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
(Germany) and Palermo
(Italy), together with chemicals companies Solvay
(Germany) and DSM
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
||Ultra high purity
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."
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,"
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,"
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."
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
- Polymerisation and polymer modification in supercritical fluids
- a novel way for cleaner manufacturing of plastics (BRPR970503)