Hydrofining method for optimizing chromatic value of bio-based terephthalic acid product

Abstract

The invention discloses a hydrofining method for optimizing the chromatic value of a bio-based terephthalic acid product, and belongs to the technical field of terephthalic acid hydrofining. The special refining process suitable for the bio-based CTA is formed by optimizing the whole process of pretreatment, hydrogenation reaction and post-treatment. The process not only solves the problem that the bio-based raw material has many impurities, but also realizes the balance of environmental protection and economy through the green solvent (water), the efficient catalyst (Pd / C) and controllable parameter design, provides a feasible path for the industrial production of bio-based PTA, and promotes the transformation of the polyester industry to sustainable development. The method provided by the invention is high in impurity removal rate, can efficiently purify the bio-based CTA to obtain a product meeting the PTA standard, is mild in reaction condition, realizes low-energy-consumption and high-stability operation under efficient catalysis, is small in process pollution, and reduces the environmental load.

Description

Technical Field

[0001] This invention belongs to the field of hydrogenation refining technology of terephthalic acid, and in particular relates to a hydrogenation refining method for optimizing the color value of bio-based terephthalic acid products. Background Technology

[0002] Purified terephthalic acid (PTA), a core raw material for the production of polyethylene terephthalate (PET), is widely used in polyester fibers, packaging flakes, and films. Its optical quality directly determines the appearance and market competitiveness of the final products. With the rapid development of the polyester industry, the continuous expansion of polyester production capacity has driven a surge in PTA demand, while simultaneously imposing more stringent requirements on its quality standards. Among numerous quality indicators, color characteristics have become a key control parameter due to their significant impact on downstream products. In polyester fiber production, a high yellow-blue index (b-value) in PTA leads to a decrease in fiber whiteness, while in flake production, abnormal color directly reduces the light transmittance and visual quality of the packaging material.

[0003] The methods for characterizing color quality have evolved from qualitative to quantitative approaches. The 1995 Chinese petrochemical industry standard (SH 1612.1-1995) only relied on visual observation to determine whether PTA was white. While the 2005 revised version (SH 1612.1-2005) added the requirement to measure the b-value using a colorimeter, it did not specify a control indicator. The current national standard (GB / T 30921.7-2016) adopts the CIE 1976 uniform color space system, specifying the tristimulus values ​​of a (red-green index), b (yellow-blue index), and L (lightness index) as comprehensive characterization indicators. Internationally renowned companies such as DuPont and Amoco, as well as domestic companies like Yizheng Chemical Fiber, all use a b-value ≤ 1.5 as a core control indicator. However, practice shows that PTA products with the same b-value can still lead to significant color differences in downstream polyester products, demonstrating the limitations of using a single indicator.

[0004] From a resource sustainability perspective, traditional PTA production relies on petroleum-based paraxylene (PX), and the extraction and processing of its feedstock, heavy naphtha, imposes a significant environmental burden. With the deepening of the global low-carbon development concept, biomass resources, represented by cellulose, have become a research hotspot for alternative carbon sources due to their renewable characteristics. Through catalytic conversion technology, biomass can be efficiently converted into bio-based chemicals, providing a new pathway for green PTA production. However, bio-based PX has lower purity due to differences in synthetic pathways (such as whole-cell catalysis), containing more non-aromatic compounds and addition intermediates, resulting in a more complex impurity profile in the crude terephthalic acid (CTA) produced by oxidation.

[0005] These impurities not only increase the difficulty of refining but also easily form colored intermediates, affecting color quality. The accumulation of metals such as iron and chromium can significantly reduce the L value and even cause polyester products to turn green. Therefore, the hydrogenation refining of bio-based CTA needs to simultaneously address the removal of conventional impurities (such as 4-CBA and P-tol) and color control. This can be achieved by optimizing hydrogenation pressure, catalyst selection, and raw material purification processes to optimize the a, b, and L values. This research not only has practical value for improving the quality stability of bio-based PTA but also provides key technical support for the large-scale application of renewable resources in the polyester industry chain. Summary of the Invention

[0006] To utilize existing biomass resources and address the issue of poor hydrogenation refining efficiency in bio-based CTA, this invention provides a hydrogenation refining method for optimizing the color value of bio-based terephthalic acid (PTA) products. This method can obtain PTA suitable for polymerization using current industrial methods, ensuring that the concentration of the main impurity p-carboxybenzaldehyde (4-CBA) in the PTA is ≤25 ppm, the concentration of p-methylbenzoic acid (p-tol) is ≤180 ppm, and the color value reaches L=95.49, a=0.17, and b=1.31, meeting the polymerization requirements.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A method for hydrogenating and refining bio-based terephthalic acid (CTA) products to optimize color values ​​includes the following steps: pre-treating bio-based crude terephthalic acid (CTA) with at least four recrystallizations; mixing the pre-treated CTA with a solvent and adding a catalyst for hydrogenation refining; performing a second recrystallization after the reaction; washing with water and drying to obtain refined terephthalic acid; the hydrogenation refining reaction time is 1.5-6 hours.

[0009] During the hydrogenation refining of bio-based crude terephthalic acid (CTA), catalyst powdering occurs, which worsens with prolonged reaction time, resulting in poor product color. This invention utilizes multiple recrystallization steps to initially remove insoluble and some soluble impurities from bio-based CTA, reducing the burden on subsequent hydrogenation reactions, shortening hydrogenation time, and minimizing catalyst powdering. This step addresses the diverse impurities in bio-based CTA by using physical separation methods to improve raw material purity, laying the foundation for subsequent hydrogenation reactions. In the hydrogenation refining stage, a Pd / C catalyst is used, leveraging its high catalytic activity and selectivity to efficiently reduce 4-CBA to p-methylbenzoic acid (easily soluble in water) under a hydrogen atmosphere, while simultaneously reducing the content of impurities such as methylbenzoic acid. After the reaction, the solvent is changed and recrystallization is performed again. Utilizing the differences in solubility of different substances in the solvent, residual 4-CBA, p-tol, and reaction byproducts are further removed, reducing impurity concentration and achieving a final product color value of L=95.49, a=0.17, and b=1.31.

[0010] Further, the recrystallization pretreatment includes the following steps: adding bio-based crude terephthalic acid to a solvent, dissolving it at 287°C, and performing crystallization using a four-stage crystallization process, wherein the mass ratio of the bio-based crude terephthalic acid to the solvent is 1:5; after changing the solvent, repeating the crystallization at least four times to obtain the pretreated bio-based crude terephthalic acid, wherein the four-stage crystallization process includes the following steps: starting from 287°C, cooling down, successively holding at 259°C for 35 min, at 219°C for 30 min, at 180°C for 30 min, and at 153°C for 25 min, and finally cooling to room temperature.

[0011] The four-stage crystallization process, through precise control of the temperature, cooling rate, and other key parameters during crystallization, helps to form uniform PTA particles suitable for polymerization, thereby improving the quality and performance of the final product.

[0012] Furthermore, the solvent for the recrystallization pretreatment is water.

[0013] Furthermore, the bio-based crude terephthalic acid contains 1500-3500 ppm of p-carboxybenzaldehyde (4-CBA) and 500-1500 ppm of p-methylbenzoic acid (p-tol). The aforementioned 4-CBA and p-tol contents are calculated based on the total weight of PTA, 4-CBA, and p-tol in the bio-based crude terephthalic acid, ignoring other impurities.

[0014] Furthermore, the mass ratio of the solvent to the pretreated bio-based crude terephthalic acid is 5:1; the mass ratio of the pretreated bio-based crude terephthalic acid to the catalyst is 3:1.

[0015] Furthermore, the solvent is water. Water, as a green solvent, has good solubility for CTA and reaction intermediates, facilitates the diffusion and transformation of impurities during the reaction, and provides compatibility for subsequent water washing steps.

[0016] Furthermore, the catalyst is a Pd / C catalyst, the active component is Pd, and the content of the active component Pd in ​​the catalyst is 1-10%.

[0017] Furthermore, the pressure of the hydrorefining reaction is 7.5 MPa, and the reaction temperature is 287°C; preferably, the hydrorefining reaction time is 1.5 h; and the hydrogen partial pressure in the hydrorefining reaction is 0.8 MPa.

[0018] The high-pressure environment of the hydrorefining reaction promotes the dissolution of hydrogen in the solvent, increases the hydrogenation reaction rate, and ensures the full reduction of impurities such as 4-CBA and p-tol. The reaction temperature is 287℃, at which the catalyst activity is optimal, and the high temperature can accelerate the chemical reaction of impurities, improve the impurity removal efficiency, and adapt to the characteristics of bio-based CTA impurities that are more difficult to convert. The reaction time is controllable to ensure that impurities react fully and avoid over-reaction that leads to energy waste or the formation of by-products.

[0019] Furthermore, the washing temperature is 90°C, and the mass ratio of solvent to washed product during the washing process is 10:1.

[0020] Water washing can effectively dissolve and remove soluble impurities. Temperature control ensures washing efficiency while avoiding product dissolution loss, ensuring that the final product contains 4-CBA ≤ 25 ppm, p-tol ≤ 180 ppm, and that the color value meets the requirements of the polyester polymerization process.

[0021] Furthermore, the bio-based crude terephthalic acid is prepared by oxidation of bio-based para-xylene (PX) obtained after processing biomass raw materials, wherein the biomass raw materials are mainly agricultural waste such as algae and wood, and the biochar content is >99%.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] (1) This invention optimizes the entire process of “pretreatment-hydrogenation reaction-posttreatment” to form a special refining process suitable for bio-based CTA. This process not only solves the problem of high impurities in bio-based raw materials, but also achieves a balance between environmental protection and economy through the design of green solvent (water), high-efficiency catalyst (Pd / C) and controllable parameters, providing a feasible path for the industrial production of bio-based PTA and promoting the transformation of the polyester industry towards sustainable development.

[0024] (2) The method of the present invention has a high impurity removal rate, can efficiently purify bio-based CTA, and obtain products that meet PTA standards. The reaction conditions are mild, and low energy consumption and high stability operation are achieved under efficient catalysis. Furthermore, the process pollution is small, reducing the environmental burden. 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 embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 Image showing the hydrogenation effect of PTA prepared in Comparative Example 1;

[0027] Figure 2 The image shows the hydrogenation effect of PTA prepared in Comparative Example 4;

[0028] Figure 3 Image showing the hydrogenation effect of PTA prepared in Comparative Example 5. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] This invention provides a method for hydrogenating and refining bio-based terephthalic acid products to optimize color values, comprising the following steps: pre-treating bio-based crude terephthalic acid with recrystallization at least four times; mixing the pre-treated bio-based crude terephthalic acid with a solvent and adding a catalyst for hydrogenation and refining reaction; performing a second recrystallization treatment after the reaction is completed; washing with water and drying to obtain refined terephthalic acid; the hydrogenation and refining reaction time is 1.5-6 hours; the catalyst is a Pd / C catalyst.

[0035] This invention involves first subjecting bio-based crude terephthalic acid to multiple recrystallization pretreatments. Then, the pretreated bio-based crude terephthalic acid is mixed with a solvent, and a catalyst is added for hydrogenation refining. After the reaction, the solvent is replaced, and the hydrogenated product is recrystallized, washed with water, and dried to obtain refined terephthalic acid. The recrystallization pretreatment of the bio-based crude terephthalic acid reduces the impurity content before hydrogenation, and the shortening of the hydrogenation time controls the shedding of the Pd / C catalyst. The hydrogenation refining method provided by this invention effectively removes impurities and improves the product quality of bio-based terephthalic acid.

[0036] In some preferred embodiments of the present invention, the bio-based crude terephthalic acid is obtained by oxidizing bio-based p-xylene (PX) obtained after processing biomass raw materials, wherein the biomass raw materials are mainly agricultural waste such as algae and wood, and the biochar content is >99%.

[0037] In some preferred embodiments of the present invention, the concentration of p-carboxybenzaldehyde (4-CBA) in the bio-based crude terephthalic acid is 1500-3500 ppm, and the concentration of p-methylbenzoic acid (p-tol) is 500-1500 ppm; the above-mentioned concentrations of 4-CBA and p-tol are based on the total weight of PTA, 4-CBA and p-tol in the bio-based crude terephthalic acid, ignoring other impurities in the bio-based crude terephthalic acid.

[0038] In some preferred embodiments of the present invention, the mass ratio of the solvent to the pretreated bio-based crude terephthalic acid is 5:1, the mass ratio of the pretreated bio-based crude terephthalic acid to the catalyst is 3:1, and the solvent is water. The catalyst is a Pd / C catalyst, and the content of the active component Pd in ​​the catalyst is 1-10%.

[0039] In some preferred embodiments of the present invention, the hydrorefining reaction is carried out under a hydrogen atmosphere, the pressure of the hydrorefining reaction is 7.5 MPa, the reaction temperature is 287°C, and the reaction time is 1.5-6 h; the partial pressure of hydrogen in the hydrorefining reaction is 0.8 MPa.

[0040] In a preferred embodiment of the present invention, the washing temperature is 90°C, and the mass ratio of solvent to washed product during the washing process is 10:1.

[0041] In a preferred embodiment of the present invention, the concentration of p-carboxybenzaldehyde in the purified terephthalic acid is ≤25ppm and the concentration of p-methylbenzoic acid is ≤180ppm.

[0042] Unless otherwise specified, all materials used in this invention are commercially available products.

[0043] In this embodiment of the invention, bio-based CTA is prepared from bio-based PX (obtained from biomass through fermentation) via liquid-phase oxidation. The specific steps are as follows: a solvent is prepared at a volume ratio of acetic acid / water of 12:1, and a catalyst (content of 400 / 200 / 600 ppm (Co / Mn / Br)) is added. This catalyst is continuously fed into a continuous oxidation reactor at a constant flow rate for oxidation (reaction conditions: 185℃; residence time 180 min; air flow rate 20 L / min; feed flow rate 5.6 mL / min). After the reaction, the collected liquid is subjected to solid-liquid separation, and the resulting solid is the bio-based CTA, which is used as a hydrogenation feedstock for purification experiments. Testing showed that the concentration of 4-CBA in the bio-based crude terephthalic acid in this embodiment ranged from 1500-3500 ppm, and the concentration of p-tol ranged from 500-1500 ppm.

[0044] The specific operation of recrystallization pretreatment of bio-based CTA in the following embodiments of the present invention is as follows: bio-based crude terephthalic acid is added to a solvent, dissolved at 287°C, and crystallized using a four-stage crystallization process, wherein the mass ratio of bio-based crude terephthalic acid to solvent is 1:5; after changing the solvent, the crystallization is repeated at least four times to obtain pretreated bio-based crude terephthalic acid. The four-stage crystallization process includes the following steps: starting from 287°C, cooling down, and successively holding at 259°C for 35 min, 219°C for 30 min, 180°C for 30 min, and 153°C for 25 min, and finally cooling to room temperature.

[0045] In this embodiment of the invention, the specific operation of recrystallizing the PTA obtained by hydrogenation is as follows: the PTA obtained by hydrogenation is added to water and dissolved at 287°C for 2 hours. Crystallization is carried out according to a four-stage crystallization gradient process (259°C for 35 minutes; 219°C for 30 minutes; 180°C for 30 minutes; 153°C for 25 minutes, and finally cooled to room temperature), wherein the mass ratio of the PTA obtained by hydrogenation to water is 1:5; after changing the solvent, the crystallization is repeated four times.

[0046] In the embodiments of the present invention, the content of the active component Pd in ​​the Pd / C catalyst is 4%.

[0047] Example 1

[0048] A hydrogenation purification method for optimizing the color value of bio-based terephthalic acid products, comprising the following steps:

[0049] First, the bio-based CTA (approximately 3000 ppm 4-CBA concentration and approximately 1000 ppm p-tol concentration) was pretreated with recrystallization four times (with fresh solvent each time). The recrystallized CTA was then collected and mixed with water at a mass ratio of 1:5, and added to a hydrogenation reactor. A Pd / C catalyst (mass ratio of bio-based CTA to Pd / C catalyst was 3:1) was also added. Before the reaction began, nitrogen gas was introduced into the reactor to purge air, and heating was started. Once the required reaction temperature was reached, hydrogen gas was introduced into the reactor to initiate the hydrogenation refining reaction (rotation speed 300 rpm, pressure 7.5 MPa, temperature 287℃, time 1.5 h, hydrogen partial pressure 0.8 MPa). After the reaction, the solvent was replaced with fresh water, and the hydrogenated PTA was recrystallized again. The PTA was then washed with water at 90℃ using water at a mass ratio 10 times that of the re-recrystallized product, and dried to obtain the final PTA product.

[0050] Example 2

[0051] A hydrogenation purification method for optimizing the color value of bio-based terephthalic acid products includes the following steps:

[0052] First, the bio-based CTA (approximately 3000 ppm 4-CBA concentration and approximately 1000 ppm p-tol concentration) was pretreated with four recrystallization cycles (using fresh solvent). The recrystallized CTA was then removed and mixed with water at a mass ratio of 1:5, and added to a hydrogenation reactor. A Pd / C catalyst (3:1 mass ratio of bio-based CTA to Pd / C catalyst) was also added. Before the reaction began, nitrogen gas was introduced into the reactor to purge air, and heating was initiated. Once the required reaction temperature was reached, hydrogen gas was introduced into the reactor to initiate the hydrogenation refining reaction (300 rpm, 7.5 MPa, 287°C, 2.5 h, hydrogen partial pressure 0.8 MPa). After the reaction, the solvent was replaced with fresh water, and the hydrogenated PTA was recrystallized again. The PTA was then washed with water at 90°C using 10 times its mass of water, and dried to obtain the final PTA product.

[0053] Example 3

[0054] A hydrogenation purification method for optimizing the color value of bio-based terephthalic acid products includes the following steps:

[0055] First, the bio-based CTA (approximately 3000 ppm 4-CBA concentration and approximately 1000 ppm p-tol concentration) was pretreated with four recrystallization cycles (using fresh solvent). The recrystallized CTA was then removed and mixed with water at a mass ratio of 1:5, and added to a hydrogenation reactor. A Pd / C catalyst (3:1 mass ratio of bio-based CTA to Pd / C catalyst) was also added. Before the reaction began, nitrogen gas was introduced into the reactor to purge air, and heating was initiated. Once the required reaction temperature was reached, hydrogen gas was introduced into the reactor to initiate the hydrogenation refining reaction (300 rpm, 7.5 MPa, 287°C, 4 hours, hydrogen partial pressure 0.8 MPa). After the reaction, the solvent was replaced with fresh water, and the hydrogenated PTA was recrystallized again. The PTA was then washed with water at 90°C using 10 times its mass of water, and dried to obtain the final PTA product.

[0056] Example 4

[0057] First, the bio-based CTA (approximately 3000 ppm 4-CBA concentration and approximately 1000 ppm p-tol concentration) was pretreated with four recrystallization cycles (using fresh solvent). The recrystallized CTA was then removed and mixed with water at a mass ratio of 1:5, and added to a hydrogenation reactor. A Pd / C catalyst (3:1 mass ratio of bio-based CTA to Pd / C catalyst) was also added. Before the reaction began, nitrogen gas was introduced into the reactor to purge air, and heating was initiated. Once the required reaction temperature was reached, hydrogen gas was introduced into the reactor to initiate the hydrogenation refining reaction (300 rpm, 7.5 MPa, 287°C, 6 hours, hydrogen partial pressure 0.8 MPa). After the reaction, the solvent was replaced with fresh water, and the hydrogenated PTA was recrystallized again. The PTA was then washed with water at 90°C using 10 times its mass of water, and dried to obtain the final PTA product.

[0058] Comparative Example 1

[0059] Similar to Example 4, except that no pretreatment for recrystallization of the bio-based CTA was performed, and the hydrogenation purification reaction product was not recrystallized again. The specific operating steps are as follows:

[0060] First, bio-based CTA (approximately 3000 ppm 4-CBA concentration and approximately 1000 ppm p-tol concentration) was mixed with water at a mass ratio of 1:5 and added to a hydrogenation reactor. A Pd / C catalyst (mass ratio of bio-based CTA to Pd / C catalyst was 3:1) was also added. Before the reaction began, nitrogen gas was introduced into the reactor to purge air, and heating was started. Once the required reaction temperature was reached, hydrogen gas was introduced into the reactor to initiate the hydrogenation purification reaction (rotation speed 300 rpm, pressure 7.5 MPa, temperature 287 °C, time 6 h, hydrogen partial pressure 0.8 MPa). After filtration, a crystalline product was obtained. The crystalline product was then washed with water at 90 °C in a 10:1 mass ratio, and dried to obtain the PTA product.

[0061] Comparative Example 2

[0062] Same as Example 4, except that no pretreatment for recrystallization of bio-based CTA was performed. The specific steps are as follows:

[0063] First, bio-based CTA (approximately 3000 ppm 4-CBA concentration and approximately 1000 ppm p-tol concentration) was mixed with water at a mass ratio of 1:5 and added to a hydrogenation reactor. A Pd / C catalyst (mass ratio of bio-based CTA to Pd / C catalyst was 3:1) was also added. Before the reaction began, nitrogen gas was introduced into the reactor to purge air, and heating was started. Once the required reaction temperature was reached, hydrogen gas was introduced into the reactor to initiate the hydrogenation refining reaction (rotation speed 300 rpm, pressure 7.5 MPa, temperature 287 °C, time 6 h, hydrogen partial pressure 0.8 MPa). After the reaction, the solvent water was replaced, and the PTA obtained from the hydrogenation refining was recrystallized again. The PTA was then washed with water at 90 °C using 10 times its mass of water, and dried to obtain the PTA product.

[0064] Comparative Example 3

[0065] Same as Example 4, except that the bio-based CTA is subjected to only one recrystallization pretreatment. The specific steps are as follows:

[0066] First, the bio-based CTA (approximately 3000 ppm 4-CBA concentration and approximately 1000 ppm p-tol concentration) was pretreated by recrystallization. The recrystallized CTA was then removed and mixed with water at a mass ratio of 1:5, and added to a hydrogenation reactor. A Pd / C catalyst (mass ratio of bio-based CTA to Pd / C catalyst was 3:1) was also added. Before the reaction began, nitrogen gas was introduced into the reactor to purge air, and heating was initiated. Once the required reaction temperature was reached, hydrogen gas was introduced into the reactor to initiate the hydrogenation refining reaction (rotation speed 300 rpm, pressure 7.5 MPa, temperature 287 °C, time 6 h, hydrogen partial pressure 0.8 MPa). After the reaction, the solvent water was replaced, and the hydrogenated PTA was recrystallized again. The PTA was then washed with water at 90 °C using 10 times its mass of water, and dried to obtain the final PTA product.

[0067] Comparative Example 4

[0068] Similar to Comparative Example 1, the only difference is that the rotation speed is 100 rpm during the hydrogenation purification reaction.

[0069] Comparative Example 5

[0070] Similar to Comparative Example 1, the only difference is that the rotation speed was 800 rpm during the hydrogenation purification reaction.

[0071] Figure 1 The image shows the PTA product after hydrogenation in Comparative Example 1, with a rotation speed of 300 rpm and minimal catalyst powder shedding. Figure 2 The image shown is of the PTA product after hydrogenation in Comparative Example 4. The reaction speed was 100 rpm, at which point the hydrogenation effect was poor due to mass transfer. Figure 3The image shows the PTA product after hydrogenation in Comparative Example 5, at a rotation speed of 800 rpm. At this speed, catalyst powder shedding was severe, and the product was heavily grayish. Figures 1-3 It can be seen that rotational speed affects the quality of the final product.

[0072] Performance testing

[0073] (1) PTA colorimetric value analysis

[0074] a, b, and L values ​​determination: 12 ± 0.2 g of PTA products prepared in Examples 1-4 and Comparative Examples 1-5 were weighed, pressed into discs with a diameter of 30 mm on a tablet press, and measured on a colorimeter. The instrument automatically gave the a, b, and L values ​​of the sample. The test results are shown in Table 1.

[0075] Table 1. Colorimetric values ​​of bio-based PTA products.

[0076]

[0077] As shown in Table 1, Examples 2-4 and Comparative Examples 1-5 have high L-values ​​of chromaticity. This is because the hydrogenation time in the comparative examples is long, and the shedding of Pd / C catalyst powder affects the brightness of the product, resulting in a grayish appearance after hydrogenation. The tristimulus values ​​of a (red-green index), b (yellow-blue index), and L (brightness index) are used as comprehensive characterization indicators.

[0078] (2) Impurity analysis in PTA

[0079] This invention uses high-performance liquid chromatography (HPLC) to analyze and test the content of target impurities 4-CBA and p-tol in the product. The specific instruments and test conditions are as follows:

[0080] The system used was a Waters e2695 high-performance liquid chromatograph with an autosampler, a Waters 2695 UV / Vis detector, and an Empower 2 data processing system.

[0081] Chromatographic conditions: Column: Zorbax Eclipse Plus C18 (4.6 × 250 mm, 5 μm); Mobile phase A: 100% acetonitrile, Mobile phase B: 0.06% phosphoric acid aqueous solution; Isocratic elution; Flow rate: 1 mL / min; Column temperature: 40℃; Detection wavelength: 254 nm / 240 nm; Injection volume: 20 μL.

[0082] Sample preparation: Weigh 0.1g of sample (PTA products prepared in Examples 1-4 and Comparative Examples 1-5), add 28% ammonia water to dissolve, then adjust the pH to 6.0-7.0 with 17% phosphoric acid, and make up to 10mL with ultrapure water. Inject the resulting liquid sample directly. The present invention uses the external standard method to determine the impurity content in the above samples. The determination results are shown in Table 1.

[0083] Table 2 Impurity content in bio-based PTA products

[0084]

[0085] Table 2 shows that the high p-tol content in the PTA product prepared in Comparative Example 1 is due to the fact that recrystallization was omitted, making it difficult to remove the impurity with just one water wash. The high 4-CBA content in the PTA product prepared in Comparative Example 4 is due to the low rotation speed, which affects mass transfer and thus the hydrogenation reaction. The low quality of the PTA product prepared in Comparative Example 5 indicates that severe catalyst powder loss occurred at high rotation speeds, affecting product quality. Example 1 reduced the 4-CBA content through multiple crystallizations and reduced catalyst powder loss by controlling the hydrogenation time.

[0086] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of optimizing the hydrofinishing of a bio-based terephthalic acid product color value, characterized by, The method comprises the following steps: The bio-based crude terephthalic acid is pretreated by at least four times of recrystallization, the pretreated bio-based crude terephthalic acid and a solvent are mixed, a catalyst is added for a hydrorefining reaction, after the reaction, the pretreated bio-based crude terephthalic acid is treated by recrystallization again, washed by water and dried to obtain refined terephthalic acid; the hydrorefining reaction time is 1.5-6h; the catalyst is a Pd / C catalyst.

2. The hydrofining process of claim 1 wherein, The recrystallization pretreatment comprises the following steps: the bio-based crude terephthalic acid is added into a solvent, dissolved at 287℃, and treated by a four-stage crystallization process, wherein the mass ratio of the bio-based crude terephthalic acid to the solvent is 1:5; after changing the solvent, the recrystallization is repeated for at least four times to obtain the pretreated bio-based crude terephthalic acid, and the four-stage crystallization process comprises the following steps: cooling from 287℃, stopping at 259℃ for 35min, stopping at 219℃ for 30min, stopping at 180℃ for 30min and stopping at 153℃ for 25min, and finally cooling to room temperature.

3. The hydrofinishing process of claim 2, wherein, The solvent for the recrystallization pretreatment is water.

4. The hydrofinishing process of claim 1 wherein, The content of p-carboxybenzaldehyde in the bio-based crude terephthalic acid is 1500-3500ppm, and the content of p-methylbenzoic acid is 500-1500ppm.

5. The hydrofinishing process of claim 1 wherein, The mass ratio of the solvent to the pretreated bio-based crude terephthalic acid is 5:1, and the mass ratio of the pretreated bio-based crude terephthalic acid to the catalyst is 3:

1.

6. The hydrofinishing process of claim 5, wherein, The solvent is water.

7. The hydrofinishing process of claim 5, wherein, The content of the active component Pd in the catalyst is 1-10%.

8. The hydrofinishing process of claim 1 wherein, The hydrorefining reaction is carried out in a hydrogen atmosphere, the pressure of the hydrorefining reaction is 7.5MPa, and the reaction temperature is 287℃; the hydrogen partial pressure in the hydrorefining reaction is 0.8MPa.

9. The hydrofinishing process of claim 1 wherein, The hydrorefining reaction time is 1.5h.

10. The hydrofinishing process of claim 1 wherein, The bio-based crude terephthalic acid is prepared by oxidizing bio-based p-xylene obtained by treating a biomass raw material.

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