Process for recovering acrylonitrile from acrylic fiber production wastewater

Abstract

The invention discloses a process for recovering acrylonitrile from acrylic fiber production wastewater, and belongs to the technical field of acrylic acid-containing wastewater treatment. In the prior art, most acrylic acid-containing wastewater treatment processes mostly adopt strong alkali treatment or biological strain treatment, have the defects of complex process and higher cost, and waste recyclable monomers. The method comprises the following steps: 1) adding a pH buffer agent into the acrylic fiber production wastewater to adjust the pH value to 6-10, and continuously stirring for 2-4 hours; 2) heating the obtained material to 60-70 DEG C, enabling the material to enter a flash tower from the bottom of the flash tower, and performing flash separation to obtain acrylonitrile; wherein the pH buffering agent 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 the specific pH by utilizing the specific pH buffer agent, acrylonitrile can be recovered by utilizing flash evaporation, the obtained acrylonitrile is high in purity, high in yield and low in energy consumption, and the method is simple.

Description

Technical Field

[0001] The invention discloses a process for recovering acrylonitrile from acrylic fiber production wastewater, belonging to the technical field of wastewater treatment containing acrylic acid. Background Art

[0002] Acrylonitrile is a common basic organic chemical raw material, widely used in acrylic fiber, nitrile rubber or latex, ABS engineering plastics, PVC processing, impact modifiers MBS, ACR and other industries. Modified functional acrylic fiber is a high-end fiber made by the polymerization of acrylic acid and acrylonitrile monomers. The composition and content of the wastewater discharged from its production process are generally: acrylonitrile about 17000mg / L, acrylic acid about 1600mg / L, pH about 3.1, conductivity about 2650uS / cm, CODcr about 26000mg / L, TOC about 9310mg / L, total nitrogen and ammonia nitrogen about 4490mg / L and 26mg / L respectively. Generally, the treatment method of this wastewater is to use alkali neutralization to neutrality and then ion exchange treatment of the polymer or incineration of oil phase substances, which causes great 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, but both sodium hydroxide and calcium hydroxide will cause the reaction of acrylonitrile monomer and are not suitable for the acrylonitrile recovery process; Patent CN103058366A discloses a method for cultivating anaerobic granular sludge for biochemical treatment of acrylic acid wastewater, which is mainly used to remove CODCr in acrylic acid wastewater. It needs to control the influent organic matter concentration, alkalinity, pH, nutrients, temperature, trace elements, and addition of flocculants. The process is complicated and the cost is high.

[0004] Most of the existing technologies for treating wastewater containing acrylic acid use strong alkali treatment or biological bacteria treatment, which has the disadvantages of complex process and high cost, or has a strong destructive effect on acrylonitrile in the wastewater, wasting acrylonitrile with recovery value. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a process for recovering acrylonitrile from acrylic fiber production wastewater, which can obtain high-purity acrylonitrile.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a process for recovering acrylonitrile from acrylic fiber production wastewater, characterized in that it comprises the following steps: 1) After adding pH buffer to acrylic fiber production wastewater to adjust the pH to 6-10, stir continuously for 2-4 hours; 2) The obtained material is heated to 60-70°C, enters the flash tower from the bottom of the flash tower, and flashes and separates to obtain acrylonitrile; Wherein, the pH buffer is one or a mixture of any proportion of sodium carbonate, sodium bicarbonate and sodium pyrophosphate.

[0007] In view of the high acrylonitrile content in the wastewater and the boiling point difference between acrylonitrile and acrylic acid of nearly 70°C, it is theoretically feasible to obtain acrylonitrile by flash distillation separation. However, in actual operation, due to the high acrylic acid content, even if the flash distillation process is used, it is inevitable that there will be a certain amount of acrylic acid in the separated acrylonitrile, and acrylic acid has a high self-polymerization property, which causes the use of the recovered acrylonitrile monomer to affect the reaction and the smooth progress of the subsequent production process. Therefore, the current treatment of acrylic fiber production wastewater does not consider acrylonitrile recovery.

[0008] The present invention uses a specific pH buffer to adjust acrylic fiber production wastewater to a specific pH, and then uses flash evaporation to recover acrylonitrile. In theory, alkaline substances can cause acrylic acid to undergo a neutralization reaction while hydrolyzing acrylonitrile to generate acrylamide, or further cause acrylamide to decompose to generate acrylic acid and release ammonia, which makes waste gas difficult to treat and has a low acrylonitrile monomer recovery rate. The above-mentioned pH buffer is combined with a specific pH end point, and after continuous stirring for the time, it can ensure that acrylic acid undergoes a neutralization reaction while preventing acrylonitrile from hydrolyzing.

[0009] Preferably, the sodium carbonate, sodium bicarbonate and sodium pyrophosphate are from a solution with a weight concentration of 3 to 10%. Too high a concentration may lead to hydrolysis of acrylonitrile, while too low a concentration may result in insufficient reaction with acrylic acid, making it impossible to recover high-purity acrylonitrile, and the reaction time will be prolonged, and the amount of wastewater will increase.

[0010] Preferably, the sodium carbonate, sodium bicarbonate and sodium pyrophosphate are from a solution with a weight concentration of 4-6%. At the preferred concentration, they can fully react with acrylic acid in a shorter time and avoid hydrolysis of acrylonitrile caused by too fast a pH increase.

[0011] Preferably, in step 1), a pH buffer is added to adjust the pH to 8 to 9. Only under the preferred pH conditions can the acrylic acid be almost fully reacted and not be carried away by the acrylonitrile vapor during the flash evaporation process, and the acrylonitrile loss is less.

[0012] Preferably, the stirring time after adjusting the pH in step 1) is 3 to 3.5 hours. During the stirring time set after adjusting the pH, a cross-linking polymerization plasma fixation reaction occurs between the sodium acrylate produced by the neutralization of acrylic acid, which can further ensure that the acrylic acid is stably present in the system after neutralization, and reduce the probability of acrylic acid ions reacting reversely to acrylic acid and being taken 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.

[0013] Preferably, after the material in step 2) enters the flash tower, steam with a pressure of 0.1-0.3 MPa is used in the flash tower to countercurrently contact the material.

[0014] Preferably, after the material in step 2) enters the flash tower, steam at a temperature of 110-130° C. is used in the flash tower to countercurrently contact the material. Too high a temperature may cause acrylic acid to evaporate, while too low a temperature may result in a low acrylonitrile yield.

[0015] 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 to 2. The preferred pH buffer can obtain the best acrylonitrile yield and purity.

[0016] Preferably, the acrylonitrile material obtained by flash separation in step 2) is decanted at a temperature below 12° C. to obtain acrylonitrile monomer. The obtained acrylonitrile monomer may contain a portion of water, so the acrylonitrile material obtained can be decanted from saturated water to separate acrylonitrile from water and obtain acrylonitrile monomer with higher purity.

[0017] Compared with the prior art, the present invention has the following beneficial effects: after adjusting the acrylic fiber production wastewater to a specific pH by a specific pH buffer, acrylonitrile can be recovered by flash evaporation. The CODcr in the wastewater, especially the content of volatile organic matter, is greatly reduced, and high-value monomers are obtained. Moreover, the obtained acrylonitrile has high purity, high yield, low energy consumption, and a simple method. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the embodiments, and Embodiment 1 is the best embodiment of the present invention.

[0019] In the following embodiments and comparative examples, unless otherwise specified, the acrylic fiber production wastewater is wastewater produced by the polymerization of acrylic acid and acrylonitrile monomers to produce acrylic fiber, wherein the component analysis is: 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.

[0020] Example 1 A process for recovering acrylonitrile from acrylic fiber production wastewater, comprising the following steps: 1) Take 1L of acrylic fiber production wastewater, slowly add pH buffer while stirring, adjust the pH to 8, and stir for 3.5h; 2) The obtained material is heated to 70°C and enters the flash tower from the bottom. 0.2Mpa, 120°C steam is sprayed on the top of the flash tower to countercurrently contact with the bottom material. The vaporized gas phase is collected from one side of the top of the flash tower. 3) After the gas phase is condensed, acrylonitrile monomer is obtained by two decantations at 11°C.

[0021] The pH buffer is a mixture of 5% by weight sodium bicarbonate and 5% by weight sodium pyrophosphate, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:2.

[0022] Example 2 A process for recovering acrylonitrile from acrylic fiber production wastewater. Based on Example 1, 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 those in Example 1.

[0023] Example 3 A process for recovering acrylonitrile from acrylic fiber production wastewater is provided. Based on Example 1, step 1) the pH adjustment end point is set to 9, the stirring time is set to 3 hours, and other conditions are the same as those in Example 1.

[0024] Example 4 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to 5% by weight concentration of sodium bicarbonate, and other conditions are the same as those in Example 1.

[0025] Example 5 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to 5% by weight of sodium pyrophosphate, and other conditions are the same as those in Example 1.

[0026] Example 6 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to 5% by weight concentration of sodium carbonate, and other conditions are the same as those in Example 1.

[0027] Example 7 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to a mixture of 5% by weight sodium carbonate and 5% by weight sodium pyrophosphate, wherein the molar ratio of sodium carbonate to sodium pyrophosphate is 1:2, and other conditions are the same as those in Example 1.

[0028] Example 8 A process for recovering acrylonitrile from acrylic fiber production wastewater is disclosed. Based on Example 1, 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 those in Example 1.

[0029] Example 9 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to a mixture of 10% by weight sodium bicarbonate and 10% by weight sodium pyrophosphate, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:2, and other conditions are the same as those in Example 1.

[0030] Example 10 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH end point is set to 6, the stirring time is set to 4 hours, and other conditions are the same as those in Example 1.

[0031] Embodiment 11 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH end point is set to 10, the stirring time is set to 2 hours, and other conditions are the same as those in Example 1.

[0032] Example 12 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to a mixture of 12% by weight sodium bicarbonate and 12% by weight sodium pyrophosphate, wherein the molar ratio of sodium bicarbonate to sodium pyrophosphate is 1:2, and other conditions are the same as those in Example 1.

[0033] Comparative Example 1 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to a 5% sodium hydroxide solution, and other conditions are the same as those in Example 1.

[0034] Comparative Example 2 A process for recovering acrylonitrile from acrylic fiber production wastewater, based on Example 1, wherein the pH buffer is set to a 5% sodium sulfide solution, and other conditions are the same as those in Example 1.

[0035] Comparative Example 3 A process for recovering acrylonitrile from acrylic fiber production wastewater is provided. Based on Example 1, in step 1), the pH adjustment end point is set to 11, the stirring time is set to 2.5 h, and other conditions are the same as those in Example 1.

[0036] Comparative Example 4 A process for recovering acrylonitrile from acrylic fiber production wastewater is provided. Based on Example 1, the reaction time of step 1) is set to 5 hours, and other conditions are the same as those of Example 1.

[0037] Comparative Example 5 A process for recovering acrylonitrile from acrylic fiber production wastewater is provided. Based on Example 1, in step 2), the material heating temperature is set to 80° C., and other conditions are the same as those in Example 1.

[0038] Performance Testing The water quality of the wastewater treated in the embodiment and the comparative example was analyzed, and the analysis results are shown in Table 1 below.

[0039] Table 1 Water quality after treatment .

[0040] The yield of acrylonitrile and the content of acrylic acid in acrylonitrile were tested for Examples 1 to 12 and Comparative Examples 1 to 5, wherein the yield was expressed as a percentage of the actual production amount to the theoretical production amount, and the acrylic acid content was compared and tested by NMR. The test results are shown in Table 2 below.

[0041] Table 2 Yield and purity test .

[0042] According to the results of the above embodiments and comparative examples, the test results of comparative examples 1 and 2 are compared with those of embodiment 1, which proves that ordinary pH regulators cannot be used to treat acrylic fiber production wastewater to recover acrylonitrile. Comparative example 3 shows that when the pH is too high, even if the reaction time is shortened, acrylonitrile may be hydrolyzed. Comparative example 4 proves that too long a reaction time may also lead to the hydrolysis of acrylonitrile. Comparative example 5 shows that the temperature entering the flash tower will also affect the distillation of acrylic acid.

[0043] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A process for recovering acrylonitrile from acrylic fiber production wastewater, characterized in that: The following steps are involved: 1) After adding pH buffer to acrylic fiber production wastewater to adjust the pH to 6-10, stir continuously for 2-4 hours; 2) The obtained material is heated to 60-70°C, enters the flash tower from the bottom of the flash tower, and flashes and separates to obtain acrylonitrile; Wherein, the pH buffer is one or a mixture of any proportion of sodium carbonate, sodium bicarbonate and sodium pyrophosphate.

2. The process for recovering acrylonitrile from acrylic fiber production wastewater according to claim 1, wherein: The sodium carbonate, sodium bicarbonate and sodium pyrophosphate are from a solution with a weight concentration of 3-10%.

3. The process for recovering acrylonitrile from acrylic fiber production wastewater according to claim 1, characterized in that: The sodium carbonate, sodium bicarbonate and sodium pyrophosphate are from a solution with a weight concentration of 4-6%.

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

5. The process for recovering acrylonitrile from acrylic fiber production wastewater according to claim 1 or 4, characterized in that: Step 1) The continuous stirring time is 3~3.5h.

6. The process for recovering acrylonitrile from acrylic fiber production wastewater according to claim 1, characterized in that: After the material in step 2) enters the flash tower, steam with a pressure of 0.1-0.3 MPa is used in the flash tower to countercurrently contact the material.

7. The process for recovering acrylonitrile from acrylic fiber production wastewater according to claim 1, characterized in that: After the material in step 2) enters the flash tower, steam at a temperature of 110-130° C. is used in the flash tower to countercurrently contact the material.

8. The process for recovering acrylonitrile from acrylic fiber production wastewater according to claim 1, characterized in that: 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.

9. The process for recovering acrylonitrile from acrylic fiber 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.