CN106955712B - A Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process and its preparation method - Google Patents

Abstract

The invention discloses an Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process and a preparation method thereof. The composite catalyst is formed by using Al ₂ O ₃ -TiO ₂ as a composite carrier and supporting active components Fe ₂ O ₃ -CeO ₂ . At the same time, it also discloses a preparation method of Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process, which includes the following steps: 1) first prepare the composite carrier Al ₂ O ₃ ‑TiO ₂ ; 2) prepare the composite Catalyst Fe ₂ O ₃ —CeO ₂ /Al ₂ O ₃ —TiO ₂ . The catalyst process prepared by this method is relatively simple, which is convenient for large-scale industrial production, and in the common industrial catalytic temperature range of 160°C-240°C, it can achieve better synchronous removal of the two, so it has the advantages of High economic value and promotion value. And in the later stage, the catalyst can be further modified, including further increasing or reducing the content of Ce and Fe, or adding trace amounts of other components, or even optimizing the reaction conditions to achieve higher conversion rates of nitrogen oxides and sulfides.

Description

A Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process Chemical agent and its preparation method

technical field

The invention relates to an Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process and a preparation method thereof.

Background technique

As we all know, a large amount of nitrogen oxides (NOx) and sulfides (mainly SO ₂ ) produced by the combustion of coal-fired boilers will lead to the aggravation of smog and photochemical smog, and cause great harm to human health. In addition, various emission standards are also increasing year by year. Therefore, it is necessary to simultaneously remove nitrogen oxides and sulfides in the flue gas so that their concentrations can reach the emission standard.

At present, the synchronous desulfurization and denitrification methods used in the industry are generally wet methods, which mainly use oxidizing solutions to oxidize insoluble NOx (mainly NO) into soluble _NOx while absorbing soluble SO2. NOx (mainly NO ₂ ) and absorb it. However, due to the fact that the equipment usually occupies a large area, the maintenance cost is high, and the absorption liquid needs to be replaced for a long time, the general cost is high, so it has not been promoted on a large scale. The catalytic desulfurization and denitrification method can overcome the above-mentioned disadvantages, so it is becoming a hot spot in current research and promotion. Among them, the single catalytic desulfurization method commonly used in industry is the Claus method, and the reducing agent used is H ₂ S. The separate catalytic denitrification is the SCR method, and the reducing agent used is NH ₃ . However, due to the different reducing agents used in the above-mentioned methods, the catalysts and process flow used are also different, so it is difficult to realize the simultaneous removal of nitrogen oxides and sulfides. In addition, H ₂ , CO, CxHy, etc. can also replace ammonia to remove nitrogen oxides. But the price of this kind of gas is relatively expensive, and storage and transportation are inconvenient. In addition, the catalysts required for this type of catalytic reaction are usually noble metal catalysts, and the cost is higher than that of ordinary oxide catalysts. The above-mentioned various technical bottlenecks also limit its further research, development and promotion to a certain extent. In fact, since the strong reducing agent H ₂ S in the Claus reaction can effectively remove SO ₂ , the inventors believe that H ₂ S can also remove NO under the action of a suitable catalyst. The reaction equation is as follows:

H ₂ S+NO→S+N ₂ +H ₂ O

It can be seen that the above reaction generates non-toxic _N2 and S, so it has the value of further research. It was reported in the early literature that the above reaction can be realized by using Al ₂ O ₃ as a catalyst. The previously invented flue gas catalytic desulfurization and denitrification process using H ₂ S as a reducing agent shows that H ₂ S can be used as a reducing agent to achieve simultaneous desulfurization and denitrification, and H ₂ S can be prepared through the sewage treatment process of industrial enterprises, which can significantly reduce The cost of flue gas desulfurization and denitrification. However, since the catalyst used in the inventive process is 4A molecular sieve, its catalytic temperature is 600°C-700°C, which reduces the cost advantage of this new technology. Therefore, it is urgent to study new catalysts, improve reaction efficiency and reduce reaction temperature.

At present, in the research of SCR catalysts, there are relatively many studies on iron (Fe). This is not only because of its low price and good denitrification effect alone, but also as an auxiliary agent or auxiliary component, it can significantly improve the performance of other catalysts while reducing temperature reflex. The rare earth element cerium (Ce) has a strong oxygen storage capacity and a good redox catalytic activity due to its special crystal structure. Therefore, in combination with the above factors, the present invention chooses to prepare various composite two-component catalysts of Fe and Ce in different proportions, and then uses the prepared catalyst in the simultaneous desulfurization and denitrification experiment of H2S to achieve simultaneous removal of _both the goal of.

Contents of the invention

The purpose of the present invention is to provide an Fe-Ce based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process and its preparation method. It aims to overcome the technical defects in the current catalytic desulfurization and denitrification technology, such as the inability to remove them at the same time, the low conversion rate at low temperature, and the high energy consumption in the high temperature section.

The technical scheme that the present invention takes is:

An Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process is formed by using Al ₂ O ₃ -TiO ₂ as a composite carrier and supporting active components Fe ₂ O ₃ -CeO ₂ .

In the composite carrier, the molar ratio of Al ₂ O ₃ to TiO ₂ is 1:1.

_The loading amount of the active component _{Fe2O3 -} CeO2 is 8wt%-12wt%.

The catalytic temperature of the catalyst is 160°C to 240°C.

The preparation method of a Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process comprises the following steps:

1) Prepare the composite carrier Al ₂ O ₃ -TiO ₂ first;

2) The composite catalyst Fe ₂ O ₃ -CeO ₂ /Al ₂ O ₃ -TiO ₂ is prepared afterwards.

In step 1), the Al ₂ O ₃ -TiO ₂ is prepared by using aluminum salt and titanate by sol-gel method.

In step 1), the aluminum salt is aluminum nitrate; the titanate is tetrabutyl titanate; the molar ratio of aluminum nitrate to tetrabutyl titanate is 2:1.

In step 2), the composite catalyst Fe ₂ O ₃ -CeO ₂ /Al ₂ O ₃ -TiO ₂ is mixed with iron salt and cerium salt, and then mixed with the composite carrier Al ₂ O ₃ -TiO ₂ by equal volume impregnation prepared by the method.

In step 2), the iron salt is iron nitrate; the cerium salt is cerium nitrate.

The mass ratio of the active component Fe ₂ O ₃ to CeO ₂ is (2-8):(8-2).

The beneficial effects of the present invention are:

The invention utilizes H ₂ S as a reducing agent, and through the method of firstly preparing a composite carrier and then preparing an Fe-Ce-based composite catalyst, the synchronous removal of nitrogen oxides and sulfides in flue gas is realized. Compared with the high installation and maintenance costs of the wet method, the singleness and limitations of the Claus and SCR technologies, as well as the higher catalyst costs faced.

The catalyst process prepared by this method is relatively simple, which is convenient for large-scale industrial production, and in the lower 160°C-240°C, which is a common industrial catalytic temperature range, it can achieve better synchronous removal of the two, so it has the advantages of High economic value and promotion value. And in the later stage, the catalyst can be further modified, including further increasing or reducing the content of Ce and Fe, or adding a small amount of other components, or changing the components to become tungsten and cerium, or iron and cobalt. The main reason is that you can continue to change the ratio through this method of loading two metals and find better catalysts. For example, the reaction conditions are even optimized to achieve higher conversions of nitrogen oxides and sulfides.

Description of drawings

Fig. 1 is the evaluation device flow chart of catalyst of the present invention;

Figure ₂ is a conversion rate diagram of NO and SO2 in the present invention.

Detailed ways

An Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process is formed by using Al ₂ O ₃ -TiO ₂ as a composite carrier and supporting active components Fe ₂ O ₃ -CeO ₂ .

Preferably, in the composite support, the molar ratio of Al ₂ O ₃ to TiO ₂ is 1:1.

Preferably, the loading amount of the active component Fe ₂ O ₃ -CeO ₂ is 8 wt % to 12 wt %; most preferably, the loading amount of the active component Fe ₂ O ₃ -CeO ₂ is 10 wt %. The loading amount is the mass fraction of the active component in the total mass of the catalyst.

Preferably, the catalytic temperature of the catalyst is 160°C to 240°C.

The preparation method of a Fe-Ce-based composite catalyst suitable for hydrogen sulfide catalytic reduction desulfurization and denitrification process comprises the following steps:

1) Prepare the composite carrier Al ₂ O ₃ -TiO ₂ first;

2) The composite catalyst Fe ₂ O ₃ -CeO ₂ /Al ₂ O ₃ -TiO ₂ is prepared afterwards.

Preferably, in step 1), the Al ₂ O ₃ —TiO ₂ is prepared by using aluminum salt and titanate by sol-gel method.

Preferably, in step 1), the aluminum salt is aluminum nitrate; the titanate is tetrabutyl titanate; the molar ratio of aluminum nitrate to tetrabutyl titanate is 2:1; further Yes, the aluminum nitrate is Al(NO ₃ ) ₃ ·9H ₂ O; the tetrabutyl titanate is Ti(OC ₄ H ₉ ) ₄ .

Preferably, in step 2), the composite catalyst Fe ₂ O ₃ -CeO ₂ /Al ₂ O ₃ -TiO ₂ is mixed with iron salt and cerium salt, and then passed through the composite carrier Al ₂ O ₃ -TiO ₂ Prepared by equal volume impregnation method.

Preferably, in step 2), the iron salt is ferric nitrate; the cerium salt is cerium nitrate; further, the ferric nitrate is Fe(NO ₃ ) ₃ ·9H ₂ O; the nitric acid Cerium is Ce(NO ₃ ) ₃ ·6H ₂ O.

Preferably, the mass ratio of the active component Fe ₂ O ₃ to CeO ₂ is (2-8): (8-2); more preferably, the mass ratio of the active component Fe ₂ O ₃ to CeO ₂ The mass ratio is one of 2:8, 5:5 or 8:2; most preferably, the mass ratio of the active component Fe ₂ O ₃ to CeO ₂ is 5:5.

The content of the present invention will be described in further detail below through specific examples.

Example:

The preparation method of a-composite carrier AT(Al ₂ O ₃ -TiO ₂ ):

(1) In a 250ml beaker, add 2.4mol C ₂ H ₅ OH, 0.9mol CH ₃ COOH, and 1.8mol deionized water in sequence, and then stir them uniformly for 1 min until completely mixed to prepare a mixed solvent.

(2) Weigh 0.2 mol of Al(NO ₃ ) ₃ ·9H ₂ O, then pour it into the mixed solvent prepared above, and stir until it is completely dissolved.

(3) 0.1 mol of Ti(OC ₄ H ₉ ) ₄ was slowly added dropwise to the above mixed solution in which Al(NO ₃ ) ₃ ·9H ₂ O was dissolved. After the addition is complete, it is stirred and allowed to stand until a single homogeneous mixed solution is formed.

(4) Put the above-mentioned solution into a magnetic stirrer and heat and stir until the solution is completely solidified into a white jelly.

(5) Aging the resulting white jelly for 12 hours, and then putting it into an oven at 110° C. for drying until white particles are formed.

(6) Put the dried white particles into a crucible, and then calcinate them in a muffle furnace at 550° C. for 4 hours.

(7) Sieve the calcined product to get particles with a size of 20-40 mesh for further use.

The preparation method of b-composite catalyst CeFe-AT ₍ the total load of active component CeO2 and _Fe2O3 is ₁₀ %):

(1) Weigh 4.5 g of the finished carrier AT prepared above, and evenly spread it on a petri dish.

(2) Weigh a number of precursors (Fe(NO ₃ ) ₃ 9H ₂ O and Ce(NO ₃ ) ₃ 6H ₂ O, the mass required for catalysts with different ratios is different, see the table below for specific values), and pour into a 10ml beaker, and then add 5ml of deionized water to dissolve it.

(3) Add the above-mentioned precursor solution onto the carrier AT evenly drop by drop to ensure that the carrier is in a completely wet state.

(4) Put the above-mentioned particulate matter into an oven at 110° C. for drying until the quality does not change any more.

(5) The dried solid was put into a crucible, and then calcined in a muffle furnace at 550° C. for 4 h.

(6) Sieve the calcined solid again to get 20-40 mesh particles, which is the finished Fe—Ce-based catalyst.

c-Evaluation device and method for catalyst performance:

Accompanying drawing 1 is the flow chart of the evaluation device of the catalyst of the present invention. In Fig. 1, 1. Ar steel cylinder; 2. H ₂ S steel cylinder; 3. SO ₂ steel cylinder; 4. NO steel cylinder; 5. O ₂ steel cylinder; 9. Temperature regulator; 10. Quartz glass reaction tube; 11. Thermocouple; 12. Sulfur powder absorption bottle; 13. Alkaline liquid absorption bottle; 14. Gas buffer bottle;

Since the molar ratio of H ₂ S and SO ₂ is 2:1, and the molar ratio of H ₂ S and NO is 1:1, the molar ratio of H ₂ S, SO ₂ and NO is 3: 1:1. In the present invention, its concentration is controlled to be 1500ppm, 500ppm and 500ppm respectively. In order to achieve this concentration, it is necessary to adjust the value in the flow indicator. The specific method is to connect the empty glass tube to the heater without heating, then turn on the carrier and three kinds of reaction gases, and measure their concentrations with a flue gas analyzer (the basis is low temperature, no catalyst, three Those who hardly react), and then adjust the flow rate by adjusting the flow display device, so that the displayed value is stable at the required concentration. In practice, through adjustment, the final actual flow rates of H ₂ S, SO ₂ and NO are 15.3ml/min, 5.0ml/min, and 2.76ml/min, respectively.

After adjusting the readings, the catalyst can be evaluated. First, fix the quartz glass reaction tube containing the catalyst on the electric heater. The catalyst in the glass tube needs to be fixed in the glass tube with quartz wool. The amount of quartz wool needs to be moderate. If the amount is too large, the airflow will be difficult to pass through. If the amount is too small, the filler will be blown away by the airflow. And the glass tube needs to be tightly fixed to prevent air leakage and cause safety accidents.

After completing the above items, turn on the flow indicator and Ar carrier gas to make the pointer of the pressure gauge reach 0.1Mpa, the purpose is to flush the pipeline, and the required time is about 30 minutes. At the same time, open the temperature regulator and set the temperature required for the reaction (due to the hysteresis of temperature control, usually the set temperature is lower than the temperature required for the reaction, and the lower the required temperature, the greater the temperature difference between the two), when When the temperature rises to the desired reaction temperature, adjust the set temperature to the reaction temperature. Simultaneously open the reaction gas cylinder to make the pointer of the pressure gauge reach 0.2Mpa.

Then, turn on the flue gas analyzer and connect the inlet pipe and the outlet pipe. After the test procedure is stable, connect one end of the inlet pipe to the outlet pipe of the reaction system to measure the gas concentration. It should be noted that because this reaction will generate a large amount of solid sulfur, and due to the large gas velocity (the flow rate of Ar is 500ml/min), a large amount of sulfur particles invisible to the naked eye will be blown out. If the instrument is directly connected, it will cause A large number of particles enter the instrument and damage the sensor, resulting in inaccurate data or even instrument failure. Therefore, it is necessary to add a filter membrane at the gas outlet of the reaction system to filter out fine sulfur particles. In addition, in order to ensure that the data is as accurate as possible, the measurement of each temperature section needs to be measured 30 minutes after the reaction temperature reaches the temperature.

The evaluation result of d-catalyst performance:

Accompanying drawing 2 is NO of the present invention and SO ₂ The conversion figure. It can be seen from Figure ₂ that within the temperature range of 160°C-240°C, the conversion rate of NO increases significantly with the increase of temperature, while the conversion rate of SO2 only slightly increases with the increase of temperature. Decline, close to or reach 100% in most of the temperature segments, and remain above 90% overall. Comparing CeFe catalysts with different ratios, it can be found that whether it is the removal rate of NO or SO ₂ , Fe5Ce5-AT is better than the other two, and in the temperature range of 220°C-240°C, it can achieve about 95 % denitrification efficiency and about 85% desulfurization efficiency. Therefore, it can be considered that Fe5Ce5-AT is a more suitable two-component catalyst, which can better realize simultaneous desulfurization and denitrification within a certain temperature range.

The most suitable synchronous desulfurization and denitrification catalyst of the present invention is Fe5Ce5-AT, and the desulfurization efficiency of the most suitable catalyst is about 95% and the denitrification efficiency is about 85% at the temperature range of 220°C-240°C.

Claims (7)

1. a kind of Fe-Ce based composite catalyst suitable for vulcanizing hydrogen catalysis reduction and desulfurization denitrating technique, it is characterised in that: be with Al₂O₃-TiO₂For complex carrier, load active component Fe₂O₃-CeO₂Made of；

In the complex carrier, Al₂O₃With TiO₂Molar ratio be 1:1；Active component Fe₂O₃-CeO₂Load capacity be 8wt% ~12wt%；The catalytic temperature of catalyst is 160 DEG C~240 DEG C.

2. a kind of Fe-Ce based composite catalyst suitable for vulcanizing hydrogen catalysis reduction and desulfurization denitrating technique described in claim 1 Preparation method, it is characterised in that: the following steps are included:

1) complex carrier Al is first prepared₂O₃-TiO₂；

2) composite catalyst Fe is prepared after₂O₃-CeO₂/Al₂O₃-TiO₂。

It is urged 3. a kind of Fe-Ce base suitable for vulcanizing hydrogen catalysis reduction and desulfurization denitrating technique according to claim 2 is compound The preparation method of agent, it is characterised in that: in step 1), the Al₂O₃-TiO₂It is solidifying by colloidal sol-with aluminium salt and titanate esters Made of the preparation of glue method.

It is urged 4. a kind of Fe-Ce base suitable for vulcanizing hydrogen catalysis reduction and desulfurization denitrating technique according to claim 3 is compound The preparation method of agent, it is characterised in that: in step 1), the aluminium salt is aluminum nitrate；The titanate esters are four fourth of metatitanic acid Ester；The molar ratio of the aluminum nitrate and butyl titanate is 2:1.

It is urged 5. a kind of Fe-Ce base suitable for vulcanizing hydrogen catalysis reduction and desulfurization denitrating technique according to claim 2 is compound The preparation method of agent, it is characterised in that: in step 2), the composite catalyst Fe₂O₃-CeO₂/Al₂O₃-TiO₂It is iron Salt and cerium salt mixing after, then with complex carrier Al₂O₃-TiO₂It is prepared by equi-volume impregnating.

It is urged 6. a kind of Fe-Ce base suitable for vulcanizing hydrogen catalysis reduction and desulfurization denitrating technique according to claim 5 is compound The preparation method of agent, it is characterised in that: in step 2), the molysite is ferric nitrate；The cerium salt is cerous nitrate.

It is urged 7. a kind of Fe-Ce base suitable for vulcanizing hydrogen catalysis reduction and desulfurization denitrating technique according to claim 6 is compound The preparation method of agent, it is characterised in that: the active component Fe₂O₃With CeO₂Mass ratio be (2~8): (8~2).