Upgrading of Bitumen in the Presence of Hydrogen and Carbon

Advanced Fuel Group, Energy Technology Research Institute, National ... (SCW) and its mixtures with hydrogen and carbon dioxide using semibatch reacto...
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Upgrading of Bitumen in the Presence of Hydrogen and Carbon Dioxide in Supercritical Water Takafumi Sato,† Tomoyuki Tomita,† Phan Hieu Trung,† Naotsugu Itoh,*,† Shinya Sato,‡ and Toshimasa Takanohashi‡ †

Department of Material and Environmental Chemistry, Utsunomiya University, 7-1-2, Yoto, Utsunomiya, 321-8585, Japan Advanced Fuel Group, Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8569, Japan

‡

ABSTRACT: Upgrading of bitumen was examined in supercritical water (SCW) and its mixtures with hydrogen and carbon dioxide using semibatch reactors. Coke formation became prominent above 673 K in SCW and 693 K for SCW + H2 + CO2. Coke yield in SCW was higher than that in SCW + H2 + CO2, implying that coke formation is suppressed in SCW + H2 + CO2. The asphaltenes obtained with SCW + H2 + CO2 had higher H/C atomic ratios than those of the raw asphaltene or asphaltene obtained with SCW. The average molecular structures of raw asphaltene, as well as asphaltene in SCW and in SCW + H2 + CO2, were estimated. From the properties of asphaltene, repolymerization during decomposition of asphaltene was probably inhibited in SCW + H2 + CO2. Furthermore, the oil formed in SCW + H2 + CO2 was removed from the reactor more easily than that in SCW. The removal of oil from the reactor and the hydrogenation of asphaltene through reverse water-gas-shift reaction probably suppressed coke formation in SCW + H2 + CO2.

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1. INTRODUCTION Development of upgrading techniques for heavy oil is important because feedstocks worldwide are becoming heavier. Oil sand bitumen recovered in Canada is one of the important heavy oil resources in the world. Nowadays, a part of bitumen is recovered with high pressure steam by steam-assisted gravity drainage (SAGD) method.1 The recovered bitumen by SAGD method is a high-temperature mixture of oil and water at 473 K, so that high-temperature water could possibly be used for the upgrading of bitumen. Supercritical water (SCW; Tc = 647 K and Pc = 22.1 MPa) including high-temperature steam is an effective solvent for heavy oil processing.2−10 SCW easily dissolves light hydrocarbons11 and disperses coke precursor in SCW.7,9 Recent research has revealed that the water molecule influences the decomposition of heavy oil in SCW primarily by physical effects such as the dispersion of heavy fractions rather than reactions such as hydrogen transfer from water to the oil.7 Treatments that enhance SCW as a solvent will probably be necessary to develop an effective upgrading process for heavy oil with SCW. Hydrogenation through the forward water-gas-shift reaction (WGSR: CO + H2O → CO2 + H2) and reverse WGSR (H2 + CO2 → CO + H2O) in SCW is one possible method for heavy oil upgrading because a reactive hydrogen molecule forms through the WGSR and reverse WGSR. The catalytic hydrogenation of dibenzothiophene, carbazole, and naphthalene proceeds with NiMo/Al2O3 catalysts through forward or reverse WGSR (SCW + CO, SCW + H2 + CO2) in SCW.12,13 The catalytic hydrodesulfurization of benzothiophene14 and dibenzothiophene15 in emulsions proceeds with dispersed Mo catalyst by reactive in situ hydrogen formed during WGSR in high-temperature water. The hydrocracking of Gudao residual oil also proceeds with catalysts through WGSR in SCW.16,17 Other than heavy oil, the hydrogenation of diesel fuel proceeds © 2012 American Chemical Society

in CO + SCW with ammonium tetramolybdate as a catalyst and hydrogen from the water molecule is incorporated into the products.18 Hydrogenation through the WGSR has been also studied via partial oxidation of hydrocarbon to form CO and hydrogenation of heavy oil and its model compounds through WGSR in SCW.12,13,19,20 Catalytic desulfurization of benzothiophene and denitrogenation of quinolone proceeds with NiMo and CoMo catalysts in the presence of hydrocarbon and oxygen in SCW.19,20 Hydrogenation through WGSR in SCW has been examined for upgrading of bitumen. The authors21 conducted noncatalytic upgrading of bitumen in SCW in the presence of HCOOH that is an intermediate of WGSR. In that work,21 it was found that the SCW + HCOOH atmosphere promotes the decomposition of asphaltene and the suppression of coke formation over that in SCW. Active hydrogen produced during the WGSR most likely reduces coke formation. A reaction model for SCW + HCOOH system is proposed by assuming the existence of water-rich phase and oil-rich phase. In that model, coke formation mainly occurs in the oil-rich phase by polymerization of asphaltene cores.8,21 Therefore, the presence of a hydrogen donor in the oil-rich phase could be effective for the suppression of coke formation in the upgrading of bitumen. Berkowitz and Calderon22 conducted the extraction of oil sand bitumen by introducing CO in SCW at 673 K with semibatchtype reactor. They reported that the coke formation was strongly suppressed in SCW + CO system, compared with that found in SCW. They also reported that bitumen containing a large amount of asphaltene was sensitive for CO introduction in SCW on coke formation. Received: September 3, 2012 Revised: December 10, 2012 Published: December 10, 2012 646

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∼50% H2, ∼40% CO2, and ∼10% CO. In the case of SCW + H2, H2 was filled at 30 MPa with a high-pressure syringe pump (ACRAFT, Natori) and was supplied to upstream of the preheater. The reaction time was defined as the time after the inside of the reactor reached reaction temperatures. The typical time to attain the reaction temperature was within 20 min. In some experiments, the amount of gas products was measured using a wet gas meter (Model W-NK-1A, Shinagawa Corporation) and the concentration of gases were analyzed by GC (GC2014, Shimadzu Corporation) equipped with a TCD detector. It is difficult to measure the accurate gas amount for SCW + H2 + CO2, because the gases pressurized in the dead volume at the inlet and outlet lines rapidly expanded when it was released. After the reaction, the products inside the reactor, inside the downstream line from the reactor, and in the receiver were mixed together and were separated into water-soluble, maltene, asphaltene, and toluene-insoluble fractions by the method reported previously.21 The toluene-insoluble fraction dried at 333 K overnight was defined as coke. The elementary analysis of CHNS (FLASH2000, Thermo Scientific) and 1H NMR analysis (NMR System 500LS, Varian) were conducted. GPC analysis system (PU-980 HPLC series equipped with RI detector, JASCO Corporation) equipped two mixed-D columns (7.6 mm ϕ × 300 mm, exclusion limit of 400000, Polymerlabs, exclusion limit of 400 000) in a series was used for asphaltene using tetrahydrofuran (THF) at a flow rate of 0.8 mL/min at 40 °C. The asphaltene and coke yields were defined by weight based on charged bitumen. In some experiments, the products inside the reactor, inside the downstream line from the reactor, and in the receiver were recovered separately using toluene. The latter two products were mixed, which is defined as an extract product, and the first one, as a raffinate product. The product was filtered with a 0.1-μm membrane filter (ADVANTEC) and separated into solid and liquid. The toluene solution was evaporated at 353 K under ∼0.02 MPa to remove toluene and obtain the recovered oil. The oil derived from raffinate product and extract product are defined as raffinate oil and extract oil, respectively. The thermal analysis of raffinate oil and extract oil was conducted with a thermogravimetric analysis (TGA) instrument (Thermo plus EVO II TG, Rigaku Corporation) under 150 cm3/min of nitrogen stream. The temperature increased from 323 K to 700 K at a heating rate of 10 K/min. The boiling point of sample was estimated using a calibration curve obtained by the analysis of several n-alkanes, and the boiling-point distribution of the oil was calculated by the integration of derivative values of weight change with temperature. The boiling point obtained from TGA should be different in the actual boiling point, because the conversion of asphaltene may occur during TGA. So we described the boiling point obtained via TGA as the apparent boiling point.

In this study, the objectives were to study the upgrading of bitumen with SCW + H2 + CO2 mixtures and to evaluate the effect of the reverse WGSR on asphaltene decomposition and coke formation. Studies in bitumen upgrading through WGSR in SCW with semibatch reactor are limited, and there is no study for SCW + H2 + CO2 mixtures as a reverse WGSR system in SCW. In particular, the fate of asphaltene, that is, the precursor of coke, should be studied. To elucidate the kinetics of asphaltene decomposition, asphaltene is analyzed in detail, an average molecular structure of asphaltene is estimated and the boiling-point distribution of products are evaluated.

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2. EXPERIMENTAL SECTION

Bitumen recovered by SAGD method was used for experiments. The bitumen consisted of maltene (pentane-soluble fraction) and asphaltene (pentane-insoluble and toluene-soluble fraction). The maltene and asphaltene were 79.0 and 21.0 wt % of the raw bitumen, respectively. Pentane (98.0+%) and toluene (99.5+%) were purchased from Wako Pure Chemical Industries, Ltd. Figure 1 shows a schematic diagram of the apparatus used for the upgrading of bitumen. The bitumen (1.0 g) was loaded in the reactor

Figure 1. Semibatch apparatus for contacting bitumen with supercritical water + H2 + CO2 mixtures.

3. RESULTS AND DISCUSSION 3.1. Asphaltene and Coke Yield. Figure 2 shows asphaltene and coke yields with temperature at a flow rate of 1 cm3/min at STP (standard temperature and pressure). At 623 K, the asphaltene yield was higher than that of raw bitumen and the coke yield was lower than 0.2 wt % in both SCW and SCW + H2 + CO2, indicating the formation of asphaltene from maltene occurred. In the case of SCW, the asphaltene yield decreased with increasing temperature while the coke yield increased above 673 K. In the case of SCW + H2 + CO2, the similar trend was observed, and the asphaltene yield was higher than that in SCW, and the coke yield was lower. The coke yield in SCW + H2 + CO2 increased with temperature. The asphaltene converted to two fractions having lower molecular weight, such as maltene, and higher molecular weight, such as coke. In the presence of H2 + CO2, those reaction pathways were suppressed and thus the coke formation was inhibited. In the literature, coke formation has been shown to be reduced

(6 cm3) made of SUS316, whose inner diameter was 8.5 mm. The reactor was oxidatively treated to make the inner wall nonreactive, according to the previous study.23 Two thermocouples were inserted into the reactor to measure the temperatures at the center and the bottom of the reactor. At first, the internal space of the reactor was filled up with water using an HPLC pump (PU-2086, JASCO Corporation) at 30 MPa using a back-pressure regulator (26-1700 series, Tescom), then the reactor was heated at 573 K. After the temperatures became stable, the reactor was heated to reaction temperature and the solvent was injected at a certain flow rate. The diameter of the injection port of the reactor was 0.59 mm at the center of the reactor. The solvent was water for SCW or 10 wt % of HCOOH aqueous solution for SCW + H2 + CO2, and it was preheated to the reaction temperature at the reactor inlet. For the case of SCW + H2 + CO2, H2 and CO2 were produced by the decomposition of HCOOH during preheating. Conversion of HCOOH in the preheating line was checked by removing the reactor from the experimental apparatus. In all cases, the conversion of HCOOH was over 99% and almost all of the HCOOH was decomposed into gases. The gas composition was 647

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asphaltene. At 653 K, the H/C atomic ratio of asphaltene in SCW was lower than that of the raw asphaltene, while in SCW + H2 + CO2, it was higher. In Figure 2, the decomposition of asphaltene proceeded with low coke formation in SCW and in SCW + H2 + CO2 at 653 K, whereas the decomposition of asphaltene did not seem to proceed. Judging from the elementary analysis, the asphaltene in SCW was dehydrogenated at 653 K and that in SCW + H2 + CO2 was hydrogenated. The H/C atomic ratio of asphaltene for experiments in SCW and in SCW + H2 + CO2 increased with temperature. Above 673 K, the H/C atomic ratio of asphaltene was in the order of in SCW + H 2 + CO2 > in SCW > raw asphaltene

Figure 2. Asphaltene and coke yields with temperature at 30 MPa and 1 cm3/min of solvent at STP for 60 min ((○) asphaltene yield in SCW, (●) asphaltene yield in SCW + H2 + CO2, (△) coke yield in SCW, (▲) coke yield in SCW + H2 + CO2).

at each temperature, which means that the hydrogenation of asphaltene occurred and the reaction was promoted more in SCW + H2 + CO2 than in SCW. Furthermore, the sulfur contents in asphaltene decreased from 653 K to 673 K and that in SCW + H2 + CO2 were always lower than that in SCW in each temperature. In the decomposition of asphalt in SCW, sulfur in asphaltene moves into coke, maltene, or hydrogen sulfide in the progress of desulfurization of asphaltene.3 In this study, the enhancement of the desulfurization of asphaltene in the high-temperature region probably indicates that a similar movement of sulfur occurred. In the case of SCW + H2 + CO2, sulfur in asphaltene mainly moved to maltene or hydrogen sulfide, because coke formation was suppressed. The hydrogenation of asphaltene probably made the amount of sulfur in asphaltene decrease by the decomposition of sulfur-containing compounds to lowermolecular-weight side to be dissolved in maltene or by the hydrogenation of sulfur to form hydrogen sulfide. Figure 3 shows the molecular weight distribution of asphaltene. After the reaction, the peak shifted to lowermolecular-weight side except that at 653 K in SCW. At 653 K, the molecular weight of asphaltene in SCW was as much as that of raw asphaltene, whereas the molecular weight of asphaltene in SCW + H2 + CO2 was lower than that of raw asphaltene. The asphaltene decomposed to a fraction having lower molecular weight in SCW + H2 + CO2. At both 673 and 693 K, the peaks of molecular weight were lower than 1100, regardless of whether SCW or SCW + H2 + CO2 was used. Figure 4 shows the hydrogen type distribution of asphaltene observed by 1H NMR analysis. The composition of aromatic hydrogen (Ha) in SCW and in SCW + H2 + CO2 was lower than that of raw asphaltene and the ratio was in the order of SCW > SCW + H2 + CO2. The decomposition of asphaltene in SCW and SCW + H2 + CO2 promoted the hydrogenation of aromatics. For the distilled residue, the composition of Ha increases after the decomposition of bitumen at 723 K in SCW.9 This trend was not observed for the case of asphaltene. The average molecular structure of asphaltene was estimated with methods in the literature24,25 from the average molecular weight, elementary analysis, and hydrogen-type distribution, as shown above. The analysis with 13C NMR can narrow the structure; however, it is reported that the carbon aromaticity required for the estimation of average molecular structure can be evaluated by H/C ratio and the hydrogen distribution with 1 H NMR even without the results of 13C NMR for C5 and C7 asphaltene.26,27 In this method, the error in the number of aromatic carbon in each asphaltene was within 5% and that in the number of carbon in model molecules was within approximately one molecule. We evaluated carbon aromaticity

during the conversion of bitumen with HCOOH in SCW without catalyst21 and in that with CO in SCW.22 In this study, we focused the discussion of the kinetics of bitumen decomposition on the information of asphaltene, although the reaction of maltene is also important when the effect of coke formation is small. For example, the amount and properties of asphaltene depends on the forward and reverse chemical alternation from asphaltene to maltene such as cracking and hydrogenation. The progress of these alternations would influence the solubility of products in oil. It is expected that the reaction of maltene will be revealed in the future, because the kinetics of maltene will improve bitumen decomposition. The amount of gas recovered in SCW was ∼10 cm3 and main gases detected were CO2, H2, and CH4. On the other hand, the amount of gas recovered in SCW + H2 + CO2 was a few thousand cubic centimeters, and the detected gases were H2, CO2, and CO, and those were derived from the decomposition of HCOOH. The compositions of H2 and CO were smaller than those without reaction of bitumen by several percent, which means that some of the H2 and CO was probably consumed during the reaction. To evaluate the effect of flow rate, experiments were performed by changing the flow rate of water in SCW at 673 K. Table 1 shows the effect of flow rate on asphaltene and coke Table 1. Effect of Flow Rate on Asphaltene and Coke Yields in SCWa Yield [wt%]

a

supplied flow rate at STP [cm3/min]

asphaltene

coke

0.7 1.0 1.2

7.2 7.4 8.1

6.4 5.6 5.4

Conditions: 673 K, 60 min, 30 MPa.

yields. The asphaltene and coke yields were not so different in the range of 0.7−1.2 cm3/min of flow rate of water at STP. The flow rate of solvent does not seem to be a major factor for the extraction behavior in SCW that was also reported by Morimoto et al.10 with their experimental apparatus. 3.2. Properties of Asphaltene. The properties of asphaltene were analyzed in detail. Table 2 shows the result of elementary analysis of asphaltene obtained above 653 K. After the reaction, the sulfur content was lower than that of raw 648

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Table 2. Elementary Analysis of Asphaltenea SCW C (wt %) H (wt %) N (wt %) S (wt %) H/C atomic ratio a

SCW + H2 + CO2

raw

653 K

673 K

693 K

653 K

673 K

693 K

80.98 8.26 1.05 7.85 1.21

81.01 7.20 1.32 7.23 1.06

83.22 8.83 0.85 5.32 1.26

82.06 9.14 0.54 5.88 1.33

81.62 8.51 1.00 6.12 1.24

82.81 9.18 0.89 4.28 1.32

82.55 9.64 0.59 4.46 1.39

1 cm3/min of solvent at STP, 60 min, 30 MPa.

LD-MS are compared with those obtained with GPC.29 The molecular weight obtained with LD-MS gives that as a molecule, because each molecular is ionized. The numberaverage molecular weight of a whole asphaltenene and all fractions are from Mn ≈ 1000 to Mn ≈ 2000 in LD-MS analysis. On the other hand, the number-average molecular weight of higher-molecular-weight fraction is from Mn ≈ 3000 to Mn ≈ 7000 in GPC analysis, whereas those of the lower-molecularweight fraction and a whole asphaltene are from Mn ≈ 1000 to Mn ≈ 1600 and are close to that obtained with LD-MS analysis. These results imply that if the aggregation of molecule in GPC occurs, it mainly affects not the average structure of fused rings, but the number of fused rings in one molecule. Furthermore, in GPC analysis, the Mn value was underestimated, because of the late asphaltene outflow in the lower-molecular-weight region. However, the result of GPC after the correction of underestimation is similar to that of LD-MS under Mn ≈ 1600,30 and we made a correction according to ref 30. From these facts, the effect of aggregation on the estimation of average molecular structure was relatively small for the analyses in this study at lower than Mn ≈ 1600. Therefore, the average molecular structure in this study would be credible, because all of the Mn values were under ∼1600. Figure 5 shows the average molecular structures of raw asphaltene, as well as asphaltene in SCW and in SCW + H2 + CO2 at 673 K, where the coke formation in SCW proceeded and that in SCW + H2 + CO2 was almost completely suppressed. The average molecular structure consisted of monomers and dimers. The raw asphaltene contained the monomer fused ring units, which consisted of 10 carbon rings, including 2 naphthene rings, and the ratio of monomer to dimer was 2:8. For SCW, the monomer fused ring units consisted of 10 carbon rings, including 7 naphthene rings, and the ratio of monomer to dimer was 1:9. The length of alkyl side chain was shorter than that of raw asphaltene. The ratio of monomer to dimer in SCW was slightly larger than that in raw asphaltene. The hydrogenation of the aromatic ring and the decomposition of alkyl side chain proceeded in SCW. In SCW + H2 + CO2, the monomer fused ring units consisted of eight carbon rings, including three naphthene rings. The hydrogenation of aromatic ring proceeded as well as the case in SCW, and the ring-opening reaction of carbon rings somewhat occurred. The ratio of monomer to dimer was 5:5, which was larger than that of raw asphaltene and the asphaltene obtained with SCW. The length of the alkyl side chain was almost the same as raw asphaltene. It is reported that the desulfurization of dibenzothiophene proceeded through reverse WGSR with a trace amount of CO formation in the presence of catalyst.12 We consider a similar reaction to have occurred in SCW + H2 + CO2. In SCW + H2 + CO2, the reverse WGSR would proceed and the active hydrogen formed during reverse WGSR was consumed by the incorporation into active site of oil such as a

Figure 3. Molecular weight distribution of the asphaltene at 30 MPa and 1 cm3/min of solvent at STP for 60 min: raw asphaltene (curve 1); SCW at 653 K (curve 2); SCW at 673 K (curve 3); SCW at 693 K (curve 4); SCW + H2 + CO2 at 653 K (curve 5); SCW + H2 + CO2 at 673 K (curve 6); SCW + H2 + CO2 at 693 K (curve 7).

Figure 4. Hydrogen-type distribution of asphaltene at 30 MPa and 1 cm3/min of solvent at STP for 60 min.

required for the estimation of average molecular structure according to refs 26 and 27. The number-average molecular weight (Mn) values were 1638, 1009, and 964 for raw asphaltene, asphaltene in SCW at 673 K and asphaltene in SCW + H2 + CO2 at 673 K, respectively. GPC can measure a combination of molecular weight and molecular aggregation, as well as a monomer. In the previous studies, the asphaltene from Maya, Kafji, and Iranian Right crude oil are fractionated with GPC28 and the molecular weight of whole asphaltene and each fraction obtained with 649

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Figure 5. Average molecular structure of asphaltene at 673 K, 30 MPa, and 1 cm3/min of solvent at STP for 60 min. (raw asphaltene, 1(a):1(b) = 2:8; in SCW, 2(a):2(b) = 1:9; and in SCW + H2 + CO2, 3(a):3(b) = 5:5).

used for the SCW + H2 + CO2 system. The flow rate of H2 in SCW + H2 was 1.25 × 10−3 mol/min, which was as large as 1.11 × 10−3 mol/min in SCW + H2 + CO2. In all experiments, the total yield, which is the sum of coke, raffinate oil, and extract oil, was ∼80 wt %. Preliminary experiments at 473 and 573 K, where the decomposition of bitumen practically does not occur, gave total yields of 101 wt % and 89 wt %, respectively, which demonstrates the low reactivity of bitumen under these conditions. The mass balance being to within ∼20 wt % probably corresponds to the volatiles released during evaporation of toluene in the analysis procedure, because the apparent boiling point of the volatiles is equivalent to temperatures up to 423 K under atmospheric pressure. The lack of mass balance was 20.2 wt %, 25.3 wt %, 16.2 wt %, and

coke precursor rather than by the complete progress of reverse WGSR to form CO. The hydrogen produced through reverse WGSR probably capped the reactive sites of fused ring units produced during the decomposition of asphaltene and thus prevented repolymerization between fused ring units that would cause coke formation. 3.3. Boiling-Point Distribution. Figure 6 shows the apparent boiling point distribution of raw bitumen, oil in SCW, oil in SCW + H2 and oil in SCW + H2 + CO2 obtained at 673 K, 30 MPa for 30 min. The supplied flow rate of water was 0.5 and 0.8 cm3/min at STP (SCW-0.5, SCW-0.8), that of 10 wt % HCOOH aqueous solution for SCW + H2 + CO2 system was 0.5 cm3/min and that for the SCW + H2 system was 0.45 cm3/min, to be comparable with the supplied flow rate of water 650

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equation of state was 11% lower than the data in ref 31. The actual flow rate under the reaction conditions in SCW + H2 and SCW + H2 + CO2 were 2.65 and 3.10 cm3/min, respectively. The actual flow rate at the reaction conditions in SCW-0.8 was almost the same as that in SCW + H2. The distribution of the oil between a raffinate and an extract in SCW-0.5 was much the same as that in SCW-0.8, whereas that the ratio of extract to raffinate in SCW + H2 was significantly larger than that in SCW-0.8. These results suggest that the flow rate was not critical and the existence of hydrogen and carbon dioxide was important to determine the distribution of the oil in a raffinate and an extract. The effect of solubility of oil to solvent is discussed next. During the extraction, there are probably two phases that are an upper water-rich phase and bottom oil-rich phase in the reactor.8,21,32 The difference in the composition of oil between the raffinate oil and the extract oil strongly indicates that the solubility of oil in the water-rich phase affects the distribution of oil, because the extract oil should be the extract of oil at least to the water-rich phase. The affinity of bitumen and solvent can be organized by solubility parameters.33,34 The Hansen solubility parameter (HSP) contain terms related to dispersive forces δD, polar interactions δP, and hydrogen bonding δH that are used to express the solubility of bitumen, in which δP and δH are important parameters.33 The HSP of bitumen is 18.4 MPa0.5, 3.9 MPa0.5, and 3.6 MPa0.5 for δD, δP, and δH, respectively.34 On the other hand, the HSP of SCW at 673 K and 30 MPa have been reported as being 5.5 MPa0.5, 9.6 MPa0.5, and 8.7 MPa0.5 for δD, δP, and δH, respectively.35 To estimate the effect of additives, we estimated HSP for CO2 in SCW + H2 + CO2, because the method of calculation of HSP for supercritical CO2 has been reported.36 The calculation of HSP for CO2 at 673 K and 0.96 MPa that was assumed by the partial pressure of CO2 being proportional to molar ratio gave 0.03 MPa0.5, 0.4 MPa0.5, and 0.8 MPa0.5 for δD, δP, and δH, respectively.36 HSP of the mixtures of SCW and inorganic gases should decrease from those for SCW due to lower HSP of inorganic gases such as CO2. The addition of CO2 or H2 to SCW probably made the important parameters of δP and δH decrease and approach those values of bitumen. In the extraction of asphaltene derived from bitumen in SCW, the solubility does not monotonically increase according to water density, and there is an optimal water density for solubility,10 because high water density gave excessively large HSP parameters. Consequently, the existence of H2 and CO2 enhanced the dissolution of bitumen in the water-rich phase and the solubility of bitumen in the water-rich phase should be in the order of

Figure 6. Apparent boiling-point distribution of raw bitumen and oil recovered for 30 min at 673 K, 30 MPa, and 0.5 or 0.8 cm3/min of water at STP in SCW (SCW-0.5 and SCW-0.8), 0.45 cm3/min of water at STP and 1.25 × 10−3 mol/min of hydrogen in SCW + H2, 0.5 cm3/min of 10 wt % formic acid aqueous solution at STP in SCW + H2 + CO2 (R = raffinate oil, E = extract oil).

25.1 wt % for SCW-0.5, SCW-0.8, SCW + H2, and SCW + H2 + CO2, respectively. These results means that light compounds probably formed during the reaction at 673 K, because there was almost no fraction whose apparent boiling point was