Handbook of Solvents - George Wypych - ChemTech - Ventech!

21.4 Alternative cleaning technologies 1499
10% polymers albumin (blood, milk), starch (food);
10% solvent soluble oils, fat, wax, grease.
The main problem in dry cleaning is the removal of pigments, water soluble material
and polymers. Apolar solvents as perc, hydrocarbons or LCD are not able to achieve this.
Drycleaning detergents (DD) will widen the activity of the drycleaning process in removing
pigments and polar substances. In order to gain a maximal benefit from DD, the
process technology must meet the special requirements. DD’s offer dispersing and
emulsifying activity to solvents, they activate water additions into micro-emulsions in order
to achieve removal of polar matter in apolar solvent. To optimize this action, a multi bath
process is used, which works under the conditions of extraction from high to low contaminated
cleaning fluids. Regeneration of cleaning fluids is realized by filtration and distillation.
For filtration a drum-pump-filter-drum circuit is used. For distillation a distilling
vessel, condensing equipment and clean solvent tank are necessary. The dimensions must
be constructed with regard to the requirements of the quantity of removed “soil” during a
full working day, which means with a 10 kg machine 750 g pigments, 600 g “salts” and
polymers, 100 g oils and fats, 1000 g DD and about 10 l of water. In order to save costs, the
cleaning baths are as short as possible, which means, about3lofsolvent per kg load, so that
per process one full bath can be distilled. In order to separate clean, average and high contaminated
cleaning fluid, most drycleaning machines are equipped with 3 tanks, a filter and
a distilling vessel with the capacity of the biggest tank.
In order to build less expensive machines, sometimes drycleaning machines are offered
which are equipped with insufficient size for distilling and less than 3 tanks. In this
case the possible cleaning result will not meet the necessary hygienic and esthetic requirements
of customers.
The same rules apply to LCD as to conventional solvents. A one tank machine and distilling
from tank to tank instead from cage to clean tank, combined with an insufficient filter
size, cannot meet the minimum requirements, even if the solvent is LCD.
21.4.1.4 Risks
The solubility of water in LCD is low (0.1%); the solubility of CO2 in water is high; at 4 bar
and 20°C 1 l of water dissolves 4 l of CO2 gas, of which about 0.1 % reacts to H2CO3, a corrosive
substance to iron and steel.
Up to now the interaction in the system LCD, surfactants, water and textiles together
with solved and dispersed contaminants has not yet been studied under practical conditions.
The influence of surfactants on the equilibrium of water in the system of high pressure without
airspace (free water, water in LCD emulsion, water adsorbed on textiles) is not yet
known. In order to achieve the removal of polar substances from textiles, in conventional
cleaning systems a desorption of moisture from textiles is necessary. If this method is compatible
with LCD is not yet known.
The low risk of shrinkage on natural textiles in dry cleaning is due to the fact, that the
adsorption of moisture is reduced, after fibers are soaked with apolar solvent beyond condensation
conditions of water. In presence of moisture within condensation conditions natural
textiles will shrink in dry cleaning more than in aqueous processes. The LCD cleaning
process works completely within condensation conditions of water. This means, that LCD
cleaning can bear a high risk of shrinkage, in particular, when water additions are used in order
to remove apolar soiling.