Method for purifying light acrylates
The present invention relates to the production of light (meth)acrylic esters by direct esterification of acrylic acid by methanol or ethanol. The invention more particularly relates to a process for the recovery/purification of C1-C2 alkyl acrylate comprising the azeotropic distillation of the crude reaction mixture using a distillation column comprising a sidestream drawing off of a fraction rich in alkyl alkoxypropionate byproduct, the boiling point of which is close to that of acrylic acid, and therefore problematic in the purification process.
1. A process for the recovery/purification of C 1 -C 2 alkyl acrylate from a reaction mixture resulting from the esterification of acrylic acid with an alcohol chosen from methanol and ethanol, said process comprising the step of azeotropically distilling said reaction mixture using an azeotropic distillation column comprising a sidestream drawoff of a fraction rich in alkyl alkoxypropionate byproduct.
2. The process as claimed in claim 1 , wherein the sidestream drawing off of the fraction rich in alkyl alkoxypropionate is carried out in liquid phase.
3. The process as claimed in claim 1 , wherein the drawing off of the fraction rich in alkyl alkoxypropionate is carried out in an upper half of the azeotropic distillation column.
4. The process as claimed in claim 1 , wherein the azeotropic distillation is carried out under vacuum pressure ranging from 200 to 600 mmHg.
5. The process as claimed in claim 1 , wherein a temperature at a bottom of the azeotropic distillation column is less than 110° C.
6. The process as claimed in claim 1 , wherein an external reflux is provided in the azeotropic distillation column using a stream comprising alkyl acrylate.
7. The process as claimed in claim 1 , wherein a fraction rich in alkyl alkoxypropionate contains alkyl alkoxypropionate at a content by weight ranging from 20% to 50%.
8. The process as claimed in claim 1 , wherein a fraction rich in alkyl alkoxypropionate contains water at a content by weight ranging from 20% to 60%.
9. The process as claimed in claim 1 , which is selected from the group consisting of continuous, semi-continuous and batch type processes.
10. The process as claimed in claim 1 , comprising:
a) azeotropically distilling the reaction mixture using a first distillation column having a top and bottom to separate, at the top, an azeotropic mixture comprising alkyl acrylate, unreacted alcohol and water and, at the bottom, a fraction comprising unreacted acrylic acid and heavy byproducts, a fraction rich in alkyl alkoxypropionate byproduct being removed by sidestream drawoff;
b) separating a bottom stream from the first distillation column into a stream comprising unreacted acrylic acid which is recycled to an esterification reactor, and a stream comprising heavy byproducts, which is subjected to a thermal cracking releasing a stream of economically upgradable products which are recycled;
c) liquid/liquid extraction of a top stream from the first distillation column with an aqueous stream which is separated into an organic phase, comprising alkyl acrylate, and an aqueous phase, the aqueous phase being distilled in order to recover, on the one hand, a fraction rich in alcohol which is recycled to the reactor and, on the other hand, a fraction rich in water which is used as aqueous stream in the liquid/liquid extraction stage;
d) purifying said organic phase to recover the purified alkyl acrylate.
11. The process as claimed in claim 10 , wherein purification step d) is carried out by distillation, using a purification system comprising at least one distillation column.
12. The process as claimed in claim 10 , wherein purification step d) is carried out using a purification system comprising at least one partition column.
13. The process as claimed in claim 1 , wherein the C 1 -C 2 alkyl acrylate is methyl acrylate.