Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-06-13
2002-11-05
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S077000, C526S317100, C526S319000
Reexamination Certificate
active
06476162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for preventing easily polymerizing substance from polymerization in a packed column, and more particularly to a method for preventing from polymerization in a packed column using a packing having undergone a water-repelling treatment or a wetting treatment from inducing polymerization and a method for the production of (meth)acrylic acid or an ester thereof in the packed column having the packing disposed therein.
2. Description of the Related Art
Such easily polymerizing compounds as acrylic acid and methacrylic acid are raw material for commercial production and are chemical substances to be produced in large volumes at plants in large scale. In the case of (meth)acrylic acid, for example, such easily polymerizing compounds are produced by the reaction of catalytic gas phase oxidation of propylene, isobutylene, t-butanol, methyl-t-butyl ether, and acrolein.
In the reaction gas which is obtained by the reaction of catalytic gas phase oxidation, however, by-products of (meth)acrylic acid, a target product, are present in a mixed state. This reaction, for example, generates mainly non-condensable gases, namely unaltered propylene and isobutylene, low-boiling organic compounds having lower boiling points than acrylic acid, namely steam, unaltered acrolein, formaldehyde produced by a side reaction, and impurities such as acetic acid, and high-boiling compounds having higher boiling points than acrylic acid, namely maleic anhydride, furfural, benzaldehyde, benzoic acid, and acrylic acid dimer. For the purpose of purifying the target product, therefore, rectification and fractional distillation are carried out with various distilling columns.
Generally, in the distilling column, the vapor abounding in the low-boiling component and ascending to the top of the distilling column is cooled and condensed, the condensate is fallen from the top of the column and allowed to contact the vapor ascending from below and induced gasification of the low-boiling component included in the condensate, and at the same time the high-boiling component in the vapor is condensed and liquefied. As a result, the distilling column increases the purity of the low-boiling component of the vapor departing from the top of the column and, at the same time, increases the purity of the high-boiling component of the liquid falling to the bottom of the column.
The packed column which is one type of the distilling column types a device in popular use because it is at an advantage in having a simple structure, allowing easy manufacture, and incurring only small pressure loss of gas. In the packed column, various kinds of packing are used as a high-performance device for mass transfer for the purpose of saving energy improving the yield of products, increasing the amount of treatment, and decreasing pressure loss and for the elimination of such troubles as foaming and entrainment of mist. Particularly in the purification of an easily polymerizing substance, the packing is used for the purpose of exalting the property of separation.
The packing is regularly or irregularly disposed inside the column, for example, and used for causing the liquid descending from the upper part of the column and the vapor ascending from the lower part thereof to establish gas-liquid contact in a cruciform or counterflow pattern on the surface of the packing. Consequently,the gas-liquid contact surface is enlarged enough to allow thorough material transfer between the vapor and the liquid and accomplish efficient material separation.
The packing heretofore used in the packed column, however, has been only required to satisfy such conditions as manifesting a wide specific surface area, a large percentage of voids, high mechanical strength, a small apparent density, and high resistance to corrosion and enjoying inexpensiveness. The operation of material transferring by gas-liquid contact in the packed column which handles a solution containing an easily polymerizing substance, therefore, has possibly given generation of a polymer owing to the inferior contact between the gas and the liquid.
When acrylic acid is produced by the catalytic gas phase oxidation of propylene and/or acrolein with a molecular oxygen-containing gas, for example, the acrylic acid-containing liquid is unusually liable to induce the acrylic acid to polymerize because it contains such impurities as water,acetic acid,and acrolein. Generally for the purpose of preventing this polymerization, various polymerization inhibitors such as hydroquinone, p-methoxy phenol, and phenothiazine are added to the process of production either singly or in the form of a combination of two or more members and enabled to repress the polymerization of acrylic acid, etc. Since these inhibitors have higher boiling points than the easily polymerizing substance and are not contained in the vapor of distillation, they fail to prevent efficiently the polymerization of the easily polymerizing substance. The column, therefore, incurs the mishap of polymerization in the interior thereof, degrades the efficiency of the purification by separation, deteriorates the quality of the product and, at the same time, obstructs the continued operation of the column owing to the adhesion of the polymer to the devices and the blockage of the gas-liquid paths.
This situation necessitates early removal of the polymer. The removal of the polymer compels the process of purification to be suspended. The removal of the polymer adhering to the inner surface of the column is generally difficult.
Further, the packed column is of ten attached a reboiler to the bottom of the column. Through this reboiler, not only the vapor but also the bottom liquid of the column being circulated via the reboiler is blown in copiously. There is a case where the vapor of the target of purification ascends the interior of the distilling column in accordance with the ascending speed in the column and, at the same time, entrains the splash of the bottom liquid of the column and carries it as far as the bed of the packing in the column. Since part of the bottom liquid of the column mingles the product of distillation through the top of the column, the efficiency of the separation by distillation is possibly deteriorated. Particularly, when the polymer adheres to the packing in the packed column, the treatment for the removal of the adhering polymer necessitates great labor.
In the packed column which is used particularly for the expulsion of the easily polymerizing substance by distillation and the purification of the product by separation, therefore, a method for obtaining the target product with a high degree of purification while maintaining the purification of the product by separation of the easily polymerizing substance and preventing the easily polymerizing substance from yielding to polymerization has been desired.
SUMMARY OF THE INVENTION
The present inventor, as a result of pursuing an elaborate study regarding the packing intended to fill the packed column, has found that, by subjecting the surface of the packing to a water repelling treatment or a wetting treatment, the mishap of polymerization of the easily polymerizing substance can be prevented without degrading the efficiency of separation owing to the gas-liquid contact. This invention has been perfected as a result.
Specifically, this invention is aimed at providing the following items (1) or (2).
(1) A method for preventing an easily polymerizing substance from exposing the substance to polymerization in a packed column handling the easily polymerizing substance, characterized by subjecting the surface of a packing disposed in the interior of the column to a water repelling treatment or a wetting treatment.
(2) A method for the production of (meth)acrylic acid or an ester thereof, characterized by purifying at least one member selected from the group consisting of acrylic acid, methacrylic acid, and esters thereof in the presence of a polymerization inhibitor in a packed column having disp
Mori Masakatsu
Nishimura Takeshi
Sakamoto Kazuhiko
Sanada Kenji
Cheung William
Mathews, Collins Shepherd & McKay, P.A.
Nippon Shokubai Co. , Ltd.
Wu David W.
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