U.S. patent application number 11/674247 was filed with the patent office on 2007-06-07 for process for producing (meth)acrylic acids.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Yasushi Ogawa, Yoshiro Suzuki, Kiyoshi Takahashi, Kenji Takasaki, Shuhei Yada.
Application Number | 20070129571 11/674247 |
Document ID | / |
Family ID | 27555026 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070129571 |
Kind Code |
A1 |
Yada; Shuhei ; et
al. |
June 7, 2007 |
PROCESS FOR PRODUCING (METH)ACRYLIC ACIDS
Abstract
A process for producing (meth)acrylic acid or (meth)acrylic acid
esters, which comprises a reaction step comprising vapor phase
catalytic oxidation of propylene, propane or isobutylene and, if
necessary, a reaction step comprising an esterification step,
characterized in that at the time when a high boiling mixture
(hereinafter referred to as a high boiling material) containing a
Michael addition product, is decomposed in a decomposition reactor
to recover (meth)acrylic acids, while forcibly imparting a liquid
flow in the circumferential direction to a liquid reaction residue
in the decomposition reactor, the liquid reaction residue is
discharged. In a process for recovering a valuable substance by
thermally decomposing the high boiling material containing the
Michael addition product of (meth)acrylic acids, it is possible to
transfer the decomposition residue from the decomposition reactor
to the storage tank without clogging, whereby a long-term
continuous operation is possible.
Inventors: |
Yada; Shuhei; (Mie, JP)
; Ogawa; Yasushi; (Mie, JP) ; Suzuki; Yoshiro;
(Mie, JP) ; Takahashi; Kiyoshi; (Mie, JP) ;
Takasaki; Kenji; (Mie, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Tokyo
JP
|
Family ID: |
27555026 |
Appl. No.: |
11/674247 |
Filed: |
February 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10859221 |
Jun 3, 2004 |
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11674247 |
Feb 13, 2007 |
|
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PCT/JP02/12709 |
Dec 4, 2002 |
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10859221 |
Jun 3, 2004 |
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Current U.S.
Class: |
562/545 ;
422/140; 562/600 |
Current CPC
Class: |
B01D 3/225 20130101;
B01J 2219/00774 20130101; B01J 2208/0084 20130101; B01D 3/24
20130101; B01J 19/006 20130101; B01J 2219/00252 20130101; B01J
2219/00006 20130101; B01D 3/322 20130101; B01J 8/228 20130101; B01J
19/0066 20130101; B01J 2219/00094 20130101; B01D 3/14 20130101;
B01J 14/00 20130101; B01J 2208/003 20130101; B01J 2219/00247
20130101; C07C 51/252 20130101; B01J 2208/00283 20130101; B01J
19/18 20130101; C07C 51/252 20130101; C07C 57/04 20130101 |
Class at
Publication: |
562/545 ;
562/600; 422/140 |
International
Class: |
C07C 51/42 20060101
C07C051/42; C07C 51/16 20060101 C07C051/16; B01J 8/18 20060101
B01J008/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2001 |
JP |
2001-369636 |
Dec 5, 2001 |
JP |
2001-371608 |
Dec 18, 2001 |
JP |
2001-385168 |
Dec 25, 2001 |
JP |
2001-392058 |
May 16, 2002 |
JP |
2002-141162 |
May 16, 2002 |
JP |
2002-141194 |
Claims
1-31. (canceled)
32. A method for installing a liquid level meter in a case where a
liquid level meter is installed at a place where a liquid
containing an easily polymerizable compound is stored, in an
installation for production of the easily polymerizable compound,
characterized in that a high pressure side detection line of the
liquid level meter is connected to a discharge line for the liquid
stored.
33. The method according to claim 32, wherein the connection angle
.alpha. between the high pressure side detection line and the
liquid discharge line is from 5 to 90.degree..
34. The method according to claim 32, wherein the dimensional ratio
D.sub.2/D.sub.1 is from 1 to 20 where D.sub.1 is the pipe diameter
of the high pressure side detection line and D.sub.2 is the pipe
diameter of the liquid discharge line.
35. The method according to claim 32, wherein the liquid discharge
line is connected to a distillation column, a reflux tank of the
distillation column, a decomposition reaction column, a thin film
evaporator, a column top gas condensed liquid tank, a vertical
storage tank, a horizontal storage tank or a tank.
36. The method according to claim 32, wherein the high pressure
side detection line and/or the low pressure side detection line of
the liquid level meter, is heated or warmed.
37. The method according to claim 32, wherein the high pressure
side detection line and/or the low pressure side detection line of
the liquid level meter, is connected with an inlet for a gas and/or
a liquid.
38. The method according to claim 32, wherein the easily
polymerizable compound is (meth)acrylic acid or its ester, and the
liquid to be measured by the liquid level meter, contains at least
one member selected from an acrylic acid dimer,
.beta.-(meth)acryloxypropionic acid esters, .beta.-alkoxypropionic
acid esters, .beta.-hydroxypropionic acid and
.beta.-hydroxypropionic acid esters, formed as byproducts when
(meth)acrylic acid or its ester is produced.
Description
TECHNICAL FIELD
[0001] The present invention relates to an industrially
advantageous process for producing (meth)acrylic acids at a high
recovery rate, while reducing the amount of industrial wastes, by
decomposing byproducts such as Michael addition products of
(meth)acrylic acid or (meth)acrylic esters, by-produced in a step
for producing (meth)acrylic acids, and recovering variable
compounds such as (meth)acrylic acid, (meth)acrylic esters and
alcohols.
[0002] In this specification, "(meth)acrylic acid" is a general
term for acrylic acid and methacrylic acid, and it may be either
one or both of them. Further, "(meth)acrylic acids" is a general
term for these acids and (meth)acrylic esters obtainable from such
acids and alcohols, and the term is meant for one comprising at
least one of them.
BACKGROUND ART
[0003] a. As a method for decomposing Michael addition products
by-produced during production of acrylic acid or acrylic esters, it
is common to employ a thermal decomposition method using no
catalyst in the case of a process for producing acrylic acid
(JP-A-11-12222), while in the case of a process for producing an
acrylic ester, a method is known to carry out the decomposition by
heating in the presence of a Lewis acid or a Lewis base
(JP-A-49-55614, JP-B-7-68168, JP-A-9-110791, JP-A-9-124552,
JP-A-10-45670). Further, as a decomposition reactive system for
Michael addition products, it is common to employ a reaction
distillation system wherein the desired decomposed reaction product
is distilled by distillation while carrying out the decomposition
reaction. Further, a method is also known wherein Michael addition
products by-produced in a step for producing acrylic acid, and
Michael addition products by-produced in a step for producing an
acrylic ester, are put together, followed by thermal decomposition.
There are a method for thermal decomposition by a reactive
distillation system in the absence of any catalyst (JP-A-8-225486)
and a method for decomposition by means of a highly concentrated
acid catalyst (JP-A-9-183753).
[0004] In order to increase the recovery rate of acrylic acid, an
acrylic ester or an alcohol useful as a product or as a raw
material for a reaction, at the top of such a decomposition
reaction column, it is necessary to increase the decomposition
reaction temperature and to suppress the bottom discharge amount,
whereby there has heretofore been a problem such that the bottom
liquid tends to be a highly viscous liquid; as the decomposition
temperature is high, an oligomer or polymer of acrylic acid or an
acrylic ester being an easily polymerizable substance, is likely to
form; and some of substances contained in the raw material for the
reaction tend to precipitate, whereby a solid will deposit at the
bottom of the decomposition reaction column, a polymer is formed
due to a liquid contained in the deposit, and such a deposit will
flow into a liquid discharge line at the time of an operational
change thereby to cause sudden clogging of the liquid discharge
line; and thus, there has been no appropriate method whereby the
decomposition reaction column can be operated constantly for a long
time. Especially when a solid has once deposited at the bottom of a
decomposition reaction column, an easily polymerizable liquid
occluded in the deposited solid tends to be extremely polymerizable
since it can not flow, and the decomposition reaction temperature
is relatively high, thus leading to a phenomenon where the amount
of the deposit will be further increased by such polymerization.
Thus, it has been desired to cope with this problem.
[0005] b. As an example to solve this problem, a method is
conceivable wherein the diameter of a pipe to transfer the bottom
liquid is reduced to transfer the liquid at a high flow rate, but
it has been impossible to adopt such a method, since the pump for
such a transfer is required to be of a high pressure type, such
being economically disadvantageous as an industrial production
method. Further, a method is also conceivable wherein in order to
lower the viscosity of the bottom liquid, waste liquid from the
production step may be added or water may be added afresh, but such
will bring about a decrease of the liquid temperature, whereby
clogging tends to be rather accelerated, or it tends to be required
to add such water in a large amount. Accordingly, it has been
practically impossible to adopt such a method.
[0006] c. On the other hand, as is well known, there is a vapor
phase oxidation method of propylene as a reaction to form acrylic
acid. For such a method of obtaining acrylic acid by oxidizing
propylene, there are a two step oxidation process wherein oxidation
to acrolein and a next step of oxidation to acrylic acid, are
carried out in separate reactors, respectively, since the oxidation
conditions are different, and a process wherein oxidation is to
acrylic acid is carried out directly by one step oxidation.
[0007] FIG. 9 shows an example of a flowchart for forming acrylic
acid by two step oxidation, followed by a reaction with an alcohol
to form an acrylic ester. Namely, propylene, steam and air are
subjected to two step oxidation via the first and second reactors
packed with e.g. a molybdenum-type catalyst to form an acrylic
acid-containing gas. This acrylic acid-containing gas is contacted
with water in a collection column to obtain an aqueous acrylic acid
solution, which is extracted in an extraction column by adding a
suitable extraction solvent, whereupon the extraction solvent is
separated in a solvent separation column. Then, acetic acid is
separated in an acetic acid separation column to obtain crude
acrylic acid, and in a fractionating column, a byproduct is
separated from this crude acrylic acid to obtain a purified product
of acrylic acid. Further, this acrylic acid (purified product) is
esterified in an esterification reaction column, and then, via an
extraction column and a light component separation column, a crude
acrylic ester is obtained. From this crude acrylic ester, a
byproduct (high boiling product) is separated in a fractionating
column to obtain a purified product of an acrylic ester.
[0008] Here, depending upon the type of the acrylic ester, there
may be a case where the flow sheet will be as shown in FIG. 10. In
such a case, the byproduct is obtained as bottoms in an acrylic
acid separation column.
[0009] In the process for producing an acrylic ester in FIG. 10,
acrylic acid, an alcohol, recovered acrylic acid and a recovered
alcohol are respectively supplied to an esterification reactor.
This esterification reactor is packed with a catalyst such as a
strongly acidic ion exchange resin. An esterification reaction
mixture comprising a formed ester, unreacted acrylic acid, an
unreacted alcohol, formed water, etc., withdrawn from this reactor,
will be supplied to an acrylic acid separation column.
[0010] From the bottom of this acrylic acid separation column, the
bottom liquid containing unreacted acrylic acid is withdrawn and
recycled to an esterification reactor. A part of this bottom liquid
is supplied to a high boiling component separation column, whereby
a high boiling component is separated from the bottom, and this is
supplied to and decomposed in a high boiling component
decomposition reactor (not shown). The decomposition product
containing a valuable substance formed by the decomposition will be
recycled to the process. A place in the process where the
decomposition product is recycled, varies depending upon the
process conditions. High boiling impurities such as polymers will
be discharged from the high boiling decomposition reactor to the
exterior of the system.
[0011] From the top of this acrylic acid separation column, an
acrylic ester, an unreacted alcohol and formed water are distilled.
A part of the distillate is recycled as a reflux liquid to the
acrylic acid separation column, and the rest is supplied to an
extraction column.
[0012] To this extraction column, water for extraction of an
alcohol is supplied. Water containing an alcohol, flowing out of
the bottom, will be supplied to an alcohol recovery column. The
distilled alcohol will be recycled to the esterification
reactor.
[0013] A crude acrylic ester discharged from the top of the
extraction column will be supplied to a light boiling component
separation column, and a light boiling material is withdrawn from
the top and recycled within a process. A place within the process
where it is recycled, varies depending upon the process conditions.
The crude acrylic ester having the low boiling material removed,
will be supplied to a purification column for an acrylic ester
product, whereby a high purity acrylic ester will be obtained from
the top. The bottom liquid contains a large amount of acrylic acid
and therefore is recycled within the process. The place within the
process where it will be recycled, varies depending upon the
process conditions.
[0014] Further, in recent years, instead of a solvent extraction
method wherein recovery of acrylic acid from the above aqueous
acrylic acid solution is carried out by means of an extraction
solvent, an azeotropic separation method is carried out wherein
distillation is carried out by means of water and an azeotropic
solvent, so that from the top of the azeotropic separation column,
an azeotropic mixture comprising water and the azeotropic solvent,
is distilled, and from the bottom, acrylic acid is recovered.
[0015] Further, also practically used is a method wherein acrylic
acid is obtained by using propane instead of propylene and using a
Mo--V--Te type composite oxide catalyst or a Mo--V--Sb type
composite oxide catalyst. In the case of methacrylic acid and a
methacrylic ester, isobutylene or t-butyl alcohol is employed
instead of propylene, and a purified product of methacrylic acid
and a purified product of a methacrylic ester are obtained via a
similar oxidation process and the subsequent esterification
process.
[0016] Further, as a method for forming a (meth)acrylic ester (an
acrylic ester or a methacrylic ester), a method is practically
employed wherein a (meth)acrylic ester of a lower alcohol and a
higher alcohol are subjected to a transesterification reaction by
using e.g. an acid as a catalyst, to produce a (meth)acrylic ester
of the higher alcohol. The crude (meth)acrylic ester obtained by
this transesterification exaction, is subjected to steps such as
catalyst separation, concentration and fractionation to obtain a
purified (meth)acrylic ester.
[0017] A useful byproduct such as a Michael addition product, is
contained in the fraction separated by distillation and
purification of the above-mentioned crude acrylic acid, the crude
methacrylic acid, the crude acrylic ester or the crude methacrylic
ester. Accordingly, this byproduct is decomposed to recover
(meth)acrylic acid or its ester, or the raw material alcohol.
[0018] Heretofore, the methods as disclosed in the above a have
been known as methods for decomposing a Michael addition product
by-produced during production of acrylic acid or an acrylic ester.
Thus, heretofore, it has been common to decompose a Michael
addition product by-produced during production of an acrylic ester
thereby to recover a valuable substance such as acrylic acid, an
acrylic ester or an alcohol. As such a decomposition and recovery
method, it has been common to employ a reactive distillation system
wherein distillation is conducted while carrying out a
decomposition reaction.
[0019] To carry out the reactive distillation system, a reactor
provided at its upper portion with a distillation column, is
employed. As such a distillation column, it is common to employ a
plate column provided internally with various trays, or a packed
column having various packing materials packed, in order to bring
about fractionating effects. The plates may, for example, be bubble
cap trays, uniflux trays, flexible trays, ballast trays, perforated
trays (sieve trays), chimney trays, ripple trays, dual flow trays
or baffle trays. The packing material may, for example, be a
ring-type packing material such as Raschig rings, spiral rings or
pall rings, or a saddle type packing material such as Berl saddle
or interlock saddle, or others such as Goodloe packing, Dixon ring,
MacMahon packing, or a vertically flat plate type regulated packing
material.
[0020] However, in both production processes for acrylic acid and
an acrylic ester, the raw material to be supplied to the step of
decomposing the byproduct, is a fraction obtained by concentrating
a high boiling component formed in the reaction system or
purification system. Further, acrylic acid and acrylic esters are
very easily polymerizable materials, and consequently, the raw
material for the decomposition reaction contains polymers formed.
Further, the decomposition reaction is carried out at a high
temperature, and therefore, there will be a polymer formed during
the decomposition reaction. Accordingly, it is likely that a solid
substance is already present in the raw material to be subjected to
decomposition, and even when no solid substance is present in the
raw material, it may precipitate anew, or there may be a solid
substance to be formed during the distillation separation operation
or in the decomposition step where a chemical reaction is
simultaneously carried out. And, adhesion, deposition or
accumulation of such a solid substance takes place on the trays or
at void spaces of the packing material in the distillation column,
whereby an increase of the differential pressure, deterioration of
the gas/liquid contact state and further clogging, may, for
example, occur. Consequently, there has been a problem that such
tends to hinder to obtain a high recovery rate of a valuable
substance or tends to hinder a constant continuous operation.
[0021] Accordingly, in both processes for producing acrylic acid
and the ester, it is desired to solve the above problems and to
develop a process for decomposing a Michael addition product,
whereby a high recovery rate can constantly be obtained.
[0022] d. Further, in a method for recovering (meth)acrylic acid or
a (meth)acrylic ester by carrying out the decomposition reaction of
a Michael addition reaction product by-produced during the process
for producing (meth)acrylic acid or a (meth)acrylic ester, if the
decomposition reaction temperature is made high in order to obtain
a high recovery rate for such (meth)acrylic acid, a (meth)acrylic
ester or an alcohol, an oligomer or polymer of (meth)acrylic acid
or a (meth)acrylic ester being an easily polymerizable substance,
will be formed. To prevent such polymerization, it is suggested to
add molecular oxygen in addition to a polymerization inhibitor such
as hydroquinone, methoxyhydroquinone, phenothiazine or
hydroxylamine, to the decomposition reactor (e.g. the
above-mentioned JP-A-10-45670, paragraphs 0012 and 0019).
[0023] However, if such a method is employed, there may sometimes
be a case where not only no adequate effect for preventing
polymerization of (meth)acrylic acid or a (meth)acrylic ester in
the decomposition product by oxygen is obtainable, but also
polymerization may be accelerated, and thus there may be a case
where the above decomposition reaction can not be constantly
continued over a long time.
[0024] e. Further, an acrylic acid-containing gas obtained by vapor
phase catalytic oxidation by molecular oxygen of propylene and/or
acrolein, usually contains maleic acid, as one of byproducts, in an
amount of from about 0.2 to 1.6 wt %, based on acrylic acid. Maleic
acid is a dicarboxylic acid represented by
HOCO--CH.dbd.CH--CO.sub.2H and is in an equilibrium state with a
carboxylic anhydride having one molecule of water dehydrated in its
molecule in its solution. Hereinafter, unless otherwise specified,
maleic acid and maleic anhydride will be together represented by
maleic acid. When an acrylic acid-containing gas is collected by a
solvent in the form of an acrylic acid-containing solution, maleic
acid will be collected at the same time. The boiling point of
maleic acid is high as compared with acrylic acid, and in the
purification step by distillation, maleic acid will be concentrated
in the bottoms.
[0025] When two molecules of acrylic acid undergo Michael addition,
an acrylic acid dimer will be formed. There is no means to prevent
formation of such an acrylic acid dimer in the acrylic acid
solution, and the formation speed increases as the temperature
becomes high. Further, a higher oligomer such as an acrylic acid
trimer will sequentially be formed by acrylic acid and an acrylic
acid dimer. In the purification step for acrylic acid, an acrylic
acid dimer (or oligomer) will be formed mostly in the distillation
column where heating is carried out, particularly at the bottom
portion where the temperature is high, and the retention time is
long.
[0026] In order to improve the recovery rate of acrylic acid in the
purification step, it is usual to recover acrylic acid from the
formed acrylic acid oligomer.
[0027] As a recovery method from an acrylic acid oligomer, there
may, for example, be a method wherein thermal decomposition is
carried out under reduced pressure in the presence or absence of a
catalyst, and acrylic acid is recovered as a distilled gas or a
distilled liquid, as disclosed in JP-B-45-19281. In such a case,
the distilled gas and the distilled liquid of acrylic acid contains
a large amount of high boiling compounds other than acrylic acid to
be recovered, such as maleic acid. In a case where the operation
temperature is increased in order to increase the recovery rate of
acrylic acid, the maleic acid concentration in the recovered
acrylic acid will also be increased.
[0028] As a method to reduce such maleic acid, in a method as
disclosed in JP-A-11-12222, a crude acrylic acid containing from 3
to 10 wt % of maleic acid and other acrylic acid oligomers, is
introduced into an acrylic acid recovery column, and acrylic acid
is distilled from the top, and the bottom liquid is thermally
decomposed, and such a bottom liquid is recycled to the recovery
column, whereby maleic acid can be reduced to a level of from 0 to
3 wt %.
[0029] In such a thermal decomposition recovery method of an
acrylic acid oligomer, maleic acid as an impurity is disposed as
bottoms of the thermal decomposition reaction apparatus or the
distillation apparatus. At that time, if the amount of maleic acid
contained in the recovered acrylic acid is large, the amount of
maleic acid recycled in the system will increase, whereby
instruments and the heat load in the purification step will
increase. The simplest method to prevent this, is to reduce the
thermal decomposition recovery amount of the acrylic acid oligomer,
but the recovery rate for acrylic acid in the purification step
will thereby be decreased, and the economical efficiency will be
deteriorated.
[0030] In order to accomplish improvement of the recovery rate of
acrylic acid and reduction of the recycling amount of maleic acid,
there is a method of adding a distillation column as in the method
disclosed in JP-A-11-1222. However, since acrylic acid is an easily
polymerizable compound, it is common to carry out distillation
under reduced pressure to prevent polymerization by lowering the
operational temperature, but as the boiling point of maleic acid is
higher than acrylic acid, even if the operation pressure is
lowered, an increase of the operational temperature can not be
avoided. This will not only facilitate clogging of the distillation
apparatus by polymerization, but also tends to accelerate formation
of an acrylic acid oligomer in the acrylic acid recovered by
thermal decomposition. Further, in order to increase the vacuuming
degree of the distillation installation, the diameter of the
distillation column is increased, whereby the load during the
construction and operation will also increase.
[0031] Further, concentrated maleic acid is discharged from the
bottom. However, maleic acid is solid at room temperature and thus
has problems such that the viscosity of the liquid tends to be high
from the lower portion to the bottom of the distillation column,
and deterioration in the separation ability due to fouling, or
deposition of a polymer or clogging is likely to result.
[0032] Such problems result as maleic acid being an impurity is
separated as a high boiling substance by distillation.
[0033] In order not to include a step of concentrating maleic acid
by distillation and to improve the thermal decomposition recovery
efficiency of acrylic acid, it is necessary to carry out, without
imparting a large heat as distillation, either {circle around (1)}
reducing the maleic acid concentration in the acrylic acid solution
to be supplied to the thermal decomposition reaction apparatus, or
{circle around (2)} reducing maleic acid in the acrylic acid
solution recovered from the thermal decomposition reaction
apparatus.
[0034] f. Further, heretofore, in an installation for producing
acrylic acid or the like, it has been common to carry out a
pressure measurement by installing a high pressure side detection
portion of a liquid level meter in direct connection to the main
body of the instrument. However, by a conventional method for
installation of a liquid level meter, a polymerization inhibitor to
be used for the preparation of an easily polymerizable compound or
a formed polymer, is supplied to the high pressure side detection
portion of the liquid level meter, and a solid substance is likely
to be accumulated, whereby an error operation of the liquid level
meter used to be observed.
[0035] Accordingly, it used to be difficult to carry out accurate
measurement continuously by a liquid level meter, whereby it has
been difficult to carry out a constant operation of the
installation for a long period of time.
DISCLOSURE OF THE INVENTION
[0036] a. It is an object of the present invention to overcome the
problems in the conventional decomposition reaction of a Michael
addition product of acrylic acid or an acrylic ester thereby not to
let deposition remain in the decomposition reaction column, to
prevent formation of a polymer in the decomposition reaction column
and to prevent sudden clogging of the discharge pipe, so that a
stabilized operation method is presented.
[0037] b. Further, it is an object of the present invention to
provide a method for decomposing a byproduct during production of
(meth)acrylic acids, whereby at the time of recovering a valuable
substance by decomposing, by a reactive distillation system, a
Michael addition product by-produced in the process for producing
(meth)acrylic acid or a (meth)acrylic ester, adhesion, deposition
or accumulation of such a solid substance is prevented, a high
recovery rate of (meth)acrylic acid, a (meth)acrylic ester and an
alcohol can be constantly maintained, and a constant continuous
operation can be carried out for a long period of time.
[0038] c. Further, it is an object of the present invention to
provide a method to eliminate recycling of maleic acid in an
acrylic acid purification system involving thermal decomposition
and recovery of an acrylic acid oligomer formed in the distillation
purification step of an acrylic acid-containing liquid and to
readily accomplish the purification without a problem of
polymerization of acrylic acid or clogging of an equipment in the
purification step.
[0039] d. Further, it is an object of the present invention to
provide a method for installing a liquid level meter on an
installation for producing an easily polymerizable compound,
whereby accurate measurement can continuously be carried out by
preventing formation and accumulation of a solid substance of the
liquid to be measured at a high pressure side detection portion of
the liquid level meter.
[0040] The present inventors have conducted various studies to
accomplish the above objects, and as a result, have arrived at the
present invention having the following gists.
[0041] (1) A process for producing (meth)acrylic acids, which
comprises a method of decomposing in a decomposition reactor a high
boiling mixture formed as a byproduct during the production of
(meth)acrylic acids, characterized in that the high boiling mixture
contains a Michael addition product having water, an alcohol or
(meth)acrylic acid added to a (meth)acryloyl group; while forcibly
imparting a liquid flow in the circumferential direction to a
liquid reaction residue in the decomposition reactor, the liquid
reaction residue is discharged; and (meth)acrylic acid or a
(meth)acrylic ester is recovered.
(2) The process according to the above (1), characterized in that
the liquid flow in the circumferential direction is imparted by
stirring vanes installed in the decomposition reactor.
(3) The process according to the above (1), characterized in that
the liquid flow in the circumferential direction is imparted by a
liquid supplied from the exterior of the decomposition reactor.
[0042] (4) The process according to the above (3), characterized in
that the liquid supplied from the exterior of the decomposition
reactor is the high boiling material supplied as raw material, or a
return liquid of the liquid reaction residue discharged from the
decomposition reactor.
(5) The process according to any one of the above (1) to (4),
characterized in that the liquid reaction residue is intermittently
discharged from the decomposition reactor.
[0043] (6) The process according to any one of the above (1) to
(5), characterized in that at the time of recovering a valuable
substance by carrying out distillation as well as thermal
decomposition of the high boiling mixture, the distillation is
carried out by means of a distillation column which is internally
provided with disk-and-donut type trays.
(7) The process according to any one of the above (1) to (6),
characterized in that an oxygen-containing gas is added to a
distillate from the decomposition reactor.
[0044] (8) The process according to any one of the above (1) to
(7), characterized in that from a liquid to be supplied to the
thermal decomposition reactor or from a liquid recovered from the
thermal decomposition reactor, maleic acid contained in said
liquid, is precipitated and separated.
[0045] (9) The process according to any one of the above (1) to
(8), characterized in that a liquid level meter is installed on the
thermal decomposition reactor, and a high pressure side detection
line of the liquid level meter is connected to a liquid discharge
line of the decomposition reactor.
[0046] The above present invention has the following preferred
embodiments (a) to (f).
[0047] a1. A process for producing (meth)acrylic acids, which is a
process for producing acrylic acid or (meth)acrylic acid (these are
hereinafter generally referred to also as (meth)acrylic acid) or a
(meth)acrylic ester ((meth)acrylic acid and a (meth)acrylic ester
may hereinafter generally referred to also as (meth)acrylic acids),
by a reaction step comprising vapor-phase catalytic oxidation of
propylene, propane or isobutylene, and, if necessary, further by a
reaction step comprising an esterification step, characterized in
that at the time when a high boiling mixture (hereinafter referred
to as a high boiling material) containing a Michael addition
product, is decomposed in a decomposition reactor to recover
(meth)acrylic acids, while forcibly imparting a liquid flow in the
circumferential direction to a liquid reaction residue in the
decomposition reactor, the liquid reaction residue is
discharged.
a2. The process according to the above a1, wherein the liquid flow
in the circumferential direction is imparted by stirring vanes
installed in the decomposition reactor.
a3. The process according to the above a1 or a2, wherein the
stirring vanes are anchor vanes, multistage puddle vanes,
multistage inclined puddle vanes or lattice vanes.
[0048] a4. The process according to the above a1 or a2, wherein the
structure of the stirring vanes is such that on a rotary shaft
vertically installed at the center portion of the reactor, radial
flow type vanes are attached in two or more stages in the
rotational axis direction, so that vanes adjacent in the rotational
axis direction are in a positional relation to the rotational axis
direction such that their phases are displaced from each other by
not more than 90.degree., and the lowest portion of the upper stage
one of the vanes adjacent in the rotational axis direction, is
located below the highest portion of the lower stage one.
a5. The process according to the above a1, wherein the liquid flow
in the circumferential direction is imparted by a liquid supplied
from the exterior of the decomposition reactor.
[0049] a6. The process according to the above a1 or a5, wherein the
liquid supplied from the exterior of the decomposition reactor is
the high boiling material supplied as raw material, or a return
liquid of the liquid reaction residue discharged from the
decomposition reactor.
[0050] b1. A process for producing (meth)acrylic acids, which is a
process for producing acrylic acid, methacrylic acid or a
(meth)acrylic ester by a reaction step comprising vapor-phase
catalytic oxidation of propylene, propane or isobutylene, and, if
necessary, further by a reaction step comprising an esterification
step, characterized in that at the time when a high boiling mixture
(hereinafter referred to as a high boiling material) containing a
Michael addition product, is decomposed in a decomposition reactor
to recover (meth)acrylic acids, a liquid reaction residue is
intermittently discharged from the decomposition reactor.
b2. The process according to the above b1, wherein the discharge
stop time is from 5 seconds to 5 minutes, and the discharge time is
from 2 seconds to 5 minutes.
b3. The process according to the above b1 or b2, wherein the liquid
high boiling material is continuously supplied to the decomposition
reactor, and (meth)acrylic acids are continuously discharged from
the vapor phase.
[0051] c1. In a process which comprises introducing a byproduct
formed during production of (meth)acrylic acid and/or a byproduct
formed during production of a (meth)acrylic ester into a reactor
provided with a distillation column, thereby to thermally decompose
the byproduct and at the same to carry out distillation for
recovering a valuable substance, a method for decomposing the
byproduct formed during production of (meth)acrylic acids,
characterized in that as said distillation column, a distillation
column which is internally provided with disk-and-donut type trays,
is used.
[0052] c2. The process according to the above c1, wherein the
byproduct formed during production of (meth)acrylic acid is the
bottom liquid of a fractionating column in the final step for
producing (meth)acrylic acid, and the byproduct formed during
production of the (meth)acrylic ester is the bottom liquid of a
fractionating column for separating a high boiling fraction in a
purification step for the (meth)acrylic ester.
[0053] c3. The process according to the above c1 or c2, wherein the
byproduct formed during production of (meth)acrylic acid and/or the
byproduct formed during production of a (meth)acrylic ester
contains a Michael addition product having water, an alcohol or
(meth)acrylic acid added to a (meth)acryloyl group.
c4. The process according to any one of the above c1 to c3, wherein
the thermal decomposition reaction temperature is from 12.degree.
to 280.degree. C., and the thermal decomposition reaction time is
from 0.5 to 50 hours.
[0054] d1. A process for decomposing a byproduct formed during
production of (meth)acrylic acids, which comprises decomposing in a
decomposition reactor a byproduct formed during production of
(meth)acrylic acid and/or a byproduct formed during production of a
(meth)acrylic ester, and distilling the decomposed product from the
decomposition reactor, characterized in that oxygen or an
oxygen-containing gas is added to the distillate from the
decomposition reactor.
[0055] d2. The process according to the above d1, wherein the
byproduct formed during production of (meth)acrylic acid is the
bottom liquid of a fractionating column in the final step for
producing (meth)acrylic acid, and the byproduct formed during
production of the (meth)acrylic ester is the bottom liquid of a
fractionating column in the final step for producing the
(meth)acrylic ester, or the bottoms of a separation column for
(meth)acrylic acid.
d3. The process according to the above d1 or d2, wherein the
byproduct to be decomposed, contains a Michael addition
product.
d4. The process according to any one of the above d1 to d3, wherein
the gas containing oxygen is air or oxygen diluted with an inert
gas.
d5. The process according to any one of the above d1 to d4, wherein
the gas containing oxygen is added to a discharge line for a
distillate from the decomposition reactor, or to the top portion of
the decomposition reactor.
[0056] e1. In a process for producing acrylic acid, which comprises
contacting with a solvent an acrylic acid-containing gas obtained
by catalytic oxidation of propane or propylene, to collect acrylic
acid in the form of an acrylic acid-containing solution, and
purifying acrylic acid by distillation of the obtained acrylic
acid-containing solution, a method for recovering acrylic acid,
characterized in that the bottoms obtained from the bottom of a
fractionating column for acrylic acid, or a liquid obtained by
heating and concentrating such bottoms, is supplied to a thermal
decomposition reactor to decompose an oligomer of acrylic acid in
the liquid, and the obtained acrylic acid is recovered in a
purification step, wherein from the liquid to be supplied to the
thermal decomposition reactor or from the liquid recovered from the
thermal decomposition reactor, maleic acid contained in the liquid
is precipitated and separated. e2. The process according to the
above e1, wherein the composition of the liquid to be supplied to
the thermal decomposition reactor or the liquid recovered from the
thermal decomposition reactor, is adjusted to become a solution
comprising at least 70 wt % of acrylic acid, from 1.6 to 28 wt % of
maleic acid and/or maleic anhydride and water having a molar ratio
of: Water Maleic .times. .times. acid + Maleic .times. .times.
anhydride .times. 2 .times. ( molar .times. .times. ratio )
.ltoreq. 1.0 ##EQU1## and maleic acid is precipitated at from 20 to
70.degree. C. within a range of from 0.5 to 5 hours, followed by
filtration and separation. e3. The process according to the above
e1 or e2, wherein at the time of the separation operation of maleic
acid, an aliphatic or aromatic hydrocarbon is added in a volume
ratio of from 1/2 to 4 times. e4. The process according to the
above e3, wherein the hydrocarbon to be added, is a solvent to be
used for collecting the acrylic acid-containing gas, or an
azeotropic agent to be used for dehydration distillation
purification of acrylic acid. f1. A method for installing a liquid
level meter in a case where a liquid level meter is installed at a
place where a liquid containing an easily polymerizable compound is
stored, in an installation for production of the easily
polymerizable compound, characterized in that a high pressure side
detection line of the liquid level meter is connected to a
discharge line for the liquid stored f2. The method according to
the above f1, wherein the connection angle .alpha. between the high
pressure side detection line and the liquid discharge line is from
5 to 90.degree.. f3. The method according to the above f1, wherein
the dimensional ratio D.sub.2/D.sub.1 is from 1 to 20 where D.sub.1
is the pipe diameter of the high pressure side detection line and
D.sub.2 is the pipe diameter of the liquid discharge line. f4. The
method according to the above f1, wherein the liquid discharge line
is connected to a distillation column, a reflux tank of the
distillation column, a decomposition reaction column, a thin film
evaporator, a column top gas condensed liquid tank, a vertical
storage tank, a horizontal storage tank or a tank. f5. The method
according to any one of the above f1 to f4, wherein the high
pressure side detection line and/or the low pressure side detection
line of the liquid level meter, is heated or warmed. f6. The method
according to any one of the above f1 to f5, wherein the high
pressure side detection line and/or the low pressure side detection
line of the liquid level meter, is connected with an inlet for a
gas and/or a liquid. f7. The method according to any one of the
above f1 to f6, wherein the easily polymerizable compound is
(meth)acrylic acid or its ester, and the liquid to be measured by
the liquid level meter, contains at least one member selected from
an acrylic acid dimer, .beta.-(meth)acryloxypropionic acid esters,
.beta.-alkoxypropionic acid esters, .beta.-hydroxypropionic acid
and .beta.-hydroxypropionic acid esters.
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] FIG. 1 shows an example of the production line by the
thermal decomposition reaction (the spiral flow is formed by a
return liquid to the decomposition reactor).
[0058] FIG. 2 shows an example of the production line by the
thermal decomposition reaction (the spiral flow is formed by the
raw material liquid supplied to the decomposition reactor).
[0059] FIG. 3 shows an example of the production line by the
thermal decomposition reaction (the spiral flow is formed by
stirring vanes).
[0060] FIG. 4 is a view showing the cross section in a horizontal
direction of the decomposition reactor A and the positional
relation for connection with the lines for forming the spiral
flow.
[0061] FIG. 5 is a view schematically showing a solid substance
accumulated at the bottom of the decomposition reactor A (a
cross-sectional view in the longitudinal direction of the
column).
[0062] FIG. 6 shows an example of the production line by the
thermal decomposition reaction.
[0063] FIG. 7(a) is a schematic cross-sectional view showing a
distillation column provided with flat plate disks and doughnuts,
suitable for carrying out the method for decomposing a byproduct
formed during the production of (meth)acrylic acids according to
the present invention.
[0064] FIG. 7(b) is an enlarged perspective view of the essential
portions of FIG. 7(a).
[0065] FIG. 8(a) is a schematic cross-sectional view showing a
distillation column provided with slanted plate disks and
doughnuts, suitable for carrying out the method for decomposing a
byproduct formed during the production of (meth)acrylic acids
according to the present invention.
[0066] FIG. 8(b) is an enlarged view of the essential portions of
FIG. 8(a).
[0067] FIG. 9 is an example of the flowchart for production of
acrylic acid and an acrylic ester.
[0068] FIG. 10 is another example of the flowchart for production
of an acrylic ester.
[0069] FIG. 11 is a flowchart for decomposition of a high boiling
liquid.
[0070] FIG. 12 is a view showing the entire installation wherein
the method for installing a liquid level meter of the present
invention is applied to a (high boiling material) decomposition
reaction column and a top gas-cooled liquid tank in the production
of acrylic acid.
[0071] FIG. 13 is a partially enlarged view showing a liquid level
meter installed on the (high boiling material) decomposition
reaction column of FIG. 11.
[0072] FIG. 14 is a partially enlarged view showing a liquid level
meter installed on the top gas-cooled liquid tank of FIG. 11.
EXPLANATION OF REFERENCE SYMBOLS
[0073] A: Decomposition reactor B: Bottom pump [0074] C: Heat
exchanger for heating D: Stirring means [0075] E: Deposition F:
Intermittent discharge control valve [0076] 1: High boiling
material supply line [0077] 2: Bottom liquid discharge line [0078]
2-1, 2-2: Residual liquid discharge lines [0079] 3: Supply line for
heat exchanger for heating [0080] 3-2: Return line for heating
[0081] 4: Reaction residue discharge line [0082] 5: Spiral
flow-forming return line [0083] 6: Valuable substance recovery line
[0084] 7: Heating medium supply line [0085] 8: Heating medium
discharge line [0086] 31, 33: Distillation columns [0087] 31D, 33D:
Bottoms discharge ports [0088] 32A, 34A: Disk trays 32B, 34B:
Doughnut trays [0089] 35: Distributor [0090] 41: Decomposition
reaction column 42,46: Pumps [0091] 43: Heat exchanger for heating
[0092] 44a: Column top gas line [0093] 44, 47: Heat exchangers 45:
Cooled liquid tank [0094] 6A: (High boiling material) decomposition
reaction column [0095] 6E: Column top gas-cooled liquid tank [0096]
H.sub.1, H.sub.2: Liquid level meters [0097] 62: Bottom liquid
discharge line [0098] 62a: Bottom liquid discharge short pipe
[0099] 62b: Bottom liquid discharge conduit [0100] 65: Bottom
liquid discharge line [0101] 65a: Bottom liquid discharge short
pipe [0102] 65b: Bottom liquid discharge conduit [0103] 11, 13:
High pressure side detection line [0104] 11a, 13a: High pressure
side detection short pipes [0105] 11b, 13b: High pressure side
detection conduits [0106] 12, 14: Low pressure side detection line
[0107] 12a, 14a: Low pressure side detection short pipe [0108] 12b,
14b: Low pressure side detection conduits [0109] .alpha.:
Connection angle between high pressure side detection line and
liquid discharge line
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment a
[0110] This Embodiment a has been accomplished on the basis of a
discovery that in a decomposition reaction of a Michael addition
product of acrylic acid or an acrylic ester, it is very effective
to make the liquid flow at the column bottom in the circumferential
direction in order to prevent accumulation of a solid substance at
the bottom of the decomposition reaction column and thereby to
avoid polymerization due to such accumulation.
1. (meth)acrylic Acid and (meth)acrylic Ester
[0111] The present invention can be applied to decomposition
treatment of a high boiling mixture (high boiling material)
obtained during production of (meth)acrylic acid or a (meth)acrylic
ester. For example, it can be applied to a process for producing
(meth)acrylic acid by vapor phase catalytic oxidation of propylene
or isobutylene in the presence of a Mo--Bi type composite oxide
catalyst to form acrolein or methacrolein, followed by vapor phase
catalytic oxidation in the presence of a Mo--V type composite oxide
catalyst. In such a case, the preliminary reaction to form mainly
acrolein or methacrolein by oxidizing propylene or the like and the
later reaction to form mainly (meth)acrylic acid by oxidizing
acrolein or methacrolein, may be carried out in separate reactors,
respectively, or such reactions may be carried out in one reactor
packed with both the catalyst for the preliminary reaction and the
catalyst for the later reaction. Further, the present invention is
also applicable to a process for producing acrylic acid by vapor
phase oxidation of propane by means of a Mo--V--Te type composite
oxide catalyst or a Mo--V--Sb type composite oxide catalyst.
Further, it is also applicable to a process for producing an
acrylic ester by reacting an alcohol to (meth)acrylic acid.
[0112] A high boiling mixture (high boiling material) obtained
after separating the desired product in these processes, is the
object to be decomposed by the present invention. As the acrylic
ester, a C.sub.1-8 alkyl or cycloalkyl ester may be mentioned. For
example, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl
acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate,
2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate or methoxyethyl
acrylate may be mentioned. Also with respect to a methacrylic
ester, esters similar to the above may be mentioned.
Michael Addition Product
[0113] The Michael addition product contained in the high boiling
material as the object to be decomposed by the present invention,
is one having an active hydrogen compound such as water, an alcohol
or (meth)acrylic acid ion-added to a carbon-carbon double bond of
(meth)acrylic acid or a (meth)acrylic ester. Specifically, the
Michael addition product in the case of producing acrylic acid,
may, for example, be an acrylic acid dimer (hereinafter the dimer),
an acrylic acid trimer (hereinafter the trimer), an acrylic acid
tetramer (hereinafter the tetramer) or .beta.-hydroxypropionic
acid, as illustrated below.
[0114] Dimer:
H.sub.2C.dbd.CH--C(.dbd.O)--O--CH.sub.2--CH.sub.2--C(.dbd.O)--OH
[0115] Trimer:
H.sub.2C.dbd.CH--C(.dbd.O)--O--CH.sub.2--CH.sub.2--C(.dbd.O)--O--CH.sub.2-
--CH.sub.2--C(.dbd.O)--OH
[0116] Tetramer:
H.sub.2C.dbd.CH--C(.dbd.O)--O--CH.sub.2--CH.sub.2--C(.dbd.O)--O--CH.sub.2-
--CH.sub.2--C (.dbd.O)--O--CH.sub.2--CH.sub.2--C(.dbd.O)--OH
[0117] .beta.-hydroxypropionic acid:
HO--CH.sub.2--CH.sub.2--C(.dbd.O)--OH
[0118] On the other hand, the Michael addition product in the case
of producing an acrylic ester, may, for example, be a Michael
addition product of acrylic acid to the above acrylic ester,
specifically a .beta.-acryloxypropionic ester (an ester of the
dimer); a Michael addition product of an alcohol, specifically an
ester of the dimer, the trimer or the tetramer,
.beta.-hydroxypropionic acid, a .beta.-hydroxypropionic esters or a
.beta.-alkoxypropionic esters.
[0119] .beta.-acryloxypropionic ester:
H.sub.2C.dbd.CH--C(.dbd.O)--O--CH.sub.2--CH.sub.2--C(.dbd.O)--OR
[0120] .beta.-alkoxypropionic ester:
RO--CH.sub.2--CH.sub.2--C(.dbd.O)--OR
[0121] Ester of the trimer:
H.sub.2C.dbd.CH--C(.dbd.O)--O--CH.sub.2--CH.sub.2--C(.dbd.O)--O--CH.sub.2-
--CH.sub.2--C(.dbd.O)--OR
[0122] .beta.-hydroxypropionic ester:
HO--CH.sub.2--CH.sub.2--C(.dbd.O)--OR
[0123] .beta.-hydroxypropionic acid:
HO--CH.sub.2--CH.sub.2--C(.dbd.O)--OH
[0124] Also with respect to methacrylic acid and a methacrylic
ester, substantially the same as the above will apply. Only the
difference is that as a result of substitution of hydrogen at the
.alpha.-position for a methyl group, propionic acid (ester) becomes
isobutyric acid (ester).
[0125] The high boiling material to be supplied to the
decomposition reactor is a high boiling mixture containing the
above Michael addition product. The content of the Michael addition
product may vary to a large extent by the production process.
However, it is common to employ a high boiling material containing
a Michael addition product in an amount of from 1 to 90 wt %,
preferably from 2 to 70 wt %. The high boiling material also
contains a compound by-produced in the step of producing
(meth)acrylic acids or a material to be used as an assisting agent
in the process. Specifically, (meth)acrylic acid, (meth)acrylic
esters, maleic acid, maleic acid esters, furfural, benzaldehyde,
polymers, oligomers, alcohols to be used as materials for producing
esters, or polymerization inhibitors, specifically, copper
acrylate, copper dithiocarbamate, a phenol compound or a
phenothiazine compound, may, for example, be mentioned.
[0126] The copper dithiocarbamate may, for example, be a copper
dialkyldithiocarbamate such as copper dimethyldithiocarbamate,
copper diethyldithiocarbamate, copper dipropyldithiocarbamate or
copper dibutyldithiocarbamate, a copper cyclic
alkylenedithiocarbamate such as copper ethylenedithiocarbamate,
copper tetramethylenedithiocarbamate, copper
pentamethylenedithiocarbamate or copper
hexamethylenedithiocarbamate, or a copper cyclic
oxydialkylenedithiocarbamate such as copper
oxydiethylenedithiocarbamate.
[0127] The phenol compound may, for example, be hydroquinone,
methoxyhydroquinone (methoquinone) pyrogallol, resorcinol, phenol
or cresol. The phenothiazine compound may, for example, be
phenothiazine, bis-(.alpha.-methylbenzyl)phenothiazine,
3,7-dioctylphenothiazine or
bis(.alpha.-dimethylbenzyl)phenothiazine. In some cases, materials
other than the above-mentioned may be contained depending upon the
process, without adversely affecting the present invention.
Process for Producing (meth)acrylic Acids
[0128] The above-mentioned high boiling material may, for example,
be obtained via a purification step such as extraction or
distillation after contacting a (meth)acrylic acid-containing gas
obtained by vapor phase catalytic oxidation of propylene or
acrolein, with water or an organic solvent to collect (meth)acrylic
acid in the form of a solution. The process for producing a
(meth)acrylic ester, for example, comprises an esterification
reaction step of reacting (meth)acrylic acid with an alcohol in the
presence of an organic acid or a cationic ion exchange resin or the
like, as a catalyst, and a purification step of carrying out
extraction, evaporation or distillation as a unit operation to
concentrate the crude (meth)acrylic ester solution obtained by the
reaction. Each unit operation is suitably selected depending upon
the raw material ratio of (meth)acrylic acid to the alcohol in the
esterification reaction, the type of the catalyst to be used for
the esterification reaction or the physical properties of the raw
materials, reaction byproducts, etc.
Flowchart for the Thermal Decomposition Reaction of the High
Boiling Material
[0129] The description will be made with reference to the drawings.
FIG. 1 is an example of the production line by the thermal
decomposition reaction of the present invention. The high boiling
material is supplied via a line 1 to a decomposition reactor A. The
supply to the decomposition reactor A may be carried out
continuously or intermittently (semi-continuously), but continuous
supply is preferred. A valuable substance formed in the
decomposition reactor and a part of materials constituting the high
boiling material will be continuously withdrawn in a gas state from
the recovery line 6 and will be returned to the production process,
as it is in the gas state or as cooled in a liquid state. In a case
where the decomposition reactor A is a column type reactor, a part
of the cooled liquid may be returned as a reflux liquid to the top
of the decomposition reactor.
[0130] The residual liquid will be withdrawn via a residual liquid
discharge line 2 and the bottom pump B, and a part thereof is
supplied to a heat exchanger C for heating via a line 3 and
returned to the decomposition reactor A. The rest will be
discharged out of the system via a line 4. The relation between the
return liquid amount and the discharge amount may suitably be set
depending upon various factors such as the heat balance at the heat
exchanger for heating and the retention time at the decomposition
reactor. The flow in the circumferential direction (hereinafter
sometimes referred to as a spiral flow) in the decomposition
reactor of the present invention is formed by the return liquid of
the line 5 in FIG. 1. The line 5 is disposed in the tangent
direction of the main body of the decomposition reactor, and the
spiral flow will be formed in the reactor by the flow of the liquid
supplied from the line 5. The return liquid amount of the line 5 is
usually selected within a range of from 0.2 to 5 times by weight,
based on the amount of the raw material supplied from the line 1.
If the return liquid amount is less than the above range, an
adequate spiral flow tends to be hardly formed. The return liquid
for heating, flowing through the line 3-2, is not related to
formation of the spiral flow, and its flow rate is determined
depending upon e.g. a heat balance.
[0131] FIG. 2 is one wherein the flow in the circumferential
direction is made by the raw material liquid supplied to the
decomposition reactor, and such is carried out by the line 1. The
line 1 is disposed in a tangent direction of the main body of the
decomposition reactor, and the spiral flow will be formed in the
reactor by the raw material liquid supplied from the line 1. In
this case, the line 1 is required to be controlled so that the
liquid surface will be below the liquid surface of the reaction
liquid retained in the decomposition reactor.
[0132] FIG. 3 is an example of an apparatus to form the spiral flow
in the decomposition reactor by means of stirring vanes.
[0133] The high boiling material is supplied from the line 1 to the
decomposition reactor A. a valuable substance and a part of
materials constituting the high boiling material, decomposed in the
decomposition reactor A will be withdrawn from a recovery line 6
and will be returned to the production process in a gas state or as
cooled in a liquid state. In a case where the decomposition reactor
A is a column type reactor, the part of cooled liquid may be
returned as a reflux liquid to the top of the decomposition
reactor. The residual liquid will be discharged from the line 4 out
of the system. The heat medium supply line 7 and the heat medium
discharge line 8 are exemplary, and depending upon the type of the
heat medium, the positions of the supply line and the discharge
line may be changed.
[0134] The flow in the circumferential direction (the spiral flow)
in the decomposition reactor of the present invention is carried
out by the residual liquid-stirring means D in FIG. 3. The stirring
means D comprises stirring vanes, a stirring shaft and a motor for
stirring, whereby the internal liquid of the decomposition reactor
is capable of forming a liquid flow in the circumferential
direction. The rotational speed of the stirring vanes is usually
suitably selected depending upon the shape or the diameter of the
vanes, so that the forward end speed of the vanes will be usually
from 0.2 to 5 m/sec. The residual liquid forming the spiral flow
will be withdrawn from the residual liquid discharge line 2-1 or
2-2. The residual liquid discharge line 2-1 represents an example
wherein it is disposed in a tangent direction of the main body of
the decomposition reactor, and the residual liquid discharge line
2-2 represents an example wherein it is disposed at the center
portion of the decomposition reactor. In the case of the discharge
line 2-1, together with the stirring effect of the vanes, a good
spiral flow may be maintained.
[0135] FIG. 4 is a view showing the cross section of the
decomposition reactor A and the positional relation of connection
with the spiral flow-forming lines. The line 5 (spiral flow-forming
return line 5) in FIG. 1 or the line 1 (high boiling
material-supply line 1) in FIG. 2, is disposed in a tangent
direction of the main body of the decomposition reactor, whereby a
flow in the circumferential direction (a spiral flow) can be formed
within the decomposition reactor. Further, the residual liquid
discharge line 2-1 in FIG. 3 is disposed in a tangent direction of
the main body of the decomposition reactor, whereby together with
the stirring effect of vanes, a good spiral flow can be
maintained.
[0136] FIG. 5 is a view (column longitudinal cross-sectional view)
schematically showing a solid substance accumulated at the bottom
of the decomposition reactor A. If the left and right accumulated
products are joined, the discharge port will be in a clogged state,
whereby withdrawal of the bottom liquid will be impossible, and the
bottom pump B may undergo cavitation.
Decomposition Reaction of the High Boiling Material
[0137] The Michael addition product contained in the high boiling
material can be decomposed to a monomer containing (meth)acrylic
acid as the main component. In a case where a (meth)acrylic ester
is contained in the high boiling material, it may be hydrolyzed to
(meth)acrylic acid and an alcohol, or may be recovered as it is in
the form of an ester without decomposition, depending upon the
conditions.
[0138] The temperature for the decomposition reaction is adjusted
to from 110 to 250.degree. C., preferably from 120 to 230.degree.
C. In FIG. 1, the high boiling material is heated in the heat
exchanger C for heating, and the temperature is controlled. Other
than the one where a heater is installed outside the decomposition
reactor A, as shown in FIG. 1, an inner coil type heater installed
in the decomposition reactor or a jacket type heater installed
around the decomposition reactor, is, for example, available, and a
heating device of any type may be used.
[0139] The retention time for the decomposition reaction varies
depending upon the composition of the high boiling material, the
presence or absence of the catalyst and the decomposition reaction
temperature. In a case where the decomposition reaction temperature
is low, it is a relatively long time, such as from 10 to 50 hours,
and in a case where the decomposition reaction temperature is high,
it is from 30 minutes to 10 hours. The reaction pressure may be
either under a reduced pressure condition or under an atmospheric
pressure condition.
[0140] The decomposition reaction can be carried out by using only
the high boiling material as the object. However, for the purpose
of accelerating the decomposition reaction, it may be carried out
in the presence of an acid catalyst or in the presence of water. As
the catalyst for the decomposition reaction, an acid or a Lewis
acid, such as sulfuric acid, phosphoric acid, methanesulfonic acid,
paratoluenesulfonic acid or aluminum chloride, is mainly used. The
catalyst and/or water may preliminarily be mixed with the high
boiling material, or may be supplied to the decomposition reactor A
separately from the high boiling material. In a case where a
polymer, a polymerization inhibitor, a catalyst, etc. are contained
in the high boiling material, they will usually remain and be
concentrated in the decomposition residue without being
decomposed.
Structure of the Decomposition Reactor
[0141] The structure of the decomposition reactor A may be any
structure such as a column type or a tank type. In the case of a
column type reactor, trays or packing materials which are commonly
used in a distillation column, may be installed as a content,
whereby not only the decomposition reaction but also a distillation
operation can be carried out, such being preferred. As the packing
material, a regular packing material such as SULZER PACKING
manufactured by SULZER BROTHERS LTD., SUMITOMO SULZER PACKING or
MELLAPACK manufactured by SUMITOMO HEAVY INDUSTRIES, LTD., GEMPAK
manufactured by GLITSCH, MONTZ PACK manufactured by MONTZ, GOODROLL
PACKING manufactured by TOKYO TOKUSHU KANAAMI K.K., HONEYCOMB
PACKING manufactured by NGK INSULATORS, LTD. or IMPULSE PACKING
manufactured by NAGAOKA INTERNATIONAL CORPORATION, may, for
example, be used.
[0142] As an irregular packing material, INTALOX SADDLE
manufactured by NORTON, TELLERETTE manufactured by Nittetu Chemical
Engineering Ltd., PALL RING manufactured by BASF, CASCADE MINI-RING
manufactured by MASS TRANSFER or FLEXIRING manufactured by JGC
CORPORATION, may, for example, be mentioned. Any one of such
packing materials may be used, or more than one of them may be used
in combination.
[0143] The trays may, for example, be bubble cap trays, perforated
plate trays, bubble trays, superflux trays or max flux trays having
a downcomer or dual trays or disk and doughnut type trays having no
downcomer. The trays or the packing materials may be used in
combination, or no such content may be present in the decomposition
reactor.
[0144] In the present invention, the liquid flow in the
circumferential direction (the spiral flow) is one which is
generated forcibly, and such can be carried out by supplying the
high boiling material or the return liquid of bottoms (the bottom
liquid) from a tangent direction of the reactor. In a case where a
supply inlet from a tangent direction is not present, the spiral
flow is formed by stirring vanes provided in the reactor. In some
cases, both means may be used in combination.
[0145] In the case of a tank type reactor provided with stirring
vanes, a baffle may be provided, as the case requires. The stirring
vanes may be of any type so long as they are capable of generating
a circumferential flow. Specifically, anchor vanes, (at least one
stage) multistage paddle vanes, (at least one stage) multistage
inclined paddle vanes, lattice vanes, MAXBLEND vanes (tradename,
manufactured by SUMITOMO HEAVY INDUSTRIES, LTD.), FULLZONE VANES
(tradename, manufactured by SHINKO PANTEC CO., LTD., etc. may be
mentioned, and at least one type may be used in at least one stage.
FULLZONE VANES are such that radial flow type vanes are attached in
two stages in a rotation axis direction on a rotational shaft
installed vertically at the center of the reactor, and vanes
adjacent in the rotational axis direction are in a positional
relation to the rotational axis direction such that their phases
are displaced from each other by not more than 90.degree., and the
lowest portion of the upper stage one of the vanes adjacent in the
rotational axis direction, is located below the highest portion of
the lower stage one (see JP-A-7-33804). Particularly preferred as
stirring vanes, are anchor vanes, lattice vanes or FULLZONE
VANES.
[0146] With respect to baffle plates (hereinafter baffles)
installed together with stirring vanes, there is no restriction in
the present invention. Any type may be employed, or no baffles may
be installed. Specifically, a rod type, a plate type, a comb type
may, for example, be mentioned, and at least one type and at least
one member may be installed. It is particularly preferred to
install one rod type or one plate type.
Discharge of the Residue of the Decomposition Reactor
[0147] The decomposition residue may be discharged from the
decomposition reactor by a suitable method. The bottom discharge
position of the decomposition reactor may be at any place so long
as it is the bottom end portion of the column. It is preferably
within a range of 1/2 of the column diameter from the lowest
portion of the bottom. If it is located above the end portion, a
solid substance will be accumulated at the end portion. The residue
is stored in e.g. a tank and then recycled to incineration
treatment or a production process. On the other hand, acrylic acid,
methacrylic acid, an alcohol, etc. as decomposition products of the
Michael addition product or the ester will be continuously
discharged from the top (the column top) of the decomposition
reactor. They are led to a purification system or recycled to a
suitable position in the production process.
Embodiment b
[0148] This Embodiment b has been accomplished on the basis of a
discovery that the decomposition reaction of the Michael addition
product of (meth)acrylic acids can be carried out without clogging
for a long time, by pulse discharge i.e. intermittent discharge of
the bottom liquid instead of continuous discharge from the bottom
of the reactor. The reason as to why clogging can effectively be
prevented, is not clearly understood. However, from the
experimental facts, the present inventors consider that the
clogging in a pipe under a constant flow, will be disturbed by the
liquid flow by intermittent flowing, and due to the disturbing
effect of the liquid flow, the clogging can extremely effectively
be suppressed in spite of the fact that the liquid flow will be
temporarily stopped.
[0149] "(Meth)acrylic acid and (meth)acrylic ester", "Michael
addition product" and "Process for producing (meth)acrylic acids"
are the same as in the case of Embodiment a.
Flowchart for the Production Line by Thermal Decomposition Reaction
of the High Boiling Material
[0150] FIG. 6 is an example of the production line by the thermal
decomposition reaction of the present invention, which is the same
as in the case of Embodiment a except that C represents a heat
exchanger for heating, F an intermittent discharge control valve,
and 3 a supply line for the heat exchanger for heating.
[0151] The high boiling material is supplied to a decomposition
reactor A from a line 1. The supply to the decomposition reactor A
may be carried out continuously or intermittently
(semicontinuously), but continuous supply is preferred. A valuable
substance and a part of materials constituting the high boiling
material, formed in the decomposition reactor is continuously
withdrawn in a gas state from a recovery line 6 and returned to the
production process, as it is in a gas state or as cooled in a
liquid state. In a case where the decomposition reactor A is a
column type reactor, a part of the cooled liquid may be returned as
a reflux liquid to the top of the decomposition reaction column.
The bottom liquid is withdrawn from the line 2, and via a pump B, a
part is supplied to a heat exchanger C for heating and returned to
the decomposition reactor A. The rest will be discharged out of the
system from the line 4 via an intermittent discharge control valve
D as the gist of the present invention. Reference numeral 5
represents a transport pipe to a storage tank.
[0152] "Decomposition reaction of the high boiling material" and
"Structure of the decomposition reactor" are the same as in the
case of Embodiment a.
Intermittent Discharge
[0153] In Embodiment b, the most significant feature is that the
decomposition residue is intermittently discharged from the
decomposition reactor. The intermittent discharge is carried out by
an intermittent discharge control valve D. The closing time of the
valve D is usually from 5 seconds to 5 minutes, preferably from 10
seconds to 2 minutes, and the opening time of the valve D is
usually from 2 seconds to 5 minutes, preferably from 3 seconds to 2
minutes. The opening ratio of the control valve D (percentage of
opening time/(opening time+closing time)) is preferably within a
range of from 2 to 50%, more preferably from 5 to 30%. If the
closing time is shorter and the opening time is longer than the
above range, the clogging suppression effect may not sufficiently
be obtained due to an inertia of the flow of the decomposition
residue. If the closing time is long and the opening time is short,
clogging of the pipeline is likely to take place due to an
influence of the static state of the liquid in the piping, such
being undesirable. In the continuous discharge (opening rate:
100%), clogging of the pipe will take place as is evident also from
a Comparative Example hereinafter.
[0154] On the other hand, acrylic acid, methacrylic acid, an
alcohol, etc. as decomposition products of the Michael addition
product or the ester, will be continuously discharged from the top
of the decomposition reactor (column top). They will be led to a
purification system, or may be recycled to an appropriate position
of the production process.
Embodiment c
[0155] In Embodiment c, as trays for the distillation column, disk
and doughnut type trays are used, whereby problems of adhesion,
deposition and accumulation of the solid substance have been
solved. Namely, disk and doughnut type trays are such that disk
trays and doughnut trays are alternately installed with a suitable
distance, and as shown in FIGS. 7 and 8, the structure is very
simple, and the opening is extremely large, whereby a solid
substance is hardly precipitated or accumulated, whereby it is
possible to solve the problems of adhesion, deposition and
accumulation of the solid substance.
[0156] Accordingly, by using a distillation column equipped with
disk and doughnut type trays, decomposition of the byproduct and
recovery of a valuable substance during the production of
(meth)acrylic acids, can be carried out constantly. The disk and
doughnut type trays have a structure which is extremely simple.
Accordingly, as compared with a distillation column employing
conventional trays or packing material, there is a merit such that
the production cost of the distillation column and construction
costs such as installation costs, can be very low.
[0157] Now, a practical embodiment of the method for decomposing
the byproduct formed during production of (meth)acrylic acids
according to Embodiment c will be described in detail. Firstly,
with reference to FIGS. 7 and 8, the construction of a distillation
column equipped with disk and doughnut type trays suitable for
Embodiment c will be described. FIG. 7(a) is a schematic
cross-sectional view showing a distillation column equipped with
flat plate type disks and doughnuts, and FIG. 7(b) is an enlarged
perspective view of the essential portions of FIG. 7(a). Further,
FIG. 8(a) is a schematic cross-sectional view showing a
distillation column equipped with sloping plate type
disk-and-doughnut trays, and FIG. 8(b) is an enlarged view of the
essential portions of FIG. 8(a).
[0158] The disk-and-doughnut type trays are such that a plurality
of disk-shaped trays and doughnut-shaped trays are alternately
disposed with a suitable distance in the distillation column, and
in distillation column 31 in FIG. 7, flat plate type disk-shaped
trays 32A and doughnut-shaped trays 32B are alternately disposed in
the column. Whereas, in the distillation column 3 in FIG. 8,
sloping plate type disk-shaped trays 34A and doughnut-shaped trays
34B slanted in the liquid flow direction, are alternately disposed.
In the distillation columns 31 and 33 in FIGS. 7 and 8, 31A and 33A
are liquid inlets, and 31B and 33B are vapor inlets. Further, 31C
and 33C are vapor outlets, and 31D and 33D are bottom liquid
outlets. 35 in FIG. 8 is a distributor (dispersing device).
[0159] The distance between the disk-shaped trays 32A and 34A and
the doughnut-shaped trays 32B and 34B (L in FIGS. 7 and 8) is
preferably at least 250 mm in order to suppress entrainment. If
this distance L is excessively large, the height of the
distillation column will have to be increased, and therefore, it is
preferably at most 500 mm.
[0160] The plan view-shape of the disk-shaped tray 32A or 34A is
preferably a perfect circle, and its center is preferably located
at the center of the distillation column. Likewise, the plan
view-shape of the doughnut-shaped tray 32B or 34B is preferably a
perfect circular ring, and the outer periphery of the
doughnut-shaped tray 32B or 34B is preferably closely in contact
with the inner wall of the distillation column 31 or 33.
[0161] The diameter of the disk-shaped tray 32A or 34A (D.sub.1 in
FIGS. 7 and 8) and the diameter of the opening of the
doughnut-shaped tray 32B or 34B (D.sub.2 in FIGS. 7 and 8)
(hereinafter sometimes referred to as "inner diameter") are
suitable selected within a range of from 55 to 74% of the inner
diameter of the distillation column 31 or 33. This size corresponds
to a range of from 30 to 55% as represented by the open area ratio
in the distillation column 31 or 33.
[0162] In order to avoid short path (short circuit) of the down
flow of the liquid in the distillation column 31 or 33, the
diameter D.sub.1 of the disk-shaped tray 32A or 34A is preferably
slightly larger than the inner diameter D.sub.2 Of the
doughnut-shaped tray 32B or 34B.
[0163] With respect to the shape of trays, simple flat plate type
trays 32A and 32B as shown in FIG. 7 are preferred. However, as
shown in FIG. 8, with trays 34A and 34B slightly slanted to the
liquid flow direction, it is possible to further suppress
accumulation of a solid substance. The sloping angle in such a case
is not particularly limited, but it is usually preferably set
within a range of from 5 to 45.degree. against a horizontal
direction.
[0164] A method of installing the disk-shaped trays 32A and 34A and
the doughnut-shaped trays 32B and 34B in the distillation columns
31 and 33 may be any method. It may, for example, be a method of
fixing them by means of supports extended from the walls of the
distillation columns, a method of welding them to the walls of the
distillation column, or a method wherein the respective disk-shaped
trays and doughnut-shaped trays are entirely fixed to a vertical
support and mounted in the distillation columns in the form of an
integral structure.
[0165] The number of plates of the disk-shaped trays and
doughnut-shaped trays to be installed in the distillation column is
not particularly limited and is suitably selected so that the
separation performance required for the particular process, can be
obtained. If the plate number is too small, the distillation amount
of the high boiling component tends to be large, and the recycling
amount will increase, and the treating ability of the decomposition
reactor will decrease, such being undesirable. On the other hand,
if the plate number is increased more than necessary, not only the
construction costs will increase, but also the distillation
concentration, at the top, of the polymerization inhibitor
contained in the raw material liquid decreases, whereby an
undesirable polymerization reaction of the distillate is likely to
take place, such being undesirable. Accordingly, the disk-shaped
trays and doughnut-shaped trays to be installed, are preferably
selected within a range of from 5 to 20 plates (for this plate
number, one disk-shaped tray or doughnut-shaped tray will be taken
as one plate).
[0166] (Meth)acrylic acid in Embodiment c is preferably one
obtained by a catalytic vapor phase oxidation reaction of propane,
propylene, acrolein, isobutylene, t-butyl alcohol or the like, and
a gaseous oxidation reaction product is rapidly cooled and quenched
with water. Then, separation of water and (meth)acrylic acid is
carried out by an azeotropic distillation method employing an
azeotropic solvent or by an extraction method employing a solvent.
Further, low boiling compounds such as acetic acid are separated,
and then a heavy component such as the Michael addition product is
separated to obtain high purity (meth)acrylic acid. Otherwise,
water and acetic acid may be separated simultaneously by means of
an azeotropic agent. The above-mentioned Michael addition product
will be concentrated in the high boiling fraction, and it is
preferred that this fraction, i.e. usually the bottom liquid of a
fractionating column, is mixed with the byproduct formed during
production of a (meth)acrylic ester, so that they are treated all
together.
[0167] The (meth)acrylic ester in Embodiment c is not particularly
limited and may, for example, be methyl (meth)acrylate,
ethyl(meth)acrylate, n-butyl (meth)acrylate, i-butyl(meth)acrylate,
n-hexyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, n-octyl
(meth)acrylate, methoxyethyl(meth)acrylate, i-nonyl (meth)acrylate
or i-decyl(meth)acrylate.
[0168] The Michael addition product is a byproduct to be formed in
a reaction step or a purification step in the production of
(meth)acrylic acid and a (meth)acrylic ester, and it is a compound
having (meth)acrylic acid, acetic acid, an alcohol or water
Michael-added at the .alpha.- or .beta.-position of a compound
having a (meth)acryloyl group present in such a production process.
The compound having a (meth)acryloyl group present in the
production process, may, for example, be (meth)acrolein, a
(meth)acrylic acid, a carboxylic acid having a (meth)acryloyl
group, such as a .beta.-acryloxypropionic acid or a
.beta.-methacryloxyisobutyric acid (hereinafter both may generally
be referred to as the dimer) having (meth)acrylic acid Michael
added to such (meth)acrylic acid, a (meth)acrylic acid trimer
(hereinafter the trimer) having (meth)acrylic acid Michael-added to
such a dimer, or a (meth)acrylic acid tetramer (hereinafter the
tetramer) having (meth)acrylic acid Michael-added to such a trimer,
or the corresponding (meth)acrylic ester having such a carboxylic
acid having a (meth)acryloyl group esterified with an alcohol.
Further, likewise, one having (meth)acrylic acid Michael-added to
(meth)acrolein may also be contained. Specifically, the Michael
addition product of the present invention includes
.beta.-acryloxypropionic acid or .beta.-methacryloxyisobutyric
acid, and its ester and aldehyde compound (.beta.-acryloxypropanal
or .beta.-methacryloxyisobutanal), a .beta.-alkoxypropionic acid
and its ester, .beta.-hydroxypropionic acid or
.beta.-hydroxyisobutyric acid, and their esters and aldehyde
compounds, as well as dimers, trimers, tetramers, etc., and their
.beta.-acryloxy compounds, .beta.-acetoxy compounds, .beta.-alkoxy
compounds and .beta.-hydroxy compounds. Further, a compound having
acetic acid Michael-added to a (meth)acryloyl group, is present
although it may be in a very small amount.
[0169] In Embodiment c, as a method for producing a (meth)acrylic
ester, it is common to employ a method of reacting an alcohol to
(meth)acrylic acid for esterification, or a method for producing an
acrylic ester of a higher alcohol, by reacting an acrylic ester of
a lower alcohol with a higher alcohol for transesterification.
Further, the production process may be either a batch system or a
continuous system. As a catalyst for such esterification or
transesterification, an acid catalyst is usually employed.
[0170] The process for producing a (meth)acrylic ester preferably
comprises the reaction step and a purification step for carrying
out washing, extraction, evaporation, distillation or the like as a
unit operation to carry out separation of the catalyst,
concentration, purification, etc. of the crude (meth)acrylic ester
obtained in such a reaction step. The starting material molar ratio
of the (meth)acrylic acid or the (meth)acrylic ester to the alcohol
in the reaction step may suitably be selected depending upon the
type and amount of the catalyst to be used for the reaction, the
reaction system, the reaction conditions, or the type of the
alcohol used as the raw material.
[0171] The Michael addition product by-produced mainly by the
reaction will be concentrated at the bottom of the distillation
column (the fractionating column) to separate a high boiling
fraction. Accordingly, in the present invention, this bottom liquid
is, as the object to be treated, subjected to thermal decomposition
together with the byproduct from the previous (meth)acrylic acid
production step, and the obtained useful component will be
recovered for the reaction step for (meth)acrylic ester or a
purification step.
[0172] Here, the distillation column to separate the high boiling
fraction may vary depending upon the type of the (meth)acrylic
ester to be produced or the process to be used, but usually, it is
one to separate (meth)acrylic acid and the high boiling fraction,
or one to separate a (meth)acrylic ester and the high boiling
fraction, or one to separate (meth)acrylic acid, an alcohol and a
(meth)acrylic ester, and the high boiling fraction. The present
invention can be applied to all of them.
[0173] In the bottom liquid of the high boiling fraction-separation
column, the above-mentioned Michael addition product is
concentrated, but in addition, substantial amounts of (meth)acrylic
acid and/or a (meth)acrylic ester are contained, and further, high
boiling components such as a polymerization inhibitor used in the
process, an oligomer or polymer formed in the process, high boiling
impurities in the raw material or their reaction products, are
contained. Further, in some cases, the catalyst used for the
esterification or transesterification step may be contained.
[0174] As mentioned above, the Michael addition product by-produced
during the step for producing (meth)acrylic acid will usually be
concentrated at the bottom of a distillation column (fractionating
column) for separating the product of (meth)acrylic acid from the
heavy fraction. In this bottom liquid, a substantial amount of
(meth)acrylic acid is also contained, and further, the
polymerization inhibitor used in the process, the oligomer formed
in the process or high boiling components are also contained.
[0175] In Embodiment c, as the reactive distillation system wherein
the decomposition reaction of the Michael addition product and
distillation and recovery of the valuable substance are
simultaneously carried out, any system such as a continuous system,
a batch system, a semi-batch system or an intermittent discharge
system may be employed, but a continuous system is preferred.
Further, the type of the reactor may be any of a completely mixing
type stirring tank reactor, a circulation type completely mixing
tank reactor or a simple hollow reactor, without being restricted
to any particular type.
[0176] As the catalyst, a known Lewis acid or Lewis base catalyst
may be used, but simple thermal decomposition employing no catalyst
may be used. As conditions for the decomposition reaction, the
temperature is usually from 120 to 280.degree. C., preferably from
140 to 240.degree. C., and the liquid retention time based on the
discharge liquid, is from 0.5 to 50 hours, preferably from 1 to 20
hours. With respect to the reaction pressure, a condition is
preferably selected so that the majority of (meth)acrylic acid, the
(meth)acrylic ester, the alcohol, etc. to be recovered, will be
distilled at the reaction temperature.
[0177] In Embodiment c, a distillation column provided with
disk-and-doughnut type trays as shown in FIG. 7 or 8 is installed
to the reactor to carry out the reactive distillation. This
distillation column portion may be a column directly connected to
the reactor, or an independent column of a system which is
connected to a vapor piping from the reactor and a liquid supply
piping from a distillation column, and thus the system is not
particularly limited. Further, the heating system for the reactive
distillation is not particularly limited and may be a coil type in
the reactor, an internal multitubular heat exchanger type, an
external jacket type or an external heat exchanger type.
[0178] In a case where the reactive distillation is carried out in
a continuous system, the raw material may be supplied to the
distillation column portion or the reactor portion at the bottom,
but it is preferred to supply it to the distillation column
portion.
[0179] Further, in the present invention, the byproduct formed
during production of (meth)acrylic acid containing the Michael
addition product, and the byproduct formed during production of a
(meth)acrylic ester, may separately be subjected to thermal
decomposition treatment, or they may be mixed and subjected to
thermal decomposition treatment.
Embodiment d
[0180] Embodiment d is one wherein oxygen or an oxygen-containing
gas is supplied directly to the distillate containing the
decomposition product formed by the decomposition reaction of the
above byproduct and one to suppress polymerization of an easily
polymerizable compound in the decomposition product by the action
of such oxygen. As a result of various studies, it has been is
found that polymerization of the easily polymerizable compound in
the decomposition product can be sufficiently suppressed by the
addition of such oxygen or an oxygen-containing gas. This is
considered to be attributable to the fact that the oxygen added
will increase the polymerization-suppressing effect of the
polymerization inhibitor usually contained in the raw material for
the decomposition reaction.
[0181] In Embodiment d, the (meth)acrylic ester is not particularly
limited, but ones similar to those disclosed in Embodiment c may be
mentioned. Further, with respect to the Michael-addition product,
ones similar to those disclosed in Embodiment c may be
mentioned.
[0182] The feed liquid (hereinafter sometimes referred to as the
high boiling liquid) to be supplied to the reaction decomposition
column also contains substances used or generated in the process
for producing acrylic acid or acrylic esters. Specifically, they
are acrylic acid, acrylic esters, maleic acid, maleic acid esters,
furfural, benzaldehyde, polymers, oligomers, alcohols to be used as
materials for production of esters, and a polymerization inhibitor
(copper acrylate, copper dithiocarbamate, a phenol compound, a
phenothiazine compound, etc.).
[0183] The above copper dithiocarbamate may be ones similar to
those disclosed in Embodiment a. Further, the above phenol compound
may be ones similar to those disclosed in Embodiment a.
[0184] Substances other than the above may sometimes be contained
depending upon the process.
[0185] (Meth)acrylic acid in Embodiment d is the same as disclosed
in Embodiment c. Further, the method for producing a (meth)acrylic
ester in Embodiment d, for example, comprises a reaction step of
reacting an alcohol to (meth)acrylic acid for esterification by
using a cationic ion exchange resin as a catalyst, and a
purification step of carrying out washing, extraction, evaporation,
distillation or the like, to carry out separation of the catalyst,
concentration, purification, etc. of the crude acrylic ester
solution obtained in the reaction step. The raw material molar
ratio of the (meth)acrylic acid or the (meth)acrylic ester to the
alcohol in the reaction step, the type and amount of the catalyst
to be used for the reaction, the reaction system, the reaction
conditions, etc., are suitably selected depending upon the type of
the alcohol raw material. The Michael addition product by-produced
mainly in the esterification reaction step, will be concentrated as
a heavy fraction at the bottom of a reaction column for recovering
a variable component.
[0186] The byproduct formed during the production of acrylic acid
and the byproduct formed during the production of an acrylic ester
may be together decomposed.
[0187] In Embodiment d, any system of a continuous system, a batch
system, a semi-batch system or an intermittent discharge system,
may be employed for the reaction process to carry out the
decomposition reaction of the Michael addition product, but a
continuous system is preferred. Also the type of the reactor is not
particularly limited, and any type such as a flow tubular type
reactor, a thin film flowing down type reactor, a completely mixing
tank type stirring tank reactor or a circulation type completely
mixing tank type reactor, may be employed. To obtain useful
components contained in the decomposition reaction product, a
method of obtaining them by evaporation or distillation during the
reaction or a method of obtaining them by evaporation or
distillation after the decomposition reaction, may either be
employed. However, in order to obtain a high recovery rate, the
former reactive distillation system is preferred.
[0188] In the case where the reactive distillation system is
employed, the reaction pressure depends substantially on the
after-mentioned reaction temperature, and a pressure is employed
such that the majority of useful components such as acrylic acid,
an acrylic ester, an alcohol, etc., produced in the decomposition
reaction and contained in the raw material for the decomposition
reaction will be evaporated.
[0189] The catalyst may be selected from a Lewis acid, a Lewis
base, an inorganic acid such as sulfuric acid or phosphoric acid,
and an organic acid such as methanesulformic acid or
p-toluenesulfonic acid. Water may be supplied to the decomposition
reaction column so that decomposition may be carried out in the
coexistence of the high boiling fraction and water.
[0190] The concentration of the acid catalyst is preferably from
0.1 to 1.0 wt %, particularly preferably from 0.2 to 0.8 wt %,
based on the charged liquid.
[0191] The decomposition reaction temperature is preferably from
110 to 250.degree. C., particularly preferably from 120 to
230.degree. C. The liquid retention time based on the discharge
liquid is preferably from 0.5 to 50 hours. Further, in a case where
the decomposition reaction temperature is lower, it is preferably
from 10 to 50 hours, and in a case where the decomposition reaction
temperature is higher, it is preferably from 0.5 to 10 hours.
Further, in a case where the decomposition reaction is carried by a
continuous reaction, with respect to the reaction time, the liquid
retention time as calculated by the discharge liquid may be
regarded as the reaction time. For example, in a case where the
liquid capacity in the reactor is 500 L, and the discharge liquid
amount is 100 L/hr, the retention time will be 5 hours.
[0192] To the distillate from the decomposition reaction column,
oxygen or an oxygen-containing gas (hereinafter sometimes referred
to as oxygen or the like) is added to prevent its polymerization.
As the oxygen or the like, pure oxygen, a gas having oxygen diluted
with an inert gas, air, or a gas having air diluted with an inert
gas, may, for example, be employed. The inert gas may, for example,
be nitrogen, carbon dioxide, argon or neon. The addition of the
inert gas is to avoid formation of an explosive gas. The inert gas
is preferably present in an amount of from 3.76 to 18.05 times by
volume to oxygen, and in the case of air, the inert gas is
preferably present in an amount of from 0.3 to 3 times by volume to
air. From the viewpoint of costs, it is apparent that air is more
inexpensive than oxygen. The oxygen or the like is preferably added
in a proportion of from 0.0001 to 0.01 volume ratio, particularly
from 0.0005 to 0.005 volume ratio as calculated as oxygen to the
distilled gas.
[0193] Further, in the present invention, the addition of the
oxygen or the like to the distilled gas of the decomposition
reaction column, may be carried out to the line after discharge
from the decomposition reaction column, or the oxygen or the like
may be added to the top portion of the decomposition reaction
column where the distilled gas is substantially formed.
[0194] FIG. 11 is a flowchart showing the decomposition reaction
process. The high boiling liquid is supplied to a decomposition
reaction column 41 and thermally decomposed. Here, this
decomposition reaction column 41 may be provided with a stirrer to
stir the liquid in the column. Further, the decomposition reaction
column 41 may be provided with a jacket for heating employing steam
or an organic heat medium as the heat source.
[0195] The bottom liquid in the decomposition reaction column 41 is
withdrawn by a pump 42, and a part thereof is, via recycling line
43a, heated by a heat exchanger 43 for heating, and recycled, and
the rest is discharged out of the system.
[0196] The distillate formed by the decomposition reaction is
distilled from the top of the decomposition reaction column 41, and
after addition of oxygen or the like, via a column top gas line
44a, cooled and liquefied by a heat exchanger 44 and introduced
into a cooled liquid tank 5. Here, in a case where a reflux line is
provided, the cooled liquid tank 45 may be omitted. In FIG. 11, the
gas component in the cooled liquid tank 45 is led from the cooled
liquid tank 45 to a heat exchanger 7 and cooled, whereby a valuable
substance will be liquefied. The non-condensed gas will be supplied
to a valuable substance-recovery installation or a vacuum
installation (not shown). The liquid in the cooled liquid tank 45
is withdrawn via a pump 46, and a part thereof will be, after
adding a polymerizing inhibitor, recycled via the heat exchanger 44
to the cooled liquid tank 45, and the rest will be taken out as the
decomposition product. This decomposition product will be returned
to the process for producing acrylic acid or an acrylic ester, as
mentioned above.
[0197] In the decomposition reactor 41, trays or a packing
material, which is commonly used in a distillation column, may be
provided. In such a case, it will be operated as a decomposition
reactive distillation column. As the packing material, a regular
packing material such as SULZER PACKING manufactured by SULZER
BROTHERS LTD., SUMITOMO SULZER PACKING manufactured by SUMITOMO
HEAVY INDUSTRIES, LTD., MELLAPACK manufactured by SUMITOMO HEAVY
INDUSTRIES, LTD., GEMPAK manufactured by GLITSCH, MONTZ PACK
manufactured by MONTZ, GOODROLL PACKING manufactured by TOKYO
TOKUSHU KANAAMI K.K., HONEYCOMB PACKING manufactured by NGK
INSULATORS, LTD. or IMPULSE PACKING manufactured by NAGAOKA
INTERNATIONAL CORPORATION, or an irregular packing material such as
INTALOX SADDLE manufactured by NORTON, TELLERETTE manufactured by
Nittetu Chemical Engineering Ltd., PALL RING manufactured by BASF,
CASCADE MINI-RING manufactured by MASS TRANSFER or FLEXIRING
manufactured by JGC CORPORATION, may be mentioned. Any one of these
packing materials may be employed, or more than one type may be
used in combination.
[0198] The trays may, for example, be bubble cap trays, perforated
plate trays, bubble trays, superflux trays, max flux trays, etc.
having a downcomer, or dual trays, etc. having no downcomer. The
trays or the packing materials may be used in combination.
[0199] Further, no such a content may be provided in the
decomposition reaction column. In such a case, a distillation
column or the like may be installed, as the case requires.
[0200] In a case where a stirring means is provided in the
decomposition reaction column 41, the stirring vanes may be of any
type, and for example, they may be anchor vanes, (at least one
stage) multistage paddle vanes, (at least one stage) multistage
inclined paddle vanes, as special ones, MAXBLEND vanes
(manufactured by SUMITOMO HEAVY INDUSTRIES, LTD.), or FULLZONE
VANES (manufactured by SHINKO PANTEC CO., LTD.). More than one type
may be used in more than one stage i.e. in multistages.
Particularly preferred are anchor vanes or lattice vanes.
[0201] Baffle plates (baffles) to be installed together with the
stirring vanes may be of any type. Specifically, they may be of a
rod type, a plate type or a comb type, and more than one type, and
more than one baffle may be installed. It is particularly preferred
to install one rod type or one plate type. However, no baffle may
be provided.
[0202] The fraction rich in (meth)acrylic acid, a (meth)acrylic
ester and an alcohol, obtained by the decomposition reaction, is
recovered in its entire amount for the step for producing an
acrylic ester. The place where the recovered fraction is to be
recycled, is not particularly limited. However, it contains a small
amount of a light fraction, and accordingly, it is preferred to
recycle it to a place prior to the step of separating the light
fraction.
Embodiment e
[0203] The invention of this Embodiment e relates to a process for
recovering acrylic acid. Particularly, in a process which comprises
contacting acrylic acid containing maleic acid, particularly an
acrylic acid-containing gas obtained by a vapor phase catalytic
oxidation of propylene, with a solvent, to collect acrylic acid in
the form of an acrylic acid-containing solution, distilling off a
low boiling point component from the acrylic acid-containing
solution by azeotropic distillation or direct distillation, then
obtaining acrylic acid by fractionation, while thermally
decomposing an oligomer of acrylic acid contained in the bottoms of
a distillation column, and recovering acrylic acid and recycling it
to a purification step, it relates to a method for efficiently
removing maleic acid as an impurity from the liquid to be supplied
to the thermal decomposition reactor or from the distillate.
[0204] The invention of Embodiment e has been accomplished on the
basis of the discovery of the following fact by the present
inventors.
[0205] Maleic acid formed together with acrylic acid by the
oxidation reactor is present in the form of a dicarboxylic acid
having two carboxyl groups, in an aqueous solution, but in acrylic
acid, it may have a form of maleic anhydride having one molecule of
water dehydrated from its molecule. Maleic acid and maleic
anhydride are in an equilibrium state, and in the acrylic acid
solution to be supplied to the recovery apparatus of the thermal
decomposition reaction of an oligomer of acrylic acid, the
concentration of water as a low boiling point component is low,
whereby the equilibrium is substantially shifted to maleic
anhydride.
[0206] When water is added to such a liquid, a part of maleic
anhydride turns into maleic acid in correspondence with the amount
of water added.
[0207] In the column top liquid (or gas) of the thermal
decomposition reactor, water formed by the thermal decomposition of
3-hydroxypropionic acid, etc. is present, and a part of maleic
anhydride will be reacted with this water to form maleic acid.
[0208] For the equilibrium reaction, it takes sometime, and the
equilibrium will be accelerated by heating.
[0209] The solubility of maleic acid in acrylic acid is low as
compared with maleic anhydride, and maleic acid is likely to
undergo precipitation.
[0210] The degree of precipitation depends on the concentration of
maleic acid or water in the liquid and the operation temperature,
and by an addition of a water-insoluble solvent, precipitation will
be accelerated.
[0211] It is possible to facilitate precipitation and separation by
reducing the solubility by converting maleic anhydride to maleic
acid in the liquid to be supplied to the thermal decomposition
reactor for acrylic acid or in the recovered liquid from the
thermal decomposition reactor.
[0212] And, by such a method, circulation in the purification
system of maleic acid involved in the thermal decomposition and
recovery of an oligomer of acrylic acid formed in the step for
distillation and purification of the acrylic acid-containing
liquid, can easily be reduced by precipitation and solid-liquid
separation utilizing the chemical equilibrium of the acid and the
acid anhydride, whereby it is made possible to recover acrylic acid
without a problem of clogging by polymerization.
[0213] Now, Embodiment e will be described in detail with respect
to each of items "Thermal decomposition reactor", "Preparation of
acrylic acid solution", "Reaction of maleic acid", "Precipitation
operation", and "Separation of the precipitate".
Thermal Decomposition Reactor
[0214] The bottom liquid of the purification (product) column for
acrylic acid or the liquid obtained by concentrating and heating
the bottom liquid by a thin film evaporator or the like, is used as
the liquid to be supplied, and heat decomposition of an oligomer of
acrylic acid is carried out within a temperature range of from 120
to 220.degree. C. The step for the thermal decomposition reaction
and the step for separating the decomposed products may be carried
out in the same equipment such as a reactive distillation column,
or in separate equipments, such as a combination of a heating tank
and an evaporator. A catalyst may be used for the thermal
decomposition reaction. As a type of the catalyst, a compound
having a secondary or tertiary amino group, or a tertiary phosphine
may, for example, be mentioned. However, the catalyst is not
limited thereto. Otherwise, the decomposition reaction may be
carried out in the absence of any catalyst.
Preparation of Acrylic Acid Solution
[0215] The liquid to be supplied to the thermal decomposition
reactor or the recovered liquid from the thermal decomposition
reactor (the distillate) is to be treated.
[0216] The concentration of maleic acid or/and maleic anhydride in
the recovered liquid is within a range of from 1.6 to 28 wt %,
preferably from 2.5 to 25 wt %. If the concentration of maleic acid
is low, the precipitation tends to be difficult, and if the
concentration is too high, the loss of acrylic acid increases at
the time of separating the precipitated maleic acid.
[0217] The concentration of water is as follows in a molar ratio:
Water Maleic .times. .times. acid + Maleic .times. .times.
anhydride .times. 2 .ltoreq. 1.0 ##EQU2##
[0218] Particularly preferably, it is within a range of [maleic
anhydride].times.0.8.ltoreq.[water].ltoreq.[maleic
acid].times.0.5+[maleic anhydride]. If the concentration of water
is too high, the precipitation amount of maleic acid decreases, and
the time required for precipitation will be long.
[0219] The concentration of acrylic acid is at least 70 wt %. If it
is lower than this, the liquid nature will be different, and there
will be a case where the effect of the present invention can not be
obtained.
Reaction of Maleic Acid
[0220] In the solution, maleic acid and maleic anhydride are
present. As compared with maleic anhydride, maleic acid has a low
solubility in acrylic acid. Accordingly, the larger the ratio of
maleic acid/maleic anhydride in the solution, the more efficient
the removal by precipitation.
[0221] To accelerate formation of maleic acid by the reaction of
maleic anhydride with water, the liquid temperature may be raised
to from 50 to 70.degree. C. If the temperature is raised beyond
this range, the speed of the formation of an oligomer of acrylic
acid will be accelerated, whereby not only the efficiency for
heating, decomposition and recovery of the oligomer will decrease,
but also polymerization of acrylic acid is likely to take place,
such being undesirable.
[0222] The reaction tank to be used is not particularly limited.
However, it is preferably provided with a system to stir the
solution, such as stirring vanes or an external circulation by a
pump, in order to prevent polymerization in the tank.
[0223] In a case where the amount of maleic acid (not including
anhydride) in the solution exceeds 2 wt %, the above operation may
be omitted.
Precipitation Operation
[0224] From the above-mentioned solution, maleic acid is
precipitated. The tank to be used for such precipitation may be one
used for the above operation or may be a separate tank. The time
required for the precipitation is preferably within a range of from
0.5 to 5 hours including the above operation. If the time is too
short, the precipitation efficiency tends to be poor. From the
viewpoint of the efficiency, the longer the required time, the
better. However, the instrument to be used is required to be large,
such being uneconomical.
[0225] The operation temperature is from 20 to 70.degree. C.,
preferably from 20 to 40.degree. C. If the operation temperature is
too low, the cooling load will be increased, such being
uneconomical. Further, the melting point of acrylic acid is
13.degree. C., and freezing of acrylic acid may occur. The higher
the temperature, the more polymerizable the acrylic acid, and the
solubility of maleic acid will increase, such being
undesirable.
[0226] A solvent capable of forming double liquid layers with
water, may be added, whereby the precipitation amount and the
precipitation speed of maleic acid can be increased. The solvent
which may be employed for this purpose, may, for example, be an
aliphatic hydrocarbon such as heptene or octene, an aromatic
hydrocarbon such as toluene, xylene or ethylbenzene, an ester such
as isopropyl acetate, or a ketone such as methyl isobutyl ketone,
but it is not limited thereto. More preferred is a low polarity
solvent such as an aromatic or aliphatic hydrocarbon. The amount is
preferably from 0.5 to 4 times by volume to the recovered acrylic
acid solution. If the amount is too small, no adequate effects for
the precipitation amount tends to be obtained. On the other hand,
an excessive amount of addition increases a load to the process
such as the size and ability of the instrument, such being
uneconomical. The same one as the azeotropic agent to be used for
the dehydration distillation step may be employed, and in such a
case, the thermal load to remove the added solvent will not be
substantially increased.
[0227] Stirring may be carried out to prevent deposition on the
tank wall of crystals precipitated in the tank. Further, crystals
having a uniform particle size will be precipitated by stirring,
which makes the subsequent separation step easy.
Separation of the Precipitate
[0228] Separation of the precipitated maleic acid may be carried
out in the tank used for precipitation. However, it is convenient
to carry out the separation against the liquid withdrawn from the
precipitation tank, so that the operation can be continuously
carried out.
[0229] As a means for removing precipitated maleic acid in the
discharged liquid, a change-over strainer may, for example, be
convenient. However, such a means is not limited thereto, and a
usual solid-liquid separator may be employed. A thickener, a
precipitation tank, a cyclone, a strainer, a centrifugal separator
or the like may be employed. The separated solid may be taken out
by opening the instrument. However, it may be dissolved by a small
amount of warm water and may be removed as waste water. Depending
upon the instrument, the separated solid may continuously be
discharged. The acrylic acid solution having the precipitate
removed, contains water or an organic solvent added for the
precipitation operation and therefore preferably recycled to a
purification step prior to the purification column for acrylic
acid.
[0230] As a result of the above operation, the concentration of
maleic acid in the recovered acrylic acid will be reduced to a
level of from 1.4 to 3 wt %. The content of this level will not
adversely affect the purity of the product, even if recycled to the
purification step.
Embodiment f
[0231] The invention of Embodiment f relates to a method for
installing a liquid level meter to be used for the equipment for
producing an easily polymerizable compound. More particularly, it
relates to a method for installing a high pressure side detection
portion of the liquid level meter and is directed to a method for
installing a liquid level meter, whereby continuous operation of
the equipment has been made possible without clogging of the
detection portion of the liquid level meter.
[0232] FIG. 12 is a view showing the entire installation wherein
the method for installing a liquid level meter of the invention of
Embodiment f is applied to the (high boiling material)
decomposition reaction column and the top gas-cooled liquid tank in
the production of acrylic acid, FIG. 13 is a partially enlarged
view showing a liquid level meter installed on the (high boiling
material) decomposition reaction column of FIG. 12, and FIG. 14 is
a partially enlarged view showing a liquid level meter installed on
the top gas-cooled liquid tank of FIG. 12.
[0233] Firstly, with reference to FIG. 12, the installation for the
production of acrylic acid will be generally described. 6A is a
(high boiling material) decomposition reaction column, and a supply
line 61 is attached to the (high boiling material) decomposition
reaction column 6A. 6B.sub.1 is a bottom pump, and the inflow side
of the bottom pump 6B.sub.1 is connected to a bottom liquid
discharge line 62 attached to the bottom of the (high boiling
material) decomposition reaction column 6A, and its outflow side is
connected to the decomposition residue discharge line 64.
[0234] 6C is a heat exchanger for heating, and the inflow side of
the heat exchanger for heating is connected to the supply line 63
for the heat exchanger for heating, branched from the decomposition
residue discharged line 64, and its outflow side is connected to a
lower side wall of the (high boiling material) decomposition
reaction column 6A by a line.
[0235] 6D is a heat exchanger for cooling the column top gas, and
the inflow side of the heat exchanger 6D for cooling the column top
gas is connected to a decomposition gas recovery line 66 attached
to the top of the (high boiling material) decomposition reaction
column 6A, and its outflow side is connected to the inflow side of
a column top gas-cooled liquid tank 6E via a line.
[0236] Further, the outflow side of the column top gas-cooled
liquid tank 6E is connected to a column top gas-cooled liquid
discharge line 68 via a tank bottom liquid discharge line 65 and a
pump 6B.sub.2, and the column top gas-cooled liquid is transferred
by this line 68 to the next installation.
[0237] A cooled liquid return line 69 branched from the column top
gas-cooled liquid discharge line 68, is connected to the inflow
side of the heat exchanger 6D for cooling the column top gas.
[0238] 6F is a heat exchanger for cooling a vent gas, and the
inflow side of the heat exchanger 6F for cooling a vent gas, is
connected to the column top gas-cooled liquid tank 6E via a line.
The vent gas flowing into the heat exchanger 6F for cooling a vent
gas, will be cooled and, after a valuable substance in the gas is
recovered, will be led to a vent gas discharge line 67.
[0239] H.sub.1 and H.sub.2 are differential pressure type liquid
level meters, and the method for installing such liquid level
meters H.sub.1 and H.sub.2 is the essential feature of the present
invention.
[0240] Namely, the high pressure side of the differential pressure
type liquid level meter H.sub.1 is connected to the bottom liquid
discharge line 62 via a high pressure side detection line 11, and
the low pressure side of the differential pressure type liquid
level meter H.sub.1 is connected to the lower side wall of the
(high boiling material) decomposition reaction column 6A via a low
pressure side detection line 12.
[0241] The high pressure side of the differential pressure type
liquid level meter H.sub.2 is connected to the tank bottom liquid
discharge line 65 via a high pressure side detection line 13, and
the low pressure side of the differential pressure type liquid
level meter H.sub.2 is connected to the upper side of the column
top gas-cooled liquid tank 6E via a low pressure side detection
line 14.
[0242] Now, specific examples of the method for installing the
above differential pressure type liquid level meters H.sub.1 and
H.sub.2 will be described in detail with reference to FIGS. 13 and
14.
[0243] In FIGS. 13(1) and (2), 6A is the (high boiling material)
decomposition reaction column, and the liquid stored at the bottom
of the (high boiling material) decomposition reaction column 6A is
withdrawn out of the column by the bottom liquid discharge line 62
constituted by the bottom liquid discharge short pipe 62a attached
to the column bottom and a bottom liquid discharge conduit 62b.
[0244] H.sub.1 is the differential pressure type liquid level
meter, and the high pressure side of the differential pressure type
liquid level meter H.sub.1 is connected to either the short pipe
62a or the conduit 62b constituting the bottom liquid discharge
line 62, by the high pressure side detection line 11 constituted by
a high pressure side detection short pipe 11a and a high pressure
side detection conduit 11b.
[0245] The connection angle .alpha. between the high pressure side
detection line 11 and the bottom liquid discharge line 62 is from 5
to 90.degree., preferably from 10 to 90.degree..
[0246] If the connection angle is less than 5.degree., connection
is practically difficult, and if the connection angle exceeds
90.degree., the solid substance in the liquid is likely to flow
into the high pressure side detection line 11, such being
undesirable.
[0247] The dimensional ratio D.sub.2/D.sub.1 is from 1 to 20,
preferably from 1.3 to 10, where D.sub.1 is the pipe diameter of
the high pressure side detection line, and D.sub.2 is the pipe
diameter of the liquid discharge line.
[0248] If the ratio D.sub.2/D.sub.1 is less than 1, the solid
substance in the liquid is likely to flow into the high pressure
side detection line 11, such being undesirable, and if
D.sub.2/D.sub.1 exceeds 20, detection of the liquid level tends to
be difficult.
[0249] The low pressure side of the differential pressure type
liquid level meter H.sub.1 is connected to the lower side wall of
the (high boiling material) decomposition reaction column 6A by a
low pressure side detection line 12 constituted by a low pressure
side detection conduit 12b and a low pressure side detection short
pipe 12a.
[0250] FIG. 13(1) is an example wherein the high pressure side
detection line 11 is connected to the vertical portion of the
bottom liquid discharge line 62, while FIG. 13(2) is an example
wherein the high pressure side detection line 11 is connected to a
horizontal portion of the bottom liquid discharge line 62.
[0251] In FIGS. 14(1) and (2), 6E is the column top gas-cooled
liquid tank, and the liquid stored in the bottom of the column top
gas-cooled liquid tank 6E is withdrawn out of the tank by the tank
bottom liquid discharge line 65 constituted by a tank bottom liquid
discharge short pipe 65a attached to the tank bottom and a tank
bottom liquid discharge conduit 65b.
[0252] H.sub.2 is the differential pressure type liquid level
meter, and the high pressure side of the differential pressure type
liquid level meter H.sub.2 is connected to either the short pipe
65a or the conduit 65b constituting the tank bottom liquid
discharge line 65, by a high pressure side detection line 13
constituted by a high pressure side detection short pipe 13a and a
high pressure side detection conduit 13b.
[0253] Further, the low pressure side of the differential pressure
type liquid level meter H.sub.2 is connected to the upper side of
the column top gas-cooled liquid tank E by a low pressure side
detection line 14 constituted by a low pressure side detection
conduit 14b and a low pressure side detection short pipe 14a.
[0254] The connection angle .alpha. between this high pressure side
detection line 13 and the tank bottom liquid discharge line 65, and
the dimensional ratio D.sub.2/D.sub.1 where D.sub.1 is the pipe
diameter of the high pressure side detection line 13, and D.sub.2
is the pipe diameter of the tank bottom liquid discharge line 65,
are acceptable, if they satisfy the relation between the high
pressure side detection line 11 and the liquid discharge line 62,
as described in detail with reference to the above example of FIG.
13.
[0255] Here, FIG. 14(1) is an example wherein the high pressure
side detection line 13 is connected to a vertical portion of the
tank bottom liquid discharge line 65, and FIG. 14(2) is an example
wherein the high pressure side detection line 13 is connected to a
horizontal portion of the tank bottom liquid discharge line 65.
[0256] The above liquid discharge line is connected to a place
where the liquid containing an easily polymerizable compound is
stored, such as a distillation column, a reflux tank for a
distillation column, a decomposition reaction column, a thin film
evaporator, a column top gas-cooled liquid tank, a vertical storage
tank, a horizontal storage tank or a tank, and the high pressure
side detection line of the liquid level meter is attached thereto,
so that the liquid level can be measured.
[0257] Further, the liquid level meter to be used in the present
invention may, for example, be a differential pressure type liquid
level meter, a glass gauge type or tubular direct vision type
liquid level meter or a displacement type level indicator.
[0258] It is preferred that an injection inlet of a gas and/or a
liquid is connected to the high pressure side detection line and/or
the low pressure side detection line of such a liquid level
meter.
[0259] In a case where by some operational change, a solid
substance in the liquid flows into such a detection line, it is
possible to quickly discharge the solid substance by the gas and/or
the liquid. Such a gas and/or a liquid may be supplied continuously
or intermittently.
[0260] The gas to be used for this purpose is preferably air
nitrogen, carbon dioxide or the like, and as the liquid, it is
preferred to use the same liquid as the liquid flowing in the
liquid discharge line, such as acrylic acid or an acrylic
ester.
[0261] Further, it is preferred that such a portion is heated or
warmed to prevent deposition of a solid substance in the liquid in
the high pressure side detection line and/or the low pressure side
detection line of the liquid level meter.
[0262] The easily polymerizable compound to be measured by means of
the method for installing a liquid level meter of the present
invention is effective when (meth)acrylic acid or its ester is to
be produced.
[0263] Further, as the liquid to be measured by the liquid level
meter, particularly effective is one containing at least one type
selected from an acrylic acid dimer, .beta.-(meth)acryloxypropionic
acid esters, .beta.-alkoxypropionic acid esters,
.beta.-hydroxypropionic acid and .beta.-hydroxypropionic acid
esters, by-produced during the production of (meth)acrylic acid or
its ester.
EXAMPLES
[0264] Now, the present invention will be described in further
detail with reference to Examples and Comparative Examples, but the
present invention is by no means restricted by such Examples. Here,
the analysis of the composition of the high boiling material was
carried out in accordance with a usual method by means of gas
chromatograph provided with a flame ionization detector (FID).
Example a1
[0265] A decomposition reaction of a high boiling material was
carried out by the installation shown in FIG. 1. As the
decomposition reactor, a column type reactor made of Hastelloy C
and having an outer diameter of 600 mm and a length of 1800 mm, was
used. As raw material, a high boiling material having the following
composition was continuously supplied from the line 1 at a rate of
580 kg/hr. TABLE-US-00001 Composition of high boiling material (raw
material) Butyl acrylate: 22 wt % Butyl .beta.-butoxypropionate: 67
wt % Butyl acryloxypropionate: 4 wt % Butyl
.beta.-hydroxypropionate: 2 wt % Hydroquinone: 3 wt %
Methoxyquinone: 2 wt %
[0266] Further, as a decomposition reaction catalyst, a 1 wt %
sulfuric acid aqueous solution was supplied at a rate of 58 kg/hr
(10 wt % to the raw material feed liquid), and a decomposition
reaction was carried out under a reaction pressure of 100 kPa at a
decomposition temperature of 190.degree. C. for a retention time of
1 hour.
[0267] From the line 6 at the top, a valuable substance composed
mainly of acrylic acid and butanol, was recovered at a rate of 438
kg/hr, while a reaction residue having the following composition
was discharged out of the system via the line 4 at a rate of 200
kg/hr. TABLE-US-00002 Composition of reaction residue Butyl
acrylate: 11.0 wt % Butyl .beta.-butoxypropionate: 68.5 wt % Butyl
acryloxypropionate: 2.0 wt % Butyl .beta.-hydroxypropionate: 0.3 wt
% Hydroquinone: 8.7 wt % Methoxyquinone: 5.8 wt % Butanol: 0.8 wt %
Sulfuric acid: 2.9 wt %
[0268] From the line 2 of the reactor A, the bottom liquid was
withdrawn at a rate of 35350 kg/hr, and from the line 5 (see FIG.
4) installed in a tangent direction to the reactor A, 350 kg/hr of
the bottom liquid was returned to the reactor A by a flow rate
control valve (not shown in FIG. 1) installed on the line 5. The
rest of 34800 kg/hr was returned to the reactor A via the heat
exchanger C for heating and the return line 3-2 for heating. At
that time, a spiral flow was formed at the bottom of the reactor A
by the return liquid from the line 5. Further, the pipe for the
line 3 was 4B, and the pipe for the line 5 was 11/2(1.5)B.
[0269] After carrying out a continuous operation for 6 months, the
operation was stopped, and the interior of the decomposition
reaction column was inspected. No accumulation was observed at the
bottom of the decomposition reaction column. Further, during the
operation, there was no clogging in the transport pipe for the
reaction residue.
Comparative Example a1
[0270] An operation was carried out by the same apparatus (FIG. 1)
as in Example a1 except that with respect to the connection of the
line 5 to the decomposition reactor, it was installed in the column
center direction i.e. not in the tangent direction. After the
operation for 2 months, cavitation occurred suddenly in the pump B.
The operation of the decomposition reaction column was terminated,
and the interior was inspected, whereby accumulation of a solid
substance was observed at the bottom of the decomposition reaction
column. The state of the solid substance accumulated at the bottom
of the decomposition reaction column, is shown in FIG. 5.
Example a2
[0271] Using the same apparatus (FIG. 1) as in Example a1, a high
boiling material having the following composition was continuously
supplied from the line 1 at a rate of 580 kg/hr. TABLE-US-00003
High boiling (raw material) composition Acrylic acid: 45.3 wt %
Maleic acid: 10.0 wt % Acrylic acid dimer 42.4 wt %
(acryloxypropionic acid): Hydroquinone: 1.3 wt % Phenothiazine: 1.0
wt %
[0272] A decomposition reaction was carried out under a reaction
pressure of 72 kPa at a decomposition temperature of 190.degree. C.
for a retention of 1 hours. From the line 6 at the top, a valuable
substance composed mainly of acrylic acid was recovered at a rate
of 449 kg/hr, while a reaction residue having the following
composition was withdrawn out of the system via the line 4 at a
rate of 131 kg/hr. TABLE-US-00004 Composition of reaction residue
Acrylic acid: 8.0 wt % Maleic acid: 14.0 wt % Acrylic acid dimer
67.2 wt % (acryloxypropionic acid): Hydroquinone: 5.8 wt %
Phenothiazine: 4.4 wt % Oligomer and polymer: 0.6 wt %
[0273] The bottom liquid of the decomposition reaction column was
withdrawn from a 3/4 B nozzle (line 2) installed at the lowest
position of the bottom portion and supplied to the pump B. Via the
pump B, it was withdrawn from the line 4 at a rate of 131 kg/hr,
while to the line 3, it was supplied at a rate of 32000 kg/hr as a
return liquid to the decomposition reaction column is via the heat
exchanger C for heating by a pipe having a diameter of 4B.
[0274] On the other hand, the bottom liquid of the decomposition
reaction column was supplied as a return liquid by the pump B from
the line 5 to form the flow in a circumferential direction in the
decomposition reaction column. The pipe diameter of the line 5 was
11/2(1.5)B, and the flow rate was 400 kg/hr, and the such a control
was carried out by a flow rate control valve (not shown in Fig.)
installed on the line 5.
[0275] After carrying out a continuous operation for 6 months, the
operation was stopped, and the interior of the decomposition
reaction column was inspected. No accumulation was observed at the
bottom of the decomposition reaction column. Further, during the
operation, no clogging was observed in the transport pipe of the
reaction residue.
Comparative Example a2
[0276] An operation was carried out by the same installation as in
Example a2 except that in Example a2, the connection of the line 5
to the decomposition reaction column was made in the center
direction instead of in the tangent direction.
[0277] After the operation for 70 days, cavitation occurred
suddenly at the pump B. The operation of the decomposition reaction
column was stopped, and the interior was inspected, whereby
accumulation of a solid substance was observed at the bottom of the
decomposition reaction column. The state of the solid substance
accumulated at the bottom of the decomposition reaction column, was
as shown in FIG. 5.
Example a3
[0278] A decomposition reaction of the same high boiling material
as in Example a2 was carried out by using a decomposition reaction
column (without a baffle) as shown in FIG. 3 having anchor vanes
installed as stirring vanes. The decomposition reaction column has
a jacket and has a diameter of 600 mm and a height of 1000 mm, and
the vane diameter of the anchor vanes was 540 mm. An operation was
carried out under the same operation conditions as in Example a2 by
adjusting the rotational speed of the anchor vanes to 20 rpm. Six
months later, the operation was stopped, and the interior was
inspected, whereby no accumulation of a solid substance was
observed in the column. Further, no clogging was observed in the
discharge line installed at the lowest portion of the column bottom
during the same period.
Example b1
[0279] A decomposition reaction of a high boiling material was
carried out by the installation shown in FIG. 6. As the
decomposition reactor, a column type reactor made of Hastelloy C
and having an outer diameter of 600 mm and a length of 1800 mm, was
used. As the raw material, a high boiling material having the
following composition was continuously supplied from a line 1 at a
rate of 580 kg/hr. TABLE-US-00005 Composition of high boiling
material (raw material) Butyl acrylate: 22 wt % Butyl
.beta.-butoxypropionate: 69 wt % Butyl acryloxypropionate: 4 wt %
Butyl .beta.-hydroxypropionate: 2 wt % Hydroquinone: 2 wt %
Methoxyquinone: 1 wt %
[0280] Further, as a decomposition reaction catalyst, a 1 wt %
sulfuric acid aqueous solution was supplied at a rate of 58 kg/hr
(10 wt % to the raw material supply liquid), and a decomposition
reaction was carried out under a reaction pressure of 100 kPa at a
decomposition temperature of 190.degree. C. for a retention time of
1 hour.
[0281] From the top of the column, a valuable substance composed
mainly of acrylic acid and butanol, was recovered at a rate of
449.5 kg/hr, and on the other hand, from the column bottom, the
reaction residue of the following composition was intermittently
withdrawn at a rate of 188.5 kg/hr. Namely, the intermittent
discharge control valve D shown in FIG. 6 was operated for a
closing time of 75 seconds and an opening time of 5 seconds (the
opening ratio: 6.3%).
[0282] The discharged liquid was sent to the reaction residue
storage tank installed in a distance of 800 m by means of a pipe
having a diameter of 3/4B (inner diameter: 22.2 mm). A continuous
operation was carried out for 3 months, but no clogging was
observed in the transport pipe for the reaction residue. The
results are shown in Table 1. TABLE-US-00006 Composition of the
reaction residue Butyl acrylate: 11.7 wt % Butyl
.beta.-butoxypropionate: 72.7 wt % Butyl acryloxypropionate: 2.1 wt
% Butyl .beta.-hydroxypropionate: 0.4 wt % Hydroquinone: 6.2 wt %
Methoxyquinone: 3.1 wt % Butanol: 0.8 wt % Sulfuric acid: 3.1 wt
%
[0283] Further, the decomposition rates of the respective
components in the high boiling material were as follows.
TABLE-US-00007 Butyl .beta.-butoxypropionate: about 67 wt % Butyl
acryloxypropionate: about 83 wt % Butyl .beta.-hydroxypropionate:
about 74 wt %
[0284] Here, with respect to each component in the high boiling
material, the decomposition rate is defined by [1-(discharged
amount from the decomposition reactor)/(supplied amount to the
decomposition reactor)].times.100 (%).
Examples b2 to b4
[0285] A reaction residual liquid obtained by the same installation
and operation as in Example b1, was sent to the reaction residue
storage tank in the same manner as in Example b1 except that the
intermittent discharge time, (opening ratio) was changed to the
condition as shown in Table 1. Under any condition, no clogging was
observed in the transport pipe as a result of the continuous
operation for 3 months. Further, the decomposition ratio of the
high boiling material was substantially the same as in Example b1
with respect to each component. The results are shown in Table
1.
Comparative Example b1
[0286] A reaction residual liquid obtained by the same installation
and operation as in Example b1, was sent continuously to the same
reaction residue storage tank as in Example b1. From about the
fifth day after initiation of the operation, gradual decrease was
observed in the transport amount of the reaction residual liquid. A
mechanical shock was given to the pipe from the exterior, clogging
was partially and temporarily resolved, but complete recovery of
the transport amount was impossible. Thereafter, the discharge
amount continuously decreased, and accordingly, the retention time
in the decomposition reactor gradually increased. As a result, the
liquid state of the reaction residue became highly viscous, and on
the 25th day, the operation of the decomposition reactor had to be
stopped. Further, the decomposition ratio of the high boiling
material during the steady operation before stopping was
substantially the same as in Example b1 with respect to each
component. The results are shown in Table 1.
Examples b5 to b8
[0287] Using the same apparatus as in Example b1, a decomposition
reaction was carried out by supplying a high boiling material
having the following composition as the raw material at a rate of
580 kg/hr. TABLE-US-00008 Composition of high boiling material (raw
material) Acrylic acid: 46.0 wt % Maleic acid: 10.0 wt % Acrylic
acid dimer 42.4 wt % (acryloxypropionic acid): Hydroquinone: 0.9 wt
% Phenothiazine: 0.7 wt %
[0288] The conditions of the decomposition reaction were a reaction
pressure of 72 kPa, a decomposition temperature of 190.degree. C.
and a retention time of 1 hour, and no decomposition catalyst was
supplied.
[0289] From the column top, a valuable substance composed mainly of
acrylic acid was recovered at a rate of 449.5 kg/hr, while from the
bottom, a reaction residue having the following composition was
intermittently discharged at a rate of 130.5 kg/hr. Namely, the
closing time and the opening time of the intermittent discharge
control valve D as shown in FIG. 6, were set as shown in Table 2,
and the operation was carried out.
[0290] The discharged liquid was sent to the reaction residue
storage tank installed in a distance of 800 m by means of a pipe
having a diameter of 3/4 B (inner diameter: 22.2 mm). A continuous
operation was carried out for 3 months, whereby no clogging was
observed in the transport pipe for the reaction residue. Further,
the decomposition ratio of the acrylic acid dimer was about 72%.
The results are shown in Table 2. TABLE-US-00009 Composition of the
reaction residue Acrylic acid: 9.0 wt % Maleic acid: 14.0 wt %
Acrylic acid dimer 69.5 wt % (acryloxypropionic acid):
Hydroquinone: 4.0 wt % Phenothiazine: 3.1 wt % Oligomer and
polymer: 0.4 wt %
Comparative Example b2
[0291] A reaction residual liquid obtained by the same installation
and operation as in Examples b5 to b8, was continuously sent to the
same reaction residue storage tank as in Examples b5 to b8. From
about the 5th day from the initiation of the operation, gradual
decrease was observed in the transport amount of the reaction
residual liquid to the storage tank. A mechanical shock was given
to the pipe from the exterior, whereby clogging was partially and
temporarily resolved, but complete recovery of the transport amount
was impossible. Thereafter, the discharge amount continuously
decreased, and the retention time in the decomposition reactor
gradually increased. As a result, the liquid state of the reaction
residue became highly viscous, and the operation of the
decomposition reactor had to be stopped on the 18th day. The
results are shown in Table 2. TABLE-US-00010 TABLE 1 Comparative
Examples Example b1 b2 b3 b4 b1 Intermittent Opening 5 3 10 20
Continuously open discharge time control (sec) valve Closing 75 60
120 180 0 time (sec) Opening 6.3 4.8 7.7 10 100 ratio (%) State of
the transport No clogging No clogging No clogging No clogging The
transport pipe for the reaction for 3 for 3 for 3 for 3 amount
gradually residual liquid months months months months decreased,
and on the 25th day, the decomposition reactor had to be
stopped
[0292] TABLE-US-00011 TABLE 2 Comparative Examples Example b5 b6 b7
b8 b2 Intermittent Opening 5 3 10 20 Continuously open discharge
time control (sec) valve Closing 60 40 90 120 0 time (sec) Opening
7.7 7 10 14.3 100 ratio (%) State of the transport No clogging No
clogging No clogging No clogging The transport pipe for the
reaction for 3 for 3 for 3 for 3 amount gradually residual liquid
months months months months decreased, and on the 18th day, the
decomposition reactor had to be stopped
Example C1
[0293] A decomposition reaction was carried out in accordance with
the present invention by using as raw material a bottom liquid of a
high boiling fraction separation column in a process for producing
methyl acrylate, having the following composition: TABLE-US-00012
Composition of the bottom liquid Acrylate acid: 20 wt %
.beta.-hydroxypropionic acid: 1 wt % Methyl
.beta.-hydroxypropionate: 8 wt % .beta.-acryloxypropionic acid: 8
wt % Methyl .beta.-acryloxypropionate: 7 wt %
.beta.-methoxypropionic acid: 41 wt % Methyl
.beta.-methoxypropionate: 12 wt % Other high boiling components,
etc.: 3 wt %
[0294] As a reactor portion at the bottom of the decomposition
reaction distillation column, a stirring tank made of Hastelloy C
having an internal diameter of 1000 mm and a height of 2000 mm, and
a heat medium was supplied to an external jacket to control the
reaction temperature at 200.degree. C., and the reaction pressure
was maintained at 130 kPa. Further, at the upper portion of this
stirring tank reactor, a distillation column having an internal
diameter of 400 mm and a height of 4000 mm and further a condenser,
were connected, whereby a decomposition reaction was carried out by
a reactive distillation system.
[0295] In the interior of the distillation column, as shown in FIG.
7, disk-shaped trays 2A having a diameter D.sub.1 of 280 mm were
installed in five stages with a distance of 600 mm from the
uppermost portion to the lowermost portion, and in-between thereof,
doughnut-shaped trays 2B with an opening having an inner diameter
D.sub.2 of 260 mm were installed in four stages with an equal
distance.
[0296] The feeding position of the raw material liquid was above
the uppermost stage disk, and the above-mentioned bottom liquid as
the raw material was supplied at a rate of 150 kg/hr. The liquid
retention time was controlled by the liquid level in the
decomposition reactor, and adjusted so that the retention time
based on the discharged liquid would be 10 hours. The operation was
continued for 1 month at a decomposition reaction temperature of
200.degree. C., whereby no increase of the differential pressure
was observed, and it was possible to carry out the operation under
a stabilized condition.
[0297] After the operation, the interior of the distillation column
was visually observed, whereby no accumulation of a solid substance
was observed. The discharge amount of the decomposition residue
during this period was 76 kg/hr on average, and the composition was
analyzed by gas chromatography, and the results were as follows.
TABLE-US-00013 Composition of the residue Water: 0.2 wt % Methanol:
0.2 wt % Methyl acrylate: 0.3 wt % Acrylic acid: 39 wt %
.beta.-hydroxypropionic acid: 0.3 wt % Methyl
.beta.-hydroxypropionate: 7 wt % .beta.-acryloxypropionic acid: 4
wt % Methyl .beta.-acryloxypropionate: 4 wt %
.beta.-methoxypropionic acid: 31 wt % Methyl
.beta.-methoxypropionate: 8 wt % Other high boiling components,
etc.: 6 wt %
Comparative Example c1
[0298] A decomposition reaction was carried out for 1 month by
using the same apparatus, raw material and reaction conditions as
in Example c1 except that as the distillation column portion, a
distillation column packed with 2000 mm of a coil pack as a packing
material instead of the disk-and-doughnut type trays, was used.
There was no distinct difference from Example c1 with respect to
the discharge amount or the composition of the residue, but during
this period, the pressure difference between the top and the bottom
of the distillation column gradually increased, and upon expiration
of 1 month, an increase of differential pressure of 2.6 kPa was
observed. Further, after 1 month, the operation was stopped, and
the packing material was taken out and visually inspected, whereby
a substantial amount of a solid substance was found to have
deposited.
[0299] As is evident from the results of the above Examples and
Comparative Examples, when the process of the present invention is
employed, it is possible to carry out a continuous operation in a
stabilized condition without a trouble of e.g. clogging or an
increase in the differential pressure and to prevent deposition or
accumulation of the solid substance.
Example d1
[0300] A decomposition reaction of a high boiling liquid was
carried out by the installation as shown in FIG. 11. The
decomposition reactor had a column diameter of 1000 mm and a column
length of 2800 mm, and the material was Hastelloy C. The
composition of the high boiling liquid was 22 wt % of butyl
acrylate, 67 wt % of butyl .beta.-butoxypropionate, 4 wt % of butyl
acryloxypropionate, 2 wt % of butyl .beta.-hydroxypropionate, 3 wt
% of hydroquinone and 2 wt % of methoxyquinone, and the liquid was
supplied at a rate of 580 kg/hr.
[0301] As a decomposition reaction catalyst, a 1 wt % sulfuric acid
aqueous solution was supplied in a weight ratio of 10% to the
supplied liquid, and the decomposition reaction was carried out
under a reaction pressure of 100 kPa at a decomposition temperature
of 190.degree. C. for a retention time of 1 hour, whereby a
decomposition gas comprising 45.8 wt % of butyl acrylate, 23 wt %
of acrylic acid, 16 wt % of butanol, 11.9 wt % of water, 2.9 wt %
of butyl .beta.-butoxypropionate, 0.003 wt % of hydroquinone, 0.007
wt % of methoxyquinone and 0.39 wt % of others was obtained from
the top of the decomposition reaction column at a rate of 437.9
kg/hr. To the heat exchanger for cooling the decomposition gas, the
liquid obtained by cooling the decomposition gas was returned at a
rate of 800 kg/hr.
[0302] As oxygen or the like, air at a rate of 3 Nm.sup.3/hr and
nitrogen as a diluting inert gas at a rate of 3 Nm.sup.3/hr were
supplied to the column top gas line 44a as shown in FIG. 11.
[0303] After carrying out a continuous operation for 3 months, the
operation was stopped, and the interior of the decomposition
reaction column was inspected. No polymer was observed in the
interior of the decomposition reaction column or in the heat
exchanger for cooling the column top gas.
Comparative Example d1
[0304] An operation was carried out by the same installation as in
Example d1 except that as oxygen or the like, air at a rate of 6
Nm.sup.3/hr and nitrogen as a diluting inert gas at a rate of 6
Nm.sup.3/hr were supplied to the recycling line 43a prior to the
heat exchanger 43 for heating, i.e. not to the column top gas line
44a.
[0305] After a continuous operation for 3 months, the operation was
stopped, and the interior of the decomposition reaction column was
inspected. A polymer was observed in the interior of the
decomposition reaction column. No polymer was observed in the heat
exchanger 44 for cooling the column top gas.
Comparative Example d2
[0306] An operation was carried out in the same manner as in
Comparative Example d1, except that air was supplied at a rate of 3
Nm.sup.3/hr, and nitrogen as a diluting inert gas was supplied at a
rate of 3 Nm.sup.3/hr.
[0307] After a continuous operation for 3 months, the operation was
stopped, and the interior of the decomposition reaction column was
inspected. A polymer was observed in the interior of the
decomposition action column, but the amount was about 1/3 of the
amount in Comparative Example d1. Further, a polymer was observed
also in the heat exchanger for cooling the column top gas.
Example d2
[0308] Decomposition of a high boiling liquid was carried out by
using the same apparatus as in Example d1. The composition of the
high boiling liquid was 5.3 wt % of acrylic acid, 10 wt % of maleic
acid, 42.4 wt % of an acrylic acid dimer (acryloxypropionic acid),
1.3 wt % of hydroquinone and 1 wt % of phenothiazine, and the
liquid was supplied at a rate of 580 kg/hr.
[0309] The decomposition reaction was carried out under a reaction
pressure of 72 kPa at a decomposition temperature of 190.degree. C.
for a retention time of 1 hour, whereby a decomposition gas
comprising 85.1 wt % of acrylic acid, 8.7 wt % of maleic acid, 2.1
wt % of an acrylic acid dimer (acryloxypropionic acid), 0.03 wt %
of hydroquinone and 4.07 wt % of others was obtained from the top
of the decomposition reaction column at a rate of 449.5 kg/hr. To
the heat exchanger for cooling the decomposition gas, the liquid
obtained by cooling the decomposition gas was returned at a rate of
500 kg/hr.
[0310] As oxygen or the like, air was supplied at a rate of 2
Nm.sup.3/hr to the column top gas line 44a as shown in FIG. 11.
[0311] After carrying out a continuous operation for 3 months, the
operation was stopped, and the interior of the decomposition
reaction column was inspected. No polymer was observed in the
interior of the decomposition reaction column or in the heat
exchanger for cooling the column top gas.
Comparative Example d3
[0312] An operation was carried out by the same installation as in
Example d1 except that as oxygen or the like, air was supplied at a
rate of 3 Nm.sup.3/hr to the recycling line 3a.
[0313] After a continuous operation for 3 months, the operation was
stopped, and the interior of the decomposition reaction column was
inspected. A polymer was observed in the interior of the
decomposition reaction column. Further, a polymer was also observed
in the heat exchanger for cooling the column top gas.
Example e1
[0314] TABLE-US-00014 Recovered liquid from the thermal
decomposition reactor Acrylic acid: 88 wt % Acrylic acid dimer: 1.1
wt % Acrylic acid trimer: 100 wt ppm Maleic acid: 1.5 wt % Maleic
anhydride: 57 wt % Water: Water Maleic .times. .times. acid +
Maleic .times. .times. anhydride .times. 2 .times. ( molar .times.
.times. ratio ) = 0.34 ##EQU3##
Operation
[0315] 20 ml of a liquid having the above composition was put into
a test tube with a stopper and subjected to horizontal shaking in
an oil bath at 70.degree. C. for 2 hours with an amplitude of 3 cm
at a cycle of 1 second. Then, toluene was added in an amount of two
times by a volume ratio, and the mixture was left to stand still at
35.degree. C. for 1 hour, whereupon a precipitated solid was
separated. The separation of the solid was carried out at room
temperature by vacuum filtration employing a filter paper of 1.mu.
mesh. The separated solid contained mixed crystals of 96% maleic
acid and maleic anhydride, and acrylic acid and very small amounts
of impurities impregnated therein. The concentration of maleic acid
including maleic anhydride after the removal of the solid was 2.6
wt % as calculated by excluding the added toluene.
Example e2
[0316] Separation of a solid was carried out under the same
conditions as in Example e1 except that no addition of toluene was
carried out. The concentration of maleic acid including maleic
anhydride after removing the solid was 3.2 wt %.
Example e3
[0317] An operation was carried out under the same conditions as in
Example e1 by adding 0.08 wt % of water at the time of heating at
70.degree. C. The amount of water at that time was: Water Maleic
.times. .times. acid + Maleic .times. .times. anhydride .times. 2
.times. ( molar .times. .times. ratio ) = 0.38 ##EQU4##
[0318] The concentration of maleic acid including maleic anhydride
after removing the solid was 2.4 wt %.
Comparative Example e1
[0319] An operation was carried out under the same conditions as in
Example e2 except that 3 wt % of water was added at the time of
heating at 70.degree. C. The amount of water at that time was:
Water Maleic .times. .times. acid + Maleic .times. .times.
anhydride .times. 2 .times. ( molar .times. .times. ratio ) = 1.63
##EQU5##
[0320] No precipitation of a solid was observed, and the
concentration of maleic acid including maleic anhydride was
unchanged at 7.2 wt %.
Example f1
[0321] A decomposition reaction of a high boiling liquid was
carried out by the installation as shown in FIGS. 12 and 13.
[0322] The composition of the high boiling liquid was 22 wt % of
butyl acrylate, 67 wt % of butyl .beta.-butoxypropionate, 4 wt % of
butyl acryloxypropionate, 2 wt % of butyl .beta.-hydroxypropionate,
3 wt % of hydroquinone and 2 wt % of methoxyquinone, and the liquid
was supplied at a rate of 580 kg/hr.
[0323] As a decomposition reaction catalyst, a 1 wt % sulfuric acid
aqueous solution was supplied in a weight ratio of 10% to the
supplied liquid, and the decomposition reaction was carried out
under a reaction pressure of 100 kPa at a decomposition temperature
of 190.degree. C. for a retention time of 1 hour, whereby from the
bottom, a reaction residue comprising 11.7 wt % of butyl acrylate,
68.5 wt % of butyl .beta.-butoxypropionate, 2 wt % of butyl
acryloxypropionate, 0.3 wt % of butyl .beta.-hydroxypropionate, 8.7
wt % of hydroquinone, 5.8 wt % of methoxyquinone, 0.8 wt % of
butanol and 2.9 wt % of sulfuric acid, was obtained at a rate of
200.1 kg/hr and discharged from the bottom.
[0324] The bottom liquid of the decomposition reaction column was
discharged from the bottom liquid discharge line 62 attached to the
lowermost position of the bottom portion. The liquid level meter
H.sub.1 at the bottom was a differential pressure type liquid level
meter and was installed as shown in FIG. 13(1) The connection angle
.alpha. between the high pressure side detection line 11 and the
bottom liquid discharge line was set to be 45.degree..
[0325] After carrying out a continuous operation for 6 months, the
operation was stopped, and the high pressure side detection short
pipe 11a and the high pressure side detection conduit 11b of the
high pressure side detection line 11 of the liquid level meter
H.sub.1, were inspected. As a result of such inspection, no
deposition was observed in either one of them.
Comparative Example f1
[0326] An operation was carried out under the same conditions as in
Example f1 except that the high pressure side detection line 11 of
the differential pressure type liquid level meter H.sub.1 was
connected horizontally to the lower side wall of the decomposition
reaction column 6A. After operation for 2 months, cavitation
occurred suddenly in the bottom pump B.sub.1. Immediately, the
operation of the decomposition reaction column 6A was stopped, and
the interior was inspected, whereby it was found that no liquid was
present at the bottom portion of the decomposition reaction column
6A, and the indication of the liquid level meter H.sub.1 was
erroneous.
[0327] The high pressure side detection short pipe 11a and the high
pressure side detection conduit 11b of the high pressure side
detection line 11 of the liquid level meter H.sub.1 were inspected,
whereby the short pipe 11a and the conduit 11b were found to be
clogged.
Comparative Example f2
[0328] An operation was carried out under the same conditions as in
Example f1 except that the high pressure side detection line 11 of
the differential pressure type liquid level meter H.sub.1 was
connected at a connection angle .alpha. of 45.degree. to the lower
side wall of the decomposition reaction column 6A.
[0329] After an operation for 3 months, cavitation occurred
suddenly in the bottom pump B.sub.1. Immediately, the operation of
the decomposition reaction column A was stopped, and the interior
was inspected, whereby it was found that no liquid was present at
the bottom portion of the decomposition reaction column A, and the
indication of the liquid level meter H.sub.1 was erroneous.
[0330] The high pressure side detection short pipe 11a and the high
pressure side detection conduit 11b of the high pressure side
detection line 11 of the liquid level meter H.sub.1 were inspected,
whereby the short pipe 11a and the conduit 11b were found to be
clogged.
Example f2
[0331] An evaporation operation satisfying the following conditions
was carried out by using a thin film evaporator.
[0332] As a raw material (crude acryl monomer) composition, a
mixture comprising 66.6 wt % of acrylic acid, 8.0 wt % of maleic
acid, 25.0 wt % of an acrylic acid oligomer, 0.5 wt % of
hydroquinone and 0.5 wt % of phenothiazine, was supplied at
85.degree. C. at a rate of 3000 kg/hr.
[0333] The operation was carried out under a column top pressure of
9 kPa under a bottom pressure of 10 kPa at a column top temperature
of 95.degree. C. and a bottom temperature of 98.degree. C., whereby
from the top of the column, 53% of the supplied amount was
withdrawn, and acrylic acid having a purity of at least 88 wt %,
was obtained.
[0334] From the bottom, a mixture comprising 41.1 wt % of acrylic
acid, 10.9 wt % of maleic acid, 46.16 wt % of an acrylic acid
oligomer, 0.92 wt % of hydroquinone and 0.92 wt % of phenothiazine,
was discharged.
[0335] The bottom liquid of the thin film evaporator was discharged
by the bottom liquid discharge line attached to the lowermost
position of the bottom portion. The liquid level meter at the
bottom was a differential pressure type liquid level meter and
installed as shown in FIG. 13(1). The connection angle .alpha.
between the high pressure side detection line 11 and the bottom
liquid discharge line was set to be 45.degree..
[0336] After carrying out a continuous operation for 6 months, the
operation was stopped, and the high pressure side detection short
pipe 11a and the high pressure side detection conduit 11b of the
high pressure side detection line 11 of the liquid level meter,
were inspected. As a result of such inspection, no deposition was
observed in either one of them.
Comparative Example f3
[0337] An evaporation operation was carried out under the same
conditions as in Example f2 except that the high pressure side
detection line 11 of the differential pressure type liquid level
meter was connected horizontally to the lower side wall of the thin
film evaporator.
[0338] After operation for 1 month, cavitation occurred suddenly in
the bottom pump. The operation of the thin film evaporator was
stopped, and the interior was inspected, whereby it was found that
no liquid was present in the thin film evaporator, and indication
of the liquid level meter was erroneous.
[0339] The high pressure side detection short pipe 11a and the high
pressure side detection conduit 11b of the high pressure side
detection line 11 of the liquid level meter, were inspected,
whereby the short pipe 11a and the conduit 11b were found to be
clogged.
INDUSTRIAL APPLICABILITY
[0340] a. According to the present invention, in a process for
recovering a valuable substance by heating and decomposing a high
boiling material containing a Michael addition product of
(meth)acrylic acids, the decomposition reaction residue can be
transported without clogging from the decomposition reactor to a
storage tank, whereby a continuous operation for a long time will
be possible.
[0341] b. Further, according to the process for decomposing a
byproduct formed during production of (meth)acrylic acids of the
present invention, at the time of recovering a valuable substance
such as (meth)acrylic acid, a (meth)acrylic ester and an alcohol by
thermally decomposing by a reactive distillation system a byproduct
formed during production of (meth)acrylic acid and/or a byproduct
formed during production of a (meth)acrylic ester, it becomes
possible to carry out a continuous operation under a stabilized
condition while preventing adhesion, deposition or accumulation of
a solid substance and while maintaining the recovery rate of the
valuable substance at a high level without bringing about a problem
such as clogging or an increase of the differential pressure of the
distillation column due to deterioration of the gas-liquid contact
state. Yet, in the present invention, a distillation column having
a very simple structure may be adopted, whereby there will be a
merit that the construction costs will be very low as compared with
other distillation columns employing trays or a packing
material.
[0342] c. Further, according to the present invention, it is
possible to carry out decomposition treatment of a Michael addition
reaction product by-produced in the step for producing
(meth)acrylic acid and/or a (meth)acrylic ester, under a stabilized
condition, whereby (meth)acrylic acid, a (meth)acrylic ester and an
alcohol, etc. can be recovered at a high recovery rate.
[0343] d. Further, according to the present invention, an acrylic
acid-containing gas obtained by catalytic oxidation of propane or
propylene, is contacted with a solvent to collect acrylic acid as
an acrylic acid-containing solution, the obtained acrylic
acid-containing solution is distilled to purify acrylic acid, while
an acrylic acid oligomer from the bottom liquid containing the
acrylic acid oligomer, obtained from the purification column, is
thermally decomposed, and acrylic acid having a small content of
maleic acid, can be recovered efficiently.
[0344] e. Further, if a method for installing a liquid level meter
of the present invention is adopted in the installation for
producing a easily polymerizable compound, it is possible to
prevent a solid substance present in the liquid of the easily
polymerizable compound from flowing into a high pressure side
detection line of the liquid level meter. Accordingly, the
detection portion of the liquid level meter will not be clogged by
the liquid to be measured, whereby an accurate continuous
measurement by the liquid level meter will be possible, whereby the
installation can be operated over a long period of time.
[0345] The entire disclosures of Japanese Patent Application No.
2001-369636 filed on Dec. 4, 2001, Japanese Patent Application No.
2001-371608 filed on Dec. 5, 2001, Japanese Patent Application No.
2001-385168 filed on Dec. 18, 2001, Japanese Patent Application No.
2001-392058 filed on Dec. 25, 2001, Japanese Patent Application No.
2002-141162 filed on May 16, 2002 and Japanese Patent Application
No. 2002-141194 filed on May 16, 2002 including specifications,
claims, drawings and summaries are incorporated herein by reference
in their entireties.
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