Surfactant Effects on Crystal Growth Dynamics and Crystal

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Surfactant Effects on Crystal Growth Dynamics and Crystal Morphology of Methane Hydrate Formed at Gas/Liquid Interface Hiroaki Hayama, Makoto Mitarai, Hiroyuki Mori, Jonathan Verrett, Phillip Servio, and Ryo Ohmura Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01124 • Publication Date (Web): 29 Aug 2016 Downloaded from http://pubs.acs.org on September 4, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20

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

Crystal Growth & Design

1

Surfactant Effects on Crystal Growth Dynamics and Crystal

2

Morphology of Methane Hydrate Formed at Gas/Liquid Interface

3 4

Hiroaki Hayama†, Makoto Mitarai†, Hiroyuki Mori†, Jonathan Verrett‡, Phillip Servio‡ and Ryo Ohmura*, †

5

†

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Department of Mechanical Engineering, Keio University, Yokohama 223-8522, Japan

‡

Department of Chemical Engineering, McGill University, 3610 University Street, Montréal, Québec, H3A 0C5, Canada. ABSTRACT This paper presents the visual observations aims to clarify the underlying physics of surfactant effects on clathrate hydrate crystal growth at the interface between methane gas and water with surfactant. Sodium dodecyl sulfate (SDS), which is commonly used in industrial process, was used in this study. Various SDS mass fractions from 0 to wSDS =100 ppm with a step of size 10 ppm were examined, where wSDS represents the mass fraction of SDS aqueous solution. The crystal growth behavior and the crystal morphology of the methane hydrate at the interface varied depending on surfactant concentration and ∆Tsub. In systems with wSDS ≤ 20 ppm, the nucleation occurred on the droplet surface (gas/liquid interface), then grew laterally and finally covered the whole droplet surface. Contrary, at wSDS ≥ 30 ppm, the shape of droplet was not maintained and the enhanced hydrate crystal growth was observed compared to those systems with wSDS ≤ 20 ppm. Individual hydrate crystals at wSDS = 20 ppm were observed to be smaller than those in a pure water system at a given ∆Tsub , which is ascribed to the enhanced hydrate nucleation by the addition of SDS.

24 25 26 27 28 29 30

Crystal growth behavior depending on SDS concentration and subcooling temperature. Ryo Ohmura Department of Mechanical Engineering, Keio University

Yokohama 223-8522, Japan Phone: +81-45-566-1813 E-mail: [email protected]

1

ACS Paragon Plus Environment


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

Page 2 of 20

31

Surfactant Effects on Crystal Growth Dynamics and Crystal

32

Morphology of Methane Hydrate Formed at Gas/Liquid Interface

33

Hiroaki Hayama†, Makoto Mitarai†, Hiroyuki Mori†, Jonathan Verrett‡, Phillip Servio‡ and

34

Ryo Ohmura*, †

35

†

Department of Mechanical Engineering, Keio University, Yokohama 223-8522, Japan

36

‡

37

Québec, H3A 0C5, Canada.

Department of Chemical Engineering, McGill University, 3610 University Street, Montréal,

38 39

ABSTRACT

40

This paper presents the visual observations aims to clarify the underlying physics of

41

surfactant effects on clathrate hydrate crystal growth at the interface between methane gas and

42

water with surfactant. Sodium dodecyl sulfate (SDS), which is commonly used in industrial

43

process, was used in this study.

44

step of size 10 ppm were examined, where wSDS represents the mass fraction of SDS aqueous

45

solution.

46

the interface varied depending on surfactant concentration and ∆Tsub.

47

20 ppm, the nucleation occurred on the droplet surface (gas/liquid interface), then grew

48

laterally and finally covered the whole droplet surface. Contrary, at wSDS ≥ 30 ppm, the

49

shape of droplet was not maintained and the enhanced hydrate crystal growth was observed

50

compared to those systems with wSDS ≤ 20 ppm.

51

ppm were observed to be smaller than those in a pure water system at a given ∆Tsub , which is

52

ascribed to the enhanced hydrate nucleation by the addition of SDS.

Various SDS mass fractions from 0 to wSDS =100 ppm with a

The crystal growth behavior and the crystal morphology of the methane hydrate at In systems with wSDS ≤

Individual hydrate crystals at wSDS = 20

53 2


Page 3 of 20

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

54 55


INTRODUCTION Clathrate hydrates (hereafter simply hydrates) are crystalline compounds formed at

56

low temperatures and high pressures.

57

bonded water molecules forming cages and guest molecules occupying the inside of the cages.

58

There has been much research interest in hydrates due to their unique properties.

59

have a large gas-storage capacity and can contain 160 times more gas in the same volume

60

compared to gas at standard temperature and pressure, a large heat of formation and

61

decomposition which is comparable to that of ice, and guest selectivity which comes from the

62

interaction of the water-molecule cages and the occupying guest molecules.

63

properties may lead to the development of the various technologies, for instance, storage and

64

transportation of natural gas1 and hydrogen2, thermal energy storage3, high efficient heat

65

pumps4 and, carbon dioxide separation5, 6, 7. With so many applications and given their slow

66

formation rate, the enhancement of hydrate formation is one of the key challenges toward

67

developing hydrate technologies.

68

compound in oil and gas industries as the formation and growth of hydrates followed by their

69

agglomeration results in plugging oil and gas pipelines8.

70

gone into finding inhibitors which prevent hydrate formation or growth which block pipelines.

71

In this way, both hydrate formation and prevention methods are necessary for their respective

72

engineering practices.

73

Their structures are constructed of the hydrogen

Hydrates

These

Meanwhile, hydrates have been viewed as a problematic

Because of this, much research has

Recently, several studies regarding the surfactant effect on the hydrate formation Aman et al.9 reported the reduction of agglomeration in surfactant

74

have been conducted.

75

system compared to pure system by measuring the adhesion force between hydrate particles.

76

On the other hand, Okutani et al.10 reported the increase in the rate of hydrate formation and

77

water-to-hydrate conversion ratio by adding surfactant.

78

surfactants have both effects for prevention of hydrate agglomeration and promotion of

These reports indicate that

3



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

Page 4 of 20

79

hydrate formation, which are apparently different effects.

Why surfactants provide two

80

different effects for hydrate formation is still not well understood.

81

of hydrate formation in the system including surfactant can be better understood using crystal

82

growth and morphology date.

83

the mechanistic aspects of hydrate crystal growth by providing crystal size and shape data11,

84

12

The physical mechanism

Crystal morphology studies provide valuable knowledge of

. It is generally known that hydrates preferentially grow at the guest/water interface13,

85 86

14

87

chemical species of the guests and the addition of surfactant.

88

critically reviewed the previous studies related the surfactant effect on the hydrate formation

89

and they mentioned that SDS would be suitable for the application in the engineering

90

technologies15.

91

methane gas, tetrahydrofuran and sodium dodecyl sulfate (SDS) at near ambient temperatures

92

for large scale natural gas storage.

93

uptake by the addition of SDS compared to the pure water system.

94

the effect of surfactant such as SDS on the hydrate growth from methane-propane gas mixture.

95

They observed the leaf-like and fiber-like hydrate crystals in the bulk water.

96

relationship between hydrate growth dynamics and the hydrate morphology was not

97

elucidated.

98

between water and cyclopentane with surfactant such as PPG, naphthenic acid, and Span 80.

99

They revealed that the hydrate crystal production increased and the size of individual hydrate

, but the hydrate growth behavior and hydrate crystal morphology changes depending on the Recently, Kumar et al.

Veluswamy et al.16 observed hydrate formation kinetics in the presence of

They reported the substantial increase in methane gas Yoslim et al.17 reported

However, the

Mitarai et al.18 observed hydrate crystal growth at the liquid/liquid interface

100

crystals was larger compared to the system without surfactants.

101

formation and the formation of smaller sized crystals were caused by the detachment of the

102

hydrate crystals from the interface in the presence of surfactant.

103

The enhanced hydrate

SDS is commonly used in industrial process because it is one of the most economical 4


Page 5 of 20

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


104

surfactants.

Though the morphology of hydrate systems with SDS have been studied, there

105

has been little work, explaining the mechanism of hydrate growth.

106

the mechanism of the SDS effect on the hydrate growth at the gas/liquid interface with the

107

visual observations of hydrate crystal growth and morphology in the methane/water system

108

with SDS.

109

were examined to understand how SDS affects hydrate crystal growth and crystal

110

morphology.

This study aims to reveal

Various SDS concentrations from 0 to wSDS =100 ppm with a step of size 10 ppm

111 112

EXPERIMENTAL SECTION

113

The fluid samples used in the experiments were deionized and distilled water and

114

methane (99.99 vol %, Takachiho Chemical, Co.). The surfactant used in the study was SDS

115

(99.0 %, Aldrich Chemical Co.). SDS aqueous solution samples were prepared at mass

116

fractions from 0 to wSDS =100 ppm with increasing step of 10 ppm, where wSDS represents the

117

mass fraction of SDS aqueous solution. The system subcooling ∆Tsub was defined as the

118

difference between the experimental temperature and the equilibrium temperature of methane

119

hydrate (∆Tsub ≡ Teq - Tex) under the given experimental pressure as an indicator of the

120

driving force for the crystal growth.

121

A schematic diagram of the main portion of the experimental apparatus was shown in

122

Fig. 1. The experimental section holding hydrate crystals and methane gas is a cylinder made

123

from stainless steel and a pair of glass windows for the observation. The internal space of test

124

section is 20 mm in axial length by 25 mm in diameter. To control the temperature of test

125

section, ethylene glycol aqueous solution was circulated in the jacket which covered the

126

experimental vessel. The experimental temperature, Tex was measured by Pt-wire

127

thermometer inserted directly under the Teflon stage which is 6 mm or 13 mm in diameter.

128

The SDS aqueous solution was deposited and hold on the Teflon stage. Methane gas 5



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

Page 6 of 20

129

is supplied and depressured repeatedly to replace the air in test section with methane gas. The

130

experimental pressure, P was set to a prescribed level by supplying methane gas. P was

131

measured by a stain gauge pressure transducer. The uncertainty of temperature and pressure

132

measurements were ±0.2 K and ±0.05 MPa, respectively.

133

It was confirmed that equilibrium temperature of the hydrate formed between

134

methane and SDS aqueous solution was equal to the methane hydrate equilibrium temperature

135

in any conditions19.

136

explained in the previous study by Mitarai et al.18

The detailed procedure of equilibrium temperature measurements was

137

After the droplet of SDS solution and methane were placed in the test cell, the

138

experimental pressure was set to P = 7.8 MPa and the experimental temperature T was first

139

decreased to approximately 270 K to form a hydrate.

140

was increased to 1 K higher than the equilibrium temperature of methane hydrate, Teq = 283.9

141

K to dissociate the hydrate under the experimental pressure.

142

dissociation of all hydrate crystals, Tex was set at a prescribed experimental temperature, such

143

that ∆Tsub was in the range from 1.3 K to 9.0 K, to observe the formation and growth of

144

hydrate crystals in each experimental condition. In this manner, the memory effect was used

145

to shorten the induction time for hydrate formation.

Then, the temperature of the test cell

After visually confirming the

146

Concurrent monitoring and recording of the formation and growth of the hydrate

147

crystals were conducted using a CCD camera (Olympus, DP72) and a microscope

148

(VZMis450i, Edmond optics).

149 150

RESULTS AND DISCUSSION

151

Hydrate crystal growth behavior

152 153

The sequential images of the methane hydrate crystal growth at the interface of methane and water with/without SDS are shown in Fig. 2.

The figure shows images of the 6


Page 7 of 20

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


154

system with SDS concentration at wSDS = 0 and wSDS = 20 ppm.

The time when the first

155

hydrate crystal was visually confirmed is defined as t = 0 and the elapsed time is shown under

156

each image in Fig. 2.

157

(gas/liquid interface) (Fig. 2 (1a, 2a)), and then laterally grew (Fig. 2 (1b, 2b)) and finally

158

covered the whole droplet surface (Fig. 2, (1c, 2c)).

159

covered the droplet, no remarkable subsequent hydrate growth was observed. The crystal

160

growth behavior was almost similar in wSDS ≤ 20 ppm system but crystal morphology was

161

distinct between pure water and wSDS = 20 ppm as described in detail below crystal

162

morphology section.

Nucleation occurred at random points on the droplet surface

After the hydrate film completely

163

The hydrate growth behavior in the systems with SDS in the range from wSDS = 30

164

ppm to wSDS = 100 ppm showed a distinct difference compared to those system where wSDS ≤

165

20 ppm.

166

shown in Fig. 3.

167

formed hydrate at the gas/liquid interface detached and migrated to the bulk (Fig. 3, 1b).

168

The accumulation of the detached hydrate crystals resulted in the conversion of the droplet of

169

SDS aqueous solution to a chunk of crystals.

170

out on the stage (Fig. 3, 1c).

171

the droplet surface after the nucleation was observed (Fig. 3, 2a), then the fiber crystals grew

172

vertically from the point of contact between the droplet of SDS aqueous solution and the stage

173

(Fig. 3, 2c).

174

compared to those in the wSDS ≤ 20 ppm systems based on visual observation.

The representative hydrate growth behavior in this range of the concentration was At ∆Tsub < 6.0 K, the hydrate crystals did not cover the droplet surface but

The droplet with the hydrate crystals spread

At ∆Tsub ≥ 6.0 K, the hydrate crystals instantaneously covered

The observation showed that the amount of formed hydrate crystals increased

175 176 177 178

Crystal morphology It was difficult to observe the crystal morphology because the droplet shape was not maintained and thus the individual crystals could not be identified at wSDS ≥ 30 ppm.

In the 7



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

Page 8 of 20

179

previous study, morphology change was observed when the surfactant such as SDS is present

180

at the condition with wSDS ≥ 25 ppm20.

181

morphology that was clearly influenced by SDS, the concentration wSDS = 20 ppm may be

182

favorable because the effect of SDS on the methane hydrate crystal growth was observed at

183

this concentration while the droplet shape was maintained.

184

morphology of the individual hydrate crystals between pure water system21 and wSDS = 20

185

ppm system.

186

The size of individual hydrate crystals was smaller and their shape varied from polygonal to

187

sword-like with increasing ∆Tsub in both concentration.

188

individual hydrate crystals in wSDS = 20 ppm system was smaller than those in the pure water

189

system at a given ∆Tsub.

190

nucleation by SDS reported in the previous studies22, 23. Crystal morphology should be fixed

191

by the rate of nucleation in this system because the hydrate growth was prevented from

192

contacting with other formed hydrates.

193

morphology was determined from the balance between the rates of nucleation and crystal

194

growth.

195

restricted and the size of hydrate crystals was smaller in comparison to pure water system.

196

These results were different from those found in Mitarai et al.18

197

explained as follows: they observed the morphology in the condition that individual crystals

198

could grow without ever contacting any other crystals as the hydrate crystals detached from

199

the interface and fell into water.

With regard to the observation of hydrate crystal

Fig. 4 shows the comparison of

The typical individual hydrate crystals were enclosed by red lines in Fig. 4.

It should be noted that the size of

This observation may be ascribed to the enhancement of hydrate

As discussed in the previous study24, hydrate

When the rate of nucleation increased, hydrate crystal growth was strongly

This difference may be

200 201 202 203

Crystal Growth Mechanism Fig. 5 shows the visual summary of the representative behavior for methane hydrate formation at various SDS concentrations.

As mentioned above, there were two types of 8


Page 9 of 20

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


204

characteristic behaviors occurring for the methane and SDS aqueous solution at the gas/liquid

205

interface.

206

growth mechanisms.

207

Covering the interface

208

The following figures from Fig. 6 through Fig. 8 further explained these hydrate

The first mechanism was observed when hydrate crystals initially forming on the

209

interface and spread to cover the whole droplet surface.

210

were in the red box in Fig. 5 at the conditions with wSDS ≤ 20 ppm, 1.3 K ≤ ∆Tsub ≤ 6.0 K, P =

211

7.8 MPa.

212

how the hydrate crystals covered the interface. These figures show how the hydrate crystal

213

covers the interface and hydrate growth stops.

214

covering the droplet surface, and this crystal barrier prevents the necessary interaction

215

between water and methane to continue methane hydrate formation.

216

Detached from the interface

217

The conditions, at which this occurs,

Fig. 6 shows the representative sequential images of hydrate growth and explains

Hydrate crystals grow on the interface with

Another mechanism observed was the detaching of hydrate crystals from the

218

interface after the crystal formed on the droplet surface.

This behavior is highlighted in the

219

blue box in Fig. 5 at the conditions with wSDS ≥ 30 ppm, 1.3 K ≤ ∆Tsub ≤ 9.0 K, P = 7.8 MPa.

220

Depending on the intensity of subcooling, the crystal growth differed.

221

crystal growth direction was tangent to the substrate, whereas at ∆Tsub ≥ 6.0 K, the crystal

222

growth direction was vertical.

223

the hydrate crystal grow, then detached from the interface and then grow tangential to the

224

substrate.

225

substrate with the SDS aqueous solution, and therefore SDS aqueous solution inside the

226

droplet permeated beyond the initial droplet edge and continued to outward crystallize newly

227

formed interfaces.

228

the increased wettability of the hydrate crystals with SDS aqueous solution.

At ∆Tsub < 6.0 K, the

Fig. 7 refers to wSDS = 100 ppm and ∆Tsub < 6.0 K, and shows

This spreading growth behavior would be caused by increased wettability of the

Why the crystals detached from the interface could also be found from When the 9



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

Page 10 of 20

229

hydrate crystals detached from the gas/liquid interface and formed new hydrate crystals on the

230

gas/liquid interface, the concentration of SDS within the droplet increased because SDS was

231

not enclosed into the hydrate.

232

wettability of the stage surface would increase in response to the decreasing interfacial tension

233

thereby resulting in the spreading of the droplet in the tangent direction.

234

interfacial tension on the SDS concentration was previously reported by Watanabe et al.25.

235

The permeated SDS aqueous solution continued to contact with methane gas. Therefore, it

236

was observed that hydrate crystal growth keeps this spreading behavior.

237

From the above, as the hydrate crystals formed in SDS system,

The dependency of

Fig. 8 is the explanatory diagram of vertical hydrate growth, which occurred for wSDS

238

= 100 ppm and ∆Tsub ≥ 6.0 K systems.

The droplet of SDS aqueous solution rapidly

239

crystalized because of the high subcooling, which promoted crystal nucleation and growth.

240

Thereafter, the droplet was elevated from the substrate by pillars of fiber hydrate crystals.

241

Similar to the aforementioned spreading mechanism, once the gas/liquid interface was

242

covered, the remaining SDS increased the wettability of the substrate.

243

permeated out of the initial droplet border.

244

hydrate crystals in the system with SDS were smaller than those in the system without SDS as

245

shown in the crystal morphology observation (Fig. 4).

246

the pores between hydrate crystals were smaller, the SDS aqueous solution tended to permeate

247

outside, contacted the methane gas and then crystallized very quickly.

248

solution inside the lower part of the droplet continued to permeate outside and contacted the

249

already formed crystal column and continue to grow by contact with the methane gas.

250

Finally, columns of fiber-like hydrate crystals were generated.

Aqueous solution

The capillary force increased because formed

Since ∆Tsub was extremely high and

The SDS aqueous

251

Macroscopic hydrate growth dynamics is known to be quite similar irrespective to

252

the chemical species of the surfactants as clearly reported by Okutani et al10. We consider that

253

the surfactant-effect mechanism found in this study would be common for the other surfactant 10


Page 11 of 20

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

254


systems but further experimental confirmation is necessary.

255 256

CONCLUSION

257

Visual observations of methane hydrate were used to understand the underlying

258

physics of the two different surfactant effects, the antiagglomeration of hydrate crystals and

259

the hydrate formation enhancement.

260

phenomena that explain the surfactant effects.

261

These observations successfully clarified the distinct

The amount of formed hydrate crystals increased, which was caused by detachment

262

of hydrate crystals from the interface because of increased wettability.

Detachment of

263

hydrate crystals is the phenomenon common both for the antiagglomeration and the enhanced

264

hydrate formation.

265

smaller compared to pure water system because of increased hydrate nucleation.

266

subcooling temperature was extremely high, the hydrates formed upright crystal fibers which

267

was distinct from the existing observed hydrate morphology in SDS system because capillary

268

force was larger due to smaller pores between hydrate crystals.

269

it is concluded that increased wettability and strong capillary action, both induced by SDS,

270

control the crystal growth and morphology in the system with surfactant.

The size of individual hydrate crystals in systems with SDS present was When the

Based on these observations,

271

11



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

Page 12 of 20

FIGURE CAPTIONS Figure 1 Schematic diagram of the experimental apparatus. Figure 2 Sequential images of typical methane hydrate growth between methane and water with/without SDS at wSDS ≤ 20 ppm, P = 7.8 MPa. Figure 3 Sequential images of typical methane hydrate growth between methane and SDS aqueous solution at wSDS ≥ 30 ppm, P = 7.8 MPa. Figure 4 Summary of crystal morphology comparison between pure water system and wSDS = 20 ppm system depending on ∆Tsub. The typical individual hydrate crystals were enclosed by red lined. Figure 5 Visual summary of crystal growth behavior on gas/liquid interface for different ∆Tsub and mass fractions. The upper images were methane hydrate crystals without SDS, P = 8.15 MPa, the middle images and lower images were methane hydrate crystals with SDS at wSDS = 20 ppm, wSDS = 100 ppm, respectively, P = 7.8 MPa. Figure 6 Sequential images and schematic illustration explaining how the hydrate crystals covered the interface at wSDS = 10 ppm, ∆Tsub = 1.3 K, P = 7.8 MPa. Figure 7 Sequential images and schematic illustration explaining how crystals form and slide to the edges of the interface at wSDS ≥ 30 ppm, ∆Tsub < 6.0 K, P = 7.8 MPa. Figure 8. Sequential photographs and schematic illustration explaining how columnar growth occurs on the edges of the interface for wSDS ≥ 30 ppm, ∆Tsub ≥ 6.0 K, P = 7.8 MPa. 272 273

12


Page 13 of 20

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


274

275 276

Figure 1. Schematic diagram of experimental apparatus.

277

278 279

Figure 2. Sequential images of typical methane hydrate growth between methane and water

280

with/without SDS at wSDS ≤ 20 ppm, P = 7.8 MPa. 13



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

Page 14 of 20

281 282

Figure 3. Sequential images of typical methane hydrate growth between methane and SDS

283

aqueous solution at wSDS ≥ 30 ppm, P = 7.8 MPa.

284

285 286

Figure 4. Summary of crystal morphology comparison between pure water system and wSDS =

287

20 ppm system depending on ∆Tsub. The typical individual hydrate crystals were enclosed by

288

red lined.

14


Page 15 of 20

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


289 290

Figure 5. Visual summary of crystal growth behavior on gas/liquid interface for different

291

∆Tsub and mass fractions. The upper images were methane hydrate crystals without SDS, P =

292

8.15 MPa, the middle images and lower images were methane hydrate crystals with SDS at

293

wSDS = 20 ppm, wSDS = 100 ppm, respectively, P = 7.8 MPa.

294

295 296

Figure 6. Sequential images and schematic illustration explaining how the hydrate crystals

297

covered the interface at wSDS = 10 ppm, ∆Tsub = 1.3 K, P = 7.8 MPa. 15



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

Page 16 of 20

298 299

Figure 7. Sequential images and schematic illustration explaining how crystals form and slide

300

to the edges of the interface at wSDS ≥ 30 ppm, ∆Tsub < 6.0 K, P = 7.8 MPa.

301 302

Figure 8. Sequential photographs and schematic illustration explaining how columnar growth

303

occurs on the edges of the interface for wSDS ≥ 30 ppm, ∆Tsub ≥ 6.0 K, P = 7.8 MPa. 16


Page 17 of 20

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


304 305

AUTHOR INFORMATION

306

Corresponding Author

307

*E-mail: [email protected]

308

Notes

309

The authors declare no competing financial interest.

310

ACKNOWLEDGMENT

311

This study was supported by a Keirin-racing-based research-promotion fund from the JKA

312

Foundation and by JSPS KAKENHI Grant Number 25289045.

313 314

REFERENCE

315

(1) Thomas, S.; Dawe, R. A. Energy 2003, 28, 1461–1477.

316

(2) Mao, W. L.; Mao, H.-K. Proc. Natl. Acad. Sci. U. S. A. 2004, 101, 708–710.

317

(3) Sakamoto, H.; Sato, K.; Shiraiwa, K.; Takeya, S.; Nakajima, M.; Ohmura, R. RSC Adv.

318

319 320

321

2011, 1, 315.

(4) Ogawa, T.; Ito, T.; Watanabe, K.; Tahara, K.; Hiraoka, R.; Ochiai, J.; Ohmura, R.; Mori, Y. H. Appl. Therm. Eng. 2006, 26 , 2157–2167.

(5) Ohmura, R.; Mori, Y. H. Environ.Sci.Technol. 1998, 32, 1120–1127. 17



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

322 323

(6) Tohidi, B.; Yang, J.; Salehabadi, M.; Anderson, R.; Chapoy, A. Environ. Sci. Technol. 2009, 44, 1509–1514.

324

(7) Brewer, P. G.; Friederich, G.; Peltzer, E. T.; Orr, F. M., Jr. Science 1999, 284, 943-945.

325

(8) Sloan, E. D. Nature 2003, 426, 353.

326

(9) Aman, Z. M.; Dieker, L. E.; Aspenes, G.; Sum, A. K.; Sloan, E. D.; Koh, C. A. Energy

327

and Fuels 2010, 24, 5441–5445.

328

(10)

Okutani, K.; Kuwabara, Y.; Mori, Y. H. Chem. Eng. Sci. 2012, 73, 79–85.

329

(11)

Darbouret, M.; Cournil, M.; Herri, J. M. Int. J. Refrig. 2005, 28, 663–671.

330

(12)

Bird, R. B.; Stewart, W. E.; Lightfoot, E. N. Transport Phenomena, 2nd ed.; John

331

332 333

Page 18 of 20

Wiley and Sons. Inc.: Hoboken, NJ, 2006; pp196-200.

(13)

Saito, K.; Kishimoto, M.; Tanaka, R.; Ohmura, R. Cryst. Growth Des. 2011, 11,

295–301.

334

(14)

Ueno, H.; Akiba, H.; Akatsu, S.; Ohmura, R. New J. Chem. 2015, 39, 8254–8262.

335

(15)

Kumar, A.; Bhattacharjee, G.; Kulkarni, B. D.; Kumar, R. Ind. Eng. Chem. Res. 2015,

336

337

54, 12217–12232.

(16)

Veluswamy, H. P.; Kumar, S.; Kumar, R.; Rangsunvigit, P.; Linga, P. Fuel 2016, 18


Page 19 of 20

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

338


182, 907–919.

339

(17)

Yoslim, J.; Linga, P.; Englezos, P. J. Cryst. Growth 2010, 313, 68–80.

340

(18)

Mitarai, M.; Kishimoto, M.; Suh, D.; Ohmura, R. Cryst. Growth Des. 2015, 15, 812–

341

342 343

821.

(19)

Nakamura, T.; Makino, T.; Sugahara, T.; Ohgaki, K. Chem. Eng. Sci. 2003, 58, 269–

273.

344

(20)

Veluswamy, H. P.; Chen, J. Y.; Linga, P. Chem. Eng. Sci. 2015, 126, 488–499.

345

(21)

Tanaka, R.; Sakemoto, R.; Ohmura, R. Cryst. Growth Des. 2009, 9, 2529–2536.

346

(22)

Kakati, H.; Mandal, A.; Laik, S. J. Ind. Eng. Chem. 2015, 35, 357–368.

347

(23)

Kumar, A.; Sakpal, T.; Linga, P.; Kumar, R. Fuel 2013, 105, 664–671.

348

(24)

Kishimoto, M.; Iijima, S.; Ohmura, R. Ind. Eng. Chem. Res. 2012, 51, 5224–5229.

349

(25)

Watanabe, K.; Niwa, S.; Mori, Y. H. J. Chem. Eng. Data 2005, 50, 1672–1676.

350

19



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

Page 20 of 20

351

For Table of Contents Use Only

352

Title: “Surfactant Effects on Crystal Growth Dynamics and Crystal Morphology of Methane

353

Hydrate Formed at Gas/Liquid Interface”

354

Author: Hiroaki Hayama, Makoto Mitarai, Hiroyuki Mori, Jonathan Verrett, Phillip Servio

355

and Ryo Ohmura

356

Table of Contents Graphic and Synopsis

357

358

Crystal growth of clathrate hydrate formed in the methane + SDS aqueous solution system

359

was visually analyzed. Based on the visual observations, the controlling mechanism of the

360

surfactant effect was discussed. It was found that the increased wettability and strong

361

capillary action, both induced by SDS, control the crystal growth and morphology in the

362

system with surfactant.

363

20


Surfactant Effects on Crystal Growth Dynamics and Crystal

Recommend Documents