Method for preparing 2, 6-dimethylaniline by depolymerizing and aminating polyphenyl ether

Abstract

The invention provides a method for preparing 2, 6-dimethylaniline by depolymerizing and aminating polyphenyl ether, which comprises the following steps: reacting polyphenyl ether, hydrogen and ammonia gas dispersed in an organic reaction medium under the action of a Pt-based catalyst at a first temperature for a first time to obtain 2, 6-dimethyl cyclohexylamine; adding a hydrogen trapping agent, and reacting at a second temperature for a second time under the action of a nitrogen atmosphere and a Pt-based catalyst to obtain 2, 6-dimethylaniline; wherein the Pt-based catalyst comprises a carrier and Pt loaded on the carrier, and the carrier is selected from at least one of metal oxide, SiO2 and activated carbon; and the particle size of Pt is 0.6 nm to 1.8 nm. The novel method for depolymerizing and aminating PPO into 2, 6-dimethylaniline through a two-step method not only provides a new thought for recovery and upgrading of PPO waste plastics, but also provides a new direction for synthesis of aromatic amines such as 2, 6-dimethylaniline with high added value.

Description

Technical Field

[0001] The present application relates to the field of industrial synthesis technology, and in particular to a method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether. Background Art

[0002] As an important aromatic amine, 2,6-dimethylaniline is widely used in medicines, dyes, agricultural chemicals and other fields, with high added value. The increasing market size of 2,6-dimethylaniline in the world in recent years shows that it has broad application prospects.

[0003] The traditional synthesis method of 2,6-dimethylaniline mainly uses aromatic hydrocarbons as raw materials, which are further coupled / hydrogenated after halogenation / nitration. With the depletion of fossil fuels, the application of aromatic hydrocarbons such as benzene and toluene is gradually limited, and the pollution problem caused by the large amount of waste generated during the halogenation / nitration process is also not optimistic.

[0004] Therefore, a novel method for preparing 2,6-dimethylaniline is urgently needed. Summary of the invention

[0005] In view of this, the purpose of the present application is to provide a method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether.

[0006] Based on the above purpose, the present application provides a method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether, comprising: reacting polyphenylene ether, hydrogen and ammonia dispersed in an organic reaction medium under the action of a Pt-based catalyst at a first temperature for a first time to perform a first reaction to obtain 2,6-dimethylcyclohexylamine; the first reaction comprises a depolymerization reaction, a hydrogenation reaction and an amination reaction;

[0007] adding a hydrogen capture agent, reacting at a second temperature for a second time under the action of a nitrogen atmosphere and the Pt-based catalyst, and performing a second reaction to obtain 2,6-dimethylaniline; the second reaction includes an aromatization reaction;

[0008] The Pt-based catalyst comprises a carrier and Pt loaded on the carrier, and the carrier is selected from at least one of metal oxides, SiO2 and activated carbon; the particle size of Pt is 0.6nm-1.8nm.

[0009] The depolymerization of polyphenylene ether to prepare 2,6-dimethylaniline places extremely high demands on the dehydrogenation activity of the active center of the catalyst. On the one hand, it needs to have high dehydrogenation activity and high selectivity for the dehydrogenation of alcohol and the dehydrogenation of the αC-H bond connected to the alcohol, and low selectivity for the ortho-carbon of the α-C connected to the alcohol to avoid the dehydrogenation of the ortho-carbon to control the dehydrogenation rate in the first reaction. On the other hand, the active center of the catalyst also needs to have high selectivity for the dehydrogenation of the NH bond and the dehydrogenation of the αC-H bond in 2,6-dimethylcyclohexylamine, and low selectivity for the ortho-carbon of the α-C connected to N to avoid the dehydrogenation of the ortho-carbon as much as possible to dehydrogenate to generate imines, which is convenient for the subsequent aromatization to form 2,6-dimethylaniline.

[0010] The Pt-based catalyst in the method for preparing 2,6-dimethylaniline by depolymerization and amination of polyphenylene ether provided in the present application has a metal site and a metal-support interface as its active center. The reaction principle is that in the first reaction, hydrogen is activated and dissociated at the metal Pt site to produce active hydrogen species to reduce and depolymerize PPO to 2,6-dimethylphenol. Then, the benzene ring in 2,6-dimethylphenol is adsorbed on the metal site, and the process of hydrogenation to 2,6-dimethylcyclohexanol is completed under the condition of the participation of active hydrogen species. The process of amination of 2,6-dimethylcyclohexanol to 2,6-dimethylcyclohexylamine follows the general mechanism of hydrogen amination, first activating the OH bond and αC-H bond in 2,6-dimethylcyclohexanol, dehydrogenating to 2,6-dimethylcyclohexanone, and then condensing with NH3 to imine and further hydrogenating to 2,6-dimethylcyclohexylamine. The dehydrogenation process takes place at the metal-support interface, the hydroxyl hydrogen in 2,6-dimethylcyclohexanol dissociates as a hydrogen proton at the carrier acid-base site, and the activation and dissociation of αC-H takes place at the metal site. In the second reaction, the NH bond and αC-H bond in 2,6-dimethylcyclohexylamine are first activated. Specifically, the activation of the NH bond and αC-H bond also takes place at the metal-support interface, that is, the hydrogen in the NH bond of 2,6-dimethylcyclohexylamine dissociates as a hydrogen proton at the carrier acid-base site, and the activation and dissociation of αC-H takes place at the metal site.

[0011] In the method for preparing 2,6-dimethylaniline by depolymerizing PPO in the embodiment of the present application, the whole process is carried out in two steps. PPO is first reduced and depolymerized to 2,6-dimethylaniline under a hydrogen atmosphere, and then further aminated to 2,6-dimethylcyclohexylamine with NH3 as an amine source after hydrogenation to 2,6-dimethylcyclohexylamine; then, under the same catalyst and reaction phase conditions, the process of dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline is completed in a nitrogen atmosphere in the presence of a hydrogen capture agent, and finally PPO is depolymerized and aminated to high value-added 2,6-dimethylaniline. Therefore, the present application provides a new method for depolymerizing PPO and aminated to 2,6-dimethylaniline in a two-step method, which not only provides new ideas for the recycling and upgrading of PPO waste plastics, but also provides a new direction for the synthesis of aromatic amines such as high value-added 2,6-dimethylaniline. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the present application or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0013] Figure 1 A schematic diagram of a method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to an embodiment of the present application;

[0014] Figure 2 This is a STEM electron microscope spectrum of an exemplary Pt-based catalyst Pt / CeO2 of an embodiment of the present application; wherein, part a and part b are distribution diagrams of the Pt-based catalyst Pt / CeO2, and part c is a distribution diagram of the Pt particle size in the Pt-based catalyst Pt / CeO2;

[0015] Figure 3 The following are the hydrogen and carbon nuclear magnetic resonance spectra of the exemplary 2,6-dimethylaniline of the embodiments of the present application. DETAILED DESCRIPTION

[0016] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0017] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should have the usual meanings understood by people with ordinary skills in the field to which the present application belongs. The words "include" or "comprise" and the like used in the embodiments of the present application mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects.

[0018] As a common type of engineering plastic, PPO is widely used in automotive parts, dashboards, wheel trims and other fields. The annual increase in its market size means that the amount of waste PPO plastics to be processed is gradually increasing, but traditional recycling methods are relatively limited. Therefore, chemical recycling of PPO and further upgrading it to high-value-added fine chemicals provide a new idea for the recycling of PPO. At present, the chemical recycling of PPO mainly focuses on the reduction depolymerization of PPO into phenols or aromatics and its oxidation depolymerization into benzoquinone.

[0019] The unique O-bridged dimethyl aromatic ring structure in the PPO plastic structure can be used to convert PPO to 2,6-dimethylaniline by amination of the hydroxyl group after reduction and depolymerization to phenolic monomers, completing the recycling of waste plastics while providing a new direction for the synthesis of high-value-added 2,6-dimethylaniline. Therefore, it is urgent to develop a new path to complete the catalytic conversion of PPO to high-value-added 2,6-dimethylaniline.

[0020] To solve the above problems, the embodiment of the present application provides a method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether, using waste plastic PPO as raw material, depolymerizing and aminating polyphenylene ether plastic, and preparing 2,6-dimethylaniline by a two-step method. In the first step (e.g., S1), hydrogen is used as a hydrogen source and ammonia is used as an amine source. PPO is reduced and depolymerized to 2,6-dimethylphenol in an organic reaction medium on a Pt-based catalyst, and then hydrogenated to 2,6-dimethylcyclohexanol, and then further aminated to obtain 2,6-dimethylcyclohexylamine; in the second step (e.g., S2), under the same catalyst and reaction medium, the obtained 2,6-dimethylcyclohexylamine is further dehydrogenated and aromatized in a nitrogen atmosphere in the presence of a hydrogen capture agent to obtain the target product 2,6-dimethylaniline. The method of the embodiment of the present application uses waste plastic PPO as a raw material to prepare 2,6-dimethylaniline, and can obtain 2,6-dimethylaniline with a yield of more than 30%. Compared with the traditional synthesis of 2,6-dimethylaniline, it not only gets rid of the excessive dependence of traditional synthesis methods on non-renewable fossil energy such as aromatic hydrocarbons as raw materials, but also provides a new idea for the synthesis of aromatic amines such as 2,6-dimethylaniline, and also provides a new direction for the recycling and upgrading of waste plastic PPO. 2,6-dimethylaniline, the product obtained by recycling waste plastic PPO, is a high-value-added aromatic amine, which is widely used in the production of drugs, dyes and agricultural chemicals and has a high market demand.

[0021] like Figure 1 As shown, the method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether provided in the embodiment of the present application may include:

[0022] In the first step S1, polyphenylene ether, hydrogen and ammonia dispersed in an organic reaction medium are reacted at a first temperature for a first time under the action of a Pt-based catalyst to perform a first reaction to obtain 2,6-dimethylcyclohexylamine; the first reaction includes a depolymerization reaction, a hydrogenation reaction and an amination reaction;

[0023] The second step S2, adding a hydrogen capture agent, reacting at a second temperature for a second time under the action of a nitrogen atmosphere and the Pt-based catalyst, and performing a second reaction to obtain 2,6-dimethylaniline; the second reaction includes an aromatization reaction;

[0024] The Pt-based catalyst comprises a carrier and Pt loaded on the carrier, and the carrier is selected from at least one of metal oxides, SiO2 and activated carbon; the particle size of Pt is 0.6nm-1.8nm.

[0025] The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether in an embodiment of the present application comprises the following steps: polyphenylene ether, hydrogen and ammonia dispersed in an organic reaction medium react at a first temperature for a first time under the action of a Pt-based catalyst to perform a first reaction to obtain 2,6-dimethylcyclohexylamine; the first reaction comprises a depolymerization reaction, a hydrogenation reaction and an amination reaction; a hydrogen capture agent is added, and the reaction is performed at a second temperature for a second time under the action of a nitrogen atmosphere and the Pt-based catalyst to perform a second reaction to obtain 2,6-dimethylaniline; the second reaction comprises an aromatization reaction; wherein the Pt-based catalyst comprises a carrier and Pt supported on the carrier, and the carrier is selected from at least one of metal oxides, SiO2 and activated carbon; the particle size of Pt is 0.6nm-1.8nm, which can inhibit the side reaction from 2,6-dimethylcyclohexylamine to 1,3-dimethylcyclohexane to a certain extent, thereby improving the obtained conversion rate, and then 2,6-dimethylaniline can be obtained with a higher yield, thereby achieving efficient conversion of polyphenylene ether to 2,6-dimethylaniline.

[0026] Among them, in the first reaction, the depolymerization reaction mainly includes depolymerizing polyphenylene ether to 2,6-dimethylphenol. The hydrogenation reaction mainly includes hydrogenating 2,6-dimethylphenol to obtain 2,6-dimethylcyclohexanol. The amination reaction mainly includes aminating 2,6-dimethylcyclohexanol to 2,6-dimethylcyclohexylamine, following the general mechanism of hydrogen amination. In the amination reaction, the OH bond and αC-H bond in 2,6-dimethylcyclohexanol are first activated, dehydrogenated to 2,6-dimethylcyclohexanone, and then condensed with NH3 to imine, and further hydrogenated to 2,6-dimethylcyclohexylamine. The entire hydrogen amination process is controlled by the first step of alcohol dehydrogenation, which has high requirements for the active metal center of the catalyst, needs to have high dehydrogenation activity, and needs to have high selectivity for alcohol dehydrogenation and dehydrogenation of αC-H bonds connected to alcohol, and has low selectivity for the ortho-carbon of αC connected to alcohol, avoiding ortho-carbon dehydrogenation.

[0027] In some embodiments, the organic reaction medium can be selected from at least one of cyclohexane, methylcyclohexane, toluene and n-octane. Further, the organic reaction medium can be selected from at least one of cyclohexane and methylcyclohexane.

[0028] In some embodiments, in the first reaction, the polyphenylene ether may be in powder form, such as waste polyphenylene ether plastic that has been crushed.

[0029] In some of the embodiments, the Pt-based catalyst may be a supported Pt-based catalyst, including at least one of a metal oxide-supported platinum-based catalyst, an activated carbon-supported platinum-based catalyst, and a silica-supported platinum-based catalyst. Wherein, the metal oxide may include at least one of a IIIA group metal oxide, a IIA group metal oxide, an IVB group metal oxide, a lanthanide metal oxide, and a VIB group metal oxide. The precursor of the platinum Pt supported on the carrier may include at least one of an aqueous solution of platinum and an alcohol solution of platinum. Wherein, the aqueous solution of platinum may include at least one of an aqueous solution of platinum nitrate and an aqueous solution of chloroplatinic acid. The alcohol solution of platinum includes at least one of a methanol solution of platinum nitrate and a methanol solution of chloroplatinic acid.

[0030] In some embodiments, the carrier may be selected from at least one of aluminum oxide Al2O3 and cerium oxide CeO2. The precursor of platinum Pt supported on the carrier may be an aqueous solution of platinum, including at least one of an aqueous solution of platinum nitrate and an aqueous solution of chloroplatinic acid.

[0031] In some embodiments, the catalyst may be Pt / CeO2, and the carrier may be cerium oxide CeO2. The precursor of the platinum Pt supported on the carrier may be an aqueous solution of platinum nitrate. Figure 2It can be seen that the Pt-based catalyst Pt / CeO2 used in the embodiment of the present application, the presence characteristics of Pt in the platinum-based catalyst obtained through the image show that the Pt species is highly dispersed on the surface of the catalyst, Pt exists in the form of particles, and the Pt particle size is between 0.6nm-1.8nm (that is, about 1nm), and is evenly dispersed.

[0032] In some embodiments, the mass ratio of the polyphenylene ether to the catalyst can be 1:(0.5-3); the mass ratio of the polyphenylene ether to the organic reaction medium is 1:(1-50); the pressure of the hydrogen is 1MPa-3MPa; the pressure of the ammonia is 0.2MPa-0.6MPa; the first temperature is 210℃-250℃; the first time is 4h-12h, for example, 8h, 10h or 12h. Wherein, the hydrogen pressure is the hydrogen pressure required for the reduction and depolymerization of PPO into monomers in the first step. Wherein, the ammonia pressure can be the pressure after the liquid ammonia is gasified. The pressure after the liquid ammonia is gasified refers to the ammonia pressure required for the amination of 2,6-dimethylcyclohexanol to 2,6-dimethylcyclohexylamine after the reduction and depolymerization of PPO to 2,6-dimethylphenol and further hydrogenation to 2,6-dimethylcyclohexanol. The first temperature can be the reaction temperature required for the reduction and depolymerization of PPO and further amination to 2,6-dimethylcyclohexylamine. The first period of time may be the reaction time required for the reduction depolymerization of PPO and the further amination to 2,6-dimethylcyclohexylamine.

[0033] In some embodiments, the mass ratio of the polyphenylene ether to the catalyst may be 1:(1-2), for example, 1:1, 1:1.5, or 1:2.

[0034] In some embodiments, the mass ratio of the polyphenylene ether to the organic reaction medium is 1:(5-30), for example, 1:10, 1:20, or 1:30.

[0035] In some embodiments, the pressure of the hydrogen may be 1MPa-2MPa, for example, 1MPa, 1.5MPa, 2MPa. The Pt-based catalyst of the present application has good activity in reducing and depolymerizing PPO, and can more efficiently complete the process of reducing and depolymerizing PPO into monomers under this hydrogen pressure.

[0036] In some embodiments, the pressure of the ammonia gas may be 0.4 MPa-0.6 MPa, for example, 0.4 MPa, 0.5 MPa or 0.6 MPa.

[0037] In some embodiments, the first temperature may be 200° C.-230° C., for example, 200° C., 210° C., 220° C. or 230° C. The first duration may be 4 h-8 h, for example, 4 h, 8 h, etc.

[0038] In some embodiments, the preparation method of the Pt-based catalyst can be selected from an equal volume impregnation method, an excess impregnation method or a deposition precipitation method. Among them, the equal volume impregnation method may include impregnating a platinum precursor onto a corresponding carrier, further calcining after drying, and then reducing at high temperature to obtain a corresponding Pt-based catalyst. The excess impregnation method may include impregnating a platinum precursor onto a corresponding carrier, stirring overnight at room temperature, then filtering, washing with deionized water, drying the resulting solid in an oven at 100°C overnight, calcining at 500°C in a muffle furnace, and then reducing in a mixture of hydrogen and argon. The deposition precipitation method may include impregnating a platinum precursor onto a corresponding carrier, stirring at room temperature, and then dropping a sodium hydroxide solution to PH = 10, stirring at room temperature overnight, filtering the resulting solid, washing with deionized water, drying overnight in an oven at 100°C, calcining at 500°C in a muffle furnace, and then reducing in a mixture of hydrogen and argon. Among them, the metal oxide type carrier can be prepared by high temperature thermal decomposition or hydrothermal method. The carrier can be selected from cerium oxide, which can be prepared by heating and decomposing hexahydrated cerium nitrate; the temperature of the heating and decomposition can be 300°C to 700°C, and can be preferably 400°C to 500°C. The loading amount of platinum in the platinum catalyst = (the mass of platinum in the platinum precursor) / (the mass of platinum in the platinum precursor + the mass of the carrier) × 100%. The loading amount of Pt in the catalyst can be 1.0%wt-2.0%wt, for example, 1.5wt%.

[0039] In some embodiments, the preparation method of the Pt-based catalyst may be an isovolumetric impregnation method. The preparation method may specifically include:

[0040] A carrier is provided; the water absorption rate of the carrier is 50% to 765%. The type of the carrier can be as described above, which will not be repeated here.

[0041] A precursor solution is provided; the concentration of the precursor solution may be 0.024 g / ml to 0.050 g / ml, and the volume may be 298 μL to 634 μL. The type of the precursor solution may be as described above, and will not be described in detail here.

[0042] pouring the carrier into the precursor solution, drying and calcining;

[0043] The calcined product is reduced in a reducing gas.

[0044] In some of the embodiments, the carrier can be selected from cerium oxide, and the cerium oxide can be prepared by high-temperature thermal decomposition of cerium nitrate hexahydrate; the temperature of the thermal decomposition is 300°C to 700°C, preferably 400°C-500°C.

[0045] In some embodiments, the calcination temperature may be 300° C. to 700° C. Preferably, the calcination temperature may be 400° C. to 500° C., for example, 400° C., 450° C. or 500° C., not specifically limited, preferably at least one of 400° C. or 500° C.

[0046] In some embodiments, the reducing gas may be a mixture of hydrogen and argon; the volume fraction of hydrogen in the reducing gas is 5%-20%. Preferably, the volume fraction of hydrogen in the reducing gas may be 10-20%, for example, 10%, 15%, 20%, not specifically limited, preferably at least one of 10% and 15%, and may be 10%-15%.

[0047] In some embodiments, the flow rate of the reducing gas can be 50-100 ml / min. -1 , preferably 60-80ml / min -1 , for example, 60 ml / min -1 、70ml / min -1 、80ml / min -1 , not limited to specific, preferably 70ml / min -1 、80ml / min -1 At least one of the above can be 70ml / min to 80ml / min.

[0048] In some embodiments, the reduction temperature may be 200°C-500°C, preferably 300°C-400°C. More preferably, it is 350-400°C; for example, it may be 350°C, 380°C, 400°C, and there is no specific limitation. The reduction temperature refers to the temperature when the Pt-based catalyst is reduced by a reducing gas.

[0049] In some embodiments, the reduction time may be 1 h-10 h, preferably 1 h-6 h, and more preferably 2 h-4 h. The reduction time is more preferably 2 h-3 h, for example, 2 h, 2.5 h, 3 h, etc., and is not specifically limited. The reduction time is the time for reduction using a Pt-based catalyst.

[0050] In some of the embodiments, in the first reaction, during the depolymerization and amination of PPO to 2,6-dimethylcyclohexylamine, the main side reaction is the hydrogenolysis of the CN bond in 2,6-dimethylcyclohexylamine, and the hydrogenolysis product 1,3-dimethylcyclohexane is the main byproduct. By optimizing the Pt-based catalyst, carrier and preparation method, as well as the main reaction parameters such as reaction time and reaction temperature, the formation of the byproduct 1,3-dimethylcyclohexane can be suppressed to a great extent, so as to obtain 2,6-dimethylcyclohexylamine with the highest possible yield.

[0051] Among them, in the second reaction, the aromatization reaction can include the activation of the NH bond and the αC-H bond in 2,6-dimethylcyclohexylamine, dehydrogenation to imine, and then further aromatization to obtain aromatic amine (ie, 2,6-dimethylaniline).

[0052] In some embodiments, the second reaction temperature may be 180°C-220°C; the second time period may be 4h-12h; and the nitrogen pressure may be 0.1-2MPa.

[0053] In some embodiments, the second reaction temperature is 180°C-200°C; the second time is 8h-12h; and the nitrogen pressure is 0.1MPa-0.5MPa.

[0054] The process for preparing aniline in a batch reactor using cyclohexanol compounds as reaction substrates provided in the present application can be: preparing a prescribed amount of cyclohexanol compounds, a platinum-based catalyst and an organic reaction medium, adding the cyclohexanol compounds, the platinum-based catalyst and the reaction phase into a batch reactor, and reacting for 10-16 hours under the conditions of an ammonia partial pressure of 0.4-0.6 MPa and a reaction temperature of 180-200°C.

[0055] The present application also provides a method for determining the conversion rate and yield of aniline during synthesis. The method can be: qualitative analysis of the reaction product by gas chromatography-mass spectrometry (GC-MS Agilent 7890A-5975C) and quantitative analysis by gas chromatography (GC Agilent 7890A), using an HP-5 chromatographic column, and the programmed temperature conditions of the chromatographic column are: maintaining 50°C for 10 mins, and heating at 10°C / min. -1 The temperature was raised to 250°C at a rate of 1000 ℃ and maintained at 250°C for 5 mins.

[0056] Pt-based catalysts can be prepared by methods such as equal volume impregnation, excess impregnation and precipitation deposition.

[0057] In some embodiments, the Pt-based catalyst can be prepared by isovolumetric impregnation, that is, the platinum precursor is impregnated onto the corresponding carrier, dried and further calcined, and then reduced at high temperature to obtain the corresponding platinum-based catalyst. Specifically, the preparation method of the Pt-based catalyst includes:

[0058] Providing the carrier; the water absorption rate of the carrier is 50% to 765%;

[0059] Providing a precursor solution; the concentration of the precursor solution is 0.022 g / ml to 0.050 g / ml, and the volume is 298 μL to 682 μL;

[0060] pouring the carrier into the precursor solution, drying and calcining;

[0061] The calcined product is reduced in a reducing gas.

[0062] The precursor of platinum in the Pt-based catalyst may include an aqueous solution of platinum or an alcohol solution of platinum. Among them, the aqueous solution of platinum may include at least one of an aqueous solution of platinum nitrate and an aqueous solution of chloroplatinic acid. The alcohol solution of platinum includes at least one of a methanol solution of platinum nitrate, a methanol solution of chloroplatinic acid and a n-butanol solution of platinum nitrate. In some embodiments, the precursor of platinum may include at least one of an aqueous solution of platinum nitrate, a methanol solution of platinum nitrate, an aqueous solution of chloroplatinic acid, a methanol solution of chloroplatinic acid and a n-butanol solution of platinum nitrate. The metal oxide type carrier can be prepared by high temperature thermal decomposition.

[0063] The concentration of the precursor solution can be adjusted according to the different saturated water absorption rates of different carriers, and the corresponding platinum precursor can be prepared into a solution of corresponding concentration. The loading amount of Pt in the Pt-based catalyst is 1.5wt%, and the corresponding volume of the precursor solution with the corresponding concentration can be taken according to the loading amount.

[0064] After the carrier is poured into the precursor solution, it can be stirred continuously and then ultrasonicated for 10-20 minutes to make Pt uniformly dispersed in the carrier. Drying can be carried out by drying in an oven at 100°C overnight. Calcination can be carried out by grinding the dried product and then calcining it at high temperature in a muffle furnace.

[0065] The calcination temperature may be 300°C-550°C, preferably 400°C-500°C. More preferably 450°C-500°C, for example 450°C, 480°C or 500°C, not specifically limited, preferably at least one of 450°C and 500°C. The calcination time is 3-12h, for example 5h, 6h, 7h, 8h, 10h, not specifically limited, preferably 5h-10h, for example at least one of 5h, 8h, 10h. More preferably 5h-8h.

[0066] The volume fraction of hydrogen in the reducing gas may be 5%-30%, preferably 10%-20%.

[0067] In the present application, reducing gas refers to a gas used to reduce a platinum-based catalyst. The reducing gas may be a mixture of hydrogen and argon. The volume fraction of hydrogen refers to the volume percentage of hydrogen in the mixture. The volume percentage may be 5-30%, preferably 10-20%, for example, 10%, 15%, 20%, etc., without specific limitation.

[0068] In some embodiments, the flow rate of the reducing gas may be 10-150 ml / min. -1 , preferably 20-80ml / min-1 ; For example, it can be 20ml / min -1 、30ml / min -1 、40ml / min -1 、60ml / min -1 、80ml / min -1 More preferably, the flow rate of the reducing gas is 30 ml / min to 80 ml / min.

[0069] Preferably, the reduction temperature may be 200-500°C, preferably 300-400°C, more preferably 350-400°C.

[0070] In the present application, the reduction temperature refers to the temperature when the platinum-based catalyst is reduced by a reducing gas, which can be 200-400°C, preferably 300°C to 400°C, and more preferably 350-400°C. For example, it can be 350°C, 370°C, 390°C or 400°C, etc., without specific limitation.

[0071] Preferably, the reduction time may be 1-5 h, preferably 3-4 h.

[0072] In the present application, the reduction time refers to the time for reducing the platinum-based catalyst, which may be 1-5 hours, preferably 3-4 hours, for example, 3 hours, 3.5 hours, 4 hours, etc., without specific limitation.

[0073] In the method for preparing 2,6-dimethylaniline by depolymerizing PPO in the embodiment of the present application, the whole process is carried out in two steps. PPO is first reduced and depolymerized to 2,6-dimethylaniline under a hydrogen atmosphere, and then further aminated to 2,6-dimethylcyclohexylamine with NH3 as an amine source after hydrogenation to 2,6-dimethylcyclohexylamine; then, under the same catalyst and reaction phase conditions, the process of dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline is completed in a nitrogen atmosphere in the presence of a hydrogen capture agent, and finally PPO is depolymerized and aminated to high value-added 2,6-dimethylaniline. Therefore, the present application provides a new method for depolymerizing PPO and aminated to 2,6-dimethylaniline in a two-step method, which not only provides new ideas for the recycling and upgrading of PPO waste plastics, but also provides a new direction for the synthesis of aromatic amines such as high value-added 2,6-dimethylaniline.

[0074] The technical solution of the present application is further explained below in conjunction with specific implementation methods.

[0075] The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0076] Unless otherwise specified, the test materials used in the following examples were purchased from conventional biochemical reagent stores.

[0077] For the first reaction, that is, in Examples 1 to 46, PPO is used as a reaction substrate, an intermittent reactor is used, hydrogen is used as a hydrogen source, and ammonia is used as an amine source. PPO is depolymerized in an organic phase on a Pt-based catalyst and aminated to 2,6-dimethylcyclohexylamine. The specific process is as follows: 0.1 g of PPO, 0.2 g of a catalyst, and 5 ml of a reaction medium are added to a 50 ml high pressure reactor, the hydrogen pressure is 0.5-3 MPa, the pressure of liquid ammonia after gasification is 0.1-1 MPa, the reaction temperature is 180-250°C, and the reaction time is 4-12 h. After the reaction is completed, the reaction product is subjected to qualitative analysis by gas chromatography-mass spectrometry (GC-MS Agilent 7890A-5975C) and quantitative analysis by gas chromatography (GC Agilent 7890A), using an HP-5 chromatographic column, and the program temperature conditions of the chromatographic column are: 50°C for 10 minutes, at 10°C / min -1 The temperature was raised to 270°C at a rate of 100°C and maintained at 270°C for 5 minutes. The molar yield of 2,6-dimethylcyclohexylamine and 1,3-dimethylcyclohexane were calculated based on the measured molar yields of 2,6-dimethylcyclohexylamine and 1,3-dimethylcyclohexane and the molar amount of the reaction substrate.

[0078] Among them, in Examples 1-4, Pt-based catalysts are prepared by an equal volume impregnation method, and the specific process may include: the theoretical loading amount of Pt is 1.5wt%, and a Pt precursor solution of corresponding concentration is prepared according to the water absorption of the carrier, the carrier is poured into the precursor solution, and stirred continuously, and then ultrasonicated for 10-20min (wherein each embodiment corresponds to a specific time), and then dried in an oven at 100°C overnight, ground and pulverized, and then calcined at high temperature in a muffle furnace, the calcination temperature is 300-600°C (wherein each embodiment corresponds to a specific calcination temperature), and then reduced in a mixture of hydrogen and argon, the volume fraction of the reducing gas is 5%-30% (wherein each embodiment corresponds to a specific volume fraction), and the gas flow rate is 50-100ml / min -1 (wherein each embodiment corresponds to a specific gas flow rate), and the reduction temperature is 200-500° C. (wherein each embodiment corresponds to a specific reduction temperature).

[0079] Example 1-Example 4 Screening of platinum precursors for Pt-based catalysts

[0080] Method: Example 1-Example 4 respectively adopts the equal volume impregnation method to prepare Pt-based catalysts, and the cerium oxide obtained by thermal decomposition of hexahydrate cerium nitrate at 500°C is used as the carrier. The catalyst preparation process is as follows: the concentration of platinum in the aqueous solution of platinum nitrate and chloroplatinic acid is 0.031g / ml, take 484 microliters of the aqueous solution, add 1g of cerium oxide, and stir continuously; the concentration of platinum in the methanol solution of platinum nitrate and chloroplatinic acid is 0.030g / ml, take 501 microliters of methanol solution, add 1g of cerium oxide, stir continuously, then ultrasonicate for 10-20min, dry in an oven at 100°C overnight, grind and crush, and calcine at high temperature in a muffle furnace, the calcination temperature is 500°C, the volume fraction of reducing gas is 10%, and the reducing gas flow rate is 70ml / min -1 , the reduction temperature is 400°C, and the reduction time is 2h. The main difference between Examples 1 to 4 is that the platinum precursors of the Pt-based catalysts are different.

[0081] In Examples 1 to 4, the Pt-based catalyst prepared by the equal volume impregnation method is used to complete the depolymerization of PPO in S1 and the amination to 2,6-dimethylcyclohexylamine. The reaction conditions are as follows: the reaction is carried out in a batch reactor, the mass of PPO is 0.1 g, the catalyst is 0.2 g, 5 ml of methylcyclohexane is used as the reaction medium, the hydrogen pressure is 2 MPa, the pressure of liquid ammonia after gasification is 0.4 MPa, the reaction temperature is 230°C, the reaction time is 8 h, and the yield of the target product 2,6-dimethylcyclohexylamine and the main by-product 1,3-dimethylcyclohexane in each example is determined after the reaction is completed.

[0082] Results: The test results are shown in Table 1.

[0083] Table 1 Product molar yields of Pt-based catalysts prepared from different Pt precursors

[0084]

[0085] Result analysis: The results in Table 1 show that the type of Pt precursor has a significant effect on the depolymerization of PPO and the amination to 2,6-dimethylcyclohexylamine. Among them, when platinum nitrate aqueous solution is used as the precursor, its catalytic activity is the best and the yield of the obtained product 2,6-dimethylcyclohexylamine is the highest.

[0086] Example 5-Example 7 Screening of Preparation Methods for Pt-Based Catalysts

[0087] Method: In Examples 5 to 7, platinum nitrate aqueous solution was used as a precursor, cerium oxide obtained by thermally decomposing cerium nitrate hexahydrate at 500°C was used as a carrier, the volume fraction of the reducing gas was 10%, and the reducing gas flow rate was 70 ml / min. -1, the reduction temperature is 400°C, the reduction time is 2h, and the main difference between Examples 5 to 7 is the different preparation methods of the Pt-based catalysts. In the process of completing the depolymerization of PPO in S1 and amination to 2,6-dimethylcyclohexylamine, the reaction conditions of the Pt-based catalysts prepared by different preparation methods in Examples 5 to 7 are the same as those of Examples 1 to 4.

[0088] Specifically, the preparation process of the equal volume impregnation method is the same as that of Examples 1-4.

[0089] Specifically, the excess impregnation method includes: the concentration of platinum in the platinum nitrate aqueous solution is 0.007 g / ml, taking 2149 microliters of the platinum nitrate aqueous solution, adding 1 g of cerium oxide, stirring at room temperature overnight, then filtering, washing with deionized water, and drying the resulting solid in an oven at 100°C overnight, calcining in a muffle furnace at 500°C, and then reducing in a mixture of hydrogen and argon.

[0090] Specifically, the deposition precipitation method includes: the concentration of platinum in the platinum nitrate aqueous solution is 0.006g / ml, taking 2511 microliters of the platinum nitrate aqueous solution, adding 1g of cerium oxide, stirring at room temperature for 2h, and then adding 0.2mol / L sodium hydroxide solution to pH=10. After the addition is completed, continue to stir at room temperature overnight, filter the obtained solid, wash with deionized water, dry it in an oven at 100°C overnight, calcine it in a muffle furnace at 500°C, and then reduce it in a mixture of hydrogen and argon.

[0091] Results: The test results are shown in Table 2. Among them, Pt / CeO2-1 is a Pt-based catalyst prepared by equal volume impregnation method. Pt / CeO2-2 is a Pt-based catalyst prepared by excess impregnation method. Pt / CeO2-3 is a Pt-based catalyst prepared by deposition precipitation method.

[0092] Table 2 Product molar yields of Pt-based catalysts obtained by different preparation methods of Pt-based catalysts

[0093]

[0094] Results analysis: As shown in Table 2, the performance of Pt-based catalysts prepared by different preparation methods in the process of PPO depolymerization and amination to 2,6-dimethylcyclohexylamine is quite different. Among them, the Pt-based catalyst prepared by the equal volume impregnation method has the best performance and the yield of the obtained product 2,6-dimethylcyclohexylamine is the highest.

[0095] Example 8-Example 11 Screening of carriers for Pt-based catalysts

[0096] Method: Pt-based catalyst was prepared by equal volume impregnation method, platinum nitrate aqueous solution was used as precursor, 1g carrier, according to the difference of water absorption of different carriers, corresponding concentration of platinum nitrate precursor aqueous solution was taken, stirred continuously after impregnation, then ultrasonicated for 10-20min, dried in an oven at 100℃ overnight, ground and calcined at high temperature in a muffle furnace, calcined at 500℃, the volume fraction of reducing gas was 10%, and the reducing gas flow rate was 70ml / min -1 , the reduction temperature is 400℃ and the reduction time is 2h.

[0097] The main difference between the embodiments in Example 8 to Example 11 lies in the different types of carriers. The concentrations and volumes of platinum nitrate aqueous solutions corresponding to different carriers are as follows: cerium oxide (0.031 g / ml, 484 μL); aluminum oxide (0.024 g / ml, 634 μL); activated carbon (0.050 g / ml, 298 μL); silicon dioxide (0.037 g / ml, 406 μL).

[0098] In Examples 8 to 11, platinum nitrate aqueous solution was used as a precursor, and the Pt-based catalysts loaded on different carriers prepared by the equal volume impregnation method completed the depolymerization of PPO in S1 and amination to 2,6-dimethylcyclohexylamine. The reaction conditions were the same as those in Examples 1 to 4.

[0099] Results: The test results are shown in Table 3.

[0100] Table 3 Product molar yields of Pt-based catalysts prepared with different supports

[0101]

[0102] Results analysis: As shown in Table 3, the Pt-based catalysts prepared with different supports have great differences in the performance of PPO depolymerization and amination to 2,6-dimethylcyclohexylamine. In general, the Pt-based catalyst supported by cerium oxide has the best performance and the yield of the obtained product 2,6-dimethylcyclohexylamine is the highest.

[0103] Example 12-Example 16 Screening of Preparation Methods for Cerium Oxide Supports for Pt-Based Catalysts

[0104] Method: Example 12-Example 16 uses platinum nitrate aqueous solution as a precursor and cerium oxide as a carrier, and adopts an equal volume impregnation method to prepare a Pt-based catalyst. After impregnation, it is continuously stirred, then ultrasonicated for 10-20 minutes, dried in an oven at 100°C overnight, ground and calcined in a muffle furnace at a high temperature of 500°C, the volume fraction of the reducing gas is 10%, and the reducing gas flow rate is 70ml / min -1, the reduction temperature is 400°C, and the reduction time is 2 hours. The main difference between Examples 12 to 16 is the different preparation methods of the cerium oxide carrier.

[0105] Among them, the high temperature thermal decomposition method (C) comprises: roasting cerium nitrate hexahydrate in a muffle furnace at 500° C. for 5 hours at a heating rate of 5° C. / min to obtain cerium oxide.

[0106] The hydrothermal method for preparing cubic cerium oxide (HC) includes: dissolving 19 grams of flaky sodium hydroxide in 70 ml of ultrapure water for standby use, dissolving 1.732 g of hexahydrated cerium nitrate in 10 ml of ultrapure water, adding the cerium nitrate solution dropwise into the sodium hydroxide solution, stirring continuously during the process, stirring at room temperature for 30 minutes after the addition is completed, then pouring the liquid into the lining of the crystallization reactor, sealing, and hydrothermal treatment at 180°C for 24 hours. After the hydrothermal treatment is completed, the obtained solid is separated by suction filtration, washed with ultrapure water until pH=7, and the filter cake is dried in an oven at 100°C for 12 hours, and then calcined in a muffle furnace at 500°C for 3 hours to obtain rod-shaped cerium oxide.

[0107] The hydrothermal method for preparing rod-shaped cerium oxide (HR) includes: the preparation process of rod-shaped cerium oxide is similar to the preparation process of cubic cerium oxide, the main difference being that the hydrothermal conditions for preparing rod-shaped cerium oxide are 100°C / 24h.

[0108] Among them, the hydrothermal method for preparing octahedral cerium oxide (HO) includes: 0.008 grams of sodium phosphate dodecahydrate is dissolved in 70 ml of ultrapure water for standby use, and 0.858 g of cerium nitrate hexahydrate is dissolved in 10 ml of ultrapure water. The aqueous solution of cerium nitrate is added dropwise to the sodium phosphate solution, and the process is continuously stirred. After the addition is completed, stirring is continued at room temperature for 30 minutes, and then the liquid is poured into the lining of the crystallization reactor, sealed, and hydrothermal at 170°C for 24 hours. After the hydrothermal process is completed, the obtained solid is separated by suction filtration, washed with ultrapure water to PH = 7, and the filter cake is dried in a 100°C oven for 12 hours, and then calcined in a muffle furnace at 500°C for 3 hours to obtain octahedral cerium oxide.

[0109] Among them, the hydrothermal method for preparing polyhedral cerium oxide (HP) includes: 2.25 grams of sodium hydroxide is dissolved in 9.5 ml of ultrapure water for standby use, 1.24 grams of hexahydrated cerium nitrate is dissolved in 21.9 grams of water, and added dropwise to the sodium hydroxide solution, stirring continuously during the process, stirring for 30 minutes after the dropwise addition is completed, and then the liquid is poured into the lining of the crystallization reactor, sealed, and hydrothermal at 90°C for 24 hours. After the hydrothermal process is completed, the obtained solid is separated by suction filtration, washed with ultrapure water to PH = 7, the filter cake is dried in a 100°C oven for 12 hours, and then calcined at 400°C in a muffle furnace for 3 hours to obtain polyhedral cerium oxide.

[0110] In Examples 12 to 16, platinum nitrate aqueous solution was used as a precursor, and the Pt-based catalysts supported on different cerium oxide supports prepared by the equal volume impregnation method were used to complete the depolymerization of PPO in S1 and amination to 2,6-dimethylcyclohexylamine. The reaction conditions were the same as those in Examples 1 to 4.

[0111] Results: The results can be shown in Table 4. Wherein, CeO2-C represents cerium oxide obtained by high temperature thermal decomposition of hexahydrated cerium nitrate, and the calcination condition is calcination at 500°C for 5h. CeO2-HC represents cubic cerium oxide prepared by hydrothermal method. CeO2-HR represents rod-shaped cerium oxide prepared by hydrothermal method. CeO2-HO represents octahedral cerium oxide prepared by hydrothermal method. CeO2-HP represents polyhedral cerium oxide prepared by hydrothermal method.

[0112] Table 4 Product molar yield of Pt-based catalysts obtained by different preparation methods of cerium oxide supports

[0113]

[0114]

[0115] Results analysis: The results in Table 4 show that the cerium oxide supports prepared by different methods have great differences in their catalytic performance in PPO depolymerization and amination to 2,6-dimethylcyclohexylamine after loading Pt. According to the results, the cerium oxide obtained by high-temperature thermal decomposition of hexahydrated cerium nitrate has the best catalytic performance after loading Pt, and the yield of the obtained product 2,6-dimethylcyclohexylamine is the highest.

[0116] Example 17-Example 21 Screening of Calcination Temperature during Preparation of Pt-Based Catalysts

[0117] Method: Example 17-Example 21 uses platinum nitrate aqueous solution as a precursor, and high-temperature thermal decomposition of cerium nitrate hexahydrate to obtain cerium oxide as a carrier. The Pt-based catalyst is prepared by an equal volume impregnation method. After impregnation, it is continuously stirred, then ultrasonicated for 10-20 minutes, dried in an oven at 100°C overnight, ground and calcined at high temperature in a muffle furnace, the volume fraction of the reducing gas is 10%, and the reducing gas flow rate is 70ml / min -1 , the reduction temperature is 400°C, and the reduction time is 2h. The main difference between Examples 17 to 21 is the different calcination temperatures during the high-temperature calcination process after the catalyst is impregnated and dried.

[0118] In the process of completing the depolymerization of PPO and amination to 2,6-dimethylcyclohexylamine in S1, the reaction conditions of the Pt-based catalysts obtained at different calcination temperatures in Examples 17-21 are the same as those in Examples 1-4.

[0119] Results: The results are shown in Table 5. Among them, Pt / CeO2-300 represents a calcination temperature of 300°C during the high temperature calcination process. Pt / CeO2-400 represents a calcination temperature of 400°C during the high temperature calcination process. Pt / CeO2-500 represents a calcination temperature of 500°C during the high temperature calcination process. Pt / CeO2-600 represents a calcination temperature of 600°C during the high temperature calcination process. Pt / CeO2-700 represents a calcination temperature of 700°C during the high temperature calcination process.

[0120] Table 5 Product molar yield of Pt-based catalysts obtained at different calcination temperatures

[0121]

[0122]

[0123] Results analysis: The results in Table 5 show that the calcination temperature has a certain influence on the catalytic performance during the catalyst preparation process. Specifically, both too low and too high calcination temperatures will have an adverse effect on the catalytic performance. In comparison, the catalyst calcined at 500°C has the best performance and the yield of the obtained product 2,6-dimethylcyclohexylamine is the highest.

[0124] Example 22-Example 33 Screening of the volume fraction of hydrogen in the reducing gas, the reducing gas flow rate, the reducing temperature and the reducing time during the preparation of the Pt-based catalyst

[0125] Method: Example 22-Example 33 uses platinum nitrate aqueous solution as a precursor, high-temperature thermal decomposition of cerium nitrate hexahydrate to obtain cerium oxide as a carrier, and uses an equal volume impregnation method to prepare a Pt-based catalyst. After impregnation, it is continuously stirred, ultrasonicated for 10-20 minutes, and then dried in an oven at 100°C overnight, ground and pulverized, and then calcined in a muffle furnace at a high temperature of 500°C, and then reduced. The main difference between each embodiment in Example 22-Example 33 is the difference in reduction conditions, mainly including at least one difference in the volume fraction of hydrogen in the reducing gas, the flow rate of the reducing gas, the reduction temperature, and the reduction time.

[0126] In Examples 22 to 33, the Pt-based catalysts obtained under different reduction conditions were used to complete the depolymerization of PPO in S1 and amination to 2,6-dimethylcyclohexylamine. The reaction conditions were the same as in Examples 1 to 4.

[0127] Results: The results are shown in Table 6.

[0128] Table 6 Product molar yields of Pt-based catalysts prepared under different reduction conditions

[0129]

[0130]

[0131] Results analysis: From the results in Table 6, it can be seen that during the catalyst preparation process, the reduction conditions have an impact on the catalyst performance. Specifically, for the volume fraction of hydrogen in the reducing gas, both too high and too low hydrogen gas volume fractions have an adverse effect on the formation of the target product 2,6-dimethylcyclohexylamine. The optimal hydrogen gas volume fraction is 10%. The reducing gas flow rate has little effect on the catalyst performance, and the performance fluctuates. At 70ml / min -1 The reduction temperature and reduction time have a significant impact on the catalyst. Too low or too high reaction temperature and too short or too long reduction time will lead to a decrease in the yield of the target product. Especially at too high a reduction temperature and too long a reduction time, the significant increase in the yield of by-products leads to a decrease in the selectivity of the target product. The optimal reduction temperature is 400°C and the reduction time is 2h. The yield of the obtained product 2,6-dimethylcyclohexylamine is the highest.

[0132] Example 34-Example 42 Screening of reaction conditions during depolymerization of PPO and amination to 2,6-dimethylcyclohexylamine

[0133] Method: The Pt-based catalysts prepared in Examples 34 to 42 are prepared by an equal volume impregnation method using an aqueous solution of platinum nitrate as a precursor and cerium oxide obtained by thermally decomposing cerium nitrate hexahydrate at 500°C as a carrier. The specific process is as follows: the concentration of platinum in the aqueous solution of platinum nitrate is 0.031 g / ml. 484 microliters of the aqueous solution are added with 1 g of cerium oxide, and the mixture is stirred continuously. The mixture is then ultrasonicated for 10-20 minutes and then dried in an oven at 100°C overnight. The mixture is ground and calcined in a muffle furnace at 500°C and then reduced. The volume fraction of hydrogen in the reducing gas is 10%, and the flow rate of the reducing gas is 70 ml / min. -1 , the reduction temperature is 400°C, and the reduction time is 2h. The main difference between each embodiment in Examples 34 to 42 is the different reaction conditions, including at least one of the hydrogen pressure, ammonia pressure, reaction temperature and reaction time.

[0134] In Example 34-Example 42, a Pt-based catalyst is used to complete the depolymerization of PPO in S1. During the amination to 2,6-dimethylcyclohexylamine, the reaction is carried out in a batch reactor. The mass of the reaction substrate PPO is 0.1 g, the mass of the catalyst is 0.2 g, and 5 ml of methylcyclohexane is the reaction medium. The main difference between each embodiment in Example 34-Example 42 is the different reaction conditions, including hydrogen pressure, ammonia pressure, reaction temperature and reaction time. After the reaction is completed, the yield of the target product 2,6-dimethylcyclohexylamine and the main by-product 1,3-dimethylcyclohexane is measured.

[0135] Results: The results are shown in Table 7.

[0136] Table 7 Product molar yield under different reaction conditions

[0137]

[0138] Result analysis: The results in Table 7 show that the reaction conditions have a great influence on the yield of the target product 2,6-dimethylcyclohexylamine in the process of PPO depolymerization and amination to 2,6-dimethylcyclohexylamine. For hydrogen pressure, both too high and too low hydrogen pressures are not conducive to the formation of the target product 2,6-dimethylcyclohexylamine. Especially under the condition of too high hydrogen pressure, the side reactions are aggravated, and the increase in the yield of by-products greatly reduces the selectivity of the target product. Therefore, the best hydrogen pressure is 2MPa.

[0139] The effect of ammonia pressure on the formation of target products is similar to that of hydrogen pressure. Both too high and too low ammonia pressures are not conducive to the formation of target products. Therefore, an ammonia pressure of 0.4 MPa is optimal.

[0140] The reaction temperature and reaction time also have a significant effect on the formation of the target product. The main manifestation is that under too high a reaction temperature and too long a reaction time, the yield of the byproduct 1,3-dimethylcyclohexane increases significantly, which greatly reduces the selectivity of the target product 2,6-dimethylcyclohexylamine. This may be related to the fact that high temperature and too long a reaction time aggravate the side reaction of the hydrogenolysis of the CN bond of the product. Too low or too short a reaction time will lead to incomplete depolymerization of PPO, which also reduces the yield of the target product. Therefore, the optimal reaction temperature is 230℃ and the optimal reaction time is 8h.

[0141] Example 43-Example 46 Screening of different organic reaction media

[0142] Method: The preparation method of the Pt-based catalysts prepared in Examples 43 to 46 is consistent with that in Examples 34 to 42. The main difference between Examples 43 to 46 is the different reaction media.

[0143] In Example 43-Example 46, a Pt-based catalyst is used to complete the depolymerization of PPO in S1. In the process of amination to 2,6-dimethylcyclohexylamine, the reaction conditions are as follows: the mass of the reaction substrate PPO is 0.1 g, the mass of the catalyst is 0.2 g, the hydrogen pressure is 2 MPa, the ammonia pressure is 0.4 MPa, the reaction temperature is 230°C, and the reaction time is 8 h. The main difference between Example 43-Example 46 is the different reaction media. After the reaction, the yields of the target product 2,6-dimethylcyclohexylamine and the main by-product 1,3-dimethylcyclohexane are measured.

[0144] Results: The test results are shown in Table 8.

[0145] Table 8 Product molar yields under different organic reaction media

[0146]

[0147] Result analysis: The results in Table 8 show that the reaction medium also has a great influence on the formation of the target product 2,6-dimethylcyclohexylamine. Among them, methylcyclohexane is the best reaction medium, and the yield of the obtained product 2,6-dimethylcyclohexylamine is the highest.

[0148] In the above examples, i.e., Examples 1 to 46, the preparation method of the Pt-based catalyst (including the type of precursor Pt, the type of carrier, the impregnation method, the calcination conditions and the reduction conditions, etc.) and the reaction conditions (including the hydrogen pressure, the ammonia pressure, the reaction temperature, the reaction time and the reaction medium, etc.) were screened for the effects of the depolymerization of PPO and the amination to 2,6-dimethylcyclohexylamine in the first step S1, and the optimal catalyst preparation method and the optimal reaction conditions were finally determined, and the optimal yield of the product 2,6-dimethylcyclohexylamine was obtained under these conditions. After the reaction of S1 is completed, the batch reactor is cooled, and after the remaining gas in the reactor is exhausted, a certain amount of hydrogen capture agent is injected into the reactor, which is then sealed, filled with nitrogen, and the process of dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to the final target product 2,6-dimethylaniline in S2 is carried out under a nitrogen atmosphere, so as to complete the depolymerization of PPO and the amination to high value-added 2,6-dimethylaniline.

[0149] The S2 process of the present invention is described in detail below through Examples 47 to 65.

[0150] In the following examples, the best catalyst preparation method and the best reaction conditions in S1 determined according to Examples 1 to 46 are used, and on this basis, the process of PPO depolymerization and amination to 2,6-dimethylcyclohexylamine is completed to obtain the best target product 2,6-dimethylcyclohexylamine yield. After S1 is completed, the intermittent kettle reactor is cooled, and after the air in the kettle is exhausted, a certain amount of hydrogen capture agent is injected, and then it is sealed and filled with nitrogen. Under a nitrogen atmosphere, the reaction of 2,6-dimethylcyclohexylamine dehydrogenation aromatization to 2,6-dimethylaniline in S2 is carried out under the same catalyst and reaction conditions as S1, and finally the process of PPO depolymerization and amination to high value-added 2,6-dimethylaniline is completed. The catalyst and reaction phase used in S2 are consistent with the optimal catalyst and reaction phase in S1. After the reaction is completed, the analysis method of the reaction product is also consistent with that in S1, that is, gas chromatography-mass spectrometry (GC-MS Agilent 7890A-5975C) is used for qualitative analysis and gas chromatography (GC Agilent 7890A) is used for quantitative analysis. The HP-5 chromatographic column is used. The program temperature condition of the chromatographic column is: 50°C for 10 minutes, and 10°C / min -1 The temperature was raised to 270°C at a rate of 100°C and maintained at 270°C for 5 minutes. The molar yield of 2,6-dimethylaniline and 1,3-dimethylcyclohexane were calculated based on the molar yields of 2,6-dimethylaniline and 1,3-dimethylcyclohexane and the molar amount of the reaction substrate. The conversion rate of the reaction substrate is the sum of the molar yield of 2,6-dimethylaniline and the molar yield of 1,3-dimethylcyclohexane.

[0151] The following examples, i.e., Examples 47 to 65, are after the end of S1, the intermittent kettle reactor is cooled, the air in the kettle is exhausted, a certain amount of hydrogen capture agent is injected, and then it is sealed and filled with nitrogen. The reaction of 2,6-dimethylcyclohexylamine dehydrogenation aromatization to 2,6-dimethylaniline in S2 is carried out under the same catalyst and reaction phase conditions as S1 under a nitrogen atmosphere, and finally the PPO is depolymerized and aminized to high value-added 2,6-dimethylaniline. The reaction conditions used in the S1 process are as follows: the mass of the reaction substrate PPO is 0.1g, the mass of the catalyst is 0.2g, 5ml of methylcyclohexane is used as the reaction medium, the hydrogen pressure is 2MPa, the ammonia pressure is 0.4MPa, the reaction temperature is 230°C, and the reaction time is 8h.

[0152] Example 47-Example 51 Screening of Hydrogen Capture Agents

[0153] Method: The preparation method of the Pt-based catalyst used in Examples 47-51 is consistent with that in Examples 34-42.

[0154] In the process of dehydrogenation aromatization of 2,6-dimethylcyclohexylamine in S2 to 2,6-dimethylaniline in Example 47-Example 51, the reaction conditions are: nitrogen pressure of 0.1 MPa, reaction temperature of 200°C, reaction time of 8 hours, and the main difference between Example 47-Example 51 is the different hydrogen capture agents used. After the reaction is completed, the yields of the target product 2,6-dimethylaniline and the main by-product 1,3-dimethylaniline are measured.

[0155] Results: The test results are shown in Table 9.

[0156] Table 9 Product molar yields under different hydrogen capture agents

[0157]

[0158] Result analysis: The results in Table 9 show that the type of hydrogen capture agent used in S2 has a certain degree of influence on the target product 2,6-dimethylaniline. The presence of the hydrogen capture agent can timely capture the hydrogen generated in situ during the dehydrogenation of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline in S2, and avoid excessive participation of the hydrogen generated in situ in the hydrogenolysis of the CN bond in the side reaction 2,6-dimethylcyclohexylamine, thereby retaining a higher yield of the target product 2,6-dimethylaniline. From the results in Table 9, it can be seen that toluene has the best effect as a hydrogen capture agent.

[0159] Example 52-Example 58 Screening of reaction conditions for the dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline

[0160] Method: The preparation method of the Pt-based catalyst used in Examples 52-58 is consistent with that in Examples 34-42.

[0161] In the process of dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline in S2, the reaction conditions are: toluene is used as a hydrogen capture agent. The main difference between Examples 52 and 58 is the different reaction conditions, including reaction temperature, reaction time and nitrogen pressure used. After the reaction is completed, the yields of the target product 2,6-dimethylaniline and the main by-product 1,3-dimethylaniline are measured.

[0162] Results: The test results are shown in Table 10.

[0163] Table 10 Product molar yield under different reaction conditions

[0164]

[0165] Result analysis: The results in Table 10 show that the reaction temperature and reaction time have a certain influence on the yield of the target product in the dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline in S2. Too low a reaction temperature and too short a reaction time will reduce the degree of dehydrogenation aromatization, and the substrate conversion is incomplete, which leads to a decrease in the yield of the target product. After reaching a certain reaction temperature and reaction time, further increasing the temperature or extending the time will not significantly change the yield of the relevant products, but the energy consumption cost will increase in actual applications. The optimal reaction temperature is 200℃ and the reaction time is 8h.

[0166] Nitrogen pressure also has a certain influence on the formation of target products in S2. Generally speaking, too high nitrogen pressure is not conducive to the dehydrogenation aromatization, and 0.1MPa is the optimal nitrogen pressure.

[0167] Performance test of Pt-based catalysts at different cycle times in Example 59-Example 65

[0168] Method: The preparation method of the Pt-based catalyst used in Examples 59 to 65 is consistent with that in Examples 34 to 42.

[0169] In the process of dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline in S2, the reaction conditions are: toluene is used as a hydrogen capture agent, the reaction temperature is 200°C, the reaction time is 8h, and the nitrogen pressure used during the reaction is 0.1MPa. Examples 59-65 are the recycling of platinum-based catalysts. Specifically, after the end of the previous kettle experiment, the reaction phase and the catalyst are centrifuged, and then the catalyst is repeatedly centrifuged and washed three times with methylcyclohexane, and then the next kettle is re-added. After the end of each kettle reaction, the yield of the target product 2,6-dimethylaniline and the main by-product 1,3-dimethylcyclohexane is measured.

[0170] Results: The test results are shown in Table 11.

[0171] Table 11 Product molar yields under Pt-based catalysts at different cycle times

[0172]

[0173] Result analysis: The results in Table 11 show that during the first application of the catalyst, the yield of the target product 2,6-dimethylaniline decreased, and the yield of the corresponding by-product 1,3-dimethylcyclohexane increased. In the subsequent application process, the yield of the target product was always maintained at more than 45%. During the application process, the catalyst was not regenerated and no new catalyst was added, which proved that the catalyst had good stability during the reaction.

[0174] Comparative Example 1

[0175] The difference between Comparative Example 1 and Example 59 is that the active ingredient in the catalyst is Fe, and an aqueous solution of iron nitrate is used as a precursor. The concentration of iron in the aqueous solution of iron nitrate (i.e., Fe(NO3)2 aqueous solution) is 0.030 g / ml, and the volume of the aqueous solution of iron nitrate (i.e., Fe(NO3)2 aqueous solution) is 500 μl.

[0176] Comparative Example 2

[0177] The only difference between Comparative Example 2 and Example 59 is that the active ingredient in the catalyst of Comparative Example 2 is Co, and a cobalt nitrate aqueous solution (i.e., Co(NO3)2 aqueous solution) is used as a precursor. The concentration of cobalt in the cobalt nitrate aqueous solution is 0.032 g / ml, and the volume of the solution is 469 μl.

[0178] Comparative Example 3

[0179] The only difference between Comparative Example 3 and Example 59 is that the active ingredient in the catalyst of Comparative Example 3 is Co, and a Ni nitrate aqueous solution (i.e., Ni(NO3)2 aqueous solution) is used as a precursor. The Ni concentration in the Ni nitrate aqueous solution is 0.028 g / ml, and the solution volume is 536 μl.

[0180] Comparative Example 4

[0181] The only difference between Comparative Example 4 and Example 59 is that the active ingredient in the catalyst in Comparative Example 4 is Pd, and a Pd nitrate aqueous solution (i.e., a Pd(NO3)2 aqueous solution) is used as a precursor. The concentration of Pd in ​​the Pd nitrate aqueous solution is 0.029 g / ml, and the volume of the solution is 517 μl.

[0182] Comparative Example 5

[0183] The only difference between Comparative Example 5 and Example 59 is that the active ingredient in the catalyst of Comparative Example 5 is Ru, and Ru chlorate aqueous solution (i.e., RuCl3 aqueous solution) is used as a precursor. The concentration of cobalt in the Ru nitrate aqueous solution is 0.031 g / ml, and the volume of the solution is 484 μl.

[0184] Results: The test results are shown in Table 12.

[0185] Table 12 Molar yields of 2,6-dimethylcyclohexylamine and 1,3-dimethylcyclohexane in Comparative Examples 1-5

[0186]

[0187] Result analysis: The results in Table 12 show that compared with Pt-based catalysts, catalysts based on other transition metal elements have poor ability to catalyze PPO to 2,6-dimethylaniline. Specifically, for Fe-based catalysts, no related products were detected. Therefore, Fe-based catalysts do not have the ability to reduce and depolymerize PPO under this condition. For Co-based and Ni-based catalysts, the target product 2,6-dimethylaniline was not detected, and the main products were 1,3-dimethylcyclohexane and 2,6-dimethylcyclohexylamine. Therefore, although both have a certain ability to reduce and depolymerize PPO, they cannot catalyze the process of dehydrogenation aromatization of 2,6-dimethylcyclohexylamine to 2,6-dimethylaniline. And from the total yield of detectable products, the ability of both to depolymerize PPO is poor. For Pd-based and Ru-based catalysts, although the degree of PPO reduction depolymerization is high and the total yield of detectable products is high, the product distribution is mainly 1,3-dimethylcyclohexane, the by-product, and the selectivity of 2,6-dimethylaniline is poor. It can be seen that the degree of side reactions on these two catalysts is high. In summary, Pt / CeO2 was determined to be the best catalyst.

[0188] Based on all the above examples, the optimal catalyst preparation method and the optimal reaction conditions in the two-step process of PPO depolymerization and amination of high value-added 2,6-dimethylaniline were finally determined, and on this basis, the target product 2,6-dimethylaniline was obtained with the optimal yield. After the reaction, the obtained reaction phase was centrifuged to separate the solid catalyst, and the liquid component was added with HCl solution, stirred and refrigerated at 0°C overnight to precipitate a white precipitate. The white solid obtained after centrifugation was dried to finally obtain the pure product of 2,6-dimethylaniline hydrochloride, and analyzed by nuclear magnetic resonance hydrogen spectrum and carbon spectrum. The relevant results are as follows: Figure 3 shown.

[0189] In summary, the present application provides a new method for depolymerizing PPO and aminating it to 2,6-dimethylaniline in two steps. The method uses PPO as a raw material. In the first step S1, hydrogen is used as a hydrogen source and ammonia is used as an amine source. PPO is reduced and depolymerized to 2,6-dimethylphenol in an organic phase on a Pt-based catalyst, hydrogenated to 2,6-dimethylcyclohexanol, and then further aminated to 2,6-dimethylcyclohexylamine; in the second step S2, under the same catalyst and reaction phase, the obtained 2,6-dimethylcyclohexylamine is further dehydrogenated and aromatized to the target product 2,6-dimethylaniline in the presence of a hydrogen capture agent under a nitrogen atmosphere. After optimization, not only can the separable target product 2,6-dimethylaniline be obtained in high yield, but the catalyst also has good stability, and can continuously and efficiently catalyze the catalytic conversion of PPO to the target product 2,6-dimethylaniline, which has certain industrial application prospects. Compared with the traditional synthesis of 2,6-dimethylaniline, this method uses waste plastic PPO as raw material, which not only gets rid of the excessive dependence on non-renewable fossil energy such as aromatic hydrocarbons as raw materials in traditional synthesis methods, but also provides a new idea for the synthesis of aromatic amines such as 2,6-dimethylaniline, and also provides a new direction for the recycling and upgrading of waste plastic PPO. The resulting product 2,6-dimethylaniline, as a high value-added aromatic amine, is widely used in the production of drugs, dyes and agricultural chemicals. The market size is increasing year by year and has a high market demand.

[0190] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples. Based on the concept of the present disclosure, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the present disclosure as described above, which are not provided in detail for the sake of simplicity.

[0191] While the disclosure has been described in conjunction with specific embodiments thereof, many alternatives, modifications and variations of these embodiments will be apparent to those skilled in the art in light of the foregoing description.

[0192] The embodiments of the present disclosure are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether, characterized in that: include: The polyphenylene ether, hydrogen and ammonia dispersed in the organic reaction medium react under the action of a Pt-based catalyst at a first temperature for a first time to perform a first reaction to obtain 2,6-dimethylcyclohexylamine; the first reaction includes a depolymerization reaction, a hydrogenation reaction and an amination reaction; adding a hydrogen capture agent, reacting at a second temperature for a second time under the action of a nitrogen atmosphere and the Pt-based catalyst, and performing a second reaction to obtain 2,6-dimethylaniline; the second reaction includes an aromatization reaction; The Pt-based catalyst comprises a carrier and Pt loaded on the carrier, and the carrier is selected from at least one of metal oxides, SiO2 and activated carbon; the particle size of Pt is 0.6nm-1.8nm.

2. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 1, characterized in that: The organic reaction medium is selected from at least one of cyclohexane, methylcyclohexane, toluene and n-octane; The metal oxide is selected from at least one of cerium oxide and aluminum oxide, and the precursor of Pt supported on the carrier is selected from at least one of an aqueous solution of platinum nitrate, a methanol solution of platinum nitrate, an aqueous solution of chloroplatinic acid, and a methanol solution of chloroplatinic acid; The hydrogen capture agent is selected from at least one of ethylene, styrene, benzyl cyanide, toluene and p-xylene.

3. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 2, characterized in that: The organic reaction medium is selected from at least one of cyclohexane and methylcyclohexane; The carrier is selected from cerium oxide; the preparation method of cerium oxide includes high temperature thermal decomposition method or hydrothermal method; The hydrogen capture agent is selected from at least one of toluene and styrene.

4. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 1, characterized in that: In the first reaction, the mass ratio of the polyphenylene ether to the catalyst is 1:(0.5-3); the mass ratio of the polyphenylene ether to the organic reaction medium is 1:(1-50); the pressure of the hydrogen is 1MPa-3MPa; the pressure of the ammonia is 0.2MPa-0.6MPa; the first temperature is 210°C-250°C; the first time is 4h-12h; In the second reaction, the second reaction temperature is 180°C-220°C; the second time length is 4h-12h; and the nitrogen pressure is 0.1-2MPa.

5. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 4, characterized in that: In the first reaction, the mass ratio of the polyphenylene ether to the organic reaction medium is 1:(5-30); the pressure of the hydrogen is 1MPa-2MPa; the pressure of the ammonia is 0.4MPa-0.6MPa; the first temperature is 210°C-230°C; the first time is 4h-8h; In the second reaction, the second reaction temperature is 180°C-200°C; the second time length is 8h-12h; and the nitrogen pressure is 0.1MPa-0.5MPa.

6. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 1, characterized in that: The preparation method of the Pt-based catalyst is selected from an equal volume impregnation method, an excess impregnation method or a deposition precipitation method.

7. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 6, characterized in that: The preparation method of the Pt-based catalyst is selected from an isovolumetric impregnation method, comprising: Providing a carrier; the water absorption rate of the carrier is 50% to 765%; Providing a precursor solution; the concentration of the precursor solution is 0.024 g / ml to 0.050 g / ml, and the volume is 298 μL to 634 μL; pouring the carrier into the precursor solution, drying and calcining; The calcined product is reduced in a reducing gas.

8. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 7, characterized in that: The calcination temperature is 300°C to 700°C; The reducing gas is a mixed gas of hydrogen and argon; the volume fraction of hydrogen in the reducing gas is 5%-20%; the flow rate of the reducing gas is 60ml / min-80ml / min; the reduction time is 1h-10h; and the reduction temperature is 200°C-500°C.

9. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 8, characterized in that: The calcination temperature is 400°C to 500°C; The volume fraction of hydrogen in the reducing gas is 10%-15%; the flow rate of the reducing gas is 70ml / min-80ml / min; the reduction time is 2h-4h; and the reduction temperature is 300°C-400°C.

10. The method for preparing 2,6-dimethylaniline by depolymerizing and aminating polyphenylene ether according to claim 6, characterized in that: The carrier is selected from cerium oxide, and the cerium oxide is prepared by high-temperature thermal decomposition of cerium nitrate hexahydrate; the temperature of the high-temperature thermal decomposition is 300°C to 700°C.

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