Method for efficiently preparing synthesis gas by frequency conversion microwave directional regulation of water-gas reaction

Abstract

The application discloses a method for efficiently preparing synthesis gas by variable frequency microwave directional regulation of water-gas reaction, and belongs to the technical field of water-gas reaction for preparing synthesis gas. The method uses biomass charcoal as a wave absorber and a reactant, and gasifies water by a preheating furnace and then feeds the water into a microwave reactor, so that water vapor passes through the charcoal bed from top to bottom to generate synthesis gas through water-gas reaction; the microwave frequency is 3550-7500 MHz. The method uses biomass charcoal as a wave absorber and a reactant, and the volume fraction of the obtained synthesis gas is higher than 99%, and the hydrogen-carbon molar ratio is 1.1. By changing the microwave emission frequency to match the intrinsic frequency of different biomass charcoals, the reaction activation energy is reduced and the reaction rate is improved under the resonance action of the two. The method solves the problems that the water-gas reaction for preparing synthesis gas is difficult to occur under conventional microwave frequency and the gas production rate is low under electric heating conditions, and the synthesis gas components are complex and difficult to separate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of preparing synthesis gas by water-gas reaction, and particularly relates to a method for preparing synthesis gas by high-efficiency water-gas reaction under the direction of variable-frequency microwave. BACKGROUND

[0002] Synthesis gas is a kind of flammable gas with H2 and CO as main components, which can be directly used as gas fuel for power supply or heat supply, or used as raw gas for synthesizing methanol, methane, dimethyl ether (DME) and other fuels and chemicals. There are many methods for preparing synthesis gas, which can be obtained by converting solid raw materials such as biomass, coal and coke, or by reforming natural gas. At present, the process for preparing synthesis gas mainly develops from natural gas reforming and coal gasification. The use of coal gasification to prepare synthesis gas will produce SO2 and other harmful gas pollution to the air, and the preparation of synthesis gas will emit CO2, which needs subsequent treatment to pollute the environment. Although the natural gas reforming process has no environmental pollution problem, the price of natural gas is high, the catalyst used is expensive, and there are problems such as catalyst deactivation in the conversion process. Using clean and abundant water resources to prepare synthesis gas has the potential to replace coal or natural gas to prepare synthesis gas, and can realize clean and efficient conversion of the synthesis gas preparation process.

[0003] At present, the methods for preparing synthesis gas from water mainly include water electrolysis, photocatalytic water splitting and water-gas reaction. The electrolysis water process is relatively mature, and the product is pure, but the introduction of noble metal catalyst is needed, and the catalyst activity and stability are difficult to solve. The research on photocatalysis has become a hot spot in recent years, but the selectivity of the catalyst is also high. The reaction formula of water-gas reaction for preparing synthesis gas includes:

[0004] C + H2O → CO + H2 ΔH = 131 kJ / mol (1);

[0005] C + 2H2O → CO2 + 2H2 ΔH = 90.2 kJ / mol (2);

[0006] C + CO2 → 2CO ΔH = 173.8 kJ / mol (3).

[0007] The above reactions are endothermic reactions, the reaction temperature is greater than 800℃, the energy consumption is high; the molar ratio of H2 to COx is difficult to reach the theoretical value of 2 due to the thermodynamic control of the reaction; and the main reaction for preparing synthesis gas is formula (1), the occurrence of side reactions (2) and (3) makes the water-carbon gasification efficiency low. Due to the lower heat required for reaction (2), the synthesis gas contains a large amount of CO2 gas due to the limitation of traditional heating methods, and the component ratio in the product is difficult to control, which affects the quality of synthesis gas, and the carbon is not fully utilized. The paper (10.19912 / j.0254-0096.2020.08.047) reported the experimental study of corn straw coke steam enhanced gasification for preparing hydrogen-rich gas. Fe2O3, CaO and Na2CO3 were mixed in a certain proportion and compressed into corn straw, and the modified biomass char obtained by pyrolysis was used as the raw material for steam gasification. The steam gasification experiment was carried out at 750-950℃, and the volume fraction of CO2 in the obtained gas product was higher than 20%. Patent CN 112063394 A discloses a method for producing hydrogen-rich synthesis gas by gasification of waste biomass. The biomass is upgraded to hydrothermal char by hydrothermal treatment, and then the hydrothermal char is gasified at 750-900℃ under the catalysis of Ni, Fe metal catalyst supported by Al2O3, clay mineral, molecular sieve, etc. to prepare hydrogen-rich gas. The highest H2 volume fraction is 72.56%, CO is 22.7%, CO2 is 2.1%, and CH4 is 2.64%. In this patent, the volume fraction of hydrogen is relatively high, but the hydrogen-carbon molar ratio control is poor. When the hydrogen-carbon molar ratio is close to 1, the volume fraction of CO2 and CH4 increases accordingly.

[0008] Microwave heating is also used for water-carbon gasification to produce hydrogen. Patent CN 114958434 A discloses a method for producing hydrogen by microwave pyrolysis and gasification of biomass. Active carbon and NiO / CaO catalyst are mixed into the biomass for microwave cracking and steam gasification. The resulting gas products are mainly H2, CO2 and CH4. Patent CN 103387853 A discloses a method for producing synthesis gas by microwave gasification of biochar. The biomass raw material is carbonized in a microwave reactor, and then steam gasification is carried out at 500-900℃ under the catalysis of K2O, SiO2, MgCO3, CuO and CaO. The value of H2+CO in the resulting gas product is up to 99.35%, the volume fraction of CO2 is 0.74%, and the volume fraction of CH4 is 0.21%. In this technology, the synthesis gas has less impurities, the proportion of synthesis gas is extremely high, and the hydrogen-carbon molar ratio is close to the theoretical value 1. However, this effect is achieved by using alkaline metals as catalysts and CO2 absorbers, which increases the consumption of catalysts and requires consideration of the stability of catalysts at high temperatures. The time for gasification and removal of volatile matter is 20-50min. In existing microwave technologies, the microwave frequency is fixed at 2450MHz, which can only act on part of the wave-absorbing materials, thereby putting high requirements on the wave-absorbing agent. In addition, a power of 500-1000W is usually required, which has low energy utilization rate and cannot achieve complete conversion of the water-gas reaction to high-quality synthesis gas. SUMMARY

[0009] To solve the above problems in the prior art, the technical problem to be solved by the present application is to provide a method for efficiently producing synthesis gas by frequency-variable microwave directional regulation of water-gas reaction, which improves the reaction rate, adjusts the gas components and directionally regulates the quality of synthesis gas.

[0010] To solve the above technical problems, the technical solution adopted by the present application is as follows:

[0011] A method for efficiently producing synthesis gas by frequency-variable microwave directional regulation of water-gas reaction, which uses biomass char as a wave-absorbing agent and a reactant, and gasifies water through a preheating furnace and into a microwave reactor. The water vapor passes through the char bed layer from top to bottom, and the water-gas reaction C+H2O=CO+H2 occurs to generate synthesis gas. The microwave frequency is 3550-5700MHz, the power is 200-500W, and the reactor temperature is 700-880℃.

[0012] The method for efficiently producing synthesis gas by frequency-variable microwave directional regulation of water-gas reaction uses biomass char, which is any one of Chinese fir char, rice husk char or bamboo char.

[0013] The method for efficiently preparing synthesis gas by variable frequency microwave directional regulation of the water gas reaction, when using Chinese fir charcoal as the wave absorber and reaction material, has a microwave frequency of 3550-4225 MHz and a power of 200 W, and the reactor temperature is 800-880 DEG C.

[0014] The method for efficiently preparing synthesis gas by variable frequency microwave directional regulation of the water gas reaction, when using rice husk charcoal as the wave absorber and reaction material, has a microwave frequency of 4400 MHz and a power of 200 W, and the reactor temperature is 713 DEG C.

[0015] The method for efficiently preparing synthesis gas by variable frequency microwave directional regulation of the water gas reaction, when using bamboo charcoal as the wave absorber and reaction material, has a microwave frequency of 4225 MHz and a power of 500 W, and the reactor temperature is 746 DEG C.

[0016] The method for efficiently preparing synthesis gas by variable frequency microwave directional regulation of the water gas reaction comprises the following steps:

[0017] In the first step, quartz wool is filled in a quartz tube with an inner diameter of 8 mm, and 3 g of activated carbon is slowly filled into the quartz tube and fixed by the quartz wool.

[0018] In the second step, the quartz tube is connected to a reaction system, the air tightness is checked, nitrogen is introduced to purge the reaction system and keep the reactor in an inert atmosphere.

[0019] In the third step, the microwave power is turned on, the variable frequency microwave is input into the microwave resonance cavity through the microwave feed port, the reaction material starts to heat after being irradiated by the microwave of different frequencies, and the temperature change of the catalyst is detected in real time by an infrared temperature detector and a thermal imager on the axial section of the quartz tube.

[0020] In the fourth step, after the reaction temperature is reached and kept stable, the nitrogen is stopped, and water is introduced into the reactor after being gasified by a preheating furnace.

[0021] In the fifth step, after the reaction is completed, the gaseous products are collected by a gas sampling bag and analyzed offline in a gas chromatograph.

[0022] Compared with the prior art, the method has the following beneficial effects:

[0023] 1. The method is based on the continuous adjustment of the microwave frequency, provides the best microwave absorption frequency for different types of biomass charcoal, first studies the wave absorption characteristics of the biomass charcoal in the variable frequency microwave, reduces the limitation of the microwave heating on the types of wave absorbers, improves the microwave utilization rate, and is conducive to reducing the pretreatment energy consumption of the biomass charcoal.

[0024] 2、The adaptability of microwave frequency to biomass charcoal material reduces the reaction activation energy. According to the reaction endothermic and exothermic effect, the microwave frequency and power are double-regulated to direct regulate the reaction equilibrium. When the microwave frequency is 4225 MHz, the Chinese pine charcoal is rapidly heated to 880 DEG C to promote the water gas reaction, the volume fraction of the obtained synthesis gas is greater than 99%, and the hydrogen-carbon molar ratio is 1.1, so that the full conversion of microwave active carbon catalytic cracking to synthesis gas is realized, and the synthesis gas quality is improved.

[0025] 3、The present application solves the problems of low reaction rate and low synthesis gas quality in the existing microwave-promoted water-carbon reaction technology.

[0026] The microwave frequency is matched with the optimal absorption frequency of various materials, the temperature is raised through resonance and the hot spot effect is generated, so that the reaction activation energy is effectively reduced, and the water gas reaction for preparing synthesis gas is efficiently promoted. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The result graph of the influence of different heating modes on the reaction results;

[0028] Figure 2 The result graph of the influence of different power strips on the reaction results;

[0029] Figure 3 The product distribution graph of water cracking catalyzed by different catalysts. DETAILED DESCRIPTION

[0030] The present application will be further described below in combination with specific examples. The frequency conversion device used in the examples is the device disclosed in the patent application with the publication number CN111117676A and the invention name of a microwave continuous frequency modulation cooperates with biomass directional depolymerization device and its use method.

[0031] Example 1

[0032] In the microwave reactor, the frequency is 2450 MHz, the power is 200 W, the Chinese pine charcoal is used as the catalyst, the loading mass is 5 g, and the influence of microwave on the preparation of synthesis gas by water-carbon reaction is investigated. The water flow is 0.2 ml / min, and the gasification temperature of water is 250 DEG C. The specific implementation steps include:

[0033] Firstly, 3 g of catalyst is loaded into the quartz tube with an inner diameter of 8 mm, and the quartz wool is fixed by loading;

[0034] Secondly, the quartz tube is connected to the reaction system, the air tightness is checked, nitrogen is introduced to purge the reaction system and keep the reactor in inert atmosphere;

[0035] Third step, open the microwave power, the frequency conversion microwave through the microwave feed input microwave resonant cavity, catalyst absorption microwave after the start of warming, through the infrared temperature detector and thermal imager real-time detection of the quartz tube axis section catalyst temperature change;

[0036] Fourth step: after reaching the reaction temperature and keeping stable, stop the nitrogen gas, adjust the flow meter control water to 0.2ml / min flow through the preheating furnace gasification after the reactor;

[0037] Fifth step: use gas sampling bag to collect gaseous products in gas chromatography off-line analysis.

[0038] In this example, the reaction system temperature is lower than 200℃, the reaction does not occur.

[0039] Example 2

[0040] In the microwave reactor, set the microwave power to 200W, the frequency is 3550MHz, other conditions and implementation steps are the same as example 1.

[0041] In this example, the reaction system temperature is 800℃, the gas component is H2: 52%, CO: 47%, the gas production rate is 120ml / min.

[0042] Example 3

[0043] In the microwave reactor, set the microwave power to 200W, the frequency is 4225MHz, other conditions and implementation steps are the same as example 1.

[0044] The reactor temperature is 880℃, the gas component is H2: 52%, CO: 47%, the gas production rate is 240ml / min.

[0045] Example 4

[0046] In the microwave reactor, set the microwave power to 200W, the frequency is 5500MHz, other conditions and implementation steps are the same as example 1.

[0047] In this example, the reaction system temperature is lower than 200℃, the reaction does not occur.

[0048] Example 5

[0049] In the microwave reactor, set the microwave power to 200W, the frequency is 7010MHz, other conditions and implementation steps are the same as example 1.

[0050] In this example, the reaction system temperature is 325℃, the reaction does not occur.

[0051] Comparative example 1

[0052] In the fixed bed reactor, the water splitting reaction for synthesis gas is carried out by electric heating, the temperature of the fixed bed reactor is set to 880℃, the catalytic water splitting gasification is carried out by using Chinese pine charcoal, the filling mass is 3g; the water flow is 0.2ml / min, and the gasification temperature of water is 250℃. The specific steps include:

[0053] Firstly, the quartz pipe with an inner diameter of 8mm is filled with quartz wool, 3g of series catalyst is loaded into the quartz pipe, and the quartz pipe is fixed by filling quartz wool; and the quartz pipe is placed in the fixed bed reactor;

[0054] Secondly, the fixed bed tube furnace is heated, the temperature is increased to the preset temperature value at a heating rate of 10℃ / min; the whole system is fully purged by a constant amount of N2, and the air tightness of the device is checked;

[0055] Thirdly, after purging, the nitrogen gas is stopped, the water flow is adjusted to 0.2ml / min, the preheated water vapor generator enters the reactor, after the reaction is completed, the product gas is collected by an aluminum foil collection bag and is introduced into a gas chromatograph for qualitative and quantitative analysis.

[0056] Since the water-carbon reaction is a strong endothermic reaction, the reaction can be carried out completely when the electric heating reaction temperature is above 850℃. In the electric heating fixed bed gasification furnace, the water-carbon reaction is carried out at a high temperature of 880℃, which can generate synthesis gas with a H2 volume fraction of more than 60%, but the CO content is low, the hydrogen-carbon molar ratio is not conducive to the subsequent use of synthesis gas, and the volume fraction of CO2 is as high as more than 20%, which puts high requirements on the subsequent separation and purification. Under the industrialization frequency of 2450MHz, the wave absorption performance of Chinese pine charcoal is poor, which is lower than the temperature at which the water-carbon reaction occurs. However, this kind of wave absorber can rapidly heat up at frequencies of 3550MHz and 4225MHz, and the catalytic water-carbon reaction proceeds violently. At the same reaction temperature, due to the fast heating rate and uniform heating of the frequency conversion microwave, the water-carbon reaction is rapidly and completely converted, the hydrogen-carbon molar ratio is close to 1, and the CO2 content is very low, which is very beneficial to the purification and use of synthesis gas. When the microwave frequency is changed to 5500MHz, the wave absorber exhibits poor wave absorption performance, and the reaction does not occur. In addition, the gas production rate at this temperature by electric heating is 76ml / min, while the microwave can significantly improve the reaction rate, and the gas production rate at 3550MHz is 140ml / min, but the reaction rate can reach 240ml / min at 4225MHz.

[0057] Example 6

[0058] In the frequency conversion microwave reactor, Chinese pine charcoal is used as the catalyst, the microwave frequency is set to 4225MHz, the power is 100-400W, the water flow is 0.2ml / min, and the water is gasified at 250℃ and then introduced into the reactor. The specific implementation steps are the same as those in Example 1.

[0059] At the fixed microwave frequency, the change of power mainly affects the product distribution by changing the temperature. When the power is too low, the slow heating rate and reaction temperature cannot meet the conditions for water-carbon reaction to occur. When the power increases to a certain extent, the reaction occurs, but the change of power has little effect on the component distribution. The main reason is that the matching of the frequency and the intrinsic frequency of the absorbing material promotes the reaction under good temperature conditions. The power of 200 W can meet the energy required for reaction equilibrium. When the power continues to increase, the dielectric properties of the material will change, and the change of temperature is not obvious, and the product distribution is basically the same. Therefore, by adjusting the appropriate microwave frequency, the reaction can occur at a lower power and obtain synthesis gas with a hydrogen-carbon molar ratio close to 1, which provides conditions for the use of synthesis gas while saving energy.

[0060] Example 7

[0061] In the variable frequency microwave reactor, the microwave emission frequency was 2500-5700 MHz, and the power was continuously adjusted within 200-500 W. The reaction temperatures of the three carbon materials were: 750℃ for Chinese pine charcoal, 713℃ for rice husk charcoal, and 746℃ for bamboo charcoal. The water flow rate was 0.2 ml / min, and the gasification was carried out at 250℃ and then introduced into the reactor. The effect of different biomass carbons on the component of water-carbon reaction was investigated. The specific implementation steps were the same as in Example 1.

[0062] The product distribution of water splitting catalyzed by different catalysts is shown in Table 1. Figure 3 The composition of gaseous products varies greatly with different types of biomass carbon. Among them, Chinese pine charcoal, as an activated carbon with high fixed carbon content and little volatile matter, has very similar volume fractions of H2 and CO in the gaseous products, the sum of the volume fractions of the two is the highest, the hydrogen-carbon molar ratio is closest to 1, and the volume fraction of CO2 is approximately 0, close to the ideal synthesis gas ratio; the hydrogen-carbon molar ratio of bamboo charcoal is second, and the volume fraction of CO2 is lower than that of electric heating; the ash content of rice husk charcoal is high, the H2 content in the water-carbon reaction is high, but the volume fraction of CO2 is about 20%, and the proportion of CO is the least, which is not conducive to the preparation of synthesis gas.

Claims

1. A method for efficient syngas production from water-gas reaction under microwave directional control, characterized in that, Using cedar charcoal as a microwave absorber and reactant, water is preheated in a furnace and then gasified before being introduced into a microwave reactor. Water vapor flows from top to bottom through the charcoal bed, undergoing a water-gas reaction to generate syngas. The microwave frequency is 4225 MHz, the power is 200 W, and the reaction temperature is 880 ℃. The gas composition is H2: 52%, CO: 47%, and the gas production rate is 240 mL / min. The process includes the following steps: The first step is to fill a quartz tube with an inner diameter of 8 mm with quartz wool, and slowly fill 3 g of cedar charcoal into the quartz tube and fix it with quartz wool. The second step is to connect the quartz tube to the reaction system, check the airtightness, purge the reaction system with nitrogen and keep the reactor in an inert atmosphere. The third step is to turn on the microwave power supply and input the microwave into the microwave resonant cavity through the microwave feed port. After the cedar charcoal absorbs the microwave, it begins to heat up. The temperature change of the cedar charcoal is detected in real time by an infrared thermometer and a thermal imager on the axial section of a quartz tube. Step 4: After reaching and stabilizing the reaction temperature, stop the nitrogen supply and adjust the flow meter to control the water flow rate to 0.2 mL / min, which is then vaporized in the preheating furnace and introduced into the reactor. Step 5: After the reaction is complete, the gaseous products are collected using a gas sampling bag and analyzed offline in a gas chromatograph.

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