CN108404922A - One kind being used for low temperature NOxThe quick regenerated catalyst of alternating sorbent-and preparation method - Google Patents

Abstract

The invention discloses a catalyst and preparation method for fast alternate adsorption-desorption/reduction of NOx at low temperature. Heat at ℃ until it is in the form of a sol, add hydrogen peroxide or acid to it, and stir well to make the pH of the system less than or equal to 5, then bake at 150-350°C for 2-5 hours, and at 450-650°C for 2- 5 hours, the carrier was prepared; the other metal salts were at least one of Fe, Ni, Mg, Mn, Co or La salts; 2) soluble copper salts or/and chromium salts were dissolved in water, and added to the step The carrier prepared in 1), add hydrogen peroxide or acid to it, and fully stir, so that the pH value of the system is less than or equal to 5, and then bake at 150-350°C for 2-5 hours, and at 450-650°C for 2-5 hours Hours, the target catalyst was prepared. The catalyst has good NOx reduction performance and fast adsorption capacity at low temperature.

Description

A catalyst for low-temperature NOx rapid alternate adsorption-regeneration and its preparation method

technical field

The invention relates to a catalyst for fast alternate adsorption-desorption/reduction of low-temperature NOx and a preparation method, and the catalyst is used for removing nitrogen oxides in flue gas.

Background technique

With the development of my country's economy and the improvement of people's quality of life, the pressure brought by environmental pollution is increasing. As one of the main pollutants of current air pollution, nitrogen oxides are closely related to the quality of my country's atmospheric environment. Coal-fired power plants are the main pollution source of concentrated emissions of nitrogen oxides. The reduction of nitrogen oxides in the flue gas emitted by them has become an important goal of governance today. Flue gas denitrification has also become an essential environmental protection facility for coal-fired power plants. This facility usually uses NH ₃ -SCR (Ammonia Selective Catalytic Reduction) denitrification technology is used for denitrification. The principle is that NH ₃ or urea is used as a reducing agent to reduce NO _x to N ₂ under the action of a catalyst to achieve the purpose of removing nitrogen oxides. At present, the NH ₃ -SCR catalysts used in industrial coal-fired power plants are generally VW-Ti catalysts, but the optimal reaction temperature of this catalyst needs to be around 350°C. However, there is no relatively mature technology for the treatment of low-temperature flue gas. The activated coke/activated carbon method is the most widely used low-temperature flue gas method. This method uses activated coke/activated carbon as a catalyst to reduce NOx in the flue gas by spraying ammonia. However, the reaction temperature of this method is low, resulting in very low NOx reduction efficiency. All are lower than 40%, unable to meet the requirements of the smoke emission standard. And the unreacted NH ₃ at low temperature will not only form ammonium sulfate with SO ₂ in the flue gas, block the catalyst, escape into the atmosphere, but also participate in the formation of smog.

As a technology with great development potential, NOx adsorption method has been widely used in the treatment of tail gas produced by nitric acid. However, the proportion of NO in flue gas in coal-fired power stations and metallurgical industries is very high, often above 90%, while the proportion of NO ₂ Very low, because common adsorbents/catalysts have weak NO adsorption capacity, far from meeting the requirements of _NOx emission standards, and it is difficult to regenerate adsorbents after adsorbing NOx. And the adsorption and regeneration of the adsorbent/catalyst requires two sets of equipment, resulting in the inability of continuous production.

Contents of the invention

In view of the above-mentioned technical problems in the prior art, the object of the present invention is to provide a catalyst and preparation method for fast alternate adsorption-desorption/reduction of NOx at low temperature. After research, the inventor found that the rare earth-based composite catalyst has good NOx reduction performance and fast adsorption capacity at low temperature. It is very suitable for NO _x removal in low temperature flue gas such as coal-fired power plants and steel plants.

In order to solve the above problems, the technical solution of the present invention is:

A method for preparing a catalyst for fast alternate adsorption-regeneration of low-temperature NOx, comprising the steps of:

1) Dissolve soluble cerium salts and other metal salts in water in a specific proportion, heat and stir, and then heat at 140°C-240°C to form a sol, the purpose of which is to accelerate the decomposition of nitrate and the formation of a network structure between metal ions , then add hydrogen peroxide or acid to it, and stir well to make the pH value of the system less than or equal to 5, to prevent metal ions from forming insoluble matter, and then roast at 150-350°C for 2-5 hours to remove undecomposed nitrate and The acid is further decomposed, and finally roasted at 450-650°C for 2-5 hours to prepare a composite metal oxide support; the other metal salts are at least one of Fe, Ni, Mg, Mn, Co or La salts ;

2) Dissolving soluble copper salt or/and chromium salt in water, and adding the carrier prepared in step 1), adding hydrogen peroxide or acid to it, and fully stirring, so that the pH value of the system is less than or equal to 5, preventing the formation of metal ions. The dissolved material is then calcined at 150-350°C for 2-5 hours to decompose the remaining nitrate and the added acid, and finally calcined at 450-650°C for 2-5 hours to prepare a composite metal oxide catalyst.

The prepared catalyst has the following characteristics: (1) The appropriate ratio of cerium and other metals as a carrier can effectively provide the lattice oxygen required for NO oxidation to NO ₂ at low temperature, and can quickly catalyze the oxidation of NO to NO ₂ , making NOx is adsorbed on the surface of the catalyst; (2) The addition of Cu or Cr as an active component can quickly desorb and reduce the NOx adsorbed on the catalyst surface to N ₂ at low temperature under the action of a reducing agent, completing the regeneration of the catalyst and the removal of NOx catalytic reduction.

Preferably, in step 1), the soluble cerium salt is one or more mixtures of cerium nitrate, cerium acetate or cerium chloride; other metal salts are one or more of nitrate, acetate or chloride A mixture of several.

Preferably, in step 1), the molar ratio of cerium and other metal elements is 8:2-4.5:5.5.

Preferably, in step 1), the mass ratio of liquid and solid in the sol-like liquid is 1:1-1:100.

Preferably, in step 1), the stirring temperature is 65-75°C. Metal salt ions are more soluble and difficult to decompose at this temperature.

Preferably, in step 1), the acid is one or a mixture of acetic acid, nitric acid or hydrochloric acid.

Preferably, in step 2), the mass ratio of the copper salt or/and chromium salt to the carrier is 1:10-1:100, preferably 1:30-1:70.

Preferably, in the system in step 2), the mass ratio of liquid to solid is 1:1-1:100, preferably 1:10-1:50.

Preferably, in step 2), the stirring temperature is 65-75°C.

The catalyst prepared by the above preparation method.

The application of the above-mentioned catalyst in low-temperature flue gas denitrification.

The beneficial effects of the present invention are:

(1) Proper proportioning of cerium and other metals as a carrier can effectively provide the lattice oxygen required for NO oxidation to NO ₂ at low temperature, and can quickly catalyze the oxidation of NO to NO ₂ , so that NOx can be adsorbed on the surface of the catalyst;

(2) The addition of Cu or Cr as an active component can quickly desorb and reduce NOx adsorbed on the surface of the catalyst to N ₂ under low temperature conditions under the action of a reducing agent, completing catalyst regeneration and catalytic reduction of NOx.

Description of drawings

The accompanying drawings constituting a part of the present application are used to provide further understanding of the present application, and the schematic embodiments and descriptions of the present application are used to explain the present application, and do not constitute improper limitations to the present application.

Figure 1 is the comparison of the adsorption amount of NOx at 100, 150 and 200°C within 60s after the adsorption breakthrough experiment of the fresh catalyst prepared in Example 1 and the continuous adsorption-regeneration of the rotary denitration reactor for a period of time; The NOx adsorption amount in the experiment and the rotary denitrification reactor is basically the same, indicating that the catalyst has excellent low-temperature NOx rapid alternate adsorption-regeneration performance.

Figure 2. The NOx removal efficiency of the catalyst in the NOx adsorption-reduction experiment at different temperatures. The NOx removal efficiency in the flue gas reaches more than 90%, indicating that the catalyst has a high NOx removal efficiency in the low-temperature NOx rapid alternate adsorption-regeneration.

Detailed ways

It should be pointed out that the following detailed description is exemplary and intended to provide further explanation to the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It should be noted that the terminology used here is only for describing specific implementations, and is not intended to limit the exemplary implementations according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural, and it should also be understood that when the terms "comprising" and/or "comprising" are used in this specification, they mean There are features, steps, operations, means, components and/or combinations thereof.

The invention provides a method for preparing a catalyst for fast alternate adsorption-regeneration of low-temperature NOx, the method comprising the following steps:

1) Preparation of carrier: dissolve a certain amount of cerium salt and a certain amount of one or more metal element salts such as Fe, Ni, Mg, Mn, Co and La in deionized water, wherein the cerium element and other metal elements The molar ratio is between 8:2~4.5:5.5, the mass ratio of liquid to solid is 1:1~1:100, fully stirred at 70°C, then heated at 140°C~240°C until it becomes a sol, and a certain amount of Hydrogen peroxide or acetic acid, nitric acid, hydrochloric acid one or more mixtures in any proportion, and fully stirred so that the pH of the solution is not greater than 5, and roasted at 150-350°C and 450-650°C for 2-5 hours respectively;

2) Active ingredient loading: Dissolve one or two soluble copper salts or chromium salts in deionized water, and add the carrier prepared in step 1), wherein the mass ratio of one or two copper salts or chromium salts to the carrier is 1:10～1:100, the mass ratio of liquid to solid is 1:1～1:100, fully stir at 70°C, and add a certain amount of hydrogen peroxide or one of acetic acid, nitric acid, hydrochloric acid or a mixture of several in any proportion , and fully stirred so that the pH of the solution is not greater than 5, and roasted at 150-350°C and 450-650°C for 2-5 hours respectively to obtain a NOx rapid alternate adsorption-regeneration catalyst at low temperature.

The technical feature of the present invention is also that: the soluble cerium salt in the method is cerium (III), cerium acetate (III) and cerium (III) chloride, one or more mixtures in any proportion, the soluble The metal salt is one of nitrate, acetate and chloride or a mixture of several in any proportion.

The catalyst that can be obtained by this method has the following characteristics: (1) the appropriate ratio of cerium and other metals can be used as a carrier to effectively provide the lattice oxygen required for NO oxidation to _NO at low temperature, and can quickly catalyze the oxidation of NO to NO _2. Make NOx adsorb on the surface of the catalyst (2) The addition of active component Cu can quickly desorb and reduce the NOx adsorbed on the catalyst surface to N ₂ at low temperature under the action of the reducing agent, completing the regeneration of the catalyst and the removal of NOx catalytic reduction.

Several specific examples are enumerated below to further understand the present invention.

Example 1:

1) Add 10g of cerium nitrate and 10g of cobalt nitrate into 20ml of deionized water, stir fully at 70°C, then heat at 185°C until it becomes a sol, add a certain amount of nitric acid, and stir well to make the solution pH less than 3 , and roasted at 200°C and 450°C for 3 hours respectively to prepare a carrier;

2) Dissolve 0.5g of copper acetate in 30ml of deionized water, add the carrier prepared above, fully stir at 70°C, add a certain amount of nitric acid, and fully stir so that the pH of the solution is less than 3, and respectively at 200 ℃ and 450 ℃ for 3 hours to prepare a carrier; obtain a catalyst for fast alternate adsorption-regeneration of NOx at low temperature, which is used in a new denitration reactor (a rotary HC-SCR denitration reactor, application publication number In CN103908892A), more than 90% of NOx in flue gas is removed at 150°C.

Example 2:

1) Add 10g of cerium nitrate and 10g of ferric nitrate into 20ml of deionized water, stir fully at 70°C, then heat at 160°C until it becomes a sol, add a certain amount of acetic acid, and stir well to make the solution pH less than 5 , and roasted at 250°C and 550°C for 5 hours respectively to prepare a carrier;

2) Dissolve 1 g of copper nitrate in 30 ml of deionized water, add the above prepared carrier, fully stir at 70 ° C, add a certain amount of acetic acid, and fully stir so that the pH value of the solution is less than 5, and respectively at 250 °C and 550 °C for 5 hours to obtain a catalyst for fast alternate adsorption-regeneration of NOx at low temperatures. Remove more than 93% of NOx in flue gas at 150°C.

Catalyst NOx breakthrough curve and NOx adsorption capacity testing methods are as follows:

Get 3ml of the catalyst of Example 1 with a particle size of 40-60 mesh and put it into a stainless steel tube, and its temperature is controlled by a tube-type resistance furnace and a temperature controller. The simulated flue gas is provided by the corresponding steel cylinder. The composition of the simulated flue gas is: C _NOx = 0.08%, _CO2 = 5%, the balance gas is N ₂ , and the volumetric space velocity is 10,000 ^-1 . The concentration values of NO and _O2 at the inlet and outlet are monitored online by HORIBAPG-350 flue gas analyzer. The NOx breakthrough curve experiment shows the relationship between NOx passing through the catalyst bed concentration and time, which represents the adsorption capacity of the catalyst for NOx; NOx adsorption The capacity indicates the molar amount of NOx adsorbed by the unit mass of the catalyst after reaching NOx adsorption saturation. The specific calculation formula is as follows:

The formula for calculating S is:

Where q _e is the NOx adsorption capacity in mmol/g, P is the reaction pressure in Pa, C ₀ is the initial concentration of NOx in 10 ^-6 , F is the gas flow rate in m ² /s, and R is Gas constant, the unit is 8.314J/(mol.k), T is the adsorption temperature, the unit is ℃, S is the NOx integral area of the adsorption breakthrough curve, Wcat is the catalyst mass, the unit is g, C _NO,out is the outlet of the reactor NOx concentration, the unit is 10 ^-6 , t is the adsorption time, the unit is s.

The NOx removal rate test method of the catalyst is as follows:

Get 3ml of the catalyst of Example 1 with a particle size of 40-60 mesh and put it into a stainless steel tube, and its temperature is controlled by a tube-type resistance furnace and a temperature controller. The simulated flue gas and simulated reducing gas are respectively provided by the corresponding steel cylinders. The simulated flue gas is composed of: C _NOx = 0.08%, _CO2 = 5%, and the balance gas is N ₂ ; in the simulated reducing gas, C _CO = 0.5%, and the balance gas is It is N ₂ ; the volumetric space velocity is 10,000 ^-1 . The concentration values of NO, _O2 and CO at the inlet and outlet are monitored online by the HORIBA PG-350 flue gas analyzer. The removal rate of NOx indicates the proportion of NOx adsorbed after the flue gas passes through the catalyst in a unit time to the total incoming NOx. Calculated as follows:

Represents the NOx removal efficiency, t0 is the initial time, t is the time after the flue gas passes through the catalyst bed, C _NOx,0 is the initial NOx concentration, C _NOx is the NOx concentration after passing through the catalyst bed.

Figure 1 shows the NOx adsorption capacity at 100, 150 and 200°C of the catalyst prepared in Example 1 in the rotary denitration reactor, after the adsorption breakthrough experiment of the fresh catalyst and the continuous adsorption-regeneration of the rotary denitration reactor for a period of time. Examples illustrate that the low-temperature NOx fast alternate adsorption-regeneration catalyst obtained by the preparation method of the present invention has higher NOx adsorption capacity and catalyst regeneration effect at low temperature.

Figure 2 shows the NOx removal efficiency of the catalyst in the NOx rapid alternate adsorption-regeneration experiment at different temperatures. In the range of 100-200°C, the NOx removal efficiency reaches more than 90%, especially at 150°C, the NOx removal efficiency is as high as 98%, indicating that the catalyst has good NOx rapid alternate adsorption-regeneration capability at low temperature.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. For those skilled in the art, various modifications and changes may be made to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this application shall be included within the protection scope of this application.

Claims (10)

1. a kind of preparation method for the regenerated catalyst of the quick alternating sorbents-of low temperature NOx, it is characterised in that：Including as follows Step：

1) soluble cerium salt and other metal salts is soluble in water in specific proportions, then heating stirring adds at 140 DEG C -240 DEG C Heat is extremely in sol form, and hydrogen peroxide or acid are added thereto, and is sufficiently stirred, and so that the pH value of system is less than or equal to 5, then successively It is roasted at 150-350 DEG C 2-5 hours, 2-5 hour is finally roasted at 450-650 DEG C, carrier is prepared；Other described gold It is at least one of Fe, Ni, Mg, Mn, Co or La salt to belong to salt；

2) soluble copper salt or/and chromic salts is soluble in water, and the carrier prepared in step 1) is added, hydrogen peroxide is added thereto Or acid, and be sufficiently stirred, so that the pH value of system is less than or equal to 5, is then roasted 2-5 hours at 150-350 DEG C successively, in 450- 2-5 hour is roasted at 650 DEG C, and final catalyst is prepared.

2. preparation method according to claim 1, it is characterised in that：In step 1), soluble cerium salt is cerous nitrate, acetic acid One or several kinds of mixtures in cerium or cerium chloride；Other metal salts are one kind in nitrate, acetate or chlorate Or several mixture.

3. preparation method according to claim 1, it is characterised in that：In step 1), Ce elements and other metallic elements Molar ratio is 8:2-4.5:5.5.

4. preparation method according to claim 1, it is characterised in that：In step 1), liquid and solid in sol form liquid Mass ratio be 1:1-1:100.

5. preparation method according to claim 1, it is characterised in that：In step 1), the temperature of stirring is 65-75 DEG C.

6. preparation method according to claim 1, it is characterised in that：In step 1), the acid is acetic acid, nitric acid or hydrochloric acid One or more of mixture.

7. preparation method according to claim 1, it is characterised in that：In step 2), the matter of mantoquita or/and chromic salts and carrier Amount is than being 1:10-1:100, preferably 1:30-1:70.

8. preparation method according to claim 1, it is characterised in that：In system in step 2), the matter of liquid and solid Amount is than being 1:1-1:100, preferably 1:10-1:50.

9. preparation method according to claim 1, it is characterised in that：In step 2), the temperature of stirring is 65-75 DEG C.

10. what any preparation methods of claim 1-9 were prepared urges for the quick alternating sorbents-of low temperature NOx to be regenerated Agent.