U.S. patent application number 09/147706 was filed with the patent office on 2001-12-13 for process for separating by distillation pure (meth)acrylic acid from mixtures.
Invention is credited to KROKER, RUPRECHT, WIEDEMANN, MANFRED.
Application Number | 20010050216 09/147706 |
Document ID | / |
Family ID | 7803824 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050216 |
Kind Code |
A1 |
KROKER, RUPRECHT ; et
al. |
December 13, 2001 |
PROCESS FOR SEPARATING BY DISTILLATION PURE (METH)ACRYLIC ACID FROM
MIXTURES
Abstract
A process for distillative separation of pure (meth)acrylic acid
from mixtures which comprise (meth)acrylic acid and dimers and
oligomers of (meth)acrylic acid and are essentially free from
aldehydes and from components whose boiling point is lower than
that of (meth)acrylic acid, using a distillation apparatus which
has a thin-film evaporator, a condenser and a connection which
contains a baffle device and links the thin-film evaporator and the
condenser.
Inventors: |
KROKER, RUPRECHT;
(BOBENHEIM-ROXHEIM, DE) ; WIEDEMANN, MANFRED;
(LUDWIGSHAFEN, DE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND
MAIER & NEUSTADT
1755 JEFFERSON DAVIS HIGHWAY
FOURTH FLOOR
ARLINGTON
VA
22202
|
Family ID: |
7803824 |
Appl. No.: |
09/147706 |
Filed: |
February 22, 1999 |
PCT Filed: |
August 26, 1997 |
PCT NO: |
PCT/EP97/04639 |
Current U.S.
Class: |
203/6 ; 203/40;
203/72; 203/78; 203/8; 203/80; 203/89; 203/DIG.21; 562/600 |
Current CPC
Class: |
Y10S 203/22 20130101;
C07C 51/44 20130101; C07C 51/44 20130101; C07C 57/04 20130101 |
Class at
Publication: |
203/6 ; 203/8;
203/40; 203/72; 203/78; 203/80; 203/89; 203/DIG.021; 562/600 |
International
Class: |
B01D 003/28; B01D
003/34; C07C 005/44 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 1996 |
DE |
19634614.2 |
Claims
We claim:
1. A process for distillative separation of pure (meth)acrylic acid
from mixtures which comprise (meth)acrylic acid and dimers and
oligomers of (meth)acrylic acid and are essentially free from
aldehydes and from components whose boiling point is lower than
that of (meth)acrylic acid, using a distillation apparatus which
has a thin-film evaporator, a condenser and a connection which
contains a baffle device and links the thin-film evaporator and the
condenser.
2. A process as claimed in claim 1, where the mixture is a bottom
product obtained in the distillative preparation of pure
(meth)acrylic acid, containing residual (meth)acrylic acid.
3. A process as claimed in claim 1 or 2, where the proportion of
residual (meth)acrylic acid in the mixture is up to 99% by
weight.
4. A process as claimed in any of the preceding claims, where the
mixture comprises, as polymerization inhibitor, phenothiazine,
hydroquinone, hydroquinone monomethyl ether, p-nitrosophenol,
pmethoxyphenol or mixtures of two or more thereof.
5. A process as claimed in any of the preceding claims, where the
pressure in the thin-film evaporator is from 1.times.10.sup.3 to
3.times.10.sup.4 Pa.
6. A process as claimed in any of the preceding claims, where the
temperature at the top of the thin-film evaporator during
distillation is from 40 to 140.degree. C.
7. A process for distillative recovery of pure (meth)acrylic acid,
comprising the following stages (a) and (b): (a) separation by way
of extractive and distillative separation techniques of pure
(meth)acrylic acid from reaction mixtures obtained in connection
with the preparation of (meth)acrylic acid, and (b) treatment of a
bottom product, obtained in step (a) in a distillative separation
technique and comprising (meth)acrylic acid, by a process as
claimed in any of claims 2 to 6.
8. A process as claimed in claim 7, where the separation of pure
(meth)acrylic acid in accordance with step (a) is conducted in a
distillation apparatus which has a distillation device, a condenser
and a connection between the distillation device and the condenser
and to which the liquid mixture that is to be separated is supplied
continuously, where at least part of the energy required to
evaporate the liquid mixture is supplied to the distillation
apparatus by continuously withdrawing from the distillation device
a fraction of its liquid contents which are at a pressure P.sub.x,
heating this fraction to a temperature T.sub.y, at a pressure
P.sub.y which is above P.sub.x, with the proviso that T.sub.y, is
above the boiling temperature T.sub.x of the liquid contents of the
distillation device when subject to the pressure P.sub.x and is
below the boiling temperature T.sub.y of the liquid contents of the
distillation device when subject to the pressure P.sub.y and
passing the liquid fraction withdrawn from the distillation device
and superheated in this manner, relative to the pressure P.sub.x,
back to the distillation apparatus.
9. A process as claimed in claim 7 or 8, where the product streams
of pure (meth)acrylic acid obtained in step (a) and (b) are
combined.
10. A process as claimed in any of the preceding claims, where a
storage stabilizer is added to the pure (meth)acrylic acid obtained
as product.
Description
[0001] The present invention relates to a process for distillative
separation of pure (meth)acrylic acid from mixtures which comprise
(meth)acrylic acid and dimers and oligomers of (meth)acrylic acid
and are essentially free from aldehydes and other components whose
boiling point is lower than that of (meth)acrylic acid.
[0002] (Meth)acrylic acid is used as an abbreviated written form
and denotes acrylic acid or methacrylic acid. (Meth)acrylic acid,
either per se or in the form of its esters, is particularly
important in the preparation of polymers for a very wide variety of
applications, for example as an adhesive, and especially in the
liquid aggregate state has a high propensity to polymerize. Safe
storage of essentially pure liquid (meth)acrylic acid is possible
even at low temperatures only with the addition of polymerization
inhibitor.
[0003] (Meth)acrylic acid is obtainable inter ail by catalytic gas
phase oxidation of alkanes, alkanols, alkenes or alkenals having 3
or 4 C atoms. (Meth)acrylic acid is obtainable with particular
advantage, for example, by catalytic gas phase oxidation of
propene, acrolein, tert-butanol, isobutene, isobutane,
isobutyraldehyde or methacrolein.
[0004] When considering possible starting compounds, however, one
should not ignore those from which the actual C.sub.3/C.sub.4
starting compound is formed only during the gas phase oxidation, as
an intermediate. An example which may be mentioned is the methyl
ether of tert-butanol.
[0005] In the reaction these starting gases, generally diluted with
inert gases such as nitrogen, CO.sub.2, saturated hydrocarbons
and/or steam, are passed in the form of a mixture with oxygen and
at elevated temperatures (usually from 200 to 400.degree. C.) at
atmospheric or superatmospheric pressure over transition metal
(containing Mo, V, W and/or Fe, for example) mixed-oxide catalysts
and are converted by oxidation to (meth)acrylic acid (cf. e.g. DE-A
44 05 059, EP-A 253 409, EP-A 92 097, DE-A 44 31 949).
[0006] Because of the numerous parallel and follow-on reactions
that occur in the course of the catalytic gas phase oxidation, and
because of the inert diluting gases that are used, the catalytic
gas phase oxidation produces not pure (meth)acrylic acid but
instead a reaction mixture which essentially comprises
(meth)acrylic acid, the inert dilution gases and byproducts and
from which it is necessary to separate the (meth)acrylic acid.
[0007] (Meth)acrylic acid is usually separated from the reaction
mixture by way of extractive and distillative separation
techniques. In such techniques, the (meth)acrylic acid formed is
typically first of all absorbed from the gas phase oxidation
reaction mixture into a suitable absorbent. Subsequent distillative
separation of the absorbate customarily gives a crude (meth)acrylic
acid which, on traversing further distillative separation stages,
frequently produces a pure (meth)acrylic acid (cf. e.g. DE-A 44 36
243, DE-C 21 36 396, DE-A 43 08 087, EP-A 297 445, EP-A 117 146,
EP-B 102 642, GB-B 1 346 737 and DE-C 22 07 184).
[0008] A feature of all of these rectificative separation
techniques, irrespective of whether the (meth)acrylic acid is
separated off at the top or at the bottom and even when
polymerization inhibitors are used, is that after a relatively
short time during the rectificative separation a deposit is formed
within the rectification devices, as a result of which
rectification, which is normally carried out continuously, must be
interrupted at intervals to allow removal of the deposit
formed.
[0009] In recent times extensive investigations have been carried
out into how to reduce the problem of the formation of deposits
during the distillative separation of (meth)acrylic acid from the
reaction mixtures or product mixtures obtained in the preparation
of (meth)acrylic acid.
[0010] For instance, DE 195 01 326.3 describes a method of
rectificative is separation of (meth)acrylic acid from a mixture
comprising (meth)acrylic acid as principal constituent and lower
aldehydes as secondary constituents in a rectification column which
consists of a stripping section and a rectifier section, where the
starting mixture comprising the (meth)acrylic acid that is to be
separated by rectification is not supplied directly to the
rectification column but instead is first of all passed into a
heated dwell vessel, connected on the vapor side with the rectifier
section of the rectification column, in which vessel the starting
mixture is held at boiling, and instead of the starting mixture per
se the bottom liquid from the residence vessel is supplied to the
rectification column. In this method, the mixture is processed to
generally liquid mixtures with a (meth)acrylic acid content of from
5 to 25% by weight, as are generally obtained following the
addition of an absorbent to the reaction mixture obtained from the
catalytic gas phase oxidation, and after subsequent desorption, as
the outgoing flow from the desorption column. In addition to
(meth)acrylic acid, these mixtures still comprise large amounts of
absorbent and lower aldehydes as secondary components.
[0011] A more recent process for the continuous distillative
separation of liquid mixtures whose principal constituent is
(meth)acrylic acid is described in DE 195 39 295.7, which is also
directed mainly toward the problem of reducing the formation of
deposits during rectification. According to this application, the
distillative separation of a mixture which in general has a content
of (meth)acrylic acid of .gtoreq.95% by weight (crude (meth)acrylic
acid) is conducted in a distillation device which has a
distillation still, a condenser and a connection between
distillation still and condenser, and to which the liquid mixture
that is to be separated is supplied continuously, wherein a
fraction of the distillation still liquid is withdrawn in
superheated form and is passed back under pressure release into the
distillation device in the course of this process.
[0012] All of the processes described in the prior art have the
common feature that the bottom product of the distillations or
rectifications, which contains up to 99% by weight (meth)acrylic
acid as the target substance, is not likewise subjected to
distillative workup. The resulting bottom product, which contains a
relatively high proportion of (meth)acrylic acid in the form of
oligomers, has to date been used as a component in a coupled
production process for butyl (meth)acrylate. Coupled production of
this kind is, however, not always possible or economic.
[0013] It is an object of the present invention, accordingly, to
provide a process which is able to isolate pure (meth)acrylic acid,
as simply as possible and with a high yield, from the (meth)acrylic
acid which is present in the bottom product. A further object, to
be achieved with the aid of this process, is to produce not only as
much pure (meth)acrylic acid as possible but at the same time to
produce a correspondingly small amount of residue requiring
landfill or incineration.
[0014] We have found, in the course of the investigations leading
to this invention, that this object is achieved, surprisingly, by a
simple distillation process.
[0015] The present invention accordingly provides a process for
distillative separation of pure (meth)acrylic acid from mixtures
which comprise (meth)acrylic acid and dimers and oligomers of
(meth)acrylic acid and are essentially free from aldehydes and from
components whose boiling point is lower than that of (meth)acrylic
acid, such as water and acetic acid, for example, using a
distillation apparatus which has a thin-film evaporator, a
condenser, and a connection which contains a baffle device and
links the thin-film evaporator and the condenser.
[0016] The term crude (meth)acrylic acid as used in the present
application refers to a (meth)acrylic acid which in general has a
purity of .gtoreq.95% by weight, frequently .gtoreq.97% by weight,
the impurities being drawn in particular from lower aldehydes (for
example formaldehyde, acetaldehyde, acrolein, methacrolein,
propionaldehyde, n-butyraldehyde, benzaldehyde, furfural or
crotonaldehyde), water, lower alkanecarboxylic acids (for example
acetic and propionic acid) and anhydrides of alkanecarboxylic acids
(for example maleic anhydride).
[0017] The term pure (meth)acrylic acid as used in this application
refers to a (meth)acrylic acid whose purity is .gtoreq.98% by
weight, frequently >99% by weight.
[0018] The term residue (meth)acrylic acid as used in this
application refers to the residual (meth)acrylic acid which remains
in the bottom product obtained in the distillative preparation of
pure (meth)acrylic acid.
[0019] The mixture which is to be treated here generally has a
content of residue (meth)acrylic acid of not more than
approximately 99% by weight, the content generally being from
approximately 20 to approximately 99% by weight, preferably from
approximately 70 to approximately 95% by weight.
[0020] The content of dimers and oligomers of (meth)acrylic acid is
generally not more than approximately 5000 ppm, preferably not more
than approximately 1000 ppm, and increases with the duration and/or
temperature of storage.
[0021] As further components, the mixture comprises processing
stabilizers which inhibit the polymerization of (meth)acrylic acid,
examples being air, hydroquinone, hydroquinone monomethyl ether,
p-nitrosophenol, p-methoxyphenol or phenothiazine, or mixtures of
two or more thereof, preference being given to the use of
phenothiazine, in an amount from approximately 50 to approximately
1000 ppm.
[0022] The amount of the processing stabilizer (polymerization
inhibitor) based on the (meth)acrylic acid (by weight) is normally
from approximately 200 to approximately 800 ppm.
[0023] Because of the inhibiting effect that atmospheric oxygen has
on the polymerization of (meth)acrylic acid it is advantageous to
operate the distillation apparatus that is used in accordance with
the invention with a throughflow of air.
[0024] The mixture also includes aldehyde-aminoguanidine adducts
and/or aldehydehydrazine adducts in an amount of up to
approximately 2000 ppm which originate from the aminoguanidine
hydrocarbonate and/or hydrazine (derivatives) added at the
beginning of the workup of the reaction mixture obtained in the gas
phase oxidation.
[0025] The term "essentially free from" used in connection with the
present invention means that the content of the aldehydes and of
the "further components", to which reference is made in this
context, especially of the aldehydes and/or low-boiling components,
for example water and lower alkanecarboxylic acids, is in each case
not more than approximately 1000 ppm, preferably approximately 500
ppm and, in particular, approximately 300 ppm.
[0026] The novel process is employed with particular advantage in
connection with the workup of a bottom product, containing residual
(meth)acrylic acid, that is obtained in the distillative
preparation of pure (meth)acrylic acid.
[0027] For the purposes of the novel process it is essential that
the distillation apparatus is designed as a thin-film evaporator
(Sambay or Luva evaporator) which can of course be configured in
one or more stages. The thin-film evaporator configuration is
essential for the advantageous implementation of the process in so
far as with other evaporators, for example tube evaporators, it is
difficult to work up the in most cases relatively viscous mixtures
that are to be worked up in this case, which generally have a
viscosity of from approximately 50 to approximately 1000 mPas at
50.degree. C., and formation of deposits or encrustation of the
apparatus is observed after only a relatively short time. Thin-film
evaporators that can be used for the purposes of the present
invention, in addition to those mentioned above, are falling film
evaporators and filmtruders.
[0028] In addition, the apparatus to be used in accordance with the
invention has a connection which has a baffle device and links the
thin-film evaporator and the condenser. Apart from the baffle
device, which prevents the entrainment of liquid droplets,
especially of the polymerization inhibitor, the connection is
essentially free from further internals. Possible baffle devices
that can be used are demistors, i.e. wire mesh packings with a very
large internal surface area, which can be fabricated, for example,
from chromium nickel steels, aluminum, copper, nickel,
polypropylene, polytetrafluoroethylene and so on, and a simple
packing of Raschig rings etc.
[0029] To minimize the temperatures during workup the distillative
separation of (meth)acrylic acid in accordance with the invention
preferably takes place under reduced pressure. In this context it
is judicious, in accordance with the invention, to operate under a
pressure .ltoreq.5.times.10.sup.4 Pa, preferably at from
approximately 0.1 to approximately 5.times.10.sup.4 Pa, more
preferably at from approximately 0.1 to approximately
3.times.10.sup.4 Pa and, in particular, at approximately
7.times.10.sup.3 Pa. The interior of the thin-film evaporator is
generally at from approximately 40 to approximately 140.degree. C.,
preferably from approximately 40 to approximately 100.degree. C.
and, in particular, at approximately 70.degree. C., while the
corresponding wall temperature of the thinfilm evaporator is from
approximately 30 to 40.degree. C. higher.
[0030] With preference, the above-described novel process for
distillative separation of pure (meth)acrylic acid is coupled with
the customary processes for obtaining pure (meth)acrylic acid from
reaction mixtures obtained in connection with the preparation of
(meth)acrylic acid, as mentioned at the outset when discussing the
prior art.
[0031] Accordingly, the present invention additionally provides a
process for distillative recovery of pure (meth)acrylic acid,
comprising the following stages (a) and (b):
[0032] (a) separation by way of extractive and distillative
separation techniques of pure (meth)acrylic acid from reaction
mixtures obtained in connection with the preparation of
(meth)acrylic acid, and
[0033] (b) treatment of a bottom product, obtained in step (a) in a
distillative separation technique and comprising (meth)acrylic
acid, by a process for distillative separation of pure
(meth)acrylic acid from mixtures, as defined above.
[0034] Pure (meth)acrylic acid is obtained both in step (a) and in
step (b) in each case at the top, or laterally (step (a)) and at
the top (step (b)).
[0035] In this connection, the product streams obtained in steps
(a) and (b), comprising pure (meth)acrylic acid, can be
combined.
[0036] In general, a storage stabilizer such as hydroquinone
monomethyl ether is added to the pure (meth)acrylic acid obtained
as product.
[0037] In a particularly preferred embodiment of the present
invention step (a) is conducted as follows:
[0038] First of all a crude (meth)acrylic acid is obtained by a
prior art process as described, for example, in EP 95 118 901 (EP-A
717 029).
[0039] The distillative preparation of pure (meth)acrylic acid in
accordance with step (a) is then carried out by means of a
single-stage distillation in which pure (meth)acrylic acid is taken
off at the top in a distillation apparatus which has a distillation
device, a condenser and a connection between the distillation
device and the condenser and to which the liquid mixture that is to
be separated, comprising crude (meth)acrylic acid, is supplied
continuously, wherein at least part of the energy required to
evaporate the liquid mixture is supplied to the distillation
apparatus by continuously withdrawing from the distillation device
a fraction of its liquid contents which are at a pressure P.sub.x,
heating this fraction to a temperature T.sub.y, at a pressure
P.sub.y which is above P.sub.x, with the proviso that T.sub.y, is
above the boiling temperature T.sub.X of the liquid contents of the
distillation device when subject to the pressure P.sub.x and is
below the boiling temperature T.sub.y of the liquid contents of the
distillation device when subject to the pressure P.sub.y, and
passing the liquid fraction withdrawn from the distillation device
and superheated in this manner, relative to the pressure P.sub.x,
back to the distillation apparatus. A process of this kind is
described in DE 195 39 295.7.
[0040] The mixture which remains as the bottom product in this
process can then be passed directly into the second apparatus, for
example by way of pumps, and can be worked up appropriately, as
described above, as step (b).
[0041] A diagram of this process is shown in FIG. 1.
[0042] In this diagram the crude (meth)acrylic acid recovered from
the extraction, which has been treated with aminoguanidine
hydrogencarbonate (AGHC) and/or hydrazine to break down the
aldehydes and contains polymerization inhibitors and a wetting
agent, for example dodecylbenzenesulfonic acid, as antifouling
agent is introduced via line (1) into a distillation unit (2)
provided if desired with a demistor (3), and is distilled, the pure
(meth)acrylic acid being taken off at the top and condensed by
means of the line (4) in a cooling circuit (5), and being provided
via feed line (6) with a stabilizer. The stabilized pure product
thus obtained is transferred to a vessel (not shown) by way of the
line (7), which (as shown) can be provided with a circulation pump
(9'").
[0043] The bottom product obtained in the distillation in unit (2),
containing residual (meth)acrylic acid, is drawn off and
transferred via a feed line (8), which can if desired be provided
with a circulation pump (9), into the thin-film evaporator (10),
which is provided with a demistor (2'), where it is subjected to a
residue distillation procedure. Pure (meth)acrylic acid is again
taken off from the top and passed via the feed line (11) to a
further cooling circuit where it is likewise treated with a
stabilizer via the supply line (13). The pure product thus obtained
is transferred into a vessel (not shown here) via the line (14),
which (as shown) can be provided with a circulation pump (9"). The
residue in the thin-film evaporator, which contains high-boiling
compounds, is removed continuously from the thin-film evaporator
via the discharge line (15), which contains a discharge pump (9'),
and is passed on for incineration. The amount of residue produced,
based on the initial amount of crude (meth)acrylic acid, is about
1-2% by weight.
[0044] As likewise shown diagrammatically in FIG. 1 by the dashed
line (16), the pure (meth)acrylic acid taken off at the top in the
residue distillation procedure can also be combined with the
distillation product stream from the unit (2), which likewise
consists of pure (meth)acrylic acid, by way of a connection
incorporating a cooling device (16), and both product streams can
be condensed together, provided with a storage stabilizer and
transferred to a vessel which is not shown here.
[0045] It is also possible--as is shown likewise--for there to be
circulation evaporators (17) at various points in the process.
[0046] Overall it should be borne in mind that the novel process
can be carried out, preferably, continuously, but also
discontinuously, and can in fact be conducted either alone or
coupled with other process stages within a process preparing pure
(meth)acrylic acid by gas phase oxidation with subsequent
purification.
EXAMPLE
[0047] A bottom product of the following composition:
[0048] 92% by weight of acrylic acid
[0049] 4000 ppm of phenothiazine (process polymerization
inhibitor)
[0050] 2% by weight of dimers and oligomers of acrylic acid
[0051] 2% by weight of adducts of AGHC and aldehydes/maleic
anhydride
[0052] 3% by weight of dodecylbenzenesulfonic acid (antifouling
agent)
[0053] 300 ppm of propionic acid
[0054] 300 ppm of acetic acid
[0055] 100 ppm of water,
[0056] which was obtained in connection with a preparation by
catalytic gas phase oxidation of acrolein and subsequent extractive
and distillative purification thereof, was supplied to a
distillation apparatus with a thin-film evaporator and a baffle
device.
[0057] The precise data for the distillation apparatus and the mode
of operation were as follows:
[0058] thin-film evaporator of the Sambay type with a wall area of
10 m.sup.2
[0059] demistor with a diameter of 700 mm and a length of 1 m
[0060] direct feed of the mixture to be separated into the
thin-film evaporator with an entry temperature of from 30 to
90.degree. C. at a rate of 0.5 m.sup.3/h;
[0061] pressure in the apparatus: 7.times.10.sup.3 Pa (70
mbar);
[0062] boiling temperature at the top of the device: approximately
70.degree. C.;
[0063] cooling circuit 80 m.sup.3/h.
[0064] In the condenser a condensate was obtained which comprised
99.7% by weight of acrylic acid and also less than 1000 ppm of
diacrylic acid, about 300 ppm of propionic acid, about 300 ppm of
acetic acid, <10 ppm of low molecular mass aldehydes and <1
ppm of phenothiazine and to which 200 ppm of hydroquinone
monomethyl ether as storage stabilizer were added directly.
[0065] The yield of acrylic acid based on the amount introduced was
approximately 90%. The bottom product, which was obtained in this
distillation in an amount of approximately 10% based on the overall
amount employed, consis-ted essentially of dimers and oligomers of
acrylic acid, process stabilizer, antifouling agent, the adducts of
AGHC and aldehydes/maleic anhydride, and a small amount of acrylic
acid.
* * * * *