Synthesis and physiochemical performance evaluation of novel sulphobetaine zwitterionic surfactants from lignin for enhanced oil recovery

Journal of Molecular Liquids 249 (2018) 73–82

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Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq

Synthesis and physiochemical performance evaluation of novel sulphobetaine zwitterionic surfactants from lignin for enhanced oil recovery Shuyan Chen a, Hongjuan Liu a, Hong Sun b, Xiang Yan a, Gehua Wang a, Yujie Zhou a,⁎, Jianan Zhang a,⁎ a b

Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China

a r t i c l e

i n f o

Article history: Received 25 September 2017 Received in revised form 2 November 2017 Accepted 2 November 2017 Available online 06 November 2017 Keywords: Zwitterionic surfactant Surface tension Interfacial tension Synthesis Alkali lignin Enhanced oil recovery

a b s t r a c t Lignin sulphobetaine zwitterionic surfactants (LSBA) were successfully synthesized by a cost-effective three-step route containing sulfonation, quaternization and alkylation reaction from renewable alkali lignin. The synthesized surfactants were characterized by FT-IR, UV and 1H NMR analysis. The physicochemical properties of synthesized surfactants had been tested to investigate the effectiveness of LSBA surfactants for enhanced oil recovery (EOR). The hydrophile lipophile balance (HLB) values of LSBA-1, LSBA-2 and LSBA-3 were 14, 11 and 10, respectively. LSBA surfactants exhibited high surface activity with low surface tension and the critical micelle concentration (cmc) of LSBA-1, LSBA-2 and LSBA-3 were 4.36 × 10−4 mg/L, 4.45 × 10−4 mg/L and 1.04 × 10−3 mg/L, respectively. The dynamic interfacial tension (IFT) between the crude oil from Huabei and Xinjiang oilfields (China) and the LSBA solution was measured. Compared with Huabei crude oil, LSBA surfactants showed better interfacial activity on Xinjiang crude oil. LSBA surfactants reduced the IFT between Xinjiang crude oil and brine down to ultra-low (b10−3 mN/m) under weak alkaline conditions. © 2017 Elsevier B.V. All rights reserved.

1. Introduction In recent years, more and more attention has been paid to surfactant flooding recovery, which is one of the promising chemical methods for enhanced oil recovery (EOR) [1–3]. Surfactants can not only decrease the oil/water interfacial tension (IFT) but also improve the capillary number, making the residual oil trapped in reservoir flow, thus the efficiency of oil recovery can be improved greatly [4–6]. At the present stage there are a lot of serious problems in surfactant flooding, such as adsorption loss, large dosage and high cost, which obviously limit the wide application of surfactants in EOR [7]. Therefore, the research and development of high efficiency and low-cost oil-displacing surfactants has become one of the major challenges for the scientific workers. The production of eco-friendly green surfactants which make full use of natural renewable resources and the green chemical synthesis technology are the hotspot and primary development direction for the current oil-displacing surfactants [8,9]. As the second abundant renewable resource in the nature, lignin is a kind of biopolymer composed by benzene propane monomer on earth after cellulose [10–12], which is expected to play an important role in ⁎ Corresponding authors. E-mail addresses: [email protected] (Y. Zhou), [email protected] (J. Zhang).

https://doi.org/10.1016/j.molliq.2017.11.021 0167-7322/© 2017 Elsevier B.V. All rights reserved.

the near future as a raw material for the production of bio-products. Most industrial lignins are produced as a by-product during the paper pulping process with a large volume of approximate 50 million tons each year [13]. And the majority of them are burnt or drained directly into rivers and lakes as waste, which not only cause the waste of resources but also seriously pollute the environment [14,15]. In addition, the molecular structure of lignin on the benzene ring and the side chains contains a number of different functional groups, such as methoxyl group (–OCH3), hydroxyl (–OH), carbonyl group (–CO–), alkyl and so on, which can be modified through a variety of chemical reactions [16–18]. The water solubility and interfacial activity of lignin will be affected by the introduction of the hydrophilic and lipophilic groups [19, 20]. Therefore, the surfactants synthesized from the biodegradable and low-cost lignin will be one of the most promising applications in EOR. Lignosulfonate is the first surface active component applied in surfactant flooding, but the industrial lignosulfonate has strong hydrophilic groups without long-chain of lipophilic group, which leads to the inhibition of interfacial activity of lignosulfonate [21]. Therefore, the lignosulfonate cannot decrease the IFT to ultralow level (b 10− 3 mN/m) between oil and water when used alone, it usually need to be compounded with other main surfactants to form oil-displacing surfactants with better interfacial performance [22,23]. In order to improve the interfacial performance of the surfactants synthesized from lignin,

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a wide range of synthesis techniques such as sulfonated, alkylation, oxidation, amination and carbonylation have been developed to alter the molecular structure of alkali lignin [24–28]. However, most of these methods can only improve the oil-soluble of lignin surfactants and the existing lignin surfactants are in general relatively hydrophilic, the modified lignin surfactants used alone still cannot decrease the IFT of oil-water to ultralow level. Moreover, multiple steps, the high modification cost and special equipments are also needed in these techniques. In the last decade zwitterionic surfactants have attracted the attention of researchers for their adaptability in EOR [29–31]. The superior properties of zwitterionic surfactants, such as good biodegradability, salt resistance, high temperature resistance, good water solubility and enough lipophilicity and good synergistic effect with some nonionic and anionic surfactants, which enable them to be effective on increasing the oil recovery efficiency [32–34]. At present, there are many different zwitterionic surfactants synthesized and the demand for this kind of surfactant is increasing each year. However, the relatively high cost of zwitterionic surfactants limits their large-scale application in EOR compared to other types of surfactants. At present, the synthesis and performance research of zwitterionic surfactants are the focus of attention for researchers, and little attention has been paid to study and synthesis of zwitterionic surfactants from low-cost and renewable lignin. Sulphobetaine and their derivatives are a class of zwitterionic surfactants containing quaternary ammonium cation and sulfonic acid anion, with excellent stability under acidic and alkaline conditions. In the present work, a new cost-efficient and high performance zwitterionic surfactants from alkali lignin as raw materials were successfully synthesized by an economic pathway, in which a three-step procedure was involved. First, the alkali lignin was selectively oxidized and sulfonated with hydrogen peroxide and sodium sulfite to obtain the product lignosulfonate. Second, (2, 3-epoxypropyl) alkyl dimethyl ammonium chloride (ADAC) was prepared by the reaction of long alkylchain dimethyl tertiary amine and epichlorohydrin. Last, this intermediate ADAC was subsequently reacted with phenolic hydroxyl groups of lignosulfonate to synthesize lignin sulphobetaine zwitterionic surfactant (LSBA). Thus, both long alkylchain and amine functional groups were introduced into the lignin molecules to improve the surface activity and solubility of lignin surfactants. The structures of target products LSBA were analyzed by FI-IR, UV and 1H NMR. The hydrophile lipophile balance (HLB) experiments for LSBA surfactants were examined. The surface active and interfacial behavior of LSBA surfactants were also evaluated by surface tension and interfacial tension measurements, respectively. 2. Experimental procedures 2.1. Materials Alkali lignin was provided by Shandong paper mills of China. Hydrogen peroxide (30 wt%), sodium sulfite, epichlorohydrin, sodium hydroxide, sulfuric acid, hydrochloric acid, sodium carbonate, isopropanol and acetone were purchased from Sinopharm Chemical Reagent Co., Ltd., Beijing, China. Decyldimethyl tert-amine, dodecyldimethyl tert-amine, tetradecyldimethyl tert-amine, p-hydroxybenzoic acid, N, Ndimethylformamide and tetra-n-butylammonium hydroxide were purchased from Sigma Chemicals. All the chemicals were analytical pure grade. Partially hydrolysed polyacrylamide (HPAM, Mw = 1800 × 104) was given from Beijing Hengju Chemical Group Co., Ltd., China. Two kinds of dewatered and degassed crude oil were provided by Xinjiang and Huabei oilfields, China. The density of crude oil from Xinjiang and Huabei oilfields was 0.85 g/cm3 and 0.78 g/cm3, respectively. The ionic composition of simulated brine from different oilfields was shown in Table 1.

Table 1 Composition of simulated brine from Huabei and Xinjiang oilfields, China. Oilfield

Ca2+ (mg/L)

Mg2+ (mg/L)

Na+ (mg/L)

K+ (mg/L)

Cl− (mg/L)

SO2− 4 (mg/L)

CO2− 3 (mg/L)

HCO− 3 (mg/L)

Huabei Xinjiang

53.6 56.9

22.0 13.4

3900.7 2085.0

32.2 –

4737.5 2577.0

117.5 131.6

– 5.8

1925.9 1156.9

2.2. Methods 2.2.1. Synthesis of oxidized sulfonated lignin The quantitative lignin (40 g) dissolved with 300 mL deionized water was added into a three-necked round-bottom flask equipped with a stirrer. After the pH of solution being adjusted to 12 with sodium hydroxide solution, 6 g hydrogen peroxide was added into the flask at 70 °C for 1 h with stirring. Then the sodium sulfite (8 g) was added into the reactor and the reaction continued for 1 h at 180 °C. After the reaction, the pH of resulting mixture was adjusted to 2 with dilute sulfuric acid and the precipitation was separated by centrifuge. Thus, a brown power of oxidized sulfonated lignin was obtained after drying in a vacuum oven. 2.2.2. Synthesis of (2, 3-epoxypropyl) alkyl dimethyl ammonium chloride The epichlorohydrin (9.25 g) and hydrochloric acid (4.38 g) were added into a three-necked round-bottom flask and agitated at 25 °C for 30 min, then decyldimethyl tert-amine (18.54 g) was added dropwise in 20 min after the reaction temperature was went up to 40 °C. After that, the pH of the mixed solution was adjusted to 9 with sodium hydroxide solution and the reaction continued for 2 h at 50 °C. Thus the intermediate (2, 3-epoxypropyl) decyldimethyl ammonium chloride (ADAC-1) was obtained after cooling to room temperature. By varying the carbon chain length of tertiary amine, the intermediates ADAC-2 and ADAC-3 were synthesized according to the above synthetic pathway using the dodecyldimethyl tert-amine and the tetradecyldimethyl tert-amine, respectively. 2.2.3. Synthesis of lignin sulphobetaine zwitterionic surfactant In a 500 mL round-bottom flask, 25.4 g oxidized sulfonated lignin which was dissolved in 200 mL acetone was added and the temperature of the mixture was raised to 40 °C gradually. Then the pH of solution was adjusted to 12 by adding sodium hydroxide and insulation for 30 min in order to fully dissolve the oxidized sulfonated lignin in acetone. After that, the intermediate ADAC-1 (30.81 g) was added dropwise into the flask with stirring after the reaction temperature increased up to 50 °C and the reaction was carried out for 2.5 h at 50 °C. After removing the solvents by rotary evaporator under reduced pressure, the 200 mL isopropanol was added into the mixture and refluxed at 70 °C for 3 h to filter off inorganic salts. Then the mixture was neutralized by distilled water and dried in a vacuum oven at 60 °C for 20 h, a light brown solid powder of lignin sulphobetaine zwitterionic surfactant (LSBA-1) was obtained. The products LSBA-2 and LSBA-3 were synthesized according to the above synthetic method using the intermediates ADAC-2 and ADAC-3, respectively. 2.2.4. Chemical analysis Fourier transform infrared spectroscopy (FT-IR) (Thermo 6700, USA) was employed to characterize the structures of alkali lignin and synthesized LSBA surfactant by potassium bromide (KBr) pellet method in the range of 500 cm−1 to 4000 cm−1 with a resolution of 4 cm−1. Ultraviolet spectrum (UV) measurements were performed in a Lambda UV–Visible Spectrometer (Perkin-Elmer co., America). Element analyses of alkali lignin and LSBA surfactant were carried out on the Vario ELL III type element analyzer (Elementar Co., Germany). Nuclear magnetic resonance (NMR) spectroscopy was used to obtain the 1H NMR spectra of

S. Chen et al. / Journal of Molecular Liquids 249 (2018) 73–82

100

point, mL; a is the theoretical titer of p-hydroxybenzoic acid in the sample, mL; c is the concentration of the titrant, mol/L; m is the quality of sample, mg.

60

3430 cm

-1

1462 cm

2.2.6. Surface tension measurement Surface tension of the samples was determined by a dynamic surface tensiometer QBZY-2 (CANY, China) at 25 ± 0.1 °C with the Wilhelmy plate method. Before testing, aging time of 30 min was necessary for each sample so that the liquid surfaces reach an equilibrium state. Three measurements were performed for each sample and the average value of equilibrium was recorded.

-1

40

20 2850 cm

-1

1610 cm

3500

3000

2500

2000

-1

1500

1000

500

-1

wavenumber (cm )

(a) 100 910 cm

Transmittance (%)

80

60

1210 cm

3430 cm

-1

721 cm 2926 cm

3500

2.2.8. IFT measurements The dynamic IFT between synthesized LSBA surfactants in brine and crude oil was conducted on the SVT20N spinning drop IFT apparatus (Eastern-Dataphy, China) with the spinning drop technique. Crude oil was from Huabei and Xinjiang oilfields of China and the measurements were taken under the reservoirs temperature of Huabei and Xinjiang oilfields, 54 °C and 28.7 °C, respectively. Each measurement lasted for 1 h until the equilibrium value of IFT was obtained.

-1

40

20 4000

-1

-1

3000

2850 cm

-1

2500

1610 cm

2000

-1

1462 cm

1500

-1

-1

1000

2.2.7. HLB measurements The HLB values of LSBA surfactants were measured using a 100 mL cylinder with stopper by the emulsification method. First, the cottonseed oil (HLB = 6) and turpentine (HLB = 16) were used to prepare a series of standard oil samples, in which the HLB values were 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16, respectively. Then 25 mL standard oil samples with different HLB value and 25 mL LSBA (0.4 wt%) solution were added into the cylinder. After that, the cylinder was shaken drastically and laid aside until the two phases were separated. The separation time of oil and water was recorded, and the HLB of tested sample was in keeping with the HLB value of standard oil owned the best emulsifying effect.

500 3. Results and discussion

-1

wavenumber (cm )

(b)

3.1. FT-IR analysis

Fig. 1. FT-IR spectra of alkali lignin (a) and the synthesized surfactant LSBA (b).

alkali lignin and synthesized surfactant LSBA using deuterated dimethyl sulfoxide (DMSO-d6) as solvent with the AVANCE III spectrometer (500 MHz) (Bruker, France). 2.2.5. Phenolic hydroxyl content determination The non-aqueous potentiometric titration method [35] was used to measure the content of phenolic hydroxyl groups in raw materials and the synthesized surfactants. A DDS-11A conductivity tester (Rex, China) equipped with platinum black electrode was employed for these experiments. First, 350 mg sample and 50 mg p-hydroxybenzoic acid were added to a 100 mL four-neck flat-bottom flask, then 2 mL distilled water, 0.2 mL hydrochloric acid and 60 mL N, N-dimethylformamide solvent were added sequentially into the flask with stirring for 5 min at 25 °C in nitrogen atmosphere. After that, the sample was titrated with tetran-butylammonium hydroxide standard solution (0.05 mol/L). At the same time the conductivity curve was recorded until two isoelectric points appeared. According to the conductivity-titrant dosage curve, the isoelectric points were determined by tangent extension method. The phenolic hydroxyl content was calculated as follows:

The FT-IR spectra of alkali lignin and synthesized surfactant LSBA were depicted in Fig. 1. IR spectrum was made up of the adsorption peak which was consistent with the functional group of the sample. And the peaks contributed to acknowledgement for the synthesis of the product after reaction. Compared with alkali lignin (Fig. 1(a)), the

0.7

255 nm

0.6

LSBA Alkali lignin

300 nm

0.5 Absorbance

Transmittance (%)

80

0 4000

75

0.4 0.3 0.2




½OH  ¼

Vz −Vy −a  c m

ð1Þ

220

240

260

280

300

320

340

360

380

Wavelength (nm) where, Vz is the dosage of titrant corresponding to the second isoelectric point, mL; Vy is the dosage of titrant corresponding to the first isoelectric

Fig. 2. UV spectra of alkali lignin and the synthesized surfactant LSBA.

400

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S. Chen et al. / Journal of Molecular Liquids 249 (2018) 73–82

absorption band of O\\H in LSBA surfactant at 3430 cm−1 was weakened due to the phenolic hydroxyl in the feedstock being involved in the alkylation reaction (Fig. 1(b)). The peaks at 2926 cm− 1 and 2850 cm−1 indicated the presence of C\\H stretching vibration in \\CH2\\ and\\CH3 groups, the absorption band at these regions was broadened because of the introduction of long alkylchain amine. The strong and wide absorption peaks at 1610 cm−1 and 1462 cm− 1 revealed the presence of benzene ring in LSBA. The C\\N stretching vibration absorption seen at 1459 cm−1 in which the peaks were overlapped with the peaks of benzene ring, the bending vibration absorption peak and small absorption peak for C\\N appeared at 721 cm− 1 and 1000 cm−1 to 910 cm− 1, respectively. These peaks were consistent with the characteristic absorption peaks of the quaternary ammonium salt. In addition, the stretching vibration absorption of S_O groups at 1370 cm−1 and 1210 cm−1 was present, revealing the introduction of sulfonate group to the alkali lignin molecule.

Table 2 The determination of phenolic hydroxyl content. Sample

Alkali lignin

Oxidized sulfonated lignin

LSBA-1

LSBA-2

LSBA-3

Content of phenolic hydroxyl (mmol/g)

0.2622

0.1933

0.1261

0.1159

0.1162

3.2. UV analysis The UV absorption spectra of alkali lignin and LSBA surfactant were shown in Fig. 2. It could be seen that the characteristic absorption appeared nearby 255 nm and 300 nm in the alkali lignin spectrum, which was the typical absorption peak of alkali lignin [36]. For the LSBA spectrum, there was no obvious absorption peak except for the weak absorption band and the UV absorption decreased to different

Fig. 3. 1H NMR spectra of alkali lignin (a) and the synthesized surfactant LSBA (b).

S. Chen et al. / Journal of Molecular Liquids 249 (2018) 73–82

77

70

Table 3 The determination of nitrogen content. Alkali lignin

LSBA-1

LSBA-2

LSBA-3

Nitrogen content (mmol/g)

0.3142

1.5357

1.6143

1.6753

LSBA-3 LSBA-2 LSBA-1

60 Surface tension (mN/m)

Sample

degrees. The absorption peak associated with the phenolic hydroxyl group of alkali lignin disappeared nearby 255 nm and 300 nm in the LSBA spectrum. As a result of comprehensive FT-IR spectra, it was found that most of the phenolic hydroxyl groups in the alkali lignin were consumed in the reaction. This proved that the phenolic hydroxyl groups of alkali lignin had been etherified with the intermediates, indicating that the quaternary ammonium groups were introduced to the phenolic hydroxyl groups of the oxidized sulfonated lignin.

50

40

30

20 -4.5

1

3.3. H NMR analysis

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

Log c The chemical shifts in 1H NMR spectra of alkali lignin and synthesized LSBA surfactant were obtained as shown in Fig. 3. The 1H NMR spectra could be used to confirm the molecule structure of compounds because of each hydrogen element of the sample could produce a corresponding absorption peak in the 1H NMR spectra. In Fig. 3(a) all the peaks ranging from δ 0.5 to 0.95 ppm were related to the methyl proton (CH3C–). The methylene proton (–CCH2C-) and methine proton (– CCHR2) were shown at δ 1.0–1.3 ppm and δ 1.4 ppm, respectively. The peak at δ 2.5 ppm was due to DMSO-d6. The intense peak centered at δ 3.4 ppm was attributed to the methoxy protons (–OCH3). The peaks appearing in the range of δ 6.0 to 7.5 ppm were due to the aromatic protons in alkali lignin. In LSBA surfactant, the peaks ranging from δ 0.6 to 1.4 ppm were obviously enhanced, which proved that the long

Fig. 5. The plots of surface tension versus log C (concentration of surfactant in g/L) at 25 °C.

alkylchain lipophilic group containing a large number of methyl and methylene groups was introduced after the alkylation reaction (Fig. 3(b)). The methyl proton at (CH3N+) and the methylene proton at (RCH2N+) for quaternary ammonium ion were shown ranging from δ 3.0 to 4.0 ppm and they had partial overlap, which also confirmed that the quaternary ammonium groups were introduced into the chemical structure of LSBA surfactant. The peak at δ 4.3 ppm was due to the proton of methylene group attached to the benzene ring and sulfonate group, indicating the introduction of sulfonate group to the alkali lignin molecule.

200

140

180

120 100

120

80

Time (min)

140 100 80 60

60 40

40 20

20 0

0 7

8

9

10

11

12

13

14

15

16

7

8

9

HLB value

10

11

12

HLB value

(a)

(b) 300 250 200 Time (min)

Time (min)

160

150 100 50 0 7

8

9

10

11

12

13

14

15

16

HLB value

(c) Fig. 4. HLB values of the synthesized surfactants LSBA-1 (a), LSBA-2 (b) and LSBA-3 (c).

13

14

15

16

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amine was introduced into the oxidized sulfonated lignin. Therefore the nitrogen content in the lignin sulphobetaine could be used as an indicator of product yields. The nitrogen contents of alkali lignin, LSBA-1, LSBA-2 and LSBA-3 were measured and the results were shown in Table 3. It was seen that the nitrogen contents of LSBA obtained after modification increased obviously compared to that of alkali lignin. The molecular weights of LSBA-1 and LSBA-2 were lower than that of LSBA-3, but the nitrogen content of LSBA-3 was relatively higher compared with the other two. This indicated that the yield of LSBA-3 was higher than that of LSBA-1 and LSBA-2.

Table 4 The calculated surface activity parameters of LSBA surfactants at 25 °C. Sample

LSBA-1

LSBA-2

LSBA-3

Ccmc (mg/L) γcmc (mN/m) Γmax (mol/cm2) Amin (nm2)

4.36 × 10−4 30.29 8.08 × 10−10 0.21

4.45 × 10−4 25.97 6.53 × 10−10 0.25

1.04 × 10−3 27.87 6.44 × 10−10 0.26

3.4. Phenolic hydroxyl content measurement The phenolic hydroxyl contents of alkali lignin, oxidized sulfonated lignin and synthesized surfactants LSBA were given in Table 2. It was found that the phenolic hydroxyl content of oxidized sulfonated lignin was lower than that of alkali lignin. The benzene ring of alkali lignin undergone a certain degree of damage after oxidation reaction and some of the hydroxyl groups were oxidized, leading to a decrease of phenolic hydroxyl content in oxidized sulfonated lignin. The phenolic hydroxyl contents of LSBA-1, LSBA-2 and LSBA-3 were 0.1261 mmol/g, 0.1159 mmol/g and 0.1162 mmol/g, respectively. It indicated that the phenolic hydroxyl groups of oxidized sulfonated lignin were involved in the reaction with the intermediates ADAC in the subsequent chemical modification, resulting in a decline of the phenolic hydroxyl content in the products. The slight difference of phenolic hydroxyl content among LSBA-1, LSBA-2 and LSBA-3 was due to the errors of measured values caused by the different chain length of surfactants.

3.5. Nitrogen content measurement The nitrogen content in the lignin sulphobetaine would be increased after alkylation reaction in which the long alkylchain dimethyl tertiary

3.6. HLB measurement HLB value is a crucial indicator which represents the hydrophilic or lipophilic degree of surfactants to some extent. The stronger the hydrophilicity of the surfactant, the higher the HLB value, and vice versa. And the HLB value is related to the interfacial properties of the surfactant [37, 38]. The surfactant with more hydrophilic is not beneficial for the adsorption of surfactant molecules on the gas/liquid interface, whereas surfactant with more lipophilic cannot be dissolved in water. Therefore, the surfactants with suitable HLB values can be used in practical applications for EOR [39]. The HLB values for LSBA-1, LSBA-2 and LSBA-3 were measured and the results were shown in Fig. 4. It could be seen that the HLB values of LSBA-2 and LSBA-3 were 11 and 10, respectively. According to the relationship between HLB value and the physicochemical properties of surfactant [40], the HLB values of LSBA-2 and LSBA-3 being in the range of 8–13 indicated that they had good emulsification in O/W system. The HLB value of LSBA-1 was 14, which was in the range of 12–15 and therefore exhibited good wetting performance. Although the lipophilic group of straight alkylchain was attached to the lignin molecule, the amino acid in acidic conditions could produce ammonium 10

Interfacial tension (mN/m)

LSBA-1 (0.6 wt%) LSBA-1 (0.4 wt%) LSBA-1 (0.2 wt%) LSBA-1 (0.1 wt%)

1

0.1

0.01

0

10

20

30

40

50

LSBA-2 (0.6 wt%) LSBA-2 (0.4 wt%) LSBA-2 (0.2 wt%) LSBA-2 (0.1 wt%)

1

0.1

0.01

1E-3

60

0

10

20

30

Time (min)

Time (min)

(a)

(b)

40

50

100

Interfacial tension (mN/m)

Interfacial tension (mN/m)

10

10

1

LSBA-3 (0.6 wt%) LSBA-3 (0.4 wt%) LSBA-3 (0.2wt%) LSBA-3 (0.1 wt%)

0.1

0.01 0

10

20

30

40

50

60

Time (min)

(c) Fig. 6. Concentration effects of LSBA-1 (a), LSBA-2 (b) and LSBA-3 (c) on the IFT between Huabei crude oil and brine at 54 °C.

60

S. Chen et al. / Journal of Molecular Liquids 249 (2018) 73–82

salt because of the introduction of more hydrophilic amino and sulfonic acid groups at the same time. And the HLB value of LSBA-1 was higher than that of the other two surfactants due to the introduction of shorter alkyl carbon chains. 3.7. Critical micelle concentration (cmc) and surface tension (γcmc) The surface tension measurements for the solutions were conducted on the dynamic surface tensiometer at 25 °C and the results were shown in Fig. 5. It could be seen that the surface tension gradually decreased and then tended to a stable region with the increase of LSBA concentration. The excessive surfactant molecules would form micelles in aqueous solutions when the break point appeared in the curves, and the further increase of surfactant concentration had little impact on the surface tension of solution, and thus the surfactant tension remained almost constant. The cmc values of LSBA-1, LSBA-2 and LSBA-3 were calculated from the break point of the curves for each sample as depicted in Fig. 5. The surface adsorption parameters including maximum surface excess concentration (Γmax) and area per molecule (Amin) were evaluated according to Gibbs adsorption equation. And the results were listed in Table 4. Γ max

    1 dγ 1 dγ ¼− ¼− RT d lnC T 2:303RT d logC T

ð2Þ

Amin ¼ ðΓ max NA Þ−1

ð3Þ

where, Γmax is the maximum surface excess concentration, R is the gas constant, T is the temperature in Kelvin, γ is the surface tension, C is the surfactant concentration, Amin is the area per molecule and NA is the Avogadro constant.

As shown in Table 4, the cmc values of LSBA-1 and LSBA-2 were 4.36 × 10− 4 mg/L and 4.45 × 10−4 mg/L, which was smaller than that of LSBA-3 (1.04 × 10−3 mg/L). This indicated that LSBA-1 and LSBA-2 were prone to forming micelles in solution compared to LSBA-3. The minimum surface tension values of LSBA-1, LSBA-2 and LSBA-3 at cmc were 30.29 mN/m, 25.97 mN/m and 27.87 mN/m, respectively. The LSBA surfactant molecules could aggregate to form micelles in solution at lower concentrations due to the introduction of long chain lipophilic groups, thus the surface activity of the modified lignin sulphobetaine surfactant was obviously improved. For LSBA-1, the value of surface excess concentration Γmax was slightly higher than that of LSBA-2 and LSBA-3 while the value of area per molecule Amin was lower than that of LSBA-2 and LSBA-3. It could be attributed to the proportion of hydrophilic head group in LSBA-1 molecule was larger compared to that of LSBA-2 and LSBA-3. In addition, the zwitterionic surfactant with positive charge would cause a smaller repulsion between the molecules, forming a closer surfactant adsorption layer at the air/water interface, and the hydrophobic carbon chains of surfactant would be partially overlapped. 3.8. IFT measurements It is well known that the ultralow IFT is an important indicator for the successful application of surfactant flooding in EOR. The IFT of oil/ water interface is strongly influenced by many factors, such as the type and concentration of surfactants, the temperature of reservoir, the salinity of liquid phase and the alkane carbon number in the crude oil [41,42]. In this work, the effects of surfactant LSBA concentration on the IFT were first investigated at 54 °C between Huabei crude oil and brine, without addition of any polymers, alkaline reagents and cosurfactants. The dynamic IFT between Huabei crude oil and brine containing lignin sulphobetaine (LSBA-1, LSBA-2 and LSBA-3) at the concentration varying from 0.1 wt% to 0.6 wt% was illustrated in Fig. 6. As

1

1 LSBA-2 (0.4 wt%) LSBA-2 (0.4 wt%)+Na2CO3(0.2 wt%)

LSBA-1 (0.4 wt%)+Na2CO3(0.4 wt%)

LSBA-2 (0.4 wt%)+ Na2CO3(0.4 wt%) LSBA-2 (0.4 wt%)+Na2CO3(0.8 wt%)

Interfacial tension (mN/m)

0.1

LSBA-1 (0.4 wt%) LSBA-1 (0.4 wt%)+Na2CO3(0.2 wt%) LSBA-1 (0.4 wt%)+Na2CO3(0.8 wt%)

0.01

1E-3 -3

IFT < 10 mN/m

1E-4

0.1

0.01

1E-3 0

10

20

30

40

50

60

70

0

10

20

Time (min)

30

40

50

60

Time (min)

(a)

(b) 10

Interfacial tension (mN/m)

Interfacial tension (mN/m)

79

1

0.1

0.01

LSBA-3 (0.4 wt%) LSBA-3 (0.4 wt%)+Na2CO3(0.2 wt%) LSBA-3 (0.4 wt%)+Na2CO3(0.4 wt%) LSBA-3 (0.4 wt%)+Na2CO3(0.8 wt%)

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(c) Fig. 7. Effects of Na2CO3 concentration on the IFT between LSBA-1 (a), LSBA-2 (b), LSBA-3 (c) and Huabei crude oil at 54 °C.

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1 LSBA-1 (0.4 wt%) LSBA-1 (0.4 wt%)+Na2CO3(0.2 wt%) LSBA-1 (0.4 wt%)+Na2CO3(0.8 wt%)

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(b) 1 LSBA-3 (0.4 wt%) LSBA-3 (0.4 wt%)+Na2CO3(0.2 wt%)

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(c) Fig. 8. Effects of Na2CO3 concentration on the IFT between LSBA-1 (a), LSBA-2 (b), LSBA-3 (c) and Xinjiang crude oil at 28.7 °C.

shown in Fig. 6(a), the IFT decreased to 10−2 mN/m within 20 min and the equilibrium IFT was achieved when the LSBA-1 concentration was 0.4 wt%. And the IFT was much lower than those used with other surfactant concentrations. Similar interfacial activity was found with LSBA-2 and LSBA-3, though the equilibrium IFT was 10−1 mN/m level for the 0.4 wt% LSBA-3. The results showed that the ability of surfactants on reducing IFT was related to the surfactant concentration, and however, IFT of water/oil could not be further decreased with higher surfactant concentration. The lowest IFT between Huabei crude oil and brine could be achieved with the appropriate surfactant concentration (0.4 wt%).

1

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Time (min) Fig. 9. The IFT between Xinjiang crude oil and the brine solutions of the LSBA-3 (0.4 wt%) or the mixed LSBA-3 (0.4 wt%)/HPAM (0.1 wt%) at 28.7 °C.

In general, when the interactions of surfactant film at the oil/water interface are balanced, the IFT of oil/water can be decreased to ultralow. It is usually difficult to obtain ultralow IFT using a single surfactant alone and alkali is occasionally added to the surfactant solution to reduce the IFT [43]. The influences of weak alkali sodium carbonate (Na2CO3) on the IFT were investigated at 54 °C between Huabei crude oil and brine, and the results were shown in Fig. 7. The surfactant with a fixed concentration of 0.4 wt% and the Na2CO3 concentrations ranging from 0.2 wt% to 0.8 wt% were included in the chemical solution. It was seen that dynamic IFT of LSBA-1/crude oil decreased after adding Na2CO3 into solution compared to that of LSBA-1 solely (Fig. 7(a)). And the IFT of LSBA-1/ crude oil decreased with increasing the Na2CO3 concentration. When the concentration of Na2CO3 was 0.4 wt%, the equilibrium IFT of LSBA1/crude oil could reach 10−3 mN/m in 10 min. The effects of Na2CO3 on the IFT of LSBA-2/crude oil and LSBA-3/crude oil were analogous to that of LSBA-1/crude oil (Fig. 7(b) and Fig. 7(c)). In addition, the IFT between LSBA-1 and Huabei crude oil was much more stable and lower than that of LSBA-2 and LSBA-3 under the same Na2CO3 concentration. It had been recognized that the alkali could effectively reduce the IFT between oil and water due to synergistic effect between the substance produced in situ by the reaction of acidic components in crude oil with alkali and the surfactant in solution [44–46]. In order to further understand the influence of crude oil on the IFT, the IFT measurements between Xinjiang crude oil and brine at 28.7 °C were conducted under different Na2CO3 concentrations. As shown in Fig. 8(a), the dynamic IFT of each system gradually decreased to the equilibrium value and held for the remaining time. The IFT of Xinjiang crude oil/brine reduced as the increase of Na2CO3 concentration. And the ultra-low IFT was obtained for LSBA-1 with 0.8 wt% Na2CO3. This interfacial behavior was similar to that of LSBA-2 and LSBA-3 in the presence of Na2CO3. Especially, the IFT between LSBA-3 and Xinjiang crude oil could reach ultra-low values with the range of Na2CO3 concentration

S. Chen et al. / Journal of Molecular Liquids 249 (2018) 73–82

from 0 to 0.8 wt%. The more effective surfactant molecules were adsorbed on the oil/water interface, a lower interfacial tension was achieved according to the Gibbs adsorption theory. The results indicated that the LSBA surfactants exhibited stable and better interfacial behavior on Xinjiang crude oil compared to that of Huabei crude oil. In the practical application of surfactant flooding in EOR, polymers were usually introduced into the surfactant solution to increase the viscosity of displacement formula, thereby increasing the swept volume of flooding solution and improving the oil displacement efficiency [47,48]. The effect of additional HPAM (0.1 wt%) on the IFT between Xinjiang crude oil and brine containing 0.4 wt% LSBA-3 was investigated. As shown in Fig. 9, there was a slight increase in the IFT of surfactant/polymer system compared to that of individual surfactant system. The polymer molecules with weak interfacial activity in solution could be adsorbed on the oil/water interface and affected the adsorption density of surfactant molecules on the interface, resulting in a slight increase of IFT. Furthermore, the surfactant/polymer system with high viscosity slowed the adsorption rate of surfactant molecules on the interface, leading to a longer time to reach stable IFT. However, the values of equilibrium IFT for both systems were in the same order of magnitude even if the additional polymer affected the ordered arrangement of surfactant molecules on the oil/water interface.

4. Conclusions In this work, a series of lignin sulphobetaine zwitterionic surfactants were synthesized through sulfonation, quaternization and alkylation reaction with low-cost and renewable alkali lignin as raw materials. FT-IR spectrum, UV spectrum and 1H NMR spectrum were employed to confirm the structure of lignin sulphobetaine surfactants. The HLB values of LSBA-1, LSBA-2 and LSBA-3 were 14, 11 and 10, which indicated that the synthesized lignin sulphobetaine surfactants were relatively hydrophilic if the carbon chain length of incoming tertiary amine was relatively short. The lignin sulphobetaine surfactants showed high surface activity with low surface tension and the cmc of LSBA-1, LSBA-2 and LSBA-3 were 4.36 × 10− 4 mg/L, 4.45 × 10−4 mg/L and 1.04 × 10−3 mg/L, respectively. For Huabei crude oil, the lowest IFT could be achieved at the appropriate surfactant concentration (0.4 wt%). LSBA-1 could effectively decrease the IFT between Huabei crude oil and brine down to 10−3 mN/ m with 0.4 wt% Na2CO3. Similar interfacial activities were found with LSBA-1 and LSBA-2 for Xinjiang crude oil. Especially, LSBA-3 could reduce the IFT between Xinjiang crude oil and brine to ultra-low level in the absence of alkali, exhibiting satisfactory interfacial activity on Xinjiang crude oil. In addition, the additional polymer had little impact on the reducing ability of IFT between Xinjiang crude oil and brine with LSBA-3. The present study demonstrated that the synthesized surfactant LSBA could be used as a prominent candidate for the practical application of surfactant flooding in EOR.

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