Process for producing acrylic acid
The process for the distillation of a gas mixture comprising (meth)acrylic acid obtained from the gas-phase oxidation of at least one (meth)acrylic acid precursors is improved through the use of coupled distillation columns. In a first column, the gaseous mixture is dehydrated while in a second column, the dehydrated gaseous mixture is distilled into product, overhead and bottoms streams.
1. A process for the recovery of (meth)acrylic acid, the process comprising:
A. Cooling a gaseous reaction mixture comprising (meth)acrylic acid, the mixture obtained from the gas-phase oxidation of at least one (meth)acrylic acid precursor;
B. Dehydrating the cooled gas mixture in a dehydration column to produce a dehydration column overhead stream and a dehydration column bottoms stream, wherein the dehydrating is carried out without using a solvent that forms an azeotrope with water;
C. At least partially condensing the dehydration column overhead stream to form a condensate, and returning at least a portion of the condensate to the dehydration column as reflux;
D. Dividing the dehydration column bottoms stream into at least first and second dehydration column bottom streams, and passing at least a portion of one of the first and second dehydration column bottoms stream to a dehydration column heater/reboiler and passing at least a portion of the other dehydration column bottoms stream to the upper half of a second column;
E. Subjecting the portion of the bottoms stream passed to the second column to distillation within the second column to produce at least a second column overhead stream and a second column bottoms stream comprising heavy components;
F. At least partially condensing the second column overhead stream to form a second overhead condensate, and passing at least a portion of the second overhead condensate to the dehydration column heater/reboiler; and
G. Passing at least a portion of the second column bottoms stream to a second column heater/reboiler.
2. The process of claim 1 further comprising recovering a side draw product stream from the second column.
3. The process of claim 2 in which at least a portion of the side draw product stream is recovered as a liquid.
4. The process of claim 2 in which at least a portion of the side draw product stream is recovered as a vapor.
5. The process of claim 2 in which the second column side draw product stream and bottoms stream are recovered at a weight ratio of side stream to bottoms stream of 5:95 to 95:5.
6. The process of claim 1 in which the heavy components of at least a portion of the second column bottoms stream are cracked to produce (meth)acrylic acid.
7. The process of claim 1 in which the second column is operated at less than atmospheric pressure.
8. The process of claim 1 in which the dehydration column is operated at a pressure of at least atmospheric and not in excess of the pressure of the gaseous reaction mixture before it is cooled.
9. The process of claim 1 in which the dehydration column bottoms stream has a temperature not in excess of 120° C.
10. The process of claim 1 in which the temperature at the top of the dehydration column is at least 40° C.
11. The process of claim 1 in which the gaseous reaction mixture is cooled within the dehydration column.
12. The process of claim 1 in which the gaseous reaction mixture is at least partially cooled within a vapor/liquid contact apparatus apart from the dehydration column.
13. The process of claim 1 in which the gaseous reaction mixture is cooled by the direct contacting of the mixture with liquid from the dehydration column heater/reboiler.
14. The process of claim 1 in which at least a portion of the dehydration column bottoms stream that passes to the second column passes through a surge tank before entering the second column.
15. The process of claim 1 in which at least a portion of the second column bottoms stream is passed to an acrylates ester production unit.
16. The process of claim 1 further comprising the addition to the dehydration column of an inhibitor package to inhibit the polymerization of (meth)acrylic acid while within the dehydrator column.
17. The process of claim 16 in which the inhibitor package comprises 4-hydroxy TEMPO and soluble manganese ions.
18. The process of claim 16 in which the (meth)acrylic acid is acrylic acid.
19. The process of claim 1 in which the at least a portion of the other dehydration column bottoms stream is passed to the top of the second column.
20. The process of claim 6 in which the heavy components are cracked within a dimer cracker.