Process for recycling printing and dyeing white mud green resources

Abstract

This invention discloses a green resource utilization process for dyeing and printing white mud. The process involves drying and dehydrating the white mud that has already been washed and deacidified, then adding it to a solvent for heating and stirring to dissolve it. Insoluble impurities are removed by filtration or centrifugation. The filtrate is then fed into a crystallization tank for addition crystallization within a specific temperature range. After complete addition crystallization, the filtrate is filtered or centrifuged again. This filtrate is then reused repeatedly as a solvent for dissolving the next batch of white mud. The filter cake is an addition crystal of terephthalic acid and the solvent. The solid obtained after drying is a high-purity terephthalic acid product. This invention utilizes addition crystallization technology to recover high-purity PTA from dyeing and printing white mud. Compared to traditional recovery methods, this invention has a simpler process flow, and the solvent can be recycled multiple times without significantly reducing product purity, greatly reducing production costs and achieving green resource utilization of dyeing and printing white mud.

Description

Technical Field

[0001] This invention belongs to the field of material purification technology, and in particular relates to a process for the green resource utilization of dyeing and printing white mud. Background Technology

[0002] Textile dyeing sludge is a type of solid waste generated during the treatment of dye wastewater in the textile dyeing industry. This solid waste contains a large amount of terephthalic acid (PTA) and small amounts of other organic and inorganic components. Due to the large production volume and high difficulty in disposal, improper treatment of textile dyeing sludge can easily cause environmental pollution. Therefore, the harmless treatment and resource utilization of textile dyeing sludge has become one of the important issues that urgently need to be addressed in the green transformation and upgrading of my country's dyeing industry.

[0003] To address this issue, several patents have proposed methods for the resource utilization of dyeing and printing white mud. Chinese patent (CN106588638B) describes a method for preparing a high-temperature slurry by mixing dyeing and printing white mud with water, high-temperature activated carbon, a descaling agent, and a composite finishing agent. This slurry is then subjected to high-temperature, high-pressure filtration, depressurization crystallization, cooling, and dehydration to obtain PTA. Chinese patent (CN113831234B) describes a method for washing alkali-reduced white mud with a dilute acid solution containing surfactants, followed by solid-liquid separation. The resulting white mud filter cake is placed in a hydrothermal reactor for hydrothermal reaction. After washing the hydrothermal product, the resulting filter cake is dried to obtain high-purity PTA. Chinese patent (CN105585475B) describes a method for obtaining high-purity terephthalic acid by high-temperature water slurrying, high-temperature solvent dissolution, high-temperature filtration, cooling crystallization, filtration, and drying.

[0004] However, the aforementioned methods generally suffer from complex processes, high energy consumption, and harsh operating conditions (such as high temperature and high pressure or hydrothermal reactions). Furthermore, some methods do not adequately consider solvent recycling, increasing production costs and environmental burden. Therefore, it is essential to develop a high-efficiency, low-energy-consumption, and environmentally friendly green resource utilization process for dyeing and printing white mud. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems in the existing technology, the purpose of this application is to provide a process for the green resource utilization of dyeing and printing white mud.

[0006] The technical solution adopted in this invention is as follows:

[0007] A process for the green resource utilization of printing and dyeing white clay includes the following steps:

[0008] S1 Drying and Dehydration: The dyeing and printing mud that has been washed and deacidified by water is dried and dehydrated;

[0009] S2 Dissolution and Impurity Removal: The dried printing and dyeing white mud is added to the solvent and heated. The mixture is stirred until dissolved, and then filtered or centrifuged under heat preservation conditions to remove insoluble impurities. The resulting filtrate is then introduced into a crystallization tank.

[0010] S3 addition crystallization: The solution in the crystallization tank is continuously stirred while the solution in the crystallization tank is slowly cooled to room temperature, so that the terephthalic acid PTA in the solution combines with the solvent to form addition crystals;

[0011] S4 Filtration and Drying: The liquid-solid mixture after addition crystallization is subjected to solid-liquid separation to obtain an addition crystal filter cake and filtrate II. The filtrate II is reused in step S2 as a solvent for dissolving the next batch of white mud. The solid obtained after drying the addition crystals is the high-purity terephthalic acid product.

[0012] Furthermore, the white mud after washing and deacidification is fed into a dryer for drying, and the moisture content of the dried white mud is controlled to be less than 3%.

[0013] Furthermore, the solvent used in step S2, the dissolution and impurity removal section, is N,N-dimethylformamide or N,N-dimethylacetamide, which can form adduct crystals with terephthalic acid (PTA).

[0014] Furthermore, the mass of the solvent used in step S2, the dissolution and impurity removal section, is 8-10 times the dry weight of the white mud, and the dissolution temperature is 80-100 ℃.

[0015] Furthermore, in step S3, a cooling jacket is provided on the inner and outer sides of the crystallization tank, and cooling water is introduced into the cooling jacket. By controlling the flow rate of the cooling water, the crystallization temperature is cooled down at a relatively uniform rate, and the cooling time to room temperature is controlled to be no less than 1 hour.

[0016] Further, in step S4, the filtration and drying section filters or centrifuges the liquid-solid mixture after addition crystallization, and dries the obtained solid crystals at a temperature of 130-160 ℃, a drying pressure of 0.5-2 kPa, and a time of 2-3 hours. The resulting solid PTA can then be bagged and stored.

[0017] Furthermore, the filtrate obtained after filtration or centrifugation in the filtration and drying section, as well as the condensate collected during the drying of the crystals, can be used together as a solvent for dissolving the white mud in the next batch.

[0018] Furthermore, the solvent recovery section will distill the solvent solution that has been reused 8-10 times or has a water content of 1.5% to recover high-purity N,N-dimethylformamide or high-purity N,N-dimethylacetamide.

[0019] Furthermore, the solvent recovery section can use plate towers, packed towers, or rotating beds for distillation to achieve a solvent recovery rate of over 98% and a purity of over 99.5%.

[0020] Furthermore, the purity of the PTA product can still be maintained above 95% even after multiple applications of the solvent.

[0021] Furthermore, by subjecting the PTA after a single purification to a second purification process involving dissolution, impurity removal, addition crystallization, filtration, and drying, the purity can be increased to over 99%.

[0022] Furthermore, the high-purity PTA obtained can be esterified with isooctanol to prepare the green plasticizer diisooctyl terephthalate (DOTP), thereby further realizing the high-value utilization of dyeing and printing white mud.

[0023] This invention abandons the traditional hydrothermal method and solvent recrystallization method, and proposes a green resource utilization process for dyeing and printing white mud by utilizing the characteristic that a specific solvent and PTA can form an adduct crystal under specific conditions.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention employs addition crystallization technology, which generates addition crystals by reacting solvent with PTA. This effectively avoids the problem of impurity accumulation after repeated use of solvent in traditional recrystallization methods, which leads to a rapid decline in PTA purity. It ensures that the solvent can maintain high PTA purity even after multiple cycles of use, and significantly reduces solvent processing costs.

[0026] 2. The process of this invention is simple. High-purity PTA can be recovered through only steps such as dissolution, filtration, crystallization and drying. Compared with the complex high temperature and high pressure or hydrothermal reaction operations in the prior art, it has lower energy consumption, milder operating conditions and is easier to apply in industrial applications. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention.

[0028] Figure 2 This is a comparison of the purity and yield of PTA products obtained through different crystallization processes in Example 2 of the present invention.

[0029] Figure 3 The purity of the PTA product obtained by addition crystallization in Example 3 of this invention varies with the number of times it is applied.

[0030] Figure 4 The purity of the PTA product obtained using dimethyl sulfoxide solvent in Comparative Example 1 of this invention varies with the number of applications. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] Example: Comparison Figure 1 This invention discloses a green resource utilization process for dyeing and printing white mud, the main steps of which include: firstly, drying and dehydrating the white mud obtained from the dyeing and printing enterprise that has already been washed and deacidified, controlling the moisture content of the dried white mud to be below 3%; then, the dried white mud enters a dissolution and impurity removal section, where N,N-dimethylformamide or N,N-dimethylacetamide is used to stir and dissolve the dried white mud at 80-100 °C; subsequently, filtration or centrifugation is performed under heat preservation conditions to remove insoluble impurities. The filtrate enters an addition crystallization section, where the cooling rate is controlled so that the crystallization temperature drops to room temperature in about 1 hour.

[0033] Further, the liquid-solid mixture after addition crystallization is filtered or centrifuged, and the resulting solid crystals are dried at a temperature of 130-160 ℃ and a pressure of 0.5-2 kPa. The resulting solid PTA is then bagged and stored. The filtrate and the condensate collected during crystal drying can be used together as the solvent for the next batch of dissolving white mud. Finally, the solvent solution, after 8-10 uses or with a water content of 1.5%, is distilled through a solvent recovery section to recover high-purity N,N-dimethylformamide or N,N-dimethylacetamide.

[0034] The white dyeing mud obtained from dyeing and printing enterprises in this invention, which has already undergone water washing and deacidification, mainly consists of terephthalic acid (approximately 75% by mass) excluding water, with the remainder being impurities such as ethylene glycol, inorganic salts, and oligomers. The white dyeing mud has a water content of 50% and a pH of 6-7.

[0035] Example 1: Using as follows Figure 1 The process shown purifies PTA from dyeing and printing white mud, including the following steps:

[0036] 1) Weigh 20 g of white dyeing mud with a moisture content of 50% and a pH of 6-7, and dry it at 110 ℃ under normal pressure for 3 hours until the moisture content is below 3%;

[0037] 2) Add 10 g of dried white mud and 90 g of N,N-dimethylacetamide to a flask, heat the liquid-solid mixture to 85 °C at a stirring speed of 100 rpm, and stir until the white PTA solid is completely dissolved; keep the liquid-solid mixture warm and filter to remove insoluble impurities, and pass the resulting filtrate into a crystallization tank;

[0038] 3) The solution in the crystallizer undergoes addition crystallization at a stirring speed of 100 rpm, while the solution is simultaneously cooled slowly and uniformly to room temperature over a period of 1 hour. This allows the PTA in the solution to combine with the solvent to form addition crystals. After the solution cools to room temperature, it is filtered to obtain an addition crystal filter cake and filtrate two. The addition crystals are dried at 30 kPa and 140 °C for 3 hours to obtain the final PTA product. The PTA purity in the product is 97.8% and the yield is 90% based on the acid value measurement. Because this embodiment uses fresh pure solvent for addition crystallization, some PTA will eventually dissolve in filtrate two, resulting in a lower yield. When filtrate two is reused in subsequent batches for addition crystallization, the PTA yield is usually greater than 95%. This is because during the recrystallization of PTA in the solvent, the amount of PTA dissolved in the solvent is basically saturated after the first use, so PTA does not continue to dissolve and be lost when the solvent is reused in subsequent batches.

[0039] Example 2: Comparison of the effects of different crystallization processes on the purification of PTA in dyeing and printing white mud:

[0040] (1) Dissolution and crystallization: Weigh 20 g of white dyeing mud with a water content of 50% and a pH of 6-7, and dry it at 110 °C under normal pressure for 3 hours; add 10 g of dried white mud and 90 g of N,N-dimethylacetamide to a flask, heat the liquid-solid mixture to 85 °C at a stirring speed of 100 rpm, and stir until the white PTA solid is completely dissolved; keep the liquid-solid mixture warm and filter to remove insoluble impurities; then add 90 g of deionized water to the filtrate and stir for 10 min, during which PTA precipitates; filter again to separate the crystals and filtrate; dry the crystals at 30 kPa and 140 °C for 3 h, and finally obtain the PTA product.

[0041] (2) Freeze-crystallization: Weigh 20 g of white mud with a water content of 50% and a pH of 6-7, and dry it at 110 °C under normal pressure for 3 hours; add 10 g of dried white mud and 100 g of N,N-dimethylformamide to a flask, heat the liquid-solid mixture to 60 °C at a stirring speed of 100 rpm, stir until the white PTA solid is completely dissolved, and then place it at room temperature; filter to remove insoluble impurities, and place the filtrate in a constant temperature bath at -25 °C for freeze-crystallization for 1 h, during which PTA precipitates; filter to separate the crystals and filtrate while cold; dry the crystals at 30 kPa and 140 °C for 3 h, and finally obtain the PTA product.

[0042] (3) Evaporation and crystallization: Weigh 20 g of white mud with a water content of 50% and a pH of 6-7, and dry it at 110 °C under normal pressure for 3 hours; add 10 g of dried white mud and 100 g of N,N-dimethylformamide to a flask, heat the liquid-solid mixture to 85 °C at a stirring speed of 100 rpm, stir until the white PTA solid is completely dissolved, and then place it at room temperature; filter to remove insoluble impurities, pour the filtrate into a flask for distillation to remove the solvent, and PTA precipitates in this process; after no obvious distillate flows out, place the liquid-solid mixture at room temperature and then filter to separate the crystals and filtrate; dry the crystals at 30 kPa and 140 °C for 3 hours, and finally obtain the PTA product.

[0043] (4) Rapid cooling addition crystallization: The experimental steps are basically the same as those in Example 1. The only difference is that in the addition crystallization process of "step 3), the cooling rate of the solution in the crystallization tank is accelerated, so that the cooling time to room temperature is shortened to 10 min". The other conditions remain unchanged.

[0044] A comparison of the purity and yield of PTA obtained by the four crystallization methods described in Example 2 and the addition crystallization method proposed in Example 1 of this invention. Figure 2 As shown, the addition crystallization method in Example 1 of this invention achieves the highest PTA product purity. Although freeze crystallization also yields similar PTA purity, this process requires continuous energy consumption to maintain the low temperature and places higher demands on the insulation performance of the equipment. Therefore, the addition crystallization method exhibits the best performance among the aforementioned crystallization methods. Furthermore, the PTA product purity of the addition crystallization method under rapid cooling in Example 2 is lower than that of the normal addition crystallization method in Example 1 of this invention. This is because excessively rapid cooling causes PTA to precipitate before the formation of the addition crystals, thereby reducing product purity. This indicates that slow cooling with sufficient cooling time is crucial for the formation of the addition crystals.

[0045] Example 3: Using as follows Figure 1 The solvent-based purification process shown includes the following steps for purifying PTA in dyeing and printing slurry:

[0046] 1) Weigh 20 g of white dyeing mud with a moisture content of 50% and a pH of 6-7, and dry it at 110 ℃ under normal pressure for 3 hours;

[0047] 2) Add 10 g of dried white mud to the flask, add 90 g of the filtrate obtained after addition crystallization in step 3) of Example 1, heat the liquid-solid mixture to 85 °C at a stirring speed of 100 rpm, and stir until the white PTA solid is completely dissolved; keep the liquid-solid mixture warm and filter to remove insoluble impurities, and pass the resulting filtrate into the crystallization tank.

[0048] 3) The solution in the crystallizer undergoes addition crystallization at a stirring speed of 100 rpm, while the solution in the crystallizer is cooled slowly and uniformly to room temperature for 1 hour. After the solution cools to room temperature, it is filtered to obtain an addition crystal filter cake and a second filtrate. The addition crystals are dried at 30 kPa and 140 °C for 3 hours to finally obtain the PTA product.

[0049] The filtrate obtained after addition crystallization was repeatedly reused 8 times in the above manner, and the yield of PTA product was always greater than 95%. The change in PTA product purity with the number of solvent reuses is as follows: Figure 3 As shown, it can be seen that when the solvent is reused more than 4 times, the PTA purity is less than 97%, and after 7 reuses, the PTA purity is less than 95%. In actual production, the number of reuses can be selected according to the product purity requirements.

[0050] Comparative Example 1: Dimethyl sulfoxide, a solvent that cannot form adduct crystals with PTA, was used as a comparison.

[0051] The experimental steps of Comparative Example 1 were repeated in Examples 1 and 3, with the only difference being that "the solvent used for each addition crystallization in Comparative Example 1 was dimethyl sulfoxide, and since dimethyl sulfoxide has a high solubility for PTA at room temperature, the mass of dimethyl sulfoxide used for each addition crystallization in Comparative Example 1 was adjusted to 40 g", with all other conditions remaining unchanged.

[0052] The experimental results obtained in Comparative Example 1 were as follows: the final PTA yield was 22% when using fresh solvent for the first time; the PTA yield was consistently greater than 95% when the solvent was repeatedly reused in subsequent batches for addition crystallization. The change in PTA product purity with the number of times dimethyl sulfoxide was used as solvent is shown in the figure. Figure 4 As shown, the purity of the PTA in the product decreases rapidly with the increase of the number of times it is reused. This is because although the process operating conditions are the same, dimethyl sulfoxide cannot form an addition crystal with PTA. Therefore, with the increase of the number of times it is reused, the impurity content in the solution gradually increases, resulting in a gradual decrease in the purity of the crystal. This further highlights the unique technical advantage of addition crystallization technology in realizing multiple solvent reuses.

[0053] Example 4: The PTA product obtained from step 3) of Example 1 after one purification was subjected to a second purification. The second purification process was repeated as in Example 1. The experimental results were: the PTA purity obtained after the second purification was 99.1%, and the yield was 92.5%.

[0054] Example 5: Using as follows Figure 1 The process shown involves distillation to recover the solvent after multiple uses:

[0055] The impurity solvent obtained from the seven reuses of N,N-dimethylacetamide in Example 3, with a water content of 1.5%, was dehydrated in the first plate distillation column under absolute pressure of 20 kPa until the water content was below 500 ppm. The dehydrated solvent was then further fed from the bottom of the column into a second plate distillation column, where N,N-dimethylacetamide was distilled off from the top under absolute pressure of 20 kPa. The resulting solvent had a purity greater than 99.5% and a recovery rate greater than 98%.

[0056] Example 6: Preparation of the green plasticizer diisooctyl terephthalate (DOTP) by esterification using PTA obtained in Example 4:

[0057] Weigh 33.2 g of the PTA product obtained in Example 4, and weigh 78 g of isooctanol. Add them together to a four-necked flask equipped with a reflux condenser. Start heating at 300 rpm with stirring. When the liquid-solid mixture reaches 180 °C and a large amount of isooctanol refluxes, add 0.3% (by weight of PTA) of tetrabutyl titanate catalyst to begin esterification. After esterification for 4 h, stop heating and cool the liquid in the flask to room temperature. Transfer the cooled liquid to an 80 °C constant temperature water bath and add 10% (by weight of oil) of 0.1% NaOH solution for alkaline washing. After standing for 30 min to separate the layers, take the oil phase and add 10% (by weight of oil) of deionized water for washing. After standing for 30 min to separate the layers, take the oil phase and add 10% (by weight of oil) of activated clay for decolorization under stirring for 30 min. After centrifugation, take the oil phase and decolorize it at 500 Pa and 80 °C. The alcohol was removed by vacuum distillation at ℃ to obtain the final DOTP product. The purity of the DOTP was analyzed by gas chromatography, and the purity was found to be 99.5% with a yield of 99.2%.

[0058] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A process for the green resource utilization of dyeing and printing white mud, characterized in that... Includes the following steps: 1) The dyeing and printing mud that has been washed and deacidified is dried and dehydrated; 2) After drying, the white mud for printing and dyeing is added to the solvent and heated. The mixture is stirred until dissolved at a temperature of 80-100 ℃. Then, under the condition of heat preservation, it is filtered or centrifuged to remove insoluble impurities. The resulting filtrate is then passed into a crystallization tank. 3) The solution in the crystallization tank is continuously stirred while the solution in the crystallization tank is slowly cooled to room temperature, so that the terephthalic acid (PTA) in the solution combines with the solvent to form adduct crystals. Then, solid-liquid separation is performed to obtain adduct crystal filter cake and filtrate 2. The filtrate 2 is reused in step 2) as a solvent for dissolving the next batch of white mud. The solid obtained after drying the adduct crystals is the high-purity terephthalic acid product. Step 2) The solvent used is N,N-dimethylformamide or N,N-dimethylacetamide, which can form adduct crystals with PTA terephthalic acid; In step 3), a cooling jacket is provided on the inside and outside of the crystallization tank, and cooling water is introduced into the cooling jacket. By controlling the flow rate of the cooling water, the crystallization temperature is cooled down at a relatively uniform rate, and the cooling time to room temperature is controlled to be no less than 1 hour. When the filtrate is reused twice, after 8-10 reuses or when the water content reaches 1.5%, it is purified by distillation to recover high-purity solvent for reuse.

2. The process for green resource utilization of dyeing and printing white mud as described in claim 1, characterized in that, After being washed and deacidified, the white mud is fed into a dryer for drying, and the moisture content of the dried white mud is controlled to be less than 3%.

3. The process for green resource utilization of dyeing and printing white mud as described in claim 1, characterized in that, Step 2) The mass of the solvent used is 8-10 times the dry weight of the white clay.

4. The process for green resource utilization of printing and dyeing white mud as described in claim 1, characterized in that, Step 3) Filter or centrifuge the liquid-solid mixture after addition crystallization, and dry the obtained solid crystals at a temperature of 130-160 ℃, a pressure of 0.5-2 kPa, and a time of 2-3 hours. The resulting solid PTA can then be bagged and stored.

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