Basf Aktiengesellschaft

Herbert Vogal

Franz Merger

Richard Krabetz

Gerd Duembgen

Fritz Thiessen

Michael Jaeger

Methacrylic acid can be prepared with advantage by gas phase oxidation of methacrolein or isobutyraldehyde over Mo- and P-containing catalysts at from 250.degree. to 400.degree. C. with cooling of the hot reaction gas to below 100.degree. C., absorption of the methacrylic acid in a water-operated absorption column, at below 100.degree. C. and partial recycling into the oxidation reactor after admixture of methacrolein or isobutyraldehyde and oxygen by feeding a quantity of methacrolein or isobutyraldehyde equal to the quantity of methacrolein or isobutyraldehyde consumed in the reaction in liquid form together with a polymerization inhibitor into the reactor gas in the lower two-thirds of the absorber column and upstream of the feed point for the fresh methacrolein or isobutyraldehyde or down-stream of the absorption column splitting off the reactor off-gas a side stream which is washed in a wash column operated with water at &lt;10.degree. C. to remove unconverted methacrolein or isobutyraldehyde which is fed as an aqueous solution to the top of the absorption column.

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Ludwigshafen, Germany

Herbert Vogal