A process for preparing low water material by microwave external field assisted catalytic dehydration reaction

Abstract

The application provides a process for preparing low-water material by microwave external field assisted catalytic dehydration reaction, and steps are as follows: (1) loading pretreated solid raw material containing crystal water into a quartz container; (2) placing the quartz container loaded with solid material into a microwave reactor, feeding raw material gas, and performing catalytic dehydration reaction by controlling microwave power and temperature in the reactor to obtain solid product and tail gas. The microwave technology is applied to the catalytic dehydration reaction, the microwave directly intensifies the vibration of crystal water molecules in a short time, rapidly increases the intramolecular energy, activates and accelerates the catalytic reaction with carbon-containing mixed gas / low-carbon small molecules. The microwave can directly act on the active hydroxyl site of the catalytic dehydration reaction, directly improve the activity of the active site, thereby greatly accelerate the reaction rate and significantly reduce the reaction temperature. The application of microwave assisted catalytic dehydration technology significantly reduces the crystal water in the solid raw material, and more efficiently obtains the product with high uniformity and high quality.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microwave technology, in particular to a process for preparing low-water materials by microwave external field assisted catalytic dehydration reaction. BACKGROUND

[0002] Dehydration drying, as a typical chemical unit operation process, is an indispensable link in the preparation of anhydrous / low-water solid materials. There are various forms of water in solid materials, among which the crystal water has strong interaction with ions or atoms in the solid material, and a high energy barrier needs to be overcome to break the chemical bond. This characteristic determines that the dehydration process is a high energy consumption process. Especially when the dehydration of certain solid materials is carried out at a higher temperature, the problem of difficult to balance dehydration accuracy and structure preservation may occur. Hydrated chloride is one of the typical representatives, and the traditional thermal dehydration process has problems such as high reaction temperature, large energy consumption, and environmental unfriendliness. Moreover, there may be hydrolysis side reactions in the dehydration process, generating by-products that affect product quality. Patent CN116553586A discloses a method for preparing low-water magnesium chloride by dehydration reaction of low-carbon small molecules and magnesium chloride, which utilizes the characteristics that the crystal water coordinated with metal cations is more easily activated, and further promotes the reaction to proceed in the forward direction by coupling low-carbon small molecules, thereby reducing the dehydration temperature and avoiding the corrosion of HCl gas to the equipment. Patent CN116395732A discloses a method and device for preparing anhydrous calcium chloride by dehydration reaction of hydrated calcium chloride and carbon-containing mixed gas self-catalysis coupling, establishes a new theory of inorganic salt dehydration self-catalysis based on the basic principle of coupling self-catalysis, and forms a new understanding of the dehydration process of hydrated calcium chloride. The above-mentioned disclosed patents confirm the method of preparing low-water materials by self-catalytic dehydration reaction of low-carbon small molecules / carbon-containing mixed gas and solid materials containing crystal water, which can reduce the reaction temperature, shorten the reaction time or / and inhibit the side reactions in the dehydration process compared with the traditional thermal dehydration method. On this basis, in order to more significantly improve the efficiency and effect of the catalytic dehydration process to promote the industrial application of the method, introducing external field assistance is a feasible way.

[0003] Microwaves are usually electromagnetic waves with a frequency of 3x10 8 Hz~3x10 11Electromagnetic wave (wavelength 1mm~1m) of 300MHz. Under the high frequency alternating effect of microwave electromagnetic field, the polar molecules change the orientation with the electric field at the frequency of billions of times per second, causing the violent movement and collision friction of the molecules, and generating a large amount of heat instantaneously. Microwave heating has considerable advantages compared with the traditional heating method, and the main advantages are as follows: (1) the heating rate is extremely fast, and the heating is uniform. The conventional heating utilizes heat conduction, convection and radiation to transfer the heat to the surface of the heated object first, and then gradually increases the center temperature through heat conduction; in order to make the center of the medium reach the required temperature, the heat conduction time is needed, and the time required for the object with poor heat conductivity is longer; in order to improve the heating speed, the external temperature needs to be increased, and the temperature difference gradient is increased, which is easy to cause the situation of external heat and internal cold. While the microwave can directly act on the molecules of the medium, uniformly penetrates the medium material, and makes the inside and outside of the medium be heated at the same time, so that the uniform heating is realized in a short time without heat conduction. (2) energy saving, clean and high efficiency. The heating chamber is a closed cavity for the microwave, and the electromagnetic wave cannot be leaked out, but can only be absorbed by the heated object, so the corresponding container and non-polar substances in the heating chamber will not be heated, and the thermal efficiency is extremely high. (3) instant on and instant off, no thermal inertia. The microwave heating does not need extra heat conduction medium, and the heating starts immediately when the microwave runs, and the heating stops immediately when the microwave stops. (4) selective heating. The higher the polarity of the material, the greater the microwave absorption loss, and the water-containing substance is easy to absorb microwave energy.

[0004] According to the CRC Handbook of Chemistry and Physics, the relative dielectric constant of water is as high as 81.5 at room temperature, and the dielectric loss coefficient is extremely high; the hydrated magnesium chloride, the hydrated calcium chloride, the hydrated strontium chloride, and the hydrated barium chloride have strong water absorption, contain a lot of adsorbed water and crystal water, and have strong polarity. Due to the high sensitivity of water molecules to microwaves, the thermal dynamic effect is significant; the wavelength of the microwave is long enough to penetrate the heated medium, ensuring the uniformity of heating; the inside and outside of the material are heated at the same time, and almost no heat conduction is needed. The application of microwave technology to the catalytic dehydration reaction can directly increase the vibration of the adsorbed water or crystal water molecules in a short time, rapidly increase the internal energy of the molecules, and activate and accelerate the catalytic reaction with the carbon-containing mixed gas / low-carbon small molecules. The self-catalytic dehydration process depends on the chemical reaction activity of water in any form and the interaction with surrounding atoms to a certain extent. Compared with the traditional heating method, the microwave can directly act on the active hydroxyl sites of the catalytic dehydration reaction, directly improve the activity of the active sites, and the influence of heat conduction on the reaction can be almost ignored, thereby greatly accelerating the reaction rate and significantly reducing the reaction temperature. It is beneficial to improve the uniformity of the solid product, continue to reduce the reaction temperature, shorten the reaction time, reduce the influence of reaction thermal inertia on the experimental results, and control the amount of by-product generated. Therefore, the reaction efficiency is improved, the energy consumption and pollution are reduced, and the production cost is greatly reduced. SUMMARY

[0005] The present application mainly aims to provide a process for preparing low-water materials by using microwave external field to assist catalytic dehydration reaction, so as to solve the problems of traditional heating mode, such as difficult to activate catalytic dehydration reaction, large thermal inertia, uneven heating of solid, uneven product property distribution, large energy consumption and low production efficiency, etc.

[0006] Specifically, the microwave heating is applied to catalytic dehydration of hydrated magnesium chloride, which is beneficial to improve product uniformity, greatly reduce reaction temperature, greatly shorten reaction time, reduce uncontrollable generation of by-products caused by large thermal inertia of traditional heating mode, reduce pollution and corrosion, improve product quality and production efficiency. The microwave heating is applied to catalytic dehydration of hydrated calcium chloride, hydrated strontium chloride, hydrated barium chloride, which is beneficial to improve product uniformity, reduce reaction temperature, shorten reaction time, improve product quality and production efficiency.

[0007] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a process for preparing low-water materials by using microwave external field to assist catalytic dehydration reaction is provided, which comprises the following steps:

[0008] A. loading the solid raw material containing crystal water after pretreatment into a quartz container; B. placing the quartz container filled with solid material in step A into a microwave reactor, introducing raw material gas, and performing catalytic dehydration reaction by controlling microwave power and temperature in the reactor to obtain solid product and tail gas.

[0009] The high-precision controllable microwave heater adjusts power by detecting the temperature in the reactor through thermocouple / thermistor transducer, and the microwave heating is started or stopped by adjusting power when the temperature in the reactor is outside the temperature control range of the set temperature. The temperature control mode is multi-segment programmable logic controller PID temperature control mode or constant power mode. The raw material gas can be pure gas, mixed gas or gas after liquid gasification. The mixed gas is two or more kinds of gas, one of which is balance gas and the other is carbon-containing gas. The mixed gas can be mixed by a gas mixing device with a propeller blade inside after being equipped with a safety valve and a matching high-precision mass flowmeter, and the mixed gas is mixed according to the principle of experimental requirements. The carbon-containing gas is CH4, CO, C2H6, C2H4 or C2H2, and the balance gas is N2 or Ar. When the carbon-containing gas is methanol, the methanol liquid is gasified by a gasification device and a heat preservation gas path to obtain methanol gas. After the gas mixing device is connected to a water removal, oxygen removal and impurity removal device, the gas is preheated, and then connected to the reactor. A pressure gauge is arranged in front of the reactor, and a gas collection tank is arranged behind the reactor. The raw material gas flow rate during reaction is 10-1000 ml / min.

[0010] Further, in step A, the pre-treatment method comprises one or more combinations of crushing, grinding, drying and sieving, wherein the mesh size of the sieving is 40-100 mesh; the solid raw material is one or more of hydrated magnesium chloride, hydrated calcium chloride, hydrated strontium chloride, and hydrated barium chloride; the volume of the quartz container can be selected according to the requirement of the loading amount; the quartz container is a crucible type container with a handle; the bottom of the quartz container can be completely closed or can be made into a sand core, and the size of the sand core is 40-400 mesh, preferably 80-200 mesh.

[0011] Further, in step B, during the reaction, microwave power is used for heating, the heating temperature is 10-1000°C, preferably 80-300°C; the holding time is 10-1000 min, preferably 10-500 min; the temperature control accuracy is 0.1-10°C, preferably 1-5°C. The raw gas flow during the reaction is 10-1000 ml / min, preferably 10-100 ml / min. The preheating temperature of the raw gas before entering the microwave reactor is consistent with the reaction temperature.

[0012] Further, a process for preparing a material by using a microwave external field assisted catalytic dehydration reaction, characterized in that the device used is as follows: it comprises a raw gas supply system and a high-precision power temperature-controlled microwave heating furnace.

[0013] Because the sensitivity of water molecules to microwave is extremely high, the thermal dynamic effect is significant; the microwave wavelength is long enough to penetrate the heated medium, ensuring the uniformity of heating; the inside and outside of the material are heated at the same time, almost without heat conduction. The application of microwave technology in catalytic dehydration reaction can directly intensify the molecular vibration of adsorbed water or crystal water in a short time, rapidly increase the internal energy of the molecules, activate and accelerate the catalytic reaction with carbon-containing mixed gas / low-carbon small molecules. The self-catalytic dehydration process depends on the chemical reaction activity of water in any form and the interaction with surrounding atoms to some extent. Compared with the traditional heating method, the microwave can directly act on the active hydroxyl sites of the catalytic dehydration reaction, directly improve the activity of the active sites, and the influence of heat conduction on the reaction can be almost ignored, thereby greatly accelerating the reaction rate and significantly reducing the reaction temperature. It is beneficial to improve the uniformity of solid products while continuing to reduce the reaction temperature, shorten the reaction time, reduce the influence of reaction thermal inertia on the experimental results, and control the amount of by-products. Therefore, the reaction efficiency is improved, the energy consumption and pollution are reduced, and the production cost is greatly reduced. The application utilizes the microwave external field to assist the catalytic dehydration reaction of low-carbon small molecules / carbon-containing mixed gas and solid raw materials containing adsorbed water or crystal water. The microwave can intensify the molecular vibration of adsorbed water or crystal water in a short time, rapidly increase the internal energy of the molecules, and accelerate the catalytic reaction with carbon-containing mixed gas / low-carbon small molecules. Compared with the traditional heating method, the microwave can directly act on the active sites of the catalytic dehydration reaction, directly improve the activity of the active sites, and under the same reaction conditions, the microwave heating can obtain products with controllable quality, higher quality and higher uniformity. The reaction temperature can be greatly reduced, the reaction time can be shortened, the production efficiency can be greatly improved, the energy consumption can be greatly reduced, and a new way for the application of microwave technology in the chemical industry is opened up. BRIEF DESCRIPTION OF DRAWINGS

[0014] The accompanying drawings, which form a part of this patent, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and explain the principles of the application. In the drawings:

[0015] Figure 1 A process flow diagram according to an embodiment of the application is shown.

[0016] Figure 2 A process device diagram according to an embodiment of the application is shown. DETAILED DESCRIPTION

[0017] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without contradiction. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0018] The microwave reactor used in the following implementation has a rated microwave power of 800w and a rated microwave frequency of 2450±50MHz.

[0019] Example 1

[0020] A. Dry the magnesium chloride hexahydrate to magnesium chloride tetrahydrate, sieve to get 60-80 mesh material, take 1 g of magnesium chloride tetrahydrate and put it into a quartz container with a carrying handle with a bottom sand core of 180-200 mesh;

[0021] B. Put the above quartz container into a microwave reactor, pass in 5% CH4 / N2 raw gas, set the reaction temperature to 200°C, the microwave power to 640 w, the temperature control accuracy to 1°C, the holding time to 2 h, the temperature of the coil heating band to 200°C, and the gas flow to 10 ml / min, and start the catalytic dehydration reaction;

[0022] C. After the reaction is completed, use inert gas N2 with a flow rate of 10 ml / min to purge for 30 min, and then collect the solid product and tail gas.

[0023] Here 5% CH4 / N2 means that CH4 accounts for 5% of the volume percentage of the raw gas, and N2 accounts for 95% of the volume percentage of the raw gas, and the following is the same.

[0024] The catalytic dehydration reaction here is:

[0025]

[0026] Here x is the average number of moles of crystal water contained in each magnesium chloride hydrate molecule in the solid product.

[0027] Example 2

[0028] A. Dry the magnesium chloride tetrahydrate to magnesium chloride dihydrate, sieve to get 80-100 mesh material, take 2 g of magnesium chloride dihydrate and put it into a quartz container with a carrying handle with a bottom sand core of 160-180 mesh;

[0029] B. Put the above quartz container into a microwave reactor, pass in 5% CO / N2 raw gas, set the reaction temperature to 180°C, the microwave power to 720 w, the temperature control accuracy to 2°C, the holding time to 3 h, the temperature of the coil heating band to 180°C, and the gas flow to 20 ml / min, and start the catalytic dehydration reaction;

[0030] C. After the reaction is completed, use inert gas N2 with a flow rate of 10 ml / min to purge for 30 min, and then collect the solid product and tail gas.

[0031] The catalytic dehydration reaction here is:

[0032]

[0033] Herein x is the average number of moles of crystal water contained in each low water calcium chloride molecule in the solid product.

[0034] Example 3

[0035] A. The calcium chloride hexahydrate was dried to calcium chloride tetrahydrate, and the 80-100 mesh material was screened. 2g of calcium chloride tetrahydrate was loaded into a bottom closed quartz container with a lifting handle;

[0036] B. The above quartz container was placed in a microwave reactor, and 5% CO / N2 raw gas was introduced. The reaction temperature was set to 120°C, the microwave power was 720w, the temperature control accuracy was 2°C, the holding time was 3h, the temperature of the coil heating band was set to 120°C, the gas flow was set to 20ml / min, and the catalytic dehydration reaction was started;

[0037] C. After the reaction was completed, the solid product and tail gas were collected after the inert gas N2 with a flow rate of 10ml / min was blown for 30min.

[0038] Herein the catalytic dehydration reaction is:

[0039]

[0040] Herein x is the average number of moles of crystal water contained in each low water calcium chloride molecule in the solid product.

[0041] Example 4

[0042] A. The calcium chloride tetrahydrate was dried to calcium chloride dihydrate, and the 80-100 mesh material was screened. 2g of calcium chloride dihydrate was loaded into a bottom sand core of 160-180 mesh quartz container with a lifting handle;

[0043] B. The above quartz container was placed in a microwave reactor, and 5% CO / N2 raw gas was introduced. The reaction temperature was set to 120°C, the microwave power was 720w, the temperature control accuracy was 2°C, the holding time was 3h, the temperature of the coil heating band was set to 120°C, the gas flow was set to 20ml / min, and the catalytic dehydration reaction was started;

[0044] C. After the reaction was completed, the solid product and tail gas were collected after the inert gas N2 with a flow rate of 10ml / min was blown for 30min.

[0045] Herein the catalytic dehydration reaction is:

[0046]

[0047] Herein x is the average number of moles of crystal water contained in each low water calcium chloride molecule in the solid product.

[0048] Example 5

[0049] A. Crush, grind, and sieve calcium chloride dihydrate to obtain 80-100 mesh material, and take 2 g of calcium chloride dihydrate and load into a quartz container with a carrying handle of 140-160 mesh at the bottom;

[0050] B. Place the above quartz container in a microwave reactor, and pass in 5% CO / N2 raw gas, set the reaction temperature to 120°C, the microwave power to 720 w, the temperature control accuracy to 2°C, the holding time to 3 h, the temperature of the coil heating band to 120°C, and the gas flow to 20 ml / min, and start the catalytic dehydration reaction;

[0051] C. After the reaction is completed, use inert gas N2 with a flow rate of 10 ml / min to purge for 30 min, and collect the solid product and tail gas.

[0052] The catalytic dehydration reaction here is:

[0053]

[0054] Here, x is the average number of moles of crystal water contained in each low-water calcium chloride molecule in the solid product.

[0055] Example 6

[0056] A. Dry strontium chloride hexahydrate to strontium chloride dihydrate, sieve to obtain 80-100 mesh material, and take 2 g of strontium chloride dihydrate and load into a quartz container with a carrying handle at the bottom;

[0057] B. Place the above quartz container in a microwave reactor, and pass in 10% C2H2 / N2 raw gas, set the reaction temperature to 80°C, the microwave power to 640 w, the temperature control accuracy to 2°C, the holding time to 3 h, the temperature of the coil heating band to 80°C, and the gas flow to 20 ml / min, and start the catalytic dehydration reaction;

[0058] C. After the reaction is completed, use inert gas N2 with a flow rate of 10 ml / min to purge for 30 min, and collect the solid product and tail gas.

[0059] The catalytic dehydration reaction here is:

[0060]

[0061] Here, x is the average number of moles of crystal water contained in each low-water strontium chloride molecule in the solid product.

[0062] Example 7

[0063] A. Dry barium chloride hydrate to barium chloride dihydrate, sieve to obtain 80-100 mesh material, and take 2 g of barium chloride dihydrate and load into a quartz container with a carrying handle at the bottom;

[0064] B. The quartz container was placed in a microwave reactor, and 5% CH3OH / N2 raw gas was introduced, the reaction temperature was set to 80°C, the microwave power was 640w, the temperature control accuracy was 2°C, the holding time was 3h, the coil type heating band temperature was set to 80°C, the gas flow was set to 20ml / min, and the catalytic dehydration reaction was started;

[0065] C. After the reaction was completed, the solid product and tail gas were collected after the inert gas N2 with a flow rate of 10ml / min was blown for 30min.

[0066] The catalytic dehydration reaction here is:

[0067]

[0068] x is the average number of moles of crystal water contained in each low-water barium chloride molecule in the solid product.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that a conventional tubular furnace reactor is used.

[0071] Comparative Example 2

[0072] The difference from Example 2 is that a conventional tubular furnace reactor is used.

[0073] The average number of moles of crystal water contained in each low-water magnesium chloride molecule in the solid product is determined by the Karl Fischer method, and the weight percentage of basic magnesium chloride impurities is titrated by iodimetry. The solid product prepared in the above examples and comparative examples was determined, and the results are shown in Table 1.

[0074] Table 1

[0075]

[0076] Comparative Example 3

[0077] The difference from Example 3 is that a conventional tubular furnace reactor is used.

[0078] Comparative Example 4

[0079] The difference from Example 4 is that a conventional tubular furnace reactor is used.

[0080] Comparative Example 5

[0081] The difference from Example 5 is that a conventional tubular furnace reactor is used.

[0082] The average molar content of crystal water contained in each low-water calcium chloride molecule of the solid product was determined by the Karl Fischer method, and the accuracy of the Karl Fischer method was verified by EDTA titration analysis. The low-water calcium chloride products prepared in the above examples and comparative examples were determined, and the results are shown in Table 2.

[0083] Table 2

[0084]

[0085]

[0086] Comparative Example 6

[0087] The difference from Example 6 is that a conventional tubular furnace reactor is used.

[0088] The average molar content of crystal water contained in each low-water strontium chloride molecule of the solid product was determined by the Karl Fischer method, and the solid products prepared in the above examples and comparative examples were determined, and the results are shown in Table 3.

[0089] Table 3

[0090]

[0091] Comparative Example 7

[0092] The difference from Example 7 is that a conventional tubular furnace reactor is used.

[0093] The average molar content of crystal water contained in each low-water barium chloride molecule of the solid product was determined by the Karl Fischer method, and the solid products prepared in the above examples and comparative examples were determined, and the results are shown in Table 4.

[0094] Table 4

[0095]

[0096] As can be seen from the above, compared with the comparative examples, the catalytic dehydration reaction of low-carbon small molecules / mixed gas containing carbon and solid raw materials containing adsorbed water or crystal water is assisted by the microwave external field in each embodiment of the present application. The molecular vibration of adsorbed water or crystal water is directly intensified in a short time by microwave, the intramolecular energy is rapidly increased, and the catalytic reaction with mixed gas containing carbon / low-carbon small molecules is activated and accelerated. At the same time, compared with the conventional heating method, the microwave can directly act on the active hydroxyl sites of the catalytic dehydration reaction, directly improve the activity of the active sites, and the influence of heat conduction on the reaction can be almost ignored. Under the same reaction conditions, the microwave heating can obtain a product with controllable quality, higher quality and higher uniformity, so as to greatly reduce the reaction temperature and shorten the reaction time, greatly improve the production efficiency, and greatly reduce the energy consumption, thereby opening up a new way for the application of microwave technology in the chemical industry.

[0097] The above presents a further detailed description of the present application in connection with specific embodiments, which are not understood as limiting the scope of the present application claimed. The above is only the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for the preparation of low water materials by microwave external field assisted catalytic dehydration reaction, characterized in that The steps are as follows: A. The solid raw material containing crystal water after pretreatment is loaded into a quartz container; the solid raw material is one or more of hydrated magnesium chloride, hydrated calcium chloride, hydrated strontium chloride, and hydrated barium chloride; B. The quartz container loaded with the solid material in step A is placed in a microwave reactor, and a raw material gas is introduced, and a catalytic dehydration reaction is carried out by controlling the microwave power and the temperature in the reactor to obtain a solid product and tail gas; A microwave heater detects the temperature in the reactor to adjust the power, and when the temperature in the reactor is outside the temperature control range of the set temperature, the microwave heating is turned on or stopped by adjusting the power; The raw material gas is a pure gas or a mixed gas or a gas after gasification of a liquid; the mixed gas is two or more gases, one of which is a balance gas and the other or more of which is a carbon-containing gas; The carbon-containing gas is CH4, CO, C2H6, C2H4, or C2H2, and the balance gas is N2 or Ar; the raw material gas flow rate during the reaction is 10-1000 ml / min.

2. The process according to claim 1, characterized in that, In step A, the pretreatment method includes one or more combinations of crushing, grinding, drying, and sieving, and the mesh size of sieving is 40-100 mesh; the bottom of the quartz container is completely closed or made into a sand core.

3. The process of claim 1, wherein, In step B, the heating temperature is 80-1000°C, the holding time is 10-1000 min, and the temperature control accuracy is 0.1-10°C; the preheating temperature of the raw material gas before entering the microwave reactor is consistent with the reaction temperature.

4. The process of claim 1, wherein, The device used is as follows: it includes a raw material gas supply system and a power-controlled microwave heating furnace.

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