MTO-grade methanol production system and method

Abstract

The invention relates to the technical field of methanol production, and discloses an MTO-grade methanol production system and method.The MTO-grade methanol production method comprises the steps that a carbon-containing raw material at least comprising natural gas, coal or biomass is obtained, sulfur, nitrogen and heavy metal impurities in the carbon-containing raw material are removed through a composite purification adsorbent, an auxiliary is added to adjust the hydrogen-carbon ratio, and then the purified raw material is pressurized; converting the pretreated raw material into synthesis gas by utilizing a plasma-assisted steam reforming, partial oxidation or autothermal reforming process; introducing the purified synthesis gas into a reactor, and carrying out methanol synthesis in the reactor; a three-tower rectification process is combined with a heat pump rectification and heat integration technology, a pre-rectification tower is used for removing light components, a pressurized rectification tower is used for separating a methanol product, a normal-pressure rectification tower is used for recovering residual methanol, the reflux ratio of each tower is optimized, a molecular rectification device is additionally arranged at the tail end of a rectification system, and trace impurities are separated by using molecular free path difference; the production cost is reduced, and continuous high yield of methanol is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of methanol production, and particularly relates to an MTO-grade methanol production system and method. Background Art

[0002] The methanol-to-olefins (MTO) process, as a key way to convert non-petroleum resources such as coal and natural gas, has extremely high requirements for methanol quality. Currently, there are many deficiencies in the conventional methanol production methods in terms of non-refined raw material treatment, low syngas preparation efficiency, limited methanol synthesis catalytic performance, and difficulty in improving rectification purity. As a result, the production cost of MTO-grade methanol is high, the output is limited, which hinders the large-scale and efficient development of the MTO industry. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems and design an MTO-grade methanol production system and method.

[0004] The first aspect of the present invention provides an MTO-grade methanol production method, and the MTO-grade methanol production method includes the following steps:

[0005] S1. Raw material pretreatment: Obtain a carbon-containing raw material including at least natural gas, coal or biomass, use a composite purification adsorbent to remove sulfur, nitrogen and heavy metal impurities in the carbon-containing raw material, add an auxiliary agent to adjust the hydrogen-carbon ratio, and then pressurize the purified raw material to 2-5 MPa;

[0006] S2. Syngas preparation: Use plasma-assisted steam reforming, partial oxidation or autothermal reforming process to convert the pretreated raw material into syngas, control the molar ratio of H2 / CO in the syngas between 2-3, and the total sulfur content of the syngas is less than 0.01 ppm;

[0007] S3. Methanol synthesis: Feed the purified syngas into a reactor loaded with a Cu-Zn-Al-based composite catalyst supported on an alumina carrier with a nanoporous structure and doped with 0.5-2% rare earth elements, and carry out methanol synthesis in the reactor;

[0008] S4. Methanol rectification: Adopt a three-column rectification process combined with heat pump rectification and heat integration technology. The pre-rectification column removes light components, the pressurized rectification column separates the methanol product, the atmospheric rectification column recovers the residual methanol, optimize the reflux ratio of each column, add a molecular rectification device at the end of the rectification system, and use the difference in molecular free path to separate trace impurities, so that the purity of the methanol product reaches more than 99.9%, the water content is less than 0.05%, and the total content of organic impurities is less than 50 ppm.

[0009] Optionally, in the first implementation manner of the first aspect of the present invention, step S1 specifically includes the following process:

[0010] Mix zinc oxide precursors with a particle size of 10 - 50 nm and molecular sieves adsorbed with nitrides in a mass ratio of 3:2 in an alcohol solvent, add an appropriate amount of acid catalyst to adjust the pH value to 3 - 5, and stir and react at 60 - 80 °C for 4 - 6 hours to form a gel-like substance. Subsequently, obtain the composite purification adsorbent through filtration, washing, drying, and calcination;

[0011] Pass the carbon-containing raw material into a fixed-bed adsorption column filled with the composite purification adsorbent. The adsorption column is made of stainless steel, with an inner diameter of 0.5 - 1 m and an adsorbent filling height of 2 - 3 m. Control the gas flow rate at 0.5 - 1 m / s, and remove impurities such as sulfur, nitrogen, and heavy metals at normal temperature and pressure, so that the sulfur content is reduced to less than 0.01 ppm, the nitrogen content is less than 1 ppm, and the total heavy metal content is less than 0.01 ppm;

[0012] Real-time monitor the composition of the carbon-containing raw material through a near-infrared spectroscopy analyzer. When coal is the main raw material, if the hydrogen content in the coal is low, add hydrogen generated by the hydrolysis of sodium borohydride to adjust the initial hydrogen-carbon ratio of the carbon-containing raw material gas to 1 - 1.5;

[0013] Pressurize the conditioned raw material through a multi-stage centrifugal pump. The number of pump stages is 2 - 3, and the motor power is 50 - 100 kW. Pressurize the raw material to 2 - 5 MPa, and control the pressure fluctuation within ±0.1 MPa.

[0014] Optionally, in the second implementation manner of the first aspect of the present invention, during the preparation of the composite purification adsorbent, the drying temperature is 100 - 120 °C, the drying time is 12 - 24 hours, the calcination temperature is 400 - 600 °C, and the calcination time is 3 - 5 hours.

[0015] Optionally, in the third implementation manner of the first aspect of the present invention, step S2 specifically includes the following process:

[0016] Select a plasma generator with a frequency range of 10 - 50 kHz and a power of 100 - 500 kW, and install it at the front end of a steam reforming, partial oxidation, or autothermal reforming reactor. The electrode spacing of the plasma generator is 5 - 10 mm, and the plasma energy density is 100 - 500 J / cm 3 ;

[0017] Pass the pretreated raw material into the plasma reaction zone at a flow rate of 0.2 - 0.5 m 3 / h. Under the action of high plasma energy, methane molecules are instantly cracked into highly active free radicals, and the reaction starting temperature is reduced to about 500 °C. Subsequently, introduce steam or oxygen into the reactor in a ratio of 1 - 2:1 to natural gas in terms of molar ratio, and combine with the reforming process to make the molar ratio of H2 / CO in the syngas stable at 2 - 3;

[0018] Collect gas composition, temperature and pressure data, use a deep learning model for dynamic prediction, and adjust the feed flow rates of oxygen and water vapor and the reactor temperature according to the prediction results.

[0019] Optionally, in the fourth implementation manner of the first aspect of the present invention, the collecting gas composition, temperature and pressure data and using a deep learning model for dynamic prediction includes:

[0020] Collect gas composition, temperature and pressure data, perform filtering processing and normalization processing on the collected original data to obtain preprocessed data;

[0021] Select a long short-term memory network as the basic model of the deep learning model, construct a multi-layer LSTM network structure, the input layer receives the preprocessed data, assuming that a total of n sensors collect data, then the input dimension is n, the hidden layer is set to 3-5 layers, each layer contains 64-128 LSTM units, the output layer corresponds to the key indicators of the syngas to be predicted, and between the LSTM units and between the hidden layer and the output layer, a fully connected layer is used for transitional connection;

[0022] Continuously input the preprocessed gas composition, temperature and pressure data into the trained LSTM model, and the model outputs the predicted values of the key indicators of the syngas according to the current moment data input and the reaction process time series characteristics learned before, to obtain the prediction results.

[0023] Optionally, in the fifth implementation manner of the first aspect of the present invention, during the reaction process of the reactor, the reaction temperature is monitored in real time by a thermocouple, the temperature fluctuation range is within ±20 °C, and the reactor pressure is monitored by a pressure sensor at 0.5-1 MPa.

[0024] Optionally, in the sixth implementation manner of the first aspect of the present invention, step S3 specifically includes the following process:

[0025] Using mesoporous silica as a template, mixing an aluminum source and a templating agent in a molar ratio of 1:0.1-0.3 in deionized water, adding an appropriate amount of ammonia water to adjust the pH value to 8-10, stirring and reacting at 80-100 °C for 12-24 hours to form a gel, after filtration, washing and drying, calcining at 500-700 °C for 5-10 hours to remove the template, to obtain an alumina support with a pore size of 5-50 nm;

[0026] The active components of the Cu-Zn-Al composite catalyst are loaded onto the nano-porous alumina support by the impregnation method. The concentration of the impregnation solution is 0.2 - 0.5 mol / L, and the impregnation time is 12 - 24 hours. Then, it is dried at 100 - 120 °C for 12 - 24 hours, and calcined at 300 - 500 °C for 3 - 5 hours to fully disperse and fix the active components on the support. Finally, 0.5 - 2% of rare earth elements are doped. The rare earth elements are added in the form of nitrates, and the doping process is completed through the steps of re-impregnation, drying, and calcination;

[0027] A shell-and-tube fixed-bed reactor is selected, with a tube diameter of 20 - 50 mm, a tube length of 2 - 3 m, and 100 - 500 tubes. The prepared catalyst is evenly filled in the reaction tubes, with a filling height of 1.5 - 2 m. During the filling process, a vibrator is used for assistance, and the filling density is 1000 - 1500 kg / m 3 ;

[0028] The purified syngas is introduced into the reactor containing the catalyst at a flow rate of 100 - 500 m 3 / h. The temperature of the reactor is controlled at 220 - 280 °C by a circulating water cooling system, with a temperature fluctuation range of ±5 °C. The pressure of the reactor is adjusted to 5 - 10 MPa by a back pressure valve, with a pressure fluctuation of ±0.2 MPa, and the gas hourly space velocity is controlled at 5000 - 10000 h -1 .

[0029] Optionally, in the seventh implementation manner of the first aspect of the present invention, step S4 specifically includes the following process:

[0030] Using the top steam of the pressurized distillation column as the heat source, a screw-type heat pump compressor is selected, with a compression ratio of 2 - 4 and a power of 50 - 100 kW. The pressure of the top steam is increased and supplied to the reboiler at the bottom of the column. Temperature and pressure sensors are installed at the inlet and outlet of the compressor, the inlet and outlet of the reboiler, and various parts of the distillation column to monitor the operating status of the system;

[0031] Conduct a comprehensive heat integration of each column in the distillation system. A molecular distillation device is added at the end of the distillation system. A wiped-film evaporator is used, with a drum diameter of the evaporator of 0.5 - 1 m and a rotation speed of 100 - 300 rpm. An oil-sealed mechanical vacuum pump and a Roots vacuum pump are selected in series, and the operating pressure can be as low as 0.001 - 0.01 Pa. A plunger metering pump is selected as the feed pump, with a flow rate of 0.1 - 0.5 m 3 / h, and the bottom material of the distillation column is accurately transported to the molecular distillation device;

[0032] The material forms a thin film in the wiped-film evaporator. Under a high-vacuum environment, light molecules volatilize and are condensed and collected, while heavy molecules flow down along the evaporator wall and enter the product collection tank. By sampling and analyzing the product at the outlet of the molecular distillation device and adjusting the parameters, the purity of the methanol product reaches over 99.9%, the water content is lower than 0.05%, and the total content of organic impurities is lower than 50 ppm.

[0033] In the second aspect of the present invention, a production system for MTO-grade methanol is provided. The MTO-grade methanol production system includes:

[0034] A raw material pretreatment unit for obtaining a carbon-containing raw material including at least natural gas, coal or biomass, removing sulfur, nitrogen and heavy metal impurities in the carbon-containing raw material by using a composite purification adsorbent, adding an auxiliary agent to adjust the hydrogen-carbon ratio, and then pressurizing the purified raw material to 2-5 MPa;

[0035] A syngas preparation unit for converting the pretreated raw material into syngas by using a plasma-assisted steam reforming, partial oxidation or autothermal reforming process, controlling the molar ratio of H2 / CO in the syngas between 2-3, and the total sulfur content in the syngas is lower than 0.01 ppm;

[0036] A methanol synthesis unit for introducing the purified syngas into a reactor loaded with a Cu-Zn-Al series composite catalyst supported on an alumina carrier with a nanoporous structure and doped with 0.5-2% rare earth elements, and performing methanol synthesis in the reactor;

[0037] A methanol rectification unit for adopting a three-column rectification process combined with a heat pump rectification and heat integration technology, removing light components in the pre-rectification column, separating the methanol product in the pressurized rectification column, recovering the residual methanol in the atmospheric rectification column, optimizing the reflux ratio of each column, adding a molecular distillation device at the end of the rectification system, and separating trace impurities by using the difference in molecular free path, so that the purity of the methanol product reaches over 99.9%, the water content is lower than 0.05%, and the total content of organic impurities is lower than 50 ppm.

[0038] In the technical solution provided by the present invention, the present invention greatly improves the purity and adaptability of the raw material, reduces the influence of impurities, lays a solid foundation for efficient production, reduces the equipment maintenance cost, the plasma-assisted reforming reduces energy consumption and improves the quality of syngas, the intelligent control ensures stability, enhances the reliability and adaptability of the process, improves the overall production efficiency, the nanostructured catalyst support greatly improves the catalytic performance, the in-situ regeneration reactor prolongs the catalyst life, reduces the production cost, ensures the continuous high yield of methanol, the heat pump rectification and heat integration significantly save energy, the molecular distillation realizes ultra-pure refining, improves the product added value, meets the high-end process requirements of MTO, and promotes industrial upgrading. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The accompanying drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention.

[0040] Figure 1 Schematic diagram of the MTO-grade methanol production method provided by the embodiment of the present invention;

[0041] Figure 2 Schematic structural diagram of the MTO-grade methanol production system provided by the embodiment of the present invention. Detailed implementation manners

[0042] The terms "first", "second", "third", "fourth", etc. (if any) in the specification, claims and above-mentioned accompanying drawings of the present invention are used to distinguish similar objects and do not have to be used to describe a specific order or sequence. It should be understood that such used data can be interchanged under appropriate circumstances so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "comprising" or "having" and any variation thereof are intended to cover non-exclusive inclusion. For example, a process, method, device, product or equipment comprising a series of steps or units does not have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or equipment.

[0043] For ease of understanding, the specific process of the embodiment of the present invention will be described below. Please refer to Figure 1 Schematic diagram of the embodiment of the MTO-grade methanol production method provided by the embodiment of the present invention. The method specifically includes the following steps:

[0044] S1. Raw material pretreatment: Obtain a carbon-containing raw material including at least natural gas, coal or biomass, use a composite purification adsorbent to remove sulfur, nitrogen and heavy metal impurities in the carbon-containing raw material, add an auxiliary agent to adjust the hydrogen-carbon ratio, and then pressurize the purified raw material to 2-5 MPa;

[0045] S2. Syngas preparation: Use plasma-assisted steam reforming, partial oxidation or autothermal reforming process to convert the pretreated raw material into syngas, control the molar ratio of H2 / CO in the syngas between 2-3, and the total sulfur content of the syngas is lower than 0.01 ppm;

[0046] S3. Methanol synthesis: Feed the purified syngas into a reactor loaded with a Cu-Zn-Al series composite catalyst supported on an alumina carrier with a nanoporous structure and doped with 0.5-2% rare earth elements, and carry out methanol synthesis in the reactor;

[0047] S4. Methanol rectification: Adopt a three-column rectification process combined with heat pump rectification and heat integration technology. The pre-rectification column removes light components, the pressurized rectification column separates methanol products, and the atmospheric rectification column recovers residual methanol. Optimize the reflux ratio of each column, and add a molecular rectification device at the end of the rectification system. Utilize the difference in molecular free path to separate trace impurities, so that the purity of the methanol product reaches more than 99.9%, the water content is less than 0.05%, and the total content of organic impurities is less than 50 ppm.

[0048] In this embodiment, step S1 specifically includes the following processes:

[0049] Mix zinc oxide precursor with a particle size of 10 - 50 nm and molecular sieve adsorbed with nitride in an alcohol solvent at a mass ratio of 3:2, add an appropriate amount of acid catalyst to adjust the pH value to 3 - 5, and stir and react at 60 - 80 °C for 4 - 6 hours to form a gel-like substance. Subsequently, obtain the composite purification adsorbent through filtration, washing, drying, and calcination.

[0050] Pass the carbon-containing raw material into a fixed-bed adsorption column filled with the composite purification adsorbent. The adsorption column is made of stainless steel, with an inner diameter of 0.5 - 1 m and an adsorbent filling height of 2 - 3 m. Control the gas flow rate at 0.5 - 1 m / s, and remove impurities such as sulfur, nitrogen, and heavy metals at normal temperature and pressure, so that the sulfur content is reduced to less than 0.01 ppm, the nitrogen content is less than 1 ppm, and the total content of heavy metals is less than 0.01 ppm.

[0051] Real-time monitor the composition of the carbon-containing raw material through a near-infrared spectroscopy analyzer. When coal is the main raw material, if the hydrogen content in the coal is low, add hydrogen generated by the hydrolysis of sodium borohydride to adjust the initial hydrogen-carbon ratio of the carbon-containing raw material gas to 1 - 1.5.

[0052] Pressurize the conditioned raw material through a multi-stage centrifugal pump. The number of pump stages is 2 - 3, the motor power is 50 - 100 kW, pressurize the raw material to 2 - 5 MPa, and control the pressure fluctuation within ±0.1 MPa.

[0053] In this embodiment, during the preparation process of the composite purification adsorbent, the drying temperature is 100 - 120 °C, the drying time is 12 - 24 hours, the calcination temperature is 400 - 600 °C, and the calcination time is 3 - 5 hours.

[0054] In this embodiment, step S2 specifically includes the following processes:

[0055] Select a plasma generator with a frequency range of 10 - 50 kHz and a power of 100 - 500 kW, install it at the front end of a steam reforming, partial oxidation, or autothermal reforming reactor. The electrode spacing of the plasma generator is 5 - 10 mm, and the plasma energy density is 100 - 500 J / cm 3 ;

[0056] The pre-treated raw materials are fed into the plasma reaction zone at a flow rate of 0.2 - 0.5 m 3 / h. Under the action of high-energy plasma, methane molecules are instantaneously cracked into highly reactive free radicals, and the initial reaction temperature is reduced to about 500 °C. Subsequently, water vapor or oxygen is introduced into the reactor in a ratio of 1 - 2:1 in terms of the molar ratio to natural gas. Combining with the reforming process, the molar ratio of H2 / CO in the syngas is stabilized at 2 - 3;

[0057] Gas composition, temperature and pressure data are collected, and a deep learning model is used for dynamic prediction. According to the prediction results, the feed flow rates of oxygen and water vapor and the reactor temperature are adjusted.

[0058] In this embodiment, collecting gas composition, temperature and pressure data and using a deep learning model for dynamic prediction includes:

[0059] Collect gas composition, temperature and pressure data, perform filtering and normalization processing on the collected raw data to obtain pre-treated data;

[0060] Select the long short-term memory network as the basic model of the deep learning model, construct a multi-layer LSTM network structure. The input layer receives the pre-treated data. Suppose there are n sensors collecting data in total, then the input dimension is n. The hidden layer is set to 3 - 5 layers, and each layer contains 64 - 128 LSTM units. The output layer corresponds to the key indicators of the syngas to be predicted. Between the LSTM units and between the hidden layer and the output layer, fully connected layers are used for transitional connection;

[0061] Continuously input the pre-treated gas composition, temperature and pressure data into the trained LSTM model. The model outputs the predicted values of the key indicators of the syngas according to the current moment data input and the time series characteristics of the reaction process learned before, and obtains the prediction results.

[0062] In this embodiment, during the reaction process of the reactor, the reaction temperature is monitored in real time by a thermocouple, and the temperature fluctuation range is within ±20 °C. The reactor pressure is monitored by a pressure sensor at 0.5 - 1 MPa.

[0063] In this embodiment, step S3 specifically includes the following process:

[0064] Using mesoporous silica as a template, mixing an aluminum source and a templating agent in deionized water at a molar ratio of 1:0.1 - 0.3, adding an appropriate amount of ammonia water to adjust the pH value to 8 - 10, stirring and reacting at 80 - 100 °C for 12 - 24 hours to form a gel. After filtration, washing and drying, it is calcined at 500 - 700 °C for 5 - 10 hours to remove the template, and an alumina support is obtained with a pore size of 5 - 50 nm;

[0065] The active components of the Cu-Zn-Al composite catalyst are loaded onto the nano-porous alumina support by the impregnation method. The concentration of the impregnation solution is 0.2 - 0.5 mol / L, and the impregnation time is 12 - 24 hours. Then, it is dried at 100 - 120 °C for 12 - 24 hours, and calcined at 300 - 500 °C for 3 - 5 hours to fully disperse and fix the active components on the support. Finally, 0.5 - 2% of rare earth elements are doped. The rare earth elements are added in the form of nitrates, and the doping process is completed through the steps of re-impregnation, drying, and calcination;

[0066] A shell-and-tube fixed-bed reactor is selected, with a tube diameter of 20 - 50 mm, a tube length of 2 - 3 m, and 100 - 500 tubes. The prepared catalyst is evenly filled in the reaction tubes, with a filling height of 1.5 - 2 m. During the filling process, a vibrator is used for assistance, and the filling density is 1000 - 1500 kg / m 3 ;

[0067] The purified syngas is introduced into the reactor filled with this catalyst at a flow rate of 100 - 500 m 3 / h. The temperature of the reactor is controlled at 220 - 280 °C by a circulating water cooling system, with a temperature fluctuation range of ±5 °C. The pressure of the reactor is adjusted to 5 - 10 MPa by a back pressure valve, with a pressure fluctuation of ±0.2 MPa, and the gas hourly space velocity is controlled at 5000 - 10000 h -1 。

[0068] In this embodiment, step S4 specifically includes the following process:

[0069] Using the top steam of the pressurized distillation column as the heat source, a screw-type heat pump compressor is selected, with a compression ratio of 2 - 4 and a power of 50 - 100 kW. The pressure of the top steam is increased and supplied to the reboiler at the bottom of the column. Temperature and pressure sensors are installed at the inlet and outlet of the compressor, the inlet and outlet of the reboiler, and various parts of the distillation column to monitor the operating status of the system;

[0070] Conduct a comprehensive heat integration of each column in the distillation system. A molecular distillation device is added at the end of the distillation system. A wiped-film evaporator is used, with a drum diameter of the evaporator of 0.5 - 1 m and a rotation speed of 100 - 300 rpm. A mechanical oil-sealed vacuum pump and a Roots vacuum pump are selected in series, and the operating pressure can be as low as 0.001 - 0.01 Pa. The feed pump is a plunger metering pump, with a flow rate of 0.1 - 0.5 m 3 / h, and the bottom material of the distillation column is accurately transported to the molecular distillation device;

[0071] The material forms a thin film in the wiped-film evaporator. Under a high-vacuum environment, light molecules volatilize and are condensed and collected, while heavy molecules flow down along the evaporator wall and enter the product collection tank. By sampling and analyzing the product at the outlet of the molecular distillation device and adjusting the parameters, the purity of the methanol product reaches over 99.9%, the water content is lower than 0.05%, and the total content of organic impurities is lower than 50 ppm.

[0072] Please refer to Figure 2 , the structural schematic diagram of the MTO-grade methanol production system provided by the embodiment of the present invention. This system includes:

[0073] A raw material pretreatment unit, which is used to obtain a carbon-containing raw material that at least includes natural gas, coal or biomass, remove sulfur, nitrogen and heavy metal impurities in the carbon-containing raw material by using a composite purification adsorbent, add an auxiliary agent to adjust the hydrogen-carbon ratio, and then pressurize the purified raw material to 2 - 5 MPa;

[0074] A syngas preparation unit, which is used to convert the pretreated raw material into syngas by using a plasma-assisted steam reforming, partial oxidation or autothermal reforming process, control the molar ratio of H2 / CO in the syngas between 2 - 3, and the total sulfur content of the syngas is lower than 0.01 ppm;

[0075] A methanol synthesis unit, which is used to introduce the purified syngas into a reactor filled with a Cu-Zn-Al-based composite catalyst supported on an alumina carrier with a nanoporous structure and doped with 0.5 - 2% rare earth elements, and carry out methanol synthesis in the reactor;

[0076] A methanol rectification unit, which is used to adopt a three-column rectification process combined with a heat pump rectification and heat integration technology. The pre-rectification column removes light components, the pressurized rectification column separates the methanol product, the atmospheric rectification column recovers the residual methanol, optimizes the reflux ratio of each column, adds a molecular distillation device at the end of the rectification system, and separates trace impurities by using the difference in molecular free paths, so that the purity of the methanol product reaches over 99.9%, the water content is lower than 0.05%, and the total content of organic impurities is lower than 50 ppm.

[0077] Through the implementation of the above solutions, through fine raw material pretreatment, impurities are deeply removed, effectively protecting the subsequent catalysts, extending their service life, and reducing production costs; precisely regulating the process parameters of syngas preparation, obtaining syngas with an appropriate ratio, improving the efficiency of the methanol synthesis reaction, and reducing raw material waste; adopting a catalyst doped with high-performance rare earth elements, significantly enhancing the activity, selectivity and stability of methanol synthesis, and increasing the methanol yield; the optimized three-column rectification process combined with high-efficiency structured packing ensures that the methanol product reaches an extremely high purity, meeting the strict quality standards of MTO-grade methanol, and providing a reliable raw material guarantee for the MTO industry.

[0078] The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for producing MTO-grade methanol, characterized in that, The described MTO-grade methanol production method includes the following steps: S1. Raw material pretreatment: Obtain a carbon-containing raw material including at least natural gas, coal or biomass, use a composite purification adsorbent to remove sulfur, nitrogen and heavy metal impurities in the carbon-containing raw material, add an auxiliary agent to adjust the hydrogen-carbon ratio, and then pressurize the purified raw material to 2-5 MPa; S2. Syngas preparation: Use plasma-assisted steam reforming, partial oxidation or autothermal reforming process to convert the pretreated raw material into syngas, control the molar ratio of H2 / CO in the syngas between 2-3, and the total sulfur content of the syngas is less than 0.01 ppm; S3. Methanol synthesis: Pass the purified syngas into a reactor loaded with a Cu-Zn-Al series composite catalyst supported on an alumina carrier with a nanoporous structure and doped with 0.5-2% rare earth elements, and carry out methanol synthesis in the reactor; S4. Methanol rectification: Adopt a three-column rectification process combined with heat pump rectification and heat integration technology. The pre-rectification column removes light components, the pressurized rectification column separates the methanol product, the atmospheric rectification column recovers the residual methanol, optimizes the reflux ratio of each column, adds a molecular rectification device at the end of the rectification system, and uses the difference in molecular free path to separate trace impurities, so that the purity of the methanol product reaches more than 99.9%, the water content is less than 0.05%, and the total content of organic impurities is less than 50 ppm.

2. The MTO-grade methanol production method according to claim 1, wherein Step S1 specifically includes the following processes: Mix zinc oxide precursor with a particle size of 10-50 nm and a molecular sieve adsorbed with nitride in an alcohol solvent according to a mass ratio of 3:2, add an appropriate amount of acid catalyst to adjust the pH value to 3-5, and stir and react at 60-80 °C for 4-6 hours to form a gel-like substance, and then obtain a composite purification adsorbent through filtration, washing, drying and calcination; Pass the carbon-containing raw material into a fixed-bed adsorption column filled with a composite purification adsorbent. The adsorption column is made of stainless steel, with an inner diameter of 0.5-1 m, an adsorbent filling height of 2-3 m, and a gas flow rate controlled at 0.5-1 m / s. Remove impurities such as sulfur, nitrogen and heavy metals at normal temperature and pressure, reduce the sulfur content to less than 0.01 ppm, the nitrogen content is less than 1 ppm, and the total heavy metal content is less than 0.01 ppm; Real-time monitor the composition of the carbon-containing raw material through a near-infrared spectroscopy analyzer. When coal is the main raw material, if the hydrogen content in the coal is low, add hydrogen generated by the hydrolysis of sodium borohydride to adjust the initial hydrogen-carbon ratio of the carbon-containing raw material gas to 1-1.5; Pressurize the conditioned raw material through a multistage centrifugal pump. The number of pump stages is 2-3, the motor power is 50-100 kW, pressurize the raw material to 2-5 MPa, and control the pressure fluctuation within ±0.1 MPa.

3. A method for producing MTO-grade methanol according to claim 2, characterized in that, During the preparation process of the composite purification adsorbent, the drying temperature is 100-120 °C, the drying time is 12-24 hours, the calcination temperature is 400-600 °C, and the calcination time is 3-5 hours.

4. A method for producing MTO-grade methanol according to claim 1, characterized in that, Step S2 specifically includes the following processes: Select a plasma generator with a frequency range of 10 - 50 kHz and a power of 100 - 500 kW, and install it at the front end of a steam reforming, partial oxidation, or autothermal reforming reactor. The electrode spacing of the plasma generator is 5 - 10 mm, and the plasma energy density is 100 - 500 J / cm 3 ; The pre-treated raw materials are introduced into the plasma reaction zone at a flow rate of 0.2 - 0.5 m 3 / h. Under the action of high-energy plasma, methane molecules are instantaneously cracked into highly active free radicals, and the initial reaction temperature is reduced to about 500 °C. Subsequently, water vapor or oxygen is introduced into the reactor in a ratio of 1 - 2:1 in terms of the molar ratio to natural gas. Combining with the reforming process, the molar ratio of H2 / CO in the syngas is stabilized at 2 - 3; Collect gas composition, temperature and pressure data, use a deep learning model for dynamic prediction, and adjust the oxygen, steam feed flow rate and reactor temperature according to the prediction results.

5. The method for producing MTO-grade methanol according to claim 4, characterized in that, The collection of gas composition, temperature and pressure data and the use of a deep learning model for dynamic prediction include: Collect gas composition, temperature, and pressure data, perform filtering and normalization processing on the collected raw data to obtain preprocessed data; Select the long short-term memory network as the basic model of the deep learning model, construct a multi-layer LSTM network structure. The input layer receives the preprocessed data. Suppose there are n sensors collecting data, then the input dimension is n. The hidden layer is set to 3 - 5 layers, and each layer contains 64 - 128 LSTM units. The output layer corresponds to the key indicators of the syngas to be predicted. Between the LSTM units and between the hidden layer and the output layer, fully connected layers are used for transitional connection; Continuously input the preprocessed gas composition, temperature, and pressure data into the trained LSTM model. The model outputs the predicted values of the key indicators of the syngas according to the currently input data and the time series characteristics of the reaction process learned before, and obtains the prediction results.

6. The MTO-grade methanol production method according to claim 4, wherein, During the reaction process of the reactor, the reaction temperature is monitored in real time through a thermocouple, and the temperature fluctuation range is within ±20°C. The reactor pressure is monitored by a pressure sensor at 0.5 - 1 MPa.

7. The MTO-grade methanol production method according to claim 1, wherein, Step S3 specifically Includes the following processes: Using mesoporous silica as a template, mix the aluminum source and the template agent in deionized water at a molar ratio of 1:0.1 - 0.3, add an appropriate amount of ammonia water to adjust the pH value to 8 - 10, stir and react at 80 - 100°C for 12 - 24 hours to form a gel. After filtration, washing, and drying, calcine at 500 - 700°C for 5 - 10 hours to remove the template and obtain an alumina support with a pore size of 5 - 50 nm; Load the active components of the Cu-Zn-Al series composite catalyst onto the alumina support with a nano-porous structure by the impregnation method. The concentration of the impregnation solution is 0.2 - 0.5 mol / L, and the impregnation time is 12 - 24 hours. Then dry at 100 - 120°C for 12 - 24 hours, and then calcine at 300 - 500°C for 3 - 5 hours to make the active components fully dispersed and fixed on the support. Finally, dope 0.5 - 2% of rare earth elements. The rare earth elements are added in the form of nitrates, and the doping process is completed through the steps of re-impregnation, drying, and calcination; A shell-and-tube fixed-bed reactor is selected, with a tube diameter of 20 - 50 mm, a tube length of 2 - 3 m, and 100 - 500 tubes. The prepared catalyst is evenly loaded into the reaction tubes, with a loading height of 1.5 - 2 m. During the loading process, a vibrator is used for assistance, and the loading density is 1000 - 1500 kg / m 3 ; The purified syngas is fed into the reactor containing the catalyst at a flow rate of 100 - 500 m 3 / h, and the reactor temperature is controlled at 220 - 280 °C with a temperature fluctuation range of ±5 °C through a circulating water cooling system. The reactor pressure is regulated at 5 - 10 MPa with a pressure fluctuation of ±0.2 MPa using a back pressure valve, and the gas hourly space velocity is controlled at 5000 - 10000 h -1 .

8. A method for producing MTO-grade methanol according to claim 1, characterized in that, Step S4 specifically includes the following processes: Using the top steam of the pressurized distillation column as the heat source, select a screw-type heat pump compressor with a compression ratio of 2 - 4 and a power of 50 - 100 kW. After increasing the pressure of the top steam, it is supplied to the reboiler at the bottom of the column. Install temperature and pressure sensors at the inlet and outlet of the compressor, the inlet and outlet of the reboiler, and various parts of the distillation column to monitor the operation status of the system; Conduct comprehensive heat integration on each column of the distillation system, add a molecular distillation device at the end of the distillation system, use a wiped film evaporator, with the diameter of the evaporator drum being 0.5 - 1 m and the rotation speed being 100 - 300 rpm. Select a series connection of an oil-sealed mechanical vacuum pump and a Roots vacuum pump, and the operating pressure can be as low as 0.001 - 0.01 Pa. Select a plunger metering pump as the feed pump, with a flow rate of 0.1 - 0.5 m 3 / h, and accurately transport the bottom material of the distillation column to the molecular distillation device; The material forms a thin film in the wiped-film evaporator. In a high-vacuum environment, light molecules volatilize and are condensed and collected, and heavy molecules flow down along the evaporator wall and enter the product collection tank. By sampling and analyzing the product at the outlet of the molecular distillation device and adjusting the parameters, the purity of the methanol product reaches more than 99.9%, the water content is less than 0.05%, and the total content of organic impurities is less than 50 ppm.

9. An MTO-grade methanol production system, characterized in that, The MTO-grade methanol production system includes: The raw material pretreatment unit is used to obtain a carbonaceous raw material containing at least natural gas, coal or biomass, remove sulfur, nitrogen and heavy metal impurities in the carbonaceous raw material by using a composite purification adsorbent, add an auxiliary agent to adjust the hydrogen-carbon ratio, and then pressurize the purified raw material to 2-5 MPa; The syngas preparation unit is used to convert the pretreated raw material into syngas by using plasma-assisted steam reforming, partial oxidation or autothermal reforming process, control the molar ratio of H2 / CO in the syngas between 2-3, and the total sulfur content of the syngas is lower than 0.01 ppm; The methanol synthesis unit is used to introduce the purified syngas into a reactor loaded with a Cu-Zn-Al-based composite catalyst supported on an alumina carrier with a nanoporous structure and doped with 0.5-2% rare earth elements for methanol synthesis in the reactor; The methanol rectification unit is used to adopt a three-column rectification process combined with heat pump rectification and heat integration technology. The pre-rectification column removes light components, the pressurized rectification column separates methanol products, the atmospheric rectification column recovers residual methanol, optimizes the reflux ratio of each column, adds a molecular rectification device at the end of the rectification system, and separates trace impurities by using the difference in molecular free path, so that the purity of the methanol product reaches more than 99.9%, the water content is lower than 0.05%, and the total content of organic impurities is lower than 50 ppm.

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