Method for preparing cycloalkane through microwave pyrolysis of lignite and hydrogen-donating solvent

Abstract

The invention provides a method for preparing cycloalkanes through microwave pyrolysis of lignite and a hydrogen-donating solvent, belongs to the technical field of microwave pyrolysis of lignite, and mainly aims to prepare C6-C10 cycloalkanes. The method comprises the following steps: firstly, microwave absorbent activated carbon is subjected to microwave irradiation treatment and then is added into a microwave pyrolysis system; then adding the upgraded lignite and a hydrogen-donor solvent into a microwave pyrolysis system according to a certain proportion, and ensuring that the microwave pyrolysis system is in a nitrogen atmosphere; then carrying out pyrolytic reaction in a microwave pyrolytic system with the microwave electric field intensity of 2.68 * 10 < 4 >-3.28 * 10 < 4 > V / m under the normal pressure condition, condensing the generated airflow, and absorbing by dichloromethane; according to the method, the synergistic effect of the lignite, the microwaves, the hydrogen-donor solvent and the microwave absorbent is utilized, the cycloalkane is generated through pyrolysis under the moderate conditions of medium and low temperature and normal pressure, and the excellent results that the lignite conversion rate can reach 70% or above and the cycloalkane yield can reach 2.5% or above can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave pyrolysis of lignite, and in particular relates to a method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen supplying solvent. Background Art

[0002] Lignite is a mineral coal with a low degree of coalification. It is an early product of peat being transformed into organic biorock through dehydration and compression, and is usually brown or dark brown in color. The physical and chemical properties of lignite are between peat and bituminous coal. Its typical characteristics include: low metamorphic degree and high water content (30-70%); low degree of aromatic nuclear condensation and high volatile content (45-55%); more acidic oxygen functional groups and high oxygen content (20-30%); shallow carbonization and low carbon content (about 25-35%); low diagenesis, many internal pores, low density; high moisture content and low calorific value. These characteristics make lignite more expensive in long-distance transportation, long-term storage, weathering and spontaneous combustion, and its direct use efficiency is poor, making it difficult to achieve large-scale and efficient application. Therefore, although lignite is cheap, its use is limited and it is not as widely used as high-quality bituminous coal. However, after upgrading, the lignite has less moisture, higher calorific value, and the coal quality gradually approaches that of high-quality coal. The upgraded lignite products can be used as coal for power, liquefaction, gasification and coking purposes. They have broad applications and market prospects, opening up new areas for the application of lignite.

[0003] The pyrolysis of lignite can also be called medium-low temperature pyrolysis (300-600℃) or dry distillation, which refers to heating under air-tight conditions to cause a series of physical and chemical changes. After the breaking of cross-linking bonds and the secondary reaction of the initial pyrolysis components, the resulting liquid (tar) has a relatively complex composition, mainly including a variety of aliphatic hydrocarbons, aromatic hydrocarbons and other high value-added products such as oxygen-containing, nitrogen-containing and sulfur-containing compounds. Cycloalkanes have high heat sink and high thermal stability, but the content is very small, so it is very meaningful to increase the content of cycloalkanes in lignite pyrolysis products.

[0004] Microwaves are electromagnetic waves between infrared and radio waves. They are composed of photons, have wave-particle duality, follow the laws of optics, and have characteristics such as reflection, interference, and diffraction. In terms of frequency, they can be divided into very high frequency (0.3-3GHz), ultra-high frequency (3-30GHz), and extremely high frequency (30-30GHz); in terms of wavelength, they can be divided into decimeter waves (10-1dm), centimeter waves (10-1cm), and millimeter waves (10-1mm). The International Radio Regulatory Committee stipulates that the frequencies of industrial microwaves are 915MHz, 2450MHz, 5800MHz, and 24124MHz. 915MHz is commonly used for industrial heating, and 2450MHz is used for household and industrial microwave heating equipment in most countries. Microwaves do not directly heat objects, but convert electromagnetic energy into heat energy. The influencing factors include power, frequency, and dielectric properties of materials. The dielectric constant of a substance is affected by frequency, composition, humidity, structure, temperature, pressure, porosity, etc. Substances are divided into conductors, insulators, and absorbers according to their ability to absorb microwaves and loss factors. Conductors such as metals reflect microwaves and are used for energy reflection and conduction; insulators such as quartz transmit microwaves and are used in microwave oven reactors; absorbers such as water can absorb electromagnetic wave energy and convert it into heat, also called dielectrics, and microwave heating is also called dielectric heating.

[0005] Microwave heating converts microwave energy into heat energy inside the material through dielectric dissipation, causing the temperature to rise. Compared with traditional heating, microwave heating has the following characteristics: fast, efficient, uniform, selective, instant and safe heating. Traditional heating requires heating the medium first, and the material heats up through heat conduction, while microwaves directly penetrate and convert into heat. Microwave heating is highly efficient because the energy is mainly absorbed by the material without heating the transmission medium. In terms of uniform heating, microwaves increase the overall temperature through energy exchange, and the temperature distribution is different inside and outside. Selective heating is based on the dielectric properties of the material. Different materials or parts have different absorption capabilities, and the parts with high water content heat up quickly. Microwave drying has automatic balance and consistent drying effect. The instant heating feature allows microwave heating to be turned on and off immediately, without thermal inertia, precise control, and easy automation. In terms of safe heating, microwaves are in a closed metal transmission system, and energy leakage meets safety standards.

[0006] At present, there are few reports on the preparation of cycloalkanes using lignite as raw material. The preparation of cycloalkanes also uses a relatively high hydrogen pressure (>5MPa) and consumes a large amount of hydrogen. During the research process, the inventor found that the content of cycloalkanes in the tar product of co-pyrolysis of lignite and hydrogen-donating solvent under microwave conditions increases, which also provides a new path for the preparation of cycloalkanes. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen supply solvent. The method has mild reaction conditions and can prepare cycloalkanes safely while achieving significant economic benefits.

[0008] In order to achieve the above-mentioned invention object, the present invention provides the following technical solution: a method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent, comprising the following steps:

[0009] (1) First, activated carbon particles with a sieved particle size of ≤0.075 mm were placed in a microwave pyrolysis system, with microwaves as the heat source, and the microwave irradiation time was 30 min and the microwave electric field intensity was 2.68×10 4 ~3.28×10 4 V / m, the activated carbon is burned to be porous and have good microwave absorption performance;

[0010] (2) sending lignite with a particle size of 2.5 to 4 mm into an oven for upgrading to obtain a dry powdered coal sample;

[0011] (3) Weigh 5 g of microwave-irradiated activated carbon and place it in a microwave pyrolysis system, and then add 5 g of dry powdered coal sample and 10 mL of decahydronaphthalene (hydrogen donor solvent);

[0012] (4) Ensure that the microwave pyrolysis system is in a nitrogen atmosphere, and then prepare for microwave pyrolysis under the protection of 50 mL / min nitrogen;

[0013] (5) Microwave pyrolysis conditions: irradiation frequency 2450 MHz, irradiation time 5-30 min and electric field intensity 2.68×10 4 V / m;

[0014] (6) The tar product obtained by condensing the oil-gas mixture obtained by pyrolysis is absorbed by dichloromethane in a flask; the lignite conversion rate and tar yield are calculated by weighing, and the tar composition is determined.

[0015] Preferably, in the method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent provided by the present invention, the particle size of the lignite is 2.5 to 4 mm.

[0016] Preferably, in the method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent provided by the present invention, the lignite is upgraded and its moisture content is gradually reduced from an initial moisture content of 48% to below 15%.

[0017] Preferably, in the method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent provided by the present invention, the hydrogen-donating solvent comprises hydrogenated naphthalene, hydrogenated anthracene and alkyl alcohol.

[0018] Preferably, in the method for preparing cycloalkanes by microwave pyrolysis of lignite and hydrogen-donating solvent provided by the present invention, the frequency of microwave irradiation is 2450 MHz, the time of microwave irradiation is 5 to 30 min, and the microwave electric field intensity is 2.68×10 4 ~3.28×10 4 V / m.

[0019] Preferably, in the method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent provided by the present invention, the microwave irradiation originates from a modified microwave heating furnace, and the structure of the microwave heating furnace mainly includes: a magnetron, a waveguide, a microwave reaction cavity, a high-voltage transformer and a heating control system, etc.

[0020] Preferably, in the method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent provided by the present invention, the lignite and the hydrogen-donating solvent are cracked under normal pressure conditions, using a self-modified household microwave oven, placing a microwave absorber in the microwave pyrolysis system, and adding the lignite and the hydrogen-donating solvent in sequence according to a certain mass ratio, generally 1:1 to 3.

[0021] Preferably, in the method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent provided by the present invention, the activated carbon as a microwave absorber is first screened, and particles with a particle size of ≤0.075 mm are selected for use, and then the activated carbon is microwave irradiated for 30 minutes to obtain the desired porous activated carbon with good microwave absorbing properties.

[0022] The present invention is a safe, mild, clean and efficient lignite utilization method, and its specific advantages are as follows:

[0023] (1) Under normal pressure conditions, safety is significantly improved compared to high-pressure hydrogenation, providing a high sense of security;

[0024] (2) Microwave pyrolysis can greatly increase the pyrolysis rate, shorten the time, and improve the efficiency;

[0025] (3) The process flow of the present invention is simple, easy to operate, and the system is safe and reliable;

[0026] (4) The saturated cycloalkane kerosene produced has better thermal stability and is more suitable as aerospace propulsion fuel. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0028] Figure 1 Flow chart of producing cycloalkanes by microwave pyrolysis of lignite and hydrogen-donating solvent;

[0029] Figure 2 This is the GC-MS analysis of tar from microwave pyrolysis of lignite without adding hydrogen-donating solvent;

[0030] Figure 3 GC-MS analysis of tar from microwave pyrolysis of lignite and decahydronaphthalene;

[0031] Figure 4 GC-MS analysis of lignite and 9,10-dihydroanthracene microwave pyrolysis tar;

[0032] Figure 5This is the GC-MS analysis chart of tar from microwave pyrolysis of lignite, decahydronaphthalene and n-dodecane. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to the accompanying drawings and specific examples.

[0034] The present invention provides a method for preparing cycloalkanes by microwave pyrolysis of lignite and hydrogen-donating solvent, the flow chart of which is as follows: Figure 1 As shown, the following steps are included:

[0035] Firstly, activated carbon particles with a sieved particle size of ≤0.075 mm were placed in a microwave pyrolysis system. Microwaves were used as the heat source. The microwave time was 30 min and the microwave electric field intensity was 2.68×10 4 ~3.28×10 4 V / m, the activated carbon is burned to be porous and have good microwave absorption performance;

[0036] The lignite with a particle size of 2.5 to 4 mm is sent into an oven for upgrading to obtain a dry powdered coal sample;

[0037] Weigh 5 g of microwave-irradiated activated carbon and place it in a microwave pyrolysis system, and then add 5 g of dry powdered coal sample and 10 mL of decahydronaphthalene (hydrogen supply solvent);

[0038] Ensure that the microwave pyrolysis system is in a nitrogen atmosphere, and then prepare for microwave pyrolysis under the protection of 50 mL / min nitrogen;

[0039] Microwave pyrolysis conditions: irradiation frequency 2450 MHz, irradiation time 30 min and electric field intensity 2.68×10 4 ~3.28×10 4 V / m;

[0040] The tar product obtained by condensing the oil-gas mixture obtained by pyrolysis is absorbed by dichloromethane in a flask; the lignite conversion rate and tar yield are calculated by weighing, and the tar composition is determined.

[0041] The method of preparing cycloalkanes by microwave pyrolysis of lignite and hydrogen-donating solvent is now described with a specific example.

[0042] Example 1

[0043] The activated carbon particles with a sieved particle size of 0.065 mm were placed in a microwave pyrolysis system. Microwaves were used as the heat source. The microwave time was 30 min and the microwave electric field intensity was 2.68×10 4V / m, the activated carbon was burned to be porous and have good microwave absorption performance; then the lignite was crushed and sieved to obtain lignite with a particle size of 2.5 mm; and it was sent to an oven for quality improvement to obtain a dry powdered coal sample; 5 g of microwave-irradiated activated carbon was weighed and placed in a microwave pyrolysis system, and then 5 g of dry powdered coal sample was added, ensuring that the microwave pyrolysis system was in a nitrogen atmosphere, and then prepared for microwave pyrolysis under the protection of 50 mL / min of nitrogen. The microwave pyrolysis conditions were: irradiation frequency 2450 MHz, irradiation time 30 min and electric field strength 2.68×10 4 V / m, the oil-gas mixture obtained by pyrolysis was condensed and absorbed by dichloromethane; the lignite conversion rate and tar yield were calculated by weighing, and the tar composition was determined by gas chromatography-mass spectrometry. The GC-MS used in the research institute is the 6890N-5970N model produced by Agilent. The test conditions are initial column temperature 40℃, retention time 2min, column temperature increased to 160℃ at a heating rate of 4℃ / min, retained for 2min, and then increased from 160℃ to 280℃ / min at a heating rate of 10℃ / min.

[0044] The results of microwave pyrolysis of lignite are shown in Figure 2 .

[0045] Example 2

[0046] The activated carbon particles with a size of 0.075 mm were placed in a microwave pyrolysis system with microwave as the heat source. The microwave time was 30 min and the microwave electric field intensity was 2.71×10 4 V / m, the activated carbon was burned to be porous and have good microwave absorption performance; then the lignite was crushed and sieved to obtain lignite with a particle size of 3 mm; and it was sent to an oven for quality improvement to obtain a dry powdered coal sample; 5g of microwave-irradiated activated carbon was weighed and placed in a microwave pyrolysis system, and then 5g of dry powdered coal sample and 10mL of decahydronaphthalene (hydrogen supply solvent) were added in sequence. Under a nitrogen atmosphere, first ensure that the microwave pyrolysis system is in a nitrogen atmosphere, and then prepare for microwave pyrolysis under the protection of 50mL / min nitrogen. The microwave pyrolysis conditions were: irradiation frequency 2450MHz, irradiation time 30min and electric field strength 2.71×10 4 V / m, the oil-gas mixture obtained by pyrolysis was condensed and absorbed by dichloromethane; the lignite conversion rate and tar yield were calculated by weighing, and the tar composition was determined by gas chromatography-mass spectrometry. The GC-MS used in the research institute is the 6890N-5970N model produced by Agilent. The test conditions are initial column temperature 40℃, retention time 2min, column temperature increased to 160℃ at a heating rate of 4℃ / min, retained for 2min, and then increased from 160℃ to 280℃ / min at a heating rate of 10℃ / min.

[0047] The microwave pyrolysis results of lignite and decahydronaphthalene are shown in Figure 3.

[0048] Example 3

[0049] The activated carbon particles with a sieved particle size of 0.070 mm were placed in a microwave pyrolysis system with microwaves as the heat source. The microwave time was 30 min and the microwave electric field intensity was 2.73×10 4 V / m, the activated carbon was burned to be porous and have good microwave absorption performance; then the lignite was crushed and sieved to obtain lignite with a particle size of 3.5 mm; and it was sent to an oven for quality improvement to obtain a dry powdered coal sample; 5g of microwave-irradiated activated carbon was weighed and placed in a microwave pyrolysis system, and then 5g of dry powdered coal sample and 10mL of 9,10-dihydroanthracene (hydrogen supply solvent) were added in sequence. First, the microwave pyrolysis system was ensured to be in a nitrogen atmosphere, and then prepared for microwave pyrolysis under the protection of 50mL / min nitrogen. The microwave pyrolysis conditions were as follows: irradiation frequency of 2450MHz, irradiation time of 30min, and electric field strength of 2.73×10 4 V / m, the oil-gas mixture obtained by pyrolysis was condensed and absorbed by dichloromethane; the lignite conversion rate and tar yield were calculated by weighing, and the tar composition was determined by gas chromatography-mass spectrometry. The GC-MS used in the research institute is the 6890N-5970N model produced by Agilent. The test conditions are initial column temperature 40℃, retention time 2min, column temperature increased to 160℃ at a heating rate of 4℃ / min, retained for 2min, and then increased from 160℃ to 280℃ / min at a heating rate of 10℃ / min.

[0050] The microwave pyrolysis results of lignite and 9,10-dihydroanthracene are shown in Figure 4 .

[0051] Example 4

[0052] The activated carbon particles with a size of 0.060 mm were placed in a microwave pyrolysis system with microwave as the heat source. The microwave time was 30 min and the microwave electric field intensity was 2.75×10 4 V / m, the activated carbon was burned to be porous and have good microwave absorption performance; then the lignite was crushed and sieved to obtain lignite with a particle size of 4 mm; and it was sent to an oven for quality improvement to obtain a dry powdered coal sample; 5g of microwave-irradiated activated carbon was weighed and placed in a microwave pyrolysis system, and then 5g of dry powdered coal sample and 10mL of decahydronaphthalene (hydrogen supply solvent) were added in sequence. First, the microwave pyrolysis system was ensured to be in a nitrogen atmosphere, and then prepared for microwave pyrolysis under the protection of nitrogen at 50mL / min. The microwave pyrolysis conditions were as follows: irradiation power 1200W, irradiation frequency 2450MHz, irradiation time 30min and electric field strength 2.75×10 4V / m, the oil-gas mixture obtained by pyrolysis was condensed and absorbed by dichloromethane; the lignite conversion rate and tar yield were calculated by weighing, and the tar composition was determined by gas chromatography-mass spectrometry. The GC-MS used in the research institute is the 6890N-5970N model produced by Agilent. The test conditions are initial column temperature 40℃, retention time 2min, column temperature increased to 160℃ at a heating rate of 4℃ / min, retained for 2min, and then increased from 160℃ to 280℃ / min at a heating rate of 10℃ / min.

[0053] The microwave pyrolysis results of lignite, decahydronaphthalene and n-dodecane are shown in Figure 5 .

[0054] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent, characterized in that: The invention comprises the following steps: the microwave co-cracking of lignite and hydrogen-donating solvent is performed to obtain tar through condensation, wherein the tar contains cycloalkanes of C6 to C10. Firstly, activated carbon particles with a sieved particle size of ≤0.075 mm are placed in a microwave pyrolysis system, and microwaves are used as a heat source. The microwave irradiation time is 5 to 30 min and the microwave electric field intensity is 2.68×10 4 ~3.28×10 4 V / m, and then the upgraded lignite and the hydrogen-donating solvent are added in sequence to ensure that the pyrolysis environment in the microwave pyrolysis system is a nitrogen atmosphere. The treated lignite and the hydrogen-donating solvent are cracked under microwave normal pressure conditions, and then absorbed by dichloromethane after condensation to obtain C6-C10 cycloalkanes.

2. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The microwave irradiation frequency is 2450 MHz, the microwave irradiation time is 5 to 30 minutes, and the microwave electric field intensity is 2.68×10 4 ~3.28×10 4 V / m.

3. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The lignite particle size is 2.5-4 mm.

4. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The upgraded lignite gradually reduces its initial moisture content from 48% to below 15%.

5. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The hydrogen-donating solvent includes, but is not limited to, hydrogenated naphthalene, hydrogenated anthracene and alkyl alcohol.

6. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The structure of the microwave heating furnace mainly includes: magnetron, waveguide, microwave reaction cavity, high-voltage transformer and heating control system.

7. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The lignite and hydrogen-donating solvent are cracked under normal pressure, the absorber is placed in the microwave pyrolysis system, and the lignite and hydrogen-donating solvent are added in sequence according to a certain mass ratio, generally 1:1 to 3.

8. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The activated carbon as the wave absorbing agent is first screened, and particles with a particle size of ≤0.075 mm are selected for use, and then the activated carbon is irradiated with microwaves for 30 minutes to obtain the activated carbon with the desired good wave absorbing performance.

9. The method for preparing cycloalkanes by microwave pyrolysis of lignite and a hydrogen-donating solvent according to claim 1, characterized in that: The raw material is lignite, which is abundant in resources but has a low utilization rate.

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