Method for preparing fumaric acid by treating maleic acid wastewater

Abstract

The invention belongs to the technical field of chemical wastewater treatment and recycling, and particularly relates to a method for preparing fumaric acid by treating maleic acid wastewater. The pretreated maleic acid wastewater passes through at least two stages of fixed bed reactors connected in series, the fixed bed reactors are filled with a thiourea supported catalyst, maleic acid is subjected to a continuous isomerization reaction, and a fumaric acid product is obtained. The thiourea supported catalyst takes mesoporous silica or alumina as a carrier, and thiourea groups are immobilized on the surface of the carrier through covalent bonds. The invention relates to an integrated system for realizing continuous catalytic reaction, intermediate product separation and efficient utilization of a catalyst by using a thiourea supported catalyst, and particularly relates to an integrated system for realizing continuous catalytic reaction, intermediate product separation and efficient utilization of the catalyst by using a multistage fixed bed reactor to catalyze epoxiconazole to produce maleic acid-containing wastewater through isomerization.

Description

Technical Field

[0001] This invention belongs to the field of chemical wastewater treatment and resource utilization technology, specifically relating to a method for treating maleic acid wastewater to prepare fumaric acid. Background Technology

[0002] Fluticasone is a highly effective triazole fungicide, but its production process generates a large amount of organic wastewater containing maleic acid. Maleic acid (cis-butenedioic acid) and fumaric acid (trans-butenedioic acid) are cis-trans isomers, but their economic values ​​differ significantly. Fumaric acid is widely used in the food, pharmaceutical, and resin synthesis industries, while maleic acid has a lower value.

[0003] The maleic acid to fumaric acid isomerization process uses thiourea as a catalyst. Thiourea is added to maleic acid wastewater for reaction. Thiourea remains in the wastewater after the reaction, requiring additional steps to treat the residual thiourea. Furthermore, the purity of fumaric acid is low due to the introduction of impurities during the separation process.

[0004] Other methods have the following problems: Liquid-phase thermal isomerization: Heating maleic acid aqueous solution at high temperature results in high energy consumption, low efficiency, and easy generation of by-products. Homogeneous catalysis: Using thiourea, hydrochloric acid, etc. as catalysts, it suffers from difficulties in catalyst separation, equipment corrosion, residual catalyst in wastewater, and high treatment costs. Traditional fixed-bed method: Although it can achieve continuous operation, the catalyst has low activity and is easily lost, especially for industrial wastewater with complex composition, exhibiting poor stability and incomplete resource recovery.

[0005] These methods all have significant shortcomings in industrial applications. Thiourea remains in the wastewater after the reaction, and because thiourea and its degradation products are difficult-to-treat nitrogen-containing organic compounds, this not only wastes catalyst but also increases the difficulty of wastewater treatment. In addition, single fixed-bed reactors are prone to reduced efficiency when treating high-concentration maleic acid wastewater due to localized catalyst blockage or saturation of active sites, resulting in limited single-stage reaction conversion rates and making continuous production impossible.

[0006] Therefore, developing a process that can operate continuously, has reusable catalysts, leaves no wastewater residue, and enables resource recovery is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the above problems, the purpose of this invention is to provide a method for treating maleic acid wastewater to prepare fumaric acid.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for treating maleic acid wastewater to produce fumaric acid involves passing pretreated maleic acid wastewater through at least two stages of fixed-bed reactors connected in series. The fixed-bed reactors are filled with a thiourea-supported catalyst, and maleic acid undergoes a continuous isomerization reaction to obtain fumaric acid product.

[0009]

[0010] The continuous isomerization reaction in the fixed-bed reactor was carried out at a temperature of 50℃-120℃, a pressure of atmospheric pressure-0.5MPa, and a liquid hourly space velocity of 0.5-3.0h. -1 .

[0011] The fixed-bed reactor consists of 2-4 stages connected in series, with the reaction temperature of each stage independently controllable, and the temperature of the first stage being higher than that of the subsequent stages. 2-3 stages connected in series are preferred. The preferred reaction temperature is 80℃.

[0012] The thiourea supported catalyst uses mesoporous silica or alumina as a support, and the thiourea groups are covalently fixed on the surface of the support, with a thiourea loading of 5%-15%.

[0013] The pretreatment of maleic acid wastewater involves extraction, light removal, and adsorption, with a maleic acid concentration of 10%-30%.

[0014] Maleic acid wastewater originates from the flutriafol production process.

[0015] The continuous isomerization reaction solution is crystallized to obtain fumaric acid product. The crystallization temperature of fumaric acid is 10℃-20℃. Part of the crystallization mother liquor is recycled, and the recycling rate of the crystallization mother liquor is 50%-80%.

[0016] A treatment and resource recovery system for preparing fumaric acid from maleic acid wastewater includes a pretreatment unit, a multi-stage fixed-bed reactor, a crystallization separation unit, a fumaric acid refining unit, and a mother liquor circulation pipeline.

[0017] When the reaction temperature is below 90℃, a filter needs to be installed after each stage of fixed-bed reactor to separate fumaric acid crystals.

[0018] The beneficial effects of this invention are: This invention utilizes a multi-stage fixed-bed reactor to catalyze the isomerization of maleic acid-containing wastewater containing flucyclotriazole to produce fumaric acid. In particular, it relates to an integrated system that uses a thiourea-supported catalyst to achieve continuous catalytic reaction, intermediate product separation, and efficient catalyst utilization.

[0019] This invention provides a multi-stage fixed-bed reactor that utilizes a fixed catalyst to catalyze isomerization reactions to convert maleic acid in industrial wastewater containing maleic acid produced during flutriafol production into fumaric acid, turning waste into a valuable resource and increasing economic benefits. This method employs a thiourea-supported catalyst and a multi-stage reaction-separation coupling system to achieve continuous catalytic reaction and in-situ product separation, improving catalyst utilization and reaction efficiency, reducing wastewater treatment difficulty and cost, achieving efficient conversion of maleic acid, high-yield recovery of fumaric acid, and long catalyst lifespan. It fundamentally reduces wastewater treatment difficulty and cost and recovers industrial fumaric acid through resource recovery. Specifically: 1. Catalyst Innovation: This is the first time that a thiourea-supported catalyst has been applied to the maleic acid isomerization reaction, solving the problems of difficult catalyst recovery, wastewater treatment difficulties, and environmental pollution caused by homogeneous catalysis. The thiourea-supported catalyst boasts high utilization and no residue: It avoids the loss of thiourea as in traditional homogeneous catalysis, with a single catalyst lifespan exceeding 1000 hours. The activity recovery rate after regeneration is high (>90%), and there is no thiourea residue at the wastewater effluent, significantly reducing the load on subsequent biochemical treatment.

[0020] 2. High fumaric acid recovery rate and reduced wastewater treatment costs: Maleic acid conversion rate >95%, fumaric acid selectivity >98%, product purity >98%. Mother liquor recycling reduces wastewater discharge by more than 60%.

[0021] 3. Continuous process and low energy consumption: The multi-stage fixed bed system enables continuous operation around the clock, and the energy consumption per unit product is reduced by about 30% compared with batch reactor.

[0022] 4. Process innovation: The design integrates multi-stage fixed-bed reactors in series with intermediate filtration separation, realizing continuous reaction-separation.

[0023] 5. Resource-based innovation: Pollutants in wastewater are converted into fumaric acid, a high-value-added product, thus realizing the resource utilization of waste.

[0024] 6. Environmental Innovation: Utilizing maleic acid from wastewater as a resource to produce high-value chemicals, this achieves a green circular economy model of "treating waste with waste and turning waste into treasure." It fundamentally solves the wastewater treatment problem in flutriafol production, achieving a COD removal rate of ≥98% and leaving no catalyst residue. Attached Figure Description

[0025] Figure 1 This is a flowchart of the process method of Embodiment 1 of the present invention. Detailed Implementation

[0026] Example 1 Fluticasone produced from maleic acid-containing wastewater to produce industrial fumaric acid (three-stage fixed bed system). Influent water quality: maleic acid concentration in the maleic acid-containing wastewater is 20.7%.

[0027] like Figure 1 The following is stated: 1) The maleic acid-containing wastewater from flutriafol production was heated to 96°C to remove light pollutants and then pretreated in a resin (LS-16G) adsorption tower to prepare a solution containing 18.3% maleic acid; COD=357600mg / L.

[0028] 2) Three fixed-bed reactors (25 mm inner diameter, 400 mm length) are connected in series, each filled with 100 g of thiourea immobilized catalyst.

[0029] 3) Preparation of thiourea supported catalyst: Weigh 100.0g of mesoporous silica SBA-15 (specific surface area 790m²) 2 Under nitrogen protection, 700 g of anhydrous toluene solution containing 20.0 g of 3-aminopropyltriethoxysilane was added, and the mixture was refluxed for 12 hours. After cooling, the mixture was filtered and washed with toluene to obtain an amino-functionalized support. This support was dispersed in an acetonitrile solution containing 15 g of phenyl isothiocyanate and stirred at 60 °C for 24 hours. After filtration, the support was washed successively with acetonitrile and water, and then dried under vacuum to obtain a thiourea-supported silica catalyst with a thiourea loading of approximately 10%.

[0030] 4) The feed flow rate is set to 60.0 g / h, the first stage reaction temperature is 83℃, the second stage is 74℃, the third stage is 69℃, and the system pressure is 0.3 MPa.

[0031] 5) The material passes through a filter between the first-stage and second-stage reactors to separate the generated crude solid fumaric acid. The liquid material in the separation transfer bottle is pumped into the second-stage reactor. (The maleic acid conversion rate at the outlet of the first-stage reactor reaches 60-70%, and after the first-stage intermediate filtration, about 40% of the fumaric acid crystals are separated).

[0032] The material is filtered between the second and third stage reactors to separate the generated crude solid fumaric acid. The liquid material in the separation transfer bottle is pumped into the third stage reactor. (The maleic acid conversion rate at the outlet of the second stage reactor reaches 85-90%. After secondary intermediate filtration, approximately 40% of the fumaric acid crystals are separated). The reaction liquid effluent from the third stage reactor is cooled to 21.3℃ for crystallization and filtration to obtain crude fumaric acid. The filtrate is then discharged into the biochemical wastewater. (The three-stage reactor completes the final conversion, with a total maleic acid conversion rate ≥96.8%. The remaining fumaric acid crystals are collected by the terminal separator.) Effluent quality: maleic acid concentration ≤1.0%; COD ≤2500mg / L; COD removal rate can reach over 98%.

[0033] After 24 hours of stable operation, samples were taken for analysis. The maleic acid conversion rate was 96.3%, and the fumaric acid selectivity was 99.2%.

[0034] The crude fumaric acid obtained by merging was added to process water, heated to reflux, cooled to 22.1℃, crystallized, filtered, and dried to obtain industrial fumaric acid product with a purity of 99.1% and a total recovery rate of 91.3%. The crystallization mother liquor was reused in the flutriafol maleic acid dissolution station.

[0035] The mother liquor was recycled, and the activity of the thiourea-supported silica catalyst remained above 88% for 500 hours of continuous operation without significant decline. No thiourea residue was detected in the effluent.

[0036] Economic benefits: 17.8 tons of industrial fumaric acid can be recovered for every 100 tons of wastewater treated.

[0037] Example 2 When the temperature is above 90℃, the solubility of fumaric acid in water is relatively high, and the intermediate filtration and separation of crude maleic acid in each reactor stage can be omitted. Specifically: 1) The maleic acid-containing wastewater from the flutriafol production in Example 1 was heated to 96°C for light removal and then pretreated in a resin (LS-16G) adsorption tower to prepare a solution containing 19.1% maleic acid; COD=369400mg / L.

[0038] 2) Three fixed-bed reactors (25 mm inner diameter, 400 mm length) are connected in series, each filled with 100 mL of thiourea immobilized catalyst.

[0039] 3) Preparation of thiourea supported catalyst: Weigh 100.0 g of γ-alumina (specific surface area 830 m²) 2 Under nitrogen protection, 700 g of anhydrous toluene solution containing 20.0 g of 3-aminopropyltriethoxysilane was added, and the mixture was refluxed for 12 hours. After cooling, the mixture was filtered and washed with toluene to obtain an amino-functionalized support. This support was dispersed in an acetonitrile solution containing 15 g of phenyl isothiocyanate and stirred at 60 °C for 24 hours. After filtration, the mixture was washed successively with acetonitrile and water, and then dried under vacuum to obtain a thiourea-supported alumina catalyst with a thiourea loading of approximately 10%.

[0040] 3) The feed flow rate is set to 60.0 g / h, the first stage reaction heating temperature is 112℃, the second stage is 102℃, the third stage is 98℃, and the system pressure is 0.5 MPa.

[0041] 4) The material sequentially passes through the first-stage reactor, the second-stage reactor, and the third-stage reactor. The reaction liquid effluent from the third-stage reactor is cooled to 20-25℃ for crystallization and filtration to obtain crude fumaric acid. The filtrate is then discharged into the biochemical wastewater. (The three-stage reactor completes the final conversion, with a total maleic acid conversion rate ≥95.7%. The remaining fumaric acid crystals are collected by the terminal separator.) Effluent quality: maleic acid content 0.3%; COD ≤3400mg / L; COD removal rate can reach over 98%.

[0042] After 24 hours of stable operation, samples were taken for analysis. The maleic acid conversion rate was 95.6%, and the fumaric acid selectivity was 99.1%.

[0043] The crude fumaric acid obtained by merging was added to process water, heated and refluxed, then cooled to 20-25℃ for crystallization, filtration, and drying to obtain industrial fumaric acid product with a purity of 99.0% and a total recovery rate of 91.2%. The crystallization mother liquor was reused in the flutriafol maleic acid dissolution station.

[0044] The mother liquor was recycled, and the activity of the thiourea-supported alumina catalyst remained above 85% for 500 hours of continuous operation without significant decline. No thiourea residue was detected in the effluent.

[0045] Economic benefits: 16.9 tons of industrial fumaric acid can be recovered for every 100 tons of wastewater treated; An experiment was conducted using maleic acid-containing wastewater from the industrial production of flutriafol. The results are as follows: Comparative Example 1: Conventional homogeneous thiourea catalysis The maleic acid-containing wastewater from the flutriafol production in Example 1 was heated to 96°C for light removal and then pretreated in a resin (LS-16G) adsorption tower to prepare a solution containing 19.1% maleic acid with a COD of 369,400 mg / L.

[0046] Then, 1.5% thiourea was added, with a COD of 399,100 mg / L, and the mixture was stirred at 100°C for 4 hours. The conversion rate was 94%, but the residual thiourea concentration in the wastewater after the reaction was 1.4%, and the maleic acid concentration was 1.1%; COD was 31,730 mg / L. After filtration, the purity of fumaric acid was only 97.3% due to the introduction of impurities during the separation process, and the total recovery rate was 89.1%.

[0047] Effluent water quality: maleic acid concentration 1.1%; COD=31730mg / L; COD removal rate can reach 92.1%.

[0048] As shown in Comparative Example 1, when thiourea is used to treat wastewater, it results in residual thiourea in the wastewater after the reaction, affecting both the conversion rate and purity of fumaric acid. Because thiourea is water-soluble and cannot be separated, residual thiourea remains in the wastewater, requiring additional treatment steps. The multi-stage fixed-bed reactor uses an immobilized thiourea catalyst, preventing thiourea loss and decomposition during the reaction. Therefore, no thiourea residue remains in the wastewater after the thiourea-supported catalyst reaction, resulting in a high maleic acid conversion rate, low COD in the treated wastewater, and the resulting wastewater can be used for biochemical treatment without further treatment.

[0049] In summary, the multi-stage fixed-bed reactor system provided by this invention successfully solves the key technical problems in the treatment of flutriafol maleic acid wastewater. Through the innovative design of fixed-bed thiourea supported catalyst and intermediate separation process, it achieves the triple goals of high-efficiency catalysis, product recovery, and wastewater treatment, and has significant environmental and economic benefits. It also has broad application prospects in the field of pesticide wastewater treatment and resource utilization.

Claims

1. A method for treating maleic acid wastewater to prepare fumaric acid, characterized in that, The pretreated maleic acid wastewater is passed through at least two fixed-bed reactors connected in series. The fixed-bed reactors are filled with thiourea-supported catalysts, and maleic acid undergoes a continuous isomerization reaction to obtain fumaric acid product.

2. The method for preparing fumaric acid from maleic acid wastewater according to claim 1, characterized in that, The temperature of the continuous isomerization reaction in the fixed-bed reactor is 50℃~120℃, the pressure is atmospheric pressure~0.5MPa, and the liquid flow rate is 50g / h~100g / h.

3. The method for preparing fumaric acid from maleic acid wastewater according to claim 1, characterized in that, The fixed-bed reactor consists of 2-4 stages connected in series, with the reaction temperature of each stage independently controllable, and the temperature of the first stage being higher than that of the subsequent stages. 2-3 stages connected in series are preferred. The preferred reaction temperature for the first stage is 80℃.

4. The method for treating maleic acid wastewater to prepare fumaric acid according to claim 1, characterized in that, The thiourea supported catalyst uses mesoporous silica or alumina as a support, and the thiourea groups are covalently fixed on the surface of the support, with a thiourea loading of 5%-15%.

5. The method for treating maleic acid wastewater to prepare fumaric acid according to claim 1, characterized in that, The pretreatment of maleic acid wastewater involves extraction, light removal, and adsorption, with a maleic acid concentration of 10%-30%.

6. The method for preparing fumaric acid from maleic acid wastewater according to claim 1, characterized in that, The continuous isomerization reaction solution is crystallized to obtain fumaric acid product. The crystallization temperature of fumaric acid is 10℃-20℃. Part of the crystallization mother liquor is recycled, and the recycling rate of the crystallization mother liquor is 50%-80%.

7. A processing and resource recycling system using the method of claim 1, characterized in that, It includes a pretreatment unit, a multi-stage fixed-bed reactor, a fumaric acid refining unit, and a mother liquor circulation pipeline.

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