阅读说明：本技术 一种从印染白泥中水热回收高纯度对苯二甲酸的方法 (Method for recovering high-purity terephthalic acid from printing and dyeing white mud through hydrothermal process ) 是由 李方 沈忱思 章耀鹏 徐晨烨 杜繆佳 于 2021-09-26 设计创作，主要内容包括：本发明公开了一种从印染白泥中水热回收高纯度对苯二甲酸的方法,属于纺织印染行业固废物资源化技术领域。本发明的回收方法包括如下步骤：使用含有表面活性剂的稀酸溶液洗涤碱减量白泥后进行固液分离,得白泥滤饼；白泥滤饼分散于水中,调节pH,置于水热釜中进行水热反应；将水热产物固液分离并使用适量纯水洗涤所得滤饼；再次进行固液分离后取固体烘干,制得高纯度对苯二甲酸。采用本发明回收制得的纯对苯二甲酸杂质含量低于1.5％,晶粒平均尺寸大于145μm,可循环使用于聚酯合成或用作于增塑剂合成,使印染白泥得到经济有效的回收利用。(The invention discloses a method for recovering high-purity terephthalic acid from printing and dyeing white mud through hydrothermal treatment, and belongs to the technical field of solid waste recycling in the textile printing and dyeing industry. The recovery method of the invention comprises the following steps: washing the alkali-reduced lime mud by using a dilute acid solution containing a surfactant, and then carrying out solid-liquid separation to obtain a lime mud filter cake; dispersing the white mud filter cake in water, adjusting the pH value, and placing the mixture in a hydrothermal kettle for hydrothermal reaction; carrying out solid-liquid separation on the hydrothermal product and washing the obtained filter cake by using a proper amount of pure water; and carrying out solid-liquid separation again, taking out the solid and drying to obtain the high-purity terephthalic acid. The impurity content of the pure terephthalic acid recovered and prepared by the method is lower than 1.5%, the average grain size is larger than 145 mu m, and the pure terephthalic acid can be recycled for polyester synthesis or plasticizer synthesis, so that the printing and dyeing white mud can be recycled economically and effectively.)

1. A method for recovering high-purity terephthalic acid from printing and dyeing white mud through hydrothermal process is characterized by comprising the following steps:

step 1: washing the printing and dyeing white mud by using a dilute acid solution containing a surfactant, and then carrying out solid-liquid separation to obtain a white mud filter cake;

step 2: dispersing the white mud filter cake obtained in the step 1 into water to obtain a white mud dispersion liquid, adjusting the pH value, and placing the white mud dispersion liquid into a hydrothermal kettle for hydrothermal reaction to obtain a hydrothermal reaction product;

and step 3: carrying out solid-liquid separation on the hydrothermal reaction product obtained in the step 2, and dispersing and washing a filter cake by using pure water to obtain a washed product dispersion liquid;

and 4, step 4: carrying out solid-liquid separation on the product dispersion liquid obtained in the step 3 again, and drying the solid to obtain high-purity terephthalic acid;

the components of the printing and dyeing white mud comprise terephthalic acid, ethylene glycol, polyethylene terephthalate oligomer, oil, acid and polyaluminium chloride.

2. The method for hydrothermally recovering high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the dilute acid solution in the step 1 is at least one of sulfuric acid, hydrochloric acid and nitric acid, and the concentration of the dilute acid solution is 0.5-2 mol/L and is 1-5 times of the volume of the white mud.

3. The method for hydrothermal recovery of high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the surfactant in the step 1 is alcohol ether acid-resistant surfactant such as fatty alcohol-polyoxyethylene ether, and the concentration of the surfactant is 0.05-0.2 mol/L.

4. The method for hydrothermally recovering high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the solid-to-liquid ratio of the white mud dispersion liquid in the step 2 is 1: 5-9 g/mL.

5. The method for hydrothermally recovering high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the pH in the step 2 is 6.5-7.5.

6. The method for hydrothermally recovering high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the temperature of the hydrothermal reaction in the step 2 is 150-180 ℃ and the time is 12-24 hours.

7. The method for hydrothermally recovering high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the filling degree of the hydrothermal kettle in the step 2 is 60-80%.

8. The method for hydrothermally recovering high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the volume of pure washing water in the step 3 is 5-10 times of the volume of the filter cake.

9. The method for hydrothermally recovering high-purity terephthalic acid from dyeing white mud according to claim 1, wherein the solid-liquid separation in steps 3 and 4 is centrifugal separation or mechanical filter pressing.

10. The method for hydrothermally recovering high-purity terephthalic acid from printing and dyeing white mud according to claim 1, wherein the drying temperature in the step 4 is 60-80 ℃.

Technical Field

The invention relates to a method for recovering high-purity terephthalic acid from printing and dyeing white mud through hydrothermal treatment, and belongs to the technical field of solid waste recycling in the textile printing and dyeing industry.

Background

The dyeing white mud (alkali weight reduction white mud) mainly comes from an alkali weight reduction process in the dyeing process of the dacron chemical fiber fabric. The alkali decrement process is an important link of the printing and dyeing production of the polyester fabric and is also a key production link. The polyester fiber is hydrolyzed to make the fabric light and the fiber diameter thin through treating the polyester fabric with high temperature and stronger caustic soda solution, thereby making the fabric soft in hand feeling and soft in luster. The decrement rate of the polyester fabric is generally 5-20%, the waste enters the wastewater in the form of terephthalic acid, ethylene glycol and polyester oligomer, and grey-white materialized sludge is formed in the processes of acidification-coagulation and the like of alkali decrement wastewater.

The printing white mud contains terephthalic acid as a main component, but cannot be directly used due to impurities such as polyester oligomer and coagulant. The method effectively recovers the high-purity terephthalic acid from the printing and dyeing white mud, reduces the printing and dyeing sludge, can utilize the terephthalic acid as resources, and has double benefits of environment and economy. At present, the methods for recovering terephthalic acid from printing and dyeing white mud mainly comprise three methods, namely a precipitation washing method, an alkali dissolution-acid precipitation method and a recrystallization method. The precipitation washing method and the alkali dissolution-acid precipitation method are relatively simple and easy to implement, but can not remove some ethylene terephthalate oligomers with the properties close to those of terephthalic acid, so that the product quality is uneven, and the water consumption and the waste water generation amount are large. The recrystallization method can obtain terephthalic acid with larger crystal grains and higher purity, but the process needs to use organic solvents such as dimethylformamide and the like, is relatively complex and is easy to cause secondary pollution.

Disclosure of Invention

The technical problem solved by the invention is as follows: the prior method for recovering the terephthalic acid in the printing and dyeing white mud has the problems that some ethylene terephthalate oligomers with the property close to that of the terephthalic acid cannot be removed, the product purity is not high, the water consumption and the waste water generation amount are large, secondary pollution is easily caused by using organic solvents such as dimethylformamide and the like, and the like.

In order to solve the technical problem, the invention provides a method for recovering high-purity terephthalic acid from printing and dyeing white mud through hydrothermal reaction, which comprises the following steps:

step 1: washing the printing and dyeing white mud by using a dilute acid solution containing a surfactant, and then carrying out solid-liquid separation to obtain a white mud filter cake;

step 2: dispersing the white mud filter cake obtained in the step 1 into water to obtain a white mud dispersion liquid, adjusting the pH value, and placing the white mud dispersion liquid into a hydrothermal kettle for hydrothermal reaction to obtain a hydrothermal reaction product;

and step 3: performing solid-liquid separation on the hydrothermal product obtained in the step 2, and dispersing and washing a filter cake by using pure water to obtain a washed product dispersion liquid;

and 4, step 4: carrying out solid-liquid separation on the product dispersion liquid obtained in the step 3 again, and drying the solid to obtain high-purity terephthalic acid;

the components of the printing and dyeing white mud comprise terephthalic acid, ethylene glycol, polyethylene terephthalate oligomer, oil, acid and polyaluminium chloride.

Preferably, the diluted acid solution in the step 1 is at least one of sulfuric acid, hydrochloric acid and nitric acid, the concentration of the diluted acid solution is 0.5-2 mol/L, and the using amount of the diluted acid solution is 1-5 times of the volume of the white mud.

Preferably, the surfactant in the step 1 is alcohol ether acid-resistant surfactant such as fatty alcohol-polyoxyethylene ether, and the concentration of the surfactant is 0.05-0.2 mol/L.

Preferably, the solid-to-liquid ratio of the white mud dispersion liquid in the step 2 is 1: 5-9 g/mL.

Preferably, the pH value in the step 2 is 6.5-7.5.

Preferably, the temperature of the hydrothermal reaction in the step 2 is 150-180 ℃ and the time is 12-24 h.

Preferably, the filling degree of the hydrothermal kettle in the step 2 is 60-80%.

Preferably, the volume of the pure water for washing in the step 3 is 5-10 times of the volume of the filter cake.

Preferably, the solid-liquid separation mode in the steps 3 and 4 is centrifugal separation or mechanical filter pressing.

Preferably, the drying temperature in the step 4 is 60-80 ℃.

The principle of the invention is as follows:

the printing and dyeing white mud contains a large amount of terephthalic acid and ethylene glycol, and also contains incompletely hydrolyzed ethylene terephthalate oligomer, oil, acid, polyaluminium chloride and other conventional coagulants. The invention utilizes the characteristic that terephthalic acid is insoluble in dilute acid and substances such as ethylene glycol, polyaluminium chloride and the like are easily soluble, and dilute acid is used for washing to separate impurities such as ethylene glycol, polyaluminium chloride and the like which are easily soluble in acid in the white mud from the terephthalic acid solid; the surfactant in the dilute acid can simultaneously emulsify the oil agent contained in the white mud, and the alcohol ether acid-resistant surfactant can effectively emulsify the oil agent and simultaneously avoid generating a large amount of foam and secondary pollution such as phosphorus, nitrogen and the like; then, the characteristics that ester bond hydrolysis is facilitated under a high-temperature condition and crystal growth is facilitated under a hydrothermal condition are utilized, the complete hydrolysis of oligomers in the white mud is promoted and the growth of terephthalic acid crystals is strengthened through a hydrothermal method under a neutral condition; finally, the high-purity terephthalic acid is obtained through solid-liquid separation and drying.

Compared with the prior art, the invention has the following beneficial effects:

1. on the basis of preliminarily washing off impurities such as ethylene glycol, oil solution, polyaluminium chloride and the like by using dilute acid containing a surfactant, the high-temperature environment of a hydrothermal method is utilized to promote the incompletely hydrolyzed ethylene terephthalate oligomer in the white mud to further generate terephthalic acid and ethylene glycol, and meanwhile, the growth of terephthalic acid crystals is enhanced by utilizing the high-temperature and high-pressure condition of the hydrothermal method, so that the efficiency of recovering the terephthalic acid from the alkali-reduced white mud and the purity of a terephthalic acid product are remarkably improved;

2. the impurity content of the pure terephthalic acid recovered and prepared by the method is lower than 1.5%, the average grain size is larger than 145 mu m, and the pure terephthalic acid can be recycled for polyester synthesis or plasticizer synthesis, so that the printing and dyeing white mud can be recycled economically and effectively.

Drawings

FIG. 1 is an X-ray diffraction spectrum of a terephthalic acid product (example 1) and a corresponding standard card.

Detailed Description

In order to make the invention more comprehensible, preferred embodiments are described in detail below.

Example 1

A process for hydrothermal recovery of high purity terephthalic acid from a printing and dyeing white mud comprising:

taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 80mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Example 2

A process for hydrothermal recovery of high purity terephthalic acid from a printing and dyeing white mud comprising:

taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of hydrochloric acid solution with the concentration of 1.5mol/L (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 80mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Example 3

A process for hydrothermal recovery of high purity terephthalic acid from a printing and dyeing white mud comprising:

taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of nitric acid solution with the concentration of 1.0mol/L (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 80mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Comparative example 1

Taking 10g of printing and dyeing white mud, washing with 30mL of pure water (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 80mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

The results of the analyses of the terephthalic acids obtained in examples 1, 2 and 3 and comparative example 1 are shown in Table 1, and the specific analysis methods are as follows:

(1) purity: determination by high performance liquid chromatography (Wanghao, Feifei Shuishuan, Chan, Li Zuoqing. high performance liquid chromatography determines terephthalic acid content [ J ] in secondary PTA 2008,21(1):16-17,38.)

(2) Average particle size: determination by means of a laser particle sizer (GB/T30921.6-2016 Industrial Purified Terephthalic Acid (PTA) test method part 6: determination of particle size distribution);

(3) yield:

yield-quality of the solid produced x purity/white mud quality.

TABLE 1 analysis of the product index of terephthalic acid in different pickling processes

As can be seen from table 1, in the case of fixing hydrothermal conditions and other preparation conditions, acid washing is a key step for improving the purity and yield of terephthalic acid products, and dilute acid solutions such as sulfuric acid, hydrochloric acid, nitric acid and the like are used for washing alkali-reduced white mud to primarily remove substances such as ethylene glycol, polyaluminum chloride and the like which are easily dissolved in the acid solution in the white mud, so that the terephthalic acid can be stably maintained in the white mud solids due to insolubility, and the dilute acid washing is helpful for improving the purity and yield of recycling the terephthalic acid from the alkali-reduced white mud.

Example 4

A process for hydrothermal recovery of high purity terephthalic acid from a printing and dyeing white mud comprising:

taking 10g of Indonesia white mud, washing with 30mL of 0.5mol/L sulfuric acid solution (containing 0.1mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 80mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Comparative example 2

Taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of sulfuric acid solution with the concentration of 0.5mol/L (without fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 80mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Comparative example 3

Taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.5mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 80mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

The results of the analyses of the terephthalic acids obtained in example 4 and comparative examples 2 and 3 are shown in Table 2, and the analytical methods were the same as those described above.

TABLE 2 analysis of the product index of terephthalic acid in different pickling processes

As can be seen from Table 2, the use of the non-foaming acid-resistant fatty alcohol-polyoxyethylene ether for removing the oil agent from the white mud during the pickling process can significantly improve the purity and yield of the product. However, the use of an excessive amount of surfactant tends to affect the growth of terephthalic acid crystals, resulting in poor crystallization of the product.

Example 5

A process for hydrothermal recovery of high purity terephthalic acid from a printing and dyeing white mud comprising:

taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 90mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 150mL for hydrothermal reaction (at 150 ℃, for 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Comparative example 4

Taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 10mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 15mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Comparative example 5

Taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 150mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the white mud filter cake into a hydrothermal kettle with the capacity of 250mL for hydrothermal reaction (150 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

The results of the analyses of the terephthalic acids obtained in example 5 and comparative examples 4 and 5 are shown in Table 3, and the analytical methods were the same as those described above.

TABLE 3 analysis of terephthalic acid product index at different solid-to-liquid ratios

As can be seen from Table 3, under the conditions of fixed acid washing and other preparation conditions, the solid-liquid ratio is a key step influencing the purity and yield of the terephthalic acid product, when the hydrothermal solid-liquid ratio is greater than 1:5, the filling degree is kept within the range of 60-66.7%, the high-purity terephthalic acid product can be obtained, and the yield is kept above 70%. The proper solid-to-liquid ratio can promote the complete hydrolysis of the low ethylene terephthalate polymer to raise the product purity and yield and strengthen the crystal growth of terephthalic acid. On the other hand, although the excessive solid-liquid ratio does not affect the purity and yield of the product, the corresponding water consumption is excessive, which is not beneficial to saving water in production.

Example 6

A process for hydrothermal recovery of high purity terephthalic acid from a printing and dyeing white mud comprising:

taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 150mL for hydrothermal reaction (180 ℃, 12 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Example 7

A process for hydrothermal recovery of high purity terephthalic acid from a printing and dyeing white mud comprising:

taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 150mL for hydrothermal reaction (at 150 ℃, for 24 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Comparative example 6

Taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 150mL for hydrothermal reaction (120 ℃, 24 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

Comparative example 7

Taking 10g of printing and dyeing white mud, washing the printing and dyeing white mud by using 30mL of 0.5mol/L sulfuric acid solution (containing 0.05mol/L fatty alcohol-polyoxyethylene ether), and performing centrifugal separation to obtain a white mud filter cake; dispersing the white mud filter cake into 50mL of pure water, adjusting the pH to 7.0 by using sodium hydroxide, and placing the mixture into a hydrothermal kettle with the capacity of 150mL for hydrothermal reaction (at 150 ℃, for 6 hours) to obtain a hydrothermal reaction product; and centrifugally separating the hydrothermal product, dispersing and washing a filter cake by using a proper amount of pure water, centrifugally separating again, taking the solid, and drying to obtain the terephthalic acid product.

The results of the analyses of the terephthalic acids obtained in examples 6 and 7 and comparative examples 6 and 7 are shown in Table 4, and the analytical methods were the same as those described above.

TABLE 4 terephthalic acid product index analysis under different hydrothermal conditions

As can be seen from Table 4, the temperature measurement time of the hydrothermal treatment is also very critical under the conditions of fixed acid washing and other preparation conditions, and when the temperature of the hydrothermal reaction is 150-180 ℃ and the reaction time is 12-24 hours, a high-purity terephthalic acid product can be obtained, and the yield is kept above 75%. The proper hydrothermal temperature can ensure that the ethylene terephthalate oligomer is completely hydrolyzed to improve the purity and yield of the product and promote the crystal growth of the terephthalic acid.

FIG. 1 shows the X-ray diffraction spectrum of a terephthalic acid product (example 1) and a corresponding standard card, and it can be seen that the method for recovering terephthalic acid by hydrothermal method of the present invention can obtain a terephthalic acid product with high crystallinity and good purity from printing and dyeing white mud.

While the invention has been described with respect to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.