Comments on Cleaning with Trichloroethylene

Question:

In your August 2001 column, I read your answer to the question on outsourcing cleaning with TCE. There is one correction and a suggestion. The correction is that TCE boils at approximately 187-190F. You may want to print a correction, as this is a 50F difference from the 237F boiling point that you stated. Regarding recommending a source for vapor degreasing outsourcing, almost all plating shops have vapor degreasers. As you probably know, there are many applications where only vapor degreasing is successful at cleaning certain soils. Plating shops see them all. Also, plating shops are pretty ubiquitous in every major city. M.B.

Answer:

The reader was asking about a shop to outsource 1,1,2-trichloroethane. The Merck Index (and probably several other chemistry references) lists the boiling point of this solvent at 237F. Since this is not one of the normal chlorinated degreasing solvents, I went on to clarify/suggest that the reader could have either been asking about 1,1,1-trichloroethane (which is now essentially extinct for metal degreasing due to its ozone depletion potential, boiling point 165F) or 1,1,2-trichloroethylene, (also known as trichloroethylene or simply TCE, boiling point 189F). Those seemingly slight differences in nomenclature are very significant to the chemist and make all the difference in the world. The solvent that the reader was asking about is a saturated structure, while the TCE is an unsaturated (double-bonded carbon) structure. That difference means that the two solvents are completely different molecules with different physical characteristics, including boiling point.

Regarding vapor degreasers in plating shops, I have not found them to be ubiquitous, actually quite the opposite. Many platers require a significantly cleaner and more active surface than vapor degreasing can do. Plating shops often go through aqueous cleaning including electrolytic cleaning to fully prepare the part prior to plating. If a plating shop has a vapor degreaser, it is more than likely used to remove gross oils prior to sending the part through for its final cleaning. I did forward the name of a job shop that I am familiar with to the reader (better late than never). I hope this clarifies things and apologize for any confusion.