Experimental Investigation into the Dissociation Behavior of CH4

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Experimental investigation into the dissociation behavior of CH4C2H6-C3H8 hydrates in sandy sediments by depressurization Youhong Sun, Kai Su, Sheng-Li Li, John J. Carroll, and You-Hai Zhu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02949 • Publication Date (Web): 04 Dec 2017 Downloaded from http://pubs.acs.org on December 5, 2017

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Experimental investigation into the dissociation behavior of CH4-C2H6-C3H8 hydrates in sandy sediments by depressurization You-Hong Sun1, Kai Su1, Sheng-Li Li1∗, John J. Carroll2, You-Hai Zhu3 1 Key Laboratory of Drilling and Exploitation Technology in Complex Conditions of Ministry of Land and Resources, College of Construction Engineering, Jilin University, Changchun, 130026, China. 2 Gas Liquids Engineering Ltd., Calgary, Canada. 3 The Key Laboratory of Unconventional Petroleum Geology, Oil and Gas Survey, China Geological Survey, Beijing, 100029, China.

ABSTRACT The dissociation kinetics of gas hydrate formed from binary CH4-C3H8 and ternary CH4-C2H6-C3H8 gas mixtures were studied by a gas-collection-analysis method at constant back pressure and different temperatures. During hydrate dissociation, the gas produced was collected first by sample bags consecutively and then analyzed by gas chromatography. It was found that the gas production of the mixed hydrates was quite different from that of methane hydrate. Interestingly, the molar composition of C3H8 in the gas mixture produced changed little as hydrate dissociation proceeded. The retainment of C3H8 in hydrates was confirmed with the calculation results of composition of hydrates remained during gas production. The preferential of CH4 and C2H6 over C3H8 molecules released from hydrate decomposition was attributed to the difference in guest-to-cavity size ratios. The heterogeneous dissociation of the multiple guests complicates the gas production process as the remaining hydrate rich in C3H8 may act as a barrier to gas diffusion.

∗

To whom correspondence should be addressed. Fax: +86 431 88502678. E-mail: [email protected] (S. L. Li). 1

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The self-preservation model for CH4 hydrate dissociation below ice point was applied to describe the heterogeneous dissociation of the mixed hydrates, suggesting that the dissociation kinetics of the mixed hydrates containing C3H8 above ice point was similar to that of CH4 hydrate below ice point. These results are of interest for the gas recovery from hydrates, and for natural gas storage and transportation in the hydrate state. Keywords: mixed hydrates; dissociation; depressurization; propane;

1. INTRODUCTION Clathrate

hydrates

are

nonstoichiometric

crystalline

compounds

composed

of

a

three-dimensional network of hydrogen-bonded water molecules that confines guest molecules in well-defined cavities of different sizes. Light hydrocarbon molecules, such as methane (CH4), ethane (C2H6), and propane (C3H8), are major components of natural gas.1 Of the two crystalline structures for gas hydrates, CH4 hydrate and C2H6 hydrate form structure I hydrates (sI), and larger guest molecules such as C3H8 form structure II hydrates (sII). The gas hydrates have generated considerable interest not only because of its complex structural and chemical properties but also due to its importance in methane recovery from natural gas hydrate reserves2 and flow assurance3. Researchers have looked into possible applications of gas hydrates in carbon dioxide capture4, gas storage5 and mixed gas separation6, 7. Potential recovery of methane from the natural gas hydrate reserves has attracted significant interest in the study of methane hydrate formation and depressurization dynamics.8-15 In addition to the methane hydrate, the mixed hydrates, which are known to be formed by the influence of thermogenic hydrocarbon and mainly includes oil-related C1–C4 hydrocarbons, was discovered in the ocean deposits such as the Gulf of Mexico outside the Caspian Sea16-18, Lake Baikal19, 20, the Qilian Mountain permafrost of China21, 22 and Pearl River Mouth Basin of the South China Sea23, 24. 2


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There are previous studies on the formation of mixed hydrates, such as methane-propane hydrates6, 25-28

, ethane-propane hydrates29, and methane-ethane-propane hydrates7,

30

. The decomposition

conditions have been measured for propane hydrate31, methane-ethane hydrates32, methane-propane hydrates33, ethyne-propane hydrates34 and methane-ethane-propane hydrates35, which were the basic data for hydrate decomposition. However, only a few reports have dealt with the decomposition kinetics of hydrates with multiple hydrocarbon guests. Clarke et al.36 measured the decomposition rate of methane-ethane hydrates in a semi-batch stirred-tank reactor. The intrinsic rate constant and activation energy for methane in structure II (sII) was found to be different from that in structure I. They proposed that it was necessary to take the hydrate structure into account when predicting the decomposition of hydrates formed from gas mixture. Kawamura et al.37,

38

investigated the

dissociation kinetics of mixed gas hydrate pellets that contain propane as a guest molecule. They deduced that the free gas composition around the dissociation surface was different from the equilibrium composition during the dissociation reaction. Unfortunately, they did not measure the gas production and did not analyze the compositional evolution of mixed gas released from hydrate dissociation. Kida et al.39 studied the dissociation behavior of methane-ethane mixed gas hydrate coexisting structures I and II by using powder X-ray diffraction and solid-state 13C NMR techniques. Their results showed there was different dissociation behavior between structures I and II. Zhong et al.40 recently reported a study on the hydrate structure type and dissociation behavior for pure methane and methane-ethane hydrates at temperatures below the ice point using in situ Raman spectroscopic analysis. The investigation showed the selectivity for self-preservation of methane over ethane led to a structure transition during hydrate decomposition process. The previous reports indicate the decomposition kinetic of mixed hydrates could be completely different from that of the conventional sI hydrates due to its structure, compositions and guest species. Thus, a close 3


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experimental measurement of the dissociation of mixed hydrates is required, primarily focusing on the release of different guest molecules from hydrate structures during the dissociation. The dissociation of mixed hydrates synthesized from the CH4-C3H8 and CH4-C2H6-C3H8 gas mixtures is studied in this work. To acquire detailed information of gas releasing features, the kinetics of mixed hydrate dissociation are studied by coupling gas production measurements with compositional analysis using gas chromatography. This information is of interest for the development of technology for hydrate exploitation, natural gas storage and transportation.

2. EXPERIMENTAL SECTION 2.1. Materials Analytical grade methane (C1, 99.999%), ethane (C2, 99.99%), and propane (C3, 99.99%) supplied by Beifang Special Gas Industry Corporation were used in preparing the (C1+C3) and (C1+C2+C3) gas mixtures. The sediment is formed by 20-40 mesh quartz sands with the porosity of 38.7%. As the composition of gas mixture released from mixed hydrate dissociation varied with the time, to our best knowledge, there were no gas flowmeters suitable for the measurement volume and composition simultaneously. Thus, the gas mixture was collected in a series of sample bags first and then analyzed by gas chromatograph. The volume of the sample bag varied from 50 mL to 1000 mL. A syringe with a maximum volume of 150 mL was used to measure the volume of gas in sample bags. The uncertainty of the gas volume measurement was ±5 mL. 2.2. Experimental apparatus. A schematic of the experimental apparatus used in this work is shown in Figure 1. The apparatus consists of the high-pressure cell, the gas cylinder, gas collector, and the data acquisition system. The pressure cell is a column made by stainless steel. The effective volume of the cell is 510 mL with a diameter of 50 mm and height of 260 mm. The temperature sensor used is a 4


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secondary platinum resistance thermometer (type pt100). Five thermometers are distributed evenly along the cell. Two pressure transducers are located at the two ends of the cell. The uncertainties of pressure and temperature measurements are 0.01 MPa and 0.1 K, respectively. Changes of the system temperature and pressure with time are recorded and displayed by a computer.

Figure 1. Schematic of the experimental apparatus. 2.3. Experimental procedures In the experiments, a known amount of quartz sands saturated with water was loaded into the cell. The system then was evacuated for approximately one hour, and the gas space of the cell was purged with gas mixture 3 times to ensure the absence of air. A gas mixture was charged into the cell from the gas cylinder until the pressure reached the desired value and then the cell was closed. The temperature of the air bath was then adjusted to the desired value. When the temperature of the system decreased to a certain value, the formation of the mixed hydrates started. As was reported that the formation of mixed hydrates may include two stages,7 In the first stage, hydrates formed with gas and water is fast. After that, gas exchange continued between gas and hydrate phase for a further equilibrium.7 In the experiments, as the hydrate formation proceeded, the pressure in the system gradually dropped. When the pressure drop in the cell was C1 (512) > C2 (51264) > C1 (51264), which indicated that the decomposition of C1 in small and large cavities and C2 in large cavities could be more easier than that of C3 in large cavities. 3.5

5.5 275.2 K 277.2 K 279.2 K

3.0

Ratio of (C1+C2)/C3 in hydrate phase

Ratio of C1/C3 in hydrate phase

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2.5 2.0 1.5 1.0 0.5 0.0

275.2 K 277.2 K 279.2 K

5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

1.0

0.8

0.6

0.4

0.2

0.0

1.0

0.8

X

0.6

0.4

X

13


0.2

0.0

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a. C1-C3 hydrates

b. C1-C2-C3 hydrates

Figure 5 The evolution of ratios of C1/C3 and (C1+C2)/C3 in binary and ternary hydrates during hydrates dissociation at three different temperatures. X presents the percentage of hydrate remained. Table 2 Ratios of molecular diameters to cavity diameters for C1, C2 and C3 in sII hydrate.1 Molecule

Guest diameter (Å)

512 (II)

51264 (II)

CH4

4.36

0.868

0.652

C2H6

5.5

1.10

0.826

C3H8

6.28

1.25

0.943

The preferential dissociation of C1 and C2 over C3 changed the average compositions of hydrates remained during hydrate dissociation. Figure 6 shows the evolution of average composition of hydrates remained with the sampling number that increased with the time (calculated by eq. 4b). It can be observed that, C3 molecules was retained with the quicker release of C1 and C2 molecules at different temperatures. At higher temperatures, the retainment of C3 was even more obvious. According to Rydzy’s results45, the onset temperature of decomposition of both sI and sII hydrates increased with an increasing number of larger guest molecules occupying the large cavities. In this work, the dissociation of hydrate was very slow at the end of the experiments, which could be partly caused by the fact that the dissociation pressure and temperature were affected during hydrate dissociation by the composition change in the hydrate phase; the richer C3 in the hydrate phase led to a higher dissociation temperature. Under higher temperature conditions, the hydrate dissociation would not stop until a higher fraction of C3 was achieved.

14


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C1

C3

80

60

40

20

0 2

3

4

5

6

7

8

9

40

20

10

1

2

3

4

5

6

7

Gas composition of hydrate phase / %

Gas composition in hydrate phase / %

C3

80

60

40

20

C1

3

4

5

6

7

8

9

40

20

10 11 12 13 14

2

4

6

8

10

C3

C1


100

80

60

40

20

0 8

10

12

16

18

20

14

16

18

20

22

C2

C3

80

60

40

20

0

6

14

b. C1-C2-C3 hydrates, 277.2 K

100

4

12

Numbers

a. C1-C3 hydrates, 277.2 K

2

C3

60

Numbers

C1

C2

80

0

0 2

9 10 11 12 13 14 15 16

b. C1-C2-C3 hydrates, 275.2 K 100

1

8

Numbers

a. C1-C3 hydrates, 275.2 K C1

C3

60

Numbers

100

C2

80

0

1

C1

100



100


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2

Numbers

4

6

8

10

12

14

16

Numbers

a. C1-C3 hydrates, 279.2 K

b. C1-C2-C3 hydrates, 279.2 K

Figure 6 The evolution of average compositions of hydrate remained during dissociation at three different temperatures. The numbers of the horizontal axis represent the serial numbers 15


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of the gas sample bags. 3.2. Modelling of the mixed hydrates dissociation kinetics As discussed above, the dissociation kinetic behavior of mixed hydrate was largely different from that of methane hydrate. In fact, the heterogeneous dissociation verified for C1-C3 and C1-C2-C3 hydrates meant the dissociation of the mixed hydrates was not completely. The partially dissociation has been observed in the preservation of hydrates below ice point.47-51 The experimental study of Prasad et al.52 also shows CH4 gas can be preserved in the form of mixed hydrates. When the mixed hydrates dissociated heterogeneously from the outer layer to the inside of hydrate particle, a hydrate layer with higher C3 concentration may remain or re-form53 below the hydrate dissociation surface and surround the hydrate core. Figure 7 shows a conception for the formation of the hydrate layer rich of C3H8 covering on the mixed hydrate particles. As the hydrate decomposition conditions for liquid water and propane31 were in range of 0.26-0.57 MPa at the temperature range of 275.2-279.2 K, the hydrate layer rich of C3 was able to keep stable under the back-pressure in this work and would thicken with the proceeding of hydrates dissociation. The thickening hydrate layer would hinder the hydrate from further decomposition when the diffusion of gas molecules through it was difficult.

Figure 7 Schematic diagram of the mixed hydrates dissociation. It was obvious that such hydrate-shielding dissociation of mixed hydrates above ice point was quite similar to the ice-shielding dissociation of methane hydrate below ice point.47-51 Therefore, the 16


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kinetic model54 for methane hydrates dissociation below the ice point (see Liang et al. 200454 for detailed information) was applied to study the dissociation behavior of the mixed hydrates:

    dnd  1 ( fe − f g ) = dt  1 nr b   +   K Ds 

(7)

where nd is the cumulative moles of gas released at time t; K is associated with the dissociation rate of hydrates: K=kdAs, where kd is the decomposition rate constant and As is the total surface area of the decomposing hydrate particles; b and Ds are empirical constants that can be determined from the experimental data (according to Liang’s model, the larger value of b implies that the diffusion resistance of the outer layer increases more rapidly and Ds is associated with the permeability feature of the hydrate layer surrounding hydrate core); fe and fg represent the fugacity of gas at the water-hydrate-vapor three-phase equilibrium pressure and the fugacity of gas in vapor phase, respectively, which were determined by PT equation of state;55 nr is the cumulative moles of gas in hydrate layer remained after dissociation, which can be evaluated by the following equation with the assumption that only C3 molecules are left in the hydrate layer after its dissociation:

nr = nd yd / xinitial − nd

(8)

where yd is the fraction of C1 in gas that have been released from C1-C3 hydrate or C1+C2 in gas released from C1-C2-C3 hydrate; nd and yd can be calculated based on eq. 3; xinitial is the fraction of C1 in C1-C3 hydrate or C1+C2 in C1-C2-C3 hydrate before dissociation (see Table 1). The decomposition kinetic model (eq. 7) was used to correlate the measured experimental data of mixed hydrates dissociation. Figure 8 shows the model can well describe the dissociation kinetic behavior of mixed hydrates at different temperatures. The values of three parameters, K, b, and Ds, in eq 7 were determined by fitting the dissociation rate data (the volume gas produced in Figure 2 17


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was transformed into the number of moles) measured at different temperatures and tabulated in Tables 3 and 4, respectively, corresponding to the two kinds of hydrates: C1-C3 hydrate and C1-C2-C3 hydrate. For comparison, the rate constant K was transformed into a specific rate constant K ' by using K '= K / mw , where mw was the mass of water. 0.10

0.10

0.08

0.08

Evolved gas / mol

Evolved gas / mol

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0.06

275.2 K Fit line 277.2 K Fit line 279.2 K Fit line

0.04

0.02

275.2 K Fit line 277.2 K Fit line 279.2 K Fit line

0.06

0.04

0.02

0.00

0.00 0

1000

2000

3000

4000

5000

0

1000

2000

3000

Time / s

4000

5000

6000

7000

Time / s

a. C1-C3 hydrates

b. C1-C2-C3 hydrates

Figure 8 Cumulative moles of gas mixture produced at different times during the hydrates dissociation at different temperatures. The symbols represent the experimental data calculated from Figure 1 and the solid curves are calculated from eq 7. From Tables 3 and 4, it was clear that the specific decomposition rate constant K ' for C1-C2-C3 hydrate increased more obviously with the temperature, which indicated that the dissociation rate of C1-C2-C3 hydrate was more sensitive to the temperature. The sensitivity might come from C2 in hydrate, since Peng’s experimental study56 on C1-C2 hydrate dissociation behavior showed that the temperature had great influence on the dissociation rate of the C1-C2 mixed hydrates. The markedly low permeability parameter Ds at 275.2 K for the two hydrates might be attributed to the temporal formation of ice with the strong endothermic effect of mixed hydrates dissociation.45 The density of pores distribution in the crust of formed hydrate layer may decrease upon decreasing the temperature.57 Therefore at 275.2 K, large percentages of hydrates remained while the increase of C3 average fraction was unapparent.(see Figures 3 and 6) By contrast to 18


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Liang’s fitting results54, the dissociation rate of C1-C3 hydrate and C1-C2-C3 hydrate at the final stage of dissociation were comparable to that of C1 hydrate below ice and the permeability of the relatively stable hydrate layer formed during C1-C3 hydrate dissociation was closer to that of ice layer formed from C1 hydrate dissociation below ice point, which may imply the similar self-preservation behavior of the mixed hydrates above ice point with that of C1 hydrate below ice point.47-51, 54

Table 3 Model parameters in eq 7 with respect to the dissociation of C1-C3 hydrates. T/K

fe / MPa

K ' ×106/mol-1·MPa-1·s-1·g-1

b

9 b+1 -1 -1 Ds ×10 /mol ·MPa ·s

275.2

2.59

4.197

3.214

0.0659

277.2

2.60

4.311

2.547

5.045

279.2

2.63

6.342

2.954

6.307

Table 4 Model parameters in eq 7 with respect to the dissociation of C1-C2-C3 hydrates T/K

fe / MPa

K ' ×106/mol-1·MPa-1·s-1·g-1

b

8 b+1 -1 -1 Ds ×10 /mol ·MPa ·s

275.2

1.84

2.348

3.929

7.29×10-3

277.2

1.86

9.566

2.118

6.962

279.2

1.89

21.976

1.989

27.98

4. CONCLUSIONS Mixed gas hydrates made from CH4-C3H8 and CH4-C2H6-C3H8 gas mixtures in partially saturated sandy sediments dissociated at temperatures of 275.2 K, 277.2 K and 279.2 K and under a constant back pressure. The rate of gas production from mixed hydrates decreased more quickly than that from methane hydrate and part of the gas hydrates remained when the gas production rate was quite small. The composition of the gas produced and the hydrate remained evolved over time. It was found that the C3H8 concentration in the gas produced change little while in hydrate phase increased obviously during in experiments. This increased the stable temperature of mixed hydrates remained and thus reduced the driving force for hydrate dissociation, which in consequence reduced 19


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the rate of hydrate dissociation. Such dissociation behavior was never observed in CH4 hydrate. It was deduced that the remained hydrate rich in C3H8 could act as a permeable barrier that hindered the diffusion of gas from hydrate core. The heterogeneous dissociation kinetic of the mixed hydrates was compared with that of CH4 hydrate below ice and a self-preservation model was applied to fit the experimental data. The result shows the permeability of assumed stable hydrate layer formed during CH4-C3H8 hydrate dissociation was closer to that of ice layer formed from CH4 hydrate dissociation below ice point. It is the first time to report he heterogeneous dissociation behavior of the mixed hydrates, which should be taken into account in the development of mixed gas hydrate recovery and natural gas storage and transport technologies.

AUTHOR INFORMATION Corresponding Author Tel.: +86 431 88502678. Fax: +86 431 88502678. Email: [email protected].

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The financial support received from National Natural Science Foundation of China (Grant Nos. 51506073 and 51474112), Key Laboratory of Unconventional Petroleum Geology, Oil and Gas Survey, China Geological Survey (No. DD20160226-01) and China Postdoctoral Science Foundation (2015M580248) are gratefully acknowledged.

REFERENCES (1) Sloan, E. D., Fundamental principles and applications of natural gas hydrates. Nature 2003, 426 (6964), 353-363. (2) Boswell, R., Is Gas Hydrate Energy Within Reach? Science 2009, 325 (21), 956-957. (3) Koh, C. A.; Sloan, E. D.; Sum, A. K.; Wu, D. T., Fundamentals and applications of gas hydrates. Annu Rev 20


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Chem Biomol Eng 2011, 2, 237-57. (4) Koh, D.-Y.; Kang, H.; Lee, J.-W.; Park, Y.; Kim, S.-J.; Lee, J.; Lee, J. Y.; Lee, H., Energy-efficient natural gas hydrate production using gas exchange. Appl. Energy 2016, 162, 114-130. (5) Sugahara, T.; Haag, J. C.; Prasad, P. S. R.; Warntjes, A. A.; Sloan, E. D.; Sum, A. K.; Koh, C. A., Increasing Hydrogen Storage Capacity Using Tetrahydrofuran. J. Am. Chem. Soc. 2009, 131 (41), 14616-14617. (6) Uchida, T.; Moriwaki, M.; Takeya, S.; Ikeda, I. Y.; Ohmura, R.; Nagao, J.; Minagawa, H.; Ebinuma, T.; Narita, H.; Gohara, K.; Mae, S., Two-step formation of methane-propane mixed gas hydrates in a batch-type reactor. AlChE J. 2004, 50 (2), 518-523. (7) Kumar, R.; Linga, P.; Moudrakovski, I.; Ripmeester, J. A.; Englezos, P., Structure and kinetics of gas hydrates from methane/ethane/propane mixtures relevant to the design of natural gas hydrate storage and transport facilities. AlChE J. 2008, 54 (8), 2132-2144. (8) Li, X.-S.; Xu, C.-G.; Zhang, Y.; Ruan, X.-K.; Li, G.; Wang, Y., Investigation into gas production from natural gas hydrate: A review. Appl. Energy 2016, 172, 286-322. (9) Feng, J.-C.; Wang, Y.; Li, X.-S., Energy and entropy analyses of hydrate dissociation in different scales of hydrate simulator. Energy 2016, 102, 176-186. (10) Wang, S.; Yang, M.; Wang, P.; Zhao, Y.; Song, Y., In Situ Observation of Methane Hydrate Dissociation under Different Backpressures. Energy Fuels 2015, 29 (5), 3251-3256. (11) Takeya, S.; Fujihisa, H.; Gotoh, Y.; Istomin, V.; Chuvilin, E.; Sakagami, H.; Hachikubo, A., Methane Clathrate Hydrates Formed within Hydrophilic and Hydrophobic Media: Kinetics of Dissociation and Distortion of Host Structure. J. Phys. Chem. C 2013, 117 (14), 7081-7085. (12) Konno, Y.; Uchiumi, T.; Oyama, H.; Jin, Y.; Nagao, J.; Masuda, Y.; Ouchi, H., Dissociation Behavior of Methane Hydrate in Sandy Porous Media below the Quadruple Point. Energy Fuels 2012, 26 (7), 4310-4320. (13) Song, Y.; Cheng, C.; Zhao, J.; Zhu, Z.; Liu, W.; Yang, M.; Xue, K., Evaluation of gas production from methane hydrates using depressurization, thermal stimulation and combined methods. Appl. Energy 2015, 145 (0), 265-277. (14) Zhao, J.; Liu, D.; Yang, M.; Song, Y., Analysis of heat transfer effects on gas production from methane hydrate by depressurization. Int. J. Heat Mass Transfer 2014, 77, 529-541. (15) Zhao, J.; Zhu, Z.; Song, Y.; Liu, W.; Zhang, Y.; Wang, D., Analyzing the process of gas production for natural gas hydrate using depressurization. Appl. Energy 2015, 142, 125-134. (16) Sassen, R.; Sweet, S. T.; Milkov, A. V.; DeFreitas, D. A.; Kennicutt, M. C., Thermogenic vent gas and gas hydrate in the Gulf of Mexico slope: Is gas hydrate decomposition significant? Geology 2001, 29 (2), 107-110. 21


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(17) Lu, H.; Seo, Y.-t.; Lee, J.-w.; Moudrakovski, I.; Ripmeester, J. A.; Chapman, N. R.; Coffin, R. B.; Gardner, G.; Pohlman, J., Complex gas hydrate from the Cascadia margin. Nature 2007, 445 (7125), 303-306. (18) Klapp, S. A.; Murshed, M. M.; Pape, T.; Klein, H.; Bohrmann, G.; Brewer, P. G.; Kuhs, W. F., Mixed gas hydrate structures at the Chapopote Knoll, southern Gulf of Mexico. Earth Planet. Sci. Lett. 2010, 299 (1–2), 207-217. (19) Kida, M.; Khlystov, O.; Zemskaya, T.; Takahashi, N.; Minami, H.; Sakagami, H.; Krylov, A.; Hachikubo, A.; Yamashita, S.; Shoji, H.; Poort, J.; Naudts, L., Coexistence of structure I and II gas hydrates in Lake Baikal suggesting gas sources from microbial and thermogenic origin. Geophys. Res. Lett. 2006, 33 (24603), 1-4. (20) Kida, M.; Hachikubo, A.; Sakagami, H.; Minami, H.; Krylov, A.; Yamashita, S.; Takahashi, N.; Shoji, H.; Khlystov, O.; Poort, J., Natural gas hydrates with locally different cage occupancies and hydration numbers in Lake Baikal. Geochem. Geophys. Geosyst. 2009, 10 (5), 3093-3107. (21) Lu, Z.; Zhu, Y.; Liu, H.; Zhang, Y.; Jin, C.; Huang, X.; Wang, P., Gas source for gas hydrate and its significance in the Qilian Mountain permafrost, Qinghai. Mar. Pet. Geol. 2013, 43, 341-348. (22) Zhu, Y.; Zhang, Y.; Wen, H.; Lu, Z.; Jia, Z.; Li, Y.; Li, Q.; Liu, C.; Wang, P.; Guo, X., Gas Hydrates in the Qilian Mountain Permafrost, Qinghai, Northwest China. Acta Geologica Sinica-English Edition 2010, 84 (1), 1-10. (23) Wei, J.; Fang, Y.; Lu, H.; Lu, H.; Liang, J.; Wang, H.; Lu, J., Coexistence of sI and sII hydrates in the South China Sea. the Ninth International Conference on Gas Hydrate, Denver, USA, 2017. (24) Cong, X.; Su, M.; Wu, N.; Qiao, S.; Sha, Z.; Lu, H.; Su, P., Discussion on the role of thermogenic gases for hydrate accumulation in marine hydrocarbon-rich depression. the Ninth International Conference on Gas Hydrate, Denver, USA, 2017. (25) Yoslim, J.; Linga, P.; Englezos, P., Enhanced growth of methane-propane clathrate hydrate crystals with sodium dodecyl sulfate, sodium tetradecyl sulfate, and sodium hexadecyl sulfate surfactants. J. Cryst. Growth

2010, 313 (1), 68-80. (26) Kini, R. A.; Dec, S. F.; Sloan, E. D., Methane plus propane structure II hydrate formation kinetics. J. Phys.

Chem. A 2004, 108 (44), 9550-9556. (27) Prado, M. R.; Cazares, Y.; Janda, K. C., Toward the Efficient Production of Methane/Propane Double Hydrate. Ind. Eng. Chem. Res. 2009, 48 (11), 5160-5164. (28) Wu, R.; Kozielski, K. A.; Hartley, P. G.; May, E. F.; Boxall, J.; Maeda, N., Methane-Propane Mixed Gas Hydrate Film Growth on the Surface of Water and Luvicap EG Solutions. Energy Fuels 2013, 27 (5), 2548-2554. (29) Al-Otaibi, F.; Clarke, M.; Maini, B.; Bishnoi, P. R., Kinetics of structure II gas hydrate formation for propane 22


Page 22 of 25

Page 23 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

and ethane using an in-situ particle size analyzer and a Raman spectrometer. Chem. Eng. Sci. 2011, 66 (11), 2468-2474. (30) Kodama, T.; Ohmura, R., Crystal growth of clathrate hydrate in liquid water in contact with methane plus ethane plus propane gas mixture. J. Chem. Technol. Biotechnol. 2014, 89 (12), 1982-1986. (31) Adeniyi, K. I.; Deering, C. E.; Marriott, R. A., Hydrate Decomposition Conditions for Liquid Water and Propane. J. Chem. Eng. Data 2017, 62 (7), 2222-2229. (32) Soltanimehr, S.; Javanmardi, J.; Nasrifar, K., Liquid Water-Hydrate-Vapor Equilibrium for Methane plus Ethane Gas Mixtures: Application of Gas Hydrates for Separation. J. Chem. Eng. Data 2017, 62 (7), 2143-2148. (33) Sowa, B.; Zhang, X. H.; Hartley, P. G.; Dunstan, D. E.; Kozielski, K. A.; Maeda, N., Formation of Ice, Tetrahydrofuran Hydrate, and Methane/Propane Mixed Gas Hydrates in Strong Monovalent Salt Solutions.

Energy Fuels 2014, 28 (11), 6877-6888. (34) Tumba, K.; Babaee, S.; Naidoo, P.; Mohammadi, A. H.; Ramjugernath, D., Phase Equilibria of Clathrate Hydrates of Ethyne plus Propane. J. Chem. Eng. Data 2014, 59 (9), 2914-2919. (35) Lee, S.; Lee, Y.; Park, S.; Kim, Y.; Cha, I.; Seo, Y., Stability conditions and guest distribution of the methane plus ethane plus propane hydrates or semiclathrates in the presence of tetrahydrofuran or quaternary ammonium salts. J. Chem. Thermodyn. 2013, 65, 113-119. (36) Clarke, M. A.; Bishnoi, P. R., Measuring and modelling the rate of decomposition of gas hydrates formed from mixtures of methane and ethane. Chem. Eng. Sci. 2001, 56 (16), 4715-4724. (37) Kawamura, T.; Sakamoto, Y.; Ohtake, M.; Yamamoto, Y.; Komai, T.; Haneda, H.; Yoon, J.-H.; Ohga, K., Dissociation behavior of pellet shaped mixed gas hydrate samples that contain propane as a guest. Energy Convers.

Manage. 2006, 47 (15–16), 2491-2498. (38) Kawamura, T.; Ohga, K.; Higuchi, K.; Yoon, J. H.; Yamamoto, Y.; Komai, T.; Haneda, H., Dissociation behavior of pellet-shaped methane-ethane mixed gas hydrate samples. Energy Fuels 2003, 17 (3), 614-618. (39) Kida, M.; Jin, Y.; Takahashi, N.; Nagao, J.; Narita, H., Dissociation Behavior of Methane-Ethane Mixed Gas Hydrate Coexisting Structures I and II. J. Phys. Chem. A 2010, 114 (35), 9456-9461. (40) Zhong, J. R.; Zeng, X. Y.; Zhou, F. H.; Ran, Q. D.; Sun, C. Y.; Zhong, R. Q.; Yang, L. Y.; Chen, G. J.; Koh, C. A., Self-preservation and structural transition of gas hydrates during dissociation below the ice point: an in situ study using Raman spectroscopy. Sci. Rep. 2016, 6, 38855. (41) Mimachi, H.; Takeya, S.; Gotoh, Y.; Yoneyama, A.; Hyodo, K.; Takeda, T.; Murayama, T., Dissociation behaviors of methane hydrate formed from NaCl solutions. Fluid Phase Equilib. 2016, 413, 22-27. (42) Chen, L.; Levine, J. S.; Gilmer, M. W.; Sloan, E. D.; Koh, C. A.; Sum, A. K., Methane Hydrate Formation 23


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

and Dissociation on Suspended Gas Bubbles in Water. J. Chem. Eng. Data 2014, 59 (4), 1045–1051. (43) Chari, V. D.; Sharma, D. V. S. G. K.; Prasad, P. S. R.; Murthy, S. R., Methane hydrates formation and dissociation in nano silica suspension. J. Nat. Gas Sci. Eng. 2013, 11, 7-11. (44) Watanabe, S.; Saito, K.; Ohmura, R., Crystal growth of cathrate hydrate in liquid water saturated with a simulated natural gas. Cryst. Growth Des. 2011, 11 (7), 3235-3242. (45) Rydzy, M. B.; Schicks, J. M.; Naumann, R.; Erzinger, J., Dissociation enthalpies of synthesized multicomponent gas hydrates with respect to the guest composition and cage occupancy. J. Phys. Chem. B 2007, 111 (32), 9539-9545. (46) Das, S.; Baghel, V. S.; Roy, S.; Kumar, R., A molecular dynamics study of model SI clathrate hydrates: the effect of guest size and guest-water interaction on decomposition kinetics. Phys. Chem. Chem. Phys. 2015, 17 (14), 9509-9518. (47) Bai, D.; Zhang, D.; Zhang, X.; Chen, G., Origin of Self-preservation Effect for Hydrate Decomposition: Coupling of Mass and Heat Transfer Resistances. Sci. Rep. 2015, 5, 14599. (48) Takeya, S.; Yoneyama, A.; Ueda, K.; Mimachi, H.; Takahashi, M.; Sano, K.; Hyodo, K.; Takeda, T.; Gotoh, Y., Anomalously Preserved Clathrate Hydrate of Natural Gas in Pellet Form at 253 K. J. Phys. Chem. C 2012, 116 (26), 13842-13848. (49) Giavarini, C.; Maccioni, F., Self-preservation at low pressures of methane hydrates with various gas contents.

Ind. Eng. Chem. Res. 2004, 43 (20), 6616-6621. (50) Falenty, A.; Kuhs, W. F.; Glockzin, M.; Rehder, G., "Self-Preservation" of CH4 Hydrates for Gas Transport Technology: Pressure-Temperature Dependence and Ice Microstructures. Energy Fuels 2014, 28 (10), 6275-6283. (51) Stern, L. A.; Circone, S.; Kirby, S. H.; Durham, W. B., Temperature, pressure, and compositional effects on anomalous or "self" preservation of gas hydrates. Can. J. Phys. 2003, 81 (1-2), 271-283. (52) Prasad, P. S. R.; Chari, V. D., Preservation of methane gas in the form of hydrates: Use of mixed hydrates. J.

Nat. Gas Sci. Eng. 2015, 25, 10-14. (53) Zhou, X.; Long, Z.; Liang, S.; He, Y.; Yi, L.; Li, D.; Liang, D., In Situ Raman Analysis on the Dissociation Behavior of Mixed CH4-CO2 Hydrates. Energy Fuels 2016, 30 (2), 1279-1286. (54) Liang, M. Y.; Chen, G. J.; Sun, C. Y.; Yan, L. J.; Liu, J.; Ma, Q. L., Experimental and modeling study on decomposition kinetics of methane hydrates in different media. J. Phys. Chem. B 2005, 109 (40), 19034-19041. (55) Patel, N. C.; Teja, A. S., A new cubic equation of state for fluids and fluid mixtures. Chem. Eng. Sci. 1982, 37 (3), 463-473. (56) Peng, B.; Sun, C.; Chen, G.; Tang, X.; Liu, P.; Chen, J.; Zhang, Y., Dissociation behavior of (CH4 + C2H4) 24


Page 24 of 25

Page 25 of 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

hydrate in the presence of sodium dodecyl sulfate. Pet. Sci. 2010, 7 (1), 112-117. (57) Misyura, S. Y., The influence of porosity and structural parameters on different kinds of gas hydrate dissociation. Sci. Rep. 2016, 6.

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Experimental Investigation into the Dissociation Behavior of CH4

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