Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
1999-07-27
2003-12-16
Rotman, Alan L. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
C562S600000, C560S205000
Reexamination Certificate
active
06664418
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for inhibiting polymerization of a vinyl compound. More particularly, the present invention relates to a method for effectively inhibiting the polymerization of (meth)acrylic acid or esters of (meth)acrylic acid during these storage, transportation and production.
2. Description of the Prior Art
Vinyl compounds such as (meth)acrylic acid (i.e., acrylic acid or methacrylic acid), esters of (meth)acrylic acid, and acrylonitrile are prone to be naturally polymerized by light or heat due to the vinyl bond they have. Therefore, there have been proposed to use various polymerization inhibitors in order to inhibit polymerization of (meth)acrylic acid or esters of (meth)acrylic acid during their storage, transportation or production process.
As an example, there has been proposed use of methoquinone. Japanese Examined Patent Publication No. 414121 discloses a method for inhibiting polymerization of vinyl compounds using an N-oxyl compound such as bis-(2,2,6,6-tetramethyl-4-piperidino oxyl) sebacate.
However, the inventors of the present application have studied the stability of a vinyl compound during storage or transportation after addition of the above-mentioned N-oxyl compound, and found that the concentration of the N-oxyl compound gradually decreases in contact with the vinyl compound, and it is difficult to prevent polymerization of vinyl compounds for a prolonged time.
In the production process of vinyl compounds, particularly in the processes of recovery, purification and synthesis of vinyl compounds, polymerization of vinyl compounds proceeds. Therefore, there have been proposed to use various polymerization inhibitors in order to inhibit the polymerization of (meth)acrylic acid or esters of (meth)acrylic acid during these processes.
For example, Japanese Examined Patent Publication No. 45-1054 discloses a method for inhibiting polymerization of acrylic acid using an N-oxyl compound such as tertiary-butyl nitroxide and 4-hydroxy-2,2,6,6-tetramethyl-4-piperidino oxyl alone, gives better polymerization inhibiting effect than that of the conventionally known hydroquinone, pheno-thiazine, and cupric chloride etc.
Japanese Examined Patent Publication No. 54-3853 discloses a method for inhibiting the polymerization using 4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl or 2,2,6,6-tetramethylpiperidino oxyl in the production process of methacrylic acid from methacrolein using a gas containing oxygen in an organic solvent.
Japanese Examined Patent Publication No. 58-46496 discloses a method for inhibiting polymerization of (meth)acrylic acid or esters of (meth)acrylic acid, using 3-oxo-2,2,5,5-tetramethyl pyrolidino oxyl or 4-acetoxy 2,2,6,6-tetramethylpiperidino oxyl.
Chinese Patent CN 1052847A discloses a method for inhibiting polymerization of acrylic acid and esters of acrylic acid, using 4-hydroxy-2,2,6,6-tetramethylpiperldino oxyl alone or used in combination with hydroquinone, which is shown to be higher than the effect of combined use of copper dibutyldithiocarboxylate and hydroquinone.
Japanese Unexamined Patent Publication No. 6-345681 discloses a method for inhibiting polymerization of acrylic acid and esters of acrylic acid, using N-oxyl compounds such as 2,2,6,6-tetramethylpiperldino oxyl, and 4,4′,4″-tris(2,2,6,6-tetramethylpiperldino oxyl) phosphate in combination with phenol compounds such as hydroquinone, and phenothiazine compound.
Japanese Unexamined Patent Publication No. 9-316026 discloses a method for inhibiting polymerization of acrylic acid and esters of acrylic acid during its production, particularly during distillation process, using an N-oxyl compound in combination with phosphorus compound.
In the use of N-oxyl compounds according to the conventional polymerization inhibiting technology in the production process, for example, to prevent polymerization during distillation of crude acrylic acid, an N-oxyl compound is dissolved in acrylic acid and the solution is transferred to a distilling column by a pump.
The inventors found that the transfer of the solution, in which the N-oxyl compound is dissolved in acrylic acid, to the distilling tower in the recovery, purification and synthesis process of vinyl compound as mentioned above does not sufficiently inhibit the polymerization of vinyl compound.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for inhibiting polymerization of a vinyl compound which has overcome the problems residing in the prior art.
It is another object of the present invention to provide a method for stabilizing and inhibiting polymerization of vinyl compounds such as (meth)acrylic acid and ester of (meth)acrylic acid which can reliably assure stabilization and inhibition of polymerization of such vinyl compounds during storage, transportation and production of them, in the presence of an N-oxyl compound and a specific amount of water.
According to an aspect of the present invention, a method for inhibiting polymerization of a vinyl compound uses an N-oxyl compound and a specific amount of water. The presence of the N-oxyl compound can inhibit polymerization of the vinyl compound more effectively.
According to another aspect of the present invention, an N-oxyl compound is dissolved in water to produce a solution, and the solution is added to a vinyl compound in a process of recovering, purifying, or synthesizing the vinyl compound. In this way, polymerization of the vinyl compound can be effectively inhibited.
The vinyl compound has a vinyl bond which is liable to cause polymerization. Also, the N-oxyl compound includes any water soluble N-oxyl compounds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to inhibition of polymerization of (meth)acrylic acid and esters of (meth)acrylic acid.
Acrylic esters include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and the like. Also, methacrylic esters include methyl methacrylate, propyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and the like.
According to the present invention, any water soluble N-oxyl compounds is useable. It is preferable to use 2,2,6,6-tetramethylpiperidino oxyls represented by the following general formula (1);
wherein R
1
represents CHOH, CHCH
2
OH, CHCH
2
CH
2
OH, CHOCH
2
OH, CHOCH
2
CH, OH, CHCOOH or C═O, R
2
represents H or CH
2
OH.
The above-mentioned 2,2,6,6-tetramethylpiperidino oxyls include 4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl, 4-oxo-2,2,6,6-tetramethylpiperidino oxyl, 4-carboxy-2,2,6,6-tetramethylpiperidino oxyl, and the like. Among these, preferably used are 4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl, 4-oxo-2,2,6,6-tetramethylpiperidino oxyl, and the like, and particularly preferably used is 4-hydroxy-2,2,6,6-tetramethylpiperidino oxyl. These N-oxyl compounds may be used singly or at least two of these compounds may be used in combination. In this case, the mixing ratio may be appropriately decided.
More specifically, an N-oxyl compound may be preferably added in an amount of 0.0005 parts by weight or more, more preferably 0.001 parts by weight or more, to 100 parts by weight of a vinyl compound in order to ensure sufficient stabilization effects. On the other hand, addition of an N-oxyl compound too much causes staining in a produced acrylic acid. Accordingly, the amount may be preferably to set an upper limit up to 0.1 parts by weight, more preferably up to 0.03 parts by weight.
The adding amount of water may be adjusted in accordance with the solubility of water in the vinyl compound. It may be, however, preferable to dissolve 0.01 parts by weight or more of water to 100 parts by weight of the vinyl compound, more preferably 0.02 parts by weight or more, more preferably 0.05 parts by weight or more. To assure the inhibiting effect, on the other hand, it may be preferable to set the upper limit amount of water at 20 parts by weight, preferably 5 parts by weight, mor
Nakahara Sei
Ohkouchi Kazuo
Sakamoto Kazuhiko
Uemura Masahiro
Ueoka Masatoshi
Nippon Shokubai Co. , Ltd.
Oh Taylor V.
Rotman Alan L.
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