CN1326620C - Process for preparing bromine blended metal oxide catalyst - Google Patents

Abstract

A preparation method of bromine-doped metal oxide catalyst, the metal oxide precursor and a certain proportion of bromine dopant are dissolved in water to obtain a mixed solution, and then the metal oxide precursor and bromine dopant are added to the mixed solution The dispersant with a total molar amount of 0 to 3 times is used to obtain a gel precursor solution, and the catalyst carrier whose weight is 1 to 100 times the total amount of the metal oxide precursor and bromine dopant is immersed in the above mixed solution or gel precursor solution In the process, the catalyst precursor is obtained after drying treatment, and then calcined in an air atmosphere at 100° C. to 800° C. to obtain a bromine-doped metal oxide catalyst. The present invention adopts bromine doping technology to synthesize bromine-doped modified metal oxide catalyst, introduces bromine element into the metal oxide crystal, and the prepared bromine-doped metal oxide has strong mercury catalytic oxidation ability, and the preparation method simultaneously Simple and has industrial application prospect.

Description

Preparation method of bromine-doped metal oxide catalyst

technical field

The invention relates to a method for preparing a bromine-doped metal oxide catalyst. The prepared catalyst can be applied to flue gas mercury removal, and belongs to the technical fields of inorganic catalytic materials, environmental protection and energy saving.

Background technique

After investigation, the U.S. Environmental Protection Agency believes that coal-fired power plants are currently the largest source of mercury emissions that have not been controlled by humans. Considering the huge amount of mercury emissions from power plants and the accumulation of mercury in fish, it is considered necessary to control them.

Oxidized mercury is easy to control and is not global, so the current mercury control technology mainly focuses on increasing the oxidation state ratio of mercury in flue gas, whether it is activated carbon adsorption injection (ACI), wet flue gas desulfurization (WFGD) method, low temperature Net electrostatic precipitator adsorption method, bag filter method (FF), electrocatalytic oxidation method (ECO) method, calcium-based and oxidant method, mercury catalytic oxidation method, selective catalytic reduction method (SCR) and non-selective catalytic reduction method (SNCR), photochemical methods, etc., the key to their performance is the ratio of the oxidation state of mercury. The influence of various factors on the effect of mercury control technology is also carried out through the impact on the form of mercury.

Activated carbon adsorption technology is the most researched at present, but its application in coal-fired power stations still has the following problems: (1) The performance is unstable, and the efficiency for power stations burning lignite is very low; (2) Activated carbon has a great influence on the quality of fly ash Large, the US Energy Bureau test shows that: the activated carbon adsorption injection method makes the fly ash can not be sold as a concrete additive; (3) The impact of mercury adsorbed by activated carbon on the environment is unknown, and research in this area is currently underway. If the impact is significant, it may also require disposal as solid waste. Therefore, the cost of directly adopting activated carbon adsorption is very high.

Other systems such as wet flue gas desulfurization, low-temperature net electrostatic precipitator adsorption, and bag dust removal are not efficient for burning lignite and sub-bituminous coal, because the proportion of oxidized mercury in the flue gas is small. The electrocatalytic oxidation method, photochemistry, oxidant method and catalytic oxidation method directly use various technical means to increase the proportion of oxidized mercury. From an economic point of view: electrocatalytic oxidation, photochemistry, and oxidant methods require continuous input of energy or chemical reagents in the treatment process. The cost of mercury control is comparable to that of activated carbon injection, which is not in line with my country's national conditions. Even American power stations cannot bear it.

Withum (Characterization of Coal Combustion By-Products for the Re-Evolution of Mercury into Ecosystems. In Proceedings of Air QualityIII: Mercury,, Trace Elements, and Particulate Matter Conference; Arlington, VA, September 9-12, 2002.) research suggests that combustion Mercury adsorbed in coal plant by-products (CUBs) such as fly ash and wet flue gas desulfurization solid waste may be re-released into the environment during waste treatment and use, causing secondary pollution. The Environmental Protection Agency (EPA), the Department of Energy (DOE) and other U.S. agencies have begun to pay attention to and invest a lot of money in research on the final fate of mercury in power station by-products, but the existing mercury control technology does not consider the impact of by-products.

Catalytic oxidation of flue gas mercury removal uses catalytic materials to oxidize elemental mercury in the flue gas into mercury oxide and then adsorbs it. The material is regenerated by heating and decomposing the adsorbed mercury oxide. The elemental mercury obtained after the decomposition of mercury oxide is cooled or other chemical reagents treatment, there is no secondary pollution. The method has low operating cost and can meet the strict mercury emission regulations in the future, so it has strong competitiveness. The catalytic oxidation method also has advantages that the traditional adsorption method does not have: it can adsorb mercury under high temperature conditions, so it is suitable for mercury treatment in a new generation of clean coal combustion systems such as gasification combined cycle power generation systems (IGCC).

Currently commonly used mercury oxidation catalysts include metal oxides, noble metals (Pd, Pt), and other natural materials. Precious metals are easily poisoned in an environment with sulfur, and general metal oxide catalysts and natural materials still have low activity problems.

Contents of the invention

The purpose of the present invention is to provide a method for preparing bromine-doped metal oxide catalysts for the problems of low metal oxide activity and easy poisoning. This preparation method has the advantages of simple process and low production cost. By doping the metal oxide with bromine, the catalytic oxidation performance and anti-poisoning ability of the metal oxide to mercury can be improved.

The present invention is achieved through the following technical scheme: dissolving the metal oxide precursor and a certain proportion of bromine dopant in water to obtain a mixed solution, and then adding the total molar amount of the metal oxide precursor and bromine dopant to the mixed solution 0 to 3 times the dispersant to obtain a gel precursor solution, immerse a catalyst carrier whose weight is 1 to 100 times the total amount of metal oxide precursor and bromine dopant in the above mixed solution or gel precursor solution, and dry The catalyst precursor is obtained after treatment, and then calcined in an air atmosphere at 100° C. to 800° C. to obtain a bromine-doped metal oxide catalyst.

Method concrete steps of the present invention are as follows:

1. Dissolve 68-99.9% by weight metal oxide precursor and 0.1-32% bromine dopant in water, stir evenly to obtain a mixed solution, add a dispersant to the above mixed solution and mix well to obtain a gel The precursor solution, wherein the molar ratio of the dispersant to the total amount of the metal oxide precursor and the bromine dopant is 0-3.

2. Immerse the catalyst carrier whose weight is 1 to 100 times the total weight of the metal oxide precursor and the bromine dopant in the above mixed solution or gel precursor solution, dry naturally in the air or use direct heating at 40 ~100°C drying to obtain the catalyst precursor. The best drying method is direct heating and drying, and the best drying temperature is 50-60°C.

3. Place the catalyst precursor in a heating device and raise the temperature to 100°C-800°C at a rate of 5-40°C/min, and keep at this temperature for 0.5-8 hours to fully decompose the catalyst precursor to obtain bromine-doped Heterometal oxide catalysts. Wherein the optimum heating rate is 9-20° C./minute, and the optimum holding time is 0.5-3 hours.

The metal oxide precursors described in the present invention include metal nitrates, metal carbonates, metal oxalates, metal acetates, and salts that are prone to pyrolysis to produce metal oxides, which can be one or both of them .

The bromine dopant is: HBr, Br ₂ , or bromine-containing inorganic salts.

The dispersant is ethylene glycol, glycerol, citric acid, gelatin, or other compounds containing more than two hydroxyl functional groups.

The catalyst carrier is various metal oxides, various rare earth minerals, various activated carbons and their fibers, artificial and natural molecular sieves, diatomaceous earth, silica gel, various natural ores, carbon nanotubes, etc., which can be one of them species or several.

The present invention adopts bromine doping technology to synthesize bromine-doped modified metal oxide catalyst, which not only doped bromine element in the metal oxide crystal lattice, but also doped bromine element in its interstitial space, bromine-doped metal oxide The content of bromine in the catalyst is 0.1-32%. Such doping will have the following effects on the catalyst:

① The p orbital of the bromine atom and the Zp orbital of the O atom are hybridized to form a new molecular orbital, while the valence band of the metal oxide is basically composed of the 2P orbital of the O atom, the p orbital of the bromine atom and the Zp orbital of the O atom After orbital hybridization, the new molecular orbital is higher than the 2P orbital energy level of the original O atom, thereby changing the electronic state of the metal oxide surface to improve its ability to oxidize mercury.

② Doping introduces impurities into the crystal and causes defects, thereby improving the catalytic activity of metal oxides.

Tests have proved that bromine-doped metal oxide catalysts have a much greater ability to oxidize mercury than undoped metal oxides. Because the doping of bromine atoms changes the electronic state of the catalyst surface, the adsorption capacity of the active center for the product mercury oxide is weakened. The stability is improved, and some oxygen atoms on the surface of the metal oxide are replaced by bromine atoms, which improves its anti-toxic performance.

The present invention has substantive features and significant progress. The catalytic performance of the bromine-doped metal oxide catalyst prepared according to the above preparation method has been greatly improved on the basis of the original oxide, and at the same time, the anti-poisoning performance is enhanced, and the preparation method is simple. , has industrial application prospects.

Description of drawings

Fig. 1 is a graph comparing the oxidation effects of bromine-doped metal oxide catalysts and metal oxide catalysts not doped with bromine on elemental mercury. Measuring instrument: AMA254 mercury meter.

Detailed ways

The weight percentage of bromine in the bromine-doped metal oxides in the following examples is selected within the range of 0.1 to 32%, and the specific salts listed do not indicate that they are the only ones in this category that can be used for the preparation of bromine-doped metal oxides. Other salts of the same class can also be used in this method.

Example 1

Weigh 33.9mg of ammonium bromide and 0.727g of cobalt nitrate in a 50ml beaker, add 25ml of deionized water to dissolve to obtain a mixed solution, weigh 3.6g of aluminum oxide, put it into the mixed solution and soak for 6 hours, filter it, and put it in the oven directly After heating and drying at 60° C. for 8 hours, the catalyst precursor was obtained and placed for use. The catalyst precursor is placed in a muffle furnace and calcined at a rate of 5°C/min to 400°C for 2 hours to obtain a bromine-doped cobalt metal oxide catalyst with high catalytic activity.

The mercury oxidation performance test of the bromine-doped cobalt metal oxide catalyst adopts a fixed reaction bed. The fixed reaction bed uses a quartz glass tube with a diameter of 6 mm, and 5 mg of quartz wool is blocked in the middle of the quartz tube. The concentration of mercury in the gas is controlled using a mercury permeation tube. Mercury concentration detection uses 4% KMnO ₄ /10% H ₂ SO ₄ solution to absorb elemental mercury and then measure it in AMA254 mercury detector, while using SG-921 dual-light digital display mercury detector to track the concentration of elemental mercury in the gas online. Weigh 30 mg of bromine-doped cobalt metal oxide catalyst in a fixed adsorption bed, place the fixed reaction bed vertically in a tubular resistance furnace, and conduct a mercury catalytic oxidation performance test at 250°C for 1 hour. The test results are shown in Figure 1, where the curve Co is the change of the ratio of elemental mercury at the outlet of the reaction bed to the imported elemental mercury over time when the catalyst is cobalt oxide not doped with bromine, and the curve CoBr is the oxidation of cobalt metal doped with bromine as the catalyst. When the material catalyst is used, the ratio of elemental mercury at the outlet of the reaction bed to the elemental mercury at the inlet varies with time. It can be seen that the cobalt oxide doped with bromine has a much higher oxidation ability to mercury than the cobalt oxide without bromine at the adsorption temperature of 250 °C.

Example 2

Dissolve 15ml of hydrogen bromide aqueous solution (0.1mol/L) and 1.01g of nickel nitrate in a 50ml beaker to obtain a mixed solution, add 0.3g of ethylene glycol and stir evenly to obtain a gel precursor solution, add 5.4g of activated carbon and stir well before placing Naturally dry in air for 10 hours and filter to obtain a bromine-doped nickel metal oxide catalyst precursor. The bromine-doped nickel metal oxide catalyst precursor was placed in a muffle furnace and calcined at a rate of 20°C/min to 300°C for 1.5 hours to obtain a bromine-doped nickel metal oxide catalyst with high catalytic activity.

In the catalytic activity test, the same as in Example 1, the test results are shown in Fig. 1, wherein the curve Ni is the change over time of the ratio of the reaction bed outlet element mercury to the import element mercury under the situation of the nickel oxide without doping bromine, and the curve NiBr When the catalyst is bromine-doped nickel oxide, the ratio of elemental mercury at the outlet of the reaction bed to the elemental mercury at the inlet varies with time. It can be seen that the oxidation ability of bromine-doped nickel metal oxide catalyst to mercury is much greater than that without nickel oxide when the adsorption temperature is 250 °C.

Example 3

Dissolve 3.7mg of sodium bromide, 0.464g of cobalt nitrate and 0.602g of copper nitrate in 50ml of water to obtain a mixed solution, add 0.9g of citric acid to the mixed solution, stir well to obtain a gel precursor solution, and add 2.5g of molecular sieves to the in the gel precursor solution, stirred evenly, and then placed in an oven to dry at 60° C. to obtain a bromine-doped cobalt-copper-oxygen composite metal oxide precursor. The bromine-doped cobalt-copper-oxygen composite metal oxide precursor is placed in a muffle furnace and heated to 600°C at a rate of 20°C/min, and kept for 2 hours to obtain the bromine-doped cobalt-copper-oxygen composite metal oxide. The mercury oxidation catalytic activity test shows that the catalyst material has a much higher oxidation effect on mercury than the undoped composite metal oxide.

Example 4

Weigh 0.23ml of Br ₂ and 2.24g of copper nitrate in a 50ml beaker, add 35ml of deionized water to dissolve to obtain a mixed solution, add 1ml of glycerol, stir well to obtain a gel precursor solution, weigh 0.43g of carbon nanotubes in the above After soaking in the solution for 8 hours, filter, put in an oven and dry at 60° C. for 5 hours, evaporate and remove water to obtain a catalyst precursor. Then the catalyst precursor was placed in a muffle furnace, raised to 540° C. at a rate of 35° C./min and kept for 8 hours to obtain a bromine-doped copper metal oxide catalyst with high catalytic activity.

Example 5

Measure 1.5ml of hydrogen bromide solution and 12ml of manganese nitrate solution in a 50ml beaker, add 25ml of deionized water to dilute to obtain a mixed solution, add 0.4g of gelatin to fully dissolve to obtain a gel precursor solution, weigh 8.4g of diatomaceous earth in Soak in the above solution, put into the air and spontaneously ignite and dry to obtain the catalyst precursor. Put the catalyst precursor into a muffle furnace, raise it to 450°C at a rate of 26°C/min, and keep it there for 4 hours to obtain a bromine-doped manganese metal oxide catalyst with high catalytic activity.

Claims (6)

1, a kind of preparation method of bromine blended metal oxide catalyst is characterized in that comprising the steps:

1) be that the bromine adulterant of 68～99.9% metal oxide precursor and 0.1～32% is soluble in water with percentage by weight, stir and obtain mixed solution, do not add dispersant in this mixed solution or further add dispersant and fully mix and obtain gel precursors solution, the mol ratio of dispersant and metal oxide precursor and bromine adulterant total amount is 0～3 in above-mentioned mixed solution that obtains or the gel precursors solution, and described metal oxide precursor is one or both in metal nitrate, metal carbonate, metal oxalate, the metal acetate;

2) be that the catalyst carrier of 1～100 times of metal oxide precursor and bromine adulterant gross weight impregnated in above-mentioned mixed solution or the above-mentioned gel precursors solution with weight, in air, dry naturally or adopt direct mode of heating to obtain catalyst precarsor in 40～100 ℃ of oven dry;

3) catalyst precarsor is positioned in the heater under speed is 5～40 ℃/minute condition and is warming up to 100 ℃～800 ℃, under this temperature, keep catalyst precarsor fully being decomposed in 0.5～8 hour, obtain bromine blended metal oxide catalyst, described metal oxide is cobalt metal oxide, nickel metal oxide, cobalt copper metal oxide, copper metal oxide or manganese metal oxide.

2, according to the preparation method of the bromine blended metal oxide catalyst of claim 1, when it is characterized in that preparing catalyst precarsor, the temperature that adopts direct mode of heating drying is 50～60 ℃.

3, according to the preparation method of the bromine blended metal oxide catalyst of claim 1, it is characterized in that the programming rate described in the step 3 is 9～20 ℃/minute, temperature retention time is 0.5～3 hour.

4, according to the preparation method of the bromine blended metal oxide catalyst of claim 1, it is characterized in that described bromine adulterant is: HBr, Br ₂, or brominated inorganic salts.

5, according to the preparation method of the bromine blended metal oxide catalyst of claim 1, it is characterized in that described dispersant is ethylene glycol, glycerine, citric acid or gelatin.

6,, it is characterized in that described catalyst carrier is for each quasi-metal oxides, various rare-earth mineral, all kinds of active carbon and fiber thereof, manually reach in natural molecule sieve, diatomite, silica gel and the CNT one or more according to the preparation method of the bromine blended metal oxide catalyst of claim 1.