Process for the regeneration of a supported bimetallic alloy catalyst in the dehydrogenation of alkanes

Abstract

The present application belongs to the field of catalyst regeneration technology, and discloses a regeneration method of a supported bimetallic alloy catalyst in alkane dehydrogenation. After the supported bimetallic alloy catalyst is calcined by oxygen, the auxiliary metal oxide is physically blended with the supported bimetallic alloy catalyst, and then the reduction treatment is carried out under high temperature using hydrogen atmosphere, so as to restore the activity of the supported bimetallic alloy catalyst. The present application can solve the problems of metal loss and bimetallic alloy structure damage of the bimetallic catalyst in the long-time high-temperature reaction environment and the regeneration process. By adding the oxide of the auxiliary metal, the auxiliary metal atoms are reduced and diffused onto the metal alloy under high-temperature conditions, so as to restore the structure and activity of the bimetallic alloy in the catalyst. The method is simple and convenient to operate, and is suitable for the supported bimetallic alloy prepared by different methods.

Description

Technical Field

[0001] This invention belongs to the field of catalyst regeneration technology, specifically, it relates to a method for regenerating catalysts in alkane dehydrogenation. Background Technology

[0002] Due to global economic development, the demand for light olefins, especially olefins, continues to grow. Light olefins are reactive and are fundamental feedstocks for the production of polymers, consumer goods, and specialty chemicals. Given the availability of light alkanes (C2-C6) as feedstocks, particularly the emergence of shale gas, the selective conversion of light alkanes (C2-C6 saturated hydrocarbons) into their corresponding olefins is a highly attractive strategy for the petrochemical industry. Dehydrogenation reactions of light alkanes (especially propane and butane) are widely used for the large-scale production of their corresponding olefins. The dehydrogenation reaction of light alkanes involves breaking two carbon-hydrogen bonds while selectively forming hydrogen and carbon-carbon double bonds. The highly endothermic nature of this reaction requires high reaction temperatures to achieve good conversion rates. However, selective control at higher temperatures is difficult. Simultaneously, higher operating temperatures make catalysts prone to sintering and carbon deposition, leading to a decrease in activity. To suppress catalyst sintering and improve catalyst stability, a second active metal is often introduced as a promoter metal to modify the geometry and electronic state of the active metal. After the alloy is formed, the catalyst becomes more stable under high temperature conditions. At the same time, the auxiliary metal changes the dispersion state of the active metal, making its dehydrogenation to olefins more selective.

[0003] Although the metal promoters significantly enhance the catalyst's resistance to sintering and improve its dehydrogenation selectivity, carbon deposition remains unavoidable. After prolonged reactions, the catalyst activity decreases markedly. To restore the catalyst's activity to its initial state, frequent high-temperature regeneration is necessary in long-range reactions to remove carbon deposits. Sintering and metal component loss during regeneration are also major causes of deactivation in alkane dehydrogenation catalysts. Due to the high regeneration temperature and the interaction between the support and different metal components, metal components are gradually lost during regeneration, leading to changes in the catalyst structure and a gradual loss of its thermal stability and activity. This is particularly true for newly developed bimetallic catalysts such as PtZn, PtIn, and PtGa, becoming a significant factor restricting their industrial application. Summary of the Invention

[0004] The present invention addresses the technical problem that existing alkane catalysts lose regenerated metal components under high-temperature conditions, resulting in irrecoverable activity. It provides a method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation, which exhibits excellent regeneration stability.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0006] This invention provides a method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation. After the supported bimetallic alloy catalyst is calcined in oxygen, an auxiliary metal oxide is physically blended with the supported bimetallic alloy catalyst, and then the catalyst is reduced at high temperature in a hydrogen atmosphere to restore the activity of the supported bimetallic alloy catalyst.

[0007] The supported bimetallic alloy catalyst includes a support on which bimetallic alloy nanoparticles are uniformly loaded. The bimetallic alloy nanoparticles are composed of an auxiliary metal and an active metal. The active metal is one of the transition metal elements from groups IIIB, IVB, VB, VIB, VIIB, VIII, IB, and IIB. The auxiliary metal is one of the transition metal elements from groups IIIB, IVB, VB, VIB, VIIB, VIII, IB, and IIB, and one of In, Ga, Sn, Bi, and Pb. Furthermore, the active metal and the auxiliary metal are different metals.

[0008] The auxiliary metal in the auxiliary metal oxide is the same metal as the auxiliary metal in the supported bimetallic alloy catalyst.

[0009] Furthermore, in the supported bimetallic alloy catalyst, the mass percentage of the active metal, calculated based on the mass of the support, is 0.025%-20%.

[0010] Furthermore, in the supported bimetallic alloy catalyst, the molar ratio of the auxiliary metal to the active metal is 0.5 to 5.

[0011] Furthermore, in the supported bimetallic alloy catalyst: the support is SiO2 or Al2O3.

[0012] Furthermore, the auxiliary metal oxide is a supported auxiliary metal oxide or an unsupported auxiliary metal oxide.

[0013] Further, proceed as follows:

[0014] (1) The fresh supported bimetallic alloy catalyst is calcined at high temperature in an oxygen atmosphere after undergoing an alkane dehydrogenation process;

[0015] (2) The auxiliary metal oxide and the supported bimetallic alloy catalyst obtained in step (1) are physically mixed evenly;

[0016] (3) The mixture obtained in step (2) is reduced at high temperature in a hydrogen atmosphere to obtain the regenerated supported bimetallic alloy catalyst.

[0017] Preferably, the high-temperature calcination in step (1) under an oxygen atmosphere is at a temperature of 400-650℃ and a time of 20-60min.

[0018] Furthermore, the auxiliary metal oxide is a supported auxiliary metal oxide or an unsupported auxiliary metal oxide, wherein the preparation method of the supported auxiliary metal oxide is as follows:

[0019] The precursor solution of the auxiliary metal in the supported bimetallic alloy catalyst is impregnated on the support while being added dropwise and stirred. Then, it is sonicated to ensure thorough impregnation. After standing at room temperature, it is completely dried to obtain the supported auxiliary metal precursor. The supported auxiliary metal precursor is calcined in air at high temperature to obtain the supported auxiliary metal oxide.

[0020] Preferably, the time for standing at room temperature after full impregnation is 6-12 hours; the temperature for high-temperature calcination in air is 400-700℃ and the time is 1-3 hours.

[0021] Preferably, the content of the auxiliary metal oxide added in step (2) is 5%-200% of the auxiliary metal content in the fresh supported bimetallic alloy catalyst in step (1).

[0022] Preferably, the high-temperature reduction in step (3) is carried out at a temperature of 300-800℃ for 1-3 hours.

[0023] The beneficial effects of this invention are:

[0024] This invention proposes a method for regenerating supported bimetallic alloy catalysts in alkane dehydrogenation, addressing the problems of prolonged high-temperature reaction environments, metal loss during regeneration, and structural damage to the bimetallic alloy. Under high-temperature conditions, conventional regeneration methods, particularly the air regeneration step, often fail to restore catalyst activity after reduction treatment due to the loss of promoter metals or alterations in the bimetallic alloy structure. This invention addresses this issue by adding oxides of promoter metals, which, under high-temperature conditions, reduce and diffuse promoter metal atoms onto the metal alloy, restoring the bimetallic alloy structure and activity within the catalyst. This method is simple and convenient to operate and applicable to supported bimetallic alloys prepared using various methods. Attached Figure Description

[0025] Figure 1 The graph shows the mass loss of Pt in the PtZn / SiO2 catalyst after continuous propane dehydrogenation reaction and regeneration cycle.

[0026] Figure 2 The diagram shows the propane dehydrogenation regeneration cycle activity of the prepared PtZn / SiO2 catalyst.

[0027] Figure 3 The diagram shows the propane dehydrogenation regeneration cycle performance of the prepared PtZn / SiO2 catalyst. Detailed Implementation

[0028] This invention provides a method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation. After the supported bimetallic alloy catalyst is calcined in oxygen, an auxiliary metal oxide is physically blended with the supported bimetallic alloy catalyst, and then the catalyst is reduced at high temperature in a hydrogen atmosphere to restore the activity of the supported bimetallic alloy catalyst.

[0029] The supported bimetallic alloy catalyst includes a support on which bimetallic alloy nanoparticles are uniformly loaded. The bimetallic alloy nanoparticles are composed of an auxiliary metal and an active metal. The active metal is one of the transition metal elements from groups IIIB, IVB, VB, VIB, VIIB, VIII, IB, and IIB. The auxiliary metal is one of the transition metal elements from groups IIIB, IVB, VB, VIB, VIIB, VIII, IB, and IIB, and one of In, Ga, Sn, Bi, and Pb. The active metal and the auxiliary metal are different metals.

[0030] In this case, the auxiliary metal in the auxiliary metal oxide is the same metal as the auxiliary metal in the supported bimetallic alloy catalyst.

[0031] Furthermore, in the supported bimetallic alloy catalyst, the mass percentage of the active metal is 0.025%-20% based on the mass of the support.

[0032] Furthermore, in the supported bimetallic alloy catalyst, the molar ratio of the promoter metal to the active metal is 0.5 to 5.

[0033] Furthermore, in the supported bimetallic alloy catalyst, the support is SiO2 or Al2O3.

[0034] Furthermore, the auxiliary metal oxide is either a supported auxiliary metal oxide or an unsupported auxiliary metal oxide.

[0035] Specifically, the regeneration method of the above-mentioned supported bimetallic alloy catalyst in alkane dehydrogenation is carried out according to the following steps:

[0036] (1) The fresh supported bimetallic alloy catalyst is subjected to alkane dehydrogenation process and then calcined at high temperature in an oxygen atmosphere; the preferred temperature for high-temperature calcination is 400-650℃ and the preferred time is 20-60min.

[0037] (2) The auxiliary metal oxide and the supported bimetallic alloy catalyst obtained in step (1) are physically mixed evenly.

[0038] Generally, the content of the added auxiliary metal oxide is 5%-200% of the auxiliary metal content in the fresh supported bimetallic alloy catalyst in step (1), and the specific amount added depends on the reaction time. As the reaction time is extended, the loss of auxiliary metal will gradually increase, and the amount added also needs to be increased accordingly, with 5%-200% being the preferred range.

[0039] Furthermore, the auxiliary metal oxide can be a supported auxiliary metal oxide or an unsupported auxiliary metal oxide.

[0040] The preparation method of the supported auxiliary metal oxide is as follows:

[0041] The precursor solution of the auxiliary metal in the supported bimetallic alloy catalyst is impregnated on the support while being added dropwise and stirred. Then, it is ultrasonicated to ensure thorough impregnation. After standing at room temperature, it is completely dried to obtain the supported auxiliary metal precursor. The supported auxiliary metal precursor is calcined in air at high temperature to obtain the supported auxiliary metal oxide. Preferably, the standing time at room temperature after thorough impregnation is 6-12 hours. The high temperature calcination in air is 400-700℃ for 1-3 hours.

[0042] The auxiliary metal oxide can also be supported on a support: the precursor solution of the auxiliary metal in the supported bimetallic alloy catalyst is impregnated on the support, and stirred dropwise. Then, it is ultrasonicated to ensure full impregnation, and after standing at room temperature, it is completely dried to obtain the supported auxiliary metal precursor; the supported auxiliary metal precursor is calcined in air at high temperature to obtain the supported auxiliary metal oxide; wherein, the standing time at room temperature after full impregnation is preferably 6-12h; the high temperature of calcination in air is preferably 400-700℃, and the time is preferably 1-3h.

[0043] (3) The mixture obtained in step (2) is reduced at high temperature in a hydrogen atmosphere to obtain the regenerated supported bimetallic alloy catalyst. The preferred high-temperature reduction temperature is 300-800℃, and the preferred time is 1-3h. It should be noted that the melting and boiling points of different auxiliary metals vary greatly. For example, Zn in the example can volatilize at 400-550℃. Other transition metals, such as Pt in the example, although used as active metals in the example, require higher reduction temperatures (600-800℃) and longer times to volatilize to a sufficient amount if they are to be used as auxiliary metals. Since the regeneration experiment is time-consuming, we only use Pt as active metal and Zn as auxiliary metal as examples. Other metals can be deduced by analogy. If the alloy structure is damaged due to the loss or segregation of auxiliary metal components, the auxiliary metal diffusion method used in this invention can also achieve a similar effect.

[0044] The present invention will be further described in detail below through specific embodiments. These embodiments will enable those skilled in the art to have a more comprehensive understanding of the present invention, but will not limit the present invention in any way.

[0045] Example 1:

[0046] (1) Dissolve 0.02 g of (NH3)4Pt(NO3)2 in 1-2 mL of deionized water, and add ammonia to adjust the pH to 11;

[0047] Dissolve 0.01 g of Zn(NO3)3·6H2O precursor in 1-2 mL of deionized water.

[0048] (2) The two solutions obtained in step (1) were added dropwise to two 1.00g portions of SiO2 while stirring, and then sonicated for 30min. They were left to stand at room temperature for 6h, and then placed in an oven at 80-100℃ to dry completely, to obtain Pt / SiO2 and Zn / SiO2 respectively.

[0049] (3) Calcine the SiO2 containing the Zn precursor obtained in step (2) in air at 500-600℃ for 1 h to obtain ZnO / SiO2.

[0050] (4) The Pt / SiO2 obtained in step (2) and the ZnO / SiO2 obtained in step (3) are physically mixed and then reduced at 550°C in a diluted hydrogen atmosphere to obtain the PtZn alloy catalyst.

[0051] Example 2

[0052] Supported bimetallic alloy catalysts were used for propane dehydrogenation to propylene: The PtZn alloy catalyst prepared in Example 1 was pressed into 20-40 mesh catalyst particles and treated in a nitrogen atmosphere, with the temperature increased from room temperature to the reduction temperature of 600°C for 1 h. Subsequently, the reaction was carried out at a reaction temperature of 600°C, a propane space velocity of 4 h⁻¹, and a hydrogen to propane feed ratio of 1:1, with nitrogen used as a dilution gas.

[0053] Example 3

[0054] The PtZn alloy catalyst used in Example 2 for propane dehydrogenation to propylene was treated with oxygen at 500°C for 30 min, followed by treatment with hydrogen at 550°C for 1 h.

[0055] Example 4

[0056] Same as Example 2, except that the propane space velocity is 20 h⁻¹. -1 .

[0057] Example 5

[0058] The PtZn alloy catalyst used in Example 2 for propane dehydrogenation to propylene was treated at 500°C for 30 min in an oxygen atmosphere. After cooling to room temperature, ZnO / SiO2 prepared in Example 1 (30% of the Zn content in the fresh PtZn alloy catalyst by elemental mass) was added and thoroughly mixed. The mixture was then treated at 550°C in a hydrogen atmosphere for 1 h.

[0059] The results of the above embodiments are discussed below:

[0060] (I) Elemental content analysis was performed on PtZn alloy catalysts after continuous propane dehydrogenation processes and regeneration cycles of different durations. The results are as follows: Figure 1 As shown, the specific preparation is the same as in Example 1, the reaction conditions are the same as in Example 2, and the regeneration conditions are the same as in Example 3.

[0061] from Figure 1 It can be seen that after continuous propane dehydrogenation and regeneration cycles, both Pt and Zn in the catalyst suffer mass loss. The mass loss of Zn is significantly higher than that of Pt under the same conditions. For the catalyst after the regeneration cycle, the percentage loss of Pt and Zn (Pt: 3%, Zn: 18%) is much higher than in the continuous propane dehydrogenation process. This indicates that the traditional oxygen-hydrogen regeneration process causes the loss of metal components, especially the auxiliary metal Zn.

[0062] (II) Activity data obtained from propane dehydrogenation and continuous regeneration cycling of the PtZn alloy catalyst are as follows: Figure 2 As shown. The specific preparation is the same as in Example 1, the reaction conditions are the same as in Example 4, the conventional regeneration conditions are the same as in Example 3, and the regeneration method using the present invention is the same as in Example 5.

[0063] from Figure 2 As can be seen, under high propane space velocity conditions, the catalyst activity decreases rapidly with increasing reaction time, and can be partially recovered after conventional regeneration. However, after four regeneration cycles, the initial activity decreased from 37.1% to 28.9%, and gradually became difficult to recover. After regeneration with ZnO / SiO2, the initial activity recovered to 34.9%.

[0064] (III) Selection data obtained for the propane dehydrogenation process and continuous regeneration cycle of the PtZn alloy catalyst are as follows: Figure 3 As shown. The specific preparation is the same as in Example 1, the reaction conditions are the same as in Example 4, the conventional regeneration conditions are the same as in Example 3, and the regeneration method using the present invention is the same as in Example 5. From Figure 3 As can be seen, under high propane space velocity conditions, the catalyst selectivity gradually decreases with the extension of reaction time. After conventional regeneration conditions, its selectivity cannot be fully recovered and decreases by about 1-2%. However, after regeneration with the addition of ZnO / SiO2, the selectivity is recovered.

[0065] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many specific modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and these modifications all fall within the scope of protection of the present invention.

Claims

1. A method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation, characterized in that, After the supported bimetallic alloy catalyst is calcined in oxygen, the auxiliary metal oxide is physically blended with the supported bimetallic alloy catalyst, and then reduced at high temperature in a hydrogen atmosphere to restore the activity of the supported bimetallic alloy catalyst. The supported bimetallic alloy catalyst includes a support on which bimetallic alloy nanoparticles are uniformly loaded. The bimetallic alloy nanoparticles are composed of an auxiliary metal and an active metal. The active metal is one of the transition metal elements from groups IIIB, IVB, VB, VIB, VIIB, VIII, IB, and IIB. The auxiliary metal is one of the transition metal elements from groups IIIB, IVB, VB, VIB, VIIB, VIII, IB, and IIB, and one of In, Ga, Sn, Bi, and Pb. Furthermore, the active metal and the auxiliary metal are different metals. Wherein, the auxiliary metal in the auxiliary metal oxide is the same metal as the auxiliary metal in the supported bimetallic alloy catalyst; Follow these steps: (1) The fresh supported bimetallic alloy catalyst is calcined at high temperature in an oxygen atmosphere after undergoing an alkane dehydrogenation process; (2) The auxiliary metal oxide and the supported bimetallic alloy catalyst obtained in step (1) are physically mixed evenly; (3) The mixture obtained in step (2) is reduced at high temperature in a hydrogen atmosphere to obtain the regenerated supported bimetallic alloy catalyst.

2. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, In the supported bimetallic alloy catalyst, the mass percentage of the active metal is 0.025%-20% based on the mass of the support.

3. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, In the supported bimetallic alloy catalyst, the molar ratio of the auxiliary metal to the active metal is 0.5 to 5.

4. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, In the supported bimetallic alloy catalyst: the support is SiO2 or Al2O3.

5. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, The auxiliary metal oxide is either a supported auxiliary metal oxide or an unsupported auxiliary metal oxide.

6. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, In step (1), the high-temperature calcination under an oxygen atmosphere is carried out at a temperature of 400-650℃ for 20-60 minutes.

7. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, The auxiliary metal oxide is either a supported auxiliary metal oxide or an unsupported auxiliary metal oxide, wherein the preparation method of the supported auxiliary metal oxide is as follows: The precursor solution of the auxiliary metal in the supported bimetallic alloy catalyst is impregnated on the support while being added dropwise and stirred. Then, it is sonicated to ensure thorough impregnation. After standing at room temperature for 6-12 hours, it is completely dried to obtain the supported auxiliary metal precursor. The supported auxiliary metal precursor is then calcined in air at 400-700℃ for 1-3 hours to obtain the supported auxiliary metal oxide.

8. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, The content of the auxiliary metal oxide added in step (2) is 5%-200% of the auxiliary metal content in the fresh supported bimetallic alloy catalyst in step (1).

9. The method for regenerating a supported bimetallic alloy catalyst in alkane dehydrogenation according to claim 1, characterized in that, In step (3), the high-temperature reduction temperature is 300-800℃ and the time is 1-3h.

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