Process for preparing methacrolein from formaldehyde and propionaldehyde and preparation plant for the purpose

A process for preparing methacrolein from formaldehyde and propionaldehyde in the presence of water and in the presence of a homogeneous catalyst based at least on an acid and a base, the process comprising:

• S1:
• introducing formaldehyde, propionaldehyde, water, and the homogeneous catalyst based at least on the acid and the base into a reactor,
• S2:
• producing, in a liquid phase, a liquid reaction mixture in the reactor, wherein the reaction mixture comprises methacrolein and accompanying components, wherein the accompanying components comprise water, the catalyst, unconverted formaldehyde, and unconverted propionaldehyde,
• S3:
• introducing the reaction mixture into a methacrolein workup plant and at least partly separating off the accompanying components present in the reaction mixture in the methacrolein workup plant, wherein the at least partly separating off comprises:
• S3.i:
• introducing at least a fraction of the reaction mixture into a first distillation column that forms part of the methacrolein workup plant and separating the at least a fraction of the reaction mixture at least into a first distillation mixture and a second distillation mixture, wherein the first distillation mixture is in a form of a gas phase at the top of the first distillation column and comprises methacrolein, and the second distillation mixture is in a form of a liquid phase at the bottom of the first distillation column and comprises water and the catalyst,
• S3.ii:
• introducing the first distillation mixture removed from the top of the first distillation column into a first condenser that forms part of the methacrolein workup plant and condensing the first distillation mixture,
• S3.iii:
• removing condensate from the first condenser, introducing the condensate into a first phase separator that forms part of the methacrolein workup plant and separating the condensate into a first separation mixture and a second separation mixture in the first phase separator, wherein the first separation mixture is in a form of an organic phase comprising methacrolein, and the second separation mixture is in a form of an aqueous phase, and
• S3.iv:
• removing the second distillation mixture from the bottom of the first distillation column,
• S4:
• introducing at least a portion of the second distillation mixture removed in S3.iv into the reactor,
• S5:
• introducing the second separation mixture into a second distillation column and separating the second separation mixture introduced at least into a third distillation mixture and a fourth distillation mixture, wherein the third distillation mixture is in a form of a gas phase at the top of the second distillation column and comprises methacrolein, and the fourth distillation mixture is in a form of a liquid phase at the bottom of the second distillation column and comprises water,
• S6:
• removing the third distillation mixture from the top of the second distillation column and introducing the third distillation mixture into the methacrolein workup plant, and
• S7:
• removing the fourth distillation mixture from the bottom of the second distillation column,
• wherein a pressure in the reactor is higher than in the first distillation column.