Preparation method of waste liquid rhodium source confined molecular sieve dehydrogenation catalyst and application thereof

Abstract

This invention relates to a method for preparing a rhodium-confined molecular sieve dehydrogenation catalyst from waste liquid, comprising the following steps: S1, adding deionized water to industrial homogeneous rhodium-containing waste liquid, adjusting the pH, and then adding an oxidant for complex-breaking oxidation; S2, adding a sulfiding agent for wet sulfidation, heating and aging to obtain a rhodium-sulfur-containing precipitate; S3, acid washing and water washing of the rhodium-sulfur-containing precipitate to obtain a rhodium-sulfur-containing precursor; S4, mixing the rhodium-sulfur-containing precursor with a silicon source, a template agent, and deionized water to form a crystallization system, and then hydrothermally crystallizing to obtain a rhodium-sulfur-containing molecular sieve crystallization product; S5, solid-liquid separation and washing of the rhodium-sulfur-containing molecular sieve crystallization product, followed by drying, calcination, and reduction to obtain a sulfur-modified molecular sieve confined rhodium dehydrogenation catalyst. This invention also discloses the application of this catalyst. This invention achieves a short-process conversion of rhodium-containing waste liquid into a high-value-added catalyst. The obtained catalyst is suitable for propane dehydrogenation to propylene, exhibiting high propylene selectivity and a low tendency for hydrogenolysis side reactions.

Description

Technical Field

[0001] This invention relates to the field of precious metal waste liquid resource utilization and alkane catalytic conversion technology, and particularly to a method for preparing a rhodium-source confined molecular sieve dehydrogenation catalyst for waste liquid and its application. Background Technology

[0002] Propylene is a crucial basic organic chemical raw material, second only to ethylene, and is widely used in the production of bulk chemicals and polymer materials such as polypropylene, acrylonitrile, propylene oxide, acrolein, and acetone. With the continued growth in demand for downstream polymers and fine chemicals, the development of technologies for the direct dehydrogenation of propane to propylene has attracted widespread attention. Existing patents indicate that the direct dehydrogenation of propane to propylene under anaerobic conditions has advantages such as a simple process, high economic efficiency, and the production of hydrogen as a byproduct, thus possessing high industrial application value in targeted propylene production. However, existing industrial routes still generally face the challenge of simultaneously achieving optimal conversion rate, selectivity, and long-term stability.

[0003] Currently, propane dehydrogenation catalysts mainly fall into two categories: noble metal systems and non-noble metal systems. Related patents indicate that noble metal catalysts, represented by Pt, possess strong CH bond activation capabilities and good initial activity and selectivity. However, they are prone to carbon deposition, sintering, and deactivation during high-temperature dehydrogenation, and require frequent regeneration, resulting in high costs. On the other hand, non-noble metal systems, represented by Cr, V, Ga, and Zn, while having lower costs, typically still suffer from deficiencies in activity, selectivity, and stability. Especially for noble metal catalysts, when the interaction between active sites and the support is weak, they are prone to migration and aggregation at high temperatures, leading not only to decreased metal utilization but also significantly impacting the selectivity of the target product, propylene, and the catalyst lifetime.

[0004] To improve the utilization rate of precious metals and suppress high-temperature sintering, molecular sieve confinement strategies have gradually become an important research direction. Existing patents have disclosed that the pore and cage structures of molecular sieves can restrict the migration and growth of metal species, thereby improving dispersion and thermal stability. Compared with traditional impregnation methods, in-situ construction or encapsulation is more conducive to introducing precious metal species into the interior of the molecular sieve, reducing the formation of large particles on the outer surface. CN116713025B points out that traditional molecular sieve-supported precious metal catalysts, which involve first preparing the molecular sieve and then impregnating it with precious metals, easily lead to problems such as large precious metal particles, poor dispersion, and poor heat resistance. CN117046504B further demonstrates that supported Pt-Sn catalysts often form large particles on the outer surface of the catalyst after impregnation and calcination, resulting in low precious metal utilization. However, confinement through molecular sieve pores can enhance the interaction between the metal and the support, improving high-temperature stability. CN116116453B and CN117046504B also disclose the application of industrial molecular sieve-confined metal catalysts and molecular sieve-confined Pt-based bimetallic catalysts in propane dehydrogenation, respectively, indicating that molecular sieve confinement has become an important technical route for developing efficient PDH catalysts.

[0005] However, most existing patented technologies still start with high-purity precious metal salts or fresh metal precursors, constructing molecular sieve-confined catalysts through in-situ hydrothermal synthesis, in-situ encapsulation, or post-impregnation. The focus is on improving metal dispersion, pore confinement, and bimetallic synergistic effects. Current technologies lack a publicly available scheme for directly introducing rhodium- and sulfur-containing precursors obtained from industrial homogeneous rhodium-containing wastewater through acidification, oxidative complex breaking, and wet sulfidation into a molecular sieve crystallization system, and further preparing sulfur-modified molecular sieve-confined rhodium catalysts for dehydrogenation of low-carbon alkanes. Especially for rhodium, a precious metal with strong CH activation ability but potentially inducing hydrogenolysis side reactions, a mature technical solution is still lacking for coupling industrial wastewater recovery, sulfur-containing precursor modulation, and molecular sieve confinement construction into a short-process preparation route. Therefore, developing a method for directly preparing sulfur-modified molecular sieve-confined rhodium dehydrogenation catalysts from industrial homogeneous rhodium-containing wastewater has significant resource utilization value and catalytic application significance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a waste liquid rhodium source confined molecular sieve dehydrogenation catalyst that is short in process and easy to implement.

[0007] Another technical problem to be solved by the present invention is to provide an application of a waste liquid rhodium source confined molecular sieve dehydrogenation catalyst.

[0008] To address the above problems, the present invention provides a method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 is prepared by adding 5% to 100% of the volume of deionized water to a homogeneous industrial rhodium-containing waste liquid to form a stirable system. The pH of the aqueous phase of the system is adjusted to 0.5 to 2.0 using an inorganic acid. An oxidant is added at 50 to 90°C to break the complex and oxidize until the redox potential (ORP) of the system reaches +550 to +850 mV, and this is maintained for 10 to 60 min. S2. Add a vulcanizing agent to the system obtained in step S1 at 50-90℃ for wet vulcanization, control the ORP of the system to drop to -30 to -150 mV, then raise the temperature to 80-95℃ and mature for 2-6 h, and obtain a rhodium-containing sulfur precipitate after solid-liquid separation. S3. The rhodium-sulfur precipitate is washed 1-3 times with a 1%-10% hydrochloric acid solution, the volume of which is 2-10 times the mass of the rhodium-sulfur precipitate. Then, it is washed 2-10 times with deionized water until the filtrate has a pH of 6.0-7.5 and a Cl- concentration of 1%. - When the content is less than 100 mg / L, a rhodium- and sulfur-containing precursor is obtained; S4 The rhodium-containing sulfur-containing precursor is mixed with a silicon source, a template agent and deionized water to form a crystallization system. The crystallization system is stirred at room temperature for 1 to 8 hours and then hydrothermally crystallized at 130 to 180°C for 48 to 120 hours to obtain a rhodium-containing sulfur-containing molecular sieve crystallization product. S5 involves solid-liquid separation of the rhodium- and sulfur-containing molecular sieve crystallization product, washing with deionized water until the pH of the filtrate is 6.0–8.0, drying at 80–120°C for 4–24 h, calcining at 450–550°C for 2–8 h at a heating rate of 0.5–5°C / min under an oxygen-containing atmosphere, and finally reducing at 400–600°C for 1–6 h under a hydrogen-containing atmosphere to obtain a sulfur-modified molecular sieve confined rhodium dehydrogenation catalyst.

[0009] In step S1, the mass concentration of Rh in the industrial homogeneous rhodium-containing waste liquid is 50 ppm to 2000 ppm. The industrial homogeneous rhodium-containing waste liquid is selected from one or more of the following: olefin hydroformylation reaction waste liquid, methanol carbonylation or acetic acid carbonylation reaction waste liquid, and washing waste liquid after homogeneous catalytic reaction in fine chemicals.

[0010] In step S1, the inorganic acid is selected from one or two of hydrochloric acid, sulfuric acid, and nitric acid, with a mass fraction of 10% to 37%; the oxidant is selected from one or two of hydrogen peroxide solution with a mass fraction of 10% to 35%, hypochlorite solution with an effective chlorine mass fraction of 5% to 15%, and chlorine gas.

[0011] In step S2, the sulfiding agent is selected from one or two of the following: a sodium sulfide aqueous solution with a mass fraction of 5% to 25%, a sodium hydrosulfide aqueous solution with a mass fraction of 5% to 25%, and hydrogen sulfide gas.

[0012] In step S3, the pickling time is 10–60 min / cycle; the deionized water washing temperature is 20–90℃.

[0013] In step S4, the molar ratio of template agent to SiO2 in the crystallization system is 0.05 to 0.50, the molar ratio of H2O to SiO2 is 10 to 100, and the Rh content introduced by the rhodium-containing and sulfur-containing precursor accounts for 0.05 wt% to 0.50 wt% of the mass of SiO2 in the final catalyst.

[0014] In step S4, the silicon source is selected from one or two of tetraethyl orthosilicate, silica sol, and water glass; the template agent is selected from one or two of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, and tetraethylammonium bromide; and the molecular sieve framework in the rhodium-containing sulfur-containing molecular sieve crystallization product has one of the MFI, BEA, or CHA topologies.

[0015] In step S5, the oxygen-containing atmosphere is air with an oxygen content of 5 vol% to 21 vol%, oxygen-enriched air, or a mixture of oxygen and inert gas; the hydrogen-containing atmosphere has a hydrogen gas fraction of 5 vol% to 100 vol.

[0016] A sulfur-modified molecular sieve-confined rhodium dehydrogenation catalyst prepared by the method described above is characterized in that: based on the total mass of the catalyst, the Rh content in the catalyst is 0.05 wt% to 0.50 wt%, the S content is 0.001 wt% to 0.10 wt%, and the remainder is a molecular sieve support; the molecular sieve support has one of the topological structures of MFI, BEA, or CHA; the Rh species are dispersed in the molecular sieve system, and trace amounts of sulfur are retained in the catalyst.

[0017] The application of a sulfur-modified molecular sieve-confined rhodium dehydrogenation catalyst, as described above, in the dehydrogenation reaction of low-carbon alkanes.

[0018] Compared with the prior art, the present invention has the following advantages: 1. This invention uses industrial homogeneous rhodium-containing waste liquid as raw material. Through steps such as acidification, oxidation and complex breaking, wet sulfidation, washing, crystallization, roasting and reduction, it eliminates the traditional processes of pyrometallurgical incineration, deep refining and salt production and reloading. It realizes the direct conversion of industrial rhodium-containing waste liquid into a high-value-added dehydrogenation catalyst precursor. The process route is shorter, the process parameters are clear and easy to control.

[0019] 2. This invention introduces the rhodium- and sulfur-containing precursors obtained by wet sulfidation directly into the molecular sieve crystallization system, which is beneficial for the better dispersion of Rh species during the crystallization process and for the retention of trace sulfur elements in the final catalyst, thereby helping to reduce the tendency of hydrogenolysis side reactions in the dehydrogenation reaction.

[0020] 3. In this invention, the molecular sieve support has one of the topological structures of MFI, BEA, or CHA, preferably the MFI topological structure. In the specific embodiments and comparative examples, the MFI topological molecular sieve is used as the confinement support, and the molar ratio of template agent / SiO2, the molar ratio of H2O / SiO2, the crystallization temperature, the crystallization time, the calcination conditions, and the reduction conditions are quantitatively controlled, which is beneficial to improving the structural stability and repeatability of the catalyst.

[0021] 4. The Rh content in the catalyst prepared by the present invention is controlled at 0.05 wt% to 0.50 wt%, preferably 0.08 wt% to 0.30 wt%. It can still be used for dehydrogenation reactions of low-carbon alkanes with a low amount of precious metals, and is especially suitable for propane dehydrogenation to propylene reaction. It also exhibits high selectivity for target products and low tendency for methane by-products. Attached Figure Description

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0023] Figure 1 This is a SEM image of Embodiment 1 of the present invention.

[0024] Figure 2 This is the XRD pattern of Embodiment 1 of the present invention. Detailed Implementation

[0025] A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst includes the following steps: S1 involves adding 5%–100% by volume of deionized water to a homogeneous industrial rhodium-containing waste liquid to form a stirable system. The pH of the aqueous phase is adjusted to 0.5–2.0 using an inorganic acid. An oxidant is then added at 50–90°C to break down the complex and induce oxidation until the system's redox potential (ORP) reaches +550–+850 mV, and this value is maintained for 10–60 min. Preferably, the ORP is controlled to reach +600–+800 mV and maintained for 20–40 min.

[0026] Among them, the mass concentration of Rh in the industrial homogeneous rhodium-containing waste liquid is 50 ppm to 2000 ppm. The industrial homogeneous rhodium-containing waste liquid is selected from one or more of the following: olefin hydroformylation reaction waste liquid, methanol carbonylation or acetic acid carbonylation reaction waste liquid, and washing waste liquid after homogeneous catalytic reaction in fine chemicals.

[0027] The inorganic acid is selected from one or two of hydrochloric acid, sulfuric acid, and nitric acid, with a mass fraction of 10% to 37%; the oxidant is selected from one or two of hydrogen peroxide solution with a mass fraction of 10% to 35%, hypochlorite solution with an available chlorine mass fraction of 5% to 15%, and chlorine gas.

[0028] S2 involves adding a vulcanizing agent to the system obtained in step S1 at 50–90°C for wet vulcanization. The vulcanizing agent is selected from one or two of the following: a 5%–25% sodium sulfide aqueous solution, a 5%–25% sodium hydrosulfide aqueous solution, and hydrogen sulfide gas. The system ORP is controlled to drop to -30–-150 mV, preferably with the vulcanization endpoint controlled at -50–-120 mV. Subsequently, the temperature is raised to 80–95°C and aged for 2–6 h, preferably at 85–95°C for 2–4 h. After solid-liquid separation, a rhodium-containing sulfur precipitate is obtained.

[0029] S3 involves washing the rhodium- and sulfur-containing precipitate 1-3 times with a 1%-10% hydrochloric acid solution, using 2-10 times the mass of the precipitate, for 10-60 minutes per wash; then washing 2-10 times with deionized water at 20-90°C until the filtrate has a pH of 6.0-7.5 and a Cl- content of 0.5. - When the content is less than 100 mg / L, a rhodium- and sulfur-containing precursor is obtained.

[0030] Preferably, acid washing is performed using a hydrochloric acid solution with a mass fraction of 3%–8%; the washing endpoint is when the pH of the filtrate is 6.5–7.2, and the Cl... - The content is less than 50 mg / L.

[0031] S4 mixes a rhodium- and sulfur-containing precursor with a silicon source, a template agent, and deionized water to form a crystallization system. After stirring the crystallization system at room temperature for 1–8 h, it is hydrothermally crystallized at 130–180 °C for 48–120 h to obtain a rhodium- and sulfur-containing molecular sieve crystallization product.

[0032] Wherein: the molar ratio of template agent / SiO2 in the crystallization system is 0.05-0.50, the molar ratio of H2O / SiO2 is 10-100, and the Rh content introduced by the rhodium-containing and sulfur-containing precursor accounts for 0.05 wt%-0.50 wt% of the mass of SiO2 in the final catalyst. Preferably: SiO2: template agent: H2O = 1:0.08-0.40:15-80; and the mass ratio of Rh introduced in the rhodium-containing and sulfur-containing precursor to SiO2 is 0.0005-0.0100:1.

[0033] The silicon source is selected from one or two of tetraethyl orthosilicate, silica sol, and water glass; the template agent is selected from one or two of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, and tetraethylammonium bromide; the molecular sieve framework in the rhodium-containing sulfur-containing molecular sieve crystallization product has one of the MFI, BEA, or CHA topologies, preferably the MFI topology.

[0034] S5 involves solid-liquid separation of the rhodium- and sulfur-containing molecular sieve crystallization product, washing with deionized water until the filtrate pH reaches 6.0–8.0, drying at 80–120℃ for 4–24 h, calcining at 450–550℃ for 2–8 h under an oxygen-containing atmosphere at a heating rate of 0.5–5℃ / min, and finally reducing at 400–600℃ for 1–6 h under a hydrogen-containing atmosphere, preferably at 500–600℃ for 1–4 h, to obtain a sulfur-modified molecular sieve confined rhodium dehydrogenation catalyst.

[0035] Among them: the oxygen-containing atmosphere is air with an oxygen content of 5 vol% to 21 vol%, oxygen-enriched air, or a mixture of oxygen and inert gas; the hydrogen-containing atmosphere has a hydrogen gas fraction of 5 vol% to 100 vol.

[0036] The sulfur-modified molecular sieve-confined rhodium dehydrogenation catalyst prepared by the above method, based on the total mass of the catalyst, contains 0.05 wt% to 0.50 wt% Rh, 0.001 wt% to 0.10 wt% S, and the remainder is a molecular sieve support; preferably, the Rh content is 0.08 wt% to 0.30 wt% and the S content is 0.005 wt% to 0.050 wt%. The molecular sieve support has one of the topologies MFI, BEA, or CHA, preferably the MFI topology; the Rh species are dispersed in the molecular sieve system, and trace amounts of sulfur are retained in the catalyst.

[0037] Application of a sulfur-modified molecular sieve-confined rhodium dehydrogenation catalyst in the dehydrogenation reaction of low-carbon alkanes: The low-carbon alkane dehydrogenation reaction is a propane dehydrogenation to propylene reaction. The reaction is carried out in a fixed-bed reactor at a temperature of 500–650 °C, a pressure of 0–0.20 MPa, and a propane mass hourly space velocity (WHSV) of 1.0–10.0 h⁻¹. -1 The volume fraction of propane in the feed is 30 vol% to 100 vol%, and the remainder is one or two of nitrogen, hydrogen, water vapor or combinations thereof.

[0038] Unless otherwise stated, all raw materials used in the embodiments of the present invention are commercially available; all percentage contents are by mass; and the Rh content and S content are based on the total mass of the catalyst.

[0039] In this embodiment of the invention, the crystal phase of the sample was determined using an X-ray diffractometer (XRD).

[0040] Example 1: A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1. Take 300 mL of rhodium-containing hydroformylation waste liquid discharged from a butanol / octanol unit. The Rh concentration was pre-tested to be 600 ppm. Add 120 mL of deionized water to the waste liquid and stir at room temperature for 10 min to form a stirable system. Add 36% hydrochloric acid to adjust the pH of the aqueous phase to 1.20. Then raise the temperature to 70℃ and add 18 mL of 30% hydrogen peroxide solution dropwise over a period of 30 min. Monitor the ORP using an online ORP electrode. Once the ORP reaches +680 mV, maintain this level for another 30 min.

[0041] S2 maintained the system temperature at 70℃ and added 22 mL of a 15% sodium sulfide aqueous solution dropwise over a period of 20 min. The addition was stopped when the system ORP dropped to -80 mV. The temperature was then raised to 90℃ and maintained for 3 h. The mixture was then filtered while hot to obtain a black rhodium- and sulfur-containing precipitate.

[0042] S3 precipitates containing rhodium and sulfur were washed once with 80 mL of 5% hydrochloric acid solution for 20 min; then washed five times with 100 mL of deionized water at 80℃ until the filtrate pH=6.8 and Cl - When the content is less than 50 mg / L, a rhodium- and sulfur-containing precursor is obtained.

[0043] S4. All of the above-mentioned rhodium- and sulfur-containing precursors were added to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 190 g of a 25% tetrapropylammonium hydroxide solution, and 180 g of deionized water. The mixture was stirred at room temperature for 4 h. The molar ratio of template agent to SiO2 was 0.22, and the molar ratio of H2O to SiO2 was 10.7. The resulting crystallization slurry was transferred to a stainless steel crystallization reactor and allowed to crystallize at 170 °C for 72 h to obtain the rhodium- and sulfur-containing molecular sieve crystallization product.

[0044] S5 cooled the rhodium- and sulfur-containing molecular sieve crystallization product to room temperature, filtered it, and washed it with deionized water until the pH of the filtrate was 7.2. It was then dried at 100℃ for 12 h. Then, it was calcined at 500℃ for 4 h in air atmosphere at a rate of 2℃ / min. Finally, it was reduced at 550℃ for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 99.3 g of catalyst, denoted as Cat-1.

[0045] Electron microscopy and X-ray diffraction tests were performed on Cat-1, and the results are as follows: Figures 1-2 As shown.

[0046] Example 2: A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 Take 300 mL of rhodium-containing waste liquid from the same source as in Example 1, add 120 mL of deionized water, and add 36% hydrochloric acid to adjust the pH of the aqueous phase of the system to 1.50; after heating to 75°C, add 20 mL of 30% hydrogen peroxide solution dropwise, controlling the dropwise addition time to 35 min, and maintain the system ORP at +720 mV for 20 min.

[0047] S2 was added dropwise at 75℃ with 18 mL of a 15% sodium sulfide aqueous solution. The addition was stopped when the ORP dropped to -60 mV. The temperature was then raised to 90℃ and allowed to mature for 3 h. After filtration, a rhodium- and sulfur-containing precipitate was obtained.

[0048] S3 washes the rhodium- and sulfur-containing precipitate once with 80 mL of 5% hydrochloric acid solution for 20 min, and then washes it five times with deionized water at 80℃ to obtain the rhodium- and sulfur-containing precursor.

[0049] S4 added the rhodium- and sulfur-containing precursor to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 190 g of 25% tetrapropylammonium hydroxide solution, and 180 g of deionized water. After stirring at room temperature for 4 h, the mixture was crystallized at 160 °C for 96 h to obtain the rhodium- and sulfur-containing molecular sieve crystallization product.

[0050] S5 cooled the rhodium- and sulfur-containing molecular sieve crystallization product to room temperature, filtered it, and washed it with deionized water until the pH of the filtrate was 7.2. It was then dried at 100℃ for 12 h. Then, it was calcined at 500℃ for 4 h in air atmosphere by raising the temperature at 2℃ / min. Finally, it was reduced at 550℃ for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 98.7 g of catalyst, which was designated as Cat-2.

[0051] Example 3: A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 Take 300 mL of rhodium-containing waste liquid from the same source as in Example 1, add 120 mL of deionized water, and add 36% hydrochloric acid to adjust the pH of the aqueous phase of the system to 1.20; add 18 mL of 30% hydrogen peroxide solution at 70°C, and maintain for 30 min after the ORP reaches +680 mV.

[0052] S2 was replaced with 24 mL of a 12% sodium hydrosulfide aqueous solution at 70℃. The addition was stopped when the ORP dropped to -90 mV. The temperature was then raised to 90℃ and allowed to mature for 3 h. After filtration, a rhodium- and sulfur-containing precipitate was obtained.

[0053] S3 washes the rhodium- and sulfur-containing precipitate twice with 60 mL of 3% hydrochloric acid solution for 15 min each time, and then washes it six times with deionized water at 80℃ to obtain the rhodium- and sulfur-containing precursor.

[0054] S4 added the rhodium- and sulfur-containing precursor to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 190 g of 25% tetrapropylammonium hydroxide solution, and 180 g of deionized water. The mixture was stirred at room temperature for 4 h and then crystallized at 170 °C for 72 h to obtain the rhodium- and sulfur-containing molecular sieve crystallization product.

[0055] S5 subjected the rhodium- and sulfur-containing molecular sieve crystallization product to solid-liquid separation, washed with deionized water until the filtrate pH=7.2, and dried at 100℃ for 12 h; then calcined at 500℃ for 4 h in air atmosphere at a rate of 2℃ / min; finally reduced at 550℃ for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 97.9 g of catalyst, denoted as Cat-3.

[0056] Example 4: A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 Take 170 mL of rhodium-containing waste liquid from the same source as in Example 1. After preliminary testing, the Rh concentration is 600 ppm. Add 70 mL of deionized water and adjust the pH of the aqueous phase of the system to 1.20 with 36% hydrochloric acid. Add 10 mL of 30% hydrogen peroxide solution at 70°C to raise the ORP of the system to +680 mV and maintain it for 30 min.

[0057] S2 was added dropwise at 70℃ with 12 mL of 15% sodium sulfide aqueous solution to reduce the system ORP to -80 mV; the system was then heated to 90℃ and aged for 3 h, and the precipitate containing rhodium and sulfur was obtained after filtration.

[0058] S3 washes the rhodium- and sulfur-containing precipitate once with 50 mL of 5% hydrochloric acid solution, and then washes it five times with deionized water at 80℃ to obtain the rhodium- and sulfur-containing precursor.

[0059] S4 added the rhodium- and sulfur-containing precursor to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 190 g of 25% tetrapropylammonium hydroxide solution, and 180 g of deionized water. The mixture was stirred at room temperature for 4 h and then crystallized at 170 °C for 72 h to obtain the rhodium- and sulfur-containing molecular sieve crystallization product.

[0060] S5 subjected the rhodium- and sulfur-containing molecular sieve crystallization product to solid-liquid separation, washed with deionized water until the filtrate pH=7.2, and dried at 100℃ for 12 h; then calcined at 500℃ for 4 h in air atmosphere at a rate of 2℃ / min; finally reduced at 550℃ for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 100.6 g of catalyst, denoted as Cat-4.

[0061] Example 5: A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 Take 500 mL of rhodium-containing waste liquid from the same source as in Example 1. The Rh concentration was pre-tested to be 600 ppm. Add 160 mL of deionized water and adjust the pH of the aqueous phase of the system to 1.20 with 36% hydrochloric acid. Add 28 mL of 30% hydrogen peroxide solution at 70°C. When the ORP reaches +680 mV, maintain for 30 min.

[0062] S2 was added dropwise at 70℃ with 35 mL of a 15% sodium sulfide aqueous solution. The addition was stopped when the ORP dropped to -85 mV. The mixture was then heated to 90℃ and allowed to mature for 3 h. After filtration, a rhodium- and sulfur-containing precipitate was obtained.

[0063] S3 washes the rhodium- and sulfur-containing precipitate once with 100 mL of 5% hydrochloric acid solution for 20 min, and then washes it 6 times with deionized water at 80℃ to obtain the rhodium- and sulfur-containing precursor.

[0064] S4 added the rhodium- and sulfur-containing precursor to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 190 g of 25% tetrapropylammonium hydroxide solution, and 180 g of deionized water. The mixture was stirred at room temperature for 4 h and then crystallized at 170 °C for 72 h to obtain the rhodium- and sulfur-containing molecular sieve crystallization product.

[0065] S5 subjected the rhodium- and sulfur-containing molecular sieve crystallization product to solid-liquid separation, washed with deionized water until the filtrate pH=7.2, and dried at 100℃ for 12 h; then calcined at 500℃ for 4 h in air atmosphere at a rate of 2℃ / min; finally reduced at 500℃ for 4 h in a 10 vol% H2 / N2 mixed gas to obtain 99.8 g of catalyst, denoted as Cat-5.

[0066] Example 6: A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 Take 300 mL of rhodium-containing waste liquid from the same source as in Example 1, add 120 mL of deionized water, and add 36% hydrochloric acid to adjust the pH of the aqueous phase of the system to 1.20; add 18 mL of 30% hydrogen peroxide solution at 70°C to make the ORP of the system reach +680 mV and maintain it for 30 min.

[0067] S2 was added dropwise at 70℃ with 25 mL of a 15% sodium sulfide aqueous solution. The addition was stopped when the ORP dropped to -100 mV. The temperature was then raised to 90℃ and allowed to mature for 3 h. After filtration, a rhodium- and sulfur-containing precipitate was obtained.

[0068] S3 washes the rhodium- and sulfur-containing precipitate once with 80 mL of 5% hydrochloric acid solution for 20 min, and then washes it five times with deionized water at 80℃ to obtain the rhodium- and sulfur-containing precursor.

[0069] S4 added the rhodium- and sulfur-containing precursor to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 190 g of 25% tetrapropylammonium hydroxide solution, and 180 g of deionized water. The mixture was stirred at room temperature for 4 h and then crystallized at 170 °C for 72 h to obtain the rhodium- and sulfur-containing molecular sieve crystallization product.

[0070] S5 subjected the rhodium- and sulfur-containing molecular sieve crystallization product to solid-liquid separation, washed with deionized water until the filtrate pH=7.2, and dried at 100℃ for 12 h; then calcined at 480℃ for 6 h in air atmosphere at a rate of 1℃ / min, and then reduced at 530℃ for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 98.5 g of catalyst, denoted as Cat-6.

[0071] Example 7: A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 Take 300 mL of rhodium-containing waste liquid from the same source as in Example 1, add 120 mL of deionized water, and add 36% hydrochloric acid to adjust the pH of the aqueous phase of the system to 1.30; add 18 mL of 30% hydrogen peroxide solution at 65°C to make the ORP of the system reach +650 mV and maintain it for 25 min.

[0072] S2 was added dropwise at 65℃ with 20 mL of a 15% sodium sulfide aqueous solution, causing the system ORP to drop to -70 mV; the temperature was then raised to 88℃ for 4 h for aging. After filtration, a rhodium- and sulfur-containing precipitate was obtained.

[0073] S3 washes the rhodium- and sulfur-containing precipitate once with 80 mL of 5% hydrochloric acid solution for 20 min, and then washes it five times with deionized water at 80℃ to obtain the rhodium- and sulfur-containing precursor.

[0074] S4 added the rhodium- and sulfur-containing precursor to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 210 g of 25% tetrapropylammonium hydroxide solution, and 200 g of deionized water. The mixture was stirred at room temperature for 5 h and then crystallized at 150 °C for 120 h to obtain the rhodium- and sulfur-containing molecular sieve crystallization product.

[0075] S5 subjected the rhodium- and sulfur-containing molecular sieve crystallization product to solid-liquid separation, washed with deionized water until the filtrate pH=7.2, and dried at 100℃ for 12 h; then calcined at 500℃ for 4 h under air atmosphere with a heating rate of 2℃ / min; finally reduced at 550℃ for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 101.2 g of catalyst, denoted as Cat-7.

[0076] Comparative Example 1 The difference between this comparative example and Example 1 is that the wet sulfidation step is omitted. Instead, the system after oxidation and complex breakdown is directly subjected to alkali precipitation to recover the rhodium precursor, followed by treatment under the same crystallization, calcination, and reduction conditions as in Example 1. Specifically, 300 mL of rhodium-containing waste liquid is taken, 120 mL of deionized water is added, the pH is adjusted to 1.20, and 18 mL of 30% hydrogen peroxide is added at 70°C to bring the ORP to +680 mV and maintain this for 30 min. Afterward, without adding a sulfiding agent, 10% ammonia solution is added dropwise under stirring until the system pH reaches 8.5. After standing for 30 min, the mixture is filtered to obtain a sulfur-free rhodium precursor. It was added to a crystallization system consisting of 350 g of tetraethyl orthosilicate, 190 g of 25% tetrapropylammonium hydroxide solution and 180 g of deionized water. The mixture was stirred at room temperature for 4 h, crystallized at 170 °C for 72 h, and then dried at 100 °C for 12 h, calcined at 500 °C for 4 h and reduced at 550 °C for 2 h to obtain 99.0 g of catalyst, denoted as Comp-1.

[0077] Comparative Example 2 This comparative example uses the traditional "recovery-salt production-impregnation-loading" route to prepare the catalyst. 300 mL of rhodium-containing waste liquid from the same source as in Example 1 was concentrated, incinerated, and acid-dissolved to obtain a rhodium salt solution. 100.0 g of commercially pure silicon MFI molecular sieve was added to 150 mL of deionized water and stirred at room temperature for 30 min. The rhodium salt solution was then added dropwise to achieve an Rh loading of 0.18 wt%, and stirring continued for 12 h. After filtration, the solution was dried at 100 °C for 12 h, calcined in air at 500 °C for 4 h, and then reduced at 550 °C for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 100.4 g of catalyst, denoted as Comp-2.

[0078] Comparative Example 3 The difference between this comparative example and Example 1 is that although a rhodium-containing sulfur-containing precursor is used, the in-situ crystallization confinement step is not employed; instead, a post-loading method is used. Specifically, the rhodium-containing sulfur-containing precursor was prepared according to the method of Example 1; 100.0 g of commercially pure silicon MFI molecular sieve was added to 150 mL of deionized water and stirred for 30 min, then the rhodium-containing sulfur-containing precursor slurry was added, and stirred at room temperature for 12 h. After filtration, it was dried at 100 °C for 12 h, calcined in air at 500 °C for 4 h, and then reduced at 550 °C for 2 h in a 10 vol% H2 / N2 mixed gas to obtain 100.1 g of catalyst, denoted as Comp-3.

[0079] The Rh content, S content, specific surface area, and pore volume of the catalysts obtained in Examples 1-7 and Comparative Examples 1-3 were determined. The Rh content was determined by ICP, the S content was determined by elemental analysis, and the specific surface area and pore volume were determined by N2 adsorption-desorption method. The results are shown in Table 1.

[0080] Table 1. Parameters of catalysts in each example and comparative example (all supports are MFI topology). The catalysts obtained in Examples 1-7 and Comparative Examples 1-3 were applied in propane dehydrogenation. The specific process is as follows: The propane dehydrogenation reaction was carried out in a quartz tube fixed-bed reactor. The catalyst was tableted, crushed, and sieved to 20-40 mesh. 5.0 g of catalyst was mixed with 10.0 g of quartz sand and then loaded into the isothermal zone of the reactor. Before the reaction, a pre-reduction was performed in a 10 vol% H2 / N2 mixed atmosphere, with a total flow rate of 200 mL / min and a heating rate of 10 °C / min, heated to 550 °C and held for 2 h, followed by N2 purging for 30 min. Unless otherwise specified, the catalytic activity evaluation conditions were as follows: reaction temperature 600 °C, reaction pressure at atmospheric pressure, feed of pure propane, propane volumetric flow rate of 170 mL / min (standard conditions), corresponding to a propane mass hourly space velocity (WHSV) of 4.0 h⁻¹. -1 The reaction products were analyzed by online gas chromatography, and the propane conversion, propylene selectivity, and CH4 selectivity were calculated. The results are shown in Table 2.

[0081] Table 2 Performance results of catalysts in propane dehydrogenation for each example and comparative example. As shown in Tables 1 and 2, under the same propane dehydrogenation evaluation conditions, the Cat-1 to Cat-7 samples prepared by directly introducing industrial homogeneous rhodium-containing wastewater into the molecular sieve crystallization system after wet sulfidation in this invention generally exhibit superior comprehensive catalytic performance compared to the comparative samples. The samples prepared in each example are all MFI topological structure molecular sieve-confined Rh catalysts. Example 1, under conditions of 0.17 wt% Rh and 0.032 wt% S, still maintained a propane conversion of 38.6%, a propylene selectivity of 97.9%, and a CH4 selectivity of 0.7% after 50 h, indicating that the route of this invention can balance activity, selectivity, and a low tendency for hydrogenolysis side reactions under relatively low Rh loading. The results of Example 2 are similar to those of Example 1, indicating that by adjusting the acidification, oxidation, and crystallization conditions within the scope defined by this invention, a high-performance MFI-confined catalyst can still be obtained. Example 4 further illustrates that when the Rh content decreases to 0.09 wt%, the propane conversion rate decreases to 30.6%, but the propylene selectivity remains at 98.2%, and the CH4 selectivity decreases to 0.4%, indicating that a lower Rh loading is beneficial for suppressing side reactions but reduces dehydrogenation activity. Example 5 shows that as the Rh content increases to 0.29 wt%, the propane conversion rate increases to 41.0%, but the propylene selectivity decreases to 95.8%, and the CH4 selectivity increases to 1.3%, indicating that there is an adjustable relationship between Rh loading and dehydrogenation activity and the tendency for hydrogenolysis side reactions. Examples 3 and 6 exhibit better overall performance, with Example 6 still showing a propane conversion rate of 36.6%, a propylene selectivity of 98.5%, and a CH4 selectivity of 0.5% after 50 h, indicating that appropriately increasing the sulfur retention and optimizing post-treatment conditions are beneficial for further reducing hydrogenolysis side reactions.

[0082] In comparison, the catalytic performance of Comparative Examples 1–3 was significantly lower. Although Comparative Example 1 achieved an initial propane conversion of 46.8%, its propylene selectivity was only 34.2%, while its CH4 selectivity was as high as 18.5%. Even after 50 h, the propylene selectivity remained at only 39.8%, indicating that the Rh site was more prone to hydrogenolysis side reactions when the sulfur-containing precursor introduced by wet sulfidation was absent. Comparative Example 2, using the traditional "recovery-salt production-impregnation loading" route, achieved a propane conversion of only 20.1% after 50 h, a propylene selectivity of only 81.2%, and a CH4 selectivity of 4.1%. Comparative Example 3, although introducing a rhodium-containing sulfur-containing precursor, did not undergo in-situ crystallization confinement; after 50 h, its propane conversion, propylene selectivity, and CH4 selectivity were 24.7%, 88.1%, and 2.3%, respectively. This suggests that the subsequent impregnation introduction of Rh, the presence of only a sulfur-containing precursor without a crystallization confinement step, are all detrimental to the effective anchoring and confined dispersion of Rh species during MFI crystal formation.

[0083] In summary, the technical route provided by this invention couples the short-process resource utilization of industrial homogeneous rhodium-containing waste liquid with the confined construction of molecular sieves, achieving confined dispersion of Rh active components and micro-modulation of S. It takes into account the simplicity of the preparation route, the operability of the system, and the catalytic performance, and has good application potential in the field of propane non-oxidative dehydrogenation to propylene.

[0084] All equivalent substitutions or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst, comprising the following steps: S1 is prepared by adding 5% to 100% of the volume of deionized water to a homogeneous industrial rhodium-containing waste liquid to form a stirable system. The pH of the aqueous phase of the system is adjusted to 0.5 to 2.0 using an inorganic acid. An oxidant is added at 50 to 90°C to break the complex and oxidize until the redox potential (ORP) of the system reaches +550 to +850 mV, and this is maintained for 10 to 60 min. S2. Add a vulcanizing agent to the system obtained in step S1 at 50-90℃ for wet vulcanization, control the ORP of the system to drop to -30 to -150 mV, then raise the temperature to 80-95℃ and mature for 2-6 h, and obtain a rhodium-containing sulfur precipitate after solid-liquid separation. S3. The rhodium-sulfur precipitate is washed 1-3 times with a 1%-10% hydrochloric acid solution, the volume of which is 2-10 times the mass of the rhodium-sulfur precipitate. Then, it is washed 2-10 times with deionized water until the filtrate has a pH of 6.0-7.5 and a Cl- concentration of 1%. - When the content is less than 100 mg / L, a rhodium- and sulfur-containing precursor is obtained; S4 The rhodium-containing sulfur-containing precursor is mixed with a silicon source, a template agent and deionized water to form a crystallization system. The crystallization system is stirred at room temperature for 1 to 8 hours and then hydrothermally crystallized at 130 to 180°C for 48 to 120 hours to obtain a rhodium-containing sulfur-containing molecular sieve crystallization product. S5 involves solid-liquid separation of the rhodium- and sulfur-containing molecular sieve crystallization product, washing with deionized water until the pH of the filtrate is 6.0–8.0, drying at 80–120°C for 4–24 h, calcining at 450–550°C for 2–8 h at a heating rate of 0.5–5°C / min under an oxygen-containing atmosphere, and finally reducing at 400–600°C for 1–6 h under a hydrogen-containing atmosphere to obtain a sulfur-modified molecular sieve confined rhodium dehydrogenation catalyst.

2. The preparation method of a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: In step S1, the mass concentration of Rh in the industrial homogeneous rhodium-containing waste liquid is 50 ppm to 2000 ppm. The industrial homogeneous rhodium-containing waste liquid is selected from one or more of the following: olefin hydroformylation reaction waste liquid, methanol carbonylation or acetic acid carbonylation reaction waste liquid, and washing waste liquid after homogeneous catalytic reaction in fine chemicals.

3. The preparation method of a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: In step S1, the inorganic acid is selected from one or two of hydrochloric acid, sulfuric acid, and nitric acid, with a mass fraction of 10% to 37%; the oxidant is selected from one or two of hydrogen peroxide solution with a mass fraction of 10% to 35%, hypochlorite solution with an effective chlorine mass fraction of 5% to 15%, and chlorine gas.

4. The preparation method of a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: In step S2, the sulfiding agent is selected from one or two of the following: a sodium sulfide aqueous solution with a mass fraction of 5% to 25%, a sodium hydrosulfide aqueous solution with a mass fraction of 5% to 25%, and hydrogen sulfide gas.

5. The preparation method of a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: In step S3, the pickling time is 10–60 min / cycle; the deionized water washing temperature is 20–90℃.

6. The preparation method of a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: In step S4, the molar ratio of template agent to SiO2 in the crystallization system is 0.05 to 0.50, the molar ratio of H2O to SiO2 is 10 to 100, and the Rh content introduced by the rhodium-containing and sulfur-containing precursor accounts for 0.05 wt% to 0.50 wt% of the mass of SiO2 in the final catalyst.

7. The preparation method of a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: In step S4, the silicon source is selected from one or two of tetraethyl orthosilicate, silica sol, and water glass; the template agent is selected from one or two of tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, and tetraethylammonium bromide; and the molecular sieve framework in the rhodium-containing sulfur-containing molecular sieve crystallization product has one of the MFI, BEA, or CHA topologies.

8. The method for preparing a waste liquid rhodium-source confined molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: In step S5, the oxygen-containing atmosphere is air with an oxygen content of 5 vol% to 21 vol%, oxygen-enriched air, or a mixture of oxygen and inert gas; the hydrogen-containing atmosphere has a hydrogen gas fraction of 5 vol% to 100 vol.

9. A sulfur-modified molecular sieve confined rhodium dehydrogenation catalyst prepared by the method according to any one of claims 1 to 8, characterized in that: Based on the total mass of the catalyst, the catalyst contains 0.05 wt% to 0.50 wt% Rh, 0.001 wt% to 0.10 wt% S, and the remainder is a molecular sieve support; the molecular sieve support has one of the topological structures of MFI, BEA or CHA; the Rh species are dispersed in the molecular sieve system, and trace amounts of sulfur are retained in the catalyst.

10. The application of the sulfur-modified molecular sieve confined rhodium dehydrogenation catalyst as described in claim 9 in the dehydrogenation reaction of low-carbon alkanes.

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