TECHNICAL FIELD
The present invention relates to a process for dehydrating a
hexafluoroacetone hydrate by hydrogen fluoride, and furthermore relates to
a process for producing a hexafluoroacetone-hydrogen fluoride adduct.
BACKGROUND TECHNIQUE
Hexafluoroacetone is produced in a large amount as an industrial
raw material of 2,2-bis(4-hydroxyphenyl)hexafluoropropane (bisphenol-AF),
which is important as a crosslinking agent of fluororubber,
hexafluoroisopropanol, which is important as a medicine intermediate, and
the like. Industrially, hexafluoroacetone is produced by a process by an
epoxidation of hexafluoropropene and a subsequent isomerization, a process
by subjecting hexachloroacetone obtained by chlorinating acetone to a
substitution fluorination with hydrogen fluoride by a chromium-supported
activated carbon catalyst or the like, etc. Hexafluoroacetone is a gas
having a boiling point of -28°C under atmospheric pressure. Therefore, in
order to meet the convenience of handling, hexafluoroacetone trihydrate,
which is obtained as a constant boiling composition of 106°C, is used as a
raw material in many reactions or served for storage. There are, however,
some cases in which existence of water is not permissible depending on the
reaction conditions, the target product and other requirements.
Furthermore, hydrates are generally lower in reactivity in many cases, as
compared with anhydrides. Therefore, anhydride of hexafluoroacetone is
requested in some cases, and upon use it is frequently conducted to convert
the hydrate to the anhydride in place.
As a process for dehydrating a hexafluoroacetone hydrate, there
have been reported processes by the contact with Molecular Sieve (a
registered trade mark) (Patent Publication 1), concentrated sulfuric acid,
sulfuric anhydride, phosphorus pentoxide (Patent Publication 2), etc. By
using concentrated sulfuric acid, sulfuric anhydride, phosphorus pentoxide,
fuming sulfuric acid or the like as the dehydrator, hexafluoroacetone
decomposition products may be produced. Furthermore, there occurs a
waste in a large amount of sulfuric acid or phosphoric acid containing water
and organic matters produced by the decomposition. Furthermore, there is
also a problem that recovery percentage of hexafluoroacetone is not
necessarily high when the dehydration is conducted by these processes
including the case of using a synthetic zeolite.
On the other hand, hydrogen fluoride may be used as a catalyst or
solvent in reactions using hexafluoroacetone as a raw material. For
example, bisphenol-AF is obtained by a dehydration reaction from a mixture
of hexafluoroacetone, phenol and hydrogen fluoride (Non-patent Publication
1).
Patent Publication 1: Japanese Patent Application Publication 59-157045
Patent Publication 2: Japanese Patent Application Publication 57-81433
Non-patent Publication 1: Isz. Akad-Nauk SSSR, Otdel. Khim, Nauk, vol. 4
pp. 686-692 (1960); English version pp. 647-653
DISCLOSURE OF THE INVENTION
TASK TO BE SOLVED BY THE INVENTION
There is provided a process of obtaining a mixture of a
hexafluoroacetone-hydrogen fluoride adduct and hydrogen fluoride by
dehydrating a hexafluoroacetone hydrate, the process generating
substantially no waste.
MEANS FOR SOLVING TASK
As a result of a study about a process for industrially producing a
hexafluoroacetone-hydrogen fluoride adduct, which shows a reaction

behavior similar to that of hexafluoroacetone in specific reactions, the
present inventors have found that a hydrogen fluoride solution of a
hexafluoroacetone-hydrogen fluoride adduct can quantitatively be produced
with good yield and substantially no generation of waste through
dehydration of a hexafluoroacetone hydrate by a simple process comprising
mixing a hexafluoroacetone hydrate with hydrogen fluoride and then
conducting distillation, thereby completing the present invention.
That is, the present invention is a process for producing a
hexafluoroacetone-hydrogen fluoride adduct, comprising separately
obtaining a component containing a hexafluoroacetone-hydrogen fluoride
adduct and hydrogen fluoride and a component containing water and
hydrogen fluoride by bringing a hexafluoroacetone hydrate into contact with
hydrogen fluoride and conducting distillation as it is.
Aspects 1-5 of the present invention are shown in the following.
Aspect 1 of the present invention is a process for dehydrating a
hexafluoroacetone hydrate, comprising introducing a hexafluoroacetone
hydrate and hydrogen fluoride either as a mixture or separately into a
distillation column, obtaining a composition containing hexafluoroacetone or
a hexafluoroacetone-hydrogen fluoride adduct and hydrogen fluoride as a
low boiling component, and obtaining a composition containing water and
hydrogen fluoride as a high boiling component.
Aspect 2 of the present invention is a dehydration process according
to Aspect 1, wherein the hexafluoroacetone hydrate and the hydrogen
fluoride are continuously introduced either as a mixture or separately into
the distillation column.
Aspect 3 of the present invention is a process for dehydrating a
hexafluoroacetone hydrate, comprising continuously introducing a
hexafluoroacetone hydrate and hydrogen fluoride either as a mixture or

separately into a distillation column, continuously obtaining a composition
containing hexafluoroacetone or a hexafluoroacetone-hydrogen fluoride
adduct and hydrogen fluoride as a low boiling component from a column top
portion, and continuously obtaining a composition containing water and
hydrogen fluoride as a high hoiling component from a column bottom
portion.
[4] A dehydration process according to any of claims 1-3, wherein the
hexafluoroacetone hydrate is hexafluoroacetone trihydrate.
Aspect 4 of the present invention is a dehydration process according
to any of Aspects 1-3, wherein the hexafluoroacetone hydrate is
hexafluoroacetone trihydrate.
Aspect 5 of the present invention is a dehydration process according
to any of Aspects 1-4, wherein the hexafluoroacetone hydrate is a
hexafluoroacetone hydrate containing water.
ADVANTAGEOUS EFFECT OF THE INVENTION
In the dehydration process of the present invention, since
hexafluoroacetone or a hexafluoroacetone-hydrogen fluoride adduct to be
obtained is in a mixture with hydrogen fluoride, it can be used as it is for a
reaction in which hexafluoroacetone is used with hydrogen fluoride as a raw
material, catalyst or solvent. Therefore, it is effective for simplification of
the steps. Furthermore, it is a superior process on the side of
environmental protection too, since it does not require a treatment of waste
such as waste sulfuric acid containing organic materials, which is inevitable
in processes conducted hitherto using concentrated sulfuric acid, fuming
sulfuric acid, and the like.
BEST MODE FOR CARRYING OUT THE INVENTION
In the following, the present invention is explained in detail.

In the description, hydrogen fluoride may be represented by HF.
In the description, hexafluoroacetone may be represented by HFA.
In the description, a hexafluoroacetone-hydrogen fluoride adduct may be
represented by HFAHF.
In the description, a hexafluroacetone hydrate refers to a hydrate or its
aqueous solution with unlimited hydration number and is a concept
containing hexafluoroacetone trihydrate.
In the description, hexafluoroacetone trihydrate may be represented by
HFA.3W.
The present invention is a process for producing a
hexafluoroacetone-hydrogen fluoride adduct, comprising separately
obtaining a component containing a hexafluoroacetone-hydrogen fluoride
adduct and hydrogen fluoride and a component containing water and
hydrogen fluoride by bringing a hexafluoroacetone hydrate into contact with
hydrogen fluoride and conducting distillation as it is. Here, "as it is" refers
to without conducting a treatment by a chemical substance that is used
generally as a dehydrator, such as concentrated sulfuric acid, sulfuric
anhydride, phosphorus pentoxide, and the like, or by an adsorbent such as
molecular sieves and the like. However, not "as it is", that is, it is natural
to be able to conduct a dehydration by these dehydrators before or after
applying the dehydration process of the present invention.
As HFA3W, which may be dealt with as an alternative reaction
reagent to hexafluoroacetone, is represented by
[Chemical Formula 1]

it is a gem-diol dihydrate resulting from a reaction between
hexafluoroacetone and water and is a liquid having a boiling point of 106°C.
Even if HFA.3W is distilled, it is not possible to release water to obtain
hexafluoroacetone.
Furthermore, hexafluoroacetone monohydrate is a compound
different from hexafluoroacetone and is represented as gem-diol. An
equilibrium of the following formula between hexafluoroacetone and water
is established, and the equilibrium shifts extremely rightward.
[Chemical Formula 2]

Hexafluoroacetone monohydrate is a solid having a melting point of
52°C, which is high in sublimation property and strong in hygroscopic
property. Although it decomposes at 46°C, it is not possible to obtain
hexafluoroacetone by distillation, similar to HFA3W.
On the other hand, a hexafluoroacetone-hydrogen fluoride adduct is
a 1:1 adduct of hexafluoroacetone and hydrogen fluoride, represented by
heptafluoroisopropanol of the following formula. Heptafluoroisopropanol
alone is a thermally unstable compound, and it is considered that there is a
partial decomposition into hexafluoroacetone and hydrogen fluoride at a
temperature not lower than boiling point (14-16°C) and that an equilibrium
of the following formula is established. The equilibrium depends on
temperature, and heptafluoroisopropanol is decomposed by 35% at 20°C and
by 70% at 100°C.
[Chemical Formula 3]

There is a report (US No. 3745093 Patent Publication) that HFAHF
can be separated by distillation under non-equilibrium condition, but it is
not possible to separate hexafluoroacetone and hydrogen fluoride even if
distillation is conducted by a normal method (French Patent No. 1372549).
In the course of completing the present invention, it has been
confirmed by NMR measurement in hydrogen fluoride by the inventors and
the like that HFAHF is heptafluoroisopropanol, and, if an excessive amount
of hydrogen fluoride is coexistent, it exists stably as it is
heptafluoroisopropanol with no decomposition even if it is left at room
temperature or higher.
It is possible to conduct dehydration of a hexafluoroacetone hydrate
of the present invention by any type of batch type, half batch type or
continuous type by using a common distillation apparatus equipped with a
distillation pot, a distillation column, a condenser and other devices As the
material of the apparatus, it is possible to use stainless steel, nickel alloy
steel, silver, fluororesin, carbon and polyethylene, or metal materials lined
or cladded with these materials. For the distillation pot, the distillation
column and the packing material, with which a hydrogen fluoride aqueous
solution of a relatively high temperature is brought in contact, it is
preferable to use silver, resin materials, such as fluororesin and the like,
resistant to a hydrogen fluoride aqueous solution, or metal materials lined
or cladded with these materials. As the distillation column, it is possible to
use any of packing-type formed of a publicly known packing material, a tray
column, etc.
The process of the present invention can be conducted under reduced
pressure or pressurized condition, specifically even under a condition of a
pressure of about 0.05-2MPa. In the following, the case of conducting it
under atmospheric pressure is explained. Conducting it under other
pressure conditions also belongs to the scope of the present invention. It is
easy for a person skilled in the art to optimize the conditions, based on the
following explanation and technical common sense in this technical field.
The batch type dehydration process is explained.
HFA3W and hydrogen fluoride are introduced into the distillation
pot (column bottom) of the distillation column. Relative to 1 mol of
HFA3W, hydrogen fluoride is necessary by 1 mol or greater, preferably
2-100 mols, more preferably 3-50 mols, still more preferably 5-30. If
hydrogen fluoride is too little, the effect of dehydration is insufficient, and
operation of the distillation does not become stable. If it is too much, there
is no problem in the effect of dehydration. With this, consumption of utility
becomes large, and it is accompanied by enlargement of the apparatus.
Each of them is not preferable. Here, it suffices that HFA.3W is a
hexafluoroacetone hydrate. It may be one having a hydration number less
than 3, such as hexafluoroacetone monohydrate. Furthermore, it may be
an aqueous solution of a hexafluoroacetone hydrate. As a raw material
used for the dehydration, it is preferably HFA.3W or one having a hydration
number less than that. As the hydrogen fluoride, anhydrous hydrogen
fluoride, which is available for industrial use, is suitable. In principle,
however, the water content is not essential. It is possible to use even one
containing about 50 mass % of water.
By increasing the column bottom temperature to exceed boiling point
of hydrogen fluoride, vapor is liquefied at the column top by the condenser to
start reflux. After a certain period of time, it gets closer to 16°C, which is
boiling point of HFA.HF. By gradually taking the reflux liquid out, the
temperature gets closer to boiling point (19.5°C) of hydrogen fluoride.
While making an adjustment to maintain the reflux condition, the reflux
liquid is taken out. In case that the amount of reflux decreases, the column
bottom temperature is gradually increased. At the initial stage of the
distillation, a component containing a lot of HFA.HF is taken out of the

column top at 16-20°C. Then, the temperature of the reflux liquid
increases gradually. The HFA HF content decreases, and a component
containing a lot of hydrogen fluoride is taken out. It is necessary to
maintain the temperature of the reflux liquid in a range not to greatly
exceed boiling point of hydrogen fluoride. Otherwise, dehydration of
hydrogen fluoride becomes incomplete, and water is contained in the column
top liquid. Although the admissible water content depends on use of the
dehydrated HFA, it is 1 mass % or lower, normally 0.01 mass % or lower.
Furthermore, the distillation is continued. It can be continued until the
column bottom temperature, depending on the composition of hydrogen
fluoride and water, increases to 112°C, the azeotropic temperature of
hydrogen fluoride aqueous solution. Upon this, the column bottom liquid
forms a maximum boiling point azeotrope of 38 mass % hydrogen fluoride
and 62 mass % water. The column bottom liquid contains substantially no
hexafluoroacetone. The admissible residual HFA depends on the use of the
hydrogen fluoride aqueous solution, but is 1 mass % or lower, normally 0.01
mass % or lower. As to the column bottom temperature, it can be
conducted until the maximum azeotropic temperature of the hydrogen
fluoride aqueous solution. It is also can be conducted at a temperature
lower than the maximum azeotropic temperature as long as it is not lower
than boiling point (19.5°C) of hydrogen fluoride. In that case, it results in
obtaining a hydrogen fluoride aqueous solution having a concentration
determined by boiling point, but the concentration may be determined by
the use of the hydrogen fluoride aqueous solution. In this way, a
component formed of hexafluoroacetone or HFA.HF and hydrogen fluoride
and a component (hydrogen fluoride aqueous solution) formed of hydrogen
fluoride and water are separately obtained.
Next, the case of conducting the process of the present invention by a
continuous process is explained.

In the above-mentioned batch type dehydration process, it is
preferable to conduct a shift to the continuous process from a condition in
which the distillation column is maintained in a stable reflux condition. In
the continuous process, it is operationally easy to use a hexafluoroacetone
hydrate that the compositional ratio of hexafluoroacetone to water is
constant, for example, HFA3W. Therefore, the case of using HFA3W is
explained in the following. In general, it is preferable not to vary the
composition ratio of hexafluoroacetone to water, but it is not necessary to be
a specific composition ratio (in this case, the molar ratio of water/HFA is 3).
HFA3W and hydrogen fluoride are continuously introduced into the
distillation column. HFAHF and hydrogen fluoride are continuously taken
out of the column top, and the hydrogen fluoride aqueous solution out of the
column bottom. It is also possible to intermittently conduct the continuous
operation of introducing hexafluoroacetone hydrate and hydrogen fluoride,
taking HFAHF and hydrogen fluoride out of the column top, and taking the
hydrogen fluoride aqueous solution out of the column bottom.
It is possible to not only introduce a hexafluoroacetone hydrate and
hydrogen fluoride into the distillation column through separate pipes, but
also introduce them after their previous mixing. It is preferable to have the
same positions for the introduction into the distillation column. It is
possible to set the position (height) for the introduction into the distillation
column at an arbitrary position from the column bottom to the column top.
It is, however, preferable to introduce them at the position (height)
corresponding to the boiling point of a mixed liquid resulting from the
theoretical amounts of water and hydrogen fluoride, which are generated by
a dehydration reaction of preferably HFA 3W and hydrogen fluoride.
The reason why dehydration can effectively be conducted in the
process of the present invention is assumed that, in the case of mixing
hexafluoroacetone trihydrate with one equivalent or more of hydrogen
fluoride, a reaction or equilibrium shown in the following formula is

established in a short period of time, and in the distillation an equilibrium
condition formed of three components of HFAHF, hydrogen fluoride and an
azeotropic composition of water and hydrogen fluoride is established.

EXAMPLES
In the following, the present invention is explained in detail by
examples, but the present invention is not limited to these examples.
[EXAMPLE 1] Batch type production process
As to material of the dehydration apparatus, a fluororesin or
polyethylene was used for all of the parts with which hexafluoroacetone,
hexafluoroacetone trihydrate and anhydrous hydrogen fluoride are brought
into contact. As the distillation pot, a polytetrafluoroethylene container of
10cm diameter x 15 cm height was used. As the distillation column, there
was used a PFA column of 3cm diameter x 45cm height packed by a length
of 35cm with polyethylene Raschig rings (4mm diameter x 4mm length) as a
packing material. As the condenser, there was used a PFA cylindrical
container of 10cm diameter x 15cm height equipped in the inside with a
coiled tube to make a refrigerant to flow. As a receiver for an effluent from
the column top, a 500ml PFA container was used.
After putting 220g of HFA3W into the distillation pot, it was cooled
with a dry ice/acetone bath to solidify it. Then, 240g of anhydrous
hydrogen fluoride was weighed and put thereinto. Under a cooled
condition (-20°C), it was set on the distillation column. It was allowed to
stand still as it was until room temperature. Then, heating was started
with a water bath and then an oil bath. During this, a conspicuous
generation of heat in the distillation pot by the mixing was not observed.
As the heating was continued, reflux was observed at an upper part
of the distillation column. Then, temperature of the reflux portion started
to become lower than boiling point (19.5°C) of hydrogen fluoride, and reflux
of HFAHF was confirmed. Upon this, it was started to take the reflux
liquid out, while securing reflux to maintain temperature of the column top
at around 19.5°C, boiling point of hydrogen fluoride. The reflux liquid
(HFAnHF) taken out was received in the receiver cooled with ice, and the
volume was recorded over time. At the time when a suitable amount was
collected, the container was changed, followed by measuring the volume and
the mass, putting into a storage container made of polyethylene, and storing
with sealing in a refrigerator.
Since the column bottom temperature increases with lowering of the
hydrogen fluoride concentration at the column bottom portion by the
progress of the distillation, the oil bath temperature was adjusted to always
have a temperature difference of 20°C or greater between the column top
and the column bottom. Temperature of the column bottom showed on
occasions temperature of the gas phase portion of the distillation pot due to
decrease of the amount of the interior content (It was the same in the
following.). Temperatures of the column bottom portion and the distillation
column increased gradually, but temperature of the column top was almost
constantly maintained at 20°C to maintain a suitable reflux. At the time
when the column bottom temperature showed 60°C, the distillation was
stopped.
After the distillation, the reflux liquid (column top effluent)
recovered from the column top was 252g (the molar ratio n of HFAnHF: 4.3,
yield of hexafluoroacetone: 99%), and the column bottom liquid was a
hydrogen fluoride aqueous solution (71 mass %) of 188g. Existence of water
was not confirmed by measuring water content of the reflux liquid by Karl
Fischer's method. Hexafluoroacetone was not detected in the column
bottom liquid.
[EXAMPLE 2] Batch type production process
(a) The distillation pot was charged with 181g of the hydrogen fluoride
aqueous solution (71 mass %) recovered from the column bottom after
termination of the distillation of Example 1, 220g of HFA3W and 344g of
anhydrous hydrogen fluoride. A distillation similar to that of Example 1
was started. While the reflux liquid of the column top was taken out, the
distillation was continued until the column bottom temperature showed
51°C. With this, the column top effluent was 249g (the molar ratio n of
HFAnHF: 4.15, yield of hexafluoroacetone: 99%), and the column bottom
liquid was a hydrogen fluoride aqueous solution (76 mass %) of 489g.
Existence of water was not confirmed by measuring water content of the
column top effluent by Karl Fischer's method. Hexafluoroacetone was not
detected in the column bottom liquid.
(b) After termination of the distillation of (a), the distillation pot was
charged with 412g of the hydrogen fluoride aqueous solution (76 mass %)
recovered from the column bottom, and a distillation similar to that of
Example 1 was started. While the reflux liquid of the column top was
taken out, the distillation was continued until the column bottom
temperature showed 85°C. With this, the column top effluent was
hydrogen fluoride of 197g, and the column bottom liquid was a hydrogen
fluoride aqueous solution (62 mass %) of 275g. Existence of water was not
confirmed by measuring water content of the column top effluent by Karl
Fischer's method. Hexafluoroacetone was not detected in the column
bottom liquid.
(c) After termination of the distillation of (b), the distillation pot was
charged with 267g of the hydrogen fluoride aqueous solution (62 mass %)

recovered from the column bottom, and a distillation similar to that of
Example 1 was started. While the reflux liquid of the column top was
taken out, the distillation was continued until the column bottom
temperature showed 116°C. With this, the column top effluent was
hydrogen fluoride of 54g, and the column bottom liquid was a hydrogen
fluoride aqueous solution (48 mass %) of 206g. Existence of water was not
confirmed by measuring water content of the column top effluent by Karl
Fischer's method. Hexafluoroacetone was not detected in the column
bottom liquid.
[EXAMPLE 3] Batch type production process
A distillation was conducted by using the same apparatus as that of
Example 1. After putting 220g of HFA 3W into the distillation pot, it was
cooled with a dry ice/acetone bath. Then, 122g of anhydrous hydrogen
fluoride was weighed and put thereinto. Under a cooled condition (-20°C),
it was set on the distillation column. Then, similar to Example 1, the
distillation was continued until the column bottom temperature showed
121°C and stopped.
After the distillation, the reflux liquid (column top effluent)
recovered from the column top was 229g (the molar ratio n of HFAnHF: 3.5,
yield of hexafluoroacetone: 99%), and the column bottom liquid was a
hydrogen fluoride aqueous solution (46 mass %) of 104g. Existence of water
was not confirmed by measuring water content of the reflux liquid by Karl
Fischer's method. Hexafluoroacetone was not detected in the column
bottom liquid.
[EXAMPLE 4] Batch type production process
A distillation was conducted by using the same apparatus as that of
Example 1. After putting 220g of HFA.3W into the distillation pot, it was
cooled with a dry ice/acetone bath. Then, 271g of anhydrous hydrogen

fluoride was weighed and put thereinto. Under a cooled condition (-20°C),
it was set on the distillation column. Then, the distillation was continued
until the column bottom temperature showed 128°C and stopped.
After the distillation, the reflux liquid (column top effluent)
recovered from the column top was 389g (the molar ratio n of HFAnHF: 11,
yield of hexafluoroacetone: 99%), and the column bottom liquid was a
hydrogen fluoride aqueous solution (38 mass %) of 96g. Existence of water
was not confirmed by measuring water content of the reflux liquid by Karl
Fischer's method. Hexafluoroacetone was not detected in the column
bottom liquid.
[EXAMPLE 5] Continuous production process
A metering pump (EH-B10SH-100PR9 made by IWAKI CO., LTD.)
as a device for supplying HFA.3W, and a device prepared by combining a
needle valve with a cylinder equipped with an inner pipe and a branch pipe,
which were made of stainless steel, as a device for supplying hydrogen
fluoride were added to the apparatus shown in Example 1, thereby using it
as the dehydration apparatus. Flow rate was adjusted by the reading of a
weighing scale.
Firstly, a distillation pot was charged with 303g of a 60 mass %
hydrogen fluoride aqueous solution prepared by mixing hydrogen fluoride
with water, and the distillation was started. At the time when reflux of
hydrogen fluoride was confirmed, 638g of a mixed liquid (the molar ratio of
hydrogen fluoride to HFA.3W: 13) of HFA.3W and hydrogen fluoride was
continuously supplied for 5 hours to the position of 1/4 of the distillation
column height from the column top, and an effluent from the column top was
collected in a receiver. During the supply of the mixed liquid, while
maintaining the column bottom temperature at about 107°C, the column top
temperature was maintained in 16.5°C to 20.5°C by adjusting the amount of
effluent.

The column top effluent of 567g recovered from the column top at the
time of termination of the dehydration treatment had a molar ratio of
hexafluoroacetone/hydrogen fluoride of 10. Existence of water was not
confirmed by measuring water content of this effluent from the column top
by Karl Fischer's method. The column bottom liquid at the time of
termination of the distillation was a hydrogen fluoride aqueous solution (48
mass %) of 370g. Hexafluoroacetone was not detected in the column bottom
liquid. The total recovery percentage (material balance) was not lower
than 99.9%, the recovery percentage of hexafluoroacetone was 99.6%, and
the recovery percentage of hydrogen fluoride was 100%.
[EXAMPLE 6] Batch type production process
A distillation was conducted by using the same apparatus as that of
Example 1. After putting 220g of HFA-3W into the distillation pot, it was
cooled with ice. Then, 271g of anhydrous hydrogen fluoride was weighed
and added to HFA-3W in the distillation pot. Temperature of the mixture
increased to about 30°C by mixing. Then, similar to Example 1, the
distillation was continued until the column bottom temperature became
127°C and stopped.
After the distillation, the reflux liquid (column top effluent)
recovered from the column top was 390g (the number n of HFAnHF-11),
and the column bottom liquid was a hydrogen fluoride aqueous solution (38
mass %) of 95g. Existence of water was not detected by measuring water
content of the reflux liquid by Karl Fischer's method. HFA was not
detected in the column bottom liquid.
[EXAMPLE 7] Batch type production process
A distillation was conducted by using the same apparatus as that of
Example 1. At room temperature (about 25°C) the distillation pot was
charged with 358g of 70 mass % hydrogen fluoride aqueous solution and
430g of HFA-3W. Then, the reflux liquid was taken out while controlling it

so that the column top temperature became 15-16°C. Similar to Example 1,
the distillation was continued until the column bottom temperature became
107°C and stopped.
After the distillation, the reflux liquid (column top effluent)
recovered from the column top was 339g (the number n of HFAnHF: 1), and
the column bottom liquid was a hydrogen fluoride aqueous solution (50
mass %) of 449g.
INDUSTRIAL APPLICABILITY
The dehydration process of the present invention has an advantage
that it generates almost no waste since hydrogen fluoride is used as a
dehydration agent. In addition, since anhydride to be obtained is a
hydrogen fluoride adduct of hexafluoroacetone, there is a characteristic that
it is particularly effective in the case of using hydrogen fluoride as a solvent
or the like in reactions.
WE CLAIM:
1. A process for dehydrating a hexafluoroacetone hydrate, comprising
introducing a hexafluoroacetone hydrate and hydrogen fluoride either as a
mixture or separately into a distillation column, obtaining a composition
containing hexafluoroacetone or a hexafluoroacetone-hydrogen fluoride
adduct and hydrogen fluoride as a low boiling component, and obtaining a
composition containing water and hydrogen fluoride as a high boiling
component.
2. A dehydration process according to claim 1, wherein the
hexafluoroacetone hydrate and the hydrogen fluoride are continuously
introduced either as a mixture or separately into the distillation column.
3. A process for dehydrating a hexafluoroacetone hydrate, comprising
continuously introducing a hexafluoroacetone hydrate and hydrogen
fluoride either as a mixture or separately into a distillation column,
continuously obtaining a composition containing hexafluoroacetone or a
hexafluoroacetone-hydrogen fluoride adduct and hydrogen fluoride as a low
boiling component from a column top portion, and continuously obtaining a
composition containing water and hydrogen fluoride as a high boiling
component from a column bottom portion.
4. A dehydration process according to any of claims 1-3, wherein the
hexafluoroacetone hydrate is hexafluoroacetone trihydrate.
5. A dehydration process according to any of claims 1-4, wherein the
hexafluoroacetone hydrate is a hexafluoroacetone hydrate containing water.

[Task] To provide a process for producing anhydrous hexafluoroacetone
from hexafluoroacetone hydrate. To provide a process taking environment
into consideration, that does not require a treatment of wastes, such as waste
sulfuric acid, containing organic substances, which is inevitable in processes
conducted hitherto using concentrated sulfuric acid, fuming sulfuric acid, and
the like.
[Solving Means] A process for dehydrating a hexafluoroacetone hydrate,
comprising introducing a hexafluoroacetone hydrate and hydrogen fluoride
either as a mixture or separately into a distillation column, obtaining a
composition containing hexafluoroacetone or a hexafluoroacetone-hydrogen
fluoride adduct and hydrogen fluoride as a low boiling component, and
obtaining a composition containing water and hydrogen fluoride as a high
boiling component.