Method for converting ultra-high concentration formaldehyde wastewater into formic acid solution

Abstract

The application discloses a method for converting ultra-high-concentration formaldehyde wastewater into formic acid solution, and comprises the following steps: S1, after heating formaldehyde wastewater, a pH regulator is added to obtain hot acidic formaldehyde wastewater; S2, after adding hydrogen peroxide, a metal catalyst and an organic acid inducer to the hot acidic formaldehyde wastewater in step S1 under ultraviolet light, the hot acidic formaldehyde wastewater is fully stirred to obtain formic acid solution. The application solves the problems of formaldehyde wastewater treatment efficiency, sewage treatment cost, formaldehyde wastewater treatment capacity and formaldehyde conversion selectivity.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and in particular relates to a method for converting ultra-high concentration formaldehyde wastewater into formic acid solution. Background Technology

[0002] Formaldehyde is a toxic and harmful chemical substance widely used in industries such as wood processing, textiles, and chemicals. However, the production process generates a large amount of formaldehyde wastewater, which, if not effectively treated, will cause serious environmental pollution.

[0003] Existing technological solutions: Current formaldehyde wastewater treatment technologies mainly include physicochemical methods, biological methods, and advanced oxidation methods. Physicochemical methods primarily use physical and chemical reactions to convert harmful substances in formaldehyde wastewater into harmless substances. Common physicochemical methods include coagulation sedimentation, air flotation, and activated carbon adsorption. Biological methods utilize the action of microorganisms to convert harmful substances in formaldehyde wastewater into harmless substances. Common biological methods include activated sludge and biofilm processes. Advanced oxidation methods utilize the generation of highly oxidizing free radicals to oxidize and decompose harmful substances in formaldehyde wastewater. Common advanced oxidation methods include the Fenton process and photocatalysis.

[0004] Existing technical problems: Although existing formaldehyde wastewater treatment technologies can effectively reduce the content of harmful substances in wastewater, these technologies suffer from the problem of metal catalyst passivation and deactivation when treating ultra-high concentration formaldehyde wastewater. Firstly, these technologies have low treatment efficiency for formaldehyde wastewater. Secondly, these technologies only treat low-concentration formaldehyde wastewater and cannot completely eliminate harmful substances in ultra-high concentration formaldehyde wastewater. Finally, these technologies require large amounts of chemical reagents and energy to treat ultra-high concentration formaldehyde wastewater, resulting in high costs. Therefore, how to efficiently and cost-effectively treat ultra-high concentration formaldehyde wastewater is a crucial problem currently facing this field. Summary of the Invention

[0005] Compared with existing technologies, this technical solution aims to solve the following technical problems:

[0006] 1. Solving the problem of formaldehyde wastewater treatment efficiency: Existing physicochemical, biological, and advanced oxidation methods have low treatment efficiency and long processing times when treating ultra-high concentration formaldehyde wastewater. This technical solution uses ultraviolet light in conjunction with Fenton to convert formaldehyde into formic acid, which can significantly improve the treatment efficiency of formaldehyde wastewater and efficiently and rapidly eliminate harmful substances in the wastewater.

[0007] 2. Solving the problem of formaldehyde wastewater treatment capacity: These technologies can only treat low-concentration formaldehyde wastewater. They cannot completely eliminate harmful substances in wastewater with ultra-high concentrations of formaldehyde. This technical solution can deeply and thoroughly treat ultra-high concentration formaldehyde wastewater.

[0008] 3. Reducing Treatment Costs: Existing formaldehyde wastewater treatment technologies require significant amounts of chemical reagents and energy to treat ultra-high concentration formaldehyde wastewater, resulting in high costs. This technology, through the synergistic effect of ultraviolet light irradiation and the Fenton reaction, greatly improves conversion efficiency, reducing the consumption of chemical reagents and energy, thereby lowering treatment costs.

[0009] 4. Solve the selectivity problem of formaldehyde to formic acid conversion: The oxidation system in the existing technology has poor selectivity and low formic acid conversion rate. In addition, it directly oxidizes aldehyde compounds into carbon dioxide and water, which wastes formic acid resources and cannot effectively recycle formic acid in high-concentration formaldehyde wastewater.

[0010] To solve the above problems, this application provides the following technical solution:

[0011] A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution includes the following steps:

[0012] S1. Formaldehyde wastewater is heated and a pH adjuster is added to obtain hot acidic formaldehyde wastewater.

[0013] S2. In step S1, hydrogen peroxide, a metal catalyst, and an organic acid inducer are added to the hot acidic formaldehyde wastewater under ultraviolet light, and then the mixture is stirred thoroughly to obtain a formic acid solution.

[0014] In step S1, the pH adjuster is a 2wt% NaOH solution, which is used to adjust the pH to 3-3.5.

[0015] In step S1, the formaldehyde wastewater is heated to 60~65℃.

[0016] In step S2, the ultraviolet wavelength is 254~282nm.

[0017] The metal catalyst in step S2 is one of ferrous sulfate, MnSO4@BC, or CuSO4@BC.

[0018] The organic acid inducer in step S2 is one of oxalic acid, tartaric acid, benzoic acid, and salicylic acid.

[0019] In step S2, the mass ratio of formaldehyde wastewater: hydrogen peroxide: metal catalyst: organic acid inducer is 1: 16%~20%: 0.02%~0.08%: 0.01%~0.03%.

[0020] The stirring time in step S2 is 0.25~2h.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1. High efficiency conversion: This invention uses ultraviolet-assisted Fenton technology to effectively convert ultra-high concentration formaldehyde wastewater into formic acid solution. The formaldehyde removal rate can reach more than 90% and the formic acid conversion rate can reach more than 90% within 2 hours, which has significant advantages over existing technologies.

[0023] 2. Strong processing capacity: This invention can completely eliminate harmful substances in ultra-high concentration formaldehyde wastewater with a formaldehyde concentration of 70,000-110,000 mg / L, and has a strong processing capacity.

[0024] 3. Low cost: The process of this invention only requires a small amount of chemical reagents and energy, resulting in low cost and a significant economic advantage compared to existing technologies.

[0025] 4. Strong adaptability: The technology of this invention has a wide range of adaptability to the treatment of ultra-high concentration formaldehyde wastewater. It can effectively treat wastewater regardless of the type and concentration of harmful substances it contains, and has a wider range of applications compared with existing technologies.

[0026] 5. Simple operation: The operation process of this invention is simple, easy to implement and control, and does not require complex equipment and processes. Compared with the prior art, it has higher operational convenience. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Unless otherwise specified, the formaldehyde concentration in the formaldehyde wastewater is 83866 mg / kg, the formic acid concentration is 290.00 mg / kg, and the remainder is water; the trace amounts of methanol in the formaldehyde wastewater are negligible, and the initial pH of the formaldehyde wastewater is 2.76.

[0028] In this invention, the hydrogen peroxide is prepared at a concentration of 30 wt%.

[0029] Example 1

[0030] A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution, the specific steps of which are as follows:

[0031] Step 1: Take 500g of formaldehyde wastewater into a three-necked flask.

[0032] Step 2: Control the reaction temperature to 30℃ and irradiate the formaldehyde wastewater with an ultraviolet light source with a wavelength of 254nm.

[0033] Step 3: Add 20 μL of 2% NaOH solution to adjust the pH of the solution to 2.85.

[0034] Step 4: Add hydrogen peroxide to the formaldehyde wastewater at a rate of 13% of the wastewater's mass; add ferrous sulfate to the formaldehyde wastewater at a rate of 0.08% of the wastewater's mass.

[0035] Step 5: The reaction time is 2 hours, with continuous stirring to ensure uniform reaction. The reaction solution is filtered, and the formaldehyde concentration in the supernatant is determined using the acetylacetone spectrophotometric method. The formaldehyde removal rate is calculated to be 60.01%.

[0036] Example 2

[0037] The methods and steps described in Example 1 were followed, with the temperatures changed to 50℃, 55℃, 60℃, 65℃, and 70℃ for the experiments. The results are shown in Table 1 below.

[0038] Table 1

[0039]

[0040] The formaldehyde removal rate first increases and then decreases with increasing temperature. This is because higher temperature accelerates the generation of •OH, which helps •OH react with formaldehyde and improves the oxidation effect. However, excessively high temperature will accelerate the decomposition of H2O2 into O2 and H2O, which is not conducive to the generation of •OH. Therefore, the preferred temperature is 60~65℃.

[0041] Example 3

[0042] Using the method and steps in Example 1, the temperature was changed to 65°C, and different amounts of regulators were added as shown in Table 2 below.

[0043] Table 2

[0044]

[0045] Formaldehyde removal rate initially increased and then decreased with increasing pH, mainly due to Fe... 2+ The form in which H2O2 exists differs at different pH levels.

[0046] In a strongly acidic environment with a pH ≤ 3, Fe 2+ It will produce [Fe(H2O)6] 2+ Fe 2+ As the amount of H₂O₂ decreases, the amount of •OH produced by catalysis also decreases. The complex ion produced under strongly acidic conditions significantly slows down the Fenton oxidation reaction. [H₂O₂] can also be generated from H₂O₂ under strongly acidic conditions. + Fe 2+ It is difficult to catalyze the formation of •OH from H2O2; [H3O2] + This will cause the target product, formic acid, to become unstable, and some of the formic acid will be directly oxidized and decomposed into carbon dioxide and water.

[0047] In a weakly acidic environment with pH 4 ≤, Fe 2+ It cannot effectively catalyze the oxidation of H2O2 to produce •OH, Fe 2+ It preferentially reacts with hydroxide ions (OH) in sodium hydroxide. - The combination produces [Fe(OH)] + And weakened Fe 2+ The catalytic ability decreases again, and the formaldehyde removal rate decreases again. Therefore, a pH of 3 to 3.5 is preferred.

[0048] Example 4

[0049] Following the method and steps in Example 1, the temperature was changed to 65°C, 200 μL of 2% NaOH solution was added to adjust the pH to 3.25, and the amount of ferrous sulfate was adjusted during the experiment. The results are as follows.

[0050] When ferrous sulfate was added at a concentration of 0.02 wt%, the formaldehyde removal rate was 91.02%.

[0051] When ferrous sulfate was added at a concentration of 0.04 wt%, the formaldehyde removal rate was 91.10%.

[0052] When ferrous sulfate was added at a concentration of 0.08 wt%, the formaldehyde removal rate was 91.18%.

[0053] When ferrous sulfate was added at a concentration of 0.10 wt%, the formaldehyde removal rate was 92.20%.

[0054] When ferrous sulfate was added at a concentration of 0.18 wt%, the formaldehyde removal rate was 92.30%.

[0055] Ferrous sulfate has almost no effect on the removal rate, while ultraviolet light irradiation can continuously promote the removal of Fe. 3+ To Fe 2+ Transformation, thereby achieving Fe 2+ with Fe 3+ The cycle between these components is as follows. The preferred dosage of ferrous sulfate is 0.02 wt% to 0.08 wt% of the formaldehyde wastewater mass. If too much ferrous sulfate is added, subsequent filtration is required, but the formaldehyde removal rate remains essentially unchanged.

[0056] Example 5

[0057] Following the method and steps in Example 1, the temperature was changed to 65℃, 200 μL of 2% NaOH solution was added to adjust the pH to 3.25, the amount of ferrous sulfate was changed to 0.08%, and the amount of hydrogen peroxide was adjusted for the experiment. The results are shown in Table 3 below.

[0058] Table 3

[0059]

[0060] The dosage of hydrogen peroxide has a significant impact on the removal rate. When the hydrogen peroxide dosage is 16 wt% to 20 wt% of the formaldehyde wastewater mass, the formaldehyde removal rate can reach over 95%, and the removal rate increases with increasing hydrogen peroxide dosage. This is because increasing the hydrogen peroxide dosage promotes the generation of •OH. However, when the hydrogen peroxide dosage exceeds 20 wt%, excessive •OH will oxidize and decompose the formic acid product into CO2 and H2O.

[0061] Example 6

[0062] A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution, the specific steps of which are as follows:

[0063] Step 1: Take 500g of formaldehyde wastewater into a three-necked flask.

[0064] Step 2: Control the reaction temperature to 65℃ and irradiate the formaldehyde wastewater with an ultraviolet light source at a wavelength of 254nm.

[0065] Step 3: Add 200μL of 2% NaOH solution to change the pH of the formaldehyde wastewater to 3.25.

[0066] Step 4: Add hydrogen peroxide to the formaldehyde wastewater at a rate of 20% of the formaldehyde wastewater mass; add ferrous sulfate to the formaldehyde wastewater at a rate of 0.04 wt% of the formaldehyde wastewater mass.

[0067] Step 5: The reaction time is 2 hours, during which the mixture should be stirred continuously to ensure a uniform reaction.

[0068] The reaction solution was filtered, and the supernatant was used to detect the formaldehyde concentration by acetylacetone spectrophotometry and the formic acid concentration by ion chromatography. The results showed that the removal rate of formaldehyde to formic acid was 98.10%, and the decomposition rate of formic acid was 3.67%.

[0069] Example 7

[0070] Brazilian iris, Latin name: Neomaricagracilis, also known as "horse butterfly flower" or "jade butterfly", is a plant of the genus Neomaricagracilis in the family Iridaceae. The Brazilian iris was purchased from Jiaxingyuan store, model: Brazilian Iris Orchid.

[0071] Preparation of manganese sulfate biochar, MnSO4@BC: 10g of Brazilian iris was chopped and dried at 60℃ for 24 h. Then, 1L of 10g / L MnSO4 aqueous solution was added, and the mixture was stirred at 100rpm for 24 h to obtain a homogeneous mixture. The mixture was placed in a crucible and thermally pyrolyzed in a muffle furnace under a N2 atmosphere. The temperature was increased to 900℃ at a rate of 17℃ / min, and the pyrolysis was carried out for 1 h. After natural cooling, the black powder obtained was taken out as crude biochar. 2g of crude biochar was weighed and added to 50 mL of 3mol / L NaOH solution. The mixture was stirred in an 80℃ water bath for 2 h, and filtered to obtain a solid filtrate. The solid filtrate was washed with distilled water until the pH was neutral, and then dried at 60℃ for 4 h until the sample was completely dry. After grinding, the sample was passed through a 100-mesh sieve to obtain the MnSO4@BC sample. The Mn content of the prepared MnSO4@BC was 15.0mg / g.

[0072] Preparation of copper sulfate biochar, CuSO4@BC: Compared with the preparation of manganese sulfate biochar, 1L of 10g / L MnSO4 aqueous solution was replaced with 1L of 10g / L CuSO4 aqueous solution, and other conditions remained unchanged. The Cu content in the obtained CuSO4@BC was 14.0mg / g.

[0073] Example 7-1

[0074] Compared with Example 6, the difference is that ferrous sulfate was replaced with 0.04 wt% manganese sulfate biochar (MnSO4@BC) composite catalyst; the degradation rate of formaldehyde was 96.59%, and the decomposition rate of formic acid was 3.31%.

[0075] Example 7-2

[0076] Compared with Example 6, the difference is that ferrous sulfate was replaced with 0.04 wt% copper sulfate biochar (CuSO4@BC) composite catalyst; the degradation rate of formaldehyde was 95.32%, and the decomposition rate of formic acid was 4.24%.

[0077] Example 8

[0078] Compared to Example 6, the difference lies in the addition of organic acid inducers, namely oxalic acid, tartaric acid, benzoic acid, and salicylic acid, to the system. The experimental results are as follows.

[0079] When 0.02 wt% oxalic acid was added and the mixture was stirred for 30 minutes, the formaldehyde removal rate was 96.32%.

[0080] When 0.02 wt% salicylic acid was added and the mixture was stirred for 30 minutes, the formaldehyde removal rate was 81.88%.

[0081] Oxalic acid or salicylic acid can improve the utilization rate of ultraviolet light in this system and shorten the reaction time of formaldehyde to formic acid. Adding oxalic acid or salicylic acid to the system is beneficial to shorten the reaction time and improve the formaldehyde removal efficiency.

[0082] When 0.02 wt% tartaric acid was added and the mixture was stirred for 30 minutes, the formaldehyde removal rate was 77.14%.

[0083] When 0.03 wt% benzoic acid was added and the mixture was stirred for 30 minutes, the formaldehyde removal rate was 65.26%.

[0084] Adding tartaric acid or benzoic acid to the system and shortening the reaction time to 30 minutes does not result in high removal efficiency.

[0085] Example 9

[0086] Compared to Example 6, the difference lies in the addition of 0.02 wt% oxalic acid in step four, and the experiment was conducted by changing the wavelength of the ultraviolet lamp. The results are as follows.

[0087] When the UV lamp wavelength is 206nm, and the reaction is stirred for 30 minutes, the formaldehyde removal rate is 87.47%.

[0088] When the UV lamp wavelength is 254nm and the reaction is stirred for 30 minutes, the formaldehyde removal rate is 96.32%.

[0089] When the UV lamp wavelength is 282nm, and the reaction is stirred for 30 minutes, the formaldehyde removal rate is 94.52%.

[0090] When the UV lamp wavelength is 468nm and the reaction is stirred for 30 minutes, the formaldehyde removal rate is 67.10%.

[0091] The preferred wavelength of ultraviolet light is 254~282nm. This is because H2O2 only significantly absorbs ultraviolet light with wavelengths below 300nm, but the shorter the wavelength of ultraviolet light, the weaker its penetrating ability in water will be, thus leading to a decrease in degradation efficiency.

[0092] Comparative Example 1-1

[0093] Compared to Example 1, the difference is that there was no ultraviolet light irradiation, and the formaldehyde removal rate was 44%.

[0094] Comparative Examples 1-2

[0095] Compared with Example 1, the difference is that ferrous sulfate was not added, and the formaldehyde removal rate of the water bath / H2O2 system was only 29%.

[0096] The above examples illustrate that this invention provides a method for converting ultra-high concentration formaldehyde wastewater into formic acid solution. Formaldehyde wastewater treated by this method can achieve a directional conversion into formic acid solution, solving the problems of high hazard, non-biodegradability, and high treatment costs associated with formaldehyde wastewater. Furthermore, the heterogeneous catalytic degradation technology of formaldehyde wastewater using transition metal-containing minerals and catalysts to activate H₂O₂, as well as general improved methods derived from this invention, can all be considered within the scope of protection of this invention.

Claims

1. A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution, characterized in that, Includes the following steps: S1. After heating the formaldehyde wastewater, a pH adjuster is added to adjust the pH to 3-3.5 to obtain hot acidic formaldehyde wastewater. S2. In step S1, hydrogen peroxide, a metal catalyst, and an organic acid inducer are added to the hot acidic formaldehyde wastewater under ultraviolet light and then stirred thoroughly to obtain a formic acid solution. In step S1, the formaldehyde wastewater is heated to 60~65℃; In step S2, the mass ratio of formaldehyde wastewater: hydrogen peroxide: metal catalyst: organic acid inducer is 1: 16%~20%: 0.02%~0.08%: 0.01%~0.03%. In step S2, the organic acid inducer is one of oxalic acid, tartaric acid, benzoic acid, and salicylic acid; The metal catalyst in step S2 is one of ferrous sulfate, MnSO4@BC or CuSO4@BC; Method for preparing MnSO4@BC or CuSO4@BC: 10g of Brazilian iris was chopped, dried at 60℃ for 24 h, and then 1L of 10g / L MnSO4 or CuSO4 aqueous solution was added. The mixture was stirred at 100rpm for 24 h to obtain a homogeneous mixture. The mixture was placed in a crucible and thermally decomposed in a muffle furnace under a N2 atmosphere. The temperature was increased to 900℃ at a rate of 17℃ / min and thermally decomposed for 1 h. After natural cooling, the black powder obtained was taken out as crude biochar. 2g of crude biochar was weighed and added to 50 mL of 3mol / L NaOH solution. The mixture was stirred in an 80℃ water bath for 2 h and filtered to obtain a solid filter. The solid filter was washed with distilled water until the pH was neutral and then dried at 60℃ for 4 h until the sample was completely dry. The sample was then ground and passed through a 100-mesh sieve to obtain the MnSO4@BC or CuSO4@BC sample.

2. The method for converting ultra-high concentration formaldehyde wastewater into formic acid solution according to claim 1, characterized in that, In step S1, the pH adjuster is a 2wt% NaOH solution.

3. The method for converting ultra-high concentration formaldehyde wastewater into formic acid solution according to claim 1, characterized in that, In step S2, the ultraviolet wavelength is 254~282nm.

4. The method for converting ultra-high concentration formaldehyde wastewater into formic acid solution according to claim 1, characterized in that, The stirring time in step S2 is 0.25~2h.

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