Chemical Separations with Liquid Membranes - ACS Publications

Chapter 2 A Tribute to Norman N. L i 1

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J. DouglasWay and W. S. Winston Ho

Downloaded by NORTH CAROLINA STATE UNIV on October 11, 2012 | http://pubs.acs.org Publication Date: May 5, 1996 | doi: 10.1021/bk-1996-0642.ch002

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Chemical Engineering and Petroleum Refining Department, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401-1887 Corporate Research, Exxon Research and Engineering Company, Route 22 East, Clinton Township, Annandale, NJ 08801

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Researchers in the fields of facilitated transport and liquid membranes owe much to Dr. Norman N. Li for his pioneering work on facilitated transport and the invention of liquid surfactant (emulsion) membrane technology when he was with Exxon Research and Engineering Company. A member of the National Academy of Engineering, Dr. Li became Chairman and President of NL Chemical Technology, Inc. after he recently retired as Director of Research and Technology at Allied Signal. Although his 30 year career has been spent entirely in industry, Dr. Li has an impressive record of publication. Dr. Li has also made important contributions to the profession through his participation in AIChE, ACS, and the North American Membrane Society. This chapter will highlight some of Dr. Li's accomplishments, briefly describe the liquid membrane technology he invented, and discuss commercial applications of the emulsion liquid membrane (ELM) and related technologies. In 1968 Dr. Norman N. Li invented a new separation technology known as the liquid surfactant or emulsion liquid membrane (7). This technique combined the conventional separation unit operations of extraction and stripping into a single process capable of extremely rapid separations and high selectivity. The emulsion liquid membrane (ELM) process technology is capable of separating an extremely wide variety of solutes from organics to metal ions for a very diverse set of applications including wastewater treatment, biotechnology, and hydrometallurgy. This chapter will briefly describe ELM technology and Dr. Li's contributions to the profession through his work in professional societies. Extensive, recent reviews of all aspects of ELM technology are available including theory, design, applications and economics (2-6). For the theory and applications, see also the chapter in this volume entitled "Recent Advances in Emulsion Liquid Membranes" by W. S. Ho and Ν. N . Li.

0097-6156/96/0642-0011$15.00/0 © 19% American Chemical Society

In Chemical Separations with Liquid Membranes; Bartsch, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

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CHEMICAL SEPARATIONS WITH LIQUID MEMBRANES


ELM Technology. As shown in Figure 1 in the chapter entitled "Recent Advances in Emulsion Liquid Membranes," ELMs are prepared by dispersing an inner receiving phase in an immiscible liquid membrane phase to form an emulsion. The emulsion is stabilized by surfactants with appropriate hydrophilic-lipophilic balance (HLB) number dissolved in the liquid membrane phase (7). The HLB is a parameter which is the percentage of hydrophilic functional groups in the surfactant molecule divided by five. The liquid membrane phase can be either aqueous or organic although the majority of work in the literature describes water-in-oil emulsions in which the liquid membrane phase is organic. In use, the ELM is dispersed in a continuous phase in a stirred tank reactor and the liquid membrane phase separates two miscible phases. Under agitation, the ELM phase separates into spherical globules of emulsion which have typical diameters of 100 urn to 1 mm. Each globule contains many droplets of encapsulated inner or receiving phase with a typical size of 1 to 3 um in diameter. The formation of many globules of emulsion produces large surface area/volume ratios of 1000 to 10 m /m for very rapid mass transfer (6, 8). Due to this dispersed emulsion configuration, ELMs or liquid surfactant membranes are commonly referred to as double emulsions. The transport of a solute from the continuous phase to the inner receiving phase can occur by a variety of mechanisms (2). The two primary mechanisms known as Type 1 and 2 facilitation are shown in Figure 2 in the chapter "Recent Advances in Emulsion Liquid Membranes." * The constituents of the ELM for extraction of a solute must be chosen in such a way that once the solute diffuses into the inner receiving phase it cannot diffuse back out into the continuous phase. The Type 1 mechanism is designed for the separation of nonionic solutes such as phenol (9-10). The phenol dissolves in the organic liquid membrane phase and diffuses to an internal aqueous droplet. A trapping reaction in the internal aqueous phase, such as the reaction of phenol with NaOH, creates an ionic species, sodium phenolate, which is insoluble in the organic liquid membrane phase. The trapping reaction also maintains the highest possible concentration driving force for diffusion. Ionic solutes, such as metal ions, are not soluble in the organic liquid membrane phase. Consequently, the Type 2 mechanism involves the addition of an organic extractant, or chelating agent, to the organic liquid membrane. Figure 2 in "Recent Advances in Emulsion Liquid Membranes" illustrates the concept of coupled transport where an ion-exchange reaction takes place at the organic liquid membrane/aqueous phase interfaces and the solute flux is linked (coupled) to the flux of another ion, usually H (77). Coupled transport is analogous to performing solvent extraction in a thin liquid film. The majority of liquid membranes for metal ion separation involve a coupled transport mechanism. 6

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Commercial Applications for ELMs. Draxler and Marr (72) discussed the application of ELM technology to remove zinc as zinc sulfate from low concentration wastewater from a textile plant in Lenzing, * NOTE: Please see Figure 2 in Chapter 15, page 209. In Chemical Separations with Liquid Membranes; Bartsch, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

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A Tribute to Norman N. Li

Austria. The ELM process was chosen over solvent extraction and ion exchange due to the low zinc concentration and the presence of interfering C a ions. Furthermore, due to the very slow stripping kinetics, the extractant used was not suitable for solvent extraction; but the slow kinetics were overcome by the extremely large interal droplet surface area of the ELM (10 m /m ). A commercial plant for Zn removal was constructed at the same location and began operation at the end of 1986. The plant used proprietary countercurrent extraction columns and electrostatic coalescers to break the emulsion prior to Zn recovery and recycle of the organic phase. The Zn concentration in the aqueous waste stream was reduced from 200 mg/L to 0.3 mg/L in less than 20 minutes average residence time in the extraction column. Concentrations in the inner droplet phase of the ELM of up to 50 g/L Zn were obtained. Proprietary design countercurrent stirred extraction columns (10 m high, 1.6 m diameter) similar to Oldshue-Rushton columns were used. The plant throughput was 75 to 100 m /hr. Zhang and coworkers described a commercial application for ELMs in China for phenol removal from wastewater (13-14). At the Nanchung Plastics Factory in Guangzhou, China, the phenol concentration in a 250 L/h wastewater stream was reduced from 1000 mg/L to 0.5 mg/L. ELM technology was also employed at the Huang-hua Mountain Gold Plant near Tian-jin China (14-15). Cyanide was removed from waste liquors generated in a hydrometallurgy process. The cyanide concentration in the waste stream was reduced from 130 mg/L to 0.5 mg/L. Finally, ELM technology was the basis for a commercial well control fluid developed by Exxon. A water-in-oil emulsion containing clay particles in the organic liquid membrane phase has a low viscosity allowing it to be pumped. Under the high shear conditions developed at the drilling bit nozzles which rupture the liquid membranes, the clay particles cause the internal water droplets to thicken the emulsion to a viscous paste. This viscous fluid prevents well blowout during drilling and can be used to seal loss zones in an oil or gas reservoir. 2+


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Potential Applications for ELMs. There are a variety of potential applications for ELM technology that have yet to be exploited commercially. These include wastewater treatment, removal and recovery of metal ions, biochemical processing, a fracturing fluid for oil and gas production. Marr and Draxler (1992a) describe the removal of heavy metals including Zn, Cd, Cu, Pb, and Hg from wasterwaters and the recovery of Ni from spent electroplating solutions and rinse waters. ELMs have been investigated for the removal of acetic acid, nitrophenols, and ammoniafromwastewater (16-18). More recently, Huang et al. (19) and Gleason et al. (20) have applied ELM technology to the removal of arsenicfromwastewater. Solvent extraction (e. g. the TRUEX Process) (21) has been used very successfully in the processing of radioactive metals such as U, Pu, and Am. ELM technology could be a complementary process to solvent extraction (SX) in the separation of radionuclides, especially in the cases where the reaction kinetics are not fast enough for SX processing. Another potential application in metal recovery is the extraction of rare earth metalsfromdilute solutions in hydrometallurgical processing (22-23). Hatton and coworkers (24-25) have shown that ELM technology can be used to recover aminoacids and other fermentation products in biochemical processes. Recently, Ho and Li (26) have reported on an emulsion-based fracturing fluid to increase oil and gas production via core-annular flow. In Chemical Separations with Liquid Membranes; Bartsch, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

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Contributions to the Profession. Researchers in the fields of facilitated transport and liquid membranes owe much to Dr. Norman N. Li for his pioneering work on facilitated transport and his invention of liquid surfactant (emulsion) membrane technology while at Exxon Research and Engineering Company. Dr. L i became Chairman and President of NL Chemical Technology, Inc. after he recently retired as Director of Research and Technology at Allied Signal. Although his 30 year career has been spent entirely in industry, Dr. Li' s publication record is impressive, including 44 U. S. patents, 100 publications and 13 edited books. His contributions to the profession by very active participation in professional societies are equally impressive. Dr. Li is a former Director of AIChE and a Fellow of AIChE. He was awarded the AIChE Alpha Chi Sigma Award in chemical engineering research in 1988 and the Ernest Thiele Award by the AIChE Chicago section. The American Chemical Society recognized Dr. Li's contributions by awarding him the ACS Award in Separation Science and Technology in 1988. He served as the Chairman of the Industrial and Engineering Chemistry Division of the American Chemical Society. He organized and chaired the Gordon Research Conference on Separation and Purification in 1973, the first Gordon Research Conference on Membranes in 1975, and the first and second Engineering Foundation Conferences on Separation Technologies in Switzerland in 1984 and in Germany in 1987. Dr. Li was chairman of the 1990 International Congress on Membranes and Membrane Processes and was president of the North American Membrane Society from 1990 to 1993. Dr. Li was recognized for both his technical and professional contributions by induction into the National Academy of Engineering. References 1. Li, N. N. U. S. Patent 3,410,794, 1968. 2. Ho, W. S. W.; Li, Ν. N. In Membrane Handbook; Ho, W. S. W.; Sirkar, Κ. K., Eds.; Chapman & Hall: New York, NY, 1992, pp. 597-610. 3. Ho, W. S. W.; Li, Ν. N. In Membrane Handbook; Ho, W. S. W.; Sirkar, Κ. K., Eds.; Chapman & Hall: New York, NY, 1992, pp. 611-655. 4. Gu, Z.; Ho, W. S. W.; Li, Ν. N. In Membrane Handbook; Ho, W. S. W.; Sirkar, Κ. K., Eds.; Chapman & Hall: New York, NY, 1992, pp. 656-700. 5. Marr, R. J.; Draxler, J. In Membrane Handbook; Ho, W. S. W.; Sirkar, Κ. K., Eds.; Chapman & Hall: New York, NY, 1992, pp. 701-717. 6. Marr, R. J.; Draxler, J. In Membrane Handbook; Ho, W. S. W.; Sirkar, Κ. K., Eds.; Chapman & Hall: New York, NY, 1992, pp. 718-724. 7. Adamson, A. W. The Physical Chemistry of Surfaces. Wiley: New York, NY, 1977. 8. Marr, R.; Kopp, A. Int. Chem. Eng. 1982, 22, 44-60. 9. Matulevicius, E. S.; Li, Ν. N. Sep. Purif. Methods 1975, 4, 73-96. 10. Li, N. N. J. Membr. Sci. 1978, 3, 265. 11. Cussler, E. L. AIChE J. 1971, 17, 1300-1303. 12. Draxler, J.; Marr, R. Chem. Eng. Process. 1986, 20, 319-329. 13. Zhang, X.-J.; Liu, J.-H.; Fan, Q.-J.; Lian, Q.-T.; Zhang, X.-T.; Lu, T.-S. In Separation Technology; Li, N. N..; Strathmann, H. Eds.; United Engineering Trustees: New York, NY, 1988, pp. 190-203.



2. WAY & HO A Tribute to Norman N. Li

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14. Jin, M.; Zhang, Y. In Proc. International Congress on Membranes and Membrane Processes, Chicago, IL, August 20-24,1990, Vol. I; pp. 676-678. 15. Jin, M.; Wen, T.; Lin, L.; Liu, F.; Liu, L.; Zhang, Y.; Zhang, C.; Deng, P.; Song, Z. Mo Kexue Yu Jishu 1994, 14, 16. 16. Yan, N.-X.; Huang, S.-A.; Shi, Y.-J. Sep. Sci. Technol. 1987, 22, 801-818. 17. Gadekar, P. T.; Mukkolath, Α. V.; Tiwari, K.K. Sep. Sci. Technol. 1992, 27, 427. 18. Lee, C. J.; Chan, C. C. Ind. Eng. Chem. Res. 1990 29, 96-100. 19. Huang, C. R.; Zhou, D. W.; Ho, W. S.; Li, Ν. N . Paper No. 89b Presented at the AIChE National Meeting, Houston, TX, March 19-23, 1995. 20. Gleason, K. J.; Yu, J.; Bunge, A. L.; Wright, J. D.; In Chemical Separations with LiquidMembranes;Bartsch, R. Α.; Way, J. D. Eds.; American Chemical Society: Washington, DC, 1996. 21. Horwitz, E. P.; Kalina, D. G.; Diamond, H.; Vandegrift, G. F.; Schulz, W. W Solvent Extr. Ion Exch. 1985, 3, 75-109. 22. Tang, J.; Wai, C. M.; J. Membr. Sci. 1989, 46, 349. 23. Goto, M.; Kakoi, T.; Yoshii, N.; Kondo, K.; Nakashio, F. Ind. Eng. Chem. Res., 1993,32,1681. 24. Thien, M. P.; Hatton, T. A. Sep Sci. Technol. 1988, 23, 819. 25. Itoh, H.; Thien, M . P.; Hatton, Τ. Α.; Wang, D. I. C. J. Membr. Sci. 1990, 51, 309. 26. Ho, W. S. W.; Li, Ν. N. AIChE J. 1994, 40, 1961-1968.


Chemical Separations with Liquid Membranes - ACS Publications

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