CN1375448A

CN1375448A - Methane oxidization catalyzing method

Info

Publication number: CN1375448A
Application number: CN 02116304
Authority: CN
Inventors: 寇元; 阎震
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2002-03-22
Filing date: 2002-03-22
Publication date: 2002-10-23
Anticipated expiration: 2022-03-22
Also published as: CN1172842C

Abstract

The method for catalyzing oxidation of methane is characterized by adding NO or/and NO2 whose additive amount is above 50 ppm in the reaction system containing methane and oxygen gas so as to reduce reaction temp. by 200-300 deg.C. Its reaction system can be one for preparing synthetic gas by using oxidation reaction of methane gas phase and one for preparing formaldehyde or methyl alcohol or ethylene by utilizing methane. Said invention possesses the advantages of low reaction temp. and proper H2/CO ratio, etc.

Description

Method for catalyzing methane oxidation

The technical field is as follows:

the invention relates to the technical field of methane conversion, in particular to a method for preparing synthesis gas or other C by direct gas phase oxidation of methane without using a solid catalyst₁、C₂Methods of using the compounds.

Background art:

natural gas is a rich and clean primary energy source, can be directly used for power generation, industry and civilian use, and is also an important raw material of modern chemical industry. With the increasing problem of oil shortage and the wide concern of human beings on globalwarming, the chemical industry of natural gas using methane as a main raw material is generally regarded worldwide. To date, there are two main routes to methane conversion. One is the direct process, i.e. methane is reacted in one step to give the desired product, e.g. methanol, formaldehyde (as MoO)₃/SiO₂As catalyst), ethylene (in V)₂O₅/SiO₂As a catalyst), etc. Due to economic issues, the direct process is still in the laboratory research phase at present.

The other is an indirect method adopted in the industry at present, namely methane is firstly converted into synthesis gas, and then the synthesis gas is used for preparing methanol, such as: h required for the reaction₂the/CO ratio is usually 2. The industrial production of synthesis gas from methane is carried out by methane-steam reforming, i.e.

The disadvantage of this process is H₂H with a CO ratio higher than that required for the synthesis of methanol₂The ratio of/CO, large equipment investment and high energy consumption.

Other routes being investigated also include methane-carbon dioxide reforming and methane partial oxidation using solid catalysts, which have in common the problem that the carbon deposition on the catalyst is relatively severe.

The invention content is as follows:

the object of the present invention is to provide a process for converting methane at lower temperatures without using a solid catalyst. The method can avoid the problems of carbon deposition, deep oxidation and the like caused by using a solid catalyst.

The technical scheme of the invention is as follows:

the method for catalyzing methane oxidation is to add methane and oxygen into a reaction systemMore than 50ppm of NO or/and NO₂。

The reaction system is used for preparing synthesis gas (CO + H) through methane gas phase oxidation reaction₂) Or a system for preparing formaldehyde or methanol or ethylene by using methane.

The concentration of methane in the reaction system is 0.4% -60%.

The volume ratio of methane to oxygen in the reaction system is (0.2-5) to 1.

In the method, NO or/and NO are added₂The concentration of (B) is preferably 200-2000 ppm.

Preparation of synthesis gas by gas phase oxidation of methane, i.e.

At the same time in CH₄-O₂Adding micro (50-2000ppm) NO into the system_x(NO/NO₂) The reaction temperature can be lowered by 200-300 ℃. Changing the reaction conditions (temperature, CH)₄/O₂Ratio, flow rate, etc.) to change CO, H in the product₂、CH₃OH、HCHO、C₂H₄To obtain one or more main products. The method has no carbon deposition problem due to gas phase reaction.

The invention has the following characteristics:

the methane oxidation reaction can take place at temperatures above 750 ℃ in the absence of a catalyst. The invention does not use a solid catalyst, and adopts the method that₄-O₂Adding micro (50-2000ppm) NO into the system_x(NO/NO₂) The reaction temperature was lowered by 200 ℃ to 300 ℃. For the partial oxidation of methane to syngas, the formation of COand H begins around 520 deg.C₂The methane conversion rate and the CO selectivity can reach 50 percent and 80 percent respectively at 650-700 ℃, and the H of the synthesis gas in the product₂The ratio of/CO is 0.8-2.0.

The invention has the advantages and positive effects that:

the invention uses methane gas phase oxidation reaction to prepare the synthesis gas, compared with the traditional methane-water vapor reforming method, the invention has the advantages of low reaction temperature, H₂The ratio of/CO is appropriate, and the like. Meanwhile, compared with a methane partial oxidation method using a solid catalyst, carbon deposition and deep oxidation of methane (generation of CO) are avoided₂)。

The invention can be used for preparing synthesis gas by partial oxidation of methane or for methane-steam reforming system, namely in CH₄-H₂Adding O into O system₂With NO_xTo reduce the reaction temperature and improve H₂The ratio of/CO.

The invention can also be used for synthesizing other methane partial oxidation products, such as formaldehyde, methanol and the like. Compared with the existing method, because of gas phase reaction, the continuous oxidation (to generate CO or CO) of the substances on the solid catalyst is avoided₂) The selectivity to the reduced matter can be improved.

The invention relates to a method for activating methane, which can be used for natural gas chemical industry, and can also be used for reactions involving other methane, such as catalytic combustion, carbon nano tube preparation by methane cracking, coal liquefaction by using methane and other systems which usually need solid catalysts, and can solve the problems of low solid-solid reaction efficiency, difficult separation of productsand catalysts and the like in the traditional method.

Description of the drawings:

FIG. 1 shows the addition of NO to CH under the conditions of synthesis gas preparation₄Effect of conversion and CO yield schematic.

FIG. 2 shows the addition of NO to CH under catalytic combustion conditions₄Effect of conversion and CO yield schematic.

In the figure, ■ and □ respectively represent CH in the absence of NO₄Conversion and CO yield ● and ○ represent CH with 600ppm NO added, respectively₄Conversion and CO yield.

FIG. 3 is an infrared spectrum of the product after reaction at different temperatures. a: 550 ℃; b: 600 ℃; c: 700 ℃.

Example (b):

the methane catalytic oxidation reaction is carried out in a quartz reaction tube with the inner diameter of 6mm, the reaction tube is heated by an electric furnace, the length of the heating section is 20cm, and the reaction temperature is controlled by an LU-900M type program temperature controller. Reactive gas (CH)₄Air, NO) flow rate is controlled by a mass flow meter, and is mixed in advance and then introduced into a reaction tube. O in the reaction product₂，N₂，H₂Detected by two gas chromatographs (molecular sieve column, thermal conductivity detector), CH₄，CO，HCHO，CH₃OH was detected on-line by a Brookfield 22 infrared spectrometer (10cm gas cell) and the concentration was corrected by chromatography. 1. Preparing synthesis gas by methane conversion:

reaction conditions are as follows: CH in the reaction system₄Concentration 20% O₂The concentration was 10%, the NO concentration was 600ppm and the flow rate was 40 ml/min.

As can be seen from FIG. 1, a clear reaction was observed at 550 deg.CAt 700 ℃ CH₄Conversion 38%, selectivity to CO 91%, H₂The ratio of/CO was 0.8. Without adding NO_xThe reaction takes 750 ℃ to occur.

Table 1 shows the different reaction conditions (flow rate, temperature, CH)₄/O₂Ratio) to CH₄Conversion, CO yield and H₂Influence of the/CO ratio. Table 1: CH (CH)₄Concentration CH₄/O₂Maximum methane conversion of CO at flow rate^*H₂/CO^*Temperature of^*(%) (ml/min) yield (%) (%) (. degree.C) 101: 14046550.4650202: 14035380.8700205: 14046.80.9650202: 120047.50.8700^*Data for maximum yield of CO2. Catalytic combustion of methane:

reaction conditions are as follows: CH in the reaction system₄Concentration of 0.4%, O₂The concentration is 2 percent, and the rest is N₂The NO concentration was 600ppm and the flow rate was 40 ml/min.

As can be seen from FIG. 2, under the catalytic combustion condition (strong oxidation condition), the initial temperature of the reaction can be reduced from 850 ℃ to 550 ℃ by adding NO, the CO yield can reach 70% at about 650 ℃, and when the CO yield is higher than 700 ℃, CH₄Near complete conversion. 3. Methane conversion to other products:

reaction conditions are as follows: CH in the reaction system₄Concentration 20% O₂The concentration is 10 percent, and the rest is N₂The NO concentration was 600ppm and the flow rate was 40 ml/min.

For the same reaction system (CH)₄-O₂-NO_x) By changing the reaction conditions, formaldehyde can be obtainedMethanol, ethylene, and the like.

FIG. 3 is a (partial) infrared spectrum of the product after reaction at different temperatures, a being the infrared spectrum of the product after reaction at 550 ℃; b is an infrared spectrogram of a product after the reaction at 600 ℃; c is an infrared spectrum of a product after 700 ℃ reaction. It can be seen that formaldehyde and methanol are advantageously produced at lower temperatures and ethylene can be obtained at elevated temperatures.

Claims

1. A method for catalyzing methane oxidation is characterized in that more than 50ppm of NO or/and NO is added into a reaction system containing methane and oxygen₂。

2. The catalytic methane oxidation process according to claim 1, wherein the reaction system is a gas phase methane oxidation reaction to produce synthesis gas (CO + H)₂) The system of (1).

3. A catalytic methane oxidation process according to claim 1, characterized in that the reaction system is a system for the preparation of formaldehyde or methanol from methane.

4. A catalytic methane oxidation process according to claim 1, characterized in that the reaction system is a system for producing ethylene from methane.

5. The catalytic methane oxidation process according to claim 1, wherein the concentration of methane in the reaction system is from 0.4% to 60%.

6. The catalytic methane oxidation processof claim 1 wherein the volume ratio of methane to oxygen in the reaction system is from 0.2 to 5: 1.

7. The catalytic methane oxidation process of claim 1, wherein NO or/and NO₂The concentration of (B) is 200-2000 ppm.