Zinc oxide-cerium oxide desulfurization catalyst and preparation method thereof

Abstract

The application relates to the field of desulfurization catalysts, in particular to a zinc oxide-cerium oxide desulfurization catalyst and a preparation method thereof. In the scheme, a zinc-cerium composite catalyst is used as a substrate, and ammonium carbonate is added as a pore former, so that a large-pore-small-pore composite form can be formed, and then the gas can be uniformly distributed in the catalyst, and the sulfur capacity of the system is greatly improved at a high space velocity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of desulfurization catalysts, in particular to a zinc oxide-cerium oxide desulfurization catalyst and a preparation method thereof. BACKGROUND

[0002] With the increasing demand for industrial gas purification, desulfurization technology has become particularly important in the fields of petrochemical industry, natural gas purification, coal gasification, etc. Hydrogen sulfide (H2S) and carbonyl sulfide (COS) are common sulfur-containing compounds in industrial gas, which not only corrode equipment and reduce catalyst activity, but also cause serious environmental pollution. Therefore, it is of great industrial significance to develop efficient and stable desulfurization catalysts.

[0003] At present, zinc oxide (ZnO) is widely used as a desulfurization catalyst due to its high sulfur capacity, good thermal stability and renewability. The main mechanism of zinc oxide desulfurization is to generate zinc sulfide (ZnS) by reacting with H2S, thereby achieving the removal of sulfur.

[0004] In order to improve the catalytic effect of zinc oxide catalyst, doping cerium oxide in it is a feasible method. Compared with traditional zinc oxide desulfurization catalyst, zinc oxide-cerium oxide composite catalyst has better sintering resistance, catalytic effect and overall stability, so it has better performance in the process of catalytic desulfurization.

[0005] The theoretical sulfur capacity of zinc oxide is 41.9wt%, which is based on the calculation result of ZnO completely reacting with H2S to generate ZnS. In fact, considering the structure of zinc oxide itself, its maximum sulfur capacity in the reaction process is usually not more than 30%, and it needs to be carried out at a lower space velocity, so it has certain adverse effects on the actual catalytic efficiency. SUMMARY

[0006] In order to improve the sulfur capacity of zinc oxide catalyst at high space velocity and thus improve its effect during catalysis, the present application provides a preparation method of zinc oxide-cerium oxide desulfurization catalyst and the zinc oxide-cerium oxide desulfurization catalyst.

[0007] Firstly, the present application provides a preparation method of zinc oxide-cerium oxide desulfurization catalyst, which comprises the following steps:

[0008] S1, a mixed solution is configured, the mixed solution at least contains zinc ions and cerium ions, and the mass ratio of zinc and cerium is 100:1-3;

[0009] S2, adding an alkali without carbonate to the above solution to form a suspension;

[0010] S3, adding polyferric sulfate as a precipitant to make the suspension in step S2 precipitate, and after separation, drying and crushing, a powder is obtained;

[0011] S4, calcining the powder, and then preparing the catalyst through post-treatment;

[0012] In step S1 or S2, alumina and ammonium carbonate are also added, the mass ratio of the alumina and zinc is 0.1-0.3:1, and the amount of the ammonium carbonate added is 3.5-6% of the mass of the zinc.

[0013] In the existing zinc oxide-cerium oxide catalyst, the main structure is still zinc oxide, and the formed cerium oxide can be attached to the zinc oxide main material in the form of an attached material during sintering. In the above preparation process, small particles and mesoporous structures can be formed by the sedimentation method, but only small pores can lead to a decrease in the gas diffusion performance during the subsequent forming process, and the gas blockage phenomenon is easily generated in the system, and part of the pores can easily deposit gas, thereby causing the internal space to be unable to be fully utilized. This phenomenon is more obvious in the catalysts pressed into blocks and sheets, thereby causing the use convenience and catalytic efficiency of the catalyst to be unable to be considered.

[0014] In the above scheme, the co-precipitation method is first used to prepare the zinc oxide material to form zinc oxide particles with mesopores, and on this basis, ammonium carbonate is added as a porogen, and the gas generated during the decomposition of the ammonium carbonate is used to leave a through-hole region with a larger pore in the system, thereby better realizing the distribution of the gas, and thereby making the gas better distributed to the inside of the catalyst. In the process of precipitation, the alumina can provide good forming performance, and at the same time, the alumina has a more stable structure, improves the reliability of the zinc oxide catalyst after forming, and also provides good renewable performance. At the same time, the use of the forming performance of the alumina can reduce the damage of the gas generated during the decomposition of the ammonium carbonate to the zinc oxide crystal system, and maintains the stability of the overall pore distribution.

[0015] In the above scheme, the specific surface area of the alumina is preferably 175-220 m 2 / g. The alumina in this range can provide better precipitation and adsorption performance, and the pores formed by the alumina itself also help the gas to better diffuse inside, and at the same time, avoid the difficulty of gas desorption caused by too high specific surface area, and help to improve the overall catalytic and regeneration effect.

[0016] Preferably, in step S3, the mass of the polymeric ferric sulfate is 0.05-0.1 times the mass of the zinc.

[0017] In this step, polymeric ferric sulfate is added as a precipitant, which helps to improve the crystalline morphology of the zinc oxide after shaping, and after calcination, the polymeric ferric sulfate can form a certain pore template, forming a medium state of large and small pores in the system, so that the gas can diffuse more uniformly in the pores. At the same time, polymeric ferric sulfate can also help to improve the sintering performance of the whole, so that the above-mentioned catalyst has better catalytic effect after subsequent sintering, and overall, the overall catalytic effect and regeneration performance are improved.

[0018] On the basis of the above, in step S3, the polymeric ferric sulfate is added at one time or in batches within 5 minutes, and the reaction temperature is controlled at 20-50°C. After the addition is completed, the reaction is continued for 30-90 minutes. By controlling the reaction system at a lower temperature, the dispersion uniformity of the polymeric ferric sulfate can be improved, and the agglomeration of the polymeric ferric sulfate itself can be reduced, thereby improving the uniformity of the distribution of zinc oxide and aluminum oxide, and making the zinc, aluminum, and iron three phases of the system more uniformly dispersed and shaped.

[0019] Preferably, in step S2, the base is sodium hydroxide, ammonia or potassium hydroxide, and the final suspension has a pH of 8-10. Further preferably, in step S2, the temperature is controlled at 40-50°C, and the base is added in at least three batches or uniformly added within 30 minutes, and then the reaction time is 1-2 hours. By controlling the addition of the base, the overall morphology stability of the shaped zinc hydroxide, cerium hydroxide and sintered zinc oxide-cerium oxide composite system can be adjusted, so that the particle size and pore distribution of the shaped catalyst are more uniform and flat, and the ammonium carbonate loaded therein can form a more uniform pore distribution, thereby improving the distribution and diffusion performance of the gas in the catalyst.

[0020] Preferably, in step S1, the solution also contains any number of cerium ions, nickel ions, cobalt ions, magnesium ions, copper ions, and silver ions. Further preferably, in step S1, the solution contains nickel ions, and the mass of nickel is 2-4% of the mass of zinc. Through experiments, a small amount of added nickel ions can adjust the catalytic effect of the system, and have the best effect on the overall catalytic effect in the above reaction.

[0021] Preferably, in step S4, the calcination is first carried out at 130-160°C for 10-30 minutes, and then at 300-400°C for 30-60 minutes.

[0022] In the above environment, low-temperature calcination is first carried out, and then high-temperature calcination is carried out, which can make the ammonium carbonate decompose at low temperature and then form a zinc oxide system through high-temperature calcination, while removing other carbon and oxides in the system. In the above process, the pores can be formed before high-temperature calcination, so that the internal materials can be fully calcined, and the uniformity of calcination is improved.

[0023] In addition, the present application also relates to a metal oxide desulfurizer prepared by the preparation method of the metal oxide desulfurizer.

[0024] In summary, the zinc oxide desulfurizer prepared by the above method is based on zinc oxide-aluminum oxide, utilizes a pore former to form a comprehensive distribution of large pores and small pores, and simultaneously utilizes polyferric sulfate to produce a pore connection effect in the system, thereby improving the distribution and diffusion performance of the gas in the catalyst, further improving the sulfur capacity of the catalyst at a higher space velocity, and further improving the catalytic effect. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 FIG. 1A is a schematic diagram of an electron scanning microscope of the experimental group 1A-4. DETAILED DESCRIPTION

[0026] The technical solutions in the present application are further described through the following specific embodiments.

[0027] In the present application, the catalytic effect of the catalyst prepared above is determined by the sulfur capacity, and the determination of the sulfur capacity refers to the national standard HG / T 6151-2023 Sulfur Capacity Test Method for Zinc Oxide Desulfurizer at Room Temperature. In order to reflect that the catalyst in the present application can still maintain good sulfur capacity at a higher space velocity, the space velocity is adjusted to 3000h-1 on the basis of the above standard. At the same time, in order to detect whether the catalyst above can still maintain good catalytic effect and sulfur capacity after being regenerated for many times, the catalytic effect of the catalyst below is also determined at 5 cycles, 10 cycles and 20 cycles. -1

[0028] Example 1, the main purpose of this embodiment is to keep the addition amount of other metal materials fixed in two cases of not adding polyferric sulfate and adding polyferric sulfate, and to study the influence of the addition of ammonium carbonate on the catalytic effect of the system. Specifically, the specific preparation method of the zinc oxide desulfurization catalyst used in this embodiment is as follows:

[0029] S1: configure an aqueous solution of zinc nitrate-cerium oxide, and add aluminum oxide to the aqueous solution, wherein the aluminum oxide is selected from γ-aluminum oxide, and the specific surface area is 220m 2 / g; specifically, the concentration of zinc nitrate is 37.88g / L (0.2mol / L), the concentration of cerium nitrate is 0.61g / L (18.7mmol / L), and the aluminum oxide is added in a proportion of aluminum:zinc mass ratio=0.2:1, that is, in each liter of zinc nitrate solution, the mass of added aluminum oxide is 4.95g, and at the same time, in order to improve the overall catalytic efficiency, nickel nitrate is also added as a nickel source in this step, and the concentration of nickel nitrate is 1.2g / L; ​

[0030] S2, ammonia water is added in the above solution, and the pH value is monitored to be in the range of 8-10. Overall, the temperature control of this step is 45±5℃, ammonia water is added by dripping, and the dripping time is controlled for 30 min. After the end, the stirring reaction is continued for 2 h. For each liter of the mixed solution prepared in step S1, the mass of ammonia water is about 20 g of NH3·H2O. The specific addition can be monitored by a pH meter and slowly dripped. When the pH reaches 8-10, it is stopped. In addition, ammonium carbonate is also added in this step. The ammonium carbonate is added to the system after the ammonia water is dripped. The specific addition amount is shown in Table 1. It should be noted that in this step, ammonia water can be replaced by sodium hydroxide or potassium hydroxide.

[0031] S3, four ways are designed in this step, respectively denoted as 3-1, 3-2, 3-3 and 3-4, as follows:

[0032] S3-1, in this step, polymeric ferric sulfate is added according to the mass ratio of polymeric ferric sulfate: zinc of 0.1:1 (i.e. for each liter of the solution prepared in step S1, the mass of polymeric ferric sulfate added is 1.31 g). The polymeric ferric sulfate is added at one time, and then the temperature is controlled at 30℃, the stirring is stopped, and the reaction is continued for 60 min. In this process, the solids in the system settle, then the above solids are separated by centrifugation, and vacuum drying is carried out at a temperature of 40℃ to obtain a powder. In this step, the polymeric ferric sulfate selected is solid polymeric ferric sulfate with a total iron content of 20%. The product obtained according to this step is denoted as Example 1A;

[0033] S3-2, the difference between this step and scheme 3-1 is that iron oxide is added instead of polymeric ferric sulfate. The iron content of the iron oxide is consistent with the iron content of the polymeric ferric sulfate in step S3-1, i.e. for 1.31 g of polymeric ferric sulfate, the addition method and reaction conditions are consistent with step S3-1. The micron-sized iron oxide is selected, and the specific surface area is determined to be 88 m 2 / g. The product obtained according to this step is denoted as Example 1B;

[0034] S3-3, no other additives are added, the reaction is stopped naturally and settled for 60 min according to the method of step S3-1, then the above solids are separated by centrifugation, and vacuum drying is carried out at a temperature of 40℃ to obtain a powder. The product obtained according to this step is denoted as Example 1C;

[0035] S4, the powder in step S3 is sintered. First, it is calcined at 130℃ for 30 min, then it is calcined at 300℃ for 60 min, then it is pressed into a tablet to obtain the target sample.

[0036] In this embodiment, the experimental results of corresponding examples 1A, 1B, 1C corresponding to different ammonium carbonate addition amounts are shown in Table 1.

[0037] Table 1

[0038]

[0039] In the above table, it can be seen that after adding ammonium carbonate in this application, using ammonium carbonate as a porogen, the sulfur capacity can be effectively improved as a whole, which is most obvious in group 1A, and there is also a certain embodiment in groups 1B and 1C. In groups 1B and 1C, the trend of the effect of adding ammonium carbonate on the improvement of sulfur capacity is similar. It can be seen that the addition of iron element has no obvious effect on the initial sulfur capacity. Comparing experimental group 1B and experimental group 1C, it shows that the addition of iron element has certain help in improving the overall sintering resistance, which can still have certain catalytic performance after the above catalysts undergo 20 cycles. The above effect also has certain embodiment in example 1A.

[0040] Compared with example 1B, the form of adding iron in example 1A is changed from adding iron oxide to adding polymeric ferric sulfate. In the system, polymeric ferric sulfate not only realizes the addition of iron element, but also adjusts the catalytic form of the finally obtained zinc oxide-cerium oxide composite catalyst by using its sedimentation performance. Overall, it forms a larger initial sulfur capacity under the condition of adding ammonium carbonate, and also provides better catalytic performance after multiple uses, which shows that the effect of polymeric ferric sulfate in the system and the pore forming effect of ammonium carbonate work together to form a more uniform pore distribution structure inside, and at the same time, a form of interconnected large and small pores is produced, which improves the diffusion performance of gas under high space velocity, and thus improves the sulfur capacity.

[0041] Example 2, on the basis of examples 1A-4, further verifies the influence of the reaction conditions and the amount of polymeric ferric sulfate added on the sulfur capacity of the system, and the influence of replacing polymeric ferric sulfate with other sedimentation agents on the system. In this embodiment, the reaction conditions in step S3 are grouped as follows:

[0042] 2A: Polymeric ferric sulfate is added at one time, then the temperature is controlled at 20°C, the stirring is stopped and the reaction is continued for 60 min, and in this process the solids in the system are settled.

[0043] 2B: On the basis of 2A, the temperature is adjusted to 30°C. This reaction step is the same as step S3-1 in example 1.

[0044] 2C: On the basis of 2A, the temperature is adjusted to 50°C.

[0045] 2D: On the basis of 2A, the temperature was adjusted to 60°C.

[0046] 2E: On the basis of 2A, the reaction time was adjusted to 90 min.

[0047] 2F: On the basis of 2A, the reaction time was adjusted to 120 min.

[0048] 2G: On the basis of 2A, the reaction time was adjusted to 30 min.

[0049] 2H: On the basis of Example 2A, the polymeric ferric sulfate was added evenly to the system within 10 min.

[0050] 2I: On the basis of Example 2A, the polymeric ferric sulfate was replaced by alum, and other reaction conditions remained unchanged.

[0051] Adjustments to the above reaction steps, different amounts of polymeric ferric sulfate were added in each step, and the experimental results obtained are shown in Table 2.

[0052] Table 2

[0053]

[0054]

[0055] Through the above experimental groups, in each group of reaction conditions, the sulfur capacity and the sulfur capacity after multiple regeneration all increase first and then decrease with the increase of the addition amount of polymeric ferric sulfate. It can be seen that after adding polymeric ferric sulfate, in addition to having certain improvement on the sintering resistance of the system, the polymeric ferric sulfate is also used to adjust the settling performance of the system, forming a better pore structure and a more firm morphology. The overall structure can form a posture with iron-aluminum crosslinked system as the center, uniform distribution of zinc and cerium, so as to make the catalyst obtain better catalytic effect. When the addition of polymeric ferric sulfate is less, it will also lead to general molding performance of the catalyst as a whole, insufficient strength, and easy to produce debris. And when the polymeric ferric sulfate is added too much, the overall system will lead to a certain decline in catalytic effect.

[0056] In the above reaction process, too high temperature will lead to the decline of the settling effect of the system, and then lead to the overall pore to present a more fine and dense posture, and then lead to the initial sulfur capacity to decline.

[0057] It is worth noting that in the experimental group 2H, the slow addition of ferric sulfate to the system over a longer period of time actually produces a less effective polymerization than the one-time addition. After experiments, when the cumulative time exceeds 5 minutes, it is easy to cause uneven sedimentation performance, part of which forms smaller iron cores, leading to a decrease in sintering resistance, and the other part has too little catalyst, leading to a decrease in catalytic performance, which overall leads to a decrease in sulfur capacity.

[0058] In addition, by comparing experimental groups 2I and 2A, it can be seen that when alum is selected to be added to the system (considering that the addition of a small amount of alum has no obvious effect on the aluminum content in the product, so the overall aluminum / zinc ratio is not adjusted), in addition to the lack of iron element addition, which causes the sintering resistance of the system to decrease to a certain extent, it also causes the sulfur capacity to decrease and the overall catalyst forming performance to decrease. In fact, considering that the coagulation of alum is relatively close to that of polymerized ferric sulfate, the difference may be due to the fact that the polymerized ferric sulfate system itself has a large and relatively extended core structure, which can better adjust the overall product pore system.

[0059] Example 3, on the basis of Examples 1A-4, experiments on the addition of alumina were conducted. By orthogonal experiment on the specific surface area and addition amount of alumina, the effect of alumina in the above system was studied. The specific experimental results are shown in Table 3.

[0060] Table 3

[0061]

[0062] From the above experiments, it can be seen that the sulfur capacity of the catalyst as a whole will first increase and then decrease with the addition of alumina. The reason may be that alumina itself provides good forming performance, which not only improves the catalyst morphology, but also improves the uniformity of the overall pore distribution, making the gas diffusion performance and the performance of the gas and zinc oxide-cerium oxide contact better. However, alumina itself does not participate in the reaction, and its excessive presence will cause some gas to remain in its pores, which will hinder the full contact of the reaction gas with the catalyst, thereby weakening the catalytic effect.

[0063] In addition, from the above experimental results, it can be seen that in this embodiment, alumina with a specific surface area of 175-220 m 2 / g range, as the specific surface area of alumina is too large, the overall pore structure changes, the overall catalyst is more likely to agglomerate, the gas diffusion performance is not good, and sintering is more likely to occur, causing a significant decrease in sulfur capacity after multiple cycles. When the specific surface area of alumina is too small, the overall sulfur capacity will decrease significantly.

[0064] Example 4, on the basis of Examples 1A-4, the conditions of the calcination step were studied, as shown in Table 4.

[0065] Table 3

[0066]

[0067] From the experimental data in Table 4, it can be seen that using step calcination, compared with directly calcining, can provide better catalytic effect, the reason may be that by low temperature calcination, the rate of gas generation can be controlled to improve the forming performance of the whole body before the whole body is not formed, the formation of the airway can be controlled, while directly using high temperature calcination can easily lead to too fast production rate, which in turn leads to poor forming performance and also has a certain influence on the overall adsorption performance. At the same time, the above experimental data can obviously see that too high calcination temperature or too long calcination time will obviously lead to the decrease of sulfur capacity.

[0068] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for producing a zinc oxide-cerium oxide desulfurization catalyst, characterized by, The method comprises the following steps: S1, preparing a mixed solution containing zinc ions and cerium ions, wherein the mass ratio of zinc to cerium is 100:1-3; S2, adding a base without carbonate to the solution to form a suspension; S3, adding polymeric ferric sulfate as a precipitant to make the suspension in step S2 precipitate, and then drying and crushing to obtain a powder; S4, calcining the powder and then preparing a catalyst through post-treatment; In step S1 or S2, aluminum oxide and ammonium carbonate are also added, wherein the mass ratio of aluminum to zinc is 0.1-0.3:1, and the amount of ammonium carbonate added is 3.5-6% of the mass of zinc; In step S3, the mass of polymeric ferric sulfate is 0.05-0.1 times the mass of zinc, and the polymeric ferric sulfate is added at one time or in batches within 5 minutes, the reaction temperature is controlled at 20-50℃, and the reaction is continued for 30-90 minutes after the addition is completed.

2. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 1, characterized by, The specific surface area of the alumina is 175 to 220 m 2 / g.

3. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 1, characterized by, In step S2, the base is sodium hydroxide, ammonia or potassium hydroxide, and the final pH of the suspension is 8-10.

4. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 3, characterized by, In step S2, the temperature is controlled at 40-50℃, the base is added in at least three batches or uniformly within 30 minutes, and then the reaction time is 1-2 hours.

5. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 1, characterized by, In step S1, the solution also contains one or more of nickel ions, cobalt ions, magnesium ions, copper ions and silver ions.

6. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 5, characterized by, In step S1, the solution contains nickel ions, and the mass of nickel is 2-4% of the mass of zinc.

7. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 1, characterized by, In step S4, the calcination is first carried out at 130-160℃ for 10-30 minutes, and then carried out at 300-400℃ for 30-60 minutes.

8. The zinc oxide-cerium oxide desulfurization catalyst prepared by the method of any one of claims 1-7.

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