Abstract: A process for preparing pure (meth)acrylic acid or a (meth)acrylate starting from a crude (meth)acrylic acid, which comprises the following stages: A: treating the crude (meth)acrylic acid with at least one compound which is able to remove aldehydes, to give an aldehyde-free crude (meth)acrylic acid; B: subjecting the aldehyde-free crude (meth)acrylic acid to imprecise distillation, to give a low-boiling fraction comprising (meth)acrylic acid and acetic acid and a high-boiling fraction comprising (meth)acrylic acid and high boilers; C: isolating a pure (meth)acrylic acid from the high-boiling fraction and, if desired, D: esterifying the low-boiling fraction comprising (meth)acrylic acid and acetic acid that is obtained in stage B by means of one or more alkanols, to give an esterification mixture comprising one or more (meth)acrylates, one or more acetic esters, and one or more alkanols.

Abstract: Crude (meth)acrylic acid is purified by a process in which a primary amine compound and an organic sulfonic acid are added to the crude (meth)acrylic acid and the latter is then worked up by distillation.

Abstract: In a process for purifying crude (meth)acrylic acid, the crude (meth)acrylic acid is worked up by distillation after addition of an organic carboxylic acid hydrazide and, if desired, an organic sulfonic acid.

Abstract: A process for the gas phase catalytic oxidation of a C.sub.3-6 alkane, alkanol, alkene or alkenal using as a catalyst multimetal oxide compositions of the formula I, [X.sup.1.sub.a X.sup.2.sub.b O.sub.x ].sub.p [X.sup.3.sub.c X.sup.4.sub.d X.sup.5.sub.e X.sup.6.sub.f X.sup.7.sub.g X.sup.2.sub.h O.sub.y ].sub.q, where X.sup.1 is bismuth, tellurium, antimony, tin and/or copper, X.sup.2 is molybdenum and/or tungsten, X.sup.3 is an alkali metal, thallium and/or samarium, X.sup.4 is an alkaline earth metal, nickel, cobalt, copper, manganose, zinc, tin, cadmium and/or mercury, X.sup.6 is iron, chromium, cerium and/or vanadium, X.sup.6 is phosphorus, arsenic, boron and/or antimony, X.sup.7 is a rare-earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, geranium, lead, thorium and/or uranium, a is from 0.01 to 8, b is from 0.

Abstract: Multimetal oxide compositions of the formula I[X.sup.1.sub.a X.sup.2.sub.b O.sub.x ].sub.p [X.sup.3.sub.c X.sup.4.sub.d X.sup.5.sub.e X.sup.6.sub.f X.sup.7.sub.g X.sup.2.sub.h O.sub.y ].sub.q(I)whereX.sup.1 is bismuth, tellurium, antimony, tin and/or copper,X.sup.2 is molybdenum and/or tungsten,X.sup.3 is an alkali metal, thallium and/or samarium,X.sup.4 is an alkaline earth metal, nickel, cobalt, copper, manganese, zinc, tin, cadmium and/or mercury,X.sup.5 is iron, chromium, cerium and/or vanadium,X.sup.6 is phosphorus, arsenic, boron and/or antimony,X.sup.7 is a rare-earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, lead, thorium and/or uranium,a is from 0.01 to 8,b is from 0.

Abstract: A process for the catalytic gas-phase oxidation of propene or isobutene to acrolein or methacrolein in a tubular fixed bed reactor or catalytically active oxides with a .gtoreq.90% conversion of the initial olefin on a single passage, wherein the temperature of the gases containing the reactants in the direction of flow along the tubes from their entrance until the conversion of the initial olefin is from 30 to 70% is from 360.degree. to 420.degree. C. and is then adjusted to from 360.degree. to 300.degree. C. until the conversion of the initial olefin is from 80 to 90% and is thereafter maintained at from 330.degree. to 390.degree. C. until the gases emerge from the tubes, is described.

Abstract: Catalyst particles of an active material of the general formula[Mo,V,W].sub.12 Bi.sub.a [Fe,Ce].sub.b [Ni,Co,Zn].sub.C [Alkali].sub.d [P,As,Sb,B].sub.e [Si,Al,Ti].sub.f O.sub.xwherea is from 0.1 to 5,b is from 0.1 to 10,c is from 1 to 15,d is from 0.01 to 2,e is from 0 to 2,f is from 0 to 30 andx is the number of oxygen atoms required to saturate the valences of the other components,have the shape of a 3-spoked to 5-spoked wheel or of a rosette which have wall thicknesses of from 0.5 to 4 mm and a diameter of from 3 to 20 mm.

Abstract: A catalytically active composition for the gas phase oxidation of propylene to acrolein and acrylic acid, of the general formulaMo.sub.12 Bi.sub.0.1-10 Fe.sub.0.8-12 [Co,Ni].sub.0.1-10 P.sub.0-2 A.sub.0-10 B.sub.0.001-1 O.sub.xwhere A is arsenic, antimony, tin, thallium, tungsten, an alkaline earth metal, zinc and/or chromium, B is at least one of the metals sodium, potassium, rubidium, cesium and/or indium and X is the number determined by the atomic valences of the individual elements, is prepared by introducing all or some of the iron and molybdenum in the form of dried pulverulent iron molybdate gel into an aqueous solution or suspension of the other constituents and gelating the mixture by stirring and possibly heating, then comminuting, drying at elevated temperatures and finally calcining.