Note: Descriptions are shown in the official language in which they were submitted.
~IL0495~7
BACKGROUND OF THE INVENTION
Methylene chloride is a highly versatile and useful
solvent for various industrial applications at both normal
and elevated temperatures. A particularly important industrial
use is the vapor degreasing of metals. Methylene chloride
is ,known to be more stable than other chlori,n~ted hydrocarbons
solvents such as perchloroethylene, trichloroethylene and
methyl chloroform when the solvents are used in unstabilized
condition. For example, methylene chloride is more resistant
to oxidation, hydrolysis and pyrolysis than other chlorinated
solvents and does not substantially react with aluminum in '~
the aluminum scratch test commonly used to indicate unstabilized
or minimally stabilized methyl chloroform. In addition,
methylene chloride may be used to greater advantage in vapor
degreasing of metals than other known degreasing solvents
since it may be used effectively at lower temperatures due
to its lower boiling point and excellent stability. MethyLene
chloride is particularly desirable for such degreasing operations
since it is substantially resistant to photochemical activity
20 and therefore does not contribute to air pollution by smog '-`
formation. However, methylene chloride when used in various
metal cleaning functions, including vapor degreasing, suffers
the disadvantage of being reactive with aromatic compounds in
the presence of metals, metal halides and combinations thereof,
including aluminum, zinc and iron, halides thereof, and com~
binations of said metals and halides which react with the
methylene chloride to produce hydrochloric acid and objection- '
able high boiling tarry substances which render the methylene
chloride unsuitable for further useO The entire reaction of
methylene chloride in the presence of aromatic compounds is
: -2-
~4~567
not completely understood but is bel.ieved to be a condensation
reaction catalyzed by metal, metal halides or combinations
thereof~ Thus, the aromatic compound reaction wit.h methylene
chloride is believed to be catalyzed, or inltiated and
catalyzed by the presence of metals such as aluminum, zinc,
iron and the like, halides of said metals and combinations ':
of said metals and halides. Such ,reactions are thought to
be of the nature of a Fxiedel-Craft type reaction. Aromatic . ~
organic compounds of this nature and metals such as aluminum, .~ ' .'
10 iron and zinc, their halides and combinations are generally ~
introduced into the methylene chloride from various cutting ~: '
oils and Iubricants used in metal fabricating operations : -
which are carried over into the methylene chloride solvent
during vapor degreasing or other cleaning of the fabricated ~;
metal parts. Solvent manufacturing, handling and storage
equipment is another source for introduction of such impuritiesO
To prevent degradation and other types of deterioration such
as oxidation, hydrolysis and pyrolysis whi.ch may occur in
some instances, it has been the practice to incorporate
~ 20 minor quantities of various organic compounds into methylene
;~ chloride, which compounds act as stabilizers to substantlally '.' ,
prevent such degradationO It is desirable to provide
methylene chloride stabilized to effectively prevent degra-
dation in various applications/ and the demand still exists
for a low cost stabilized methylene chloride composition that
can be easily prepared and which provides optimum stabiliza-
tion under many different operating conditions~
. SUMM~RY OF THE INVENTI_ .
An object of this invention is to prevent deterloration
30 or degradation of methylene chloride in assocat.ion with metals, ~'
:
.
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~49567
metaL halides and combinatl.ons inclu,ding aluminum, iron and
zinc, halides oE sai.d metals and combinations and an aromatic
compound capable of reacting w.ith methylene chlo:ride in the
presence of said metals, metal halides and combinations.
A further object of this invention is to provide a
stabilized methylene chlo:ride composition in which the
stabilizers are low in cost. and capable of being incorporated
with ease into ~he methylene chlorideO
A still further object of this invention is to provide
a process for the degreasing of metals b,y contacting the
metals with methylene chloride stabilized to prevent degrada-
tion of the methylene chlor.ide in the presence of metals,
metal halides and combinations thereof including aluminum,
iron and zinc r halides of said metals and combinations and
aromatic compounds which react w.ith the meth,ylene chloride
in the presence of said metalsl metal halides and combinations
thereof.
Still another object of this inven.tion ,is to provide a
process for the degreasing of metals by contacting the metals
20 with methylene chlo.ride stabilized to prevent deg.radation ; ::-
of the methylene chloride in the presence of impurities such
as reactive aromatic compounds and metals including aluminum, : '
iron, zinc and the like~ halides of said metals and comb.ina~
tions of the individual metals and salts thereof. ~ ~
These and additional objects of the present invention - :-
will become apparent to those skilled in the art from the ,~,'. ,~
description and claims which follows~
DESCRIPTIO_ OF THE PREFER~ED EMBODIMÆNTS .
The objects set fo.rth above have been found to be
attained by provid.ing a compositlon consisting essentialLy
. .~ .
; - :
:~L049567
of methylene chloride containing stabilizing amount of from
about 0.001 to about 2.0 percent by weight of tne methylene
chloride of each of diisopropylamine, N-metnyl pyrolle, butylene
oxide, propylene oxide, methyl acetate, acetone, tertiary
amylenes and optionally methyl alcohol. ;~
The quantity of the stabilizing agents useful in the
practice of this invention will vary depending upon the con-
ditions of use, the identity and ~uantity of other stabilizers
incorporated into the methylene chloride and other practical ;
operating considerations. ~ach stabilizing agent or compound
may generally be used within the range of from about .001 to
about 2.0 percent and preferably from about 0.002 to about
1.0 percent by weight of the methylene chloride. Although
higher concentrations may be used, if desired, no additional
benefit is obtained and the cost is unnecessarily increased.
While the above composition containing stabilizing agents
provides optimum prevention of degradation of the methylene
chloride under a variety of operating conditions it is also
possible to stabilize methylene chloride by deleting the
propylene oxide depending on the stabilization required for
the particular operating conditions.
Tne stabilized composition may be used for the degreasing
` of metals by contacting the metals with the stabilized
composition. Thus, the process for vapor degreasing metals
comprises contacting the metals to be degreased with the
above described stabilized methylene chloride compositions
i wherein the methylene chloride contains an admixture of
`li stabilizing amounts of diisopropylamine, N-methyl pyrolle,
butylene oxide, propylene oxide,methyl acetate, acetone,
tertiary amylenes and optionally methyl alcohol. In degreasing
`~ metals with the above described preferred stabilized methylene
_5_
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10495~7
chloride in the presence of an aromatic compound which
reacts with methylene chloride in the presence of metals,
metal halides and combinations thereof including aluminum,
iron, zinc, halides of said metals and combinations, there
exists upon contact of the metal with the stabilized methy-
lene chloride a composition comprising methylene chloride, a
stabilizing amount of from about 0.001 to about 2.0 weight
percent of the methylene chloride of each of diisopropylamine,
N-methyl pyrolle, butylene oxide, propylene oxide, methyl
acetate, acetone, tertiary amylenes, optionally methyl
alcohol, and an organic compound which reacts with methylene
chloride in the presence of said metals, metal halides and
combinationsO The metals, metal halides and combinations may
be present from any source such as chloride formed by drilling -.
or other machining of aluminum or aluminum-containing materials
with various working fluids such as cutting oils, lubricants : -
and the like, or aluminum chloride may be present from the
reaction of methylene chloride with aluminumO The reactive
aromatic compounds include toluene, mesitylene, napthalene,
and the like~
In order that those skilled in the art may readily
understand the present invention and certain specific embodi- .. -
ments by which it may be carried into effect the following ~ :
illustrative examples are presented. .
In Examples 1 and 2, respectively, of Table I, 15 ml.
of substantially water free methylene chloride and methylene .;
chloride stabilized with the specified quantities of diiso-
propylamine, N-methyl pyrolle~ propylene oxide, butylene
. oxide, methyl acetate, acetone, tertiary amylenes and methyl
; 30 alcohol were placed in glass vials containing a 1 cm2 aluminum
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-6-
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9St;'7
coupon 1~64" thick. The vials were tightly capped and allowed
to stand at ambient conditionsO After 16 hours no changes
had taken place in the appearance of the solvent, the pH or
the aluminum in each vial. Toluene in an amount of 5~ by
volume and about 0.04 grams of anhydrous aluminum chloride
were then added to each vial, the contents stirred, changes
in the contents recorded, and the vials loosely capped and
allowed to stand. After four hours and after twenty-two
hours changes in the appaarance of the aluminum coupons and
the solvents, and relative pH values of the solvents, were
recorded. The procedure of Examples 1 and 2 was followed
in Examples 3 to 7 of Table I. In the latter Examples various
compounds reported in ths prior literature to be useful in
stabilizing chlorinated solvents were evaluated for their ability
to stabilize methylene chlorideO In Examples 3 to 7 after
the tightly capped vials had been standing for 16 hours no
changes had occurred in the appearance of the solvent, the
pH or the aluminum coupons. The results of the tests of
Examples 1 to 7 are set forth in Table Io
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~049567
From Table I it will be readily observed that after four
hours the methylene chloride without the stabilizing composition
of this invention had undergone a degradation reaction
resulting in a dark orange coloration, evolvement of hydrogen
chloride gas and complete loss of utility of the solvent.
Examples 3 to 7 inclusive of Table I show that various com-
pounds frequently used as solvent stabilizers are not as
effective as the stabilizing composition of this invention in :
inhibiting degradation of methylene chloride by reaction of
aromatic compounds with methylene chloride in the presence of
~ ,: . -: -
metals, metal salts and combinations thexeof.
In Examples 8 to 12 of Table II, below, aluminum reflux ~ :
., . - . .
stability tests were carried out by placing 200 ml of methylene
chloride in a 300 ml flask, adding about 1.0 grams of 20 mesh
granular aluminum and suspending a bright aluminum coupon
about 2 x 7 cmO in a condenser fitted to the flaskD Methylene
chloride and the solvent containing 5~ by volume of Mesitylene,
5% by volume of Mesitylene with the stabilizing composition ~
of this invention and 5% by volume of Durene were refluxed for :: .
varying time periods. In the tests the pH and acid content,
as HCl, were determined and visual observations of the aluminum
condenser coupon were made at the completion of the test~ The .
results of these tests are set forth in Table II below.
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The tests in Table II were conducted by venting the
condenser to room air and without the addition of water.
Also in Table II the pH determinations were made with a portion
of the water layer obtained by extraction of the solvent with
water equal to the volume of the solvent system.
Table II illustrates the prevention of degradation of
methylene chloride by the stabilizing components of this ' ~ -
invention in the presence of aluminum and the aromatic com-
pound Mesitylene in Example lOo Examples 9 and 11 to 12 show
degradation of methylene chloride in the presence of the
aromatic compounds Mesitylene and Durene (tetramethyl benzene)
when refluxed with aluminum in the absence of the stabilizing
composition of this invention.
In Table III hydrolytic stability tests were made by
placing 150 ml. of methylene chloride in Example 13 and 150 ml.
of methylene chloride containing the stabilizing composition
specified in Example 14 into a 300 ml. boiling flask. The
flask was fitted with a Soxhlet extractor equipped with a
syphon break and a condenser vented to room air. Fifty milli-
liters of the solvent of each Example were first introducedinto the Soxhlet and 50 ml. of water was then added. One gram
of 20 mesh granular aluminum, about one gram of 30 mesh -~
granular zinc and about 0.1 g of iron powder were placed in
the flask. A 2 x 7 cm. zinc coupon of known weight was
positioned in the Soxhlet and a 2 x 7 cm. weighed steel coupon
was mounted in the condenser. The contents of the flask were
refluxed for the period of time specified by heating the
boiling flask with an electric heater. At the end of the
reflux period the pH and alkalinity, as NaOH, of the solvent
contents of the So~hlet and of the flask were determined from
-12-
1049S67
a portion of the aqueous phase obtained by extraction of the
solvent with an equal volume of neutral distilled water after
the solvent system had been refluxed for the time specified~
The zinc and iron coupons were cleaned of any accumulated
corrosion products, weighed and the difference in initial and
f.inal weight recorded as weight loss,
The results are shown below in Table III.
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~L~49567
The superiority of the stabilizing composition of
this invention is evident ~rom a comparison of the results of
Example 14, the composition of the present invention, and
Example 13, a stabilizing composition of known good stabilizing
characteristics formulated by the applicant hereinO Much less
corrosion of the zinc coupon in the Soxhlet and the iron
coupon located in the condenser occurred in the use of the
composition of this invention during the 15 day reflux period.
In Examples 15 and 16 of Table IV reflux stability
tests were conducted by following Federal Specification
O-T-236b modified by the use of 200 ml. of the solvent
system in place of 100 ml. and by positioning a 6-watt ultra-
violet lamp about one inch from the vapor tube of the Soxhlet
extractor. A 300 ml. boiling flash was fitted with a Soxhlet
extractor, a condenser connnected to the extractor, about 1.0
gram of granular zinc and about 0.5 ml. of water was added . ~-
to the flask and a 2 x 7 cm~ zinc coupon was inserted in the
extractor and the condenser. The condenser was vented to a
water scrubber.
The results of the tests are presented in Table IV
: , . . .
95167
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~o~5~;7
Storage stability tests of stabilized methylene ,
chloride carried out in Examples 17 ko 19 of Table 5O About
250 ml each of three stabilized methylene chloride composition~
specified in the Examples was placed in a pint bottle contain-
ing three lJ16" diameter x 5" rusty steel rods and two 1/2" x
6" x 0,003" gauge rusty steel coupons. About lo 32 ml ~0~4 WtD%~
of distilled water was added and the entire contents of the
bottle thoroughly agitated at the start of the test period.
In Example 17 an additional 0. 4 wto % was added to the bottle
after one day~ The capped bottles were permitted to stand
for five days after which visual observations of the steel
coupons, the solvent and the surface of the solvent were
made and recordedO The bottles were then uncapped and any
detectable objectionable odor noted.
The results of the tests are included in Table V.
-17-
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1~4956t7
The superiority of the compos.it.ion of this i.nvention
in stabilizing methylene chloride on exposure to water and
rusty steel storage conditions is evidenced by the .result.s
of Example 19 as compared to the results of the tests in
Examples 17 and 18 in which two different stabllizing compo-
sitions known in the axt were usedO In Example 19 no uncharac
teristic odor was detected but both Examples 17 and 18 had an
objectionable putrid odor.
- Although the present invention has been described with .
detailed reference to specific embodiments thereofl it is
not intended to be so limited since modiflcations and alter-
ations may be made therein which are wit.hin the complete
intended scope of this invention as defined by the appended
claims.
-19
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