A method for separating terephthalic acid from methyl methacrylate oxidation waste residue

Abstract

The present invention discloses a method for separating terephthalic acid from methyl methacrylate oxidation waste residue. The terephthalic acid is coated with a complex formed by vanillic acid, alkyl chain-modified vanillic acid, and metal ions, and then flotation is performed. This significantly improves its floatability. The complex coating can not only be used to recover solid terephthalic acid, but also to treat terephthalic acid wastewater, thereby capturing and removing trace amounts of terephthalic acid. Compared with traditional processes, this preparation process is simple, the preparation conditions are mild, and the use of organic solvents and the generation of high-salt wastewater are avoided, making it widely applicable to industrial production.

Description

Technical Field

[0001] The invention relates to the field of chemical waste residue recovery, and in particular to a method for separating terephthalic acid from methyl methacrylate oxidation waste residue. Background Art

[0002] Methyl methacrylate (MMA) is widely used in defense / construction and fine chemicals. It is an important polymer monomer. Its polymer (PMMA) can be used to produce organic glass, and can also be copolymerized with monomers such as acrylates / styrene to produce coatings / igniters and other products. It can also be used as a cross-linking agent to further copolymerize with unsaturated polyesters to produce other polymer materials.

[0003] Currently, the traditional acetone cyanohydrin (ACH) process is the primary method for producing MMA in my country. This complex synthesis route, high production costs, and the generation of large amounts of waste acid solutions pose significant environmental risks have led to the cessation of production in many small and medium-sized enterprises. Since the 1970s, rapid technological advancements have led to the emergence of the C4 process, a greener route for producing MMA. Using isobutylene and tert-butyl alcohol as raw materials, the C4 process produces methacrylic acid (MAA) through a two-step oxidation process, which is then esterified to produce MMA. This process utilizes readily available raw materials, offers advanced technology, and offers low production costs. However, the isobutylene oxidation process generates a significant amount of byproducts, such as terephthalic acid, maleic acid, and fumaric acid. These byproducts are first quenched in the oxidation reaction gas, where they are deposited as solids. Filtering the resulting residue yields an oxidation residue, and the use of a filter aid before filtration can improve filtration efficiency. According to incomplete statistics, C4-process MMA plants nationwide generate over 5,000 tons of waste residue annually. The main components of this waste residue are methacrylic acid (MAA), terephthalic acid (PTA), diatomaceous earth, benzoic acid, maleic acid (MA), and fumaric acid (FA). MAA and PTA are high in content, accounting for over 80%. Due to technological limitations, the current treatment method for the oxidized waste residue generated by MMA plants is to regularly discharge the residue, bag it, and incinerate it. However, since the residue primarily contains high-boiling-point organic matter, combustion efficiency is low, environmental pollution is severe, and raw material utilization is low, resulting in serious resource waste.

[0004] Terephthalic acid is an important raw material for synthesizing polyester, and polyester is an important raw material for manufacturing polyester fibers, coatings, films and engineering plastics. In particular, polyethylene terephthalate (PET), which is synthesized from terephthalic acid and ethylene glycol (EG), has excellent properties such as good mechanical properties, electrical insulation, fatigue resistance and easy recycling, and is increasingly replacing aluminum, glass, ceramics and other synthetic materials.

[0005] Currently, terephthalic acid waste and wastewater are typically disposed of through landfill, incineration, and water treatment. Due to its inherent resistance to degradation, landfill and incineration are both environmentally polluting, while water treatment is costly and difficult to commercialize. Meanwhile, PTA is a key industrial raw material, and disposing of it as waste not only poses serious environmental risks but also represents a significant waste of resources. Therefore, new technologies for PTA recycling are urgently needed.

[0006] With the advancement of technology, it is a general trend to develop green new energy solid waste treatment processes. If the useful components in the waste residue can be recycled and reused, the amount of waste residue treatment can be greatly reduced and the waste residue resource utilization can be realized. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for separating terephthalic acid from methyl methacrylate oxidation waste residue, recovering terephthalic acid from the residue, thereby reducing waste emissions, improving product utilization, and realizing resource utilization of the residue.

[0008] A method for separating terephthalic acid from methyl methacrylate oxidation waste residue comprises the following steps:

[0009] (1) Residue pretreatment:

[0010] The residue from the MMA oxidation process is washed with alcohol and filtered to obtain a treated residue A;

[0011] (2) Centrifugal separation

[0012] The residue after alcohol washing is added to water for ultrasonic dispersion, and then centrifuged to separate the silica and terephthalic acid by utilizing the particle size and density difference. At the same time, a certain amount of high-pressure water is added to the centrifuge at regular intervals. The heavy phase settles quickly and the light phase flows out with the water. The light phase is recorded as slurry B.

[0013] (3) Preparation of alkyl chain-modified vanillic acid

[0014] A halogen element or halogenated hydrogen is added to a long-chain alkane organic compound, and the mixture is stirred at 30-90°C for more than 60 minutes to fully react to obtain a halogenated long-chain organic compound; a certain amount of vanillic acid (VA) solution and the halogenated long-chain organic compound are mixed, and the mixture is stirred and heated at 25-60°C for 30-120 minutes to prepare an alkyl chain-modified vanillic acid (M-VA);

[0015] (4) Separation of terephthalic acid

[0016] Add the metal compound solution to slurry B, adjust the pH to 2.0-7.0, and stir thoroughly;

[0017] A mixture of vanillic acid (VA) and alkyl chain-modified vanillic acid (M-VA) is added to the above slurry and stirred thoroughly. Air is then introduced into the slurry, causing bubbling. The terephthalic acid moves in the direction of the bubbles and is carried out of the flotation machine, which is recorded as slurry C.

[0018] Since some carboxyl groups on the surface of terephthalic acid solid will dissociate, thus carrying a certain degree of negative charge, under the action of electrostatics, Y n+ It will be selectively adsorbed on the surface of terephthalic acid solid.

[0019] VA and M-VA will react with Y adsorbed on the surface of terephthalic acid. n+ Complexation occurs, forming a network structure coating the terephthalic acid surface. Due to the presence of hydrophobic segments in the M-VA, the coating exhibits amphiphilic properties, thereby enhancing the floatability of the terephthalic acid. When air is introduced into the slurry, the presence of some free M-VA causes bubbling. The terephthalic acid particles coated by the complex network migrate toward the bubbles due to the presence of a certain density of hydrophobic segments on their surfaces. This constant bubbling action carries them out of the flotation cell. Due to the hydrophilic surface of diatomaceous earth, it cannot migrate with the bubbles. Furthermore, its particle density is greater than that of terephthalic acid, so it ultimately remains in the flotation cell, achieving efficient separation of diatomaceous earth and terephthalic acid.

[0020] (5) Purification of terephthalic acid:

[0021] VA, M-VA and Y n+ The complex system formed is acid-sensitive. The pH of the obtained terephthalic acid slurry C is adjusted to 2.0-6.0 and stirred thoroughly. The complex structure is automatically decomposed. After filtration and drying, high-purity terephthalic acid can be recovered. The remaining Y n+ The solutions of VA and M-VA can be returned to step (4) for recycling.

[0022] Preferably, in step (1), the MMA oxidation process residue is discharged from the MMA oxidation process filter and conveyed to the upper entrance of the alcohol washing tank via a belt. The upper part of the belt is sealed with a plastic cover to prevent the escape of volatile gases. An alcohol solvent is added to the oxidation residue in a certain proportion and stirred at room temperature in the alcohol washing tank for more than 30 minutes. After the soluble substances are fully dissolved, the solid-liquid mixture is centrifuged to collect the residue free of MAA, FA, MA, etc., and the filtrate is returned to the device for reuse.

[0023] Preferably, the main components of the residue from the MMA oxidation process in step (1) are 10-25% methacrylic acid, 40-70% terephthalic acid, 2-20% water, 0.5-5% diatomaceous earth, 2-9% maleic acid, 0.1-1% fumaric acid and less than 0.5% polymerization inhibitor.

[0024] Preferably, the alcohol used for alcohol washing in step (1) is selected from one or more of methanol, ethanol, n-propanol, isopropanol, etc., the mass ratio of the amount of alcohol used to the residue is 5:1 to 50:1, preferably 10:1 to 20:1, the stirring time is controlled at 30 to 120 minutes, and the rotation speed is controlled at 50 to 300 rpm / min.

[0025] The main components of the filtrate are alcohol solvents, MAA, MA, FA, etc., and the main components of the filter residue are terephthalic acid and diatomaceous earth, etc.

[0026] Preferably, during ultrasonic dispersion in step (2), the mass ratio of the alcohol-washed residue to water is 1:1 to 1:20, preferably 1:1 to 1:5, and the ultrasonic dispersion time is 30 to 120 minutes. The centrifugal speed is controlled at 200 to 500 r / min, and the amount of high-pressure water added each time is 120 to 200 L, with each addition every 10 to 15 seconds, for a total of 1 to 5 additions.

[0027] Preferably, the long-chain alkane organic matter in step (3) is a C8-C16 alkane or a C9-C13 aldehyde, preferably one or more of nonane, decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane or decanal, n-undecane, n-dodecanal, or tridecanal.

[0028] The halogen element or halogenated hydrogen is preferably one or more of Cl2, Br2, I2, HCl, HBr or HI. When the added substance is a gas, it can be diluted with air, wherein the mass concentration of the halogen element or halogenated hydrogen is 1% to 5%.

[0029] Preferably, the added molar amount of the halogen element or halogenated hydrogen is 0.02 to 1 times the molar amount of the halogenated long-chain alkane organic matter.

[0030] Preferably, in step (3), the concentration of the vanillic acid solution is 5-20%.

[0031] Preferably, the molar ratio of the vanillic acid to the long-chain alkane organic matter is 1:1 to 1:10.

[0032] Preferably, the metal compound in step (4) is a metal ion Fe 3+ Cr 3+ 、Cu 2+ 、Zn 2+ 、Zr 4+ One or more compounds, preferably Fe 3+ 、Cu 2+The compound is added in an amount of 0.02% to 0.5% of the mass of the treated initial residue. Preferably, the metal compound comprises one or more of FeCl3, CrCl3, CuCl2, ZnCl2, and ZrCl2.

[0033] Preferably, in step (4), the mass ratio of vanillic acid (VA) to alkyl chain-modified vanillic acid (M-VA) is 1:5 to 1:20.

[0034] Preferably, in step (5), the drying time is 60 to 400 minutes, and the drying temperature is 120 to 300° C. Preferably, the drying time is 100 to 150 minutes, and the drying temperature is 140 to 200° C.

[0035] The PTA product is obtained through filtration and drying, with a purity of over 99%, which can meet the standards for external sale.

[0036] Preferably, in the present invention, the synthesis reaction route of M-VA is as follows:

[0037]

[0038] VA, M-VA and Y n+ The formed complex network structure is shown below:

[0039]

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] (1) The present invention synthesizes a complex with adjustable hydrophobicity, which can achieve selective coating of terephthalic acid solid particles. The modified vanillic acid and metal ions form a strong intermolecular force with terephthalic acid after complexation, which greatly improves the flotation efficiency. It can not only be used for the recovery of terephthalic acid solids, but also for the capture of trace terephthalic acid in wastewater. The purity of PTA after final drying is greater than 99%, meeting the standard for external sale.

[0042] (2) The process is simple, energy-saving, and environmentally friendly. The alcohol washing-primary centrifugation-secondary flotation separation technology is used to achieve complete separation of MAA, PTA, and diatomaceous earth.

[0043] (3) Compared with traditional terephthalic acid recovery technology, it avoids the use of organic solvents and high-concentration acids and alkalis, has mild process conditions, high separation efficiency, and the raw materials can be recycled, which greatly reduces the discharge of salt-containing wastewater. It is a more green, environmentally friendly and sustainable process. DETAILED DESCRIPTION

[0044] The following is a clear and complete description of the technical solution of this patent in conjunction with the examples of this patent. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without making any creative work are within the scope of protection of this invention.

[0045] Source of raw materials: residue from the oxidation process of methyl methacrylate, its main components are 15% methacrylic acid, 60% terephthalic acid, 10% water, 5% diatomaceous earth, 9% maleic acid, 0.2% fumaric acid and less than 0.5% polymerization inhibitor, etc.

[0046] Example 1

[0047] (1) Residue pretreatment: 100 kg of oxidation residue was transported to the entrance of the alcohol washing tank via a conveyor belt, and methanol was added at a mass ratio of 5:1 to the residue. The mixture was stirred and dissolved at room temperature for 30 min at a speed of 200 rpm / min. The solid-liquid mixture was centrifuged and the filtrate was returned to the device for reuse. The filter cake A entered the next process step.

[0048] (2) Centrifugal separation: For the filter cake A in step (1), 100 kg of deionized water was added thereto to prepare a 50% slurry. After ultrasonic dispersion, the slurry was transferred to a centrifuge via a screw feeder. The speed was controlled at 500 r / min. 120 L of high-pressure water was added to the centrifuge at intervals of 10 s for a total of 5 times. The light phase (referred to as slurry B) flowing out of the centrifuge entered the next step.

[0049] (3) Preparation of alkyl chain-modified vanillic acid: A mixture of Cl2 and air was continuously introduced into 1 kg of n-dodecane, wherein the Cl2 mass concentration was 1%, the introduction time was 50 min, and the introduction rate was 120 L / min (the actual molar ratio of Cl2 to long-chain organic matter was 1:50), and the mixture was stirred at 60°C for 60 min to allow for sufficient reaction; 10 kg of 10 wt% vanillic acid solution was added, i.e., the molar ratio of vanillic acid to long-chain organic matter was 1:1, and the mixture was stirred at room temperature for 30 min to prepare alkyl chain-modified vanillic acid (M-VA);

[0050] (4) Separation of terephthalic acid: 2 kg of 10% FeCl3 solution was added to slurry B, and the pH was adjusted to 6.0. 170 g of 10 wt% vanillic acid solution and 830 g of alkyl chain-modified vanillic acid solution of the same concentration were added. The mixture was stirred thoroughly, and air was introduced into the slurry at a flow rate of 120 L / h. After a period of time, terephthalic acid (slurry C) was carried out of the flotation machine by the bubbles.

[0051] (5) Purification of terephthalic acid:

[0052] The pH of the terephthalic acid slurry obtained in step (4) was adjusted to 3.0, fully stirred, filtered, and dried at 120° C. for 60 min to obtain high-purity terephthalic acid with a purity of 99.3%.

[0053] Examples 2 to 11

[0054] According to the method of Example 1, 100 kg of methyl methacrylate oxidation residue was prepared and transported to the inlet of the alcohol washing tank via a conveyor belt, wherein:

[0055] In step (1), the residue is first pretreated, and the pretreatment conditions are changed to obtain treated residues A1 to A11, as shown in Table 1.

[0056] In step (2), the centrifugal separation conditions were changed to obtain slurries B1 to B11, as shown in Table 2.

[0057] In step (3), the preparation conditions for the preparation of alkyl chain-modified vanillic acid are shown in Table 3.

[0058] In step (4), the preparation process of the adjustable complexes C1 to C11 in the separation of terephthalic acid is shown in Table 4.

[0059] In step (5), the terephthalic acid purification process is to obtain the final terephthalic acid products P1 to P11, and the preparation conditions are shown in Table 5.

[0060] Table 1 Residue pretreatment conditions

[0061]

[0062]

[0063] Table 2 Centrifugal separation conditions, slurries B1 to B11

[0064]

[0065] Table 3 Preparation conditions of alkyl chain modified vanillic acid

[0066]

[0067] Table 4 Preparation process of adjustable complexes C1-C11 in terephthalic acid separation

[0068]

[0069] Table 5 Terephthalic acid purification process, that is, obtaining the final terephthalic acid products P1 to P11

[0070] Slurry C Purification pH Drying temperature / ℃ Drying time / min Terephthalic acid purity% Example 1 C1 6 120 120 99.3 Example 2 C2 6 150 300 99.5 Example 3 C3 6 120 400 99.6 Example 4 C4 4 200 240 99.3 Example 5 C5 4 250 60 98.7 Example 6 C6 2 300 60 98.9 Example 7 C7 2 120 300 97.3 Example 8 C8 2 240 180 97.3 Example 9 C9 6 240 210 99.8 Example 10 C10 6 150 300 99.1 Example 11 C11 4 300 210 98.1

Claims

1. A method for separating terephthalic acid from methyl methacrylate oxidation waste residue, characterized in that: The following steps are involved: (1) Residue pretreatment: The residue from the MMA oxidation process is washed with alcohol and filtered to obtain a treated residue A; (2) Centrifugal separation The residue after alcohol washing is added to water for ultrasonic dispersion, and then centrifuged. At the same time, a certain amount of high-pressure water is added to the centrifuge at regular intervals. The heavy phase settles quickly and the light phase flows out with the water. The light phase is recorded as slurry B. (3) Preparation of alkyl chain-modified vanillic acid Adding a halogen element or a halogenated hydrogen to a long-chain alkane organic substance, stirring at 30-90° C. for more than 60 minutes to fully react, thereby obtaining a halogenated long-chain alkane organic substance; mixing a certain amount of vanillic acid solution and the halogenated long-chain alkane organic substance, stirring and heating at 25-60° C. for 30-120 minutes, thereby preparing an alkyl chain-modified vanillic acid; the long-chain alkane organic substance in step (3) is a C8-C16 alkane or a C9-C13 aldehyde; (4) Separation of terephthalic acid Add the metal compound solution to slurry B, adjust the pH to 2.0-7.0, and stir thoroughly; A mixture of vanillic acid and alkyl chain-modified vanillic acid is added to the above slurry and stirred thoroughly. Vanillic acid, alkyl chain-modified vanillic acid and metal ions form a complex. Air is then introduced into the slurry, causing bubbling. Terephthalic acid moves in the direction of the bubbles and is carried out of the flotation machine, which is recorded as slurry C. The metal compound in step (4) is the metal ion Fe 3+ Cr 3+ 、Cu 2+ 、Zn 2+ 、Zr 4+ One or more compounds of (5) Purification of terephthalic acid: The pH of the obtained terephthalic acid slurry C is adjusted to 2.0-6.0 and stirred thoroughly. The complex structure thereof is automatically decomposed. After filtration and drying, high-purity terephthalic acid can be recovered. The remaining vanillic acid, alkyl chain-modified vanillic acid and metal ion solution can be returned to step (4) for recycling.

2. The separation method according to claim 1, wherein In the step (1), the residue from the MMA oxidation process is discharged from the MMA oxidation process filter and transported to the upper inlet of the alcohol washing tank via a belt. The upper part of the belt is sealed with a plastic cover to prevent volatile gas from escaping.

3. The separation method according to claim 1, characterized in that The main components of the residue from the MMA oxidation process in step (1) are 10-25% methacrylic acid, 40-70% terephthalic acid, 2-20% water, 0.5-5% diatomaceous earth, 2-9% maleic acid, 0.1-1% fumaric acid and less than 0.5% polymerization inhibitor.

4. The separation method according to claim 1, wherein The alcohol used for alcohol washing in step (1) is selected from one or more of methanol, ethanol, n-propanol, and isopropanol, the mass ratio of the alcohol used to the residue is 5:1 to 50:1, the stirring time is controlled at 30 to 120 minutes, and the rotation speed is controlled at 50 to 300 rpm / min.

5. The separation method according to claim 4, characterized in that The mass ratio of the amount of alcohol to the residue is 10:1 to 20:

1.

6. The separation method according to claim 1, characterized in that During the ultrasonic dispersion in step (2), the mass ratio of the alcohol-washed residue to water is 1:1 to 1:20, and the ultrasonic dispersion time is 30 to 120 minutes.

7. The separation method according to claim 6, characterized in that During the ultrasonic dispersion in step (2), the mass ratio of the alcohol-washed residue to water is 1:1 to 1:

5.

8. The separation method according to claim 1, characterized in that In step (2), the centrifugal speed is controlled at 200-500 r / min, the amount of high-pressure water added each time is 120-200 L, and the addition is performed once every 10-15 seconds, for a total of 1-5 times.

9. The separation method according to claim 1, characterized in that The long-chain alkane organic matter in step (3) is one or more of nonane, decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane or decanal, n-undecane, n-dodecanal, and tridecanal.

10. The separation method according to claim 1, characterized in that The halogen element or halogenated hydrogen is selected from one or more of Cl2, Br2, I2, HCl, HBr or HI.

11. The separation method according to claim 1, characterized in that The added molar amount of the halogen element or halogenated hydrogen is 0.02 to 1 times the molar amount of the halogenated long-chain alkane organic matter.

12. The separation method according to claim 1, characterized in that The molar ratio of the vanillic acid and the long-chain alkane organic matter added is 1:1 to 1:

10.

13. The separation method according to claim 1, characterized in that The metal compound in step (4) is the metal ion Fe 3+ 、Cu 2+ One or more compounds.

14. The separation method according to claim 1, characterized in that The amount of the metal compound added to the metal compound solution is 0.02% to 0.5% of the mass of the treated initial residue.

15. The separation method according to claim 1, characterized in that The metal compound is one or more of FeCl3, CrCl3, CuCl2, ZnCl2, and ZrCl2.

16. The separation method according to claim 1, characterized in that In step (4), the mass ratio of vanillic acid (VA) to alkyl chain-modified vanillic acid (M-VA) is 1:5 to 1:

20.

17. The separation method according to claim 1, characterized in that In step (5), the drying time is 60 to 400 minutes, and the drying temperature is 120 to 300°C.

18. The separation method according to claim 17, characterized in that In step (5), the drying time is 100 to 150 minutes, and the drying temperature is 140 to 200°C.

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