Basf Aktiengesellschaft

Johannes E Schmidt

Heinz Hohenschutz

Hans Kiefer

Rolf Seubert

Friedrich Wirth

Matthias Schwarzmann

Herwig Hoffmann

Wilhelm Ruppel

Heinrich Aichinger

Friedrich Sauer

Karl Fischer

Karl-Heinz Boehning

Ernest Miesen

Eckehard Danz

Dieter Stockburger

Walter Scheidmeir

Klaus Wintermantel

Bernhard Holzknecht

Horst Buelow

Dieter Zimmerling

Werner Sachsze

Wilhelm Schultz

Gerd Dumbgen

Gerhard Michl

Phthalic anhydride is prepared in a multiple tube reactor provided with separate salt baths, the temperature of the salt bath used for cooling the first layer of catalyst, as regarded in the direction of flow of the reaction mixture, being from 2.degree. to 20.degree. C. higher than that of the salt bath(s) associated with the following layer(s).

Preparation of phthalic anhydride from o-xylene

Anhydrous or substantially anhydrous formic acid is prepared by hydrolyzing methyl formate in the presence of a formamide and then obtaining the formic acid from the hydrolysis mixture by distillation, by a method in which the hydrolysis is carried out in the presence of 0.5-3 moles, per mole of methyl formate, of a water-soluble formamide of the general formula I ##STR1## where R.sup.1 and R.sup.2 are each alkyl or together form an alkylene group, giving a 5-membered to 7-membered ring, with the proviso that the sum of the carbon atoms in R.sup.1 and R.sup.2 is 5 or 6 and, in the case of an alkylene group, a carbon atom which is not directly bonded to the N atom can be replaced by an oxygen atom.

Preparation of formic acid

Very pure maleic anhydride having a stable color is obtained by fractional distillation of crude maleic anhydride by a method in which the maleic anhydride vapor separated off from low boilers and high boilers is partially condensed so that from 0.5 to 15% by weight of the maleic anydride vapor is separated off from the vapor phase as a liquid precondensate, and the remaining very pure maleic anhydride vapor is then completely condensed.

Obtaining very pure maleic anhydride from crude maleic anhydride

Process for obtaining maleic anhydride that is not prone to discolor by treating crude maleic anhydride with oxygen, a gas mixture containing oxygen, or a substance that releases oxygen before or while it is distilled.

Obtaining maleic anhydride not prone to discolor

A process for the continuous isolation of phthalic anhydride and maleic anhydride from the reaction gases obtained by catalytic oxidation of o-xylene or naphthalene with air, wherein the reaction gases are treated with a hydrocarbon of boiling range from 115.degree. to 175.degree. C. as the solvent in a column, and are then treated with an organic solvent of boiling range from 180.degree. to 290.degree. C. in a second column, the phthalic anhydride and maleic anhydride being isolated from the liquid bottom product of the first column.

Continuous isolation of phthalic anhydride and maleic anhydride from

A process for the preparation of phthalic anhydride (PA) of catalytic oxidation of naphthalene or o-xylene with air, a preheated mixture of air and naphthalene or o-xylene being passed into a reactor charged with the catalyst, and the reaction gas leaving the reactor being passed through a separator in which the PA is separated out as a solid, in which process the air fed to the reactor is preheated, before or after the admixture of naphthalene or of o-xylene, by using it to cool the reaction gas in the PA separator.

Preparation of phthalic anhydride

Formic acid is prepared by hydrolyzing methyl formate, the hydrolysis being carried out in the presence of from 0.5 to 3.0 moles, per mole of methyl formate, of a base which contains tertiary nitrogen atoms, boils at not less than 180.degree. C. under atmospheric pressure and has a pKa from 4 to 9, N-substituted imidazole derivatives being the preferred bases.

Carboxylic acids of the general formula I

Isolation of formic acid from its aqueous solutions

Formic acid is purified by extractive distillation of its aqueous solutions using a basic extractant, followed by distillation of the bottom mixture first obtained, the extractant used being N-formylmorpholine.

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Johannes E Schmidt