Four-stage purification device for producing refined acrylic acid by crystallization method

Abstract

The utility model discloses a four-stage purification device for producing refined acrylic acid by a crystallization method, which is characterized by comprising a falling film crystallizer, a receiving tank, a product tank, a first-section storage tank, a second-section storage tank, a third-section storage tank, a fourth-section storage tank and a static crystallizer, a bottom discharge port of the receiving tank is respectively connected with the product tank, the falling film crystallizer, the first-section storage tank, the second-section storage tank, the third-section storage tank and the fourth-section storage tank, and a bottom discharge port of the product tank is connected with an output pump; the upper end of the fourth-section storage tank is connected with a crude acrylic acid raw material inlet pipe, the fourth-section storage tank, the third-section storage tank and the second-section storage tank are respectively connected with a feed port at the upper end of the receiving tank, the first-section storage tank is connected with a feed port at the top of the static crystallizer, and a discharge port at the bottom of the static crystallizer is connected with the second-section storage tank, the first-section storage tank and a residual acid collecting pipe; the method has the advantages of realizing production continuity and improving the yield of a refined acrylic acid product.

Description

Technical Field

[0001] The utility model relates to the field of technology for producing refined acrylic acid by a crystallization method, in particular to a four-stage purification device for acrylic acid. Background Art

[0002] Refined acrylic acid refers to acrylic acid with a high purity of more than 99.95% acrylic acid content, which is mainly used to produce super absorbent resin. Super absorbent resin is mainly used in baby diapers, sanitary napkins, and adult incontinence products, so the purity of the main raw material acrylic acid is required to be high. The other impurities in the required raw material acrylic acid: acrolein, furfural, benzaldehyde, acetic acid, propionic acid, maleic anhydride, dimer content is very small, especially the content of aldehydes that are irritating to infant skin must be less than 1ppm. There are two ways to produce refined acrylic acid: distillation and crystallization.

[0003] Distillation method: The main equipment of the distillation method for producing high-purity acrylic acid includes a reactor, an acrylic acid distillation tower, and an acrylic acid recovery tower. The boiling point of some impurities in crude acrylic acid (such as acrolein) is very close to that of acrylic acid. Therefore, when preparing high-purity acrylic acid by distillation, it is necessary to first add a chemical (such as hydrazine, thiol, etc.) to convert these impurities into high-boiling point substances, and then remove the impurities by distillation. Due to the complex equipment and the disadvantages of acrylic acid being easy to polymerize under high temperature conditions, the distillation method is gradually being eliminated. Crystallization method: The crystallization method is a new type of crystallization separation technology, which includes three steps of crystallization, sweating and melting. This method does not use solvents and has simple equipment. It has unique advantages in the separation and refining of easy-to-polymerize, difficult-to-distill, and high-boiling point organic matter. It has almost completely replaced the distillation method to produce refined acrylic acid.

[0004] At present, most of the refined acrylic acid at home and abroad is produced by crystallization method, which is divided into two types: static crystallization method and falling film crystallization method. The static crystallizer used in the static crystallization method is equivalent to a plate heat exchanger, without forced material circulation and stirring. The material is precipitated on the surface of the crystallization plate through crystallization. The heat exchange medium methanol (ethylene glycol) aqueous solution circulates inside the plate and provides the necessary cooling or heating energy. The advantages are: flexible and convenient production and low energy consumption. The disadvantages are: 1. Low production capacity and low yield (about 60%) of a single device; 2. Unable to achieve continuous production. Therefore, at present, only some small factories at home and abroad that use refined acrylic acid as raw material and do not use much adopt this method to provide fresh refined acrylic acid raw materials for downstream. This can solve the problem of acrylic acid being difficult to store (the growth rate of dimers in refined acrylic acid storage is 100ppm / day).

[0005] Falling film crystallization is the main crystallization method for refined acrylic acid devices at home and abroad. The falling film crystallizer used is composed of multiple bundles of vertical tubes. The methanol (ethylene glycol) aqueous solution is heated or cooled, and the methanol (ethylene glycol) aqueous solution flows as a falling film on the outside of the tubes. Acrylic acid crystallizes in the tubes. The collection tank under the tubes is attached to the lower part of the crystallizer, where the downward flowing liquid is collected, and then pumped into the top of the crystallizer through the material circulation pump and distributed into the tube again. The film flow rate is much higher than the crystallization growth rate.

[0006] Most acrylic acid manufacturers at home and abroad use two-stage falling film crystallization to produce refined acrylic acid, which has the following disadvantages: 1. The yield of refined acrylic acid is low, between 65% and 70%. The remaining residual acid (acrylic acid content is about 98%) is discharged to the butyl acrylate unit to produce butyl acrylate. Although this reduces energy consumption, it has more impurities. When producing butyl acrylate, there are more by-products such as diol butyl ester and di-acid butyl ester, which increases the load of subsequent distillation and purification. In addition, the distillation tower is prone to polymerization, and long-term operation cannot be guaranteed. 2. There is no stage storage tank, and the raw materials directly enter the falling film crystallizer from the tank area. The feeding time of the falling film crystallizer is long, and the corresponding crystallization time is extended, which affects the production capacity, and it is impossible to achieve production continuity and the yield of refined acrylic acid products is low. Summary of the invention

[0007] The technical problem to be solved by the utility model is to provide a four-stage purification device for producing refined acrylic acid by a crystallization method, which can realize production continuity and improve the yield of refined acrylic acid products.

[0008] The utility model solves the above technical problems by adopting the following technical scheme: a four-stage purification device for producing refined acrylic acid by crystallization method, comprising a falling film crystallizer, a receiving tank, a product tank, a first-stage storage tank, a second-stage storage tank, a third-stage storage tank, a fourth-stage storage tank and a static crystallizer, wherein the falling film crystallizer, the receiving tank and the product tank are sequentially connected from top to bottom, and the bottom discharge port of the receiving tank is respectively connected to the feed port of the product tank, the top feed port of the falling film crystallizer, the upper feed port of the first-stage storage tank, the upper feed port of the second-stage storage tank, the upper feed port of the third-stage storage tank and the fourth-stage storage tank. The upper end feed port of the tank is connected, and the bottom discharge port of the product tank is connected to an output pump for outputting refined acrylic acid products; the upper end of the four-stage storage tank is connected to a crude acrylic acid raw material inlet pipe, the bottom discharge port of the four-stage storage tank, the bottom discharge port of the three-stage storage tank, and the bottom discharge port of the two-stage storage tank are respectively connected to the upper end feed port of the receiving tank, the bottom discharge port of the one-stage storage tank is connected to the top feed port of the static crystallizer, and the bottom discharge port of the static crystallizer is connected to the upper end feed port of the two-stage storage tank, the upper end feed port of the one-stage storage tank and the residual acid collection pipe.

[0009] Preferably, the bottom discharge port of the receiving tank is connected to the upper feed port of the first storage tank, the upper feed port of the second storage tank, the upper feed port of the third storage tank and the upper feed port of the fourth storage tank respectively through the falling film crystallizer metering tank and the falling film crystallizer metering pump in sequence, so that the feed metering of each storage tank is more accurate.

[0010] Preferably, the bottom discharge port of the static crystallizer is connected to the upper feed port of the second-stage storage tank, the upper feed port of the first-stage storage tank and the residual acid collection pipe respectively through the static crystallizer metering tank and the static crystallizer metering pump, so that the feed metering of each storage tank is more accurate.

[0011] Preferably, the upper end of the falling film crystallizer is connected to a heat medium inlet and outlet pipe and the lower end is connected to a coolant inlet and outlet pipe.

[0012] Preferably, one end of the heat exchange tube of the static crystallizer is connected to the heat medium inlet and outlet pipes and the other end of the heat exchange tube is connected to the refrigerant inlet and outlet pipes.

[0013] Preferably, a circulation pump is provided between the bottom discharge port of the receiving tank and the top feed port of the falling film crystallizer.

[0014] Preferably, the falling film crystallizer, the receiving tank and the product tank are connected in sequence from top to bottom, the four-stage storage tank is connected in an integral manner with the one-stage storage tank, and the three-stage storage tank is connected in an integral manner with the two-stage storage tank, forming three high towers in a three-dimensional form, and the design advantage is that the floor space is reduced.

[0015] Compared with the prior art, the utility model has the following advantages: the utility model is a four-stage purification device for producing refined acrylic acid by crystallization method, which combines a falling film crystallizer with a static crystallizer, and four-stage storage tanks are matched to perform four-stage purification, so that the yield of refined acrylic acid reaches 98.5%, and a small amount of residual liquid is incinerated as a heavy component. The energy consumption cost of the product is reduced, the floor space is reduced, the production continuity can be achieved, and the yield of refined acrylic acid products is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The schematic diagram of the structure of the four-stage purification device of acrylic acid of the utility model is shown in the figure. The markings in the figure are as follows: 1-falling film crystallizer, 2-receiving tank, 3-product tank, 4-first stage storage tank, 5-second stage storage tank, 6-third stage storage tank, 7-fourth stage storage tank, 8-static crystallizer, 9-output pump, 10-crude acrylic acid raw material inlet pipe, 11-residual acid collection pipe, 12-falling film crystallizer metering tank, 13-falling film crystallizer metering pump, 14-static crystallizer metering tank, 15-static crystallizer metering pump, 16-heat medium inlet and outlet pipe, 17-refrigerant inlet and outlet pipe, 18-circulation pump. DETAILED DESCRIPTION

[0017] The present invention will be described in further detail below in conjunction with the accompanying drawings.

[0018] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the embodiments of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature. 1. Specific embodiments

[0020] A four-stage purification device for producing pure acrylic acid by crystallization method, such as Figure 1 As shown, it includes a falling film crystallizer 1, a receiving tank 2, a product tank 3, a first-stage storage tank 4, a second-stage storage tank 5, a third-stage storage tank 6, a fourth-stage storage tank 7 and a static crystallizer 8. The falling film crystallizer 1, the receiving tank 2 and the product tank 3 are connected in sequence from top to bottom. The bottom discharge port of the receiving tank 2 is connected to the feed port of the product tank 3, the top feed port of the falling film crystallizer 1, the upper feed port of the first-stage storage tank 4, the upper feed port of the second-stage storage tank 5, the upper feed port of the third-stage storage tank 6 and the upper feed port of the fourth-stage storage tank 7 respectively. The bottom of the product tank 3 The discharge port is connected to an output pump 9 for outputting refined acrylic acid products; the upper end of the four-stage storage tank 7 is connected to a crude acrylic acid raw material inlet pipe 10, the bottom discharge port of the four-stage storage tank 7, the bottom discharge port of the three-stage storage tank 6, and the bottom discharge port of the two-stage storage tank 5 are respectively connected to the upper feed port of the receiving tank 2, the bottom discharge port of the one-stage storage tank 4 is connected to the top feed port of the static crystallizer 8, and the bottom discharge port of the static crystallizer 8 is connected to the upper feed port of the two-stage storage tank 5, the upper feed port of the one-stage storage tank 4 and the residual acid collection pipe 11.

[0021] In this specific embodiment, the bottom discharge port of the receiving tank 2 is connected to the falling film crystallizer metering tank 12 and the falling film crystallizer metering pump 13 in sequence, and the falling film crystallizer metering pump 13 is respectively connected to the upper feed port of the first stage storage tank 4, the upper feed port of the second stage storage tank 5, the upper feed port of the third stage storage tank 6 and the upper feed port of the fourth stage storage tank 7. The bottom discharge port of the static crystallizer 8 is connected to the static crystallizer metering tank 14 and the static crystallizer metering pump 15 in sequence, and the static crystallizer metering pump 15 is respectively connected to the upper feed port of the second stage storage tank 5, the upper feed port of the first stage storage tank 4 and the residual acid collection pipe 11. The upper end of the falling film crystallizer 1 is connected to the heat medium inlet and outlet pipe 16 and the lower end thereof is connected to the refrigerant inlet and outlet pipe 17. One end of the heat exchange tube of the static crystallizer 8 is connected to the heat medium inlet and outlet pipe 16 and the other end of the heat exchange tube is connected to the refrigerant inlet and outlet pipe 17. A circulation pump 18 is provided between the bottom discharge port of the receiving tank 2 and the top feed port of the falling film crystallizer 1. The falling film crystallizer 1, the receiving tank 2 and the product tank 3 are connected integrally from top to bottom in sequence, the four-stage storage tank 7 is connected integrally with the first-stage storage tank 4 up and down, and the three-stage storage tank 6 is connected integrally with the second-stage storage tank 5 up and down, forming three high tower three-dimensional forms, and its design advantage is that the floor space is reduced.

[0022] 2. Application Examples

[0023] Primary purification: 99.5% of the crude acrylic acid raw material is continuously fed into the four-stage storage tank 7, and then from the four-stage storage tank 7 to the falling film crystallizer 1 via the receiving tank 2 to be purified to 99.95% of qualified refined acrylic acid. The purified residue is uncrystallized residue and sweating liquid, and the acrylic acid purity is 98.18%. The uncrystallized residue and sweating liquid are fed into and stored in the three-stage storage tank 6, and the qualified refined acrylic acid with a purity of ≥99.95% obtained after melting is sent out via the product tank 3.

[0024] Secondary purification: When the three-stage storage tank 6 reaches the set liquid level, the crude acrylic acid with a purity of 98.18% in the three-stage storage tank 6 is sent to the falling film crystallizer 1 through the receiving tank 2 to be purified to 99.5% crude acrylic acid. The purified residue is uncrystallized residue and sweating liquid, and the acrylic acid purity is 94.24%. The uncrystallized residue and sweating liquid are sent to and stored in the second-stage storage tank 5, and the crude acrylic acid with a purity of 99.5% obtained after melting is sent to the fourth-stage storage tank 7 to repeat the primary purification to 99.95% qualified refined acrylic acid.

[0025] Three-stage purification: When the second-stage storage tank 5 reaches the set liquid level, the crude acrylic acid with a purity of 94.24% in the second-stage storage tank 5 is sent to the falling film crystallizer 1 through the receiving tank 2 to be purified to 98.18% crude acrylic acid. The purified residue is an uncrystallized residue and a sweating liquid, and the acrylic acid purity is 87.21%. The uncrystallized residue and the sweating liquid are sent to and stored in the first-stage storage tank 4. The crude acrylic acid with a purity of 98.18% obtained after melting is sent to the third-stage storage tank 6 to repeat the secondary purification to 99.5% crude acrylic acid. After the three-stage purification in the falling film crystallizer 1, the product yield reaches 95%.

[0026] Four-stage purification: When the first-stage storage tank 4 reaches a certain liquid level, the crude acrylic acid with a purity of 87.21% in the first-stage storage tank 4 is sent to the static crystallizer 8 for four-stage purification. After crystallization in the static crystallizer 8, the 87.21% crude acrylic acid in the first-stage storage tank 4 is purified to 94.24%, and sent to and stored in the second-stage storage tank 5 for further purification in the falling film crystallizer 1. The remaining very small amount of residual acid contains a large amount of heavy components and has almost no utilization value. It enters the heavy component incinerator of the acrylic acid device for incineration. The purpose of using the static crystallizer 8 for four-stage purification is to increase the yield of acrylic acid to 98.5% to reduce the amount of residual acid produced.

[0027] Table 1 Acrylic acid and other impurities content in storage tanks at each stage

[0028]

[0029] The above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by a person skilled in the art within the essential scope of the present invention shall also fall within the protection scope of the present invention.

Claims

1. A four-stage purification device for producing pure acrylic acid by a crystallization method, characterized in that: The invention comprises a falling film crystallizer, a receiving tank, a product tank, a first-stage storage tank, a second-stage storage tank, a third-stage storage tank, a fourth-stage storage tank and a static crystallizer. The falling film crystallizer, the receiving tank and the product tank are connected in sequence from top to bottom. The bottom discharge port of the receiving tank is respectively connected with the feed port of the product tank, the top feed port of the falling film crystallizer, the upper feed port of the first-stage storage tank, the upper feed port of the second-stage storage tank, the upper feed port of the third-stage storage tank and the upper feed port of the fourth-stage storage tank. The bottom discharge port of the product tank is connected with the feed port of the product tank, the top feed port of the falling film crystallizer, the upper feed port of the first-stage storage tank, the upper feed port of the second-stage storage tank, the upper feed port of the third-stage storage tank and the upper feed port of the fourth-stage storage tank. The outlet of the four-stage storage tank is connected to an output pump for outputting refined acrylic acid products; the upper end of the four-stage storage tank is connected to a crude acrylic acid raw material inlet pipe, the bottom discharge port of the four-stage storage tank, the bottom discharge port of the three-stage storage tank, and the bottom discharge port of the two-stage storage tank are respectively connected to the upper feed port of the receiving tank, the bottom discharge port of the one-stage storage tank is connected to the top feed port of the static crystallizer, and the bottom discharge port of the static crystallizer is connected to the upper feed port of the two-stage storage tank, the upper feed port of the one-stage storage tank and the residual acid collection pipe.

2. A four-stage purification device for producing pure acrylic acid by a crystallization method according to claim 1, characterized in that: The bottom discharge port of the receiving tank is connected to the upper feed port of the first storage tank, the upper feed port of the second storage tank, the upper feed port of the third storage tank and the upper feed port of the fourth storage tank respectively through the falling film crystallizer metering tank and the falling film crystallizer metering pump.

3. The four-stage purification device for producing pure acrylic acid by a crystallization method according to claim 1, characterized in that: The bottom discharge port of the static crystallizer is connected to the upper feed port of the second-stage storage tank, the upper feed port of the first-stage storage tank and the residual acid collection pipe respectively through the static crystallizer metering tank and the static crystallizer metering pump.

4. The four-stage purification device for producing pure acrylic acid by a crystallization method according to claim 1, characterized in that: The upper end of the falling film crystallizer is connected with a heat medium inlet and outlet pipe, and the lower end thereof is connected with a coolant inlet and outlet pipe.

5. A four-stage purification device for producing pure acrylic acid by a crystallization method according to claim 4, characterized in that: One end of the heat exchange tube of the static crystallizer is connected to the heat medium inlet and outlet pipes, and the other end of the heat exchange tube is connected to the cold medium inlet and outlet pipes.

6. The four-stage purification device for producing pure acrylic acid by a crystallization method according to claim 1, characterized in that: A circulation pump is arranged between the bottom discharge port of the receiving tank and the top feed port of the falling film crystallizer.

7. A four-stage purification device for producing pure acrylic acid by a crystallization method according to any one of claims 1 to 6, characterized in that: The falling film crystallizer, the receiving tank and the product tank are integrally connected from top to bottom in sequence, the four-stage storage tank is integrally connected with the one-stage storage tank up and down, and the three-stage storage tank is integrally connected with the two-stage storage tank up and down.

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