Process for the purification of acrolein

2:

• The process according to claim 1, wherein a mass flow ratio of the first liquid stream to the second liquid stream ranges from 95:5 to 50:50.

3:

• The process according to claim 1, wherein a mass flow ratio of the first liquid stream to the second liquid stream ranges from 75:25 to 50:50.

4:

• The process according to claim 1, wherein the temperature T2 of the second liquid stream in said introducing c) is 10° C. at the most.

5:

• The process according to claim 1, wherein the first liquid stream is heated prior to its introduction into the distillation column.

6:

• The process according to claim 5, wherein the first liquid stream is heated to the temperature T1 of from more than 10° C. to 95° C.

7:

• The process according to claim 5, wherein the first liquid stream is heated by heat exchange with the bottom stream from the distillation column.

8:

• The process according to claim 1, wherein the process is performed under reduced pressure.

9:

• The process according to claim 1, wherein the process is performed at a pressure of from 400 to 800 mbara.

10:

• The process according to claim 1, wherein the overhead vapor stream withdrawn from the distillation column is further processed without any condensation of said vapor stream.

11:

• The process according to claim 1, further comprising
• g) condensing a part of the overhead vapor stream withdrawn from the distillation column to give a liquefied stream and a residual vapor stream, and
• h) feeding at least a part of the liquefied stream as reflux back into the distillation column at the top of said distillation column.

12:

• The process according to claim 11, wherein the liquefied stream is fed back as reflux to the top of the distillation column at a smaller mass flow than the mass and/or volume of the second liquid stream introduced at the top of the distillation column.

13:

• The process according to claim 12, wherein a mass flow ratio of the liquefied stream to the second liquid stream ranges from 5:95 to 45:55.

14:

• The process according to claim 1, further comprising
• g′) condensing at least a part of the overhead vapor stream withdrawn from the distillation column to give a liquefied stream, and, if applicable, a residual vapor stream, and
• h′) feeding the liquefied stream to a further processing or to a storage tank.

15:

• A process for preparing 3-methyl-mercaptopropionaldehyde, the process comprising
• i) purifying the liquid feed stream comprising acrolein by the process according to claim 1 to provide the overhead vapor stream enriched in acrolein, a residual vapor stream, enriched in acrolein and/or a liquefied stream enriched in acrolein, and
• ii) reacting said overhead vapor stream enriched in acrolein, said residual vapor stream, enriched in acrolein and/or said liquefied stream enriched in acrolein with at least one selected from the group consisting of methyl mercaptan, the hemithioacetal of methyl mercaptan and 3-methylthiomercaptopropionaldehyde to give 3-methylmercaptopropionaldehyde.