Magnetic iron oxide catalyst for wet catalytic oxidation of sludge and preparation method of magnetic iron oxide catalyst

Abstract

The invention discloses a magnetic iron oxide catalyst for wet catalytic oxidation of sludge and a preparation method of the magnetic iron oxide catalyst, and belongs to the field of preparation of catalyst materials. The method specifically comprises the following steps: dissolving a trivalent iron salt and a divalent iron salt in water in proportion to obtain a mixed solution; under the protection atmosphere of inert gas, adding an alkaline solution into the mixed solution, and adjusting the pH value to be 8-12; sequentially washing off impurities by using water and an organic detergent to obtain a reactant; and carrying out vacuum drying on the reactant, and grinding to obtain the magnetic iron oxide catalyst. The catalyst can effectively reduce the content of organic substances in the sludge pyrolysis liquid in the catalytic wet oxidation process, and has good magnetism and recoverability before and after the reaction. After five times of circulation, the catalyst still keeps a stable organic matter removal effect and good magnetism. The method is expected to be applied to the fields of sludge resource utilization, environmental water pollutant removal and the like.

Description

Technical Field

[0001] The invention belongs to the field of catalyst material preparation, and in particular relates to a magnetic iron oxide catalyst for sludge wet catalytic oxidation and a preparation method thereof. Background Art

[0002] my country's activated sludge production is huge, and has been on an upward trend in recent years. In 2019, the production of activated sludge reached 60Mt, and it is expected to exceed 90Mt (80% water content) in 2025. Therefore, it is particularly important to harmlessly treat and recycle activated sludge. The main components of activated sludge include organic matter, heavy metals and pathogens, among which the content of organic matter can reach 40%.

[0003] Catalytic wet oxidation technology is a technology that produces strong oxidative free radicals through oxygen activation under high temperature, high pressure and catalyst, and oxidizes pollutants into small molecular organic or inorganic substances. Compared with traditional sludge treatment methods, this technology can better achieve sludge reduction, harmlessness and resource utilization. The selection of catalysts is the key to this technology. The catalyst must not only be efficient but also cheap. If the catalyst is easy to recover and regenerate during use, it will greatly reduce the loss of the catalyst and avoid secondary pollution, thereby reducing the cost of repair and treatment and improving the atomic economy of the catalyst.

[0004] Therefore, there is an urgent need to develop a catalyst that can be recycled and reused and has high efficiency in catalyzing wet oxidation. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies in the prior art and to provide a magnetic iron oxide catalyst for sludge wet catalytic oxidation and a preparation method thereof.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] In a first aspect, the present invention provides a method for preparing a magnetic iron oxide catalyst for wet catalytic oxidation of sludge, comprising dissolving a trivalent iron salt and a divalent iron salt in water in proportion to obtain a mixed solution; adding an alkaline solution to the mixed solution under an inert gas protective atmosphere to adjust the pH value to alkaline; subsequently, washing away impurities with water and an organic detergent in turn to obtain a reactant; and vacuum drying and grinding the reactant to obtain a magnetic iron oxide catalyst.

[0008] Preferably, the molar ratio of ferric iron to ferrous iron in the mixed solution is (0.1-10):1.

[0009] Preferably, the ferric iron salt is ferric chloride hexahydrate or ferric sulfate, and the ferrous iron salt is ferrous chloride tetrahydrate or ferrous sulfate.

[0010] Preferably, the alkaline solution is sodium hydroxide, potassium hydroxide or calcium hydroxide solution.

[0011] Furthermore, the concentration of the alkaline solution is 0.01-10 mol / L.

[0012] Preferably, the inert gas is nitrogen or argon.

[0013] Preferably, the pH value is adjusted to be in the range of 8 to 12.

[0014] Preferably, the vacuum drying temperature of the reactants is set at 50° C. to 120° C., and the drying time is 0.5 to 12 hours.

[0015] Preferably, the organic detergent is ethanol or acetone.

[0016] In a second aspect, the present invention provides a magnetic iron oxide catalyst obtained by the preparation method described in the first aspect.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The preparation method provided by the present invention has simple process, low raw material price and little environmental pollution. The prepared magnetic iron oxide catalyst can achieve a removal rate of 40% for organic matter in sludge pyrolysis liquid, which is much higher than the removal rate of 17% of the control group without catalyst. In addition, the magnetic iron oxide catalyst can be recovered by high-temperature heating to achieve recycling. Experiments show that after the magnetic iron oxide catalyst is recycled 5 times, it can still maintain a stable organic matter removal effect and good magnetic properties, and is expected to be applied to the resource recovery process of sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A flow chart of the method for preparing the magnetic iron oxide catalyst provided by the present invention;

[0020] Figure 2 This is a schematic diagram of the magnetic properties of the magnetic iron oxide catalyst prepared in Example 1;

[0021] Figure 3 This is a scanning electron microscope image of the magnetic iron oxide catalyst prepared in Example 1;

[0022] Figure 4 This is a diagram showing the effect of the magnetic iron oxide catalyst prepared in Example 1 on the removal rate of organic matter in the sludge pyrolysis liquid;

[0023] Figure 5 This is a comparison chart of the removal rate of organic matter in sludge pyrolysis liquid by the magnetic iron oxide catalyst after different cycles in Example 2;

[0024] Figure 6Schematic diagram of the magnetic properties of the magnetic iron oxide catalyst after 5 cycles in Example 2;

[0025] Figure 7 This is a scanning electron microscope image of the magnetic iron oxide catalyst after 5 cycles in Example 2. DETAILED DESCRIPTION

[0026] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0027] Example 1

[0028] This embodiment provides a method for preparing a magnetic iron oxide catalyst, which is as follows:

[0029] (1) Ferric chloride hexahydrate and ferrous chloride tetrahydrate are dissolved in water to obtain a mixed solution, wherein the molar ratio of trivalent iron ions to divalent iron ions in the mixed solution is 1:1, and the ferric chloride solution and the ferrous chloride solution are both 0.5 mol / L.

[0030] (2) Under an inert gas atmosphere, a 5 mol / L sodium hydroxide solution was added to the mixed solution to adjust the pH value to 10, and the reaction was carried out.

[0031] (3) Then, the remaining salt ion impurities are washed away with water and ethanol in turn to obtain the reactant.

[0032] (4) placing the reactants in a vacuum drying oven, setting the drying temperature to 50° C. for 12 hours, and finally grinding to obtain a magnetic iron oxide catalyst.

[0033] like Figure 2 As shown, the magnetic iron oxide catalyst prepared in this embodiment can be adsorbed by a magnet and has magnetic properties. Figure 3 This is a scanning electron microscope image of the magnetic iron oxide catalyst prepared in this example. Figure 3 It can be seen that the surface of the sample is spherical, which is consistent with the microscopic characteristics of the material.

[0034] In order to verify the performance of the magnetic iron oxide catalyst prepared in this example for sludge wet catalytic oxidation, the following experiment was conducted:

[0035] Take 30mL of sludge pyrolysis liquid, put it into the reactor, add a certain amount of catalyst, start the pressure control system, set the agitator speed and reaction temperature, and start heating. When the target temperature is reached, open the ventilation valve to allow oxygen to flow into the reactor to start the reaction. After the reaction is completed, close the oxygen inlet valve and heating switch of the reactor to cool it down.

[0036] according to Figure 4It can be seen that compared with the case without adding a catalyst, the degradation rate of organic matter increased from the original 17% to 38%, which indicates that the organic matter was significantly degraded after adding the magnetic iron oxide catalyst.

[0037] Example 2

[0038] In this embodiment, the magnetic iron oxide catalyst used for wet catalytic oxidation of sludge in embodiment 1 is recovered and then subjected to multiple cycles of catalysis. The reacted magnetic iron oxide catalyst is vacuum dried at 50° C. for 12 hours and then heated at 450° C. for half an hour to complete the recovery of the catalyst.

[0039] Figure 5 This is a diagram of the catalyst's cycle effect. From the figure, we can see that the catalytic effect does not show a significant decrease after multiple cycles. Figure 6 This is a schematic diagram of the magnetism of the catalyst after five cycles. After multiple reactions, the material still has strong magnetism. Figure 7 is a schematic diagram of the SEM of the catalyst after 5 cycles. Figure 3 In comparison, there was no obvious change in the microstructure, indicating that the catalyst has good recyclability.

[0040] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing a magnetic iron oxide catalyst for wet catalytic oxidation of sludge, characterized in that: The trivalent iron salt and the divalent iron salt are dissolved in water in proportion to obtain a mixed solution; an alkaline solution is added to the mixed solution under an inert gas protection atmosphere to adjust the pH value to be alkaline; then impurities are washed away with water and an organic detergent in turn to obtain a reactant; the reactant is vacuum dried and ground to obtain a magnetic iron oxide catalyst.

2. The method for preparing a magnetic iron oxide catalyst according to claim 1, characterized in that: The molar ratio of trivalent iron to divalent iron in the mixed solution is (0.1-10):

1.

3. The method for preparing a magnetic iron oxide catalyst according to claim 1, characterized in that: The ferric iron salt is ferric chloride hexahydrate or ferric sulfate, and the ferrous iron salt is ferrous chloride tetrahydrate or ferrous sulfate.

4. The method for preparing a magnetic iron oxide catalyst according to claim 1, characterized in that: The alkaline solution is sodium hydroxide, potassium hydroxide or calcium hydroxide solution.

5. The method for preparing a magnetic iron oxide catalyst according to claim 4, characterized in that: The concentration of the alkaline solution is 0.01-10 mol / L.

6. The method for preparing a magnetic iron oxide catalyst according to claim 1, characterized in that: The inert gas is nitrogen or argon.

7. The method for preparing a magnetic iron oxide catalyst according to claim 1, characterized in that: Adjust the pH value to 8-12.

8. The method for preparing a magnetic iron oxide catalyst according to claim 1, characterized in that: The vacuum drying temperature of the reactants is set to 50° C. to 120° C., and the drying time is 0.5 to 12 hours.

9. The method for preparing a magnetic iron oxide catalyst according to claim 1, characterized in that: The organic detergent is ethanol or acetone.

10. A magnetic iron oxide catalyst obtained by the preparation method according to any one of claims 1 to 9.

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