t-Butyl Acetate: VOC Exemption
Barbara Kanegsberg, BFK Solutions
t-butyl acetate (TBAC) is another promising candidate for a variety of
applications related to cleaning and surface preparation. It has
been delisted as a VOC.
However, TBAC performance, materials compatibility, stability, and long-term
toxicity must be established.
Background, early studies
TBAC shows promise of utility in aerospace and other precision cleaning
applications (including military and aerospace), for brake cleaners,
and as a component
of coatings and inks. TBAC is now exempt as a VOC at the Federal level
(please see article on Methyl Ethyl Ketone for a brief explanation of
VOC-exemption); and progress is being made in various state regulatory
agencies, even in
California. This makes TBAC potentially useful in areas of poor air quality.
There were initial indications of promising TBAC performance for precision
cleaning applications (1,2). For example, TBAC appeared useful for
certain silicone removal applications (2); and additional studies
were recommended.
However, the VOC-exemption process was slower than one would have wished
for. The Federal VOC-exemption application started in 1997; Federal
exemption occurred in 2004. This probably slowed the progress of
performance studies.
Inhalation Studies
We have obtained a bit of information about TBAC toxicity. Specifically,
a 28 day inhalation study has been performed and that Lyondell is
conducting 90 day inhalation studies; the results will be subject to
independent
peer review.
Terry Keating, Senior Scientist at the U.S. EPA Office of Air and
Radiation, indicates that Lyondell has committed to completing
the 90 day testing
by the fall of 2006. After result evaluation and peer consultation,
the results
are expected to be provided to the EPA sometime in 2007 (3).
Perspective
I realize that mentioning that toxicity studies are being conducted
may cause unjustified angst on the part of engineers and managers.
That’s really
unfortunate, because such studies are more productively thought of as providing
a level of assurance to workers, regulators, management, and safety/environmental
professionals. To me, it is counter-productive to favor a chemical that has
zero information about worker exposure, because it has never been studied,
over a chemical where the worker exposure profile is better defined.
For chemicals that are widely-used in industry, a 90 day study
or even a multi-generation study is often considered desirable.
Publication
of the
peer-reviewed data associated with long-term inhalation studies,
if
it occurs, will provide a level of assurance for this potentially
useful chemical.
Additional Concerns and Reports
There are also additional toxicity concerns; and some of these
concerns may have impeded the exemption process. Some concerns
relate to TBAC;
others relate to t-butyl alcohol. Because TBAC is an ester,
it can break down
to
an acid and an alcohol. This breakdown can occur when the chemical
is metabolized by the body; so the potential impact of breakdown
products have to be considered.
A large report with a good summary of the California state
view of the
issues by the staff at the California Air Resources Board (CARB)
can be downloaded
(4).
You should also be aware that TBAC has a low flashpoint, and
a distinct odor. There are some indications that it may hydrolyze
after long-term
storage
under basic conditions (pH > 10), (2).
As with all other chemicals, TBAC should be handled respectfully
and cautiously.
What’s next?
As indicated in a recent review, TBAC is definitely a promising
tool for cleaning and coating in terms of solvency, soil
removal, and
lower cleaning
agent residue (5). Now that the VOC exemption hurdles appear
to be resolved and even while inhalation and other studies
are in
progress,
it is appropriate
to consider where TBAC might have utility.
References:
(1) Elias, W.E., “Real Life Applications With Environmentally
Compliant Solvents for
Electronic Assembly”, Nepcon West, February 2000,
Anaheim, Ca.
(2) Foreman, J.E. Tertiary Butyl Acetate: A Potential VOC Exempt Solvent
for Hand Wipe Cleaning and Coatings Applications, presentation at
the Tenth Annual International Workshop on Solvent Substitution and
the Elimination
of Toxic Substances and Emissions, September, 1999, Scottsdale, AZ.
(3) We appreciate the comments of Terry Keating, U.S. EPA. Terry
can be contacted at: keating.terry@epa.gov.
(4) California Environmental Protection Agency Air Resource Board, “Environmental
Impact Assessment of Tertiary-Butyl Acetate,” Staff Report, January,
2006.
http://www.arb.ca.gov/research/reactivity/tbacf.pdf
(5) Pourreau, D.B. “Tertiary-Butyl Acetate (TBAC): A Technical Overview
and Regulatory Update on the Latest VOC-Exempt Solvent,” Process
Cleaning Magazine, June, 2006.
