This paper evaluates simple tests to be used as criteria for determining the condition of cold dipping (Stoddard solvent), vapor degreasing (chlorinated solvents), and precision cleaning solvents (Freon-113 and isopropanol), and for identifying when a solvent should be changed, thereby extending its usage life cycle. The use of these tests to monitor the quality of reclaimed solvent is also explored.
Several physico-chemical solvent properties were selected on the basis of sensitivity to solvent contamination, and the reliability and simplicity of the methodology for measuring these properties. Visible absorbance spectrometry was the most reliably measured property, followed by specific gravity, viscosity, and electrical conductivity. Additional testing is required for chlorinated solvents to determine inhibitor concentrations. These properties were monitored for several spent solvent batches and found to yield consistent results. The use of only one criterion based on one property would be adequate in most cases; however, the identification of when a solvent becomes spent can be determined more accurately when two or more criteria are used.
The major inhibitors present in trichloroethylene, tetrachloroethylene, and 1,1,1 -trichlo-roethane were identified using gas chromatography-mass spectrometry. These inhibitors can be classified as antioxidants, acid acceptors, and metal stabilizers. The inhibitor concentrations were monitored with usage time. Batch kinetic studies show that the reactions between the acid acceptors (butylene oxide, cyclohexene oxide, and epichlorohydrin) and hydrochloric acid, and between the metal stabilizers (1,4-dioxane and 1,3-dioxolane) and aluminum chloride were each second-order overall when tetrachloroethylene was used as a solvent. A simple test was also devised to determine the metal stabilizer concentration in a solvent.
Solvent reclamation by batch distillation is a viable option for significantly reducing solvent replacement and disposal costs. Batch distillation is most feasible when the same unit is used to reclaim multiple solvents. Simple physico-chemical tests, for example, absorbance, electrical conductivity, acid acceptance, and so forth, can be used to monitor the condition of reclaimed solvent, and to determine additive requirements. Reclamation studies on spent chlorinated solvents were carried out by using distillation and a carbon adsorption method.