Patent ID: 8877966
Filing Date: 2014-11-04
Classification: B01J,C07B,C07C

Abstract:
1. A process for preparing acrylic acid from methanol and acetic acid, which comprises the following measures: a stream of a reaction gas input mixture A comprising the methanol and molecular oxygen reactants and at least one inert diluent gas other than steam is conducted through a first reaction zone A charged with at least one oxidation catalyst A and, in the course of passage through reaction zone A, methanol present in the reaction gas input mixture A is oxidized under heterogeneous catalysis to formaldehyde and steam so as to form a product gas mixture A comprising formaldehyde, steam and at least one inert diluent gas other than steam, with or without excess molecular oxygen, and a stream of product gas mixture A leaves reaction zone A, producing a stream of a reaction gas input mixture B by mixing the stream of product gas mixture A and at least one further stream comprising acetic acid such that reaction gas input mixture B comprises acetic acid, steam, at least one inert diluent gas other than steam and formaldehyde, with or without molecular oxygen, and in which the molar amount n the stream of reaction gas input mixture B is passed through a second reaction zone B charged with at least one aldol condensation catalyst B and formaldehyde present in reaction gas input mixture B, as it flows through reaction zone B, is condensed with acetic acid present in reaction gas input mixture B under heterogeneous catalysis to give acrylic acid and H the stream of product gas mixture B leaving reaction zone B is fed to a separation zone T and separated in separation zone T into at least three streams X, Y and Z, the acrylic acid content in percent by weight present in stream X being greater than the acrylic acid content in percent by weight present in streams Y and Z together, the acetic acid content in percent by weight present in stream Y being greater than the acetic acid content in percent by weight present in streams X and Z together, the content in percent by volume of inert diluent gas other than steam present in stream Z being greater than the content in percent by volume of inert diluent gas other than steam present in streams X and Y together, and stream Y is recycled into reaction zone B and used to obtain reaction gas input mixture B wherein product gas mixture B is separated in separation zone T by a method selected from the group consisting of: product gas mixture B is separated in separation zone T by passing product gas mixture B into a condensation column equipped with separating internals and fractionally condensing it within the condensation column and conducting streams X, Y and Z out of the condensation column as separate fractions, product gas mixture B is separated in separation zone T by passing product gas mixture B into an absorption column equipped with separating internals in countercurrent to an organic solvent with a higher boiling point than acrylic acid at standard pressure, and absorbing the acetic acid and acrylic acid present in product gas mixture B into the solvent to obtain an absorbate, while a stream Z leaves the absorption column at the top thereof, and then removing streams X and Y from the absorbate as separate fractions by fractional distillation thereof in a rectification column, and product gas mixture B is separated in separation zone T by passing product gas mixture B into an absorption column equipped with separating internals in countercurrent to an aqueous solution as an absorbent, and absorbing the acetic acid and acrylic acid present in product gas mixture B into the solvent to obtain an absorbate, while a stream Z leaves the absorption column at the top thereof, and then removing streams X and Y as separate fractions from the absorbate by fractional distillation thereof in a rectification column.