U.S. patent application number 10/058459 was filed with the patent office on 2002-07-25 for liquid withdrawing tray for purification column, purification column, and method for purification.
Invention is credited to Inada, Misao, Matsumoto, Hajime, Matsumoto, Yukihiro, Nakahara, Sei, Nishimura, Takeshi.
Application Number | 20020098123 10/058459 |
Document ID | / |
Family ID | 17580199 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020098123 |
Kind Code |
A1 |
Matsumoto, Hajime ; et
al. |
July 25, 2002 |
Liquid withdrawing tray for purification column, purification
column, and method for purification
Abstract
In the purification of an easily polymerizable compound such as
(meth)acrylic acid by the use of a purification column adapted to
withdraw a liquid from the middle portion of the column, a novel
liquid withdrawing tray adapted to prevent the compound from
polymerization effectively and permit the purification to be stably
performed for a long time, a purification column using this tray,
and a method for purifications using this purification column are
provided. The liquid withdrawing tray for the purification column
is composed of a liquid receiving plate and a liquid withdrawing
tube for withdrawing the liquid from the liquid receiving
plate.
Inventors: |
Matsumoto, Hajime; (Hyogo,
JP) ; Nishimura, Takeshi; (Hyogo, JP) ;
Matsumoto, Yukihiro; (Hyogo, JP) ; Nakahara, Sei;
(Hyogo, JP) ; Inada, Misao; (Hyogo, JP) |
Correspondence
Address: |
Mathews, Collins,
Shepherd & Gould, P.A.
100 Thanet Circle, Suite 306
Princeton
NJ
08540
US
|
Family ID: |
17580199 |
Appl. No.: |
10/058459 |
Filed: |
January 28, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10058459 |
Jan 28, 2002 |
|
|
|
09667283 |
Sep 22, 2000 |
|
|
|
Current U.S.
Class: |
422/400 |
Current CPC
Class: |
C07C 57/04 20130101;
C07C 67/54 20130101; B01D 3/4205 20130101; Y10S 203/11 20130101;
B01D 3/20 20130101; C07C 67/54 20130101; C07C 51/44 20130101; C07C
69/54 20130101; C07C 51/44 20130101 |
Class at
Publication: |
422/100 |
International
Class: |
B01L 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 1999 |
JP |
11-277199 |
Claims
What is claimed is:
1. A liquid withdrawing tray for a purification column, comprising
a liquid receiving plate and a liquid withdrawing tube
communicating with said liquid receiving plate and serving the
purpose of withdrawing the liquid.
2. A tray according to claim 1, wherein said receiving plate has
the shape of a funnel.
3. A tray according to claim 1, wherein said liquid receiving plate
is provided in the upper outer periphery thereof with notches.
4. A tray according to claim 1, wherein the angle of the downward
slope of said liquid withdrawing tube from the horizontal direction
is in the range of 0.5-80.degree..
5. A purification column provided in the column interior thereof
with a liquid withdrawing tray according to any one of claims
1-4.
6. A purification column according to claim 5, wherein the largest
cross sectional area, S1, of said liquid withdrawing tray is in the
range of 10-90% of the cross sectional area, S2, of said
purification column.
7. A purification column according to claim 5, wherein said liquid
receiving plate is provided thereunder with at least one spray
nozzle for spraying the lower side of said liquid receiving plate
with a liquid.
8. A purification column according to claim 5, wherein said liquid
receiving plate is provided thereover with at least one liquid
injecting nozzle for injecting a liquid into the liquid surface in
said liquid receiving plate.
9. A method for purifying an easily polymerizable compound, which
comprises effecting the purification by the use of a purification
column set forth in claim 5.
10. A method according to claim 9, wherein said easily
polymerizable compound is at least one member selected from the
group consisting of (meth)acrylic acid and esters thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a liquid withdrawing tray for a
purification column, a purification column, and a method for
purification. More particularly, it relates to a tray for
withdrawing a liquid from a middle portion or middle level of a
purification column, a purification column furnished with the tray,
and a method for purification an easily polymerizable compound such
as (meth)acrylic acid by the use of the purification column.
[0003] 2. Description of the Prior Art
[0004] As a method for production of acrylic acid and esters
thereof, the method by oxidizing propylene and/or acrolein with a
molecular oxygen-containing gas in vapor phase, recovering a
reaction product gas thus obtained with a solvent, and subjecting a
reaction product-containing solution thus obtained purification in
a purification column to obtain purified acrylic acid or esters
thereof (JP-A-9-227445).
[0005] In the purification column, such operations as withdrawing
as withdrawing reflux liquid in the column from the middle portion,
generally the middle level, of the column for the purpose of
withdrawing an intermediate product, and cooling or heating the
reflux liquid are routine. Then, for the purpose of withdrawing the
liquid from the middle portion of the purification column, the
chimney tray which is composed of a vapor conduit (gas riser), an
umbrella covering the conduit, and a liquid withdrawing tube has
been popularly used (refer, for example, to Henry Z. Kister,
"Distillation Operation," pp. 102-116 [published in 1990 by McGraw
Hill, Inc.]). The chimney tray which is concurrently provided with
a vapor conduit and a liquid withdrawing tube is also available for
the purpose of the withdrawal of interest.
[0006] In purification of such an easily polymerizable compound as
(meth)acrylic acid, the measure taken to polymerize the easily
polymerizable compound is important for operating the purification
column stably. For inhibiting this polymerization, the practice of
adding such a polymerization inhibitor as phenothiazine,
hydroquinone, or methoquinone has been in vogue.
[0007] When the purification column provided with the chimney tray
is used in purifying the easily polymerizable compound, however,
the polymerization of the compound occurs throughout the entire
chimney tray inclusive of the vapor conduit and the umbrella in
spite of the use of the polymerization inhibitor and the polymer
brings the problem of clogging the chimney tray and preventing it
from being stably operated for a long time. Then, in the case of
the chimney tray provided concurrently with a vapor conduit and a
liquid withdrawing tube, since the descending liquid comes into
counterflow contact with the vapor in motion at a relatively high
speed, this vapor entrains liquid splash to the upper part of the
purification column and impairs the separating effect of the
purification column. This impairment possibly results in increasing
the content of impurities in the target product of purification
obtained via the top of the column.
[0008] An object of this invention, therefore, is to provide a
novel liquid withdrawing tray for the purification column, a
purification column utilizing the tray, and a method for
purification.
[0009] Another object of this invention is to provide a tray for
withdrawing the liquid from the middle portion or middle level of
the purification column, a purification column provided with the
tray, and a method for purification such an easily polymerizable
compound as (meth)acrylic acid by the use of this purification
column.
[0010] Still another object of this invention is to provide, in
purification such an easily polymerizable compound as (meth)acrylic
acid, a novel liquid withdrawing tray adapted to allow effective
prevention of the polymerization and enable the purification to be
performed stably for a long time, a purification column provided
with the tray, and a method for purifying the easily polymerizable
compound by using the purification column.
SUMMARY OF THE INVENTION
[0011] The objects mentioned above are accomplished by the
following items (1)-(10).
[0012] (1) A liquid withdrawing tray for a purification column,
comprising a liquid receiving plate and a liquid withdrawing tube
communicating with the liquid receiving plate and serving the
purpose of withdrawing the liquid.
[0013] (2) A tray set forth in (1) above, wherein the receiving
plate has the shape of a funnel.
[0014] (3) A tray set forth in (1) or (2) above, wherein the liquid
receiving plate is provided in the upper outer periphery thereof
with notches.
[0015] (4) A tray set forth in any one of (1)-(3) above, wherein
the angle of the downward slope of the liquid withdrawing tube from
the horizontal direction is in the range of
0.5.degree.-80.degree..
[0016] (5) A purification column provided in the column interior
thereof with a liquid withdrawing tray set forth in any one of
(1)-(4) above.
[0017] (6) A purification column set forth in (5) above, wherein
the largest cross sectional area, S1, of the liquid withdrawing
tray is in the range of 10-90% of the cross sectional area, S2, of
the purification column.
[0018] (7) A purification column set forth in (5) or (6) above,
wherein the liquid receiving plate is provided thereunder with at
least one spray nozzle for spraying the lower side of the liquid
receiving plate with a liquid.
[0019] (8) A purification column set forth in any one of (5) -(7)
above, wherein the liquid receiving plate is provided thereover
with at least one liquid injecting nozzle for injecting a liquid
into the liquid surface in the liquid receiving plate.
[0020] (9) A method for purifying an easily polymerizable compound,
which comprises effecting the purification by the use of a
purification column set forth in any one of (5)-(8) above.
[0021] (10) A method set forth in (9) above, wherein the easily
polymerizable compound is at least one member selected from the
group consisting of (meth)acrylic acid and esters thereof.
[0022] In the purification column, the polymerization inhibitor is
present mainly in the liquid phase and hardly ever in the gas
phase. When the vapor in the gas phase condenses in the dry part of
the interior of the purification column, therefore, the condensate
readily polymerizes because it is exposed in a state destitute of
the polymerization initiator at a relatively high temperature in
the purification column.
[0023] In the case of the chimney tray, the lower (reverse) surface
of the umbrella covering the vapor conduit is not always kept wet
with the condensate and, therefore, is possibly suffered to permit
the appearance of a dry part. More often than not, the
polymerization occurs in the dry part under the umbrella.
[0024] The study further continued has brought a discovery that the
use of a funnel-shaped tray devoid of an umbrella in the place of
the conventional chimney tray deprives the tray surface of the dry
part and consequently permits effective prevention of the
occurrence of the polymerization. The present invention has been
perfected on the basis of this knowledge.
[0025] By adopting the liquid withdrawing tray of this invention
and using the purification column provided with this tray in
purifying an easily polymerizable compound such as (meth)acrylic
acid, for example, it is made possible to prevent effectively the
occurrence of the polymerization in the tray part. The purification
of the easily polymerizable compound, therefore, can be stably
carried out for a long time. In this invention, the purification
column effects the separation with high efficiency because the
entrainment of liquid splash to the upper part of the purification
column is reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a cross section illustrating one preferred
embodiment of the liquid withdrawing tray according to this
invention.
[0027] FIG. 2 is a cross section illustrating another preferred
embodiment of the liquid withdrawing tray according to this
invention.
[0028] FIG. 3 is a cross section illustrating still another
preferred embodiment of the liquid withdrawing tray according to
this invention.
[0029] FIG. 4 is a cross section illustrating yet another preferred
embodiment of the liquid withdrawing tray according to this
invention.
[0030] FIG. 5 is a cross section illustrating another preferred
embodiment of the liquid withdrawing tray according to this
invention.
[0031] FIG. 6 is a cross section illustrating still another
preferred embodiment of the liquid withdrawing tray according to
this invention.
[0032] FIG. 7 is a plan view of the liquid withdrawing tray shown
in FIG. 6.
[0033] FIG. 8 is a cross section illustrating yet another preferred
embodiment of the liquid withdrawing tray according to this
invention.
[0034] FIG. 9 is a cross section illustrating another preferred
embodiment of the liquid withdrawing tray according to this
invention.
[0035] FIG. 10 is a cross section illustrating still another
preferred embodiment of the liquid withdrawing tray according to
this invention.
[0036] FIG. 11 is a partial side view illustrating one preferred
embodiment of the liquid receiving plate in the liquid withdrawing
tray according to this invention, wherein the plate is provided in
the lateral face part thereof with notches.
[0037] FIG. 12 is a partial cross section illustrating one
preferred embodiment of the purification column of this invention
provided with the liquid withdrawing tray.
EXPLANATION OF THE PREFERRED EMBODIMENTS
[0038] Now, the preferred embodiments of this invention will be
explained below with reference to the accompanying drawings.
[0039] FIG. 1 is a cross section illustrating one preferred
embodiment of the liquid withdrawing tray according to this
invention. A liquid withdrawing tray 11 is composed of a liquid
receiving plate 12 and a liquid withdrawing tube 13 communicating
with the bottom part of the liquid receiving plate and serving the
purpose of withdrawing the liquid in the liquid receiving plate out
of a purification column (not shown). The lateral shape (the shape
of longitudinal cross section) of this liquid receiving plate 12
does not need to be particularly discriminated but has only to be
capable of accommodating the liquid in the purification column (not
shown) and allowing the liquid to overflow the liquid receiving
plate 12 in the proximity of the upper end part thereof, wet the
lower lateral face of the tray, and prevent the lower lateral face
from producing a dry part. Generally, this lateral shape is
preferred to resemble a funnel as illustrated in FIG. 1 and the
plan view of the liquid receiving plate 12 is a circle, for
example. The liquid withdrawing tube 13 in this case is so
constructed as to extend in the perpendicular direction from the
lowermost part of the liquid receiving plate 12, begin to slope
down at a point halfway along the entire length thereof, and
communicate with the exterior of the purification column (not
shown).
[0040] The plan shape of the liquid receiving plate 12 has no
particular restriction either but has only to be capable of being
set in the purification column. As typical examples of the plan
shape, a circle, a semicircle, an ellipsis, a square, and a broken
circle may be cited. Among other shapes mentioned above, the circle
is used particularly advantageously.
[0041] FIGS. 2-8 are schematic cross sections illustrating
preferred embodiments of the liquid withdrawing tray using the same
liquid receiving plates as the funnel-shaped liquid receiving plate
illustrated in FIG. 1.
[0042] Specifically, in a liquid withdrawing tray 21 illustrated in
FIG. 2, a liquid receiving plate 22 has a funnel-shaped
longitudinal cross section similarly in the embodiment of FIG. 1
and a liquid withdrawing tube 23 descends in an oblique direction
from the bottom part of the liquid receiving plate 22.
[0043] In a liquid withdrawing tray 31 illustrated in FIG. 3, a
liquid receiving plate 32 has a cylindrical shape containing a
converging part in the lower portion thereof. From the bottom part
of the liquid receiving plate 32, a liquid withdrawing tube 33
descends and turns in a substantially horizontal direction at a
point halfway along the entire length thereof and communicates with
the exterior.
[0044] In a liquid withdrawing tray 41 illustrated in FIG. 4, a
liquid receiving plate 42 is shaped like a funnel similarly in the
embodiment of FIG. 1 and a liquid withdrawing tube 43 descends from
the bottom part of the liquid receiving plate 42 and turns in a
substantially horizontal direction at a point halfway along the
entire length thereof and communicates with the exterior similarly
in the embodiment of FIG. 3.
[0045] In a liquid withdrawing tray 51 illustrated in FIG. 5, a
liquid receiving plate 52 is shaped like a bowl and a liquid
withdrawing tube 53 is similar to the liquid withdrawing tubes of
FIG. 3 and FIG. 4.
[0046] A liquid withdrawing tray 61 illustrated in FIG. 6 is
constructed by providing a liquid withdrawing tube 63 similar to
those of FIG. 3-FIG. 5 for a liquid receiving plate 62 comprising
one side inclined from a perpendicular plane at a point halfway
along the entire length thereof, the another side inclined from the
upper through the lower end thereof (See FIG. 7).
[0047] In a liquid withdrawing tray 71 illustrated in FIG. 8, a
liquid receiving plate 72 is shaped like a pot having a narrow
opening and a liquid withdrawing tube 73 is similar to those of
FIG. 3-FIG. 6. Then, the liquid receiving plate 72 is provided
below the lower lateral side thereof with at least one spray nozzle
74 for spraying a liquid to the lower lateral side thereof,
preferably a plurality of such spray nozzles spaced by an equal
interval, to ensure the wetting of the lower lateral side. This
liquid receiving plate 72 communicates with a liquid supply conduit
75.
[0048] In a liquid withdrawing tray 81 illustrated in FIG. 9, a
liquid receiving plate 82 is shaped like a wine glass having a
narrow opening and a liquid withdrawing tube is similar to those of
FIG. 3-FIG. 8. Then, the liquid receiving plate 82 is provided
below the lower lateral side thereof with at least one spray nozzle
84 for spraying a liquid to the lower lateral side thereof,
preferably a plurality of such spray nozzles spaced by an equal
interval, to ensure the wetting of the lower lateral side. This
liquid receiving plate 82 communicates with a liquid supply conduit
85.
[0049] Above mentioned Figures show embodiments of funnel type
liquid receiving plate, and the funnel type means a liquid
receiving plate having a tapered portion at least one portion of
the bottom. The liquid in the liquid receiving plate flows down
smoothly without storage, so polymerization of the liquid is
inhibited.
[0050] FIG. 10 shows an embodiment of a dish type liquid receiving
plate and the liquid receiving plate 92 has the shape of a cylinder
or a square cup and a liquid withdrawing tube 93 is similar to
those of FIG. 3-FIG. 9. Then, the liquid receiving plate 92 is
provided below the lower lateral side thereof with at least one
spray nozzle 94 for spraying a liquid to the lower lateral side
thereof, preferably a plurality of such spray nozzles spaced by an
equal interval, to ensure the wetting of the lower lateral side.
This liquid receiving plate 92 communicates with a liquid supply
conduit 95.
[0051] In the liquid receiving plates illustrated in FIG. 1-FIG.
10, those illustrated in FIG. 1-FIG. 6 are used particularly
advantageously because their lower lateral sides are wetted
throughout with the liquid overflowing the liquid receiving plates
near the upper ends thereof and are substantially incapable of
producing a dry part. They also enable their pertinent purification
columns to effect the expected separation with an exalted
efficiency because they reduce the entrainment of liquid splash to
the upper parts of the purification columns.
[0052] The liquid receiving plates illustrated in FIG. 8-FIG. 10,
for the purpose of ensuring the wetting of the lower lateral sides
thereof, may be provided with at least one spray nozzle 74 for
spraying the liquid or a plurality of such spray nozzles spaced
with an equal interval. As the liquid used for spraying, it is
advantageous to withdraw the liquid in the liquid receiving plate
through the liquid withdrawing tube and circulate it to the spray
nozzle because the use of this liquid in this manner has only
sparing effect to bear on the material balance within the
purification column.
[0053] The liquid withdrawing tube is commended to be inclined
downward from the horizontal direction with an angle, (refer to
FIG. 1), in the range of 0.5.degree.-80.degree., preferably
1.degree.-70.degree., and particularly preferably
2.degree.-40.degree., lest the liquid should remain on the surface
of the liquid withdrawing tube during a suspension of the operation
of the purification column. If this angle is less than 0.5.degree.,
the shortage will be at a disadvantage in suffering the liquid to
remain readily because of insufficient descent of the liquid.
Conversely, if the angle exceeds 80.degree., the excess will be at
a disadvantage in the fact that a certain distance for a height
direction in the column is required until the liquid is discharged,
and as a result storage time in the gas phase becomes long, so the
gas is apt to polymerize in the gas phase.
[0054] The liquid withdrawing tray according to this invention is
referred to be provided in the outer peripheral edge thereof with
notches so as to promote the overflow of the liquid from the liquid
receiving plate and keep the lateral side of the tray wet
throughout the surface. FIG. 11 is a partially longitudinal cross
section of a liquid receiving plate 102 which is provided with
notches 106. Though the intervals between the notches and the
widths and the largest depths of the notches are not generally
definite because they are variable as with the size of the liquid
receiving plate, the intervals between the notches (the distances
between the bottom parts of the adjacent notches) are preferred to
be in the range of 2-100 mm, preferably 5-50 mm, the widths of the
notches to be in the range of 2-100 mm, preferably 5-50 mm, and the
largest depths of the notches to be in the range of 2-100 mm,
preferably 5-50 mm.
[0055] Incidentally, the shape of such notches does not need to be
particularly limited and may be properly selected as from among a
triangle (V-shape), a square, and a semicircle.
[0056] FIG. 12 is an explanatory cross section of the purification
column of this invention which is furnished with the liquid
withdrawing tray mentioned above. Specifically, in a shelf type
purification column 130 provided with a tray 131, a liquid
withdrawing tray 121 provided with a liquid receiving plate 122
having a liquid withdrawing tube 123 connected to the bottom part
thereof is supported by a liquid withdrawing tray-supporting plate
133.
[0057] As regards the size of the liquid withdrawing tray, the
largest cross section (such as the area denoted by the reference
numeral S1 in FIG. 3 and FIG. 8) is properly in the range of
10-90%, preferably 20-80%, of the cross section (S2) of the
purification column. That is, the quotient of S1/S2 (.times.100) is
preferred to fall in the range mentioned above. If the quotient
exceed 90%, the excess will beat a disadvantage in increasing the
pressure loss due to a decrease in the vapor flow path and tending
to induce the entrainment of liquid splash due to an increase in
the linear velocity of the vapor. Conversely, if the quotient is
less than 10%, the shortage will be at a disadvantage in preventing
the purposes of such actions as mixing, cooling, heating, and
drawal of an intermediate product from being fully attained.
[0058] Part of the liquid received in the liquid withdrawing tray
121 is withdrawn in a prescribed unit volume from the purification
column and the remainder thereof is left overflowing the tray 121
across the upper edge thereof. For the purpose of enabling the
liquid to overflow the tray 121, it suffices to fix the amount of
the liquid to be withdrawn to the exterior in the range of 5-80%,
preferably 20-70%, of the amount of the reflux liquid in the
column. The overflowing liquid keeps falling into the tray laid
beneath while wetting the lower lateral side of the liquid
withdrawing tray 121. By there flux liquid containing the
polymerization inhibitor, the lateral side of the liquid
withdrawing tray 121 is kept wet and protected against
polymerization. This overflow is promoted by the provision of the
notches mentioned above.
[0059] For the purpose of effectively preventing the
polymerization, the purification column may be provided with spray
nozzles 124 adapted to spray part of the liquid withdrawn from the
purification column against the lower lateral side of the tray 121.
The nozzles communicate with a liquid supply conduit 125. Besides
or simultaneously with the spray nozzles 124, the purification
column may be provided with at least one liquid injection nozzle
135 adapted to inject the liquid into the liquid surface in the
liquid withdrawing tray 121. This nozzle communicates with a liquid
supply conduit 136. By injecting the liquid through this liquid
injecting nozzle 135, it is made possible to keep the liquid in the
liquid receiving plate stirred and prevent the liquid from
stagnating and inducing polymerization. Incidentally, a spray
nozzle is advantageously used as the liquid injection nozzle 135.
When a separate feed liquid is simultaneously sprayed, the
efficiency of separation is improved because the mixing of the
reflux liquid in the column with the feed liquid is promoted.
[0060] When the liquid withdrawing tray in accordance with the
present invention is used, in the purification column for the
easily polymerizable compound, it is useful for the following
objects. In a system where polymer generates, it is possible to
discharge the liquid form the column, to separating a polymer by a
solid-liquid separator and to return only the liquid into the
column. Further, when a liquid composition between a reflux liquid
in the column and a fed liquid is considerably different or the
reflux liquid has two liquid phases, polymerization in the column
can be inhibited by mixing uniformly. Furthermore, it becomes
possible to inhibit the polymerization and proceed the reaction by
withdrawing the liquid in the column, adding the polymerization
inhibitor and a reaction product, and returning it to the tray.
[0061] The method of this invention for the purification of an
easily polymerizable compound can be implemented in an ordinary way
except that the use of the purification column mentioned above. In
this specification, the "purification" means distillation
(rectification), stripping and absorption, and the "purification
column" means distillation (rectification) column, stripper and
absorber.
[0062] The liquid withdrawing tray and the purification column in
accordance with this invention are used particularly advantageously
in handling an easily polymerizable compound. The easily
polymerizable compounds include (meth)acrylic acid and esters
thereof. As typical examples of the compound, alkyl esters having
alkyl groups of 1-8 carbon atoms such as methyl esters, ethyl
esters, n-propyl esters, isopropyl esters, n-butyl esters, n-hexyl
esters, and 2-ethylhexyl esters, cycloalkyl esters such as
cyclohexyl esters, hydroxyalkyl esters of 2-3 carbon atoms such as
2-hydroxyethyl esters, 2-hydroxypropyl esters, and 3-hydroxypropyl
esters, and alkyl or dialkylaminoalkyl esters such as
methylaminoethyl esters, ethylaminoethyl esters, dimethylaminoethyl
esters, and diethylaminoethyl esters may be cited. These compounds
may be used for purification either singly or in the form of a
mixture or a in the form of a solution containing them.
[0063] Now, this invention will be described more specifically
below with reference to working examples.
EXAMPLE 1
[0064] A funnel-shaped liquid withdrawing tray fulfilling the
following particulars and illustrated in FIG. 1 was installed
between the 15.sup.th and the 16.sup.th shelf of a distillation
column made of stainless steel (SUS 304) having an inside diameter
of 1500 mm and containing a total of 50 shelves.
[0065] Diameter of the uppermost part (outer peripheral edge): 1100
mm
[0066] Cross section of tray/cross section of column (S1/S2):
0.54
[0067] Notches in the outer peripheral edge: V notches 10 mm in
width, 10 mm in pitch, and 10 mm in depth
[0068] Inclination (.alpha.) of withdrawing tube: 1.degree.
[0069] The distillation column mentioned above was kept supplied
with acrylic acid containing maleic acid as impurity at a
concentration of 0.8% by weight at a feed rate of 9 tons per hour
and was operated fir continuous distillation under the conditions
of 0.6 of reflux ratio, 35 mmHg of working pressure, and 63.degree.
C. of working temperature. The liquid withdrawn to the exterior
from the funnel-shaped liquid withdrawing tray was sprayed on the
lateral side of the tray and the liquid surface respectively at a
rate of 1 ton per hour.
[0070] During the course of the distillation, phenothiazine as a
polymerization inhibitor was added to the feed liquid to the
distillation column in an amount calculated to account for a
concentration of 100 ppm. A gas containing oxygen was continuously
supplied in a prescribed amount to the interior of the distillation
column via the bottom thereof.
[0071] This apparatus was used to continue the distillation for 1
month. In this while, the distillate from the column top was found
to contain maleic acid as an impurity at a concentration of 0.1% by
weight. When the interior of the column was visually inspected
after 1 month's operation, the amount of a polymer formed in the
vicinity of the funnel-shaped withdrawing tray inclusive of the
liquid withdrawing tube was found to be about 1 kg.
EXAMPLE 2
[0072] Continuous distillation was carried out by following the
procedure of Example 1 while omitting the spray of the liquid to
the lateral side of the funnel-shaped liquid withdrawing tray.
[0073] When the interior of the column was visually inspected after
1 month's continuous distillation, the amount of a polymer formed
in the vicinity of the funnel-shaped withdrawing tray inclusive of
the liquid withdrawing tube was found to be about 1.2 kg.
EXAMPLE 3
[0074] Continuous distillation was carried out by following the
procedure of Example 1 while using a funnel-shaped liquid
withdrawing tray containing no notch in the outer peripheral edge
(with no other change).
[0075] When the interior of the column was visually inspected after
1 month's continuous distillation, the amount of a polymer formed
in the vicinity of the funnel-shaped withdrawing tray inclusive of
the liquid withdrawing tube was found to be about 1.2 kg.
EXAMPLE 4
[0076] Continuous distillation was carried out by following the
procedure of Example 1 while using a funnel-shaped liquid with
drawing tray having no inclination in a liquid withdrawing tube
(.alpha.=0) (with no other change).
[0077] When the interior of the column was visually inspected after
1 month's continuous distillation, the amount of a polymer formed
in the vicinity of the funnel-shaped withdrawing tray inclusive of
the liquid withdrawing tube was found to be about 1.1 kg.
[0078] Control 1
[0079] Continuous distillation was carried out by following the
procedure of Example 1 while using a chimney tray (cross section of
tray/cross section of column=0.56, equivalent to a funnel-shaped
liquid withdrawing tray measuring 1100 mm in inside diameter)
provided with a vapor conduit 1000 mm in diameter in the place of
the funnel-shaped liquid withdrawing tray.
[0080] Duringthelmonth's continued operation, the distillate
emanating from the column top was found to contain maleic acid as
an impurity at a concentration of 0.2% by weight. When the interior
of the column was visually inspected after 1 month's continuous
purification, the amount of a polymer formed in the vicinity of the
chimney tray inclusive of the liquid withdrawing tube was found to
be about 3 kg.
[0081] The results of the examples 1-4 and the control 1 are
collectively shown in Table 1.
1 TABLE 1 Example 1 Example 2 Example 3 Example 4 Control 1 Inside
diameter of distillation column mm 1500 .rarw. .rarw. .rarw. .rarw.
Number of shelves 50 .rarw. .rarw. .rarw. .rarw. Shelves used for
intermediate extraction 15-16 .rarw. .rarw. .rarw. .rarw. Liquid
withdrawing tray mm funnel type .rarw. .rarw. .rarw. riser type
Inside diameter of tray 1100 .rarw. .rarw. .rarw. 1100 mm Working
pressure mmHg 35 .rarw. .rarw. .rarw. .rarw. Working temperature
.degree. C. 63 .rarw. .rarw. .rarw. .rarw. Spray of lateral side of
tray yes no yes .rarw. .rarw. Notch yes .rarw. no yes .rarw.
Inclination of withdrawing nozzle yes .rarw. .rarw. no yes Maleic
acid contained in feed liquid to Wt % 0.8 .rarw. .rarw. .rarw.
.rarw. distillation column Polymerization inhibitor (phenothiazine)
ppm 100 .rarw. .rarw. .rarw. .rarw. (After completion of 1 month's
continued operation) Maleic acid in distillate Wt% 0.1 .rarw.
.rarw. .rarw. 0.2 Polymer in column kg 1 1.2 1.2 1.1 3
[0082] Comparison of the results of the working examples and those
of the control reveals that the use of the liquid withdrawing tray
of this invention permitted prevention of polymerization and
allowed improvement in the efficiency of separation in the
distillation column.
[0083] The entire disclosure of Japanese Patent Application No.
11-277199 filed on Sep. 29, 1999 including specification, claims
and summary are incorporated therein by reference in its
entirely.
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