CN109107578B - Preparation method of monolithic catalyst for catalytic oxidation of VOCs - Google Patents
Preparation method of monolithic catalyst for catalytic oxidation of VOCs Download PDFInfo
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- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/78—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with alkali- or alkaline earth metals
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- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
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Abstract
The invention discloses a preparation method of an integral catalyst for catalytic oxidation of VOCs. Dissolving inorganic salts of Co and Al in water according to a proportion to prepare a solution A; mixing NaOH and Na2CO3Dissolving in water to obtain solution B. Solution A, B was added dropwise to 100ml of deionized water with vigorous stirring at 40 ℃ to control the pH of the mixture at 8-11. And (3) continuing stirring for 30min after dripping, crystallizing in a dark place for 12h, performing suction filtration to obtain a filter cake, washing the filter cake to be neutral by using deionized water, drying the filter cake in an oven, and grinding the filter cake to obtain the Co/Al hydrotalcite precursor. Mixing water, citric acid and glycol according to a certain proportion, heating and stirring, and dispersing the catalyst precursor into the solution to obtain a colloidal solution. Immersing the pretreated cordierite carrier into the colloidal solution for 12h, taking out, blowing away the redundant solution in the carrier pore channel, drying and roasting. The catalyst prepared by the method has the advantages of high catalytic activity, strong selectivity, strong hydrothermal stability and the like, and has good application value and prospect.
Description
Technical Field
The invention relates to a preparation method of a catalyst, in particular to a preparation method of an integral catalyst for catalytic oxidation of VOCs.
Background
VOCs (volatile Organic Compounds), volatile Organic pollutants. At room temperature, such organic materials are present as liquids or solids, but have a saturated vapor pressure greater than 0.0007 atm (0.01psia) and a boiling point below 260 ℃. The atmospheric fine particulate matter (PM2.5) is a core pollutant polluted by dust haze and photochemical smog, and the VOCs are important precursor substances of the PM2.5, and the past experience shows that the emission of the VOCs can be controlled to effectively reduce the dust haze and the photochemical smog.
The sources of the VOCs are mainly divided into artificial sources and natural sources, wherein the natural sources comprise plant emission, forest fire, wild animal emission, wetland anaerobic process and the like; artificial sources include industrial sources, traffic sources, agricultural sources, and the like. Research shows that the discharge amount of industrial sources is not only huge and accounts for more than half of the total amount of the artificial sources, but also the types and the amounts of the generated VOCs are different due to complex and various production processes. In recent years, research on the emission conditions and characteristics of industrial-source VOCs mainly focuses on both the key industry and the key areas. Wherein the key industries mainly comprise petroleum refining, synthetic materials, coatings, pharmacy, printing and the like; the key areas mainly include the areas of bead triangle, Long triangle and Jingjin Ji.
With the continuous and deep research, the human beings have more profound understanding on the harm of the VOCs. Firstly, the direct threat to human health is caused, most of VOCs gases have high toxicity and carcinogenicity, and long-term contact can not only cause damage to the skin of a human body, but also seriously affect the nervous system, the respiratory system and the immune system of the human body. Secondly, VOCs pollute the ecological environment, and under the irradiation of ultraviolet rays, VOCs can react with SO in the atmosphere2、NOxAnd other polluted gases react to generate secondary pollutants such as photochemical smog, secondary organic aerosol and the like, and damage the ozone layer of the earth.
There are two main approaches to the end-treatment of VOCs. One is destruction and conversion, i.e., complex VOCs are collected and converted into non-toxic and harmless inorganic small molecule compounds such as carbon dioxide and water by chemical or biochemical reactions in the presence of light, heat, catalysts or microorganisms. And the other is recovery, wherein the principle of the recovery path is enrichment recycling, VOCs are collected by changing temperature and pressure or adopting physical methods such as selective adsorbent, selective permeable membrane and the like, and the VOCs are returned to the system for recycling after simple treatment.
The most common and most efficient method of destruction and conversion technology is catalytic oxidation, and catalysts for catalytic oxidation of VOCs can be broadly classified into three types: noble metal catalysts, non-noble metal oxide catalysts, and mixed metal catalysts. Among them, the metal oxide catalyst has received extensive attention from researchers due to its excellent low-temperature catalytic activity, relatively low cost, and low susceptibility to poisoning, and thus is applied to catalytic oxidation of VOCs. The prior non-noble metal oxide catalyst has the problem that the catalyst prepared by the traditional method is a granular catalyst and is inconvenient for large-scale industrial application.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and develop a preparation method of a catalyst for catalytic oxidation of VOCs, which has the advantages of high efficiency, small wind resistance, strong stability, wide application range and long service life.
In order to solve the technical problem, the preparation method of the monolithic catalyst for catalytic oxidation of VOCs provided by the invention specifically comprises the following steps:
step one, adding Co (NO)3)2·6H2O and Al (NO)3)3·9H2Dissolving O in deionized water to obtain solution A, wherein Co is2+And Al3+The molar ratio of (1) to (4) is 0.4:1-14:1, and the concentration of total metal ions is 0.48 mol/L; mixing NaOH and Na2CO3Dissolving in deionized water to obtain solution B, wherein NaOH is 0.96mol/L, and Na is added2CO3The concentration is twice of the concentration of the trivalent ions;
step two, simultaneously dripping the solution A and the solution B into a beaker filled with a proper amount of deionized water, simultaneously violently stirring at 40 ℃, adjusting the dripping speed of the solution A and the solution B to control the pH of the mixed solution to be 8-11, continuously stirring for 30min after dripping is finished, placing the obtained suspension in a dark place for crystallization, and then carrying out suction filtration to obtain a filter cake;
washing the obtained filter cake with deionized water for 3-5 times until the washing liquid is neutral, drying and grinding into powder to obtain a Co/Al hydrotalcite precursor of the monolithic catalyst for catalytic oxidation of VOCs; the grinding process is as uniform and full as possible, and the stability of the subsequent preparation of colloidal solution is ensured.
Step four, mixing water, citric acid and glycol according to the molar ratio of 15 (0.5-2) to 1, and stirring at the temperature of 80-100 ℃ to obtain a transparent and viscous solution; generally, the higher the temperature, the greater the viscosity of the solution.
Step five, dispersing the Co/Al hydrotalcite precursor ground into powder into the transparent and viscous solution prepared in the step four, and stirring for 3-4 hours to form a uniform and stable colloidal solution;
step six, immersing the cordierite carrier in a nitric acid solution with the concentration of 10 wt% for 2-4h for pretreatment, taking out, drying and weighing for later use;
and step seven, putting the pretreated cordierite carrier into the colloidal solution obtained in the step five, soaking for 10-12h, drying for 4h at 110 ℃, and then roasting for 4h at 200-600 ℃, wherein the obtained product is the monolithic catalyst for catalytic oxidation of VOCs.
Compared with the prior art, the invention has the beneficial effects that:
(1) the present invention utilizes cordierite as carrier material to artificially synthesize cordierite (2 MgO)2·Al2O3·5SiO2) It is a synthetic material with low expansion coefficient, good thermal stability and low dielectric constant, and can be widely used as refractory material, porous material and composite material. The cordierite is used as the carrier of the monolithic catalyst, so that the pressure drop in the organic waste gas treatment process can be effectively reduced, the catalytic efficiency of the catalyst is improved, and the treatment cost is reduced.
(2) The invention adopts Co/Al hydrotalcite as the active component of the catalyst, Co/Al hydrotalcite ([ Co ] Al hydrotalcite)1-x 2+Alx 3+(OH)2]x+(CO3 2-)x/2·mH2O) has higher low-temperature catalytic activity on the VOCs components, and has comprehensive excellent characteristics of high stability, corrosion resistance, difficult poisoning and the like, thereby becoming one of popular catalytic materials in the VOCs treatment field.
(3) The invention prepares water, citric acid and glycol into viscous transparent solution under the condition of heating and stirring, disperses active ingredient hydrotalcite into the transparent viscous solution to form uniform and stable colloidal solution, and then carries out dipping operation. In this way, the active component can be coated on the surface of the cordierite carrier more uniformly and stably, and simultaneously the blockage of the channel of the cordierite carrier can be effectively avoided.
Drawings
FIG. 1 is a graph of acetone conversion for example 1 monolithic catalyst prepared according to the present invention;
FIG. 2 is a graph of the conversion of ethyl acetate for monolithic catalyst example 2 prepared in accordance with the present invention.
Detailed Description
The invention will be described in more detail with reference to the following figures and embodiments, but the scope of the invention is not limited thereto.
The preparation method of the invention has the design idea that: dissolving inorganic salts of Co and Al in water according to a proportion to prepare a solution A; mixing NaOH and Na2CO3Dissolving in water to obtain solution B. Under the condition of vigorous stirring at 40 ℃, the solution A, B is dropwise added into a proper amount of deionized water (the amount of the deionized water is suitable for being submerged in a magnetic stirrer), and the pH of the mixed solution is controlled by adjusting the dropwise adding speed of the solution to be about 10 +/-2. And after titration, continuously stirring for 30min, then placing in a dark place for crystallization for 12h, carrying out suction filtration to obtain a filter cake, washing with ultrapure water to be neutral, placing in an oven for drying, and grinding into powder to obtain the Co/Al hydrotalcite precursor. Mixing water, citric acid and glycol according to a certain proportion, stirring under a heating condition to obtain a transparent and sticky solution, dispersing the prepared powdery catalyst precursor into the solution, and stirring to obtain a uniform and stable colloidal solution. Immersing the pretreated (acid-washed and dried) cordierite carrier into the colloidal solution for 12h, taking out, blowing off redundant solution in the carrier pore channel by using compressed air, drying, and roasting at high temperature. The catalyst prepared by the method has the advantages of high catalytic activity, strong selectivity, strong hydrothermal stability and the like, and has good application value and prospect.
Example 1: preparing a monolithic catalyst for the catalytic oxidation of VOCs by the following steps:
step one, 29.103g of Co (NO)3)2·6H2O and 7.5026g of Al (NO)3)3·9H2Dissolving O in deionized water to obtain 250ml solution A, wherein Co is2+And Al3+The molar ratio of (1) to (5), the concentration of total metal ions is 0.48 mol/L; 0.24mol, 9.6g of NaOH and 0.04mol, 4.2396g of Na were added2CO3Dissolved in deionized water250ml of solution B was prepared in water.
Step two, simultaneously dripping the solution A and the solution B into a beaker filled with 100ml of deionized water (the amount of the deionized water is determined by the fact that a magnetic stirrer is not used), meanwhile, violently stirring at 40 ℃, adjusting the dripping speed of the solution A and the solution B to control the pH of the mixed solution to be 10-11, continuously stirring for 30min after dripping is finished, placing the obtained suspension in a dark place for crystallization for 12h, and then carrying out suction filtration to obtain a filter cake;
washing the obtained filter cake with deionized water for 3-5 times until the washing liquid is neutral, drying and grinding into powder to obtain a Co/Al hydrotalcite precursor of the monolithic catalyst for catalytic oxidation of VOCs;
step four, mixing 27g of water, 28.812g of citric acid and 6.2068g of ethylene glycol (the molar ratio of the water to the citric acid to the ethylene glycol is 15:1.5:1), and stirring for 3 hours at 80 ℃ to obtain a transparent and viscous solution;
step five, dispersing the Co/Al hydrotalcite precursor ground into powder into the transparent and viscous solution prepared in the step four, and stirring for 3 hours to form a uniform and stable colloidal solution, wherein the colloidal solution is coating slurry of the catalyst;
step six, immersing the cordierite carrier in a nitric acid solution with the concentration of 10 wt% for 4 hours for pretreatment, taking out, drying for 4 hours, and weighing for later use;
and step seven, putting the pretreated cordierite carrier into the colloidal solution obtained in the step five, soaking for 12 hours, drying for 4 hours at the temperature of 110 ℃, and then roasting for 4 hours at the temperature of 300 ℃, wherein the obtained product is the monolithic catalyst for catalytic oxidation of VOCs.
The monolithic catalyst prepared in the example 1 is subjected to fixed bed reaction, the mixed gas contains 1000ppm of VOCs gas, and the space velocity is 1500h-1And under the condition of the reaction temperature of 100 ℃ and 320 ℃, respectively testing the inlet concentration and the outlet concentration of the fixed bed reactor, and calculating the conversion rate of the VOCs according to (inlet concentration-outlet concentration)/inlet concentration multiplied by 100%.
As shown in figure 1, a fixed bed catalytic oxidation reaction evaluation device is adopted to perform a catalytic activity test on the prepared catalyst, so that the acetone conversion rate of the catalyst can reach more than 80% at the temperature of about 230 ℃, the acetone conversion rate of the monolithic catalyst can reach more than 99% at the temperature of 280 ℃, and the activity of the catalyst can be repeatedly tested for many times without obvious reduction.
Example 2: preparing a monolithic catalyst for the catalytic oxidation of VOCs by the following steps:
step one, 26.1927g of Co (NO)3)2·6H2O and 11.2539g of Al (NO)3)3·9H2Dissolving O in deionized water to obtain 250ml solution A, wherein Co is2+And Al3+The molar ratio of (A) to (B) is 3:1, and the concentration of total metal ions is 0.48 mol/L; 0.24mol, 9.6g of NaOH and 0.06mol, 6.3594g of Na were added2CO3Dissolved in deionized water to prepare 250ml of solution B.
Step two, simultaneously dripping the solution A and the solution B into a beaker filled with 100ml of deionized water, stirring vigorously, adjusting the dripping speed of the solution A and the solution B to control the pH of the mixed solution to be 8-10, continuing stirring for 30min after dripping is finished, placing the obtained suspension in a dark place for crystallization for 12h, and then carrying out suction filtration to obtain a filter cake;
washing the obtained filter cake with deionized water for 3-5 times until the washing liquid is neutral, drying and grinding into powder to obtain a Co/Al hydrotalcite precursor of the monolithic catalyst for catalytic oxidation of VOCs;
step four, mixing 27g of water, 19.2140g of citric acid and 6.2068g of ethylene glycol (the molar ratio of the water to the citric acid to the ethylene glycol is 15:1:1), and stirring for 3 hours at the temperature of 100 ℃ to obtain a transparent and viscous solution;
step five, dispersing the Co/Al hydrotalcite precursor ground into powder into the transparent and viscous solution prepared in the step four, and stirring for 3 hours to form a uniform and stable colloidal solution, wherein the colloidal solution is coating slurry of the catalyst;
step six, immersing the cordierite carrier in a nitric acid solution with the concentration of 10 wt% for 4 hours for pretreatment, taking out and drying for 4 hours for later use;
and step seven, putting the pretreated cordierite carrier into the colloidal solution obtained in the step five, soaking for 12 hours, drying for 4 hours at the temperature of 110 ℃, and then roasting for 4 hours at the temperature of 300 ℃, wherein the obtained product is the monolithic catalyst for catalytic oxidation of VOCs.
The monolithic catalyst prepared in the example 2 is subjected to fixed bed reaction, the mixed gas contains 1000ppm of VOCs gas, and the space velocity is 1500h-1And respectively testing the inlet concentration and the outlet concentration of the fixed bed reactor at the reaction temperature of 90-300 ℃, and calculating the conversion rate of the VOCs according to (inlet concentration-outlet concentration)/inlet concentration multiplied by 100%.
A fixed bed catalytic oxidation reaction evaluation device is adopted to perform catalytic activity test on the prepared catalyst, as shown in figure 2, when the temperature is about 230 ℃, the conversion rate of the catalyst to ethyl acetate can reach more than 80%, and when the temperature reaches 260 ℃, the conversion rate of the monolithic catalyst to ethyl acetate can reach more than 99%, and the activity of the catalyst can be repeatedly tested for many times without obvious reduction.
In the preparation method, the ratio change of the divalent element and the trivalent element of the solution A in the step one can influence the catalytic activity of the prepared monolithic catalyst in a low temperature range. In the fourth step, the temperature of the mixture of water, citric acid and glycol during heating also affects the dispersibility of the hydrotalcite precursor powder in the mixture. The firing temperature in step seven also affects the layered structure of the active component, and too high a temperature may collapse the structure of the active component.
While the present invention has been described with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments, which are illustrative only and not restrictive, and various modifications which do not depart from the spirit of the present invention and which are intended to be covered by the claims of the present invention may be made by those skilled in the art.
Claims (1)
1. A preparation method of an integral catalyst for catalytic oxidation of VOCs is characterized by comprising the following steps:
step one, adding Co (NO)3)2·6H2O and Al (NO)3)3·9H2Dissolving O in deionized water to obtain solution A, wherein Co is2+And Al3+The molar ratio of (1) to (4) is 0.4:1-14:1, and the concentration of total metal ions is 0.48 mol/L; mixing NaOH and Na2CO3Dissolving in deionized water to obtain solution B, wherein NaOH is 0.96mol/L, and Na is added2CO3The concentration is twice of the concentration of the trivalent ions;
step two, simultaneously dripping the solution A and the solution B into a beaker filled with a proper amount of deionized water, simultaneously violently stirring at 40 ℃, adjusting the dripping speed of the solution A and the solution B to control the pH of the mixed solution to be 8-11, continuously stirring for 30min after dripping is finished, placing the obtained suspension in a dark place for crystallization, and then carrying out suction filtration to obtain a filter cake;
washing the obtained filter cake with deionized water for 3-5 times until the washing liquid is neutral, drying and grinding into powder to obtain a Co/Al hydrotalcite precursor of the monolithic catalyst for catalytic oxidation of VOCs;
step four, mixing water, citric acid and glycol according to the molar ratio of 15 (0.5-2) to 1, and stirring at the temperature of 80-100 ℃ to obtain a transparent and viscous solution;
step five, dispersing the Co/Al hydrotalcite precursor ground into powder into the transparent and viscous solution prepared in the step four, and stirring for 3-4 hours to form a uniform and stable colloidal solution;
step six, immersing the cordierite carrier in a nitric acid solution with the concentration of 10 wt% for 2-4h for pretreatment, taking out, drying and weighing for later use;
and step seven, putting the pretreated cordierite carrier into the colloidal solution obtained in the step five, soaking for 10-12h, drying for 4h at 110 ℃, and then roasting for 4h at 200-600 ℃, wherein the obtained product is the monolithic catalyst for catalytic oxidation of VOCs.
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