WO2003040029A1

WO2003040029A1 - Method for hydrogen production by catalytic decomposition of hydrocarbons, method and installation for electric power production using same

Info

Publication number: WO2003040029A1
Application number: PCT/FR2002/003755
Authority: WO
Inventors: Cyrille Millet; Claude Mirodatos; Carlos Marquez-Alvarez; Yves Schuurman
Original assignee: Centre National De La Recherche Scientifique
Priority date: 2001-11-08
Filing date: 2002-10-31
Publication date: 2003-05-15
Also published as: FR2831880A1

Abstract

The invention concerns a method for producing hydrogen comprising at least steps which consist in: a) contacting an initial gas and a catalytic system, so as to prepare a hydrogen-rich gas, by catalytic decomposition of at least a hydrocarbon present in the initial gas, b) generating the catalytic system using an oxygen-containing regenerating gas. The catalytic system comprises a catalyst and a support capable of storing and restoring at least oxygen and oxycarbon species, and bearing the catalyst. Said method can be advantageously used in combination with a fuel cell (5), in a process and an installation for electric power production.

Description

Process for the production of hydrogen by catalytic decomposition of hydrocarbons, process and installation for the production of electrical energy, comprising application

The present invention relates to a process for the preparation of a gas rich in hydrogen, by catalytic decomposition of at least one hydrocarbon present in an initial gas, as well as to a process and an installation in which this process for the preparation of a gas rich in hydrogen is used to produce electrical energy.

Various processes, such as steam methane reforming, are currently used industrially to produce hydrogen from a gas which contains at least one hydrocarbon, such as natural gas. These processes, suitable for mass production, are cumbersome. In other words, the installations for their implementation represent substantial investments, require significant and qualified personnel for their maintenance and their operation, consume a lot of energy and include auxiliary equipment to produce for example steam or compressed air.

A process which does not have these drawbacks is known from document FR-2-790 750. It is of the type in which a gas rich in hydrogen is produced, by catalytic decomposition of at least one hydrocarbon present in an initial gas, the decomposition being ^'' carried out using a catalytic system comprising a support and a catalyst carried by this support, this process comprising at least the steps in which: a) the initial gas is brought into contact with the catalytic system, and b) regenerates the catalytic system using a regenerating gas containing oxygen.

In the latter process, the catalyst is formed by nickel powder associated with a support made of silicon oxide Si0 ₂ . During the catalytic decomposition of the hydrocarbon molecules, hydrogen is released, while that the carbon atoms initially present in the hydrocarbon molecules are grouped together in the form of “nanotubes” or “nanofilaments” inside the support. The gradual reduction in the yield of this decomposition reaction leads to the need to carry out a regeneration of the catalyst, for example by means of an air sweep.

For more details on the mechanisms which then come into play, we will refer in particular to the following documents:

- the article by ZHA G et Al. published in "APPLIED CATALYSIS A", 1998, volume 167, pages 161 to 172;

- the article by MURADOV published in “ENERGY AND FUELS”, 1998, volume 12, pages 41 to 48; - the article by CHEN et Al. published in the review

"CARBON", 1997, volume 35, pages 1495 to 1501; the article by POIRIER et Al. published in “INTERNATIONAL JOURNAL OF HYDROGEN ENERGY”, 1997, volume

22, pages 429 to 433; or even ^" .- the article by STEINBERG published in" INTERNATIONAL JOURNAL OF HYDROGEN ENERGY ", 1998, volume

23, pages 419 to 425.

The continuation of experiments in this way has however shown that despite the regeneration phases, the support is clogged with soot after several cycles, which is not satisfactory in the case of industrial exploitation.

The invention therefore aims to remedy the rapid fouling of the support with soot. To this end the invention relates to a process of the aforementioned type, characterized in that the support of the catalyst is capable of storing and restoring at least oxygen and oxycarbonaceous species. The subject of the invention is also a process for producing electrical energy, characterized in that it includes the preparation process as defined above, as well as stages in which: c) the gas rich in is recovered hydrogen, and d) a fuel cell is supplied essentially directly with the hydrogen-rich gas.

According to other advantageous characteristics of this method of producing electrical energy: - before step d), this hydrogen-rich gas is passed through a refill of a trap intended to eliminate any harmful impurities in the cell , including possible traces of carbon monoxide;

- the fuel cell is of the proton exchange membrane type;

it comprises stages in which: e) a waste gas produced during stage d) is recovered and containing an undecomposed part of the hydrocarbon present in the initial gas, and f) this waste gas is subjected to the process, as defined above, for the production of a gas rich in hydrogen;

- Before step d), the hydrogen-rich gas is cooled. Furthermore, the subject of the invention is an installation for producing electrical energy, characterized in that it comprises:

a catalytic reactor intended for the implementation of the process, as defined above, for the production of a gas rich in hydrogen, this catalytic reactor containing a catalytic system which comprises a support and a catalyst carried by this support, said support being capable of storing and restoring at least oxygen and carbon-containing species, and a fuel cell, placed downstream of the catalytic reactor.

According to other advantageous characteristics of this installation: - it includes a recharging trap, which is intended to remove possible harmful impurities in the batteries, including possible traces of carbon monoxide, and which is placed between the catalytic reactor and the fuel cell; - It includes a return line, connecting a point downstream of the fuel cell to a point upstream of the catalytic reactor;

- The return line is provided with means for driving the waste gas to the point upstream of the catalytic reactor;

- It includes a drain connecting to a portion of the installation comprising the return pipe and connecting the cell to said point upstream of the catalytic reactor; - It includes means for cooling the hydrogen-rich gas, these cooling means being placed between the catalytic reactor and the fuel cell.

The invention will be clearly understood on reading the description which follows, given solely by way of example and made with reference to the single appended figure which represents an installation, according to the invention, for producing electrical energy. .

The method according to the invention is intended to be implemented to produce a gas rich in hydrogen by catalytic decomposition at least one hydrocarbon present in an initial gas.

By hydrocarbon is meant any hydrocarbon, in the form of gas under the conditions implemented for the process according to the invention, or any mixture of hydrocarbons. The preferred hydrocarbons are methane, ethane, propane and butane. Of course, any other known hydrocarbon which can be catalytically converted mainly into carbon and hydrogen can be used in the present invention. The initial gas in which the hydrocarbon (s) are present may be a pure gas or a mixture such as natural gas or liquefied petroleum gas (LPG). The process considered comprises two main steps. In the first step, the decomposition of at least part of the hydrocarbon results from the contacting of the initial gas with a catalytic system comprising a support and a catalyst carried by this support. The decomposition of the hydrocarbon releases hydrogen which escapes in gaseous form H ₂ and carbon which is stored by the support in a manner which will be specified later.

During the second step of the process, the support is regenerated, that is to say that it gets rid of the carbon which is there _. accumulated, by reaction with a regenerating gas comprising _. advantageously oxygen, but which may include other oxidants such as carbon dioxide and water. For example, this regeneration step can be carried out by sweeping the support with a stream of pure oxygen, or more simply with air, or alternatively with any other gas comprising oxygen. The oxygen of the regenerating gas reacts with the carbon present on the support to form carbon dioxide in gaseous form C0 ₂ .

According to the invention, the support of the catalyst is an oxide capable of storing and restoring at least oxygen and / or oxy-carbon species. Thanks to a diffuse reflection infrared spectroscopy implemented for determine the nature of the chemical species forming on the surface of the catalytic system and to follow the evolution of these species, it has been observed that with such a support, the carbons of the hydrocarbons at least partially dehydrogenated during the catalytic decomposition are then stored by partial oxidation, by combining with the supporting oxygen, and not by forming carbon nanotubes or nanofilaments. In fact, on the surface of the support, the presence of adsorbed oxycarbon C0 _X species and of adsorbed hydro-oxycarbon species H _y CO _x has been observed.

Tests have shown that, thanks to the mechanism which has just been mentioned, the support does not clog up, nor does it deactivate after several cycles, in accordance with the aim which the invention intends to achieve.

They also showed that still using this mechanism, it was possible to produce, both in the first stage and in the second stage of the process, gases devoid of almost carbon monoxide, which represents a considerable advantage especially when the hydrogen produced is intended to operate a proton exchange membrane cell.

The catalytic system can be in any form known for this type of reaction. For an industrial implementation of the process, it will preferably be in the form of grains forming one or more fluidized or fixed beds, inside a catalytic reactor totally or partially filled. This reactor can also contain an inert material, for example in the form of ceramic balls which support or retain between them one or more layers of grains of catalytic system.

The support material is advantageously porous. Surprisingly, it has been highlighted that the supports to _. based on rare earth oxides are entirely suitable for the present invention, by their capacity to store and restore at least oxygen and oxy-carbon species, the rare earths being able to change valence. Thus the rare earth oxides which can be used in the preparation of the support for the catalytic system are for example chosen from the oxides of elements from the lanthanide group. Mention will preferably be made of the lanthanum, cerium and ytterbium oxides and, more generally, the oxides of variable valence from the lanthanide family. Very good results have been obtained with cerium dioxide, also called cerine Ce02. It goes without saying, however, that any support capable of storing and restoring at least oxygen and oxycarbon species is suitable for the process of the invention, the aim being essentially that the support does not promote the formation of nanotubes or nanofila ents of carbon.

Chosen from the group VIII metals and combinations of these metals, the catalyst may for example be nickel Ni or, preferably, a platinoid, that is to say a metal which is part of both the noble metals and the group VIII. The use of one of the platinoids which are ruthenium (Ru), rhodium (Rh), palladium (Pd), osmiun (Os), iridium (Ir) and platinum (Pt) presents l 'advantage of resulting in a lowering of the activation temperature of the catalytic decomposition of the hydrocarbon. Preferably, the catalyst is platinum. The use of mixtures and / or alloys of metals comprising at least one aforementioned metal may also be suitable for the process of the present invention. ^•

Preferably, thanks to the use of a catalyst chosen from noble metals, the catalytic decomposition is carried out at a temperature below 600 ° C., advantageously less than 500 ° C, for example of the order of 400 ° C, when it is desired to produce a gas rich in hydrogen which is substantially free of carbon monoxide. Indeed, it is then a question of finding the best possible compromise: a rise in temperature beyond the activation temperature of the catalytic decomposition promotes the latter, while the release of carbon monoxide by the support is inhibited by a sufficiently low temperature. Still when it is desired to prevent a release of carbon monoxide, the step of catalytic decomposition of the hydrocarbon is carried out at a pressure advantageously between atmospheric pressure and 20 bars, preferably between 2 bars and 12 bars, for example of the order of 3 bars.

The stage of regeneration of the support, preferably in air, is carried out at a pressure slightly higher than atmospheric pressure and at a temperature between 300 ° C and 600 ° C. We will now describe an example of implementation

_the process according to the invention. In this example, the hydrocarbon is methane CH ₄ .

The support consists of porous cerium oxide, with a large specific surface (344 m ² g ^_1 ), while the catalyst is platinum, at a rate of 1.1 g per 100 g of catalytic system.

This catalytic system is in the form of grains. It is prepared by impregnation with an aqueous solution of Pt (OH) ₂ (NH ₃ ) ₄ . Calcination using helium heated to 650 ° C. follows and allows the surface carbonates to be decomposed. The whole is then reduced to the state of pellets, then ground and finally passed through sieves so as to keep only the grains whose size is between 0.2 mm and 0.3 mm. These grains are placed at inside a reactor, into which hydrogen is injected at 400 ° C, for two hours, to reduce the precursors to metallic platinum.

The interior chamber of the catalytic reactor is cylindrical. The grains of the catalytic system form there a fixed bed intended to be traversed by an axial flow.

During the tests, the length of the catalytic bed, fixed at 0.5 mm and 15 mm, the internal diameter of the reactor chamber, fixed at 4 mm and 10 mm, the quantity of the catalytic system used, fixed at 50, is varied. mg and 250 mg, the hourly volume velocity of the initial gas, fixed at 16,000 h ^-1 and 79,800 h ^-1 . The reactor is placed in an oven, the temperature of which is regulated either around 400 ° C. or around 450 ° C. The durations of the successive power supply sequences of the reactor are of the order of ten seconds. At each cycle, from 6.10 ¹⁹ to 1.4.10 ²¹ molecules of methane per gram of catalytic system are introduced. For all of the tests, the catalytic decomposition step is carried out at a pressure of the order of 1 bar, while the regeneration step was carried out at a pressure of the order of 1 bar.

During a cycle, the reactor is sequentially fed by the initial gas, which is a mixture of methane and pure helium, followed by a neutral gas, namely pure helium ^'and finally by the regenerating gas, consisting of a mixture of oxygen and pure helium.

The results of the various tests carried out are grouped in the following table:

T WH Q CH ₄ Q d 'o ₂ X ^e t q3H2 ^d q ^d

(° C) (h ^"1 ) (μmol) (μmol) (%) (%) (%)

400 79 800 ^a 9. 0 204 88. 0 19. 0 100

- 79800 ^a 9. 5 102 82. 0 23. 0 100

- 79800 ^a 21 102 44. 0 64. 0 100 79800 "20 81 37.0 44.5 100 79 800 ¹ 118 81 10.5 64.5 100 79 800 * 117 27 10.5 62.5 100 16 000 111 81 41.0 41.5 100

16000 "112 107 41.0 44.0 100

450 16000 "87 81 54.0 44.0 99.9

16000 "59 81 72.0 36.0 99.9

T = temperature

WH = hourly volume speed

Q = quantity introduced into the reactor during a cycle ^a Internal diameter of the reactor chamber = 10 mm. Inside diameter of the reactor chamber = 4 mm.

X ^e Methane conversion rate

S ^d Selectivities of hydrogen and carbon dioxide.

For each of the tests presented in the table above, the selectivity rate for carbon monoxide is less than 0.1%. This carbon monoxide is therefore practically absent from the gases leaving the reactor, or is found in trace amounts in these gases (a few ppm).

Surface analysis by diffuse reflection infrared spectroscopy (DRIFT) shows that carbonate species corresponding respectively to infrared absorption bands equal to 1460 cm ^"1 , 1380cm ^{" 1} , 1070 cm ^"1 , and formates corresponding respectively to bands infrared absorption equal to 1560 cm ^"1 , 1300 cm and

2850 cm ^"1 are formed on the surface of the catalytic system, on the partially reduced cerine support, during the catalytic decomposition step of methane. These species are stable in an inert atmosphere. During the regeneration step at 400 ° C or 450 ° C depending on the test, they react with oxygen to produce carbon dioxide C0 ₂ and water H ₂ 0. The single figure shows an installation according to the invention and intended to produce electrical energy from natural gas GN. This installation comprises a main pipe 1 which successively connects a catalytic reactor 2 placed at the head, a cooler 3 disposed downstream of this reactor 2, a recharging trap 4 placed downstream of the cooler 3 and a fuel cell 5, placed at the outlet .

A return line 6, connecting a point downstream of the fuel cell 5 to a point upstream of the catalytic reactor 2, is provided with a blower 7 designed to entrain the fluid present in this return line 6 to the inlet of reactor 2.

A purge P is provided downstream of the fuel cell 5. In the example shown, it consists of the downstream end of the main pipe 1.

Upstream of reactor 2, the main pipeline 1 is connected to a source of compressed natural gas GN. It is provided with a valve 8 and a valve 9 respectively arranged at the inlet and at the outlet of the reactor 2.

A pipe 10 for supplying a regenerating fluid, namely air, is provided with a valve 11 and is connected to the main pipe 1, between the valve 8 and the reactor 2. A pipe 12 for evacuation of. gas resulting from the regeneration of reactor 2 by air is provided with a valve 13 and is connected to the main pipe 1, between the reactor 2 and the valve 9.

The catalytic reactor 2, with a fixed bed, contains grains of a catalytic system comprising platinum on a cerine support as described above. As for the fuel cell, it is of the proton exchange membrane type. By means of valves 8 and 11, the catalytic reactor 2 is supplied alternately with natural gas and then with air, which is used to implement the catalytic decomposition process which has been previously described in detail. Valves 9 and 13 are used to alternately direct the hydrogen-rich gas produced during the catalytic decomposition step of methane, in the cooler 3, and the gas resulting from the regeneration of reactor 2, in the evacuation pipe 12 The hydrogen-rich gas, which leaves the reactor 2 at a temperature of the order of 400 ° C., is cooled using the cooler 3 to 90 ° C., a temperature at which it cannot damage the fuel cell 5. Like any proton exchange membrane cell, cell 5 must not be supplied with a gas containing carbon monoxide, otherwise it will deteriorate. However, the process implemented in reactor 2 has the advantage of producing a gas which is both rich in hydrogen and free or almost free of carbon monoxide. Also, in the installation shown, this advantage is taken advantage of, since the reactor 2 feeds essentially directly the cell 5 which thereby supplies electrical energy by consuming hydrogen.

In the sense understood here, the expression "essentially directly" means that the hydrogen-rich gas which leaves the reactor 2 does not undergo a heavy purification treatment, such as a purification process by cyclic variation of pressure. Indeed, the element referenced 4 is a simple refill trap, which is intended to eliminate possible infinitesimal traces of carbon monoxide, but which is not intended to eliminate large quantities of it. It is also intended to retain any other impurities harmful to the cell 5, such as sulfur. As a variant, when the conditions for implementing the catalytic decomposition process are such that the hydrogen-rich gas is produced while being practically free of impurities harmful to the cell, the trap 4 is removed, and the hydrogen-rich gas, immediately produced by the reactor 2, is introduced directly into the stack 5.

In reactor 2, a fraction of the methane present in natural gas is not broken down. It therefore forms part of the constituents of the hydrogen-rich gas and, therefore, passes into the cell 5, without this affecting the proper functioning of the latter. In order to reduce as much as possible the share of non-decomposed methane and the share of unconsumed hydrogen which escape from the installation shown, most of the gas escaping from the cell 5 is reinjected, at using the return pipe 6 and the fan 7, upstream of the reactor 2, in order to be recycled.

Natural gas GN does not only contain hydrocarbons. In particular, it also contains nitrogen which would constantly accumulate in the loop over the cycles if the purge P did not exist. Also, the flow rate evacuated by this purge P is regulated as a function of the nitrogen content present in the gas mixture at the outlet of the hydrogen cell 5.

Claims

1. Process for the preparation of a gas rich in hydrogen, by catalytic decomposition of at least one hydrocarbon present in an initial gas, the decomposition being carried out using a catalytic system comprising a support and a catalyst carried by this support, this process comprising at least the steps in which: a) the initial gas is brought into contact with the catalytic system, and b) the catalytic system is regenerated using a regenerating gas containing oxygen, characterized in that the catalyst support is able to store and restore at least oxygen and oxycarbon species.

2. Method according to claim 1, characterized in that said support is made of a material comprising a rare earth oxide.

3. Method according to claim 2, characterized in that the rare earth oxide is a cerium oxide.

4. Method according to any one of the preceding claims, characterized in that said support is porous.

5. Method according to any one of the preceding claims, characterized in that the catalyst comprises a material chosen from metals from group VIII, preferably from platinoids.

6. Method according to any one of the preceding claims, characterized in that the catalyst comprises platinum.

7. Method according to any one of the preceding claims, characterized in that step a) is carried out at a temperature below 600 ° C, preferably of the order of 400 ° C.

8. Method according to any one of the preceding claims, characterized in that step a) is carried out at a pressure between 1 and 20 bars.

9. A method of producing electrical energy, characterized in that it includes the preparation method according to any one of the preceding claims, as well as stages in which: c) the gas rich in hydrogen is recovered, and d ) a fuel cell (5) is supplied essentially directly with the hydrogen-rich gas.

10. Method according to claim 9, characterized in that before step d), this hydrogen-rich gas is passed through a refill of a trap (4) intended to remove possible impurities harmful to the battery ( 5), including possible traces of carbon monoxide.

11. A method according to reseller! Catipn 9 or 10, characterized in that the fuel cell (5) is of the proton exchange membrane type.

12. Method according to any one of claims

9 to 11, characterized in that it comprises stages in which: e) a residual gas produced during stage d) is recovered and containing an undecomposed part of the hydrocarbon present in the initial gas, and f ) this waste gas is subjected to the process according to any one of claims 1 to 8.

13. Method according to any one of claims 9 to 12, characterized in that before step d), the hydrogen-rich gas is cooled.

14. Installation for producing electrical energy from an initial gas containing at least one hydrocarbon, characterized in that it comprises: - a catalytic reactor (2) provided for the implementation of the method according to any one of claims 1 to 8, this catalytic reactor (2) containing a catalytic system which comprises a support and a catalyst carried by this support, said support being capable of storing and restoring at least oxygen and carbon-containing species, and

- a fuel cell (5), placed downstream of the catalytic reactor (2).

15. Installation according to claim 14, characterized in that it comprises a refill trap

(4), which is intended to remove possible impurities harmful to the cell (5), including possible traces of carbon monoxide, and which is' placed between the catalytic reactor (2) and the fuel cell (5) .

16. Installation according to one of claims 14 or 15, characterized in that it comprises a return line (6), connecting a point downstream of the fuel cell (5) to a point upstream of the catalytic reactor ( 2).

17. Installation according to claim 16, characterized in that the return pipe (6) is provided with means (7) for driving the waste gas towards the point upstream of the catalytic reactor (2). ,

18. Installation according to claim 16 or 17, characterized in that it comprises a drain (P) connecting to a portion of the installation comprising the return pipe (6) and connecting the stack (5) to said point upstream of the catalytic reactor (2). 19 Installation according to any one of claims 14 to 18, characterized in that it comprises means (3) for cooling the hydrogen-rich gas, these cooling means (3) being placed between the catalytic reactor (2) and the fuel cell (5).