Method for the production of bio-sourced acrylic acid
The present invention relates to the manufacture of biobased acrylic acid from glycerol as starting material, the term “biobased acid” indicating that the acrylic acid is essentially based on a carbon source of natural origin.
1. A process free of external organic solvent for recovering biobased acrylic acid from a gaseous reaction mixture obtained by gas-phase oxidation of a stream containing acrolein generated by a glycerol dehydration reaction in a first reactor, comprising the steps of:
(i) subjecting the stream containing acrolein to separation, resulting in an aqueous phase substantially depleted of acrolein and a gaseous reaction mixture rich in acrolein and substantially depleted of water and methyglyoxal, thereby controlling water content,
(ii) subjecting said gaseous reaction mixture rich in acrolein to a gas-phase catalytic oxidation reaction in a second reactor obtaining a gaseous reaction mixture wherein said gaseous reaction mixture comprises a water/acrylic acid weight ratio of less than 1.6,
(iii) subjecting the gaseous reaction mixture from step (ii) comprising a water/acrylic acid weight ratio of less than 1.6 to dehydration in a first dehydration column, resulting in a dehydration column top stream, a part of which is condensed and returned to the dehydration column in the form of reflux, and to a dehydration column bottom stream;
iv) at least partly distilling the dehydration column bottom stream in a second purification column, resulting in a purification column top stream which is at least partly condensed and returned to the dehydration column, and in a purification column bottom stream containing heavy compounds;
v) recovering a final stream comprising more than 98% by weight of acrylic acid by side take-off from the purification column.
2. A process according to claim 1 wherein the gaseous reaction mixture comprises a water/acrylic acid weight ratio of between 0.3 and 1.5.
3. A process according to claim 1 wherein the gaseous reaction mixture is at least partially condensed using a condenser internal to the dehydration column and is optionally precooled.
4. A process according to claim 1 wherein the gaseous reaction mixture is at least partly condensed using a condenser external to the dehydration column and is optionally precooled.
5. A process according to claim 1 wherein at least part of the dehydration column bottom stream is sent to a heat exchanger, which may be a reboiler or a cooler, before being returned to the dehydration column.
6. A process according to claim 1 wherein part of the dehydration column bottom stream is brought into contact with the gaseous reaction mixture and the resulting stream is sent to step i).
7. A process according to claim 1 wherein the purification column top stream is at least partly sent to a condenser, the stream leaving the condenser being partly or totally returned to the dehydration column.
8. A process according to claim 1 wherein at least part of the dehydration column top stream is subjected to oxidation, and energy produced vaporizes glycerol prior to the dehydration reaction in the first reactor.
9. A process according to claim 1 wherein at least part of the purification column bottom stream is brought to a purification column heater/reboiler.
10. A process according to claim 1 wherein at least part of the purification column bottom stream is subjected to thermal cracking to produce acrylic acid.
11. A process according to claim 1 wherein at least part of the final stream taken off from the side of the purification column is subjected to crystallization.
12. The process according to claim 1 wherein separation of step i) is a partial condensation carried out at a pressure of between 10 5 and 5×10 5 Pa, and at a temperature of between 40° C. and 90° C.
13. The process according to claim 1 wherein at least part of the aqueous phase depleted of acrolein of step i) is subjected to oxidation before being recycled and the energy produced vaporizes glycerol prior to the dehydration reaction.