CN1590297A

CN1590297A - Method of synthesizing ammonia and fuel oil using methane and nitrogen gas

Info

Publication number: CN1590297A
Application number: CN 200310120888
Authority: CN
Inventors: 白敏冬; 白希尧; 杨波; 张芝涛; 白敏菂
Original assignee: Dalian Maritime University
Current assignee: Dalian Maritime University
Priority date: 2003-12-31
Filing date: 2003-12-31
Publication date: 2005-03-09
Anticipated expiration: 2023-12-31
Also published as: CN1280195C

Abstract

A process for synthesizing NH3 and fuel oil from methane and N2 with low cost includes applying an alternative voltage to plasma generator to create a strong discharging electric field, passing the gas mixture (CH4+N2) through the electric field for ionizing and decomposing it into atoms, molecular fragments, CH3, CH2, CH, C, H and N2H4, and reacting to obtain NH3, fuel oil and organic gases.

Description

Method for synthesizing ammonia and fuel oil by using methane and nitrogen

The invention belongs to the field of gas discharge and chemical synthesis, and relates to a method for synthesizing ammonia and fuel oil from methane and nitrogen without using a catalyst.

Background artas petroleum resources are increasingly in shortage, people pay more and more attention to the development and utilization of natural gas resources. It is predicted that the proportion of natural gas in the world's energy structure will rise from 25% to around 40% in the middle of the 21 st century. Therefore, the development and utilization of natural gas have wide prospects. Methane has been used as the main component of natural gas, and its development and research have been in the past hundred years, and mainly includes indirect oxidation of methane to prepare synthetic gas and oxidation/hydrogenation coupling of methane to prepare C₂、C₃The compound and aromatization, the catalytic oxidation of methane to prepare oxygen-containing compound.

The conventional methane catalytic synthesis is a high energy-consuming process and requires scale and efficiency, thus the development of synthesis gas routes is always restricted. Much work has been done on the research of catalytic oxidation of methane to oxygenates, but it is difficult to achieve higher conversion under high selectivity conditions, and therefore there is a certain distance from industrial application. Due to the high stability of the methane molecule, the direct synthesis of carbo-hydrocarbons from natural gas is thermodynamically difficult, and conventional catalytic conversion and oxidative coupling have not made a breakthrough progress. The research on the direct coupling synthesis of carbo-hydrocarbons from natural gas by using new technology and new process is currently a very challenging subject. The research on the methane hydrogenation coupling has been carried out in China at the university of great graduates and Tianjin university in the last decade by using low-temperature plasma. They mainly adopt pulsed corona discharge and dielectric barrier discharge to generate low-temperature plasma under normal pressure, and although certain progress is made, the conversion rate of methane is not high, and the energy consumption is high, so that the coupling of methane in engineering is difficult to use. Microwave plasma adopted by Chinese academy of sciences organic chemistry is used for researching conversion of methane and nitrogen, and products of the microwave plasma mainly comprise HCN and C₂Hydrocarbons and small amounts of cyanide-containing compounds, but the desired ammonia or amines and higher hydrocarbons are not obtained.

NH₃Is an important chemical product. The conventional ammonia synthesis process is N₂And H₂Directly obtained by using iron as a catalyst at a high temperature of 480-520 ℃ and a high pressure of more than 150 atm. The energy consumption is huge and accounts for 70 percent of the total cost, and the large size of the synthesis tower and the complex process flow cause the synthetic ammonia industry to have the defects of large investment, huge energy consumption, difficult production stop and maintenance, high operation cost and the like. Therefore, the energy consumption of the synthetic ammonia is reduced, the process is simplified, and the method becomes the research direction of the current synthetic ammonia.

In recent years, many researchers have conducted studies on the synthesis of ammonia by a plasma method.

In 1983, Khin Swe Yin et Al conducted a research on synthetic ammonia under a low-pressure glow discharge condition, and the experiment analyzed the influence of Pt, SS, Ag, Fe, Cu, Al, Zn and other metals as electrodes on the synthetic effect, and the synthetic ammonia concentration was only 0.31-1.46 mmol/h after the gas reaction for 1 hour. N is a radical of₂The conversion rate is 1.8-8.3%.

In 1993, Haruo Uyama et al studied the effect of iron wire as a catalyst in RF (13.56MHz) or microwave (2450MHz) discharge on synthetic ammonia, and the experimental conditions were as follows: pressure, 650 Pa; an iron wire with the purity of 99.99 percent, the diameter of 0.5mm and the length of 50 mm; the volume ratio of the nitrogen to the hydrogen is 4: 1; the gas flow rate is 1.2dm³h^-1(ii) a After the gas is reacted in the reactor for 2 hours, the final synthetic ammonia concentration is only 1.1 mmol/g.

The above studies are carried out under low pressure, and therefore, the gas is thin and needs to be evacuated, and extremely trace amount of NH can be generated₃It has only research significance and has a larger distance from engineering.

The invention aims to provide a method for synthesizing ammonia and fuel oil by using methane and nitrogen, which has low cost, easy operation and simplified process flow.

The technical conception of the invention is as follows: the ionization energy of methane and nitrogen is 12.98eV and 15.8eV respectively. The average energy obtained by electrons in the strong ionization discharge is 10-30 eV, and high-energy electrons pass through the N₂And CH₄Non-elasticcollisionHit and will N₂And CH₄Gas excitation, ionization and dissociation into N, CH₃·，CH₂H, CH, C, H, and N₂H₄Plasma reaction processes of plasma radicals and active substances are carried out as follows:

these radicals and active species play a major role in the synthesis of ammonia and fuel oil, the product of the synthesis being ammonia and hydrazine, with ammonia concentrations of 8000ppm, and synthetic organic gases including acetylene, ethylene, ethane, propylene, propane, n-butane and isobutane. The synthesized fuel oil contains liquid olefin, alkyne, heterocyclic compound such as pyrrole, pyrazine and pyridine and polycyclic organic matter with molecular weight of 475. The reaction is summarized as follows:

the method adopts CH rich in nature₄And N₂Synthesizing important chemical raw material NH by green chemical strong ionization discharge method as raw material₃And fuel oil, and provides a green new method for industrial synthesis of ammonia and methane conversion.

The technical solution of the invention is as follows: CH (physical channel)₄+N₂Synthesis of NH₃And a fuel oil process. The method is realized by firstly applying an alternating voltage to the plasma generator, establishing a strong discharge electric field with a folding electric field strength of 300-800Td in the plasma generator when CH is generated₄+N₂When the mixed gas passes through a discharge electric field, the mixed gas is ionized and dissociated into atoms, molecular fragments and CH₃·、CH₂ ^·、CH^·、C^·、H^·Isoradical and active substance hydrazine N₂H₄Etc. these particles further react to form NH₃And fuel oil and some organic gases. Wherein the frequency of the alternating voltage is 400-20 kHz. Synthetic organic gases include acetylene, ethylene, ethane, propylene, propane, n-butane and isobutane. The synthesized fuel oil comprises liquid olefin, alkyne, heterocyclic compound such as pyrrole, pyrazine, pyridine and polycyclic organic matter.

The invention has the beneficial effects that:

1. the raw material adopted by the invention is CH rich in nature₄And N₂；

2. A catalyst, an absorbent and a solvent are not used, so that the problems of pollution and energy consumption in the process of using or producing the catalyst, the absorbent and the solvent are avoided;

3. zero pollution, zero waste discharge and zero byproduct green one-step synthesis of ammonia and fuel oil are realized;

4. the equipment for processing ammonia and fuel oil has small volume, simple and convenient operation and low operation cost;

5. the conversion rate of methane is high, and carbon deposition phenomenon on a discharge electrode is avoided.

Description of the drawingsthe invention will be further described with reference to the following drawings and examples.

FIG. 1 is a schematic diagram of the process for synthesizing ammonia and fuel oil according to the present invention.

In fig. 1: 1N₂A gas; 2, adjusting a valve; 3, a gas flow meter; 4, a pressure gauge; 5 heating the tube; 6 plasma reactionA machine; 7 a pressure sensor; 8, a temperature sensor; 9 a humidity sensor; 10 energizing a power supply; 11 an electrostatic voltmeter; a 12 high voltage divider; 13 current probe; 14 sampling the capacitor; 15 gas analyzer; 16, an oscilloscope; 17 a fuel oil collector; 18 a product gas outlet; 19 methane gas;

FIG. 2 is gas flow vs. NH₃Influence of Concentration (CH)₄∶N₂3: 1) relationship graph.

FIG. 3 gas flow vs. CH₄Effect of Conversion (CH)₄∶N₂3: 1) relationship graph.

FIG. 4 gas volume ratio CH₄The effect of conversion (Q ═ 0.5L/min) is plotted.

FIG. 5 shows the unit power consumption and NH₃Concentration dependence (Q ═ 0.5L/min, CH)₄∶N₂3: 1) relationship graph.

Detailed Description

The regulating valve 2 and the gas flowmeter 3 in FIG. 1 are used for controlling and reading the gas flow, the pressure gauge 4 is used for reading the pressure of the gas, and the raw material gas N₂1 and CH₄19, flowing into a heating pipe 5 through the regulating valve 2 and the gas flowmeter 3, heating and fully mixing, and then entering a plasma reactor 6 for synthesis, wherein the reacted gas isThe reaction gas outlet 18 is used for collecting, part of the gas after reaction is taken out to be analyzed on line in the gas analyzer 15, and the generated fuel oil is contained by the fuel oil collector 17. The excitation power source 10 is used to supply high-voltage high-frequency electricity to the plasma reactor. The electrostatic voltmeter 11, the high voltage divider 12, the current probe 13 and the sampling capacitor 14 form a discharge diagnosis part for measuring discharge parameters of the plasma reactor 16 and calculating parameters such as electric energy consumed in the reaction process, energy flow density of discharge and the like according to the parameters. The reaction is carried out at normal pressure and the environmental parameters are detected by a pressure sensor 7, a temperature sensor 8 and a humidity sensor 9.

The different CHs are given in FIG. 2₄And N₂At volume ratio of (2) of total gas mixtureThe influence of the flow rate on the concentration of the synthetic ammonia can be seen from the graph, and as the total flow rate of the mixed gas increases, the different CH₄And N₂To synthesize NH at a volume ratio of₃The concentration of (c) is reduced. This is because the increase in the flow rate of the mixed gas reduces the residence time of the mixed gas in the plasma reaction chamber, i.e., the time during which the mixed gas is subjected to the electric field is short, and therefore, the concentration of the synthetic ammonia is reduced. It can also be seen from FIG. 2 that the total amount of the mixed gas is the same, and the CH is different₄And N₂The volume ratio of(a) has a certain influence on the concentration of synthetic ammonia. CH (CH)₄And N₂When the volume ratio of (A) to (B) is 3: 1, the highest concentration of the synthetic ammonia can reach 8000 ppm.

The graph 3 shows the effect of the total flow rate of the mixed gas on the methane conversion rate, and it can be seen that the methane conversion rate is reduced with the increase of the total flow rate of the gas, because the increase of the flow rate of the mixed gas reduces the residence time of the mixed gas in the plasma reaction chamber, i.e. the time for which the mixed gas is subjected to the electric field is short. Therefore, the conversion rate of methane is reduced, and the conversion rate of the methane obtained at present can reach 90 percent at most. And no carbon deposition phenomenon on the electrode of the plasma reactor is observed, which indicates that strong electric field ionization discharge is adopted to act on CH₄And N₂The gas, because the average energy obtained by electrons in discharge is large, generates more free radicals and active particles, so that the methane can fully react and be converted into organic gas and fuel oil.

The influence of the different gas volume ratios on the methane conversion is given in FIG. 4, from which it can be seen that CH₄And N₂The highest methane conversion, 90%, was obtained at a volume ratio of 3: 1. It can also be seen from the figure that the discharge gaps of the plasma reaction chamber are different, the conversion rate of methane is different, and the conversion rate of methane with the discharge gap width of 0.47mm is higher than that with the discharge gap width of 0.64mm, which indicates that the narrow gap is beneficial to the conversion of methane.

The effect of the fluence of the discharge on the concentration of the synthetic ammonia is shown in FIG. 5. As can be seen fromthe graph, the energy flux density when discharging reached 0.8W/cm²Then, the power density is increasedThe ammonia concentration increases slowly. It is explained that when the high frequency and high voltage applied to the plasma reaction chamber make the discharge reach a certain degree, the energy actually acting on the gas is not increased any more, and the increased energy is consumed in the temperature rise of the dielectric and the electrode of the plasma reaction chamber.

Claims

1. A process for synthesizing ammonia and fuel oil from methane and nitrogen includes such steps as applying an alternative voltage with 400-20kHz to plasma generator, generating a discharge electric field with the folding electric field intensity of 300-800Td while CH is generated₄+N₂When the mixed gas passes through a discharge electric field, the mixed gas is ionized and dissociated into atoms, free radicals and an active substance hydrazine N₂H₄Finally synthesizing ammonia, fuel oil and organic gas.

2. The method for synthesizing ammonia and fuel oil from methane and nitrogen according to claim 1, wherein the methane and nitrogen are directly synthesized into ammonia, fuel oil and organic gas at normal temperature and pressure without using a catalyst in the ionization discharge process of a strong electric field.

3. A process for the synthesis of ammonia and fuel oil from methane and nitrogen as claimed in claim 1, wherein the radical critical in the synthesis reaction is CH₃、CH₂、CH、H、C。

4. The method for synthesizing ammonia and fuel oil from methane and nitrogen according to claim 1, wherein the organic gas comprises acetylene, ethylene, ethane, propylene, propane, n-butane and isobutane.

5. A process for the synthesis of ammonia and fuel oil from methane and nitrogen as claimed in claim 1, wherein the fuel oil comprises heterocyclic compounds, liquid hydrocarbons and polycyclic organic compounds.

6. A process for the synthesis of ammonia and fuel oil from methane and nitrogen as claimed in claim 1, wherein the heterocyclic compound comprises pyrrole, pyrazine or pyridine.

7. The process for the synthesis of ammonia and fuel oil from methane and nitrogen as claimed in claim 1, wherein the liquid hydrocarbon is an alkene, alkyne including 2-methyl-1, 4-pentadiene, 1-hexyne, 1, 4-heptadiene.

8. A process for the synthesis of ammonia and fuel oil from methane and nitrogen as claimed in claim 1, wherein the polycyclic organic compound has a molecular weight of 450.