Abstract: An inhibitor mixture containing, as components, a) at least one nitroxyl radical (derivative), b) at least one phenol (derivative) and c) at least one chemical compound which contains at least one phosphorus atom which has the oxidation state +3 is preferably used for stabilizing compounds capable of free radical polymerization.

Abstract: (Meth)acrylic acid is worked up in the presence of at least one stabilizer by a process in which a stabilizer-containing mixture originating from the working-up and substantially freed from (meth)acrylic acid is passed into a distillation apparatus and a stabilizer-containing low boiler stream obtained from said apparatus is recycled to the working-up.

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: 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 method for measuring the temperature of fluid masses being treated in a tubular reactor apparatus which comprises carrying out the treatment in reactor apparatus comprises at least two same-type tubular reactors which are filled with solid particles, at least one tubular reactor containing a temperature measuring unit, the tubular reactors being designed such that both the ratio of the mass of the solid particles to the free cross-sectional area of the respective tubular reactor and the pressure drop measured by an inert gas being conducted transversely to the free cross-sectional area are each substantially identical across the respective tubular reactor. The apparatus is suitable for treating fluid masses while generating or consuming thermal energy, the temperature being measured.

Abstract: A process for the fractional condensation of a gas mixture which, in addition to acrylic acid or methacrylic acid, also contains at least one further condensable component and additionally a high proportion of one or more noncondensable components, wherein the gas mixture is passed through a column having separatory internals and the condensable components are condensed by cooling.

Abstract: A process for preparing acrylic acid or methacrylic acid comprises (a) preparing a gaseous product mixture having essentially the composition of a reaction mixture of the catalytic gas phase oxidation of C3-/C4-alkanes, -alkenes, -alkanols and/or -alkanals and/or precursors thereof to form acrylic acid or methacrylic acid, characterized by (b) condensing said product mixture, (c) crystallizing acrylic acid or methacrylic acid from the solution obtained in step (b), and (d) removing the resulting crystals from the mother liquor.

Abstract: An inhibitor mixture containing, as components, a) at least one nitroxyl radical (derivative), b) at least one phenol (derivative) and c) at least one chemical compound which contains at least one phosphorus atom which has the oxidation state +3 is preferably used for stabilizing compounds capable of free radical polymerization.

Abstract: In a process for stabilizing chemical compounds having at least one ethylenically unsaturated bond to undesired free radical polymerization, a nitroxyl radical and a chemical compound containing phosphorus in chemically bonded form are added to the unsaturated compound present as pure substance or as a component of a mixture.

Abstract: An article having a metallic surface treated with polymeric complexing agent is described. Particularly suitable polymeric complexing agents are phosphonoalkylated polyethyleneimines and/or carboxyalkylated polyethyleneimines and/or vinylimidazole polymers. As a rule, the treated metallic surface forms the total inner surface or a part of the inner surface of a process apparatus or of a container. The surface is protected by the treatment, in particular from the adhesion of polymer.

Abstract: An inhibitor mixture containing, as components, a) at least one nitroxyl radical (derivative), b) at least one phenol (derivative) and c) at least one chemical compound which contains at least one phosphorus atom which has the oxidation state +3 is preferably used for stabilizing compounds capable of free radical polymerization.

Abstract: A process for preparing acrylic acid or methacrylic acid comprises preparing a gaseous product mixture having essentially the composition of a reaction mixture of the catalytic gas phase oxidation of C3-/C4-alkanes, -alkenes, -alkanols and/or -alkanals and/or precursors thereof to form acrylic acid or methacrylic acid. The product is removed from the gaseous product mixture by a process comprising the following steps: (a) condensing said gaseous product mixture, (b) crystallizing acrylic acid or methacrylic acid from the solution obtained in step (a), (c) removing the resulting crystals from the mother liquor, and (d) recycling at least a portion of said mother liquor from step (c) into step (a).

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.

Abstract: A process for the continuous recovery of (meth)acrylic acid from a liquid starting mixture containing (meth)acrylic acid, a high-boiling organic solvent and low boilers, medium boilers and high boilers is proposed, the mixture being separated into a first part-stream (a), which, in addition to (meth)acrylic acid, contains the low boilers and a part each of the medium boilers and high boilers, and a second part-stream (b), which contains the predominant part of the (meth)acrylic acid and is completely or virtually completely free of low boilers, and the (meth)acrylic acid being recovered from the part-stream (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.

Abstract: A reactor apparatus comprises at least two same-type tubular reactors which are filled with solid particles, at least one tubular reactor containing a temperature measuring unit, the tubular reactors being designed such that both the ratio of the mass of the solid particles to the free cross-sectional area of the respective tubular reactor and the pressure drop measured by an inert gas being conducted transversely to the free cross-sectional area are identical across the respective tubular reactor. The apparatus is suitable for treating fluid masses while generating or consuming thermal energy, the temperature being measured.

Abstract: A process for the continuous recovery of (meth)acrylic acid from a liquid starting mixture containing (meth)acrylic acid, a high-boiling organic solvent and low boilers, medium boils and high boils is proposed, the mixture being separated into a first part-stream (a), which, in addition to (meth)acrylic acid, contains the low boilers and a part each of the medium boilers and high boilers, and a second part-stream (b). which contains the predominant part of the (meth)acrylic acid and is completely or virtually completely free of low boilers, and the (meth)acrylic acid being recovered from the part-stream (b).

Abstract: In a process for the disposal of low, mediun, and high-boiling secondary components formed during the preparation of (meth)acrylic acid the gaseous low-boiling secondary components are burned, whilst low-boiling and medium-boiling secondary components that are dissolved in water optionally together with high-boiling secondary components treated with solvent are added.

Abstract: A reactor apparatus comprises at least two same-type tubular reactors which are filled with solid particles, at least one tubular reactor containing a temperature measuring unit, the tubular reactors being designed such that both the ratio of the mass of the solid particles to the free cross-sectional area of the respective tubular reactor and the pressure drop measured by an inert gas being conducted transversely to the free cross-sectional area are identical across the respective tubular reactor. The apparatus is suitable for treating fluid masses while generating or consuming thermal energy, the temperature being measured.