CA2026487A1 - Ternary azeotropic compositions of 1,1-dichloro-1,2-difluoroethane and trans-1,2-dichloroethylene with methanol, ethanol or isopropanol - Google Patents

Abstract

TITLE
TERNARY AZEOTROPIC COMPOSITIONS OF
1,1-DICHLORO-1,2-DIFLUOROETHANE AND
TRANS-1,2-DICHLOROETHYLENE WITH
METHANOL, ETHANOL OR ISOPROPANOL
ABSTRACT OF THE INVENTION
Azeotropic mixtures of 1,1-dicloro-1,2-difluoroethane (HCFC-132c) with trans-1,2-ddichloroethylene (T-CFC-1130) and methanol or ethanol or isopropanol, the azeotropic mixtures being useful in solvent cleaning applications.

Description

~ 2~26 48 ~

TERNARY AZEOTROPIC COMPOSITIONS OF
1,1-DICHLORO-1,2-DI~ W OROETHANE AND
TRANS-1,2-DICHLOROETHYLENE WITH
S NET~ANOL, ETHANOL OR ~SOPROPANOL
INVENTIO~ BACXGROUND
As modern electronic circuit boards evolve toward increased circuit and component densities, thorough ~oard cleaning after soldering becomes a more important criterion. Current industr~al processes for soldering electronic components to circuit boards involve coating the entire circuit side of the board with flux and thereafter passing the flux-coated board over preheaters and through molten solder. The flux c~eans the conductive metal parts and promotes solder fusion. Co~monly used solder fluxes generally consist of rosin, either used alone or with activating additives, such as amine hydrochlorides or oxalic acid derivatives.
After soldering, which thermally degrades part of the rosin, the flux-residues are often removed from th-~ci~cuit boards with an organic solvent. The re~ulrements for such~solvents are very stringent.
Defluxing~solvents should have the following chara~teristics: a low ~oiling point, be nonflammable, have low toxicity and have high solvency power, so th~t~lùx~and~ flux-residues can be removed without damaging the~substrate being cleaned.
While boiling point, flammability and 30~ solvent power characteristics can often be adjusted by preparlng solvent~mixtures, these mixtures ~re often unsatisfactory because they fractionate to an undesirable degree during use. Such solvent mixtures ` also fractionate dur~ng solvent d~stillation, wh~ch : ~

2~2~87 ~akes it virtually impossible to recover a solvent mixture with the original composition.
On the other hand, azeotropic ~xtures, with their constant boiling points and const~nt compositions, have been found to be very use~ul for these applications. Azeotropic mixtures exhibit either a maximum or minimum boiling point and they do not fractionate on boiling. These characteristics are also important when using solvent compocitions to --remove solder ~lux-s and flux-residues from printed circuit boards. Preferential evaporation of the more volatile solvent mixture components would occur, i~
the mixtures were not azeotropic and would result in mixtures with changed compositions, and with -less-desirable solvency properties, such as lower rosin flux solvency and lower inertness toward the electrical components being cleaned. The azeotropic character is also desirable in vapor degreasing operations, where redistilled solvent is generally 20 employed for final rinse cleaning. -~
In summary, vapor defluxing and degreasing systems act as~a still. Unless the solvent composition~exhibLts a constant-boiling point, i.e., is~a~ingle -aterial, or Ls~an azeotrope, 25~ fractionation will occur and undesirable solvent distributions will result, which could detrimentally affect the~-afety and~efficacy of the cleaning operation.
; A number of halocar~on based azeotropic ;30 ~composLtio~ns hav- b~-en disoovered and in some cases ' used as solvents for ~older~flux and flux-residue ; removal ~rom printed c~rcuit boards and àlso for ` m~scellaneous~d-greasing~applications. For example:
U.S. Patent No. 3,903,009 discloses the ternary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane : :

2~2~487 with ethanol and nitromethane; U.S. Patent No.
2,999,815 discloses the binary azeotrope of 1,1,2-trichloro-1,2,2-trifluoroethane and acetone.
U.S. Patent No. 2,999,816 discloses the binary azeotrope of 1,1,2-trichloro-1,2,2-tri~luoroethane and methyl alcohol. U.S. Patent No. 4,767,561 discloses the ternary azeotrope of 1,1,2-trtchloro-1,2,2-trifluoroethane, methanol and 1,2-dichloroethylene.
Some o~ the ¢hIorofluorocarbons which are currently used for cleaning and other applications have been theoretically linked to depletion of the earth,s ozone layer. As early as the mid-1970,s, it was known that introduction of hydro~en into the chemical structure of pr-viously ~ully-halogenated chlorofluorocarbons reduced the chemical stability of these compounds. Hence, these now destabilized compounds would be expected to degrade in the lower atmosphere and not reach the tratospheric ozone layer in-tact. What is also needed, t~erefore, are , substitute chlorofluorocarbons which have low theoretical ozone depletion potentials.
Unfortunately, as recognized in the art, it s~not poss~ible~to predict the formation of 25~ az-otropes. This~fact obviously complicates the 8 rch for new a~zeotropic compositions, which have application;~in the~field.~ Nevertheless, there is a constant effort in the art to discover new azeotropic compositions, which~have desirable solvency ~characteristics~and particularly greater versatilities ln~solvency power.
StlMMARY OF T~?E INVENTION
According to the presént invention, azeotropic compositions have been discovered ;; ~ 35 compri-ing admiYtures of effective amounts o~

:

- 4 ~
1,1-dichloro-1,2-difluoroethane with tranc-1,2-dichloroethylene plus an alcohol from the group consisting of methanol, ethanol and ~sopropanol.
More specifically, the azeotropic mixtures -are: an admixture of about 51-61 weight percent 1,1-dichloro-1,2-difluoroethane and about 31-41 weight percent trans-1,2-dichloroethylene and about 4-10 weight percent methanol: an admixture of about 65-75 weight percent 1,1-dichloro-1,2-difluoroethane and about 19-29 weight percent trans-1,2-dichloroethylene and about 3-7 weight percent ethanol; an admixture of -~
about 61-71 weight percent 1,1-dichloro-1,2-difluoroethane and about 27-37 weight percent trans-1,2-dichloroethylene and about 0.7-1.7 ~-15 weight percent isopropanol. - -~
The present invention provides nonflammable azeotropic compositions which are well suited for so~vent clea~ning applications.
DETAIL~D~DESCRIP$~ON
20 ~ The ¢ompos1tions of the instant invention comprise~admixtures of effective amounts of dichloro-1,2-difluoroeth~ne ~CFCI2CH2F, boiling point ~ 48~-4-C) with~trans~ 2-dichloroethylene (bo~l~ing point ~ 48-~C)~and an alcohol selected~rom ;

5~ the group~consistlng ot~methanol (CH30H~,~boiling point 6~4-6-C)~or~ethanol ~CH3 ~ 0H, boi}ing point~ 8'C) or lsopropanol~(CH3CHOHCH3,;boiling point~-~82-C) to form azeotropic~ompositions~ The~ha~ogenated ' materials~are known as HCFC-132c and T-HCC-1130, 30~ #Sp-ctiV~ly~ :~n th- nomenclature convèntional to the halocarbon~ield;,~
By~az-otrople composition is meant, a -~
constant boiling liquid admixture of three or more substances, whose~admlxture behaves as a single 35 ~ subs~tanc-, ln that~th- vapor, produc-d by partial , ~ , 2~26~87 e~aporation or distillation of the liquid has substantially the same composition as the liquid, i.e., the admixture distills without substantial compositional change. Constant boiling compositions, which are characterized as azeotropic, exhibit either a maximum or minimum bo~ling point, as compared with that of the nonazeotropic m~xtures o~ the same substance~.
For purposes o~ this invention, effective amount is defined as the amount of each component of the instant invention admixture which, when combined, ~ results in the formation of the azeotropic - compositions of the instant invention. This definition includes the amounts of each component, which amounts may ~ary depending upon the pressure applied to the composition so long as the azeotropic compositions continue to exist at the different pressures, but with poæsible different boiling points.
Therefore, effective amount includes each components, weight percentaqe for each composition of the instant invention,~ which form azeotropic compositions at pressures othes than atmospheric pressure.`
The language ~an azeotropic composition ¢onslsting essentially of.,.~ is not intended to 5~;eYclud-~the~lnclusion of minor amounts of other ;ma~terials~wh~ch do not iignificantly alter the azeotroplc ch~aracter o~ the composition.
It is~-possibIe to characterize, in effect, a constant boiling adm~xture, which may appear under 30~ many~guises, dep-nd~ng upon the conditions chosen, by any of several criteria: ~
* The composition can ~e defined as an azeotrope of~A, B, and C sinc- th- very ~-te~rm~azeotrope~ is at once both definitive and limitative, and requires ,~ , . .
~ ~ - 5 - ~

`"` 2026:~g7 that effective amounts of A, B and C form this unique composition of matter, which is a constant boiling admixture ~ It is well known by those skilled in the art that at dif~erent pressures, the composition of ~ given azeotrope will vary - at least to some degree - and changes in pressuro will also change - at ~ -least to some degree - the bo~l$ng point temperature Thus ~n azeotrope of A, B
and C represents a unique type o~
relationsh~p but with a variable composition which depends on temperature and/or pressure Therefore compositional ranges, rather than ~ixed compositions, ar- oten used to de~ine~azeotropes * $he composition can be def~ned~as a particular~weight percent relationShip or mole percont relationship of A,~B and~C, 9;~ ~ =whi~le recognizing that such sp-cific ; valueg~point~out only one particulàr such ;~
relati~onship~and that in~actuality,~a~
serles~o~such~relationsh~ps,~ r~-presented by~A~ B~and~C~actually exi~t~for a~g~ven e, varied by~the 1nfluence of~

*~Az-trope~A,~B~and C;oan~be characterlzed by;~defining the compositlon as an azeotrope~characterized ~y a boil$ng 30 ~ point~at~a~given pressure, thus~giving ident~fyIng~characteristics w~thout undùly~ ~1t1ng the -cop- of~the ~ -invent~on~by a~speci~¢~;~numer~cal~
composition,~which is limited~by and is~

,, ~ :
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202~487 only as accurate as the analytical equipment available.
Ternary mixtures o~ about 51-61 weight percent l,l-dichloro-1,2-difluoroethane and about 31-41 weight percent trans-1,2-dichloroethylene and about 4-10 weight percent ~ethanol are characterized as azeotropic, in that mixtures within th$s range exhibit a substantially constant boiling po~nt at constant pressure. Being substantially constant boiling, the ~ixtures do not tend to rractionate to any great extent upon evaporation. A~ter evaporation, ~; ~ only a small difference exists between the co~position of the vapor and the composition of th~ inltial liquid phase. This difference is such that the co~positions lS o~ the vapor and liguid phases are considered substantial}y identical. Accordingly, any mixture within this range exhibits properties which are characteristic of a true ternary azeotrope. Tbe ternary composition consisting of about 56.5 weight percent 1,1-dichloro-1,2-difluoroethane, a~out 36.~5 wei~ht~percent trans-1,2-dichloroethylene and abo~ut 7.0~weight percent ~ethanol has b-en established, within;the~accuracy~of~the fractional distillat~'on method,~s a true ternary azeotrope, boiling at about 2~5~ ~41.~0-~C-, at substantially atmospherio pressure.
Al~o,~according~to the~instant~im ention, ternary~;mi ~ es of~about~;65-~5 weight~percent dichloro-1~,2-di~luoroethane, about 19-29 weight ' percent'trans-1,2-d~chloroethylene and about 3-7 30 ~weight~percent ethanol;~are characterized as azeotropic,~in~that~mixtur-s within this~r~nge exhib~t '~
ubs*antially'constant ~oiling point~at constant pre~ure~ ~e~ng~substantially constant boil~ng~ thQ
m~xtures do not tend to fractionate to any great 35 extent upon e~aporat~on. After evaporation, only a ;~

..
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small difference exists between the composition of the vapor and the composition of the initial liquid phase.
This difference is such that the compositions o~ the vapor and liquid phases are considered substantially S identical. Accordingly, any mixture within this range exhibits properties which are characteristic of a true ternary azeotrope. The ternary composition consisting of about 70.0 weight percent 1,1-dichloro-1,2-difluoroethane, about 24.6 weight percent trans-1,2-dichloroethylene and about 5.4 weight percent ethanol has been established, within the accuracy o~ the fractional distillation method, as a true ternary azeotrope, boiling at about 44.S-C, at substantially atmospheric pressure.
lS Also, accordinq to the instant invention, ternary mixtures of about 61-71 weight percent ;-~
1,1-dichloro-1,2-difluoroethane, about 27-37 weight percent trans-1,2-dichloroethylene and about 0.7-1.7 weight percent isopropanol are characterized as azeotropic, in that mixtures within this range exhibit a substant~ally constant boiling point at constant pr-ssure. Being substantially constant boiling, the mixtures do not tend to ~ractionate to any great ext~nt upon evaporation. After evaporation, only a ~small difference exists between the composition of the vapor and the composition of the initial liquid phase.
This differenc- is such that the compositions of the vapor and liquid phases are considered substantia}ly identical. Accordingly, any mixture within this range exhibits properties which are characteristic of a~true ternary azeotrope. Tbe ternary compositioh consisting of about 66.3 weight percent dichloro-1,2-difluoroethane, about 32.5 weight percent trans-1,2-dichloroethylene and about 1.2 weight percent isopropanol has been established, ::

. 1; . , . , . ~ - . ~;, 2~2G487 within the accuracy of the fractional distillation method, as a true ternary azeotrope, boiling at about 46.5-C, at substantially atmospheric pressure.
The a~orestated azeotropes have low S ozone-depletion potentials and are expected to decompose almost completely, prior to reaching the stratosphere.
The azeotropic compositions of the present invention permiit easy recovery and reuse o~ the solvent ~rom vapor defluxing and degreasing operations because o~ tbeir azeotropic nature. As an example, the azeotropic mixtures of this invention can be used in cleaning processes such as described in U.S. Patent No. 3,881,949, which is incorporated herein by lS referenCe-The azeotropic compositions of the instantinvention can be prepared by any convenient method including mixing or combining the desired component amounts. A preferred method is to weigh the desired component amounts and thereafter combine them in an appropriate container.
EXAMPL~S
a~ple 1 A;solution which contained 61.7 weight 5~ percent 1,~1-dichloro-1,2-dif~uoroethane, 31.8 weight ' ' "
percent tran~-~,2-dichloroethylene and 6.S weight pérc-nt metbanol~was~ prepared in a 'suitab~le contalner and mlxed thoroughly. -~
' ; The solution was distilled in a Perkin-Elmer ~odel 251~autoannular spinning band still (200 plate ' "~
3~ fractionatlng capability)~ u ing about a 10:1 reflux '' ~ -to ta~e-o~f ratio. Head temperatures were read~
directly to O.l-C~. All temperatures were adjusted to 760 mm pressure. Distillate compositions were ~ ~P'~
; 3S

.

,.

. ~ :.' :, . ~.' 202G~87 determined by gas chromatography. Results obtained are summarized in Table 1.

DISTILLATION OF:
~61.7 + 31.8 + 6.5) 51,1-D}CHLORO-1,2-DIFLUOROETHANE (DCDFE), T~ANS-1,2-DICHLOROETHYLENE (T-9CE) AND METHANOL (MEOH) WT.%
DISTILLED
TEMPE~ATURE,C OR
CUTS POT RECOVERED-- DCDFE T-DCE MEOH
1 41.1 2.6 57.1 35.7 7.2 2 41.0 10.3 56.1 36.9 7.0 3 41.1 15.0 56.1 36.8 7.1 -4 41.1 20.0 56.5 36.5 7.0 S 41.1 22.0 56.6 36.4 7.0 6 41.1 25.0 56.8 36.3 6.9 7 41.1 30.0 S6.9 36.2 6.9 HEEL -- 79.8 63.4 29.5 7.1 ~ nalysis of the above data indicates ~ery small differences among head temperatures and distillate compositlons, as the distillation progressed. A statistical analysis of the data ~ndicates that the true ternary azeotrope o~ dichloro-1,2-difluoroethane, trans-1,2-dichloroethylene and methanol has the following~characteristic- at atmospheric pressure (99 p-rcent~confidence limits):
Dichloro-1,2-d~fluoroethane = 56.5 * I.3 wt.~
trans-1,2-Dichloroethylene - 36.5 1 1.1 wt.%
Methanol ~ 7.0 ~ 0.3 wt.%
Boiling point, C ~ 41.0 1 0.1 Example 2 A solution which contained 76.3 weight percent 1,~1-dichloro-1,2-difluoroethane, 16.~ weight perc-nt trans-1,2-d~chloroethylene 6.9 weight percent ~ ethanol was prepared in a suitable container and ~ixed ;;~ thoroughly.

,, ;- . , . . ~. . , . . i ,~

2026 ~7 The solution was distilled in a Perkin-Elmer Model 251 autoannular spinning band still (200 plate ~ractionating capa~ility), using about a 10:1 reflux to take-off ratio. Head temperatures were read directly to O.l-C. All temperatures were adjusted to 760 mm pressure. Distillate compositions were determined by gas chromatography. Results obtained are summarized in Table 2.

DISTILLATION OF:
~76.3 + 16.8 + 6.9) 1,1-DICH~ORO-1,2-DIFLUOROETHANE (DCDFE), TRANS-1,2-DICHLOROETHYLENE (T-DCE) AND ETHANOL (ETOH) WT.%
D~STILLED
TEMPE~ATURE,C OR
CUTSHEADRECOVERED DCDFE T-DCE ETOH
1 44.5 5.0 70.0 24.6 5.4 2 44.5 9.8 69.6 25.0 5.4 -3 44.5 14.6 69.8 24.9 5.3 ~ ;~
4. 44.5 20.0 69.7 24.8 5.5 44.5 24.4 70.2 24.5 5.3 6 44.5 28.6 70.8 23.8 5.4 7 50.0 32.9 72.4 22.4 5.2 HEEL -- 93.5 86.2 S.6 8.2 Analysis of the a~ove data indicates very -small differences among head temperatures and distillat- compos~itions, as the distillation progressed. A statistical analysis of the data -indicates that the true ternary azeotrope of dlchloro-1,2-dirluoroethane, trans-1,2-dichloroethylene and ethanol has the following characterlstics at atmospheric pressure (99 percen~ donfidence limits)~
Dichloro~ 2-difluoroethane ~ 70.0 + 1.9 wt.%
trans-1,2-Dichloroethylene - 24.6 1 1.9 wt.~
Ethanol - 5.4 + 0.3 wt.%
Boiling point, C ~ ~ 44.5 ~ 0.1 , ~ :' ~ :-20264~7 ExamDle 3 A solution which contained 64.6 weightpercent l,l-dichloro-1,2-difluoroethane, 30.0 weight percent trans-1,2-dichloroethylene and 5.4 weight percent isopropanol was prepared in a suitable container and mixed thoroughly.
Tbe solution was distilled in a Perkin-Elmer Model 251 autoannular spinning band still (200 plate ~ractionating capabi~ity), using a~out a 10:1 re~lux to take-off ratio. Head temperatures were read directly to O.l-C. All temperatures were ad~usted to 760 mm pressure. D~stillate compositions were determined by gas chromatography. Results o~tained are su~arized in Table 3.

DISTILLATION OF: `
(64.6 ~ 30.0 ~ 5.4) DICH~ORO-1,2-DIFLUOROETHANE (DCDFE), TRANS-1,2~DICHLOROETHYLENE (T-DCE) AND
ISOPROPANOL(IPROH) ,~;, ` ~ WT.%
DISTILLED
TEMPERATURE,-C OR
CUTSHEADRECOVERED DCPFP T-DCE IPROH
1 45.g ~4.7 64.6 34.4 1.0 2 46.4 29.8 65.8 32.9 1.3 3 46.4 41.6 65.9 32~9 1.2 4 46.3 65.2 ~66.8 31.9 1.3 5 46.7 72.8 66.5 32.4 1.1 6~46.~9 87.6 69.3 29.3 1.4 EE~ ~ 100.0 63.8 12.423.8 Analysis of the above data indicates very small~di~er-nces among head temperatures and distillate~ compositions, as the distillation progressed. A statisticàl analysis o~ the data --~ lnd~cates~t~at the true ternary azeotrope Or diohloro-1,2-difluoroethane, trans-1,2-d$chloroethylene and isopropanol has the ; .

.. .:.~. .; . . - . ~

following characterlstics at atmospheric pressure (99 percent conridence limits):
l,l-Dichloro-1,~-difluoroethane - 66.3 1 2.2 wt.%
trans-1,2-Dichloroethylene ~ 32.5 + 2.2 wt.
Isopropanol ~ 1.2 + 0.3 wt.%
Boiling point, C ~ 46.5 + 0.8 ExamDle 4 Several single sided circuit boards were coated with activated rosin flux and soldered by passing the board over a preheater to obtain a top side board temperature of approximately 200-F (93-C) and then through 500-F (260'C) molten solder. The s~ldered boards were defluxed separately with the -three azeotropic mixtures cited in Examples 1, 2 and 3 abo~e, ~y suspending a circuit board, first, for three minutes in the boiling sump, which contained the azeotropic m~xture, then, for one minute in the rinse sump, which contained the same azeotrop1o mixture, a~nd finally, ~or one minute in the solvent vapor above the -;~
boiling sump. The boards cleaned in each azeotropic mixture had no visible resldue remaining thereon. ` ;

.:, ~. . .

.: . :~:. , :

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Claims (13)

1. An azeotropic composition comprising effective amounts of: 1,1-dichloro-1,2-difluoroethane with trans-1,2-dichloroethylene plus an alcohol selected from the group consisting of methanol, ethanol and isopropanol.

2. The azeotropic composition of Claim 1, consisting essentially of about 51-61 weight percent 1,1-dichloro-1,2-difluoroethane, about 31-41 weight percent trans-1,2-dichloroethylene, and about 4-10 weight percent methanol.

3. The azeotropic composition of Claim 1, consisting essentially of about 65-75 weight percent 1,1-dichloro-1,2-difluoroethane and about 19-29 weight percent trans-1,2-dichloroethylene and about 3-7 weight percent ethanol.

4. The azeotropic composition of Claim 1, consisting essentially of about 61-71 weight percent 1,1-dichloro-1,2-difluoroethane, and about 27-37 weight percent trans-1,2-dichloroethylene and about 0.7-1.7 weight percent isopropanol.

5. The azeotropic composition of Claim 2, consisting essentially of about 56.5 weight percent 1,1-dichloro-1,2-difluoroethane, and about 36.5 weight percent trans-1,2-dichloroethylene and about 7.0 weight percent methanol.

6. The azeotropic composition of Claim 2, wherein the composition has a boiling point of about 41.0°C at substantially atmospheric pressure.

7. The azeotropic composition of Claim 3, consisting essentially of about 70.0 weight percent 1,1-dichloro-1,2-difluoroethane, and about 24.6 weight percent trans-1,2-dichloroethylene and about 5.4 weight percent ethanol.

8. The azeotropic composition of Claim 3, wherein the composition has a boiling point of about 44.5°C, at substantially atmospheric pressure.

9. The azeotropic composition of Claim 4, consisting essentially of about 66.3 weight percent 1,1-dichloro-1,2-difluoroethane and about 32.5 weight percent trans-1,2-dichloroethylene and about 1.2 weight percent isopropanol.

10. The azeotropic composition of Claim 4, wherein the composition has a boiling point of about 46.5°C, at substantially atmospheric pressure.

11. A process for cleaning a solid surface which comprises treating said surface with the azeotropic composition of Claim 1.

12. The process of Claim 11, wherein the solid surface is a printed circuit board contaminated with flux and flux-residues.

13. The process of Claim 12, wherein the solid surface is a metal.