- Supercritical carbon dioxide
DuPont Co. (Wilmington, DE) has begun construction of a $40 million, 2.5 million lb/y development and manufacturing facility to make melt-processable fluoropolymers using a process based on supercritical carbon dioxide. Should the demonstration prove successful, the company will spend $275 million over the next seven years to build a worldscale fluoropolymer and fluoromonomer facility.
The company says it has been testing the technology at a $2-million pilot plant it brought on stream in 1999 at the DuPont Experimental Station in Wilmington, DE. It expects the Fayetteville unit to open in late 2000 and produce fluorinated ethylene propylene (FEP) and perfluoroalkoxy resin (PFA). The company plans to demonstrate the technology for two to three years before building a larger plant.
The technology gives DuPont the ability to make new grades with specialized properties. It also promises to be more efficient, more flexible, and less costly than existing processes.
It was developed through a partnership between DuPont and Joseph DeSimone, a chemistry professor at University of North Carolina-Chapel Hill. He is a pioneer in polymer synthesis using supercritical fluids, gases that turn liquid and show tremendous solvating power under high pressures. DuPont has supported his research since 1990.
DuPont's Teflon FEP is widely used for plenum cable insulation because of its excellent insulating properties, fire resistance, and light weight, which makes it easier to string over long distances. A new production technology based on supercritical carbon dixoide promises more specialized grades and improved process economics.
Supercritical carbon dioxide (back to top)
Supercritical carbon dioxide has several advantages, says DeSimone. "Fluoropolymers can't have hydrogen present in the solvent because it's chain transfer agent," he explains. "Carbon dioxide doesn't have any hydrogen, and so it's inert to free radical chemistry." This simplifies some reactions and makes other economically feasible.
Supercritical carbon dioxide is a powerful solvent that works especially well with fluoromonomers, which are insoluble in most solvents except chlorofluorocarbons. "It's easy to dissolve comonomers," DeSimone continues, "and it's easy to isolate the polymer after synthesis." When pressure is released on supercritical carbon dioxide, it turns into a gas and evaporates, leaving behind the products of the reaction.
"It lets us make a lot of the same polymers in a more environmentally friendly way," says DeSimone. "Water or chlorofluorocarbons, which are typically used to make fluoropolymers, get contaminated. Here, there's a lot less waste, and it's easier to isolate and dispose of. When you dry polymer made in water, it takes a lot energy because water has a high heat of vaporization. Here, the energy consumption is much less."
DeSimone says his group reported the first successful homogeneous free radical polymerization in an inert supercritical fluid (SCF) in 1992. Since then, he has expanded synthesis technology to include dispersion, cationic, ring-opening metathesis, step-growth, and additional heterogeneous polymerizations.
He is also codirector of the Kenan Center for the Utilization of Carbon Dioxide in Manufacturing, a joint UNC-North Carolina State University research center with 16 corporate sponsors. It focuses on industrial use of supercritical carbon dioxide that range from coatings to textile dyeing. The center has more than 20 faculty and 40 students and post-doctoral associates.
DeSimone's own research group at UNC currently consists of 16 graduate students, five postdocs, and a visiting professor. Under a licensing agreement, DuPont will provide UNC with royalty payments when production begins, as well as continue its financial support for related technology and research efforts.
DuPont's Fayetteville plant (which is north of the city in Bladen County) produces Butacite polyvinyl butyral protective laminates for automotive windshields, and Nafion polymer membrane for chloralkali production. It currently employs 515 people.
Although DuPont wants to scale up the technology to construct a worldscale fluoropolymer and fluoromonomer facility, it is not yet committed to building the unit in North Carolina. A DuPont press release says plans "are contingent upon successful passage of legislation now before the North Carolina General Assembly."
The bill (back to top)
The bill, a package of financial incentives for the company, was introduced by North Carolina State Senator Tony Rand. DuPont also says that construction will depend on resolution of "other logistical factors in North Carolina." A company spokesperson would not elaborate on what, exactly, that means.
"We're the fluoropolymer market and technology leader, and part of that leadership is introducing new polymers, driving costs, and improving quality," says DuPont Fluoroproducts global business manager Henry B. Voigt. Some of our competitors have announced plans for new capacity, but I really expect this plant to be more significant than that."
"The additional capacity and new products we will gain from this investment will strongly support our customers in the rapidly growing data communications, semiconductor and automotive markets," he says.
The world's largest producer of fluoropolymers, DuPont operates facilities in United States, Europe and Japan. DuPont Fluoroproducts serves industries as diverse as telecommunications, aerospace, refrigeration, air conditioning, pharmaceutical, automotive, electronics, chemical processing, and home furnishings. Its brands include Teflon fluoropolymers, SilverStone nonstick finishes, and Suva refrigerants.
For more information: Joseph M. DeSimone, University of North Carolina at Chapel Hill, Dept. of Chemistry, B-5 Venable Hall, CB 3290, Chapel Hill, NC 27599. Phone: 919-962-2166. Fax: 919-962-5447. Email: email@example.com.
By Nick Basta