Abstract: A process for the separation of acrylic acid from the reaction gases from the catalytic oxidation of propylene and/or acrolein by countercurrent absorption using a mixture of from 70 to 75 wt % of diphenyl ether and from 25 to 30 wt % of diphenyl plus from 0.1 to 25 wt % of o-dimethyl phthalate, based on said mixture.

Abstract: Acrolein and methacrolein are prepared advantageously by oxidizing propylene or isobutylene, respectively, with an oxygen-containing gas mixture under conventional conditions over a supported catalyst possessing a firmly adhering coating, from 150 to 1,500 .mu.m thick, which contains calcined catalytic material based on molybdenum oxide and has a carrier core with a surface area of less than 15 m.sup.2 /g and a diameter of more than 100 .mu.m, if a coated catalyst is used which has been prepared by applying calcined catalytic material having a particle size of from 0.1 to 300 .mu.m, in an amount of from 1 to 40 g/min/liter of carrier and water in a weight ratio of catalytic material to water of from 1:1 to 8:1, continuously and separately from one another, each at a constant speed, at below 100.degree. C.

Abstract: Catalysts which consist of a molded carrier, the surface of which is coated with an active catalyst composition of the general formula Mo.sub.12 A.sub.a B.sub.b C.sub.c D.sub.d O.sub.x, where A is V and/or W, B is Cu and/or Fe and/or Mn and/or Ni and/or Cr, C is Nb and/or Ta and/or Bi and/or Sb and/or Sn and/or Th and/or Ce and/or U, D is Li and/or Na and/or K and/or Rb and/or Cs and/or Tl and a is from 0.1 to 18, b is from 0 to 8, c is from 0 to 10, d is from 0 to 2 and x is from 36 to 135, which are particularly active and selective for the oxidation of acrolein and methacrolein with oxygen-containing gases to give acrylic acid and methacrylic acid, respectively, are obtained by first manufacturing the catalyst composition, before applying it to the carrier, from thermally easily decomposed salts of the components by mixing aqueous solutions, slurries or moist solid masses of the salts of the components, drying the mixture and calcining the dried composition at from 140.degree. to 600.degree. C.

Abstract: In the oxidation of propylene and/or acrolein, high-boiling or non-volatile byproducts are separated from the solvents used for absorbing the acrylic acid by treating the said solvents laden with byproducts with the hot reaction gases in such amounts that the major portion of the solvents evaporates, the residual solvent containing a high percentage of said byproducts then being discarded or worked up.

Abstract: In the oxidation of .alpha.-olefins in the gas phase to .alpha.,.beta.-olefinically unsaturated aldehydes and carboxylic acids with molecular oxygen in the presence of an inert gas using a catalyst containing molybdenum and bismuth with elements as oxides or mixed oxides at from 280.degree. to 450.degree. C a content of indium and/or aluminum and/or lanthanum and/or gallium as oxide or mixed oxide results in an improvement in the conversion and/or activity and/or life of the catalyst.

Abstract: In the oxidation of propylene to acrylic acid in the gas phase in two spatially separate oxidation stages, a part of the off-gas, which has been freed from condensable products, is fed to the oxidation stages in addition to freshly charged propylene and air, under the following conditions:A. The recycled off-gas and air are in part fed to the first oxidation stage and in part to the second oxidation stage,B. The molar ratio of propylene : oxygen : residual gases fed to the first stage is 1 : 1.5-2.3 : 11-19,C. The molar ratio of the total propylene fed in, to the total oxygen fed in, in the form of air or off-gas, before and after the first stage, and to the total residual gases fed in is 1 : 1.9-2.5 : 13-25, with the proviso thatD. The air and the recycled off-gas are divided between the two feed points in such a way that from 10 to 50% by volume of the total quantity of air and off-gas fed in are added after the first stage andE.

Abstract: Acrylic acid practically devoid of water, acrolein, formaldehyde and acetic acid is obtained at particularly low cost by countercurrent scrubbing and quenching of the reaction gas formed in the catalytic oxidation of propylene and/or acrolein with a high-boiling, extremely hydrophobic solvent followed by processing of the extract.