CN109759078B - Gamma-Fe load 2 O 3 Preparation method of molded SCR catalyst - Google Patents
Gamma-Fe load 2 O 3 Preparation method of molded SCR catalyst Download PDFInfo
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Abstract
The invention relates to a gamma-Fe loaded composite material 2 O 3 The preparation method of the low-temperature forming SCR catalyst is mainly used for removing NOx in low-temperature (lower than 200 ℃) flue gas of industrial kilns in the field of environmental protection. In the invention, a honeycomb industrial SCR catalyst is used as a substrate, and the method comprises the following steps of 4: preparation of binder, surface binder treatment of formed catalyst, and gamma-Fe 2 O 3 Coating and roasting to prepare gamma-Fe 2 O 3 And the molded SCR catalyst is uniformly and firmly coated on the surface. Coating with gamma-Fe in contrast to the procatalyst 2 O 3 The low-temperature denitration performance of the catalyst is greatly improved, and the cost required by low-temperature flue gas of the kiln can be greatly reduced. The method has simple process and easy realization, and is very suitable for being used in industrial catalysts.
Description
Technical Field
The invention relates to a low-temperature denitration material, in particular to a gamma-Fe-loaded material 2 O 3 A method for preparing a shaped SCR catalyst.
Background
One of main pollutants in the atmosphere of nitrogen oxide is also one of main pollutants causing photochemical smog, and the nitrogen oxide and various VOCs in the atmosphere undergo a series of reactions to cause the photochemical smog and seriously affect the environment. The Selective Catalytic Reduction (SCR) technology is currently the most mature and widely used technology for removing nitrogen oxides from stationary sources, and NOx generates harmless components under the action of a reducing agent and a catalyst.
The catalyst is the key of SCR technology, the catalyst used for treating the flue gas of the industrial kiln is mainly based on vanadium, the reducing agent mostly causes the urea to be thermally decomposed or ammonia gas generated by ammonia water, and the catalyst usually needs to be at the temperature of more than 300 ℃ to have good NOx removal efficiency. Fe 2 O 3 Having NH 3 SCR denitration activity, fe-based catalyst has good NOx removal effect, fe 2 O 3 The acid sites of (A) promote NH 3 Adsorption on the surface of the catalyst, thereby increasing the denitration activity of the catalyst, and gamma-Fe 2 O 3 With higher NH content 3 -SCR denitration Activity, nano gamma-Fe 2 O 3 Compared with the common grain diameter gamma-Fe 2 O 3 Has higher thermal stability. The invention loads nano gamma-Fe on the surface of the honeycomb-shaped SCR catalyst 2 O 3 The material greatly improves the low-temperature denitration performance of the catalyst, and the low-temperature industrial flue gas does not need to be heated to the activation temperature of the catalyst by an air preheater. In addition, the catalyst operates at low temperature, so that the sintering speed of active components of the catalyst can be effectively delayed, the chemical life of the catalyst is prolonged, and the catalyst cost of the SCR denitration device is reduced.
At present, no nano gamma-Fe exists in China 2 O 3 Material in NH 3 -patents applied in SCR denitration field, laboratory preparation of nano gamma-Fe 2 O 3 The invention aims to provide a relatively simple and convenient industrial implementation method for preparing nano gamma-Fe by adopting a sol-gel method which is difficult to industrially solve the technical problems and the defects in the prior art 2 O 3 The catalyst is loaded on an industrial SCR catalyst, so that the low-temperature activity of the catalyst is improved.
Disclosure of Invention
The working temperature of the catalyst is further expanded to a low-temperature region. The invention provides a gamma-Fe-loaded material 2 O 3 A method for preparing a shaped SCR catalyst.
The invention is realized by the following scheme:
the invention relates to nano gamma-Fe 2 O 3 The method is based on industrial honeycomb-shaped SCR catalyst, and then through preparing binder, treating the surface of the shaped catalyst with the binder, and carrying out gamma-Fe treatment 2 O 3 Spraying, coating, baking and roasting a series of processes to obtain gamma-Fe 2 O 3 Supported on a shaped catalyst.
The method for preparing the supported catalyst is as follows:
1. preparation of the binder: 30wt% silica sol, hydroxymethyl cellulose and water were mixed in a ratio of 25. Excessive temperature and time of the water bath can cause the silica sol gel in the adhesive to block, and the adhesive can not be used.
2. And (3) treating the surface binder of the formed catalyst: immersing the formed SCR catalyst in the binder in the amount of 1, putting the mixture into a water bath at 60 ℃, performing ultrasonic treatment for 30min to obtain a sample, taking out the sample, and performing gamma-Fe treatment before the surface of the catalyst is not completely dried 2 O 3 Coating. The reason why the time and temperature need to be controlled is the same as in 1.
3、γ-Fe 2 O 3 Coating: mixing gamma-Fe 2 O 3 The powder is filled into a dust generator, the dust generation rate is related to the mass of the formed catalyst and is 4 to 8 percent of the mass of the formed catalyst per minute, the dust generation is continued for 3 to 5 minutes, and the gamma-Fe is enabled to be generated 2 O 3 The powder was uniformly loaded onto the surface of a laboratory shaped catalyst, after which the sample was oven dried in a 105 ℃ oven for 3h. The gamma-Fe can be obviously changed by changing the dust generation rate and the dust generation time 2 O 3 An excessively high loading of Fe 2 O 3 The degree of adhesion firmness of (2) is drastically reduced.
4. Roasting: and (3) putting the dried catalyst into a muffle furnace, roasting for 2h at 250 ℃, and naturally cooling to room temperature to finish the preparation. The formed catalyst and the adhesive layer, the adhesive layer and the gamma-Fe are formed in the roasting process 2 O 3 The bonding is firmer, and the hydroxymethyl cellulose component, alpha-Fe, in the bonding agent can be removed 2 O 3 gamma-Fe with low-temperature denitration activity ratio 2 O 3 Low, this temperature is much lower than gamma-Fe 2 O 3 To alpha-Fe 2 O 3 Conversion temperature, no alpha-Fe during the calcination process 2 O 3 And (4) generating.
The invention has the following advantages:
1. the invention has no nano gamma-Fe at home 2 O 3 Material in NH 3 Under the condition of the patent applied in the field of SCR denitration, a set of complete Fe coating on the surface of the formed catalyst is provided 2 O 3 The process of (1). Under the process condition, the method does not relate to gamma-Fe which is difficult to apply industrially 2 O 3 The sol-gel preparation method of (1). In the process, gamma-Fe is not changed 2 O 3 The high denitration activity of the catalyst is high,and enable Fe 2 O 3 Firmly adhered to the surface of the formed catalyst. The process method is simple, low in cost and beneficial to rapid large-scale production of production enterprises.
2. The invention is through gamma-Fe 2 O 3 The reduction of the industrial catalyst use temperature window is realized, the promotion of catalyst low temperature performance is favorable to changing the industrial current situation that the SCR device is arranged with the high dust and is given first place to, makes the device can install after dust removal, desulfurization, promotes the life of catalyst by a wide margin, when practicing thrift the cost, has reduced the production of industry hazardous waste.
Description of the drawings:
FIG. 1 shows a device for detecting denitration efficiency of a supported catalyst under the detection conditions of gas flow of 1.8L/min and O 2 5vol% NO X 700ppm, ammonia nitrogen ratio 1:1 (volume ratio) and space velocity of 6000h -1 And the NOx detection device is a Thermo 42i-HL smoke analyzer.
FIG. 2 shows the support of gamma-Fe 2 O 3 Catalyst and procatalyst detection results.
FIG. 3 different gamma-Fe 2 O 3 Efficiency of supported catalyst versus procatalyst.
Detailed Description
Example 1:
250g of 30wt% silica sol was taken, 10g of hydroxymethyl cellulose was mixed, and placed in 740g of deionized water, heated to 60 ℃ in a water bath and stirred continuously for 25min to form a relatively clear solution.
Immersing 20mm x 100mm honeycomb vanadium titanium-based formed catalyst (in order to adapt to the size of a reaction tube of a detection device) in the preparation solution for 30min, simultaneously carrying out water bath at 60 ℃ and carrying out ultrasound, and placing the SCR catalyst in a closed container within 5min after the immersion to prepare gamma-Fe 2 O 3 Coating is carried out, namely nano gamma-Fe is filled 2 O 3 The dust-generating mouth of the dust generator of the powder is communicated with the container, and then the nano gamma-Fe is sprayed at the speed of (8 percent of the mass of the formed catalyst)/min 2 O 3 Powder for 5min, placing into oven before the catalyst surface is completely dried, taking care not to make the catalyst surface dryGamma-Fe which is not firmly bonded on the surface of the catalyst 2 O 3 The powder falls off, the mixture is baked for 3 hours at 105 ℃ to lead the silica sol to gel rapidly, and then the dried catalyst is put into a muffle furnace to be baked for 2 hours at 250 ℃, wherein the temperature is far lower than gamma-Fe 2 O 3 Phase change to alpha-Fe 2 O 3 The desired temperature. The supported catalyst was weighed after calcination to a loading of 5.27% (40.210 g → 42.329 g).
Carrying out efficiency detection on the filter cloth in the following device, wherein the device is shown in figure 1, and the detection condition is that the air flow is 1.8L/min, O 2 5vol%, NOx 700ppm, ammonia nitrogen ratio 1:1 (volume ratio), space velocity 6000h -1 The results are shown in FIG. 2 (space velocity =6000 h-1. Gamma. -Fe loading) 2 O 3 Catalyst), it can be seen that nano-gamma-Fe is supported 2 O 3 The low-temperature performance of the powder catalyst is greatly improved, and simultaneously the airspeed has great influence on the catalyst efficiency and is 6000h -1 The nitrogen oxide removal efficiency can reach 90% at 160 ℃, and the nitrogen oxide removal efficiency of the original catalyst can reach 90% only at 200 ℃.
Example 2:
the difference from example 1 is γ -Fe 2 O 3 The load rate is 5.35% (39.260 g → 41.36 g), and the denitration efficiency detection condition airspeed is increased to 12000h -1 。
The detection result is shown in figure 2 (space velocity =12000h-1 loading gamma-Fe) 2 O 3 Catalyst), the space velocity has a significant effect on the denitration effect of the catalyst.
Example 3:
directly taking a honeycomb-shaped vanadium-titanium-based forming catalyst of 20mm to 100mm at an air amount of 1.8L/min, O 2 5vol%, NOx 700ppm, ammonia nitrogen ratio 1:1 (volume ratio), space velocity 6000h -1 The efficiency test is carried out under the condition, the result is shown in figure 2 (space velocity =6000h-1 original catalyst), and the catalyst loading gamma-Fe can be seen 2 O 3 There is a large difference in the front and rear low temperature activities.
Example 4:
the difference from the example 3 is that the detection condition airspeed of the denitration efficiency is increased to 12000h -1 . The detection results are shown in FIG. 2 (empty)Speed =6000h-1 load gamma-Fe 2 O 3 Catalyst) and loading gamma-Fe under the same space velocity condition 2 O 3 By contrast of the catalyst, gamma-Fe can be found 2 O 3 Has a great influence on the activity at low temperature.
Example 5:
the difference from example 1 is γ -Fe 2 O 3 The load was 5.19% (39.244 g → 41.281 g), and the denitration efficiency detection condition space velocity was changed to 18000h -1 The results are shown in FIG. 3 (space velocity =18000 h-1. Gamma. -Fe) 2 O 3 Loading 5.19% catalyst).
Example 6:
the same as example 5, except that the dust generation rate was adjusted to (7% by mass of the molded catalyst)/min, γ -Fe 2 O 3 The loading was 4.60% (38.622 g → 40.399 g) and the results are shown in fig. 3 (space velocity =18000h-1 γ -Fe) 2 O 3 Loading 4.60% catalyst).
Example 7:
the same as example 5, except that the dust generation rate was adjusted to (5% by mass of the molded catalyst)/min, the dust generation time was 3min, and γ -Fe 2 O 3 The loading was 2.63% (39.021 g → 40.047 g) and the results are shown in fig. 3 (space velocity =18000h-1 γ -Fe) 2 O 3 Loading 2.63% catalyst).
Example 8:
the same as example 5, except that the dust generation rate was adjusted to (4% by mass of the molded catalyst)/min, the dust generation time was 3min, and γ -Fe 2 O 3 The loading was 2.04% (38.764 g → 39.555 g) and the results are shown in fig. 3 (space velocity =18000h-1 γ -Fe) 2 O 3 Loading 2.04% catalyst).
Example 9:
the difference from the example 3 is that the detection condition airspeed of the denitration efficiency is increased to 18000h -1 . The results are shown in FIG. 3 (space velocity =18000h-1 unsupported catalyst).
Claims (4)
1. Gamma-Fe load 2 O 3 The preparation method of the formed SCR catalyst is characterized in that the forming is carried out firstlyCoating a binder on the surface of the SCR catalyst, wherein the binder is prepared by mixing 30wt% of silica sol, hydroxymethyl cellulose and water in a mass ratio of 25:1:74, heating and stirring in a water bath at 60 ℃ for 25min; immersing the formed SCR catalyst in a binder, putting the binder into a water bath at 60 ℃, and carrying out ultrasonic treatment for 30min to obtain a sample; then the gamma-Fe is sprayed by a spray coating method before the surface of the catalyst is not completely dried 2 O 3 Uniformly coating the surface of the formed SCR catalyst; finally roasting for 2h at the roasting temperature of 250 ℃ to form gamma-Fe on the surface of the formed SCR catalyst 2 O 3 Coating; gamma-Fe 2 O 3 Is powder with nano-grade grain diameter;
γ-Fe 2 O 3 the spray coating method comprises the following steps: mixing gamma-Fe 2 O 3 The powder is filled into a dust generator and gamma-Fe is sprayed at a dust generation rate of 4-8% of the mass of the formed SCR catalyst per minute 2 O 3 Continuously generating dust for 3-5min to make gamma-Fe 2 O 3 Uniformly loading the powder on the surface of the formed SCR catalyst, and then drying the sample in an oven at 105 ℃ for 3 hours; the gamma-Fe can be obviously changed by changing the dust generation rate and the dust generation time 2 O 3 At a high loading level, too high loading level would result in gamma-Fe 2 O 3 The degree of adhesion firmness of (2) is drastically reduced.
2. The method of claim 1, wherein the shaped SCR catalyst is a honeycomb shaped catalyst.
3. The method of claim 1, wherein the shaped SCR catalyst to be coated is placed in a closed container and gamma-Fe is sprayed using a dust blower 2 O 3 The powder is uniformly coated.
4. gamma-Fe-supported material prepared by the method according to claim 1 2 O 3 Shaped SCR catalyst for removing NO in flue gas x Characterized in that the removal conditions are NO x 700ppm、NH 3 700ppm、O 2 5vol％、CHSV＝6000h -1 、160℃。
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