HYDRATE

1. Formation kinetics of sII and sH gas
hydrates, surface phenomenon point
of view
AMIR ERFANI
SUPERVISOR: DR. F. VARAMINIAN
SEPTEMBER 2015
Semnan University

2. Scopes
1. Gas hydrate: an introduction
(Hydrate formers and hydrate structures, pros and cons)
2. Experimental
(Atmospheric and high pressure hydrate formations, pendant drop method)
3. Results and discussion
4. Conclusions and future plans
2

3. 1. Gas hydrate: an introduction
 Gas hydrate or clathrate hydrates: crystalline ice-like solid [1-2]
 Guest molecules are trapped in cages formed by water molecules
Formed at:
 Low temperatures (slightly above freezing point of water)
 High pressures
Guest molecules:
C1,C2,C3, CO2, H2S, …..
3

4. 1. Gas hydrate: an introduction
Gas hydrate Structures [3-4]:
1. sI: 46 water molecules, cages: 2 small (512) and 6 large (51262)
2. sII: 136 water molecules: 16 small (512 ) cages 8 large cages (51264).
3. sH: 34 water molecules: 3 small 512,
2 small ones of type 435663 and
one huge of type 51268
4

5. 1. Gas hydrate: an introduction
Structures:
 the quest molecule define which structure is formed
 The equilibrium pressure of hydrate formation is different for these structures
 The water content is different!
5
sH gas hydrate

6. 1.Gas hydrate: an introduction
 Why study of gas hydrates is of importance:
1. natural gas hydrates: potentially vast energy resource [1]
(6.4×1012 tonnes of methane is trapped on ocean floor)
2. cause problems for the petroleum industry [1,5]
(form inside gas pipelines, drilling operations)
3. Gas separation [6-7]
4. CO2 capture [8-9]
5. Transportation of natural gas or hydrogen [10-13]
6. Gas hydrate as cold storage material [14-17]
7. Desalination of water [18-20]
 Why kinetics of hydrate formation is of importance??
 Help us introducing new technologies!!!
6

7. 1.Gas hydrate: an introduction
Among these technologies we are concerned with:
Use of gas hydrate as a medium for
1. Gas transportation and storage: sH is best structure [21]
2. Cold storage material: hydrate that form at moderate conditions
7

8. 1. Gas hydrate: an introduction
 The kinetics of sII and sH hydrate are poorly understood.
 No account for promotion of sH hydrate in published literature
 The promotion (and inhibition) mechanisms: not well understood
8
Kinetics of hydrate formation for
MCH/methane/ water system at 3°C
[11]

9. 1. Gas hydrate: an introduction
In promotion section we deal with surfactant!
 Surfactant types : anionic, cationic, non-ionic [22-24]
 Non-ionic surfactants: more environmental friendly and less toxic
 Macroscopic properties of surfactants [25-26]
9
HLB =
𝑚𝑜𝑙𝑒 𝐸𝑂 ×44
𝐴𝑣𝑒𝑟𝑎𝑔𝑒.𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟.𝑤𝑡
× 20

10. 1. Gas hydrate: an introduction
Our research goals:
 A better understanding of hydrate formation and promotion mechanism
 How surfactants affect the interfacial tension and hydrate formation
 Help introducing hydrate based technologies
10

11. 2. Experimental
 2.1. Atmospherics hydrate formation in stirred reactor
 2.2. Atmospheric hydrate formation on subcooled cylinder
 2.3. High pressure hydrate formation in stirred reactor
 2.4. liquid-liquid interfacial tension measurements
 2.5. Materials
11

12. 2. Experimental
2.1. Atmospherics hydrate formation in stirred
reactor
 Mixture: 100 cc
 Ratios: hydrate stoichiometric ratio
 Stirrer speed: 550 rpm
 Procedure
12

13. 2. Experimental
2.2. Atmospheric hydrate formation on
subcooled cylinder
 2.2. Atmospheric hydrate formation on subcooled cylinder
13
Setup figure, 1: outer jacket, 2: hydrate
3:former solution, 4:formed hydrate, 5:
subcooled cylinder, 6:refrigeration cycle

14. 2. Experimental
2.3 High pressure hydrate formation in stirred
reactor
 600 cc stirred reactor
 Controllable stirrer speed
 Calibrated temperature and pressure transmitters
 With 0.1°C and 0.1 bar accuracies
 Stirrer speed: 650 rpm
 Solution: 250 or 300 cc
14

15. 2. Experimental
 2.3 High pressure hydrate formation in stirred reactor
15
Pressure vs. time for the system of water/MCH/Methane at 2°C in
presence of 1%w/wNPE6EO

16. 2. Experimental
2.4. liquid-liquid surface tension measurements
 2.4 liquid-liquid surface tension measurements [27-29]
16
𝛾 =
∆𝜌𝑔𝑑𝑒
2
𝐻
1
𝐻
= 𝑓
𝑑𝑠
𝑑𝑒
e
s
d
d
S 
0
1
2
2
3
3
4
1
B
S
B
S
B
S
B
S
B
H a






17. 2. Experimental
2.4. liquid-liquid surface tension measurements
 Pendant drop apparatus:
1. Liquid pump
2. Pendant drop
3. Sessile bubble
4. Small cylinder
5. Gas supply
6. Digital microscope
7. Light source
8. 8,9,12: pressure and temperature transmitter
10. Temperature controlled bath
13. Drain
14. To vacuum pump
15. Computer
16. Needle valve
17

18. 18

19. 2. Experimental
2.5 Materials
 Liquid hydrate formers:
 Gas hydrate former:
19
Cyclopentane Methyl Cyclopentane Methyl Cyclohexane Tert Butyl Methyl Ether
Methane
Tetrahydrofuran

20. 2. Experimental
2.5 Materials
 Additives:
1: Surfactants:
2: Polymers:
20
Nonyl Phenol
Ethoxylates (NPE)
Butyl phenol ethoxylates
(TritonX-100)
Lauryl alcohol ethoxylates
(LAE)
polyoxyethylene (20)
sorbitan
monopalmitate
(Tween 40)
Sodium
Dodecyl
Sulphate
(SDS)
Ethylene Oxide Propylene
Oxide copolymer (EO/PO)
Poly Ethylene
Glycol (PEG)

21. Methodology
Methodology:
 Firstly the hydrate formation reactions are conducted
 Secondly the interfacial tension of desired systems are measured
 Finally the hydrate formation rates are compared with the interfacial tension datas.
21

22. 3. Results and discussion:
3.1. interfacial tension
 CP/water system:
 CP droplet in continuous water phase
 Left: in presence of TritonX100,
Interfacial tension: 3.7 mN/m
 Right: no surfactants,
interfacial tension: 31 mN/m
22
Needle outer diameter: 1.22 mm

23. 3. Results and discussion:
3.1. interfacial tension
 CP/water system:
23
CP/water interfacial tension, surfactants at 1%w/w

24. 3. Results and discussion:
3.1. interfacial tension
 MCH/water system:
24
TritonX-100
LAE8EO
EO/PO

25. 3. Results and discussion:
3.1. interfacial tension
 TBME/water system:
25
TritonX-100
LAE8EO
EO/PO

26. 3. Results and discussion:
3.1. interfacial tension
 Highest interfacial tension: MCP
 Lowest interfacial tension: TBME
 Lower interfacial tension: due to hydrogen bounding (ether
oxygen and water hydrogen)
 At high temperatures: the hydrogen bounding less
important
26

27. 3. Results and discussion:
3.2. CP hydrate
 Effect of surfactants on CP hydrate formation:
 (Family of NPE)
 Steeper slope: higher rate
27

28. 3. Results and discussion:
3.2. CP hydrate
 Surfactants at 1% w/w
28

29. 3. Results and discussion:
3.2. CP hydrate
 Effect of studied polymers:
29

30. 3. Results and discussion:
3.2. CP hydrate
 best promoters : TritonX-100, NPE6EO and LAE8EO;
 Rate : 1533% increase
 Induction time: 0.04 of its original value
 The rate is mass transfer controlled
30
Rate
(°C/60sec)
Induction time
(sec)
System
0.3
1244
No surfactant
2.8
94
LAE2EO
2.9
4
LAE3EO
3.9
41
LAE7EO
3.7
31
LAE8EO
4.6
56
TritonX100
4
7
NPE6EO
3.7
42
NPE10EO
0.6
113
NPE30EO
1.3
50
NPE40EO
2
50
EO/PO
copolymer
0.3
210
PEG 600
1.9
120
Tween40

31. 3. Results and discussion:
3.2. CP hydrate
 On the promotion mechanism:
 Bancroft's law: the phase which the emulsifier is more soluble is the continuous phase
of an emulsion
 Best promoters: optimum O/W emulsifiers
31

32. 3. Results and discussion:
3.2. CP hydrate
Visual observations:
 Hydrate are in form of aggregates
 The hydrate formed in presence of surfactants: more slurry-ish
 The surfactants can affect the particle adhesion forces
32
CP hydrate aggregates,
light microscopy 100X magnification left: the cyclopentane and water Right: addition of NPE6EO

33. 3. Results and discussion:
3.3. THF hydrate
THF hydrate formation
 Mechanisms: Rayleigh number [30]
 Ra=590
Thus: only conduction!
 ρCp
𝜕T
𝜕t
=𝛻. k𝛻T
 An enthalpy based heat transfer model is developed
33
Thickness of hydrate formed, T (out): 4°C
L
L
H
eq
i
L D
T
T
g
Ra


 3
)
( 


34. 3. Results and discussion:
3.4. THF hydrate
34
A. Thot=8.2 ℃ ,Tini=8.2℃ , Tcold=0.1 ℃, relative
absolute error:12.2%
B. Thot=Tini=6.7 ℃ ,Tcold=0.1 ℃, relative absolute
error: 8.6%
C. Tcold=3.5 ℃ , Thot=Tini=4.5, relative absolute
error: 12.1%
D. Tcold=2.35 ℃ , Thot=Tini=4.5 ℃, relative absolute
error:11.7%
E. Tcold=1.3 ℃ , Thot=Tini=4.5 ℃, relative absolute
error: 10.5%
F. Tcold=0.35 ℃ , Thot=Tini=4.5 ℃, relative absolute
error:11.3%
 THF hydrate formation: (a soluble hydrate
former)Is heat transfer controlled!!!!

35. Results and discussion:
3.4. sH methane hydrate
 MCH/methane/ water:
 No sH is formed
 Methane/water :
35

36. Results and discussion:
3.4. sH methane hydrate
 First account for sH promotion:
 Effect of TritonX-100
 Much lower induction time
 Higher rate
 Single stage process
36

37. Results and discussion:
3.4. sH methane hydrate
 Effect of other additives:
 SDS in not a sH promoter
 This might be due to affect of identical charge repulsion
37

38. Results and discussion:
3.4. sH methane hydrate
 NPE6EO and Triton X-100:best promoters
 The tritonX-100 also exhibit the lowest
interfacial tension
 The induction time is lower to 0.04 of its
original value
 Rate: 424% increase
38
Rate
(bar/3000sec)
Induction
time
(sec)
Surfactant
concentration
w/w
surfactant
System
2.5
50000
--
--
MCH+ water
4.7
12000
--
--
MCH+ water
(twice
stoichiometric
ratio)
12.2
2100
1%
TritonX100
MCH+ water
(twice
stoichiometric
ratio)
12.5
17100
1%
TritonX100
MCH+ water
12.2
16800
0.5%
TritonX100
MCH+ water
12.5
21100
0.25%
TritonX100
MCH+ water
10.2
12300
1%
LAE8EO
MCH+ water
12.3
4670
1%
NPE6EO
MCH+ water
10.6
2550
1%
EO/PO block
copolymer
MCH+ water
8.7
31000
1%
Tween40
MCH+ water
13.1
2150
0.5% + 0.5%
NPE6EO+
Tritonx100
MCH+ water

39. Results and discussion:
3.4. sH methane hydrate
MCP/methane water:
 The sH hydrate does nor form in timescale of the experiment
 (more than 16 hours)
 Effect of NPE6EO :
39
Rate
(bar/3000sec)
Induction time
(sec)
Surfactant
concentration
w/w
surfactant
System
1.5
27100
--
--
MCP+ water
1.7
5420
--
--
MCP+ water
(twice
stoichiometric
ratio)
2.8
16500
1%
NPE6EO
MCP+ water

40. Results and discussion:
3.4. sH methane hydrate
 MCP/methane water:
 Effect of initial pressure:
 The induction time is not pressure dependent!!
 Higher pressures: higher rate!
 For sI: induction time is pressure dependent!
 The liquid/liquid solubility control the induction time
40

41. Results and discussion:
3.4. sH methane hydrate
 Kinetics of TBME/methane/water
 Effect of surfactants:
 Two stage hydrate formation!
41

42. Results and discussion:
3.4. sH methane hydrate
 Kinetics of three studied systems
42
In presence of 1% NPE6EO at 2°C

43. Results and discussion:
3.4. sH methane hydrate
 The TBME is kinetically favorable
 The MCH and MCP are thermodynamical favorable
 Mixture of two large guest molecules
43

44. Conclusions:
 NPE6EO, TritonX-100 and LAE8EO can significantly promote CP hydrate
formation kinetics: much higher interfacial surface
 The presence of surfactant can lower the particle adhesion forces: more slurry-
ish
 THF hydrate formation is a heat transfer controlled process due to its high
solubility in water
 Proposed enthalpy based heat transfer model can easily predict THF hydrate
formation rate
44

45. Conclusions:
 The CP/water MCP/water and MCH/water interfacial tension can be
lowered by an order of magnitude using non-ionic surfactants
 While the EO/PO can increase the effective diffusivity of the CP in water,
anionic surfactant might lower the effective diffusivity
 Mixed TBME/MCH and TBME/MCP systems are kinetically and
thermodynamically favorable systems
 Presence of surfactants: can change kinetic path for sH hydrate formation
45

46. Future plans:
 Experimental an modeling investigation of THF hydrate formation: falling
film
 Study of rheology and particle adhesion force for THF,TBAB and CP
hydrate
with and without additives
 Study of sH and sII hydrogen clathrate hydrate for hydrogen
transportation and storage
 Study of hydrate formation in CP/methane/ water and CP/CO2/water
systems
46

47. References
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135-136.
4. Susilo, Robin, Saman Alavi, Igor L. Moudrakovski, Peter Englezos, and John A. Ripmeester. 2009. Guest–Host Hydrogen Bonding in
Structure H Clathrate Hydrates. ChemPhysChem 10: 824-829.
5. Naeiji Parisa, Akram Arjomandi, and Farshad Varaminian.2014. Amino acids as kinetic inhibitors for tetrahydrofuran hydrate formation:
experimental study and kinetic modeling. Journal of Natural Gas Science and Engineering, 21: 64-70.
6. Eslamimanesh A, Mohammadi AH, Richon D, Naidoo P, Ramjugernath D. 2012. Application of gas hydrate formation in separation
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formation. Separation and Purification Technology.
8. ZareNezhad Bahman, and Mona Mottahedin. 2012. A rigorous mechanistic model for predicting gas hydrate formation kinetics: the case
of CO 2 recovery and sequestration. Energy Conversion and Management, 53: 332-336
47

48. References
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dissociation kinetics in a flow loop. International journal of refrigeration.
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processes", Energy conversion and management.
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Energy Conversion and Management.
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(SDS) and polyoxyethylene (20) sorbitan monopalmitate (Tween (R) 40) on ethane hydrate formation kinetics: Experimental and
modeling studies. Journal of Natural Gas Science and Engineering.
13. Roosta H., S. Khosharay, and F. Varaminian. 2013. Experimental study of methane hydrate formation kinetics with or without additives
and modeling based on chemical affinity. Energy Conversion and Management.
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refrigerants. International Journal of Refrigeration.
15. Li, Gang, Yunho Hwang, and Reinhard Radermacher.2012.Review of cold storage materials for air conditioning application. International
journal of refrigeration.
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Meeting, Arlington.
48

49. References
17. Ogoshi, Hidemasa, and Shingo Takao. 2004.Air-conditioning system using clathrate hydrate slurry." JFE Tech. Rep 3.
18. Javanmardi, M. Moshfeghian.2003. Energy consumption and economic evaluation of water desalination by hydrate phenomenon.
Applied thermal engineering.
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macroscopic kinetic model. International Journal of Refrigeration.
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subcooling driving force. Journal of Industrial and Engineering Chemistry.
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49

50. References
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Computers & Chemical Engineering.
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50

51. Thank you for your attention
(a.erfani@students.semnan.ac.ir)
51

52. Results and discussion:
3.4. sH methane hydrate
 Kinetics of TBME/methane/water
52

53. Results and discussion:
3.4. sH methane hydrate
 Induction time is lowere to 0.15 of its original value
 Rate: 162% increase
53
Rate
(bar/3000sec)
Induction time
(sec)
Surfactant
concentration
w/w
surfactant
System
11
670
--
--
TBME+ water
17
420
--
--
TBME+ water
(twice
stoichiometric
ratio)
18.8
68
1%
TritonX100
TBME+ water
(twice
stoichiometric
ratio)
17.8
100
1%
TritonX100
TBME+ water
12.4
80
1%
LAE8EO
TBME+ water
11.6
150
1%
NPE6EO
TBME+ water