Water in CO2 emulsion 형성을 위한 hybrid fluorocarbon-hydrocarbon

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

surfactants 합성 및 초임계 CO2 내의 용해도 측정

박지영, 이윤우, 이창하,* 임종성

한국과학기술연구원 국가지정 초임계유체 연구실, 연세대학교 화학공학과*

Synthesis of hybrid fluorocarbon-hydrocarbon surfactants for water in CO2 emulsion and the measurement of solubility in supercritical CO2

Ji-Young Park, Youn Woo Lee, Chang-Ha Lee,* Jong Sung Lim

National Research Lab. for Supercritical Fluid, KIST,

Dept. of Chem. Eng., Yonsei University*

Introduction

Carbon dioxide (CO2) has been regarded as a useful chemical having many advan- tages that it is cheap, nonflammable, nontoxic, inexpensive, chemically inert, recyclable, and readily accessible to supercritical region (TC=31oC, PC=7.38 MPa)[1], but the other hand CO2 which is nonpolar also regarded as a poor solvent because the solubility of polar chemicals in CO2 is low[2]. Recently, the researches to solve this disadvantage of CO2 are lively carried out by many chemists and engineers. One of these is the research about the formation of emulsion that polar chemicals of nano (nm) or micro (□m) size droplets in diameter were dispersed in CO2. It is desired that many polar chemicals will be soluble in CO2 to reduce the interfacial tension between two types of chemicals by a proper surfactant.

In this study, we synthesized the fluorocarbon-hydrocarbon (F-H) hybrid nonionic surfactants[3], the sodium salt of bis (2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate (di-HCF4), and the sodium salt of bis (3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro- octyl)-2-sulfosuccinate (di-HCF7) with with both 'CO2 philic' chain and 'hydrophilic' chain and form water (polar) in CO2 (nonpolar) emulsion by using these surfactants[4]. We confirmed the two surfactants were soluble in CO2 as well as water by measurement of surfatant and compared the degree of the solubility between them.

The surfactants synthesied were characterized by 1H NMR, 13C NMR, 19F NMR and DEPT NMR analysis.

Experimental

Chemicals  Carbon dioxide (CO2, □99.99%, Duck Yang, Korea), 3,3,4,4,5,5,6,6,7,7,8,8,8- tridecafluoro-1-octanol (CF3(CF2)5CH2CH2OH, □97%, Aldrich) 2,2,3,3,4,4,5,5-octafluoro- 1-pen-tanol (F2CH(CF2)3CH2OH, □98%, Aldrich), 1,4-dioxane (C4H8O2, □99%, Junsei chem. co.),  p-toluenesulfonic acid monohydrate (CH3C6H4SO3H□H2O, □99%, Yakuri chem. co.), sodium hydrogen sulfite (NaHSO3, a reagent, Hayashi chem.co.), maleic anhydride (C4H2O3, □98%, Junsei chemical co.), toluene (C6H5CH3, □99.8%, J.T. Baker), acetone-d6 (CD3COCD3, □99.5%, Aldrich), trifluoroacetic acid-d (CF3COOD, □99.5%, Aldrich).

Preparation of the sodium salt of bis (2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate (and the sodium salt of bis (3,3,4,4,5,5,6,5,7,7,8,8,8-tridecafluorooctyl)-2-sulfosuccinate )

Step 1> 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (3,3,4,4,5,5,6,5,7,7,8,8,8-tridecafluoro-1-octanol), maleic anhydride, and p-toluene sulfonic acid monohydrate were mixed in toluene. After the reaction ( ; 'esterification'), bis (2,2,3,3,4,4,5,5-octafluoro-1-pentyl) maleate (bis(3,3,4,4,5,5,6,6,- 7,7,8,8,8-tride- ca fluorooctyl) maleate) was gained by separation and purification.

화학공학의 이론과 응용 제8권 제1호 2002년

Step 2> A solution of bis (2,2,3,3,4,4,5,5-octafluoro-1-pentyl) maleate (bis(3,3,4,4,5,5,6,6,7,7,- 8,8,8-tridecafluorooctyl) maleate) that was synthesiez in Step 2 in 1,4-dioxane was added to an aqueous sodium hydrogen sulfite in water. Then this mixture was refluxed for 2 days. After the reaction, a white color solid, the sodium salt of bis (2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate (the sodium salt of bis(3,3,4,4,5,5,- 6,6,7,7,8,8,8-trideca-fluorooctyl)-2-sulfosuccinate) was gained. Synthetic procedure of surfactants was represented in scheme 1. These surfactants were characterized by 1H NMR, 13C NMR, 19F NMR and DEPT and the results of di-HCF7 of these were shown in Fig.3 (a~e)

Experimental procedure The apparatus for 1) formation of water/CO2 emulsion, and 2) measurement of cloud point was a variable-volume view cell and shown in Fig. 1. The experimental procedure to form water/CO2 emulsion in supercritical CO2 was as follows. The reactor cell was evacuated and a constant molar ratio  of water to surfactant (WO=[water]/[surfactant]) of the water and surfactant solution was introduced into the reactor. To remove any entrapped air present in the cell, the cell was purged at least three times with low-pressure CO2. A certain amount of liquid CO2 was charged into the cell through the inlet line. The solution in the cell was continuously pressurized using the pressure generator. At the same time, the solution was well agitated by a stirring bar to form emulsion. As the pressure increases, the solution in the cell finally becomes the emulsion with a milky color. The procedure for measurement of cloud point in sc CO2 is explained in detail in other paper [5] and omitted in this paper.

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

화학공학의 이론과 응용 제8권 제1호 2002년

Fig. 1. Schematic diagram of experimental apparatus

Results and discussion

Formation of W/CO2 emulsion  Two surfactants contain a long hydro fluorocarbon chain plus an ionic end. The hydro fluorocarbon portion of the molecule is hydrophobic and soluble in the nonpolar substances, while the ionic end is hydrophilic and water soluble. Because of the hydro fluorocarbon chain, these surfactants arenot truly soluble in water. However, these are readily suspended in CO2 because it forms micelles. In other words, the hydro fluorocarbon chains of these molecules are dissolves in CO2, (SO3Na+) of these molecules are attractive to water. The phenomena of CO2-water emulsion are shown in Fig 2. Surfactant lowers the surface tension of water by disrupting the hydrogen bonding in the surface of water and hydrophobic tails contact with CO2. As a result, the surface tension of water-CO2 was reduced. The present writer will publish the result of this research.

Measurement of solubility  We measured both the two chemicals with the only CO2 philic group (bis(2,2,3,3,4,4,5,5-octafluoro-1-pentyl) maleate and (bis(3,3,4,4,5,5,6,6,7,7,8,8,8- trideca fluorooctyl) maleate and the two chemicals with CO2 philic and hydrophilic group (bis(2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate, the sodium salt of bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl)-2-sulfosuccinate). Solubility of bis(2,2,3,3, 4,4,- 5,5-octafluoro-1-pentyl) maleate in CO2 was in range of 8.616MPa (T=47.31oC)~14.926 MPa(T=128.34oC) and that of bis(3,3,4,4,5,5,7,7,7,8,8,8-tride cafluoro) maleate was in range of 7.72MPa(T=34.60oC)~16.41MPa (T=116.39oC). The di-HCF4 with a short hydro fluorocarbon chain was more soluble than di-HCF7. □P of cloud point between two materials was in range of 2.10MPa(T=48oC)~3.27MPa(T=116.39oC) and the degree of increment of □P was 0.2bar per 10oC. The solubility of bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tride- cafluorooctyl)-2-sulfosuccinate) in CO2 was in the range of 12.04MPa (T=48.12oC) ~20.11MPa(T=130oC), specially in 50~60oC that is optical temperature for experiment in supercritical CO2, the solubility was the range of 12.6MPa~14.2MPa. The solubility of (bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl) maleate with CO2 philic group was higher than that of bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-octyl)-2-sulfosuccinate) with both CO2 philic tail and hydrophilic head. □P of cloud point between two materials was in range of 2.10(T=48)~3.27(T=116.39) and the degree of increment of □P was 1.6 bar per 10oC. The solubility in CO2 was decresed because the hydrophilic group (SO3Na+) was added to (bis(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro octyl) maleate. These results were shown in Fig. 3.

Conclusion

In this research, two nonionic H-F hybrid surfactants which have CO2 philic tail and hydrophilic tail to increase the solubility power of CO2 were synthesized and water in CO2 emulsion was formed by using these surfactants. We offer possibility to improve solubility of polar chemical in CO2 (nonpolar). Now that the research for using CO2 (especially, sc CO2) have been active, the result of this study will be up to the expectation of a great help for other researches.

(a)                                       (b)

(d)

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Acknowledgement

This work has been supported by the National Research Laboratory (NRL) Program for Supercritical Fluid and the authors would like to thank to the Ministry of Science and Technology, Korea.

Literature Cited

1. S. Angus, B. Armstrong, K. M. de Reuck, international thermodynanic tables of the     fluid state (CO2), pergamon press, 1976.

2. K. P. Johnston, K. L. Harrison, et al., Science, 271, 1996.

3. K. Harison, J. Goveas, K. P. Johnston, et al, Langmuir, 10, 3536, 1994.

4. J. L. Fulton, R. D. Smith, J. Phys. Chem., 92, 2903, 1988.

5. Y. M. Kuk, B. C. Lee, J. S. Lim, J. of Chem. and Eng. Data, 1344, 46(5), 2001.