A method and system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol

Abstract

The application provides a method and system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, which adopts a gas-liquid separator with an internal thread on the inner wall, ensures efficient separation of dimethyl ethylene ketone, reduces the content of isobutyric anhydride and isobutyric acid entering the subsequent system, and effectively protects the hydrogenation catalyst. At the same time, the hydrogen-rich tail gas is partially recycled to the cracking stage as a mixed carrier gas, which can provide a weak reducing atmosphere, optimize the cracking reaction path, inhibit the cracking side reaction of isobutyric anhydride, reduce the production of carbon deposition, and improve the selectivity of dimethyl ethylene ketone. The reaction heat recycles the high-grade heat energy inside the system, greatly reducing the consumption of external energy supply. In addition, the hydrogenation catalyst used in the method has a dual functional system of hydrogenation and in-situ conversion of trace impurities, improving the hydrogenation reaction conversion rate and selectivity.

Description

Technical Field

[0001] This invention belongs to the field of polymer synthesis technology, and in particular relates to a method and system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. Background Technology

[0002] 2,2,4,4-Tetramethyl-1,3-cyclobutanediol (CBDO) is an important diol polyester monomer, mainly used in the production of high-performance polyester materials. Copolyesters synthesized from CBDO have characteristics such as high melt viscosity, high glass transition temperature, and ease of processing. Their main applications include: replacing harmful bisphenol A-containing polyester materials in baby products and medical devices; preparing polyester materials that are easily processed into films and sheets; and acting as antibacterial agents in water-based coatings, personal care, medical, and household care products.

[0003] The current mainstream industrial method for synthesizing CBDO involves the thermal cracking of isobutyric anhydride or isobutyric acid to produce dimethyl ketene, followed by dimerization to obtain 2,2,4,4-tetramethyl-1,3-cyclobutanedione, and finally catalytic hydrogenation to obtain the target product CBDO. This process suffers from problems such as a long process flow, high energy consumption, and inconsistent optimization goals for each step (patent CN117486703A). For example, the cracking step, aiming for high conversion and selectivity, inevitably increases the cracking temperature (CN117342934A), leading to continuous carbon deposition and accumulation. The subsequent hydrogenation step requires higher temperatures and pressures (CN105732329B), while the overall energy utilization efficiency of the entire process has significant room for improvement. Furthermore, if isobutyric acid in the cracking products cannot be effectively removed or converted in existing technologies, it may affect the activity of subsequent hydrogenation catalysts.

[0004] Therefore, it is of great significance to develop an integrated process that can synergistically optimize the entire process, reduce energy consumption, and improve overall economic efficiency. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method and system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol to solve the above problems.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows: A method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, the method comprising the following steps: I. Preparation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione The raw material is preheated and then pyrolyzed. The pyrolysis residence time is 0.1-2 s, and the pressure is 10-101 kPa, to obtain a mixed gas containing dimethyl ketene. The pyrolysis residence time is related to the pressure; that is, under the same gas volume, the lower the pressure, the shorter the residence time. The extremely short residence time can effectively prevent dimethyl ketene from regenerating isobutyric anhydride, thereby improving the conversion rate. The mixed gas is then condensed, gas-liquid separated, and absorbed. The absorbent is dimerized to obtain a reaction liquid containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione. The gas-liquid separation uses a gas-liquid separator with internal threads on the inner wall to efficiently separate the dimethyl ketene gas produced by pyrolysis from the condensed isobutyric acid and isobutyric anhydride liquids. II. Hydrogenation The reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione is directly mixed with hydrogen and preheated without separation. A hydrogenation reaction is then carried out under the action of a hydrogenation catalyst to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The heat released by the hydrogenation reaction is recovered through a heat exchange system for preheating of the raw materials. The hydrogen-rich tail gas from the hydrogenation reaction is recycled to the cracking stage and mixed with the existing carrier gas for reuse, thereby suppressing the cracking side reactions of isobutyric anhydride, reducing carbon deposition, and improving the selectivity of dimethyl ketene. The hydrogenation catalyst used is the hydrogenation catalyst described above. The hydrogenation catalyst is a functional core-shell structure catalyst, comprising a core support and a shell layer. The core support is loaded with an active metal, which includes a main metal and a secondary metal. The main metal and the secondary metal are alternately deposited on the core support using atomic layer deposition technology to form an alternating metal alloy layer.

[0007] Furthermore, the molar ratio of the main metal is 60-90%, and the molar ratio of the auxiliary metal is 10-40%. The alternating deposition method is as follows: after the main metal is deposited for 15-25 seconds, the auxiliary metal is deposited for another 10-15 seconds, and the alternating deposition cycle is repeated 5-10 times; the main metal is deposited for a longer time to ensure the deposition effect, while the auxiliary metal is used in smaller quantities and has a shorter deposition time. And / or, the thickness of the alternating metal alloy layer is 2-10nm. The thickness of the alternating metal alloy layer should not be too thick, as too thick a layer will cause metal layer accumulation, and too thin a layer will cause a decrease in catalytic effect.

[0008] Furthermore, the raw material for the core carrier is selected from one of silicon oxide, titanium oxide, zirconium oxide, and magnesium oxide, with silicon oxide being preferred; the diameter of the core carrier is 50-100 nm; if the particle size of the core carrier is too large, the metal loading rate will be low, and if the particle size is too small, it will not be suitable for loading. And / or, the raw material of the shell is selected from one of alumina, calcium oxide, silicon-aluminum composite oxide, and calcium-magnesium composite oxide, preferably alumina; the thickness of the shell is 1-5 nm; if the shell is too thick, it will affect the contact efficiency between the substrate and the catalyst; if it is too thin, it will not play a stabilizing and protective role for the metal. And / or, the shell accounts for 5-10% of the mass of the core carrier.

[0009] Furthermore, the mass percentage of the active metal relative to the core carrier is 1-10%, preferably 2-5%; And / or, the main metal is one or more of Ru, Pt, Rh, and Pd, and the auxiliary metal is one or more of Ni, Cu, Zn, Co, Fe, Sn, Cr, and Mn; Preferably, the combination of the main metal and the auxiliary metal is Pd-Co, Rh-Co, Pd-Co-Ni, or Pt-Co-Ni.

[0010] Furthermore, the hydrogenation catalyst is prepared by the following method: first, nanospheres are prepared using the sol-gel method as the core support; then, the main metal and auxiliary metal are cyclically deposited at 200-300℃ using atomic layer deposition technology to form an alternating metal alloy layer; then, the outer shell is deposited; finally, the prepared catalyst is calcined to stabilize the structure.

[0011] Furthermore, the specific method of the sol-gel method is as follows: the raw material of the core carrier is reacted with the silane coupling agent in a solvent at 80-100℃ for 5-10 hours, filtered, washed with ethanol, and vacuum dried for 8-12 hours to obtain the core carrier; wherein, the mass percentage of the silane coupling agent relative to the raw material of the core carrier is 0.5-2%; The method for depositing the outer shell is as follows: at 150-200℃, the raw material of the outer shell is deposited on the surface of the core carrier to form a thin layer, and then softened and annealed at 150-200℃ for 30-60 minutes. The final catalyst was calcined at 200-400℃ for 12-48 hours.

[0012] Furthermore, the catalyst powder can be processed into the required particle size by methods such as tableting.

[0013] Specifically, the catalyst powder is pressed into sheets or cylinders, which are then placed in a fixed-bed reactor for hydrogenation.

[0014] Furthermore, the raw material for pyrolysis is isobutyric anhydride or isobutyric acid, and the raw material is mixed with an inert gas at a volume ratio of 1:100-1000 and preheated at a temperature of 100-400℃, and the pyrolysis temperature is 400-700℃; the inert gas is nitrogen or helium, preferably nitrogen; And / or, the condensation temperature is -20-40℃, the absorption temperature is -20-40℃, and the absorption pressure is 100-600kPa; the absorbent used for absorption is one or more of ethyl acetate, n-butyl acetate, isobutyl acetate, or isobutyl isobutyrate; the absorption liquid contains 5-50% dimethyl ketone by mass. And / or, the dimerization is carried out at a temperature of 80-150°C, a reaction pressure of 100-600 kPa, a reaction time of 30-120 min, and in an inert gas atmosphere.

[0015] Furthermore, the hydrogenation reaction conditions are as follows: temperature 100-200℃, pressure 2.0-6.0MPa, molar ratio of hydrogen to 2,2,4,4-tetramethyl-1,3-cyclobutanedione 150-500:1, and residence time 0.5-10s.

[0016] Furthermore, the volume ratio of the hydrogen-rich tail gas to the original carrier gas is 1:10-100.

[0017] Too little hydrogen-rich tail gas will not be effective in suppressing cracking side reactions; too much hydrogen-rich tail gas will produce hydrogenation byproducts.

[0018] Preferably, the pyrolysis residence time is 0.1-0.3 s.

[0019] This invention also provides a system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, the system being used in the method described above. The system comprises a cracking reaction unit, a gas-liquid separation and absorption unit, a dimerization reaction unit, and a hydrogenation reaction unit connected in sequence. The cracking reaction unit includes a preheater and a cracking reactor; the gas-liquid separation and absorption unit includes a gas-liquid separator and an absorption reactor; the inner wall of the gas-liquid separator is provided with internal threads; the hydrogenation reaction unit is a fixed-bed hydrogenation reactor; the heat released by the hydrogenation reaction is recovered to the preheater through a heat exchange system for preheating the raw materials; the hydrogen-rich tail gas from the hydrogenation reaction is recycled to the preheater of the cracking reaction unit and mixed with the existing carrier gas for utilization. Online chromatographic analyzers are also installed at the cracked gas outlet, dimerization reaction liquid outlet, and hydrogenation feed to monitor the concentration of components in real time.

[0020] The components include isobutyric anhydride, dimethyl ketone, and 2,2,4,4-tetramethyl-1,3-cyclobutanedione.

[0021] Compared with the prior art, the method and system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol described in this invention have the following advantages: (1) This invention creatively couples the hydrogenation reaction (exothermic) with the preheating of the cracking feedstock (endothermic), effectively recovering and utilizing the high-grade thermal energy within the system, significantly reducing the consumption of external energy, and reducing the energy consumption of the entire process by more than 20% compared to the traditional segmented process. At the same time, the dimerization reaction liquid is directly hydrogenated, avoiding the steps of separation, purification, and redissolution of the intermediate product cyclobutanedione, greatly simplifying the process flow.

[0022] (2) The method of this invention first controls the pyrolysis conditions, namely specific temperature, pressure, and residence time, to ensure a high conversion rate of pyrolysis. Secondly, the recovery and utilization of hydrogen-rich tail gas reduces pyrolysis side reactions and improves the selectivity of the pyrolysis product dimethyl ketene, resulting in a very high selectivity of dimethyl ketene in the dimerization reaction solution, greater than 96%. Furthermore, thanks to the control of temperature, pressure, and time conditions during the dimerization reaction, the obtained 2,2,4,4-tetramethyl-1,3-cyclobutanedione has a high selectivity, greater than 95%, and can be directly used for hydrogenation without further purification, simplifying the system reaction process. Finally, this application uses a specific core-shell structured hydrogenation catalyst to improve the hydrogenation selectivity of cyclobutanedione, and shortens the hydrogenation time and improves the hydrogenation efficiency by optimizing the reaction conditions. In contrast, existing methods result in hydrogenation reaction solution products with lower purity and more complex post-processing.

[0023] (3) The hydrogenation catalyst used in this invention first modifies the surface of the raw material on the core support with a silane coupling agent to facilitate its bonding with metal atoms. Secondly, it uses atomic layer deposition (ALD) technology to load the active metal. ALD technology can achieve atomic-level thickness control of the metal, avoiding metal agglomeration, and simultaneously achieving a bimetallic or multimetal alternating active catalyst layer, overcoming the problem of inhomogeneous alloy phase caused by inter-metal diffusion in the traditional impregnation method. The alternating metal alloy layer can greatly improve the metal utilization rate and regulate the electronic structure of the multimetals, optimizing the activation ability of hydrogen. For example, metal Pd can promote the dissociation of hydrogen to generate active hydrogen atoms, while another metal Ni regulates the nucleophilicity of hydrogen atoms, making them more inclined to attack carbonyl groups (C=O) to generate target products, thereby improving the conversion rate and selectivity of the hydrogenation reaction. Finally, the weakly basic shell acts as a "sieve," which can regulate the contact frequency and contact time between 2,2,4,4-tetramethyl-1,3-cyclobutanedione molecules and the active metal surface, accelerating the separation of raw materials and products and improving hydrogenation efficiency. This catalyst is a dual-function system that combines hydrogenation and in-situ conversion of trace impurities. Specifically, while hydrogenating 2,2,4,4-tetramethyl-1,3-cyclobutanedione to 2,2,4,4-tetramethyl-1,3-cyclobutanediol, it converts the trace amounts of isobutyric acid remaining in the reaction solution into isobutyric anhydride, thereby reducing the impact of acidic materials on the active site and extending the catalyst lifetime.

[0024] (4) The method of the present invention introduces an online analysis system, which can adjust the process parameters in real time according to the actual concentration and impurity content of the material, so as to realize dynamic optimization and stable control of the process window. For example, the purity and content of the cracking product dimethyl ketene can be detected online. If the content is low, the feed rate and preheating temperature can be increased; if the purity decreases, the amount of hydrogen-rich tail gas can be appropriately increased to suppress side reactions and improve selectivity.

[0025] (5) The present invention employs a gas-liquid separator with internal threads on its inner wall, which ensures efficient separation of dimethyl ketene, reduces the content of isobutyric anhydride and isobutyric acid entering the subsequent system, and effectively protects the hydrogenation catalyst. At the same time, the hydrogen-rich tail gas is partially recycled to the cracking stage as a mixed carrier gas, which can provide a weakly reducing atmosphere, optimize the cracking reaction path, suppress the cracking side reaction of isobutyric anhydride, reduce carbon deposition, and improve the selectivity of dimethyl ketene.

[0026] (6) In the method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol described in this invention, the conversion rate of the cracking reaction feedstock is ≥50%, the selectivity of dimethyl ketene is ≥95%; the absorption efficiency of the absorbent is ≥90%; the conversion rate of dimethyl ketene is ≥98%, the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol is ≥95%; the conversion rate of the hydrogenation feedstock 2,2,4,4-tetramethyl-1,3-cyclobutanediol is ≥98%, the selectivity of the hydrogenation product 2,2,4,4-tetramethyl-1,3-cyclobutanediol is ≥95%; and the final hydrogenation product 2,2,4,4-tetramethyl-1,3-cyclobutanediol is purified by distillation or recrystallization to a purity of ≥99.5%. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart of the method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to the present invention. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0029] In this document, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0030] In this document, when values ​​are described as ranges, it should be understood that such disclosure includes disclosure of all possible subranges within that range, as well as the specific numerical values ​​that fall within that range, regardless of whether the specific numerical value or specific subrange is explicitly specified.

[0031] In this article, the terms "multiple" or "more than" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0032] In this document, the terms "preferred" and "more preferred" are used only to describe implementation methods or embodiments with better effects, and should be understood as not constituting a limitation on the scope of protection of this invention.

[0033] In this document, terms such as "further" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0034] In this article, the terms "and / or" or "and / or" describe an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0035] In this document, the term "about" means a specified value of + / - 10%, preferably + / - 5%, and more preferably + / - 1%.

[0036] In this article, the terms “include,” “including,” “have,” “contain,” etc., are all open-ended terms, meaning that they include but are not limited to.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1 I. Preparation of Hydrogenation Catalysts The hydrogenation catalyst is a functional core-shell structure catalyst, comprising a core support and a shell. The core support is made of silicon oxide and has a diameter of 80 nm. The core support is loaded with active metal Pd-Co, with a Pd-Co molar ratio of 8:2. The active metal accounts for 3% of the mass percentage of the core support. The active metal is alternately deposited on the core support using atomic layer deposition technology to form alternating metal alloy layers with a thickness of 3 nm. The shell is an alumina shell with a thickness of 2 nm. The alumina shell accounts for 5% of the mass percentage of the silicon oxide core support.

[0040] The preparation method of the hydrogenation catalyst is as follows: (1) Monodisperse mesoporous silica nanospheres were prepared as the core support using the sol-gel method. Subsequently, the core support and a silane coupling agent (3-aminopropyltriethoxysilane) were reacted in tetrahydrofuran solvent at 80°C for 5 h. After filtration, the mixture was washed with ethanol and vacuum dried for 12 h to obtain the silica core support. The silane coupling agent accounted for 1% of the mass of silica and was used to improve the loading and dispersion of the metal active centers.

[0041] (2) Subsequently, the active metal was loaded using atomic layer deposition technology.

[0042] Pd and Ru metal precursors were deposited alternately in cycles at 250°C. The main metal was deposited for 15 seconds, and the auxiliary metal was deposited for 10 seconds. The alternating deposition cycle was repeated 10 times to form an alternating metal alloy layer.

[0043] (3) Then, the alumina surface of the outer shell is deposited. At 160°C, the alumina is deposited on the catalyst shell to form a thin layer of alumina. The alumina is then softened and annealed at 160°C for 45 minutes to eliminate microcracks or stress during the deposition process, while retaining the weak alkaline properties of the alumina.

[0044] (4) The catalyst was calcined at 250°C for 14 hours to stabilize its structure. Finally, the catalyst powder was processed into the required particle size by means of tableting or other methods.

[0045] II. Preparation of 2,2,4,4-Tetramethyl-1,3-cyclobutanediol The preparation method includes the following steps: S1, pyrolysis: Isobutyric anhydride was mixed with nitrogen at a rate of 0.05 mL / min and preheated to 180 °C before being fed into a 400 °C pyrolysis furnace for pyrolysis. The residence time was 0.19 s and the pressure was 40 kPa (absolute pressure), yielding a mixed gas containing dimethyl ketene.

[0046] S2. Separation and Absorption: The mixed gas obtained in step S1 is condensed to 20°C and then enters a gas-liquid separator with internal threads. The separated gas components are mainly dimethyl ketone (DMK) and inert gas (nitrogen). The separated gas is absorbed by ethyl acetate at an absorption temperature of 20°C and an absorption pressure of 200 kPa (absolute pressure) to obtain an absorbent liquid with a DMK mass fraction of approximately 32%.

[0047] S3, dimerization: The absorbent containing dimethyl ketene (DMK) obtained in step S2 was subjected to a dimerization reaction at 80°C under an inert gas (nitrogen) atmosphere, with a reaction pressure of 200 kPa and a reaction time of 120 min, to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione (TMCD).

[0048] S4, Hydrogenation: The reaction solution obtained in step S3 was directly mixed with hydrogen (H2 / TMCD molar ratio 150) without separation. After preheating, it was fed into a fixed-bed reactor packed with a hydrogenation catalyst. The hydrogenation reaction was carried out under the action of the prepared hydrogenation catalyst to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The hydrogenation reaction conditions were: temperature 180℃, pressure 4.0 MPa, and residence time 1 s.

[0049] The system used in the above-described method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, such as Figure 1 As shown, the system includes a pyrolysis reaction unit, a gas-liquid separation and absorption unit, a dimerization reaction unit, and a hydrogenation reaction unit connected in sequence. The pyrolysis reaction unit includes a preheater and a pyrolysis reactor; the gas-liquid separation and absorption unit includes a gas-liquid separator and an absorption reactor; the gas-liquid separator has internal threads on its inner wall; the hydrogenation reaction unit is a fixed-bed hydrogenation reactor. The heat released by the hydrogenation reaction is recovered to the preheater through a heat exchange system (such as a heat exchanger) for preheating the feedstock. The hydrogen-rich tail gas from the hydrogenation reaction is recycled to the preheater of the pyrolysis reaction unit and mixed with the existing carrier gas for utilization, thereby suppressing the pyrolysis side reactions of isobutyric anhydride, reducing carbon deposition, and improving the selectivity of dimethyl ketene. The volume ratio of the hydrogen-rich tail gas to the existing carrier gas is 1:50.

[0050] Online chromatographic analyzers are also installed at the cracked gas outlet, dimerization reaction liquid outlet, and hydrogenation feed to monitor the concentration of components in real time.

[0051] Online chromatographic analysis showed that the isobutyric anhydride pyrolysis conversion rate was 50%, and the selectivity for dimethyl ketene was 98%. After dimerization, the dimethyl ketene conversion rate was 99%, and the selectivity for 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 96%. In the hydrogenation stage, the 2,2,4,4-tetramethyl-1,3-cyclobutanedione conversion rate was 99%, and the hydrogenation product, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, had a selectivity of 97%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 99.8%.

[0052] Example 2 I. Preparation of Hydrogenation Catalysts The hydrogenation catalyst is a functional core-shell structure catalyst, comprising a core support and a shell. The core support is made of silicon dioxide and has a diameter of 50 nm. The core support is loaded with an active metal, Rh-Co, with a molar ratio of 6:4. The active metal accounts for 5% of the mass of the core support. The active metal is alternately deposited on the core support using atomic layer deposition technology to form alternating metal alloy layers with a thickness of 5 nm. The shell is an alumina shell with a thickness of 3 nm. The alumina shell accounts for 10% of the mass of the silicon dioxide core support.

[0053] The preparation method of the hydrogenation catalyst is as follows: (1) Monodisperse mesoporous silica nanospheres were prepared as the core support using the sol-gel method. Subsequently, the core support and a silane coupling agent (3-aminopropyltriethoxysilane) were reacted in tetrahydrofuran solvent at 80 °C for 6 h. After filtration, the mixture was washed with ethanol and vacuum dried for 12 h to obtain the silica core support. The silane coupling agent accounted for 2% of the mass of silica and was used to improve the loading and dispersion of the metal active centers.

[0054] (2) Subsequently, the active metal was loaded using atomic layer deposition technology.

[0055] Rh and Co metal precursors were deposited alternately in cycles at 200°C. The main metal was deposited for 20 seconds, and the auxiliary metal was deposited for 12 seconds. The alternating deposition cycle was repeated 7 times to form an alternating metal alloy layer.

[0056] (3) Then, the alumina surface of the outer shell is deposited. At 150°C, the alumina is deposited on the catalyst shell to form a thin layer of alumina. The alumina is then softened and annealed at 150°C for 50 min to eliminate microcracks or stress during the deposition process, while retaining the weak alkaline properties of the alumina.

[0057] (4) The catalyst was calcined at 200°C for 20 h to stabilize its structure. Finally, the catalyst powder was processed into the required particle size by means of tableting or other methods.

[0058] II. Preparation of 2,2,4,4-Tetramethyl-1,3-cyclobutanediol The preparation method includes the following steps: S1, pyrolysis: Isobutyric anhydride was mixed with nitrogen at a rate of 0.1 mL / min and preheated to 200 °C before being fed into a 500 °C pyrolysis furnace for pyrolysis. The residence time was 0.25 s and the pressure was 60 kPa (absolute pressure), yielding a mixed gas containing dimethyl ketene.

[0059] S2. Separation and Absorption: The mixed gas obtained in step S1 is condensed to 0°C and then enters a gas-liquid separator with internal threads. The separated gas components are mainly dimethyl ketone (DMK) and inert gas (nitrogen). The separated gas is absorbed by isobutyl acetate at an absorption temperature of -0°C and an absorption pressure of 400 kPa (absolute pressure) to obtain an absorbent liquid with a DMK mass fraction of approximately 38%.

[0060] S3, dimerization: The absorbent containing dimethyl ketene (DMK) obtained in step S2 was dimerized at 120°C and 400 kPa absolute pressure for 80 min under an inert gas (nitrogen) atmosphere to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione (TMCD).

[0061] S4, Hydrogenation: The reaction solution obtained in step S3 was directly mixed with hydrogen (H2 / TMCD molar ratio 300) without separation. After preheating, it was introduced into a fixed-bed reactor packed with a hydrogenation catalyst. The hydrogenation reaction was carried out under the action of the prepared hydrogenation catalyst to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The hydrogenation reaction conditions were: temperature 200℃, pressure 3.5 MPa, and residence time 1.6 s.

[0062] The system used in the method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol described above is the same as in Example 1. The volume ratio of hydrogen-rich tail gas to the original carrier gas is 1:20.

[0063] Online chromatographic analysis showed that the isobutyric anhydride pyrolysis conversion rate was 58%, and the selectivity for dimethyl ketene was 97.8%. After dimerization, the dimethyl ketene conversion rate was 99%, and the selectivity for 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 96.8%. In the hydrogenation stage, the 2,2,4,4-tetramethyl-1,3-cyclobutanedione conversion rate was 99%, and the selectivity for 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 97.3%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 99.9%.

[0064] Example 3 I. Preparation of hydrogenation catalysts The hydrogenation catalyst is a functional core-shell structure catalyst, comprising a core support and a shell. The core support is made of silicon dioxide and has a diameter of 100 nm. The core support is loaded with active metal Pd-Co-Ni, with a Pd-Co-Ni molar ratio of 7:2:1. The active metal accounts for 4% of the mass percentage of the core support. The active metal is alternately deposited on the core support using atomic layer deposition technology to form alternating metal alloy layers with a thickness of 7 nm. The shell is an alumina shell with a thickness of 4 nm, and the alumina shell accounts for 6% of the mass percentage of the silicon dioxide core support.

[0065] The preparation method of the hydrogenation catalyst is as follows: (1) Monodisperse mesoporous silica nanospheres were prepared as the core support using the sol-gel method. Subsequently, the core support and a silane coupling agent (3-aminopropyltriethoxysilane) were reacted in tetrahydrofuran solvent at 80 °C for 10 h. After filtration, the mixture was washed with ethanol and vacuum dried for 12 h to obtain the silica core support. The silane coupling agent accounted for 0.5% of the mass of silica and was used to improve the loading and dispersion of the metal active centers.

[0066] (2) Subsequently, the active metal was loaded using atomic layer deposition technology.

[0067] Rh and Co metal precursors were deposited alternately in cycles at 300°C. After the main metal was deposited for 25 seconds, the auxiliary metal was deposited for 14 seconds. The alternating deposition cycle was repeated 8 times to form an alternating metal alloy layer.

[0068] (3) Then, the alumina surface of the outer shell is deposited. At 180°C, the alumina is deposited on the catalyst shell to form a thin layer of alumina. The alumina is then softened and annealed at 180°C for 50 minutes to eliminate microcracks or stress during the deposition process, while retaining the weak alkaline properties of the alumina.

[0069] (4) The catalyst was calcined at 300°C for 24 hours to stabilize its structure. Finally, the catalyst powder was processed into the required particle size by means of tableting or other methods.

[0070] II. Preparation of 2,2,4,4-Tetramethyl-1,3-cyclobutanediol The preparation method includes the following steps: S1, pyrolysis: Isobutyric anhydride was mixed with nitrogen at a rate of 0.02 mL / min and preheated to 250 °C before being fed into a pyrolysis furnace at 600 °C for pyrolysis. The residence time was 0.22 s and the pressure was 80 kPa (absolute pressure) to obtain a mixed gas containing dimethyl ketene.

[0071] S2. Separation and Absorption: The mixed gas obtained in step S1 is condensed to -10°C and then enters a gas-liquid separator with internal threads. The separated gas components are mainly dimethyl ketone (DMK) and inert gas (nitrogen). The separated gas is absorbed by isobutyl acetate at an absorption temperature of -10°C and an absorption pressure of 500 kPa (absolute pressure) to obtain an absorbent liquid with a DMK mass fraction of approximately 31%.

[0072] S3, dimerization: The absorbent containing dimethyl ketene (DMK) obtained in step S2 was dimerized at 150°C and 500 kPa absolute pressure for 50 min under an inert gas (nitrogen) atmosphere to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione (TMCD).

[0073] S4, Hydrogenation: The reaction solution obtained in step S3 was directly mixed with hydrogen (H2 / TMCD molar ratio 400) without separation. After preheating, it was introduced into a fixed-bed reactor packed with a hydrogenation catalyst. The hydrogenation reaction was carried out under the action of the prepared hydrogenation catalyst to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The hydrogenation reaction conditions were: temperature 200℃, pressure 5.0 MPa, and residence time 1.2 s.

[0074] The system used in the method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol described above is the same as in Example 1. The volume ratio of hydrogen-rich tail gas to the original carrier gas is 1:100.

[0075] Online chromatographic analysis showed that the isobutyric anhydride pyrolysis conversion rate was 66%, and the selectivity for dimethyl ketene was 97.3%. After dimerization, the dimethyl ketene conversion rate was 99%, and the selectivity for 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 96.6%. In the hydrogenation stage, the 2,2,4,4-tetramethyl-1,3-cyclobutanedione conversion rate was 99%, and the selectivity for 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 97.4%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 99.9%.

[0076] Example 4 I. Preparation of hydrogenation catalysts The hydrogenation catalyst is a functional core-shell structure catalyst, comprising a core support and a shell. The core support is made of silicon dioxide and has a diameter of 85 nm. The core support is loaded with active metal Pt-Co-Ni, with a Pt-Co-Ni molar ratio of 6:2:2. The active metal accounts for 2% of the mass percentage of the core support. The active metal is alternately deposited on the core support using atomic layer deposition technology to form alternating metal alloy layers with a thickness of 6 nm. The shell is an alumina shell with a thickness of 3 nm, and the alumina shell accounts for 5% of the mass percentage of the silicon dioxide core support.

[0077] The preparation method of the hydrogenation catalyst is as follows: (1) Monodisperse mesoporous silica nanospheres were prepared as the core support using the sol-gel method. Subsequently, the core support and a silane coupling agent (3-aminopropyltriethoxysilane) were reacted in tetrahydrofuran solvent at 80°C for 8 h. After filtration, the mixture was washed with ethanol and vacuum dried for 12 h to obtain the silica core support. The silane coupling agent accounted for 1% of the mass of silica and was used to improve the loading and dispersion of the metal active centers.

[0078] (2) Subsequently, the active metal was loaded using atomic layer deposition technology.

[0079] Rh and Co metal precursors were deposited alternately in cycles at 260°C. After the main metal was deposited for 20 seconds, the auxiliary metal was deposited for another 10 seconds. The alternating deposition cycle was repeated 7 times to form an alternating metal alloy layer.

[0080] (3) Then, the alumina surface of the outer shell is deposited. At 160°C, the alumina is deposited on the catalyst shell to form a thin layer of alumina. The alumina is then softened and annealed at 160°C for 45 minutes to eliminate microcracks or stress during the deposition process, while retaining the weak alkaline properties of the alumina.

[0081] (4) The catalyst was calcined at 280°C for 30 h to stabilize its structure. Finally, the catalyst powder was processed into the required particle size by means of tableting or other methods.

[0082] II. Preparation of 2,2,4,4-Tetramethyl-1,3-cyclobutanediol The preparation method includes the following steps: S1, pyrolysis: Isobutyric acid was mixed with nitrogen at a rate of 0.04 mL / min and preheated at 400 °C before being fed into a pyrolysis furnace at 700 °C for pyrolysis. The residence time was 0.12 s and the pressure was 100 kPa (absolute pressure) to obtain a mixed gas containing dimethyl ketene.

[0083] S2. Separation and Absorption: The mixed gas obtained in step S1 is condensed to -20°C and then enters a gas-liquid separator with internal threads. The separated gas components are mainly dimethyl ketone (DMK) and inert gas (nitrogen). The separated gas is absorbed by isobutyl isobutyrate at an absorption temperature of -20°C and an absorption pressure of 600 kPa (absolute pressure) to obtain an absorbent liquid with a DMK mass fraction of about 30%.

[0084] S3, dimerization: The absorbent containing dimethyl ketene (DMK) obtained in step S2 was dimerized at 150°C and 600 kPa absolute pressure for 30 min under an inert gas (nitrogen) atmosphere to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione (TMCD).

[0085] S4, Hydrogenation: The reaction solution obtained in step S3 was directly mixed with hydrogen (H2 / TMCD molar ratio 500) without separation. After preheating, it was fed into a fixed-bed reactor packed with a hydrogenation catalyst. The hydrogenation reaction was carried out under the action of the prepared hydrogenation catalyst to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The hydrogenation reaction conditions were: temperature 200℃, pressure 6.0 MPa, and residence time 1.5 s.

[0086] The system used in the method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol described above is the same as in Example 1. The volume ratio of hydrogen-rich tail gas to the original carrier gas is 1:70.

[0087] Online chromatographic analysis showed that the isobutyric acid degradation conversion rate was 60%, and the selectivity for dimethyl ketene was 97.0%. After dimerization, the dimethyl ketene conversion rate was 99%, and the selectivity for 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 96.5%. In the hydrogenation stage, the 2,2,4,4-tetramethyl-1,3-cyclobutanedione conversion rate was 99%, and the selectivity for 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 97.6%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 99.9% after distillation.

[0088] Comparative Example 1 The difference from Example 1 is that the hydrogenation catalyst uses a conventional loading method, that is, a soluble salt precursor solution containing a metal is impregnated and loaded onto a silica support, and the metal ratio in the resulting catalyst is Pd / SiO2=5 / 95, while other conditions remain unchanged.

[0089] During the hydrogenation reaction stage, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 85%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 85%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 96.8%.

[0090] It is evident that the hydrogenation catalyst prepared by conventional methods is less effective than the hydrogenation catalyst prepared according to the method described in this application. The core-shell structured hydrogenation catalyst of this application outperforms conventional hydrogenation catalysts in both feedstock hydrogenation conversion and product selectivity, and the purity of the cyclobutanediol product obtained is superior to that obtained by conventional methods.

[0091] Comparative Example 2 The difference from Example 1 is that the hydrogenation catalyst uses a single metal deposition method, the mass of metal Pd is 3% of the silica core support, and finally an alumina shell is deposited, which is 5% of the silica core support, while other conditions remain unchanged.

[0092] During the hydrogenation reaction stage, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 88%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 89%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 97.6%.

[0093] It is evident that the catalytic effect of a single active metal is significantly reduced, while bimetals can better enhance the catalytic effect. The bimetallic catalyst of this application can better promote hydrogen dissociation, optimize the hydrogenation pathway, and improve the conversion rate and selectivity of the hydrogenation reaction.

[0094] Comparative Example 3 The difference from Example 1 is that the hydrogenation catalyst does not have an alumina shell, while other conditions remain the same.

[0095] During the hydrogenation reaction stage, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 84%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 82%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 92.6%.

[0096] It is evident that the presence or absence of an alumina shell also affects conversion rate and selectivity. The alumina shell in this application acts as a molecular sieving agent, controlling the contact time between the substrate cyclobutanedione molecule and the active metal surface, separating the hydrogenation feedstock and product, and improving hydrogenation efficiency.

[0097] Comparative Example 4 The difference from Example 1 is that the residence time of the pyrolysis reaction is 3s, the pressure is 200kPa (absolute pressure), and other conditions remain the same.

[0098] The isobutyric anhydride pyrolysis conversion rate was 20%, and the selectivity for dimethyl ketene was 77.0%.

[0099] It is evident that pyrolysis reaction time and pressure affect the pyrolysis conversion rate and the selectivity of dimethyl ketene. An extremely short residence time can effectively prevent the regeneration of isobutyric anhydride from dimethyl ketene, thus improving the conversion rate. Conversely, a prolonged pyrolysis residence time results in longer material exposure at high temperatures, increased byproducts, and lower pyrolysis efficiency.

[0100] Comparative Example 5 The difference from Example 1 is that the pyrolysis gas is condensed to 20°C and then enters a gas-liquid separator without internal threads, while other conditions remain unchanged.

[0101] An absorbent solution with a DMK mass fraction of approximately 8% was obtained.

[0102] It is evident that gas-liquid separators with internal threads improve the gas-liquid separation effect of dimethyl ketene (DMK), while separators without internal threads cause the product DMK to be carried away with nitrogen, reducing the absorption effect.

[0103] Comparative Example 6 The difference from Example 1 is that the heat released by the hydrogenation reaction was not recovered and utilized, resulting in an overall energy consumption increase of 20%. The hydrogen-rich tail gas from the hydrogenation reaction was not recycled to the cracking stage. The isobutyric anhydride cracking conversion rate was 25%, and the selectivity of dimethyl ketene was 75.0%.

[0104] It is evident that recycling a portion of the hydrogen-rich tail gas to the pyrolysis stage as a mixed carrier gas can provide a weakly reducing atmosphere, optimize the pyrolysis reaction pathway, suppress the pyrolysis side reactions of isobutyric anhydride, reduce carbon deposit formation, and improve the selectivity of dimethyl ketene.

[0105] Comparative Example 7 The difference from Example 1 is that the main metal and auxiliary metal of the hydrogenation catalyst are atomically deposited simultaneously at a Pd-Co molar ratio of 8:2, without alternating deposition, while other conditions remain unchanged.

[0106] During the hydrogenation reaction stage, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 90%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 91%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 98.2%.

[0107] It is evident that when a mixed metal layer is deposited simultaneously with a primary metal and a secondary metal, the hydrogenation selectivity is reduced. In contrast, alternating metal alloy layers can significantly improve metal utilization and regulate the electronic structure of the multi-metal, thereby optimizing the activation ability of hydrogen and enhancing hydrogenation selectivity.

[0108] Comparative Example 8 The difference from Example 1 is that the number of main metal and auxiliary metal cyclic depositions of the hydrogenation catalyst is reduced from 10 times in Example 1 to 3 times, while other conditions remain unchanged.

[0109] During the hydrogenation reaction stage, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 92%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 90%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 98.4% after recrystallization.

[0110] It is evident that if the number of alternating depositions of the main metal and auxiliary metal is too small, it is similar to a mixed metal layer, which fails to achieve the optimization and screening effect of the alternating metal layer, thereby reducing the hydrogenation selectivity.

[0111] Comparative Example 9 The difference from Example 1 is that the metal combination of the hydrogenation catalyst is different. Atomic layer deposition technology is used to load Zn / Cr metals with a Zn / Cr molar ratio of 8:2, while other conditions remain the same.

[0112] During the hydrogenation reaction stage, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 81%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 78%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 80.5%.

[0113] It is evident that the selection of the metal active center is crucial for the hydrogenation reaction, and the bimetallic hydrogenation catalyst system in this application exhibits excellent hydrogenation performance.

[0114] Comparative Example 10 The difference from Example 1 is that the metal combination of the hydrogenation catalyst is different. Pd / Mn metal is loaded using atomic layer deposition technology with a Pd / Mn molar ratio of 8:2, while other conditions remain unchanged.

[0115] During the hydrogenation reaction stage, the conversion rate of 2,2,4,4-tetramethyl-1,3-cyclobutanedione was 84%, and the selectivity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol was 83%. Finally, the purity of 2,2,4,4-tetramethyl-1,3-cyclobutanediol after recrystallization was 85.8%.

[0116] It is evident that the selection of the metal active center is crucial for the hydrogenation reaction, and the bimetallic hydrogenation catalyst system in this application exhibits excellent hydrogenation performance.

[0117] As can be seen from the above examples and comparative examples, the preparation of 2,2,4,4-tetramethyl-1,3-cyclobutanediol using the catalyst, method, and system designed in this invention effectively reduces energy consumption, optimizes the process flow, and achieves high hydrogenation efficiency. In contrast, the unoptimized process, whether for cracking or hydrogenation, exhibits relatively low efficiency.

[0118] This invention is simple and easy to implement, providing an efficient and low-consumption method and system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. It is economically beneficial, environmentally friendly, and suitable for industrial production.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, characterized in that: The method includes the following steps: I. Preparation of 2,2,4,4-tetramethyl-1,3-cyclobutanedione The raw material is preheated and then pyrolyzed. The pyrolysis residence time is 0.1-2 s and the pressure is 10-101 kPa to obtain a mixed gas containing dimethyl ketene. The mixed gas is then condensed, gas-liquid separated and absorbed, and the absorbent is dimerized to obtain a reaction liquid containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione. The gas-liquid separation is performed using a gas-liquid separator with internal threads on the inner wall. II. Hydrogenation The reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanedione was directly mixed with hydrogen and preheated without separation. A hydrogenation reaction was then carried out under the action of a hydrogenation catalyst to obtain a reaction solution containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol. The heat released by the hydrogenation reaction was recovered through a heat exchange system for preheating of the raw materials. The hydrogen-rich tail gas from the hydrogenation reaction was recycled to the cracking stage and mixed with the existing carrier gas for reuse. The hydrogenation catalyst is a functional core-shell structure catalyst, comprising a core support and a shell layer. The core support is loaded with an active metal, which includes a main metal and a secondary metal. The main metal and the secondary metal are alternately deposited on the core support using atomic layer deposition technology to form an alternating metal alloy layer.

2. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 1, characterized in that: The molar ratio of the main metal is 60-90%, and the molar ratio of the auxiliary metal is 10-40%. The alternating deposition method is as follows: after the main metal is deposited for 15-25 seconds, the auxiliary metal is deposited for another 10-15 seconds, and the alternating deposition cycle is repeated 5-10 times. And / or, the thickness of the alternating metal alloy layers is 2-10 nm.

3. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 1, characterized in that: The raw material for the core carrier is selected from one of silicon oxide, titanium oxide, zirconium oxide, and magnesium oxide, with silicon oxide being preferred; the diameter of the core carrier is 50-100 nm. And / or, the raw material of the shell is selected from one of alumina, calcium oxide, silicon-aluminum composite oxide, and calcium-magnesium composite oxide, preferably alumina; the thickness of the shell is 1-5 nm; And / or, the shell accounts for 5-10% of the mass of the core carrier.

4. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 1, characterized in that: The mass percentage of the active metal relative to the core carrier is 1-10%, preferably 2-5%; And / or, the main metal is one or more of Ru, Pt, Rh, and Pd, and the auxiliary metal is one or more of Ni, Cu, Zn, Co, Fe, Sn, Cr, and Mn; Preferably, the combination of the main metal and the auxiliary metal is Pd-Co, Rh-Co, Pd-Co-Ni, or Pt-Co-Ni.

5. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 1, characterized in that: The hydrogenation catalyst was prepared by the following method: first, nanospheres were prepared using the sol-gel method as the core support; then, the main metal and auxiliary metal were alternately deposited at 200-300℃ using atomic layer deposition technology to form an alternating metal alloy layer; then, the outer shell was deposited; finally, the prepared catalyst was calcined to stabilize the structure.

6. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 5, characterized in that: The specific method of the sol-gel method is as follows: the core carrier raw material and the silane coupling agent are reacted in a solvent at 80-100℃ for 5-10 hours, filtered, washed with ethanol, and vacuum dried for 8-12 hours to obtain the core carrier; wherein, the mass percentage of the silane coupling agent relative to the core carrier raw material is 0.5-2%; The method for depositing the outer shell is as follows: at 150-200℃, the raw material of the outer shell is deposited on the surface of the core carrier to form a thin layer, and then softened and annealed at 150-200℃ for 30-60 minutes. The final catalyst was calcined at 200-400℃ for 12-48 hours.

7. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 1, characterized in that: The raw material for pyrolysis is isobutyric anhydride or isobutyric acid. The raw material is mixed with an inert gas at a volume ratio of 1:100-1000 and preheated at a temperature of 100-400℃. The pyrolysis temperature is 400-700℃. The inert gas is nitrogen or helium, preferably nitrogen. And / or, the condensation temperature is -20-40℃, the absorption temperature is -20-40℃, and the absorption pressure is 100-600kPa; the absorbent used for absorption is one or more of ethyl acetate, n-butyl acetate, isobutyl acetate, or isobutyl isobutyrate; the absorption liquid contains 5-50% dimethyl ketone by mass. And / or, the dimerization is carried out at a temperature of 80-150°C, a reaction pressure of 100-600 kPa, a reaction time of 30-120 min, and in an inert gas atmosphere.

8. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 1, characterized in that: The hydrogenation reaction conditions are as follows: temperature 100-200℃, pressure 2.0-6.0MPa, molar ratio of hydrogen to 2,2,4,4-tetramethyl-1,3-cyclobutanedione 150-500:1, and residence time 0.5-10s.

9. The method for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol according to claim 1, characterized in that: The volume ratio of the hydrogen-rich tail gas to the original carrier gas is 1:10-100.

10. A system for preparing 2,2,4,4-tetramethyl-1,3-cyclobutanediol, characterized in that: The system is used in the method according to any one of claims 1-9, the system comprising a cracking reaction unit, a gas-liquid separation and absorption unit, a dimerization reaction unit and a hydrogenation reaction unit connected in sequence; wherein, the cracking reaction unit includes a preheater and a cracking reactor, the gas-liquid separation and absorption unit includes a gas-liquid separator and an absorption reactor, the inner wall of the gas-liquid separator is provided with internal threads, the hydrogenation reaction unit is a fixed-bed hydrogenation reactor, the heat released by the hydrogenation reaction is recovered to the preheater through a heat exchange system for preheating of the raw materials, and the hydrogen-rich tail gas of the hydrogenation reaction is recycled to the preheater of the cracking reaction unit and mixed with the original carrier gas for utilization; Online chromatographic analyzers are also installed at the cracked gas outlet, dimerization reaction liquid outlet, and hydrogenation feed to monitor the concentration of components in real time.

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