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US00530685OA
United States Patent [191
[11]
[45]
Darago
[54] PURIFICATION PROCESS FOR A
HYDROFLUOROALKANE
[75] Inventor: Gilles Darago, Tavaux, France
[30]
Mar. 31, 1993
Foreign Application Priority Data
Apr. 3, 1992 [FR]
5,122,294
6/1992
Logsdon et a1. .................. .. 570/121
5,200,431
4/1993
Dattaniet al. .................... .. 570/178
Int. Cl.5 ..................... .. C07C 17/38; C07C 19/02
US. Cl. ............................... .. 570/178; 570/175
[58]
Field of Search ....................................... .. 570/178
References Cited
.
.
.
.
1625861
2/1991
U.S.S.R. ............................ .. 570/178
1031409
6/1966
United Kingdom .............. .. 570/178
OTHER PUBLICATIONS
France .............................. .. 92 04277
[51]
[52]
[56]
Apr. 26, 1994
0361578 4/1990 European Pat. Off.
0395793 11/1990 European Pat. Off.
0395898 1l/1990 European Pat. Off.
0472391 2/ 1992 European Pat. Off.
9118852 12/1992 PCT Int’lAppl. .
,
[21] Appl. No.: 40,992
[22] Filed:
5,306,850
FOREIGN PATENT DOCUMENTS
[73] Assignee: Solvay (Société Anonyme), Brusse
Belgium
Patent Number:
Date of Patent:
Chemical Abstracts, vol. 111, Dec. 25, 1989, No. 26,
“35-Chemistry of Synthetic High Polymers”, p. 145.
Primary Examiner-Joseph E. Evans
Attorney, Agent, or Firm-Spencer, Frank & Schneider
U.S. PATENT DOCUMENTS
[57]
2,831,902
4/1958
3,689,373
9/1972 Hutchinson
4,548,701 10/1985
Wolff ........... ..
4,766,261
Bierl ................. ..
8/1988
-
ABSTRACT
Hamilton et al. ................. .. 570/178
4,973,774
4,968,850 11/1990 Rozen
Franklin
et et
a].a1...... ..
5,001,287
3/1991
5,120,461
6/1992 Logsdon et a1.
.. 570/178
570/178
Process for purifying a hydro?uoroalkane with respect
to impurities which are less volatile than the hydro
?uorocarbon, by distillation in the presence of an acid
scavenger, for example a C3-C3 ole?n.
Fernadez et a1. ..
18 Claims, No Drawings
1
5,306,850
2
pounds. Because their boiling point is lower than that of
their precursors, these degradation compounds contam
inate the hydro?uoroalkane removed at the top of the
heavy-component column in the conventional process
PURIFICATION PROCESS FOR A
HYDROFLUOROALKANE
of puri?cation by distillation.
The present invention relates to an improved puri?
cation process for a hydro?uoroalkane.
Whatever its method of preparation, a hydrof luo
roalkane collected at the output of the synthesis reactor
Another object of the invention is then to provide a
process for purifying a hydrofluoroalkane with respect
to heavy impurities by distillation, in which the degra
dation of the hydro?uoroalkane and/or of the heavy
impurities in the distillation column is greatly reduced.
is generally contaminated with impurities comprising in
particular unconverted reactants and/or various sub
products generated during the reaction or introduced
with the reactants. The hydro?uoroalkane must there
fore be subjected to a puri?cation in order to separate
The present invention relates then to a puri?cation
process for a hydrofluoroalkane, according to which
the hydro?uoroalkane is subjected to a distillation in
order to separate therefrom the impurities which are
less volatile than the said hydroiluoroalkane, character
ized in that the distillation is performed in the presence
of an acid-scavenger.
therefrom, on the one hand, components which are
more volatile than the hydro?uoroalkane, convention
ally called light impurities, and, on the other hand,
components which are less volatile than the hydro
fluoroalkane, conventionally called heavy impurities.
It is observed that, when the distillation is performed
A well known conventional puri?cation process for
according to the invention, in the presence of an acid
hydrofluoroalkane consists of a separation by distilla 20 scavenger, neither the hydrofluoroalkane nor the or
tion in several steps. At the top of a ?rst column, usually
ganic impurities which accompany it (in particular halo
genated organic impurities) are perceptibly degraded
called the light-component column, the components
which are more volatile than the hydro?uoroalkane are
during the distillation, even when it is done in the pres
removed from the reaction mixture, the hydrofluoroal
ence of small quantities of Lewis acids.
kane leaving this column at the bottom, in a mixture 25
The term hydro?uoroalkanes is generally intended to
with the heavy impurities. The puri?cation of the hy
designate saturated hydrocarbons of the acyclic or ali
drofluoroalkane with respect to the heavy impurities is
cyclic type, comprising at least one hydrogen atom and
then conducted in a second distillation column, called
at least one ?uorine atom. They may possibly also com
the heavy-component column, supplied with the flux
prise at least one chlorine atom. Hydrofluoroalkanes as
removed at the bottom of the light-component column, 30 de?ned hereinabove generally comprise l to 6 carbon
in which the puri?ed hydrofluoroalkane constitutes the
atoms. They generally conform to the formula
top fraction, and the heavy impurities constitute the
CnHbFCCld, in which a is an integer from 1 to 6, b is an
bottom fraction.
integer from 1 to 13, c is an integer from 1 to 13 and d
This conventional process of puri?cation by distilla
is an integer from O to 8, with b+c+d= 2a+2 when the
tion has however proved unsatisfactory for obtaining a 35 compound is acyclic, and with b+c+d=2a when the
hydrofluoroalkane satisfying the purity speci?cations
compound is alicyclic. The process according to the
currently required.:Hydro?uoroalkanes puri?ed by this
invention is applicable in particular to acyclic com
conventional process are in fact usually contaminated
pounds comprising from 1 to 4_carbon atoms, compris
by a few ppm of proton acids and organic impurities,
ing at least one hydrogen atom and at least one ?uorine
principally unsaturated halogenated organic impurities,
atom. These compounds may furthermore contain at
least one chlorine atom. They conform to the above
formula in which a is an integer from 1 to 4, b is an
integer from 1 to 9, c is an integer from 1 to 9 and d is
an integer from O to 5. The process is most especially
which are particularly problematic in the ?nal product
because of their possible toxicity. The removal of such
impurities then generally requires a subsequent ?nishing
treatment.
The invention aims to remedy the shortcomings of 45 applicable to acyclic compounds having the above gen
the conventional process de?ned hereinabove by pro
eral formula, in which a is an integer equal to 2 or 3, b
viding an improved process for purifying a hydro
is an integer from 1 to 6, c is an integer from 1 to 6 and
?uoroalkane by distillation, which makes it possible
d is an integer from 1 to 4. As examples of hydro
directly to obtain a hydrofluoroalkane which is almost
?uoroalkanes which can be treated by the process of the
free from halogenated organic purities and proton acids. 50 invention, mention may be made of the compounds with
It has now been observed that, in the conventional
structural formula CH3CCl2F, CH3CC1F2, CH3CHF2,
process de?ned above, during the step of purifying the
hydro?uoroalkane with respect to heavy impurities by
CH3CF3,
distillation, a fraction of the hydro?uoroalkane and/or a
fraction of some heavy impurities, principally haloge
nated organic compounds, may undergo degradation
leading to the appearance of unsaturated halogenated
organic compounds and proton acids. A possible cause
of this degradation is the presence of traces of Lewis
acids in the mixture to be separated. It has furthermore
been observed that, even at room temperature, the pres
ence of only 1 ppm of FeCl3 in l,l-dichloro-l-?uoroe
thane is suf?cient to induce the dehydrochlorination of
a signi?cant fraction of this product to give l-chloro-l
?uoroethene and hydrogen chloride. Another possible
CH2FCH2F,
CHZFCHFZ,
CH2FCF3,
CHF2CCl3, CHF2CF3, CHClzCF 3, CHClFCF3,
55
CHFZCHFZ,
CF3CFZCHFZ,
CF3CF2CHCl2,
CFzClCFzCI-ICIF, CF3CF1CH3, CF3CH2CF2CH3 and
CF3CH2CH2CF3. Good results have been obtained
with the process according to the invention when it is
applied to the puri?cation of l, l-dichloro-l-?uoroe
thane.
Hydrofluoroalkanes such as de?ned hereinabove, to
which the process according to the invention is applica
ble, are generally obtained by reaction of d halogen, a
proton acid or hydrogen with a saturated or unsaturated
hydrocarbon which is possibly halogenated. By way of
65 examples of such reactions, mention may be made of the
cause of this degradation is linked with the use of metal
synthesis of l,l-dichloro-l-?uoroethane by hydro?uori
distillation columns, some metals being capable of in
ducing a certain degradation of halogenated com
nation of vinylidene chloride or of l,l,l-trichloroe
thane. Mention may also be made of the synthesis of
5,306,850
3
l,l,l,2-tetra?uoroethane by catalytic hydrofluorination
of a compound of structural formula CX3CH2Cl, with
X being C1 or F. The operational conditions under
which these reaction are implemented are well known
in the prior art. Whatever the hydroiluoroalkane syn
thesised and the method of preparation used, the hydro
fluoroalkane leaving the synthesis reactor is generally
contaminated by various impurities. These impurities
may have varied origins and their nature depends on the
hydro?uoroalkane synthesised and on the method of
preparation used. They may involve in particular reac
tants which are not converted during the synthesis of
the hydro?uoroalkane, impurities or derivatives of im
purities present in the reactants, sub-products formed
during the synthesis or alternatively reactants used or
products obtained in a treatment subsequent to the syn
thesis for chemically converting some impurities ac
companying the hydrofluoroalkane.
4
rated hydrocarbon most particularly preferred as the
acid-scavenger is Z-methylbut-Z-ene. In this case, very
good results have been obtained with industrial 2
methylbut-Z-ene, usually called amylene, which further
more contains a little 2-methylbut-l-ene.
All other things being equal, moreover, the optimum
quantity of acid-scavenger to be used will depend on
the nature of the hydrofluoroalkane to be puri?ed, on
the nature of the heavy impurities and on their concen
tration with respect to the hydro?uoroalkane to be
puri?ed, as well as on the acid-scavenger selected. It
must then be determined in each particular case by
routine laboratory work. In practice, it is recommended
to use a quantity by weight of acid-scavenger at least
equal to approximately 0.005 g per kilo of hydro
?uoroalkane subjected to the distillation, and preferably
greater than or equal to approximately 0.01 g. It is not
generally advantageous for this quantity to exceed ap
In the process according to the invention, the impuri
proximately 1 g per kilo of hydro?uoroalkane subjected
ties which are less volatile than the hydro?uoroalkane 20 to the distillation, and preferably approximately 0.1 g.
are chemical compounds, generally organic chemical
Quantities between approximately 0.025 g and approxi
compounds, whose boiling point is higher than the boil
mately 0.075 g per kilo of hydro?uoroalkane subjected
ing point of the hydrofluoroalkane subjected to the
puri?cation. As a general rule, it'is desirable, for eco
nomic reasons, for the relative volatility, that is to say
the ratio between the volatility of the hydro?uoroal
kane and the volatility of the impurities which are less
volatile than the hydro?uoroalkane, to be at least 1.05,
and preferably at least 1.1.
In the rest of the text, the impurities which are less
volatile than the hydro?uoroalkane, as described here
inabove, will be referred to as heavy impurities. The
heavy impurities are normally C2-C3 halogenated or
ganic compounds, principally saturated aliphatic hydro
carbons, and in particular hydro?uoroalkanes other
than the one subjected to the puri?cation.
In order effectively to inhibit the degradation of the
hydro?uoroalkane to be puri?ed and of the heavy im
to the distillation are recommended.
In the process according to the invention, the distilla
tion is generally performed in one or more distillation
columns, which are well known in the ?eld of the art. In
this embodiment of the process according to the inven
tion, the best results are obtained when the acid
scavenger is distributed homogeneously throughout the
distillationv column. The acid-scavenger may be intro
duced at'different levels in the column. In order to
ensure maximum efficiency, it is sometimes desirable to
introduce the acid~scavenger at several points of the
35 column. The acid-scavenger may be introduced periodi
cally into the column or, preferably, continuously.
In a ?rst variant of the aforementioned embodiment
of the process, the acid-scavenger is introduced at the
purities during the distillation, the acid-scavenger used
top of the distillation column, for example by injecting
of diethylamine, dipropylamine, diisopropylamine, di
butylamine, diisobutylamine, triethylamine and tri
markedly higher than that of the hydrofluoroalkane to
be puri?ed, for example a compound whose boiling
point is greater by approximately 15° C. to approxi
mately 50° C. with respect to the boiling point of the
hydrofluoroalkane to be puri?ed. This variant of the
in the process according to the invention must be highly 40 it into a fraction of the condensed hydro?uoroalkane
which is returned into the column as a re?ux.
reactive with respect to proton acids and halogens and
In a second variant of this embodiment of the process,
have a vapor pressure which is sufficient for it to be
the acid-scavenger is introduced at the bottom of the
distributed efficiently in the column where the distilla
distillation column, for example by injecting it into a
tion is performed. Acid-scavengers which can be used
in the process according to the invention are in particu 45 boiling vessel of the column.
In a third variant of this embodiment of the process,
lar epoxides, amines and unsaturated hydrocarbons. As
the acid-scavenger is added to the hydro?uoroalkane
epoxides, mention may be made in particular of 1,2
upstream of the distillation column.
epoxypropane, 1.2-epoxybutane, l,2-epoxypentane, 1,2
In the aforementioned ?rst variant of the process, it is
epoxycyclohexane, 1,2-epoxyethylbenzene, epichloro
possible to use an acid-scavenger having a boiling point
hydrin and glycidol. As amines, mention may be made
propylamine. As unsaturated hydrocarbons, mention
may be made in particular of propenes, butenes, methyl
butenes, dimcthylbutenes, pentenes, methylpentenes,
dimethylpentenes, trimethylpentenes, hexanes, cyclo
process is preferred when the level of content of acid
scavenger in the hydro?uoroalkane collected from the
puri?cation is to remain very low, for example less than
5 ppm.
are C3-C3 unsaturated hydrocarbons. Among these
unsaturated hydrocarbons, 2-methylbut-2-ene, 2 60 When it is sought to obtain a residual level of content
pentene, cyclohexene and methylcyclopentene. Ac
cording to the invention, the preferred acid-scavengers
methylbut-l-ene, 3-methylbut-l-ene, 2- ethylbut-l-ene,
pent-l-ene, pent-Z-ene, Z-methylpent-llene, 2-methyl
pent-2-ene, 3-methylpent-l-ene, 3-mcthylpent-2-ene,
of acid~scavenger in the hydro?uoroalkane, collected
from the puri?cation, which is greater than 5 ppm, for
example of the order of 10 to 100 ppm, according to the
invention, an acid-scavenger is chosen whose boiling
4-methylpent-l-ene, 2,4,4-trimethylpentl-ene, hex
l-ene, hex-2-ene and hex-S-ene are particularly pre 65 point is close to that of the hydro?uoroalkane, for ex
ferred.
ample, a compound whose boiling point differs from
that of the hydro?uoroalkane to be puri?ed by no more
In the case in which the process is applied to the
than 15° C., preferably, a compound whose boiling
puri?cation of l,l-dichloro-l-?uoroethane, the unsatu
5
5,306,850
6
point differs from that of the hydro?uoroalkane to be
lation column, of unsaturated organic products and
puri?ed by no more than 10' C.
In a particularly preferred manner, an acid-scavenger
would rather be used whose boiling point is l to 5° C.
proton acids which are lighter than the hydro?uoroal
kanes subjected to the puri?cation, makes it possible to
recover the latter at the top of the column, which oper
ation is easier than withdrawal from an intermediate
tray. The absence of compounds which are more vola
greater than that of the hydro?uoroalkane to be puri
?ed. Such an acid-scavenger may be used in all three
variants of the process described hereinabove. The
third variant of the process appears particularly advan
tile than the hydro?uoroalkane in the column further
more removes the necessity for purging the top of the
tageous, and is therefore preferred.
column, which improves the overall yield of the pro
In the process according to the invention, it is neces
cess. The invention furthermore makes it possible to
conduct the distillation at higher pressures and tempera
tures than in the absence of the acid-scavenger, without
sary for the hydro?uoroalkane subjected to the distilla
tion to be substantially free from impurities which are
more volatile than it.
any degradation of the hydro?uoroalkane or of the
Impurities which are more volatile than the hydro
heavy impurities being observed. It also makes it possi
?uoroalkane are inorganic or organic chemical com 15 ble to obtain a hydro?uoroalkane satisfying the strictest
pounds whose boiling point is less than the boiling point
of purity speci?cations without needing to implement a
?nishing treatment for the product.
of the hydro?uoroalkane subjected to the puri?cation.
In the rest of the text, impurities which are less vola
The examples whose description follows serve to
tile than the hydro?uoroalkane, as de?ned hereinabove,
illustrate the invention. Example 1, produced according
are referred to as light impurities. Typically, light impu
rities in the hydro?uoroalkane comprise inert gases
to a conventional process of puri?cation by distillation,
is given by way of reference. Examples 2 and 3 are in
accordance with the invention.
such as nitrogen, proton acids such as hydrogen ?uo
ride and hydrogen chloride, halogens such as chlorine
and fluorine, hydrogen as well as certain organic com
pounds, principally C1-C4 organic compounds, most
often halogenated, and possibly unsaturated.
25
EXAMPLE 1 (FOR REFERENCE)
1, l-Dichloro-l-fluoroethane obtained by hydrofluori
nation of vinylidene chloride then having undergone a
The light impurities are removed from the hydro
fluoroalkane by any appropriate technique, before in
treatment of chlorination of the unsaturated impurities,
in the presence of FeCl3, is subjected to a predistillation
troduction of the acid-scavenger into the mixture.
In one preferred embodiment of the process accord 30 in order to purify it with respect to the light impurities.
For this purpose, it is introduced into a ?rst stripping
ing to the invention, before the distillation, the hydro
column (light-component column) under a pressure of
?uoroalkane is subjected to a predistillation in order to
2.1 bar. The excess chlorine used in the preceding chlo
separate light impurities therefrom. The predistillation
rination step is removed at the top of the column, and
is a distillation which precedes the one intended to
the
mixture of l,l-dichloro-l-fluoroethane and the
separate the heavy impurities from the hydro?uoroal 35
heavy impurities comprising in particular chlorinated
kane, and which is carried out under controlled condi
tions in order to separate the light impurities from the ' saturated compounds produced in the step of chlorina
hydro?uoroalkane. The predistillation is performed in ' . tion of the unsaturated impurities, leaves the light-com
ponent column at the bottom. This mixture is then intro
one or more distillation columns.
duced into a second distillation column (heavy-compo
It is generally desirable to add the acid-scavenger as
nent column), operating at a pressure of 1.5 bar. In this
rapidly as possible after the separation of the light impu
column, the mixture undergoes a distillation in order to
rities from the hydro?uoroalkane. For this purpose, in
separate the l,l-dichloro-l-fluoroethane from the impu
the preferred embodiment described hereinabove in
rities which accompany it. The l,l-dichloro-1 -?uoroe
which the light impurities are removed by a predistilla
tion, the acid-scavenger may be injected into the boiling
45 thane is there withdrawn at the top of the column and
the heavy impurities are removed at the bottom. The
re?ux ratio is equal to 2.
The mean concentration of l-chloro-l-?uoroethene
longer contaminated with signi?cant quantities of light
in the 1,1-dichloro-l-fluoroethane withdrawn at the top
impurities, in particular halogens or proton acids.
As described hereinabove, according to the embodi 50 is 5 mg per kilo of l,l-dichloro-l-iluoroethane.
ment variants of the process and the nature of the acid
EXAMPLE 2 (ACCORDING TO THE
scavenger used, the process according to the invention
vessel of the column in which the predistillation is per
formed, at which place the hydro?uoroalkane is no
INVENTION)
makes it possible to obtain the puri?ed hydro?uoroal
kane either almost free from the acid-scavenger, or
Every point of the above Example 1 is repeated, but
containing small quantities by weight of acid-scavenger,
55 30 mg of amylene per kilo of mixture is injected into the
for example of the order of 10 to 100 ppm. At this level
boiling vessel of the light-component column. The
of concentration, the acid-scavenger then performs the
function of stabilizing the hydro?uoroalkane, both for
mean concentration of l-chloro-l-fluoroethene in the
storage and for subsequent uses, in particular as a sol~
vent.
The invention has numerous advantages. It makes it
possible in particular to perform the distillation in a
column made of ordinary steel. It also makes it possible
to perform the distillation in the presence of Lewis
acids, which are regularly present in hydro?uoroal 65
l,l-dichloro-l-tluoroethane withdrawn at the top is less
than 0.2 mg per kilo of l,l-dichloro-l-?uoroethane.
The puri?ed l, l-dichloro-l-?uoroethane contains on
average 20 mg of amylene per kilo.
EXAMPLE 3 (ACCORDING .TO THE
INVENTION)
Every point of the above Example l is repeated, but
kanes to be puri?ed because of their frequent use as
30 mg of amylene per kilo of l,l-dichloro-l-?uoroe
catalysts, during the synthesis of the hydro?uoroal
thane returned to the heavy-component column as re
kanes. The inhibition of the formation, within the distil
flux is injected.
7
5,306,850
The mean concentration of l-chloro-l-?uoroethene
I in the l, l-dichloro-l-?uoroethane withdrawn at the top
higher than that of the hydro?uoroalkane to be puri?ed.
is less than 0.2 mg per kilo of l,l-dichloro-l-fluoroe
thane and the puri?ed l,l-dichloro-l-?uoroethane con
tains on average 50 mg of amylene per kilo.
I claim:
1. A puri?cation process for a hydro?uoroalkane,
8. The process according to claim 6, wherein the
acid-scavenger is added to the hydro?uoroalkane up
stream of the column in which the distillation is per
formed.
9. The process according to claim 1, wherein said
comprising:
distilling said hydro?uoroalkane to separate there
from impurities which are less volatile than said
hydro?uoroalkane, said distillation performed in
the presence of approximately 0.005 g to'approxi
mately l g of an acid-scavenger per kilo of hydro
?uoroalkane subjected to the distillation, and
separating said impurities from said hydro?uoroal
8
7. The process according to claim 6, wherein an acid
scavenger is used whose boiling point is from 1° to 5'‘ C.
hydro?uorocarbon is 1,1-dich1oro-1-?uoroethane.
10
10. The process according to claim 9, wherein 2
niethylbut-Z-ene is the acid-scavenger.
11. The process according to claim 6 wherein said
hydro?uoroalkane after said impurities are separated
15
contains from 10 to 100 mg of acid-scavenger per kilo.
12. The process according to claim 7 wherein said
hydro?uoroalkane after said impurities are separated
kane.
contains
from 10 to 100 mg of acid-scavenger per kilo.
2. The process according to claim 1, wherein a hydro
13. The process according to claim 8 wherein said
?uoroalkane is used which has undergone a predistilla
hydro?uoroalkane after said impurities are separated
tion in order to separate therefrom impurities which are 20
contains from 10 to 100 mg of acid-scavenger per kilo.
more volatile than the said hydro?uoroalkane.
14. The process according to claim 9 wherein said
3. The process according to claim 1, wherein the
hydro?uoroalkane after said impurities are separated
acid-scavenger is a C3-C3 unsaturated hydrocarbon.
contains from 10 to 100 mg of acid-scavenger per kilo.
4. The process according to claim 1, wherein the
15. The process according to claim 10 wherein said
quantity of acid-scavenger is approximately 0.01 g to
0.1 g per kilo of hydro?uoroalkane subjected to the
distillation.
5. The process according to claim 1, wherein the
25
hydro?uoroalkane after said impurities are separated
contains from 10 to 100 mg of acid-scavenger per kilo.
16. A puri?cation process for 1,1-dichloro-l-l
?uoroethane, comprising
acid-scavenger has a boiling point higher by approxi
mately 15'’ C. to approximately 50° C. than the boiling 30
point of the hydro?uoroalkane to be puri?ed, and said
acid-scavenger is introduced at the top of the column in
which the distillation is performed.
distilling said l,l-dichloro-l-?uorethane to separate
therefrom impurities which are less volatile than
said 1,1-dichloro-l-?uoroethane, said distillation
performed in the presence of an acid-scavenger.
17. The process according to claim 16, wherein the
6. The process according to claim 1, wherein an acid
scavenger is a C3-C3 unsaturated hydrocarbon.
scaven'ger is used whose boiling point differs from that 35 ‘18. The process according to claim 16, wherein the
of the hydro?uoroalkane to be puri?ed by no more than
acid-scavenger is 2-methylbut-2-ene.
it
t
i
i
1
15° C.
45
50
55
65