Method for purifying terephthalic acid

Abstract

A process for purifying terephthalic acid. The method comprises: contacting unpurified terephthalic acid with graphite, activated carbon and a molecular sieve to provide a reaction mixture; stirring the reaction mixture for a first specific period of time; filtering the reaction mixture to provide a reaction mixture filtrate; providing graphite, activated carbon, and a molecular sieve to the reaction mixture filtrate; stirring the reaction mixture filtrate for a second specific period of time; filtering the reaction mixture filtrate to provide a reaction output solution; and precipitating purified terephthalic acid from the reaction output solution.

Description

Technical Field

[0001] This disclosure generally relates to methods for purifying terephthalic acid (TPA). Specifically, this disclosure relates to methods for purifying terephthalic acid (TPA) at room temperature, which methods include the use of graphite, activated carbon, and molecular sieves. Background Art

[0002] PCT Application Publication No. WO2020173961A1 (the entire disclosure of which, except for any definitions, disclaimers, denials, and inconsistencies, is incorporated herein by reference) provides a method for alkaline hydrolysis of one or more plastic polymers into terephthalic acid (TPA) and / or ethylene glycol (EG) and / or other monomers that form one or more plastic polymers, the method comprising: a) contacting one or more plastic polymers with a metal oxide in solution in the presence of a base to provide a reaction mixture; b) stirring the reaction mixture under ultraviolet light for a suitable period of time; c) recovering terephthalic acid, ethylene glycol, and / or other monomers from the reaction mixture.

[0003] The method of PCT Application Publication No. WO2020173961A1 can output contaminated terephthalic acid or terephthalic acid of a quality that requires further purification before further processing and use. Current methods for purifying TPA are energy-intensive and economically inefficient.

[0004] Accordingly, there is a need for improved methods for purifying TPA. Summary of the Invention

[0005] According to one embodiment, a method for purifying terephthalic acid is described herein. The method comprises: contacting unpurified terephthalic acid with graphite, activated carbon, and molecular sieves to provide a reaction mixture; stirring the reaction mixture for a first specific period of time; filtering the reaction mixture to provide a reaction mixture filtrate; providing graphite, activated carbon, and molecular sieves to the reaction mixture filtrate; stirring the reaction mixture filtrate for a second specific period of time; filtering the reaction mixture filtrate to provide a reaction output solution; and precipitating purified terephthalic acid from the reaction output solution.

[0006] According to some embodiments, the reaction mixture is stirred at a pH of 14.

[0007] According to some embodiments, the reaction mixture filtrate is stirred at a pH of 7.

[0008] According to some embodiments, graphite, activated carbon, and molecular sieves are provided in a ratio of 1:6:2 for contact with unpurified terephthalic acid.

[0009] According to some embodiments, graphite, activated carbon, and molecular sieve are provided to the reaction mixture filtrate in a ratio of 1:6:2.

[0010] According to some embodiments, purified terephthalic acid is precipitated from the reaction output solution using an acid.

[0011] According to some embodiments, the acid is hydrochloric acid or sulfuric acid.

[0012] According to some embodiments, the first time period is between 10 and 120 minutes.

[0013] According to some embodiments, the first time period is 30 minutes.

[0014] According to some embodiments, the second time period is between 10 and 120 minutes.

[0015] According to some embodiments, the second time period is 30 minutes.

[0016] According to some embodiments, the method is performed at room temperature.

[0017] According to some embodiments, the molecular sieve in contact with the unpurified terephthalic acid is zeolite 13X.

[0018] According to some embodiments, the molecular sieve provided to the reaction mixture filtrate is zeolite 13X.

[0019] After reviewing the following description of some exemplary embodiments, other aspects and features will become apparent to those of ordinary skill in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings included herein are used to illustrate various embodiments of the articles, methods, and apparatuses of the present specification. In the drawings:

[0021] Figure 1 is a flow chart of a method for purifying terephthalic acid according to one embodiment;

[0022] Figure 2 is a table detailing the chemical and physical properties of terephthalic acid prepared by the method using Figure 1 according to one embodiment;

[0023] Figure 3 is a table detailing the chemical and physical properties of terephthalic acid prepared by the method using Figure 1 according to another embodiment; and

[0024] Figure 4 is a table detailing the chemical and physical properties of terephthalic acid prepared by the method using Figure 1 according to another embodiment. Detailed Implementation Modes

[0025] Various devices or processes will be described below to provide examples of each claimed implementation mode. The implementation modes described below do not limit any claimed implementation mode, and any claimed implementation mode may cover processes or devices different from those described below. The implementation modes claimed herein are not limited to devices or processes having all the features of any one of the devices or processes described below, or to the common features of multiple or all of the devices described below.

[0026] In addition, although process steps, method steps, algorithms, etc. may be described (in this disclosure and / or the claims) in a sequential order, such processes, methods, and algorithms may be configured to work in an alternating order. In other words, any order or sequence of steps that can be described does not necessarily indicate that the steps are required to be executed in that order. The steps of the processes described herein can be executed in any practical order. In addition, some steps can be executed simultaneously.

[0027] When a single device or article is described herein, it will be apparent that more than one device / article (whether or not they cooperate) can be used instead of the single device / article. Similarly, in cases where more than one device or article (whether or not they cooperate) are described herein, it will be apparent that a single device / article can be used instead of the more than one device / article.

[0028] Related to the screw conveyor reactor system described herein is a method of degrading plastic materials into terephthalic acid (TPA), ethylene glycol, and / or other monomers that form the plastic materials.

[0029] The method includes: contacting one or more plastic polymers with a metal oxide in solution in the presence of a base to provide a reaction mixture;

[0030] stirring the reaction mixture under ultraviolet light for an appropriate time; and

[0031] recovering terephthalic acid, ethylene glycol, and / or other monomers from the reaction mixture.

[0032] The method includes the alkaline hydrolysis of a polymer (i.e., polyethylene terephthalate (PET)). Compared with other methods of degrading polymers into their constituent monomers, this process can be implemented at room temperature with relatively high efficiency.

[0033] In some implementation modes, the solvent is ethanol or an ethanol - water mixture.

[0034] In some implementation modes, the polymer is polyethylene terephthalate (PET).

[0035] In some embodiments, the metal oxide is TiO2.

[0036] In some embodiments, the base is NaOH.

[0037] In some embodiments, the initial pH of the reaction mixture is 14.

[0038] In some embodiments, the reaction mixture is stirred at room temperature.

[0039] After recovering terephthalic acid at the end of the process, the terephthalic acid may be of low purity and may need to be further processed to obtain commercially useful terephthalic acid, where the terephthalic acid can be provided to a process configured to require the original terephthalic acid.

[0040] Common methods for purifying TPA typically include a recrystallization step, which requires heating to a high temperature (e.g., 200 °C), which is energy-intensive and requires the use of harmful solvents such as dimethylformamide. Such solvents can endanger the safety of the operator and require expensive, time-consuming, and complex procedures for handling and management.

[0041] Methods for purifying TPA and other compounds are described herein. While the systems and methods described herein may be particularly well-suited for purifying TPA prepared by the room-temperature alkaline polymer hydrolysis process described above and in PCT Application Publication No. WO2020173961A1, in some embodiments, the TPA purification methods described herein can be applied to TPA from other sources as well as compounds other than TPA. By using three adsorbent materials (each in significant excess) and applying two adsorption steps at different pH levels, the adsorbent materials remove a high proportion of the contaminants associated with TPA derived from contaminated PET. The methods described herein can reliably output purified TPA with a purity up to 1% higher than the original TPA and a whiteness chroma 5% brighter than the original TPA. In embodiments where compounds other than TPA are purified, additional pH adjustment can be performed.

[0042] The methods described herein can be suitable for purifying other compounds, such as low molecular weight (<200 g / mol) monomers, such as lactic acid. In other embodiments, water (e.g., wastewater, air, proteins, and other substances) can be purified by the methods described herein.

[0043] Now refer to Figure 1 , which depicts a flowchart outlining a method 100 for purifying TPA according to one embodiment. Method 100 includes steps 102, 104, 106, 108, 110, 112, and 114.

[0044] The methods described herein can be implemented in a batch operation and are carried out in a reactor vessel, which is preferably equipped with a stirrer and a plug drain filter. In some embodiments, the methods described herein can be implemented in a batch operation through a plurality of reaction vessels in a series configuration. In some embodiments, the methods described herein can be modified to operate in a continuous process.

[0045] At step 102, the unpurified terephthalic acid is contacted with graphite, activated carbon, and molecular sieves. The unpurified terephthalic acid can be sourced from the output of a polymer recycling process, such as the room temperature alkaline polymer hydrolysis process described in PCT Application Publication No. WO2020173961A1. In some embodiments, the contacting process of step 102 can be carried out within a reaction vessel.

[0046] In some embodiments, such unpurified terephthalic acid may contain contaminants, which include dyes (such as azo dyes, including Pigment Yellow 13, Sudan Black B, Sudan Red G, or anthraquinones, such as Disperse Red 11); solid pigments, such as carbon black, isomers (such as phthalic acid, isophthalic acid); and molecules that can be present as contaminants in PET, such as benzoic acid, p-toluic acid, bisphenol A, 4-carboxybenzaldehyde, metal ions (such as chromium, iron, nickel, antimony, sodium, titanium, aluminum, barium, calcium, cobalt, manganese, molybdenum, lithium, potassium, zinc), and / or other contaminants.

[0047] The graphite provided at step 102 can include amorphous, crystalline, or flaky graphite with a purity of 99% and a particle size range of 5 to 30 μm (micrometers). In other embodiments, graphite with different purity levels, forms, and particle sizes can alternatively be provided.

[0048] In some embodiments, the graphite of step 102 may include a very fine black powder with a crystal height of 60 to 100 nm, an interlayer distance of 0.25 to 0.35 nm, a D90 particle size of 5 to 30 microns, a BET surface area of 10 to 15 m 2 / g, an ash content of less than 0.05%, and a total metal content of individual metals generally less than 2 ppm.

[0049] The activated carbon provided at step 102 can include activated carbon in the form of particles with a surface area of 500 to 1500 m 2 / g and a particle size less than 1 mm.

[0050] In other embodiments, activated carbon of different purity levels, forms, surface areas, and particle sizes can alternatively be provided. In some embodiments, the activated carbon of step 102 can comprise 70% by weight of grinding fineness (less than 40 μm), an iodine value of 900 to 1500 mg / g, and a surface area of 800 to 1500 m 2 / g.

[0051] The molecular sieve provided at step 102 can comprise an aluminosilicate crystal molecular sieve, such as zeolite 13X molecular sieve. Zeolite 13X comprises an average pore measured at 9 angstroms and can adsorb molecules with a kinetic diameter less than 9 angstroms.

[0052] In some embodiments, the molecular sieve provided at step 102 can comprise 3 to 5 μm particles with an average surface area of 700 m 2 / g. In other embodiments, other molecular sieves with similar compositions and / or specifications can alternatively be provided. In other embodiments, other molecular sieves with different compositions and / or specifications can alternatively be provided.

[0053] The graphite, activated carbon, and molecular sieve provided at step 102 can be provided in a mass ratio of graphite:activated carbon:molecular sieve of 1:6:2, respectively. In other embodiments, other ratios of graphite, activated carbon, and molecular sieve can be provided.

[0054] In some embodiments, the unpurified terephthalic acid can be in the form of M-TPA dissolved in water with a pH of 14 (where "M" represents a metal, such as Na + or K + , which can be derived from a hydrolysis process), close to the maximum solubility of M-TPA in the solution (about 13% by weight). In some embodiments, after step 102, the 210 L total solution comprises 3 kg of activated carbon, 1 kg of zeolite 13X, and 0.5 kg of graphite.

[0055] All three components added at step 102 allow the capture of pollutants through an adsorption process. Activated carbon can remove dyes by adsorbing the dyes inside the pores of the large-sized material. Compared with activated carbon, the relatively smaller pores of zeolite 13X allow the capture of organic molecules with smaller molecular weights. The surface of graphite also allows non-chemical soft bonding of organic and metal ions. By changing the pH from alkaline to neutral, the surface charge of the absorbent material changes, from negative charge to neutral charge and then to positive charge, or from positive charge to neutral charge and then to negative charge, allowing for easier adsorption of organic molecules with slightly negative or positive charges on the molecular surface in addition to heavy metals.

[0056] At step 104, the reaction mixture is stirred for a first specific period of time. The reaction mixture can be stirred using an integrated stirrer component within the reaction vessel or by another similar device.

[0057] The reaction mixture can be stirred for a time range between 10 and 120 minutes. In some embodiments, the reaction mixture can be stirred for 60 minutes at step 104. In other embodiments, the reaction mixture can be stirred for different time periods.

[0058] At step 104, the reaction mixture can be stirred at an alkaline pH. Prior to stirring, a pH adjusting compound (such as HCl, NaOH, or another compound) can be added to the reaction mixture to adjust the pH of the reaction mixture. In some embodiments, the reaction mixture can be stirred at a pH of 14.

[0059] At step 106, the reaction mixture is filtered to provide a reaction mixture filtrate. In some embodiments, a plunger discharge filter can be used to filter the reaction mixture, the plunger discharge filter being coupled to or integrated into the reaction vessel in which steps 102 and / or 104 are performed. The filter can separate the solid components of the reaction mixture from the liquid components. The filter can comprise a pore size that is slightly smaller than the diameter of the smallest solid component of the reaction mixture. For example, if the smallest solid particles have a diameter of 5 μm (micrometers), the filter can comprise a pore size of 4 μm.

[0060] After filtration, the reaction mixture filtrate can be provided to another container for further processing.

[0061] In some embodiments of the methods described herein, steps 102 to 106 can each be divided into a plurality of sub-steps that are performed in sequence. For example, only one of graphite, activated carbon, and molecular sieve can be provided at step 102, and then the mixture can be stirred and filtered (in accordance with steps 104 and 106). After filtration, another one of graphite, activated carbon, and molecular sieve can be provided (e.g., one that has not been provided in the method), and then the mixture can be stirred and filtered (in accordance with steps 104 and 106). After the second filtration, another one of graphite, activated carbon, and molecular sieve can be provided (e.g., the last one that has not been provided in the method), and then the mixture can be stirred and filtered one last time (in accordance with steps 104 and 106), thereby preparing the reaction mixture filtrate mentioned at step 106.

[0062] In some embodiments, steps 102 to 106 can each be divided into two sub-steps, where two of graphite, activated carbon, and molecular sieve are provided in the first sub-step, and the remaining materials can be provided in the second sub-step. In some embodiments, the second sub-step can occur before the first sub-step.

[0063] In some embodiments, steps 102 to 106 can each be divided into three sub-steps, where in the first sub-step, one of graphite, activated carbon, and molecular sieve can be provided, in the second sub-step, one of the two remaining materials can be provided, and in the third sub-step, the third remaining material can be provided. In some embodiments, the first, second, and third sub-steps can be performed in any order.

[0064] In some embodiments, a stepwise column filtration system can be used to perform steps 102 to 106.

[0065] At step 108, graphite, activated carbon, and molecular sieve are provided to the reaction mixture filtrate. The graphite provided at step 108 can include amorphous, crystalline, or flaky graphite with a purity of 99% and a particle size range of 5 to 30 μm (micrometers). In other embodiments, graphite with different purity levels, forms, and particle sizes can alternatively be provided.

[0066] In some embodiments, the graphite of step 108 can include very fine black powder with a crystal height of 60 to 100 nm, an interlayer distance of 0.25 to 0.35 nm, a D90 particle size of 5 to 30 μm, a BET surface area of 10 to 15 m 2 / g, an ash content of less than 0.05%, and a total metal content of individual metals of generally less than 2 ppm.

[0067] The activated carbon provided at step 108 can include activated carbon in the form of particles with a surface area of 500 to 1500 m 2 / g and a particle diameter of less than 1 mm. In other embodiments, activated carbon with different purity levels, forms, surface areas, and particle sizes can alternatively be provided.

[0068] In some embodiments, the activated carbon of step 108 can include 70% by weight of grinding fineness (less than 40 μm), an iodine value of 900 to 1500 mg / g, and a surface area of 800 to 1500 m 2 / g.

[0069] The molecular sieve provided at step 108 can include an aluminosilicate crystal molecular sieve, such as zeolite 13X molecular sieve. Zeolite 13X contains an average pore measured at 9 Å and can absorb molecules with a kinetic diameter less than 9 Å.

[0070] In some embodiments, the molecular sieve of step 108 can include 3 to 5 μm particles with an average surface area of 700 m 2 / g. In other embodiments, other molecular sieves having similar composition and / or specifications may alternatively be provided. In other embodiments, other molecular sieves having different composition and / or specifications may alternatively be provided.

[0071] The graphite, activated carbon, and molecular sieve provided at step 108 may be provided in a mass ratio of 1:6:2 for graphite, activated carbon, and molecular sieve, respectively. In other embodiments, other ratios of graphite, activated carbon, and molecular sieve may be provided, e.g., as described above with reference to step 108.

[0072] At step 110, the reaction mixture filtrate is stirred for a second specific time period. The reaction mixture filtrate may be stirred using an integrated stirrer component within the reaction vessel.

[0073] The reaction mixture filtrate may be stirred for a time range between 10 and 120 minutes. In some embodiments, the reaction mixture filtrate may be stirred for 30 minutes at step 110. In other embodiments, the reaction mixture filtrate may be stirred for different time periods.

[0074] At step 110, the reaction mixture filtrate may be stirred at a neutral pH. Prior to stirring, a pH adjusting compound (e.g., HCl, NaOH, or another similar compound) may be added to the reaction mixture to adjust the pH of the reaction mixture filtrate. In some embodiments, the reaction mixture may be stirred at a pH of 7.

[0075] At step 112, the reaction mixture filtrate is filtered to provide a reaction output solution. In some embodiments, the reaction mixture filtrate may be filtered using a plunger discharge filter that is coupled to or integrated into the reaction vessel in which any of steps 102 to 110 are performed. The filter may separate the solid components from the liquid components of the reaction mixture filtrate. The filter may comprise a pore size slightly smaller than the diameter of the smallest solid component of the reaction mixture. For example, if the smallest solid particles (e.g., graphite particles) have a diameter of 5 μm, the filter may comprise a pore size of 4 μm.

[0076] Once the reaction mixture filtrate is filtered at step 112, the reaction output solution may be provided to another container or returned to the same container for further processing.

[0077] In some embodiments of the methods described herein, steps 108 to 112 may each be divided into a plurality of sub-steps that are performed in sequence. For example, only one of graphite, activated carbon, and molecular sieve may be provided at step 102, and then the mixture may be stirred and filtered (in accordance with steps 110 and 112). After filtration, another one of graphite, activated carbon, and molecular sieve may be provided (e.g., one that has not been provided in the method), and then the mixture may be stirred and filtered again (in accordance with steps 110 and 11). After the second filtration, another one of graphite, activated carbon, and molecular sieve may be provided (e.g., the last one that has not been provided in the method), and then the mixture may be stirred and filtered one last time (in accordance with steps 110 and 112) to prepare the reaction output solution mentioned at step 112.

[0078] In some embodiments, steps 108 to 112 may each be divided into two sub-steps, where two of graphite, activated carbon, and molecular sieve are provided in the first sub-step, and the remaining material may be provided in the second sub-step. In some embodiments, the second sub-step may occur before the first sub-step.

[0079] In some embodiments, steps 108 to 112 may each be divided into three sub-steps, where one of graphite, activated carbon, and molecular sieve is provided in the first sub-step, one of the two remaining materials is provided in the second sub-step, and the third remaining material is provided in the third sub-step. In some embodiments, the first, second, and third sub-steps may be performed in any order.

[0080] In some embodiments, a stepwise column filtration system may be used to perform steps 108 to 112.

[0081] At step 114, purified terephthalic acid is precipitated from the reaction output solution. In some embodiments, purified terephthalic acid may be precipitated by adding an acid to the reaction output solution. In some embodiments, the acid may comprise hydrochloric acid or sulfuric acid. In other embodiments, any other suitable acid may be used to facilitate precipitation.

[0082] If sulfuric acid is provided, the concentration of the acid provided at step 114 may be 98%. If hydrochloric acid is provided, the concentration of the acid provided at step 114 may be 33%. Other suitable acids (if provided) will have comparable concentrations, with a concentration range of 1 to 98%.

[0083] Once the purified terephthalic acid is precipitated from the reaction output solution, the purified terephthalic acid can be separated from the solution by means such as filtration. In some embodiments, the purified terephthalic acid can be subjected to additional processing steps (e.g., heating, vacuum drying, or other processing steps). For example, the purified terephthalic acid can be subjected to a grinding step to produce the purified terephthalic acid in the form of a free-flowing powder. Such free-flowing powder can be transferred to a storage medium and vacuum sealed, or stored in some other manner.

[0084] Once extracted by applying Method 100, the purified terephthalic acid can be applied to subsequent chemical processes and applications that require terephthalic acid of the original quality.

[0085] Now refer to Figure 2 , in which Table 200 is shown that details the specifications of the purified terephthalic acid prepared using Method 100 described herein. The specifications detailed in Table 200 include the contaminant concentrations and properties of two samples of the purified terephthalic acid. The samples can be compared with the PTA reference standard, as Figure 2 shown.

[0086] Now refer to Figure 3 , in which Table 300 is shown that details the specifications of the purified terephthalic acid prepared using Method 100 described herein. The specifications detailed in Table 300 include the concentration of contaminants in the sample of the purified terephthalic acid. The samples can be compared with the listed reference standards, as Figure 3 shown.

[0087] Now refer to Figure 4 , in which Table 400 is shown that details the specifications of the purified terephthalic acid prepared using Method 100 described herein. The specifications detailed in Table 400 include the concentration of contaminants in the sample of the purified terephthalic acid. The samples can be compared with the listed reference standards, as Figure 4 shown.

[0088] Although the above description provides one or more embodiments of devices, methods, or systems, it should be understood that other devices, methods, or systems may be within the scope of the claims as interpreted by those skilled in the art.

Claims

1. A method for purifying terephthalic acid, the method comprising: Contact unpurified terephthalic acid with graphite, activated carbon, and molecular sieves to provide a reaction mixture; Stir the reaction mixture for a first specific period of time; Filter the reaction mixture to provide a reaction mixture filtrate; Provide graphite, activated carbon, and molecular sieves to the reaction mixture filtrate; Stir the reaction mixture filtrate for a second specific period of time; Filter the reaction mixture filtrate to provide a reaction output solution; And Precipitate purified terephthalic acid from the reaction output solution.

2. The method according to claim 1, wherein the reaction mixture is stirred at a pH of 14.

3. The method according to claim 1 or 2, wherein the reaction mixture filtrate is stirred at a pH of 7.

4. The method according to any one of claims 1 to 3, wherein graphite, activated carbon, and molecular sieve are provided in a ratio of 1:6:2 for contact with the unpurified terephthalic acid.

5. The method according to any one of claims 1 to 4, wherein graphite, activated carbon, and molecular sieve are provided to the reaction mixture filtrate in a ratio of 1:6:

2.

6. The method according to any one of claims 1 to 4, wherein acid is used to precipitate the purified terephthalic acid from the reaction output solution.

7. The method according to claim 6, wherein the acid is hydrochloric acid or sulfuric acid.

8. The method according to any one of claims 1 to 7, wherein the first time period is between 10 and 120 minutes.

9. The method according to claim 6, wherein the first time period is 30 minutes.

10. The method according to any one of claims 1 to 9, wherein the second time period is between 10 and 120 minutes.

11. The method according to claim 10, wherein the second time period is 30 minutes.

12. The method according to any one of claims 1 to 11, wherein the method is carried out at room temperature.

13. The method according to any one of claims 1 to 12, wherein the molecular sieve in contact with the unpurified terephthalic acid is zeolite 13X.

14. The method according to any one of claims 1 to 13, wherein the molecular sieve provided to the reaction mixture filtrate is zeolite 13X.

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