Laboratory Experiments and Field Test of a Difunctional Catalyst for

Jan 22, 2012 - Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China ... catalytic aquathermolysis of super heavy oil in...
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Laboratory Experiments and Field Test of a Difunctional Catalyst for Catalytic Aquathermolysis of Heavy Oil Kun Chao,† Yanling Chen,‡,§,* Huachao Liu,‡ Xianmin Zhang,‡ and Jian Li† †

Faculty of Resources, China University of Geosciences, Wuhan 430074, PR China Faculty of Materials Science and Chemical Engineering, China University of Geosciences, Wuhan 430074, PR China § Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, PR China ‡

S Supporting Information *

ABSTRACT: A kind of difunctional catalystalkyl ester sulfonate copper, which not only has the catalytic center but also has the hydrogen precursor structurewas synthesized for the first time. It has been used for catalytic aquathermolysis of super heavy oils both in the laboratory and field. The laboratory experimental results show that, although its viscosity is about 1.81 × 105 mPa·s at 70 °C, the viscosity of heavy oil could be reduced by 90.72% using 0.3 wt % catalyst at 240 °C for 24 h, with 10.12% in conversion of heavy content to light content. To evaluate the catalyst’s high performance, the structure and group compositions of the oil were characterized by Fourier transform infrared (FT-IR), elemental analysis (EL), gel permeation chromatrography (GPC), 1H nuclear magnetic resonance (1H-NMR), and gas chromatography−mass spectrometry (GC−MS). It is found that the catalyst can not only enhance the viscosity reduction of heavy oil, but also remove some heteroatoms from its molecules, finally make the flow properties better and the quality upgrading. In field tests of the F10223 well of the Xinjiang Oilfield, the preliminary result has also proved the evident effects of the catalyst. Additionally, in view of the environmentally friendly and low toxicity of the catalyst, it will be beneficial for supporting a vast array of environmental, health, and safety (HSE) standards and is likely to have some good application prospects.

1. INTRODUCTION Nowadays, abundant heavy oil resources have attracted worldwide attention for satisfying the world’s growing oil demands.1 Due to the high viscosity and composition complexity of heavy oils, their exploitation is usually difficult and expensive.2 Many enhanced oil recovery (EOR) techniques have been developed for handling them, such as thermal recovery, chemical flooding, microbial recovery, etc., in which the steam stimulation/steam flooding technology is one of the most extensive and effective ones in use.3−6 By the chemical interactions of steam and heavy oil, named “aquathermolysis”, not only can the viscosity of heavy oil be reduced but also the quality can be upgraded slightly.7 Combining steam stimulation with a chemical recovery technique, catalytic aquathermolysis has been a new exploitation technology of heavy oil with great potential.8 With the energy and power provided by the superheated steam, the catalyst can accelerate the pyrolysis reactions and remove some heteroatoms of heavy oil, leading to the further improvement of the aquathermolysis effect.9−13 Obviously, the catalyst plays an important part in this method. How to choose a suitable catalyst, according to the oil properties and final requirements, is the key for this technique.14 To date, many researchers have investigated different catalysts and evaluated their catalytic aquathermolysis effects on heavy oil.15,16 Generally speaking, the catalysts could be divided roughly into four categories: mineral,17,18 water−soluble catalysts,11,19 oil−soluble catalysts,20−22 and dispersed catalysts.23,24 It is reported that they have good aquathermolysis effects on many heavy oils or even extra heavy oils in the laboratory, but not all. In some cases, the viscosities of reacted heavy oils might © 2012 American Chemical Society

regress rapidly after reaction. That might be caused by the repolymerization of the free radicals which were generated during the aquathermolysis process, such as the cleavage of C-R (R = S, N, O, etc.) bonds.25 Learning that hydrogen donors can inhibit free radicals in the coal liquefaction and residuum hydrocracking processing, people have begun using them to further enhance the catalytic aquathermolysis effect. Several solvents have been used as hydrogen donors in the catalytic aquathermolysis method, such as tetralin, methylcyclohexane, formic acid, toluene, etc. Ovalles et al.26 have investigated the upgrading effect on the Hamaca (Venezuelan) extra heavy oil using tetralin as the hydrogen donor. The results showed that the viscosity was decreasing from 9870 to 2900 mPa·s with 50% w/w hydrogen donor after aquathermolysis reaction at 280 °C for 24 h, and the asphaltene content decreased about 8%. Fan et al.27 have also researched the effect of tetralin on catalytic aquathermolysis of super heavy oil in China. They found that the viscosity of the oil sample (8.85 × 104 mPa·s at 50 °C) decreased by 80% using 0.2 wt % catalyst (contained VO2+, Ni2+, Fe3+) and 0.8 wt % tetralin at 240 °C for 24 h. Li et al.28 have prepared the nano-nickel catalyst in a methylcyclohexane−water−n-octanol−AEO9 microemulsion system and used it for catalytic aquathermolysis of heavy oil. They claimed that the methylcyclohexane can convert to toluene and hydrogen at reaction temperature, which can be used as a hydrogen donor and improve the H/C ratio of the upgraded crude oil. Received: November 22, 2011 Revised: January 20, 2012 Published: January 22, 2012 1152

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Liu et al.29 have used formic acid as a hydrogen donor for catalytic aquathermolysis of extra−heavy oils, and the results have proven that the viscosities of the oil samples decreased by 69.16%−87.02% with 0.1 wt % organic nickel salt catalyst and 1.0−7.0 wt % formic acid, respectively. Liu et al.30 have also used toluene as a hydrogen donor for catalytic aquathermolysis of heavy oil, the viscosity reduction rate is over 85% at 240 °C for 24 h with 0.2 wt % catalyst and 0.8 wt % toluene. They said that toluene plays the double roles of solvent and radical donor in the aquathemolysis reaction system, and the later is dominant. All above are based on the theory that free radicals can be generated during aquathermolysis process,26 the hydrogen donors can stabilize them and enhance the viscosity reduction with slight upgrading of heavy oil. However, oil exploration is not easy work after all. In a field test, an extra step for adding a hydrogen donor does not respond well to the environmental, health, and safety (HSE) standards for its toxicity, acid corrosion, combustion, volatility, and cost. How to synthesize a novel catalyst, which not only has the catalytic center but also owns the hydrogen precursor, has attracted our interest greatly. Therefore, we have designed and synthesized the difunctional catalyst, alkyl ester sulfonic copper. In its molecular structure, the element copper is an excellent hydrogenation catalytic center, and the formate ester group could play as a hydrogen precursor during the aquathermolysis process.31 Besides, with the ready biodegradability of the ester group,32 this catalyst is also an environmentally friendly catalyst. To evaluate its performance, we have used it for catalytic aquathermolysis of a kind of super heavy oil (1.81 × 105 mPa·s at 70 °C) at 240 °C in the laboratory and characterized the structure and group compositions of the oil by Fourier transform infrared (FT-IR), elemental analysis (EL), gel permeation chromatrography (GPC), 1H nuclear magnetic resonance (1H-NMR), and gas chromatography−mass spectrometry (GC−MS). In addition, the field test of F10223 well in the Xinjiang Oilfield has also been implemented and investigated.

the reaction was completed, the heating was stopped, and then, the reaction mixture was cooled by cooling water. When the mixture comes to about 50 °C, we dumped the mixture in a 150 mL baker and decanted the water, thereby the oil sample was obtained to be tested and analyzed. The viscosities of oil samples were recorded by the BROOKFIELD DV-2+ programmable Viscometer at 70 °C. The rate of viscosity reduction obtained was calculated by the method Δη = (η0 − η)/η0) × 100%, where Δη (%) was the rate of viscosity reduction, η0 (mPa·s) was the viscosity of original oil, and η (mPa·s) was the viscosity of oil after the reaction. The orthogonal experiments were conducted for 24 h according to Table 1 and 2, which show the orthogonal experimental conditions for

Table 1. Factors and Levels of Orthogonal Experiments A

B

item temperature (°C) 1 2 3

240 220 200

C

W/O

D

concentration of the catalyst (wt %) pH

7:3 8:2 9:1

0.3 0.2 0.1

7 8 9

Table 2. Orthogonal Experiments item

A

B

C

D

viscosity reduction (%)

1 2 3 4 5 6 7 8 9

240 240 240 220 220 220 200 200 200

7:3 8:2 9:1 7:3 8:2 9:1 7:3 8:2 9:1

0.3 0.2 0.1 0.2 0.1 0.3 0.1 0.3 0.2

7 8 9 9 7 8 8 9 7

89.82 90.09 86.47 83.08 83.57 83.63 76.39 78.31 76.92

the sample. W/O is the mass ratio of water to oil; the pH was adjusted by adding a certain volume of the 0.1% NaOH solution. As is shown in Table 3, the single−factor experiments were conducted for 6, 12, 24,

Table 3. Single-Factor Experiments of the Reaction Time

2. EXPERIMENTAL SECTION

reaction time (h)

2.1. Synthesis and Characterization of the Catalyst. In a typical synthesis: (a) Portions of 0.1 mol cetanol (AR, Sinopharm Chemical Reagent Co., Ltd. (SCRC)) and 0.6 mol formic acid (AR, SCRC) were put into a 250 mL three-necked flask and stirred for 5 min. Twenty drops of concentrated sulfuric acid (AR, SCRC) were added into the flask, and then, the temperature was raised to 80 °C for 2.0 h. The products were put into a separating funnel and cooled to room temperature. A 0.2 mol portion of chloroform (AR, SCRC) was added to dissolve the products. After the residual formic acid in the under layer was separated, the formate ester was obtained. (b) The formate ester was sulfonated by chlorosulfonic acid (CR, SCRC) at 50 °C for 0.5 h. Then, we raised the temperature to 90 °C for 2.0 h. (c) A 0.025 mol portion of copper hydroxide (AR, SCRC) was added to the sulfonated products to react at 120 °C for 1.0 h. After standing, the mixture separated into layers, the upper layer product was what we need. The synthesis experiments have repeated 5 times, and their productivities were all around 80%. We got the final products (alkyl ester sulfonic copper) after solvent evaporation and characterized it by Fourier transform infrared spectroscopy (FT−IR, Nicolet 5700). 2.2. Laboratory Work on Catalytic Aquathermolysis. A kind of super heavy oil was used in the experiments, which was obtained from the Shengli Oilfield of China. All the experiments were carried out by adding successively 100 g oil, water (liquid) in a designed mass ratio, the catalyst in designed mass concentration, into the FYX-0.5 high pressure reactor (the volume is 500 mL). The original pressure was kept to 3 MPa by aerating N2. Then the reaction mixture was heated to the designed temperature for aquathermolysis reaction. After

viscosity reduction (%)

6

12

24

48

72

45.80

72.17

90.72

90.75

90.77

48, and 72 h under the optimum reaction conditions from the orthogonal experiments. Furthermore, four group compositions including saturated hydrocarbon (saturated HC), aromatic hydrocarbon (aromatic HC), resin, and asphaltene were separated from the samples by a chromatography column according to the industrial standard of China Petroleum SY/T 5119. And the changes of resin and asphaltene before and after reaction were characterized by FT-IR using the KBr disk method. The elemental analyses for resin and asphaltene before and after reaction were determined by elemental analyzer (EL, vario EL cube), in which the oxygen content was calculated by difference. On the basis of calibration with polystyrene standards, the number average molecular weights (MW) of asphaltene before and after reaction were characterized by gel permeation chromatography (GPC, Waters 2690 D) using tetrahydrofuran (THF) as solvent. The resin and asphaltene before and after reaction were characterized by 1H nuclear magnetic resonance spectroscopy (1H− NMR, Bruker ARX300) using CDCl3 as solvent, whose chemical shift is referred to the TMS standard. The analyses for the pyrolytic gas without and with catalysts were carried out on a gas chromatography−mass spectrometry instrument (GC−MS, Agilent 7890A/5975C). 2.3. Field Test. A field test for the catalytic aquathermolysis of a kind of super heavy oil was conducted in the Xinjiang Oilfield of 1153

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China. The F10223 oil well was chosen for the test, whose basic petrophysical properties of its oil-bearing formation are as follows: the average porosity is about 30.0%, the average oil saturation is about 73.3%, the average permeability is about 1052 mD, the average vertical permeability is about 834 mD, the reservoir depth range is about 159.5−189.5 m, the thickness of the pay zone is about 10.0 m, and the viscosity is about 8.5 × 104 mPa·s at 50 °C. In this technology, the mass of oil was calculated according to the exploitation radius and some parameters of the oil layers like infiltration ratio, pole ratio, etc. The water was added by injecting the high temperature and pressure steam to make the oil floor conditions the same as laboratory conditions. The catalyst was injected with superheated steam into the oil floor, which was used as a natural reactor when the steam was injected. The parameters of field tests were as follows: 1200 m3 steam was injected into the oil floor; then the well was closed for 6 days; after reopening, the viscosity reduction and four group compositions of the produced oil were analyzed to evaluate the efficiency of field test.

Table 4. Viscosity−Temperature Relations of Crude Oil viscosity (mPa·s) oil sample

50 °C

60 °C

70 °C

80 °C

90 °C

crude oil

1670000

530000

181000

71000

26500

Therefore, the ordinary techniques are not suitable for its exploitation, such as water flooding, chemical flooding, etc. Table 5 shows that the heavy content (resin and asphaltene) of crude oil is about 57.98%, which is higher than many other Table 5. Viscosity Reduction and Group Compositions of Oil Samples by Different Catalysts oil sample crude oil blank experiment catalyst 1 catalyst 2 catalyst 3 catalyst 4 catalyst 5 difunctional catalyst

3. RESULTS AND DISCUSSION 3.1. Characterization of the Catalyst. The FT-IR spectra for (a) formate ester, (b) formate ester sulfonic acid, and (c) the prepared catalyst are shown in Figure 1. In Figure 1a, the bands

viscosity saturated aromatic resin asphaltene reduction (%) HC (%) HC (%) (%) (%) 16.79 16.92 17.86 19.07 20.25 20.11 20.27 20.34

33.51 63.70 77.26 77.98 78.26 78.94 90.72

25.23 26.18 29.15 29.61 29.69 29.84 30.12 31.79

32.70 32.51 31.79 31.08 29.74 30.12 29.63 29.22

25.28 24.39 21.20 20.24 20.32 19.93 19.98 18.65

heavy oils. Apparently, the light content (saturated HC and aromatic HC) is not abundant enough to make the oil keep flowing, and the oil is a solid gel at ambient temperature. GPC result shows that MW of the asphaltene is about 8841 g/mol, which is also much higher than many other heavy oils. EL analysis results of resin and asphaltene are listed in Table 6. The amounts of heteroatoms in the resin and asphaltene are Table 6. Element Content of Resin and Asphaltene before and after Aquathermolysis composition (%)

Figure 1. FT-IR spectra of (a) formate ester, (b) formate ester sulfonic acid, and (c) the prepared catalyst.

at 2925, 2852, and 1460 cm−1 are the characteristic absorption peaks of methyl and methylene group. The adsorption peaks at 673 and 595 cm−1 indicate that the length of side alkyl chain of the catalyst is larger than 4. The bands at 1724 and 1630 cm−1 indicate that the catalyst contains an aldehyde carbonyl group (CO). Besides, the adsorption peak at 1170 cm−1 could also confirm that it is the formate ester group. Figure 1b shows that, after the sulfonation reaction, the important band at 1043 cm−1 is the characteristic absorption peak of sulfonic acid group (SO). Figure 1c shows that the above peak has shifted to 1072 cm−1 and become stronger. This notable blue shift indicates that the sulfonic acid group had chelated with the copper. As a result, the prepared catalyst agrees well with what we have designed. 3.2. Results of Laboratory Study of Catalytic 3.2.1. Aquathermolysis. 3.2.1. Properties of Crude Oil. The viscosities at different temperatures, the group compositions, and the EL results of crude oil are shown in Table 4, 5, and 6, respectively. Table 4 shows that the viscosity of crude oil is about 1.81 × 105 mPa·s at 70 °C, so its flow prosperity is very bad.

group

N

C

H

S

O

resin before reaction resin after reaction asphaltene before reaction asphaltene after reaction

1.62 1.79 1.93 2.21

81.23 81.36 80.54 82.27

9.220 9.039 8.468 8.288

2.858 1.646 2.704 2.558

5.071 6.169 6.354 4.674

about 9.55% and 10.99%, respectively. This reveals that many free radicals will be generated during aquathermolysis by cleavage of C−R (R = S, N, O) bonds, so an effective catalyst will be necessary for enhancing the aquathermolysis reactions. 3.2.2. Results of Laboratory Study of Viscosity Reduction. From the orthogonal experiments and single-factor experiments as shown in Tables 1−3, we have found that the efficient consequence of the factors are as follows: temperature > the concentration of the catalyst > W/O > pH. The optimum conditions are as follows: the temperature is 240 °C, the ratio of heavy oil to water is 8:2 (w/w), the percentage of catalyst is 0.3 wt %, the acidity of system is pH = 7, and the reaction time is 24 h. As is shown in Table 5, the viscosity of heavy oil could be reduced by 90.72% under the optimum reaction conditions, while it is only 33.51% without catalyst in the blank experiment. 3.2.3. Change of the Group Compositions before and after Reaction. Table 5 also lists the group compositions of heavy oil before and after reaction. It can be seen that the resin and asphaltene have decreased by 3.49% and 6.63%, while the saturated HC and aromatic HC have increased by 3.55% and 6.56% after reaction; after the blank experiment without 1154

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Meanwhile, the adsorption peak at 752 cm−1 indicates the length of alkyl side chains in the oil sample is larger than 4. Figure 3 shows the IR spectra of resins (a) before and (b) after reaction. The structures of the resin are similar to that of

catalyst, the resin and asphaltene have decreased by 0.19% and 0.89%, while the saturated HC and aromatic HC have increased by 0.13% and 0.95%. The comparison of results of the reactions with and without catalyst verifies that the catalyst could catalyze the heavy content (asphaltene and resin) to pyrolyze to the light content (saturated HC and aromatic HC). It also reveals that the catalyst is likely to act on the asphaltene than the resin. The GPC results of the asphaltene before and after reaction show that its MW has decreased from 8841 to 1845 g/mol after aquathermolysis, which have further confirmed the conversion of heavy content into light content. 3.2.4. Activity Evaluation of the Difunctional Catalyst. To evaluate the activity of the difunctional catalyst, we have done five contrast experiments with the following catalysts (without or with hydrogen donor): CuSO4, copper naphthenate, copper naphthenate and formic acid, copper naphthenate and cyclohexane, copper naphthenate and toluene (catalysts 1−5, respectively). They all have done under the above reaction conditions (the concentration of the catalysts or the hydrogen donors are 0.3 wt %), and their viscosity reduction and group compositions are also shown in Table 5. It can be seen from Table 5 that the difunctional catalyst has reduced the viscosity of heavy oil by 90.72% after reaction, with 10.12% in conversion of heavy content to light content; while the other catalysts have only reduced the viscosity by 63.70%, 77.26%, 77.98%, 78.26%, and 78.94%, with 4.99%, 6.66%, 7.92%, 7.93%, and 8.37% in conversion of heavy content to light content, respectively. The results of the contrast experiments demonstrate the superiority of the new catalyst. 3.2.5. FT−IR Spectra of Asphaltene and Resin before and after Reaction. Figure 2 exhibits the IR spectra of asphaltene

Figure 3. IR spectra of resin (a) before and (b) after reaction.

the asphaltene, but their changes are unapparent comparing with the latter’s. It can be concluded that the asphaltenes and resins consist primarily of condensed aromatic rings, alkyl side chains, and heteroatoms, etc. The above changes have also indicated that some of the heteroatom oxygen might be removed and some condensed aromatic rings have partly associated with each other after catalytic aquathermolysis. 3.2.6. Elemental Analysis of Resin and Asphaltene before and after Reaction. The EL results of resin and asphaltene before and after reaction are listed in Table 6. It can be seen that the amounts of sulfur in the resin and asphaltene have decreased from 2.858 and 2.704 to 1.646 and 2.558 after reaction, respectively. A significant difference is that the nitrogen contents of resin and asphaltene are higher than those in the crude oil, which have increased from 1.62 and 1.93 to 1.79 and 2.21 after reaction. After calculation, the ratio of hydrogen to carbon (NH/NC) of resin and asphaltene have decreased from 1.3526 and 1.2529 to 1.3239 and 1.2073 after reaction. The C−S bond is one of the weakest bonds of the oil molecules, the removal of the sulfur could be attributed to the hydrodesulfurization of the catalyst during the catalytic aquathermolysis process. When many heavy oil moleculars break down into fragments, some of saturated fragments will release out into the light content, and the other aromatic units will partly associate with each other, leading to the decrease of NH/NC. Besides, the C−N bond is relatively stable to thermolysis, so most of the nitrogen will enrich in the reacted resin and asphaltene molecules resulting the increase of its content. 3.2.7. 1H−NMR Analysis of Resin and Asphaltene before and after Reaction. Figure 4 shows the 1H−NMR spectra of resin (a) before and (b) after reaction, and asphaltene (c) before and (d) after reaction. On the basis of the concept of Brown−Ladner method, the integrated area percentages were listed in Table 7.33,34 Two important structural parameters, the aromaticity (fA) and the aromaticity condensation (HAU/CA) of resin and asphaltene are shown in Table 8, and

Figure 2. IR spectra of asphaltene (a) before and (b) after reaction.

(a) before and (b) after reaction. As seen from Figure 2, the bands at 2925, 2852, and 1459 cm−1 are the characteristic absorption peaks of methyl and methylene group. The weak peak at 1680 cm−1 indicates that the oil sample contains some carboxyl groups (CO), and it disappears after reaction, which could be attributed to the decarboxylation during reaction, such as the probable pyrolysis of CO. The absorption peaks at 1607, 1375, 868, and 816 cm−1 indicate that the asphaltene contains condensed aromatic rings, and the new peaks at 1265 cm−1 reveal that it has partly aggregated after aquathermolysis. 1155

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Figure 4. 1H-NMR spectra of (a) resin before reaction, (b) resin after reaction, (c) asphaltene before reaction, and (d) asphaltene after reaction.

Table 7. 1H-NMR of Resin and Asphaltene before and after Aquathermolysis

Table 9. Average Structural Parameters of Asphaltene before and after Aquathermolysis

composition (%) group

HA

Hα

Hβ

Hγ

resin before reaction resin after reaction asphaltene before reaction asphaltene after reaction

18.66 19.49 15.47 12.94

20.91 21.41 19.84 19.14

45.23 44.55 50.58 52.58

15.20 14.55 14.11 15.33

the the the the the the the the

Table 8. FA and HAU/CA of Resin and Asphaltene before and after Aquathermolysis

fA HAU/CA

resin before reaction

resin after reaction

asphaltene before reaction

asphaltene after reaction

0.450 0.875

0.467 0.856

0.470 0.676

0.477 0.566

total carbons (CT) aromatic carbons (Ca) non-bridgehead aromatic carbons (CP) total rings (RT) aromatic rings (RA) naphthenic rings (RN) amount of aromatic ring substitution (n) average length of aliphatic chains (l)

before reaction

after reaction

593.38 279.15 190.08 83.07 45.53 37.54 74.27 5.46

126.49 60.39 34.42 21.37 13.98 7.39 14.64 6.73

before and after reaction to further investigate the structural changes. Table 9 shows that, not only the number of total carbons (CT), aromatic carbons (Ca) and non-bridgehead aromatic carbons (CP) decreased, but also the number of total rings (RT), aromatic rings (RA), naphthenic rings (RN), and the amount of aromatic ring substitution (n) decreased after reaction. These changes further explain that some alkyl side chains or naphthenic rings have ruptured from the asphaltene molecules by the pyrolysis of some C−C bonds. The increase of average length of aliphatic chains (l) might be attributed to some bridge bonds or naphthenic rings opening and reconstruction.25,35 It suggests that catalytic aquathermolysis is different from the conventional refinery catalytic cracking processing, the activation energy at 240 °C for 24 h is not sufficient enough to pyrolyze the C−C bonds on a large scale. 3.2.8. GC−MS of Pyrolytic Gas after Aquathermolysis without and with the Catalyst. Figure 5 shows the GC− MS spectra of pyrolytic gas after aquathermolysis (a) without and (b) with the difunctional catalyst, comparing (c) with both of copper naphthenate and toluene. (Their compounds

several average structural parameters of asphaltene are listed in Table 9.35,36 (The equations are shown in Formula S1−S10, see the Supporting Information.) It is easy to see from Table 8 that, for the resin and asphaltene after reaction, the aromaticity increased and HAU/CA decreased. According to the law of conservation of mass, the increase of aromaticity means some higher HT/CT components, such as saturated alkyl side chains or naphthenic rings, rupture to the light content. Referencing the results of EL analysis, catalytic hydrogenation reactions have happened during the aquathermolysis process. The decrease of HAU/CA means the aromaticity condensation increased and demonstrates that some aromatic units have partly aggregated each other coinciding with the results of IR analysis. Since the catalyst tents to act on the asphaltene, we have calculated the average structural parameters of the asphaltene 1156

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principle of soft and hard [Lewis] acids and bases (HSAB) by Pearson R.G., copper(II) is also a borderline acid, which is likely to interact with the soft, borderline, and hard bases (such as S, N, and O-containing groups), leading to the pyrolysis of some C−R bonds. Furthermore, as the long alkyl chain on one side of the ester could increase the oil solubility of the catalyst, and the formate ester group on the other side could act as a hydrogen precursor druing the aquathermolysis process, their synergistic effects would improve the dispersion and thereby enhance the catalytic effect of the catalyst, such as hydrogenation and hydrodesulfurization, etc. Because even a small fraction of bond breakage can lead to huge improvement of its flow properties, the total above actions of the catalyst will enhance the cleavage of some C−R (R = S, N, O, etc.) bonds in the oil molecules and reduce the viscosity eventually with the quality slightly upgraded after aquathermolysis. Figure 6 shows the possible process of the catalytic aquathermolysis. 3.3. Results of Field Tests of Catalytic Aquathermolysis. Before the field test, the F10223 well had already been exploited for two cyclic steam stimulation (CSS) periods, and its production conditions have declined obviously. To postpone the declining trend, the new catalyst has added in the third CSS period. During the first month (31 days), it is found that the viscosity of the produced oil was reduced by 84.82% on average after the catalytic aquathermolysis reaction, and the oil production is about 136 t. Table 10 lists the group compositions

Figure 5. GC−MS spectra of the pyrolytic gas after reaction (a) without and (b) with the difunctional catalyst and (c) with both of the copper naphthenate and toluene.

are shown in Table S1−S3, respectively, see the Supporting Information.) Comparing with the compounds in Table 1−3, we can find that, after aquathermolysis with the catalyst, there are not only olefins, alkanes, benzene homologues, and CO2 appearing (they are same to the compounds of pyrolytic gas after aquathermolysis without catalyst), but also some oxygen- and nitrogen-containing compounds existing, such as acetophenone and 5h-1-pyrindine. What important is that more compositions have been found with the difunctional catalyst than with both of copper naphthenate and toluene, such as indene, 1-methylindan, etc. It means that the difuncitonal catalyst had a relatively deep pyrolysis of the heavy oil without needing any hydrogen donors. In the catalytic aquathermolysis process, carbon dioxide could prove that the water−gas shift reaction has taken place and a small quantity of acetophenone and pyrindine could be attributed to the breakage of a few C−R bonds. Meanwhile, benzenes, naphthalenes, and indenes could be the results of the pyrolysis of some bridge bonds. From the above results and discussion, the catalyst could mainly react to the heteroatoms, side aliphatic chains, and bridge bonds of the heavy oil molecules during aquathermolysis process. As it is known that copper(II), a transition metal cation, can arouse the dynamic inductive effect in some polar bonds of asphaltene by the electrostatic effect,18 which will reduce the active energy of adjacent C−C bonds, thus leading to the breakdown of some C−C bonds. And following the

Table 10. Viscosities and Group Compositions of F10223 Oil before and after Field Test oil sample

viscosity (mPa·s)

saturated HC (%)

aromatic HC (%)

resin (%)

asphaltene (%)

before field test after field test

85000 12900

31.21 49.29

20.85 24.50

34.33 18.82

13.61 7.39

of the produced oil before and after the field test. It can be seen from it that the resin and asphaltene have decreased by 15.51% and 6.22%, while the saturated HC and aromatic HC have increased by 18.08% and 3.65% after the field test. These results proved that the catalytic aquathermolysis method has an evident effect for exploitation of F10223 heavy oil and the new catalyst has excellent efficiency in the field test.

4. CONCLUSIONS In summary, we have developed a new type of difunctional catalyst, alkyl ester sulfonate copper, and used it for catalytic aquathermolysis of super heavy oil both in the laboratory and field. For its excellent catalytic activity, the laboratory

Figure 6. Simple process of the catalytic aquathermolysis. 1157

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experimental results show that the viscosity of heavy oil could be decreased by 90.72% using 0.3 wt % catalyst at 240 °C for 24 h, with 10.12% in conversion of heavy content to light content. Further analysis of the structure and group compositions indicates that the catalyst could not only enhance the viscosity reduction of heavy oil, but also remove some heteroatoms from its molecules, finally making the flow properties better and the quality upgraded. The preliminary results of the field test have also proved the evident effects of the catalyst in the catalytic aquathermolysis technology. In view of its excellent efficiency for exploitation of heavy oil both in the laboratory and field, it is likely to have some good application prospects.

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ASSOCIATED CONTENT

* Supporting Information S

Equations for the structural parameters of resin and asphaltene (Formula S1−S10) and compounds of the pyrolytic gas after aquathermolysis without and with the catalyst by GC−MS (Table S1−S3, respectively). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: 86-13886113362. Fax: 86027-87801763. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No. 51174179) and the Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education (China University of Geosciences).

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