ISOPROPYL ALCOHOL (IPA) is widely accepted as a good liquid for keeping cleanroom surfaces in pristine condition. But what about methyl, ethyl, or butyl alcohol? Why aren’t these types of alcohols considered for cleanroom cleaning, too? It all comes down to performance, safety, and price.
Methyl Alcohol and Evaporation
At room temperature, methyl alcohol has three times the vapor pressure than that of IPA. This means methyl alcohol will evaporate at a much more rapid pace, making it difficult to keep wipers damp enough to efficiently remove surface particles. In addition, the higher vapor pressure of methyl alcohol means more of the alcohol will be in the vapor state, which means increased exposure to stringent alcohol fumes for cleanroom operators.
Ethyl Alcohol and Regulation
Though ethyl alcohol, like methyl alcohol, presents a much higher vapor pressure at room temperature than that of IPA (about 36 percent), the biggest problem with ethyl alcohol is that is a substance regulated by the Federal government.
Because some people have been known to drink ethyl alcohol, the Federal government requires it be denatured (i.e., rendered undrinkable through contamination with such solvents as methyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.).
In order to use pure ethyl alcohol (un-denatured) for wiping purposes would require applying for government permits and complying with usage tracking procedures — more trouble than it’s worth.
Butyl Alcohol and Solubility
Interestingly, butyl alcohol actually carries a lower vapor pressure. As a larger molecule, its vapor pressure is about one-eighth that of IPA. The problems, though, are in its odor and solubility.
The banana-like odor of butyl alcohol would render it objectionable to most cleanroom operators for long-term use. More importantly, the higher hydrocarbon content of butyl alcohol limits its solubility in water to about a 10 percent solution. By comparison, IPA is miscible in water at all concentrations.
IPA and Economies of Scale
IPA has achieved popularity for cleaning applications across many different industries — so many, in fact, that it is manufactured in high quantities with high levels of high purity. The volume and quality of its production presents economies of scale. Price advantages and accessibility make it an attractive choice.
IPA also presents the proper balance between polarity (for removal of oils and greases), vapor pressure (for acceptable evaporation rate and odor), and miscibility with water.
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