Magnetically supported catalyst and preparation method and application thereof

Abstract

The invention discloses a magnetic-supported catalyst as well as a preparation method and application thereof. The magnetically supported catalyst comprises a magnetic core, a compact PDA coating layer coating the magnetic core, and an active component supported on the compact PDA coating layer, and the compact PDA coating layer is formed by coating and densifying polydopamine (PDA). The coating layer with a compact structure is prepared on the surface of the magnetic core, and compared with a traditional porous structure and porous channel carrier, when active components are loaded, the active components are not wrapped in the channels, only the active components are loaded on the surface, the loading amount of a noble metal catalyst is reduced in a multiplied or order of magnitude manner, and the loading capacity of the noble metal catalyst is improved. Even if the loading capacity of the active component is very low, the catalyst still has high activity, and the hydrogenation degree can reach 90% or above; the active components are in a structure with the scale of several to dozens of nanometers, so that the hydrogenation activity is high, all the components can be magnetically recycled, and the use cost of the catalyst is low.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial catalysis, and in particular to a magnetically supported catalyst and a preparation method and application thereof. Background Art

[0002] Synthetic rubber, plastics and chemical fibers are the three traditional synthetic materials in the petrochemical industry and are very important pillar materials in modern industrial production. Nitrile rubber (NBR) is a copolymer of butadiene and acrylonitrile. It is widely used in automobiles, aviation, navigation, oil extraction and other fields due to its good air tightness, water resistance, oil resistance, temperature resistance and wear resistance. There are C=C and C≡N in the polymer chain structure of nitrile rubber (NBR); the presence of C≡N makes the rubber have excellent properties such as oil resistance, high tensile strength and high modulus, while the presence of C=C double bonds will cause hidden dangers in the rubber's aging resistance and chemical corrosion resistance.

[0003] In order to improve the performance and application range of nitrile rubber, hydrogenation is often used to eliminate the C=C double bond. However, how to remove the precious metal catalyst after hydrogenation and purify the hydrogenation product requires a combination of one or more methods such as centrifugation, filtration and extraction. The process is quite cumbersome and difficult to remove completely. How to achieve this goal efficiently has always been one of the hot topics in the research of this technology.

[0004] CN101703936A discloses a magnetically supported catalyst in which a magnetic carrier and an active component are supported on a long-chain organic polymer and a preparation method thereof. From the preparation process, a large amount of active components are wrapped into the polymer, resulting in the loss of active components and increasing the cost of the catalyst.

[0005] CN112023939A discloses a magnetic core-shell hydrogenation catalyst and method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, wherein the catalyst is represented by Fe3O4@S / M; wherein Fe3O4 is the core layer, S is the shell layer carrier, and M is the main active metal and / or auxiliary metal loaded on the shell layer carrier; the active metal is one or more of Ru, Ni, Ir, Pd and Pt, and the loading amount is 1-50wt% of the catalyst; the auxiliary metal is one or more of Cu, Fe, Co, Zn and Sn, and the molar ratio of the auxiliary metal to the main active metal is 0.1-10:1. The catalyst prepared by this method has a porous structure and a large active component loading amount, but in a high-viscosity system such as nitrile rubber with a large molecular weight, the active component entering the pores is quickly blocked by the nitrile rubber and cannot function.

[0006] CN104785301A discloses a magnetic palladium composite catalyst and its preparation method and use. The magnetic palladium composite catalyst uses superparamagnetic Fe3O4@SiO2 microspheres as carriers, and the surface is covalently modified with amino Pd(II) particles. The method is carried out by sequentially preparing Fe3O4 nanoparticles, core-shell structured magnetic nanomicrospheres Fe3O4@SiO2, Fe3O4@SiO2@APTES, and finally obtaining Fe3O4@SiO2@APTES@Pd catalyst by loading Pd(II) particles. The surface structure of the final catalyst prepared is still a porous structure.

[0007] KR102436881B1 discloses a magnetic Fe3O4 / PDA / Pd catalyst for Suzuki-Miyaura coupling reaction, Sonogashira coupling reaction and Heck coupling reaction and a preparation method thereof. The preparation method comprises the following steps: preparing a hydrophobic compound polydopamine (PDA) for introducing a hydrophobic alkyl group, preparing a magnetic base carrier, reacting the hydrophobic compound with the base carrier, introducing a hydrophobic alkyl group to connect to the base carrier, and loading metal nanoparticles in the base carrier introduced with the hydrophobic alkyl group. Summary of the invention

[0008] One object of the present invention is to provide a magnetically supported catalyst and a preparation method thereof, specifically a magnetic core@PDA@active hydrogenation component type magnetically supported catalyst that can be used in the hydrogenation process of a latex, a gel or a viscous solution of an unsaturated polymer.

[0009] Another object of the present invention is to provide an application of the magnetically supported catalyst in the hydrogenation process of polymers containing unsaturated olefin double bonds, especially in the hydrogenation of nitrile rubber.

[0010] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0011] On one hand, the present invention provides a magnetic-supported catalyst, in particular a magnetic-supported catalyst for hydrogenation of nitrile rubber; the magnetic-supported catalyst comprises a magnetic core, a dense PDA coating layer coated on the magnetic core, and an active component supported on the dense PDA coating layer;

[0012] The dense PDA coating layer is formed by coating with polydopamine (PDA) and undergoing a densification treatment;

[0013] The active component is selected from at least one of Pd, Rh, Ru, Ni and Mo.

[0014] In some preferred embodiments of the present invention, the densification treatment is a heat treatment at 180-500° C. in a protective gas atmosphere. The protective gas used in the present invention can be nitrogen and an inert gas, such as argon.

[0015] The present invention adopts polydopamine (PDA) to coat the magnetic core. Due to the excellent adhesiveness of PDA, it can be firmly combined with almost all inorganic and organic bodies, and its adhesion mechanism has two explanations; First, polydopamine (PDA) contains sulfhydryl and amino groups that are easy to form covalent bonds, so it is easy to form covalent bonds with other material molecules; Second, polydopamine (PDA) contains sulfhydryl and amino groups that are easy to form ion coordination and chelation. Therefore, polydopamine (PDA) is selected as the coating material of the magnetic core, and the magnetic core and the active component can be reliably combined as a whole, and after the surface densification treatment, it is conducive to the separation from the reaction system after the hydrogenation reaction. In addition, according to the needs of the catalyst particle size and bulk density, the number of coating layers of polydopamine (PDA) can be controlled, coating at least one or more layers and forming a dense surface, and finally forming a catalyst particle size, bulk density and specific surface area The final form of controllable final form.

[0016] The coating method of polydopamine (PDA) can adopt general methods such as dopamine hydrochloride hydrolysis method and layered assembly method, and the dopamine hydrochloride hydrolysis method is preferred.

[0017] In some preferred embodiments of the present invention, the particle size of the magnetic catalyst is 70nm to 600nm, and the specific surface area is 45m 2 / g~91m 2 / g, bulk density is 0.6g / cm 3 ~1.25g / cm 3 .

[0018] In some preferred embodiments of the present invention, the particle size of the magnetically supported catalyst is 70 nm to 300 nm, more preferably 80 nm to 250 nm.

[0019] In some preferred embodiments of the present invention, the specific surface area of ​​the magnetically supported catalyst is 50 m 2 / g~90m 2 / g, more preferably 60m 2 / g~80m 2 / g.

[0020] In some preferred embodiments of the present invention, the bulk density of the magnetically supported catalyst is 0.7 g / cm 3 ~1.0g / cm 3 .

[0021] In some preferred embodiments of the present invention, the active component is selected from at least one of Pd, Rh and Ru.

[0022] In some preferred embodiments of the present invention, the active component is more preferably Pd element.

[0023] In some preferred embodiments of the present invention, the loading amount of the active component is 0.01 wt% to 6 wt% of the catalyst.

[0024] In some preferred embodiments of the present invention, the loading amount of the active component is 0.02 wt% to 1 wt% of the catalyst.

[0025] In some preferred embodiments of the present invention, the loading amount of the active component is 0.05 wt% to 0.5 wt% of the catalyst.

[0026] In some preferred embodiments of the present invention, the active component is loaded by an impregnation method or an in-situ synthesis method. The in-situ synthesis method includes different preparation methods such as a titration method and an in-situ reduction method. The present invention is not particularly limited thereto, and any preparation method that can ultimately form active points of several nanometers to tens of nanometers on the surface of the dense coating layer can be adopted; the titration method and the in-situ reduction method are preferred.

[0027] In some preferred embodiments of the present invention, the magnetic core is selected from at least one of magnetic nanopowders having ferromagnetism, for example, at least one of Fe3O4, Fe3S4 and FeNi; the magnetic core can be purchased commercially or prepared in a laboratory.

[0028] In some preferred embodiments of the present invention, the particle size of the magnetic core is 50 nm to 500 nm.

[0029] In some preferred embodiments of the present invention, the magnetic core is selected from Fe3O4 magnetic nanopowder with a particle size of 50nm to 300nm.

[0030] In some preferred embodiments of the present invention, the magnetic core is selected from Fe3O4 magnetic nanopowder with a particle size of 50nm to 150nm.

[0031] Another aspect of the present invention provides a method for preparing the magnetically supported catalyst as described above, wherein the preparation method comprises the following steps:

[0032] The magnetic core is coated with polydopamine (PDA) by using the hydrolysis reaction of dopamine hydrochloride to obtain magnetic microspheres coated with polydopamine (PDA), namely, magnetic core@PDA.

[0033] The magnetic microspheres coated with polydopamine (PDA) are subjected to heat treatment at 180-500° C. for 1-4 hours in a protective gas atmosphere to form the dense PDA coating layer; when the catalyst particle size and density cannot meet the hydrogenation requirements, the coating is repeated multiple times to form multiple layers of the dense PDA coating layer;

[0034] The active component is loaded to obtain the magnetic-supported catalyst, namely, magnetic core@PDA@active component.

[0035] The thickness of the dense coating layer outside the magnetic core of the present invention can be controlled by adjusting the thickness and number of polydopamine (PDA) coating. If the final particle size and bulk density are not satisfactory, the polydopamine (PDA) coating process can be repeated once or multiple times to adjust until a satisfactory effect is achieved, and finally a dense structure with a suitable specific surface area and particle size is formed.

[0036] Since the rubber system targeted by the magnetically supported catalyst of the present invention is a high-viscosity system, the purpose of coating the magnetic core is not to prepare a porous system, but to form a surface dense structure by coating polydopamine (PDA) and performing a densification treatment. On the one hand, the densified surface can reduce the loading amount of the active component while maintaining the hydrogenation activity in the high-viscosity system; on the other hand, it can reduce the adhesion between the catalyst surface and the high-viscosity system, which is beneficial to the separation and recovery of the catalyst. In addition, for high-viscosity systems with different viscosities, the particle size, bulk density and specific surface area of ​​the final catalyst can be adaptively adjusted by adjusting the number of PDA coating layers, so as to facilitate the magnetic separation and reuse of the catalyst (for high-viscosity systems, catalyst particles with too small a particle size will be difficult to separate).

[0037] In some preferred embodiments of the present invention, the coating process of the magnetic core comprises:

[0038] The magnetic core is added into a buffer solution, and then dopamine hydrochloride is added, and stirred at 12 to 35° C. for 4 to 12 hours. After the reaction is completed, the precipitate is separated and recovered by a magnet, washed, and dried to obtain the magnetic core@PDA.

[0039] In some preferred embodiments of the present invention, the drying can be performed by freeze drying, drying, etc., wherein the drying temperature does not exceed 60° C. The washing is performed sequentially using water and ethanol. The buffer solution is preferably a Tris buffer solution, more preferably a Tris buffer solution with a pH of 8 to 9.

[0040] The dopamine hydrochloride is generally added in excess. In some preferred embodiments of the present invention, the mass ratio of the magnetic core to the dopamine hydrochloride is 1:(0.5-6.0). The coating thickness of the PDA layer can be controlled by adjusting the amount of dopamine hydrochloride and the buffer solution, as well as the hydrolysis time.

[0041] In some preferred embodiments of the present invention, the active component loading process includes:

[0042] The magnetic core coated with a dense PDA coating layer is dispersed in a solvent, and a precursor of an active component is added to react. After the reaction is completed, the solid is separated and recovered by a magnet, washed, and dried. The obtained solid powder is the magnetic-supported catalyst, i.e., magnetic core@PDA@active component.

[0043] The precursor of the active component is generally added in excess. In some preferred embodiments of the present invention, the mass ratio of the magnetic core coated with the dense PDA coating layer to the precursor of the active component is 1:(0.02-1.03).

[0044] In some preferred embodiments of the present invention, the precursor of the active component is selected from at least one of palladium, rhodium, ruthenium and other noble metal elements and acetates, halides, ammonium salts, etc. of nickel and molybdenum elements. The catalyst prepared by the present invention, except for rhodium and ruthenium noble metals, should be reduced and activated with hydrogen at 200-400°C before use.

[0045] In some preferred embodiments of the present invention, the solvent in the process of loading the active component is water.

[0046] The magnetic core of the present invention can be purchased commercially or prepared in the laboratory; the particle size can be between 50 and 500 nm, and the shape is better if it is closer to a sphere. This is related to the evaluation device and evaluation method used in the present invention. The slurry bed evaluation device is used in the embodiment of the present invention, and the final particle size of the catalyst cannot be too large. Since the density of the magnetic core is relatively large, for example, Fe3O4 reaches 5.18 g / cm 3 If the particle size is too large, sedimentation will occur and it cannot be well dispersed in the colloidal solution. Therefore, the sedimentation problem of the catalyst can be solved by controlling the appropriate coating layer thickness and ultimately by controlling the particle size of the catalyst.

[0047] For example, Fe3O4 magnetic microspheres can be prepared as magnetic cores by a solvothermal method, which can be prepared by a thermal reaction of iron salt and a reducing agent, and organic sodium salt, polyethylene glycol and caustic soda can be added during the preparation process.

[0048] Specifically, the preparation method of Fe3O4 magnetic microspheres includes:

[0049] Add a reducing agent, iron salt, organic sodium salt, polyethylene glycol and caustic alkali into a reactor according to a mass ratio, mix them evenly at 10-45° C., prepare an initial reaction mixture and add it into a reactor, heat and react at 80-220° C. for 12-24 hours to obtain a mixture of Fe3O4 magnetic microspheres and a reaction solvent, cool it to 12-35° C., then separate and recover it with a magnet, wash it, freeze-dry it, and store it for later use.

[0050] Wherein, the reducing agent may be an organic alcohol, preferably ethylene glycol and / or propylene glycol. The iron salt may be ferric chloride and / or ferric chloride. The organic sodium salt may be at least one of sodium acetate, sodium stearate, and sodium benzoate. Polyethylene glycol may be a commercially available product, such as polyethylene glycol 6000, and the present invention has no particular limitation on polyethylene glycol. The caustic alkali may be at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0051] The mass ratio of the reducing agent, iron salt, organic sodium salt, polyethylene glycol and caustic soda is preferably (5-20):1:(1-5):(4-10):(0.1-0.5), and more preferably (6-18):1:(2-4):(3-9):(0.15-0.45).

[0052] The particle size of the prepared Fe3O4 magnetic microspheres can be controlled by adjusting the material ratio, reaction time, reaction temperature, etc.

[0053] In another aspect, the present invention provides the use of any one of the above magnetically supported catalysts in the hydrogenation process of polymers containing unsaturated olefin double bonds, especially the hydrogenation of nitrile rubber.

[0054] The magnetically supported catalyst of the present invention can be used to meet the different requirements of NBR rubber, SBR rubber and other latex systems for the catalyst system. By utilizing the differences in formulation and catalyst particle size, the catalyst can be efficiently separated and reused through an external magnetic field while achieving highly selective hydrogenation of unsaturated double bonds. The invention is a convenient method for hydrogenating NBR to prepare HNBR and for hydrogenation and saturation treatment of different latexes using a magnetically supported precious metal catalyst.

[0055] In some preferred embodiments of the present invention, the organic solvent in the hydrogenation process is selected from at least one of ethers, chlorinated aromatics and ketones; more preferably, it is one of the ketones, such as acetone and butanone; the weight ratio of the nitrile rubber to the magnetically supported catalyst is (1-2):1, and more preferably (1-1.5):1.

[0056] In some preferred embodiments of the present invention, hydrogenation is carried out in a stirred tank or a slurry tank, preferably a stirred tank; the hydrogenation temperature is 70-120°C, preferably 70-110°C, more preferably 70-100°C; the hydrogen pressure is 2-16MPa, preferably 2-10MPa, more preferably 4-8MPa; the reaction time is 2-10 hours, more preferably 4-8 hours. The reaction is carried out under stirring conditions, and the stirring speed is preferably 180-600rpm, more preferably 200-450rpm; after the reaction, the original NBR can obtain HNBR with a hydrogenation degree greater than 95%.

[0057] After use, the magnetically supported catalyst of the present invention can be recovered and separated by applying an external electromagnetic field or a permanent magnetic field, preferably by a permanent magnet. The recovery efficiency of the catalyst is not less than 98%, and the recovered catalyst can be reused after washing with a solvent.

[0058] The magnetically supported catalyst of the present invention can realize highly selective hydrogenation of olefin double bonds of nitrile rubber, latex or emulsion, while having low catalyst use cost, low active component content in HNBR and long service life; the catalyst can be efficiently separated by an external magnetic field, has high separation efficiency and is easy to operate, and is a convenient method for preparing HNBR by hydrogenating NBR using a magnetically supported noble metal catalyst.

[0059] The beneficial effects of the present invention include:

[0060] 1) The method for preparing the magnetic-supported catalyst of the present invention is simple and the preparation cost is low; the active component loading amount of the prepared magnetic-supported catalyst is low, which can greatly reduce the cost of using the catalyst. The catalyst prepared by the present invention has a dense surface structure. Since the catalyst body phase is not a conventional porous structure, that is, the body phase has no pores, the catalyst efficiency is high; but since the catalyst particle size is nanometer-scale, the hydrogenation effect is close to that of a homogeneous catalyst, and the hydrogenation effect can be guaranteed.

[0061] 2) The magnetically supported catalyst of the present invention is used in the hydrogenation of NBR to prepare HNBR, which can improve the separation efficiency of the catalyst, prolong the service life of the catalyst, and improve the final performance of the HNBR product.

[0062] Compared with the existing homogeneous method, the present invention does not require complicated separation processes such as extraction or ion exchange of the catalyst after hydrogenation; compared with the existing heterogeneous method, the present invention does not require time-consuming separation processes such as catalyst centrifugation and sedimentation, and can complete the magnetic recovery of the catalyst; and the recovered catalyst can be washed to remove the HNBR colloid attached to the surface, and can be reused, and the catalyst has a long service life. Therefore, the present invention has advantages in terms of catalyst use cost and separation efficiency, and significantly reducing the final catalyst residue of HNBR. DETAILED DESCRIPTION

[0063] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0064] The key to the technical solution of the present invention is that by densifying the magnetic core coating layer, its surface is different from the conventional porous structure and multi-porous channel carrier. When the active hydrogenation component is loaded on the dense coating layer, the active component will not be wrapped into the inside of the pore, and the active component is only loaded on the surface, which reduces the loading amount of the precious metal catalyst by multiples or orders of magnitude. Even when the loading amount of the active component is very low, it still has high activity, and the degree of hydrogenation can reach more than 90%; because the active component is a few to ten nanometers in size and structure, the hydrogenation activity is high and can be fully recovered by magnetic force, and the cost of using the catalyst is low. In addition, the number of coating layers of the dense PDA layer in the magnetic catalyst of the present invention can be regulated to form a final form with a dense surface and controllable catalyst particle size and specific surface area. The magnetic-supported catalyst prepared by the present invention not only has a high hydrogenation activity for nitrile rubber, but also can be applied to the harsh hydrogenation environment of nitrile rubber, and because the catalyst has superparamagnetism, the catalyst can be efficiently recovered by an external magnetic field for reuse, reducing the cost of hydrogenation.

[0065] The magnetically supported catalyst of the present invention comprises a magnetic core, a dense PDA coating layer coated on the magnetic core, and an active component supported on the dense PDA coating layer;

[0066] The dense PDA coating layer is formed by coating with polydopamine (PDA) and undergoing a densification treatment;

[0067] The active component is selected from at least one or more elements selected from the group consisting of precious metal elements such as Pd, Rh, and Ru and elements with high hydrogenation activity such as Ni and Mo, and preferably at least one active component selected from the group consisting of precious metal palladium with high hydrogenation activity and Ni and Mo.

[0068] The densification treatment is a heat treatment at 180-500° C., preferably 220-380° C., under a protective gas atmosphere. The protective gas used in the present invention may be nitrogen and other inert gases, such as argon.

[0069] The magnetic catalyst is prepared by the following steps:

[0070] The magnetic core is coated with polydopamine (PDA) by using the hydrolysis reaction of dopamine hydrochloride to obtain magnetic microspheres coated with polydopamine (PDA), namely, magnetic core@PDA.

[0071] The magnetic microspheres coated with polydopamine (PDA) are subjected to heat treatment at 180-500° C. for 1-4 hours in a protective gas atmosphere to form the dense PDA coating layer; when the catalyst particle size and density cannot meet the hydrogenation requirements, the coating is repeated multiple times to form multiple layers of the dense PDA coating layer;

[0072] The active component is loaded to obtain the magnetic-supported catalyst, namely, magnetic core@PDA@active component.

[0073] The particle size of the magnetic catalyst prepared by the present invention is 70nm to 600nm, preferably 70nm to 300nm, more preferably 80nm to 250nm; the specific surface area is 45m 2 / g~91m 2 / g, preferably 50m 2 / g~90m 2 / g, more preferably 60m 2 / g~80m 2 / g; bulk density is 0.6g / cm 3 ~1.25g / cm 3 , preferably 0.7 g / cm 3 ~1.0g / cm 3 The active component loading amount accounts for 0.01wt% to 6wt% of the catalyst, preferably 0.02wt% to 1wt%, and more preferably 0.05wt% to 0.5wt%.

[0074] The magnetic core is coated with at least one or more layers of dense PDA layer to form a final form with a dense surface and controllable catalyst particle size and specific surface area. The final carrier surface is dense rather than traditional multi-porous form, with a specific surface area of ​​45m 2 / g~91m 2 / g, much lower than the 80m / g of conventional porous surfaces 2 / g~600m 2 / g; bulk density is 0.6g / cm 3 ~1.25g / cm 3 , much higher than the 0.4g / cm of conventional catalysts 3 ~0.6g / cm 3 The active component loading is 0.01wt% to 6wt% of the catalyst, which is much wider than the 1wt% to 5wt% loading of conventional catalysts. The catalyst concentration can be flexibly adjusted in different concentrations of gel solution according to actual needs. However, since the catalyst particle size is nanometer-scale, the hydrogenation effect is close to that of homogeneous catalysts. Since the active components can be completely recovered, the catalyst cost is low under the same hydrogenation activity.

[0075] The active component is loaded by an impregnation method or an in-situ synthesis method. The in-situ synthesis method includes different preparation methods such as a titration method and an in-situ reduction method. The present invention does not make any special limitation. Any preparation method that can ultimately form active points of several nanometers to tens of nanometers on the surface of the dense coating layer can be adopted; the titration method and the in-situ reduction method are preferred.

[0076] The magnetic core is selected from at least one of ferromagnetic magnetic nanopowders, for example, at least one of Fe3O4, Fe3S4 and FeNi; the magnetic core can be purchased commercially or prepared in a laboratory. The particle size of the magnetic core is 50nm to 500nm. The magnetic core is preferably a low-cost commercially purchased or laboratory-synthesized Fe3O4 magnetic nanopowder with a particle size of 50nm to 300nm, and more preferably a Fe3O4 magnetic nanopowder with a particle size of 50nm to 150nm.

[0077] The magnetic core of the present invention can be purchased commercially or prepared in the laboratory; the particle size can be between 50 and 500 nm, and the shape is better if it is closer to a sphere. This is related to the evaluation device and evaluation method used in the present invention. The slurry bed evaluation device is used in the embodiment of the present invention, and the final particle size of the catalyst cannot be too large. Since the density of the magnetic core is relatively large, for example, Fe3O4 reaches 5.18 g / cm 3 If the particle size is too large, sedimentation will occur and it cannot be well dispersed in the colloidal solution. Therefore, the sedimentation problem of the catalyst can be solved by controlling the appropriate coating layer thickness and ultimately by controlling the particle size of the catalyst.

[0078] For example, Fe3O4 magnetic microspheres can be prepared as magnetic cores by a solvothermal method, which can be prepared by a thermal reaction of iron salt and a reducing agent, and organic sodium salt, polyethylene glycol and caustic soda can be added during the preparation process.

[0079] Specifically, the preparation method of Fe3O4 magnetic microspheres includes:

[0080] Add a reducing agent, iron salt, organic sodium salt, polyethylene glycol and caustic alkali into a reactor according to a mass ratio, mix them evenly at 10-45° C., prepare an initial reaction mixture and add it into a reactor, heat and react at 80-220° C. for 12-24 hours to obtain a mixture of Fe3O4 magnetic microspheres and a reaction solvent, cool it to 12-35° C., then separate and recover it with a magnet, wash it, freeze-dry it, and store it for later use.

[0081] Wherein, the reducing agent may be an organic alcohol, preferably ethylene glycol and / or propylene glycol. The iron salt may be ferric chloride and / or ferric chloride. The organic sodium salt may be at least one of sodium acetate, sodium stearate, and sodium benzoate. Polyethylene glycol may be a commercially available product, such as polyethylene glycol 6000, and the present invention has no particular limitation on polyethylene glycol. The caustic alkali may be at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0082] The mass ratio of the reducing agent, iron salt, organic sodium salt, polyethylene glycol and caustic soda is preferably (5-20):1:(1-5):(4-10):(0.1-0.5), and more preferably (6-18):1:(2-4):(3-9):(0.15-0.45).

[0083] The particle size of the prepared Fe3O4 magnetic microspheres can be controlled by adjusting the material ratio, reaction time, reaction temperature, etc.

[0084] In some specific embodiments of the present invention, the coating process of the magnetic core includes:

[0085] The magnetic core is added to the buffer solution, and then dopamine hydrochloride is added, and stirred at 12 to 35°C for 4 to 12 hours; after the reaction is completed, the precipitate is separated and recovered by a magnet, washed and dried to obtain the magnetic core@PDA. The magnetic core@PDA is then subjected to densification treatment.

[0086] The drying can be performed by freeze drying, drying, etc., wherein the drying temperature does not exceed 60°C. The washing is performed sequentially using water and ethanol. The dopamine hydrochloride is generally added in excess, and preferably the mass ratio of the magnetic core to the dopamine hydrochloride is 1:(0.5-6.0). The coating thickness of the PDA layer can be controlled by adjusting the amount of dopamine hydrochloride and the buffer solution, as well as the coating time. The buffer solution is preferably a Tris (tris (hydroxymethyl) aminomethane) buffer solution, more preferably a Tris buffer solution with a pH of 8-9, for example a Tris buffer solution with a pH of about 8.5.

[0087] The thickness of the dense coating layer outside the magnetic core of the present invention can also be controlled by adjusting the thickness and number of polydopamine (PDA) coating. If the final particle size and bulk density are not satisfactory, the polydopamine (PDA) coating process can be repeated once or multiple times to adjust until a satisfactory effect is achieved, and finally a dense structure with a suitable specific surface area and particle size is formed.

[0088] Since the rubber system targeted by the magnetically supported catalyst of the present invention is a high-viscosity system, the purpose of coating the magnetic core is not to prepare a porous system, but to form a surface dense structure by coating polydopamine (PDA) and performing a densification treatment. On the one hand, the densified surface can reduce the loading amount of the active component while maintaining the hydrogenation activity in the high-viscosity system; on the other hand, it can reduce the adhesion between the catalyst surface and the high-viscosity system, which is beneficial to the separation and recovery of the catalyst. In addition, for high-viscosity systems with different viscosities, the particle size, bulk density and specific surface area of ​​the final catalyst can be adaptively adjusted by adjusting the number of PDA coating layers, so as to facilitate the magnetic separation and reuse of the catalyst (for high-viscosity systems, catalyst particles with too small a particle size will be difficult to separate).

[0089] In some preferred embodiments of the present invention, the coating process of the magnetic core includes:

[0090] Tris was added to deionized water to prepare a Tris buffer solution with a pH of 8.5, Fe3O4 was added and dispersed evenly, and then dopamine hydrochloride was added to form a mixed solution, which was stirred at room temperature for 4 to 12 hours. After the reaction was completed, the solution and the solid were separated by a magnet, and the obtained black solid was washed with deionized water and ethanol in turn, and freeze-dried to obtain Fe3O4@PDA.

[0091] In some specific embodiments of the present invention, the active component loading process includes:

[0092] The magnetic core coated with a dense PDA coating layer is dispersed in a solvent (preferably distilled water or ethanol), and the precursor of the active component is added to react. After the reaction is completed, the solid is separated and recovered by a magnet, washed and dried, and the obtained solid powder is the magnetic-supported catalyst, that is, the magnetic core@PDA@active component.

[0093] The precursor of the active component is selected from at least one of palladium, rhodium, ruthenium and other noble metal elements and acetates, halides, ammonium salts of nickel and molybdenum. Except for rhodium and ruthenium noble metals, the catalyst prepared by the present invention should be reduced and activated with hydrogen at 200-400°C before use.

[0094] The precursor of the active component is generally added in excess. Preferably, the mass ratio of the magnetic core coated with the dense PDA coating layer to the precursor of the active component is 1:(0.02-1.03).

[0095] The reaction temperature during the active component loading process is generally 25 to 120°C, and the reaction time is generally 4 to 10 hours. In the case of a heating reaction, after the reaction is completed, the solid can be separated and recovered using a magnet after cooling to 12 to 35°C (room temperature). The washing includes deionized water washing and ethanol washing.

[0096] The magnetically supported catalyst prepared by the present invention can be used in the hydrogenation process of NBR rubber, SBR rubber, latex, latex and the like containing unsaturated olefin double bonds. The NBR hydrogenation process is preferred. The organic solvents in the hydrogenation process include: ethers, chlorinated aromatics and ketones, preferably chlorinated aromatics and ketones, and more preferably ketones such as acetone and butanone; the weight ratio of the rubber amount to the catalyst is (1-2):1, and more preferably (1-1.5):1.

[0097] In some specific embodiments of the present invention, hydrogenation is carried out in a stirred kettle or a slurry kettle, preferably a stirred kettle; the hydrogenation temperature is 70-120°C, preferably 70-110°C, more preferably 70-100°C; the hydrogen pressure is 2-16MPa, preferably 2-10MPa, more preferably 4-8MPa; the reaction time is 2-10 hours, more preferably 4-8 hours. The reaction is carried out under stirring conditions, and the stirring speed is preferably 180-600rpm, more preferably 200-450rpm; after the reaction, the original NBR can obtain HNBR with a hydrogenation degree greater than 95%.

[0098] After use, the magnetically supported catalyst of the present invention can be recovered and separated by applying an external electromagnetic field or a permanent magnetic field, preferably by a permanent magnet. The recovery efficiency of the catalyst is not less than 98%, and the recovered catalyst can be reused after washing with a solvent.

[0099] The magnetically supported catalyst of the present invention can realize highly selective hydrogenation of olefin double bonds of nitrile rubber, latex or emulsion, while having low catalyst use cost, low active component content in HNBR and long service life; the catalyst can be efficiently separated by an external magnetic field, has high separation efficiency and is easy to operate, and is a convenient method for preparing HNBR by hydrogenating NBR using a magnetically supported noble metal catalyst.

[0100] Some specific examples are provided below for more specific description, wherein all numerical values ​​specified (such as temperature, time, concentration and weight, etc., including the range of each thereof) are generally appropriately changed by (+) or (-) approximate values ​​in increments of 0.1 or 1.0. All numerical values ​​specified can be understood as being preceded by the term "about".

[0101] Example 1

[0102] This embodiment prepares a magnetic catalyst, including the following process:

[0103] 1) Preparation of Fe3O4 nanoparticles:

[0104] Add 500 mL of ethylene glycol to a reaction container, then add 32 g of FeCl3·6H2O, 63 g of anhydrous sodium acetate, 138 g of polyethylene glycol-6000, and 6.3 g of sodium hydroxide, stir evenly at 25°C, then add to a reactor for reaction, heat the reaction at 200°C for 15 hours to obtain 150 nm Fe3O4 nanoparticles, cool to 25°C, separate and recover with a magnet, wash, and freeze-dry.

[0105] 2) Preparation of Fe3O4 / PDA magnetic nanoparticles:

[0106] 1.2 g of Tris was weighed and added to 600 mL of deionized water to dissolve to prepare a buffer solution of pH = 8.5, and then 1.5 g of Fe3O4 nanoparticles with a particle size of 150 nm were added and dispersed evenly, and then 50 mL of a 15% dopamine hydrochloride aqueous solution was added dropwise within 10 minutes, and stirring was continued at 25°C for 12 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 10 nm. After completion, the particles were separated and recovered with a magnet, washed with deionized water and ethanol in turn, and freeze-dried; the particle size can be characterized by a laser particle size analyzer and a transmission electron microscope.

[0107] 3) Densification treatment:

[0108] The dried Fe3O4 / PDA magnetic nanoparticles were densified at 280°C for 1 hour under nitrogen protection.

[0109] 4) Loading active components:

[0110] Then weigh 1g of densely coated magnetic nanoparticles and disperse them again in 350mL of distilled water, then add 0.02g of palladium chloride (PdCl2·2H2O) and stir evenly. Then add the evenly mixed reactants into the reactor and stir at 25°C for 6 hours. After the mixture is separated and recovered by a magnet, washed and freeze-dried to obtain the Fe3O4 / PDA / Pd magnetically supported catalyst.

[0111] 5) Hydrogenation reduction:

[0112] The obtained Fe3O4 / PDA / Pd magnetic catalyst was reduced with hydrogen at 380°C for 2h. Finally, a supported Fe3O4@PDA@Pd catalyst with hydrogenation activity was obtained.

[0113] The catalyst particle size was measured to be 170 nm, containing 0.01 wt% Pd, and a specific surface area of ​​86 m 2 / g; bulk density is 0.82g / cm 3 .

[0114] The final catalyst loading amount can be obtained by performing a digestion reaction on the prepared catalyst, or by analyzing the palladium content of the residual liquid of the catalyst precursor. The present invention obtains the catalyst loading amount by performing a digestion reaction on the prepared catalyst.

[0115] 6) Evaluation of hydrogenation degree:

[0116] Weigh 1.02g of 3304 grade NBR, add it to 200g acetone solution, stir thoroughly, dissolve completely, and then transfer the glue solution to a high-pressure reactor; add 0.51g of Fe3O4@PDA@Pd magnetic catalyst to the high-pressure reactor, introduce nitrogen 3 times to replace the air in the reactor, and then introduce H2 to replace it 2 times; heat to 120℃, increase the hydrogen pressure to 4MPa at this temperature, and react for 6h at a stirring rate of 400r / min. After the reaction, the reactor is cooled to room temperature, slowly vented, and the reactor is opened for sampling after the hydrogen gas is emptied. The glue solution and catalyst after the reaction are separated by magnetic separation to separate the solid catalyst, and the catalyst recovery rate is measured to be 99.1%; the glue solution is collected in a reagent bottle to obtain a mixture of HNBR and acetone. The degree of hydrogenation of HNBR is 91.2 by infrared analysis. See Table 1.

[0117] Example 2

[0118] This embodiment prepares a magnetic catalyst, including the following process:

[0119] 1) Preparation of Fe3O4 / PDA magnetic nanoparticles:

[0120] 1.2 g of Tris was weighed and added to 600 mL of deionized water to dissolve to prepare a buffer solution of pH = 9.0, and then 1.8 g of commercially available magnetic core Fe3O4 with a particle size of 200 nm was added and dispersed evenly, and then 70 mL of a 15% dopamine hydrochloride aqueous solution was added dropwise within 10 minutes, and stirring was continued at 25°C for 12 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 15 nm. After completion, the particles were separated and recovered using a magnet, washed with deionized water and ethanol in turn, and freeze-dried; the particle size can be characterized by a laser particle size analyzer and a transmission electron microscope.

[0121] 2) Densification treatment:

[0122] The dried Fe3O4 / PDA magnetic nanoparticles were densified at 300°C for 3 hours under nitrogen protection.

[0123] 3) Loading active components:

[0124] Then weigh 1g of densely coated magnetic nanoparticles and disperse them again in 350mL of distilled water, then add 0.78g of rhodium chloride (RhCl3·3H2O) and stir evenly. Then add the evenly mixed reactants into the reactor and stir at 30°C for 4 hours. After the mixture is separated and recovered by a magnet, washed and freeze-dried to obtain the Fe3O4 / PDA / Rh magnetically supported catalyst.

[0125] The catalyst has a particle size of 230 nm, contains 0.1 wt% Rh, and has a specific surface area of ​​74 m 2 / g; bulk density is 0.91g / cm 3 .

[0126] 4) Evaluation of hydrogenation degree:

[0127] 1.01g of 3604 grade NBR was added to 200g of acetone solution, stirred thoroughly and dissolved completely, then added to the autoclave together with 1.0g of Fe3O4@PDA@Rh, and 10mL of 1mol / L triphenylphosphine acetone solution was added at the same time; 0.4MPa nitrogen was replaced 3 times, and 2MPa H2 was replaced 2 times. The temperature was raised to 70℃, the hydrogen pressure was 16MPa, and the stirring rate was 380r / min, and the reaction was carried out for 2h. The catalyst recovery rate and hydrogenation degree are shown in Table 1.

[0128] Example 3

[0129] This embodiment prepares a magnetic catalyst, including the following process:

[0130] 1) Preparation of Fe3S4@PDA magnetic nanoparticles:

[0131] 1.2 g of Tris was weighed and added to 600 mL of deionized water to dissolve to prepare a buffer solution of pH = 8.25, and then 1 g of commercially available Fe3S4 with a particle size of 50 nm was added and dispersed evenly, and then 70 mL of a 15% aqueous dopamine hydrochloride solution was added dropwise within 10 minutes, and stirring was continued at 15°C for 8 hours to prepare Fe3S4 / PDA magnetic nanoparticles with a coating thickness of 10 nm. After completion, the particles were separated and recovered using a magnet, washed with deionized water and ethanol in turn, and freeze-dried; the particle size can be characterized by a laser particle size analyzer and a transmission electron microscope.

[0132] 2) Densification treatment:

[0133] The dried Fe3S4 / PDA magnetic nanoparticles were densified at 250°C for 3 hours under nitrogen protection.

[0134] 3) Loading active components:

[0135] Then weigh 1g of densely coated magnetic nanoparticles and disperse them again in 350mL of distilled water, then add 0.02g of palladium chloride (PdCl2·2H2O) and 1.24g of nickel chloride (NiCl2·2H2O). After stirring evenly, add the evenly mixed reactants into the reactor and stir at 25°C for 4 hours. After the mixture is separated and recovered with a magnet, washed, and freeze-dried, the Fe3S4@PDA@Pd+Ni magnetically supported catalyst is obtained.

[0136] 4) Hydrogenation reduction:

[0137] The obtained Fe3S4@PDA@Pd+Ni magnetically supported catalyst was reduced with hydrogen at 200°C for 6h. Finally, a supported Fe3S4@PDA@Pd+Ni catalyst with hydrogenation activity was obtained.

[0138] The catalyst has a particle size of 70 nm, contains 0.01 wt% Pd, 0.3% Ni, and has a specific surface area of ​​95 m 2 / g; bulk density is 0.6g / cm 3 .

[0139] 5) Evaluation of hydrogenation degree:

[0140] Weigh 1.0g of 3304 grade NBR, add it to 201g of acetone solution, stir thoroughly to completely dissolve the NBR, and then transfer the glue solution to a high-pressure reactor; add 1g of Fe3S4@PDA@Pd+Ni magnetic catalyst to the high-pressure reactor; replace it with 0.4MPa nitrogen 3 times and 2MPa H2 2 times. Heat to 90℃, hydrogen pressure of 12MPa, stirring rate of 389r / min, and react for 10h. Catalyst recovery rate and hydrogenation degree are shown in Table 1.

[0141] Example 4

[0142] This embodiment prepares a magnetic catalyst, the magnetic core is 1g of commercially available 500nm Fe3O4; due to the large particle size of the magnetic core, in order to obtain a suitable density, the magnetic core is coated and heat treated three times, and the final coating thickness is 50nm; the coating process is first coating 10nm and then heat treating at 250℃; then coating 20nm and heat treating at 270℃; finally coating 20nm and heat treating at 350℃, the purpose of this is to obtain a suitable density of the final catalyst. Specifically including the following processes:

[0143] 1) Primary coating and densification treatment:

[0144] 1.2 g of Tris was weighed and added to 600 mL of deionized water to dissolve to prepare a buffer solution with pH = 8.58.0, and then 1 g of commercially available magnetic core Fe3O4 with a particle size of 500 nm was added and dispersed evenly, and then 70 mL of a 15% dopamine hydrochloride aqueous solution was added dropwise within 10 minutes, and stirring was continued at 25° C. for 6 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 10 nm. After the separation and recovery by a magnet, the particles were washed with deionized water and ethanol in turn, and freeze-dried; the dried Fe3O4 / PDA magnetic nanoparticles were subjected to a densification treatment at 250° C. for 1 hour under nitrogen protection.

[0145] 2) Secondary coating and densification treatment:

[0146] The magnetic core treated in step 1) is coated with a 20 nm PDA layer again using the same method, and then subjected to a densification treatment at 270° C. for 2 hours.

[0147] 3) Three-time coating and densification treatment:

[0148] The magnetic core treated in step 2) is again coated with a 20 nm PDA layer using the same method, and then subjected to a densification treatment at 350° C. for 1 hour.

[0149] 4) Loading active components:

[0150] Weigh 1g of the magnetic nanoparticles densely coated three times above and disperse them again in 350mL of 25% ethanol aqueous solution, then add 0.39g of rhodium chloride (RhCl3·3H2O) and 0.64g of ruthenium chloride (RuCl3·3H2O). After stirring evenly, add the evenly mixed reactants into a reactor and stir at 25°C for 5 hours. After separation and recovery with a magnet, wash, and freeze-dry to obtain Fe3S4@PDA@Rh+Ru magnetically supported catalyst.

[0151] The catalyst has a particle size of 600 nm, contains 0.1 wt% Rh, 0.3 wt% Ru, and has a specific surface area of ​​45 m 2 / g; bulk density is 1.25g / cm 3 .

[0152] 5) Evaluation of hydrogenation degree:

[0153] 1.06g of 3604 grade NBR was added to 203g of acetone solution, stirred thoroughly and dissolved completely, then added to the autoclave together with 1.05g of Fe3O4@PDA@Rh+Ru, and 10mL of 1mol / L triphenylphosphine acetone solution was added at the same time; 0.4MPa nitrogen was replaced 3 times, and 2MPa H2 was replaced 2 times. The temperature was raised to 100℃, the hydrogen pressure was 2MPa, and the stirring rate was 401r / min, and the reaction was carried out for 8h. The catalyst recovery rate and hydrogenation degree are shown in Table 1.

[0154] Example 5

[0155] In this embodiment, a magnetic catalyst is prepared. The magnetic core is a commercially available 300nm Fe3O4. Due to the large particle size of the magnetic core, in order to obtain a suitable density, the magnetic core is coated with 20nm twice and heat-treated. The heat treatment temperatures are 220℃ and 380℃ respectively. The specific process includes the following:

[0156] 1) Primary coating and densification treatment:

[0157] 1.2 g of Tris was weighed and added to 600 mL of deionized water to dissolve to prepare a buffer solution of pH = 8.75, and then 1 g of commercially available magnetic core Fe3O4 with a particle size of 300 nm was added and dispersed evenly, and then 70 mL of a 15% dopamine hydrochloride aqueous solution was added dropwise within 10 minutes, and stirring was continued at 12° C. for 12 hours to prepare Fe3O4 / PDA magnetic nanoparticles with a coating thickness of 20 nm. After completion, the Fe3O4 / PDA magnetic nanoparticles were separated and recovered with a magnet, washed with deionized water and ethanol in turn, and freeze-dried; the dried Fe3O4 / PDA magnetic nanoparticles were subjected to a densification treatment at 220° C. for 2.5 hours under nitrogen protection.

[0158] 2) Secondary coating and densification treatment:

[0159] The magnetic core treated in step 1) is coated with a 20 nm PDA layer again using the same method, and then subjected to a densification treatment at 380° C. for 1 hour.

[0160] 3) Loading active components:

[0161] Weigh 1 g of the magnetic nanoparticles densely coated twice and disperse them again in 350 mL of distilled water, then add 0.11 g of palladium chloride (PdCl2·2H2O) and stir evenly. Then, add the mixed reactants into a reactor and stir at 25°C for 5 hours. After the mixture is stirred, separate and recover with a magnet, wash, and freeze-dry to obtain the Fe3O4@PDA@Pd magnetically supported catalyst.

[0162] 4) Hydrogenation reduction:

[0163] The obtained Fe3O4 / PDA / Pd magnetically supported catalyst was reduced with hydrogen at 370°C for 1.5h, and finally a supported Fe3O4@PDA@Pd catalyst with hydrogenation activity was obtained.

[0164] The catalyst has a particle size of 380 nm, contains 6 wt% Pd, and has a specific surface area of ​​66 m 2 / g; bulk density is 0.97g / cm 3 .

[0165] 5) Evaluation of hydrogenation degree:

[0166] Weigh 1.02g of 3304 grade NBR, add it to 201g of acetone solution, stir thoroughly to dissolve NBR completely, and then transfer the glue solution to a high-pressure reactor; add 1g of Fe3O4@PDA@Pd magnetic catalyst to the high-pressure reactor; replace it with 0.4MPa nitrogen 3 times and 2MPa H2 2 times. Heat to 85℃, hydrogen pressure of 6MPa, stirring rate of 503r / min, and react for 4h. Catalyst recovery rate and hydrogenation degree are shown in Table 1.

[0167] Example 6

[0168] This embodiment prepares a magnetic catalyst, including the following process:

[0169] 1) Preparation of FeNi@PDA magnetic nanoparticles:

[0170] 1.2 g of Tris was weighed and added to 600 mL of deionized water to dissolve to prepare a pH = 8.5 buffer solution, and then 1 g of commercially available FeNi with a particle size of 100 nm was added and dispersed evenly, and then 70 mL of a 15% dopamine hydrochloride aqueous solution was added dropwise within 10 minutes, and stirring was continued at 23° C. for 7 hours to prepare FeNi / PDA magnetic nanoparticles with a coating thickness of 10 nm. After completion, the particles were separated and recovered using a magnet, washed with deionized water and ethanol in turn, and freeze-dried; the particle size can be characterized by a laser particle size analyzer and a transmission electron microscope.

[0171] 2) Densification treatment:

[0172] The dried FeNi / PDA magnetic nanoparticles were densified at 500°C for 1 hour under nitrogen protection.

[0173] 3) Loading active components:

[0174] Then weigh 1g of densely coated magnetic nanoparticles and disperse them again in 350mL of distilled water, then add 0.02g of palladium chloride (PdCl2·2H2O) and 0.99g of ammonium molybdate (NH4)2MoO4. After stirring evenly, add the evenly mixed reactants into the reactor and stir at 20°C for 5.5 hours. After the reaction, separate and recover with a magnet, wash, and freeze-dry to obtain the Fe3O4@PDA@Pd+Mo magnetically supported catalyst.

[0175] 4) Hydrogenation reduction:

[0176] The obtained Fe3O4@PDA@Pd+Mo magnetic supported catalyst was reduced with hydrogen at 400°C for 1.5h. Finally, a supported Fe3O4@PDA@Pd+Mo catalyst with hydrogenation activity was obtained.

[0177] The catalyst has a particle size of 120 nm, contains 0.01 wt% Pd, 0.5 wt% Mo, and has a specific surface area of ​​91 m 2 / g; bulk density is 0.73g / cm 3 .

[0178] 5) Evaluation of hydrogenation degree:

[0179] Weigh 1.02g of 3304 grade NBR, add it to 201g of acetone solution, stir thoroughly to completely dissolve the NBR, and then transfer the glue solution to a high-pressure reactor; add 1.01g of FeNi@PDA@Pd+Mo magnetic catalyst to the high-pressure reactor; replace it with 0.4MPa nitrogen 3 times and 2MPa H2 2 times. Heat to 90℃, hydrogen pressure of 6MPa, stirring rate of 380r / min, and react for 10h. Catalyst recovery rate and hydrogenation degree are shown in Table 1.

[0180] Example 7

[0181] This embodiment prepares a magnetic catalyst, including the following process:

[0182] 1) Preparation of FeNi@PDA magnetic nanoparticles:

[0183] 1.2 g of Tris was weighed and added to 600 mL of deionized water to dissolve to prepare a pH = 8.5 buffer solution, and then 1 g of commercially available FeNi with a particle size of 200 nm was added and dispersed evenly, and then 70 mL of a 15% dopamine hydrochloride aqueous solution was added dropwise within 10 minutes, and stirring was continued at 35° C. for 4 hours to prepare FeNi / PDA magnetic nanoparticles with a coating thickness of 10 nm. After completion, the particles were separated and recovered using a magnet, washed with deionized water and ethanol in turn, and freeze-dried; the particle size can be characterized by a laser particle size analyzer and a transmission electron microscope.

[0184] 2) Densification treatment:

[0185] The dried FeNi / PDA magnetic nanoparticles were densified at 180°C for 4 hours under nitrogen protection.

[0186] 3) Loading active components:

[0187] Then, 1 g of densely coated magnetic nanoparticles was weighed and dispersed again in 350 mL of distilled water, and then 0.033 g of palladium chloride (PdCl2·2H2O) was added. After stirring evenly, the evenly mixed reactants were added to the reactor and stirred at 25°C for 4 hours. After the reaction, they were separated and recovered with a magnet, washed, and freeze-dried to obtain the FeNi@PDA@Pd magnetically supported catalyst.

[0188] 4) Hydrogenation reduction:

[0189] The obtained FeNi@PDA@Pd magnetically supported catalyst was reduced with hydrogen at 370°C for 2h. Finally, a supported FeNi@PDA@Pd catalyst with hydrogenation activity was obtained.

[0190] The catalyst has a particle size of 220 nm, contains 2.0 wt% Pd, and has a specific surface area of ​​67 m 2 / g; bulk density is 0.97g / cm 3 .

[0191] 5) Evaluation of hydrogenation degree:

[0192] Weigh 1g of 3304 grade NBR, add it to 200g of acetone solution, stir thoroughly and dissolve completely, then add 1g of FeNi@PDA@Pd into the autoclave; replace with 0.4MPa nitrogen 3 times and 2MPa H2 2 times. Heat to 80℃, hydrogen pressure of 2MPa, stirring rate of 380r / min, react for 2 hours. Catalyst recovery rate and hydrogenation degree are shown in Table 1.

[0193] Comparative Example 1

[0194] Use commercially available 200nm Fe3O4, then directly impregnate with 5wt% palladium acetate, and then carry out hydrogen reduction at 280℃. The Pd loading of the active component of the magnetic-supported catalyst obtained in this way is 3.1wt%, which is much higher than the Pd loading of 0.01wt% in Example 1. It is used to hydrogenate 3304NBR, and the hydrogenation effect is evaluated under the same hydrogenation conditions with the same amount of catalyst and glue added. The hydrogenation activity is acceptable and can reach 98.7%. However, further tests show that after the hydrogenation reaction, 49.9wt% Pd falls off from the surface of Fe3O4 and enters the glue, and it requires extremely complex separation steps to separate it. It shows that the method of directly impregnating Fe3O4 nanopowder will cause the active component to fall off during the hydrogenation process, causing pollution to the final HNBR product, while the magnetic-supported catalyst coated with the magnetic core surface provided by the present invention can solve this problem.

[0195] Comparative Example 2

[0196] This comparative example attempts to prepare Fe3O4@PDA@Pd type magnetic catalyst by the same method as the preparation steps of Example 1. The only difference is that the surface of this catalyst is not densified after Fe3O4 coating, and the active component Pd loading is as high as 3wt%. Although the loading of active components is high, the hydrogenation activity does not show good effect when 3304NBR is hydrogenated, only 88.3%, and 27.5% of the active components fall off into the glue. The analysis results show that some active components (about 68.1%) have entered the coating layer, and these active components are all blocked by the glue and cannot play their due role. Therefore, although the nominal loading is high, the hydrogenation effect is not good.

[0197] Comparative Example 3

[0198] This comparative example attempts to prepare Fe3O4@PDA@Pd type magnetic catalyst by the same method as the preparation steps of Example 1, but uses Fe3O4 magnetic cores with an average particle size of 20nm. For the 3304NBR high viscosity system, the hydrogenation activity is 99.5%, and the catalyst recovery rate after the single catalyst is used is only 80%. After several times of recovery, it only reaches 91%, because some magnetic cores are too small in particle size, and the viscosity of the glue is large and they are retained in the glue, which ultimately leads to a low catalyst recovery rate.

[0199] Table 1 Hydrogenation and magnetic separation results of examples and comparative examples

[0200]

[0201] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A magnetically supported catalyst, wherein: The magnetically supported catalyst comprises a magnetic core, a dense PDA coating layer coated on the magnetic core, and an active component supported on the dense PDA coating layer; The dense PDA coating layer is formed by coating with polydopamine and undergoing a densification treatment.

2. The magnetically supported catalyst according to claim 1, wherein: The densification treatment is a heat treatment at 180-500° C. in a protective gas atmosphere.

3. The magnetically supported catalyst according to claim 1, wherein: The particle size of the magnetic catalyst is 70nm to 600nm, and the specific surface area is 45m 2 / g~91m 2 / g, bulk density is 0.6g / cm 3 ~1.25g / cm 3 .

4. The magnetically supported catalyst according to claim 1, wherein: The loading amount of the active component accounts for 0.01 wt% to 6 wt% of the catalyst.

5. The magnetically supported catalyst according to claim 1, wherein: The active component is selected from at least one of Pd, Rh, Ru, Ni and Mo.

6. The magnetically supported catalyst according to claim 1, wherein: The magnetic core is selected from at least one of Fe3O4, Fe3S4 and FeNi.

7. The magnetically supported catalyst according to claim 1, wherein: The particle size of the magnetic core is 50nm to 500nm.

8. A method for preparing the magnetically supported catalyst according to any one of claims 1 to 7, wherein: The preparation method comprises the following steps: The polydopamine-coated magnetic core is coated with polydopamine by using the hydrolysis reaction of dopamine hydrochloride to obtain the polydopamine-coated magnetic microspheres; The magnetic microspheres coated with polydopamine are subjected to heat treatment at 180-500° C. for 1-4 hours in a protective gas atmosphere to form the dense PDA coating layer; when the catalyst particle size and density cannot meet the hydrogenation requirements, the coating is repeated multiple times to form multiple layers of the dense PDA coating layer; The active component is loaded to obtain the magnetically supported catalyst.

9. The preparation method according to claim 8, wherein: The coating process of the magnetic core includes: The magnetic core is added into the buffer solution, and then dopamine hydrochloride is added, and stirred at 12-35° C. for 4-12 hours. After the reaction is completed, the precipitate is separated and recovered by a magnet, washed and dried to obtain polydopamine-coated magnetic microspheres.

10. The preparation method according to claim 9, wherein: The buffer solution is a Tris buffer solution with a pH of 8-9.

11. The preparation method according to claim 8, wherein: The active component loading process includes: The magnetic core coated with a dense PDA coating layer is dispersed in a solvent, and a precursor of an active component is added to react. After the reaction is completed, a magnet is used to separate and recover the solid, and the solid powder obtained is washed and dried, and the magnetically supported catalyst is obtained.

12. The preparation method according to claim 11, wherein The precursor of the active component is selected from at least one of acetates, halides and ammonium salts of palladium, rhodium, ruthenium, nickel and molybdenum.

13. Use of the magnetically supported catalyst according to any one of claims 1 to 7 in the hydrogenation process of a polymer containing unsaturated olefin double bonds.

14. The use according to claim 13, wherein: The magnetically supported catalyst is used in hydrogenation of nitrile rubber.

15. The use according to claim 14, wherein: The weight ratio of the nitrile rubber to the magnetically supported catalyst is (1-2):

1.

16. The use according to claim 14, wherein: The hydrogenation is carried out in a stirred kettle or a slurry kettle; the hydrogenation temperature is 70-120° C., the hydrogen pressure is 2-16 MPa, and the reaction time is 2-10 hours.

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