CN103537273B - Denitrating catalyst of a kind of collaborative demercuration and preparation method thereof - Google Patents

Abstract

A denitrification catalyst for synergistic mercury removal, comprising 5%-10% of vanadium pentoxide, 5%-10% of molybdenum trioxide, and titanium dioxide as the rest. The preparation method of the above-mentioned catalyst is as follows: mixing and shaking n-tetrabutyl titanate, absolute ethanol, ammonia water and citric acid solution to obtain a titanium-containing sol; dissolving metavanadic acid and molybdenum trioxide in ammonia water to obtain a mixed solution, Then, the mixed solution is introduced into the sol, shaken and dried to obtain a gel; the catalyst is obtained after the gel is calcined and ground. The synergistic denitrification catalyst for mercury removal provided by the invention can significantly improve the efficiency of catalyzing mercury oxidation and control the ratio of SO ₂ oxidized to SO ₃ , and the catalyst has simple components, reasonable ratio and low cost. The sol-gel method used for preparing the catalyst provided by the invention has good dispersibility of each component in the prepared catalyst, and well realizes uniform doping of each active component at the molecular level.

Description

A denitrification catalyst for synergistic mercury removal and preparation method thereof

technical field

The invention relates to a denitrification catalyst for synergistic mercury removal and a preparation method thereof, belonging to the technical field of air pollution purification.

Background technique

Coal is the most abundant fossil fuel resource. China is the world's largest coal producer and consumer. Since the 1990s, my country's coal production and consumption have been ranked first in the world for a long time. The burning of coal, especially the operation of coal-fired power plants, will bring about serious environmental pollution problems. Mercury and nitrogen oxides emitted by coal-fired power plants are the main sources of human-induced emissions into the atmosphere. Mercury released into the atmosphere will accumulate in the human body after entering the biosphere, causing damage to the nervous system of the human body and seriously endangering human health. Nitrogen oxides (NO _x ) will cause local environmental problems such as acid rain and photochemical smog, and pose a serious threat to human survival. Based on this, the emission standards of mercury and nitrogen oxides were stipulated for the first time in the thermal power plant pollutant emission standards promulgated by the state in 2011. The emission standard of mercury is 0.03mg/Nm ³ and the emission standard of nitrogen oxides is 100mg/Nm ³ .

Mercury mainly exists in three forms in coal-fired flue gas: elemental mercury (Hg ⁰ ), particulate mercury (Hg ^p ) and divalent mercury (Hg ²⁺ ). Among them, particulate mercury (Hg ^p ) is easily removed by electrostatic precipitator or bag filter along with particulate matter, and divalent mercury (Hg ²⁺ ) is easily removed by wet desulfurization device (FGD) because it is easily soluble in water. Elemental mercury (Hg ⁰ ) is difficult to remove by existing flue gas purification devices due to its strong volatility and insolubility in water. Therefore, the technical problems of mercury removal in coal-fired flue gas mainly focus on the removal of elemental mercury in flue gas. At present, there are two main methods for controlling the removal of elemental mercury in coal-fired power plants: adsorption and oxidation. Activated carbon injection is a good adsorption mercury removal method, but it is expensive, and the fly ash mixed with high carbon content is difficult to be effectively utilized. Oxidative mercury removal is to use a catalyst to catalytically oxidize elemental mercury into divalent mercury, and then use a wet desulfurization device (WFGD) to remove divalent mercury. Oxidative mercury removal is currently the main method for elemental mercury removal from coal-fired flue gas.

The NO _x removal method in coal-fired flue gas generally adopts the selective catalytic reduction method. In order to improve the reaction efficiency, a denitrification catalyst (with vanadium pentoxide as the main active component and titanium dioxide as the substrate, also known as SCR catalyst) is generally used as an auxiliary. The denitrification catalyst has the performance of oxidizing elemental mercury while reducing _NOx . However, under the typical SCR temperature window (350°C-400°C), although the _NOx reduction rate of the denitrification catalyst can reach more than 80%, it is not suitable for elemental mercury. However, the oxidation efficiency of mercury can only reach 20%-50%. The main reason is that the optimum temperature for mercury oxidation of the denitrification catalyst is lower than 300°C, so it cannot be achieved at the suitable working temperature (350°C-400°C) for _NOx reduction. Ideal mercury oxidation efficiency.

In addition, because in the denitrification catalyst, if the content of the main active component vanadium pentoxide is high, the ratio of _SO2 in the coal-fired flue gas to be oxidized to _SO3 will increase significantly, and _SO3 will make the metal on the surface of the denitrification catalyst Oxide reacts to generate sulfate, which poisons the catalyst. Therefore, in traditional SCR denitration catalysts, the content of vanadium is generally lower than 3%. Since the content of the active substance vanadium pentoxide in the denitrification catalyst is relatively small, the oxidation active sites that can be provided to the elemental mercury are relatively few, resulting in a further reduction in the oxidation efficiency of the elemental mercury. Therefore, it is difficult to make the elemental mercury in the flue gas meet the emission standards stipulated by the state by using the flue gas purification device of the existing coal-fired power plant and the traditional denitrification catalyst.

Invention patent application "a denitration catalyst with mercury removal", publication date: 2012.3.7, publication number: CN102366722A, discloses a denitration catalyst with mercury removal, the general chemical formula is: MX _n -V ₂ O ₅ - Y/TiO ₂ , wherein, M is selected from metal elements Fe, Cu, Mn or Co; X is a halogen Cl or Br; Y is WO ₃ or MoO ₃ , n=2~4; the weight ratio is: M1~10, V1～1.5, W or Mo7.5～8.5, TiO ₂ 75～100. The catalyst is prepared by impregnating V ₂ O ₅ -WO ₃ /TiO ₂ or V ₂ O ₅ -MoO ₃ /TiO ₂ with MCl _n or MBr _n , drying and roasting. Due to the addition of transition metal halides, the catalyst can oxidize zero-valent mercury Hg ⁰ into Hg ²⁺ by utilizing the strong oxidation of Cl or Br and the redox properties of transition metal elements, which overcomes the traditional K and Na barriers. The influence of halide on the acid active point of SCR catalyst ensures the catalytic activity, so that the catalyst maintains a high denitrification efficiency under the flue gas of 300-450 °C, and at the same time, the oxidation rate of Hg is increased from the traditional below 30% to 85.1% to 93.8%, which greatly improves the catalytic efficiency. At the same time, the SCR denitration catalyst treated with transition metal halides will not increase the SO ₂ /SO ₃ conversion rate, avoiding catalyst poisoning and secondary pollution.

However, the above catalysts also have obvious defects and deficiencies: first, the addition of transition metal halides as oxidants greatly increases the cost of the catalyst; second, the content of the main active component V ₂ O ₅ is low (1-1.5%), V The oxidation efficiency of ₂ O ₅ to oxidize elemental mercury is low; the third is that although WO ₃ or MoO ₃ is added to the catalyst, its catalytic effect and catalytic effect in the reaction of reducing NO _x and oxidizing elemental mercury have not been clarified. Therefore, the reasonable proportion of the above-mentioned substances in the catalyst cannot be given.

Contents of the invention

The technical purpose of the present invention is to solve the defects and deficiencies such as high cost and unreasonable distribution ratio of active components in existing denitrification catalysts that use transition metal halides as oxidants to oxidize elemental mercury, and provide a synergistic denitration denitrification catalyst Catalyst and preparation method thereof, the active ingredient of the catalyst is composed of vanadium pentoxide and molybdenum trioxide, through the addition of molybdenum trioxide and a reasonable proportion, the catalyst can significantly improve catalytic mercury oxidation while maintaining good catalytic denitrification performance The efficiency, and can effectively control the ratio of SO ₂ oxidation to SO ₃ , and the catalyst components are simple, the ratio is reasonable, and the cost is low.

The technical solution adopted by the present invention to achieve the technical purpose is: a denitrification catalyst for synergistic mercury removal, characterized in that: the catalyst includes vanadium pentoxide with a mass percentage of 5% to 10%, and the mass percentage is 5% to 10% % molybdenum trioxide, and the remainder of the catalyst is titanium dioxide.

A denitrification catalyst for synergistic mercury removal, the catalyst is ground into 100-325 mesh.

A method for preparing a denitrification catalyst for synergistic mercury removal, comprising the following steps:

(1) Uniformly mix a quantitative volume of n-tetrabutyl titanate and an equal volume of absolute ethanol at 40°C to obtain a mixed solution;

(2) According to the ratio of ammonia water and n-tetrabutyl titanate at a volume ratio of 1:3, introduce ammonia water into the mixed solution obtained in step (1), and shake at 40°C for 1 hour to obtain titanium-containing sol A;

(3) Prepare a citric acid solution with a mass concentration of 10%, take a citric acid solution equal in volume to the ammonia water in step (2), introduce it into sol A, shake it at 40°C for 10 minutes, and obtain sol B;

(4) Weigh the metavanadium solid with a vanadium element content of 5 to 10 parts by weight, dissolve it in a nitric acid solution equal to the volume of ammonia in step (2) to obtain solution A, and weigh 5 to 10 parts by weight of Molybdenum trioxide is dissolved in ammoniacal water equal to the volume of ammoniacal water in step (2) to obtain solution B;

(5) Introduce the solutions A and B obtained in step (4) into sol B with a titanium element content of 80-90 parts by weight, then add concentrated nitric acid to adjust the pH value to 1, and shake at 40°C for 5 hours, Then the temperature was raised to 70°C and dried at 70°C for 48 hours to obtain a gel;

(6) Put the gel obtained in step (5) in a muffle furnace, raise the temperature to 400°C, calcinate for 5 hours, and grind to obtain the catalyst.

A method for preparing a denitrification catalyst for synergistic mercury removal, in the step (5), the gel is heated at a heating rate of 6° C./min.

Although titanium-vanadium-molybdenum catalysts have been used in the prior art, the prior art has not carried out relevant theoretical research on the effect of molybdenum addition on mercury oxidation, and thus the catalytic principle and mechanism of molybdenum in vanadium-titanium catalysts have not been obtained. Catalytic effect naturally also fails to obtain the reasonable ratio of molybdenum in the catalyst.

The applicant of the present invention has found through research that after adding molybdenum trioxide to the traditional titanium vanadium catalyst, it is beneficial to improve the structural characteristics of the catalyst and increase the surface density of the catalyst. acid sites, in the titanium vanadium catalyst, the main active substance capable of oxidizing mercury is vanadium pentoxide, and in the titanium vanadium molybdenum catalyst, in addition to the role of vanadium pentoxide, molybdenum trioxide and vanadium molybdenum complexes will It is beneficial to the oxidation of mercury, so it can significantly improve the oxidation efficiency of elemental mercury. More importantly, molybdenum will not participate in the oxidation of _SO2 , and the addition of molybdenum leads to the improvement of the catalyst structure, which is not conducive to the adsorption _{of SO2} on the catalyst surface, thus preventing the further conversion of _SO2 to _SO3 , so the addition of molybdenum Not only will it not increase, but it will reduce the conversion level of SO ₂ to SO ₃ . Therefore, on the premise of adding molybdenum, the content of vanadium pentoxide, the main active component, can be further increased, so that the oxidation rate of SO ₂ to SO ₃ can be maintained at a low level, and the oxidation efficiency of elemental mercury can be significantly improved. .

The applicant of the present invention has studied the effect of adding molybdenum on the catalyst's mercury oxidation under high temperature and high _SO2 conditions through a large number of experiments. The experimental results show that when 5% to 10% of molybdenum is added, even if the content of vanadium pentoxide reaches 5% to 10% (generally not more than 3% in the prior art), the ratio of SO ₂ to SO ₃ is still maintained The low level within 2%, while at the same time, the NO _x reduction rate can reach 85-90%, and the mercury oxidation rate can reach 75-82%. The experimental results also show that when the content of molybdenum is 5% to 10%, the oxidation efficiency of mercury remains high and roughly similar; when the content of molybdenum is lower than 5% or higher than 10%, the oxidation efficiency of mercury is all the same. lower. Therefore, the optimal ratio of molybdenum in the catalyst is 5% to 10%.

Compared with the titanium-vanadium-molybdenum catalyst in the prior art, the catalyst provided by the invention does not need to add transition metal halides, only by rationally proportioning the content of molybdenum trioxide and simultaneously increasing the content of vanadium pentoxide, the active component can be trioxidized Molybdenum and vanadium pentoxide achieve the best catalytic effect, thereby solving technical problems such as the low mercury oxidation rate under high temperature conditions, and the high proportion of _SO2 oxidized to SO3 when the oxidant content is high, and significantly reduces the product cost of the catalyst.

The preparation method of the catalyst among the present invention is the sol-gel method, and then the catalyst sample is calcined and shaped, while the preparation method of the SCR catalyst in the prior art is generally the impregnation method, and the advantage of the sol-gel method over the impregnation method is that each catalyst in the prepared catalyst is The dispersion of the components is good, and the uniform doping of each active component in the catalyst at the molecular level is well realized.

Detailed ways

The preparation of embodiment 1 catalyst of the present invention (TV ₅ M ₅ )

Follow these steps:

(1) Uniformly mix a quantitative volume of n-tetrabutyl titanate and an equal volume of absolute ethanol at 40°C to obtain a mixed solution;

(2) According to the ratio of ammonia water and n-tetrabutyl titanate at a volume ratio of 1:3, introduce ammonia water into the mixed solution obtained in step (1), and shake at 40°C for 1 hour to obtain titanium-containing sol A;

(3) Prepare a citric acid solution with a mass concentration of 10%, take a citric acid solution equal in volume to the ammonia water in step (2), introduce it into sol A, shake it at 40°C for 10 minutes, and obtain sol B;

(4) Take by weighing the metavanadic acid solid with a vanadium element content of 5 parts by weight, dissolve it in a nitric acid solution equal in volume to the ammoniacal liquor in step (2), obtain solution A, take by weighing 5 parts by weight of molybdenum trioxide, Dissolved in ammonia water of equal volume to the ammonia water in step (2), to obtain solution B;

(5) Introduce the solutions A and B obtained in step (4) into sol B with a titanium content of 90 parts by weight, then add concentrated nitric acid to adjust the pH value to 1, shake at 40°C for 5 hours, and then heat up to 70°C and drying at 70°C for 48 hours to obtain a gel;

(6) Put the gel obtained in step (5) in a muffle furnace, raise the temperature to 400°C at a heating rate of 6°C/min, calcinate for 5 hours, grind, and then grind the calcined product to 100-325 mesh , to obtain catalyst TV ₅ M ₅ .

Embodiment 2 Preparation of the catalyst of the present invention (TV ₅ M ₁₀ )

Follow these steps:

Steps (1) to (3) are the same as in Example 1;

(4) Take by weighing the metavanadic acid solid with a vanadium element content of 5 parts by weight, dissolve it in a nitric acid solution equal in volume to the ammoniacal liquor in step (2), obtain solution A, and weigh 10 parts by weight of molybdenum trioxide, Dissolved in ammonia water of equal volume to the ammonia water in step (2), to obtain solution B;

(5) Introduce the solutions A and B obtained in step (4) into sol B with a titanium element content of 85 parts by weight, then use concentrated nitric acid to adjust the pH value of the mixed solution to 1, and shake it at 40°C for 5 hours, then Raise the temperature to 70°C and dry at 70°C for 48 hours to obtain a gel;

(6) Put the gel obtained in step (5) in a muffle furnace, raise the temperature to 400°C at a heating rate of 6°C/min, calcinate for 5 hours, grind, and then grind the calcined product to 100-325 mesh , to obtain catalyst TV ₅ M ₁₀ .

Example 3 Preparation of catalyst of the present invention (TV ₁₀ M ₅ )

Follow these steps:

Steps (1) to (3) are the same as in Example 1;

(4) Take by weighing the metavanadic acid solid with a vanadium element content of 10 parts by weight, dissolve it in a nitric acid solution equal to the volume of ammonia in step (2), to obtain solution A, and take by weighing 5 parts by weight of molybdenum trioxide, Dissolved in ammonia water of equal volume to the ammonia water in step (2), to obtain solution B;

(5) Introduce the solutions A and B obtained in step (4) into sol B with a titanium element content of 85 parts by weight, then use concentrated nitric acid to adjust the pH value of the mixed solution to 1, and shake it at 40°C for 5 hours, then Raise the temperature to 70°C and dry at 70°C for 48 hours to obtain a gel;

(6) Put the gel obtained in step (5) in a muffle furnace, raise the temperature to 400°C at a heating rate of 6°C/min, calcinate for 5 hours, grind, and then grind the calcined product to 100-325 mesh , to obtain catalyst TV ₁₀ M ₅ .

Example 4 Preparation of catalyst of the present invention (TV ₁₀ M ₁₀ )

Follow these steps:

Steps (1) to (3) are the same as in Example 1;

(4) Take by weighing the metavanadic acid solid with a vanadium element content of 10 parts by weight, dissolve it in a nitric acid solution equal in volume to the ammoniacal liquor in step (2), obtain solution A, take by weighing 10 parts by weight of molybdenum trioxide, Dissolved in ammonia water of equal volume to the ammonia water in step (2), to obtain solution B;

(5) Introduce the solutions A and B obtained in step (4) into sol B with a titanium element content of 80 parts by weight, then use concentrated nitric acid to adjust the pH value of the mixed solution to 1, and shake it at 40°C for 5 hours, then Raise the temperature to 70°C and dry at 70°C for 48 hours to obtain a gel;

(6) Put the gel obtained in step (5) in a muffle furnace, raise the temperature to 400°C at a heating rate of 6°C/min, calcinate for 5 hours, grind, and then grind the calcined product to 100-325 mesh , to obtain catalyst TV ₁₀ M ₁₀ .

Preparation of comparative example 1 catalyst (TV ₅ )

Follow these steps:

Steps (1) to (3) are the same as in Example 1;

(4) Weighing the metavanadic acid solid with a vanadium element content of 5 parts by weight, and dissolving it in a nitric acid solution equal to the volume of ammonia in step (2), to obtain solution A;

(5) Import solution A obtained in step (4) into sol B with a titanium element content of 95 parts by weight, then use concentrated nitric acid to adjust the pH value of the mixed solution to 1, shake at 40°C for 5h, and then heat up to 70°C °C and dried at 70 °C for 48 hours to obtain a gel;

(6) Put the gel obtained in step (5) in a muffle furnace, raise the temperature to 400°C at a heating rate of 6°C/min, calcinate for 5 hours, grind, and then grind the calcined product to 100-325 mesh , to obtain catalyst TV ₅ .

Preparation of comparative example 2 catalyst (TV ₁₀ )

Follow these steps:

Steps (1) to (3) are the same as in Example 1;

(4) Weigh the metavanadic acid solid with a vanadium element content of 10 parts by weight, and dissolve it in a nitric acid solution equal to the volume of ammonia in step (2) to obtain solution A;

(5) Import solution A obtained in step (4) into sol B with a titanium element content of 90 parts by weight, then use concentrated nitric acid to adjust the pH value of the mixed solution to 1, shake at 40°C for 5h, and then heat up to 70°C °C and dried at 70 °C for 48 hours to obtain a gel;

(6) Put the gel obtained in step (5) in a muffle furnace, raise the temperature to 400°C at a heating rate of 6°C/min, calcinate for 5 hours, grind, and then grind the calcined product to 100-325 mesh , to obtain catalyst TV ₁₀ .

Catalyst activity test experiment

Test the activity of six catalysts prepared by four embodiments of the present invention and two comparative examples respectively on the fixed-bed reactor, and the test items include: mercury oxidation rate, NO _x reduction rate and SO ₂ oxidized to SO ₃ ratio . The test conditions are: the simulated flue gas flow rate is 0.9Nm ³ /h; the simulated flue gas composition is 0.04%NO, 0.04%NH ₃ , 6%O ₂ , 13%CO ₂ , 8%H ₂ O, 0.08%SO ₂ , 0.002% HCl, 55μg/Nm ³ ; the reaction temperature is 350°C; the catalyst dosage for a single test is 0.3g. The test results are shown in the table below:

Example contrast real Example Example 2 contrast real Example 1 Example 2

Example 1 1 Example 2 catalyst TV ₅ TV ₅ M ₅ TV ₅ M ₁₀ TV ₁₀ TV ₁₀ M ₅ TV ₁₀ M ₁₀ Mercury oxidation rate 53% 81% 75% 49% 82% 78% NO _x reduction rate 89% 90% 85% 91% 86% 88% _SO2 oxidation rate 3% 2% 1.5% 6% 1.5% 1.8%

It can be seen from the above table: under the premise of no molybdenum added, when the content of vanadium is increased to 5-10%, although the NO _x reduction rate can reach a high level of about 90%, the mercury oxidation rate can only reach 50%, and the SO ₂ oxidation rate reaches 3% to 6%, which is far beyond the specified standard; when 5 to 10% molybdenum is added and the vanadium content is increased to 5 to 10%, the titanium vanadium catalyst is in the typical SCR temperature window (350°C-400°C), the _NOx reduction rate can maintain a high level of 85-91%, while the efficiency of mercury oxidation is greatly increased to 75-82%, and the _SO2 oxidation rate is maintained at a low level within 2%. Apparently, the various performance indexes of the vanadium-titanium-molybdenum catalyst provided by the present invention have reached a very satisfactory level.

Claims (2)

1. prepare the method for the denitrating catalyst of collaborative demercuration for one kind, it is characterized in that: described catalyst comprises the vanadic anhydride that mass percent is 5% ~ 10%, mass percent is the molybdenum trioxide of 5% ~ 10%, all the other compositions in described catalyst are titanium dioxide, and the preparation method of described catalyst comprises the following steps:

(1) Homogeneous phase mixing under 40 DEG C of conditions by positive for the metatitanic acid of determined volume four butyl esters and isopyknic absolute ethyl alcohol, obtains mixed liquor;

(2) according to ammoniacal liquor and positive four butyl esters of metatitanic acid with volume ratio be the ratio of 1:3, ammoniacal liquor steps for importing (1) obtained in mixed liquor, in 40 DEG C of environment, shakes 1h, obtain the Sol A of titaniferous;

(3) configuration quality concentration is the citric acid solution of 10%, gets and the isopyknic citric acid solution of ammoniacal liquor in step (2), imports in Sol A, shake 10min, obtain sol B under 40 DEG C of conditions;

(4) the inclined vanadium propylhomoserin solid that v element content is 5 ~ 10 weight portions is taken, be dissolved in the isopyknic salpeter solution of ammoniacal liquor in step (2), obtain solution A, take the molybdenum trioxide of 5 ~ 10 weight portions, be dissolved in the isopyknic ammoniacal liquor of ammoniacal liquor in step (2), obtain solution B;

(5) it is in the sol B of 80 ~ 90 weight portions that solution A step (4) obtained, B successively import titanium elements content, then add red fuming nitric acid (RFNA) and will regulate pH value to 1, and under 40 DEG C of conditions, shake 5h, be then warming up to 70 DEG C and under 70 DEG C of conditions dry 48h, obtain gel;

(6) gel that step (5) obtains is placed in Muffle furnace, is warming up to 400 DEG C, calcining 5h, grinding, obtains this catalyst.

2. a kind of method preparing the denitrating catalyst of collaborative demercuration according to claim 1, is characterized in that: in described step (6), gel heats up according to the heating rate of 6 DEG C/min.