The present invention relates to an optimized process for preparing methacrylic acid, wherein methacrolein is prepared in a first stage from propionaldehyde and formaldehyde by means of a Mannich reaction and oxidized in a second stage to methacrylic acid. More particularly, the present invention relates to the reduction in the amounts of catalyst to be used in the first stage, especially to the reduction in the amounts of acid to be used here, by virtue of the additional installation of recycling streams suitable for the purpose.

The present invention relates to an optimized process for preparing methacrylic acid, wherein methacrolein is prepared in a first stage from propionaldehyde and formaldehyde by means of a Mannich reaction and oxidized in a second stage to methacrylic acid. More particularly, the present invention relates to the reduction in the amounts of catalyst to be used in the first stage, especially to the reduction in the amounts of acid to be used here, by virtue of the additional installation of recycling streams suitable for the purpose.

Disclosed is a method for linkage recovery of an organic acid in an aqueous organic acid solution. The method comprises: mixing a solution with an organic acid concentration lower than 20 wt % with a specific extractant and then subjecting same to counter-current extraction so as to obtain an extract phase and a raffinate phase; and subjecting the extract phase together with a solution with an acid concentration higher than 70 wt % to an azeotropic rectification so as to recover an organic acid. When the concentration of the aqueous organic acid solution is 20 wt %-70 wt %, the aqueous organic acid solution is extracted and concentrated to make the concentration of the aqueous organic acid solution higher than 70 wt %.

Disclosed is a method for linkage recovery of an organic acid in an aqueous organic acid solution. The method comprises: mixing a solution with an organic acid concentration lower than 20 wt % with a specific extractant and then subjecting same to counter-current extraction so as to obtain an extract phase and a raffinate phase; and subjecting the extract phase together with a solution with an acid concentration higher than 70 wt % to an azeotropic rectification so as to recover an organic acid. When the concentration of the aqueous organic acid solution is 20 wt %-70 wt %, the aqueous organic acid solution is extracted and concentrated to make the concentration of the aqueous organic acid solution higher than 70 wt %.

Disclosed is a method for linkage recovery of an organic acid in an aqueous organic acid solution. The method comprises: mixing a solution with an organic acid concentration lower than 20 wt % with a specific extractant and then subjecting same to counter-current extraction so as to obtain an extract phase and a raffinate phase; and subjecting the extract phase together with a solution with an acid concentration higher than 70 wt % to an azeotropic rectification so as to recover an organic acid. When the concentration of the aqueous organic acid solution is 20 wt %-70 wt %, the aqueous organic acid solution is extracted and concentrated to make the concentration of the aqueous organic acid solution higher than 70 wt %.

The present invention provides a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in an organic solvent, comprising the steps of: i) separating a vent gas from an oxidation stage into an organic solvent-rich liquid stream and a water-rich vapour stream in a distillation stage; and ii) separating an aqueous purific ation mother liquor comprising organic compounds from purified aromatic dicarboxylic acid crystals in a separation stage, characterised in that the process further comprises the steps of: iii) transferring the aqueous purification mother liquor from the separation stage to an extraction stage; iv) extracting said organic compounds from the aqueous purification mother liquor by contacting the aqueous purification mother liquor at a temperature of at least 90° C. with an organic liquid in the extraction stage to form an aqueous phase and an organic phase, wherein the concentration of said organic compounds in the aqueous phase is lower than the concentra tion of said organic compounds in the aqueous purification mother liquor; and v) transferring the aqueous phase to said distillation stage. The present invention further provides an apparatus for carrying out the process.

The present invention provides a process for the production of an aromatic dicarboxylic acid comprising the catalytic oxidation of a hydrocarbon precursor in an organic solvent, comprising the steps of: i) separating a vent gas from an oxidation stage into an organic solvent-rich liquid stream and a water-rich vapour stream in a distillation stage; and ii) separating an aqueous purific ation mother liquor comprising organic compounds from purified aromatic dicarboxylic acid crystals in a separation stage, characterised in that the process further comprises the steps of: iii) transferring the aqueous purification mother liquor from the separation stage to an extraction stage; iv) extracting said organic compounds from the aqueous purification mother liquor by contacting the aqueous purification mother liquor at a temperature of at least 90° C. with an organic liquid in the extraction stage to form an aqueous phase and an organic phase, wherein the concentration of said organic compounds in the aqueous phase is lower than the concentra tion of said organic compounds in the aqueous purification mother liquor; and v) transferring the aqueous phase to said distillation stage. The present invention further provides an apparatus for carrying out the process.

Method for isolating carboxylic acid from an aqueous metal carboxylate-containing side stream of an organic peroxide production process, involving the protonation of the carboxylate, separation of liquid and organic phases, and the removal of residual peroxides.

Method for isolating carboxylic acid from an aqueous metal carboxylate-containing side stream of an organic peroxide production process, involving the protonation of the carboxylate, separation of liquid and organic phases, and the removal of residual peroxides.

The disclosure relates to a method for producing levulinic acid in a molten salt hydrate from cellulose hydrolysis. An inorganic molten salt hydrate was prepared by mixing an inorganic salt with water, cellulose is added and stirred to dissolve, a solid catalyst is added and heated up for reaction to obtain a reactant, the reactant is cooled and subjected to a separation to obtain the levulinic acid, and the inorganic molten salt hydrate and the solid catalyst obtained after the separation are recycled, wherein the inorganic salt is one or more selected from the group consisting of LiCl, LiBr, CaBr.sub.2, Ca(NO.sub.3).sub.2, LiNO.sub.3 and KNO.sub.3.