PROCESS FOR REMOVING OLEFINIC IMPURITIES FROM FLUORINATED C3-C6-HYDROCARBONS

PROCEDE D'ELIMINATION DES IMPURETES OLEFINIQUES DANS LES HYDROCARBURES EN C3-C6 FLUORES

English Abstract

Process for removing olefinic impurities from fluorinated
C3-C6-hydrocarbons
The invention relates to a process for removing olefinic
impurities from fluorinated C3-C6-hydrocarbons, with the
exception of 1,1,1,2,3,3,3-heptafluoropropane (R 227), by
bringing the contaminated fluorinated C3-C6-hydrocarbons
into contact with an alcohol and a base and, simultaneously
or subsequently, distilling off the fluorinated
C3-C6-hydrocarbons.

Claims

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CLAIMS:
1. A process for removing an olefinic impurity of the
formula C n H m F p C l q, where n = 2 - 6 , m = 0 - 8 , p = 1 - 12,
q = 0 - 8 and m + p + q = 2n, from a fluorinated C3-C6-
hydrocarbon, with the exception of 1,1,1,2,3,3,3-
heptafluoropropane (R 227), which comprises bringing the
contaminated fluorinated C3-C6-hydrocarbon into contact with
an alcohol and a base at a temperature of -20 to 100°C and a
pressure of 1 to 50 bar and, simultaneously or subsequently,
distilling off the fluorinated C3-C6 hydrocarbon.
2. The process as claimed in claim 1, wherein the
fluorinated C3-C6-hydrocarbon is 1,1,1,3-tetra-fluoropropane,
1,1,1,4,4,4-hexafluorobutane, 1,1,1,2,3,4,4,4-
octafluorobutane, 1,1,2,2,3,3,4,4-octafluorobutane or
1,1,1,2,3,4,5,5,5-nonafluoro-2-(trifluoromethyl)-pentane.
3. The process as claimed in claim 1 or 2, wherein
the alcohol is of formula C n Han+1OH, C n H2n (OH) 2, C n H2n-1OH or
C n H2n-2 (OH) 2 where n = 1 to 6.
4. The process as claimed in claim 3, wherein
n = 1 to 3.
5. The process as claimed in claim 1 or 2, wherein
the alcohol is ethylene gylcol, methanol, ethanol or
i-propanol.
6. The process as claimed in any one of claims 1
to 5, wherein the base has a pK of 8 to 14.
7. The process as claimed in any one of claims 1
to 6, wherein the base is NaOH, KOH or Na phenolate.

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8. The process as claimed in any one of claims 1
to 7, wherein the temperature is 0 to 50°C and the pressure
is 1 to 10 bar.
9. The process as claimed in any one of claims 1 to
8, wherein 0.5 to 20% by weight of the alcohol and 0.01 to
10% by weight of the base are used, based on the fluorinated
C3-C6-hydrocarbon.

Description

HOECHST AKTIENGESELLSCHAFT HOE 92/F 170 Dr. MA/wo
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Description
Process for removing olefinic impurities from fluorinated
C3-C6-hydrocarbons
The invention relates to a process for removing olefinic
impurities from fluorinated C3-C6-hydrocarbons. These
compounds are provided as substitutes for the ozone-
endangering completely halogenated chlorofluorocarbons.
In order to be able to use the fluorinated C3-C6-hydro-
carbons in the refrigeration technology area or as
propellants for pharmaceutical aerosols or rigid
polyurethane foams, interfering and toxic olefinic
impurities, which are formed in the synthesis - some only
in traces - must be completely removed. This is not
possible on an economically tolerable scale by
conventional physical methods such as distillation or
adsorption. Therefore a possible method must be sought of
converting the interfering impurities into non-toxic
compounds by reaction with suitable substances or of
converting them into those compounds which can be
separated off from fluorinated C3-C6-hydrocarbons by a
physical route with small expenditure.
It has now proved to be expedient to react the olefins,
such as1,1,1,3,4,4,5,5,5-nonafluoro-2-(trifluoromethyl)-
2-pentene (HFH), which are formed in the preparation of,
for example, isodihydroperfluorohexane (IDPH;
1,1,1,2,3,4,5,5,5-nonafluoro-2-(trifluoromethyl)-
pentane), with alcohols in the presence of bases. Tn this
case, only compounds are formed which can easily be
separated off from IDPH by distillation. Moreover, IDPH
is not attacked and the reaction proceeds rapidly and
quantitatively.
The removal o.f olefinic impurities from
1,1,1,2,3,3,3-heptafluoropropane (R 227) by reaction with
alcohols in the presence of salts is already described in
German Patent Application P 4 115 025.2, which is not a

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prior publication. O ~. ~:r..a
Although Chemical Abstracts 1971, volume 13: 60600w
discloses that a mixture of higher-boiling ethers and
esters can be prepared from 2-H-pentafluoropropene and
alcohols in the presence of KOH, the conversion rates are
not quantitative. Therefore, it was not to be expected
that traces of HFH and other olefins, dissolved in IDPH,
can be quantitatively removed by reaction with alcohols.
Moreover, azeotrope formation with alcohols was to be
feared.
The invention relates to a process for removing olefinic
impurities of the formula CnIimFpCl9, where n = 2 - 6,
m = 0 - 8, p = 1 - 12, q = 0 - 8 and m + p + q = 2n, from
fluorinated C3-C6-hydrocarbons, with the exception of
1,1,1,2,3,3,3-heptafluoropropane (R 227), which comprises
bringing the contaminated fluorinated G3-C6-hydrocarbons
into contact with an alcohol and a base at temperatures
of -20 to 100°C and pressures of 1 to 50 bar and,
simultaneously or subsequently, distilling off the
fluorinated C3-C6-hydrocarbons.
The fluorinated G3-C6-hydrocarbon used is preferably
1,1,1,3-tetrafluoropropane, 1,1,1,4,4,4-hexafluorobutane,
1,1,1,2,3,4,4,4-octafluorobutane, 1,1,2,2,3,3,4,4-octa
fluorobutane or 1,1,1,2,3,4,5,5,5-nonafluoro-2-(tri
fluoromethyl)-pentane.
A alcohol is preferably used of the formula
CaHaa+~OH, CBHZa ( OH ) 2, CaH2a-lOH or C8H28_Z ( OH ) 2, where a = 1 to
6, in particular where a = 1 to 3. Methanol, ethanol,
i-propanol and ethylene glycol (glycol) are particularly
suitable.
The bases used are preferably those whose pK is 8 to 14,
in particular NaOH, KOH or Na phenolate.
The temperature is preferably at 0 to 50°C and the

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pressure is preferably 1 to 10 bar. Based on fluorinated
C3-C6-hydrocarbon, the amount of alcohol is preferably 0.5
to 20~ by weight, in particular 0.5 to 10~ by weight, and
the amount of base is preferably 0.01 to 10~ by weight,
in particular 0.01 to 5$ by weight.
The invention is intended to be described in more detail
by means of the following examples.
Examples 1 to 9:
A heatable stirred autoclave (V = 300 ml) was charged
with 100 g of isodihydroperfluorohexane (IDPH), which
contained approximately 500 ppm of
1,1,1,3,4,4,5,5,5-nonafluoro-2-(trifluoromethyl)-2
pentene (HFH), and with 10 g of an alcohol and 1 g of a
base. The autoclave was then heated to 50°C and stirred
for 8 hours at this temperature. The content of HFH was
followed by gas chromatography. The alcohols and bases
used and the results are presented in Table i.
Table 1
Alcohol Base Content of HFH ~p~anL after
8 hours
Methanol NaOH B.D.L.'
Methanol KOH B.D.L.'
Methanol Na acetate 380
-
Methanol Na2HIa03 450
Methanol Pyridine 280
NSethanol Na phenolate 50
Ethanol NaOH B.D.L.'
i-Propanol NaOH 40
Glycol NaOH B.D.L.'
Example 10:
A distillation vessel was charged with 80 kg of IDPH,
which contained approximately 500 ppm of HFH, and with
800 g of methanol and 50 g of KOH. The vessel was then
' B.D.L. = Below e~etection limit (< 1 ppm)

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heated to ~0°C and stirred for 12 hours at this tempera-
ture. The content of HRH had afterwards fallen to below
ppm.