Note: Descriptions are shown in the official language in which they were submitted.
CA 0221~44 1997-09-1~
PROCESS FOR PRODUCING BUTANEDIOL
FIELD OF THE INVENTION
This invention relates to a process for producing
butanediol having high purity. More particularly, it relates
to an improved process which comprises hydrolyzing
diacetoxybutane, which is obtained by acetoxylating and
hydrogenating butadiene, to thereby give butanediol.
BACKGROUND OF THE INVENTION
Butanediol is a compound which is useful as a solvent
or the starting material in synthesizing polyester resins, ~-
butyrolactone, tetrahydrofuran, etc.
A known process for producing butanediol comprises
hydrolyzing diacetoxybutane, which is obtained by reacting
butadiene with acetic acid and oxygen in the presence of a
palladium catalyst to obtain diacetoxybutene, and then
hydrogenating the diacetoxybutene using a palladium catalyst or
a nickel catalyst, to thereby give butanediol (see, JP-A-52-
7909, JP-A-52-133912, JP-A-7-82191, etc.; the term "JP-A" as
used herein means an "unexamined published Japanese patent
application").
In the above-mentioned method starting from butadiene,
a large amount of acetic acid is used in the acetoxylation of
butadiene. It is necessary to eliminate the unreacted excess
acetic acid and the water which is formed as a by-product.
Furthermore, in the hydrolysis of diacetoxybutane, a large
CA 0221~44 1997-09-1~
amount of water is used, and it is therefore necessary to
eliminate the unreacted excess water and the acetic acid which
is formed as a by-product. Various proposals have been made to
recover and reuse the water and acetic acid while maintaining
the purity of the product at a satisfactory level (see the
patents cited above).
The purity of butanediol is particularly important
when, for example, it is used for producing tetrahydrofuran,
which is the starting material for the production of polyester
resins and polyethers such as polytetramethylene ether glycol,
etc. When used in the production of tetrahydrofuran,
butanediol must have sufficiently high purity so as not to
affect the polymerization reaction, since impurities in the
butanediol adversely affect the rate of the polymerization
reaction and the molecular weight of the polymer product.
In the above-mentioned prior art method for producing
butanediol, diacetoxybutane is hydrolyzed and the reaction
product is subjected to distillation. After thus distilling
off water, acetic acid and other low-boiling compounds,
components containing butanediol are generally obtained as the
bottom settlings. These bottom settlings are then further
distilled to thereby eliminate remaining low-boiling compounds
as the overhead products and diacetoxybutane, hydroxy-
acetoxybutane, etc. as the upper side stream. The butanediol
is distilled off as the middle side stream, lower side stream
CA 0221~44 1997-09-1~
or bottom settlings, and is then rectified to thereby give
highly pure butanediol. However, this process does not always
result in sufficient elimination of impurities.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an
industrially advantageous process for producing butanediol
having high purity, which is appropriate as the starting
material for producing polyester resin, tetrahydrofuran, etc.,
the process comprising hydrolyzing diacetoxybutane obtained by
acetoxylating butadiene followed by hydrogenation.
The present inventors have conducted extensive studies
on processes for producing butanediol having high purity. As
a result, they have successfully found that butanediol obtained
from butadiene is contaminated with impurities which are
difficult to remove by distillation. One such impurity is
monoacetoxyoctanol, which is formed by the hydrolysis of
diacetoxyoctane contained as an impurity in diacetoxybutane.
When examined by gas-llquid equilibration, it is more difficult
to distill off monoacetoxyoctanol than expected on the basis of
the difference (about 40~C) between the boiling point of 1j4-
butanediol (230~C) and that of monoacetoxyoctanol (estimated as
about 270~C).
Accordingly, the present invention provides a process
for producing butanediol by hydrolyzing diacetoxybutane,
wherein the diacetoxybutane to be hydrolyzed contains not more
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than about 0.5% by weight of diacetoxyoctane.
According to the process of the present invention,
highly pure 1,4-butanediol contaminated with not more than
about 1% by weight of monoacetoxyoctanol (i.e., having a purity
of about 99% by weight or more) can be obtained by regulating
the content of diacetoxyoctane in diacetoxybutane to not more
than about 0.5% by weight, preferably from about 0.01 to about
0.2% by weight, hydrolyzing the diacetoxybutane, subjecting the
hydrolysis product to distillation in a conventional manner,
thus eliminating water, acetic acid and other low-boiling
compounds therefrom, and then distilling the bottom settlings
to thereby rectify the butanediol fraction from which the low-
boiling compounds have been eliminated.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 schematically shows an example of a preferred
apparatus for performing the process of the present invention,
wherein each reference numeral has the following meaning:
1 . . . acetoxylation reactor
2 . . . first distillation column
3 . . . second distillation column
4 . . . hydrogenation reactor
5 . . . third distillation column
6 . . . hydrolysis reactor
7 . . . fourth distillation column
8 . . . fifth distillation column
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9 . . . sixth distillation column.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The content of diacetoxyoctane in diacetoxybutane can
be regulated to not more than about 0.5% by weight by one of
the following methods:
(a) reacting butadiene with acetic acid and oxygen and
recovering diacetoxybutene from the reaction product by
distillation wherein, during recovery, the amount of
diacetoxyoctadiene in the obtained diacetoxybutene is regulated
to a predetermined level (for example about 0.5% by weight or
less);
(b) hydrogenating diacetoxybutene and regulating the
content of diacetoxyoctane in the obtained diacetoxybutane
(i.e., the hydrogenation product) at or below a predetermined
level by distillation; and
(c) partly or totally combining the procedures for
reducing the impurities in the above-mentioned methods (a) and
(b) so as to regulate the diacetoxyoctane content in
diacetoxybutane at or below a predetermined level. It lS
preferred to distill off diacetoxyoctadiene by method (a) from
the viewpoint of simplifying and reducing the overall energy
consumption of the process.
Preferred embodiments of the process of the invention
are now described below.
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(1) Acetoxylation step comprising reacting butadiene with
acetic acid and molecular oxygen to thereby give
diacetoxybutene:
The acetoxylation reaction is performed in a reactor 1
(see Fig. 1) by a conventional method which comprises reacting
butadiene with acetic acid and molecular oxygen in the presence
of a palladium catalyst. As the palladium catalyst, use is
preferably made of metallic palladium or salts thereof.
Preferred palladium salts are those selected from the group
comprising organic palladium salts such as palladium acetate,
and inorganic palladium salts such as palladium chloride and
palladium nitrate. The palladium catalyst may either be used
alone or in combination with a promoter. Preferred promoters
are selected from the group comprising metals such as bismuth,
selenium, antimony, tellurium, copper, etc. and metal salts,
metal oxides or metal acids thereof such as bismuth oxide,
selenic acid, tellurium oxide, antimony chloride, orthotelluric
acid, copper chloride, etc. It is preferred that the catalyst
is supported on a carrier, with preferred carriers belng
selected from the group comprising silica, alumina, active
carbon, etc. The palladium content in the catalyst supported
on a carrier preferably ranges from about 0.1 to about 20% by
weight, while the content of the promoter, if present,
preferably ranges from about 0.01 to about 30% by weight.
The acetoxylation reaction may be performed by a number
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of different methods. Preferred methods of the reaction
include the conventional fixed bed method, fluidized bed method
and catalyst-suspending method.
The reaction is preferably carried out within a temper-
ature range of from about 40 to about 180~C, more preferably
from about 60 to about 150~C. Preferably, the reaction is
performed under atmospheric pressure or higher, more preferably
not more than about 300 kg/cm2 (29.4 MPa), and most preferably
from about 30 to about 150 kg/cm2 (2.94 - 14.7 MPa).
Since the acetoxylation reaction product thus obtained
in the reactor contains the unreacted butadiene, etc., it is
preferably degassed and then distilled to thereby give
diacetoxybutene.
Preferably, distillation of the acetoxylation reaction
product is carried out in the following manner, described with
reference to Figure 1. First, water and acetic acid are
distilled off as the overhead products from first distillation
column 2. The bottom settlings from column 2 are then supplied
to second distillation column 3, where diacetoxybutene is
obtained from the column top while high-boiling fractions
containing diacetoxyoctadiene are drawn out from the bottom.
It may be preferred to supply the bottom settlings distillation
column 3 to a thin film evaporator to thereby elevate the
separation efficiency of the high-boiling fractions (as
described in detail in JP-A-6-321861).
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The amount of diacetoxyoctadiene contained in the
diacetoxybutene recovered from the top of column 3 is at least
partially dependent on the content of diacetoxyoctadiene in the
diacetoxybutene supplied to distillation column 3 and the
operation conditions of distillation column 3. Preferably, the
diacetoxybutene supplied to distillation column 3 contains
about 3% by weight of diacetoxyoctadiene. Distillation column
3 is preferably operated at a theoretical plate number of from
about 5 to about 10, under a column top pressure of from about
5 to about 200 mmHg (0.7 to 26.7 kPa), at a column bottom
temperature of not more than about 190~C, a reflux ratio of
from about 0.1 to about 1 and a distilling ratio of from about
70 to about 99%.
The diacetoxybutene drawn from the top of column 3
preferably contains from about 0.1 to about 2.5% by weight of
diacetoxyoctadiene. When the process of the invention also
includes distilling off diacetoxyoctane contained in the
diacetoxybutane, the distillation conditions following the
acetoxylation are set so that the diacetoxyoctadiene content is
regulated to from about 1.0 to about 2.5% by weight, preferably
not more than about 1.5% by weight. When diacetoxyoctadiene
alone is distilled off such that the process does not include
a diacetoxyoctane removal step, the distillation conditions
following acetoxylation are preferably set so that the
diacetoxyoctadiene content is regulated to not more than about
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0.5% by weight, preferably not more than about 0.1% by weight.
In order to sharply reduce the amounts of impurities
contained in the diacetoxybutene, it may be preferred to vary
one or more of the distillation conditions. For example, it
may be preferred to increase the theoretical plate number or
the reflux ratio and lower the distillation ratio. More
particularly speaking, distillation column 3 may preferably be
operated at a theoretical plate number of from about S to about
20, a reflux ratio of from about 0.1 to about lO and a
distillation ratio from the column top of from about 70 to
about 97%.
(2) Hydrogenating the reaction product obtained in the
acetoxylation step to thereby give diacetoxybutane:
The diacetoxybutene obtained from the top of
distillation column 3 in the acetoxylation step is subjected to
hydrogenation to thereby form diacetoxybutane. The
hydrogenation reaction is preferably carried out by bringing
the diacetoxybutene into contact with hydrogen in the presence
of a precious metal catalyst such as a palladium, nickel or
ruthenium catalyst and reacting within a temperature range of
from about 40 to about 180~C, preferably under atmospheric
pressure or higher, more preferably up to about 150 kg/cm2
(14.7 MPa).
The hydrogenation reaction may be performed by a
number of different methods including, for example, the
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conventional fixed bed method, fluidized bed method or
catalyst-suspending method.
The hydrogen used in the hydrogenation reaction may
preferably either have high purity or be diluted with another
gas exhibiting no undesirable effect on the reaction. Hydrogen
is preferably employed in an amount of from about 1 to about 50
mol, more preferably from about 2 to about 20 mol, per mol of
diacetoxybutene.
The hydrogenation product is degassed to thereby
eliminate the unreacted hydrogen therefrom and is then
subjected to distillation in the third distillation column 5 to
thereby give diacetoxybutane. In this distillation step, the
diacetoxybutane is obtained as the overhead product while high-
boiling fractions containing diacetoxyoctane, which is the
hydrogenation product of diacetoxyoctadiene, are obtained as
the bottom settlings.
Distillation column 5 is preferably operated at a
theoretical plate number of from about 5 to about 10, under a
column top pressure of from about 5 to about 200 mmHg (0.7 to
26.7 kPa), at a column bottom temperature of not more than
about 190~C, a reflux ratio of from about 0.1 to about 1 and a
distillation ratio from the column top of from about 70 to
about 99%.
The diacetoxyoctane content in the diacetoxybutane
supplied to distillation column 5 is at least partially
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dependent on the operation conditions of distillation column 3.
Under the said conditions, the diacetoxyoctane content is about
0.1 to 2.5% by weight prior to distillation in column 5. When
the diacetoxyoctadiene content is reduced at or below 0.5% by
weight in distillation column 3, the diacetoxyoctane content is
less than about 0.5% by weight, and more preferably not more
than about 0.1% by weight. When only a portion of the
diacetoxyoctadiene is eliminated in distillation column 3, the
diacetoxyoctane content is preferably from about 1.0 to about
2.5% by weight, and more preferably not more than about 1.5% by
weight.
If the diacetoxyoctadiene content in distillation
column 3 is more than 2.5% by weight, the content has to be
reduced at or below 0.5% by weight by the distillation in
distillation column 5.
When the procedure for eliminating diacetoxyoctadiene
in distillation column 3 is combined with the procedure for
eliminating diacetoxyoctane in distillation column 5, the
predetermined level to which the content of diacetoxyoctadiene
or diacetoxyoctane is reduced in each column is appropriately
determined by taking the balance between the distillation loads
in columns 3 and 5 into consideration. For example, it is
preferred that the amount of diacetoxyoctadiene eliminated in
distillation column 2 exceeds 50% of the total amount
eliminated.
CA 0221~44 1997-09-1~
When distillation column 3 is operated under the
preferred conditions described above, the diacetoxybutane drawn
from the top of column 5 contains from about 1.0 to about 2.5%
by weight of diacetoxyoctane. In the process of the present
invention, the operation conditions of distillation column 5
are preferably set so that the diacetoxyoctane content is
regulated to not more than about 0.5% by weight, and more
preferably not more than about 0.2% by weight.
More particularly speaking, distillation column 5 is
preferably operated at a theoretical plate number of from about
5 to about 20, a reflux ratio of from about 0.1 to about 10 and
a distillation ratio from the column top of from about 70 to
about 97%.
When the diacetoxyoctane content in the diacetoxybutane
exceeds 0.5% by weight, the butanediol obtained by hydrolyzing
it contains the same content of monoacetoxyoctanol which is
difficult to remove by distillation.
(3) Hydrolyzing hydrogenation product to thereby give
butanediol:
Preferably, the hydrolysis reaction is performed by
bringing diacetoxybutane into contact with water in the
presence of a solid acid catalyst such as a cation exchange
resin within a temperature range of from about 30 to about
110~C, and more preferably from about 40 to about 90~C, under
such a pressure as to prevent boiling or serious bubbling due
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to dissolved gases, etc. in the course of the reaction, i.e.,
preferably from about atmospheric pressure to about 10 kg/cm ~G
~0.098 to 1.08 MPa).
In this reaction, water is preferably employed in an
amount of from about 2 to about 100 mol, preferably from about
4 to about 50 mol, per mol of diacetoxybutane. When water is
used in an excessively small amount, the reaction ratio is
lowered. On the other hand, it is not preferred to use too
much water, since increased heat energy would be required to
recover butanediol from the reaction product.
The reaction may be carried out by a number of
different methods which, for example, are conducted either
batchwise or continuously. When an ion exchange resin is used
in the hydrolysis reaction, it may be in a suspended state.
Alternatively, the reactants may be passed through a column
packed with the ion exchange resin. From an industrial
viewpoint, it is preferred to employ a continuous fixed bed
method.
When the reaction is performed by using a suspended
bed, the ion exchange resin is preferably employed in an amount
of from about 0.1 to about 50% by weight, and more preferably
from about 1 to about 10% by weight, based on the weight of the
liquid (water and the diacetoxybutane).
When using the continuous fixed bed method, the
reaction may be carried out by continuously supplying water and
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diacetoxybutane to a reactor 6 packed with the ion exchange
resin, which is preferably kept at a predetermined temperature,
and simultaneously drawing out the butanediol thus formed as a
mixture with acetic acid and the excess water.
The diacetoxybutane and water may be supplied either
separately or as a mixture thereof. It is also possible to
supply these materials as a homogeneous liquid phase which
further contains butanediol (i.e., the reaction product),
together with impurities such as monohydroxyacetoxybutane, etc.
When using the fixed bed method, it is preferred to supply
these materials in the form of a homogeneous liquid phase so as
to accelerate the smooth progress of the reaction.
The liquid product formed by the reaction contains the
desired butanediol together with acetic acid, water, partial
hydrolyzates and some by-products such as teterahydrofuran.
After the completion of the reaction, the catalyst is filtered
off from the reaction mixture and the filtrate is distilled to
thereby give butanediol.
The distillation is preferably effected in the
following manner. In the fourth distillation column 7, water
and acetic acid are eliminated as the overhead products. Then
the bottom settlings are supplied to the fifth distillation
column 8 from which the unreacted diacetoxybutane and its
isomers are eliminated as the overhead products. Next, the
bottom settlings, comprising 1,4-butanediol as the major
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component thereof, are supplied to the sixth distillation
column 9. From the top of distillation column 9, the desired
1,4-butanediol product is obtained, while high-boiling
compounds are drawn out as the bottom settlings. The 1,4-
butanediol product preferably contains not more than about 1%
by weight, and more preferably from about 0 to about 0.5% by
weight, of monoacetoxyoctanol.
To further illustrate the present invention, the
following Examples will be given wherein all "parts" and "%
are by weight.
(Reference Example 1) Acetoxylation reaction
Into an acetoxylation reactor were supplied 170 part/hr
of 1,3-butadiene, 3,000 part/hr of acetic acid and 530 part/hr
of oxygen. In the presence of a catalyst comprising 3% of
palladium and 0.6% of tellurium supported on active carbon, the
mixture was reacted under 9 MPa at 100~C and degassed to
thereby give a reaction product containing 14.2% of
diacetoxybutene and 0.6% of diacetoxyoctadiene.
This reaction product was supplied to distillation
column 2 at a rate of 3,100 part/hr. Thus, water and most of
the acetic acid were distilled off from the column top at a
rate of 252 part/hr, while bottom settlings containing 84.5% by
weight of diacetoxybutene and 3.2% by weight of diacetoxy-
octadiene were drawn off at a rate of 580 part/hr.
CA 0221~44 1997-09-1
(Example 1)
The bottom settlings obtained in the above Reference
Example 1 were supplied to distillation column 2 (practical
plate number: 20) at a rate of 580 part/hr and distilled
therein under a column top pressure of 2.7 kPa at a reflux
ratio of 0.5. Thus a solution containing 86.3% of diacetoxy-
butene and 1.0% of diacetoxyoctadiene was distilled off from
the column top at a rate of 550 part/hr.
The diacetoxybutene fraction thus obtained was supplied
to a hydrogenation reactor packed with a palladium catalyst and
a ruthenium catalyst and hydrogenated therein under a hydrogen
gas stream at 70~C and a reaction pressure of 5 kPa. Thus a
reaction mixture containing 86.5% of diacetoxybutane and 1.0%
of diacetoxyoctane was obtained.
Next, the reaction mixture was subjected to gas/liquid
separation and then supplied to distillation column 5
(practical plate number: 20) at a rate of 550 part/hr and
distilled therein under a column top pressure of 2.0 kPa at a
reflux ratio of 0.25. Thus a solution containing 87.1% of
diacetoxybutane and 0.2% of diacetoxyoctane was distilled off
from the column top at a rate of 520 part/hr.
The hydrogenation reaction mixture thus obtained was
supplied to a hydrolysis reactor packed with a strongly acidic
ion exchange resin (Diaion SK-lB ; manufactured by Mitsubishi
Chemical Corporation) at a rate of 520 part/hr together with
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-
500 part/hr of water. Then hydrolysis was effected at a
temperature of 50~C to thereby give a reaction mixture
containing 10.2% of 1,4-butanediol and 0.04% of monoacetoxy-
octanol.
This reaction mixture was supplied to the distillation
column 7 at a rate of 1,020 part/hr. Then water and most of
the acetic acid were distilled off from the column top at 660
part/hr, while the bottom settlings containing 28.9% of 1,4-
butanediol and 0.1% of monoacetoxyoctanol were drawn out from
the column bottom at a rate of 360 part/hr. Then the bottom
settlings were supplied to distillation column 8. After
distilling off the unreacted diacetoxybutane from the column
top, the bottom settlings of distillation column 8 were
supplied to distillation column 9. The high-boiling compounds
were drawn out from the column bottom and 1,4-butanediol with
a purity of 99.3% was obtained from the column top. This 1,4-
butanediol contained 0.4% of monoacetoxyoctanol.
(Example 2)
Distillation was performed in the same manner as
described in Example 1 but the reflux ratio of distillation
column 3, into which the bottom settlings obtained in Reference
Example 1 were supplied, was adjusted to 5. Thus a distillate
containing 87.1% of diacetoxybutene and 0.1% of diacetoxy-
octadiene was obtained from the column top.
The diacetoxybutene fraction thus obtained was
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subjected to hydrogenation in the same manner as in Example 1
to thereby give a reaction mixture containing 87.3% of
diacetoxybutane and 0.1% of diacetoxyoctane.
After gas/liquid separation, the hydrogenation reaction
mixture thus obtained was not supplied to distillation column
5 as in Example 1, but rather was hydrolyzed under the same
conditions as those employed in Example 1. Thus a reaction
mixture containing 10.4% of 1,4-butanediol and 0.02% of
monoacetoxyoctanol was obtained.
This reaction mixture was supplied successively to
distillation columns 7, 8 and 9 in the same manner as in
Example 1. From the top of distillation column 9, 1,4-
butanediol with a purity of 99.5% was obtained. This product
contained 0.2% of monoacetoxyoctanol.
(Comparative Example 1)
Distillation was performed in the same manner as
described in Example 1, but the reflux ratio of distillation
column 3 was adjusted to 0.05. Thus a distillate containing
85.0% of diacetoxybutene and 1.7% of diacetoxyoctadiene was
obtained from the column top.
The diacetoxybutene fraction thus obtained was
subjected to hydrogenation in the same manner as in Example 2.
The hydrogenation reaction mixture containing 85.1% of
diacetoxybutane and 1.6% of diacetoxyoctane was then subjected
to gas/liquid separation. After gas/liquid separation, the
- 18 -
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-
reaction mixture was not supplied to distillation column 5 as
in Example 2, but rather was hydrolyzed under the same
conditions as those employed in Example 1 to thereby give a
reaction mixture containing 9.9% of 1,4-butanediol and 0.3% of
monoacetoxyoctanol.
This reaction mixture was supplied successively to
distillation columns 7, 8 and 9 in the same manner as in
Example 1. From the top of distillation column 9, 1,4-
butanediol with a purity of 95.1% was obtained. This product
contained 3.2% of monoacetoxyoctanol.
The process of the present invention makes possible the
industrial production of highly pure 1,4-butanediol containing
not more than 1% by weight of monoacetoxyoctanol, which is
suitable as a starting material for producing polyester,
teterahydrofuran, etc.
While the invention has been described in detail and
with reference to specific embodiments thereof, it will be
apparent to one skilled in the art that various changes and
modifications can be made therein without departing from the
spirit and scope thereof.
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