Note: Descriptions are shown in the official language in which they were submitted.
_ 2~4~838
PROCESS FOR SEPARATING METHANOL AND METHYL ACRYLATE
OR METHYL METHACRYLATE
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a process for
efficiently separating methanol from a mixture of methyl
acrylate or methyl methacrylate with methanol. It also
relates to a process for efficiently separating methanol
from a mixture of methyl acrylate or methyl methacrylate
with methanol and water. Hereafter, the term
(meth)acrylic acid may be used to refer to either acrylic
acid or methacrylic acid and the term methyl
(meth)acrylate refers to either methyl acrylate or methyl
methacrylate.
DESCRIPTION OF THE RELATED ART
It is known in the art that esterification of
(meth)acrylic acid with methanol or ester exchange of an
alcohol with methyl (meth)acrylate yields a mixture of
methanol, methyl (meth)acrylate, and water.
The esterification reaction, which normally calls
for an excess molar amount of methanol with respect to
(meth)acrylic acid, essentially consumes all of the
(meth)acrylic acid leaving no unreacted (meth)acrylic
acid. Therefore, the liquid reaction mixture after the
reaction is a liquid mixture comprising excess methanol,
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the reaction product methyl (meth)acrylate, and the
reaction side product water.
The ester exchange reaction, which normally uses an
excess molar amount of methyl (meth)acrylate with respect
to an alcohol, consumes essentially all of the alcohol by
the ester exchange reaction. Thus, the liquid reaction
mixture after the reaction is a liquid mixture of the
reaction side product methanol, unreacted methyl
(meth)acrylate, and the reaction product ester. From
among these components, the reaction product ester, which
has a large boiling point difference from methanol and
methyl (meth)acrylate, is relatively easy to separate,
thereby providing a liquid mixture of the methanol and
methyl (meth)acrylate free of the ester.
Several proposals have been made whereby an organic
solvent capable of generating an azeotropic mixture with
methanol is added to a mixture mainly comprising methyl
(meth)acrylate and methanol, optionally containing water,
followed by distilling to separate into methanol and
methyl (meth)acrylate.
For example, a process is known in which a liquid
mixture comprising methanol, water, and methyl
(meth)acrylate is azeotropically distilled in the presence
of an organic solvent and the entire,amount of methanol is
essentially stripped off the top of the distillation
column and it is mostly free of water (see, e.g., U.S.
Patent 2,916,512; Japanese Laid-Open Publication
57-9740). The process, which strips off the methanol by
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azeotropic distillation, gives a distillate which contains
the organic solvent. The process discloses that the
distillate is fed to a decanter for separation into a
layer mainly comprising the organic solvent and a layer
mainly comprising methanol, and the organic solvent layer
is returned to the distillation column. However, such a
previously-known method, which efficiently distills and
separates methanol from methyl (meth)acrylate, gives a
distillate which still contains methyl (meth)acrylate, the
distillate separating into two layers, with the lower
layer mostly comprised of methanol mixed with methyl
(meth)acrylate. Particularly, in the case of methyl
acrylate, its low boiling point will give results in which
the amount of contaminating methyl acrylate is more than
negligible.
The esterification reaction recycles the separated
methanol back to the reaction so that any contamination
with methyl (meth)acrylate essentially poses no problem.
However, the ester exchange reaction requires withdrawing
out of the system the reaction by-product methanol, so
that any methyl (meth)acrylate contained in the methanol
gives rise to a recovery loss.
A proposal is given in Japanese Laid-Open
Publication 57-9740 for reducing such recovery losses,
which calls for controlling the type and amount of the
organic solvent which forms an azeotropic mixture with
methanol, and the number of plates for the methanol
condensation section of the distillation column. The
process, while exhibiting some effect, is still deficient
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in that the amount of methyl (meth)acrylate distillate
cannot be substantially decreased. Japanese Laid-Open
Publication 58-203940 teaches a process for recovering
methanol, which comprises separating the distilled
methanol and azeotropic solvent into two layers, feeding
the upper layer mainly comprising the azeotropic solvent
to the upper-most plate of the distillation column and
feeding the lower layer, mostly comprised of methanol,
into another distillation column (hereafter a second
distillation column), recovering from the top of the
second distillation column the azeotropic solvent that
was dissolved in methanol, and recovering methanol from
the bottom of the second distillation column. However,
that process, which makes it possible to recover the
azeotropic solvent, feeds a liquid mainly comprised of
methanol to the second distillation column, where the
contaminating methyl (meth)acrylate is not separated and
contaminates the methanol which is recovered from the
bottom of the second distillation column.
Such methanol before use in other applications must
be freed of any impurities with boiling points higher
than methanol by distillation so that any methyl
(meth)acrylate contained in the methanol would be
discarded with the impurities, creating a recovery loss
and making the process deficient.
SUMMARY OF THE INVENTION
The primary object of the present invention is to
overcome the above deficiencies. The present invention
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provides a process for recovering methanol using an
azeotropic solvent from a mixture of methyl
(meth)acrylate and methanol, sometimes containing water,
which substantially reduces the amount of methyl
(meth)acrylate contamination of methanol and which
readily separates methanol from a distillation-separated
liquid mixture of methanol and the azeotropic solvent.
The present invention is a process for separation
by distillation of methanol from a mixture of methyl
acrylate or methyl methacrylate and methanol, or a mixture
of methyl acrylate or methyl methacrylate and methanol
and water, using an azeotropic solvent that generates an
azeotropic mixture with methanol, which comprises
distilling such a mixture by the use of a distillation
column, further comprising the steps of:
(1) returning part of the condensate of vapors
distilled over from the top of a distillation column to
the top of the column;
(2) separating the remaining condensate into two
layers;
(3) feeding the upper layer essentially comprising
the azeotropic solvent, separated from the said two
layers, to an intermediate portion of the distillation
column;
(4) withdrawing the lower layer essentially
comprised of methanol separated from the above two layers
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out of the distillation system; and
(5) recovering from the bottom of the column methyl
acrylate or methyl methacrylate, or methyl acrylate or
methyl methacrylate and water, thereby separating methanol
from methyl acrylate or methyl methacrylate, or methanol
from methyl acrylate or methyl methacrylate and water.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features and advantages of the
present invention will become better understood by making
reference to the following description, attendant claims,
and accompanying drawings.
FIG. 1 is a diagrammatic flow sheet for one type
of apparatus used for recovering methanol by a continuous
process from a mixture of methyl (meth)acrylate and
methanol in the process of the present invention:
1...Distillation Column; 2...Condenser; 3...Liquid
Distributor; 4...Decanter; and 5,6,7,8,9,10,11,12,13,14,
and 15...Delivery Tubes.
FIG. 2 is a diagrammatic flow sheet for a type of
apparatus used in accordance with prior art by a
continuous process from a mixture of methyl (meth)acrylate
and methanol: 1...Distillation Column; 2...Condenser;
4...Decanter; and 5,6,7,13,14, and 15...Delivery Tubes.
FIG. 3 is a diagrammatic flow sheet showing an
ester exchange reactor equipped with a distillation column
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2~4~838
used in an embodiment of this invention: l...Distillation
Column; 2...Condenser; 3...Liquid Distributor;
4...Decanter; 6,7,8,9,10,11,13, and 15...Delivery Tubes;
and 16...Ester Exchange Reactor.
FIG. 4 is a diagrammatic flow sheet showing an
ester exchange reactor equipped with a distillation column
used in prior art: l...Distillation Column;
2...Condenser; 4...Decanter; 6,7,11,13, and 15...Delivery
Tubes; and 16...Ester Exchange Reactor.
DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention uses azeotropic solvents
capable of forming azeotropes with methanol, which are
aliphatic saturated hydrocarbons, aliphatic unsaturated
hydrocarbons, alicyclic hydrocarbons, organic halides,
ethers, esters, and others.
Azeotropic solvents which may be used in this
invention are required to have the following properties:
(1) to form a minimum azeotropic mixture with
methanol boiling below the boiling point of methanol, with
the azeotropic temperature as low as possible;
(2) to form no azeotropic mixture with methyl
(meth)acrylate;
(3) to give an azeotropic mixture with methanol
which is capable of forming two liquid layers on standing
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and of having the density difference substantial enough
for separation; and
(4) to undergo no chemical reaction during
distillation with methanol or methyl (meth)acrylate.
Those which are provided with the above properties
(1)-(4), have low cost, and are readily available are
linear or branched aliphatic saturated hydrocarbons,
preferably aliphatic saturated hydrocarbons with 5-8
carbon atoms, such as n-pentane, n-hexane, n-heptane,
n-octane, 2,3-dimethylbutane, 2,5-dimethylhexane,
2,2,4-trimethylpentane, and the like. Table 1 lists the
azeotropic temperatures and azeotropic compositions of
methanol with these aliphatic saturated hydrocarbons.
Table 1
Azeotropic temperatures and azeotropic compositions
of methanol with aliphatic unsaturated hydrocarbons
(edited by Yuki Gosei Kagaku Kyokai [Organic Synthetic
Chemical Association]: "Yozai Pocketbook" ["Solvent
Pocketbook"], OHM Company, Japan, 1967)
30
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214 X838
Aliphatic Saturated Azeotropic Azeotropic
Hydrocarbons Temperature Composition
n-pentane 30.8 91
n-hexane 50.6 72
n-heptane 59.1 48.5
n-octane 63.0 28
2,3-dimethylbutane 45.0 80
2,5-dimethylhexane 61.0 40
2,2,4-trimethylpentane 59.4 47
NOTE: In the table, the azeotropic temperature
refers to a temperature at 760 mmHg with the unit in °C.
NOTE: In the table, the azeotropic composition is
$ by weight of organic solvents.
The present invention requires that the separation
of methanol by distillation with an azeotropic solvent be
carried out in such a manner that the top of the
distillation column has an azeotropic composition of
methanol and the azeotropic solvent.
In accordance with this invention, returning part
of the condensate of mixed vapors of methanol and the
azeotropic solvent distilled over from the top of the
distillation column to the top of the distillation column,
preferably in an amount of at least 15$ by weight, more
particularly at least 20$ by weight of the condensate,
makes it easy to maintain an azeotropic composition at the
top of the column, which advantageously decreases the
temperature of the top of the column, thereby preventing
any methyl (meth)acrylate from distilling over. Returning
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part of the condensate to the top of the distillation
column, may be carried out by first condensing the
distillate and separating it into two layers, an upper
layer essentially comprising the azeotropic solvent and
a lower layer essentially comprising methanol, followed by
returning the upper and lower layers at a flow ratio
corresponding to the azeotropic composition, thereby
achieving the same effect.
In order to decrease any loss in methyl
(meth)acrylate by distilling over, it is preferred to
operate and control the distillation column at least ten
or more plate from the top of the distillation column, at
a temperature essentially the same as the azeotropic
temperature of the azeotropic compositional mixture of
methanol and the azeotropic solvent. This operation and
control can be carried out by adjusting the reflux ratio
when returning part of the condensate.
The above-mentioned related art comprises
separating the distillate into two layers and then
returning only the upper layer mainly comprised of an
azeotropic solvent. That is a sensible operation from the
standpoint of removing methanol, but such a method will
result in a distillate extensively contaminated with
methyl (meth)acrylate. The reason for this, although not
completely understood, may be that the contamination is
caused by the liquid composition at the top of the column
deviating from the azeotropic composition, resulting in an
increased temperature, which in turn, increases the amount
of methyl (meth)acrylate distilling over.
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~145~~~
After returning part of the distillate in this
invention, the remaining condensate, mainly comprising a
mixture of methanol and azeotropic solvent, is then
allowed to separate into two layers: the upper layer is
essentially comprised of the azeotropic solvent and the
lower is essentially comprised of methanol.
The upper layer is returned to an intermediate
portion of the distillation column, preferably to a
portion of the column where the azeotropic solvent
concentration is highest; the portion at which the
azeotropic solvent concentration is the highest in the
column differs depending upon the number of plates of the
column and the amount of the azeotropic solvent present.
The lower layer essentially comprised of methanol
is then withdrawn out of the distillation system, but
depending upon the type of azeotropic solvent, there may
be cases in which the separation into two layers, methanol
and the azeotropic solvent, is not easy or the mutual
solubility of the components may be high even if a two-
layer separation is achieved, resulting in a lower layer
which contains a substantial amount of the azeotropic
solvent. The recovering and recycling of methanol and the
azeotropic solvent in such cases requires separating the
two, where a method may be used to employ a second
distillation column for that purpose, so as to recover
from the top of the column the azeotropic solvent which is
dissolved in methanol and to recover methanol from the
bottom of the column. In this case, the lower layer
liquid mainly comprised of methanol which is led to the
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2I4~838
second distillation column is not contaminated with methyl
(meth)acrylate so that the methanol recovered in the
second distillation column is free of methyl
(meth)acrylate. This method is effective when recovering
and recycling methanol in a large scale unit, or the like.
However, having a second distillation column is too
costly in capital investment to be preferred merely for
reducing the loss of an azeotropic solvent in the case of
a small-scale unit, where methanol recovery is not
economical and methanol is disposed of by incineration.
In such a case where there is no need for methanol
recovery and capital costs should be reduced as much as
possible, water may be added to the condensate, which is
the azeotropic mixture remaining after being partially
returned to the top of the distillation column, so as to
facilitate a two-layer separation into methanol and the
azeotropic solvent and also to substantially decrease the
concentration of the azeotropic solvent in the methanol.
The latter method which does not require a second
distillation column, but involves adding only water, can
remove methanol essentially free of any azeotropic solvent
from a mixed liquid of methanol and an azeotropic solvent,
minimizing the loss of the azeotropic solvent. This
method is suitably used, particularly in a small-scale
unit for the separation of methyl acrylate and methanol.
The amount of water added by weight is 0.1-10
times, preferably 0.5-5 times the weight of methanol,
where the methanol is recovered in the form of an aqueous
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2~4~838
methanol solution, and is then withdrawn out of the
distillation system.
In this manner, removal of methanol permits
recovering methyl (meth)acrylate from the bottom of the
column. If the feed to the distillation column comprises
methyl (meth)acrylate, methanol and water, both methyl
(meth)acrylate and water are recovered from the bottom of
the column.
Thus, even if water may be present in a liquid
mixture of methyl (meth)acrylate and methanol,
distillation with an azeotropic solvent permits
discharging water together with methyl (meth)acrylate from
the bottom of the column, so that whether or not water is
present in the feed to the distillation column essentially
does not affect the extent of loss of methyl
(meth)acrylate into the methanol.
The embodiment of this invention as described above
is now explained by referring to the attached drawing
(FIG. 1). It should be noted that the present invention
is not limited to an embodiment depicted in FIG. 1.
A mixture of methanol and methyl (meth)acrylate is
fed through delivery tube 5 and is distilled in
distillation column 1. Essentially methanol-free methyl
(meth)acrylate is recovered through delivery tube 14 from
the bottom of distillation column 1. Methanol and the
azeotropic solvent are stripped as azeotropic mixed vapors
and are led through delivery tube 6 and condensed by
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condenser 2 to give a condensate, which is then led
through delivery tube 7 into liquid distributor 3. The
liquid distributor separates the mixture of methanol and
the azeotropic solvent into two parts. Part of the
condensate is led through delivery tube 8 and returned to
the top of distillation column 1, while the remaining part
of the condensate is led through delivery tube 9 into
decanter 4. Whether or not the amounts of liquid
distributed by the liquid distributor 3 are optimum can
be readily judged by a variation in the number of plates
with respect to the azeotropic composition of distillation
column 1, but the liquid distribution ratio can also be
set up by using the following Equation (I):
WT - 1 - (p/q) (1+r) (WF/W~)
W~
wherein WT, W", WF. p~ q. and r are defined as follows:
WT: rate of condensate distributed from liquid
distributor 3 to the top of distillation column (g/hr);
W~: rate of condensate condensed by passage through
delivery tube 6 in condenser 2 (g/hr);
WF: rate of liquid (g/hr) of a mixture of methanol
and methyl (meth)acrylate fed through delivery tube 5 to
the distillation column 1.
p: methanol concentration in mixture WF fed from
the delivery tube 5 to the distillation column 1;
q: methanol concentration in an azeotropic mixture
of azeotropic solvent and methanol;
r: Rate of methanol(g/hr) in the upper layer from (W"- WT)
3 0 pWf
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[ where the upper layer from ( W"- W.r ) is fed to the
intermediate portion of the distillation column]
Decanter 4 performs layer separation, and the upper
layer, which is mainly comprised of the azeotropic
solvent, is fed from delivery tube 10 through delivery
tube 11 into the intermediate part of distillation column
1, and the lower layer mainly comprised of methanol is
allowed to flow through delivery tube 13 out of the
distillation system.
If the mixture of methanol and methyl
(meth)acrylate which is fed from delivery tube 5 contains
water, essentially methanol-free methyl (meth)acrylate and
water are recovered through delivery tube 14 from the
bottom of distillation column 1. As described above, if
water is added to the condensate remaining after partially
returning to the top of the distillation column, in order
to facilitate a two-layer separation in decanter 4, the
water is then fed through delivery tube 15 into decanter
4. In this case, an aqueous methanol solution is allowed
to flow out of delivery tube 13.
The azeotropic solvent for replenishing is fed
through delivery tube 12 into distillation column 1.
As illustrated in FIG. 1, the present invention
can be suitably used for recovering methanol by a
continuous process from a mixture of methyl (meth)acrylate
with methanol optionally containing water. However, as
illustrated in FIG. 3, this invention can also be suitably
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2~4~838
used to strip off, with essentially no loss of methyl
(meth)acrylate, the methanol which is formed in ester
exchange reactor 16 that is provided with distillation
column 1.
The present invention can be carried out either at
atmospheric pressure or at reduced pressure.
ERAMPLES
The present invention is further explained in
detail by the following examples. However, these examples
in no way limit the scope of this invention. In these
examples, percent is based on weight.
EXAMPLE 1
An experiment was carried out using an apparatus
shown in FIG. 1. Ose was made of an i.d. 35 mm, 30-plate
Oldershaw column as the distillation column and n-hexane
as an azeotropic solvent. Distillation was carried out
at atmospheric pressure.
An azeotropic mixture (containing 54~ methanol) of
methyl acrylate and methanol was fed through delivery tube
5 at a rate of 117.4 g/hr to the 25th plate from the top
of the distillation column 1, while 99.50 pure methyl
acrylate was withdrawn at a rate of 53.59 g/hr from the
bottom of the column through delivery tube 14.
Vapors distilling off the top of the column were
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led through delivery tube 6 and cooled in condenser 2
(with the use of a -10°C refrigerant) to give a
condensate, which was then led through delivery tube 7 at
a rate of about 400 g/hr into liquid distributor 3.
Liquid distributor 3 was operated to return part of the
condensate through delivery tube 8 to the top of the
distillation column in such a manner that the temperature
from the top of the column to the 15 th plate was held at
50.6°C and the remaining condensate was fed through
delivery tube 9 to decanter 4. The distribution of the
condensate for the column top: decanter was equal to about
2:3. The condensate led to decanter 4 was separated into
two layers in decanter 4 and the upper layer of decanter 4
was introduced from delivery tube 10 through delivery tube
11 into the 20th plate from the top of the column, while
the lower layer of decanter 4 was withdrawn through
delivery tube 13, with the liquid level in the separated
layers within the decanter held constant. Water was at
the same time fed to the decanter 4 through delivery tube
15 at a rate of 168.0 g/hr.
In this case, the lower layer of decanter 4
provided 231.8 g/hr of methanol containing 0.003$ of
n-hexane, 0.29$ of methyl acrylate, and 72.47 of
water. The methyl acrylate recovery loss amounted to
1.26$.
EXAMPLE 2
An experiment was carried out using an apparatus
shown in FIG. 1. Use was made of an i.d. 35 mm, 30-plate
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2~~5838
Oldershaw column as the distillation column and n-hexane
as an azeotropic solvent. Distillation was carried
out at atmospheric pressure.
An azeotropic mixture (containing 54$ methanol) of
methyl acrylate and methanol was fed through delivery tube
5 at a rate of 121.0 g/hr to the 25th plate from the top
of the distillation column 1, while 99.36$ pure methyl
acrylate was withdrawn at a rate of 54.43 g/hr from the
bottom of the column through delivery tube 14.
Vapors distilling off the top of the column were
led through delivery tube 6 and cooled in condenser 2
(with the use of a -10°C refrigerant) to give a
condensate, which was then led through delivery tube 7 at
a rate of about 385 g/hr into liquid distributor 3.
Liquid distributor 3 was operated to return part of the
condensate through delivery tube 8 to the top of the
distillation column in such a manner that the temperature
from the top of the column to the 15th plate was held at
50.6°C and the remaining condensate was fed through
delivery tube 9 to decanter 4. The distribution of the
condensate for the column top: decanter was equal to about
1:3. The condensate fed to decanter 4 was separated
into two layers in decanter 4 and the upper layer of
decanter 4 was introduced from delivery tube 10 through
delivery tube 11 into the 20th plate from the top of the
column, while the lower layer of decanter 4 was withdrawn
through delivery tube 13, with the liquid level in the
separated layers within the decanter held constant. In
this case, the lower layer of decanter 4 provided
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214 58,38
98.04 g/hr of methanol containing 32.47 of n-hexane and
1.61$ of methyl acrylate. The methyl acrylate recovery
loss amounted to 2.84$.
COMPARATIVE EXAMPLE 1
An experiment was carried out using an apparatus
shown in FIG. 2. Use was made of an i.d. 35 mm, 30-
plate Oldershaw column as the distillation column and the
n-hexane was an azeotropic solvent. Distillation was
carried out at atmospheric pressure.
An azeotropic mixture (containing 54$ methanol) of
methyl acrylate and methanol was fed at a rate of 118.0
g/hr through delivery tube 5 to the 20th plate counting
from the top of the distillation column 1, and 99.37$ pure
methyl acrylate was withdrawn from the bottom of the
column through delivery tube 14 at a rate of 43.07 g/hr.
Vapors stripped off the top of the column were led
through delivery tube 6 and cooled in condenser 2 (with
the use of a -10°C refrigerant) to give a condensate
which was then led through delivery tube 7 directly to
decanter 4. The condensate introduced into decanter 4 was
separated into .two layers in decanter 4 followed by
feeding the upper layer from decanter 4 through delivery
tube 11 to the top of the column while the lower layer of
decanter 4 was withdrawn through delivery tube 13 with
the liquid levels of the separated layers within decanter
4 held constant. Water was at the same time fed to
decanter 4 through delivery tube 15 at a rate of 155.0
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g/hr.
The lower layer of decanter 4 gave 229.95 g/hr of
methanol containing 0.007$ of n-hexane, 4.99$ of
methyl acrylate, and 67.41$ of water. The methyl acrylate
recovery loss amounted to 21.15.
COMPARATIVE EXAMPLE 2
Comparative Example 1 was repeated for this
experiment except for feeding no water to decanter 4.
Immediately after starting to return the upper layer of
decanter 4 to the top of the column, the material in
decanter 4 became a homogeneous layer.
EXAMPLE 3
An experiment was carried out using an apparatus
shown in FIG. 1. Use was made of an i.d. 35 mm, 30-plate
Oldershaw column as the distillation column and n-hexane
as an azeotropic solvent. Distillation was carried out
at atmospheric pressure.
An azeotropic mixture (containing 82$ methanol) of
methyl methacrylate and methanol was fed through delivery
tube 5 at a rate of 78.1 g/hr to the 25th plate from the
top of the distillation column 1, while 14.09 g/hr of
99.80 pure methyl methacrylate was withdrawn from the
bottom of the column through delivery tube 14.
Vapors distilling off the top of the column were
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led through delivery tube 6 and cooled in condenser 2
(with the use of a -10°C refrigerant) to give a
condensate, which was then led through delivery tube 7 at
a rate of about 450 g/hr into liquid distributor 3.
Liquid distributor 3 was operated to return part of the
condensate through delivery tube 8 to the top of the
distillation column in such a manner that the temperature
from the top of the column to the 15th plate was held at
50.6°C and the remaining condensate was led through
delivery tube 9 to decanter 4. The distribution of the
condensate for the column top: decanter was equal to about
1:1.2. The condensate led to decanter 4 was separated
into two layers in decanter 4 and the upper layer of
decanter 4 was introduced from delivery tube 10 through
delivery tube 11 into the 20th plate from the top of the
column, while the lower layer of decanter 4 was withdrawn
through delivery tube 13, with the liquid level in the
separated layers within the decanter held constant. Water
was at the same time fed to decanter 4 through delivery
tube 15 at a rate of 168.0 g/hr.
In this case, the lower layer of decanter 4
provided 232.1 g/hr of methanol containing 0.002$ of
n-hexane and 70.4$ of water. The lower layer had no
detectable methyl methacrylate.
EXAMPLE 4
An experiment was carried out by repeating Example
3, except for feeding no water to decanter 4. The lower
layer in decanter 4 showed no detectable methyl
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methacrylate.
COMPARATIVE EXAMPLE 3
An experiment was carried out using an apparatus
shown in FIG. 2. Use was made of an i.d. 35 mm, 30-plate
Oldershaw column as the distillation column and the
n-hexane was an azeotropic solvent. Distillation was
carried out at atmospheric pressure.
An azeotropic mixture (containing 82$ methanol) of
methyl methacrylate and methanol was fed at a rate of 81.5
g/hr through delivery tube 5 to the 20th plate counting
from the top of the distillation column 1 and withdrawing
from the bottom of the column, 99.45$ pure methyl
methacrylate through delivery tube 14 at a rate of 14.49
g/hr.
Vapors stripped off the top of the column were led
through delivery tube 6 and cooled in condenser 2 (with
the use of a -10°C refrigerant) to give a condensate which
was then fed through delivery tube 7 directly to decanter
4. The condensate introduced into decanter 4 was
separated into two layers in decanter 4 followed by
feeding the upper layer from decanter 4 through delivery
tube 11 to the top of the column while the lower layer of
decanter 4 was withdrawn through delivery tube 13 with the
liquid levels of the separated layers within decanter 4
held constant. Water was at the same time fed to decanter
4 through delivery tube 15 at a rate of 176.0 g/hr.
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The lower layer of decanter 4 gave 243.0 g/hr of
methanol containing 0.007 of n-hexane, 0.11$ of
methyl methacrylate, and 72.42$ of water. The methyl
methacrylate recovery loss amounted to 1.77.
COMPARATIVE EXAMPLE 4
An experiment was carried out using an apparatus
shown in FIG. 2. Use was made of an i.d. 35 mm, 30-plate
Oldershaw column as the distillation column and the
n-hexane was an azeotropic solvent. Distillation was
carried out at atmospheric pressure.
An azeotropic mixture (containing 82~ methanol) of
methyl methacrylate and methanol was fed at a rate of 76.6
g/hr through delivery tube 5 to the 25th plate counting
from the top of the distillation column 1, and 99.78 pure
methyl methacrylate was withdrawn from the bottom of the
column through delivery tube 14 at a rate of 13.52 g/hr.
Vapors stripped off the top of the column were led
through delivery tube 6 and cooled in condenser 2 (with
the use of a -10°C refrigerant) to give a condensate
which was then fed through delivery tube 7 directly to
decanter 4. The condensate introduced into decanter 4 was
separated into two layers in decanter 4 followed by
feeding the upper layer from decanter 4 through delivery
tube 11 to the top of the column while the lower layer of
decanter 4 was withdrawn through delivery tube 13 with the
liquid levels of the separated layers within decanter 4
held constant. The lower layer of decanter 4 gave
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2.~ 4 5838
69.09 g/hr of methanol containing 8.7$ of n-hexane, and
0.44$ of methyl methacrylate. The methyl methacrylate
recovery loss amounted to 2.2$.
EXAMPLE 5
An experiment was carried out using an apparatus
shown in FIG. 3. Use was made of an i.d. 35 mm, 30-plate
Oldershaw column as the distillation column and a 2-L
flask as an ester exchange reactor. The azeotropic
solvent was n-hexane.
Ester exchange reactor 16 was charged with 998 g of
methyl acrylate, 552 g of dimethyl aminoethanol, 22 g of
dibutyltin oxide, and 1.76 g of phenothiazine so as to
carry out a reaction at atmospheric pressure.
Vapors stripped from the top of distillation column
1 were led through delivery tube 6 and cooled in condenser
2 (with the use of a -10°C refrigerant) to give a
condensate which was then led through delivery tube 7 into
liquid distributor 3. Liquid distributor 3 was operated
to return part of the condensate through delivery tube 8
to the top of the distillation column so as to maintain
the temperatures from the column top to the 15th plate at
50.6°C and the remaining condensate liquid was led through
delivery tube 9 to decanter 4. The condensate led to
decanter 4 was separated into two layers in decanter 4.
The upper layer of decanter 4 was fed from delivery tube
10 to delivery tube 11 to the 20th plate counting from the
top of the column, while the lower layer from decanter 4
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214838
was discharged through delivery tube 13, while the liquid
levels in the separated layers within the decanter 4 were
maintained constant. Water was at the same time fed to
the decanter 4 through delivery tube 15 at a rate of 80
g/hr. Reactor 16 was fed with 22 g/hr of methyl acrylate.
The reaction was completed in 8.5 hours, resulting
in the ester exchange reactor 16 having a reaction liquid
mixture containing 841 g of dimethylaminoethyl acrylate.
The distillate from decanter 4 was 873.4 g of methanol
containing 0.002 of n-hexane, 0.23 of methyl
acrylate, and 77.9$ of water. The methyl acrylate loss
amounted to 0.17.
COMPARATIVE EXAMPLE 5
An experiment was carried out using an apparatus
shown in FIG. 4. Use was made of an i.d. 35 mm, 30-
plate Oldershaw column as the distillation column and a
2-L flask as an ester exchange reactor. The azeotropic
solvent was n-hexane.
Ester exchange reactor 16 was charged with 998 g of
methyl acrylate, 552 g of dimethyl aminoethanol, 22 g of
dibutyltin oxide, and 1.76 g of phenothiazine so as to
carry out a reaction at atmospheric pressure.
Vapors stripped from the top of distillation column
1 were led through delivery tube 6 and cooled in condenser
2 (with the use of a -10°C refrigerant) to give a
condensate which was then led through delivery tube 7
- 25 -
2I4~838
directly into decanter 4. The condensate led to decanter
4 was separated into two layers in decanter 4 and the
upper layer of decanter 4 was fed through delivery tube
11 to the top of the column, while the lower layer from
decanter 4 was discharged through delivery tube 13, with
the liquid levels in the separated layers within the
decanter 4 held constant. Water was fed at the same time
to decanter 4 through delivery tube 15 at a rate of 80
g/hr.
The reaction was completed in 8.5 hours, resulting
in the ester exchange reactor 16 having a reaction liquid
mixture containing 841 g of dimethylaminoethyl acrylate.
The distillate from decanter 4 was 906.0 g of methanol
containing 0.002$ of n-hexane, 3.81 of methyl
acrylate, and 75.1 of water. The methyl acrylate
recovery loss amounted to 2.91.
As described above, the present invention can
separate methanol by distillation from a mixture of methyl
(meth)acrylate and methanol with essentially no loss of
methyl (meth)acrylate. The addition of water to a
distillate mixture of methanol and the azeotropic solvent
permits an efficient separation of methanol from the
azeotropic solvent without the use of a second
distillation column, giving a substantial economic
advantage.
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