Mitsui Toatsu Chemicals, Incorporated

Kuraray Co., Ltd.

Kyowa Gas Chemical Industry Company, Ltd.

Mitsui Chemicals, Inc.

Takeshi Isobe

Hirozo Segawa

Morimasa Kuragano

Katsuji Yoguchi

Yoshihiro Sezaki

Rensuke Ikarashi

Minoru Koshibe

Kozo Iwasaki

Isao Fukada

Nobutaka Ueda

Kazuo Wakimura

Yoshio Koyama

Shin-ichi Tadokoro

Koji Fujita

Tadaharu Hase

A process for producing refined methacrylic acid comprising the steps of oxidizing methacrolein and the like catalytically in a vapor phase to form a methacrylic acid-containing gas, cooling and condensing the gas to an aqueous methacrylic acid solution, adding to the solution an organic solvent that forms two liquid phases with water to carry out an extraction operation and thereby to obtain an extract, bringing the extract into contact with water to mix them together, separating the mixture into an organic phase and a water phase, and distilling the organic phase. According to this process, highly refined methacrylic acid containing little dibasic acids such as maleic acid and citraconic acid can be obtained economically and without increasing wastes that are unrecoverable to the process.

Process for refining methacrylic acid

A process is provided for the purification of methacrylic acid. The process can easily remove dibasic acids and aldehydes containing in trace amounts as impurities. According to the process, crude methacrylic acid obtained as an aqueous solution by vapor-phase catalytic oxidation of isobutylene, tertiary butanol, methacrolein or isobutyl aldehyde is treated with at least one compound selected from the group consisting of m-aminophenol, m-phenylenediamine, 2,4-diaminotoluene and 2,4-diamino-diphenylamine, followed by distillation, optionally, in the presence of a p-phenylene diamine.

Purification process of methacrylic acid

In order to recover methacrolein and/or methacrylic acid by quenching a reaction product gas obtained by catalytic oxidation of isobutylene or the like, the reaction product gas is charged into a quench column through a double-wall pipe and is then brought into contact with a condensate as a cooling medium. Deposition of terephthalic acid and the like inside the column is prevented by controlling the temperature of a bottom in the quench column and that of an overhead gas of a quench column unit. An aromatic carboxylic acid, aromatic aldehyde, metal powder is added to an aqueous solution of methacrylic acid, which contains terephthalic acid and the like, so that the terephthalic acid and the like are caused to precipitate for their removal.

Quenching process of reaction product gas containing methacrylic acid

This invention provides a method for the prevention of oxidation of resulting methacrolein immediately after its discharge from a reaction tube upon production of the methacrolein by vapor-phase oxidation of isobutylene, tertiary butanol or methallyl alcohol with a molecular-oxygen-containing gas in the presence of a catalyst. An inert gas and/or recirculated reaction gas or a mixed gas of an inert gas and/or recirculated reaction gas and air is fed and mixed with a reaction product gas immediately after an outlet of the reaction tube.

Method for the prevention of post oxidation of methacrolein

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Takaishi, Japan

Takeshi Isobe