MEK No Longer a HAP
Barbara Kanegsberg
It may seem as unlikely as water flowing up-hill. However, in terms of
regulatory restrictions, Methyl ethyl ketone (MEK) is now a more
accessible option for
general and critical cleaning applications, albeit with definite provisos.
MEK is an aggressive cleaning agent with many applications for removing
adherent soils. However, at the Federal level, MEK had been listed
as one of nearly
200 hazardous air pollutants (HAPs).
Background
Just to be sure we are on the same page: MEK or 2-butanone has the CAS
number of 78-93-3; a CAS number is useful for unambiguously identifying
chemicals
that might have different names; it’s sort of like a social security
number for chemicals.
The status of MEK as a HAP prompted a number of solvent substitution
studies. Compounds such as methyl propyl ketone (MPK) and methyl iso-butyl
ketone
(MIBK) were tested, with partial success. This is not surprising; solvency
properties are fairly specific. Further, other properties such as evaporation
rate and odor limit the utility of proposed substitutes. “Drop-in” substitutes
are not the norm; and some of the proposed substitutes have other regulatory
constraints. In fact, MIBK appears on the “EPA 17” list.
MEK HAP status
The good news is that MEK has been delisted as a HAP (1). The delisting
as a HAP occurred because the American Chemical Council (formerly the
Chemical Manufacturers Association) petitioned the EPA to do so. MEK
was delisted
at the end of 2005.
Prop 65 & ODC status
MEK has other favorable regulatory properties. MEK is not listed
under California Proposition 65. It is not an ozone depleting chemical
(ODC).
ODC’s
destroy stratospheric ozone; or desirable ozone.
Low-level Ozone
Unfortunately, MEK is a volatile organic compound (VOC); and it
is likely to remain a VOC. Very often, solvents (organic compounds)
are either
ODC’s
or VOC’s; the chemical properties tend to favor an “either/or” situation.
There are few that are neither. Those that react near the earth’s surface
and produce ozone are VOC’s. Those that survive until they reach the
upper atmosphere may destroy ozone and therefore are ODC’s. At the
Federal level, all organic compounds are classed as VOC’s unless
compelling evidence to the contrary is presented to the EPA. Further,
interested parties
have to gather this evidence and apply to the EPA for VOC-exemption.
Not all VOC’s are created equal. Classically, reactivity is judged
relative to ethane, where ethane serves as a “line-in-the sand.” That
is, compounds with a lower reactivity than ethane are more likely to be exempt
as VOC’s. VOC-exempt chemicals may still make smog, but they
are looked on more favorably by regulatory agencies.
MEK has a relatively high tropospheric reactivity (i.e. it
can react with light and other air contaminants to produce
ground-level
ozone).
Recent
maximum incremental reactivity (MIR) numbers are:
MEK = 1.48
Ethane = 0.31
While there has been some impetus to look at the actual reactivity
numbers rather than use ethane as an “off/on” switch,
the bottom line is that it is not likely that the EPA would consider
MEK for a VOC
exemption
(2). This means there will continue to be restrictions, particularly
in areas of poor air quality.
Use MEK Responsibly
Delisting MEK as a HAP is NOT synonymous with “use as much as you want
without worker safety or engineering controls.” As
with all chemicals, MEK must be used thoughtfully and responsibly.
MEK is flammable, with a very low flashpoint (various MSDS
indicate minus 3 to minus 9 Deg. C.) This means that
ignition sources
must be eliminated.
Please keep in mind that ignition sources can come not
only from your process but also from nearby processes. By contrast,
acetone
has a
lower flashpoint
of minus 20 degrees C; MEK is still definitively a flammable
solvent.
Worker exposure should be controlled and minimized. MEK
is an eye and skin irritant; and it can cause dermatitis.
Even
though
it
is no longer
a HAP,
and even though MEK has a relatively high inhalation
level (200 ppm TWA, PEL), inhalation exposure should
be minimized.
Excess
exposure
to MEK can
result in CNS (central nervous system) depression. Of
course, no one should ingest MEK.
Consider the process
MEK can be an option for cleaning, if other regulatory,
worker safety, and process-specific issues are addressed.
Like acetone, MEK is a ketone. This means it has a
carbon portion (good for dissolving oils) and a double-bonded
oxygen portion
(more water-like).
This
double-punch gives MEK a high solvency range. It
has a boiling point of 80 Deg C and it has an evaporation
rate of 2.7;
this means it sticks
around
long enough before evaporating to interact with the
soil
and the part being cleaned. In contrast, acetone
has a lower boiling
point
(57 Deg.
C); and
a much higher evaporation rate; so some people consider
acetone to be a less
effective cleaning agent, because it may evaporate
before it removes the soil.
As we indicated, it is also a rather aggressive solvent.
Aggressive solvents can react with the substrate
(the material being cleaned);
you do not want
to have materials compatibility issues. Therefore,
even if you think you remember how MEK behaved,
test it again
with
your current
product
line.
Note: Data are obtained from published MSDS and
from regulatory sources and are believed to be
accurate.
Please check all
physical and chemical
properties
prior to using in your process. Please confirm
your local regulatory constraints, as well as
any company
or customer
constraints.
Ref:
(1) http://www.access.gpo.gov/su_docs/fedreg/a051219c.html
(2) MIR numbers are from recent studies by W.
Carter, U.C. Riverside; the information was
kindly provided
by William
Johnson, U.S.
EPA.
