Nippon Shokubai Kagaku Kogyo Co., Ltd.

Kunihiro Kubota

Takashi Ohara

Noboru Shimizu

Sadao Yoshida

Daizo Kobayashi

A method for inhibiting the polymerization of acrylic acid or acrylic esters during the distillation for separating or purifying the acrylic acid obtained by the vapor phase catalytic oxidation of propylene or acrolein, or the acrylic esters derived from said acrylic acid, said method comprising carrying out the distillation operation in the presence of (A) at least one compound selected from the group consisting of hydroquinone, hydroquinonemonomethyl ether, cresols, phenols, t-butyl catechol, diphenylamine, phenothiazines and methylene blue (B) at least one compound selected from the group consisting of copper dimethyldithiocarbamate, copper diethyldithiocarbamate copper dibutyldithiocarbamate and copper salicylate: and (C) molecular oxygen.

Method for inhibiting the polymerization of acrylic acid or its esters

A method of distilling a polymerizable vinyl compound selected from the group consisting of acrolein, methacrolein, acrylic acid, methacrylec acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, glycidyl acrylate and glycidyl methacrylate, the method comprising distilling the polymerizable vinyl compound in the presence of a polymerization inhibitor using a distillation tower having perforated trays without downcomers and wherein the temperature of the inner wall of the tower is maintained at a temperature sufficient to prevent the condensation of the vapor being distilled, whereby the polymerizable vinyl compound is distilled without the formation of polymer.

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Takatsuki, Japan

Kunihiro Kubota