CN113426478A - Dehydrogenation catalyst and preparation method thereof - Google Patents
Dehydrogenation catalyst and preparation method thereof Download PDFInfo
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- CN113426478A CN113426478A CN202110713490.XA CN202110713490A CN113426478A CN 113426478 A CN113426478 A CN 113426478A CN 202110713490 A CN202110713490 A CN 202110713490A CN 113426478 A CN113426478 A CN 113426478A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J29/00—Catalysts comprising molecular sieves
- B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
- B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
- B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
- B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
- B01J29/44—Noble metals
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
- C07C5/32—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen
- C07C5/327—Formation of non-aromatic carbon-to-carbon double bonds only
- C07C5/333—Catalytic processes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
Abstract
The invention discloses a dehydrogenation catalyst and a preparation method thereof, and the dehydrogenation catalyst comprises a carrier, wherein the carrier has a three-layer structure from inside to outside, the innermost layer (namely a core) is inert alumina doped with a molecular sieve, the middle layer is active alumina or the molecular sieve, and the outermost layer is active alumina; one or two of the middle layer and the outermost layer are doped with alkali metal, alkaline earth metal or rare earth metal elements; the intermediate layer supports a catalytically active component. After the compact core is prepared, an intermediate layer with an active shell and carbon deposition resistance is coated on the surface of the compact core, then a catalytic active component is loaded, and the outermost layer is coated on the surface of the compact core to protect the catalyst. The three-layer structure of the catalyst effectively improves the carbon deposition resistance, the catalytic activity and the abrasion resistance of the catalyst; the catalyst effectively reduces the dosage of the noble metal component and the production cost.
Description
Technical Field
The invention relates to the technical field of catalytic cracking, in particular to a low-carbon alkane dehydrogenation catalyst based on a multilayer structure and a preparation method thereof.
Background
The main processes for producing low-carbon olefins at present include catalytic cracking technology, steam cracking technology, coal-to-olefin technology, methanol-to-olefin technology and direct dehydrogenation reaction-to-olefin technology. The most market competitive process in the existing main processes for producing low-carbon olefins is a direct dehydrogenation olefin preparation technology, and compared with other olefin preparation technologies, the technology has the advantages of low energy consumption, high olefin yield, low cost and the like in the production process. So far, the direct dehydrogenation reaction for preparing olefin is the most effective means for obtaining light alkane.
The direct dehydrogenation process mainly comprises the Catofin fixed bed process by Lummus and the Oleflex moving bed process by UOP. Wherein, the Camofin fixed bed process of Lummus adopts a bar-shaped catalyst of Cr/Al2O3, and Cr in the catalyst is heavy metal which has certain pollution to the environment and is a highly carcinogenic substance, and the application of the catalyst is limited to a certain extent at present when the environmental protection problem is serious.
Compared with Cr-series catalysts, the catalysts use noble metal atoms as active sites, have high reaction activity, high olefin yield and good economical efficiency, and are environment-friendly, and noble metals can be recycled. However, since the carrier of the moving bed catalyst is limited to be spherical, the carrier produced by the current process has low strength, and the prepared catalyst has high abrasion rate, thereby causing the reduction of the service life and stability of the catalyst. In addition, more seriously, the carrier of the current industrial catalyst is high-activity spherical alumina, and the diffusion speed of the carbon deposit in the ball core is lower than that of the outer layer of the ball due to the multi-level pores of the carrier, so that the carbon deposit in the ball core is accumulated too much to form core coke, thus the activity of the catalyst is reduced, and the service life of the catalyst is shortened.
In view of the above, in order to improve the activity and service life of the light alkane dehydrogenation catalyst, it is important to develop a noble metal dehydrogenation catalyst which can suppress the formation of core coke and has high crush strength.
Disclosure of Invention
So far, the noble metal dehydrogenation catalyst has been developed to some extent, but there is no related patent report on the preparation of low-carbon alkane dehydrogenation catalyst by using a carrier with a ball core as a molecular sieve and a metal organic framework component and an outer layer as an alumina component.
The invention aims to provide a low-carbon alkane dehydrogenation catalyst with a multilayer structure and a preparation method thereof, and aims to solve the problems of serious carbon deposition, low strength, poor stability and short service life of the conventional dehydrogenation catalyst.
The technical scheme for solving the technical problems is as follows:
a dehydrogenation catalyst comprises a carrier, wherein the carrier has a three-layer structure from inside to outside, the innermost layer (namely a core) is inert alumina doped with a molecular sieve, the middle layer is active alumina or the molecular sieve, and the outermost layer is active alumina; one or two of the middle layer and the outermost layer is doped with alkali metal, alkaline earth metal or rare earth metal elements; the intermediate layer supports a catalytically active component.
The innermost layer of the carrier of the catalyst is an inert component layer, has no distribution of active components of the catalyst, is a compact phase with stable property, and is not easy to form core coke. The middle layer of the carrier is a catalyst layer, active ingredients of the catalyst are distributed in the part, the part has the characteristics of large specific surface area, large aperture and high pore volume, and the active ingredients are highly dispersed and have good catalytic activity. The outermost layer of the carrier is a protective layer, so that the catalyst is stable in structure and good in wear resistance, and plays a role in improving the stability and wear resistance of the catalyst.
The innermost layer of the carrier is a molecular sieveDoped inert alumina, molecular sieves preferred for use are AlPO4One or more of-n (an aluminum phosphate molecular sieve), SAPO-n (a silicoaluminophosphate molecular sieve), ZSM-5 or Zr-MOFs, wherein the innermost layer of the carrier takes pseudo-boehmite and a molecular sieve as main raw materials, and a dense phase is formed by high-temperature roasting.
The intermediate layer of the carrier can be activated alumina or a molecular sieve, and the molecular sieve is one or more of AlPO4-n, SAPO-n and ZSM-5. The intermediate layer is preferably activated alumina doped with an alkali metal, alkaline earth metal or rare earth metal element.
The dehydrogenation catalyst supports the following catalytic active components by mass percentage of 100 percent: 0.01 to 1 percent of core component, preferably 0.1 to 0.6 percent; 0.01 to 10 percent of first auxiliary agent, preferably 0.5 to 4 percent; 0.1-10% of second auxiliary agent, preferably 0.8-4%; all the components are highly dispersed in the intermediate layer of the carrier.
The core component of the active component of the catalyst is one or a mixture of more of Pt, Pd, Ag and Rh elements; the core component element is derived from one or more of metal powder, oxide and halide of noble metal elements.
The first auxiliary agent is one or a mixture of more of rare earth metal elements, and the rare earth metal elements are one or more of rare earth metal powder, rare earth metal halide, rare earth metal oxide, rare earth metal nitrate, rare earth metal acetate and rare earth metal oxalate.
The rare earth metal element in the first auxiliary agent is selected from the following 17 elements: scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu).
The second auxiliary agent is one or a mixture of more of alkali metal elements or alkaline earth metal elements. The alkali metal element or alkaline earth metal element is one or more of alkali metal or alkaline earth metal powder, alkali metal or alkaline earth metal halide, alkali metal or alkaline earth metal nitrate, alkali metal or alkaline earth metal acetate and alkali metal or alkaline earth metal oxalate.
The alkali metal elements in the second auxiliary agent comprise: six elements, namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr); the alkaline earth metal elements include: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra).
The component of the outermost layer of the support is preferably activated alumina doped with an alkali metal, alkaline earth metal or rare earth metal element.
The rare earth metal elements doped in the middle layer and the outermost layer are derived from one or more of rare earth metal powder, rare earth metal halide, rare earth metal oxide, rare earth metal nitrate, rare earth metal acetate and rare earth metal oxalate. The outermost layer doped with alkali metal or alkaline earth metal is derived from one or more of alkali metal or alkaline earth metal powder, alkali metal or alkaline earth metal halide, alkali metal or alkaline earth metal nitrate, alkali metal or alkaline earth metal acetate, and alkali metal or alkaline earth metal oxalate. Wherein the rare earth metal elements include 17 elements of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The alkali metal elements include: six elements, namely lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr); the alkaline earth metal elements include: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra).
The thickness of each layer of the catalyst is based on the diameter R of the support, the radius of the innermost layer of the catalyst: (10% to 30%) R/2, catalyst interlayer thickness: (69-89%) R/2, and (1-20%) R/2 of catalyst outermost layer thickness.
The low-carbon alkane catalyst with the multilayer structure is applied to propane dehydrogenation.
The catalyst is applied to a fixed bed, the reaction pressure is 0.01 MPa-1 MPa, the temperature is 500-700 ℃, and the mass space velocity is 0.1h-1～20h-1。
The preparation method of the low-carbon alkane dehydrogenation catalyst based on the multilayer structure comprises the following steps of preparing the innermost layer of the catalyst, preparing the middle part of the catalyst and preparing the outermost layer of the catalyst:
(1) preparation of the innermost layer of the support
Mixing pseudo-boehmite and a molecular sieve according to the mass ratio of 3-7: 1, adding a binder, mixing to obtain a mixture, kneading the mixture, rolling the ball, drying for 4-6 hours at the temperature of 100-120 ℃, and roasting for 4-8 hours at the temperature of 900-1400 ℃ to prepare a carrier precursor (namely a mother ball) with the diameter of 0.2-4.5 mm;
pseudo-boehmite: specific surface area of 50m2/g～500m2A concentration of 100 to 200m2(ii)/g; the aperture range is 4 nm-40 nm, preferably 15-30 nm; the pore volume range is 0.4-0.7 cm3Per g, preferably 0.5 to 0.6cm3/g；
The molecular sieve being AlPO4-one or more of n, SAPO-n, ZSM-5 or Zr-MOFs;
the adhesive is kneading glue or spraying glue, or both kneading glue and spraying glue. The kneading glue is prepared by mixing citric acid and concentrated nitric acid according to the mass ratio of 1: 1-3, and the spraying glue is prepared by stirring one or more of sesbania powder, polyvinyl alcohol or methyl cellulose and deionized water into a sprayable glue. The pseudo-boehmite and the molecular sieve rolling balls are easy to be formed by using a proper amount of the adhesive, and the dosage of the adhesive is adjusted according to the material ball forming shape in a kneading machine and a ball rolling machine.
(2) Preparation of intermediate layer of support
Selecting active alumina or a molecular sieve with proper specific surface area and pore size, adding a binder, adding the carrier precursor, rolling the ball, forming, controlling the thickness of the middle layer to be 0.1-4.5 mm, drying for 4-6 hours at 100-120 ℃, and roasting for 4-8 hours at 450-600 ℃ to prepare the middle layer carrier with an active shell and carbon deposition resistance;
the specific surface area of the activated alumina or molecular sieve is 50m2/g～500m2(ii)/g; the aperture range is 4 nm-40 nm.
In the preparation of the intermediate layer carrier, a compound containing a rare earth metal element, an alkali metal element, and an alkaline earth metal element may be kneaded together with the activated alumina or the molecular sieve.
(3) Supported catalytically active component
Preparing a soluble mixed solution containing a core component, a first auxiliary agent and a second auxiliary agent, impregnating the intermediate layer carrier and the soluble mixed solution, stirring, removing redundant impregnating solution in vacuum, drying, and roasting at 450-750 ℃ for 2-8 hours to obtain a catalyst precursor;
the core component element is preferably one of metal powder and oxide of Pt, Pd, Au and Rh elements.
The first auxiliary agent is preferably yttrium or lanthanum element, and one of yttrium-containing chloride, lanthanum-containing nitrate and lanthanum-containing sulfate is used for preparing a soluble solution containing the yttrium or lanthanum element.
The second auxiliary agent is preferably calcium element, and the soluble solution containing the calcium element is prepared by using one of calcium-containing chloride, calcium-containing nitrate and calcium-containing sulfate.
The solid-to-liquid ratio (mass ratio) of the intermediate layer carrier to the soluble mixed solution is 1:1 to 4.
The aging time is 4-12 hours; the drying is carried out for 4-12 hours at the temperature of 80-120 ℃.
(4) Preparation of the outermost layer of the support
Selecting active alumina with proper specific surface area and pore size as a carrier substrate, adding a binder, adding a soluble solution containing alkali metal or alkaline earth metal elements or a soluble solution containing rare earth metal elements or a mixture of the soluble solutions, adding acid to prepare an aluminum sol, spraying the aluminum sol on the catalyst precursor, rolling ball forming, controlling the thickness of the outermost layer to be 0.1-2 mm, drying for 4-6 hours at 100-120 ℃, and roasting for 4-8 hours at 450-600 ℃ to prepare the dehydrogenation catalyst with a protective shell, an active intermediate layer and an anti-carbon deposition core.
The specific surface area of the activated alumina is 100-500 m2Per g, preferably 150 to 300m2(ii)/g; the aperture of the activated alumina is 5-40 nm, preferably 8-15 nm; the acid is one or more of citric acid, nitric acid, formic acid, acetic acid, hydrochloric acid, and trichloroacetic acid.
When the support is spherical, the thickness of each layer of the catalyst is based on the diameter R of the support, preferably the radius of the innermost layer of the catalyst: (10% to 30%) R/2, catalyst interlayer thickness: (69-89%) R/2, and (1-20%) R/2 of catalyst outermost layer thickness. In preparing the carrier, the thickness of each layer is controlled within this range by a roll-ball molding process.
Compared with the prior art, the invention has at least the following beneficial effects:
the multilayer structure of the catalyst effectively improves the carbon deposition resistance, the catalytic activity and the abrasion resistance of the catalyst.
The carrier of the invention effectively reduces the consumption of the noble metal component of the catalyst and reduces the production cost.
The low-carbon alkane dehydrogenation catalyst based on carrier modification is suitable for a fixed bed process, and the low-carbon alkane dehydrogenation catalyst modified by the carrier not only keeps the advantages of good activity, high selectivity and the like, but also solves the problems of serious carbon deposition, poor stability and short service life of the catalyst in industrial production.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
Preparing the SAPO-n molecular sieve: pseudo-boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water are mixed according to the mass ratio of 1: 0.6: 1: 1: 50, adding the mixture into a reaction kettle under the condition of stirring, crystallizing for 24 hours at the temperature of 250 ℃, filtering and washing a product, and drying at the temperature of about 100 ℃ to obtain SAPO-n raw powder.
Preparing a kneading glue: citric acid and nitric acid (the concentration is 71%) are mixed according to the mass ratio of 2:3 to obtain mixed acid, and the mixed acid is stirred for 3 hours at the temperature of 25 ℃ to obtain the kneading gum.
Preparing spray glue: pulverizing sesbania powder on a pulverizer to obtain powder of less than 150 meshes, putting the powder into deionized water of which the mass is 30 times that of the powder, and stirring the materials into colloid at 30 ℃ to obtain the spray adhesive.
The mass of each component of silicon, platinum, calcium, yttrium, potassium and lanthanum relative to the dry-based alumina is as follows: 10% of silicon, 0.35% of platinum, 2.5% of calcium, 2% of yttrium, 1.5% of potassium and 2% of lanthanum.
Preparing an innermost layer of the carrier: 500g of alumina powder (specific surface area 150 m)2Per g, pore diameter of 20nm and pore volume range of 0.6cm3And 125g of SAPO-n raw powder (mass ratio of 4: 1) putting into a kneading machine, stirring at the rotating speed of 30r/min, pouring 150g of kneading gum into the kneading machine twice, continuing kneading for 1 hour to obtain homogenized powder, putting the powder into a grinder for grinding, and then screening to obtain powder below 150 meshes. And (2) feeding the powder into a shaping machine to carry out ball rolling molding, spraying spray glue by using a high-efficiency sprayer while using the amount of the spray glue of about 120mL, operating for 3h, screening qualified balls with the diameter of 0.3-0.7 mm, shaping the qualified balls for 6 h, aging for 8h, drying for 4h at 100 ℃, and roasting for 4h at 1200 ℃ to obtain a carrier precursor (namely a mother ball).
Preparing a carrier intermediate layer: calcium chloride and yttrium chloride were prepared according to the percentage by mass of calcium and yttrium relative to the dry alumina, 500g of activated alumina (specific surface area 150 m)2Per g, pore diameter of 20nm) and a predetermined amount of calcium chloride and a predetermined amount of yttrium chloride are put into a kneading machine, the rotating speed is 30r/min, 150g of kneading gum is poured into the kneading machine for two times, and is kneaded for 1 hour to obtain homogenized powder, the powder is put into a pulverizer to be pulverized, and then the powder below 150 meshes is sieved. And feeding the powder and the mother balls into a shaping machine for rolling ball forming, operating for 3h, screening qualified balls with the diameter of 1.8-2.2 mm, shaping the qualified balls for 6 h, ageing for 8h, drying for 4h at 100 ℃, and roasting for 4h at 550 ℃ to obtain the intermediate layer carrier with an active shell and carbon deposition resistance.
Carrying a catalytic active component: preparing chloroplatinic acid, lanthanum chloride and potassium chloride according to the mass percentages of platinum, lanthanum and potassium relative to dry alumina; soaking the carrier in hydrochloric acid solution of chloroplatinic acid, lanthanum chloride and potassium chloride in certain amount to required Pt, La and K contents in the soaking liquid, relative to the total dry alumina mass, in the solution at liquid/solid ratio of 1.8, soaking for 4 hr, evaporating the residual soaking liquid at 80 deg.c in vacuum condition, drying at 120 deg.c for 10 hr, and roasting at 550 deg.c in air condition for 6 hr to obtain the catalyst precursor.
Preparing the outermost layer of the carrier: preparing a predetermined amount of lanthanum chloride solution to obtain a soluble solution, and adding activated alumina (specific surface area 150 m)2The pore diameter is 20nm), an adhesive, citric acid and a soluble solution are prepared into an aluminum sol, the aluminum sol can be sprayed, the soluble solution is repeatedly sprayed and coated on the catalyst precursor in a ball rolling machine, qualified spheres with the diameter of 1.9-2.3 mm are screened, the qualified spheres are shaped for 6 hours, then aged for 8 hours, dried for 4 hours at 100 ℃, and roasted for 4 hours at 550 ℃, so that the dehydrogenation catalyst A with a protective shell, an active intermediate layer and an anti-carbon deposition core is obtained.
Example 2
The preparation of the innermost layer and the intermediate layer of the carrier and the steps of supporting the catalytically active component were the same as in example 1.
Preparing the outermost layer of the carrier: preparing a soluble solution obtained by mixing predetermined amounts of alumina sol, magnesium chloride solution and potassium chloride solution, repeatedly spraying the soluble solution on a catalyst precursor in a ball rolling machine, screening qualified balls with the diameter of 1.9-2.3 mm, shaping the qualified balls for 6 hours, aging for 8 hours, drying for 4 hours at 100 ℃, and roasting for 4 hours at 550 ℃ to obtain the catalyst B with a protective shell, an active intermediate layer and an anti-carbon deposition core.
The relative dry alumina mass of each component is as follows: 10% of silicon, 0.35% of platinum, 2.5% of calcium, 2% of yttrium, 1.5% of potassium and 1.2% of magnesium.
Example 3
Preparing a molecular sieve: preparing tetrahydroxy ammonium hydroxide, ethyl orthosilicate and deionized water according to a mass ratio of 0.25: 1: 100, adding the mixture into a reaction kettle under the condition of stirring, crystallizing for 48 hours at the temperature of 100 ℃, filtering and washing a product, and drying at the temperature of about 100 ℃ to obtain the molecular sieve raw powder full-silicon ZSM-5.
The process for preparing spray and knead was the same as in example 1.
Preparing an innermost layer of the carrier: putting 500g of pseudo-boehmite powder and 83.33g of molecular sieve raw powder (mass ratio is 6: 1) into a kneading machine, rotating at the speed of 30r/min, pouring 150g of kneading gum into the kneading machine twice, kneading for 1 hour to obtain homogenized powder, putting the powder into a pulverizer for pulverizing, and sieving to obtain powder below 150 meshes. And (2) feeding the powder into a ball rolling machine for ball rolling forming, spraying spray glue by using high-efficiency spray, operating for 3 hours, screening qualified balls with the diameter of 0.3-0.7 mm, shaping the qualified balls for 6 hours, aging for 8 hours, drying for 4 hours at 100 ℃, and roasting for 4 hours at 1200 ℃ to obtain a carrier precursor (namely a mother ball).
The procedures of preparing the catalyst intermediate layer, loading the catalytically active component, and preparing the catalyst outermost layer were the same as in example 1, and finally, the catalyst C having the protective shell, the active intermediate layer, and the anti-carbon core was obtained.
The relative dry alumina mass of each component is as follows: 10% of silicon, 0.35% of platinum, 2.5% of calcium, 2% of yttrium, 1.5% of potassium and 2% of lanthanum.
Comparative example 1
Putting 500g of pseudo-boehmite powder into a kneading machine, pouring 150g of kneading gum into the kneading machine at the rotating speed of 30r/min for kneading for 1 hour to obtain homogenized powder, putting the powder into a grinder for grinding, and then screening the powder with the particle size below 150 meshes. And (3) putting the powder into a shaping machine for rolling ball forming, operating for 9 hours, screening qualified balls with the diameter of 1.9-2.3 mm, shaping the qualified balls for 4 hours, aging for 8 hours, drying for 4 hours at 100 ℃, and roasting for 4 hours at 550 ℃ to obtain the carrier with a single component.
The specific preparation method of the catalyst comprises the following steps:
soaking in hydrochloric acid solution of chloroplatinic acid, calcium chloride and yttrium chloride in certain amount in the liquid/solid ratio of 1.8 to obtain soaking liquid with platinum content in required amount relative to the total dry alumina mass, evaporating the soaking liquid to dryness at 80 deg.c and drying at 120 deg.c for 10 hr. Then roasting for 6 hours at 550 ℃ under the air condition to obtain the catalyst.
The relative dry alumina mass of each component is as follows: 0.35% of platinum, 2.5% of calcium and 2% of yttrium.
The nitrogen adsorption and desorption experiment of the catalyst is carried out on ASAP2020 type full-automatic physicochemical adsorption analysis, the specific surface area of a sample is calculated by adopting a BET method, and the pore volume and the average pore diameter are calculated by adopting a BJH model; the particle strength of the catalyst was measured on an automated particle strength instrument model KD-4. The catalyst properties of the examples and comparative examples are shown in table 1.
TABLE 1 physicochemical Properties of the catalyst
It can be seen from Table 1 that the specific surface areas of examples 1 to 3 are all lower than those of the comparative example. In the embodiment, the innermost layer structure is calcined at high temperature, so that the overall specific surface area of the catalyst is reduced, and the crushing strength is increased.
The dehydrogenation catalysts prepared in the examples and the comparative examples are applied to a fixed bed, the adopted process flow is the existing process flow, and the control parameters in the process flow are as follows: the space velocity of the propane is 3h-1Introducing a proper amount of nitrogen, keeping the partial pressure of propane at 0.06MPa, and keeping the total pressure of the reaction system at normal pressure; the bed temperature is 580 ℃; the analytical results obtained after 168 hours of use of the catalyst in the fixed bed are shown in Table 2. And the carbon deposition condition of the catalyst after the reaction is characterized by adopting a thermogravimetric analyzer. The model is as follows: STA 449F 3; thermogravimetric analyzer analysis mode: temperature Programmed Oxidation (TPO). The specific test process is as follows: first, the catalyst was freed of H at 200 ℃ under a helium atmosphere (40m L/min)2O (time: 1h), then the temperature was reduced to 30 ℃ after which the gas was switched to 20% O2/N2The temperature is increased to 40 to 800 ℃ and the temperature increasing rate is 10 ℃/min. And (4) detecting the weight loss condition of the catalyst. The reaction products were analyzed using a GC-2014 type gas chromatograph, in which Al is present2O3Packed column, equipped with hydrogen flame detector (FID), analysis C3H8、C3H6、C2H6、C2H6、CH4The content of (a).
The conversion of propane and the selectivity of propylene were calculated by normalization:
Ai＝fr*Cn*A’i；
ai is the correction peak area;
cn is carbon number;
a' i is the true peak area;
fr: relative molar correction molecules;
percent conversion of propane ∑ ΣAi/(ΣAi+APropane in the product)*100％；
Selectivity% for propaneAi*100％；
Yield of propane (% propane conversion) selectivity 100%.
TABLE 2 catalytic performance of the catalyst and amount of carbon deposition after reaction
As can be seen from Table 2, the present invention utilizes a multilayer catalyst to perform well in propane and catalytic dehydrogenation, propane has better propane conversion and propane selectivity, and the amount of by-products and carbon deposits is small. The catalyst prepared by the invention has good catalytic activity, high selectivity and good stability.
Although the invention has been described herein with reference to illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.
Claims (10)
1. The dehydrogenation catalyst is characterized by comprising a carrier, wherein the carrier has a three-layer structure from inside to outside, the innermost layer is inert alumina doped with a molecular sieve, the middle layer is active alumina or a molecular sieve, and the outermost layer is active alumina; one or two of the middle layer and the outermost layer is doped with alkali metal, alkaline earth metal or rare earth metal elements; the intermediate layer supports a catalytically active component.
2. The dehydrogenation catalyst of claim 1, wherein the innermost layer of the support is doped with a molecular sieve selected from the group consisting of AlPO4-n, SAPO-n, ZSM-5, and Zr-MOFs.
3. The dehydrogenation catalyst of claim 1, wherein the molecular sieve used in the intermediate layer of the support is one or more of AlPO4-n, SAPO-n, and ZSM-5.
4. The dehydrogenation catalyst according to claim 1, wherein the catalytically active component comprises 0.01% to 1% of the core component, 0.01% to 10% of the first auxiliary agent, and 0.1% to 10% of the second auxiliary agent, calculated as 100% by mass of the dehydrogenation catalyst; the core component is one or a mixture of more of Pt, Pd, Ag and Rh elements; the first auxiliary agent is one or a mixture of more of rare earth metal elements; the second auxiliary agent is one or a mixture of more of alkali metal elements or alkaline earth metal elements.
5. The dehydrogenation catalyst of claim 1 or 4, wherein the rare earth metal element comprises 17 elements of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium; the alkali metal elements comprise six elements of lithium, sodium, potassium, rubidium, cesium and francium; the alkaline earth metal elements comprise beryllium, magnesium, calcium, strontium, barium and radium.
6. The dehydrogenation catalyst according to claim 1, wherein the total doping amount of alkali metal and alkaline earth metal elements in the intermediate layer and the outermost layer of the carrier is 2-6% of the mass of dry aluminum oxide in the dehydrogenation catalyst; the total doping amount of the rare earth gold elements in the intermediate layer and the outermost layer of the carrier is 2-6% of the mass of the dry aluminum oxide in the dehydrogenation catalyst.
7. A process for the preparation of a dehydrogenation catalyst according to any of claims 1-6 comprising the steps of:
(1) preparation of the innermost layer of the support
Kneading pseudo-boehmite, a molecular sieve and an adhesive, rolling ball forming, drying and roasting to obtain a carrier precursor;
(2) preparation of intermediate layer of support
Kneading activated alumina or a molecular sieve with an adhesive and the carrier precursor, rolling ball forming, drying and roasting to obtain an intermediate layer carrier;
(3) supported catalytically active component
Dipping the intermediate layer carrier in a soluble mixed solution containing a core component, a first auxiliary agent and a second auxiliary agent, stirring, drying and roasting to obtain a catalyst precursor;
the core component is one or more of Pt, Pd, Au and Rh elements;
the first auxiliary agent is one or a mixture of more of rare earth metal elements;
one or a mixture of more of alkali metal elements or alkaline earth metal elements of the second auxiliary agent;
(4) preparation of the outermost layer of the support
Preparing active alumina, adhesive and soluble solution containing alkali metal or alkaline earth metal element or soluble solution containing rare earth metal element or mixture of the above soluble solutions into alumina sol, then spraying the alumina sol on the catalyst precursor, rolling ball forming, drying and roasting to obtain the dehydrogenation catalyst.
8. The method for preparing a dehydrogenation catalyst according to claim 7, wherein the binder is one or both of a spray gum and a kneading gum; the spray glue is prepared by stirring one or more of sesbania powder, polyvinyl alcohol or methyl cellulose and deionized water; the kneading glue is prepared by stirring citric acid and concentrated nitric acid according to the mass ratio of 1: 1-3.
9. The method for preparing a dehydrogenation catalyst according to claim 7, wherein the calcination conditions in step (1) are 900-1400 ℃ for 4-8 h; the roasting conditions from the step (2) to the step (4) are that the roasting is carried out for 4-8h at the temperature of 450-.
10. The method for producing a dehydrogenation catalyst according to claim 7, wherein the thickness of each layer of the catalyst is set based on the diameter R of the support, and the radius of the innermost layer of the catalyst is: (10% to 30%) R/2, catalyst interlayer thickness: (69-89%) R/2, and (1-20%) R/2 of catalyst outermost layer thickness.
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