Several companies, such as Separex in France and Messer in Germany, have also
developed a number of technologies that use supercritical CO 2 in the production of
extremely fine particles. One recently commercialized process dissolves a variety of
compounds ranging from pharmaceuticals to paint pigments in supercritical CO 2 .
When the pressure is suddenly released, the material precipitates as particles smaller
than 10 lm with a very homogeneous size distribution.
The same process allows for controlled precipitation of polymers with narrow
bands of molecular weight distribution.
8.3.5 Dry-Cleaning Fluid
SC-CO 2 can be used as substitute of NH 3 or perchloroethene (PERC) in dry
cleaning of cloths, a large industrial activity that only in Europe employs 180 000
workers. There is a great environmental benefit in such change as both ammonia
and PERC have a larger environmental impact than CO 2 itself. The dry-cleaning
sector currently has 75 000 cleaning machines using PERC or CFC 113 as cleaning
solvents. The substitution with SC-CO 2 is not straightforward and requires the
development of the right detergents/additives and operative conditions (T, P,
fluid-flow, fluid-textile w/w ratio, etc.) in order to guarantee that textiles and garments are not damaged. In particular, it is necessary to guarantee an excellent
cleaning effect with soil and stains removal, greying–shrinkage–colorfading
avoidance [10].
All such parameters are still under study for a full exploitation of such applications of CO 2 .
8.3.6 Cleaning Agent in the Metal- and Electronic Industry
SC-CO 2 finds diversified applications in the metal and electronic industry. The
major use for carbon dioxide in the metal industry is for welding on ships, construction sites, and in manufacturing operations. Carbon dioxide is used alone or
with Ar or He as a shielding gas to protect the welding zone from the deleterious
effects of oxygen, nitrogen, and hydrogen. Although slightly less effective (He
produces the hottest arc and Ar is best cleaner), carbon dioxide finds large use
because of its lower cost. Moreover, when used as a shielding gas with
semi-automatic micro-wire welding equipment, CO 2 speeds up by 10 times the
welding speed and cleans the weld surface avoiding wire brushing.
An earlier use (now very limited) was as binding agent, in combination with
other additives, in the production of sand moulds and cores for casting iron and
other metals.
Messer Group GmbH (Bad Soden, Germany) commercializes a SC-CO 2 process
for separating sludge formed in metalworking into clean oil (soluble in SC-CO 2 )
and metal particles. Oils, metal, and CO 2 can be easily separated, collected, and
recycled.
8.3 Uses of CO 2 and Its Quality
131
developed a number of technologies that use supercritical CO 2 in the production of
extremely fine particles. One recently commercialized process dissolves a variety of
compounds ranging from pharmaceuticals to paint pigments in supercritical CO 2 .
When the pressure is suddenly released, the material precipitates as particles smaller
than 10 lm with a very homogeneous size distribution.
The same process allows for controlled precipitation of polymers with narrow
bands of molecular weight distribution.
8.3.5 Dry-Cleaning Fluid
SC-CO 2 can be used as substitute of NH 3 or perchloroethene (PERC) in dry
cleaning of cloths, a large industrial activity that only in Europe employs 180 000
workers. There is a great environmental benefit in such change as both ammonia
and PERC have a larger environmental impact than CO 2 itself. The dry-cleaning
sector currently has 75 000 cleaning machines using PERC or CFC 113 as cleaning
solvents. The substitution with SC-CO 2 is not straightforward and requires the
development of the right detergents/additives and operative conditions (T, P,
fluid-flow, fluid-textile w/w ratio, etc.) in order to guarantee that textiles and garments are not damaged. In particular, it is necessary to guarantee an excellent
cleaning effect with soil and stains removal, greying–shrinkage–colorfading
avoidance [10].
All such parameters are still under study for a full exploitation of such applications of CO 2 .
8.3.6 Cleaning Agent in the Metal- and Electronic Industry
SC-CO 2 finds diversified applications in the metal and electronic industry. The
major use for carbon dioxide in the metal industry is for welding on ships, construction sites, and in manufacturing operations. Carbon dioxide is used alone or
with Ar or He as a shielding gas to protect the welding zone from the deleterious
effects of oxygen, nitrogen, and hydrogen. Although slightly less effective (He
produces the hottest arc and Ar is best cleaner), carbon dioxide finds large use
because of its lower cost. Moreover, when used as a shielding gas with
semi-automatic micro-wire welding equipment, CO 2 speeds up by 10 times the
welding speed and cleans the weld surface avoiding wire brushing.
An earlier use (now very limited) was as binding agent, in combination with
other additives, in the production of sand moulds and cores for casting iron and
other metals.
Messer Group GmbH (Bad Soden, Germany) commercializes a SC-CO 2 process
for separating sludge formed in metalworking into clean oil (soluble in SC-CO 2 )
and metal particles. Oils, metal, and CO 2 can be easily separated, collected, and
recycled.
8.3 Uses of CO 2 and Its Quality
131