Handbook of Solvents - George Wypych - ChemTech - Ventech!

884 Kaspar D. Hasenclever
than 55°C (130°F) were at first used in Japanese and German dry cleaning operations since
1990.
Also, alternatives to conventional dry cleaning were developed. Wet cleaning was introduced
by Kreussler in 1991 (Miele System Kreussler) and textile cleaning in liquid carbon
dioxide was exhibited by Global Technologies at the Clean Show Las Vegas in 1997.
Development of dry cleaning machines
In the beginning, dry cleaning was done manually in wooden tubs filled with turpentine or
benzene. About 1860, the Frenchman Petitdidier developed a wooden cylindrical cage,
which was rotated in a tub filled with solvent. The apparel to be dry cleaned was brought
into the cage and moved through the solvent by the rotation of the cylinder. This machine
got the name “La Turbulente”.
The next step was the addition of a centrifuge to the wooden machine. The dry cleaned
apparel was transferred from the machine into the centrifuge and then dried by vaporizing
the solvent in the open air.
About 1920, a tumble dryer was used for drying the dry cleaned textiles. Fresh air was
heated up, blown through the dryer, where the air was saturated with solvent vapor and then
blown out to be exhausted into the environment. The used solvent was cleaned to be recycled
by separation of solid matter by centrifugal power with a separator and to be cleaned
from dissolved contamination by distilling.
In 1950, dry to dry machines were developed by Wacker in Germany for use with
TCE. The principle of working is as follows: The cage, filled with textiles, is rotating in a
closed steel cylinder. The dry cleaning solvent is pumped from the storage tank into the cylinder
so that the textiles in the cage are swimming in the solvent. After ending the cleaning
process, the solvent is pumped back into the storage tank and the cage rotates with high
speed (spinning) in order to separate the rest of the solvent from the textile. Then air is circulated
through a heat exchanger to be heated up. This hot air is blown into the rotating cage in
order to vaporize the remaining solvent from the textiles. The air saturated with solvent vapor
is cleaned in a condenser, where the solvent is condensed and separated from the air.
The air now goes back into the heat exchanger to be heated up again. This circulation continues
until textiles are dry. The separated solvent is collected in a tank to be reused.
In order to reduce solvent losses and solvent emissions, since 1970 charcoal filters
have been used in the drying cycle of dry cleaning machines, so that modern dry cleaning
systems are separated from the surrounding air.
14.7.1.2 Basis of dry cleaning
Dry cleaning means a cleaning process for textiles, which is done in apolar solvents instead
of water. If water is used, such cleaning process is called “washing” or “laundering”.
Natural textile fibers, such as wool, cotton, silk and linen, swell in water because of
their tendency to absorb water molecules in themselves. This causes an increase of their diameter
and a change of the surface of yarns and fabrics. The result is shrinkage, felting and
creasing.
Apolar solvents, such as hydrocarbons, are not absorbed by natural textile fibers because
of the high polarity of the fibers. So there is no swelling, no shrinkage, no felting and
no creasing. From the solvent activity, dry cleaning is very gentle to textiles, with the result
that the risk of damaging garments is very low.
Because of the apolar character of dry cleaning solvents cleaning activity also deals
with apolar contamination. Oils, fats, grease and other similar substances are dissolved in