Simple vanillin wastewater treatment method

Abstract

The invention relates to a vanillin wastewater treatment process. The vanillin wastewater treatment process comprises ultraviolet (UV) oxidation and sodium sulfate crystallization. The novel soluble titanate catalyst is synthesized and is matched with the hydrogen peroxide and the UV for use, so that the decomposition efficiency of phenolic substances can be greatly improved, and COD in the vanillin wastewater can be basically and completely removed after the vanillin wastewater is subjected to ultraviolet oxidation (UV). Inorganic salt in the waste water is removed by adopting a sodium sulfate crystallization process, the residual water is continuously recycled, and the dried sodium sulfate is sold, so that waste is turned into wealth, and no waste water is discharged.

Description

Technical Field

[0001] The invention belongs to the field of phenol-containing wastewater treatment, and specifically relates to a highly efficient ultraviolet oxidation method, and the method is used for treating vanillin wastewater. Background Art

[0002] Vanillin, also known as vanillin, has a strong milky aroma and is mainly used as a food additive and pharmaceutical intermediate. It is known as the king of edible spices. The current mainstream process routes are synthesized using glyoxylic acid and guaiacol as raw materials. The route includes steps such as glyoxylic acid condensation, mandelic acid oxidation, acid decarboxylation, distillation crystallization and wastewater treatment. Although the reaction conditions of this process are mild, the biggest problem is the huge amount of wastewater. The production of one ton of vanillin produces about 40 tons of phenolic wastewater, and the wastewater has the characteristics of high salt content and high COD. The average COD of the wastewater is about 10,000-20,000, and the sodium sulfate content in the wastewater is about 10-15%. How to simply, efficiently and cost-effectively treat vanillin wastewater has become an unstable factor restricting the production of vanillin.

[0003] In order to treat high-concentration COD vanillin wastewater, patent CN110590037A discloses a treatment process for vanillin production wastewater. Vanillin wastewater undergoes iron-carbon reaction, oxidation reaction, complex reaction and MVR concentration evaporation, etc., which can effectively reduce the COD and salt content in the wastewater; however, this method has a long process flow, cumbersome operation, and a large amount of acid, alkali, oxidant, etc. must be added during the reaction, and the entire wastewater treatment cost is high. Patent CN101580319A discloses a wastewater treatment technology for synthesizing vanillin by glyoxylic acid method. This method uses macroporous resin to adsorb wastewater, and can selectively adsorb more than 95% of aromatic compounds in wastewater to the resin surface, and the remaining wastewater is treated by Fe / C oxidation technology. Although the above method can effectively remove or recover phenolic derivatives, the traditional biochemical and oxidation treatment process is still used for subsequent wastewater. For the glyoxylic acid process with a huge amount of wastewater, its treatment cost is high and it is difficult to meet the discharge standards. Patent CN106630297A discloses a wet catalytic oxidation treatment method for vanillin production wastewater. After the vanillin production wastewater is treated by macroporous resin adsorption, the less polar organic matter in the wastewater is adsorbed onto the resin, the desorbed wastewater is mixed with a small amount of formaldehyde for reaction, and after filtering to remove the polymer, the CODCr of the wastewater is reduced to below 500 mg / L by a wet oxidation method. Although this method is relatively simple, the overall equipment investment of the wet oxidation method is relatively high, the cost of wastewater treatment remains high, and the final high-salt wastewater is still difficult to treat. Summary of the invention

[0004] In order to reduce the treatment cost of vanillin wastewater, the present invention proposes a new wastewater treatment scheme, in which the COD in the vanillin wastewater is removed by ultraviolet oxidation (UV), and then the inorganic salts in the wastewater are removed by sodium sulfate crystallization process, the remaining water is continuously reused, and the dried sodium sulfate can be sold, thus turning waste into treasure without discharging wastewater.

[0005] The present invention adopts the following technical solutions:

[0006] The first aspect of the present invention provides a catalyst that can be used in ultraviolet catalytic treatment of vanillin wastewater. The catalyst is a soluble titanate catalyst, and the structure is as follows:

[0007]

[0008] Wherein, R1 is H or an alkyl group having 1 to 3 carbon atoms.

[0009] Another aspect of the present invention provides a method for preparing the above catalyst.

[0010] A method for preparing the catalyst comprises the following steps:

[0011] Step 1: After stirring and refluxing the solvent containing catechol, titanate is added and the reaction is continued for 3-5 hours.

[0012] Step 2: Add a benzoic acid derivative to the above reaction solution, and after a certain reaction time, obtain a soluble titanate derivative, which is the catalyst.

[0013] The synthetic route is as follows:

[0014]

[0015] In step (1) of the present invention, the solvent is one of water, acetone, DMF, and DMSO, preferably water or DMF;

[0016] Preferably, the mass ratio of catechol to solvent is 1:(3-10), and the preferred mass ratio is 1:(5-8).

[0017] In step (1) of the present invention, the titanate is preferably one of tetraethyl titanate, tetrabutyl titanate, and tetraisopropyl titanate;

[0018] Preferably, the mass ratio of titanate to catechol is (1-8):1, and the preferred mass ratio is (3-5):1.

[0019] In step (1) of the present invention, the reaction temperature is 50-180°C, and the preferred reaction temperature is 80-120°C.

[0020] The reaction in step (1) of the present invention is preferably carried out in a nitrogen atmosphere.

[0021] After the reaction of step (1) of the present invention is completed, the reaction solution does not need to be separated and can be directly subjected to the next reaction.

[0022] In step (2) of the present invention, the benzoic acid derivative is one of benzoic acid, p-toluic acid, p-ethylbenzoic acid, and p-propylbenzoic acid;

[0023] Preferably, the mass ratio of the benzoic acid derivative to catechol is (0.8-2.5):1, and the preferred mass ratio is (1-1.4):1.

[0024] In step (2) of the present invention, the reaction temperature is 80-200°C, and the preferred reaction temperature is 100-150°C.

[0025] The reaction time of step (2) of the present invention is 1-3h.

[0026] After the reaction in step (2) of the present invention is completed, the reaction solution is cooled to room temperature, and the solvent and small molecular substances are removed by reduced pressure distillation to obtain a catalyst.

[0027] The invention also relates to the application of the catalyst in treating vanillin wastewater.

[0028] A process for treating vanillin wastewater, including an ultraviolet oxidation process and a sodium sulfate crystallization process, specifically comprising:

[0029] (1) Vanillin wastewater, catalyst and hydrogen peroxide are mixed and then enter the ultraviolet oxidation process to remove COD in the wastewater;

[0030] (2) Use sodium sulfate crystallization process to remove inorganic salts from wastewater.

[0031] In the method of the present invention, the vanillin wastewater refers to the vanillin wastewater produced by the guaiacol and glyoxylic acid synthesis process, the COD of the wastewater is about 10000-20000, the sodium sulfate content in the wastewater is about 10-15%, the color is black or brown, and the main impurities are vanillin, vanillic acid, o-vanillin, vanillin dimer, guaiacol, etc.

[0032] In step (1), the concentration of hydrogen peroxide is 27.5%-50%;

[0033] Vanillin wastewater: hydrogen peroxide: catalyst mass ratio = 1: (0.04-0.15): (0.00005-0.0003).

[0034] In the ultraviolet oxidation process of the present invention, the suitable pH value is 1-6, and the preferred pH value is 2-4.

[0035] In the ultraviolet oxidation process of the present invention, the reaction temperature is 40-80° C. and the residence time is 5-24 hours.

[0036] In the ultraviolet oxidation process of the present invention, the ultraviolet light source is an ultraviolet lamp, and the reaction process is completed under the irradiation of the ultraviolet lamp.

[0037] In the crystallization process of the present invention, the temperature needs to be controlled at -5 to 15°C, preferably 0 to 10°C.

[0038] In the crystallization process of the present invention, a large amount of inorganic salt is precipitated in the form of mirabilite (sodium sulfate decahydrate), and a centrifugal device is used for solid-liquid separation and washing. The sodium sulfate content of the wastewater mother liquor after separation is about 2-6%.

[0039] The washed thenardite is heated to 30-60°C, and then the thenardite is slowly dehydrated to obtain anhydrous sodium sulfate. The preferred heating temperature is 32°C-40°C. The anhydrous sodium sulfate can be dried and then sold.

[0040] After treatment by this method, the COD of vanillin wastewater can be reduced to below 100 ppm and can be reused as process water.

[0041] Beneficial effects achieved by the technical solution of the present invention:

[0042] The invention proposes an efficient treatment method for vanillin wastewater, which only includes two major processes, namely ultraviolet oxidation and sodium sulfate crystallization, to achieve harmless treatment of high-salt, high-COD vanillin wastewater. The wastewater can be reused, truly achieving zero emission. The whole process is simple in process flow, high in resource utilization, low in device investment, and a certain amount of sodium sulfate product is produced as a by-product, thus turning waste into treasure.

[0043] The present invention proposes a new soluble titanate catalyst, which has good water solubility, so that the active component titanium ion of the catalyst can better contact with hydrogen peroxide, and under the action of ultraviolet light source, the hydrogen peroxide is decomposed into hydroxyl free radicals with strong oxidizing ability. In addition, the new titanate catalyst contains a large aromatic group, which can form a certain spatial effect, can highly selectively consume phenolic substances in wastewater, and can greatly improve the removal efficiency of phenolic substances. DETAILED DESCRIPTION

[0044] The following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the rights claimed by the present invention.

[0045] Vanillin wastewater: Wanhua Chemical Vanillin Plant;

[0046] Test method and instrument: COD: Spectrophotometry: In an acidic solution, reducing substances react with potassium dichromate to generate trivalent chromium ions, and the COD value is calculated by measuring the absorbance of trivalent chromium.

[0047] UV oxidation reactor: CME-RPR-100 UV from Zhongke Micro Energy.

[0048] Example 1

[0049] Catalyst preparation: Under nitrogen atmosphere, add 50g of catechol and 250g of water to a three-necked flask, turn on stirring, heat to 100°C, add 350g of tetrabutyl titanate to the reaction bottle, and react for 3h. Then add 60g of benzoic acid to the three-necked flask, continue to react for 2h, cool down, and stop the reaction. The small molecules in the reaction solution are removed by vacuum distillation to obtain a titanate catalyst. The catalyst was subjected to nuclear magnetic resonance analysis, and the H spectrum results are as follows: 6.78 (2H), 6.84 (2H), 7.66 (4H), 7.79 (2H), 8.21 (4H).

[0050] Wastewater treatment: Take 10kg of vanillin wastewater, its COD is 12569ppm, sodium sulfate content is 12.5%, color is black, and pH is 4.

[0051] 10kg of vanillin wastewater was mixed with 500g of hydrogen peroxide (27.5%) and 1g of titanate catalyst, heated to 60°C and put into the ultraviolet oxidation reactor. The ultraviolet lamp was turned on. After about 6 hours of reaction, the color of the wastewater dropped to colorless and transparent, and its COD was measured to be 85.4ppm. The wastewater was cooled to 2°C, and a large amount of sodium sulfate solid was precipitated. After centrifugation, separation and washing, the solid was heated to 40°C to obtain anhydrous sodium sulfate solid. The crystallized mother liquor was reused, and the sodium sulfate concentration was 4.3%, which was used as process water for vanillin reaction.

[0052] Example 2

[0053] Catalyst preparation: In a nitrogen atmosphere, add 50g of catechol and 450g of acetone to a three-necked flask, turn on stirring, heat to 100°C, add 200g of tetraethyl titanate to the reaction bottle, and react for 3h. Then add 120g of p-methylbenzoic acid to the three-necked flask, continue to react for 1.5h, cool down, and stop the reaction. Remove small molecules in the reaction solution by vacuum distillation to obtain a titanate catalyst.

[0054] Wastewater treatment: Take 10kg of vanillin wastewater, its COD is 18954ppm, sodium sulfate content is 11%, color is black, and pH is 3.

[0055] 10kg of vanillin wastewater was mixed with 1000g of hydrogen peroxide (27.5%) and 2g of titanate catalyst, heated to 45°C and put into the ultraviolet oxidation reactor. The ultraviolet lamp was turned on. After about 22 hours of reaction, the color of the wastewater dropped to colorless and transparent, and its COD was measured to be 66.4ppm. The wastewater was cooled to 12°C, and a large amount of sodium sulfate solid was precipitated. After centrifugation, separation and washing, the solid was heated to 35°C to obtain anhydrous sodium sulfate solid. The crystallized mother liquor was reused, and the sodium sulfate concentration was 5.6%, which was used as process water for vanillin reaction.

[0056] Example 3

[0057] Catalyst preparation: In a nitrogen atmosphere, add 50g of catechol and 180g of DMF to a three-necked flask, start stirring, heat to 80°C, add 90g of tetraisopropyl titanate to the reaction bottle, and react for 5h. Then add 50g of p-propylbenzoic acid to the three-necked flask, continue to react for 2.5h, cool down, and stop the reaction. Remove small molecules in the reaction solution by vacuum distillation to obtain a titanate catalyst.

[0058] Wastewater treatment: Take 10kg of vanillin wastewater, its COD is 15540ppm, sodium sulfate content is 14.2%, color is brown, and pH is 5.

[0059] 10kg of vanillin wastewater was mixed with 1200g of hydrogen peroxide (27.5%) and 1.5g of titanate catalyst, heated to 70°C and put into the ultraviolet oxidation reactor. The ultraviolet lamp was turned on. After about 8 hours of reaction, the color of the wastewater dropped to colorless and transparent, and its COD was measured to be 51.5ppm. The wastewater was cooled to 5°C, and a large amount of sodium sulfate solid was precipitated. After centrifugation, separation and washing, the solid was heated to 38°C to obtain anhydrous sodium sulfate solid. The crystallized mother liquor was reused, and the sodium sulfate concentration was 5.3%, which was used as process water for vanillin reaction.

[0060] Comparative Example 1

[0061] Wastewater treatment: Take 10kg of vanillin wastewater, its COD is 15540ppm, sodium sulfate content is 14.2%, color is brown, and pH is 5.

[0062] After mixing 10kg of vanillin wastewater and 1200g of hydrogen peroxide (27.5%), the temperature was raised to 70°C and entered into the ultraviolet oxidation reactor. The ultraviolet lamp was turned on. After about 8 hours of reaction, the COD of the wastewater was 2213.2ppm. The wastewater was cooled to 5°C, and a large amount of sodium sulfate solid was precipitated. After centrifugation, separation and washing, the solid was heated to 38°C to obtain anhydrous sodium sulfate solid. The crystallized mother liquor was reused, and the sodium sulfate concentration was 5.3%.

[0063] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A soluble titanate catalyst, the structure of which is shown below: in, R1 is H or an alkyl group having 1 to 3 carbon atoms.

2. A method for preparing the catalyst according to claim 1, comprising the following steps: Step 1: After stirring and refluxing the solvent containing catechol, titanate is added to continue the reaction; Step 2: adding a benzoic acid derivative to the above reaction solution to obtain the catalyst after reaction; The synthetic route is as follows:

3. The method according to claim 2, wherein: In step (1), the solvent is one of water, acetone, DMF, and DMSO, preferably water or DMF; Preferably, the mass ratio of catechol to solvent is 1:(3-10), preferably 1:(5-8).

4. The method according to claim 2, wherein: In step (1), the titanate is one of tetraethyl titanate, tetrabutyl titanate, and tetraisopropyl titanate; Preferably, the mass ratio of titanate to catechol is (1-8):1, and the preferred mass ratio is (3-5):

1.

5. The method according to any one of claims 2 to 4, wherein: In step (1), the reaction temperature is 50-180°C, preferably 80-120°C.

6. The method according to any one of claims 2 to 4, wherein: In step (2), the benzoic acid derivative is one of benzoic acid, p-toluic acid, p-ethylbenzoic acid, and p-propylbenzoic acid; Preferably, the mass ratio of the benzoic acid derivative to catechol is (0.8-2.5):1, preferably (1-1.4):

1.

7. The method according to any one of claims 2 to 6, wherein: In step (2), the reaction temperature is 80-200°C, preferably 100-150°C, and the reaction time is 1-3h.

8. A process for treating vanillin wastewater, comprising: (1) Vanillin wastewater, catalyst and hydrogen peroxide are mixed and then enter the ultraviolet oxidation process to remove COD in the wastewater; The catalyst is the catalyst according to claim 1; (2) Use sodium sulfate crystallization process to remove inorganic salts from wastewater.

9. The process according to claim 8, wherein: In step (1), the vanillin wastewater refers to the vanillin wastewater produced by the guaiacol and glyoxylic acid synthesis process, wherein the COD of the wastewater is 10,000-20,000 and the sodium sulfate content of the wastewater is 10-15%; In step (1), the concentration of hydrogen peroxide is 27.5%-50%; Preferably, the mass ratio of vanillin wastewater: hydrogen peroxide: catalyst = 1: (0.04-0.15): (0.00005-0.0003); Preferably, the reaction temperature is 40-80°C and the residence time is 5-24h; Preferably, the ultraviolet light source is an ultraviolet lamp.

10. The process according to claim 8, wherein: In step (2), the temperature is controlled at -5 to 15°C, preferably at 0 to 10°C.

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