Abstract: In a process for preparing acrylic acid, an acrylic acid-containing product gas mixture obtained by catalytic gas phase partial oxidation of a C3 precursor of acrylic acid, after direct cooling with a quench liquid, is fractionally condensed in a separating column provided with internals, rising into itself with sidestream takeoff of crude acrylic acid, and the acrylic acid oligomers which form are dissociated and the resulting dissociation gas is subjected to a countercurrent rectification before it is recycled.

Abstract: Acrylic acid or methacrylic acid is purified by crystallization to obtain crystals and a mother liquor, by a process in which the crystals are washed with a wash liquid containing the acid and having a temperature from 15 to 40° C. Furthermore, a process for the preparation of acrylic acid or methacrylic acid comprises the abovementioned purification process.

Abstract: (Meth)acrylic acid is purified by crystallization by a process in which the (meth)acrylic acid is purified by a combination of at least two different dynamic crystallization processes, in particular a suspension crystallization and a layer crystallization.

Abstract: Acrylic acid or methacrylic acid is purified by crystallization to obtain crystals and a mother liquor, by a process in which the crystals are washed with a wash liquid containing the acid and having a temperature from 15 to 40° C. Furthermore, a process for the preparation of acrylic acid or methacrylic acid comprises the abovementioned purification process.

Abstract: The invention describes a process for the isolation of pure N-vinylpyrrolidone from N-vinylpyrrolidone-containing crude products, comprising a single-stage or multistage crystallization process, which comprises passing the mother liquor from the first crystallization stage either to a distillative and/or extractive purification, or returning it to an N-vinylpyrrolidone-containing product stream of the preparation process.

Abstract: Acrylic acid or methacrylic acid is purified be crystallization to obtain crystals and a mother liquor, by a process in which the crystals are washed with a was liquid containing the acid and having a temperature from 15 to 40° C. Furthermore, a process for the preparation of acrylic acid or methacrylic acid comprises the abovementioned purification process.

Abstract: A process for the production of tablet-shaped granular material from a melt, in which (i) a melt is prepared, (ii) the prepared melt is shaped to droplets, (iii) the droplets are deposited on a cooling surface, and (iv) the deposited droplets solidify to give the granular material, wherein the melt comprises an alcohol, and the melt has a melting point of 30° C. or above.

Abstract: A process for the preparation of acrylic acid by: (a) preparation of a gaseous product mixture which essentially has the composition of a reaction mixture of catalytic gas-phase oxidation of C3-alkanes, C3-alkenes, C3-alkanols and/or C3-alkanals and/or intermediates thereof to acrylic acid, which comprises (b) condensation of the gaseous product mixture, (c) crystallization of the acrylic acid from the solution obtained in stage (b), with partial evaporation of the solution under reduced pressure, (d) isolation of the resulting crystals from the mother liquor, (e) recycling of at least a part of the mother liquor from stage (d) to stage (b) and (f) recycling of at least a part of the evaporated solution from stage (c) to stage (b).

Abstract: In a process for purifying acrylic acid by crystallization by means of vacuum evaporation, a solution which contains acrylic acid and water and may contain further components is crystallized by means of vacuum evaporation with formation of a liquid phase, consisting of a mother liquor containing more than 10% by weight of water and of the crystals, and a vapor phase, the vapor phase is introduced into a liquid material in a condensation zone with formation of a liquid condensation mixture, and the liquid condensation mixture is recycled at least partly to the condensation zone, the operating conditions in the condensation zone being established so that no solid is precipitated.