Abstract: In process for cleaning tray columns which are used for the purposes of rectifiying liquids comprising (meth)acrylic compounds, a basic liquid is conveyed downward through the tray column and a gas is passed through the column in countercurrent to the basic liquid at an average gas phase differential pressure over all trays of at least 0.5 mbar/tray.

Abstract: In a process for preparing at least one partial oxidation and/or ammoxidation product of propylene, the propylene is obtained from crude propane by dehydrogenating and subjected in the presence of unconverted propane as a constituent of a gas mixture 2 which comprises a total C4-hydrocarbon content of ?3% by volume to a heterogeneously catalyzed gas phase partial oxidation and/or partial gas phase ammoxidation.

Abstract: A process for rectificatively separating a liquid which comprises acrylic acid, methacrylic acid or a mixture thereof, and additionally comprises low molecular weight aldehydes and acetone.

Abstract: The invention relates to a method for purifying a raw melt of at least one monomer by crystallization, wherein suspension crystallization is initially used and the resulting remaining melt or the suspension crystals that have been molten once again and separated are subjected to a mechanical separation operation before undergoing subsequent purification by crystallization.

Abstract: This invention relates to a process for preparing a low-odor hydrogel-forming acrylic acid polymer, which comprises the steps of: a) preparing a polymeric hydrogel by free-radically polymerizing a monomer composition comprising at least 50% by weight of acrylic acid in an aqueous polymerization medium and converting said hydrogel into a particulate hydrogel or into hydrogel-forming powder; and optionally b) treating said particulate hydrogel or said hydrogel-forming powder with a crosslinking substance which, actually or latently, contain at least two functional groups capable of reacting with the carboxyl groups on the addition polymer; characterized by the acrylic acid used in step a) containing less than 400 ppm of acetic acid and propionic acid. It further relates to the hydrogel-forming addition polymers obtainable by the process and to their use.

Abstract: Crude acrylic acid is purified batchwise by crystallization by a process which comprises at least one purification stage and at least one stripping stage and in which at least the first stripping stage is carried out in a different crystallizer from the first purification stage.

Abstract: Process for preparing at least one partial oxidation and/or ammoxidation product of propylene, in which the propylene is produced from crude propane by dehydrogenation and is subjected to a heterogeneously catalyzed gas-phase partial oxidation and/or partial gas-phase ammoxidation in the presence of unreacted propane as constituent of a gas mixture 2 containing <1% by volume of 1-butene.

Abstract: In a process for heterogeneously catalyzed partial gas phase oxidation of propene to acrolein, the starting reaction gas mixture is oxidized over a fixed catalyst bed which consists of at least two fixed catalyst bed zones and is accommodated in two successive temperature zones A, B, and the transition from temperature zone A to temperature zone B does not spatially coincide with a transition from one fixed catalyst bed zone to another fixed catalyst bed zone.

Abstract: A process for the long-term operation of a two-stage heterogeneously catalyzed gas phase partial oxidation of propene to acrylic acid, in which the temperature of the fixed catalyst beds is increased over the time and the gas phase partial oxidation is interrupted from time to time and an oxygen-containing gas mixture is conducted through the fixed catalyst beds at elevated temperature of the fixed catalyst beds.

Abstract: Acrolein is prepared by a process of heterogeneous catalyzed partial gas phase oxidation, by passing a starting reaction gas mixture which comprises propene, molecular oxygen and at least one inert gas, in which the molecular oxygen to propene (O2:C3H6) mole ratio is ?1, and carbon dioxide and saturated hydrocarbons together in a total amount of at most 15 mol %, at elevated temperature and at an hourly space velocity on the fixed catalyst bed of propene present in the starting reaction gas mixture of ?120 l (STP)/l·h through a fixed catalyst bed whose catalysts are comprised of annular unsupported catalysts whose active component is at least one multimetal oxide of formula I, Mo12WaCobFecBidSieKfOn??(I) wherein a ranges from ?1 to ?3, b ranges from ?3 to ?8, c ranges from ?1 to ?4, d ranges from ?0.5 to ?1.5, e ranges from ?0 to ?10, and f ranges from ?0 to ?0.

Abstract: In a process for preparing water-absorbent resins based on acrylic acid, crude acrylic acid is firstly isolated from the reaction gases from the catalytic gas-phase oxidation of propane, propylene and/or acrolein. This is treated with an aldehyde scavenger and pure acrylic acid is separated by distillation from the treated crude acrylic acid, and this pure acrylic acid can be subjected directly to a free-radical polymerization.

Abstract: A process prepares methacrolein from isobutane by subjecting isobutane to a partial catalytic dehydrogenation in the gas phase and using the isobutenic product gas mixture to charge an oxidation zone in which the isobutene is oxidized to methacrolein in the gas phase with heterogeneous catalysis using molecular oxygen accompanied by molecular nitrogen as the oxygen source.

Abstract: In a process for heterogeneously catalyzed partial gas phase oxidation of propene to acrylic acid, the propene-containing starting reaction gas mixture is oxidized in a first reaction stage using a fixed catalyst bed 1 which consists of a plurality of fixed catalyst bed zones and is accommodated in two successive temperature zones A, B, and the acrolein-containing product gas mixture of the first reaction stage is then oxidized in a second reaction stage using a fixed catalyst bed 2 which consists of a plurality of fixed catalyst bed zones and is accommodated in two successive temperature zones C, D, and the transition from one temperature zone to another temperature zone within one reaction stage does not spatially coincide with a transition from one fixed catalyst bed zone to another fixed catalyst bed zone.

Abstract: A process prepares an aqueous alkali metal acrylate solution by distillatively removing acrylic acid from a mixture as vapors and taking up the vapors immediately from the gas phase into an aqueous alkali solution.

Abstract: In a process for heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid, the starting reaction gas mixture is oxidized over a fixed catalyst bed 1 which consists of at least two fixed catalyst bed zones and is accommodated in two successive temperature zones A, B, and the transition from temperature zone A to temperature zone B does not coincide with a transition from one fixed catalyst bed zone to another fixed catalyst bed zone.

Abstract: A process for the long-term operation of a heterogeneously catalyzed gas phase partial oxidation of propene to acrolein, in which the temperature of the fixed catalyst bed is increased over the time and the gas phase partial oxidation is interrupted at least once per calendar year and the gas mixture G consisting of molecular oxygen, inert gas and optionally steam is conducted through the fixed catalyst bed at a temperature of the fixed catalyst bed of from 250 to 550° C.

Abstract: The invention relates to a method for the production of a purified melt of a monomer melt obtained by condensation, absorption or extraction in a crystallizer, wherein the inlet to the crystallizer is subjected to a mechanical solid/liquid separation operation.

Abstract: A process for the heterogeneously catalyzed gas-phase partial oxidation of an organic compound over a fixed catalyst bed present in a fixed-bed reactor having a plurality of catalyst tubes, in which the reduction of the quality of the catalyst load with increasing duration of operation is restored by a partial catalyst change, is described.

Abstract: In a process for the purification of a crude acrylic acid melt, the crude acrylic acid melt is converted, under the action of low temperatures, into a crude acrylic acid suspension consisting of acrylic acid crystals and residual melt, and the acrylic acid crystals of the crude acrylic acid suspension are freed from remaining residual melt in a wash column, the production of the acrylic acid crystals of the crude acrylic acid suspension being carried out in the presence of water, the wash column being a wash column with forced transport of the acrylic acid crystals and the wash liquid used being the melt of acrylic acid crystals purified in the wash column.

Abstract: In a process for the heterogeneously catalyzed dehydrogenation in one or more reaction zones of one or more dehydrogenatable C2-C30-hydrocarbons in a reaction gas mixture comprising them, with at least part of the heat of dehydrogenation required being generated directly in the reaction gas mixture in at least one reaction zone by combustion of hydrogen, the hydrocarbon or hydrocarbons and/or carbon in the presence of an oxygen-containing gas, the reaction gas mixture comprising the dehydrogenatable hydrocarbon or hydrocarbons is brought into contact with a Lewis-acid dehydrogenation catalyst which has essentially no Brönsted acidity.