Cleaning solvent selection

I now shall present a summary of an application of decision analysis to a specific chemical, perchloroethylene (PCE), a widely used dry cleaning solvent (also called tetrachloroethylene). Full details of this application are presented in an EPA report (5). Perchloroethylene was selected for us by the staff of the EPA Office of Toxic Substances as representative of chemicals on which EPA needed to make an unreasonable risk determination under TSCA. Our analysis was carried out as an exercise in methodology development and not to support any specific regulatory activities by EPA concerning perchloroethylene. 

Recommended Solvent Selection Procedure. Resin contaminants have been identified only recently. Until 1977, only the following resin contaminants were identified naphthalene, ethylbenzene, and benzoic acid (36). The resin cleaning procedure of Junk et al. (5), which uses a series of three solvents of decreasing polarity, removes the widest possible variety of organic contaminants from the resins. This method is necessary when many compounds must be removed. 

The main outlet of the vessel should be at least 75 mm in diameter to allow for a fast flow of the prepolymer. The outlet can be connected either to a recirculating pump or directly to a filter prior to the drum filling. The pump must be capable of pumping the most viscous material quickly. Another key point to be noted when selecting a pump is that it has to have suitable glands. It also must be able to withstand the cleaning solvents and be readily stripped for clearing any buildup in the pump. 

Jimenez-Gonzalez, C., A. Curzons, and V. Cunningham. 2004. Expanding GSK s solvent selection guide-application of life cycle assessment to enhance solvent selections. J. Clean. Tech. Environ. Policy 1 42-50. 

A. D. Curzons, D. C. Constable and V. L. Cunningham, Solvent Selection Guide A Guide to the Integration of Environmental, Health and Safety Criteria into the Selection of Solvents, Clean Products and Processes, 1, 82-90 (1999). 

Solvent selection will often predetermine the order of addition. For example, although inverse addition of 2,6-dibromopyridine to one equivalent of -BuLi at -78°C has been reported to provide clean monolithiation via reequilibration of the initially formed 2,6-dihthiopyridine, the use of dichloromethane, a much less basic solvent, allowed addition of -BuLi to 2,6-dibromopyridine to produce the desired 2-bromo-6-lithiopyridine directly (Scheme 12.2, eq. A)P... 

Selective Crystal Dissolution. An effective method for distinguishing bulk (lattice trapped) versus surface impurities involves the selective dissolution of a crystal sample while testing the liquid and/or crystalline phases for relative purity. In this technique, a small sample of crystals of a narrow size fraction is washed with successive small amounts of clean solvent until most of the crystalline phase is dissolved. The filtrate and/or crystalline phase are analyzed after each washing to discern whether impurities reside predominantly at the surface, or are more evenly distributed throughout the crystalline phase. The general approach is described by Narang and Sherwood (1978) for quantifying caproic acid incorporation in adipic crystals, and by Addadi et al. (1982) for amino acid separations. 

The brand of the HPLC system does not matter, many manufacturers produce excellent apparatus. A few key specifications are important, however, to perform the methods presented here. If large diameter columns (25-mm) are to be used, the pumps should support flow rates of 9 mL/min and the UV detector cell must be able to withstand back pressures generated by these high flow rates (refer to the appropriate operating manual or contact the manufacturer s technical representative). A solvent selection manifold, at least on the B pump, is helpful for sample loading (otherwise, the B pump solvent lead and filter must be cleaned after sample loading prior to introduction of the B solvent see Section 3.2.1.)... 

The amount of heat required depends on the weight and specific heat of the work to be cleaned, radiation losses of the tank, amount of heat desired for the distillation rate or for the sprays, and the solvent selected for use. 

The waste cleaning solvent is handled differently by different shipyards. Facilities that use different type solvents for cleaning and thinning, or utilize multiple cleaners may select disposal rather than recycling for re-use. This decision is typically based on cost. Other facili-... 

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