The Man Who Taught CO2 to Clean

In the big-time arenas of research, hitting the pages of Science or Nature is a slam dunk. Bring out the cameras, cut down the nets. And anyone who can do it four times in five years is burning up the league.

So picture a chemist with that kind of winning streak. He is tall, and young, and he sizes you up with a calm, predatory gaze that tells you he thrives under pressure. He prowls a big office full of honey-colored wood. He goes to the board and boils things down. He doesn’t try to impress anybody with how difficult the chemistry is. He makes it look easy.

He begins with a simple idea: Carbon dioxide, the gas we are always exhaling, the gas that comes out of our smokestacks and tailpipes, has an alter ego. Under pressure, it cleans.

It cleans because Joe DeSimone, professor of chemistry, has invented a soap. Mixed with this soap, compressed carbon dioxide will dry clean your clothes. It will clean computer parts, or textiles, or a dozen other things.

When you force carbon dioxide under pressure, it becomes a liquid, like the stuff in fire extinguishers. Mix this dense CO2 with the soap, and it lifts away the grime. Release the pressure, the carbon dioxide reverts to its pure, gaseous self, ready for more. Meanwhile, the dirt and grease are locked up in an innocent puddle of soap. No more nasty dry-cleaning fluids, no more toxic turtlenecks.

That’s the idea, and it’s made DeSimone’s new company, MiCELL, Inc., a draw for investors and a headline-maker in the business press. For the moment, at least, no one can say why DeSimone’s inventions shouldn’t help clean up a whole lot of toxin-heavy industries, reducing the 30 billion tons of hazardous solvents they use each year. If that were to happen, the environment could breathe a little easier. And so could all of us.

The idea has a powerful appeal: Clean up the cleaning industry. But how did the business of cleaning become so toxic in the first place? As DeSimone explains it, it’s a matter of simple chemistry.

If you take your clothes to a dry cleaner,” he says, “they use a liquid. They can’t use water because your garments absorb too much water and that leaves them wrinkled, and you can’t use water with silk and wool. So you have to use a non-water-based solvent.”

But the water-free solvents are made from hydrocarbons, flammable organic compounds associated with fossil fuels such as oil, gas, and coal. To make these hydrocarbons non-flammable—so that people are safe to use them—chlorines are added.

The trouble is,” DeSimone says, “chlorine also makes the solvents toxic. So, if you can’t use water, and you don’t want chlorine, and you don’t want to burn anyone, there’s nothing left.” Nothing but carbon dioxide.

It seems such a modest, low-tech task—to invent a soap. Something old-fashioned, like boiling up tallow and lye. But there’s nothing low-tech about a soap to work with CO2. Ordinary soap will not mix with carbon dioxide. In fact, they repel one another. That’s where the chemistry gets interesting. And so difficult that, according to Eric Beckman, a University of Pittsburgh chemical engineer quoted in Science, “Lots of people gave up.”

Joe DeSimone did not set out to reform the cleaning industry, or to put his name on a soap. No, he was finding ways to make polymers—plastics. Since his arrival at Carolina in 1990, much of the work in DeSimone’s lab has been funded by giants of the chemical industry—first by DuPont and 3M, then by a consortium including DuPont, Hoechst Celanese, Air Products, BFGoodrich, Eastman Chemical, Xerox, General Electric, and Bayer.

One of the goals of the research was to find ways to reduce the use of special chlorinated solvents—”chlorofluorocarbons” (CFCs)—which are being banned world-wide by the Montreal Protocol because they deplete the ozone layer. CFCs are used in air conditioners and also in the manufacture of several kinds of plastics.

In 1992, DeSimone broke into the pages of Science with the discovery that certain plastics, a group of fluorinated polymers traditionally manufactured in CFCs, were soluble in liquid carbon dioxide. This meant that environmentally dangerous CFCs could be replaced with liquid carbon dioxide in manufacturing. DeSimone wanted to extend this breakthrough to other kinds of plastics.

Most polymers are oil-based hydrocarbons,” he explains. “They are oil-soluble. The fluorinated polymers we were working with turned out to be an exception. The only other solvents these polymers dissolved in were chlorofluorocarbons, CFCs. So it looked like CO2 and CFCs were a drop-in replacement for one another in polymer synthesis.”

This finding had commercial implications, and DuPont recently licensed the technique for use in manufacturing. But DeSimone and his research group wanted to make other kinds of polymers in CO2, including acrylic latex, the stuff you find in latex paint. And that’s where we come to the soap.

Latex paint,” DeSimone explains, “is a polymer dispersed in water with a soap. If the soap weren’t there, it wouldn’t look like milk. It would look like white powder in the bottom of a container of water.”

At the board, he diagrams a soap molecule for latex paint. One side of the molecule likes water (it is hydrophilic). The other side likes oil, and therefore the oil-based plastic particles in latex paint. So the soap molecule, with its split personality, links the water and the plastic. Soap molecules are so good at this, they keep grabbing water on one side and plastic on the other until the particles are thoroughly dispersed.

DeSimone was not the first chemist to imagine how handy it would be if you could do the same thing without water, using carbon dioxide instead. The trouble was, the soaps they tried just wouldn’t work in CO2.

Which means,” DeSimone says, “that we had to redesign this thing, the soap molecule. Instead of making it hydrophilic, we had to make it CO2-philic. And what dissolves in CO2? Well, we showed that in 1992. It’s those fluorinated polymers we were using.”

The next question, DeSimone says, was, “Can we make these molecules, and will they stabilize these plastic particles?”

Yes, they could, and DeSimone’s second Science paper, published in 1994, reported it to the world. The soap molecule was made of a CO2-loving acrylic compound linked with a strand of polystyrene, a plastic-loving polymer.

What we learned how to do was analogous to making acrylic latex paint in CO2 instead of water,” DeSimone says. “So we designed a soap to do this, and it worked. Beautifully. And this is actually a hard problem. A very hard problem.”

So DeSimone and his research group knew they could make acrylic latex paint in dense carbon dioxide. And the soap they’d invented made it work. Then they remembered that soap is good for something else. It cleans.

For cleaning, the process is a little different, but the principle is the same. If you take away the plastic particles, the oil-loving ends of the soap molecules begin to band together to try and hide from CO2. The result is a cluster of soap molecules with the oil-loving sides densely massed in the center, trying to avoid the CO2, and the CO2-loving sides radiating outward from the core.

Think about how soap works in water,” DeSimone says. “When you clean something, the soap molecules come together, they assemble, into something called a `micelle,’ with the oil-loving ends packed together in a core. And then when you introduce a surface that has oil on it, or grease, like in your frying pan, this grease doesn’t like water. It’s not soluble in water. What happens is, it goes inside the core, to the part of the micelle that likes oil, and the thing just swells, the interior swells. So you lock up all of the grease inside the micelles. And that’s how soap works.”

By analogy, he assumed that micelles might work the same way in dense carbon dioxide. “So we laid out probably the only cleaning experiment ever reported in the journal Science,” DeSimone says. “We showed that in the absence of the polymer particles, the soap molecules formed micelles. They acted like soaps do. We took a surface that had a contaminant on it, and we labeled it with isotopes. Then we watched this isotopically labeled stuff come off of the surface and go into the core, using a technique known as `neutron scattering,’ so that we could see where it went. And it worked. The core grew eight hundred percent in its volume, and sucked the contaminant off the surface.”

The commercial potential was obvious, and DeSimone and two of his graduate students, Jim McClain and Tim Romack, began talking about forming a company. They attracted the interest of Brad Lienhart, a former manager at Dow Chemical. With help from students in the Kenan-Flagler Business School, DeSimone, McClain, Romack, and Lienhart launched MiCELL Technologies, Inc. in 1996, attracting more than $5 million in start-up capital.

Using variations on the carbon-dioxide cleaning process, the company is developing techniques for cleaning and degreasing machinery and computer parts, for cleaning and treating textiles, and for coating metals and fibers. In June, MiCELL and American Dryer Corporation announced plans to manufacture a line of CO2-based dry-cleaning machines. In addition to the commercial potential, there’s hope for reducing the use of perchloroethylene (“perc”) in the nation’s $6 billion garment-cleaning industry. The U.S. Environmental Protection Agency (EPA) is asking the industry to reduce or eliminate its use of perc, a suspected carcinogen that leaves noxious fumes in clothing and generates toxic wastes requiring costly disposal.

Removing perc is the pressure point,” DeSimone says. “And the EPA thinks maybe we can help.”

Botanists tell us that many green things grow faster, and yield more fruit, in an environment enriched with CO2. That’s certainly been the case with green chemistry at UNC-Chapel Hill. The growth and the breakthroughs keep coming. In September, DeSimone and several of his students and colleagues in chemistry at UNC-CH made news with an article in the journal Nature, describing a process for separating liquid chemicals. The process, a further development in the use of specialized soaps and dense carbon dioxide, could dramatically affect a broad range of industries producing pharmaceuticals, textiles, chemicals, and natural extracts such as Taxol, a product derived from the yew tree and used to fight cancer.

CO2 isn’t the answer for every industry,” DeSimone says. “And there’s a lot more we need to learn. But there’s a very good chance that some of those thirty billion tons of toxic solvents the world is using are about to become unnecessary. And that would be good for business, and good for the environment, too.”

Cleaner, Cheaper, Smarter

Last June, Joe DeSimone, the Mary Ann Smith professor of chemistry at UNC-Chapel Hill, received the 1997 Presidential Green Chemistry Challenge Award from the U.S. Environmental Protection Agency. President Clinton established the award in 1995 to honor individuals, groups, and organizations involved in “fundamental breakthroughs in cleaner, cheaper, smarter chemistry.” DeSimone, believed to be the youngest person ever to hold a chair at UNC-Chapel Hill, was the only academic chemist to receive the green chemistry award in 1997. He has also received a National Science Foundation Young Investigator Award (1992) and the Discover Magazine Environment Award (1995). In 1993, the White House named him one of 30 U.S. Presidential Faculty Members.

UNC-Chapel Hill does not have an exclusive on Joe DeSimone. He is also a professor of chemical engineering at North Carolina State University (NCSU), and his company, MiCELL Technologies, Inc., has its headquarters on NCSU’s Centennial Campus. With Ruben Carbonell of NCSU, DeSimone leads the new Kenan Center for the Utilization of Carbon Dioxide in Manufacturing, a joint venture of Carolina and NCSU. While some of the engineering aspects of the CO2 work are being developed at NCSU, DeSimone’s research group at Carolina continues to pursue the basic science of polymer chemistry and carbon dioxide.

The Sense in Going Green

Saving money and waste, industries make green chemistry a serious business.

Convenience can be costly—to the environment. The hidden cost of plastic gallon milk bottles, for example? Four pounds of waterborne waste and 27 pounds of airborne emissions for every thousand made.

But what if we could have the bottles without the mess?

That’s what green chemistry is about, says Bill Glaze, former chair of environmental sciences and engineering at UNC-CH’s School of Public Health and current head of the Carolina Environmental Program.

In a broad sense, green chemistry includes anything that improves our quality of life and helps the environment, Glaze says. But, in the narrow sense, green chemistry refers to industry and implies pollution prevention rather than clean-up. “It means applying new chemistry—new science, in general—to deliver the products and services we are used to, but in a more environmentally friendly way,” he says.

The work began in the 1970s, when new environmental laws required industry to curb pollution, Glaze says. Companies cut back by recycling chemicals, substituting less hazardous materials, or using the byproducts created during manufacturing.

Some companies saved a lot of money with this kind of “housekeeping,” Glaze says, and their success encouraged others to start or expand their own pollution-reduction programs. Now, such programs are standard.

But further reductions probably will depend on decreasing the need for hazardous chemicals in the first place, he says.

One approach is to abandon the old ways of making products and start over. Joe De-Simone’s ground-up enterprise is a good example.

But in many industries, there are no alternate technologies yet. Companies must clean up their current processes, which means breaking them down, identifying the dirty steps, and handling each problem individually. That’s called control technology, and it’s the kind of work Glaze has been doing for 20 years for waste-water treatment facilities.

For instance, the traditional approach to treatment has been to combine waste from many sources and let microbes break down the toxins, Glaze says. But different sources contribute different pollutants, and some can’t be treated with microbes. The new approach is to treat sources individually, maybe add a filter to remove a certain toxin, or use chemicals to pre-treat the waste from another source. The goal is to increase efficiency and, ultimately, “zero discharge”—not releasing anything from the main plant.

Zero discharge is an inspirational goal,” Glaze says. “It challenges every operating unit to devise ways to best handle its own problem.”

And, with any luck, that approach will mean industry can take care of the environment and still furnish the luxuries that come with technology.

Green Light

Artificial photosynthesis is, for the moment, what-if.

What if you could shine light into seawater, move some electrons around, and crank out a clean-burning hydrogen fuel? What if the same sort of process would also yield new materials, or nutrients, or compounds for treating disease?

These aren’t just wild-eyed dreams in search of funding. They are on the agenda. For more than two decades, the intellectual quest for a basic understanding that could lead to artificial photosynthesis has made Tom Meyer, Kenan professor of chemistry, one of the best-funded and most-cited chemists in the world.

First, the idea.

Think about a tree,” Meyer says. “Sunlight comes into the leaves, and the tree uses it to make sugars and oxygen out of water and carbon dioxide. If we want to use the energy from this tree, we cut it down and burn it. Or the tree dies and a hundred million years later we are burning the oil and the coal.”

But the burning, he says, makes a mess.

Every time you burn a fossil fuel, you are releasing more CO2 into the atmosphere, more greenhouse gases. Even if you use catalytic systems and control the burning, it’s an inefficient, clumsy process that involves rudimentary chemistry, crude smokestacks, boilers, and catalytic converters, and lots of other big, expensive stuff. The idea of artificial photosynthesis is to capture the energy now, in a neat little closed system using much more sophisticated chemistry.”

For Tom Meyer, there’s something offensive about a crude, messy system. So it’s not at all surprising to find that the model for his life’s work is so elegant and clean: a green leaf, lit with sunlight. “The fascination,” he says, “is how to do what happens in that green leaf, to understand the basic principles. How do you tap the energy in a molecule?”

It was a simple question that opened a wilderness of new territory. With his research teams of students and post-docs, he has proceeded step-by-step through the tangles and thickets, mapping the terrain.

The first step was to control electron transfer (see the illustration, “Electron transfer”), using light to excite electrons and then learning how to move them from one molecule to the next. Meyer and his team found molecules that could absorb light efficiently, converting its energy to molecular energy. The next step was to store this energy, to keep the electrons moving in a useful and orderly way.

To get an idea how tough this is to manage, imagine a bunch of excitable children playing musical chairs. When the music plays, the children hop up and go looking for a new place to land. One kid lands on somebody’s lap.

So the problem, unfortunately, is not solved yet,” Meyer says. “If you let this sit, all that’s going to happen is that the electron is just going to slowly drift back to where it came from. So you’ve got to fight against this back-transfer of electrons.”

On this topic, Meyer’s research group has become a world leader, both in theory and experimentation. Using work on electron-transfer rates by Rudolph A. Marcus, who won the 1992 Nobel Prize in Chemistry, Meyer’s team is designing molecules that can avoid the back-transfer.

To do this, he says, you’ve got to make the molecule fancier, and add a catalyst or two. He uses the example of ethylene, derived from petroleum. Adding oxygen to ethylene is one step in making plastics. The trouble is, oxygen and ethylene won’t get together on their own. They need a catalyst—a molecule that binds to both oxygen and ethylene.

Finding or making the right catalysts takes a lot of experimentation, and many of the catalysts Meyer employs are artificial—designer molecules called “transition metal complexes.” Because these molecules are so useful in electron transfer, Meyer’s research group has worked a great deal with some fairly exotic metallic chemistry. In fact, each new step toward artificial photosynthesis has demanded a new branch of expertise, a new base of information. Rather than drop everything each time they hit a blind spot, the team has for years taken a “modular approach,” pushing ahead in those parts of the system for which they had good information, plugging in components as they could.

With each new set of students and post-docs, each new round of funding and research publications, the shape of artificial photosynthesis grows more and more distinct. Meyer is close, tantalizingly close, to revealing the whole. But he knows that it will probably be many years before the chemistry will be ready for industries and engineers. The most dramatic application, of course, would be energy production. But other uses, such as technologies for manufacturing new chemicals using sunlight, might be first in line.

Meanwhile, the intensive work with chemical reactions to light already has led to several breakthroughs. A Swiss scientist, Michael Graetzel, created a new medium for photovoltaics—using sunlight to generate electricity, as in solar heaters or solar-powered instruments and machines. Graetzel has developed a thin film coated with chemicals that Meyer and his group helped to invent.

As dramatic as such applications might be, they are not what drives Tom Meyer. For him, the attraction is that missing piece of knowledge, that basic insight into how something works. These pieces aren’t easy to come by. They resist. And that’s how he knows when he’s onto something—when he feels the resistance.

On my team, when we reach a kind of comfort level, that’s when I worry,” he says. “When the science gets hard, and we’re really struggling, I know we’re onto something good.”