin SCW and SCW + H2, indicating that hydrogenation of bitumen through the water-gas shift reaction probably occurred.Furthermore, the lightest extracted oil was obtained at 693 K in SCW + CO.The distribution of oil between the water-rich phase and oil-rich phase in the reactor governed the stability of the coke precursor in the oil-rich phase and the temperature determinedtheoil decomposition rate and the coke formation rate.The optimal upgrading condition was dependent on these factors.

Key words Heavy oil; Supercritical Water;Water-gas shift reaction; Hydrogenation; Bitumen

3

Introduction Upgrading of heavy oil has attracted attention as a fundamental technology forproviding energy resourcesbecause feedstock oil is becoming heavier.Oil sand bitumen is a heavy oil that is commercially mined and upgraded.About one-third of bitumen is recovered by steam assisted gravity drainage (SAGD), which requires high temperatures and pressurized steam [1].Bitumen is recovered as a mixture with high-temperature water at about 473 K in a well;high-temperature water can be useful as a solvent for upgrading of bitumen [2].For this purpose, supercritical water (SCW; Tc=647 K, Pc=22.1 MPa) is also a promising solvent because of its unique properties.For example, SCW dissolves gases and light hydrocarbons,and its polarity is lower than that of liquidwater and similar tothat of polar organic solvents [3].Noncatalytic conversion of heavy oil has been examined in SCW and steam [4-14].Coke precursorscan be dispersed in SCW[7,11] and it has been proposed that some of the hydrogen in water participatesin the reactionin heavy oil conversion [4,5,13].Some researchers have arguedthat there isa vapor phase and a liquid phase in the reactor,and that these phasesaffect the kinetics of oil decomposition and coke formation [8,10,13,14].Coke formation is suppressed in SCW rather than that through pyrolysis [4,7,8].However, water mainly functions as a non-reactive solvent to disperse 4

the coke precursorrather than asa hydrogen donor throughconsumption ofits hydrogen atoms [11]. Hydrogenation viathe water-gas shift reaction (WGSR; CO+ H2O=CO2+ H2) uses water as hydrogen donor throughthe reaction of water with CO.Some studies have examined catalytic hydrogenation through the WGSR in SCW [15-18].These studies focused onthe kinetics of desulfurization and denitrogenation rather than on the kineticsof oil decomposition.The kinetics of bitumen decomposition through non-catalytic hydrogenation by the WGSR in SCW has been studied in a batch system.Formic acid (HCOOH) is an intermediate of the WGSR.Increasing theratio of water to of HCOOH in SCW increases the conversion of asphaltene during bitumen upgrading in a batch system, and coke formation is suppressed [19].Water promotes the decomposition of oil to lower molecular weight compounds in the presence of HCOOH. The semi-batch system is also effective for upgrading bitumen.In SCW that contains H2 and CO2, which are the starting materials for the reverse WGSR, the coke yield is lower than that in SCW, and the H/C atomic ratio of asphaltene is higher than those of raw asphaltene and asphaltene in SCW with the semi-batch system [20].The gas enhancesthe hydrogenation of asphaltene and promotes the extraction of oil outside the reactor.In bitumen conversion with CO in SCW (SCW + CO) using a semi-batch reactor, 5

coke formation is suppressed in SCW + CO compared with SCW at 673 K andSCW + H2 + CO2[21,22].The operational parameters, such as temperature, extraction time, and solvent flow rate,are expected to affect the properties of oil inside and outside the reactor; however, the effect of these parameters on the reaction kinetics in SCW + CO is still unknown. In this study, the conversion of bitumen in SCW + CO in a semi-batch reactor was examined and the oil produced inside and outside of the reactor was analyzed.The reaction in SCW + CO was compared with the reactions in SCW and SCW + H2 to clarifythe characteristicsof theSCW + CO system.Next, the effects of temperature and extraction time in SCW + CO were evaluated,and thereaction kinetics wasanalyzed based on the results.

Material and methods Bitumen recovered by the SAGD method was used for experiments.Distilled waterwas prepared with water distillation apparatus (WG-222, Yamato Co.).CO (99.95%), and H2 (99.95%) were used as thegases.Toluene (>99.5%) was purchased from Wako Pure Chemical Industries Ltd. Fig.1 shows thesemi-batch type apparatus for upgrading of bitumen.The experiment 6

was similar to that inthe previous study [22].The reactor was made of stainless steel 316 and its volume was 6 cm3.Bitumen (1.0 g)was loaded in the reactorandthen the reactor was connected to the pipe from the preheater and the pipeto filter.Water was supplied by an HPLC pump (PU-2086, JASCO) to fill the internal space of the reactor at 30 MPa using a back-pressure regulator (26-1700, Tescom) and the reactor was heated to 573 K, whichbelow the temperature at which the reaction occurred.After the temperatures became stable, the reactor was heated to the reaction temperature, water was re-injected at a flow rate 0.5 or 1.0 g/min, and gas was supplied by a high-pressure syringe pump (ACRAFT, Natori) at 1.110-3mol/min.The experimentsperformed by supplying SCW, SCWand CO, and SCWand H2 are referred to as SCW, SCW + CO, and SCW + H2, respectively.It usually took less than30 min to reach the reaction temperature. The reaction time was measuredafter the interiorof the reactor reached the reaction temperature.After the reaction, the reactor was air-cooled, andthe products inside the reactor, and the products in thedownstream line from the reactor, including the receiver, were recovered separately by using toluene.The product in the reactoris defined as the raffinate product and thatin the lines and receiverisdefined as the extract product.Theraffinateproduct was filtered with a 0.1μm membrane filter(ADVANTEC) and separated into the solid and the liquid product.The solid was dried at 333 K 7

overnight and was defined as coke.The toluenesolutionswere evaporated at 353 K under 0.02 MPa to remove tolueneand obtain the recovered oil.The oils derived from the raffinate productand the extract product weredefined as residual oil and extract oil,respectively.In some experiments, the gas produced was sampled and analyzed by gas chromatography with a thermal conductivity detector(GC-2014, Shimadzu). Thermogravimetric and differential thermal analysis (Thermo plus EVO2, Rigaku) of the oil was conducted under a nitrogen flow of 150 cm3/min,from room temperature to 1073 K at 10 K/min.The apparent boiling point of the oil was evaluated by using a calibration curve obtained fromthe analysis of several n-alkanes [20].For some samples, CHNS elemental analysis (FLASH2000, ThermoScientific) and 1H NMR (NMR system 500, Varian) were carried out.Gel permeation chromatographywasalso conducted with a refractive indexdetector (RI-104,Shodex) and a series of two columns (4.6 mm  × 250 mm;403HQ,Shodex) using THF at 313 K.Polystyrenes (Mw=43900, 19600, 9500, 5400, 2800,

580),

decacyclene

(Mw=451),

and

2,9,16,23-tetra-t-butyl-29H,31H-phthalocyanine (Mw=739) were used as calibration standards to determine the weight average molecular weight, and the number average molecular weight was calculated from the weight average molecular weight and the peak signal. 8

Results Fig. 2 shows the apparent boiling-point distribution of raw bitumen andof the products in SCW, SCW + CO, and SCW + H2at 673 K.The average reproducibility errorwas less than 3wt % in SCW + CO at 673 Kand 0.5 g/min water.In this study, the mass balance calculated for the recovered coke and oil were above 53and 72wt %, respectively, on average.The losses from the mass balance wereattributedtolight volatile compounds with apparent boiling pointsbelow 423 K and to theproducts being extracted outside the reactor with solvent.The light volatile compoundsevaporatedwith the toluene as it was removed from the recovered oil.In this study, the conversion of CO was below 10%based on themoles of carbon fed in,andH2 and CO2 were produced. In all conditions, almost all theproducts inside the reactor were coke and oil and hadapparent boilingpoints greater than 773 K.The residual oil yield was significantly larger in SCW than in SCW + CO and SCW + H2, whereasthe extract oil yield decreasedin the order of SCW + CO, SCW + H2, and SCW.The extraction of heavy compounds from the reactor in SCW was more inhibitedthan the extractionin SCW + CO and SCW + H2.These results indicate thatCO and H2increasedthe extraction of oil from the reactor, similar toSCW + H2 + CO2 [20].Further, the coke yield was 6.6, 1.7, 9

and 4.9 wt % in SCW, SCW + CO, and SCW + H2, respectively.Hydrogen donation through WGSRin SCW + CO was more effective inpreventingcoke formation than the direct injection of H2 in SCW + H2.Catalytic hydrogenation is more effective in SCW + CO through the WGSR than in SCW + H2 [15].This principlecould be used for thenon-catalytic hydrogenation of bitumen.Theeffect of the flow rate of water in SCW + COwas small at 673 K,although the coke and residual oil yieldsdecreased slightly with increasing flow rate. Table 1 shows the elemental analysis and the number average molecular weight ofoil at 673 K.In general, oil with a low number average molecular weight is light.The H/C atomic ratio of the extract oil was 1.51 in all cases and was larger than that of raw bitumen.The number average molecular weight of the extract oil obtained under all conditions was lower than that of raw bitumen and the residual oil.The lighter component of the oil was preferentially extracted from the reactor.The numberaverage molecular weightsof the residualoil obtained in SCW were lower than thoseof raw bitumen and residualoilobtained inSCW + CO and SCW + H2.In SCW, the oil in the reactor became lighter to compensate for the formation of coke from the heavy components in the oil.The H/C atomic ratio of residualoil in SCW + CO was slightly lower than that in SCW + H2, whereasthose of extract oil in SCW + CO and SCW + H2 10

were the same.In SCW + CO, the WGSR hydrogenated the heavier components,such as the coke precursor,stabilizing them so they remained as oil rather than polymerizingto form coke. Fig. 3 shows the hydrogen type distribution of raw bitumen, residual oil, and extractoilat 673 K.The trend of properties of the extract oil can be discussed althoughthe hydrogen distribution of the extract oil did not reflectallof the oil extracted from the reactor because of the lack of the light fraction with an apparent boiling point below 423 K.Ha, H, H and Hrefer toaromatic hydrogen, hydrogen at the position, hydrogen on themethyl end groups, and other hydrogen, respectively.The ratioof Hin the extract oil was larger than that of residual oil, regardless of the conditions. Fig. 4 shows the coke, residualoil,and extract oilyieldsas a function of reaction timein SCW and SCW + CO at 673 K.In both cases, theresidualoil yield decreased with reaction time,whereasthe extract oil yield increased.The extract oil yield in SCW + CO was slightly higher than that in SCW.CO enhanced the extraction of oil regardless of reaction time.The coke yield was below 1%at a reaction time of30 min and then increased.In the absence of CO, the coke yield reached more than 6% and was almost constant.In the presence of CO, the coke yield was suppressed at 1.8% at 60 min, although the coke yieldincreased to 5.4% at 90 min, whichwas the same as that in the 11

absence of CO.The formation of coke proceeded in the presence of CO overlong reaction times. Next, the effect of temperature at 0.5g/min in SCW + CO was evaluatedbecause it was found that the oil in the reactor was easily extracted with solvent in the high-temperature region in SCW + CO during preliminary experiments, and this elimination of oil made analysis of residual oil difficult.To avoid theelimination, a slow flow rate (ca. 0.5 g/min) was used for evaluatingthe effect of temperature in SCW + CO.Theeffect of the oil on the WGSR is discussed next.CO conversion was 3.7% at 723 K and 0.5 g/min of water.Estimated CO conversion in the absence of bitumenby the rate constant was calculated from the literature [23] and the residence time was estimated by using the solvent density of SCW + CO obtained by the Peng-Robinson equation of state [20].The calculated CO conversion was 5.9% at 723 K and 0.5 g/min of water.The similar experimental and calculated conversions indicate that the effect of bitumen onthe WGSR was small. Fig. 5 shows the product yieldsas a function oftemperature.In SCW, the extract oil yield monotonically increased with increasing temperature,the coke yield increased and then remainedalmost constant, whereasthe residual oil yield decreased.In SCW + CO, the extract oil yield was always above 74wt % and reached97wt % at 723 K.Most of the 12

oil was extracted outsidethe reactor regardless of temperature.The coke yield increased with increasing temperature but decreased at 723 K.The residual oil yield was constant from 673 to 713 K and decreased to zero at 723 K.These results indicate that the oil in the reactor should be quickly extracted before coke formation at 723 K.Furthermore, the extract oil yield in SCW + CO was consistentlyhigh at more than74 wt % and was higher than that in SCW, and the recovery of oil was easier in SCW + CO than in SCW. Next, the quality of the extract oil that isconsideredthe target product in this process obtained in SCW + CO is discussed.Fig. 6 shows the ratio of products in the extract oil based on the apparent boiling point ofthe extract oil in SCW + CO.The ratio of oil with an apparent boiling point of less than 423 K increased from 673 to 693 K whereas the ratio of oil with an apparent boiling point of more than 423 K increased from 693 K to 723 K.The lightest extract oil wasobtained at 693 K.

Discussion Fig. 7showstheproposed upgrading scene occurring inside the reactor forSCW + CO system based on previous studies [8,19,20,22].In the reactor, there is an oil-richphase and a water-rich phase [8,10,13,14,24].The oil inside the reactor isdistributed inthe oil-rich phase and in the water-rich phase, which contains most of the water and gas.The 13

coke precursor, which is a heavy fraction,is mainly presentin the oil-rich phase.If themolecular weight of the heavy fractionincreases substantially by polymerization during the reaction, it will becomeinsoluble in the oil-rich phase, resulting in coke.The presenceof CO2 in SCW makesthesolvent solubility parameter of SCWsimilar to that of bitumen [20].The effect in the addition of CO toSCW issimilar to the effect CO2, although it is difficult to evaluate the solubility of SCW + CO athigh temperatures.Therefore, the introduction of CO,which is less polar than water,toSCW would alsodecrease the polarity of watertothat of bitumen [20].Consequently, the transfer of oil fromthe oil-rich phase to the water-rich phase wasincreased, which facilitated the extraction of oil outside the reactor.Coke formation in SCW + CO was suppressed more than that in SCW becausethe transferof the coke precursor from the oil-rich phase to the water-rich phase was increasedin the presence of CO.Furthermore, we propose that the formation of coke in SCW + CO over along reaction time was similar to that in SCW because the light fraction that can extractthe coke precursor from the oil-rich phase to the water-rich phase was extracted, destabilizing thecoke precursor in the oil-rich phase. One of the differences between SCW + CO and SCW + H2 isthe hydrogen donation through the WGSR in SCW + CO.The WGSR can supply 2.46  10-3 mol of hydrogen 14

under 3.7% CO conversion for 60 min at 723 K.However, 1.0 g of bitumen divided by the number average molecular weight of bitumencorresponded to1.16  10-3 mol.Considering that there are several active sites in a molecular unit of bitumen, the amount of hydrogen supplied from WGSR was roughlycomparable to the number of active sites in bitumen, although the actual amount of hydrogen consumed was unknownbecause hydrogen was formed by the WGSR and bythe decomposition of bitumen.These results mean that the WGSR partly contributed to the decomposition of bitumen.The hydrogenation of the coke precursor by the WGSR probably occurred in oil-rich phase.The enhancementofthe extraction and the WGSR were characteristic ofupgrading of bitumen in SCW + CO. The polarity of water decreases with increasing temperature under constant pressure.For example, the dielectric constant of water decreasesfrom 5.91 to 2.97 when temperature increases from 673 to 723 K at 30 MPa [25].This decrease in the polarityof water probably increasesthe affinity of SCW + COfor that of oil and increasesthe distribution of oil from the oil-rich phase to the water-rich phase.The increased distribution decreases the amount of oil in the oil-rich phase and the retention time of oil in the reactor also decreases because the oil in the water-rich phase can easily move outside the reactor in the high-temperature region.The extract oil yield increased with 15

temperature in SCW (Fig. 5), and thehigh-temperature conditions accelerated the polymerization of the coke precursor,increasingcoke formation. At 723 K in SCW + CO, there wasalmost no oil in the reactor and the ratio of heavy products with apparent boiling points of 723–773 K and of more than773 K in the extract oil was higher than under the other conditions.In this case, the distribution of oil from the oil-rich phase to the water-rich phase wasincreased considerablyby the high temperature.Almost all theoil containingcoke precursorswas probably distributed in thewater-rich phase and quickly passed through the reactor without much reaction.However, the coke yield reached its maximum at 713 K.The transfer of oil from the oil-rich phase to the water-rich phase was increased at 713 K, althoughvery heavy fractions, such as coke precursors,maynot have entered thewater-rich phase and remained in the oil-rich phase.Thesecoke precursorscould not dissolve in the small amount of oil in the oil-rich phaseand became coke.The lightest extract oil was obtained at 693 K.At 693 K, the amount of oil in the oil-rich phase was sufficientto dissolve the coke precursor effectively.The coke formation was suppressed by the high solubility of the coke precursors in oil, and coke formationproceededslowly because of thelow temperature.The decomposition of oil proceeded overa long retention time where the transfer of oil from the oil-rich phase to the water-rich phase was less than that above 16

693 K.Furthermore, the long retention time probably improved the hydrogenation of the coke precursor in the oil-rich phase through the WGSR.These factorsmay have contributed tothe effective upgrading of oil at 693 K. Finally, we compared the results in this study with previous resultsobtained in SCW.Morimoto et al. compared various results for oil sand bitumen cracking [26].They focused the relationship between coke yield and conversion based on the boiling point of oil.We compared our results with other results in SCW according to their method.The conversion and coke yield aresummarized in Table 2.The conversion was defined by the amount of oil withhigher boiling points than the cut point.The trends can be discussed to some extent, although the definition of conversion was different under each set of conditions. For semi-batch treatment at 673 K, the conversion did not proceed in SCW at 1.0 g/min, whereas the conversions were 0.32, 0.34 and 0.43 for SCW + CO at 1.0 g/min, SCW + CO at 0.5 g/min,and SCW + H2 + CO2, respectively.The addition of CO and H2 + CO2 clearly enhanced the decomposition of bitumen to lighter components.In SCW + CO, the conversion reached its maximum of 0.62 and the coke yield was 4.1 wt % at 693 K.However,the conversion and coke yield were 0.41 and 3.9 wt %, respectively, for SCW-Batch at 693 K.At 713 and 723 K, the conversionsfor SCW-Batch, SCW-CSTR, 17

and SCW + CO were similar from 0.52 to 0.64, whereas the coke yield of SCW + CO was significantly lower than the yields in SCW-Batch and SCW-CSTR.The addition of CO and treatment with the semi-batch system in SCW gave higher conversionswith similar coke yields in thelow-temperature region, and it suppressed the formation of cokeforsimilar oil conversions in the high-temperature region.In addition, the coke formation was completely suppressed by controlling the residence time in the water-rich phase and the oil-rich phase at 703 and 723 K in SCW [27], which indicates the importance of residence time inthe decomposition of bitumen.

Conclusion Bitumen was decomposed with a semi-batch type reactor in SCW, SCW + CO, andSCW + H2 at 30 MPa.At 673 K, the residual oil yield in SCW was significantly larger than the yieldsin SCW + CO and SCW + H2.The extract oil yield increasedin the order of SCW + CO, SCW + H2 and SCW.CO and H2 facilitated the extraction of oil from inside the reactor to outside.It was assumed that there were two phases in the reactor, and the transfer of oil from the oil-rich phase to the water-rich phase was increased byCO and H2.The coke yield in SCW + CO was lower than the yieldsin SCW and SCW + H2, indicating that bitumen was probably hydrogenatedby theWGSR.The 18

number average molecular weight of the extract oil was lower than that of raw bitumen, indicating that the lighter component of the oil was preferentially extracted from the reactor.The atomic H/C ratio of the residual oil in SCW + CO was slightly lower than that in SCW + H2.The hydrogenation of the oil probably stabilized the heavier components,such as coke precursors,allowing them to remain as oil instead ofbecomingcoke. The effect of temperature on product distribution was elucidated in SCW + CO from 673 to 723 K.Most of the oil was extracted outside the reactor regardless of temperaturebecause the extract oil yield was always above 74wt %.In addition, the extract oil was the lightest at 693 K.The distribution of oil between the water-rich phase andthe oil-rich phaseaffected the stability of the coke precursor and the retention time, and the temperature governed both the oil decompositionrateand coke formation rate.These were themain factors that determinedthe upgrading of bitumen.Comparing our results withpreviousresults forSCW revealed that the addition of CO gave a high conversion with similar coke yields in the low-temperature region and suppressed the formation of coke withsimilar oil conversion in the high-temperature region.

Acknowledgements 19

This work was partly supported by JSPS KAKENHI Grant Number 26420778.The authors are grateful to Dr. Shinya Sato and Dr. ToshimasaTakanohashi at Research Institute of Energy Frontier, Non-conventional Carbon Resources Group in National Institute of Advanced Industrial Science and Technology (AIST)for part of the analyses.

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References [1] J. G. Speight, The Chemistry and Technology of Petroleum fourth edition, Boca Raton, CRC Press.(2007) 163-167.

[2] D. Barson, S. Bachu, P. Esslinger, Flow systems in the Mannville Group in the east-central Athabasca area and implications forsteam-assisted gravity drainage (SAGD) operations for in situ bitumen production. Bulletin of Canadian Petroleum Geology 49 (2001) 376-392.

[3] N. Akiya,P. E. Savage,The roles of water for chemical reactions in high-temperature water. Chemical Reviews 102 (2002) 2725-2750.

[4] R. P. Dutta,W. C. McCaffrey,M. R. Gray, K.Muehlenbachs, Thermal cracking of Athabasca bitumen: Influence of steam on reaction chemistry. Energy and Fuels 14 (2000) 671-676.

[5] L. Q. Zhao,Z. M. Cheng,Y. Ding,P. Q. Yuan,S. X. Lu,W. K. Yuan,Experimental study on vacuum residuum upgrading through pyrolysis in supercritical water. Energy and Fuels 20 (2006) 2067-2071.

21

[6] M. Meng, H. Hu, Q. Zhang, M. Ding, Extraction of Tumuji oil sand with sub- and supercritical water, Energy and Fuels 20 (2006) 1157-1160.

[7] Z.-M. Cheng, Y. Ding,L.-Q.Zhao,P.-Q.Yuan,W.-K.Yuan, Effects of supercritical water in vacuum residue upgrading, Energy and Fuels 23 (2009) 3178-3183.

[8] M. Watanabe, S. Kato, S. Ishizeki, H. Inomata, R. L. SmithJr., Heavy oil upgrading in the presence of high density water: Basic study, J. Supercritical Fluids 53 (2010) 48-52.

[9] Wahyudiono, T. Shiraishi, M. Sasaki, M. Goto, Non-catalytic liquefaction of bitumen with hydrothermal/solvothermal process, J. Supercritical Fluids, 60 (2011) 127-136.

[10] J. Vilcáez, M. Watanabe, N. Watanabe, A. Kishita, T. Adschiri, Hydrothermal extractive upgrading of bitumen without coke formation, Fuel 162 (2012) 379-385.

[11] M. Morimoto,Y. Sugimoto, Y. Saotome, S. Sato, T. Takanohashi, Effect of supercritical water on upgrading reaction of oil sand bitumen, J. Supercritical Fluids 55 (2010) 223-231.

22

[12] M. Morimoto, S. Sato, T. Takanohashi, Effect of water properties on the degradative extraction of asphaltene using supercritical water, J. Supercritical Fluids 68 (2012) 113-116.

[13] Y. Liu, F. Bai, C.-C.Zhu, P.-Q.Yuan, Z.-M.Cheng, W.-K. Yuan, Upgrading of redsidual oil in sub- and supercritical water: An experimental study, Fuel Processing Technology 106 (2013) 281-288.

[14] R. O. Caniaz and C. Erkey, Process intensification for heavy oil upgrading using supercritical water, Chemical Engineering Research and Design 92 (2014) 1845-1863.

[15]

T.

Adschiri,

R.

Shibata,

T.

Sato,

M.

Watanabe,

K.

Arai,

Catalytichydrodesulfurization of dibenzothiophene through partial oxidationand a water-gas shift reaction in supercritical water, Industrial and Engineering Chemistry Research 37 (1998) 2634-2638.

[16] K. Arai, T. Adschiri, M. Watanabe, Hydrogenation of hydrocarbons through partial oxidation in supercritical water, Industrial and Engineering Chemistry Research 39 (2000) 4697-4701.

23

[17] P.-Q. Yuan, Z.-M.Cheng, W.-L.Jiang, R. Zhang, W.-K.Yuan, Catalytic desulfurization of residual oil through partial oxidation in supercritical water, J. Supercritical Fluids 35 (2005) 70-75.

[18] P.-Q. Yuan, Z.-M.Cheng, X.-Y.Zhang, W.-K.Yuan, Catalytic denitrogenation of hydrocarbons through partial oxidation in supercritical water, Fuel 85 (2006) 367-373.

[19] T. Sato, S. Mori, M. Watanabe, M. Sasaki, N. Itoh, Upgrading of bitumen with formic acid in supercritical water, J. Supercritical Fluids 55 (2010) 232-240.

[20] T. Sato, T. Tomita, P. H. Trung, N. Itoh, S. Sato, T. Takanohashi, Upgrading of bitumen in the presence of hydrogen and carbon dioxide in supercritical water, Energy and Fuels 27 (2013) 646-653.

[21] N. Berkowitz, J. Calderon, Extraction of oil sand bitumens with supercritical water, Fuel Processing Technology 25 (1990) 33-44.

[22] T.Sato, Upgrading of heavy oil by hydrogenation through partial oxidation and water-gas shift reaction in supercritical water, J. of the Japan Petroleum Institute 57 (2014) 1-10.

24

[23] M. Watanabe, T. Sato, H. Inomata, R. L. Smith, Jr., K. Arai, A. Kruse, E. Dinjus, Chemical reactions of C1 compounds in near-critical and supercritical water, Chemistry Reviews 104 (2004) 5803-5821.

[24] T. Sato, P. H. Trung, T. Tomita, N. Itoh, Effect of water density and air pressure on partial oxidation of bitumen in supercritical water, Fuel 95 (2012) 347-351.

[25] M. Uematsu and E. U. Franck, Static dielectric constant of water and steam. Journal of Physical Chemistry Reference Data 9 (1980) 1291-1306.

[26] M. Morimoto, Y. Sugimoto, S. Sato, T. Takanohashi, Comparison of thermal cracking process for Athabasca oil sand bitumen: Relationship between conversion and yield, Energy and Fuels 28 (2014) 6322-6325.

[27] S. Nagamatsu, T. Kayukawa, H. Egami, T. Fujimoto, Japan Patent Kokai 2011-88964 (2011.05.06).

25

Figure captions Fig. 1Experimental apparatusfor upgrading bitumen in SCW with CO and H2. Fig. 2 Apparent boiling point distribution of raw bitumen, and products in SCW, SCW + CO, and SCW + H2 obtained at 673 K, 30 MPa, and 1.0 g/min of water for 60 min (SCW + CO (0.5): 0.5 g/min of water; R = residual oil, E = extract oil; a: above 773 K, b: from 723 to 773K, c: from 623 to 723 K, d: from 523 to 623 K, e: from 423 to 523 K, f: below 423K, g: coke). Fig. 3 Hydrogen type distribution of raw bitumen, residual oil, and extract oil obtained at 673 K, 30 MPa and 1.0 g/min of water for 60 min(R = residual oil, E = extract oil; a:Ha, b: H, c:H, d: H). Fig. 4Yields of coke, residual oil, and extract oil as a function of reaction time in SCW and SCW + CO obtained at 673 K and 1.0 g/min of water(○: coke; ∆: residual oil; □: extract oil; open symbolsand solid lines: in SCW+CO; filled symbolsand dashed lines: in SCW). Fig. 5Yields of coke, residual oil, and extract oil as a function of temperature in SCW and SCW + CO obtained at 30 MPa and 0.5 g/min of water for 60 min (○: coke; ∆: residual oil; □: extract oil; open symbolsand solid lines: in SCW+CO; filled symbolsand dashed lines: in SCW). 26

Fig. 6Ratio of products based on apparent boiling point for extract oil in SCW + CO obtained at 30 MPa and 0.5 g/min of water for 60 min(a: above 773 K, b: from 723 to 773K, c: from 623 to 723 K, d: from 523 to 623 K, e: from 423 to 523 K, f: below 423K). Fig. 7Proposed upgrading scene occurring inside the reactor when supercritical water and CO solvent system is used

Back pressure regulator

Filter

Trap

Reactor

Preheater CO, H2

Distilled water

High-pressure syringe pump

Fig. 1

27

Fig. 2

28

Fig. 3

29

100

Yield [wt%]

80 60 40 20 0 0

20 40 60 80 Reaction time [min]

100 Fig. 4

100

Yield [wt%]

80 60 40 20 0

680 700 720 Temperature [K]

Fig. 5

30

Fig. 6

31

Extract oil + Solvent

Water rich phase ・Enhancing the extraction of oil in high temperature region ・Proceeding hydrogenation of coke precursor through the water-gas shift reaction at long retention time

Oil rich phase

Coke

・Promoting coke formation in high temperature region

Solvent (Supercritical water + CO)

Fig. 7 Graphical abstract

Upgraded Oil

water rich phase

oil rich phase

・Enhancement of extraction

Coke precursor

・Suppression of coke formation

Supercritical water + CO

32

Table 1 Elemental analysis and number average molecular weight of oil obtainedat 673 K, 30 MPa, and 1.0 cm3/min for 60 min (R= residualoil, E= extract oil).

Sample

Raw

SCW

SCW+CO

SCW+H2

R

E

R

E

R

E

C [wt%]

83.2

84.2

83.6

82.7

83.5

83.2

83.8

H [wt%]

10.2

10.3

10.6

8.30

10.6

9.30

10.6

N [wt%]

0.45

0.42

0.31

0.98

0.31

0.70

0.33

S [wt%]

5.07

4.52

4.31

6.05

4.43

5.51

4.38

O[wt%]

1.13

0.55

1.23

1.96

1.18

1.35

0.87

Ratio of H/C

1.46

1.46

1.51

1.20

1.51

1.33

1.51

860

786

658

990

751

946

711

Number average molecular weight

33

Table 2Conversion and coke yield forvarious processes in SCW

Solvent

Tempera

Pressure

Flow rate

Conversion

Coke yield

Ref.

ture [K]

[MPa]

[g/min]

[-]

[wt%]

SCW+COb

673

30

1.0

0.32

1.8

This work

SCW+COb

673

30

0.5

0.34

2.8

This work

b

693

30

0.5

0.62

4.1

This work

SCW+COb

723

30

0.5

0.52

3.3

This work

SCWb

673

30

1.0

-c

6.6

This work

a

693

27-30

-

0.41

3.9

26

a

SCW-Batch

723

27-30

-

0.56

6.0

26

SCW-CSTRa

713

30

-

0.64

9.7

26

30

d

0.43

0.6

20

SCW+CO

SCW-Batch

SCW+H2+CO2b

673

0.5

a

b

Cut point for the definition of conversion was 798 K, semi batch system, cut point for definition of

conversion was 773 K and extraction time was 60 min,

c

amount of coke + fraction over cut point

was larger than the fraction over cut point of raw bitumen, dSCW+H2+CO2 was supplied as 10wt% HCOOH aq. at 0.5 cm3/min through the preheater.

34