A method for rapidly converting acrylonitrile in a wastewater containing acrylonitrile

Abstract

The application provides a method for rapidly converting acrylonitrile in acrylonitrile-containing wastewater, and relates to the technical field of industrial wastewater treatment. The acrylonitrile-containing wastewater is added into a reaction kettle, stirring is started, and then an aqueous sulfite solution is added, while continuously adding an aqueous pH buffer solution, so that the pH value of the system is kept at 10.0-10.5, so that the acrylonitrile in the acrylonitrile-containing wastewater is rapidly converted; wherein the pH buffer is a weak acid or a weakly acidic inorganic salt. The method realizes rapid conversion of sodium sulfite and acrylonitrile, prevents acrylonitrile from escaping to affect the health of personnel, and has low operation cost.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method for rapidly converting acrylonitrile in nitrile-containing wastewater. Background Technology

[0002] In recent years, the production and demand of acrylonitrile have continued to rise, bringing with it the industry-wide challenge of treating large amounts of production wastewater. Although most raw materials can be reused through recycling, acrylonitrile still remains in the wastewater, typically at concentrations of several hundred mg / L. Highly toxic acrylonitrile has low solubility in water, posing a risk of leaching and seriously endangering human health. Achieving rapid conversion of acrylonitrile in nitrile-containing wastewater is crucial. Simultaneously, the treated wastewater requires anaerobic biological treatment. Maintaining the C / N / P ratio within an appropriate range during treatment, avoiding the introduction of other ions that could disrupt the biological water quality balance, and ensuring stable biological operation are also economically viable.

[0003] Among the existing technologies involving the treatment of acrylonitrile in nitrile-containing wastewater, Chinese Patent Publication No. CN103787538A discloses a method for the recovery and treatment of nitrile rubber wastewater: a) distilling the nitrile rubber wastewater under conditions where acrylonitrile is distilled off; b) contacting the treated nitrile rubber wastewater with ozone and / or hydrogen peroxide under conditions where acrylonitrile is oxidized. While this method is not limited by the concentration of acrylonitrile in the wastewater, it is energy-intensive and poses a risk of polluting the operating environment.

[0004] Chinese Patent Publication No. CN104556538A discloses a method for treating wastewater from nitrile rubber production, comprising: a) mixing nitrile rubber production wastewater with a polymerization initiator under polymerization reaction conditions; b) subjecting the reacted wastewater to magnetic flocculation; and c) mixing the magnetically flocculated wastewater with activated sludge. Although the acrylonitrile residue in the water treated by this method is essentially eliminated and the effluent quality is high, the reaction process is time-consuming, energy-intensive, and has low treatment efficiency.

[0005] Chinese Patent Publication No. CN104556539A discloses a method for treating wastewater from nitrile rubber production, comprising the following steps: a) mixing the nitrile rubber production wastewater with sulfite to convert acrylonitrile into a non-volatile substance; b) subjecting the wastewater mixed with sulfite to advanced oxidation and separating the solid and liquid phases; c) mixing the liquid phase obtained in step b with activated sludge to complete biochemical treatment. Although the acrylonitrile content in the treated water is low, effectively preventing acrylonitrile from escaping from the wastewater and avoiding air pollution, it cannot achieve rapid conversion.

[0006] The method disclosed in Chinese Patent Publication No. CN105461156A includes: a) adjusting the pH of wastewater to above 7 and mixing it with borohydride and aluminum chloride to reduce acrylonitrile in the wastewater; b) subjecting the reduced wastewater to coagulation-flotation, hydrolysis-acidification, activated sludge treatment, and aerated biological filter purification treatment in sequence. The water treated by this method is essentially free of acrylonitrile residue, but the reaction process is time-consuming, and the risk of acrylonitrile escape still exists.

[0007] The treatment method disclosed in Chinese Patent Publication No. CN105384301A includes the following steps: a) mixing nitrile rubber production wastewater with horseradish peroxidase and hydrogen peroxide for oxidation, wherein the amount of horseradish peroxidase is 0.2-1 U / mL of nitrile rubber production wastewater; b) subjecting the wastewater after acrylonitrile oxidation to magnetic flocculation; c) mixing the magnetically flocculated wastewater with activated sludge. This patent has the same problem as CN105461156A. Summary of the Invention

[0008] The purpose of this invention is to address the problems of highly toxic acrylonitrile easily escaping from nitrile-containing wastewater, the inability to achieve rapid conversion, high processing costs, and the lack of energy conservation and cost reduction. This invention provides a method that uses a specific pH buffer to control the pH value of the system, achieving rapid conversion between sodium sulfite and acrylonitrile, preventing acrylonitrile escape and its impact on personnel health, while also having lower operating costs. Furthermore, by controlling the C / N / P ratio of the treated system within a suitable range, anaerobic biological treatment can be directly carried out, avoiding the introduction of other impurity ions that could affect the normal operation of the biological treatment process.

[0009] The purpose of this invention is to provide a method for rapidly converting acrylonitrile in nitrile-containing wastewater.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0011] This invention provides a method for rapidly converting acrylonitrile in nitrile-containing wastewater, comprising the following steps:

[0012] Add the acrylonitrile-containing wastewater to the reactor, start stirring, then add an aqueous solution of sulfite, while continuously adding an aqueous solution of pH buffer to maintain the pH of the system at 10.0 to 10.5, so as to rapidly convert acrylonitrile in the acrylonitrile-containing wastewater; wherein the pH buffer is a weak acid or a weak acid inorganic salt.

[0013] The nitrile-containing wastewater described in this invention includes wastewater generated from acrylonitrile production and industries that use acrylonitrile, such as wastewater generated during the production of nitrile rubber. As long as its main component is acrylonitrile (e.g., acrylonitrile mass fraction of 1-10%), it is applicable to the content of this invention.

[0014] Sulfites include, but are not limited to, at least one of sodium sulfite, potassium sulfite, sodium bisulfite, and potassium bisulfite.

[0015] pH buffers are reagents that adjust and maintain the pH stability of a system, keeping the pH value at, for example, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, etc.

[0016] The inventors discovered that the Michael addition reaction between sodium sulfite and acrylonitrile to produce sodium cyanoethyl sulfonate is an effective method for converting acrylonitrile in wastewater. However, during this reaction, the pH value of the system tends to rise as the alkalinity of the product increases, affecting the reaction process, resulting in a longer conversion time and less product, thus hindering the rapid conversion of highly toxic acrylonitrile. Using a suitable pH buffer to control the system pH value within a certain range will be beneficial for the rapid conversion of acrylonitrile.

[0017] To address this, the inventors studied the pH changes of sodium sulfite aqueous solutions. The results showed that within the solubility range, the pH value of sodium sulfite solutions of different concentrations ranged from 10.0 to 10.5. Therefore, by adding a pH buffer during the reaction of sodium sulfite with acrylonitrile to maintain the system pH between 10.0 and 10.5, the rapid conversion of acrylonitrile into sodium cyanoethyl sulfonate can be achieved, thus achieving the goal of rapid conversion. However, excessively low pH will also cause sodium sulfite decomposition, increasing the amount required. Choosing a weak acid or a weakly acidic inorganic salt as the pH buffer can achieve stable pH control of the reaction system. Using strong acids such as hydrochloric acid, sulfuric acid, or nitric acid will cause a sudden drop in pH, resulting in a reaction with sodium sulfite to produce SO2, affecting the reaction efficiency.

[0018] In some implementations, the stirring speed is 50-500 rpm.

[0019] In some embodiments, the mass ratio of sulfite to acrylonitrile in the nitrile-containing wastewater is 1-5:1; the concentration of the pH buffer aqueous solution is 5%-15%.

[0020] In some implementations, samples are taken at regular intervals, and acrylonitrile in the wastewater is analyzed by headspace gas chromatography-mass spectrometry until it is undetectable. The required reaction time is recorded, and the reaction time is within 30 minutes.

[0021] In some embodiments, the method further includes subjecting the converted nitrile-containing wastewater to an anaerobic biochemical reaction.

[0022] By analyzing the COD, total nitrogen, and total phosphorus in the effluent, and calculating the C / N / P ratio, it can be determined whether other additives need to be added to reach the required range before proceeding with subsequent anaerobic biological reactions.

[0023] In some embodiments, the pH buffer is at least one selected from acetic acid, phosphoric acid, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium bicarbonate, and potassium bicarbonate.

[0024] Considering that the nitrile-containing wastewater after conversion still requires anaerobic treatment, the C / N / P ratio in this process is preferably around 500:5:1 (e.g., a C:N:P ratio of 480-520:4.5-5.5:1). This invention only uses pH buffers containing the above-mentioned elements, and recommends the use of weak acids such as acetic acid and phosphoric acid, as well as weak acid inorganic salts such as sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium bicarbonate, and potassium bicarbonate. Using other pH buffers requires the addition of additives such as acetic acid, urea, and phosphates to adjust the C / N / P ratio, and can easily introduce other impurities, even disrupting the water quality balance of the biological process, which is detrimental to the biological process.

[0025] Technical effects:

[0026] This invention addresses acrylonitrile-containing wastewater by eliminating the need for complex and time-consuming processes. Instead, it employs a specific pH buffer to maintain the system's pH within a fixed range, enabling rapid conversion of acrylonitrile and eliminating the impact of highly toxic components on the environment and personnel. Simultaneously, it controls the C / N / P ratio of the produced water within an appropriate range to facilitate direct anaerobic biological treatment and avoids introducing other impurities that could damage the biological water quality, thus offering significant economic benefits.

[0027] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Detailed Implementation

[0028] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0029] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0030] The acrylonitrile content was determined by headspace gas chromatography-mass spectrometry (Agilent 7890B-5977A), with a headspace equilibrium temperature of 130℃, an equilibrium time of 30 min, and a column of HP-50+30m×0.25mm×0.25μm.

[0031] The method for determining COD value is the dichromate method (GB 11914-89);

[0032] The method for determining total nitrogen content is BS EN 12260-2003;

[0033] The method for determining the total phosphorus content is the ammonium molybdate spectrophotometric method (GB / T 11893-1989).

[0034] The wastewater from the nitrile rubber production unit originates from the nitrile rubber production facility.

[0035] Example 1

[0036] One L of wastewater from the external discharge of nitrile rubber was placed in a reaction vessel, and the acrylonitrile concentration in the water was measured to be 500 mg / L. Stirring was started at 260 rpm, and then 14 ml of a pre-prepared 10% sodium sulfite aqueous solution was added. Timing was started, and simultaneously, a 10% acetic acid aqueous solution was added dropwise to control the pH of the system to approximately 10.3. Samples were continuously taken after 10 minutes, and the acrylonitrile content in the wastewater was determined by headspace gas chromatography-mass spectrometry until it became undetectable. The total reaction time was recorded as 19 minutes.

[0037] Subsequent analysis of the COD, total nitrogen, and total phosphorus in the produced water yielded a C / N / P ratio of 492.8:5.1:1.0, indicating that it can be directly introduced into the anaerobic reactor for biochemical treatment.

[0038] Example 2

[0039] The same amount of wastewater and treatment process as in Example 1 were used, except that the amount of 10% sodium sulfite aqueous solution was 17 ml, and the acetic acid aqueous solution was replaced with 10% phosphoric acid aqueous solution. The rest was the same as in Example 1, and the total reaction time was recorded as 16 minutes.

[0040] Subsequent analysis of the COD, total nitrogen, and total phosphorus in the produced water revealed a C / N / P ratio of 505.9:4.8:1.0, indicating that it can be directly introduced into the anaerobic reactor for biochemical treatment.

[0041] Example 3

[0042] The same amount of wastewater and treatment process as in Example 1 were used, except that the amount of 10% sodium sulfite aqueous solution was 12 ml, and the acetic acid aqueous solution was replaced with 10% sodium bicarbonate aqueous solution. The rest was the same as in Example 1, and the total reaction time was recorded as 25 minutes.

[0043] Subsequent analysis of the COD, total nitrogen, and total phosphorus in the produced water revealed a C / N / P ratio of 513.2:5.2:1.0, indicating that it can be directly introduced into the anaerobic reactor for biochemical treatment.

[0044] Example 4

[0045] The same amount of wastewater and treatment process as in Example 1 were used, except that the amount of 10% sodium sulfite aqueous solution was 10 ml, and the acetic acid aqueous solution was replaced with 10% potassium dihydrogen phosphate aqueous solution. The rest was the same as in Example 1, and the total reaction time was recorded as 28 minutes.

[0046] Subsequent analysis of the COD, total nitrogen, and total phosphorus in the produced water revealed a C / N / P ratio of 483.8:5.1:1.0, indicating that it can be directly introduced into the anaerobic reactor for biochemical treatment.

[0047] Example 5

[0048] The same amount of wastewater and treatment process as in Example 1 were used, except that the amount of 10% sodium sulfite aqueous solution was 14 ml, and the acetic acid aqueous solution was replaced with 10% hypochlorous acid aqueous solution. The rest was the same as in Example 1, and the total reaction time was recorded as 25 minutes.

[0049] Subsequent analysis of the COD, total nitrogen, and total phosphorus in the produced water revealed a C / N / P ratio of 532.5:9:1:1.0, indicating that it could be directly introduced into the anaerobic reactor for biochemical treatment. However, the residual hypochlorous acid in the water emitted a pungent, chlorine-like odor, causing respiratory discomfort.

[0050] Comparative Example 1

[0051] The same amount of wastewater and treatment process as in Example 1 were used, except that no pH buffer was added to control the pH value of the system in the range of 10.0 to 10.5, and only a 10% sodium sulfite aqueous solution was used for acrylonitrile removal, with a required amount of 14 ml and a total reaction time of 59 minutes.

[0052] The COD, total nitrogen, and total phosphorus of the produced water were then analyzed, and the C / N / P ratio was calculated to be 298.6:5.4:1.0. It is necessary to add 3 ml / L of acetic acid carbon source until the C / N / P ratio meets the requirements before the anaerobic reaction can proceed.

[0053] Comparative Example 2

[0054] The same amount of wastewater and treatment process as in Example 1 were used, except that the pH buffer solution was replaced with a 5% hydrochloric acid solution. The rest was the same as in Example 1. During the experiment, bubbles were detected escaping from the reactor, with a distinct pungent SO2 odor.

[0055] Subsequent analysis of the COD, total nitrogen, and total phosphorus in the produced water revealed a C / N / P ratio of 675.8:4.0:1.0. Acetic acid and urea need to be added simultaneously to adjust the ratio to approximately 500:5:1 before anaerobic reaction can proceed. Furthermore, the added hydrochloric acid disrupts the water quality balance of the biological process, preventing microorganisms from functioning properly.

[0056] Comparative Example 3

[0057] The same amount of wastewater and treatment process as in Example 1 were used, except that the amount of pH buffer acetic acid aqueous solution was increased to control the pH at 7.5. The rest was the same as in Example 1. During the experiment, bubbles were detected escaping from the reaction vessel, with a distinct pungent SO2 odor.

[0058] Subsequent analysis of the COD, total nitrogen, and total phosphorus in the produced water revealed a C / N / P ratio of 612.5:4.4:1.0. The C / N / P ratio needs to be adjusted to approximately 500:5:1 before anaerobic reaction can proceed.

[0059] In summary, a comparison of the results of the examples and comparative examples shows that by using the specific type of pH buffer of the present invention to control a specific pH, the characteristic pollutant acrylonitrile in nitrile-containing wastewater can be rapidly converted, avoiding the risk of acrylonitrile escape; at the same time, the produced water has a suitable C / N / P ratio, which can be directly subjected to anaerobic biological treatment, avoiding the introduction of other additives and disruption of the biological water quality balance, thus having good economic benefits.

[0060] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for rapidly converting acrylonitrile in nitrile-containing wastewater, characterized in that, Includes the following steps: The acrylonitrile-containing wastewater is added to the reactor, and stirring is started. Then, an aqueous solution of sulfite is added, while a pH buffer solution is continuously added dropwise to maintain the pH value of the system at 10.0-10.5, so as to rapidly convert acrylonitrile in the acrylonitrile-containing wastewater. The mass ratio of sulfite to acrylonitrile in the acrylonitrile-containing wastewater is 1-5:

1. The pH buffer is at least one selected from acetic acid, phosphoric acid, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium bicarbonate, and potassium bicarbonate. The concentration of the pH buffer solution is 5%-15%; The rapid conversion time of acrylonitrile in nitrile-containing wastewater is within 30 minutes.

2. The method according to claim 1, characterized in that, The sulfite is selected from at least one of sodium sulfite, potassium sulfite, sodium bisulfite, and potassium bisulfite.

3. The method according to claim 1, characterized in that, The stirring speed is 50-500 rpm.

4. The method according to claim 1, characterized in that, The method further includes: analyzing the COD, total nitrogen, and total phosphorus of the nitrile-containing wastewater after conversion, calculating the C:N:P ratio, and then carrying out anaerobic biochemical reactions.

5. The method according to claim 4, characterized in that, The C:N:P ratio is 480-520:4.5-5.5:1.