Method for converting ultrahigh-concentration formaldehyde wastewater into formic acid solution

Abstract

The invention discloses a method for converting ultrahigh-concentration formaldehyde wastewater into a formic acid solution, which comprises the following steps: S1, heating formaldehyde wastewater, and adding a pH regulator to obtain hot acidic formaldehyde wastewater; s2, adding hydrogen peroxide, a metal catalyst and an organic acid inducer into the hot acidic formaldehyde wastewater in the step S1 under ultraviolet, and fully stirring to obtain a formic acid solution. The invention solves the problem of formaldehyde wastewater treatment efficiency, the problem of sewage treatment cost, the problem of formaldehyde wastewater treatment capacity and the problem of selectivity of conversion from formaldehyde to formic acid.

Description

Technical Field

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

[0002] Formaldehyde is a toxic and harmful chemical substance, which is widely used in wood processing, textile, chemical and other industries. However, a large amount of formaldehyde wastewater will be generated in the production process, which will cause serious pollution to the environment if it is not effectively treated.

[0003] Solutions of existing technologies: Existing formaldehyde wastewater treatment technologies mainly include physical and chemical methods, biological methods, advanced oxidation methods, etc. The physical and chemical method mainly converts harmful substances in formaldehyde wastewater into harmless substances through physical and chemical reactions. Common physical and chemical methods include coagulation and sedimentation method, flotation method, activated carbon adsorption method, etc. The biological method converts harmful substances in formaldehyde wastewater into harmless substances through the action of microorganisms. Common biological methods include activated sludge method, biofilm method, etc. The advanced oxidation method oxidizes and decomposes harmful substances in formaldehyde wastewater by generating strongly oxidizing free radicals. Common advanced oxidation methods include Fenton method, photocatalysis method, etc.

[0004] Problems with existing technologies: Although existing formaldehyde wastewater treatment technologies can effectively reduce the content of harmful substances in wastewater, these technologies have the problem of metal catalyst passivation and deactivation when treating ultra-high concentration formaldehyde wastewater. First, these technologies have low treatment efficiency for formaldehyde wastewater. Secondly, these technologies treat formaldehyde wastewater with lower concentrations, and cannot completely eliminate harmful substances in the wastewater when treating ultra-high concentration formaldehyde wastewater. Finally, these technologies consume a large amount of chemical reagents and energy when treating ultra-high concentration formaldehyde wastewater, and the cost is relatively high. Therefore, how to treat ultra-high concentration formaldehyde wastewater efficiently and at low cost is an important issue currently facing this field. Summary of the invention

[0005] Compared with the prior art, this technical solution aims to solve the following technical problems: 1. Solve the problem of formaldehyde wastewater treatment efficiency: Existing physical and chemical methods, biological methods, advanced oxidation methods and other technologies have low treatment efficiency and long treatment time when treating ultra-high concentration formaldehyde wastewater. This technical solution converts formaldehyde into formic acid through ultraviolet assisted Fenton, which can significantly improve the treatment efficiency of formaldehyde wastewater and eliminate harmful substances in wastewater efficiently and quickly.

[0006] 2. Solve the problem of the ability to treat formaldehyde wastewater: These technologies treat formaldehyde wastewater with lower concentrations. When treating ultra-high concentration formaldehyde wastewater, they cannot completely eliminate harmful substances in the wastewater. This technical solution can deeply and thoroughly treat ultra-high concentration formaldehyde wastewater.

[0007] 3. Reduce treatment costs: Existing formaldehyde wastewater treatment technologies consume a lot of chemical reagents and energy when treating ultra-high concentration formaldehyde wastewater, which is very costly. This technical solution greatly improves the conversion efficiency through the synergistic effect of ultraviolet light irradiation and Fenton reaction, which can reduce the consumption of chemical reagents and energy, thereby reducing treatment costs.

[0008] 4. Solve the selectivity problem of formaldehyde conversion to formic acid: The oxidation system in the prior art has poor selectivity and low formic acid conversion rate, and 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.

[0009] In order to solve the above problems, the present application is implemented through the following technical solutions: A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution comprises the following steps: S1. After the formaldehyde wastewater is heated, a pH regulator is added to obtain hot acidic formaldehyde wastewater; S2. Add hydrogen peroxide, a metal catalyst and an organic acid inducer to the hot acidic formaldehyde wastewater in step S1 under ultraviolet light and stir the mixture sufficiently to obtain a formic acid solution.

[0010] In step S1, the pH adjuster is a 2 wt % NaOH solution, and the pH is adjusted to 3-3.5.

[0011] In step S1, the formaldehyde wastewater is heated to 60-65°C.

[0012] In step S2, the ultraviolet wavelength is 254-282 nm.

[0013] The metal catalyst in step S2 is ferrous sulfate, MnSO 4 @BCorCu 2 SO 4 @BC one of a kind.

[0014] In step S2, the organic acid inducer is one of oxalic acid, tartaric acid, benzoic acid and salicylic acid.

[0015] In the step S2, the mass ratio is: formaldehyde wastewater: hydrogen peroxide: metal catalyst: organic acid inducer = 1: 16%~20%: 0.02%~0.08%: 0.01%~0.03%.

[0016] The stirring time in step S2 is 0.25-2h.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. Efficient conversion: The present invention adopts ultraviolet synergistic Fenton technology, which can effectively convert ultra-high concentration formaldehyde wastewater into formic acid solution. The formaldehyde removal rate can reach more than 90% within 2 hours, and the formic acid conversion rate can reach more than 90%. Compared with the existing technology, it has significant advantages.

[0018] 2. Strong processing capability: The present 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 capability.

[0019] 3. Low cost: In the process of the present invention, only a small amount of chemical reagents and energy are consumed, and the cost is low. Compared with the existing technology, it has obvious economic advantages.

[0020] 4. Strong adaptability: The technology of the present invention has wide adaptability to the treatment of ultra-high concentration formaldehyde wastewater. No matter what the type and concentration of harmful substances contained in the wastewater are, it can be effectively treated. Compared with the existing technology, it has a wider range of applications.

[0021] 5. Simple operation: The operation process of the present invention is simple, easy to implement and control, does not require complicated equipment and processes, and has higher operational convenience compared to the prior art. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail in conjunction with the following examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Unless otherwise specified, the formaldehyde mass 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 methanol contained in the formaldehyde wastewater is negligible, and the initial pH of the formaldehyde wastewater is 2.76.

[0023] In the present invention, the hydrogen peroxide is prepared at 30wt%.

[0024] Example 1 A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution, the specific steps are as follows: Step 1: Take 500g of formaldehyde wastewater into a three-necked flask.

[0025] Step 2: Control the reaction temperature to 30°C and irradiate the formaldehyde wastewater with an ultraviolet light source with an ultraviolet wavelength of 254nm.

[0026] Step 3: Add 20 μL of 2% NaOH solution to adjust the solution pH to 2.85.

[0027] Step 4: adding hydrogen peroxide to the formaldehyde wastewater in an amount of 13% of the mass of the formaldehyde wastewater; adding ferrous sulfate to the formaldehyde wastewater in an amount of 0.08% of the mass of the formaldehyde wastewater.

[0028] Step 5: The reaction time is 2 hours, and stirring is continued during the reaction to ensure uniform reaction. The reaction solution is filtered, and the supernatant is taken to detect the formaldehyde concentration by acetylacetone spectrophotometry. The formaldehyde removal rate is calculated to be 60.01%.

[0029] Example 2 The method and steps in Example 1 were used to perform experiments at temperatures of 50°C, 55°C, 60°C, 65°C, and 70°C. The results are shown in Table 1. Table 1

[0030] The formaldehyde removal rate shows a trend of first increasing and then decreasing with the increase of temperature. This is because the increase of temperature will accelerate the generation rate of •OH, which is conducive to the reaction of •OH with formaldehyde and improves the oxidation effect. However, too high a temperature will accelerate the generation of H 2 O 2 Decompose into O 2 and H 2 O is not conducive to the formation of •OH, so the preferred temperature is 60~65℃.

[0031] Example 3 The method and steps in Example 1 were used, the temperature was changed to 65° C., and different amounts of regulators were added, as shown in Table 2 below.

[0032] Table 2

[0033] The formaldehyde removal rate showed a trend of first increasing and then decreasing with the increase of pH, which was mainly attributed to the Fe 2+ and H 2 O 2 The existence form is different at different pH.

[0034] In a strongly acidic environment with a pH value of ≤3, Fe 2+ It will produce [Fe(H 2 O) 6 ] 2+ , Fe 2+ The amount of catalytic H 2 O 2 The amount of •OH produced also decreases. This complex ion produced under strong acidic conditions greatly reduces the rate of Fenton oxidation reaction. 2 O 2 [H 3 O 2] + , Fe 2+ Difficult to catalyze H 2 O 2 Generate •OH; [H 3 O 2 ] + This will cause the target product formic acid to be unstable, and part of the formic acid will be directly oxidized and decomposed into carbon dioxide and water.

[0035] In a weakly acidic environment of pH 4 ≤, Fe 2+ Cannot effectively catalyze the oxidation of H 2 O 2 Produce •OH, Fe 2+ Preferentially reacts with the hydroxide ions OH in sodium hydroxide - Combined to produce [Fe(OH)] + The Fe 2+ The catalytic ability and formaldehyde removal rate decrease again, therefore, the preferred pH value is 3~3.5.

[0036] Example 4 The method and steps in Example 1 were used, the temperature was changed to 65°C, 200 μL of 2% NaOH solution was added to change the pH to 3.25, and the amount of ferrous sulfate was adjusted to conduct the experiment. The results are as follows: When the amount of ferrous sulfate added was 0.02 wt %, the formaldehyde removal rate was 91.02%; When the amount of ferrous sulfate added was 0.04 wt %, the formaldehyde removal rate was 91.10%; When the amount of ferrous sulfate added was 0.08 wt %, the formaldehyde removal rate was 91.18%; When the amount of ferrous sulfate added was 0.10 wt %, the formaldehyde removal rate was 92.20%; When the amount of ferrous sulfate added was 0.18 wt %, the formaldehyde removal rate was 92.30%; Ferrous sulfate has almost no effect on the removal rate, and ultraviolet light irradiation can continuously promote the removal of Fe 3+ Fe 2+ Conversion to achieve Fe 2+ with Fe 3+ The preferred amount of ferrous sulfate added is 0.02 wt % to 0.08 wt % of the mass of the formaldehyde wastewater. If too much ferrous sulfate is added, filtration is required in the later stage, and the formaldehyde removal rate remains basically unchanged.

[0037] Example 5 The method and steps in Example 1 were used, the temperature was changed to 65°C, 200 μL of 2% NaOH solution was added to change the pH to 3.25, the amount of ferrous sulfate was changed to 0.08%, and the amount of hydrogen peroxide was adjusted to conduct experiments. The results are shown in Table 3 below. Table 3

[0038] The amount of hydrogen peroxide has a significant effect on the removal rate. When the amount of hydrogen peroxide is 16 wt%~20 wt% of the mass of formaldehyde wastewater, the formaldehyde removal rate can reach more than 95%, and as the amount of hydrogen peroxide added increases, the removal rate also increases. This is because the increase in hydrogen peroxide can promote the production of •OH. However, when the amount of hydrogen peroxide exceeds 20 wt%, too much •OH will oxidize the product formic acid into CO 2 and H 2 O.

[0039] Example 6 A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution, the specific steps are as follows: Step 1: Take 500g of formaldehyde wastewater into a three-necked flask.

[0040] Step 2: Control the reaction temperature to 65°C and irradiate the formaldehyde wastewater with an ultraviolet light source at a wavelength of 254nm.

[0041] Step 3: Add 200 μL of 2% NaOH solution to change the pH of the formaldehyde wastewater to 3.25.

[0042] Step 4: adding hydrogen peroxide to the formaldehyde wastewater in an amount of 20% by weight of the formaldehyde wastewater; adding ferrous sulfate to the formaldehyde wastewater in an amount of 0.04wt% by weight of the formaldehyde wastewater.

[0043] Step 5: The reaction time is 2 hours, during which time the mixture is stirred continuously to ensure that the reaction proceeds evenly.

[0044] The reaction solution was filtered, and the supernatant was used to detect the formaldehyde concentration by acetylacetone spectrophotometry, and the formic acid concentration was detected by ion chromatography. The removal rate of formaldehyde into formic acid was calculated to be 98.10%, and the decomposition rate of formic acid was 3.67%.

[0045] Example 7 Brazilian iris, Latin name: Neomaricagracilis, also known as "horse butterfly flower, jade butterfly", is a plant of the genus Brazilian iris in the family Iridaceae. Brazilian iris was purchased from Jiaxingyuan store model: Brazilian iris orchid.

[0046] Preparation of manganese sulfate biochar, MnSO 4 @BC: Cut 10g of Brazilian iris into pieces, dry and dehydrate at 60℃ for 24h, and then add 1L of 10g / L MnSO 4 The aqueous solution was stirred at 100 rpm for 24 h to obtain a uniform mixture, and the mixture was placed in a crucible and heated in a muffle furnace at N 2The crude biochar was thermally cracked under a gas atmosphere, and the temperature was raised to 900 °C at a rate of 17 °C / min. The sample was thermally cracked for 1 h and then naturally cooled and taken out. The resulting black powder was the crude biochar. 2 g of crude biochar was weighed and added to 50 mL of 3 mol / L NaOH solution. The mixture was stirred for 2 h in an 80 °C water bath. The solid filter was filtered to obtain a solid filter. The solid filter was washed with distilled water until the pH was neutral, and then dried at 60 °C for 4 h until the sample was completely dry. The sample was ground and passed through a 100-mesh sieve to obtain MnSO. 4 @BC sample. Prepared MnSO 4 @BC Mn content is 15.0 mg / g.

[0047] Preparation of copper sulfate biochar, CuSO 4 @BC: Compared with the preparation of manganese sulfate biochar, 1L 10g / L MnSO 4 The aqueous solution was replaced with 1L 10g / L CuSO 4 Aqueous solution, other conditions remain unchanged, the prepared CuSO 4 @The Cu content in BC is 14.0 mg / g.

[0048] Example 7-1 Compared with Example 6, the difference is that ferrous sulfate is replaced with 0.04wt% manganese sulfate biochar (MnSO 4 @BC) composite catalyst; the degradation rate of formaldehyde is 96.59%, and the decomposition rate of formic acid is 3.31%.

[0049] Example 7-2 Compared with Example 6, the difference is that ferrous sulfate is replaced with 0.04wt% copper sulfate biochar (CuSO 4 @BC) composite catalyst; the degradation rate of formaldehyde is 95.32%, and the decomposition rate of formic acid is 4.24%.

[0050] Example 8 Compared with Example 6, the difference is that organic acid inducers, oxalic acid, tartaric acid, benzoic acid and salicylic acid are added to the system respectively. The experimental results are as follows: When 0.02 wt % oxalic acid was added and stirred for 30 min, the formaldehyde removal rate was 96.32%. When 0.02 wt % salicylic acid was added and stirred for 30 min, the formaldehyde removal rate was 81.88%; Oxalic acid or salicylic acid can improve the utilization rate of ultraviolet light in the system and shorten the reaction time of converting formaldehyde into formic acid. Adding oxalic acid or salicylic acid to the system is beneficial to shortening the reaction time and improving the formaldehyde removal efficiency.

[0051] When 0.02 wt % tartaric acid was added and stirred for 30 min, the formaldehyde removal rate was 77.14%.

[0052] When 0.03 wt % benzoic acid was added and stirred for 30 min, the formaldehyde removal rate was 65.26%.

[0053] After adding tartaric acid or benzoic acid to the system and shortening the reaction time to 30 min, the removal efficiency was not high.

[0054] Example 9 Compared with Example 6, the difference is that 0.02wt% oxalic acid is added in step 4, and the wavelength of the ultraviolet lamp is changed to conduct experiments. The results are as follows: When the wavelength of the UV lamp was 206nm and the reaction was stirred for 30min, the formaldehyde removal rate was 87.47%; When the wavelength of the UV lamp was 254nm and the reaction was stirred for 30min, the formaldehyde removal rate was 96.32%; When the wavelength of the UV lamp was 282nm and the reaction was stirred for 30min, the formaldehyde removal rate was 94.52%; When the wavelength of the UV lamp was 468nm and the reaction was stirred for 30min, the formaldehyde removal rate was 67.10%; The wavelength of ultraviolet light is preferably 254-282 nm. This is because H 2 O 2 It only significantly absorbs ultraviolet light with a wavelength below 300nm, but the shorter the wavelength of ultraviolet light, the greater its ability to penetrate water will be, resulting in lower degradation efficiency.

[0055] Comparative Example 1-1 Compared with Example 1, the difference is that there is no ultraviolet light irradiation, and the formaldehyde removal rate is 44%.

[0056] Comparative Example 1-2 Compared with Example 1, the difference is that no ferrous sulfate is added, the water bath / H 2 O 2 The formaldehyde removal rate of the system is only 29%.

[0057] The above examples illustrate that the method of converting ultra-high concentration formaldehyde wastewater into formic acid solution of the present invention can realize the directional conversion of formaldehyde wastewater treated by the method of the present invention into formic acid solution, thus solving the problems of formaldehyde wastewater being harmful, non-biodegradable, and having high treatment cost. 2 O 2 The treatment technology of heterogeneous catalytic degradation of formaldehyde wastewater and the general improved method derived from the present invention can be regarded as the protection scope of the present invention.

Claims

1. A method for converting ultra-high concentration formaldehyde wastewater into formic acid solution, characterized in that: The following steps are involved: S1. After the formaldehyde wastewater is heated, a pH regulator is added to obtain hot acidic formaldehyde wastewater; S2. Add hydrogen peroxide, a metal catalyst and an organic acid inducer to the hot acidic formaldehyde wastewater in step S1 under ultraviolet light and stir the mixture sufficiently to obtain a formic acid solution.

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 2 wt % NaOH solution, and the pH is adjusted to 3-3.

5.

3. The method for converting ultra-high concentration formaldehyde wastewater into formic acid solution according to claim 1, characterized in that: In step S1, the formaldehyde wastewater is heated to 60-65°C.

4. 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 254-282 nm.

5. The method for converting ultra-high concentration formaldehyde wastewater into formic acid solution according to claim 1, characterized in that: The metal catalyst in step S2 is one of ferrous sulfate, MnSO4@BC or Cu2SO4@BC.

6. The method for converting ultra-high concentration formaldehyde wastewater into formic acid solution according to claim 1, characterized in that: In step S2, the organic acid inducer is one of oxalic acid, tartaric acid, benzoic acid and salicylic acid.

7. The method for converting ultra-high concentration formaldehyde wastewater into formic acid solution according to claim 1, characterized in that: In the step S2, the mass ratio is: formaldehyde wastewater: hydrogen peroxide: metal catalyst: organic acid inducer = 1: 16%~20%: 0.02%~0.08%: 0.01%~0.03%.

8. 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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