Process and Apparatus for Purification of Acrylic Acid

Abstract

A process and an apparatus for the purification of a crude acrylic acid composition containing maleic anhydride as an impurity comprising the following steps: (a) carrying out at least one dynamic melt crystallization stage (14, 14a, 14b, 14c, 14d) with the crude acrylic acid composition to prepare a first purified acrylic acid composition and a first residue containing at least 3.5% by weight maleic anhydride, (b) adding a solvent (26) which is capable of dissolving maleic anhydride to the first residue in an amount that the weight ratio of the solvent to the maleic anhydride is 0.3 or more to prepare a ratio-adjusted residue and (c) carrying out at least one further dynamic melt crystallization stage and/or at least one static melt crystallization stage (18, 18a, 18b) with the ratio-adjusted residue to prepare a second purified acrylic acid composition and a second residue.

Claims

1. A process for the purification of a crude acrylic acid composition containing maleic anhydride as an impurity, the process comprising the steps of: (a) carrying out at least one dynamic melt crystallization stage (14, 14a, 14b, 14c, 14d) with the crude acrylic acid composition to prepare a first purified acrylic acid composition and a first residue containing at least 3.5% by weight maleic anhydride, (b) adding a solvent (26) which is capable of dissolving maleic anhydride to the first residue in an amount that the weight ratio of the solvent to the maleic anhydride is 0.3 or more to prepare a ratio-adjusted residue and (c) carrying out at least one further dynamic melt crystallization stage and/or at least one static melt crystallization stage (18, 18a, 18b) with the ratio-adjusted residue to prepare a second purified acrylic acid composition and a second residue.

2. The process of claim 1, wherein the concentration of maleic anhydride in the first residue prepared in step (a) is at least 4% by weight based on 100% by weight of the first residue.

3. The process of claim 1, wherein the weight ratio of the solvent to the maleic anhydride in step (b) is adjusted to a range of from 0.3 to 2.0.

4. The process of claim 1, wherein the solvent is water.

5. The process of claim 1, wherein the second purified acrylic acid composition obtained in step (c) (18, 18a, 18b) is at least partially recycled (30) to the dynamic melt crystallization of step (a) (14, 14a, 14b, 14c, 14d).

6. The process of claim 1, wherein two to four dynamic melt crystallization stages (14a, 14b, 14c, 14d) are used to prepare the first purified acrylic acid composition and the first residue in step (a) and wherein one to three static melt crystallization stages (18a, 18b) are carried out with the ratio-adjusted residue in step (c).

7. The process of claim 6, wherein at least one of the dynamic melt crystallization stages (14a, 14b, 14c, 14d) of step (a) is carried out as falling film crystallization.

8. The process of claim 1, wherein the crude acrylic acid composition is produced from propylene.

9. The process of claim 1, wherein the crude acrylic acid composition is obtained by a synthesis process comprising at least one fermentation step.

10. The process of claim 1, wherein no additional solvent is added to the crude acrylic acid composition before it is subjected to step (a).

11. The process of claim 1, wherein in steps (a) to (c) no separation of a precipitated maleic anhydride by a separation means from the crude acrylic acid composition or from the first residue is conducted.

12. An apparatus (10) for the purification of a crude acrylic acid composition containing maleic anhydride as an impurity using a melt crystallization process, preferably a melt crystallization process of claim 1, the apparatus (10) comprising: a first melt crystallization section (12) for carrying out at least one dynamic melt crystallization stage (14, 14a, 14b, 14c, 14d) with the crude acrylic acid composition to prepare a first purified acrylic acid composition and a first residue, wherein the first melt crystallization section (12) has an inlet for the crude acrylic acid composition, an outlet for the first purified acrylic acid composition and an outlet for the first residue, wherein the outlet for the first purified acrylic acid composition and the outlet for the first residue may be the same, means (26) for adding a solvent to the first residue and for adjusting a predetermined weight ratio of the solvent to the first residue to prepare a ratio-adjusted residue and a second melt crystallization section (16) for carrying out at least one further dynamic melt crystallization stage or at least one static melt crystallization stage (18, 18a, 18b) with the first residue to prepare a second purified acrylic acid composition and a second residue, wherein the second melt crystallization section (16) has an inlet being arranged downstream of the means (26) for introducing the solvent to the first residue and the inlet being in fluid communication with the outlet for the first purified acrylic acid composition.

13. The apparatus (10) of claim 12, wherein the at least one dynamic melt crystallizer (14) is a falling film crystallizer.

14. The apparatus (10) of claim 12, wherein the means (26) for introducing the solvent comprise a piping for supplying the solvent, a control valve and a flow meter.

15. The apparatus (10) of claim 12, wherein the apparatus (10) does not comprise any separation means for separating a precipitated maleic anhydride from the crude acrylic acid composition or from the first residue.

Description

[0062] Specific embodiments in accordance with the present invention are subsequently described with reference to the appended drawings, in which:

[0063] FIG. 1 schematically shows an apparatus for conducting the process for the purification of the crude acrylic acid composition in accordance with an embodiment of the present invention.

[0064] FIG. 2 schematically shows an apparatus for conducting the process for the purification of the crude acrylic acid composition in accordance with another embodiment of the present invention.

[0065] FIG. 1 shows an apparatus 10 for conducting the process for the purification of the crude acrylic acid composition in accordance with an embodiment of the present invention. The apparatus includes a first melt crystallization section 12 which comprises only one falling film crystallizer 14 as a dynamic melt crystallizer. In addition, the apparatus 10 comprises a second melt crystallization section 16 having only one static melt crystallizer 18. The falling film crystallizer 14 is connected with a feed conduit 20 which is suitable for feeding a crude acrylic acid composition into the falling film crystallizer 14. In addition, the falling film crystallizer 14 has a discharge conduit 22 for the discharge of a first purified acrylic acid composition from the falling film crystallizer 14 and from the apparatus 10. The static melt crystallizer 18 is connected with the falling film crystallizer 14 via a transfer conduit 24 which is suitable for transferring a first residue obtained by crystallization in the falling film crystallizer 14 into the static melt crystallizer 18. With this respect, the transfer conduit 24 is in fluid communication with both the falling film crystallizer 14 and the static melt crystallizer 18. A solvent conduit 26, which is configured for feeding a solvent, discharges into the transfer conduit 24 such that a solvent can be added to the first residue while it is transferred from the falling film crystallizer 14 to the static melt crystallizer 18. The static melt crystallizer 18 comprises a discharge conduit 28 which serves for discharging a second residue, which is obtained by the crystallization in the static melt crystallizer 18 from the static melt crystallizer 18 and from the apparatus 10. A recycle conduit 30 provides a fluid communication between the static melt crystallizer 18 and the falling film crystallizer 14 and therefore allows to recycle at least a part of the second purified acrylic acid composition, which results from the crystallization in the static melt crystallizer 18, back into the falling film crystallizer 14.

[0066] During operation of the apparatus 10 shown in FIG. 1, a crude acrylic acid composition is introduced into the falling film crystallizer 14 through the feed conduit 20. A falling film crystallization is performed in the falling film crystallizer 14, which leads to a first purified acrylic acid composition and a first residue. The first purified acrylic acid composition is removed from the falling film crystallizer 14 and from the apparatus 10 via the discharge conduit 22, whereas the first residue is discharged from the falling film crystallizer 14 via the transfer conduit 24. In the transfer conduit 24 a solvent, preferably water, is added to the first residue via the solvent conduit 26 so that the weight ratio of the solvent to the maleic anhydride is adjusted to 0.3 or more in order to prepare a ratio-adjusted residue. The ratio-adjusted residue is fed via the transfer conduit 24 into the static melt crystallizer 18, where it is subjected to static melt crystallization, which leads to the preparation of a second purified acrylic acid composition and a second residue. While the second residue is discharged from the static melt crystallizer 18 and from the apparatus 10 via the discharge conduit 28, the second purified acrylic acid composition obtained in the static crystallization leaves the static melt crystallizer 18 through the recycle conduit 30 and is recycled back into the falling film crystallizer 14.

[0067] In FIG. 2 an apparatus 10 is shown, wherein the first melt crystallization section 12 comprises four falling film crystallization stages 14a, 14b, 14c and 14d and wherein the second melt crystallization section 16 includes two static melt crystallization stages 18a and 18b. There are provided transfer conduits 32a, 32b and 32c between the falling film crystallization stages 14a, 14b, 14c and 14d, through which a residue obtained by falling film crystallization can be transferred from one of the falling film crystallization stages to the respective downstream falling film crystallization stage. In addition, the falling film crystallization stages 14a, 14b, 14c and 14d are connected via recycle conduits 34a, 34b and 34c suitable for recycling at least a part of the purified acrylic acid composition from one of the falling film crystallization stages to the respective upstream falling film crystallization stage. A feed conduit 20 is connected to the falling film crystallization stage 14c such that a crude acrylic acid composition can be introduced into the falling film crystallization stage 14c. A discharge conduit 22 is provided at the falling film crystallization stage 14d in order to remove a first purified acrylic acid composition from the apparatus 10. A transfer conduit 24 provides a fluid communication between the falling film crystallization stage 14a of the first melt crystallization section 12 and the static melt crystallization stage 18b of the second melt crystallization section 16 so that a first residue obtained by the crystallization in the falling film crystallization stages 14a, 14b, 14c and 14d can be transferred into the static melt crystallization stage 18b. A solvent conduit 26, which is suitable for feeding a solvent, discharges into the transfer conduit 24 such that a solvent can be added to the first residue while it is transferred from the falling film crystallization stage 14a to the static melt crystallization stage 18b. The static melt crystallization stages 18a and 18b are connected via a transfer conduit 36 for transferring a residue obtained by crystallization from the static melt crystallization stage 18b to the static melt crystallization stage 18a. In addition, the static melt crystallization stage 18a and the static melt crystallization stage 18b are connected via a recycle conduit 38 allowing for transferring a purified acrylic acid composition, which results from the crystallization in the static melt crystallization stage 18a, into the static melt crystallization stage 18b. Furthermore, the static melt crystallization stage 18a comprises a discharge conduit 28 for discharging a second residue, which is obtained by crystallization in the static melt crystallization stages 18a and 18b, from the apparatus 10. A recycle conduit 30 provides a fluid communication between the static melt crystallization stage 18b and the falling film crystallization stage 14a, which is suitable for transferring a second purified acrylic acid composition resulting from the crystallization in the static melt crystallization stages 18a and 18b of the second melt crystallization section 16, back into the falling film crystallization stage 14a of the first melt crystallization section 12.

[0068] During operation of the apparatus 10 shown in FIG. 2 a crude acrylic acid composition is fed into the falling film crystallization stage 14c via the feed conduit 20. In each of the falling film crystallization stages 14a, 14b, 14c and 14d a purified acrylic acid composition and a residue are prepared. Each of the residues obtained in one of the falling film crystallization stages 14b, 14c and 14d is transferred via the transfer conduits 32a, 32b and 32c to the respective downstream falling film crystallization stage. In addition, each of the purified acrylic acid compositions obtained in one of the falling film crystallization stages 14a, 14b and 14c is at least partially recycled via the recycle conduits 34a, 34b and 34c to the respective upstream falling film crystallization stage. The residue obtained after the crystallization in the falling film crystallization stage 14a of the first melt crystallization section 12 is the first residue and is transferred via the transfer conduit 24 into the static melt crystallization stage 18b of the second melt crystallization section 16. During the transfer a solvent, preferably water, is added to the first residue via the solvent conduit 26 so that the weight ratio of the solvent to the maleic anhydride is adjusted to 0.3 or more to prepare a ratio-adjusted residue. The ratio-adjusted residue undergoes static melt crystallization in the static melt crystallization stages 18a and 18b, wherein in each of the static melt crystallization stages 18a and 18b a purified acrylic acid composition and a residue are prepared. The residue obtained in the static melt crystallization stage 18b is transferred via the transfer conduit 36 to the downstream static melt crystallization stage 18a. In addition, the purified acrylic acid composition obtained in the static melt crystallization stage 18a is at least partially recycled via the recycle conduit 38 into the upstream static melt crystallization stage 18b. The purified acrylic acid composition obtained after the crystallization in the static melt crystallization stage 18b, which is the second purified acrylic acid composition, is recycled via the recycle conduit 30 into the falling film crystallization stage 14a of the first melt crystallization section 12. A finally purified acrylic acid composition, which is the first purified acrylic acid composition, is removed from the falling film crystallizer 14d and from the apparatus 10 via the discharge conduit 22, while a final residue, which is the second residue, is removed from the static melt crystallization stage 18a and from the apparatus 10 via the discharge conduit 28.

[0069] Subsequently, the present invention is described by means of an illustrative but non-limiting example and a comparative example.

EXAMPLE

[0070] The following example is provided to illustrate the invention and does not limit the scope of the claims. Unless stated otherwise, all parts and percentages are by weight.

[0071] A crude acrylic acid composition containing maleic anhydride as an impurity was produced by a propylene route and subsequently purified by means of dynamic melt crystallization to prepare a first purified acrylic acid composition and a first residue. The first residue obtained in this way contained 3.92% of maleic anhydride and 0.69% of water, leading to a weight ratio of water to maleic anhydride of 0.18, which is less than 0.3.

[0072] Water as a solvent was added to the first residue in an amount that the weight ratio of the solvent to the maleic anhydride was 0.80. Due to this, at least part of the maleic anhydride was hydrolyzed to maleic acid, whereas the rest was reliably kept in solution. The resulting ratio-adjusted residue was further purified by means of static melt crystallization to prepare a second purified acrylic acid composition and a second residue.

[0073] The compositions of the feed, of the 1.sup.st purified acrylic acid composition, of the 1.sup.st residue, of the ratio-adjusted residue, of the 2.sup.nd purified acrylic acid composition and of the 2.sup.nd residue are summarized in the subsequent table.

TABLE-US-00001 1.sup.st purified Ratio- 2.sup.nd purified acrylic acid adjusted acrylic acid Feed composition 1.sup.st residue residue composition 2.sup.nd residue Acrylic acid 99.46 99.94 87.50 85.43 94.50 50.50 Dimer 0.02 0.00 0.45 0.44 0.19 1.39 Maleic anhydride/ 0.16 0.00 3.92 3.82 1.71 12.06 Maleic acid Water 0.03 0.02 0.69 3.05 0.62 12.51 Furfural 0.03 0.00 0.76 0.74 0.33 2.35 Benzaldehyde 0.02 0.00 0.55 0.53 0.24 1.69 Propionic 0.04 0.01 0.88 0.86 0.39 2.69 acid Acetic acid 0.08 0.01 1.60 1.57 0.71 4.92 Acrolein 0.12 0.00 2.94 2.87 1.28 9.04 Others 0.04 0.02 0.71 0.69 0.03 2.85 Water to maleic 0.18 0.80 anhydride

COMPARATIVE EXAMPLE

[0074] The same method as described above for the example was repeated except that no water as a solvent was added to the first residue.

[0075] The further purification of the first residue by means of static melt crystallization resulted in an accumulation of maleic anhydride in the crystallization equipment thereby blocking the conduits and valves of the same.

REFERENCE NUMERAL LIST

[0076] 10 Apparatus [0077] 12 First melt crystallization section [0078] 14, 14a, 14b, 14c, 14d Falling film crystallizer/falling film crystallization stages [0079] 16 Second melt crystallization section [0080] 18, 18a, 18b Static melt crystallizer/static melt crystallization stages [0081] 20 Feed conduit [0082] 22 Discharge conduit [0083] 24 Transfer conduit between falling film crystallizer/falling film crystallization stage and static melt crystallizer/static melt crystallization stage [0084] 26 Solvent conduit [0085] 28 Discharge conduit [0086] 30 Recycle conduit between static melt crystallizer/static melt crystallization stage and falling film crystallizer/falling film crystallization stage [0087] 32a, 32b, 32c Transfer conduit between falling film crystallizers/falling film crystallization stages [0088] 34a, 34b, 34c Recycle conduit between falling film crystallizers/falling film crystallization stages [0089] 36 Transfer conduit between static melt crystallizers/static melt crystallization stages [0090] 38 Recycle conduit between static melt crystallizers/static melt crystallization stages