Effect of Demulsification for Crude Oil-in-Water ... - ACS Publications

Jan 2, 2018 - Engineering Research Center of Oilfield Chemistry, Ministry of Education, Chengdu 610500, P. R. .... the crude oil transportation indust...
0 downloads 0 Views 2MB Size
Subscriber access provided by UNIV OF NEW ENGLAND ARMIDALE

Article

Effect of Demulsification for Crude Oil-In-Water Emulsion: Comparing CO and Organic Acids 2

Dongfang Liu, Yuxin Suo, Jihe Zhao, Peiyao Zhu, Jiang Tan, Baogang Wang, and Hongsheng Lu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b03334 • Publication Date (Web): 02 Jan 2018 Downloaded from http://pubs.acs.org on January 3, 2018

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.

Energy & Fuels 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 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

1

Effect of Demulsification for Crude Oil-In-Water Emulsion:

2

Comparing CO2 and Organic Acids

3

Dongfang Liu, † Yuxin Suo, †Jihe Zhao, † Peiyao Zhu, † Jiang Tan, † Baogang Wang †

4

and Hongsheng Lu *, †, ‡

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

*Corresponding author: College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China. Email: [email protected]; Fax: +86-28-83037330; Tel: +86-28-83037330.

College of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu 610500, P. R. China ‡ Engineering Research Center of Oilfield Chemistry, Ministry of Education, Chengdu 610500, P. R. China

1

ACS Paragon Plus Environment

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

38

ABSTRACT

39

Acidic substances (naphthenic acids) were found in crude oil, which provides

40

favorable conditions for the formation of surfactants. N, N-Dimethylcyclohexylamine

41

(DMCHA) can activate the naphthenic acid in the crude oil to form the surfactant by

42

noncovalent bonding. This process has an unusual meaning for the crude oil pipelines

43

transportation by the method of forming a low viscosity oil-in-water emulsion. At the

44

same time, CO2 can be used as a demulsifier to separate crude oil and water at the end

45

of pipeline transportation because of the surfactant has a CO2 stimulus response

46

characteristic. In our study, it was found that crude oil-in-water emulsion can be

47

formed and has very good stability. CO2 has a high demulsification efficiency in

48

emulsions with lower crude oil content. For high oil content conditions, the emulsion

49

cannot be demulsified completely by CO2. Since sulfuric acid, hydrochloric acid and

50

the like are liquid and corrosive, this is not conducive to its application as a

51

demulsifier in crude oil pipeline transportation. Organic acids in this area have a

52

stronger advantage obviously, so citric acid, oxalic acid, acetic acid and lactic acid

53

were used as demulsifiers in this article, all of them have good demulsification

54

performance in high crude oil content emulsions, especially citric acid. Meanwhile,

55

DMCHA can be recycled and reused by adding NaOH to the lower aqueous solution

56

after demulsification.

57

Keywords: DMCHA; citric acid; crude oil emulsion; demulsification.

2

ACS Paragon Plus Environment

Page 2 of 25

Page 3 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

58

1. INTRODUCTION

59

In general, reducing the viscosity of the crude oil is necessary during its pipeline

60

transportation1. Many methods to reduce the viscosity of crude oil have been studied,

61

such as heating2, dilution3, emulsification4, 5 and so on. However, a green, low energy

62

consumption and low-cost solution are always the pursuits of goals. Thus, how to

63

achieve these goals in the field of crude oil pipeline transportation? We have provided

64

a very good solution based on our research about stimuli-responsive materials6-9.

65

The study of stimulus-response has been extensively studied. In general, the

66

stimulus-response is mainly focused on pH10, 11, CO212, 13, light14, 15, temperature16, 17,

67

magnetic18, 19 and redox20, 21 response. CO2 has been extensively studied because it is

68

considered to be an ideal switchable trigger factor, including its green, abundant, does

69

not accumulate in the system and easy to remove22. Recently, CO2 stimuli-responsive

70

materials have received extensive attention and research. For example, CO2

71

responsive micelles23, 24, emulsions25, 26, polymers27, 28, etc. In 2006, Jessop group

72

reported the study of switchable surfactants29. The long-chain alkyl amidine

73

compound can be reversibly converted to a positively charged surfactant in the

74

presence of CO2. Hexadecane, water, and long-chain alkyl amidine can form stable

75

emulsions in the presence of CO2 and the demulsification occurs in the presence of

76

argon. Emulsification is an effective means of reducing the viscosity of crude oil. If

77

the crude oil emulsions with the characteristics of the CO2 switch can be prepared, we

78

can solve the problems encountered in the pipeline transportation. At the beginning of

79

transport, the crude oil emulsions with lower viscosity were prepared by using CO2 3

ACS Paragon Plus Environment

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

80

switchable surfactants and the crude oil and water can be separated at the end of

81

transport under CO2 stimulation. In addition, naphthenic acids are common in crude

82

oil30, and even high acid crude oil will cause serious corrosion of equipment. The

83

naphthenic acids can form a surfactant when combined with a CO2 stimuli-responsive

84

tertiary amine or amidine. Not only can emulsify the crude oil to form emulsions but

85

also can reduce the corrosion of equipment in the pipeline transportation. In the crude

86

oil pipeline transportation process, the amount of crude oil in the emulsion determines

87

the transport costs directly. In general, the crude oil content in the emulsion should be

88

above 70 wt%31 during the pipeline transportation process. However, the increase of

89

oil content in emulsions also affects the stability of the emulsion and demulsification

90

performance. It cannot break the emulsion effectively with high oil content by CO2

91

because with the introduction of CO2, a large amount of crude oil will cover the upper

92

layer, which makes CO2 difficult to escape. This will undoubtedly increase the

93

difficulty of the operation. Due to the strong acid, such as hydrochloric acid and

94

sulfuric acid are corrosive and not suitable for use as a demulsifier. On the contrary,

95

organic acids are undoubtedly the best choice, especially citric acid. Solid acid citric

96

acid can greatly reduce transportation costs and improve demulsification efficiency at

97

room temperature.

98

In this paper, hydrophobic tertiary amine N, N-Dimethylcyclohexylamine

99

(DMCHA) with CO2 response was used to emulsify the crude oil. CO2 is an effective

100

demulsifier for emulsions with low oil content. On the contrary, if the crude oil

101

content in the emulsion increases, the crude oil cannot be effectively separated with 4

ACS Paragon Plus Environment

Page 4 of 25

Page 5 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

102

CO2 bubbling. At the meanwhile, organic acids such as acetic acid, oxalic acid, lactic

103

acid and citric acid play the vital role in demulsifier. DMCHA can emulsify crude oil

104

to form an emulsion that facilitates pipeline transportation. Organic acids can be used

105

as demulsifiers to achieve separation of crude oil and aqueous solutions at the end of

106

transport. This process has important guiding significance for crude oil transportation

107

industry.

108

2. EXPERIMENTAL SECTION

109

2.1 Chemicals and materials

110

Tertiary amines N, N-Dimethylcyclohexylamine (DMCHA, 98%) was purchased

111

from Aladdin Reagents of China. Oxalic acid (99.8%) was purchased from Shanghai

112

Macklin Biochemical Co., Ltd. Acetic acid (99.5%), lactic acid (90%) and citric acid

113

(99.8%) were purchased from Chengdu Kelong Chemical Factory. CO2 (>99%) were

114

purchased from Chengdu Jinli gas Co., Ltd. The crude oil sample was obtained from

115

the Xinjiang China. The parameters of the crude oil are shown in Table 1. All the

116

chemicals without further purification before use.

117

Table 1. The specifications of crude oil Entry Amount Unit o Density (20 C) 0.98 g/cm3 Viscosity (50oC) 113.42 Pa·s Acid number 3.78 mg KOH/g Asphaltene 1.27 wt% Resin 11.48 wt% Saturates 60.14 wt% Aromatics 25.63 wt% Water content 13.10 wt%

5

ACS Paragon Plus Environment

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

118

2.2 Preparation of crude oil-in-water emulsion

119

At room temperature, weigh the crude oil, DMCHA, and water, respectively, into

120

the 50 mL plug cylinder. Then put the plug cylinder in the ultrasonic environment for

121

30min at 50oC. After the full action of DMCHA and naphthenic acids, crude oil

122

emulsion was formed. The type of emulsion was judged by drop test6, a drop of crude

123

oil emulsion was dropped into the water. If the droplets were dispersed immediately in

124

water, the emulsion was an oil-in-water emulsion and vice versa was a water-in-oil

125

emulsion.

126

2.3 The demulsification process of crude oil emulsions

127

The stability of the crude oil emulsion was illustrated by observing the rate of

128

separation of the aqueous phase. The volume of the separated aqueous solution was

129

recorded as V1. The total volume of water (contains the water content of the crude oil

130

itself) and DMCHA were recorded as V. =

 × 100% (1) 

131

S represents the demulsification rate. Under the same conditions, the smaller of

132

the S value corresponds to the more stable emulsions; on the contrary, the larger of the

133

S value corresponds to the unstable emulsions. For the demulsification process, the

134

greater the value of S per unit time corresponds to the higher the demulsification

135

efficiency.

136

Two methods of demulsification were used in this paper. (1) At room temperature,

137

CO2 was bubbled into the crude oil emulsion at a rate of 100 mL·min-1 for 10 min,

138

and then the volume of the separated water was recorded. (2) The organic acid 6

ACS Paragon Plus Environment

Page 6 of 25

Page 7 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

139

aqueous solution was added as a demulsifier to the crude oil emulsion. After fully

140

mixed in an ultrasonic environment at 50oC, the volume of the separated aqueous

141

phase was recorded.

142

2.4 The recovery of DMCHA after emulsion breaking

143

DMCHA can be recovered by adding NaOH to the aqueous solution after

144

demulsification. The volume change of the DMCHA was recorded with the addition

145

of NaOH. When the volume of DMCHA no longer changes, it is the maximum

146

volume of the recovered. The ratio of the recovered volume of DMCHA to the total

147

volume added is the recovery rate of DMCHA.

148

3. RESULTS AND DISCUSSION

149

3.1 Preparation of crude oil-in-water emulsions with low oil content

150

Tertiary amine DMCHA and naphthenic acid self-assembled to form a surfactant,

151

which plays an important role in the formation of crude oil emulsions. In order to find

152

the optimum concentration of DMCHA, the following emulsions were prepared

153

(Table 2).

154

Table 2. The proportion of each component in the crude oil emulsion Entry

Crude oil/g

Water/g

DMCHA/g

T/min

Oil content/wt%

Emulsion type

A

2

40

0.2

30

4.74

O/W

B

2

40

0.5

26

4.71

O/W

C

2

40

1

17

4.65

O/W

7

ACS Paragon Plus Environment

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

155

Page 8 of 25

D

2

40

1.5

13

4.60

O/W

E

2

40

2

12

4.55

O/W

T: The minimum time required to form the emulsion.

156

As showed in Table 2, Emulsions A, B, C, D, and E can be formed, but the time

157

to form the emulsion was different. The lower the DMCHA concentration, the longer

158

it takes to form the emulsion. The higher the concentration of DMCHA means that the

159

higher the concentration of surfactant that promotes emulsion formation and the

160

shorter the time required for emulsion formation. What about the stability of the five

161

emulsions prepared? Freshly prepared crude oil emulsions A, B, C, D, and E were

162

placed at room temperature to observe and record the volume changes with time.

163

Since the demulsifier was not added, the oil and water phases cannot be clearly

164

separated. The single phase O/W emulsion began to be divided into two phases, and

165

the volume of the upper phase gradually increased with the prolongation of time. The

166

ratio of the volume of the upper phase to the total volume of the emulsion was used to

167

indirectly represent the stability of the emulsion. The demulsification efficiency of the

168

emulsion was shown in Figure 1.

8

ACS Paragon Plus Environment

Page 9 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

169 170

Figure 1. Stability of crude oil emulsion with various DMCHA concentration.

171

It can be seen from Figure 1 that the stability of the emulsions was closely

172

related to the concentration of DMCHA. It is clear see that the stability of the

173

emulsions D and E was better than A, B, and C. The higher the surfactant

174

concentration will not only contribute to the rapid formation of the emulsion but also

175

help to improve the stability of the emulsion. The curves D and E in Figure 1 were

176

very close, indicating that the concentration of DMCHA can only affect the stability

177

of the emulsions within a certain range and not at all of the concentration range.

178

3.2 CO2 as a demulsifier for low crude oil content emulsions

179

Before refinery, it is necessary to separate the crude oil from the crude oil

180

emulsions at the end of the pipeline transportation. Whether the emulsion can quickly

181

and thoroughly demulsify is an important factor affecting the transport efficiency of

182

crude oil pipelines. At room temperature, CO2 was bubbled into the five emulsions at

183

a rate of 100 mL·min-1 for 10 min, then the demulsification process was observed for 9

ACS Paragon Plus Environment

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

184

standing and the volume of the aqueous phase was recorded. Figure 2 shows

185

photographs of emulsions A, B, C, D and E after 10 min of CO2 treatment.

186 187

Figure 2. Demulsification of emulsions A, B, C, D and E with CO2 treatment.

188

It can be seen clearly from Figure 2 that emulsions A, B, C, D, and E have been

189

demulsified after treatment with CO2, but the final state after demulsification was

190

obviously different. Emulsions D and E have almost completely separated the crude

191

oil and water, and demulsification efficiency was over 90% (Table 3) in the case of

192

CO2 for ten minutes. Emulsion C also has an obvious two-phase separation, but the

193

separation efficiency of the emulsion was significantly lower than that of the emulsion

194

D and E at the same time, and the lower phase of the emulsion C was more turbid.

195

The emulsions A and B have the lowest demulsification efficiency under the same

196

conditions.

10

ACS Paragon Plus Environment

Page 10 of 25

Page 11 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

197 198 199

Scheme 1. A schematic diagram of the chemical principle based on the DMCHA and naphthenic acid (RCOOH).

200

As depicted in Scheme 1, DMCHA can be self-assembled with naphthenic acid

201

in crude oil to form surfactants. This process was an emulsification process where

202

crude oil emulsions can be prepared. As the acidity of carbonic acid is stronger than

203

naphthenic acid, in the presence of CO2, the assembled surfactant was destroyed and

204

the emulsion was demulsified. Naphthenic acid was dissolved in the oil phase and the

205

aqueous phase was ammonium bicarbonate solution. At the same time, DMCHA can

206

be recovered by treating the lower aqueous phase with N2, which can greatly reduce

207

the cost of consumption. It can be seen from Figure 2 that the concentration of

208

DMCHA has an effect not only on the formation of the emulsion but also the

209

demulsification process. At the moment, when CO2 was bubbled into the emulsion A

210

and B, a portion of the crude oil in the emulsions A and B accumulates in the upper

211

layer first. With the continuous entry to CO2, the crude oil and water were mixed and

212

cannot be effectively separated. This may be caused by incomplete emulsification due

213

to the low concentration of the surfactant. The demulsification process of the

214

emulsions D and E was different from those of the emulsions A and B, the O/W

215

droplets of emulsions D and E gradually disintegrate with the CO2 continuous bubbles. 11

ACS Paragon Plus Environment

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

Page 12 of 25

216

The crude oil was separated from the emulsion in the form of small droplets and

217

finally gathered in the upper layer, so the separation effect was more obvious.

218 219

220

Table 3. The demulsification efficiency of emulsions A, B, C, D and E after CO2 treatment. Entry

A

B

C

D

E

V1/mL

-

-

-

40.5

41.0

V/ mL

40.2

40.6

41.2

41.7

42.3

S/%

-

-

-

97.12

96.93

3.3 Organic acids as demulsifier for high crude oil content emulsions

221

For crude oil emulsions with low oil content, CO2 can be used as an efficient

222

demulsifier for effective separation of crude oil and water from emulsions. However,

223

the oil content of the emulsions was much higher than the oil content in section 3.1 in

224

practice. So what about the formation and demulsification process for high oil content

225

emulsions?

226

Crude oil emulsion (7g crude oil + 3g H2O + 2g DMCHA,) can be formed and

227

can last more than a week without breaking. The oil content of this emulsion is

228

58.33%. The type of the emulsion was O/W determined by the drop test. The effects

229

of CO2 and organic acids on the demulsification performance of emulsions were

230

investigated. Figure 3 shows the results of the demulsification of crude oil emulsions

231

with CO2 and organic acids as demulsifiers.

12

ACS Paragon Plus Environment

Page 13 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

232 233 234 235 236 237 238

Figure 3. The picture of crude oil emulsions was standing for 24h after the demulsification. (a) Crude oil-in-water emulsion, (b) The emulsion was treated with CO2 for 10 min at a rate of 100 mL·min-1. Organic acids are used as demulsifiers to treat crude oil-in-water emulsions, (c) Citric acid solution 10 mL (5wt%), (d) Oxalic acid solution 10 mL (5wt%), (e) Acetic acid solution 10 mL (5wt%), (f) Lactic acid solution 10 mL (5wt%).

239

As showed in Figure 3, the phase separation of the crude oil emulsion was very

240

clear in the presence of CO2 and organic acids. Naphthenic acid is a mixture of weak

241

acids. It will become an uncharged molecular state in the presence of strong acids, and

242

then the electrostatic interaction between DMCHA was disappeared. Based on this

243

principle, strong acid, such as carbonic acid, citric acid, oxalic acid, acetic acid, and

244

lactic acid can play the role of demulsifier. However, citric acid and acetic acid have

245

the highest demulsification efficiency and the lowest demulsification efficiency of

246

CO2 at the same time (Figure 4).

13

ACS Paragon Plus Environment

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

Page 14 of 25

247 248 249

Figure 4. Demulsification efficiency of crude oil emulsion under different demulsifiers.

250

It is well known that weak acids correspond to larger pka values. Table 4 lists the

251

pka values for all acids32. The organic acids mentioned in this article have stronger

252

acidity than carbonic acid, which means higher demulsification efficiency than CO2.

253

At the same time, three pka values of citric acid were 3.13, 4.76, and 6.40 (Table 4),

254

respectively. These three values are less than or close to the carbonic acid pka1, which

255

means that citric acid has more carboxyl groups can participate in the reaction,

256

demulsification efficiency higher than other acids. This is why citric acid and oxalic

257

acid have the highest efficiency of demulsification.

258

Table 4. Dissociation constants of different acids (298k). Entry

pKa1

pKa2

pKa3

Carbonic acid

6.35

10.33

-

Citric acid

3.13

4.76

6.40

14

ACS Paragon Plus Environment

Page 15 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

Oxalic acid

1.25

4.27

-

Acetic acid

4.76

-

-

Lactic acid

3.86

-

-

259

The above experiment mentions that CO2 can be used as a demulsifier for crude

260

oil-water separation. In practice, the efficiency of CO2 as a gas participating in the

261

reaction is limited, and some of the CO2 is not directly involved in the reaction but is

262

released directly into the air. At the CO2 access time increases, the separated crude oil

263

will cover the surface in the first time, which increases the CO2 gas release pressure.

264

It may cause the demulsification operation cannot proceed smoothly. Organic acids do

265

not have these problems as demulsifiers and citric acid can be used as an excellent

266

demulsifier. Citric acid is a kind of material that is inexpensive, non-irritating odor,

267

non-toxic, environmentally friendly and present in the solid state at room temperature.

268

The tricarboxylic structure of citric acid gives it a higher demulsification efficiency

269

than CO2 (Scheme 2).

270 15

ACS Paragon Plus Environment

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

271 272 273

Scheme 2. Schematic diagram of the demulsification efficiency of citric acid and CO2 as demulsifier Table 5. Composition of crude oil-in-water emulsion Emulsions Crude oil/g Water/mL DMCHA/mL Oil content/wt% (a) 10 3 3.5 62.50 (b) 12 3 3.5 66.67 (c) 14 3 3.5 70.00 (d) 16 3 3.5 72.73 (e) 18 3 3.5 75.00

274

In order to study the effect of citric acid on the demulsification efficiency of high

275

oil content emulsions, five crude oil emulsions were prepared with different oil

276

content in Table 5. The stability and viscosity reduction of crude oil-in-water

277

emulsions in Table 5 were showed in supporting information (Fig.S2, Fig.S3, and

278

Tab.S1).Citric acid solution (20 mL, 11.63wt %) was added to the five stable

279

emulsions. The demulsification was carried out after thorough mixing, and then the

280

volume change of the oil phase and the water phase was observed and recorded. After

281

demulsification for 24 hours, the photographs of the five emulsions were shown in

282

Figure 5.

283 284 285

Figure 5. The picture of demulsification after 24h with 11.63 wt% citric acid solution (20mL) as a demulsifier. The composition of emulsions was shown in Table 5.

16

ACS Paragon Plus Environment

Page 16 of 25

Page 17 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

286 287 288

Figure 6. Effect of concentration of demulsifier (citric acid) on separation efficiency of crude oil.

289

It can be seen from Figure 5 that citric acid has a very good demulsification

290

performance for crude oil emulsions. Figure 6 shows the effect of different

291

concentrations of the citric acid solution on demulsification efficiency. When the

292

concentration of citric acid increased from 11.63wt% to 17.39wt%, the

293

demulsification rate has been significantly improved. The crude oil and water were

294

almost completely separated in the Emulsion (a). Obviously, the higher the crude oil

295

content of the emulsion requires a higher concentration of citric acid to achieve

296

complete demulsification. Crude oil content of 70wt% in Emulsion (c),

297

demulsification efficiency up to 91.19%. This provides a viable option for the

298

separation of crude oil at the end of pipeline transportation.

17

ACS Paragon Plus Environment

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

299

3.4 Analysis of DMCHA recovery mechanism

300

DMCHA plays a vital role in emulsifying and demulsifying processes. It is

301

highly necessary to recycle and reuse of the DMCHA. DMCHA has a pka value of

302

10.5033, which is capable of switching between ionic and molecular states at different

303

pH conditions as shown in Figure 7.

304 305 306

Figure 7. Molecule state distribution of DMCHA in aqueous solution with different pH value.

307

It can be clearly seen from Figure 7 that when pH < 9, DMCHA is a mainly

308

hydrophilic cationic state, pH > 12 is a mainly hydrophobic molecular state, 9 < pH

309

9,

323

the DMCHA gradually separated from the solution at this time the solution appears to

324

be turbid. When pH=10.50, there was divided into two layers, the upper layer was

325

DMCHA and the recovery rate of DMCHA was about 50%. When pH=11.94, the

326

recovery rate of DMCHA was close to 100%. For ease of observation, the upper layer 19

ACS Paragon Plus Environment

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

327

of DMCHA was stained with the Nile red in Figure 8. The 1H NMR spectrum of the

328

upper layer was found to be the same as that of DMCHA, indicating that DMCHA can

329

be recovered from the solution (ESI, Figure S1). In short, it is possible to recover the

330

DMCHA by adjusting the pH of the lower layer aqueous solution with the NaOH

331

solution.

332

3.5 Recycling of DMCHA from high oil content emulsions

333

The lower layer of the crude oil emulsion is an ammonium citrate aqueous

334

solution in Figure 5. DMCHA can be regenerated by adding NaOH to the aqueous

335

solution. Figure 9 shows the recovery of DMCHA from emulsion (a). When NaOH

336

was added, the solution is immediately divided into two layers, the upper layer was

337

the recovered DMCHA, and the lower layer was the ammonium citrate solution and

338

the excess NaOH.

339 340

Figure 9. The photograph of DMCHA recovered from emulsion (a).

341

The pH of the lower aqueous solution in Figure 9 was 12.26, and almost all of

342

the DMCHA can be recovered in this strongly alkaline environment (Figure 7). 20

ACS Paragon Plus Environment

Page 20 of 25

Page 21 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

343

Finally, the recovery rate of DMCHA was obtained by calculating the ratio of the

344

volume of recovered DMCHA to the total volume of DMCHA added (Figure 10). The

345

highest recovery rate of DMCHA in the five emulsions was 85.71% for Emulsion (a).

346

With the increase of crude oil content, the recovery rate of DMCHA gradually

347

decreased (Figure 10). This is associated with the demulsification rate of the emulsion.

348

The higher the demulsification rate, the higher the recovery rate of DMCHA.

349

However, the lowest recovery rate of DMCHA in the five emulsions was more than

350

70%.

351 352 353

Figure 10. The recovery of DMCHA in five emulsions after demulsification.

4. CONCLUSION

354

DMCHA can emulsify crude oil to form crude oil-in-water emulsion and the

355

stability of the emulsion is closely related to the concentration of DMCHA which is

356

critical to the stability of crude oil emulsions. It is relatively easy to achieve efficient 21

ACS Paragon Plus Environment

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

357

separation of crude oil and water in emulsions with low oil content using CO2 as a

358

demulsifier. However, the demulsification efficiency of CO2 decreased significantly

359

when the oil content was 58.33%. The advantages of organic acids as demulsifiers are

360

obvious, especially citric acid. When the oil content of 70%, the use of concentration

361

of 17.39% citric acid solution as a demulsifier can make the demulsification

362

efficiency of more than 90%. As an important role in the formation of a crude oil

363

emulsion, DMCHA recovery and reuse are very necessary. In this article, the

364

regeneration of DMCHA can be achieved by adding NaOH to the lower aqueous

365

solution after demulsification. The recovery rate of DMCHA can be greater than 80%

366

when the oil content of 70% in the crude oil emulsion after breaking. Through the

367

emulsification and efficient demulsification of crude oil, we provide a viable solution

368

for crude oil pipeline transportation. At the beginning of transport, the crude

369

oil-in-water emulsions can be formed by DMCHA. Organic acids, especially citric

370

acid, have excellent demulsification efficiency for high crude oil content emulsions at

371

the end of pipeline transportation. Finally, the DMCHA can be recovered by NaOH.

372

ASSOCIATED CONTENT

373

Supporting Information

374

The following contents can be found in the supporting information: (a) The

375

1

376

crude oil emulsions without demulsifier.

377

AUTHOR INFORMATION

378

Corresponding author

HNMR spectrum analysis of DMCHA. (b) The stability and viscosity reduction of

22

ACS Paragon Plus Environment

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

379

*Email: [email protected]; Fax: +86-28-83037330; Tel: +86-28-83037330.

380

ORCID

381

Hongsheng Lu: 0000-0003-3201-0855

382

Notes

383

The authors declare no competing financial interest.

384

ACKNOWLEDGEMENTS

385

This work was done with the support of the National Natural Science Foundation of

386

China (NSFC, NO. 21403173), and we would like to express our heartfelt thanks.

387

REFERENCES

388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413

1.

2. 3. 4.

5.

6.

7.

8.

9.

Taborda, E. A.; Franco, C. A.; Ruiz, M. A.; Alvarado, V.; Cortes, F. B., Experimental and Theoretical Study of Viscosity Reduction in Heavy Crude Oils by Addition of Nanoparticles. Energy & Fuels 2017, 31, (2), 1329-1338. Al-Besharah, J. M.; Salman, O. A.; Akashah, S. A., Viscosity of crude oil blends. Industrial & engineering chemistry research 1987, 26, (12), 2445-2449. Argillier, J. F.; Henaut, I.; gateau, p.; Heraud, J.-P.; Glenat, P., Heavy Oil Dilution. In Society of Petroleum Engineers. Martinez-Palou, R.; Mosqueira, M. d. L.; Zapata-Rendon, B.; Mar-Juarez, E.; Bernal-Huicochea, C.; Clavel-Lopez, J. d. l. C.; Aburto, J., Transportation of heavy and extra-heavy crude oil by pipeline: A review. Journal of Petroleum Science and Engineering 2011, 75, (3-4), 274-282. Tao, J.; Shi, P.; Fang, S.; Li, K.; Duan, M.; Liu, P., Effect of acidic returned fluid on the electric demulsification of crude oil emulsions. RSC Advances 2015, 5, (31), 24591-24598. Lu, H.; Guan, X.; Wang, B.; Huang, Z., CO2-Switchable Oil/Water Emulsion for Pipeline Transport of Heavy Oil. Journal of Surfactants and Detergents 2015, 18, (5), 773-782. Lu, H.; Shi, Q.; Huang, Z., pH-Responsive Anionic Wormlike Micelle Based on Sodium Oleate Induced by NaCl. The Journal of Physical Chemistry B 2014, 118, (43), 12511-12517. Lu, H.; Zheng, C.; Xue, M.; Huang, Z., pH-regulated surface properties and pH-reversible micelle transition of a zwitterionic gemini surfactant in aqueous solution. Phys Chem Chem Phys 2016, 18, (47), 32192-32197. Lu, H.; He, Y.; Huang, Z., Foaming Properties of CO2-Triggered Surfactants for Switchable Foam Control. Journal of Dispersion Science and Technology 2014, 35, (6), 832-839. 23

ACS Paragon Plus Environment

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

414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457

10. Chu, Z.; Feng, Y., pH-switchable wormlike micelles. Chem Commun (Camb) 2010, 46, (47), 9028-9030. 11. Ren, G.; Wang, L.; Chen, Q.; Xu, Z.; Xu, J.; Sun, D., pH Switchable Emulsions Based on Dynamic Covalent Surfactants. Langmuir 2017, 33, (12), 3040-3046. 12. Han, D.; Boissiere, O.; Kumar, S.; Tong, X.; Tremblay, L.; Zhao, Y., Two-Way CO2-Switchable Triblock Copolymer Hydrogels. Macromolecules 2012, 45, (18), 7440-7445. 13. Liu, P.; Lu, W.; Wang, W.-J.; Li, B.-G.; Zhu, S., Highly CO2/N-2-Switchable Zwitterionic Surfactant for Pickering Emulsions at Ambient Temperature. Langmuir 2014, 30, (34), 10248-10255. 14. Levskaya, A.; Weiner, O. D.; Lim, W. A.; Voigt, C. A., Spatiotemporal control of cell signalling using a light-switchable protein interaction. Nature 2009, 461, (7266), 997-1001. 15. Eastoe, J.; Sanchez Dominguez, M.; Cumber, H.; Wyatt, P.; Heenan, R. K., Light-sensitive microemulsions. Langmuir 2004, 20, (4), 1120-1125. 16. Yoshimatsu, K.; Lesel, B. K.; Yonamine, Y.; Beierle, J. M.; Hoshino, Y.; Shea, K. J., Temperature-Responsive "Catch and Release" of Proteins by using Multifunctional Polymer-Based Nanoparticles. Angewandte Chemie-International Edition 2012, 51, (10), 2405-2408. 17. Ranka, M.; Katepalli, H.; Blankschtein, D.; Hatton, T. A., Schizophrenic Diblock-Copolymer-Functionalized Nanoparticles as Temperature-Responsive Pickering Emulsifiers. Langmuir 2017, 33, (46), 13326-13331. 18. Klee, A.; Prevost, S.; Kunz, W.; Schweins, R.; Kiefer, K.; Gradzielski, M., Magnetic microemulsions based on magnetic ionic liquids. Physical Chemistry Chemical Physics 2012, 14, (44), 15355-15360. 19. Brown, P.; Butts, C. P.; Eastoe, J.; Glatzel, S.; Grillo, I.; Hall, S. H.; Rogers, S.; Trickett, K., Microemulsions as tunable nanomagnets. Soft Matter 2012, 8, (46), 11609-11612. 20. Zhou, Y.; Jie, K.; Huang, F., A redox-responsive supramolecular amphiphile fabricated by selenium-containing pillar 5 arene-based host-guest recognition. Organic Chemistry Frontiers 2017, 4, (12), 2387-2391. 21. Zhang, R.; Li, X.; He, K.; Sheng, X.; Deng, S.; Shen, Y.; Chang, G.; Ye, X., Preparation and properties of redox responsive modified hyaluronic acid hydrogels for drug release. Polymers for Advanced Technologies 2017, 28, (12), 1759-1763. 22. Darabi, A.; Jessop, P. G.; Cunningham, M. F., CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications. Chemical Society Reviews 2016, 45, (15), 4391-4436. 23. Jiang, J. Z.; Wang, G. Z.; Ma, Y. X.; Cui, Z. G.; Binks, B. P., Smart worm-like micelles responsive to CO2/N-2 and light dual stimuli. Soft Matter 2017, 13, (15), 2727-2732. 24. Zhang, Y.; Feng, Y.; Wang, Y.; Li, X., CO2-switchable viscoelastic fluids based on a pseudogemini surfactant. Langmuir 2013, 29, (13), 4187-92. 25. Liu, D.; Suo, Y.; Tan, J.; Lu, H., CO2-Switchable microemulsion based on a 24

ACS Paragon Plus Environment

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

458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481

26.

27.

28.

29. 30.

31. 32. 33.

pseudogemini surfactant. Soft Matter 2017, 13, (20), 3783-3788. Liu, P.; Lu, W.; Wang, W.-J.; Li, B.-G.; Zhu, S., Highly CO2/N2-switchable zwitterionic surfactant for Pickering emulsions at ambient temperature. Langmuir 2014, 30, (34), 10248-10255. Yan, B.; Han, D.; Boissière, O.; Ayotte, P.; Zhao, Y., Manipulation of block copolymer vesicles using CO 2: dissociation or “breathing”. Soft Matter 2013, 9, (6), 2011-2016. Liu, H.; Guo, Z.; He, S.; Yin, H.; Fei, C.; Feng, Y., CO 2-driven vesicle to micelle regulation of amphiphilic copolymer: random versus block strategy. Polymer Chemistry 2014, 5, (16), 4756-4763. Liu, Y.; Jessop, P. G.; Cunningham, M.; Eckert, C. A.; Liotta, C. L., Switchable Surfactants. Science 2006, 313, (5789), 958-960. Juan, S. L.; Xian, S. B., Separation and Characterization of Naphthenic Acids Contained in Penglai Crude Oil. Petroleum Science and Technology 2009, 27, (14), 1534-1544. Pilehvari, A.; Saadevandi, B.; Halvaci, M.; Clark, P. E., Oil/Water Emulsions for Pipeline Transport of Viscous Crude Oils. In Society of Petroleum Engineers. Featherstone, J.; Lussi, A., Understanding the chemistry of dental erosion. In Dental erosion, Karger Publishers: 2006; Vol. 20, pp 66-76. Lindegård, B.; Jönsson, J. Å.; Mathiasson, L., Liquid membrane work-up of blood plasma samples applied to gas chromatographic determination of aliphatic amines. Journal of Chromatography B: Biomedical Sciences and Applications 1992, 573, (2), 191-200.

25

ACS Paragon Plus Environment