PROPERTIES OF gAS CLATHRATE HYDRATES

Carolyn A. Koh and E. Dendy Sloan

Gas clathrate hydrates (also known as gas hydrates) are crys-

talline inclusion compounds composed of hydrogen-bonded

water cavities (host) which encage small gas (guest) molecules .

Generally, a maximum of one guest molecule occupies each water

cavity . Typical guest molecules that form gas hydrates are meth-

ane, ethane, carbon dioxide, and propane (see gas hydrate phase

equilibria data in Table II) . The structural and physical properties

of gas hydrates are given in Tables Ia and Ib . Data have been taken

from the references indicated .

Table Ia. gas Hydrate Structural Properties (Ref. 1)

Structure

sI

sII

sH

Crystal system

Cubic

Cubic

Hexagonal

Space group

Pm3n (No . 223)

b

Fd3m (No . 227)

b

P6/mmm (No . 191)

b

Lattice description

Primitive

Face centered

Hexagonal

Lattice parameters

a

a = 12 Å

α

=

β

=

γ

= 90

o

a = 17 .3 Å

α

=

β

=

γ

= 90

o

a = 12 .2 Å, c = 10 .1 Å

α

=

β

=

90

ο

,

γ

= 120

o

Ideal unit cell formula

6(5

12

6

2

)·2(5

12

)

.

46H

2

O

8(5

12

6

4

)·16(5

12

)·136H

2

O

1(5

12

6

3

)·3(5

12

)·2(4

3

5

6

6

3

)·34H

2

O

Cavity

Small

Large

Small

Large

Small

Medium

Large

Description

5

12

5

12

6

2

5

12

5

12

6

4

5

12

4

3

5

6

6

3

5

12

6

8

Number of cavities/unit cell

2

6

16

8

3

2

1

Average cavity radius

c

(Å)

3 .95

4 .33

3 .91

4 .73

3 .94

d

4 .04

d

5 .79

d

H

2

O molecules/cavity

e

20

24

20

28

20

20

36

a

Lattice parameters are a function of temperature, pressure, and guest composition . Typical average values given .

b

Space group reference numbers from the International Tables of Crystallography .

c

The average cavity radius will vary with temperature, pressure, and guest composition .

d

From the atomic coordinates measured using single crystal x-ray diffraction on 2,2-dimethylpentane·5(Xe,H

2

S)·34H

2

O at 173 K (Ref . 2) . The Rietveld refinement package,

GSAS was used to determine the atomic distances for each cage oxygen to the cage center .

e

Number of oxygen atoms at the periphery of each cavity .

Table Ib. Physical Properties of sI, sII Hydrates Compared to Ice, Ih (Ref. 1,3,4,5)

Property

Ice

sI

sII

Dielectric constant at 273 K

94

~58

~58

H

2

O reorientation time at 273 K (µs)

21

~10

~10

H

2

O diffusion jump time (µs)

2 .7

>200

>200

Isothermal Young’s modulus at 268 K (10

9

Pa)

9 .5

8 .4

est

8 .2

est

Poisson’s ratio

0 .3301

f

0 .31403

f

0 .31119

f

Bulk modulus (GPa)

9 .097

f

8 .762

f

8 .482

f

Shear modulus (GPa)

3 .488

f

3 .574

f

3 .6663

f

Compressional velocity, V

p

(m/s)

3870 .1

f

3778

f

3821 .8

f

Shear velocity, V

s

(m/s)

1949

f

1963 .6

2001 .14

g

Linear thermal expansion at 200 K (K

–1

)

56 x 10

–6

77 x 10

–6

52 x 10

–6

Thermal conductivity (W m

–1

K

–1

) at 263 K

2 .18

±

0 .01

h

0 .51

±

0 .01

h

0 .50

±

0 .01

h

Adiabatic bulk compression at 273 K (GPa)

12

14

est

14

est

Heat capacity (J kg

–1

K

–1

)

1700

±

200

h

2080

2130

±

40

h

Refractive index (632.8 nm, –3°C)

1 .3082 (Ref . 9) 1 .346 (Ref . 9) 1 .350 (Ref . 9)

Density (g/cm

3

)

0 .91

j

0 .94

1 .291

k

f

At 253–268 K, 22 .4–32 .8 MPa (ice, Ih), 258–288 K, 27 .1–62 .1 MPa (CH

4

, sI), 258–288 K, 30 .5–91 .6 MPa (CH

4

–C

2

H

6

, sII), Ref . 6 .

g

At 258–288 K, 26 .6–62 .1 MPa, Ref . 7 .

h

At 248–268 K (ice, Ih), 253–288 K (CH

4

, sI), 248–265 .5 K (THF, sII), Ref . 8 .

j

Fractional occupancy (calculated from a theoretical model) in small (S) and large (L) cavities: sI = CH

4

: 0 .87 (S) and CH

4

: 0 .973 (L); sII = CH

4

: 0 .672 (S), 0 .057 (L); C

2

H

6

:

0 .096 (L) only; C

3

H

8

: 0 .84 (L) only .

k

Calculated for 2,2-dimethylpentane

.

5(Xe,H

2

S)

.

34H

2

O, Ref . 2; est = estimated .

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References for Table I

1 . Sloan, E .D . and Koh, C .A ., Clathrate Hydrates of Natural Gases, 3rd

Edition, CRC Press, 2008 .

2 . Udachin, K .A ., Ratcliffe, C .I ., Enright, G .D ., and Ripmeester, J .A .,

Supramol. Chem., 8, 173, 1997 .

3 . Davidson, D .W ., Natural Gas Hydrates (Cox, J .L ., Ed .) Butterworths,

Boston, 1, 1983 .

4 . Davidson, D .W ., Handa, Y .P ., and Ripmeester, J .A ., J. Phys. Chem ., 90,

6549, 1986 .

5 . Ripmeester, J .A ., Ratcliffe, C .I ., Klug, D .D ., and Tse, J .S ., in Proc. First

International Conference on Natural Gas Hydrates, (Sloan, E .D .,

Happel, J ., and Hnatow, M .A ., eds .) Annals of the New York Academy

of Sciences, 715, 161, 1994 .

6 . Helgerud, M .B ., Circone, S ., Stern, L ., Kirby, S ., and Lorenson, T .D .,

in Proc. Fourth International Conference on Gas Hydrates, Yokohama

May 19–23, 2002, 716, 2002 .

7 . Helgerud, M .B ., Waite, W .F ., Kirby, S .H ., and Nur, A ., Can. J. Phys ., 81,

47, 2003 .

8 . Waite, W .F ., Gilbert, L .Y ., Winters, W .J ., and Mason, D .H ., in Proc.

Fifth International Conference on Gas Hydrates, Trondheim, Norway,

June 13–16, Paper 5042, 2005 .

9 . Bylov, M . and Rasmussen, P ., Chem. Eng. Sci., 52, 3295, 1997 .

Table II: Phase equilibria Data of gas Clathrate Hydrates

This table gives measured phase equilibria data of sI and sII gas

clathrate hydrates (see Table I for gas hydrate structure and physical

property data) . The temperature and pressure conditions at which gas

hydrates are stable are listed here for typical guest molecules (Tables

IIa–d) . For example, data for methane hydrate show that at 277 .1 K

methane hydrate will dissociate at pressures below 3 .81 MPa .

Table IIa. Methane Hydrate (Ref. 1)

I–H–V

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

262 .4

1 .79

266 .5

2 .08

268 .6

2 .22

270 .9

2 .39

264 .2

1 .90

L

W

–H–V

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

273 .7

2 .77

275 .9

3 .43

280 .4

5 .35

282 .6

6 .77

274 .3

2 .90

277 .1

3 .81

280 .9

5 .71

284 .3

8 .12

275 .4

3 .24

279 .3

4 .77

281 .5

6 .06

285 .9

9 .78

275 .9

3 .42

Ref . 2

L

W

-H-V

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

295 .7

33 .99

295 .9

35 .30

301 .0

64 .81

302 .0

77 .50

Ref . 3

L

W

–H–V

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

285 .7

9 .62

285 .7

9 .62

295 .9

34 .75

300 .9

62 .40

286 .3

10 .31

289 .0

13 .96

298 .7

48 .68

301 .6

68 .09

286 .1

10 .10

292 .1

21 .13

Ref . 4

L

W

-H-V

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

275 .4

2 .87

277 .2

3 .90

279 .2

4 .90

281 .2

6 .10

276 .2

3 .37

278 .2

4 .50

Ref . 5

I–H–V

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

190 .2

0 .08251

208 .2

0 .222

243 .2

0 .9550

262 .4

1 .798

198 .2

0 .1314

218 .2

0 .3571

Ref . 6

Properties of gas Clathrate Hydrates

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Table IIb. ethane Hydrate (Ref. 1)

T (K)

P (kPa)

Phases

T (K)

P (kPa)

Phases

260 .8

294

I–H–V

285 .8

2537

L

w

–H–V

260 .9

290

I–H–V

287 .0

3054

L

W

–H–V

269 .3

441

I–H–V

287 .7

4909

L

W

–H–L

E

273 .4

545

L

W

–H–V

287 .8

3413

L

W

–H–L

E

275 .4

669

L

W

–H–V

287 .8

4289

L

W

–H–L

E

277 .6

876

L

W

–H–V

288 .1

3716

L

W

–H–L

E

279 .1

1048

L

W

–H–V

288 .1

6840

L

W

–H–L

E

219 .7

1131

L

W

–H–V

288 .2

4944

L

W

–H–L

E

281 .1

1317

L

W

–H–V

288 .2

5082

L

W

–H–L

E

282 .8

1641

L

W

–H–V

288 .3

4358

L

W

–H–L

E

284 .4

2137

L

W

–H–V

288 .4

6840

L

W

–H–L

E

Ref . 7

284 .6

2055

L

W

–H–V

I–H–V

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

263 .6

313

266 .5

357

269 .3

405

272 .0

457

L

W

–H–V

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

273 .7

510

278 .7

931

280 .4

1165

283 .2

1689

273 .7

503

278 .7

931

280 .9

1255

284 .3

1986

274 .8

579

279 .3

1007

281 .5

1345

285 .4

2303

275 .9

662

279 .8

1083

282 .1

1448

285 .4

2310

277 .6

814

280 .4

1165

282 .6

1558

286 .5

2730

Ref . 2

L

W

–H–V

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

277 .5

780

279 .9

1040

283 .3

1660

286 .5

2620

278 .1

840

281 .5

1380

284 .5

2100

Ref . 8

Table IIc. Propane Hydrate (Ref. 1)

I–H–V

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

261 .2

100

267 .4

132

269 .8

149

272 .9

172

264 .2

115

267 .6

135

272 .2

167

L

W

–H–V

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

273 .7

183

274 .8

232

275 .9

301

277 .1

386

273 .7

183

275 .4

270

Ref . 2

I–H–V

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

T (K)

P (kPa)

247 .9

48 .2

251 .6

58 .3

258 .2

81 .1

260 .9

94 .5

251 .4

58 .3

255 .4

69 .6

260 .8

90 .5

262 .1

99 .4

Ref . 9

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Properties of gas Clathrate Hydrates

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Feed composition:

x

H O

2

= 0.9503,

x

C H

3 8

= 0.0407

Q

2

at T = 278.62, P = 0.6 MPa

L

W

–H–V

L

W

–H–L

x

C H

3 8

T (K)

P (MPa)

T (K)

P (MPa)

276 .77

0 .368

278 .71

0 .643

277 .01

0 .377

278 .75

0 .893

277 .22

0 .405

278 .75

1 .393

277 .36

0 .425

278 .75

1 .891

277 .44

0 .433

278 .78

1 .893

277 .87

0 .473

278 .80

2 .391

278 .01

0 .527

278 .80

2 .891

278 .22

0 .483

278 .79

2 .893

278 .55

0 .547

278 .75

3 .891

278 .77

3 .391

278 .81

4 .391

278 .79

5 .892

278 .86

6 .392

278 .88

6 .892

278 .80

8 .393

278 .84

8 .893

278 .89

9 .893

Ref . 10

Table IId. Carbon Dioxide Hydrate (Ref. 1)

L

W

–H–V

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

279 .6

2 .74

282 .1

4 .01

282 .8

4 .36

l –H–l

W

CO

2

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

T (K)

P (MPa)

282 .9

5 .03

283 .1

6 .47

283 .6

11 .98

283 .9

14 .36

282 .9

5 .62

283 .2

9 .01

Ref . 11

Overall feed composition:

x

x

H O

CO

2

2

= 0.8668,

= 0.1332

Q

2

at 283.27 K and 4.48 MPa

L

W

–H–V

l –H–l

W

CO

2

T (K)

P (MPa)

T (K)

P (MPa)

276 .52

1 .82

283 .33

5 .97

277 .85

1 .95

283 .36

7 .35

278 .52

2 .21

279 .49

2 .62

280 .44

2 .88

281 .49

3 .35

281 .97

3 .68

282 .00

3 .69

282 .45

3 .85

282 .50

4 .01

Ref . 12

Properties of gas Clathrate Hydrates

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References for Table II

1 . Sloan, E .D . and Koh, C .A ., Clathrate Hydrates of Natural Gases, 3rd

Edition, CRC Press, 2008 .

2 . Deaton, W .M . and Frost, E .M ., Jr ., Gas Hydrates and Their Relation

to the Operation of Natural-Gas Pipe Lines, U .S . Bureau of Mines

Monograph 8, p . 101, 1946 .

3 . Kobayashi, R . and Katz, D .L ., Trans AIME, 186, 66, 1949 .

4 . McLeod, H .O . and Campbell, J .M ., J. Petl Tech ., 222, 590, 1961 .

5 . Thakore, J .L . and Holder, G .D ., Ind. Eng Chem. Res ., 26, 462, 1987 .

6 . Makogon, T .Y . and Sloan, E .D ., J. Chem. Eng. Data, 39, 351, 1994 .

7 . Roberts, O .L ., Brownscombe, E .R ., and Howe, L .S ., Oil Gas J ., 39, 37,

1940 .

8 . Holder, G .D . and Grigoriou, G .C ., J. Chem. Thermodyn ., 12, 1093,

1980 .

9 . Holder, G .D . and Godbole, S .P ., AIChE J., 28, 930, 1982 .

10 . Mooijer-van den Heuvel, M .M ., Peters, C .J ., and de Swaan Arons, J .,

Fluid Phase Equilib., 193, 245, 2002 .

11 . Ng, H .-J . and Robinson, D .B ., Fluid Phase Equilib., 21, 145, 1985 .

12 . Mooijer-van den Heuvel, M .M ., Witteman, R ., and Peters, C .J ., Fluid

Phase Equilib., 21, 145, 1985 .

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