Note: Descriptions are shown in the official language in which they were submitted.
CA 02226~34 1998-01-09
PROCESS FOR PURIFYING CRUDE 1,4-BUTANEDIOL
FIELD OF THE INv~NlION
This invention relates to a process for purifying
crude 1,4-butanediol (hereinafter sometimes referred to
simply as crude 1,4-BG). More particularly, it relates to an
improvement in the purification process which comprises
hydrogenating crude 1,4-BG.
BACKGROUND OF THE INVENTION
1,4-Butanediol is a compound which is useful as the
starting material in synthesizing polyester resins, ~-
butyrolactone, tetrahydrofuran, etc.
A known process for producing 1,4-butanediol
comprises, for example, reacting butadiene, acetic acid and
oxygen in the presence of a palladium catalyst to thereby
give diacetoxybutene, then hydrogenating diacetoxybutene with
the use of a palladium catalyst or a nickel catalyst to
thereby give diacetoxybutane, and then hydrolyzing the
diacetoxybutane thereby giving 1,4-butanediol (JP-A-52-7909
(published on January 21, 1977), JP-A-52-133912 (published on
November 9, 1977), JP-A-7-82191 (published on March 28,
1995); the term ~JP-A~ as used herein means an "unexamined
published Japanese patent application").
The 1,4-butanediol thus obtained is contaminated with
various impurities such as 2-(4'-hydroxybutoxy)tetrahydro-
furan, 2-(4'-oxobutoxy)tetrahydrofuran and 1,4-di-(2'-tetra-
hydrofuroxy)butane which cannot be eliminated by
-- 1 --
CA 02226~34 1998-01-09
distillation.
It has been found that 1,4-butanediol contaminated
with these impurities is unsuitable as the starting material
for producing resins, fibers, etc., since it causes the
coloration of products or insufficient reactivity in the
production process. Therefore, various proposals have been
made to eliminate these impurities.
For example, JP-A-61-197534 (published on September
1, 1986) has proposed a process for purifying crude 1,4-
butanediol which comprises hydrogenating crude 1,4-butanediol
cont~ining at least one of 2-(4'-hydroxybutoxy)tetrahydro-
furan, 2-(4'-oxobutoxy)tetrahydrofuran and 1,4-di-(2'-
tetrahydrofuroxy)butane in the presence of a hydrogenating
catalyst. However, the activity of the hydrogenating
catalyst is seriously reduced during prolonged continuous
operation of this process due to the heavy impurities having
high boiling point contained in the crude 1,4-butanediol,
thus making it difficult to stably produce 1,4-butanediol of
acceptable purity. To overcome this difficulty, JP-A-6-
172235 (published on June 21, 1994) discloses a process
wherein high-boiling compounds are separated by distillation
and crude 1,4-butanediol obtained from the lower side stream
of the distillation column is hydrogenated.
However, the improved process described in JP-A-6-
172235 is not completely satisfactory, since the 1,4-butane-
diol produced by the process still contains about 0.2 % by
CA 02226~34 1998-01-09
weight of 2-(4'-hydroxybutoxy)tetrahydrofuran (hereinafter
sometimes referred to simply as BGTF), which is the major
component of the impurities. Particularly during prolonged
continuous operation of the process, there arises a problem
that the content of BGTF exceeds 0.2 % by weight and is
accumulated in the 1,4-butanediol product, thus making it
impossible to produce 1,4-butanediol of high purity.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
purification process whereby the problem in the above-
mentioned improved process described in JP-A-6-172235 is
solved and highly pure 1,4-butanediol, which contains 0.2 %
by weight or less of BGTF and 99.80 % by weight or more of
1,4-butanediol, can be obtained.
The present inventors have found that the crude 1,4-
butanediol to be distilled according to the process of JP-A-
6-172235 contains a fine powder of hydrogenating catalyst
from the hydrogenation step in the process. When this
hydrogenated 1,4-butanediol is supplied into the distillation
column, the presence of catalyst causes BGTF to be formed
from 1,4-but~ne~iol in the distillation column, thus
resulting in unacceptable levels of BGTF in the distilled
product.
Accordingly, the present invention provides a process
for purifying crude 1,4-butanediol obtained by hydrolyzing
CA 02226~34 1998-01-09
diacetoxybutane which comprises the following purification
steps (1) to (3):
(1) hydrogenating the crude 1,4-butanediol in the
presence of a hydrogenating catalyst;
(2) removing a fine powder of the hydrogenating
catalyst from the hydrogenation mixture; and
(3) distilling the hydrogenation mixture, from which
the fine powder has been lel..oved, in a distillation column to
obtain 1,4-butanediol of high purity from the side stream of
the distillation column.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a flow chart showing the purification steps
of the present invention.
Fig. 2 is a flow chart showing the steps of prior art
process for producing diacetoxybutane.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the present invention will
now be described in detail below.
1. Hydrolysis of Diacetoxybutane
The crude 1,4-butanediol employed as the-starting
material in the process of the present invention is the
reaction product obtained from the hydrolysis of diacetoxy-
butane. Preferably, diacetoxybutane is obtained by
hydrogenating diacetoxybutene, and diacetoxybutene is
obtained by reacting butadiene, acetic acid and oxygen in the
presence of a palladium catalyst (JP-B-55-45051 (published on
CA 02226~34 1998-01-09
November 15, 1980), JP-B-55-16489 (published on May 2, 1980),
JP-B-55-17016 (published on May 8, 1980); the term "JP-B" as
used herein means an "examined Japanese patent publication ).
Therefore, the diacetoxybutane to be hydrolyzed
preferably comprises 1,4-diacetoxybutane as the major
component, and preferably includes isomeric mixtures of 1,4-
diacetoxybutane with 3,4-diacetoxybutane, 1,3-diacetoxy-
butane, etc. and optionally cont~ining monohydroxyacetoxy-
butane, etc., depending on the production and purification
processes. It may also be preferred in some cases to use a
mixture of 1,4-diacetoxybutane, 1,4-monohydroxyacetoxybutane
and 1,4-butanediol which is obtained by performing the
hydrolysis to a certain extent and then removing water and
acetic acid from the reaction mixture.
In the hydrolysis reaction of diacetoxybutane, it is
preferred to use a cation exchange resin as the catalyst to
achieve a high rate of hydrolysis with little formation of
by-products such as tetrahydrofuran (hereinafter referred to
simply as THF).
Nore preferably, a strongly acidic cation exchange
resin of the sulfonic acid type, made of a styrene/divinyl-
benzene copolymer as the base, is used. The cation exchange
resin may preferably be either a gel resin or a porous resin.
Particularly preferred examples of such strongly
acidic cation exchange resin of the sulfonic acid type
include gel type resins sold under the trade marks SKlB,
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SK104, SX106, SKllO and SK112 and porous type resins sold
under the trade marks PK208, PK216, PK228, RCP160H, RCP170H
and RCP145H (manufactured by Mitsubishi Chemical
Corporation).
The hydrolysis of diacetoxybutane is preferably
performed in a temperature range of from about 30 to about
110 ~C, more preferably from about 40 to about 90 ~C.
The reaction pressure in the hydrolysis of diacetoxy-
butane is not particularly restricted. However, the reaction
is preferably carried out under a pressure ranging from about
atmospheric pressure to about 10 kg/cm2G (0.1 to 1.08 MPa).
With respect to the ratio of diacetoxybutane to
water, water, which serves both as a starting material and
the solvent, is preferably employed in at least a
stoichiometric amount. More preferably, water is used in an
amount of from about 2 to about 100 mol, most preferably from
about 4 to about 50 mol, per mol of diacetoxybutane.
Although the hydrolysis reaction of diacetoxybutane
may be performed in various manners, it is preferred to use a
system wherein diacetoxybutane and water are passed through a
fixed bed packed with an acidic cation exchange resin.
2. Crude 1,4-Butanediol
Preferably, low-boiling compounds and high-boiling
compounds are removed from the hydrolysis product obtained by
the above process to thereby give crude 1,4-BG. These
compounds can be distilled off by known methods, for example,
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those described in JP-A-6-172235.
Referring to Fig. 1, it is preferred that the
hydrolysis product obtained by hydrolyzing diacetoxybutane in
a hydrolysis reactor (1), is supplied into a first distil-
lation column (2) and low-boiling fractions (4) comprising
water and acetic acid are substantially completely distilled
off from the column top, while the bottom settlings (5) are
supplied into a second distillation column (3).
The water and acetic acid (4) distilled off from the
top of column (2) are preferably further distilled and
purified to thereby obtain water and acetic acid of
sufficient purity to be employed as the starting materials in
the hydrolysis of diacetoxybutane and the acetoxylation of
butadiene, respectively.
The first distillation column (2) is preferably
operated at a theoretical plate number of from about 2 to
about 10, under a column top pressure of from about S0 to
about 200 mmHg (6.6 to 26.7 kPa), at a column bottom
temperature of from about 100 to about 200 ~C (more
preferably from about 120 to about 180 ~C) and a reflux ratio
of from about 0.01 to about 1 (more preferably from about 0.1
to about O.S).
From the bottom settlings (S) supplied into the
second distillation column (3), a fraction containing
diacetoxybutane and mainly 1,2- or 1,3-isomers of hydroxy-
acetoxybutane is distilled off from the column top (7), a
CA 02226~34 1998-01-09
fraction primarily containing the 1,4-monomer of hydroxy-
acetoxybutane is distilled off from the upper side stream (6)
and is recirculated into the hydrolysis reactor (1), while
crude l,4-BG is removed as a vapor phase from the lower side
stream (8).
The upper side stream (6) is preferably located above
the inlet through which the liquid (5) is supplied from the
first distillation column (2), while the lower side stream
(8) is preferably located below the inlet.
The bottom settlings (9) of the second distillation
column (3), which contain a large amount of high-boiling
compounds, may preferably be purged from the reaction system.
Alternatively, bottom settlings (9), usually containing 1,4-
butanediol as the major component, may preferably be supplied
into a fourth distillation column (10). The vapor distillate
(11) from column (10) is then preferably circulated into the
second distillation column (3) to thereby improve the yield
of l,4-butanediol.
The second distillation column (3) is preferably
operated at a theoretical plate number of from about 50 to
about 150, under a column top pressure of from about 50 to
about 200 mmHg (6.6 to 26.7 kPa), at a column bottom
temperature of from about 150 to about 220 ~C and a reflux
ratio of from about 0.1 to about 10. From distillation
column (3), the crude 1,4-BG fraction (8) is supplied into
hydrogenation reactors (12, 12').
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3. Purifying Treatment
The crude 1,4-BG (8) obtained from distillation
column (3) preferably contains from about 97 to about 98 % of
1,4-butanediol together with 2 to 3 % of impurities such as
4-hydroxy-1-butanal and 1,4-butanedial which are mono- and
dialdehydes respectively of 1,4-butanediol; 2-(4'-hydroxy-
butoxy)tetrahydrofuran (BGTF), 2-(4'-oxobutoxy)tetra-
hydrofuran (BDTF) and 1,4-di-(2'-tetrahydrofuroxy)butane
(BGDTF) which are adducts of dihydrofuran (i.e., the
dehydration/cyclization products of the above-mentioned
aldehydes) and 1,4-butanediol and high-boiling compounds.
These impurities are converted into 1,4-butanediol or
compounds easily separated from 1,4-butanediol by distil-
lation (tetrahydrofuran, butanol and ditetramethylene glycol)
by step (1) of the present invention wherein the crude 1,4-
butanediol is hydrogenated.
As the hydrogenating catalyst in the hydrolysis of
crude 1,4-butanediol according to the invention, use can be
made of catalysts commonly employed in hydrogenation.
Preferred examples of these catalysts include precious metals
such as Pd, Pt, Ru and Rh, with Pd and Ru being particularly
preferred.
It is not necessary that hydrogen (13, 13') used in
the hydroganation of crude 1,4-BG be pure. The hydrogen may
be diluted with an inert gas and a saturated hydrocarbon.
The hydrogenation of crude 1,4-BG is preferably
CA 02226~34 1998-01-09
performed under a hydrogen pressure of from about 5 to about
20 kg/cm2 and at a reaction temperature of from about 40 to
about 250 ~C, more preferably from about 80 to about 180 ~C.
It may be preferred that the hydrogenation step (1)
of the process of the invention is performed by a multistage
system, as shown in Fig. 1, in which the hydrogenation of
crude 1,4-BG is performed in first and second hydrogenation
reactors 12 and 12' connected in series.
In step (2) of the process of the invention, the
hydrogenation product (14) obtained from reactors 12 and 12'
is subjected to gas/liquid separation with the use of a
gas/liquid separator (15).
The liquid phase (16) obtained from gas/liquid
separator (15) is then treated to remove the finely powdered
hydrogenating catalyst.
In order to remove the fine powder of the
hydrogenating catalyst from the hydrogenation product, the
liquid phase (16) is preferably filtered through a porous
plate or filter (17) packed with a filtering medium, etc.
It is preferred that the filtering medium is
chemically resistant to 1,4-butanediol and is heat resistant
to temperatures exceeding the hydrogenation temperature. The
filter (17) is preferably selected from the group comprising
porous plates made of sintered metals, porous plates made of
carbon or graphite, filters made from alundum, silica,
ceramics, etc., or filters packed with glass wool or
-- 10 --
CA 02226~34 1998-01-09
asbestos. It is particularly preferred that the filter
comprise a glass wool filter or a porous sintered metal
plate.
The pore size of the filter is preferably about 10 ~m
or less, more preferably from about l to about 5 ~m.
In step (3) of the process of the invention, the
hydrolysis mixture (18), from which the fine powder of the
hydrogenating catalyst has been removed by filter (17), is
supplied into a third distillation column (19) and 1,4-
butanediol of high purity is obtained from the side stream
(20) thereof.
The third distillation column (19) is operated at a
theoretical plate number of from about 10 to about 100, under
a column top pressure of from about 10 to about 100 mmHg, at
a column top temperature of from about 100 to about 200 ~C
and a reflux ratio of from about 0.1 to about 10.
The 1,4-butanediol product is preferably distilled
out from the lower side stream (20) of third distillation
column (19), while low-boiling compounds (22) such as water,
tetrahydrofuran and butanol are distilled off from the top of
column (19). The high-boiling compounds (21) are drawn from
the bottom of column (19). In some cases it may be preferred
that the distillation is performed using a plurality of third
distillation columns (19).
When oxygen enters third distillation column (l9)
during the above-mentioned distillation process, 2-hydroxy-
CA 02226~34 1998-01-09
tetrahydrofuran, 4-hydroxybutylaldehyde, etc. are formed as
by-products and are difficult to separate from 1,4-butanediol
by distillation. Thus, the entry of oxygen into column (19)
should preferably be ~ini~i zed by regulating the oxygen
pressure at the top of third distillation column (19) to
about 10 mmHg or below, more preferably from about 0 to about
5 mmHg.
- The following examples further illustrate preferred
aspects of the present invention in greater detail. However,
it is to be understood that the present invention is not
restricted to the embodiments described therein. In the
following examples, all "parts" and "%" are by weight.
Unless otherwise noted, the values given below are
analytical data obtained by gas chromatography carried out 5
days after the initiation of the process, i.e., during steady
operation of the process.
REFERENCE EXAMPLE
Into an acetoxylation reactor (101) were supplied 170
part/hr of butadiene, 3,000 part/hr of acetic acid which was
contA~inAted with 0.8 % of 1,4-hydroxyacetoxybutane and 0.6 %
of 1,2-hydroxyacetoxybutane, and 530 part/hr of oxygen as
shown in Fig. 2. 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 by gas-li~uid separator (102) to thereby give a
reaction product containing 12.5 % of 1,4-diacetoxybutene.
CA 02226~34 1998-01-09
This reaction product was supplied into a first
distillation column (103) at a rate of 3,100 part/hr. Water
and a portion of the acetic acid were distilled off from the
column top at a rate of 250 part/hr, while the bottom
settlings containing 74.8 % of 1,4-diacetoxybutene were drawn
off at a rate of 580 part/hr.
The bottom settlings from the first column were
supplied into a second distillation column (104) (practical
plate number: 20) at a rate of 580 part/hr and distilled
therein under the column top pressure of 2.7 kPa at a reflux
ratio of 0.5. Thus, a solution cont~;ning 75.5 % of 1,4-
diacetoxybutene was distilled off from the column top at a
rate of 550 part/hr.
The diacetoxybutene fraction thus obtained was
supplied into a hydrogenation reactor (105) packed with a
palladium catalyst and a ruthenium catalyst and hydrogenation
was performed under a hydrogen gas stream and a reaction
pressure of 5 MPa and a temperature of 70 ~C to thereby give
a reaction mixture containing 75.6 % of 1,4-diacetoxybutane.
This reaction mixture was subjected to gas/liquid
separation and then supplied into a third distillation column
(106) (practical plate number: 20) at a rate of 550 part/hr.
The mixture was then distilled therein under a column top
pressure of 2.0 kPa at a reflux ratio of 0.25. Thus a
solution containing 75.9 % of 1,4-diacetoxybutane as shown in
Table 1 was distilled off from the column top at a rate of
CA 02226~34 1998-01-09
520 part/hr.
EXAMPLE 1
The 1,4-diacetoxybutane-containing solution obtained
above, having the composition shown in the first column of
Table 1, was supplied into a hydrolysis reactor (1) packed
with 100 1 of a cation exchange resin SKlB (manufactured by
Mitsubishi Chemical Corporation) at a rate of 520 part/hr
together with 250 partJhr of a 28 % aqueous solution of
acetic acid. Hydrolysis was then carried out at a
temperature of 50 ~C. The second column of Table 1 shows the
composition of the hydrolysis product thus obtained,
excluding water.
TABLE 1
Initial Content in
content hydrolyzed
Component (%) product (%)
1,4-diacetoxybutane 75.9 8.0
1,4-hydroxyacetoxybutane 5.2 32.5
1,4-butanediol 0.5 27.8
1,2-diacetoxybutane 8.3 0.7
1,2-hydroxyacetoxybutane 4.3 1.8
1,2-butanediol 0.2 4.7
acetic acid 2.2 20.4
others 3.4 4.1
This hydrolysis product mixture in hydrolysis
reactor (1) was supplied into the first distillation column
- 14 -
CA 02226~34 1998-01-09
(2) as shown in Fig. 1 and distilled therein. The first
distillation column (2) was made of SUS 316 and had an inner
diameter of 200 mm. This column was packed with a Raschig
ring made of SUS 316 at a height of 3000 mm. A liquid inlet
was provided 500 mm below the top of the pack layer. The
first distillation column (2) was operated under a column top
pressure of 70 mmHg, a column bottom temperature of 160 ~C
and a reflux ratio of 0.5. From the column top, water,
acetic acid and a small amount of other low-boiling compounds
were distilled off and the bottom settlings were supplied
into the second distillation column (3).
The second distillation column (3) was made of SUS
304 and had an inner diameter of 100 mm. This column was
packed with a McMahon Packing at a height of 5000 mm. A side
stream outlet (6) was provided 1000 mm below the top of the
pack layer and a liquid inlet was provided 1000 mm
therebelow. Further, a vapor outlet (8) was provided 1000 mm
below the liquid inlet. The bottom settlings from first
distillation column (2) were distilled in second distillation
column (3) under a column top pressure of 300 mmHg, a reflux
ratio of 80 and a column bottom temperature of 210 ~C.
From the column top, a fraction comprising 9.S % of
1,2-diacetoxybutane, 25.2 % of 1,2-hydroxyacetoxybutane and
65.3 % of 1,2-butanediol was distilled off. From the side
stream, another fraction comprising 0.4 % of 1,2-diacetoxy-
butane, 0.9 % of 1,2-hydroxyacetoxybutane, 2.4 % of 1,2-
- 15 -
CA 02226~34 1998-01-09
butanediol, 15.9 % of 1,4-diacetoxybutane, 64.1 % of 1,4-
hydroxyacetoxybutane and 11.4 % of 1,4-BG was taken out.
This fraction was recirculated as a part of the starting
materials into the above-mentioned hydrolysis reactor (1).
Further, crude 1,4-butanediol was taken out as a
vapor phase (8) from the vapor outlet.
The above-mentioned crude 1,4-butanediol, which
contained 2.05 % of BGTF and 0.1 % of impurities including
BDTF, BGDTF and other high-boiling compounds, and had a
carbonyl value of 6.2 mg-KOH/g and a purity of 97.5 %, was
supplied at a rate of 1874 part/hr together with 0.5 part/hr
of hydrogen into two hydrogenation reactors (12, 12')
connected in series. Hydrogenation reactors (12, 12') were
each 500 mm in inner diameter and 1300 mm in height and
packed with a catalyst comprising 0.5 ~ of ruthenium
supported on active carbon in the first hydrogenation reactor
(12) and another catalyst comprising 1.0 % of palladium
supported on active carbon in the second hydrogenation
reactor (12'). The hydrogenation was conducted under a
pressure of 9.5 kg/cm2 and a temperature of 100 ~C.
The hydrogenation reaction product mixture was then
supplied into a gas/liquid separator (15) where excess
hydrogen was separated from the reaction mixture. Next, the
reaction mixture was filtered through a glass wool filter
(17) of 5 ~m pore size to thereby remove the fine powder of
the catalyst. Then the reaction mixture was distilled in
CA 02226~34 1998-01-09
third distillation column (19).
The third distillation column (19) was made of carbon
steel and had an inner diameter of 100 mm. This column was
packed with a McMahon Packing at a height of 2000 mm. The
line (20) for drawing the side stream was exclusively made of
SUS 304.
A side stream outlet (20) was provided 300 mm below
the top of the pack layer and a liquid inlet (18) was
provided 700 mm therebelow. Distillation was then performed
under a column top pressure of 200 mmHg, a column top oxygen
pressure of 0 mmHg, a reflux ratio of 90 and a column bottom
temperature of 215 ~C. After continuously operating the
process for 100 hours and 1,000 hours, the 1,4-butanediol
taken out from the side stream of third distillation column
(19) contained 0.11 % and 0.12 % of BGTF, respectively. The
purity of the obtained 1,4-butanediol was 99.8 % in each
case.
COMPARATIVE EXAMPLE 1
The procedure of Example 1 was repeated but
filtration through a filter was omitted. After continuously
operating the process for 100 hours and 1,000 hours, the 1,4-
butanediol taken out from the side stream of the third
distillation column contained 0.21 % and 0.25 % of BGTF,
respectively. The purity of the obtained 1,4-butanediol was
99.7 % in each case.
CA 02226~34 1998-01-09
TABLE 2
Purity of 1,4- BGTF (impurity) content
butanediol after 100 hr after 1 000 hr
Ex. 1 99.8 wt. % 0.11 wt. % 0.12 wt. %
Comp. Ex. 1 99.7 wt. % 0.21 wt. % 0.25 wt. %
APPLICATION EXAMPLE
To 73.7 parts of BGTF-containing 1,4-butanediol
obtained after continuously operating the process of Example
1 for 1,000 hours, and to 73.7 parts of BGTF-containing 1,4-
butanediol obtained after continuously operating the process
of Comparative Example 1 for 100 hours, in combination with
132.4 parts of dimethyl phthalate, was added 37 ppm (in terms
of metallic titanium) of tetrabutyl titanate to prepare two
mixtures. Each mixture was subjected to esterification at
150 to 215 ~C for 3 hours. 15 minutes before the completion
of the esterification, 600 ppm of a hindered phenol anti-
oxidant (Irganox 1010~ manufactured by Ciba-Geigy) was added
to the reaction mixture. Successively, 69 ppm (in terms of
metallic titanium) of tetrabutyl titanate was added thereto
and polycondensation was performed while slowly reducing the
pressure from atmospheric pressure to 3 Torr over 85 minutes
and, at the same time, elevating the temperature from 215 to
245 ~C. Subsequently, the polycondensation was continued at
245 ~C and 3 Torr. When a predetermined stirring torque was
attained, the reaction was stopped and the PBT polymer was
- 18 -
CA 02226~34 1998-01-09
taken out. Table 3 summarizes the polymerization time and
the intrinsic viscosity and colour of the obtained polymer.
TABLE 3
Origin of 1,4- Polymerization Intrinsic
butanediol time (hr:min) viscosity (dl/g) Colour
Ex. 1 2:54 0.946 white
Comp. Ex. 1 3:05 0.943 yellowish
- 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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