Abstract: A process and an apparatus for the purification of a crude acrylic acid composition containing maleic anhydride as an impurity comprising the following steps: (a) carrying out at least one dynamic melt crystallization stage (14, 14a, 14b, 14c, 14d) with the crude acrylic acid composition to prepare a first purified acrylic acid composition and a first residue containing at least 3.5% by weight maleic anhydride, (b) adding a solvent (26) which is capable of dissolving maleic anhydride to the first residue in an amount that the weight ratio of the solvent to the maleic anhydride is 0.3 or more to prepare a ratio-adjusted residue and (c) carrying out at least one further dynamic melt crystallization stage and/or at least one static melt crystallization stage (18, 18a, 18b) with the ratio-adjusted residue to prepare a second purified acrylic acid composition and a second residue.

Abstract: A process and an apparatus for the purification of a crude acrylic acid composition containing maleic anhydride as an impurity comprising the following steps: (a) carrying out at least one dynamic melt crystallization stage (14, 14a, 14b, 14c, 14d) with the crude acrylic acid composition to prepare a first purified acrylic acid composition and a first residue containing at least 3.5% by weight maleic anhydride, (b) adding a solvent (26) which is capable of dissolving maleic anhydride to the first residue in an amount that the weight ratio of the solvent to the maleic anhydride is 0.3 or more to prepare a ratio-adjusted residue and (c) carrying out at least one further dynamic melt crystallization stage and/or at least one static melt crystallization stage (18, 18a, 18b) with the ratio-adjusted residue to prepare a second purified acrylic acid composition and a second residue.

Abstract: Disclosed is a method to prepare a polylactic acid comprising the steps of performing a ring opening polymerization using a catalyst and either a catalyst killer compound or an endcapping additive to obtain a raw polylactic acid of MW greater than 10,000 g/mol, purifying the raw polylactic acid by removing and separating low boiling compounds comprising lactide and impurities from the raw polylactic acid by devolatization of the low boiling compounds as a gas phase stream, and purifying the lactide from the devolatization and removing the impurities from the gas phase stream of evaporated low boiling compounds by means of crystallization by desublimation from the gas phase, wherein the lactide is purified and the removed impurities include a catalyst residue and a compound containing at least one hydroxyl group such that the purified lactide is then polymerized by feeding it back into the ring opening polymerization.

Abstract: Disclosed is a method to prepare a polylactic acid comprising the steps of: performing a ring opening polymerization using a catalyst and either a catalyst killer compound or an endcapping additive to obtain a raw polylactic acid of MW greater than 10,000 g/mol, purifying the raw polylactic acid by removing and separating low boiling compounds comprising lactide and impurities from the raw polylactic acid by devolatization of the low boiling compounds as a gas phase stream, purifying the lactide from the devolatization and removing the impurities from the gas phase stream of evaporated low boiling compounds by means of condensing the evaporated gas phase stream to give a condensed stream and a subsequent melt crystallization of the condensed stream, wherein the lactide is purified and the removed impurities include a catalyst residue and a compound containing at least one hydroxyl group such that the purified lactide is polymerized by feeding it back into the ring opening polymerization.

Abstract: Disclosed is a method to prepare a polylactic acid comprising the steps of: performing a ring opening polymerization using a catalyst and either a catalyst killer compound or an endcapping additive to obtain a raw polylactic acid of MW greater than 10,000 g/mol, purifying the raw polylactic acid by removing and separating low boiling compounds comprising lactide and impurities from the raw polylactic acid by devolatization of the low boiling compounds as a gas phase stream, purifying the lactide from the devolatization and removing the impurities from the gas phase stream of evaporated low boiling compounds by means of condensing the evaporated gas phase stream to give a condensed stream and a subsequent melt crystallization of the condensed stream, wherein the lactide is purified and the removed impurities include a catalyst residue and a compound containing at least one hydroxyl group such that the purified lactide is polymerized by feeding it back into the ring opening polymerization.

Abstract: Disclosed is a method to prepare a polylactic acid comprising the steps of performing a ring opening polymerization using a catalyst and either a catalyst killer compound or an endcapping additive to obtain a raw polylactic acid of MW greater than 10,000 g/mol, purifying the raw polylactic acid by removing and separating low boiling compounds comprising lactide and impurities from the raw polylactic acid by devolatization of the low boiling compounds as a gas phase stream, and purifying the lactide from the devolatization and removing the impurities from the gas phase stream of evaporated low boiling compounds by means of crystallization by desublimation from the gas phase, wherein the lactide is purified and the removed impurities include a catalyst residue and a compound containing at least one hydroxyl group such that the purified lactide is then polymerized by feeding it back into the ring opening polymerization.

Abstract: The present invention relates to a method for the purification of an ionic liquid by means of fractional crystallization in which a part of the ionic liquid is crystallized and the crystallizate formed is separated from the liquid remainder. In this respect the ionic liquid is charged with a certain amount of at least one entrainer substance.

Abstract: The present invention relates to a method of purifying an ionic liquid by means of fractional crystallization in which a part of the ionic liquid is crystallized and the crystals formed are separated off from the residual liquid. In this process a certain amount of at least one entrainer substance is added to the ionic liquid.