Environmental Engineering Reference
In-Depth Information
1960; Richtzenhain and Stephan, 1975; Irani, 1977; Blum, 1984; Smallwood, 1993). The ideal sta-
bilizer must
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Adequately inhibit deleterious reactions to prevent solvent breakdown caused by the action
of light, air, or temperature on the solvent
Protect the solvent from the action of small amounts of strong acid or from metals and their
•
salts
Correct any incipient localized breakdown of the solvent
•
•
Not impart increased toxicity to the solvent or endanger worker health and safety
•
Remain stable through use in the expected industrial process
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Stand up to repeated phase transitions from liquid to vapor and back to liquid
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Remain stable at high temperatures
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Partition to the vapor phase to provide sufi cient stability in degreasing
•
Be sufi ciently volatile to exist in both the liquid and the vapor phases of the solvent and to
be recoverable from distillation residues
Boil at temperatures not more than 15°C higher or lower than the solvent boiling point
•
•
Not be consumed by reactions
•
Prevent the solvent from taking on the character of a mixture of solvents, not require addi-
tion in large quantities
Not stain the metal part, textile, or clothing being cleaned
•
•
Not leave deposits on the parts being cleaned
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Not promote the formation of corrosion products or insoluble sludge
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Be fully soluble in the solvent
•
Be at least more soluble in the solvent than in water so that water would not extract the
stabilizer
Be inexpensive
•
•
Not react with other stabilizers
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Be compatible with the metals used in the construction of the degreaser and with the many
and varied contaminants encountered in the cleaning of metal parts from modern fabricat-
ing operations
Not weaken textile i bers
•
•
Not shrink textile i bers
•
Not bleed dyes
•
Not be malodorous or leave residual odor
•
Be compatible with soaps and detergents if used in dry-cleaning applications
•
Not react with free fatty acids
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Not be so strongly alkaline that its volatility is reduced in the presence of acids
•
Be easily measurable to coni rm its concentration during use
1.2.3.2 Selection of Solvent Stabilizers
Selection of stabilizers was determined by the conditions of the particular application. The many
permutations of the various requirements placed on solvents led to decades of competitive inven-
tions of solvent stabilizer packages that would improve solvent performance in specii c applications.
For example, operations that cut and polish metals may use bufi ng compounds and drawing oils that
must be removed from the metal parts by a vapor degreaser. Bufi ng compounds and drawing oils
are sources of fatty acids. Bufi ng compounds contain 50% stearic acid, whereas drawing oils can
contain 5-10% oleic acid (Klabunde, 1949). The stabilizer package must therefore not react with
fatty acids.
As detailed in the i rst half of this chapter, perchloroethylene has been used in a great variety of
applications, for example, in dry cleaning, in electrical transformers as a heat-transfer medium, in
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