Process for recovering acrylonitrile from acrylic fiber production wastewater

Abstract

The application discloses a process for recovering acrylonitrile from acrylic fiber production wastewater, and belongs to the technical field of wastewater treatment containing acrylic acid. Most of the existing wastewater treatment processes containing acrylic acid mostly adopt strong alkali treatment or biological strain treatment, and have the defects of complex process, high cost and waste of recyclable monomers. The application comprises the following steps: 1) adding a pH buffer into acrylic fiber production wastewater to adjust the pH to 6-10, and continuously stirring for 2-4 hours; 2) heating the obtained material to 60-70 DEG C, and making the material enter a flash tower from the bottom of the flash tower to obtain acrylonitrile through flash separation; wherein the pH buffer is a mixture of one or more of sodium carbonate, sodium bicarbonate and sodium pyrophosphate in any proportion. After the acrylic fiber production wastewater is adjusted to a specific pH by using a specific pH buffer, acrylonitrile can be recovered through flash, the obtained acrylonitrile has high purity, high yield and low energy consumption, and the method is simple.

Description

Technical Field

[0001] A process for recovering acrylonitrile from acrylic fiber production wastewater belongs to the field of acrylic acid-containing wastewater treatment technology. Background Technology

[0002] Acrylonitrile is a common basic organic chemical raw material, widely used in the production of acrylic fibers, nitrile rubber or latex, ABS engineering plastics, as well as PVC processing, impact modifiers such as MBS and ACR, etc. Modified functional acrylic fibers are a high-end fiber produced by polymerizing acrylic acid and acrylonitrile monomers. The wastewater from its production process typically contains the following components and concentrations: acrylonitrile approximately 17000 mg / L, acrylic acid approximately 1600 mg / L, pH approximately 3.1, conductivity approximately 2650 uS / cm, CODcr approximately 26000 mg / L, TOC approximately 9310 mg / L, total nitrogen approximately 4490 mg / L, and ammonia nitrogen approximately 26 mg / L. Treatment methods for this wastewater generally involve neutralization to neutral pH followed by ion exchange to remove polymers or incineration of the oil phase, resulting in significant environmental pollution.

[0003] Patent CN202110661322.0 discloses a method for treating acrylic acid wastewater, which uses sodium hydroxide and calcium hydroxide to treat acrylic acid. However, both sodium hydroxide and calcium hydroxide can cause acrylonitrile monomer to react, making them unsuitable for acrylonitrile recovery processes. Patent CN103058366A discloses a method for cultivating anaerobic granular sludge for the biochemical treatment of acrylic acid wastewater. It is mainly used to treat the removal of CODcr in acrylic acid wastewater. It requires control over the concentration of organic matter in the influent, alkalinity, pH, nutrients, temperature, trace elements, and the addition of flocculants. The process is complex and costly.

[0004] Most existing wastewater treatment processes containing acrylic acid employ strong alkali treatment or biological treatment, which have drawbacks such as complex processes and high costs, or they have a strong destructive effect on acrylonitrile in the wastewater, wasting acrylonitrile with recycling value. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a recycling process for acrylonitrile production wastewater, which can recover acrylonitrile from acrylonitrile production wastewater with high purity.

[0006] The technical solution adopted by this invention to solve its technical problem is: a process for recovering acrylonitrile from acrylonitrile production wastewater, characterized by including the following steps:

[0007] 1) After adding pH buffer to the acrylonitrile production wastewater to adjust the pH to 6-10, stir continuously for 2-4 hours;

[0008] 2) The material is heated to 60~70℃ and enters the flash tower from the bottom of the flash tower for flash separation to obtain acrylonitrile;

[0009] The pH buffer is one or a mixture of sodium carbonate, sodium bicarbonate and sodium pyrophosphate in any proportion.

[0010] Given the high acrylonitrile content in the wastewater and the nearly 70°C boiling point difference between acrylonitrile and acrylic acid, flash evaporation to separate acrylonitrile is theoretically feasible. However, in practice, due to the high acrylic acid content, even with flash evaporation, a certain amount of acrylic acid inevitably remains in the separated acrylonitrile. Acrylic acid has strong self-polymerizing properties, causing issues that affect the reaction and subsequent production processes when the recovered acrylonitrile monomer is used. Therefore, acrylonitrile recovery is not currently considered in the treatment of acrylonitrile production wastewater.

[0011] This invention utilizes a specific pH buffer to adjust the acrylonitrile production wastewater to a specific pH, enabling flash evaporation to recover acrylonitrile. Theoretically, alkaline substances would cause acrylic acid to neutralize while simultaneously hydrolyzing acrylonitrile to form acrylamide, or further decompose acrylamide to release ammonia gas. This waste gas is difficult to treat and the acrylonitrile monomer recovery rate is low. However, the aforementioned pH buffer, combined with a specific pH endpoint and continuous stirring for the specified time, ensures both the neutralization of acrylic acid and prevents acrylonitrile hydrolysis.

[0012] Preferably, the sodium carbonate, sodium bicarbonate, and sodium pyrophosphate are derived from a solution with a weight concentration of 3-10%. Excessive concentration may lead to the hydrolysis of acrylonitrile, while insufficient concentration may result in incomplete reaction with acrylic acid, preventing the recovery of high-purity acrylonitrile, and prolonging the reaction time and increasing wastewater volume.

[0013] Preferably, the sodium carbonate, sodium bicarbonate, and sodium pyrophosphate are derived from a solution with a weight concentration of 4-6%. At this preferred concentration, the reactants can react fully with acrylic acid in a shorter time, and the hydrolysis of acrylonitrile caused by a rapid increase in pH is avoided.

[0014] Preferably, in step 1), a pH buffer is added to adjust the pH to 8-9. This preferred pH condition ensures that the acrylic acid reacts nearly completely without being carried away by acrylonitrile vapor during flash evaporation, while also minimizing acrylonitrile loss.

[0015] Preferably, the stirring time after pH adjustment in step 1) is 3~3.5h. During the stirring time set after pH adjustment, the sodium acrylate produced by the neutralization of acrylic acid undergoes cross-linking polymerization and other ion fixation reactions, which can further ensure that acrylic acid remains stably present in the system after neutralization, reducing the probability of acrylic acid ions reacting back to form acrylic acid and being carried out of the system during the flash evaporation stage. The preferred stirring time can ensure the stability of acrylic acid and avoid excessive hydrolysis of acrylonitrile.

[0016] Preferably, after the material mentioned in step 2) enters the flash tower, the material is contacted countercurrently with steam at a pressure of 0.1~0.3MPa inside the flash tower.

[0017] Preferably, after the material described in step 2) enters the flash evaporator, the material is contacted countercurrently with steam at a temperature of 110~130℃ inside the flash evaporator. Excessive temperature may cause acrylic acid to evaporate, while excessively low temperature will result in a low acrylonitrile yield.

[0018] Preferably, the pH buffer is a mixture of sodium bicarbonate solution and sodium pyrophosphate solution, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:1~2. This preferred pH buffer achieves optimal acrylonitrile yield and purity.

[0019] Preferably, the acrylonitrile material obtained in step 2) through flash evaporation is decanted at a temperature below 12°C to obtain acrylonitrile monomer. The obtained acrylonitrile monomer may contain some water; therefore, decantation of the obtained acrylonitrile material with saturated water can separate acrylonitrile from water, resulting in acrylonitrile monomer with higher purity.

[0020] Compared with existing technologies, the beneficial effects of this invention are: by adjusting the acrylonitrile production wastewater to a specific pH using a specific pH buffer, flash evaporation is achieved to recover acrylonitrile. This significantly reduces the CODcr in the wastewater, especially the content of volatile organic compounds, and yields high-value monomers. Furthermore, the obtained acrylonitrile has high purity, high yield, low energy consumption, and a simple method. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments, wherein Embodiment 1 is the preferred embodiment of the present invention.

[0022] Unless otherwise specified, the acrylonitrile production wastewater in the following examples and comparative examples is wastewater from the polymerization of acrylic acid and acrylonitrile monomers to produce acrylonitrile, with the following composition analysis: acrylonitrile 17003.6 mg / L, acrylic acid 1603 mg / L, pH 3.1, conductivity 2650 uS / cm, BOD5 / COD value less than 0.1, and ammonia nitrogen 26 mg / L.

[0023] Example 1

[0024] A process for recovering acrylonitrile from wastewater from acrylic fiber production includes the following steps:

[0025] 1) Take 1L of acrylonitrile production wastewater, slowly add pH buffer while stirring, adjust the pH to 8, and stir for 3.5h;

[0026] 2) The obtained material is heated to 70°C and enters the flash tower from the bottom. 0.2 MPa, 120°C steam is sprayed from the top of the flash tower and comes into countercurrent contact with the material at the bottom. The vapor phase is collected from one side of the top of the flash tower.

[0027] 3) Acrylonitrile monomer was obtained by two decantations at 11°C after vapor-phase condensation.

[0028] The pH buffer is a mixture of 5% sodium bicarbonate and 5% sodium pyrophosphate by weight, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:2.

[0029] Example 2

[0030] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, except that the molar ratio of sodium bicarbonate to sodium pyrophosphate in the pH buffer is set to 1:1, and other conditions are the same as in Example 1.

[0031] Example 3

[0032] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, except that the pH adjustment endpoint in step 1) is set to 9, the stirring time is set to 3 hours, and other conditions are the same as in Example 1.

[0033] Example 4

[0034] A process for recovering acrylonitrile from wastewater from acrylic fiber production is based on Example 1, with the pH buffer set to a 5% (by weight) sodium bicarbonate concentration, and other conditions being the same as in Example 1.

[0035] Example 5

[0036] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, with the pH buffer set to a 5% (by weight) sodium pyrophosphate concentration, and other conditions being the same as in Example 1.

[0037] Example 6

[0038] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, with the pH buffer set to a 5% (by weight) sodium carbonate concentration, and other conditions being the same as in Example 1.

[0039] Example 7

[0040] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, wherein the pH buffer is a mixture of sodium carbonate and sodium pyrophosphate with a weight concentration of 5%, wherein the molar ratio of sodium carbonate to sodium pyrophosphate is 1:2, and other conditions are the same as in Example 1.

[0041] Example 8

[0042] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, except that the molar ratio of sodium bicarbonate to sodium pyrophosphate in the pH buffer is set to 2:1, and other conditions are the same as in Example 1.

[0043] Example 9

[0044] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, wherein the pH buffer is a mixture of sodium bicarbonate and sodium pyrophosphate with a weight concentration of 10%, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:2, and other conditions are the same as in Example 1.

[0045] Example 10

[0046] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, with the pH endpoint set to 6, the stirring time set to 4 hours, and other conditions being the same as in Example 1.

[0047] Example 11

[0048] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, with the pH endpoint set to 10, the stirring time set to 2 hours, and other conditions being the same as in Example 1.

[0049] Example 12

[0050] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, wherein the pH buffer is a mixture of sodium bicarbonate and sodium pyrophosphate with a weight concentration of 12%, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:2, and other conditions are the same as in Example 1.

[0051] Comparative Example 1

[0052] A process for recovering acrylonitrile from wastewater from acrylic fiber production is based on Example 1, except that the pH buffer is set as a 5% sodium hydroxide solution, and other conditions are the same as in Example 1.

[0053] Comparative Example 2

[0054] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, except that the pH buffer is set as a 5% sodium sulfide solution, and other conditions are the same as in Example 1.

[0055] Comparative Example 3

[0056] A process for recovering acrylonitrile from acrylonitrile production wastewater is based on Example 1, except that the pH adjustment endpoint in step 1) is set to 11, the stirring time is set to 2.5 h, and other conditions are the same as in Example 1.

[0057] Comparative Example 4

[0058] A process for recovering acrylonitrile from wastewater from acrylic fiber production is based on Example 1, with the reaction time in step 1) set to 5 hours, and other conditions remaining the same as in Example 1.

[0059] Comparative Example 5

[0060] A process for recovering acrylonitrile from wastewater from acrylic fiber production, based on Example 1, with step 2) material heating temperature set to 80°C, and other conditions the same as in Example 1.

[0061] Performance testing

[0062] Water quality analysis was performed on the wastewater after treatment in the examples and comparative examples. The results are shown in Table 1 below.

[0063] Table 1 Water quality after treatment

[0064] .

[0065] The yield of acrylonitrile and the content of acrylic acid in acrylonitrile were tested for Examples 1-12 and Comparative Examples 1-5. The yield was expressed as the percentage of actual production to theoretical production, and the acrylic acid content was compared by NMR. The test results are shown in Table 2 below.

[0066] Table 2 Yield and Purity Tests

[0067] .

[0068] Based on the results of the above examples and comparative examples, compared with the test results of Example 1, Comparative Examples 1 and 2 prove that ordinary pH adjusters cannot be applied to the treatment and recovery of acrylonitrile from acrylonitrile production wastewater. Comparative Example 3 shows that if the pH is too high, even if the reaction time is shortened, it may lead to the hydrolysis of acrylonitrile. Comparative Example 4 proves that an excessively long reaction time may also lead to the hydrolysis of acrylonitrile. Comparative Example 5 shows that the temperature entering the flash tower also affects the evaporation of acrylic acid.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A process for recovering acrylonitrile from wastewater from acrylic fiber production, characterized in that: Includes the following steps: 1) After adding pH buffer to the acrylonitrile production wastewater to adjust the pH to 6-10, stir continuously for 2-4 hours; 2) The material is heated to 60~70℃ and enters the flash tower from the bottom of the flash tower for flash separation to obtain acrylonitrile; The pH buffer is a mixture of sodium bicarbonate and sodium pyrophosphate solution, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:1~2; After the material mentioned in step 2) enters the flash tower, the material is contacted countercurrently with steam at a pressure of 0.1~0.3MPa inside the flash tower; After the material mentioned in step 2) enters the flash tower, the material is contacted countercurrently with steam at a temperature of 110~130℃ inside the flash tower.

2. The process for recovering acrylonitrile from acrylonitrile production wastewater according to claim 1, characterized in that: Step 1) Add pH buffer to adjust the pH to 8-9.

3. The process for recovering acrylonitrile from acrylonitrile production wastewater according to claim 1, characterized in that: Step 1) The continuous stirring time is 3~3.5h.

4. The process for recovering acrylonitrile from acrylonitrile production wastewater according to claim 1, characterized in that: Step 2) The acrylonitrile material obtained by flash separation is decanted at a temperature below 12°C to obtain acrylonitrile monomer.