Zinc oxide-cerium oxide desulfurization catalyst and preparation method thereof

Abstract

The invention 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, the zinc-cerium composite catalyst is used as a substrate, and ammonium carbonate is added as a pore-foaming agent, so that a large pore channel-small pore channel composite form can be formed, further, gas can be better and uniformly distributed in the catalyst, and the sulfur capacity of a system is greatly improved at a relatively high air speed.

Description

Technical Field

[0001] This application relates to the field of desulfurization catalysts, and particularly to a zinc oxide-cerium oxide desulfurization catalyst and a preparation method thereof. Background Art

[0002] With the increasing demand for industrial gas purification, desulfurization technology has become particularly important in fields such as petrochemical industry, natural gas purification, and coal gasification. Hydrogen sulfide (H 2 S) and carbonyl sulfide (COS) are common sulfur-containing compounds in industrial gases. They not only corrode equipment, reduce the activity of catalysts, but also cause serious environmental pollution. Therefore, developing efficient and stable desulfurization catalysts has important industrial significance.

[0003] Currently, 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 react with H 2 S to form zinc sulfide (ZnS), thereby achieving sulfur removal.

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

[0005] The theoretical sulfur capacity of zinc oxide is 41.9 wt%, which is the calculation result based on the complete reaction of ZnO with H 2 S to form ZnS. In fact, considering the structure of zinc oxide itself, its maximum sulfur capacity during the reaction usually does not exceed 30%, and it needs to be carried out at a lower space velocity, so it has a certain adverse effect on the actual catalytic efficiency. Summary of the Invention

[0006] In order to improve the sulfur capacity of zinc oxide catalysts at high space velocities and thus improve their catalytic effect, this application provides a preparation method of a zinc oxide-cerium oxide desulfurization catalyst and the zinc oxide-cerium oxide desulfurization catalyst.

[0007] First, this application provides a preparation method of a zinc oxide-cerium oxide desulfurization catalyst, including the following steps:

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

[0009] S2. Add a carbonate-free base to the above solution to form a suspension;

[0010] S3. Add polyferric sulfate as a sedimentation agent to cause the suspension in step S2 to coagulate, separate, dry, and pulverize to obtain a powder.

[0011] S4. Calcinate the powder and then prepare a catalyst through post-treatment.

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

[0013] In the existing zinc oxide-cerium oxide catalyst, its main structure is still zinc oxide, and the formed cerium oxide can adhere to the zinc oxide main material in the form of an adherent material during the sintering process. In the above preparation process, smaller particles and mesoporous structures can be formed by the sedimentation method. However, during the subsequent forming and using process, only small pores will lead to a decrease in the gas diffusion performance, and gas blockage is likely to occur inside the system. Some of the pores are easily deposited with gas, resulting in the inability to fully utilize the internal space. This phenomenon is more obvious in the catalysts pressed into blocks or sheets, thus making it impossible to balance the convenience of use and the catalytic efficiency of the catalyst.

[0014] In the above solution, the coprecipitation method is first used to prepare zinc oxide materials to form zinc oxide particles with mesopores. On this basis, by adding ammonium carbonate as a pore-forming agent and using the gas generated during its decomposition, through-hole regions with larger pores are left in the system, thereby better realizing gas distribution, so that the intake air can be better distributed into the catalyst interior. During the precipitation process, based on alumina, alumina itself can provide good forming performance, and at the same time it has a more stable structure, improving the reliability of the formed zinc oxide catalyst and also providing good renewable performance. At the same time, using the forming performance of alumina can reduce the damage of the gas generated during the decomposition of ammonium carbonate to the zinc oxide crystal system and maintain the stability of the overall pore distribution.

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

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

[0017] In this step, adding polyferric sulfate as a sedimentation agent, on the one hand, helps the sedimentation state to occur, so that the overall crystal form of zinc oxide is better after molding, and at the same time, polyferric sulfate can form a certain channel template after calcination, forming an intermediate form of large channels and small channels in the system, so that the gas can be diffused more evenly in the channel. At the same time, polyferric sulfate also helps to improve the overall sinterability, so that the above catalyst has a better catalytic effect after subsequent sintering, and generally improves the overall catalytic effect and regeneration performance.

[0018] On the basis of the above, in step S3, polyferric sulfate is added all at once or in batches within 5 minutes, the reaction temperature is controlled to be 20-50°C, and the reaction is continued for 30-90 minutes after the addition is completed. By controlling the reaction system to proceed at a lower temperature, the dispersion uniformity of polyferric sulfate can be improved, the agglomeration of polyferric sulfate itself can be reduced, and the uniformity of the distribution of zinc oxide and aluminum oxide can be improved, so that the overall zinc, aluminum and iron phases of the system can be more evenly dispersed and formed.

[0019] Preferably, in step S2, the alkali is sodium hydroxide, ammonia water or potassium hydroxide, and the pH value of the final suspension is 8 to 10. Further preferably, in step S2, the temperature is controlled to be 40 to 50°C, the alkali is controlled to be added in at least three batches or evenly added within 30 minutes, and then the reaction time is 1 to 2 hours. By controlling the addition of alkali, the overall morphological stability of the 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 catalyst after molding are more uniform and smooth, 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, adding a small amount of nickel ions to adjust the catalytic effect of the system has the best effect on the overall catalytic effect in the above reaction.

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

[0022] Calcination is carried out under the above environment, and low-temperature calcination is adopted followed by further calcination at a higher temperature. Ammonium carbonate can be decomposed by low temperature and then formed into a zinc oxide system by high-temperature calcination, while other carbon and oxides in the system are removed. In the above process, pores can be preformed before high-temperature calcination, so that the internal material can be fully calcined, thereby improving the uniformity of calcination.

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

[0024] In summary, the zinc oxide desulfurizer prepared by the above method is based on zinc oxide-aluminum oxide, and uses a pore-forming agent to form a comprehensive distribution of large pores and small pores. At the same time, polyferric sulfate is used to generate a pore connection effect in the system, improving the distribution and diffusion performance of gas in the catalyst, thereby improving the sulfur capacity of the catalyst at a higher space velocity, and further improving the catalytic effect. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of an electron scanning microscope of Experimental Group 1A-4. Detailed Embodiments

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

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

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

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

[0030] S2, add ammonia water to the above solution, and monitor the pH value to the range of 8 to 10. In general, the temperature of this step is controlled to 45±5°C, and the ammonia water is added by dripping, and the dripping time is controlled to be 30min. After the end, the stirring reaction is continued for 2h. For each liter of the mixed solution prepared in step S1, the added mass of ammonia water is about 20g of NH3·H2O. The specific addition can be monitored by a pH meter and slowly dripped, and stopped when the pH reaches the range of 8 to 10; in addition, ammonium carbonate is also added in this step, and 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 also be replaced by sodium hydroxide or potassium hydroxide.

[0031] S3. In this step, four methods are designed, which are respectively recorded as 3-1, 3-2, 3-3 and 3-4, as follows:

[0032] S3-1, in this step, polyferric sulfate is added at a mass ratio of 0.1:1 (i.e., for each liter of the solution prepared in step S1, 1.31 g of polyferric sulfate is added), wherein the polyferric sulfate is added all at once, and then the temperature is controlled to 30° C., stirring is stopped, and the reaction is continued for 60 min. During this process, the solid in the system settles, and then the solid is separated by centrifugation, and vacuum dried at a temperature of 40° C. to obtain a powder; in this step, the polyferric sulfate selected is a solid polyferric sulfate with a total iron content of 20%. The product obtained according to this step is recorded as Example 1A;

[0033] S3-2, in which the difference from the 3-1 scheme is that iron oxide is added instead, and the iron content in the iron oxide is controlled to be consistent with the iron content of the polyferric sulfate in step S3-1, that is, for 1.31g of polyferric sulfate, the addition method and reaction conditions are also consistent with step S3-1, and the iron oxide is micron-sized iron oxide, and the specific surface area is measured to be 88m 2 / g, and the product obtained according to this step is recorded as Example 1B;

[0034] S3-3, without adding other additives, stopping the reaction according to the method of step S3-1 and allowing the mixture to settle naturally for 60 minutes, then separating the solid by centrifugation, and vacuum drying at 40° C. to obtain a powder; the product obtained according to this step is recorded as Example 1C;

[0035] S4. Sintering the powder in step S3, first heating to 130° C. and calcining for 30 min, then heating to 300° C. and calcining for 60 min, and then pressing into tablets to obtain the target sample.

[0036] In this embodiment, the experimental results of Embodiments 1A, 1B, and 1C corresponding to different amounts of ammonium carbonate added 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 can effectively increase the sulfur capacity as a whole. The phenomenon is most obvious in group 1A, and it is also reflected 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 has no obvious effect on the initial sulfur capacity. Comparing experimental group 1B and experimental group 1C, it is shown that the addition of iron is helpful in improving the overall sintering resistance, and the above catalyst can still have a certain catalytic performance after 20 cycles. The above effect is also reflected in Example 1A.

[0040] In Example 1A, compared with Example 1B, the addition of iron in the form of directly adding iron oxide is changed to adding polyferric sulfate. In the system, polyferric sulfate not only realizes the addition of iron element, but also adjusts the catalytic form of the zinc oxide-cerium oxide composite catalyst obtained by using its sedimentation performance. On the whole, it forms a larger initial sulfur capacity with the addition of ammonium carbonate, and also provides better catalytic performance after repeated use, indicating that the coagulation effect of polyferric sulfate in the system and the pore-forming effect formed by 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 the gas at a higher air velocity, thereby improving the sulfur capacity.

[0041] Example 2, based on Example 1A-4, this example further verifies the effect of the reaction conditions after the addition of polyferric sulfate and the amount of addition on the sulfur capacity of the system, as well as the effect of replacing polyferric sulfate with other sedimentation agents on the system through orthogonal experiments. In this example, the reaction conditions in step S3 are grouped into the following groups:

[0042] 2A: Polyferric sulfate was added all at once, and then the temperature was controlled at 20°C. Stirring was stopped and the reaction was continued for 60 minutes. During this process, the solid in the system settled.

[0043] 2B: Based on 2A, the temperature was adjusted to 30° C. This reaction step is the same as the step of S3-1 in Example 1.

[0044] 2C: Based on 2A, adjust the temperature to 50°C.

[0045] 2D: Based on 2A, adjust the temperature to 60°C.

[0046] 2E: Based on 2A, adjust the reaction time to 90 min.

[0047] 2F: Based on 2A, adjust the reaction time to 120 min.

[0048] 2G: Based on 2A, adjust the reaction time to 30 min.

[0049] 2H: Based on Example 2A, uniformly add polymeric ferric sulfate to the system within 10 min.

[0050] 2I: Based on Example 2A, replace polymeric ferric sulfate with alum, and keep other reaction conditions unchanged.

[0051] For the adjustments of the above reaction steps, different amounts of polymeric ferric sulfate are 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, under the reaction conditions of each group, the sulfur capacity and the sulfur capacity after multiple regenerations both change with the increase of the addition amount of polymeric ferric sulfate in a trend of first increasing and then decreasing. It can be seen that after adding polymeric ferric sulfate, in addition to improving the sintering resistance of the system to a certain extent, the regulation of the sedimentation performance of the system by polymeric ferric sulfate is also utilized to form a better pore structure and a more solid morphology. The overall structure can form an attitude with an iron-aluminum cross-linked system as the center and zinc and cerium evenly distributed, so that the catalyst can obtain better catalytic effects. When the addition amount of polymeric ferric sulfate is small, it will also lead to general molding performance of the catalyst, insufficient strength, and easy generation of debris. When the addition amount of polymeric ferric sulfate is too large, on the contrary, it will cause a certain decline in the catalytic effect of the system.

[0056] During the above reaction process, too high temperature will lead to a decline in the sedimentation effect of the system, and then lead to a finer and denser attitude of the overall pores, and further lead to a decline in the initial sulfur capacity.

[0057] It should be noted that in experimental group 2H, after ferric sulfate was slowly added to the system over a long period of time, the polymerization effect was actually worse than that of adding it all at once. After experiments, when the cumulative time exceeded 5 minutes, it was likely to cause uneven sedimentation performance. A part formed smaller iron nuclei, resulting in a decrease in its sintering resistance, and the other part carried too little catalyst, leading to a decrease in its catalytic performance. Overall, both led to a decrease in sulfur capacity.

[0058] In addition, by comparing experimental group 2I with 2A, it can be seen that when alum was selected and added to the system (considering that the addition of a small amount of alum had little obvious effect on the aluminum content in the product, so the overall aluminum / zinc ratio was not adjusted additionally), in addition to a certain decrease in the sintering resistance of the system due to the lack of iron element addition, it also caused a decrease in sulfur capacity and a decrease in the overall shaping performance of the catalyst. In fact, considering that the flocculation property of alum was relatively close to that of ferric sulfate, the reason for this difference may be that the ferric sulfate system itself has a relatively large and extended core structure, which can better adjust the pore system of the overall product.

[0059] Example 3, on the basis of Examples 1A - 4 of this embodiment, experiments on the addition of alumina were carried out. Through orthogonal experiments on the specific surface area and addition amount of alumina, the effects of alumina in the above system were studied. The specific experimental results are shown in Table 3.

[0060] Table 3

[0061]

[0062] From the above experiments, it can be seen that overall, the sulfur capacity of the catalyst will show a trend of first increasing and then decreasing with the addition of alumina. The reason may be that alumina itself provides good shaping performance. In addition to improving the morphology of the catalyst, it also improves the uniformity of the overall pore distribution, making the gas diffusion performance and the performance of gas contacting with zinc oxide - cerium oxide better. However, alumina itself does not participate in the reaction, and too much of its presence will instead cause a certain amount of gas to remain in its pores, and this part of the gas will hinder the full contact between the reaction gas and the catalyst, instead resulting in a weakening of 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 in the range of 175 - 220 m 2 / g needs to be used. If the specific surface area of alumina is too large, it will cause changes in the overall pore structure, making it easier to agglomerate as a whole. At the same time, the gas diffusion performance in it is poor, and sintering is also more likely to occur, resulting in 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. Based on Examples 1A - 4, the conditions of the calcination step were studied, as specifically shown in Table 4.

[0065] Table 3

[0066]

[0067] From the experimental data in Table 4, it can be seen that using step - by - step calcination can provide better catalytic effects compared to direct calcination. The reason may be that by low - temperature calcination, the rate of gas generation can be controlled before the overall shaping to improve the overall shaping performance, which can play a regulatory role in the formation of the air channels. While directly using high - temperature calcination easily leads to too fast a production rate, resulting in poor shaping performance and also having a certain impact on the overall adsorption performance. At the same time, it can be clearly seen from the above experimental data that too high a calcination temperature or too long a calcination time will significantly lead to a decrease in sulfur capacity.

[0068] This specific embodiment is only an explanation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, 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 preparing a zinc oxide-cerium oxide desulfurization catalyst, characterized in that: The steps include: S1. preparing a mixed solution, wherein the mixed solution contains at least zinc ions and cerium ions, and the mass ratio of zinc to cerium is 100:1-3; S2, adding a carbonate-free base to the above solution to form a suspension; S3, adding polyferric sulfate as a precipitant to flocculate the suspension in step S2, and drying and crushing after separation to obtain a powder; S4, calcining the powder, and then preparing a catalyst through post-treatment; Wherein, in step S1 or S2, aluminum oxide and ammonium carbonate are also added, 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.

2. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 1, characterized in that: 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 in that: In step S3, the mass of the polyferric sulfate is 0.05 to 0.1 times the mass of zinc.

4. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 3, characterized in that: In step S3, polyferric sulfate is added all at once or in batches within 5 minutes, the reaction temperature is controlled at 20-50° C., and the reaction is continued for 30-90 minutes after the addition is completed.

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

6. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 5, characterized in that: In step S2, the temperature is controlled at 40-50°C, the base is added in at least three batches or evenly within 30 minutes, and then the reaction time is 1-2 hours.

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

8. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 7, characterized in that: In step S1, the solution contains nickel ions, and the mass of nickel is 2-4% of the mass of zinc.

9. The method for preparing a zinc oxide-cerium oxide desulfurization catalyst according to claim 1, characterized in that: In the step S4, the calcination is first performed at 130-160° C. for 10-30 min, and then at 300-400° C. for 30-60 min.

10. The zinc oxide-cerium oxide desulfurization catalyst prepared by the method for preparing the zinc oxide-cerium oxide desulfurization catalyst according to any one of claims 1 to 9.

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