A method for regenerating a noble metal catalyst for the dehydrogenation of low-carbon alkane

Abstract

This invention discloses a method for regenerating a noble metal catalyst for dehydrogenation of low-carbon alkanes, comprising the following steps: (1) treating the deactivated noble metal catalyst for dehydrogenation of low-carbon alkanes with an oxygen-supplying solvent under an inert gas atmosphere; (2) introducing carbon dioxide into the deactivated catalyst system after step (1) to obtain a regenerated catalyst. The method of this invention features low regeneration temperature, short regeneration time, complete carbonization, good dispersion of active components, avoids loss of alkali metal promoters, and the catalytic activity of the regenerated catalyst reaches the level of a fresh catalyst.

Description

Technical Field

[0001] This invention belongs to the field of catalyst regeneration, specifically relating to a method for regenerating noble metal catalysts for the dehydrogenation of low-carbon alkanes, particularly a method for regenerating propane dehydrogenation and isobutane dehydrogenation catalysts. Background Technology

[0002] Propylene is an important organic chemical raw material, widely used in the production of polypropylene, acrolein, acrylic acid, glycerol, isopropanol, polyacrylonitrile, butanol, octanol, and other chemical products. In recent years, with the development of the market economy, the demand for downstream propylene products has risen rapidly, greatly boosting global demand for propylene.

[0003] Propylene is primarily derived from the catalytic cracking of petroleum and the cracking of diesel and naphtha. With the dwindling supply of petroleum resources, traditional propylene production technologies can no longer meet the growing demand, making the search for new propylene production technologies a major development trend in the petrochemical industry. Propane dehydrogenation to propylene has become one of the important ways to increase propylene sources. Propane dehydrogenation technology has significant advantages, including high product quality, high conversion rate, high overall yield, fewer byproducts, and lower equipment costs. Currently, the main industrialized propane dehydrogenation to propylene production process is UOP's Olflex process, which uses a precious metal Pt catalyst.

[0004] However, propane dehydrogenation is a strongly endothermic reaction (C3H8→C3H6+ H2, ΔH=124KJ / mol), requiring temperatures above 600℃ to proceed effectively. High temperatures lead to side reactions such as deep cracking, aromatization, and polymerization of propane, reducing propylene selectivity. Simultaneously, the catalyst is prone to deactivation due to coking, shortening its lifespan and necessitating repeated regeneration. This is especially true for noble metal-based dehydrogenation catalysts, which are costly. The regeneration method directly impacts the activity, selectivity, and lifespan of the regenerated catalyst, making a suitable regeneration method particularly important.

[0005] Currently, most Pt-based dehydrogenation catalyst regeneration methods involve first performing a carbonization process, then burning off the carbon deposits on the catalyst surface at a high regeneration temperature, followed by halogen treatment to redisperse the Pt. In all these regeneration methods, oxygen is used as a combustion aid during the carbonization process, and the oxygen content must be strictly controlled to remove the carbon deposits from the catalyst.

[0006] CN1589970A discloses a method for regenerating a catalyst for the dehydrogenation of alkyl aromatics to produce alkenyl aromatics. This method uses simultaneous introduction of steam and air to regenerate the catalyst. This method requires a high regeneration temperature to completely burn off the carbon deposits on the catalyst. However, when the regeneration temperature is below 500°C, the carbon deposits on the catalyst cannot be completely burned off.

[0007] CN101940959A discloses a method for regenerating a low-carbon alkane dehydrogenation catalyst. This method first regenerates the catalyst at a low temperature in an air atmosphere to burn off the carbon deposits on the catalyst surface and most of the carbon deposits inside the pores. Then, the catalyst is further regenerated in a mixed atmosphere of water vapor and air. Both of these methods require the conversion of water into water vapor during catalyst regeneration, wasting energy. Furthermore, the introduction of water vapor not only causes a phase transformation of the alumina support but also leads to the loss of alkali metals from the low-carbon alkane catalyst and, to some extent, metal aggregation.

[0008] CN104923258A discloses a method for regenerating Pt-based dehydrogenation catalysts. This method utilizes CO methanation and disproportionation reactions to reduce the hydrogen-to-carbon ratio of catalyst coke. Simultaneously, low-carbon oxygen-containing hydrocarbons are used in conjunction with HCl to redisperse and dechlorinate the active sites. Finally, a mixed gas containing a low concentration of oxygen is used to remove the coke at a relatively low temperature. This method introduces HCl, which is highly acidic and corrosive to the reactor, and still requires dechlorination and carbon removal processes.

[0009] CN105032503A discloses a method for regenerating a noble metal catalyst. First, a deactivated catalyst is treated with a hydrogen-donating solvent under a hydrogen atmosphere. Then, the treated deactivated catalyst is treated in a mixed atmosphere containing carbon dioxide and nitrous oxide to obtain a regenerated catalyst. This method does not require the introduction of water vapor, but the regeneration time is too long, and it is difficult to ensure the dispersion of the active metal.

[0010] CN105289757A discloses a method for regenerating charcoal using hydrogen peroxide solution as a combustion aid. This charcoal regeneration method does not require the introduction of oxygen, but only utilizes the thermal decomposition of H2O2 to supply oxygen. The charcoal burning speed is fast, but water vapor is still present, which causes changes in the crystal form of the carrier and damages the pore structure. In addition, the process consumes a large amount of H2O2.

[0011] CN103801330A, CN103801331A, and CN104107704A disclose a method for regenerating a low-carbon alkane dehydrogenation catalyst, in which carbonization is carried out in stages using a mixed atmosphere of oxygen and nitrogen. The carbonization temperature during regeneration is high, the regeneration time is too long, and the oxygen content needs to be strictly controlled, which brings difficulties to the actual operation.

[0012] As can be seen from the above regeneration methods of noble metal-based dehydrogenation catalysts, oxygen, halogens, carbon dioxide or water vapor are usually introduced purposefully during the regeneration process. Although this solves the problems of carbon deposition, metal accumulation and alkali metal loss to a certain extent, it often brings other side effects and cannot simultaneously address the above three problems. This inevitably leads to the degradation of the performance and shortening of the lifespan of the low-carbon alkane dehydrogenation regeneration catalyst. Summary of the Invention

[0013] To address the shortcomings of existing technologies, this invention provides a method for regenerating noble metal catalysts for the dehydrogenation of low-carbon alkanes. The method of this invention features low regeneration temperature, short regeneration time, complete carbonization, good dispersion of active components, avoids the loss of alkali metal promoters, and achieves catalytic activity of the regenerated catalyst at the level of a fresh catalyst.

[0014] The regeneration method of the noble metal catalyst for dehydrogenation of low-carbon alkane of the present invention includes the following:

[0015] (1) Under an inert gas atmosphere, oxygen-supplying solvents are used to treat deactivated low-carbon alkane dehydrogenation noble metal catalysts;

[0016] (2) Carbon dioxide is introduced into the deactivated catalyst system after step (1) to treat it and obtain the regenerated catalyst;

[0017] In the method of the present invention, the inert atmosphere in step (1) is nitrogen and / or an inert gas, wherein the inert gas is one or more of helium, neon, and argon; the oxygen-supplying solvent is a sodium peroxide solution in chloroform, wherein the mass ratio of sodium peroxide to chloroform is 1:10 to 1:120, preferably 1:60 to 1:90.

[0018] In the method of this invention, the processing conditions in step (1) are: processing temperature 50-150℃, pressure 1-5MPa, processing time 0.5-2h, and oxygen-supplying solvent flow rate based on catalyst volume hourly space velocity (VHSV) of 0.5-3.0h. -1 The space velocity of the inert gas is 200 h⁻¹. -1 ~800h -1 .

[0019] In the method of this invention, the carbon dioxide treatment conditions in step (2) are as follows: under the conditions of step (1), the temperature is further increased to 380~450℃, preferably 380~430℃, and carbon dioxide is introduced for a treatment time of 1-12 hours, preferably 2-4 hours; the pressure is 1MPa-6MPa, preferably 2.5MPa-4.5MPa; and the carbon dioxide volume hourly space velocity is 500 h⁻¹. -1 -5000h -1 Preferably 1000h -1 -2000h -1 .

[0020] The present invention provides a method for regenerating low-carbon alkane dehydrogenation catalysts, applicable to the regeneration of low-carbon alkane dehydrogenation catalysts such as propane and isobutane.

[0021] In the method of this invention, the low-carbon alkane dehydrogenation noble metal catalyst is a platinum group metal supported catalyst, using a high-temperature resistant inorganic oxide as a support. The active component is one or more of platinum, palladium, iridium, rhodium, or osmium from the platinum group metals, preferably platinum. The platinum group metals constitute 0.01% to 1.5% of the support weight in the catalyst, based on elemental composition. The high-temperature resistant inorganic oxide includes: alumina, magnesium oxide, chromium oxide, zinc oxide, zirconium oxide, or a mixture of two of the above oxides. A preferred high-temperature resistant inorganic oxide support is Al₂O₃, which can be in the form of γ-Al₂O₃, θ-Al₂O₃, or η-Al₂O₃, preferably γ-Al₂O₃.

[0022] The low-carbon alkane dehydrogenation noble metal catalyst of the present invention contains both promoters, such as Group IVA elements and alkali metal elements. The Group IVA elements are preferably tin and / or germanium, more preferably tin, and the weight percentage of the Group IVA elements in the catalyst is 0.1%-1%; the alkali metal elements are preferably sodium and / or potassium, more preferably potassium, and the weight percentage of the alkali metal elements in the catalyst is 0.1%-1%.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention uses sodium peroxide chloroform solution as combustion aid and performs charring treatment in stages at low temperature to avoid the agglomeration of active components at high temperature. The method of the present invention does not require the introduction of halogen to redisperse the active center, and completes the charring and chlorine redispersing process at the same time. Moreover, the CHCl3 chlorine supplementation is relatively mild, avoiding equipment corrosion, and does not involve the use of water vapor, thus reducing the rate of alkali metal loss.

[0025] (2) The regeneration conditions used in the method of this invention are relatively mild, and the regeneration time is short, further reducing the production cost of the catalyst. On the one hand, sodium peroxide has strong oxidizing properties, which can oxidize the carbon deposits on the catalyst surface at low temperatures, achieving the effect of removing carbon deposits. On the other hand, when carbon dioxide is introduced, sodium peroxide reacts with carbon dioxide to generate O2, and carbon dioxide will react with the untreated carbon deposits in a Boudouard reaction, further removing the carbon deposits from the catalyst. In addition, the reaction of sodium peroxide with carbon dioxide is exothermic, which can provide heat for the carbonization and chlorination processes.

[0026] (3) The regeneration method of the present invention can achieve the same level of dehydrogenation activity as fresh catalyst after regeneration. At the same time, the temperature change during the regeneration process is small, which makes it easy to operate and extends the service life of the catalyst. Detailed Implementation

[0027] The technical content and effects of the present invention are further illustrated below with reference to embodiments, but these embodiments do not limit the scope of the present invention.

[0028] In the specific implementation of this invention, the dehydrogenation performance evaluation of the fresh catalyst and the regenerated catalyst is carried out on a continuous flow fixed-bed microreactor. The fresh catalyst undergoes reduction treatment before the reaction under the following conditions: pure hydrogen atmosphere, 0.1 MPa, 500 °C, and a volume hourly space velocity (VHSV) of 1000 h⁻¹. -1 The performance evaluation conditions for fresh catalyst and regenerator were as follows: the feed gas was a mixture of hydrogen and propane (volume ratio 0.5:1), and the volume hourly space velocity was 1000 h⁻¹. -1 The reaction was carried out at 600℃ and 0.1MPa; the fresh catalyst and the regenerated catalyst were reacted for 72 hours and then regenerated. The composition of the reaction products was analyzed by gas chromatography, and the conversion and selectivity were calculated.

[0029] Example 1

[0030] Weigh out commercially available alumina support (γ phase, spherical, 0.5 mm in diameter, 0.71 cm³ pore volume) with a Sn element content of 0.3% by weight. 3 / g, specific surface area 153m² 2 30g of Pt was weighed, and an appropriate amount of chloroplatinic acid was prepared to prepare an aqueous solution, based on a final Pt content of 0.3%. The Sn-containing alumina support was impregnated in the aqueous solution containing chloroplatinic acid at 60℃ for 6h, then dried at 120℃ for 8h, and calcined at 500℃ for 4h. An appropriate amount of potassium nitrate was weighed, and an aqueous solution was prepared, based on a final K content of 1%, and added to the calcined platinum-supported catalyst precursor. The precursor was impregnated at 60℃ for 2h and dried under the same conditions as after Pt impregnation. The resulting catalyst had the following weight contents: Pt 0.3%, Sn 0.3%, K 1%. The obtained catalyst is designated as D-1. The fresh catalyst reactivity of D-1 is shown in Table 1.

[0031] Example 2

[0032] Weigh out an alumina support (γ phase, spherical, 0.5 mm in diameter, 0.71 cm³), calculated as 0.4% Sn by weight in the commercially available catalyst. 3 / g, specific surface area 122m² 2 30g of Pt was weighed, and an appropriate amount of chloroplatinic acid was prepared to prepare an aqueous solution, based on a final Pt content of 0.25%. The Sn-containing alumina support was impregnated in the aqueous solution containing chloroplatinic acid at 70℃ for 6h, then dried at 120℃ for 4h, and calcined at 500℃ for 4h. An appropriate amount of potassium nitrate was weighed, and an aqueous solution was prepared, based on a final K content of 0.8%, and added to the calcined platinum-supported catalyst precursor. The precursor was impregnated at 70℃ for 1h and dried under the same conditions as after Pt impregnation. The weight contents of each component in the obtained catalyst were: Pt 0.25%, Sn 0.4%, K 0.8%. The obtained catalyst is designated as D-2. The fresh catalyst reactivity of D-2 is shown in Table 1.

[0033] Example 3

[0034] After the D-1 fresh catalyst reacted for 72 hours, the feed gas was switched to nitrogen, and the mixture was purged and cooled to 70°C. The pressure was increased to 0.8 MPa, and then nitrogen and a sodium peroxide chloroform solution were simultaneously introduced. The sodium peroxide chloroform solution was introduced at a catalyst volume hourly space velocity (VHSV) of 1.5 h⁻¹. -1 The mass ratio of sodium peroxide to chloroform was 1:70, and the treatment time was 2 hours. After treatment, the temperature was increased to 400℃ and the pressure to 3 MPa, and then carbon dioxide gas was introduced at a volume hourly space velocity (VHSV) of 2000 h⁻¹. -1 The processing time was 1 hour. D-1 primary regenerant was obtained, and its reactivity is shown in Table 1.

[0035] Example 4

[0036] After the D-1 primary regenerator reaction lasted 72 hours, the feed gas was switched to nitrogen, and the temperature was purged to 80°C. The pressure was then increased to 0.8 MPa. Nitrogen and a sodium peroxide solution in chloroform were then simultaneously introduced, with the sodium peroxide solution in chloroform at a catalyst volume hourly space velocity (VHSV) of 1.5 h⁻¹. -1 The mass ratio of sodium peroxide to chloroform was 1:50, and the treatment time was 2 hours. After treatment, the temperature was increased to 380℃, the pressure was controlled at 3 MPa, and then carbon dioxide gas was introduced at a volume hourly space velocity (VHSV) of 1000 h⁻¹. -1 The processing time was 2 hours. D-1 secondary regenerator was obtained. The reactivity of D-1 secondary regenerator is shown in Table 1.

[0037] Example 5

[0038] After the D-1 secondary regenerator reacts for 72 hours, the feed gas is switched to nitrogen and purged for 1 hour. Then, the temperature is lowered to 90°C and the pressure is increased to 1 MPa. Simultaneously, nitrogen and a sodium peroxide solution in chloroform are introduced, with the sodium peroxide solution in chloroform at a catalyst volume hourly space velocity (VHSV) of 1.0 h⁻¹. -1 The mass ratio of sodium peroxide to chloroform was 1:50, and the treatment time was 3 hours. After treatment, the temperature was increased to 420℃, the pressure was controlled at 3.5 MPa, and then carbon dioxide gas was introduced at a volume hourly space velocity (VHSV) of 3000 h⁻¹. -1 The processing time was 0.5 hours. D-1 tertiary regenerant was obtained. The reactivity of D-1 tertiary regenerant is shown in Table 1.

[0039] Example 6

[0040] After the D-1 regenerator reacted for 72 hours, the feed gas was switched to nitrogen and purged for 1 hour. Then, the temperature was lowered to 100°C and the pressure was increased to 1.5 MPa. Subsequently, nitrogen and a sodium peroxide solution in chloroform were simultaneously introduced, with the sodium peroxide solution in chloroform at a catalyst volume hourly space velocity (VHSV) of 2.0 h⁻¹. -1The mass ratio of sodium peroxide to chloroform was 1:80, and the treatment time was 3 hours. After treatment, the temperature was increased to 450°C, the pressure was controlled at 4 MPa, and then carbon dioxide gas was introduced at a volume hourly space velocity (VHSV) of 500 h⁻¹. -1 The processing time was 3 hours. D-1 four-stage regenerator was obtained. The reactivity of D-1 four-stage regenerator is shown in Table 1.

[0041] Example 7

[0042] After reacting with the D-1 fourth regenerator for 72 hours, it was regenerated according to the method in Example 3 to obtain the D-1 fifth regenerator.

[0043] The reactivity of D-1 five-times regenerator is shown in Table 1.

[0044] Example 8

[0045] After reacting with D-2 fresh agent for 72 hours, it was regenerated according to the method in Example 3, and its performance was evaluated. This process was repeated five times.

[0046] The reactivity of D-2 regenerator is shown in Table 1.

[0047] Comparative Example 1

[0048] Charcoal regeneration is performed using conventional methods.

[0049] After reacting with D-1 fresh agent for 72 hours, the mixture was purged with nitrogen for 1 hour and then cooled to 350°C. The reaction was then switched to a mixture of oxygen and nitrogen, with an oxygen volume concentration of 0.5% and a volume hourly space velocity (VHSV) of 2000 h⁻¹. -1 The mixture was treated for 6 hours; then the temperature was increased to 450℃ at a rate of 1℃ / min to raise the oxygen volume concentration in the mixture to 5%, with a volume hourly space velocity (VHSV) of 1000 h⁻¹. -1 The mixture was treated for 4 hours; then the temperature was increased to 500℃ at a rate of 1℃ / min to raise the oxygen volume concentration in the mixture to 10%, with a volume hourly space velocity of 500 h⁻¹. -1 The process was repeated for 2 hours to obtain D-1 regenerant, which was then evaluated for performance five times.

[0050] Comparative Example 2

[0051] After reacting with fresh catalyst D-1 for 72 hours, the catalyst bed was purged with nitrogen for 1 hour and then cooled to 200°C. A 10 wt% hydrogen peroxide solution was then introduced into the catalyst bed at a mass hourly space velocity (HHSV) of 3 h⁻¹. -1 The regeneration time is 1 hour; then the temperature is raised to 300℃, and an 8 wt% hydrogen peroxide solution is introduced into the catalyst bed at a hydrogen peroxide solution mass hourly space velocity (HHSV) of 3 h⁻¹. -1 The regeneration time was 1 hour. D-1 regenerator was obtained and its performance was evaluated, repeated five times. The regeneration catalyst reaction performance is shown in Table 1.

[0052] Table 1 Reaction performance of regenerated catalyst

[0053]

[0054] As shown in Table 1, after regeneration using the method disclosed in this invention, the regenerated catalyst showed virtually no change in propane conversion and propylene selectivity after 1 hour of reaction compared to the fresh catalyst; after 72 hours of reaction, the performance of the regenerated catalyst was also essentially the same as that of the fresh catalyst. In contrast, in the comparative examples, regeneration methods using conventional oxygen-based stepwise carbonization or hydrogen peroxide-based carbonization resulted in a gradual decrease in conversion and selectivity after 1 hour of reaction, indicating poor regeneration effectiveness.

Claims

1. A method for regenerating a noble metal catalyst for dehydrogenation of lower alkanes, characterized in that The method comprises the following steps: (1) treating the deactivated low-carbon alkane dehydrogenation noble metal catalyst with an oxygen-supplying solvent under an inert atmosphere; (2) introducing carbon dioxide into the deactivated catalyst system treated in step (1) to obtain a regenerated catalyst; the oxygen-supplying solvent in step (1) is a sodium peroxide solution in chloroform; the treatment conditions in step (1) are as follows: the treatment temperature is 50-150 DEG C, the pressure is 1-5 MPa, and the treatment time is 0.5-2 hours.

2. The method of claim 1, wherein: The inert atmosphere in step (1) is nitrogen and / or an inert gas.

3. The method of claim 1, wherein: In step (1), the mass ratio of sodium peroxide to chloroform is 1:10-1:

120.

4. The method of claim 1, wherein: In step (1), the mass ratio of sodium peroxide to chloroform is 1:60-1:

90.

5. The method of claim 1, wherein: The oxygen-supplying solvent is introduced at a volume space velocity of 0.5-3.0 h -1 with respect to the catalyst, and the volume ratio of inert gas to oxygen-supplying solvent is 100-1000:

1.

6. The method of claim 1, wherein: The treatment conditions in step (2) are as follows: the treatment temperature is 30-100 DEG C, the treatment time is 1-12 hours, and the pressure is 0.1-2 MPa.

7. The method of claim 1, wherein: The carbon dioxide volumetric space velocity in step (2) is 500 h -1 - 5000 h -1 .

8. The method of claim 1, wherein: The low-carbon alkane dehydrogenation noble metal catalyst is a platinum group supported catalyst, the support is a high-temperature-resistant inorganic oxide, the active component is one or more of platinum, palladium, iridium, rhodium or osmium in the platinum group, and the active component accounts for 0.01-1.5% of the weight of the support in terms of elements; the high-temperature-resistant inorganic oxide is selected from one or more of alumina, magnesia, chromia, zinc oxide and zirconia.

9. The method of claim 1, wherein: The low-carbon alkane dehydrogenation noble metal catalyst also contains an additive selected from group IVA elements and / or alkali metal elements; the group IVA elements are tin and / or germanium; the alkali metal elements are sodium and / or potassium; and the additive accounts for 0.1-1% of the weight of the catalyst in terms of elements.

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