CN100439238C - Metal magnesium and its mixture doped with other metals catalyze the decomposition of hydrocarbons to produce hydrogen - Google Patents

Abstract

The invention discloses a new method for directly catalyzing and decomposing hydrocarbons to produce hydrogen and charcoal by using metal magnesium and its mixture doped with other metals as a catalyst. The pressure of the reaction is between 0.01 and 10 atmospheres, and the reaction temperature is between 200 and 1500°C. After the reaction is completed, the catalyst and the product are automatically separated and can be recycled and reused. The produced hydrogen does not contain impurities such as CO and _CO2 .

Description

Metal magnesium and its mixture doped with other metals catalyze the decomposition of hydrocarbons to produce hydrogen

technical field

The invention relates to a method for producing hydrogen from hydrocarbons by using a catalyst, in particular to a method for producing hydrogen by using a metal catalyst to catalyze and decompose hydrocarbons.

Background technique

As an efficient and clean secondary energy source, hydrogen is widely used in aerospace, oil refining, metallurgy and fine organic synthesis industries; in the ammonia synthesis industry, hydrogen is one of the important synthetic raw materials. In recent years, with the rise of fuel cells, the preparation of high-purity hydrogen as fuel for cells has attracted widespread interest. At present, there are many industrial hydrogen production processes, among which natural gas hydrogen production method has become the main hydrogen production method due to the cheap and easy-to-obtain raw materials and relatively simple process flow, including methane steam reforming method, partial oxidation method, and carbon dioxide reforming method. method and direct decomposition method, among which steam reforming is the most widely used.

In the steam reforming process of methane, methane reacts with water vapor under high temperature and pressure to generate synthesis gas, namely carbon monoxide and hydrogen, and the generated carbon monoxide continues to react with water vapor to generate carbon dioxide and hydrogen. Through the separation and purification process, hydrogen gas is obtained. At present, there are many patents and literature reports on the research progress of this process. For example, US patent US5496859, US6312658 and US6328945 are all patents related to hydrogen production. Keiichi Tomishige [Energy & Fuels2001, 15, 571-574] reported that nickel supported on aluminum oxide reacted with methane and water vapor to produce hydrogen, and carbon monoxide and hydrogen were generated at 800-1100 °C. Giuseppe Barbieri [Ind.Eng.Chem.Res.2001, 40, 2017-2026] reported steam reforming on a palladium membrane reactor and performed a theoretical analysis of the reaction model.

In the partial oxidation of methane, methane reacts with oxygen to form carbonaceous compounds and hydrogen. US patents US5149516 and US5447705 describe the successful realization of this reaction on perovskite at a temperature of 600-900° C. and a pressure of 0.1 MPa. U.S. Patent No. 4,973,486 reported that hydrogen bromide was used as a catalyst to react methane with oxygen at 850° C. to generate carbon monoxide, hydrogen, ethylene and acetylene. After the reaction, the amount of hydrogen bromide remained unchanged. Korada Supat [Ind.Eng.Chem.Res.2003, 42, 1654-1661] used circular current to supply energy, so that partial oxidation reaction and steam reforming reaction occurred simultaneously, and achieved good results.

In the carbon dioxide reforming of methane, carbon dioxide reacts with methane to form carbon monoxide and hydrogen. Usually this kind of reforming reaction without the participation of water vapor is called dry gas reforming. U.S. Patent No. 5,753,143 reported that on rhodium-supported silica-alumina molecular sieve catalysts, methane and carbon dioxide reacted at 500 ° C and 1 atmosphere to generate synthesis gas. The conversion rate of methane was between 10% and 34%, and hydrogen and carbon monoxide were the highest in the product. The ratio reached 0.92:1. Another US patent, US6355219, carries out carbon dioxide reforming of methane on a nickel-aluminum catalyst, the maximum conversion rate of methane can reach 70%, and the service life of the catalyst exceeds 30 hours. Mahesh V.lyer [Ind.Eng.Chem.Res.2003, 42, 2712-2721] reported that on cobalt-tungsten carbide [Co ₆ W ₆ C], methane and carbon dioxide at a temperature of 500-600 ° C and 5 The reaction produces synthesis gas at atmospheric pressure. TatsuakiYamaguchi [Energy & Fuels 2001, 15, 571-574] reported that the carbon dioxide reforming reaction was carried out on an aluminum column reactor with nickel-loaded activated carbon as a catalyst, and the methane conversion rate exceeded 65%.

However, in all these processes of producing hydrogen from methane, the products inevitably contain carbon and oxygen compounds that pollute the environment, especially carbon monoxide, although they are separated, it is difficult to remove them. However, the concentration of carbon monoxide in the high-purity hydrogen required by fuel cells cannot exceed 20ppm. Therefore, the hydrogen produced by reforming methane cannot be directly used in fuel cells. It must undergo secondary separation to remove carbon monoxide, and reduce carbon monoxide to 20ppm. Complicated process and a lot of energy.

In addition, there are some other processes to produce hydrogen. US Patent No. 4,064,740 discloses a method for direct thermal cracking of water. The method has simple raw materials and directly decomposes water at high temperature. However, the reaction requires a high temperature above 2000°C, which requires huge energy consumption. U.S. Patent U84024230 introduces the use of ferric oxide and chlorine as catalysts to finally decompose water into hydrogen and oxygen after a catalytic cycle. This method successfully reduces the temperature of water decomposition, but requires an expensive reactor resistant to chlorine gas corrosion . U.S. Patents US6017425, US6077497, US6300274 and US6297190 disclose a method, which uses zinc sulfide or cadmium sulfide loaded with metals such as iron, nickel, ruthenium, and platinum as a catalyst to decompose water under ultraviolet light or visible light to produce hydrogen. At room temperature, but the conversion rate is very low. U.S. Patents US5958297 and US6673270 use Group VIII metals such as nickel and cobalt as catalysts to catalyze hydrocarbons such as kerosene and oxygen to react to produce hydrogen. This method can handle a wide range of hydrocarbons, from carbon-1 compound methane to carbon-10 Compounds such as naphthalene can react with different hydrocarbons to produce hydrogen, but there are disadvantages of complex products, low selectivity, and difficult separation. U.S. Patents US6059995 and US5837217 have introduced dimethyl ether or methanol as raw materials for steam reforming to produce hydrogen. Because the price of raw materials is relatively expensive, the economic benefits are not significant. In addition, this method needs to oxidize part of the hydrogen to provide heat for the reforming reaction, which also reduces the efficiency of hydrogen production. U.S. Patents US4372833 and US4507185 use visible light to decompose formate and water to produce hydrogen, but also limited by the source of raw materials, the application prospect of this method is not great.

In recent years, the splitting of alkanes, especially methane, for hydrogen production has attracted extensive interest. Since there is no oxygen element involved in the whole process, the reaction product does not contain carbon and oxygen compounds, and the hydrogen after a separation can be directly used in fuel cells, thus greatly reducing the production cost and expanding the application field of natural gas chemical industry. For example, US Pat. No. 6,315,977 utilizes the decomposition of hydrocarbons to produce hydrogen, while US Pat. No. 5,028,307 describes the use of organic cellulose to decompose and produce hydrogen. Lu Yuan of Dalian Institute of Chemical Physics introduced in Chinese patent CN1179878 that Fe, Co, and Ni were used as catalysts to decompose methane at 400-700°C; Cao Xuewu of Shanghai Jiaotong University and others used sodium-cooled fast reactors as heat sources to crack methane to produce hydrogen. In terms of literature, Huffman et al. [Energy&Fuels 2001, 15, 1528-1534] reported that the bimetallic system Fe-M (M=Pd, Mo, Ni) was used as a catalyst to decompose methane at 400-1200°C to generate hydrogen and carbon; Mohamed [Ind.Eng.Chem.Res.2004, 43, 4864-4870] used a supported catalyst Ni/TiO ₂ to decompose methane, which was also successful. R.Terry [J.Phys.Chem.B2004, 108, 20273-20277] reported that methane was decomposed on a three-component catalyst Ni-Cu-MgO at a temperature of 665-725°C to obtain hydrogen and nano-scale carbon powder.

However, in these traditional reaction processes, as the alkane decomposes, more and more carbon is generated and cannot be removed at any time, but stays and accumulates on the surface of the catalyst, gradually covering the active center of the catalyst and isolating it from the reactants. The catalytic activity is greatly reduced, which eventually leads to deactivation. Therefore, the life of catalysts in these processes is generally short, generally no more than 10 hours, or even only a few minutes. In addition, since the surface of the generated carbon-supported catalyst is very firm, it is not easy to remove, which brings great trouble to the regeneration and reuse of the catalyst.

Contents of the invention

The present invention adopts metal magnesium or magnesium and Ca, Li, Na, Al, K, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ge, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, Tl, Pb, Bi, La, Ce and Sm as a mixture of one or more of them are used as catalysts to directly catalyze the decomposition of hydrocarbons to produce hydrogen and carbon. The hydrocarbons may be one or a mixture of alkanes, alkenes, alkynes, carbocyclic compounds, aromatic compounds, waste plastics, waste rubber and asphalt. The reaction temperature of the catalytic reaction is between 200°C and 1500°C, preferably the reaction temperature is between 300°C and 1100°C, and the best reaction temperature is between 600°C and 900°C; the operating pressure is between 0.01 Between 0.02 and 8 atmospheres, preferably between 0.02 and 8 atmospheres, preferably between 0.1 and 5 atmospheres; the reactor used is a bubbling reactor.

Since metal magnesium and its mixture doped with other metals are directly used as catalysts, they can be directly added to the reactor, thus greatly reducing the pretreatment process and saving cost and time. The reaction conditions can be selected in a wide range, especially under relatively mild conditions to obtain higher yields. For example, when methane is used as a raw material, the maximum single-pass conversion rate of the reaction can reach 35%, and the products of the reaction are hydrogen and carbon powder. The feature of the present invention is that the life of the catalyst is much longer than that of the reported catalyst, which can reach more than 120 hours. In addition, after the reaction is completed, the catalyst and the product are automatically separated, which is very convenient for separation, and the recovered catalyst can be reused without reducing the activity.

Description of drawings

Figure 1 is a schematic diagram of a catalytic decomposition device for hydrocarbons

Figure 2 is a schematic diagram of a two-stage catalytic decomposition reactor for hydrocarbons

Detailed ways

Embodiments 1 to 5 take a certain amount of metal catalyst and cocatalyst, and put them into a reactor 14 (as shown in Figure 1) with a stainless steel inner cylinder 15 closed at one end, so that the air inlet pipe 7, thermocouple 11, catalyst Keeps good contact and seals well. Then the reactor is put into the heating furnace 19, and the height of the reactor is adjusted to ensure uniform heat transfer. Connect the methane cylinder 1 and the reaction pipeline, plug the rubber stopper 9 tightly, and check the device for leaks. Adjust the pressure reducing valve 2 to feed the material so that the air pressure reaches 0.1MPa, open the control valve and use the flow meter 3 and the display device 4 to control the flow rate to 5ml/min. Ventilate for 20 minutes to ensure that other gases in the reactor are flushed out. The heating device includes a temperature controller 5, a thermocouple 11, heating components 12, 13, insulation materials 17, 18, etc. Turn on the temperature controller 5 and raise the temperature to 700°C. The sampling point 8 on the 10 is sampled and analyzed with a gas chromatography-mass spectrometer. After the reaction, close the temperature controller and stop heating. Continue to pass methane until the temperature cools down to room temperature, then stop the ventilation. Take out the reactor 14 from the stainless steel inner sleeve 15, pour out the generated carbon powder, and weigh it. Change different main catalysts and cocatalysts to react. The reaction results are shown in Table 1.

Table 1 Conversion rate of methane under different catalysts

Embodiments 6-9 The reaction device, operation method, reaction pressure and flow rate are the same as in Example 1. Weigh 4 grams of catalyst and change the reaction temperature to react at 300°C, 400°C, 500°C, and 600°C. The reaction results are shown in Table 2 shown.

Table 2 Conversion rate of methane at different temperatures

Example 10 Weighed 4 grams of magnesium metal catalyst. The reaction device, operation method, reaction pressure and flow rate were the same as in Example 1, and the reaction temperature was 680° C. After 20 hours of reaction, the analysis results showed that the methane conversion was still stable at 22.0%.

Example 11 Weighed 4 grams of magnesium metal catalyst. The reaction device, operation method and flow rate were the same as in Example 1. The reaction temperature was 700° C. After 20 hours of reaction, the analysis results showed that the methane conversion rate was still stable at 23.0%.

Example 12 Weighed 4 grams of magnesium metal catalyst, the reaction device, operation method and flow rate were the same as in Example 1, the reaction temperature was 720° C., and the analysis results after 25 hours of reaction showed that the methane conversion was still stable at 27%.

Example 13 Weighed 4 grams of metal magnesium catalyst, the reaction device, operation method and flow rate were the same as in Example 1, the reaction temperature was 740°C, and the analysis results after 25 hours of reaction showed that the methane conversion rate was still stable at 32.0%.

Example 14 Weighed 4 grams of metal magnesium catalyst, the reaction device, operation method and flow rate were the same as in Example 1, the reaction temperature was 760° C., and the analysis results after 20 hours of reaction showed that the methane conversion rate was still stable at 31%.

Example 15 Weighed 4 grams of metal magnesium catalyst, the reaction device, operation method and flow rate were the same as in Example 1, the reaction temperature was 700° C., and the analysis results after 15 hours of reaction showed that the ethane conversion was still stable at 62.0%.

Example 16 Weighed 4 grams of metal magnesium catalyst, the reaction device, operation method, reaction pressure and flow rate were the same as in Example 1, and the reaction temperature was 700°C. The propane conversion rate is stable at 90.0%, the hydrogen selectivity is 80.0%, and the by-product is methane.

Embodiment 17 takes by weighing 2 gram metal magnesium catalysts and 1 gram of asphalt, for making asphalt decompose thoroughly, what adopt is two-stage reactor (as shown in Figure 2, each reactor is specifically described and sees embodiment 1), in the first The first-stage reactor is connected to the second-stage reactor for further decomposition reaction. Connect the reaction pipeline and check the device for leaks. Pass inert gas for 20 minutes to ensure that other gases in the reactor are flushed away. Turn on the temperature control system, and program the temperature of the front-stage reactor to 700°C at a rate of 1°C per minute. During the heating process, samples are continuously taken from the analysis ports 1 and 2 and quantitatively analyzed with a gas chromatograph. The asphalt is completely decomposed, and the hydrogen selectivity is More than 80.0%, the by-product is methane.

Example 18 Weigh 2 grams of metal magnesium catalyst and 1 gram of plastic rice, and put them into a reactor equipped with a stainless steel inner cylinder, so that the air inlet pipe, thermocouple, and catalyst are kept in good contact and sealed well. Then put the reactor and the heating sleeve into the heating furnace, and adjust the height of the reactor to ensure uniform heat transfer. In order to completely decompose the plastic rice, a two-stage reactor (as shown in Figure 2) is used, and the second-stage reactor is connected after the first-stage reactor to further carry out the decomposition reaction. Connect the reaction pipeline and check the device for leaks. Pass inert gas for 20 minutes to ensure that other gases in the reactor are flushed away. Turn on the temperature control system, and program the temperature of the front-stage reactor to 700°C at a rate of 1°C per minute. During the heating process, samples are continuously taken from the analysis ports 1 and 2 and quantitatively analyzed with a gas chromatograph. The plastic rice is completely decomposed and the hydrogen is selective. It is more than 90.0%, and the by-product is methane.

Example 19 Weigh 2 grams of metal magnesium catalyst and 1 gram of rubber, and put them into a reactor equipped with a stainless steel inner cylinder, so that the inlet pipe, thermocouple, and catalyst are kept in good contact and sealed well. Then put the reactor and the heating sleeve into the heating furnace, and adjust the height of the reactor to ensure uniform heat transfer. In order to completely decompose the rubber, a two-stage reactor (as shown in Figure 2) is used, and the second-stage reactor is connected after the first-stage reactor to further carry out the decomposition reaction. Connect the reaction pipeline and check the device for leaks. Pass inert gas for 20 minutes to ensure that other gases in the reactor are flushed away. Turn on the temperature control system, and program the temperature of the pre-reactor to 700°C at a rate of 1°C per minute. During the temperature rise process, samples are continuously taken from analysis ports 1 and 2 and quantitatively analyzed by gas chromatography. The rubber is completely decomposed, and the hydrogen selectivity is More than 90.0%, the by-product is methane.

Claims (11)

1. a method of using thing hydrogen manufacturing of metal catalyst catalyzed decomposing and carbon is characterized in that described metal catalyst is the mixture of MAGNESIUM METAL or magnesium and other metals.

2. the method for use metal catalyst catalyzed decomposing according to claim 1 thing hydrogen manufacturing and carbon is characterized in that described hydrocarbon polymer is wherein one or several a mixture of alkane, alkene, alkynes, isocyclic compound, aromatics, waste or used plastics, waste old and pitch.

3. the method for use metal catalyst catalyzed decomposing according to claim 1 thing hydrogen manufacturing and carbon is characterized in that described other metals are wherein one or more mixtures of Ca, Li, Na, Al, K, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ge, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Cs, Ba, Tl, Pb, Bi, La, Ce and Sm.

4. the method for use metal catalyst catalyzed decomposing according to claim 3 thing hydrogen manufacturing and carbon is characterized in that described other metals are Rh.

5. according to the method for thing hydrogen manufacturing of arbitrary described use metal catalyst catalyzed decomposing and carbon in the claim 1～4, the temperature of reaction that it is characterized in that this method is between 200 to 1500 ℃.

6. the method for use metal catalyst catalyzed decomposing according to claim 5 thing hydrogen manufacturing and carbon, the temperature of reaction that it is characterized in that this method are between 300 to 1100 ℃.

7. the method for use metal catalyst catalyzed decomposing according to claim 6 thing hydrogen manufacturing and carbon, the temperature of reaction that it is characterized in that this method are between 600 to 900 ℃.

8. according to the method for thing hydrogen manufacturing of arbitrary described use metal catalyst catalyzed decomposing and carbon in the claim 1～4, the working pressure that it is characterized in that this method is between 0.01 to 10 normal atmosphere.

9. the method for use metal catalyst catalyzed decomposing according to claim 8 thing hydrogen manufacturing and carbon, the working pressure that it is characterized in that this method are between 0.02 to 8 normal atmosphere.

10. the method for use metal catalyst catalyzed decomposing according to claim 9 thing hydrogen manufacturing and carbon, the working pressure that it is characterized in that this method are between 0.1 to 5 normal atmosphere.

11., it is characterized in that the employed reactor of this method is a kind of bubbling reactor according to the method for thing hydrogen manufacturing of arbitrary described use metal catalyst catalyzed decomposing and carbon in the claim 1～4.

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