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Graphic element Research > Growth > Research projects > Cross-disciplinary projects > Supercritical fluids clean up polymer manufacture
Graphic element Supercritical fluids clean up polymer manufacture

New production methods employing supercritical fluids - gases subjected to very high pressures - can drastically reduce the large amounts of toxic waste generated in the conventional manufacture of plastics. Additionally, because the processes avoid undesirable side reactions, they can result in polymers of exceptionally high purity.

The European Commission-funded SUPERPOL BRITE-EURAM project was established to examine the use of supercritical CO2 (SCO2) in achieving more environment-friendly polymerisation processes. This three-year collaboration, taking place between 1997 and 2000, involved the universities of Thessaloniki (Greece), Liège (Belgium), Ulm (Germany) and Palermo (Italy), together with chemicals companies Solvay (Belgium), Goldschmidt (Germany) and DSM (The Netherlands).

The main aim was to undertake basic research into the feasibility of introducing the technology within the European plastics industry - and the first commercial application is likely to be for fluoropolymers. However, both the success of this project and competitive pressures worldwide are driving further developments at a fast pace.

A cleaner environment

At present the manufacture of polymers - including fluoropolymers -- involves either an aqueous phase, or an organic phase consisting of chlorfluorocarbons, as the dispersion medium. When water is used, the quality of the product suffers and large amounts of polluting wastewater are discharged. Although conventional chlorfluorocarbon solvents yield a higher quality polymer, they pose such severe environmental hazards that their use is becoming unacceptable.

SCO2 offers several advantages as an alternative. It not only eliminates the discharge of ground waste streams, but also reduces the emissions of volatile organic compounds by replacing these with environmentally friendlier carbon dioxide (CO2 ). Under the high pressures (up to 200 bar) that produce the supercritical state, CO2 behaves like a liquid -- but at lower pressures it reverts to a gaseous form. This property greatly facilitates the separation and purification of the final product in the reaction medium, at the same time making substantial energy savings.

Ultra high purity

Fluoropolymers are high-grade speciality products used in a wide range of industries - a large proportion going to aerospace. "There is a premium placed on their purity, particularly in electronic semiconductor manufacture," says project co-ordinator Costas Kiparissides of the University of Thessaloniki. "Companies that can produce the highest grade fluoropolymers will control the markets for semiconductors and other high tech applications. The winners will be the companies using the new SCO2 technology."

DuPont de Nemours, the world's biggest producer, has constructed in the USA the first plant for the manufacture of fluoropolymers using SCO2 as the reaction medium. The company has announced that production will come on-stream during 2001, at a modest capacity of 1,100 tonnes. However, there are already plans in place to scale this up dramatically within five years.

"All the fluoropolymer producers in Europe are trying to develop their own patents. They realise that in five to ten years, SCO2 technology could dominate. They have to move in this direction, otherwise they could go out of business," insists Kiparissides.

Various assessments have been made of the cost savings accompanying the use of SCO2 technology for fluoropolymer production. But these do not take into account the economic benefits of new, superior quality products - which could be considerable.

"We estimate that applying the new technology could reduce manufacturing costs by around 20%," says Kiparissides. "In Europe this amounts to about € 0.5 per kilo of product, meaning a total saving of some € 3.5 million a year. An additional economy in the region of € 1 million per year will come from the elimination of wastewater treatment."

   Exciting new developments

Of the numerous potential uses for supercritical fluids, one of the most profitable may well be in cleaning services - for tank cars, valves, pipes and factory equipment; in fact wherever solvents are currently used. One application that has already become a reality in the USA, but not yet in Europe, is the dry cleaning of clothes for the general public.

"In 10 to 15 years, I'm sure we are going to see this technology to some extent in a very wide range of applications. In both the automotive and aerospace industries, for instance, it could easily reach a prominent position within ten years," adds Kiparissides.

Following the success of SUPERPOL, several former participants have joined with new partners in a proposal to build pilot plants over the next three years for fluoropolymer production using SCO2. At the same time, the University of Thessaloniki is forming a separate consortium to investigate the production of nanoparticles with the technology. In this form, extremely efficient catalysts become available to the chemical industry.

"One exciting medical application of nanoparticles is as polymeric carriers for drug delivery," says Kiparissides. "The active ingredient is encapsulated in the nanoparticles, permitting its release in a slow, controlled way over a week or even longer. There is nothing like that available at present."

See also
Growth programme shows new ways to sustainable development
A cleaner environment
Ultra high purity
Exciting new developments

Key data

Cleaner production is an important element of the Innovative products, processes and organisation key action of GROWTH. The SUPERPOL project consortium studied the replacement of solvents by supercritical CO2 as a route to more environment-friendly production of high-purity polymers.


SUPERPOL - Polymerisation and polymer modification in supercritical fluids - a novel way for cleaner manufacturing of plastics (BRPR970503)

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