Abstract: Process for the synthesis of a cyclic diester of an alpha-hydroxyacid, comprising the following steps: an alkalino-earth salt of the corresponding alpha-hydroxyacid is mixed with said alpha-hydroxyacid and water; the mixture is treated by evaporation-crystallization, so that a hydrate of the alkalino-earth salt of the linear dimer of the corresponding alpha-hydroxyacid precipitates; the hydrated salt is dehydrated to give the corresponding anhydrous salt; and the anhydrous salt is pyrolyzed, releasing the cyclic diester of the corresponding alpha-hydroxyacid and leaving the alkalino-earth hydroxide as solid residue.

Abstract: Process for the synthesis of a cyclic diester of an alpha-hydroxyacid, comprising the following steps: an alkalino-earth salt of the corresponding alpha-hydroxyacid is mixed with said alpha-hydroxyacid and water; the mixture is treated by evaporation-crystallization, so that a hydrate of the alkalino-earth salt of the linear dimer of the corresponding alpha-hydroxyacid precipitates; the hydrated salt is dehydrated to give the corresponding anhydrous salt; and the anhydrous salt is pyrolyzed, releasing the cyclic diester of the corresponding alpha-hydroxyacid and leaving the alkalino-earth hydroxide as solid residue.

Abstract: The raw material used in most process for the production of cyclic diesters of alpha—hydroxiacids, such as Lactide and Glycolide, is a 10% solution of Hydroxyacid. During the evacuation of the solution and condensation reaction water, the organic molecules may be damaged. The present process is characterized by the use of reactants that bring as little water as possible to the reactor. In particular, for the production of Lactide, the main reactant may be anhydrous Calcium Lactate, that will react at about room temperature, for instance, with Sulfuric Anhydride, to give a solid mixture of Lactide, Calcium Sulfate Dihydrate and Calcium Sulfate Hemihydrate. Partial dehydration of the Dihydrate under mild temperature is followed by distillation of the Lactide out of the remaining powder of Calcium Sulfate Hemihydrate, and desublimation of the Lactide. Purification of the Lactide is done in situ in the desublimator.

Abstract: Process for manufacturing a cyclic diester of an ?-hydroxy acid comprising the following steps: a substantially anhydrous salt of a divalent metal and of an ?-hydroxy acid is mixed with a strong acid, the pKa of which is less than that of the ?-hydroxy acid and the salt of which with the divalent metal is hygroscopic; and the mixture is left to react for a sufficient time in order to obtain the cyclic diester dispersed in the hygroscopic salt.

Abstract: A process and installation for the integrated treatment of concentrated residual solutions resulting from the anodization of aluminium parts is described, in which caustic soda is employed in the pickling process and sulphuric acid in the anodization bath.The process comprises three sets of operations:(1) Production of aluminium sulphate in concentrated solution or in hydrated crystals, by the treatment of part of the residual solution from the anodization.(2) Production of precipitated aluminium hydroxide and a solution of sodium sulphate from residual anodization and pickling solutions.(3) Production of sodium aluminate from residual pickling solutions and aluminium hydroxide producted in (2). (FIG. 1.