A bifunctional molecular sieve and its preparation method and a method for directly preparing ketones from olefins

Abstract

The present invention relates to a bifunctional molecular sieve catalyst comprising a dehydrogenation active center and a Lewis acid center, wherein the Lewis acid center is provided by a molecular sieve structure. Specifically, the present invention relates to an all-silicon molecular sieve catalyst encapsulating the Cu dehydrogenation active center and a preparation method thereof. The method comprises the following steps: in the presence of an aqueous solvent, a silicon source, a copper source, a dispersant, a nitrogen-containing heterocyclic compound, and an alkali source are mixed in proportion to obtain a mixed system; the mixed system is hydrothermally treated, and then filtered, dried, calcined, and reduced to obtain the all-silicon molecular sieve catalyst encapsulating the Cu dehydrogenation active center. The present invention also provides a method for directly preparing ketones from olefins, using the aforementioned bifunctional molecular sieve catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic ketone preparation, and particularly relates to a catalyst used for directly preparing ketone from olefin and a preparation method thereof. Background Art

[0002] Ketones are compounds consisting of a carbonyl group linked to two hydrocarbon groups. Ketones are chemically active and readily undergo nucleophilic addition reactions with hydrocyanic acid, Grignard reagents, hydroxylamine, and alcohols, and can also be reduced to alcohols. Due to the polarization of the carbonyl group, ketones with α-H groups can undergo halogenation reactions; under alkaline conditions, ketones with methyl groups can undergo haloform reactions. Furthermore, low-carbon ketones, such as acetone and methyl ethyl ketone, can also be used as solvents. Therefore, organic ketones have a wide range of applications, with acetone and cyclohexanone being particularly important chemical raw materials.

[0003] Typically, the preparation methods of organic ketones include oxidation / dehydrogenation of secondary alcohols, acylation of aromatic hydrocarbons, and reaction of carboxylic acid derivatives with organometallic compounds. Acetone is typically produced using the cumene process, where propylene and benzene are alkylated to produce cumene, which is then oxidized to produce cumene hydroperoxide. The hydrolysis of cumene hydroperoxide produces acetone and phenol. Methyl ethyl ketone is produced using a two-step hydration and dehydrogenation process, where n-butene is directly hydrated under acid catalysis to produce sec-butanol, or to produce a sulfate ester intermediate, which is then hydrolyzed to produce sec-butanol. Finally, the sec-butanol is dehydrogenated to produce methyl ethyl ketone. Cyclohexanone is produced through two methods: cyclohexane oxidation and cyclohexene hydration. In the oxidation process, cyclohexane is oxidized to produce a mixed solution of cyclohexanol and cyclohexanone. In the hydration process, cyclohexene is hydrated under an acid catalyst to produce cyclohexanol, which is then dehydrogenated to produce cyclohexanone.

[0004] Based on the above analysis, olefins are key precursors for organic ketone production, and olefin hydration to secondary alcohols and secondary alcohol dehydrogenation are important processes in organic ketone production. However, due to thermodynamic equilibrium limitations, the single-pass conversion rates of both n-butene direct hydration and cyclohexene hydration are difficult to reach 10%, which reduces the production efficiency of organic ketones and increases the energy consumption of the olefin cycle. Therefore, process innovation is urgently needed to improve the production efficiency and economic efficiency of organic ketones. Since the conversion rate of secondary alcohol dehydrogenation can reach over 50% under the action of dehydrogenation catalysts, coupling the hydration reaction with the dehydrogenation reaction is expected to promote the hydration reaction, thereby increasing the single-pass conversion rate of olefins and the production efficiency of organic ketones. However, the hydration reaction is typically carried out below 200°C (160°C for n-butene and 130°C for cyclohexene), while the dehydrogenation reaction is usually carried out above 220°C. If the coupling reaction is below 200°C, the dehydrogenation efficiency of the secondary alcohol is low, and the dehydrogenation has a poor effect on promoting the hydration reaction; if the coupling reaction is above 200°C, the olefins are likely to aggregate or react with the alcohol ketone, thereby reducing the selectivity of the ketone and the effective utilization of the olefins. Summary of the Invention

[0005] In response to the existing problems of low conversion rate and production efficiency in the olefin hydration and secondary alcohol dehydrogenation reactions in the preparation of ketones from olefins, one object of the present invention is to provide a method for the direct catalytic synthesis of ketones from olefins. This method uses a bifunctional catalyst with both hydration and dehydrogenation active sites to directly convert olefins into ketones. A second object of the present invention is to provide a bifunctional molecular sieve with both hydration and dehydrogenation active sites and a method for its preparation.

[0006] In a first aspect of the present invention, a bifunctional molecular sieve is provided. The bifunctional molecular sieve comprises a dehydrogenation active center having a dehydrogenation function and a Lewis acid center having a hydration catalytic function.

[0007] Specifically, the dehydrogenation active center is selected from at least one of Group IB metals.

[0008] Preferably, the dehydrogenation active center is selected from at least one of Cu, Ag, and Au metals, and its content is 0.01 to 60 wt.%; more preferably, at least one of Cu and Ag, and its content is 0.5 to 32 wt.%. The structural characteristics of Group IB metals Cu, Ag, and Au are (n-1)d10ns1, belonging to the ds region. The ns electrons of Group IB elements and the sub-outer (n-1)d electrons have similar abilities. When combined with other elements, not only can the ns electrons participate in bonding, but the (n-1)d electrons can also partially participate in bonding under different reaction conditions. Since the sub-outer layer has 18 electrons, the attraction to the outermost s electrons is strong, making Cu, Ag, and Au inactive in the environment, having high stability, resisting oxidation at the corresponding temperature, and having high catalytic activity.

[0009] Specifically, the Lewis acid center is provided by a molecular sieve structure. The molecular sieve should have good hydrothermal stability and be selected from one of the all-silicon molecular sieves.

[0010] Preferably, the all-silicon molecular sieve is at least one selected from all-silicon Silicalite-1 and Beta molecular sieve.

[0011] Furthermore, the bifunctional molecular sieve is at least one of an all-silicon molecular sieve encapsulating Cu or an all-silicon molecular sieve encapsulating Ag; the all-silicon molecular sieve encapsulating Cu is at least one of an all-silicon Silicalite-1 molecular sieve encapsulating Cu or an all-silicon Beta molecular sieve encapsulating Cu; the all-silicon molecular sieve encapsulating Ag is at least one of an all-silicon Silicalite-1 molecular sieve encapsulating Ag or an all-silicon Beta molecular sieve encapsulating Ag.

[0012] Specifically, the bifunctional molecular sieve is a crystal with a multi-level pore structure, a Lewis acid content of 1 to 200 μmol / g, and a specific surface area of ​​40 to 679 m2 / g, pore volume of 0.05~0.45cm 3 / g, the dehydrogenation active center is located inside the molecular sieve crystal and / or outside the molecular sieve crystal.

[0013] Molecular sieves, with their molecular-scale crystalline pore structure and unique Lewis / Bronsted acidity, are commonly used heterogeneous catalytic materials. The Lewis acid centers of the bifunctional molecular sieves provided by the present invention can coordinate with carbon-carbon double bonds. The Lewis acid centers, acting in concert with the dehydrogenation active centers, promote olefin hydration through the dehydrogenation of secondary alcohols, enabling the direct conversion of olefins to ketones.

[0014] In a second aspect, the present invention further provides a Cu-encapsulated all-silicon molecular sieve, with respect to the aforementioned bifunctional molecular sieve. The Cu-encapsulated all-silicon molecular sieve has Cu as its dehydrogenation active center, Lewis acid centers provided by the all-silicon molecular sieve, and the dehydrogenation active centers, Cu, located within the all-silicon molecular sieve crystals. The all-silicon molecular sieve is selected from at least one of all-silicon Silicalite-1 and Beta molecular sieve.

[0015] The third aspect of the present invention provides a method for preparing the above-mentioned Cu-encapsulated all-silicon molecular sieve. Specifically, the Cu-encapsulated all-silicon molecular sieve is prepared by a hydrothermal synthesis method, which comprises the following steps:

[0016] Step 1: mixing a silicon source, a copper source, a dispersant, a nitrogen-containing heterocyclic compound, an alkali source, and H2O in proportion to obtain a mixed system;

[0017] Step 2: Add the mixed system of step 1 into the reactor, perform hydrothermal treatment, and then filter, dry, roast and reduce to obtain the all-silicon molecular sieve encapsulating Cu.

[0018] Furthermore, in the step 1, the silicon source is selected from at least one of organic silicate, silica gel, white carbon black, and silica sol; in order to reduce the influence of heteroatoms in the silicon source on the molecular sieve crystallization product, a single silicon source is preferred; further preferred is organic silicate, such as at least one of methyl orthosilicate, isopropyl silicate, ethyl silicate, tetraethoxysilane, and tetraethyl orthosilicate.

[0019] Furthermore, in step 1, the copper source is selected from at least one of copper nitrate, copper chloride, tetraphenylporphyrin copper, and copper acetylacetonate.

[0020] Furthermore, the dispersant in step 1 is a soluble compound containing nitrogen, sulfur, or the like having lone pair electrons, and the dispersant is selected from at least one of ethylamine, ethylenediamine, propylenediamine, hexamethylenediamine, aniline, pyridine, thiophene, thiol, thiophenol, and sulfide; preferably at least one of ethylenediamine, hexamethylenediamine, and aniline.

[0021] Furthermore, the nitrogen-containing functional group in the nitrogen-containing heterocyclic compound in step 1 is selected from at least one of a pyrrole ring, an imidazole ring, a pyrazole ring, a pyridine ring, a pyrimidine ring, a quinoline ring, and a pyrimidine ring.

[0022] Specifically, the nitrogen-containing heterocyclic compound in step 1 is selected from at least one of theophylline, guanosine, adenosine, guanine, adenine, and adefovir; preferably, it is a mixture of theophylline and adenine, and the molar ratio of theophylline to adenine in the mixture is (0.4-3):1.

[0023] Furthermore, in step 1, the alkaline source is selected from at least one of alkali metal hydroxide, ammonia water, urea, hydrazine hydrate, sodium carbonate, sodium bicarbonate, aliphatic amine, aliphatic alcohol amine, and quaternary ammonium base.

[0024] Specifically, the general structural formula of the quaternary ammonium hydroxide is:

[0025]

[0026] Wherein, R1, R2, R3, and R4 are each at least one C1-C4 alkyl group, wherein the C1-C4 alkyl group is selected from at least one of a C1-C4 linear alkyl group and a C3-C4 branched alkyl group. R1, R2, R3, and R4 can independently be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl.

[0027] Specifically, the aliphatic amine has the general structural formula R5(NH2)n, where n is an integer of 1 or 2. When n is 1, R5 is at least one C1-C6 alkyl group, and the C1-C6 alkyl group is selected from at least one of a C1-C6 straight-chain alkyl group and a C3-C6 branched-chain alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, neopentyl, isopentyl, tert-pentyl, or n-hexyl group. When n is 2, R5 is at least one C1-C6 alkylene group, and the C1-C6 alkylene group is selected from at least one of a C1-C6 straight-chain alkylene group and a C3-C6 branched-chain alkylene group, such as methylene, ethylene, n-propylene, n-butylene, n-pentylene, or n-hexylene.

[0028] Preferably, the alkali source is selected from at least one of tetraethylammonium hydroxide, tetramethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tripropylamine, triethylamine, tributylammonium, hexylamine, and hexylene diamine; more preferably, it is at least one of tetraethylammonium hydroxide and tetrapropylammonium hydroxide. When the alkali source is tetraethylammonium hydroxide, a Cu-encapsulated all-silicon Beta molecular sieve is prepared; when the alkali source is tetramethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tripropylamine, triethylamine, tributylammonium, hexylamine, or hexylene diamine, a Cu-encapsulated all-silicon Silicalite-1 molecular sieve is prepared. The alkali source serves as a template in the molecular sieve synthesis process. By selecting alkali sources from different sources and adjusting the corresponding temperature and time during the preparation process, different types of all-silicon molecular sieves, namely, all-silicon Beta molecular sieves or all-silicon Silicalite-1 molecular sieves, are prepared.

[0029] Furthermore, the molar ratio of the silicon source, copper source, dispersant, nitrogen-containing heterocyclic compound, alkali source, and H2O in step 1 is 1:(0.005-0.4):(0.05-1.6):(0.08-2.2):(0.15-3):(10-200).

[0030] Preferably, the molar ratio of the silicon source, copper source, dispersant, nitrogen-containing heterocyclic compound, alkali source and H2O in step 1 is 1:(0.01-0.25):(0.08-1.2):(0.11-1.6):(0.2-1.8):(15-80).

[0031] In the present invention, the temperature and time of the hydrothermal reaction in step 2 are one of the important factors affecting the crystal form, crystal size and product morphology of the hydrothermal product. Specifically, the hydrothermal treatment temperature in step 2 is 50-190°C, and the hydrothermal treatment time is 3-10 days; preferably, the hydrothermal treatment temperature is 70-170°C, and the hydrothermal treatment time is 5-8 days; the hydrothermal treatment conditions are further preferably: first, hydrothermal treatment at a temperature of 170-180°C for 0.5-1 day; then, hydrothermal treatment at a temperature of 100-130°C for 1-2 days. In addition, the pressure of the hydrothermal reaction system is another important factor affecting the crystal form and crystallization rate of the product, and the autogenous pressure of the reaction system depends on the size of the free volume in the reactor. In order to improve the efficiency of the hydrothermal reaction, preferably, the total volume of the mixed system in step 1 is 60-85% of the capacity of the reactor, wherein the reactor is preferably a polytetrafluoroethylene reactor.

[0032] Specifically, the drying temperature in step 2 is 80-120°C.

[0033] Specifically, the calcination temperature in step 2 is 400-850°C, and the calcination time is 1-6 hours; preferably, the calcination temperature is 500-650°C, and the calcination time is 2-4 hours. To further improve the performance of the bifunctional molecular sieve, the calcination is carried out under a water vapor atmosphere. The water vapor atmosphere preferably has a volume fraction of water vapor of 30-80%, more preferably 50%. The alkali source and nitrogen-containing heterocyclic compound in the molecular sieve are removed by calcination, and the calcination temperature needs to reach the decomposition temperature of the alkali source and the nitrogen-containing heterocyclic compound.

[0034] Specifically, the reduction temperature in step 2 is 160-300°C, and the reduction time is 12-72 hours. The reduction reaction is carried out in an atmosphere with a H2 volume fraction of 10-20%. During the reduction process, the CuO encapsulated in the molecular sieve is reduced to Cu, preparing an all-silicon molecular sieve encapsulating Cu dehydrogenation active centers.

[0035] Furthermore, the Lewis acid content of the all-silicon molecular sieve encapsulating the Cu dehydrogenation active center is 13.3 to 76.1 μmol / g, and the specific surface area is 79 to 624 m 2 / g, pore volume of 0.11~0.38cm 3 / g; preferably the Lewis acid content is 8.5 to 126.6 μmol / g, and the specific surface area is 122 to 567 m 2 / g, pore volume of 0.17~0.31cm 3 / g.

[0036] The present invention provides a Cu-encapsulated all-silicon molecular sieve. A key factor influencing its performance in the direct catalytic synthesis of ketones from olefins is the content of dehydrogenation active centers and Lewis acid centers in the catalytic material, namely, the molar ratio of copper to silicon in step 1. Furthermore, another important factor influencing the catalytic performance of the molecular sieve is the Lewis acid content, specific surface area, and pore volume of the molecular sieve.

[0037] The fourth aspect of the present invention provides an application of a bifunctional molecular sieve in the direct preparation of ketones from olefins.

[0038] The fifth aspect of the present invention further provides a method for directly preparing ketones from olefins, wherein the method uses the above-mentioned bifunctional molecular sieve.

[0039] Specifically, the method for directly preparing ketones from olefins comprises the following steps:

[0040] At a reaction temperature of 100-400°C, a reaction pressure of 0.05-5 MPa, and an olefin mass space velocity of 0.1-1000 h -1Under the conditions of , olefin and water are mixed in a molar ratio of 1: (0.5-50), and then contacted with the bifunctional molecular sieve to carry out a catalytic reaction; the obtained reaction material is condensed and then separated into water and oil, the aqueous phase enters the reaction cycle, the oil phase is separated and the reactants olefin, alcohol and ketone are obtained, wherein the olefin enters the reaction cycle.

[0041] In the method for directly preparing ketone from olefin, the reaction temperature is preferably 130-350°C, the reaction pressure is 0.09-2.6 MPa, and the mass space velocity of olefin is 1-100 h -1 , the molar ratio of olefin to water is 1: (2 to 30); further preferably, the reaction temperature is 160 to 300 ° C, the reaction pressure is 0.1 to 1.6 MPa, and the mass space velocity of olefin is 2 to 40 h -1 , the molar ratio of olefin to water is 1:(3~15).

[0042] Specifically, the olefin is selected from at least one of chain olefins and cycloolefins; the carbon number of the carbocyclic ring in the cycloolefin is C5 to C16; the chain olefin is at least one of terminal olefins and internal olefins.

[0043] Furthermore, the structural formula of the terminal olefin is as follows:

[0044]

[0045] Wherein, R6 or R7 are each independently one of H or C1-C16 alkyl, wherein the C1-C16 alkyl is selected from at least one of C1-C16 straight-chain alkyl and C3-C16 branched-chain alkyl, and R6 or R7 cannot be H at the same time. R6 or R7 can independently be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc.

[0046] Furthermore, the structural formula of the internal olefin is as follows:

[0047]

[0048] Wherein, R8 or R9 are each independently H or C1-C16 alkyl, R 10 or R 11 Each independently represents H or a C1-C16 alkyl group; the C1-C16 alkyl group is selected from at least one of a C1-C16 straight-chain alkyl group and a C3-C16 branched-chain alkyl group; R8 or R9 cannot be H at the same time, R 10 or R 11 Cannot be H at the same time. R8, R9, R 10 、R 11 They may independently be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, and the like.

[0049] The bifunctional molecular sieve provided by the present invention, which combines hydration and dehydrogenation, solves the problem of coupling olefin hydration and secondary alcohol dehydrogenation reactions in the olefin-to-ketone process. It can directly produce organic ketones at the same reaction temperature, simplifying the process flow. Compared with existing olefin-to-ketone technologies, the present invention uses the bifunctional molecular sieve to catalyze the direct production of ketones from olefins, increasing the olefin conversion rate from 10% to over 25%, and the selectivity of the product organic ketone is over 90%. While ensuring high selectivity for organic ketones, it improves the effective utilization rate of olefins and the production efficiency of the product, reduces the cycle energy consumption of the substrate olefin, and makes the production process of olefin-to-ketone more economical. DETAILED DESCRIPTION

[0050] The following describes the embodiments of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0051] The present invention will be described in detail below through specific examples. In the following examples and comparative examples, the X-ray diffraction (XRD) phase diagrams were obtained by measuring with a Philips Panalytical X'pert, under the following test conditions: Cu target, Kα radiation, Ni filter, super energy detector, tube voltage 30KV, tube current 40mA; the morphology and size of the molecular sieve were measured with a Hitachi S4800 scanning electron microscope, with an accelerating voltage of 20KV; the specific surface area and pore volume of the molecular sieve were measured by nitrogen adsorption, and the nitrogen adsorption and desorption curves were measured using a Micromeritics tristarⅡ3020-M specific surface analyzer. The specific surface area and pore volume were calculated using the BET and t-plot methods, with specific data shown in Table 4; the acid content was analyzed by a BIQ-RADFTS3000 Fourier transform infrared spectrometer, with specific data shown in Table 4; and the distribution of copper was analyzed by projection electron microscopy.

[0052] In the following examples and comparative examples, the specific results of conversion rate and target product selectivity are shown in Table 4, and the corresponding calculation formulas are as follows:

[0053]

[0054]

[0055] Example 1

[0056] In the presence of an aqueous solvent, tetraethyl orthosilicate (a silicon source) and tetrapropylammonium hydroxide (an alkali source) were uniformly mixed and hydrothermally treated at 60°C for 8 hours to obtain solution 1. Copper nitrate (a copper source) and aniline (a dispersant) were mixed in appropriate proportions to form a uniform, transparent solution 2. Solutions 1 and 2 were mixed, and a nitrogen-containing heterocyclic compound, i.e., a 1:1 molar ratio of theophylline and adenine, was added to obtain a mixed system. The molar ratios of the silicon source, copper source, dispersant, nitrogen-containing heterocyclic compound, alkali source, and H2O in the mixed system were 1:0.04:0.12:0.1:0.23:15.

[0057] After transferring the mixed system to a reactor, it was hydrothermally treated, first at 165°C for 12 hours and then at 100°C for 48 hours. After filtration, the resulting solid was dried at 110°C for 12 hours and then calcined at 450°C in a 50% steam atmosphere for 6 hours to obtain the CuO-encapsulated all-silicon Silicalite-1 molecular sieve.

[0058] The CuO-encapsulated all-silicon Silicalite-1 molecular sieve was tableted and crushed to obtain 20-40 mesh particles. 2 g of the particles were weighed and loaded into the reaction tube of a fixed-bed reactor. The particles were reduced at 220°C and a H2 concentration of 15% for 24 hours to prepare the Cu-encapsulated all-silicon Silicalite-1 molecular sieve.

[0059] The fixed bed reactor was further heated to 250°C and the system pressure was increased to 0.5 MPa under anaerobic conditions. A mixture of cyclohexene and H2O was introduced into the fixed bed reactor at a molar ratio of cyclohexene to H2O of 1:10 and contacted with the Cu-encapsulated all-silicon Silicalite-1 molecular sieve. The mass space velocity of cyclohexene was 1.2 h -1 The obtained reaction mass is condensed and then separated into water and oil, the water phase enters the reaction cycle, and the oil phase is fractionated to obtain the reactants cyclohexene, cyclohexanol and cyclohexanone; the cyclohexene enters the reaction cycle.

[0060] Example 2

[0061] In the presence of an aqueous solvent, tetraethyl orthosilicate (a silicon source) and tetrapropylammonium hydroxide (an alkali source) were uniformly mixed in proportion and hydrothermally treated at 40°C for 8 hours to obtain solution 1. Copper (a copper source) copper acetylacetonate and dispersant ethylenediamine were mixed in proportion to form a uniform, transparent solution 2. Solutions 1 and 2 were mixed, and a nitrogen-containing heterocyclic compound, i.e., a 1:1 molar ratio of theophylline and adenine, was added to obtain a mixed system. The molar ratios of the silicon source, copper source, dispersant, nitrogen-containing heterocyclic compound, alkali source, and HO in the mixed system were 1:0.06:0.20:0.15:0.45:20.

[0062] After transferring the mixed system to a reactor, it was hydrothermally treated, first at 165°C for 15 hours and then at 115°C for 44 hours. After filtration, the resulting solid was dried at 110°C for 12 hours and then calcined at 450°C in a 50% steam atmosphere for 6 hours to obtain the CuO-encapsulated all-silicon Silicalite-1 molecular sieve.

[0063] The CuO-encapsulated all-silicon Silicalite-1 molecular sieve was tableted and crushed to obtain 20-40 mesh particles. 2 g of the particles were weighed and loaded into the reaction tube of a fixed-bed reactor. The particles were reduced at 220°C and a H2 concentration of 15% for 24 hours to prepare the Cu-encapsulated all-silicon Silicalite-1 molecular sieve.

[0064] The fixed bed reactor was further heated to 280°C and the system pressure was increased to 0.3 MPa under anaerobic conditions. A mixture of cyclohexene and H2O was introduced into the fixed bed reactor at a molar ratio of cyclohexene to H2O of 1:5 and contacted with the Cu-encapsulated all-silicon Silicalite-1 molecular sieve. The mass space velocity of cyclohexene was 6 h -1 The obtained reaction mass is condensed and then separated into water and oil, the water phase enters the reaction cycle, and the oil phase is fractionated to obtain the reactants cyclohexene, cyclohexanol and cyclohexanone; the cyclohexene enters the reaction cycle.

[0065] Example 3

[0066] In the presence of an aqueous solvent, tetraethyl orthosilicate (a silicon source) and tetrapropylammonium hydroxide (an alkali source) were uniformly mixed in proportion and hydrothermally treated at 40°C for 8 hours to obtain solution 1. Copper chloride (a copper source) and hexamethylenediamine (a dispersant) were mixed in proportion to form a uniform, transparent solution 2. Solutions 1 and 2 were mixed, and a nitrogen-containing heterocyclic compound, i.e., a 1:1 molar ratio of theophylline and adenine, was added to obtain a mixed system. The molar ratios of the silicon source, copper source, dispersant, nitrogen-containing heterocyclic compound, alkali source, and HO in the mixed system were 1:0.15:0.5:0.8:0.9:40.

[0067] After transferring the mixed system to a reactor, it was hydrothermally treated, first at 170°C for 24 hours and then at 110°C for 30 hours. After filtration, the resulting solid was dried at 110°C for 12 hours and then calcined at 500°C for 5 hours in a 50% steam atmosphere to obtain the CuO-encapsulated all-silicon Silicalite-1 molecular sieve.

[0068] The CuO-encapsulated all-silicon Silicalite-1 molecular sieve was tableted and crushed to obtain 20-40 mesh particles. 2 g of the particles were weighed and loaded into the reaction tube of a fixed-bed reactor. The particles were reduced at 220°C and a H2 concentration of 15% for 24 hours to prepare the Cu-encapsulated all-silicon Silicalite-1 molecular sieve.

[0069] The fixed bed reactor was heated to 225°C and the system pressure was increased to 0.11 MPa under anaerobic conditions. A mixture of cyclohexene and H2O was introduced into the fixed bed reactor at a molar ratio of cyclohexene to H2O of 1:3 and contacted with the Cu-encapsulated all-silicon Silicalite-1 molecular sieve. The mass space velocity of cyclohexene was 2 h -1 The obtained reaction mass is condensed and then separated into water and oil, the water phase enters the reaction cycle, and the oil phase is fractionated to obtain the reactants cyclohexene, cyclohexanol and cyclohexanone; the cyclohexene enters the reaction cycle.

[0070] Examples 4 to 7

[0071] Examples 4-7 provide a Cu-encapsulated all-silicon Silicalite-1 molecular sieve, its preparation method, and a method for directly preparing ketones from olefins. Compared to Example 1, Examples 4-7 use the same steps for preparing the Cu-encapsulated all-silicon Silicalite-1 molecular sieve, but differ in the raw materials, raw material ratios, and some preparation conditions. Details are shown in Table 1. In the methods for directly preparing ketones from olefins, the raw material used is cyclohexene, but the preparation conditions vary. Details are shown in Table 1.

[0072] Table 1. Examples 4 to 7

[0073]

[0074] Examples 8 to 10

[0075] Examples 8-10 provide a Cu-encapsulated all-silicon Silicalite-1 molecular sieve, its preparation method, and a method for directly preparing ketones from olefins. The steps for preparing the Cu-encapsulated all-silicon Silicalite-1 molecular sieve in Examples 8-10 are the same as in Example 1, but differ in the raw materials, raw material ratios, and some preparation conditions. Details are shown in Table 2. The raw materials and preparation conditions in the method for directly preparing ketones from olefins vary; details are shown in Table 2.

[0076] Table 2. Examples 8 to 10

[0077]

[0078] Examples 11-12

[0079] Examples 11-12 provide a Cu-encapsulated all-silicon beta molecular sieve, its preparation method, and a method for directly preparing ketones from olefins. The steps for preparing the Cu-encapsulated all-silicon beta molecular sieve in Examples 11-12 are the same as in Example 1, but differ in the raw materials, raw material ratios, and some preparation conditions. Details are shown in Table 3. The raw materials and preparation conditions in the method for directly preparing ketones from olefins vary; details are shown in Table 3.

[0080] Table 3. Examples 11-12

[0081]

[0082] Table 4 Crystal structure and catalytic effect of Cu-encapsulated all-silicon molecular sieve

[0083]

[0084] The present invention provides a Cu-encapsulated all-silicon molecular sieve. An important factor affecting its performance in the direct catalytic synthesis of ketones from olefins is the content of dehydrogenation active centers and Lewis acid centers in the catalytic material, that is, the molar ratio of silicon to copper in the step 1. In addition, another important factor affecting the catalytic performance of the molecular sieve is the Lewis acid content, specific surface area and pore volume in the molecular sieve. Combining Table 4 and Examples 6 to 7, it can be seen that when the molar ratio of copper in the molecular sieve is less than or equal to 0.005 and the specific surface area of ​​the molecular sieve is greater than or equal to 624m 2 / g, pore volume greater than or equal to 0.38cm 3 / g, the catalytic effect of the corresponding all-silicon molecular sieve encapsulated with Cu will be affected to a certain extent, but the selectivity of the product organic ketone is still higher than 98%. Combining Table 4 and Examples 8 to 10, it can be seen that the selection of molecular sieve raw material silicon source and nitrogen-containing heterocyclic compound will also affect the specific surface area of ​​the molecular sieve (≤79m 2 / g) and pore volume (0.11 cm 3 / g) and thus affect its catalytic performance.

[0085] The present invention provides a Cu-encapsulated all-silicon molecular sieve that combines hydration and dehydrogenation functions, resolving the problem of coupling olefin hydration and secondary alcohol dehydrogenation reactions in the olefin-to-ketone process. Organic ketones can be directly produced at the same reaction temperature, simplifying the process flow. Compared to existing olefin-to-ketone technologies, the present invention utilizes the bifunctional molecular sieve to catalyze the direct production of ketones from olefins, increasing the olefin conversion rate to as high as 37.5%, and achieving a selectivity of 94% or higher for the product organic ketones. This improves the effective utilization of olefins while ensuring high selectivity for organic ketones, significantly improving product production efficiency and reducing the recycling energy consumption of the substrate olefins, making the olefin-to-ketone production process more economical.

[0086] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection of the present invention.

Claims

1. A method for directly preparing ketones from olefins, characterized in that: The method uses a bifunctional molecular sieve; the bifunctional molecular sieve includes a dehydrogenation active center and a Lewis acid center; the dehydrogenation active center is selected from at least one of Group IB metals, and its content is 0.01-60wt.%; the Lewis acid center is provided by a molecular sieve structure, and the molecular sieve is selected from one of the all-silicon molecular sieves.

2. The method according to claim 1, characterized in that The dehydrogenation active center is selected from at least one of Cu, Ag, and Au metals; and the all-silicon molecular sieve is selected from at least one of all-silicon Silicalite-1 and all-silicon Beta molecular sieve.

3. The method according to claim 2, characterized in that The bifunctional molecular sieve is at least one of an all-silicon molecular sieve encapsulating Cu or an all-silicon molecular sieve encapsulating Ag; the all-silicon molecular sieve encapsulating Cu is at least one of an all-silicon Silicalite-1 molecular sieve encapsulating Cu or an all-silicon Beta molecular sieve encapsulating Cu; the all-silicon molecular sieve encapsulating Ag is at least one of an all-silicon Silicalite-1 molecular sieve encapsulating Ag or an all-silicon Beta molecular sieve encapsulating Ag.

4. The method according to any one of claims 1 to 3, characterized in that: In the bifunctional molecular sieve, the Lewis acid content is 1 to 200 μmol / g, and the specific surface area is 40 to 679 m 2 / g, pore volume of 0.05~0.45cm 3 / g, the dehydrogenation active center is located inside the molecular sieve crystal and / or outside the molecular sieve crystal.

5. The method according to claim 3, characterized in that The preparation method of the Cu-encapsulated all-silicon molecular sieve comprises the following steps: Step 1: Mixing a silicon source, a copper source, a dispersant, a nitrogen-containing heterocyclic compound, an alkali source, and H2O in proportion to obtain a mixed system; Step 2: subjecting the mixed system of step 1 to hydrothermal treatment, and then filtering, drying, calcining and reducing to obtain the Cu-encapsulated all-silicon molecular sieve.

6. The method according to claim 5, characterized in that In the step 1, the silicon source is selected from at least one of organic silicate, silica gel, white carbon black, and silica sol; the copper source is selected from at least one of copper nitrate, copper chloride, tetraphenylporphyrin copper, and copper acetylacetonate; the dispersant is selected from at least one of ethylamine, ethylenediamine, propylenediamine, hexamethylenediamine, aniline, pyridine, thiophene, thiol, thiophenol, and thioether; the alkali source is selected from at least one of alkali metal hydroxide, ammonia water, urea, hydrazine hydrate, sodium carbonate, sodium bicarbonate, aliphatic amine, aliphatic alcoholamine, and quaternary ammonium base; and the nitrogen-containing heterocyclic compound is selected from at least one of theophylline, guanosine, adenosine, guanine, adenine, and adefovir.

7. The method according to claim 6, characterized in that In the step 1, the nitrogen-containing heterocyclic compound is a mixture of theophylline and adenine, and the molar ratio of theophylline to adenine in the mixture is (0.4-3):

1.

8. The method according to claim 5, characterized in that The molar ratio of the silicon source, copper source, dispersant, nitrogen-containing heterocyclic compound, alkali source and H2O in step 1 is 1: (0.005-0.4): (0.05-1.6): (0.08-2.2): (0.15-3): (10-200); the silicon source is calculated as SiO2, the alkali source is calculated as N or OH - count.

9. The method according to claim 1, characterized in that At a reaction temperature of 100-400°C, a reaction pressure of 0.05-5 MPa, and an olefin mass space velocity of 0.1-1000 h -1 Under the conditions of olefin and water in a molar ratio of 1: (0.5-50), the reaction is carried out in the presence of the bifunctional molecular sieve and the product is recovered.

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