CN108404922B

CN108404922B - NO used at low temperaturexCatalyst for rapid alternate adsorption-regeneration and preparation method thereof

Info

Publication number: CN108404922B
Application number: CN201810122092.9A
Authority: CN
Inventors: 程星星; 张兴宇; 马春元; 王志强; 王美霞; 孙培亮; 常景彩
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2018-02-07
Filing date: 2018-02-07
Publication date: 2020-01-14
Anticipated expiration: 2038-02-07
Also published as: CN108404922A

Abstract

The invention discloses a catalyst for low-temperature NOx rapid alternate adsorption-desorption/reduction and a preparation method thereof, 1) soluble cerium salt and other metal salts are dissolved in water according to a specific proportion, heated and stirred, then heated to be sol at 140-240 ℃, added with hydrogen peroxide or acid, fully stirred to ensure that the pH value of the system is less than or equal to 5, then sequentially roasted at 150-350 ℃ for 2-5 hours, and roasted at 450-650 ℃ for 2-5 hours to prepare a carrier; the other metal salt is at least one of Fe, Ni, Mg, Mn, Co or La salt; 2) dissolving soluble copper salt or/and chromium salt in water, adding the carrier prepared in the step 1), adding hydrogen peroxide or acid into the carrier, fully stirring the mixture to ensure that the pH value of the system is less than or equal to 5, then sequentially roasting the mixture at the temperature of 150-350 ℃ for 2-5 hours and roasting the mixture at the temperature of 450-650 ℃ for 2-5 hours to prepare the target catalyst. The catalyst has good NOx reduction performance and quick adsorption capacity at low temperature.

Description

Catalyst for low-temperature NOx rapid alternate adsorption-regeneration and preparation method thereof

Technical Field

The invention relates to a catalyst for low-temperature NOx rapid alternate adsorption-desorption/reduction and a preparation method thereof.

Background

With the development of economy in China, the requirements of the quality of life of the nation are improved, the pressure brought by environmental pollution is increased day by day, and the treatment level of nitrogen oxide is closely related to the quality of the atmospheric environment in China as one of the main pollutants of the current atmospheric pollution. The coal-fired power plant is used as a main pollution source for concentrated emission of nitrogen oxides, emission reduction of the nitrogen oxides in the emitted flue gas becomes an important target for treatment at present, flue gas denitrification also becomes a necessary environment-friendly facility for the coal-fired power plant, and the facility usually adopts NH₃Denitration by SCR (ammonia Selective catalytic reduction) denitration technology based on NH₃Or urea is used as a reducing agent to react NO under the action of a catalyst_xReduction to N₂Thereby achieving the purpose of removing nitrogen oxide. NH adopted by industrial coal-fired power plant at present₃The SCR catalyst is generally a V-W-Ti catalyst, but the optimum reaction temperature of the catalyst needs to be about 350 ℃. At present, no mature technology exists for treating low-temperature flue gas. The most applied low-temperature flue gas is an active coke/active carbon method, the method adopts active coke/active carbon as a catalyst, NOx in the flue gas is reduced by spraying ammonia, but the reaction temperature of the method is low, so that the NOx reduction efficiency is very low and is generally lower than 40%, and the requirement of a flue gas emission standard cannot be met. And unreacted NH at low temperature₃Except for SO in the flue gas₂And the like, so that the ammonium sulfate salt is formed, the catalyst is blocked, and the haze can be formed after the ammonium sulfate salt escapes to the atmosphere.

The NOx adsorption method is widely applied to the treatment of tail gas produced by nitric acid preparation as a technology with great development potential, but the NO ratio in the flue gas of a coal-fired power plant and the metallurgical industry is very high and is often more than 90 percent, and NO is in the flue gas₂The occupied proportion is very low, and the adsorption capacity of the common adsorbent/catalyst to NO is weak, so that NO is far from the adsorption capacity of the common adsorbent/catalyst_xEmission standards, and difficult regeneration of the adsorbent after adsorbing NOx. And the adsorption and regeneration of the adsorbent/catalyst are requiredTwo sets of equipment are needed, so that the production cannot be continuously carried out.

Disclosure of Invention

In view of the technical problems in the prior art, the present invention aims to provide a catalyst for rapid and alternate adsorption-desorption/reduction of low-temperature NOx and a preparation method thereof. The inventor finds that the rare earth-based composite catalyst has good NOx reduction performance and quick adsorption capacity at low temperature, is combined with a novel rotary denitration reactor (a rotary HC-SCR denitration reactor, application publication No. CN103908892A), and is very suitable for NO in low-temperature flue gas of coal-fired power plants, iron and steel plants and the like_xAnd (4) removing.

In order to solve the problems, the technical scheme of the invention is as follows:

a preparation method of a catalyst for low-temperature NOx rapid alternate adsorption-regeneration comprises the following steps:

1) dissolving soluble cerium salt and other metal salts in water according to a specific proportion, heating and stirring, then heating at 140-240 ℃ to form a sol state, aiming at accelerating the decomposition of nitrate and forming a network structure between metal ions, then adding hydrogen peroxide or acid into the sol state, fully stirring to ensure that the pH value of the system is less than or equal to 5, preventing the metal ions from forming insoluble matters, roasting at 150-350 ℃ for 2-5 hours, further decomposing the undecomposed nitrate and the added acid, and finally roasting at 450-650 ℃ for 2-5 hours to prepare a composite metal oxide carrier; the other metal salt is at least one of Fe, Ni, Mg, Mn, Co or La salt;

2) dissolving soluble copper salt or/and chromium salt in water, adding the carrier prepared in the step 1), adding hydrogen peroxide or acid into the carrier, fully stirring the mixture to ensure that the pH value of the system is less than or equal to 5, preventing metal ions from forming insoluble matters, then sequentially roasting the mixture at the temperature of 150-350 ℃ for 2-5 hours to decompose residual nitrate and the added acid, and finally roasting the mixture at the temperature of 450-650 ℃ for 2-5 hours to prepare the composite metal oxide catalyst.

The prepared catalyst has the following characteristics: (1) cerium and other metals in proper proportion are matched as a carrier, so that the oxidation of NO into NO can be effectively provided at low temperature₂Required lattice oxygen to rapidly catalyze the oxidation of NO to NO₂Adsorbing NOx on the surface of the catalyst; (2) the addition of the active component Cu or Cr can lead the NOx adsorbed on the surface of the catalyst to be quickly desorbed and reduced into N under the low-temperature condition under the action of a reducing agent₂Regeneration of the catalyst and catalytic reduction of NOx are completed.

Preferably, in step 1), the soluble cerium salt is one or a mixture of cerium nitrate, cerium acetate or cerium chloride; the other metal salt is one or a mixture of more of nitrate, acetate or chloride.

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

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

Preferably, in step 1), the stirring temperature is 65-75 ℃. At this temperature the metal salt ions are more soluble and less prone to decomposition.

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

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

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

Preferably, in step 2), the temperature of stirring is 65-75 ℃.

The catalyst prepared by the preparation method.

The catalyst is applied to low-temperature flue gas denitration.

The invention has the beneficial effects that:

(1) cerium and other metals in proper proportion are matched as a carrier, so that the oxidation of NO into NO can be effectively provided at low temperature₂Required lattice oxygen to rapidly catalyze the oxidation of NO to NO₂Adsorbing NOx on the surface of the catalyst;

(2) the active component Cu or Cr can be adsorbed on the surface of the catalyst under the action of a reducing agentFast desorption and reduction of facial NOx to N at low temperature₂Regeneration of the catalyst and catalytic reduction of NOx are completed.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.

FIG. 1 is a graph showing a comparison of NOx adsorption amounts at 100, 150 and 200 ℃ for 60s after adsorption breakthrough experiments and continuous adsorption-regeneration of a rotary denitration reactor for a period of time for fresh catalysts prepared in example 1; the NOx adsorption amount of the catalyst in an adsorption penetration experiment and a rotary denitration reactor is basically consistent, and the low-temperature NOx rapid alternate adsorption-regeneration performance of the catalyst is excellent.

FIG. 2 shows that the NOx removal efficiency of the catalyst in the NOx adsorption-reduction experiment at different temperatures is higher than 90% in the flue gas, which indicates that the NOx removal efficiency of the catalyst in the low-temperature NOx rapid alternate adsorption-regeneration process is higher.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. 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 is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The invention provides a preparation method of a catalyst for low-temperature NOx rapid alternate adsorption-regeneration, which comprises the following steps:

1) preparation of the carrier: dissolving a certain amount of cerium salt and a certain amount of one or more of metal element salts of Fe, Ni, Mg, Mn, Co, La and the like in deionized water, wherein the molar ratio of cerium to other metal elements is (8): 2-4.5:5.5, the mass ratio of liquid to solid is 1:1-1:100, fully stirring at 70 ℃, then heating at 140-240 ℃ to form sol, adding a certain amount of hydrogen peroxide or one or more of acetic acid, nitric acid and hydrochloric acid in any proportion, fully stirring to ensure that the pH of the solution is not more than 5, and roasting at 150-350 ℃ and 450-650 ℃ for 2-5 hours respectively;

2) loading active ingredients: dissolving one or two of soluble copper salt or chromium salt in deionized water, and adding the carrier prepared in the step 1), wherein the mass ratio of one or two of copper salt or chromium salt to the carrier is 1:10-1:100, the mass ratio of liquid to solid is 1:1-1:100, fully stirring at 70 ℃, adding a certain amount of hydrogen peroxide or one or a mixture of more of acetic acid, nitric acid and hydrochloric acid in any proportion, fully stirring to ensure that the pH of the solution is not more than 5, and roasting at 350 ℃ and 450-650 ℃ for 2-5 hours respectively to obtain the rapid and alternative NOx adsorption-regeneration catalyst for low temperature.

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

The catalyst obtained by the method has the following characteristics: (1) cerium and other metals in proper proportion are matched as a carrier, so that the oxidation of NO into NO can be effectively provided at low temperature₂Required lattice oxygen to rapidly catalyze the oxidation of NO to NO₂The addition of the active component Cu which enables the NOx to be adsorbed on the surface of the catalyst (2) can lead the NOx adsorbed on the surface of the catalyst to be rapidly desorbed and reduced into N under the low-temperature condition under the action of a reducing agent₂Regeneration of the catalyst and catalytic reduction of NOx are completed.

The following examples are presented to provide a further understanding of the invention.

Example 1:

1) adding 10g of cerium nitrate and 10g of cobalt nitrate into 20ml of deionized water, fully stirring at 70 ℃, then heating to be in a sol state at 185 ℃, adding a certain amount of nitric acid, fully stirring to ensure that the pH of the solution is less than 3, and roasting at 200 ℃ and 450 ℃ for 3 hours respectively to prepare a carrier;

2) dissolving 0.5g of copper acetate in 30ml of deionized water, adding the prepared carrier, fully stirring at 70 ℃, adding a certain amount of nitric acid, fully stirring until the pH of the solution is less than 3, and roasting at 200 ℃ and 450 ℃ for 3 hours respectively to prepare the carrier; the catalyst for quickly and alternately adsorbing and regenerating NOx at low temperature is obtained, and the catalyst removes more than 90 percent of NOx in flue gas at 150 ℃ in a novel denitration reactor (a rotary HC-SCR denitration reactor, application publication No. CN 103908892A).

Example 2:

1) adding 10g of cerium nitrate and 10g of ferric nitrate into 20ml of deionized water, fully stirring at 70 ℃, then heating to form sol at 160 ℃, adding a certain amount of acetic acid, fully stirring to ensure that the pH of the solution is less than 5, and roasting at 250 ℃ and 550 ℃ for 5 hours respectively to prepare a carrier;

2) 1g of copper nitrate is dissolved in 30ml of deionized water, the prepared carrier is added, the mixture is fully stirred at 70 ℃, a certain amount of acetic acid is added, the mixture is fully stirred, the pH value of the solution is less than 5, the mixture is roasted at 250 ℃ and 550 ℃ for 5 hours respectively, and the catalyst for quickly and alternately adsorbing and regenerating NOx at low temperature is obtained, and the catalyst removes more than 93 percent of NOx in smoke at 150 ℃ in a novel denitration reactor (a rotary HC-SCR denitration reactor, application publication No. CN 103908892A).

The method for testing the NOx penetration curve and the NOx adsorption capacity of the catalyst comprises the following steps:

3ml of the catalyst of example 1 having a particle size of 40 to 60 mesh was charged into a stainless steel tube, and the temperature thereof was controlled by temperature programming using a tube resistance furnace and a temperature controller. The simulated smoke is provided by a corresponding steel cylinder, and the simulated smoke comprises the following components: c_NOx＝0.08％,C_O25% of balance gas N₂(ii) a Volume space velocity of 10,000^-1. Import and export NO and O₂The concentration value of the NOx is monitored on line by a HORIBAPG-350 flue gas analyzer, and a penetration curve experiment of the NOx shows the relation between the concentration of the NOx passing through a catalyst bed layer and time, and represents the adsorption capacity of the catalyst to the NOx; the NOx adsorption capacity represents the molar quantity of NOx adsorbed after the catalyst per unit mass reaches NOx adsorption saturation, and the specific calculation formula is as follows:

the calculation formula of S is as follows:

wherein q is_eIn terms of NOx adsorption capacity in mmol/g, and P in terms of reaction pressure in Pa, C₀Is the initial concentration of NOx in 10^-6F is the gas flow rate in m²R is a gas constant with the unit of 8.314J/(mol.k), T is an adsorption temperature with the unit of ℃, S is an adsorption breakthrough curve NOx integral area, Wcat is a catalyst mass with the unit of g and C_NO,outIs the reactor outlet NOx concentration, in units of 10^-6And t is the adsorption time in s.

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

3ml of the catalyst of example 1 having a particle size of 40 to 60 mesh was charged into a stainless steel tube, and the temperature thereof was controlled by temperature programming using a tube resistance furnace and a temperature controller. The simulated flue gas and the simulated reducing gas are respectively provided by corresponding steel cylinders, and the simulated flue gas comprises the following components: c_NOx＝0.08％,C_O25% of balance gas N₂(ii) a Simulating C in reducing gas_CO0.5% of balance gas N₂(ii) a Volume space velocity of 10,000^-1. Inlet and outlet NO, O₂The concentration value of CO and the CO is monitored on line by a HORIBA PG-350 flue gas analyzer, and the removal rate of NOx represents the ratio of NOx absorbed after the flue gas passes through the catalyst in unit time to the total introduced NOxFor example, the specific calculation formula is as follows:

representing the NOx removal efficiency, t0 is the initial time, t is the time after the flue gas passes through the catalyst bed, C_NOx,0As initial NOx concentration, C_NOxIs the NOx concentration after passing through the catalyst bed.

FIG. 1 shows NOx adsorption capacities of the catalyst prepared in example 1 at 100, 150 and 200 ℃ in a rotary denitration reactor, after fresh catalyst in adsorption breakthrough test and continuous adsorption-regeneration in the rotary denitration reactor for a period of time. The examples illustrate that the low-temperature NOx rapid alternate adsorption-regeneration catalyst obtained by the preparation method of the present invention has a higher NOx adsorption capacity and a higher catalyst regeneration effect at low temperatures.

FIG. 2 shows the NOx removal efficiency of the catalyst in the NOx rapid alternate adsorption-regeneration experiment at different temperatures, which reaches over 90% in the range of 100 ℃ and 200 ℃, particularly 98% at 150 ℃, indicating that the catalyst has good NOx rapid alternate adsorption-regeneration capability at low temperature.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A preparation method of a catalyst for low-temperature NOx rapid alternate adsorption-regeneration is characterized by comprising the following steps: the method comprises the following steps:

1) dissolving soluble cerium salt and other metal salts in water according to a specific proportion, heating and stirring, then heating at 140-240 ℃ to be in a sol state, adding hydrogen peroxide or acid into the sol state, fully stirring to ensure that the pH value of the system is less than or equal to 5, then sequentially roasting at 150-350 ℃ for 2-5 hours, and finally roasting at 450-650 ℃ for 2-5 hours to prepare the carrier; the other metal salt is at least one of Fe, Ni, Mg, Mn, Co or La salt;

2) dissolving soluble copper salt or/and chromium salt in water, adding the carrier prepared in the step 1), adding hydrogen peroxide or acid into the carrier, fully stirring the mixture to ensure that the pH value of the system is less than or equal to 5, then sequentially roasting the mixture at the temperature of 150-350 ℃ for 2-5 hours and roasting the mixture at the temperature of 450-650 ℃ for 2-5 hours to prepare the target catalyst.

2. The method of claim 1, wherein: in the step 1), the soluble cerium salt is one or a mixture of several of cerium nitrate, cerium acetate or cerium chloride; the other metal salt is one or a mixture of more of nitrate, acetate or chloride.

3. The method of claim 1, wherein: in the step 1), the molar ratio of the cerium element to other metal elements is 8:2-4.5: 5.5.

4. The method of claim 1, wherein: in the step 1), the mass ratio of the liquid to the solid in the sol liquid is 1:1-1: 100.

5. The method of claim 1, wherein: in the step 1), the stirring temperature is 65-75 ℃.

6. The method of claim 1, wherein: in the step 1), the acid is one or a mixture of acetic acid, nitric acid or hydrochloric acid.

7. The method of claim 1, wherein: in the step 2), the mass ratio of the copper salt or/and the chromium salt to the carrier is 1:10-1: 100.

8. The method of claim 7, wherein: in the step 2), the mass ratio of the copper salt or/and the chromium salt to the carrier is 1:30-1: 70.

9. The method of claim 1, wherein: in the system in the step 2), the mass ratio of the liquid to the solid is 1:1-1: 100.

10. The method of claim 9, wherein: in the system in the step 2), the mass ratio of the liquid to the solid is 1:10-1: 50.

11. The method of claim 1, wherein: in the step 2), the stirring temperature is 65-75 ℃.

12. NO for low temperature produced by the process of any of claims 1 to 11_xFast alternate adsorption-regeneration of the catalyst.