perkin
medal tion that she contracted during child birth. Drugs weren't available to save her. To this day, the 67-year-old Li re counts the incident with sadness and says the somber event caused him to look to science to improve quality of life. Also instrumental in guiding Li to ward science was Li's father, who warned his college-aged son that the ca reer outlook for a writer in post-World War II China was dismal at best. Li also points out that he enjoyed his science classes and was doing just as well in chemistry as he was in his liberal arts director of research and technology at Al- courses, and therefore it was easy to liedSignal. But Li says that, during his commit himself to pursuing science and youth in China, he didn't aspire to be a engineering. Engineering in particular, he adds, was considered very relevant chemist or a chemical engineer. "When I was young, I wanted to be a and was highly regarded at that time by writer," Li insists. "My father was a writ Chinese society. In 1954, Li completed an undergrad er and professor of French literature. My mother [had been] a liberal arts per uate degree in chemical engineering at son, too. And I wanted to follow in their National Taiwan University, Taipei, and footsteps." But a number of key factors then moved to the U.S. to continue his directed Li toward a lifetimefilledwith education. He received a master's de gree in chemical engineering from science and technology. To begin with, Li learned as a young Wayne State University, Detroit, in boy that his mother died when he was 1957, and a Ph.D. degree, also in chemi just two weeks old because of an infec- cal engineering, from Stevens Institute of Technology, Hoboken, N.J., in 1963. As a Ph.D. student in the 1960s, Li in vestigated the nature of gas diffusion Reactions in liquid through polymer membranes at high membranes enhance pressures. Nearly all studies until that separation efficiency time dealt with gas diffusion at very low pressures or under vacuum. But many practical applications, like chemical sep Liquid arations in high-pressure gas streams membrane from industrial plants, required an un derstanding of diffusion behavior at sev eral atmospheres of pressure or higher. Ii's graduate studies laid the ground work for much of the career he was about to begin and even landed him a consulting job on the Apollo lunar-land + H< ing program, working with a company that studied the diffusion of liquid fuels M+ = metal ion through polymers. RH = complexing agent Fresh out of graduate school, Li began Using liquid solutions as membranes working at Exxon's corporate research in place of solid polymer films can labs on using polymer membranes for hy drastically improve chemical separa drocarbon separations. Li recalls that, tions. In metal-contaminated water, during a routine experiment in which he metal ions in a feed solution on one was measuring interfacial tension be side of a membrane (yellow) react tween a water and an oil phase, he hap with complexing agents in the mem brane to form organometallic species pened to notice a thinfilmadhering to his (RM). Upon diffusing to the other apparatus. That "chance observation," as side, agents in a strip solution reverse Ii describes it, ultimately led to his inven the complexation reaction. The metal tion of liquid membranes. ions enter the strip solution, and the Liquid membranes are ultrathin complexing agents are freed to trans films of water or an organic material port more metal ions through the membrane. that are stabilized by the presence of surfactant molecules and other addi-
NORMAN LI WINS PERKIN MEDAL
Chemical separations specialist to be honoredfor invention of liquid membranes and innovations in facilitated transport Mitch Jacoby C&EN Chicago
T
alk with Norman N. Li about research and technology, and you're sure to be infected with his enthusiasm for scientific discovery. Li's numerous innovations in membrane development, which he talks about modestly but with excitement, were made throughout a three-and-a-half-decade career in the U.S. chemical industry during which Li earned an international reputation as a leader in the field of chemical separations. For his commitment to industrial research in membrane technology and his invention of liquid membranes, Li has been named winner of the 2000 Perkin Medal. Li's contributions to the development of membrane science have had wideranging commercial impact His advances have led to applications in environmental remediation, for example, including techniques for recovering phenol and toxic metals from wastewater. Considered one of the U.S. chemical industry's highest honors, the Perkin Medal will be presented to Ii this week at a Society of Chemical Industry (SCI) banquet at the Plaza Hotel in New York City. The Perkin Medal is awarded annually by the American Section of Londonbased SCI to a scientist or engineer for outstanding contributions in applied chemistry. The recipient is selected by a panel of representatives from several organizations: the American Section of SCI, the American Chemical Society, the American Institute of Chemists, the American Institute of Chemical Engineers, the Electrochemical Society, and the American Section of the Société de Chemie Industrielle. Li spent more than 35 years working in the chemical industry,firstas a senior research scientist at Exxon, later as director of separations science and technology at UOP, Des Plaines, ΠΙ., and later still as 60
MARCH 6, 2000 C&EN
tives. In today's commercial applications, liquid membranes are prepared via emulsion techniques as agglomerations of micrometer-sized droplets. They can be placed inside the pores of polymer films or inside or outside hollow fibers. All of the methods aim at maximizing membrane surface area. Li is quick to point out that, although it may sound romantic to credit a discovery to good luck or chance, serendipity plays just one role in the invention process. "You need to have the right background," he says, "or the idea just won't click." In Li's case, years of work with solid polymeric membranes and a clear understanding of advantages and disadvantages of that type of material in chemical separations provided him with the experience to recognize that the film clinging to his lab equipment wasn't simply an experimental nuisance. Rather, it held promise as an effective separation medium for several reasons. To begin with, surface-active molecules conveniently self-assemble into thin films at an oil-water interface. By contrast, polymer films require casting and coating processing, Li asserts. In addition, the effectiveness of plasticfilmsin separation processes may be compromised by pinholes that form as a result of manufacturing procedures, whereas interfacialfilmsthat form in situ are expected to be very uniform, Ii says. But perhaps the most striking feature of liquid membranes is that they can offer enormous improvements in separation efficiency compared with their solid-phase counterparts. The rea-
Li: the right background
son for the enhancement is that rates of diffusion in liquids can be 100,000 times faster than in solids. Li acknowledges that it was only after working with the new membranes for sometimethat he recognized how to capitalize on the high diffusion rates. The key is using liquid membranes as facilitated-transport systems. Facilitated transport is a process by which a membrane not only serves as a medium for physical separation, but actively transports material across its boundaries. What's the secret? Building a reversible chemical reaction directly into a stabilized liquid membrane. That advance is regarded as one of Li's major contributions to membrane science and technology.
SCI to announce Perkin Medal Scholarship The Society of Chemical Industry (SCI) will unveil a new scholarship program at the Perkin Medal banquet in New York City this week. According to SCI, a $ 5 , 0 0 0 stipend will be awarded to a graduate student in applied chemistry or a related field at an institution chosen by the medalist The prize money will be drawn from the award dinner proceeds. This year's Perkin Medal winner, Norman N. Ii, has selected the department of chemical engineering and materials science at Wayne State University, Detroit, where Li was a student in the 1950s, to receive the first annual award. Li and a panel of judges appointed by Wayne State have begun soliciting applications for a candidate "of academic excellence" from that department and expect to announce a winner in the next few weeks. Wayne State's chemical en-
gineering department chairman, Esin Gulari, will accept the award certificate in New York. William S. Stavropoulos, chief executive officer of Dow Chemical and chairman of the American Section of SCI, explains that the purpose of the scholarship program is twofold: "to recognize and reward outstanding performance and potential in the advanced study of applied chemistry or related sciences, and to broaden awareness of the Perkin Medal and the contributions to society that this prestigious award represents." SCI seeks to honor graduate students who demonstrate potential for outstanding contribution to applied chemistry and the chemical industry. "We hope to foster the study of science and help people pursue career ambitions," Stavropoulos adds.
In one type of facilitated-transport application, droplets of a reactive aqueous phase, known as strip solution, are coated with a liquid membrane that contains organic complexing agents. As wastewater containing zinc, strontium, or other metals is fed to the droplet suspension, organometallic complexes form at the membrane's feedsolution side (exterior) and diffuse rapidly toward the strip-solution side (interior). The strip solution contains agents that decomplex the metalorganic species. The metal ions are captured by the strip solution, and the organic molecules are freed to form complexes once again with metal ions in the feed solution. Two groundwater treatment facilities based on this technology (using liquid membranes inside hollow fibers) have recently been built in Baltimore, Md. Used for hexavalent chromium cleanup, one plant went into commercial operation in March 1999. Startup operations are planned for April at the other location. Units of this type are able to reduce metal-ion concentrations from the 100to 1,000-ppm range to approximately 0.05 ppm and produce spent strip solutions that are sufficiently concentrated—up to 20% Cr(VD—to be suitable for sale or reuse. After 18 years of service at Exxon, Li joined UOP in 1981 as its director of separations science and technology at the invitation of Mary Lowe Good, who at that time was UOFs director of research. Li subsequently followed Good to AlliedSignal. Li considers his career highlights to be developing applications for UOP's Sorbex adsorption technology and devising procedures for separating vinylidene chloride and other unwanted byproducts from hydrochlorofluorocarbons at AlliedSignal. In 1995, Li established a consulting company, NL Chemical Technology, in Mount Prospect, 111., where he currently investigates composite polymers for use as reverse-osmosis membranes. One of the company's main goals is developing effective membranes for use in highoutput seawater desalination and wastewater treatment systems that are less expensive and easier to operate than today's high-pressure units. Li holds nearly 50 U.S. patents and has published more than 100 technical papers. He is a fellow of the American Institute of Chemical Engineers and a member of ACS and the U.S. National Academy of Engineering.^ MARCH 6, 2000 C&EN 6 1
