CN100395021C - Application of a Rare Earth Composite Oxide Catalyst in Catalytic Wet Oxidation Process - Google Patents

Abstract

The invention relates to a rare earth composite oxide catalyst in catalytic wet oxidation process and a preparation method thereof, belonging to the fields of water treatment technology and environmental functional materials. In order to reduce the temperature and pressure of the wet oxidation reaction and increase the total organic matter wet oxidation reaction speed, the invention discloses a rare earth composite oxide catalyst, which is in the form of solid powder, and its components are composite oxides of _ZrO2 and _CeO2 , The molar ratio of Zr and Ce is 1:1˜1:11. The invention also discloses a preparation method of the catalyst: preparing a mixed solution of zirconium salt and cerium salt, slowly adding the mixed solution dropwise into a vigorously stirred alkaline solution to obtain a gel precipitate, filtering it; Adjust the pH value to alkaline in ionized water, reflux in hot lye, then dry and calcinate to obtain the catalyst. The catalyst of the invention has good activity and high stability for waste water containing high-concentration refractory small molecule organic acid, and has low production cost.

Description

Application of a Rare Earth Composite Oxide Catalyst in Catalytic Wet Oxidation Process

technical field

The invention is used for treating waste water containing high-concentration refractory small molecular organic acids in a catalytic wet oxidation process, and belongs to the field of water treatment technology and environmental functional materials.

Background technique

Wet oxidation technology is a very effective advanced chemical oxidation water treatment technology, especially suitable for the treatment of toxic, harmful and high-concentration organic wastewater. Wet oxidation technology has attracted extensive attention due to its advantages of high treatment efficiency, low secondary pollution, fast oxidation speed, small equipment size and recoverable energy, and has a good application prospect. However, wet oxidation technology needs to operate under higher temperature and pressure. Scientists and technicians overcome these shortcomings by adding catalysts to the reaction system and using catalytic wet oxidation technology. Therefore, the development of efficient, stable, cheap and water-separated heterogeneous catalysts has become one of the key technologies of catalytic wet oxidation technology. In addition, the effect of wet oxidation on small molecule organic acids (especially acetic acid) is poor, and small molecule organic acids are important intermediate products in the decomposition of most organic matter, and their oxidative decomposition speed often determines the total speed of organic matter wet oxidative decomposition. Therefore, the development of catalysts that can efficiently treat small molecule organic acids in wastewater is one of the hotspots in the research of catalytic wet oxidation at home and abroad.

The heterogeneous catalysts currently studied in the catalytic wet process mainly include noble metal series catalysts, metal copper (including iron, manganese, cobalt, etc.) series catalysts, and rare earth series catalysts.

Noble metal series catalysts have high catalytic activity and stability, especially for small molecule organic acids that are difficult to degrade. However, the high price of noble metals themselves leads to high catalyst costs.

Although metal copper series catalysts have good catalytic activity, there is a serious dissolution phenomenon of catalyst active components in the reaction, which reduces the catalyst activity and causes secondary pollution problems.

Rare earth series catalysts mainly use metal zirconium and cerium, which are relatively low in price, have certain activity and good stability in wet oxidation, but the removal rate of rare earth metals for small molecule organic acids is relatively low.

Contents of the invention

The purpose of the present invention is to propose a rare earth catalyst and its preparation method which is applied in the catalytic wet oxidation process and has high activity, good stability and low production cost for treating refractory small molecule organic acids, so as to reduce the temperature and temperature of the wet oxidation reaction. The pressure increases the reaction rate of the total organic matter wet oxidation.

Technical scheme of the present invention is as follows:

An application of a rare earth composite oxide catalyst in a catalytic wet oxidation process, characterized in that: the rare earth composite oxide catalyst is in the form of a solid powder, and the components are composite oxides of ZrO _{and CeO} , and the moles of Zr and Ce The ratio is 1:1 to 1:11.

Preferably, in the ZrO ₂ and CeO ₂ components of the rare earth composite oxide catalyst, the molar ratio of Zr and Ce is 1:9.

Wherein, the preparation method of the rare earth composite oxide catalyst is as follows: firstly prepare a mixed solution of zirconium salt and cerium salt, the molar concentration ratio of zirconium salt and cerium salt is 1:1～1:11, adopt co-precipitation method, and The mixed solution is slowly added dropwise to the alkaline solution, the volume ratio of the mixed solution to the alkaline solution is 1:4 to 1:20, vigorously stirred while adding dropwise, and the obtained gel precipitate is filtered; then the precipitate Redisperse the material in deionized water, adjust the pH value to 9-11, and then reflux in hot lye for 24-36 hours; then dry it in an oven for 24 hours in an air atmosphere, and then place it in a muffle furnace for 300 hours in an air atmosphere. Calcining at ~600°C for 3-8 hours to obtain a ZrO ₂ -CeO ₂ composite oxide catalyst.

Preferably, when preparing the mixed solution of zirconium salt and cerium salt, the molar concentration ratio of zirconium salt and cerium salt is 1:9.

In a 1L high-pressure reactor, with high-concentration, refractory small molecule carboxylic acids—acetic acid and butyric acid as targets, at a reaction temperature of 230°C and a total pressure of 5 MPa, the ZrO ₂ -CeO ₂ catalyst of the present invention is used A study on the degradation of organic acids by wet oxidation was carried out. And utilize ICP-MS to measure the stripping situation of Zr and Ce ion in catalyst wet type oxidation degradation organic acid process, research result shows that catalyst of the present invention has the following advantages:

(1) The catalyst of the present invention is used in the catalytic wet oxidation process, and has good activity for wastewater containing high-concentration refractory small molecule organic acids. It can effectively reduce the operating temperature and pressure of the wet oxidation process, and accelerate the oxidation rate of small molecular organic acids that are difficult to degrade in wastewater.

(2) ICP-MS was used to measure the dissolution of Zr and Ce ions in the process of catalytic wet oxidation degradation of organic acids. It was found that the dissolution of metal ions was very small, which indicated that the catalyst had good stability.

(3) The catalyst of the present invention uses relatively cheap Zr and Ce as the active components of the catalyst, and the production process is simple and easy, so the production cost of the catalyst is relatively low.

The above-mentioned advantages of the catalyst of the present invention can promote the popularization and application of wet oxidation technology.

Description of drawings

Figure 1 is a diagram of the COD removal rate of catalytic wet oxidation of wastewater containing acetic acid.

Figure 2 is a graph showing the change in COD removal rate of catalytic wet oxidation of wastewater containing n-butyric acid.

Detailed ways

The invention provides a rare earth composite oxide catalyst used in catalytic wet oxidation process, which is in the form of solid powder, and its components are composite oxides of _ZrO2 and _CeO2 , and the molar ratio of Zr and Ce is 1:1～ 1:11. Its preparation method comprises the following steps: first prepare the mixed solution of zirconium salt and cerium salt, the molar concentration ratio of zirconium salt and cerium salt is 1:1～1:11, adopt co-precipitation method, slowly drop the mixed solution into alkali In the alkaline solution, the volume ratio of the mixed solution to the alkaline solution is 1:4 to 1:20, and the mixture is added dropwise while stirring vigorously, and the resulting gel precipitate is filtered; then the precipitate is redispersed in deionized water , after adjusting the pH value to 9-11, reflux in hot lye for 24-36 hours; then dry in an oven for 24 hours in an air atmosphere, and then place it in a muffle furnace and bake at 300-600°C for 3-8 hours in an air atmosphere , to obtain ZrO ₂ -CeO ₂ composite oxide catalyst.

The present invention will be described in detail below in conjunction with the embodiments and the accompanying drawings.

Embodiment one

Prepare 0.1mol/L ZrOCl ₂ ·8H ₂ O and 0.9mol/L Ce(NO ₃ ) ₃ ·6H ₂ O mixed solution 50ml and 0.5mol/L ammonia water 1000ml, slowly drop the salt solution into the vigorously stirred ammonia water , the resulting gel precipitate was filtered and redispersed in 400ml of deionized water. After the pH value was adjusted to 10, it was refluxed in hot lye for 24h, and then dried in an oven at a drying temperature of 100°C. In a muffle furnace, calcined at 400°C for 6h in an air atmosphere to obtain a ZrO ₂ -CeO ₂ composite oxide catalyst.

Then utilize the catalyst prepared by the above method to catalyze wet oxidation containing high-concentration acetic acid wastewater:

Prepare an acetic acid solution with a COD concentration of about 5000mg/L, add 2.7g of ZrO ₂ -CeO ₂ catalyst, put it in the reactor and heat it to 230°C, then stop heating, feed oxygen until the total pressure is 5MPa, and wait until the temperature drops to 230°C Continue to heat and maintain the temperature at 230±3°C, and the reaction time is 2h. The results are shown in Figure 1. It can be seen from Figure 1 that when no catalyst is used, acetic acid is degraded by wet oxidation. After _{2 hours} of reaction, acetic acid is hardly degraded; The removal rate reached 76%.

Embodiment two:

Prepare 0.1mol/L ZrOCl ₂ ·8H ₂ O and 0.9mol/L Ce(NO ₃ ) ₃ ·6H ₂ O mixed solution 50ml and 0.5mol/L ammonia water 1000ml, slowly drop the salt solution into the vigorously stirred ammonia water , filter the obtained gel precipitate, and redisperse it in 400ml deionized water, adjust the pH value to 10, reflux in hot lye for 24h, then dry in an oven at a drying temperature of 100°C, and then place In a muffle furnace, calcining at 400° C. for 6 h in an air atmosphere to obtain a ZrO ₂ -CeO ₂ composite oxide catalyst.

Then use the catalyst catalytic wet oxidation prepared by the above method to contain high-concentration n-butyric acid wastewater:

Prepare a n-butyric acid solution with a COD concentration of about 9000mg/L, add 2.0g of ZrO ₂ -CeO ₂ catalyst, place it in the reactor and heat it to 230°C, then stop heating, feed oxygen until the total pressure is 5MPa, wait until the temperature drops to Continue heating at 230°C and maintain the temperature at 230±3°C, and the reaction time is 2h. The results are shown in Figure 2. It can be seen from the figure that when ZrO ₂ -CeO ₂ catalyst is added, after 2 hours of reaction, the COD removal rate reaches 87%, which is much higher than the degradation effect without catalyst.

Embodiment three:

Prepare 0.1mol/L ZrOCl ₂ ·8H ₂ O and 1.1mol/L Ce(NO ₃ ) ₃ ·6H ₂ O mixed solution 50ml and 0.5mol/L ammonia water 1000ml, slowly drop the salt solution into the vigorously stirred ammonia water , filter the obtained gel precipitate, and redisperse it in 400ml deionized water, adjust the pH value to 11, reflux in hot lye for 36h, and then dry in an oven at 80°C, then place In a muffle furnace, calcining at 600° C. for 8 hours in an air atmosphere to obtain a ZrO ₂ -CeO ₂ composite oxide catalyst.

Then with the catalyst prepared by the above method, carry out the test of removing acetic acid effect according to the test method in embodiment one, the result shows that can obtain better removal effect, carry out the test of removing n-butyric acid effect according to the test method in embodiment two, It can also achieve better removal effect.

Embodiment four:

Prepare 0.2mol/L ZrOCl ₂ 8H ₂ O and 0.2mol/L Ce(NO ₃ ) ₃ 6H ₂ O mixed solution 250ml and 0.5mol/L ammonia water 1000ml, slowly drop the salt solution into the vigorously stirred ammonia water , filter the obtained gel precipitate, and redisperse it in 400ml deionized water, adjust the pH value to 9, reflux in hot lye for 24h, and then dry in an oven at a drying temperature of 120°C, then place In a muffle furnace, calcining at 600° C. for 3 h in an air atmosphere to obtain a ZrO ₂ -CeO ₂ composite oxide catalyst.

Then with the catalyst prepared by the above method, carry out the test of removing acetic acid effect according to the test method in embodiment one, the result shows that can obtain better removal effect, carry out the test of removing n-butyric acid effect according to the test method in embodiment two, It can also achieve better removal effect.

Similarly, when using salt solutions such as Zr(NO ₃ ) ₄ 5H ₂ O, Ce(NO ₃ ) ₃ 6H ₂ O, and alkaline solutions such as NaOH solution or KOH solution as raw materials, adopt the above preparation method to obtain Catalysts have been tested to achieve better treatment effects.

Claims (3)

1. The application of a rare earth composite oxide catalyst in catalytic wet oxidation process, characterized in that: the rare earth composite oxide catalyst is a solid powder, and the components are ZrO ₂ and CeO ₂ composite oxides, Zr and Ce The molar ratio is 1:1～1:11. 2. the application of _the rare earth composite oxide catalyst according to claim 1 in catalytic wet oxidation process, is characterized in that: in the ZrO of described rare earth composite oxide catalyst and CeO _{In the} component, the mole of Zr and Ce The ratio is 1:9. 3. the application of the rare earth composite oxide catalyst according to claim 1 in catalytic wet oxidation process, is characterized in that, the preparation method of described rare earth composite oxide catalyst is as follows: first prepare the mixed solution of zirconium salt and cerium salt , the molar concentration ratio of zirconium salt and cerium salt is 1:1～1:11, and the mixed solution is slowly added dropwise into the alkaline solution by coprecipitation method, and the volume ratio of the mixed solution and the alkaline solution is 1:4～ 1:20, stir vigorously while adding dropwise, filter the obtained gel precipitate; then redisperse the precipitate in deionized water, adjust the pH value to 9~11, and reflux in hot alkali solution for 24~ 36 hours; then dry in an oven for 24 hours in an air atmosphere, then place in a muffle furnace, and bake at 300-600°C for 3-8 hours in an air atmosphere to obtain a ZrO ₂ -CeO ₂ composite oxide catalyst.

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