form have quite limited solubility in water, while
Table 1. Types of pressurized water systems (from Sum-
the micelles are highly soluble. Thus, ionic sur-
mers 1982).
factants will dissolve more readily and to a great-
Flow rate
er extent in heated water. The effects of tempera-
Type
Pressure
(L/min)
ture can be quite different for some nonionic
surfactants. For some nonionic surfactants, the
Low pressure
689 kPa
38 to 378
cmc has been found to decrease with increasing
(100 psi)
(10 to 100 gal/min)
temperature, and others are less soluble in hot
Intermediate pressure
3445 to 20,700 kPa
18.8 to 94.5
water than in cold.
(500 to 3,000 psi)
(5 to 25 gal/min)
The presence of other substances in the clean-
ing solution, such as ions (e.g., metals) or organic
High-pressure jets
68.9 to 138 MPa
18.8 to 94.5
contaminants, can also affect removal efficiencies.
(10,000 to 20,000 psi)
(5 to 25 gal/min)
According to Osipow (1962), electrolytes lower the
cmc and increase the size and alter the charge of
burns, corrosion of metal surfaces, and liberation
the micelles of ionic surfactants. Thus, electrolytes
of toxic vapors (if sufficient quantities are present).
increase the solubilization of nonpolar materials
With high-pressure water washers, high-pres-
and may increase or decrease the solubilization of
sure pumps produce solid water streams rather
polar materials, depending upon the compound
than the small droplets produced by steam clean-
being solubilized (Osipow 1962).
ing. The advantages over steam cleaning are that
In some studies there is mention of adding or-
there is increased force available and that the en-
ganic solvents to cleaning solutions to aid in the
ergy requirements are lower because water does
dissolution of sorbed organic contaminants. Al-
not have to be converted to steam. Summers (1982)
though not much data on the effectiveness of this
placed pressurized-water washing systems into
approach was found, some examples of organic
three categories: 1) those with relatively low pres-
solvents that have been used for this purpose in-
sure and high flow rates, 2) those with intermedi-
clude ethanol, acetone, and butanol. According to
ate pressure and flow rates, and 3) those with rel-
Osipow (1962), added organic compounds in-
atively high pressure jets and intermediate flow
crease the micelle volume of ionic surfactants, and
rates (see Table 1 for specific pressures and flow
the increased volume of this "pseudophase" is
expected to have an increased solvent action on
rates).
other organic materials. (Concentrations of exam-
Summers (1982) found that adding long-chain
ples given by Osipow were 0.1 to 0.3 moles/1000
polymers (such as Polyox [Union Carbide], Nalco
g surfactant.) Organic compounds may also af-
[Nalco Corp.], and Superwater [Berkley Chemi-
fect the cmc of surfactants. Long-chain alcohols
cal Corp.]) to the wash water improved perfor-
and amines will lower the cmc, and short-chain
mance. Although the function of these polymers
alcohols may increase or decrease the cmc de-
is not fully understood, Summers believed that
pending upon the temperature (Osipow 1962).
they reduced the flow resistance of the liquids and
maintained the integrity of the jet stream for a
Pressurized water cleaning
longer distance after it left the nozzle. The effi-
With steam cleaning, pressure developed in the
ciency of high-pressure water jets can also be en-
steam boiler imparts a high velocity to a mixture
hanced with other additives, such as abrasive or
of water droplets and steam, which is directed
nonabrasive particulates (abrasive cleaning),
from a nozzle onto the target surface. Detergent
surfactants, or other additives that affect the phys-
and heat from the steam weaken the bonds be-
ics of interaction between the liquid jet spray and
tween the dirt and surface while the high velocity
contaminant residue (Cante et al. 1980).
of the water droplets has sufficient power to re-
move the debris from the surface (Summers 1982).
Cleaning or rinsing with
Depending upon the contaminant, steam can also
organic solvents
facilitate volatilization, thermal decomposition,
Typically, organic solvents are used where 1)
and hydrolysis. Esposito et al. (1985) felt that long-
water is undesirable (e.g., for electrical and elec-
term exposure to steam should theoretically aid
tronic devices or where humidity might corrode
in the removal of subsurface contaminants as well.
neighboring equipment), 2) contaminants consist
Problems associated with steam cleaning include
of grease, tar, oil, and rosins, 3) fast evaporation is
5
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