A method for converting and extracting phthalic acid using a by-product

Abstract

The application discloses a method for converting by-products and extracting phthalic acid, which comprises the following steps: evaporating and concentrating salt-containing wastewater containing phthalimide and sodium salt decomposition substances; adding an impurity removal agent, stirring, and entering an automatic candle filter at a temperature of 50-80 DEG C to separate and filter fine impurities; adding the filtrate into an acidification kettle, heating, adding hydrochloric acid into the filtrate at a water temperature of 50-90 DEG C to acidify, and converting sodium phthalate and a series of substances into phthalic acid; cooling, completely separating phthalic acid, and effectively separating salt and water-soluble impurities, and obtaining phthalic acid through solid-liquid centrifugal separation and elution desalting. The method can convert high-COD and high-salt wastewater series organic matters into phthalic acid, can decolorize and purify in the extraction process, can obtain higher-quality phthalic acid, can effectively realize resource utilization, and can reduce wastewater COD to below 5000 mg / L.

Description

Technical Field

[0001] This invention relates to the field of treatment and resource utilization of rubber additive wastewater, and in particular to a method for converting and extracting phthalic acid using by-products. Background Technology

[0002] The condensation wastewater generated during the synthesis of the anti-scorching agent CTP has a COD of 30,000-50,000 mg / L. Qualitative analysis of this high-COD, high-salt wastewater revealed that the main organic matter contained within is phthalimide and its sodium salt decomposition derivatives. During the synthesis process, the condensation of sodium phthalimide with cyclohexylsulfenyl chloride is difficult to avoid due to alkaline or acidic media and temperature rises. This results in sodium phthalimide, in addition to participating in the main reaction, partially hydrolyzing under alkaline and high-temperature conditions into aqueous compounds such as anthranilic acid and sodium phthalate (which converts to phthalic acid under acidic conditions). The presence of these substances leads to a high COD, and in wastewater evaporation treatment, it not only affects evaporation efficiency and increases treatment costs but also causes the co-precipitation of organic matter and salt, impacting the quality of the by-product salts.

[0003] Currently, in the production of CTP (calcification-resistant plating agent), the extraction and resource utilization of decomposition products of phthalimide and its sodium salt from condensation wastewater are still lacking. Most methods focus on separation and transfer to reduce the impact on evaporation and desalination, without considering the resource reuse of byproducts, leading to the waste of many components in the wastewater. Furthermore, even when existing methods for treating phthalimide and its sodium salt from condensation wastewater separate these organic compounds, their complex composition, poor appearance, color, and odor, and low purity present a bottleneck problem hindering their resource reuse. Summary of the Invention

[0004] This invention overcomes the shortcomings of the prior art and provides a method for converting and extracting phthalic acid using byproducts.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: a method for converting and extracting phthalic acid using byproducts, comprising the following steps:

[0006] Step S1: Evaporation and concentration. The saline wastewater containing phthalimide and its sodium salt decomposition products is evaporated and concentrated to a high concentration of saline wastewater with a salt content of 15%-20%.

[0007] Step S2: Decolorization and impurity removal: Add impurity removal agent, stir for 10-30 minutes, and then pass it into an automatic candle filter at a temperature of 50-80℃ for the separation and filtration of fine impurities.

[0008] Step S3: High-temperature acidification. Add the filtrate to the acidification kettle, heat it, and add 10%-30% hydrochloric acid to the filtrate at a water temperature of 50℃-90℃ for acidification until the pH range is between 2 and 6. The decomposition products sodium phthalate and its series in the filtrate are converted into phthalic acid.

[0009] Step S4: Crystallize by gradually cooling down to 20℃-40℃, so that phthalic acid is completely precipitated and salt and water-soluble impurities are effectively separated;

[0010] Step S5: Solid-liquid separation, through solid-liquid centrifugation and rinsing to remove salt again, phthalic acid is obtained.

[0011] In a preferred embodiment of the present invention, in step S2, the impurity removal agent is a compound whose main components are any one or more of aluminum sulfate, polyaluminum chloride and polysilicon.

[0012] In a preferred embodiment of the present invention, the sum of the mass fractions of aluminum sulfate, polyaluminum chloride and polysilicon in the impurity removal agent is 0.02%-0.5%.

[0013] In a preferred embodiment of the present invention, in step S2, hydrogen peroxide is added to the filtrate while the impurity removal agent is being added.

[0014] In a preferred embodiment of the present invention, in step S3, after the filtrate is added to the acidification kettle, the stirring mechanism is started, and the jacket is supplemented with steam circulation heating.

[0015] In a preferred embodiment of the present invention, step S4, the stepwise cooling crystallization includes the following steps: Step S41, firstly, cooling circulating water is added to the temperature control chamber to cool the filtrate at a rate of 20°C per hour until the temperature of the filtrate drops from 80-90°C to 50°C; Step S42: Cryogenic brine is added to the filtrate to deeply cool the filtrate, controlling the cooling rate to be between 10°C and 20°C per hour until the temperature of the filtrate drops from 50°C to between 20°C and 40°C.

[0016] In a preferred embodiment of the present invention, after step S5, the centrifuged mother liquor is transferred to a storage tank for centralized processing.

[0017] In a preferred embodiment of the present invention, liquid alkali is added to the centrifuged mother liquor until the pH of the centrifuged mother liquor is 7, and then the liquor is evaporated and concentrated again and centrifuged to remove the salt, thereby obtaining solid sodium chloride.

[0018] In a preferred embodiment of the present invention, before step S1, the waste liquid to be treated is preliminarily purified by adsorbing iron ions with resin.

[0019] In a preferred embodiment of the present invention, the acidification vessel is an enamel-lined vessel with an external jacket, and a stirring mechanism is coaxially arranged inside the acidification vessel.

[0020] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0021] (1) This invention converts a series of organic compounds in high COD and high salt wastewater into phthalic acid through a series of steps such as evaporation, concentration, decolorization, impurity removal, high-temperature acidification, and step-by-step cooling and crystallization. Moreover, the decolorization and purification process during extraction can yield higher quality phthalic acid, effectively realizing resource utilization, while reducing the COD of the wastewater to below 5000 mg / L.

[0022] (2) This invention significantly improves the quality of the by-product sodium chloride by subjecting the brine from which phthalic acid has been extracted through conversion to subsequent evaporation, concentration, crystallization, and centrifugation, thereby meeting the requirements for by-product salt sales. Furthermore, the above-mentioned by-product extraction method simultaneously optimizes the quality of organic matter and waste salt in wastewater, achieving the dual benefits of resource utilization. On the other hand, the extraction steps in this invention do not generate any secondary pollution, demonstrating good practicality and promising application prospects.

[0023] (3) In step S4 of the present invention, the different saturated solubilities of phthalic acid and sodium chloride in water and the different precipitation rates of phthalic acid and sodium chloride during the cooling process are utilized, that is, the principle that phthalic acid is more likely to precipitate first with sodium chloride. By gradually cooling and crystallizing, phthalic acid is completely precipitated and sodium chloride and water-soluble impurities are effectively separated, thereby obtaining phthalic acid with higher purity.

[0024] (4) During the high-temperature acidification process of the present invention, by adding hydrochloric acid to the filtrate, a series of substances that can promote the decomposition of sodium phthalimide salt can be converted into phthalic acid under acidic conditions. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the process flow of a preferred embodiment of the present invention. Detailed Implementation

[0027] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0029] like Figure 1 As shown, a method for converting and extracting phthalic acid using byproducts includes the following steps:

[0030] Step S1: Evaporation and concentration. The saline wastewater containing phthalimide and its sodium salt decomposition products is evaporated and concentrated to a high concentration of saline wastewater with a salt content of 15%-20%.

[0031] Step S2: Decolorization and impurity removal: Add impurity removal agent, stir for 10-30 minutes, and then pass it into an automatic candle filter at a temperature of 50-80℃ for the separation and filtration of fine impurities.

[0032] Step S3: High-temperature acidification. Add the filtrate to the acidification kettle, heat it, and add 10%-30% hydrochloric acid to the filtrate at a water temperature of 50℃-90℃ for acidification until the pH range is between 2 and 6. The decomposition products sodium phthalate and its series in the filtrate are converted into phthalic acid.

[0033] Step S4: Crystallize by gradually cooling down to 20℃-40℃, so that phthalic acid is completely precipitated and salt and water-soluble impurities are effectively separated;

[0034] Step S5: Solid-liquid separation. After solid-liquid centrifugation and rinsing to remove salt again, phthalic acid is obtained. Liquid alkali is added to the centrifugation mother liquor until the pH of the centrifugation mother liquor is 7. The liquor is then evaporated and concentrated again and centrifuged to remove salt, resulting in solid sodium chloride.

[0035] In a preferred embodiment of the present invention, the quality of the by-product sodium chloride is significantly improved by subsequently evaporating, concentrating, crystallizing, and centrifuging the brine from which phthalic acid has been extracted, thereby meeting the requirements for by-product salt sales. Furthermore, this by-product extraction method simultaneously optimizes the quality of both organic matter and waste salt in wastewater, achieving the dual benefits of resource utilization. On the other hand, the extraction steps in this invention do not generate any secondary pollution, demonstrating good practicality and promising application prospects.

[0036] In a preferred embodiment of the present invention, in step S2, an impurity removal agent is added, stirred for 10-30 minutes, and then introduced into an automatic candle filter at a temperature of 50-80°C for the separation and filtration of fine impurities. The impurity removal agent is a compound with any one or more of the following components as the main components: aluminum sulfate, polyaluminum chloride, and polysilicon. The sum of the mass fractions of aluminum sulfate, polyaluminum chloride, and polysilicon in the impurity removal agent is 0.02%-0.5%.

[0037] In a preferred embodiment of the present invention, in step S2, hydrogen peroxide is added to the filtrate while adding the impurity removal agent. This has a certain flocculation effect, which removes components such as nickel ions, chromium ions, and iron ions, thereby further improving the purification effect of the filtrate.

[0038] In a preferred embodiment of the present invention, a series of steps, including evaporation, concentration, decolorization, impurity removal, high-temperature acidification, and stepwise cooling crystallization, are performed on high-COD and high-salt wastewater to convert a series of organic compounds in the wastewater into phthalic acid. Moreover, the decolorization and purification treatment during the extraction process can yield higher quality phthalic acid, effectively realizing resource utilization, while reducing the COD of the wastewater to below 5000 mg / L.

[0039] In a preferred embodiment of the present invention, step S4, the stepwise cooling crystallization, includes the following steps: Step S41: First, cooling circulating water is added to the temperature-controlled chamber to cool the filtrate at a rate of 20°C per hour until the filtrate temperature drops from 80-90°C to 50°C. At this point, phthalic acid gradually precipitates out, while sodium chloride remains in the aqueous phase. Step S42: Cold brine is added to the filtrate to deeply cool it, controlling the cooling rate to between 10°C and 20°C per hour until the filtrate temperature drops from 50°C to between 20°C and 40°C. Stage 1: Circulating cooling is used. At this point, phthalic acid precipitates completely, while sodium chloride and water-soluble impurities remain in the aqueous phase. By utilizing the different saturated solubilities of phthalic acid and sodium chloride in water, and the different precipitation rates of phthalic acid and sodium chloride during the cooling process (i.e., phthalic acid precipitates more readily than sodium chloride), a stepwise cooling crystallization method is used to completely precipitate phthalic acid and effectively separate sodium chloride and water-soluble impurities, thereby obtaining phthalic acid with higher purity.

[0040] In a preferred embodiment of the present invention, the acidification vessel is an enamel-lined vessel with an external jacket, and a stirring mechanism is coaxially arranged inside the acidification vessel. During the high-temperature acidification process, the filtrate is added to the acidification vessel, the stirring mechanism is started, and steam is replenished and circulated in the jacket for heating, raising the temperature inside the acidification vessel. Hydrochloric acid of 10%-30% concentration is added to the filtrate at a water temperature of 50℃-90℃ for acidification until the pH range is between 2 and 6. By adding hydrochloric acid to the filtrate, the conversion of sodium phthalimide salt to phthalic acid under acidic conditions can be promoted. Therefore, during the synthesis process, the chemical reaction environment of sodium phthalimide salt is always kept acidic, effectively avoiding the co-precipitation of organic matter and salt, thereby ensuring the quality of the by-product salt. Moreover, by acidifying the sodium phthalimide salt solution at high temperature, the evaporation efficiency can be improved and the processing cost reduced in the subsequent evaporation treatment.

[0041] In a preferred embodiment of the present invention, before step S1, the waste liquid to be treated is preliminarily purified by adsorbing iron ions with resin, and then further purified by a series of subsequent steps such as evaporation and concentration, which can further improve the purity of phthalic acid and sodium chloride.

[0042] Example 1:

[0043] The saline wastewater containing phthalimide and sodium salt decomposition products was added to the decolorization kettle. After evaporation and concentration, 4000L of wastewater with a salt content of 15% and a temperature of 60℃ was obtained. 1Kg of polyaluminum chloride was added and stirred for 10min. The solution is pumped into a candle filter for filtration and impurity removal. The filtrate is then added to an acidification reactor, where the stirring mechanism is activated. During stirring, a certain amount of steam is added to the jacket for heating until the reactor temperature reaches 70°C. Then, 300-350L of 20% hydrochloric acid is added until the pH of the filtrate is adjusted to 3. The filtrate is stirred for 30 minutes, during which sodium phthalate and its derivatives are converted into phthalic acid. The solution then enters a stage of gradual cooling and crystallization. First, cooling circulating water is added to the temperature-controlled chamber to cool the filtrate until the temperature drops to 40°C. Then, chilled brine is added to further cool the filtrate, controlling the cooling rate at 10°C per hour until it reaches 25°C. The filtrate is then centrifuged and washed with water to obtain 210 kg of grayish-white phthalic acid with a moisture content of 6.0%. Liquid chromatography analysis shows a purity of 96.28% and a salt content of 0.51%. The centrifuged mother liquor is added to a storage tank for centralized processing.

[0044] Example 2:

[0045] The saline wastewater containing phthalimide and sodium salt decomposition products was added to the decolorization kettle. After evaporation and concentration, 5000L of wastewater with a salt content of 20% and a temperature of 70℃ was obtained. 5Kg of aluminum sulfate was added and stirred for 20min. Add 5 kg of 8% hydrogen peroxide, stir for 10 minutes, and then pump the solution into a candle filter for filtration to remove impurities. Add the filtrate to an acidification reactor, and start the stirring mechanism inside the reactor. During stirring, add a certain amount of steam to the jacket for heating until the temperature inside the reactor reaches 80°C. Then add 350-400 L of 15% hydrochloric acid until the pH of the filtrate is adjusted to 5. Stir the filtrate for 30 minutes. The decomposition products, sodium phthalate and its series, in the filtrate are converted into phthalic acid. The process then enters a stage of gradual cooling and crystallization. First, add cooling circulating water to the temperature-controlled chamber to cool the filtrate until the temperature drops to 40°C. Then add chilled brine to the filtrate for deep cooling, controlling the cooling rate at 15°C per hour until it reaches 20°C. Centrifuge and wash the filtrate with water to obtain 230 kg of grayish-white phthalic acid with a moisture content of 5.2%. Liquid chromatography analysis showed a purity of 95.55% and a salt content of 0.64%. The centrifuged mother liquor was transferred to a storage tank for further processing.

[0046] Example 3:

[0047] The saline wastewater containing phthalimide and sodium salt decomposition products was added to the decolorization kettle. After evaporation and concentration, 5000L of wastewater with a salt content of 18% and a temperature of 60℃ was obtained. 3Kg of polysilicon was added and stirred for 30min. The solution is pumped into a candle filter for filtration and impurity removal. The filtrate is then added to an acidification reactor, where the stirring mechanism is activated. During stirring, a certain amount of steam is added to the jacket for heating until the reactor temperature reaches 80°C. Then, 200-250L of 30% hydrochloric acid is added until the pH of the filtrate is adjusted to 6. The filtrate is stirred for 30 minutes, during which sodium phthalate and its derivatives are converted into phthalic acid. The solution then enters a stage of gradual cooling and crystallization. First, cooling circulating water is added to the temperature-controlled chamber to cool the filtrate until the temperature drops to 40°C. Then, chilled brine is added to further cool the filtrate, controlling the cooling rate at 20°C per hour until it reaches 30°C. The filtrate is then centrifuged and washed with water to obtain 220 kg of grayish-white phthalic acid with a moisture content of 6.5%. Liquid chromatography analysis shows a purity of 97.25% and a salt content of 0.58%. The centrifuged mother liquor is added to a storage tank for centralized processing.

[0048] In Example 4, the mother liquor collected and stored after centrifugation in Examples 1, 2, and 3 was adjusted to pH 7 with the addition of liquid alkali, and then re-entered into the evaporation system for evaporation, concentration, and centrifugation to obtain 2400 kg of solid by-product sodium chloride. Testing showed that its main technical indicators were: whiteness (R457) of 65%, sodium chloride content of 98.80%, and TOC of 52 mg / kg. The obtained by-product sodium chloride met the sales standards for by-product industrial salt.

[0049] In summary, the method for extracting phthalic acid using byproducts in this invention not only yields phthalic acid with high purity but also extracts byproduct salts with high purity, achieving the dual benefits of quality optimization and resource utilization for both organic matter and waste salts in wastewater.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0051] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for converting and extracting phthalic acid using byproducts, characterized in that, Includes the following steps: Step S1: Evaporation and concentration. The saline wastewater containing phthalimide and its sodium salt decomposition products is evaporated and concentrated to a high concentration of saline wastewater with a salt content of 15%-20%. The saline wastewater originates from the condensation wastewater generated during the synthesis of the anti-scorching agent CTP. Step S2: Decolorization and impurity removal: Add impurity removal agent, stir for 10-30 minutes, and then pass the mixture into an automatic candle filter at a temperature of 50-80℃ for separation and filtration of fine impurities; the impurity removal agent is mainly composed of aluminum sulfate and polyaluminum chloride. Step S3: High-temperature acidification. Add the filtrate to the acidification kettle, heat it, and add 10%-30% hydrochloric acid to the filtrate at a water temperature of 50℃-90℃ for acidification until the pH range is between 2 and 6. The decomposition products sodium phthalate and its series in the filtrate are converted into phthalic acid. Step S4: Crystallize by gradually cooling down to 20℃-40℃, so that phthalic acid is completely precipitated and salt and water-soluble impurities are effectively separated; In step S4, the stepwise cooling crystallization includes the following steps: Step S41: First, add cooling circulating water into the temperature control chamber to cool the filtrate at a rate of 20°C per hour until the temperature of the filtrate drops from 80-90°C to 50°C. Step S42: Add chilled brine to the filtrate and use chilled brine to deeply cool the filtrate, controlling the cooling rate to be between 10°C and 20°C per hour, until the temperature of the filtrate drops from 50°C to between 20°C and 40°C. Step S5: Solid-liquid separation, followed by solid-liquid centrifugation, rinsing and desalting again to obtain phthalic acid; The centrifuged mother liquor is placed in a storage tank for centralized treatment. Liquid alkali is added to the centrifuged mother liquor until the pH of the centrifuged mother liquor reaches 7. It is then evaporated and concentrated again, and the salt is centrifuged to obtain solid sodium chloride.

2. The method for converting and extracting phthalic acid using byproducts according to claim 1, characterized in that: The total mass fraction of aluminum sulfate and polyaluminum chloride in the impurity removal agent is 0.02%-0.5%.

3. The method for converting and extracting phthalic acid using byproducts according to claim 1, characterized in that: In step S2, hydrogen peroxide is added to the filtrate while the impurity removal agent is being added.

4. The method for converting and extracting phthalic acid using byproducts according to claim 1, characterized in that: In step S3, after the filtrate is added to the acidification kettle, the stirring mechanism is started, and steam is replenished and heated in the jacket at the same time.

5. The method for converting and extracting phthalic acid using byproducts according to claim 1, characterized in that: Before step S1, the waste liquid to be treated is preliminarily purified by adsorbing iron ions through resin.

6. The method for converting and extracting phthalic acid using byproducts according to claim 1, characterized in that: The acidification vessel is an enamel-lined vessel with an external jacket, and a stirring mechanism is coaxially arranged inside the acidification vessel.

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