CN101050158B

CN101050158B - Method for producing acetylene for cracking natural gas by micro discharge

Info

Publication number: CN101050158B
Application number: CN2007100102541A
Authority: CN
Inventors: 白敏冬; 张芝涛; 白敏菂; 杨波; 薛晓红; 白希尧
Original assignee: Dalian Maritime University
Current assignee: Dalian Maritime University
Priority date: 2007-01-28
Filing date: 2007-01-28
Publication date: 2010-08-18
Anticipated expiration: 2027-01-28
Also published as: CN101050158A

Abstract

This invention discloses a method for preparing acetylene by micro-discharge pyrolysis of natural gas. The conversion rate of methane is higher than 70%. The selectivity of acetylene is 80-90%. The selectivity of C2 is 85-95%. The energy consumption of acetylene is lower than 10 kWh/kg. The method can avoid electrode ablation problem faced by acetylene preparation by plasma pyrolysis of natural gas. Besides, the method lowers the energy consumption, and increases the conversion rate of methane as well as the selectivity of acetylene. The method can also be used in synthesis of other novel organic and inorganic matters.

Description

The method of producing acetylene for cracking natural gas by micro discharge

Technical field

The invention belongs to technical fields such as gas ionization discharge, atmospheric pressure plasma physics and organic chemistry, relate to the method for producing acetylene for cracking natural gas by micro discharge.

Background technology

Along with the minimizing day by day of petroleum resources, switching through of natural gas straight preparation C ₂The research of hydrocarbon and other chemical products with high added-value becomes the problem that industrial sector generally is concerned about.The main component of Sweet natural gas is a methane, because methane has stable molecular structure, conventional catalysis means must could realize the activation and the conversion of methane under hot conditions, and high temperature of reaction causes the stability of catalyzer to reduce and the yield of target product is low, is difficult to realize industrial applications.

As far back as the forties in last century, arc discharge method just has been applied to switching through of natural gas straight system acetylene (Huels technology) process, owing to shortcomings such as there is temperature of reaction height (being up to 15000K) in traditional thermic arc plasma body, electrode erosion is serious, energy consumption is high, process is difficult to control fail to be applied on a large scale so far.People utilize the low temperature plasma technique that the activation of methane has been carried out a large amount of research with conversion in recent years.Heintze etc. have studied the influence of working parameter to microwave plasma conversion methane system acetylene reaction, is 70W in operating pressure for the 3000Pa discharge power, during methane flow 150mL/min, methane conversion and acetylene selectivity reach 94.3% and 71.2% respectively, but keeping plasma body, negative pressure can not satisfy production-scale needs, keep negative pressure simultaneously and increase the economy reduction that extra power consumption makes reaction process, Kado etc. utilize the spark discharge of high frequency direct current to transform methane system acetylene, higher acetylene selectivity (85%) and low acetylene energy consumption 12kWh/kg on several watts～tens watts power levels, have been obtained), but its methane conversion has only 20%, the low power density of atmospheric low-temperature plasma makes this method be difficult to obtain satisfied methane conversion and acetylene yield, and increase transformation efficiency with gas flow and descend rapidly, be difficult to realize the industry amplification.

The acetylene chemical industry is an important component part of China's chemical industry, it is the needs that the huge chlorine industry of balance China is produced, be again to be that raw material carries out polyvinyl chloride (PVC), vinyl acetate between to for plastic, vinylformic acid, 1, bulk chemical synthetic industrial production system such as 4-butyleneglycol with acetylene.Only be example with PVC, at present China PVC production capacity is 4,000,000 tons/year, demand is 6,000,000 tons/year, wherein is that to adopt acetylene be raw material production more than 70%.For a long time, domestic all is to adopt calcium carbide route to produce acetylene basically.But calcium carbide route is produced acetylene and is had energy consumption height, the serious problem of environmental pollution, is difficult to continue development.In recent years, country has carried out strict control to the production of calcium carbide, and it is 10000 kilowatts calcium carbide production equipment that time limit has been closed power capacity, causes the acetylene raw material in short supply, and the product percentage of import such as PVC rise significantly.The acetylene clearer production technology that exploitation can be applied has become the only way that ensures China's acetylene chemical industry realization Sustainable development.

Conversion of natural gas system acetylene is the clean production technology of the acetylene industrialized, that be fit to China's national situation of unique in the world realization at present.The method of the Sweet natural gas system of utilization acetylene mainly contains gas by partial oxidation of natural (co-production synthesis gas and acetylene) method and high-temperature electric arc cracking process.

But because the natural gas source utilization ratio low (below 30%) of partial oxidation process technology could produce scale and benefit in the time of must uniting with other chemical process.The disposable input that this had both increased equipment has reduced the scale adaptability of its technology again, thereby has limited applying of this technology.Advantage such as facility investment is few though high-temperature electric arc cracking legal system acetylene technology has, natural gas source utilization ratio height, adaptability to raw material are strong, but there is the shortcoming of lacking energy consumption height, electrode life in arc process, thereby has also seriously restricted this technology applying in China.

The auspicious grade of Xu Xing people had carried out the research work of low-temperature plasma preparation of acetylene by cracking natural gas device and technology in 2005.Invented the compound direct current of microwave (DC) low-temperature plasma exciting technique, utilizing microwave is thread plasma body with the cracking of column direct-current plasma, reduced the ablation of anode surface significantly, improved anodic work-ing life, electrode life, accumulative total surpassed 200 hours, than improving more than 39% the electrode life (144 hours) of conventional thermic arc plasma body.And by the plasma reaction chamber structure optimization design, direct-current plasma is operated under the high-tension operating mode of low current, system has high capacity usage ratio, thereby has reduced the energy consumption of reaction process, has improved the economy of plasma process process.Result of study shows: methane conversion is 71%, the selectivity average out to 85.3% of acetylene, C ₂Selectivity (acetylene+ethene) is stabilized in 90.3%, and the acetylene energy consumption is stabilized in 11.65kWh/kg (the minimum 10.8kWh/kg of reaching), acetylene output average out to 8.34kg/h (60t/), C ₂Yield average out to 64.2%.Compare with heat plasma technology both domestic and external, the capacity usage ratio of reaction unit improves more than 10%; Increase more than 39% the work-ing life of electrode, and reaction process is stable; Have only in equal-wattage scale and Sweet natural gas under the condition of methane, energy consumption reduces more than 30%.The new way that the research of microwave low temperature plasma preparation of acetylene by cracking natural gas device and technology provides a gas chemical industry to utilize for China.Though this technology has had bigger improvement than conventional thermic arc preparation of acetylene by cracking natural gas with plasma technology, also exist also to show electrode life less than normal, it is also bigger than normal to consume energy, and because the stable problem that electrode erosion brings.

Summary of the invention

The objective of the invention is to solve plasma natural gas cracking and produce the problem that acetylene exists, the method for dielectric impedance producing acetylene for cracking natural gas by micro discharge is provided.This method is to adopt dielectric impedance little (time) discharge means, reprocess on molecular level at the discharging gap cracking natural gas and synthesizes acetylene, and methane conversion is greater than 70%, and the acetylene selectivity is greater than 80%, C ₂Selectivity (acetylene+ethene) is 85%～95%, and the acetylene energy consumption is lower than 10kWh/kg, and electrode life is greater than 20000h.New technology, novel process that this will become the acetylene cleaner production that can apply have ensured China's acetylene chemical industry Sustainable development.

Technical scheme of the present invention is: the present invention is the method that adopts the dielectric impedance micro discharges, makes to form the dense ionization electric field in the discharging gap, and strength of electric field is 50kV/cm～100kV/cm, and electron density reaches 10 ¹⁴/ cm ³More than, electronics has mean momentum and reaches more than the 10eV (116000K), and the electron energy in the plasma body distributes by Maxwell, for natural gas pyrolysis provides a large amount of active particles.

Methane and H-H reaction:

H ₂→H+H

CH ₄→CH ₃+H

CH ₃→CH ₂+H

CH ₂→CH+H

CH→C+H

CH ₃, CH ₂Compoundly can form ethane and ethene:

CH ₃+CH ₃→C ₂H ₆

CH ₂+CH ₂→C ₂H ₄

Ethene derives from CH on the one hand ₂Compound, derive from ethane dehydrogenation on the other hand:

C ₂H ₆→C ₂H ₄+H ₂(2H)

Acetylene derives from two aspects equally, ethene dehydrogenation and free radical reaction:

C ₂H ₄→C ₂H ₂+H ₂(2H)

CH+CH→C ₂H ₂

In addition, acetylene also polymerization form various carbene:

nC ₂H ₂→C2nH ₂+(n-1)H ₂

N is the integer greater than 1 in the formula.

From the following formula reaction process as can be seen, along with the raising of hydrogen alkane ratio, can suppress the further conversion of acetylene well, improve the selectivity of acetylene, but too high hydrogen alkane ratio not only causes methane conversion to reduce, and makes concentration of acetylene decline in the product, and this will increase the later separation cost.

Because dielectric medium adopts α type Al ₂O ₃Fine powder smelting is coated with is processed into thin dielectric layer, its volume specific resistance＞10 ¹⁶Ω cm, critical breakdown electric field intensity＞300kV/cm, water-intake rate are 0%, relative permittivity is 10, dielectric loss＜3.9 * 10 ^-4, hardness＞1000 (Hv).Under the state of micro discharges, its export license is almost 0.

Effect of the present invention and benefit are: there is not the electrode erosion problem in (1) the present invention, has solved the electrode erosion problem that plasma natural gas cracking is produced acetylene; (2) solved the stability problem of plasma pyrolysis; (3) further reduce energy consumption, improved the selectivity of methane conversion and acetylene.

Description of drawings

Accompanying drawing is the technology block diagram of dielectric impedance producing acetylene for cracking natural gas by micro discharge.

Among the figure: 1 Sweet natural gas, 2 valves, 3 under meters, 4 intermediate frequency high-voltage power supplies, 5 discharge electrodes, 6 earthing poles, 7 dielectric layers, 8 plasma reactors, 9 discharging gaps, 10 insulators, 11 quenching devices, 12 gas composition analyzers, gases such as 13 synthetic acetylene.

Embodiment

Be described in detail specific embodiments of the invention below in conjunction with technical scheme and accompanying drawing.

In the step 1. figure ionic medium precursor reactant device 8, the dielectric barrier discharge parts have been placed, wherein the metal discharge electrode 5 peripheral smeltings of being processed into are coated with thin layer of dielectric 7, the earthing pole 6 that is made of metal abuts against on the reactor casing, smelting is coated with the thin dielectric layer of one deck on the another side, its thickness is 0.2mm～1mm, forms discharging gap 9 between discharge electrode, earthing pole, and its distance is 0.2～2mm.

The frequency of the intermediate frequency high-voltage power supply 4 of step 2. in Fig. 1 is 400Hz～10kHz, the high-voltage of carrying is added on the discharge electrode 5 by insulator 10, set up the strong ionization discharge electric field with earthing pole 6, highly dense little (time) discharge takes place in discharging gap 9, electron density reaches 10 ¹⁴/ cm ³More than, electronics has average energy and reaches more than the 10eV, is CH ₄Cracking, synthetic acetylene provide the active particle and the free radical of a large amount of highly dense intensities.

Step 3. Sweet natural gas 1 enters plasma reactor 8 by valve body 2 and under meter, carry out fierce plasma chemical reaction in the micro discharge channels of discharging gap 9, gases 13 such as the synthetic acetylene of Sweet natural gas 1 cracking, gas analyzer 12 is to its gaseous constituent prosecution.

Claims

1. the method for a producing acetylene for cracking natural gas by micro discharge is that Sweet natural gas is made acetylene gas by cracking in the dielectric impedance micro discharges gap process of dielectric substance formation, and methane conversion is greater than 70%, and the acetylene selectivity is characterized in that greater than 80%:

A. all be coated with smelting one deck α type Al at discharge electrode, earthing pole ₂O ₃Fine powder is made dielectric layer, and its thickness is 0.2mm～1mm;

B. formed distance between discharge electrode, the earthing pole and be the discharging gap of 0.2mm～2mm, the ionizing electric field intensity that forms in discharging gap is 50kV/cm～100kV/cm, and electrode life is greater than 20000h;

C. the power supply of discharge employing is the intermediate frequency high-voltage power supply of frequency 400Hz～10kHz.