Azeotrope-like compositions of trichlorotrifluoroethane, nitromethane and acetone

#Fluorocarbon solvents, such as trichlorotrifluoroethane, are widely used as degreasing agents due to their excellent solvent power for greases and some emulsion-type lubricants. Trichlorotrifluoroethane also finds wide use in removing solder fluxes from printed circuit boards due to its selective solvency and non-flammability. Since trichlorotrifluoroethane is non-polar, however, it does not remove polar contaminates. Thus, to overcome this inability, trichlorotrifluoroethane has, in the past, been mixed with polar components, such as aliphatic alcohols.

#The art has looked towards azeotropic compositions including desired fluorocarbon components, such as trichlorotrifluoroethane, which include the desired polar components, and other components which contribute desired characteristics, such as stabilizers. Azeotropic compositions are desired because they exhibit a minimum boiling point and do not fractionate upon boiling. This is desirable because in vapor degreasing equipment, in which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Unless the solvent composition exhibits a constant boiling point, i.e. is an azeotrope or is azeotrope-like, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. This is also important in the use of the solvent compositions to remove solder fluxes from printed circuit boards. Preferential evaporation of the more volatile components of the solvent mixtures, which would be the case if they were not azeotropic, or azeotropic-like, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency for rosin fluxes, less inertness toward the electrical components and increased flammability.

#A number of trichlorotrifluoroethane based azeotropic compositions have been discovered which have been tested and in some cases employed as solvents for miscellaneous vapor degreasing applications and for the removal of solder fluxes from printed circuit boards. For example, U.S. Pat. No. 2,999,815 discloses the azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with acetone; U.S. Pat. No. 3,903,009 discloses a ternary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane and ethanol; U.S. Pat. No. 3,573,213 discloses the binary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane; U.S. Pat. No. 3,789,006 discloses the ternary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with nitromethane and isopropanol; and U.S. Pat. No. 3,728,268 discloses the ternary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane with acetone and ethanol.

#A distillation pot was charged with about 11 pounds of a mixture which comprised about 89.5 weight percent of 1,1,2-trichloro-1,2,2-trifluoroethane, about 10 weight percent acetone and about 0.5 weight percent of nitromethane and the mixture was heated. The barometric pressure was measured at 754.4mm Hg. A constant boiling fraction at 44.0.degree. C. was collected and found to contain all three components. Hence this fraction was determined to be azeotrope-like. Analysis by gas chromatography determined that the weight percentages of the components of this constant boiling fraction were:

#______________________________________ 1,1,2-trichloro-1,2,2-trifluoroethane 90.25 wt.% nitromethane 0.33 wt.% acetone 9.42 wt.% ______________________________________

#The boiling point of this constant boiling mixture at 760mm Hg is 44.5.degree. C.