RU2799191C1 - Method for producing hydrogen from hydrocarbon raw materials and a reactor for its implementation - Google Patents

Abstract

FIELD: chemical technology.

SUBSTANCE: invention can be used to produce hydrogen from hydrocarbon stock by sequential decomposition in metal melts. The method for producing hydrogen in a reactor includes supplying hydrocarbon gas to a quartz cup located in the lower part of the reactor and containing a heated metal melt. Next, the hydrocarbon gas is decomposed by bubbling it through a layer of heated metal melt and getting into the gas space of the reactor. The gas is then allowed to pass through the solid catalyst for its catalytic decomposition. The invention also relates to a reactor capable of carrying out said process.

EFFECT: achievement of high conversion of hydrocarbon gas at relatively low temperatures and high productivity of the reactor.

6 cl, 1 dwg

Description

The present invention relates to the field of chemical technology and can be used to produce hydrogen from hydrocarbon feedstock by sequential decomposition in metal melts.

From the prior art such methods for producing hydrogen from natural gas are known, such as steam reforming, steam-oxygen reforming, adiabatic reforming. However, during these processes, a significant amount of carbon dioxide is formed, while only hydrogen and solid carbon are formed during the pyrolysis of methane, which makes this method of hydrogen production more environmentally friendly. A known method of non-catalytic pyrolysis of methane, during which carbon oxides are not formed. However, acceptable rates of methane conversion are achieved only at high temperatures, which makes the process of methane pyrolysis energy-intensive. There is also known a method for the catalytic decomposition of methane on solid catalysts, which occurs at relatively low temperatures. However, the carbon particles deposited on the surface of the catalysts, which are formed during decomposition, lead to their deactivation.

From RU 2408529, 04.06.2009, a method for producing synthesis gas and hydrogen is known, including high-temperature thermal treatment of the source hydrocarbon gas, carried out in a liquid heat carrier at a temperature of 1250-1800°C. The supply of the initial hydrocarbon gas is carried out by at least two immiscible flows in the bubbling mode into the lower part of the reactor containing a liquid coolant, which is a melt of inorganic salts or a metal or an alloy, for example, copper, iron, aluminum or nickel. The resulting synthesis gas is removed from the area above the surface of the melt and cooled by any known method. The disadvantage of this method and the device that implements it is the need to maintain high temperatures.

From US 2019055173, February 21, 2019, a system and method for pyrolysis using a liquid metal catalyst is known, including the supply of a hydrocarbon-containing gas mixture to a reactor containing a catalytically active molten metal or a catalytically active molten metal alloy, where the metal or alloy catalyzes the reaction of decomposition of the hydrocarbon-containing composition into a hydrogen gas phase and a solid carbon phase which is insoluble in the metal or alloy. The reactor can operate at temperatures of 1000°C, providing a conversion efficiency of more than 50%. The plant is a bubble column containing a catalytically active molten metal alloy (nickel-gallium, copper-gallium, iron-gallium, copper-tin, nickel-tin, or combinations thereof). The molten metal contained in the reactor can fill no more than 40% of the volume. Auxiliary devices such as stirrers or scrapers are placed in the gas space of the reactor to remove the carbon nanomaterial. The interior of the reactor may be lined with a metal oxide layer which provides a limited supply of oxygen to modulate the surface tension of the molten metal and protects the reaction vessel from corrosion by the molten metal. The method for decomposing a hydrocarbon-containing gas mixture includes: supplying gases to a reactor containing a metal melt, which catalyzes the decomposition reaction into a hydrogen-containing gas mixture and a solid carbon phase; regulation of interfacial tension inside the reactor using metal oxides, while the solid carbon phase is minimally soluble in the metal or alloy. However, the disadvantage of this solution is the use of auxiliary devices (scrapers or stirrers) to remove the carbon nanomaterial from the surface of the metal melt, which complicates the design.

The technical result of the invention is the creation of a method for producing hydrogen from hydrocarbon feedstock, as well as a reactor for implementing this method, which make it possible to achieve high conversion of hydrocarbon gas at lower temperatures and high reactor productivity.

The achievement of the technical result is ensured by a method for producing hydrogen in a reactor by successive decomposition of hydrocarbon gas, in which hydrocarbon gas is first supplied to a quartz glass located in the lower part of the reactor and containing a heated metal melt, then the hydrocarbon gas is decomposed by bubbling it through a layer of heated metal melt and its entry into the gas space of the reactor, after which the passage of the gas through the solid catalyst is ensured for its catalytic decomposition.

In one embodiment of the method, the solid catalyst is a bulk catalyst placed on perforated trays.

In one of the embodiments of the method, the carbon nanomaterial accumulating on the surfaces of the melted metals and the solid catalyst is removed from the reactor by purging the reactor with an inert gas.

In one of the embodiments of the method, the carbon nanomaterial is removed periodically as the volume of the reactor is filled without stopping the process of gas decomposition.

Also, the achievement of the technical result is ensured by a reactor for producing hydrogen by sequential decomposition, containing a housing, a hydrocarbon gas supply hose, a quartz glass for containing metal, which, when heated, forms a metal melt, a quartz tube for supplying hydrocarbon gas to the lower part of the glass, a heating element for heating metal and/or molten metals in a quartz glass, perforated plates for placing a solid catalyst on them, located in the gas space of the reactor above the quartz glass, a tube for removing hydrogen-containing gas from the reactor, and said reactor is configured to implement the above method.

In one of the embodiments, the reactor further comprises an inert gas supply valve connected to a tube exiting the gas space of the reactor, and a carbon nanomaterial outlet tube connected to the outlet gas valve to enable the reactor to be purged and carbon nanomaterial accumulating on the surfaces to be removed. molten metals and solid catalyst.

The essence of the invention is as follows. A metal is loaded into a reactor glass made of quartz glass, the temperature of which is brought to the temperature of the process using a heating element, and the metal passes into a liquid state of aggregation. The choice of quartz as a material for the reactor glass is due to the fact that the metal elements of the reactor, in contact with the molten metal, corrode very quickly and partially dissolve in it. Quartz is chemically and mechanically stable in the considered temperature range (from 500°C to 1000°C). The preferred metal for use as a heat transfer medium and to create a metal melt is tin due to its high thermal conductivity and relatively low melting point, high density compared to carbon, non-toxicity and long-term chemical stability. Alloys of nickel and bismuth (90% Ni / 10% Bi), nickel and bismuth in eutectic proportion, or other metal alloys can also be used as a heat transfer medium.

Further, hydrocarbon gas (natural gas or pure methane) is bubbled through the layer of molten metals, ie molten metal. The time of contact of the formed gas bubbles with the metal melt can be varied by changing one of two parameters: the gas flow rate (operational control) and the height of the metal melt layer (determined at the stage of loading the metal into the reactor). Gas bubbles are heated to the temperature of the metal melt (from 500°C to 1000°C), and the first stage of the decomposition process occurs with the formation of hydrogen, carbon and, if natural gas is used as a hydrocarbon gas, ethane, ethylene and acetylene. Accordingly, the operating temperatures in the invention are lower than in prior art solutions that also use the bubbling method.

Metal melts are a good medium for carrying out the process of hydrocarbon decomposition. When mixing inactive metals with a low melting point and catalyst metals active in the conversion of hydrocarbons, a metal alloy is formed, which is both a heat carrier and a catalyst for the decomposition of hydrocarbon gas to produce hydrogen and carbon. At the same time, carbon undissolved in this alloy floats to the surface in the form of a carbon nanomaterial, from where it can be removed, thereby preventing carbon deposition on the catalyst surface, and, accordingly, loss of catalyst activity is excluded.

The products formed as a result of this, as well as the unreacted hydrocarbon gas having a high temperature, enter the gas space of the reactor. Here they pass through perforated plates with sides, on the surface of which a solid metal catalyst is distributed on a substrate. The substrate is used to reduce the speed of the gas flow and its uniform distribution over the volume of the catalyst. Nickel on diatomaceous earth or other catalysts can be used as a catalyst. Here, the second stage of the decomposition process is carried out, which makes it possible to achieve a higher conversion of hydrocarbon gas.

Carbon particles (carbon nanomaterial) accumulating on the surface of the melted metals and bulk catalyst are periodically removed from it by purging the reactor with an inert gas. Nitrogen or argon can be used as inert gas. When implementing the claimed method, it is possible to organize continuous operation of the reactor by creating a technological cycle that includes 2 stages: hydrocarbon gas decomposition (98% of the cycle time) and inert gas purge (2% of the cycle time). Thus, there is no need to use any auxiliary cleaning means, for example, stirrers, since the carbon nanomaterial is removed from the surface of the heated metal melt by purging the reactor with an inert gas (the inert gas enters the reactor through the inert gas supply valve and exits through the carbon nanomaterial outlet tube). ).

To clean the gaseous reaction products from solid carbon particles, a two-stage filtration system is provided, including a vortex cyclone and a replaceable filter.

In FIG. 1 illustrates an exemplary scheme of a reactor for producing hydrogen by successive decomposition, first in a heated melt of metals, and then in the gas phase, where:

1 hydrocarbon gas supply hose;

2 clamp;

3 sealing gasket;

4 tube removal of hydrogen-containing gas;

5 reactor cover;

6 steel tube;

7 reactor cover body;

8 quartz tube;

9 rods;

10 plates for catalyst;

11 bolt;

12, 16 washers;

13, 15 steel rings;

14 sealing gasket;

17 nut;

18 thermocouple;

19 safety valve;

20 safety valve tube;

21 carbon nanomaterial outlet tubes;

22 outlet gas cock;

23 steel plate;

24 quartz glass;

25 reactor vessel;

26 layer of asbestos insulation;

27 layer of mineral wool insulation;

28 heating element;

29 metal melt;

30 asbestos gasket;

31 layers of asbestos insulation;

32 steel plate;

33 bracket;

34 bolt;

35 manometer;

36 steel tube;

37 inert gas supply valve;

38 steel tube;

39 bolt;

40 tin cylinders fastening thermal insulation;

41 welding units;

42 sides for emergency containment of molten metal.

The reactor is arranged as follows.

The hydrocarbon gas supply hose 1 is fastened with a clamp 2 through a sealing gasket 3 to a quartz tube 8. The reactor cover 5 is connected to the body 25 by four bolts 11 and a nut 17, which ensure tight contact between the steel rings 13, 15 using washers 12, 16 and a sealing gasket 14 .

In the lower part of the body 25 there is a glass 24, which is made of quartz, and in which there is a melt 29 of metals with a tube 8 immersed in it, also made of quartz. Rods 9 are attached to the upper part of the quartz glass 24 with the help of bolts 39, which are necessary for the convenience of immersing the glass and removing it from the reactor. In the lower part of the reactor, under the quartz glass 24, there is an asbestos gasket 30, which excludes the possibility of damage to the quartz glass when it is immersed.

To create the required temperature (from 500°C to 1000°C), a heating element 28 is used in the reactor. To reduce heat loss to the environment, an asbestos insulation layer 26 and a mineral wool insulation layer 27 are located in the space between the three tin cylinders 40. Another layer 31 of asbestos insulation is also provided to reduce heat loss through the bottom of the reactor. The heating element and the layers of insulation from above and below are limited by steel plates 23 and 32, attached with brackets 33 to the outer surface of the tin cylinder 40. The lower steel plate is equipped with special sides 42 to hold the melted metals in case of an emergency. To remove the carbon nanomaterial formed on the surface of the melted metals, periodic purging with an inert gas is performed, supplied through the inert gas supply valve 37 through the tube 38 and discharged together with the particles of the carbon nanomaterial through the carbon nanomaterial removal tube 21 when the outlet gas valve 22 is fully opened. To measure the pressure inside the reactor is provided with a pressure gauge 35.

Hydrocarbon gas is supplied through a quartz tube 8 to the lower part of the quartz glass 24 and bubbling through the layer of melted metals in the form of gas bubbles, decomposing into ethane, ethylene, acetylene, hydrogen and carbon. The carbon nanomaterial formed in the melt of metals floats up due to its lower density and collects on the surface of the melt of metals. With a certain periodicity, particles of carbon nanomaterial or soot are removed from the surface of the metal melt by a purge inert gas. The unreacted gas and its derivatives (ethane, ethylene, acetylene) after leaving the melt of metals enter the gas space of the reactor, where the second stage of pyrolysis is carried out on a catalyst located on perforated plates 10. Thus, the decomposition of the initial hydrocarbon gas into hydrogen and carbon particles.

In the event of emergency situations during the operation of the reactor and an increase in pressure inside it above a certain critical value, the safety valve 19 is activated, and through the pipe 20 of the safety valve, excess gas is released into the environment with the shutdown of the reactor.

Below are data demonstrating the effectiveness of the claimed invention. Methane was chosen as the hydrocarbon gas.

When carrying out the process of methane pyrolysis in a bismuth melt (the height of the molten metal column is 10 cm) at a constant methane flow rate of 10 l/h and a temperature of 850°C, the amount of hydrogen in the product gas is 0.7%, and at 950°C it increases to 11.3 %.

When carrying out the process of pyrolysis of methane in a nickel-bismuth melt (90% Ni, 10% Bi) at a molten metal column height of 10 cm and a methane consumption of 3 l/h at a temperature of 850°C, the amount of hydrogen in the product gas is 0.66%, and at 950°C and 1000°C is 12.2% and 32.3%, respectively.

When carrying out the process of bubbling methane in liquid tin (column height 35 cm) at a constant methane flow rate of 15 l/h at a temperature of 850°C, the amount of hydrogen in the product gas is 22.9%, and at 950°C and 1000°C this value is 60.5% and 65.5%, respectively.

In addition to the possibility of increasing the amount of hydrogen in the gas produced in the reactors by increasing the height of the metal melt or adding catalyzing metals to the melt, the claimed solution provides for the installation of a catalyst in the gas space of the reactor - immediately after the pyrolysis of hydrocarbons in the metal melt, which gives a significant increase in the amount of hydrogen for such a method for pyrolysis of hydrocarbons at a lower temperature. For example, when using pure bismuth 10 cm high together with a catalyst additionally placed above the surface of liquid bismuth in the gas space, the amount of hydrogen in the produced gas increases several times. Thus, compared with pure bismuth (at a temperature of 850°C, the hydrogen concentration was 0.7%), when a nickel-on-kieselguhr catalyst is placed in the gas phase, the amount of hydrogen increases to 2% at 700°C, to 15% at 800°C. and up to 28% at 850° C. In addition, the possibility of purging the reactor with an inert gas greatly accelerates the process of removing carbon nanomaterial from the surfaces of the melted metals and solid catalyst.

In the claimed method, natural gas can also be used as a hydrocarbon gas, which makes it possible to implement the method in the processing of natural and associated gases. The gas produced is a methane-hydrogen mixture, characterized by a hydrogen content maintained at the outlet of about 75% after the first stage (bubbling) and about 93% after the second stage (catalytic decomposition).

Claims (17)

1. A method for producing hydrogen in a reactor by sequential decomposition of a hydrocarbon gas, in which: - hydrocarbon gas is fed into a quartz glass located in the lower part of the reactor and containing the heated melt of metals; - ensure the decomposition of hydrocarbon gas by bubbling it through a layer of heated metal melt and its entry into the gas space of the reactor, - provide the passage of gas through the solid catalyst for its catalytic decomposition. 2. The method of claim 1 wherein the solid catalyst is a bulk catalyst placed on perforated trays. 3. The method according to claim 1 or 2, in which the carbon nanomaterial accumulating on the surfaces of the molten metals and solid catalyst is removed from the reactor by purging the reactor with an inert gas. 4. The method according to claim 3, in which the carbon nanomaterial is removed periodically as the volume of the reactor is filled without stopping the process of gas decomposition. 5. Reactor for producing hydrogen by sequential decomposition, containing: - frame, - hydrocarbon gas supply hose, - a quartz glass for containing metal, when heated, a melt of metals is formed, - a quartz tube for supplying hydrocarbon gas to the lower part of the glass, - a heating element for heating metal and/or molten metals in a quartz glass, - perforated trays for placing a solid catalyst on them, located in the gas space of the reactor above the quartz glass, - gas outlet pipe from the reactor, moreover, the specified reactor is made with the possibility of implementing the method according to any one of claims 1, 2. 6. The reactor according to claim 5, additionally containing an inert gas supply valve connected to a tube exiting the gas space of the reactor, and a carbon nanomaterial outlet pipe from the reactor connected to the outlet gas valve to enable the reactor to be purged and the accumulated carbon nanomaterial to be removed on the surfaces of molten metals and solid catalyst.

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