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BACKGROUND OF INVENTION
1,1,1-Trichloroethane is a widely used industrial cleaning solvent. With
the recent restrictions placed on the use of trichloroethylene, as for
example, vapor degreasing, more people are substituting
1,1,1-trichloroethane into uses to which the trichloroethylene was
employed. Many of these uses place a severe stress on the
1,1,1-trichloroethane. Previous inhibitor systems for the
1,1,1-trichloroethane have been found weak or ineffective in protecting
the solvent and/or the parts being cleaned. Thus, it is necessary to find
new inhibitor systems for the 1,1,1-trichloroethane which will permit the
extended uses industry is making of this useful solvent.
The prior art has added numerous members from most classes of organic
compounds in attempts to improve the stability of 1,1,1-trichloroethane to
degradation in the presence of heat, metals (particularly aluminum) and
water. For example, esters, ethers, amines, cyano compounds, alcohols,
ketones, aldehydes and the like have been suggested alone and in
combination in the literature and in patents. However, commercial grades
of 1,1,1-trichloroethane used in the major industrial countries contain at
least one inner ether (an epoxide and/or dioxane, dioxolane, or trioxane),
usually a nitroalkane (nitromethane and/or nitroethane) then one or more
of the following acetylenic alcohol, nitrile (acetonitrile or
.beta.-methoxypropionitrile), ortho ester (trimethyl ortho formate), lower
alkanol (t-butyl or t-amyl alcohol), a ketone (methyl ethyl ketone). These
compounds account for the components used in the main in the present day
inhibitor systems.
One of the largest suppliers used dioxane, nitromethane and butylene oxide
for years. However, even this recognized superior system has shown
weaknesses in certain fields of use wherein trichloroethylene was
previously employed. Such weaknesses are a result of operator's lack of
care in maintenance of their equipment, a chore not usually undertaken on
a regular basis when trichloroethylene was employed. However, any rusting,
heavy metals fines, particularly aluminum, grinding and buffing compounds,
lubricant oils and fluxes such as employed in miniature printed circuits
increase the degradation of the solvent and create corrosive atmospheres
which attack the metal parts being cleaned. In the past, the manufacturers
have been able to screen the new uses and monitor the uses. Such is not
possible with the widespread usage to which the solvent has been put in
recent months.
It is, therefore, an object of the present invention to provide a
stabilized grade of 1,1,11-trichloroethane suitable for the severe use
conditions encountered in the substitution of 1,1,1-trichloroethane for
trichloroethylene
BRIEF DESCRIPTION OF INVENTION
In accordance with the present invention it has been found advantageous to
combine 1,4-dioxane, tertiary amyl alcohol, nitromethane and/or
nitroethane, and butylene oxide in the hereinafter proportions to
stabilize 1,1,1-trichloroethane for industrial usage as a vapor degreasing
solvent in applications wherein 1,1,2-trichloroethylene was previously
employed.
As aforestated in the Background of Invention, 1,1,1-trichloroethane is a
unique chlorinated hydrocarbon solvent having low toxicity and good
ecological properties and is gradually replacing trichloroethylene in the
vapor degreasing field. In the new use as a vapor degreasing solvent the
1,1,1-trichloroethane comes under severe use conditions, i.e., contact
with metal parts containing aluminum, iron, copper, zinc and alloys
thereof, acid compositions used in metal finishing operations, oils and
resins, i.e., as in printed circuitry manufacture, and the like. Some of
these conditions have been met before in the special uses to which
1,1,1-trichloroethane have been put, but the manufacturers and their
distributors have taken care to monitor these uses. Today, however, with
the widespread and expanding usage attributable largely to the general ban
on use of trichloroethylene, monitoring becomes substantially humanly
impossible or extremely expensive. Therefore, extensive efforts have been
undertaken to prepare a stabilized grade of 1,1,1-trichloroethane which
will be suitable for total replacement of trichloroethylene in the
industrial area. A further effort was undertaken to employ as inhibitors,
compounds in small quantities, compounds which presently appear to have no
ecological or safety hazards, and employ only a minor number of compounds
and a major proportion of 1,1,1-trichloroethane. Such a formulation has
been found in the above set forth invention, to wit:
1 to 3 volume percent 1,4-dioxane;
1 to 3 volume percent t-amyl alcohol;
0.2 to 0.6 volume percent nitromethane, or a mixture of nitromethane and
nitroethane containing up to 75 volume percent nitroethane;
0.5 to 1 volume percent butylene oxide.
wherein the total of dioxane and t-amyl alcohol must be 3 volume percent
and the total inhibitor concentration must be 3.6 volume percent. It is
contemplated the total maximum inhibitor volume will be 7.6 volume percent
in order to eliminate any vapor or liquid health hazards which the
inhibitors might exhibit in the ambient atmosphere or bodily contact
toward humans as well as maintain the potential of creating a flammability
problem to the minimum.
It is to be understood that various combinations of the inhibitors named
are known to prevent degradation of the 1,1,1-trichloroethane but that
they have not been combined in the aforesaid manner or amounts. The
results of the enumerated combination establish an unexpected and unique
property of the combination in that while the boiling points of the
inhibitor components would indicate loss of nitro--methane and butylene
oxide, in fact this does not occur. Repeated usage, that is vaporization
and condensation in a vapor degreasing operation, drag-out of solvent
vapors on parts, with periodic make-up of inhibited solvent to operating
volumes have confirmed that each component of the inhibitor systems
remains in a sufficient quantity to stabilize the solvent in both the
liquid and vapor state over extended continuous periods of time without
build-up of high boilers or loss of low boilers.
The preferred composition consists of
2 to 3 percent dioxane;
1 to 2 percent t-amyl alcohol;
0.3 to 0.6 percent nitromethane, or a mixture of nitromethane and
nitroethane containing up to 75 volume percent nitroethane;
0.6 to 0.8 percent butylene oxide.
DETAILED DESCRIPTION OF THE INVENTION
A series of glassware experiments were performed in the laboratory to
determine the feasibility of a dioxane/t-amyl alcohol system as the
primary aluminum inhibitor. Also, a nitromethane/nitroethane combination
was investigated as the secondary metal stabilizer. The following
abbreviations will be used throughout: Diox = 1,4-Dioxane, TAA = t-amyl
alcohol, BO = 1,2-butylene oxide, NM = nitromethane, NE = nitroethane,
bottom = liquid phase, top = vapor condensate phase.
The following 1,1,1-trichloroethane solutions were formulated for testing
(all concentrations are as volume percent):
______________________________________
Formu-
lation
Code # Formulation Composition
______________________________________
A 3.2% Diox, ------, 0.75% BO, 0.4% NM
B 3% Diox, 1% TAA, 0.75% BO, 0.4% NM
C 2% Diox, 2% TAA, 0.75% BO, 0.4% NM
D 2% Diox, 2% TAA, 0.75% BO, 0.2% NM, 0.2% NE
E 2% Diox, 2% TAA, 0.75% BO, ------, 0.4% NE
F 1% Diox, 3% TAA, 0.75% BO, 0.4% NM
G ------, 4% TAA, 0.75% BO, 0.4% NM
______________________________________
DESCRIPTION AND RESULTS OF EXPERIMENTS
There are three steps in this series of experiments: (1) partitioning; (2)
aluminum hot scratch; and, (3) 7-day reflux.
(1) Partitioning (Table I) -- each formulation is distilled into two equal
fractions (top and bottom) to obtain solutions with inhibitor profiles
similar to that found in vapor degreasers. Adequate concentrations of
inhibitors in both the boiling liquid phase and the vapor phase of a vapor
degreaser is a very important requirement of a good inhibitor package.
Therefore the use of inhibitors with proper boiling point ranges and
partitioning profiles is important in designing an adequate inhibitor
combination. Various combinations of dioxane, t-amyl alcohol, butylene
oxide, nitromethane, and nitroethane dissolved in 1,1,1-trichloroethane at
various concentrations were distilled into two equal fractions (liquid and
vapor phases) to obtain inhibitor profiles from solutions and vapors
similar to that found in vapor degreasers. The resulting inhibitor
concentrations were obtained by gas chromatographic analysis. Listed below
are the average partitioning from the results obtained in the partitioning
of the compositions listed in Table I:
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% In Vapor Phase
% In Liquid Phase
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Dioxane 27 73
t-Amyl Alcohol
42 58
Nitromethane
62 38
Nitroethane 34 66
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It can be seen that the distribution of a combination of dioxane and t-amyl
alcohol would afford superior protection in both phases than would dioxane
alone. Also, it is evident that a 50/50 mix of the two nitroalkanes would
give almost equal protection in the two phases.
(2) Aluminum Hot Scratch (Table I) -- a series of hot scratch tests were
run with 2024 aluminum coupons (Al/Cu alloy) using each original
formulation and each top and bottom fraction. This test demonstrates the
ability of a stabilizer system to inhibit the 1,1,1-trichloroethane
reaction with the aluminum in both the liquid and vapor phases.
Specifically, 50 cc of the formulation is placed in a Pyrex petri dish (9
cm diameter by 2.5 cm deep) and placed on a hot plate. The solvent is
allowed to heat to just below rolling boil and then taken off the hot
plate. A 2024 Al coupon (21/2 .times. 1/2 .times. 1/8 inches thick) is
immediately placed in the petri dish and the surface of the coupon is
scratched with a stylus while the coupon is submerged. Three scratches are
made lengthwise of the coupon and five scratches across the coupon. The
petri dish is then removed from the hot plate, covered, and observed for
one hour. After one hour a "scratch rating" is given to that solution
according to the appearance of the scratch sites:
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"Scratch Rating"
Description
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0 Scratches are completely inhibited
with no reaction products visible
to the eye.
1 Scratches immediately cure with
isolated sites of reaction product.
2 Scratches rapidly cure but with
some formation of reaction products.
3 Scratches slowly cure with much
formation of reaction products.
4 Little inhibition at scratch sites
with a slow continuing reaction.
5 "Runaway" reaction during the
one-hour observation period; the - solution turns black,
HCl is gener-
ated, and a fast ongoing reaction
is present at scratch sites.
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TABLE I
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Partitioning Hot Scratch Rating
Form. Bot- Bot-
# Inhibitor
Original Top tom Original
Top tom
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% Diox 3.30 1.78 4.73
A % NM 0.54 0.66 0.42 0 0 0
% BO 0.71 0.83 0.59
% Diox 2.96 1.65 4.20
B % TAA 1.06 0.90 1.20 0 0 0
% NM 0.53 0.63 0.44
% BO 0.71 0.83 0.57
% Diox 1.99 1.04 2.95
C % TAA 1.93 1.60 2.17 0 1 0
% NM 0.50 0.63 0.38
% BO 0.72 0.83 0.60
% Diox 1.95 1.13 2.87
% TAA 2.04 1.79 2.20
D % NM 0.25 0.35 0.21 0 2 0
% NE 0.21 0.17 0.29
% BO 0.71 0.82 0.62
% Diox 2.20 1.17 2.99
E % TAA 2.02 1.73 2.21 0 3 0
% NE 0.44 0.29 0.58
% BO 0.71 0.80 0.60
% Diox 1.06 0.56 1.52
% TAA 2.73 2.31 3.16
F % NM 0.52 0.70 0.36 1 2 0
% BO 0.71 0.82 0.62
% TAA 3.71 3.07 4.34
G % NM 0.42 0.60 0.50 4 5 3
% BO 0.72 0.81 0.60
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It is observed that:
1. As the dioxane concentration decreases and the t-amyl alcohol increases,
the ability of the formulation to inhibit the solvent/aluminum reaction
decreases.
2. The bottom fraction aluminum hot scratch ratings are better than the
ratings for the top fractions due to the higher total primary metal
stabilizer present, caused by the partitioning behavior of dioxane and
t-amyl alcohol.
3. More protection is afforded due to better partitioning in the vapor
phase utilizing dioxane/t-amyl alcohol combinations rather than dioxane
alone.
4. Substitution of nitroethane for nitromethane (#C vs. #E) results in less
protection in the top fraction due to partitioning of nitroethane favoring
the bottom fraction.
5. A 50/50 mix of NM/NE (#D) gives better distribution of nitroalkane in
both phases.
6. Tertiary amyl alcohol as the principal inhibitor without dioxane is not
an adequate Al stabilizer.
(3) 7-Day Reflux Test -- This test consists of refluxing each top and
bottom fraction in the presence of metal chips for 7 days. It is a good
indication of how effective a stabilizer system would be in preventing
1,1,1-trichloroethane reactions with metals. Each 100 cc fraction was
refluxed in the presence of two different sets of metals: (a) 5 grams each
1100 and 2024 aluminum chips and, (b) 5 grams each 70/30 brass chips and
iron filings. After 7 days reflux the solutions are filtered and analyzed
via gas chromatography for inhibitor losses (Table II).
TABLE II
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% Lost After 7-Day Reflux
Initial With Fe+
Form. Inhibitor With Al Chips Brass Chips
# Concentration
Top Bottom
Top Bottom
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3.2% Diox No Loss (NL)
NL NL NL
A 0.4% NM 2 NL 1 6
0.75% BO NL 1 2 7
3% Diox NL NL NL NL
1% TAA NL NL NL NL
B 0.4% NM 5 11 5 13
0.75% BO 2 2 11 14
2% Diox NL NL NL NL
2% TAA NL NL 6 NL
C 0.4% NM 1 NL 5 5
0.75% BO 2 3 19 12
2% Diox 4 NL 7 NL
2% TAA 9 NL 6 NL
D 0.2% NM 11 10 17 20
0.2% NE 9 NL 15 4
0.75% BO NL 4 13 10
2% Diox 3 NL NL NL
2% TAA NL NL 6 NL
E 0.4% NE NL 19 NL 4
0.75% BO 20 58 12 6
1% Diox NL NL NL NL
3% TAA NL NL NL NL
F 0.4% NM 12 NL 13 NL
0.75% BO 2 2 17 17
4% TAA NL 1 3 40
G 0.4% NM 8 44 3 40
0.75% BO 3 41 24 98
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it is observed that:
1. Inhibitor losses of <20 percent during the 7 days are considered
acceptable since the hot scratch tests show protection, i.e., ratings of
0-2, while losses of >20 percent are considered to have failed in
preventing metal/1,1,1 reactions since the hot scratch tests show lack of
protection. This pass/fail inhibitor loss level is not entirely arbitrary
but is based on our wide experience with inhibitor system behavior in
industrial vapor degreasing where stabilizer losses of greater than 20-25
percent indicate some solvent decomposition.
2. Comparing #C and #E, it is evident that NE alone is not as effective a
secondary inhibitor for Al/ 1,1,1 reaction as is NM alone. However, an
NM/NE mix (#D) is an effective secondary Al stabilizer.
3. TAA alone is not as effective as metal/1,1,1 primary inhibitor as is
DIOX alone (#G vs. #A).
4. Combinations of DIOX/TAA do prevent metal/1,1,1 reactions (#B, #C, #D,
and #F) and afford better overall inhibitor distribution in top and bottom
phases.
DEGREASER TEST
The following formulation was tested in a laboratory-sized vapor degreaser:
0.72 percent BO, 1.65 percent TAA, 2.58 percent DIOX, 0.46 percent NM,
balance 1,1,1-trichloroethane. This degreaser had a 4-gallon boil sump and
a 3-gallon clean dip side (fed from condensed solvent vapors). The
degreaser was run at the solvent boiling point uncovered, 24 hours/day,
for 24 days. Daily additions of fresh solvent were added to maintain a
constant volume. Every effort was made to simulate actual degreasing
operations and to subject the solvent formulations to many of the stresses
that commonly occur in the field. Various metal alloys (100 g each) were
placed in both the boil sump and warm dip. These metals are 2024 aluminum
turnings, 70/30 brass turnings, and coarse steel wool; all of which expose
a large metal surface area with potential reactive sites to the solvent. A
lubricating oil (commonly used in metal machining operations) was added to
the boil sump (constituting about 10 percent of the liquid volume of the
boil sump). Finally, water was added to the boil sump on the 18th day of
the test (constituting about 1 percent of the total degreaser charge).
ANALYTICAL TEST PROCEDURE
Both the boiling sump and the warm dip tank were sampled about every other
day. Inhibitor distribution profiles were than obtained by vapor phase
chromatography. Also, some of the samples were analyzed via emission
spectroscopy for metal ion concentrations (Al, Cu, Fe, Zn). This reveals
any metal corrosion problems and potential reactions between the solvent
and particular metals due to inadequate stabilization.
RESULTS OF DEGREASER TEST
The distribution of the four inhibitors in the boiling sump and the warm
dip tank is detailed in drawings, FIGS. 1 through 4. The partitioning of
the inhibitors followed expected patterns and there were no unusual losses
during the 24 days.
Results of metal ion analysis are listed in Table III. The low levels of
metal ions present in the solvent samples indicates negligible reaction
between the metal chips and the solvent. Thus, the 24-day vapor degreaser
test was successful and this combination of inhibitors provides excellent
stability.
TABLE III
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Metal Analysis
During Degreaser Test
ppm ppm ppm ppm
Sample Description
Fe Cu Al Zn
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Virgin formulation
<1 <0.2 <1 <3
Warm dip tank after 18 days
<1 <0.2 <1 <3
Boiling sump after 18 days
<1 <0.2 <1 <3
Warm dip tank after 24 days
5 0.2 <1 5
Boiling sump after 24 days
7 0.4 <1 5
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DEGREASER TEST
A 2 .times. 51/2 foot two-chamber, open-top Manpro vapor degreaser was
charged with a stabilized 1,1,1-trichloroethane solvent having the
following composition:
2.5 volume percent 1,4-dioxane
1.5 volume percent t-amyl alcohol
0.15 volume percent nitromethane
0.15 volume percent nitroethane
0.75 volume percent 1,2-butylene oxide.
25 Gallons to the sump, 31 gallons to the warm dip and 29 gallons to a
still associated with the degreaser. The degreaser was operated for 38
days. Solvent was pumped to and from the still although the still was not
operated until the 22nd day of the test run. Solvent make-up was added on
the 9, 14, 17, 24, 30 and 34 days and 1/2 gallon of a white cutting oil
added on each of the 8, 9, 10, 13, 14, 22, 23, 24, 27, 30 and 35 days of
operation. On the 16th day metals were added to the sump and the warm dip,
viz;
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Warm Dip Sump
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2024 Al 200 gm 200 gm
Steel wool 65 gm 65 gm
Mossy zinc 500 gm 300 gm
70/30 Brass chips
500 gm 500 gm
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At the end of 38 days the test was stopped, the metals and solvent
examined. The test was considered successful as a result of this
examination.
Samples of the final composition in the warm dip and sump were taken and
each sample subjected to reflux for seven days with metals as follows:
One hundred milliliters of each compartment were refluxed with either 5
grams each of 2024 Al chips, 1100 Al pellets and iron filings or 5 grams
each of zinc fines and 70/30 brass. The aluminum and iron showed no
evidence of attack although the zinc and brass did evidence a small amount
of corrosion.
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