1. The present invention relates to chemical industry separation technical field, particularly relate to a kind of preparation method of  ice crystal acrylic acid.

2. Acrylic acid is an unsaturated organic acid, which contains carbon-carbon double bond and carboxyl structure in the molecule, so a series of compounds can be derived to form a large class of acrylic acid products. At present, a unique acrylic acid industry has formed in the field of modern chemical industry, and it has become an important derivative of propylene like polypropylene, acrylonitrile, and propylene oxide. The excellent polymerization and esterification ability of acrylic acid provides an extremely important intermediate for the synthesis and preparation of various fine chemicals. The hydrogens at the α and β positions of acrylic acid are easily substituted, and its carboxyl group can generate ester, amide, acid chloride, acid anhydride, etc.; its double bond has double bond connectivity, is chemically active, and can be homopolymerized and copolymerized. The polymer has a wide range of uses , is an important chemical raw material; acrylic acid and its esters can be used as polymer monomers; in addition, it can also be used as raw materials for adhesives, coatings, resins, etc.; the resin synthesized by this product can be used in pharmaceuticals, Leather, textile, paper, chemical fiber, rubber, building materials, plastics, packaging materials, water treatment, oil extraction and other industries. In recent years, the demand for superabsorbent resins is increasing, so the purity requirements for raw acrylic acid are also increasing. Therefore, new requirements for the purification of acrylic acid are also put forward. However, because acrylic acid contains carbon-carbon double bonds, it is easy to polymerize under high temperature environment, which affects product quality and yield. Therefore, it is very important to develop a purification technology applied to the production of high-purity acrylic acid.

3. In view of the above-mentioned shortcoming of the prior art, the object of the present invention is to provide a kind of preparation method of ice crystal acrylic acid, the present invention is raw material with acrylic acid solution, by extraction, evaporation and crystallization operation, obtains the ice crystal acrylic acid of high purity.

4. In order to achieve the above-mentioned purpose and other related purposes, the invention provides a kind of preparation method of ice crystal acrylic acid, comprising the steps:

5. (1) Use crude acrylic acid aqueous solution as raw material, add extractant, carry out extraction, separate water phase (raffinate phase) and organic phase (extraction phase), keep water-soluble impurities in water phase, acrylic acid and other oils Soluble impurities are enriched into the organic phase;

6. (2) Add polymerization inhibitor to organic phase, decompression distillation, isolate extraction agent and acrylic acid solution;

7. (3) The obtained acrylic acid solution is melted and crystallized to obtain a high-purity ice crystal acrylic acid product.

8. Further, in the step (1), the crude acrylic acid aqueous solution is an acrylic acid aqueous solution prepared by bio-based.

9. Further, the crude acrylic acid aqueous solution includes, by weight percentage: 25-45% of water and 50-70% of acrylic acid.

10. Further, in the step (1), the extractant is selected from at least one of ethyl acetate, propyl acetate, and triethyl citrate.

11. Further, in the step (1), the amount of the extractant added is 0.5-1.0 times the mass of the crude acrylic acid aqueous solution, preferably 0.6-0.8 times.

12. Further, in the step (2), the polymerization inhibitor is selected from at least one of hydroquinone, hydroquinone monomethyl ether, and phenothiazine compounds.

13. Further, in the step (2), the vacuum distillation process is as follows: first distill out the extractant at a distillation pressure of 8-12 kPa, then reduce the pressure to 2-5 kPa, and distill out the acrylic acid solution.

14. Further, in the step (2), when the extractant is distilled, the distillation temperature is 80-320°C, preferably 100-320°C; more preferably, when the extractant is selected from ethyl acetate and/or propyl acetate , the distillation temperature is 100-150°C, and when the extractant is triethyl citrate, the distillation temperature is 294-320°C.

15. Further, in the step (2), when distilling the acrylic acid solution, the distillation temperature is 30-100°C.

16. Further, in the step (2), in the acrylic acid solution obtained by distillation, the mass percentage of acrylic acid is more than 96%, preferably 97-99%.

17. Further, in the step (3), the melting and crystallization method is as follows: slowly cool down the acrylic acid solution in a stirring state to precipitate acrylic acid crystals, and when the crystal content (i.e. solid content) reaches 25-50%. Filtrate under constant temperature to obtain crystals and mother liquor; separate crystals and mother liquor, crystals continue to repeat the aforementioned crystallization operation to obtain high-purity ice crystal acrylic acid crystals, and after the mother liquor is recovered, through repeated crystallization, the finally obtained raffinate is recovered to the step ( 1) in the crude acrylic acid aqueous solution, extraction, vacuum distillation and melt crystallization were carried out together.

18. Optionally, lower the temperature to -20-13°C to precipitate acrylic acid crystals, preferably -10-10°C, more preferably 3-5°C.

19. Optionally, the filtering method is rotary centrifugation.

20. Optionally, the constant temperature during filtration is -20-10°C, preferably -10-10°C, more preferably 3-5°C.

21. Further, in the step (3), the purity of the obtained ice crystal acrylic acid crystals is ≥99.7%, preferably ≥99.8%.

22. As mentioned above, the preparation method of ice crystal acrylic acid of the present invention has the following beneficial effects:

23. The present invention uses acrylic acid solution as a raw material to obtain a high-purity ice crystal acrylic acid product through extraction, distillation, and crystallization purification operations. The method has the advantages of high product purity, stable product index, convenient continuous production, and low operating energy consumption. At the same time, during the crystallization process, there is no precipitation of impurities such as succinic anhydride to affect the crystallization process and the purity of acrylic acid. The method is suitable for purifying the aqueous acrylic acid solution, and is especially suitable for the crude acrylic acid aqueous solution produced from bio-based raw materials. Description of drawings

24. The implementation of the present invention will be described below through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation modes, and various modifications or changes can be made to the details in this specification based on different viewpoints and applications without departing from the spirit of the present invention.

25 The present invention provides a method for preparing ice crystal acrylic acid, which uses crude acrylic acid aqueous solution as a raw material, first undergoes extraction, and separates the water phase from the organic phase, so that water-soluble impurities remain in the water phase, and acrylic acid and other oil-soluble impurities are enriched to the organic phase; after the extraction and liquid separation is completed, add a polymerization inhibitor to the extraction phase, mix evenly, and then carry out vacuum distillation on the extraction phase to separate the extraction agent and acrylic acid; then melt and crystallize the obtained acrylic acid Under the condition of stirring, the temperature of the acrylic acid melt is gradually lowered, and the crystal part of the acrylic acid is analyzed. 

When the solid content reaches about 25-50%, the temperature of the crystallization liquid is controlled, and the slurry enters a temperature-controlled state at a constant temperature. In the filtration device, the mother liquor and crystals are separated, and the acrylic acid in the mother liquor is further recovered and purified through repeated crystallization after the mother liquor is recovered, and the centrifuged The filter cake (i.e. crystal) is melted and crystallized again, and according to the purity requirements of acrylic acid, it is subjected to the next stage of purification treatment until the high-purity ice crystal acrylic acid product is achieved.

27. Specifically, the crude acrylic acid aqueous solution is an acrylic acid aqueous solution prepared by bio-based. 

28. Specifically, the crude acrylic acid aqueous solution includes, by weight percentage: 25-45% of water and 50-70% of acrylic acid.

29. Specifically, the extractant is selected from at least one of ethyl acetate, propyl acetate, and triethyl citrate, and the amount of the extractant added is 0.5-1.0 times the mass of the crude acrylic acid aqueous solution; the polymerization inhibitor is selected from hydrogen At least one of quinone, hydroquinone monomethyl ether, and phenothiazine compounds.

30. Specifically, the vacuum distillation process is as follows: first distill the extractant at a distillation pressure of 8-12 kPa, then reduce the pressure to 2-5 kPa, and distill the acrylic acid solution. Wherein, when the extractant is distilled off, the distillation temperature is 80-320°C, preferably 100-320°C; more preferably, when the extractant is ethyl acetate and/or propyl acetate, the distillation temperature is 100-150°C, When the extractant is triethyl citrate, the distillation temperature is 294-320°C. When distilling out the acrylic acid solution, the distillation temperature is 30-120°C.

31. Specifically, in the acrylic acid solution obtained by distillation, the mass percentage of acrylic acid is more than 96%, preferably 97-99%.

32. Specifically, the melting and crystallization method is as follows: slowly cool the acrylic acid solution to -20-13°C under stirring, and precipitate acrylic acid crystals. In the state (-20 ~ 10 ℃), filter to obtain crystals and mother liquor; separate the crystals and mother liquor, crystals continue to repeat the crystallization operation mentioned above to obtain high-purity ice crystal acrylic acid crystals, and the mother liquor is recovered through repeated crystallization, and finally obtained The residual liquid is recovered into the crude acrylic acid aqueous solution, and extraction, vacuum distillation and melting crystallization are carried out together.