A chromium-based catalyst for dehydrogenation of alkanes and a method for preparing the same

Abstract

This invention relates to a chromium-based catalyst for alkane dehydrogenation and its preparation method. The catalyst comprises promoter microspheres, an active component, and a support; wherein the promoter microspheres have a particle size of 100–200 μm, the active component is Cr₂O₃, and the support is alumina; the promoter microspheres comprise promoter A and binder B; promoter A is a mixture of lithium oxide, copper oxide, manganese oxide, and calcium oxide; based on oxide content, the active component accounts for 10–35% of the total catalyst weight; based on oxide content, the promoter microspheres account for 0.1–20% of the total catalyst weight; the balance is the support. In this invention, the promoter microspheres are introduced as oxide microspheres, which can better supplement the heat required for the dehydrogenation reaction, improve the severity and process stability of the alkane dehydrogenation reaction, and make the temperature distribution of the catalyst bed more uniform.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to an alkane dehydrogenation catalyst, specifically a chromium-based catalyst for alkane dehydrogenation and its preparation method. Background Technology

[0002] Alkane dehydrogenation technology has been industrialized, with several processes already in operation. Among them, the Oleflex and Catofin processes are currently the most widely used internationally. Alkane dehydrogenation is a strongly endothermic reaction, and the reaction temperature significantly affects the alkane conversion rate. Sufficient heat utilization and heat balance are crucial factors for enhancing the reaction process and improving efficiency. Heat replenishment during the reaction is extremely beneficial for promoting the reaction. In the Oleflex process, the effluent from the previous reactor is reheated by an interstage heater to increase the material temperature. After leaving the last reactor, the effluent exchanges heat with the mixed feedstock, thus replenishing the heat required for the alkane dehydrogenation reaction. The Catofin process uses a parallel adiabatic fixed-bed reactor, which does not receive heat replenishment during the reaction. Therefore, the temperature difference between the reactor inlet and outlet is large, resulting in a lower reactor outlet temperature and a lower alkane conversion rate.

[0003] CN104072325A discloses a method for improving the performance of dehydrogenation reactions of low-carbon alkanes. This method employs a fixed-bed reactor with built-in electric heating tubes in the dehydrogenation process to provide heat to the catalyst during the dehydrogenation reaction, reducing the temperature drop in the catalyst bed caused by the strongly endothermic dehydrogenation reaction, and lowering the heat load of the electric heater before the reactor. This reduces the thermal cracking of low-carbon alkanes in the electric heater, ultimately improving the performance of the dehydrogenation reaction and increasing the yield of the target dehydrogenation product, olefins.

[0004] CN105120997A uses a catalyst regeneration reaction to transfer heat to an integrated fluidized bed reactor, where at least a portion of the transferred heat is used for an endothermic reaction to dehydrogenate alkanes. CN103003221A utilizes a reaction in the presence of a mixture of inert heat exchange particles and catalyst particles. The heat exchange particles are heated in a heating zone and returned to the reaction zone to provide the required heat of reaction, while the catalyst particles are regenerated in a non-oxidizing atmosphere. CN108176405A and CN108300430A achieve catalyst bed temperature stability by physically mixing an alkane reaction enhancer or exothermic agent with the catalyst particles. However, this physical mixing method occupies part of the catalyst bed space, reducing the reactor's processing capacity, or requiring a larger reactor to achieve higher processing capacity, thus increasing equipment investment. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a chromium-based catalyst for alkane dehydrogenation. This catalyst is a novel Cr-based alkane dehydrogenation catalyst that allows the dehydrogenation reaction to proceed at higher temperatures and exhibits higher activity.

[0006] Another objective of this invention is to provide a method for preparing a chromium-based catalyst for alkane dehydrogenation as described above, which is simple and easy to implement.

[0007] To achieve the above-mentioned objectives, the specific technical solution of this invention is as follows:

[0008] A chromium-based alkane dehydrogenation catalyst, comprising promoter microspheres, an active component, and a support; wherein the active component is Cr2O3, and the support is alumina; the promoter microspheres comprise promoter A and binder B; based on oxide content, the active component accounts for 10-35% of the total weight of the catalyst; based on oxide content, the promoter microspheres account for 0.1-20% of the total weight of the catalyst; the balance is the support, and the total mass percentage is 100%.

[0009] In a preferred embodiment of this application, the particle size of the additive microspheres is 100-200 μm.

[0010] In a preferred embodiment of this application, the precursor material of the active component Cr2O3 is chromium nitrate.

[0011] In a preferred embodiment of this application, the additive A in the additive microspheres is a mixture of four substances: lithium oxide, copper oxide, manganese oxide, and calcium oxide.

[0012] In a preferred embodiment of this application, the binder B is any one or a mixture of two of alumina and silicon oxide.

[0013] In a preferred embodiment of this application, the additive microspheres contain, by oxide content, lithium oxide accounting for 15-40% of the total weight of the additive microspheres (specifically, 15%, 20%, 25%, 30%, 35%, 40%, etc.), copper oxide accounting for 5-20% of the total weight of the additive microspheres (specifically, 5%, 10%, 15%, 20%, etc.), manganese oxide accounting for 5-20% of the total weight of the additive microspheres (specifically, 5%, 10%, 15%, 20%, etc.), calcium oxide accounting for 15-30% of the total weight of the additive microspheres (specifically, 15%, 20%, 25%, 30%, etc.), with the remainder being binder B.

[0014] As a preferred embodiment of this application, the preparation method of the chromium-based alkane dehydrogenation catalyst described above includes the following steps:

[0015] a. The precursors of lithium oxide, copper oxide, manganese oxide, and calcium oxide in additive A are mixed evenly with binder B, and spray-dried into microspheres. After calcination, the additive microspheres with a particle size of 100-200 μm (specifically 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, etc.) are sieved.

[0016] b. Mix the pseudoboehmite, the auxiliary microspheres obtained in step a, an appropriate amount of acid, and chromium nitrate, knead them evenly, extrude them into strips, dry them, and calcine them to obtain the catalyst.

[0017] In a preferred embodiment of this application, the precursors of lithium oxide, copper oxide, manganese oxide, and calcium oxide are metal oxides, nitrates, or chlorides.

[0018] In a preferred embodiment of this application, the calcination temperature in step a is 500-800℃ (specifically, it can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, etc.), and the calcination time is 2-10h (specifically, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.).

[0019] In a preferred embodiment of this application, the drying temperature in step b is 60-100℃ (specifically, it can be 60℃, 70℃, 80℃, 90℃, 100℃, etc.), and the drying time is 4-20h (specifically, it can be 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, etc.).

[0020] In a preferred embodiment of this application, the calcination temperature in step b is 600–1000℃ (specifically, it can be 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, etc.), and the calcination time is 4–10h (specifically, it can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, etc.).

[0021] In a preferred embodiment of this application, the acid in step b is any one or a mixture of nitric acid, citric acid, acetic acid, sulfuric acid, hydrochloric acid, and formic acid; the amount of acid added is 2 to 5% of the mass of boehmite.

[0022] Compared with the prior art, the positive effects of the present invention are reflected in:

[0023] The alkane dehydrogenation catalyst provided by this invention contains a certain amount of promoter microspheres. These promoter microspheres do not cover the active sites of the catalyst, ensuring that the active sites can function normally, while also providing heat for the reaction. The promoter microspheres contain oxides that can react with hydrogen and release heat, promoting the forward direction of the dehydrogenation reaction. The promoter microspheres also contain oxides with high specific heat, which can act as heat carriers, releasing heat when needed for the reaction. Furthermore, the promoter microspheres contain oxides that can combine with water, absorbing water and releasing heat. Through these three methods, the heat required for the dehydrogenation reaction is replenished, resulting in a more uniform temperature distribution in the catalyst bed within the reactor, improving the severity and stability of the process operation, and allowing the dehydrogenation reaction to proceed at higher temperatures. Therefore, the catalyst exhibits higher activity. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Test conditions: Performance evaluation was conducted on a fixed-bed device with an alkane to nitrogen volume ratio of 1:1, a reaction inlet temperature of 625℃, and an alkane mass hourly space velocity of 0.7 h⁻¹. The evaluation results were instantaneous data at 13 min after feeding, and the reactor outlet temperature was also measured.

[0026] Example 1

[0027] Weigh out 4.56g of copper nitrate trihydrate, 1.5g of manganese oxide, 10.38g of lithium nitrate, and 13.18g of calcium nitrate, mix them evenly with 67.50g of aluminum sol, spray dry them into microspheres, calcine them at 600℃ for 6 hours, and then sieve the microspheres with a particle size of 100-200μm.

[0028] Weigh 335.82g of pseudoboehmite and the aforementioned 100-200μm auxiliary microspheres, 10.92g of concentrated nitric acid, 138g of water, and 60g of chromium trioxide, mix them evenly, extrude them into strips, dry them at 60℃ for 18h, and calcine them at 800℃ for 4h to obtain the catalyst.

[0029] Catalyst evaluation results: alkane conversion rate was 42.34%, selectivity was 90.68%, and reactor outlet temperature was 587℃.

[0030] Example 2

[0031] Weigh out 6.0g of copper oxide, 6.18g of manganese nitrate, 13.96g of lithium oxide, and 17.82g of calcium chloride, mix them evenly with 144.77g of silica sol, spray dry them into microspheres, calcine them at 550℃ for 4h, and then sieve the microspheres with a particle size of 100-200μm.

[0032] Weigh 335.82g of pseudoboehmite and the 100-200μm auxiliary microspheres obtained above, 6.92g of concentrated nitric acid, 6.43g of citric acid, 138g of water, and 237.48g of chromium nitrate nonahydrate, mix them evenly, extrude them into strips, dry them at 80℃ for 8h, and calcine them at 700℃ for 8h to obtain the catalyst.

[0033] Catalyst evaluation results: alkane conversion rate was 42.88%, selectivity was 90.12%, and reactor outlet temperature was 589℃.

[0034] Example 3

[0035] Weigh out 6.3g of copper oxide, 8.18g of manganese oxide, 27.0g of lithium oxide, and 18.0g of calcium chloride, mix them evenly with 152.34g of silica sol, spray dry them into microspheres, calcine them at 720℃ for 6 hours, and then sieve the microspheres with a particle size of 100-200μm.

[0036] Weigh 300g of pseudoboehmite and the 100-200μm auxiliary microspheres obtained above, 10.48g of concentrated nitric acid, 129g of water, and 62.53g of chromium trioxide, mix them evenly, extrude them into strips, dry them at 100℃ for 12h, and calcine them at 1000℃ for 5h to obtain the catalyst.

[0037] Catalyst evaluation results: alkane conversion rate was 41.46%, selectivity was 91.62%, and reactor outlet temperature was 592℃.

[0038] Example 4

[0039] Weigh out 6.36g of copper nitrate trihydrate, 7.40g of manganese nitrate, 3.6g of lithium oxide, and 13.08g of calcium nitrate. Mix them evenly with 41.0g of silica sol and 41.0g of aluminum sol. Spray dry the mixture into microspheres. After calcining at 680℃ for 4 hours, sieve the microspheres with a particle size of 100-200μm.

[0040] Weigh 313g of boehmite and the 100-200μm auxiliary microspheres obtained above, 9.6g of concentrated hydrochloric acid, 3.2g of formic acid, 129g of water, and 75g of chromium trioxide, mix them, knead them evenly, extrude them into strips, dry them at 70℃ for 12h, and calcine them at 900℃ for 4h to obtain the catalyst.

[0041] Catalyst evaluation results: alkane conversion rate was 43.72%, selectivity was 90.22%, and reactor outlet temperature was 582℃.

[0042] Comparative Example 1

[0043] The catalyst was prepared using the same method as in Example 3, except that step a (i.e., microspheres were not prepared) was omitted, and the catalyst was prepared directly according to the preparation method in step b (without adding microspheres). The catalyst evaluation results were as follows: alkane conversion rate was 38.42%, selectivity was 92.86%, and reactor outlet temperature was 566°C.

[0044] The comparison between Example 3 and Comparative Example 1 shows that the introduction of the auxiliary microspheres in Example 3 can slow down the reaction temperature drop in the reactor and increase the outlet temperature, allowing the catalyst to react at a more uniform temperature.

[0045] Comparative Example 2

[0046] The catalyst preparation method is the same as in Example 3, except that in Comparative Example 2, the materials in step a and step b are directly mixed evenly to prepare the catalyst. Specifically, 6.3g of copper oxide, 8.18g of manganese oxide, 27.0g of lithium oxide, and 18.0g of calcium chloride are weighed and mixed with 152.34g of silica sol, 300g of boehmite, 10.48g of concentrated nitric acid, 129g of water, and 62.53g of chromium trioxide. The mixture is kneaded evenly, extruded into strips, dried at 100℃ for 12h, and calcined at 1000℃ for 3h to obtain the catalyst.

[0047] Catalyst evaluation results showed that the alkane conversion rate was 28.33%, the selectivity was 93.64%, and the reactor outlet temperature was 598℃.

[0048] A comparison between Comparative Example 2 and Example 3 shows that the catalyst prepared in Comparative Example 2 has a lower conversion rate, a larger amount of auxiliary agent, and covers more Cr active centers.

[0049] Comparative Example 3

[0050] The catalyst was prepared in the same way as in Example 3, except that lithium oxide was not added in Comparative Example 3, while the other steps were the same.

[0051] Catalyst evaluation results showed that the alkane conversion rate was 39.68%, the selectivity was 91.77%, and the reactor outlet temperature was 589℃.

[0052] A comparison between Comparative Example 3 and Example 3 shows that the catalyst prepared in Comparative Example 3 has a slightly lower conversion rate and the reactor outlet temperature is slightly lower than that in Example 3.

[0053] Comparative Example 4

[0054] The catalyst was prepared in the same way as in Example 3, except that copper oxide and manganese oxide were not added in Comparative Example 4, while the other steps were the same.

[0055] Catalyst evaluation results showed that the alkane conversion rate was 39.85%, the selectivity was 91.42%, and the reactor outlet temperature was 587℃.

[0056] A comparison between Comparative Example 4 and Example 3 shows that the catalyst prepared in Comparative Example 4 has a slightly lower conversion rate and the reactor outlet temperature is slightly lower than that in Example 3.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A chromium-based catalyst for alkane dehydrogenation, characterized in that: The catalyst comprises auxiliary microspheres, an active component, and a support; wherein the particle size of the auxiliary microspheres is 100~200μm, the active component is Cr2O3, and the support is alumina; The additive microspheres contain additive A and binder B; additive A in the additive microspheres is a mixture of lithium oxide, copper oxide, manganese oxide and calcium oxide; the active component accounts for 10-35% of the total weight of the catalyst based on oxide content; the additive microspheres account for 0.1-20% of the total weight of the catalyst based on oxide content; the remainder is a carrier.

2. The chromium-based catalyst for alkane dehydrogenation according to claim 1, characterized in that: The precursor material for the active component Cr2O3 is any one of chromium nitrate, chromium trioxide, and chromium trioxide.

3. A chromium-based catalyst for alkane dehydrogenation according to claim 1, characterized in that... The binder B is any one or a mixture of two of alumina and silicon dioxide.

4. A chromium-based catalyst for alkane dehydrogenation according to claim 1, characterized in that: In the aforementioned additive microspheres, based on oxide content, lithium oxide accounts for 15-40% of the total weight of the additive microspheres, copper oxide accounts for 5-20% of the total weight of the additive microspheres, manganese oxide accounts for 5-20% of the total weight of the additive microspheres, calcium oxide accounts for 15-30% of the total weight of the additive microspheres, and the remainder is binder.

5. A method for preparing a chromium-based catalyst for alkane dehydrogenation according to any one of claims 1-4, characterized in that... Includes the following steps: a. Mix the precursor of additive A and binder B evenly, spray dry to form microspheres, calcine and then sieve to obtain additive microspheres; b. Mix boehmite, the additive microspheres prepared in step a, acid, and chromium nitrate, knead evenly, extrude into strips, dry, and calcine to obtain the catalyst.

6. The method for preparing a chromium-based catalyst for alkane dehydrogenation according to claim 5, characterized in that: The precursors of lithium oxide, copper oxide, manganese oxide, and calcium oxide in additive A are their metal oxides, nitrates, or chlorides.

7. The method for preparing a chromium-based catalyst for alkane dehydrogenation according to claim 5, characterized in that: Step a: The calcination temperature is 500~800℃, and the calcination time is 2~10h; sieve the auxiliary microspheres with a particle size of 100~200μm for later use.

8. The method for preparing a chromium-based catalyst for alkane dehydrogenation according to claim 5, characterized in that: The acid mentioned in step b is any one or a mixture of nitric acid, citric acid, acetic acid, sulfuric acid, hydrochloric acid, and formic acid; the amount of acid added is 2 to 5% of the mass of boehmite.

9. The method for preparing a chromium-based catalyst for alkane dehydrogenation according to claim 5, characterized in that: The drying temperature in step b is 60~100℃ and the drying time is 4~20h; the calcination temperature is 600~1000℃ and the calcination time is 4~10h.

10. A chromium-based catalyst for alkane dehydrogenation prepared by any one of claims 6-9, characterized in that: This catalyst is used in the process of dehydrogenating alkane to olefins.