Mitsui Toatsu Chemicals, Incorporated

Kousuke Yamamoto

Shinji Takenaka

Kazuo Maeda

Teruyuki Nagata

Ryuichi Yamamoto

Kenji Obata

Michio Mituta

Ahinji Takenaka

An improved process for preparing organic isocyanates is disclosed. An organic amine is reacted with phosgene to yield a reaction product, through which hydrogen chloride gas is passed in the presence of an inert organic solvent whereby the gas included in the reaction product is removed and the acid substances and hydrolyzable chlorine-containing substances included therein are minimized.

Process for preparing organic isocyanates

A process for preparing stable anhydrous sodium dithionite which comprises reacting formic acid or sodium formate, sodium hydroxide, and sulfurous acid anhydride in hydrous methanol, wherein an aqueous solution of sodium carbonate or sodium hydroxide is added to the slurry after the reaction, and stabilized anhydrous sodium dithionite is separated from the slurry.

Process for preparing stable anhydrous sodium dithionite

A process for continuously producing anhydrous sodium dithionite in the form of large granules which comprises reacting formic acid, sodium formate, sodium hydroxide and sulfurous acid anhydride in hydrous methanol using a multi-stage reaction apparatus, wherein all the required amounts of the formic acid or sodium formate, sodium hydroxide, methanol and water, and at least 60%, based on the required amount, of sulfurous acid anhydride are introduced into a first reactor, and the residence time in the first reactor is adjusted so that the conversion of the sulfurous acid anhydride to anhydrous sodium dithionite is within the range of 25 to 50%; the remainder of the sulfurous acid anhydride is introduced into a second reactor; and the reaction temperature in any given reactor is maintained at a point not lower than the reaction temperature in the immediately preceding reactor.

Process for continuously producing anhydrous sodium dithionite

In the production of anhydrous sodium dithionite by reacting sodium formate, an alkaline sodium compound and sulfurous acid anhydride in hydrous methanol, a process for treating the mother liquor, which comprises cooling the mother liquor left after the separation of the resulting anhydrous sodium dithionite to a temperature in the range of +5.degree. to -30.degree. C, and separating the precipitated sodium thiosulfate by filtration.

Process for treating the mother liquor by cooling in the production of

In the production of anhydrous sodium dithionite by reacting sodium formate, an alkaline sodium compound and sulfurous acid anhydride in hydrous methanol, a process for treating the mother liquor, which comprises adding an alkali to the mother liquor left after the separation of the resulting anhydrous sodium dithionite to adjust its pH to at least 8, separating the solids precipitated, and oxidizing the filtrate with an oxidizing agent.

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Ohmuta, Japan

Kousuke Yamamoto