Distillation: processes – separatory – Spraying of distilland into vaporization zone
Reexamination Certificate
1999-02-19
2001-09-25
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
Spraying of distilland into vaporization zone
C203S091000, C203SDIG002, C202S158000, C202S236000, C261S097000, C261S114500, C562S600000
Reexamination Certificate
active
06294056
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus for distilling (meth)acrylic acid and/or (meth)acrylic ester in a distillation tower.
Distillation is an operation in which a raw liquid composed of two or more liquids in a mixed manner each having a different boiling point is heated for vaporization and the gas (or vapor) mainly composed of a component having a lower boiling point is condensed to separate the components of the mixture of liquids. In the case where the relative volatility between the components is great, the separation of the components is easy. However, there comes a problem that, in a normal state, the components cannot be separated with a desired concentration by merely vaporizing and condensing part of the mixture of liquids. Accordingly, it is a general practice in the art of distillation that part of the condensed liquid is returned (refluxed) from the top of the distillation tower while passing a tray or a surface of a packing provided in the tower to render the gas rising up through the distillation tower into contact with the reflux liquid returning from the top of the tower in an adequate manner so as to withdraw the component having a lower boiling point through the top of the distillation tower while withdrawing the component having a higher boiling point through the bottom of the distillation tower. The efficiency (distillation performance) of the distillation tower can be theoretically calculated according to the specification of the tower, the flow rate of the liquid and the gas to be supplied through the tower, and the property thereof.
If, however, the distributing ability of a liquid to be supplied into the distillation tower (hereinafter, also referred to as “supply liquid”) such as a raw liquid and a reflux liquid is low, the supply liquid unevenly flows through the distillation tower. Accordingly, it takes a plurality of trays when the apparatus/method adopts the tray tower, or a packing with a thickness of several ten millimeters is required when the apparatus/method adopts the packed tower system to evenly distribute the liquid.
Namely, in the conventional method and apparatus, a certain level of distillation performance that would have been obtained according to the theory could not be obtained occasionally. Especially, if the diameter of the distillation tower is large, or the surface tension of the supply liquid is great, or the viscosity of the supply liquid is high, or the supply liquid has a property that the liquid is easily separated into two liquid phases of oil phase and water phase, a problem has been pointed out that the liquid is liable to unevenly pass through the distillation tower, which would lower the distillation efficiency. Especially, the prior art apparatus/method has suffered from a problem that the distillation efficiency is gradually lowered in the case of distilling (meth)acrylic acid and/or (meth)acrylic ester.
FIG. 1
is a cross sectional view exemplifying a tray tower
10
which is generally used in the prior art when distilling (meth)acrylic acid and (meth)acrylic ester (hereinafter, also simply referred to as “(meth)acrylic acid” as a general term for (meth)acrylic acid and (meth)acrylic ester). In this embodiment, described is a case where a raw liquid in which (meth)acrylic acid is contained as a main component and acetic acid is contained as an impurity is used for distillation. The raw liquid is supplied into the distillation tower
10
through a line L
1
. Acetic acid having a lower boiling point rises up through the distillation tower
10
while being vaporized by heating, and is introduced into condensing means
20
via the top of the distillation tower
10
through a line L
2
. After condensation by the condensing means 20, the condensed liquid is drawn out through a line L
3
.
On the other hand, (meth)acrylic acid, having a higher boiling point, is drawn out from the bottom of the distillation tower
10
to a next step through a line L
4
. Part of a refined liquid obtained by the above distillation is returned to the distillation tower
10
via a reboiler
30
through a line L
5
. Since the condensed liquid by the condenser
20
contains (meth)acrylic acid as well as acetic acid (impurity), part of the condensed liquid is returned into the distillation tower
10
through a line L
6
as a reflux liquid to improve collecting efficiency of (meth)acrylic acid. After subject to gas-liquid contact in the distillation tower
10
, (meth)acrylic acid in the reflux liquid flows down onto the bottom of the distillation tower
10
and is drawn out to the next step.
Since (meth)acrylic acid is a compound liable to be polymerized quite easily, it is a general practice to add a polymerization inhibitor such as hydroquinone and phenothiazine to the raw liquid and the reflux liquid. Also, there has been adopted a method for supplying oxygen through a line L
7
to the bottom portion of the distillation tower
10
to suppress polymerization.
Despite of the above countermeasures, however, polymerization of (meth)acrylic acid cannot be completely prevented. Containment of polymerized matters in the distillation tower
10
lowers purification performance in the distillation tower
10
. Accordingly, what frequently happened was to suspend operation of the distillation tower
10
for removing the polymerized matters accumulated in the distillation tower
10
.
SUMMARY OF THE INVENTION
In view thereof, an object of this invention is to provide a method and an apparatus for distilling (meth)acrylic acid and/or (meth)acrylic ester that enables distillation of supply liquid with high purification efficiency for a long operating time, while preventing polymerization of (meth)acrylic acid in the distillation tower.
To achieve the above object, an aspect of this invention is directed to a method for distilling (meth)acrylic acid and/or (meth)acrylic ester in a distillation tower, comprising the step of uniformly distributing a supply liquid to be supplied into the distillation tower over an entirety of a horizontal cross sectional area in the distillation tower to prevent polymerization of (meth)acrylic acid in the distillation tower.
According to the distillation method of this invention, the supply liquid may include a raw liquid before distillation, a reflux liquid which is returned into the distillation tower after condensation outside the distillation tower, and a refined liquid obtained after the distillation.
Preferably, according to the distillation method of this invention, at least one of the supply liquids may be supplied into the distillation tower through at least two supply ports.
More preferably, according to the distillation method of this invention, at least one of the supply liquids may be supplied into the distillation tower in a spraying manner.
In the case where the distillation tower is a tray tower, the concentration of a composition in a liquid existing at any location of a tray immediately below the supply port may vary within the range of ±30% of the average concentration of the liquid on the tray. It may be preferable to set a pressure loss at the supply port of the liquid at 50 mmH
2
O or more so as to uniformly distribute the liquid.
Another aspect of this invention is directed to an apparatus for distilling (meth)acrylic acid and/or (meth)acrylic ester in a distillation tower comprising: supply means for supplying at least one of supply liquids including a raw liquid, reflux liquid, and a refined liquid into the distillation tower, the supply means including at least two supply ports through which the liquid is supplied into the distillation tower.
Preferably, the supply port may be provided with a pressure loss generator (e.g., an orifice plate).
More preferably, the supply means for supplying at least one of the supply liquids including a raw liquid, a reflux liquid, and a refined liquid may include an atomizer.
The above and other objects, features and advantages of the present invention will become more apparent upon a reading of the following detailed descri
Arakawa Kazukiyo
Dodo Osamu
Iwato Hiroo
Matsumoto Yukihiro
Takamura Mamoru
Manoharan Virginia
Nippon Shokubai Co. , Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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