Process for the purification of acrolein

1. A process for purifying acrolein, the process comprising

a) splitting a liquid feed stream comprising acrolein into at least a first liquid stream and a second liquid stream,

b) introducing the first liquid stream with a temperature T1 into a distillation column at a point between the top and the bottom of the distillation column,

c) introducing the second liquid stream with a temperature T2 into the distillation column at the top of the distillation column,

d) withdrawing an overhead vapor stream enriched in acrolein from the distillation column, and

e) withdrawing a bottom stream depleted in acrolein from the distillation column,

wherein the temperature T2 of the second liquid stream in said introducing c) is lower than the temperature T1 of the first liquid stream in said introducing b).

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 The process according to claim 1 , wherein the overhead vapor stream withdrawn from the distillation column is further processed without any condensation of said vapor stream.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g) condensing a part of the overhead vapor stream withdrawn from the distillation column to give a liquefied stream and a residual vapor stream, and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-methylmercaptopropionaldehyde, 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.