CH642394A5 - CARBONACEOUS MATERIAL, ITS MANUFACTURING PROCESS AND ITS USE FOR THE PRODUCTION OF A HIGH CALORIFIC GAS. - Google Patents

Description

The invention relates to a carbonaceous material with high reactivity, and it also relates to a process for the manufacture of such carbonaceous material and its use for the production of a gas of high calorific value, containing methane.

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Various carbonaceous materials are well known and have been used as pigments, coke sources, chemical absorbents, etc. A type of carbonaceous material is formed as a result of disproportionation (or disproportionation) reactions or carbon deposition from carbon monoxide in the presence of a catalyst-type substance based on an iron group metal. The term disproportionation as used here should be understood to mean any of the reactions accompanied by the formation of a carbon deposit from carbon monoxide, reactions such as the following: 2c0-c + c02

co + h2- »c + h2o

During many chemical operations, the formation of such a carbonaceous material as a result of a disproportionation reaction of carbon monoxide is an undesirable side reaction and can even deactivate the catalyst, used to carry out such operations, as a result of the formation of a carbon deposit on the catalyst. Generally, the carbonaceous material thus formed has only a low commercial value. It has been found that carbonaceous materials can react with hydrogen to form methane, the main constituent of natural gas. However, known carbonaceous materials have a reaction rate so small that they do not lend themselves to the implementation of industrial processes. However, industrial demand for methane has increased to the point of exceeding supply. It has been proposed that methane can be produced from hard coal and therefore extensive research has been carried out to find ways to economically convert hard coal into methane. For example, researchers have previously synthesized methane from carbon monoxide and hydrogen. Carbon monoxide and hydrogen are produced by burning coal in a mixture of oxygen and water vapor. Oxygen is used rather than air because the mixture of carbon monoxide and hydrogen used for the synthesis of methane should not contain considerable proportions of nitrogen, since nitrogen does not can be easily separated neither from the synthesis gas, nor from the methane product. One drawback of this process is that it requires the use of large and expensive oxygen production plants. In addition, the carbon dioxide produced during the elementary pre-methanation operations of the process is eliminated from the feed stream to be treated which constitutes the mixture of carbon monoxide and hydrogen, in order to obtain, as end product, a gas with high calorific value. It is relatively expensive to remove carbon dioxide gas from the feed stream of the mixture of carbon monoxide and hydrogen, since such removal involves a gas separation operation.

A new carbonaceous material has been discovered which has a high reactivity, in particular with hydrogen, to form methane, as defined in claim 1. It can be in two forms, the first being a carbonaceous material not activated by one promoter, and the other being a carbonaceous material activated by hydrogen. The latter is formed by passing hydrogen over the non-activated material. The carbon material in question comprises an intimate association, with multiple phases, of a main phase rich in carbon and of one or more phases, present in lesser proportions, rich in metal of the iron group and which are dispersed in the carbon. and are at least partially linked to carbon. The iron group metal-like components catalyze the reactions for carbon formation from carbon monoxide and methane formation due to the hydrogenation of carbonaceous material. To achieve this catalytic activity, it appears necessary that the metal type component of the iron group be present in a proportion by weight equal to at least 0.5% based on the total weight of the carbonaceous material, and this proportion is preferably equal to at least 1% of the total weight of said material. In carbonaceous material not activated by a promoter, the proportion by weight of metal group component of the iron group is preferably between 1 and 3.5%, based on the total weight of the material. When the iron group metal is present in this proportion, it is capable of catalyzing the reaction between the carbon present in the composition and the hydrogen to form methane at a methanation rate equal to at least 0.1 mol of methane formed per hour and per mole of carbon present when the carbon is brought into contact with hydrogen at a temperature of 550 ° C., under a pressure of 1 atm and at a minimum rate of supply of hydrogen 2 mol of hydrogen per hour and per mole of carbon present. This reactivity with respect to hydrogen is a characteristic characteristic of the materials according to the invention, and it is notably higher than that of other forms of carbon. In addition, the materials in question retain their high reactivity even after being considerably depleted or enriched in carbon. Water has an effect on the reactivity of a material of the genus in question and, under certain conditions, it can delay the rate of formation of methane. Therefore, under atmospheric pressure, hydrogen should contain, by volume, less than about 1% water.

The iron group metals appear to be transported into the partially crystallized carbon network, and they become randomly dispersed in this network. At least a portion of the metal thus dispersed is linked to the carbon. A portion of the metal can occupy spaces between the reticular planes of the carbon. Whatever the structure, it appears that the carbonaceous materials in question are of a new and original type.

The form not activated by a promoter of a carbonaceous material according to the invention is formed by passing carbon monoxide over an initiator of disproportionation of carbon monoxide based on iron group metal. The carbonaceous material forms on the surface of the disproportionation initiator when this initiator is exposed to a gas containing carbon monoxide at a temperature between 300 and about 700 ° C, and preferably between 400 and 600 "C. The pressure can vary between about 1 and about 100 atm, but the preferred pressure range is between 1 and 25 atm. Preferably, the gas containing carbon monoxide also contains a significant proportion of hydrogen. iron group metal carbides, but as the reaction progresses, carbonaceous material begins to accumulate on the surface of the disproportionation initiator. Carbon monoxide is kept in contact with the initiator of disproportionation until substantial proportions of carbonaceous material not activated by a promoter have been deposited on the initiator.

The initiators of disproportionation of carbon monoxide based on metal of the iron group are chosen from the group constituted by iron, cobalt and nickel, mixtures of these metals, oxides of iron, cobalt and nickel, such cobalt oxide, nickel oxide, ferrous oxide, ferric oxide and mixtures of these oxides, alloys of iron, cobalt and nickel and mixtures of these alloys, such as iron / nickel alloys, and iron, cobalt and nickel ores. These initiators of disproportionation of carbon monoxide based on iron group metal will be designated by the expression metal by mass, in order to distinguish them from the metal dispersed in the carbon and at least partially bound to the carbon forming the minor phase in the carbonaceous material according to the invention. Only the dispersed and bonded metal forms part of the new catalytic compositions of the material in question.

As examples of the initiators based on metal of the iron group, and of the forms which these initiators can take, one can in particular quote: powder of ferric oxide, iron ore of the hematite type mainly composed of Fe203, chips of electro iron -lytic, carbon steel spheres, steel wool, nickel oxide, cobalt oxide, high purity nickel shavings, high purity cobalt shavings, buttons or grains in iron / nickel alloy or iron / cobalt, and an alloy commonly known as stainless steel. Various ferrous metal ores can be used to initiate the formation of carbonaceous matter. For example, we used

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successfully, with good results, an iron ore from a deposit called Mesabi Range. The use of such an ore or the like is advantageous because it is readily available and inexpensive. Alternatively, the bulk metal can be on a support consisting, for example, of silica, alumina or a similar substance without the formation of carbonaceous material being adversely affected. One of the advantages of the two types of carbonaceous material (non-activated, and activated by hydrogen) lies, however, in the fact that it is not necessary to use a support in order to increase the developed surface, because carbonaceous matter itself has a high developed surface. For example, the developed surface of the carbonaceous material can be between 50 m2 / g and a value as high as 500 m2 / g, the normal range extending between approximately 150 and approximately 300 m2 / g.

In order for the carbonaceous material to have the desired degree of reactivity, it appears that it must be formed in situ. In other words, the fact of simply mixing the metal in mass with carbon does not lead to obtaining the carbonaceous material according to the invention.

Consequently, the process for manufacturing the carbonaceous material is characterized in that carbon monoxide gas is brought into contact with a group of ferrous metal which initiates disproportionation of carbon monoxide to form the carbonaceous material on the metal group. ferrous initiator.

Typically, the growth of the carbonaceous material takes place from the surface of the mass metal in the form of fibers, and possibly of hollow fibers. Typically, these fibers have a diameter between about 0.02 | i and about 2.0 n, with a length to diameter ratio greater than about 10. These fibers have been analyzed and found that most contain tiny particles of '' a metallic component (minor phases) such as iron a, iron carbide or iron / nickel alloys. Apparently, the ferrous metal component is transported into the carbon fibers. This component of the ferrous metal type transported then ceases to be physically associated with the ferrous metal in bulk and constitutes an essential part of the carbonaceous material endowed with a high reactivity. When we methanate the carbon material in question with an iron base until converting more than 95% of its free carbon into methane, when we mix the resulting low carbon material with carbon particles and when we expose this mixing with hydrogen using the pressure and temperature intervals in which one normally operates to carry out methanation, no methane is formed.

It should be borne in mind that it is difficult to distinguish between the component of the ferrous metal type active in the carbonaceous material and the ferrous metal in mass when small particles of ferrous metal in mass are used. During the characterization of the carbonaceous material in question, a series of tests is carried out using plates of iron, nickel, cobalt and an iron / nickel alloy as initiator of the disproportionation reaction of carbon monoxide , and the carbonaceous material is deposited on these plates. The carbonaceous material is formed by taking on the appearance of wavy mounds of fibers on the plate, allowing the plate to be simply physically separated from the carbonated material. This allows analysis of the carbonaceous material separately from the mass metal. From an iron plate, the carbonaceous material (separated) formed in situ appears to contain, by weight, from approximately 1% to approximately 3.5% of component of the dispersed iron type, the analytical determinations being carried out at both by spectroscopy and by weighing of the ashes. The rest of the material is mainly made up of carbon, accompanied by traces of hydrogen.

The carbon is partially graphitized. Partially graphitized carbon has been described in detail by R.E. Franklin in his article published in "Acta Cryst.", Vol. 4, p. 253 (1951).

Carbonaceous fibers formed on an iron plate were examined using a scanning electron microscope. Fig. 2 of the accompanying drawings is a micrograph showing fibers of the material according to the invention as seen in a scanning electron microscope using a relatively low magnification. Fig. 1 is a micrograph showing, in more detail, some of the fibers seen under higher magnification also using a scanning electron microscope. The fibers shown in Figs. 1 and 2 are of the non-activated type, that is to say, non-hydrogenated. In a fiber constituting a representative sample, designated in A, an area with a high concentration of iron was positively identified. Using an electron microprobe type analyzer, a B nodule was positively identified as containing iron. This nodule is approximately 3000 Å long and approximately 1000 Å wide. This analysis is carried out using the procedures described by J.R. Ogren in “Electron Microprobe”, chapter 6, in “Systematic Materials Analysis”, vol. 1, Academic Press, Inc., New York 1975. Assuming that the fiber is full and has an intermediate density between that of amorphous carbon and that of completely graphitized carbon, we can calculate that the limit of precision with which analysis by microprobe is capable of detecting the presence of iron is equal to about 1.5% by weight.

An X-ray analysis of samples of non-activated carbonaceous material (deposited on iron plates en masse) shows that iron is present in the form of iron carbide and, possibly,

also in the form of iron a. The Debye-Scherrer method (on powders) is used to obtain diffraction spectra by powders using a General Electric model XRD-5 X-ray spectrometer. By using the same method to analyze a material activated by hydrogen, it is found that the iron detectable by X-rays in the hydrogenated material is present there only in the form of iron a.

As shown in the micrograph reproduced in fig. 1, the iron component is linked to carbon. Attempts have been made to break this bond and separate the iron component from the carbon by simple physical means such as sieving through fine wire cloths and separating the iron from the carbon using magnets. However, it can be seen that these methods do not achieve the desired separation. Since the iron component in carbonaceous matter cannot be separated from carbon by the use of simple physical means, this tends to prove that at least part of the iron is intimately associated with carbon and that at least one part of the iron is linked to carbon, possibly on an atomic or molecular scale. Or, perhaps, the iron is in the form of a solid solution in carbon. If this is the case, the interfaces of the solid iron / carbon solution and the crystals of the iron component can constitute active sites which are responsible for the rapid rate of reaction. Whatever the nature of the bond established between iron and carbon, it has been found that the iron itself, the activated carbon itself, the commercial cementite (Fe3C) and a simple physical mixture of iron and carbon activated do not have the advantageous properties of the carbonaceous material according to the invention. None of these substances or any of these mixtures, when brought into contact with hydrogen at high temperatures, is capable of forming methane at rates approaching that which is reached when the carbonaceous material is used according to the invention. This fact is clearly highlighted in Table I. - "

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Table I

Carbonaceous matter

Report

Appearance of methanation

Raw material separated from the inside

C / Fe

(mol of CH4 / h / mol

(iron)

(in atoms)

of carbon)

1. Carbon deposited from a CO / H2 gas stream at

550 "C and 1 atm on a thin sheet of high purity iron.

no

27.3 *

0.10

2. Carbonaceous matter coming from a sample 1 separated from the

thin sheet and rehydrogenated.

Yes

176

0.10

3. Carbonaceous matter deposited on steel spheres at

3.175mm carbon at 500 ° C from a gas stream

CO / H2 under a pressure of 1 atm.

Yes

220

0.28

4. Carbonaceous matter ** initially prepared by several

carbon and hydrogen deposition cycles

tion at 550 ° C and under a pressure of 7 to 17.5 bar on

4.762 mm carbon steel spheres. Separate sample

from spheres and carbon deposited from a current

CO / H2 gas under 1 atm.

Yes

12.6

0.49

5. Iron ore from the Mesabi Range pre-reduced in H2, then

used to catalyze the formation of a carbon deposit at

from a CO / H2 gas mixture at 500 ° C and under 1 atm.

no

7 *

0.24

6. Identical to sample 5, except that it was

exposed to ambient air for 96 h at 25 "C before hydrogenated

nation.

no

7 *

0.20

7. Commercial Fe3C cementite.

-

0.33

<0.05

(CH4 not detected)

8. Norit A activated carbon.

-

> 1000

<0.0004

9. Coal from coal gasification.

-

> 1000

<0.0004

10. Norit A activated carbon mixed with iron powder

electrolytic in a 50:50 weight ratio.

-

4.7 *

<0.0004

11. Graphite powder of spectroscopic purity.

-

> 10,000

approx. 10-7

* Contains iron in bulk.

** Material activated using hydrogen as promoter.

Fig. 9 reproduces a micrograph obtained using a scanning electron microscope on another of the carbonaceous materials according to the invention, prepared by disproportionation of carbon monoxide on a bulk metal alloy plate containing essentially 40 % nickel and about 50% iron. After separation of the carbonaceous fibrous material from the alloy plate, it is found that this carbonaceous material contains 98.42% of carbon, 0.48% of iron, 0.73% of nickel and 0.94% of hydrogen (this is non-standard data whose sum 45 is not exactly equal to 100%). The area marked with a circle on the micrograph was analyzed using an electron microprobe; it has thus been found that it contains both iron and nickel in approximately equal proportions. An X-ray analysis carried out on a representative sample of the fibers reveals the presence of an iron / nickel alloy. It also appears that the nodule visible inside the circle in fig. 9, nodule designated by the letter C, is actually constituted by an iron / nickel alloy. That the nodule C visible in fig. 9 whether or not it is a real alloy of the solid solution type of iron and nickel, the analysis carried out clearly proves that 55 very small crystallites or nodules containing both iron and nickel are transported from the plate of metallic alloy in mass up to carbon fibers and become intimately associated with these fibers, to which they are probably linked.

One hypothesis regarding the nature of the carbon material in question is to admit that the active component which is the iron group metal is a catalyst which is dispersed through a carbon matrix. This component (iron group metal) catalyzes the reaction of carbon, contained in the matrix,

with other reagents. The material depletes in carbon as the reaction progresses, but it can be regenerated and enriched in carbon by exposing it to a gas containing carbon monoxide. When exposed to high temperatures at

carbon monoxide, the active component catalyzes the disproportionation of carbon monoxide.

It has been discovered that even if the material is depleted of carbon as a result of a reaction with hydrogen, it retains its high value of specific methanation rate. It is surprisingly observed that one can eliminate almost all of the carbon from the carbonaceous material and see the latter still retain a relatively high value of the specific methanation appearance. This property of the material in question is illustrated in FIG. 3 which represents the variation in the specific methanation rate (in moles of CH4 / h / mol of carbon), plotted on the ordinate, as a function of the percentage of carbon eliminated by hydrogenation of the material (plotted on the abscissa). The methanation paces indicated on the graph in fig. 3 were determined by carrying out the methanation at a temperature of 570 to 600 ° C. in an atmosphere of hydrogen admitted at a constant flow rate, of 110 cm 3 / min, the pressure being 1 atm. The carbon-rich material (that is to say containing approximately 96% of carbon) has an initial reactivity of approximately 0.30 mol of CH 4 / h / mol of carbon. This reactivity gradually increases to about 0.63 mol of CH4 / h / mol of carbon when about 88% (by weight) of carbon has been eliminated. When about 90% of the carbon has been removed, or when the material contains (by weight) about 25% of the iron component, its reactivity decreases rapidly. If the carbon-rich material initially contained, by weight, 95% carbon and 5% iron, the final material, after removal of approximately 90% of the carbon, would contain, by weight, approximately 35% iron.

The new carbonaceous material in question retains its important and advantageous properties after numerous carbon enrichment / carbon depletion cycles. Using iron as the metallic component of the iron group, 55 of these cycles were thus carried out and the original material in question was obtained, activated by the hydrogen serving as promoter each time.

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The new carbonaceous materials in question also retain their properties after long periods of storage, whether stored in the carbon-enriched state or in the carbon-depleted state. However, since the exposure of these materials to oxygen can oxidize the metallic components of the iron group and thus harm their catalytic activity, it is avoided to expose them to the air during storage. After having stored such an iron-based carbon material for 24 h at ordinary room temperature, there is no change in its appearance of methanation.

Based on the experiments referred to above, it has been found that the composition of the carbonaceous material in question can vary approximately as follows:

Weight content

General interval

Preferred interval

Partially graphitized carbon Metallic component (of the iron group) dispersed

65-99.5% 0.5-35%

75-99% 1-25%

The weight percentages were determined after the carbonaceous material had been separated from the iron group metal by mass. For iron-based materials, it is preferred that the carbonaceous material not activated by a promoter contains by weight between about 1% and about 3.5% of ferrous metal component and between about 99 and 96.5% of carbon.

The material activated by hydrogen serving as promoter is described below.

It has been discovered that at least some of the carbonaceous materials in question exhibit, when they are subsequently hydrogenated, better values of the rate of formation of carbon deposition and of the rate of methanation. More particularly, when the metallic component of the iron group is iron, the carbonaceous material activated by hydrogen has a value for the rate of formation of a carbon deposit exceeding 10 g of carbon deposited per hour and by gram of dispersed iron present, and a value of the methanation rate exceeding 0.3 mol of methane formed per hour and per mole of carbon present. The rate of formation of a carbon deposit is measured at 500 ° C., under a pressure of 1 atm, and at a supply rate of 10 mol of carbon monoxide per hour and per gram of dispersed iron. using a feed gas containing by volume 80% carbon monoxide and 20% hydrogen. The methanation rate is measured at 550 ° C., under a pressure of 1 atm, and at a minimum rate of supply of hydrogen of 2 mol of hydrogen per hour and per mole of carbon present.

Although the charge stream used to prepare the carbonaceous material may contain hydrogen, the hydrogen-activated material is not produced as long as conditions prevail accompanied by the formation of a carbon deposit on the mass metal. When the initially formed carbonaceous material is subjected to hydrogenation to produce methane, then the carbonaceous material in question, activated by hydrogen serving as a promoter, begins to form. The formation of this material was observed when about 15% by weight of the carbon was removed by hydrogenation of the carbonaceous material initially prepared. In addition, the hydrogen used should normally not contain more than about 1% water, by volume.

We separated the material, activated by hydrogen, from the mass metal, and we found that this material has the same general physical appearance as that of the material initially prepared, but the identification by X-rays proves that, when the metal component of iron is iron, said iron is iron a rather than carburized iron. The hydrogenated material, when it is subjected to several cycles of formation of a carbon deposit and methanation, has even a higher reactivity than before such a cyclic treatment. On the other hand, when it is subjected to such a cyclic treatment, its composition can vary approximately as indicated below:

% in weight

Partially graphitized carbon Component of the ferrous metal type Hydrogen

65-99.5 0.5-35 0.1-3.0

Hydrogen, in the new materials in question, is in a strongly associated state. When a carbonaceous material of the kind in question, based on iron, is heated in a stream of nitrogen gas from a temperature equal to approximately 200 ° C. to a temperature equal to approximately 950 ° C., and when analyzes the conveying gas stream to dose the desorbed gases, mainly hydrogen and carbon monoxide, it is found that the amount of hydrogen present in the carbonaceous material according to the invention is more than fifty thousand times greater than the amount which can dissolve in iron a. In addition, more than two thirds of the hydrogen released during such experiments are released at temperatures above 700 ° C.

It should also be emphasized that, when percentages by weight are specified in the carbonaceous material according to the invention, it may be both the material activated by hydrogenation and the non-activated material, after it has been separated from the mass metal.

When iron oxides such as iron ore are used as the raw material for the disproportionation initiator, they are first reduced by using a mixture of carbon monoxide and hydrogen as the feed gas, after which the carbonaceous material begins to accumulate on the mass iron. Consequently, the duration of the contact time between the bulk iron and the gas containing carbon monoxide is important. If, for example, Fe304 is used and the gas containing carbon monoxide is at a temperature of 600 ° C and under a pressure of 1 atm, initially the iron oxide is at least partially reduced to iron. This is indicated by weight loss of iron oxide due to loss of oxygen. For example, after the iron oxide has been contacted with pure carbon monoxide gas for 15 min, the sample shows a weight loss of about 22% (oxygen represents, by weight, about 27 , 6% of the weight of the ferrous catalyst) and there is only little carbon deposited on the iron in mass. The carbon thus deposited is in the form of Fe3C. After 30 min of contact, the sample shows a weight loss of 15% and the carbon which is deposited there is in the form of carbide, mainly in the form of Fe3C. Even after 60 min of contact of the iron oxide with the carbon monoxide, the sample still shows a weight loss of 10%, and practically all the carbon deposited on the iron oxide is in the form of carbide, and here again mainly in the form of Fe3C. After 4 h, however, the sample shows a weight gain of about 75%, and the deposited carbon is partially graphitized. The samples obtained after the above periods of 15 min, 30 min and 60 min do not have the required value of the methanation appearance. Unlike these samples, the fourth sample (the one obtained after 4 h) forms methane at the rate of at least 0.1 mol of methane per hour and per mole of carbon when it is brought into contact with hydrogen. at 550 ° C, under a pressure of 1 atm, and at a hydrogen supply rate equal to 2 mol of hydrogen per hour and per mole of carbon present.

The invention also encompasses a process for the production of a gas of high calorific value, from coal or other carbonaceous fuels, using the new carbonaceous material. Methane can be produced without the need for oxygen or the removal of nitrogen, carbon dioxide or other gases inert to

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from the charge gas stream. During the implementation of the method according to the invention, carbon monoxide and hydrogen are extracted from the charge current as a result of the formation of the new carbonaceous material in question on the ferrous metal in bulk. A gas containing hydrogen is then brought into contact with the carbonaceous material at a temperature, under a pressure and at a space speed such that it results in the production of a gaseous product containing methane, containing by volume at least 20% methane. Due to the fact that the reactivity of the carbonaceous material is so high towards hydrogen, the duration of the residence time of the hydrogen in contact with this carbonaceous material can be very short. It has been found that the carbonaceous material requires only a short residence time with hydrogen to produce a gas containing a proportion by volume as high as 75% of methane, or even more. For example, the duration of the residence time can vary from 1 s to 50 s to produce such a methane-rich gas. The preferred duration of the hydrogen residence time is between 5 s and 30 s. The desirable value of the minimum temperature at which methanation should be carried out is 350 "C. This temperature is preferably between approximately 400 and approximately 700 ° C. The pressure can be between approximately 1 and approximately 100 atm, and preferably between 1 and 25 atm.

Almost any gas containing carbon monoxide can be used to produce a high calorific gas containing methane. Particular examples of gases which can be used during the implementation of the process in question are those which are produced by gasification of the coal using air or a mixture of air and steam in order to produce a gas of gasifier of low calorific value, between approximately 623 and approximately 1335 kcal / m3. For example, coal can be burned in situ (that is to say without extracting it from the veins of the deposit) in order to produce a gas having a calorific value equal to approximately 89 kcal / m3. A gasifier gas such as that used here is a gas mixture containing carbon monoxide, hydrogen, nitrogen, and carbon dioxide. Preferably, coal is burned in a mixture of air and water vapor in order to obtain a gasifier gas rich in carbon monoxide and hydrogen. For example, gasifier gases can normally contain, when calculated in the dry state, between approximately 15% and approximately 30% of carbon monoxide, between approximately 5% and approximately 30% of hydrogen, between approximately 40% and approximately 60% nitrogen, and between about 2% and about 10% carbon dioxide. All these gases containing carbon monoxide are convertible into a gas rich in methane analogous to a natural gas and having a calorific value whose value is at least 4450 kcal / m3 and can reach up to 8900 kcal / m3.

In general, such gasifier gases also contain water and small proportions of other gases such as methane, hydrogen sulfide, carbonyl sulfide, etc. To operate under atmospheric pressure, the water vapor content should be lowered to a value less than about 6% by volume,

while the sulfur content is less than about 10 parts per million. If the feed gas containing carbon monoxide contains hydrogen, the molar ratio of carbon monoxide to hydrogen should be greater than about 1: 2, and preferably be greater than 1: 1. The preferred molar ratio of carbon monoxide to hydrogen is preferably between about 1: 1 and about 100: 1. When the feed gas contains carbon dioxide, it is preferable that the molar ratio of carbon monoxide to carbon dioxide is high. In general, the molar ratio of carbon monoxide to carbon dioxide should be greater than or at least 1: 1, and preferably greater than 2: 1 - 3: 1. However, carbon deposits form at acceptable rates even when the ratio of carbon dioxide to carbon monoxide is as high as 3.

It has been found that the initial feed gas containing carbon monoxide should not contain appreciable proportions of sulfur. More particularly, the feed gas containing carbon monoxide should not contain more than about 20, and preferably not more than 10 parts of sulfur per million, this sulfur being calculated as hydrogen sulfide. When necessary, sulfur removal can be achieved using well-known methods, such as using amine-based systems, or contacting the feed gas with an aqueous solution of a carbonate. alkali metal or alkaline earth metal such as a hot solution of potassium carbonate. In addition to the use of conventional methods of removing hydrogen sulfide from feed gas, it has also been found that it is possible to remove hydrogen sulfide by passing the feed gas over the carbonaceous material. or on a mixture of this carbonaceous material and the iron group metal by mass. When this is done, the ferrous metal reacts with the sulfur to form metallic sulfides inside the material. This reaction deactivates the carbonaceous material. Therefore, if this method is used to remove sulfur from the feed gas, the carbonaceous material containing sulfur becomes unusable for producing methane.

Since nitrogen-containing gases can be used in relatively large proportions (for example, nitrogen can be present therein in volume proportions as high as 70%, or even greater), there is n It is not necessary to form the gas containing carbon monoxide by operating in a nitrogen-free oxygen atmosphere. In other words, it is possible to use air, to burn coal, rather than pure oxygen. What makes this process economically attractive is that the combustible portion of the charge stream, mainly carbon monoxide, is extracted or separated inexpensively from the inert or non-combustible portion of said charge stream as a result of the formation of solid carbonaceous material as an intermediate product. A methane-rich gas is subsequently produced simply by bringing said carbonaceous material into contact with hydrogen. This solid carbonaceous material need not be immediately allowed to react with hydrogen, since it retains its reactivity for a time of considerable duration. For example, a sample was kept for 5 d, then reacted with hydrogen and thus methane was formed at the same high rates as when using a freshly prepared carbonaceous material. This allows energy to be stored until it is needed.

A partially depleted gasifier gas can be used to produce the carbonaceous material in question, subsequently convertible into methane. In this case, coal is burned in air by operating under controlled conditions in order to form the gasifier gas which is brought into contact with iron oxides in order to reduce these oxides mainly in iron, iron carbides and iron oxides of lower oxygen content, and in order to produce partially depleted gasifier gas. For example, the partially depleted gasifier gas can contain about half as much carbon monoxide and about half as much hydrogen as the gasifier gas initially contacted with the iron oxides. The partially depleted gasifier gas is used to prepare the carbonaceous material by bringing it into contact with the disproportionation initiator that constitutes the iron group metal in bulk under conditions allowing the carbonaceous material to be formed. Hydrogen can be produced by contacting the reduced iron oxides with water vapor. This hydrogen is then brought into contact with the carbonaceous material in order to produce methane.

The carbonaceous material (ordinarily mixed with the ferrous metal in mass) can be allowed to traverse a cycle between two reaction zones, in the first of which the carbonaceous material is brought into contact with the gas of gas partially depleted while, in the other, the material is brought into contact with the hydrogen-rich gas to prepare methane. Consequently, the material undergoes a transition between a carbon-rich state and a low-carbon state. The material that is brought to the methane production area is rich in carbon. A notable portion

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(at least 15% by weight) of the carbon is removed from this material during the methane formation in order to produce the low carbon material which is transferred to the other zone where it is again enriched in carbon by contacting with the gasifier gas. The low-carbon material (that is to say the carbonaceous material activated by hydrogen) may contain, during the first cycle, between approximately 5 and 35% by weight of dispersed ferrous metal, between approximately 95 and 65 % by weight of carbon, and between approximately 0.1 and 3% by weight of hydrogen. The carbonaceous material can however remain in one zone and the gas streams admitted to pass in the two zones are then switched in order to alternately deliver passage to the gasifier gas stream and to the hydrogen-rich gas stream.

The carbonaceous matter entrained in the fluids on which one operates can be separated from these fluids by using a magnetic field. The metallic component of the iron group contained in the carbonaceous material retains its ferromagnetic properties, thereby making said material magnetic.

Substantial amounts of energy can be produced from depleted gasifier gas or another gas used as a source of carbon monoxide. Therefore, after the gasifier gas has been used to make the new carbonaceous material in question, and to produce hydrogen by the steam / iron process, the depleted gases are preferably then burnt in air, in order to oxidize any remaining fuels, and the resulting gases are allowed to expand in a gas turbine in order to recover their energy in the form of electricity.

The best mode of implementation currently envisaged is schematically shown in FIG. 8. In an installation such as that shown in said fig. 8, a desulfurized gasifier gas from a source 100 constitutes the charging current. This gas can contain, for example, in a supposed dry state, 50% of nitrogen, 25% of carbon monoxide, 18% of hydrogen, 6% of carbon dioxide and 1% of methane. Its sulfur content should be less than about 20 parts per million.

The gasifier gas is transferred via a pipe 101 to a fluidized bed reactor 102 where the formation of a carbon deposit takes place, this reactor containing low carbon solids which are based on a ferrous metal such as iron. The formation of a carbon deposit occurs in the reactor 102 as a result of a disproportionation of the carbon monoxide, contained in the gasifier gas, at a temperature of approximately 650 ° C. and under a pressure of between approximately 10.5 and 17.5 bar.

The carbonaceous material formed in the reactor 102 is transferred by a line 103 to a methane generator 104. In this methane generator, at a temperature between approximately 525 and approximately 700 ° C., the carbon contained in the carbonaceous material reacts with dry hydrogen allowed to enter the methane generator 104 through a line 106 in order to form a mixture of methane and hydrogen. Because methane formation is highly exothermic and because lower temperatures favor the formation of mixtures with higher methane concentrations, methane formation is carried out in several stages, cooling the solids and gases between stages. Depending on the composition of the desired product, it may be necessary to provide one or more coolers between stages. In the present case, the cooling is carried out by bringing water into the methane generator 104 through a pipe 107 and allowing the exit of water vapor through a pipe 108.

The methane / hydrogen gas mixture leaves the methane generator 104 via a pipe 109 and is allowed to pass through a cooler 110, and it leaves it via a pipe 111, ready for further processing operations.

The partially depleted gasifier gas from reactor 102 for the formation of a carbon deposit is transferred therefrom through a line 112 to a heat exchanger 13 inside which the temperature of said gas is high, for example from 670 to 'at about 920 ° C, and the residual methane contained in the mixture is converted into a mixture of water, carbon monoxide and carbon dioxide. The partially depleted gasifier gas coming out of the heat exchanger 113 has a lower value of the ratio of carbon monoxide to carbon dioxide, and it mainly contains nitrogen, carbon monoxide, hydrogen, water and carbon dioxide. Although the value is lower, the C0 / C02 ratio is high enough to allow the use of this gas to effect the reduction of iron oxides.

The partially depleted gasifier gas leaves the heat exchanger 113 through a line 114 which transfers it to a reducer 115 of iron oxides. Inside this reducer 115, the mixture reduces ferric oxide to ferrous oxide, and it oxidizes carbon monoxide to carbon dioxide and hydrogen to water. The reduced iron oxides are transferred from the reducing agent 115 through a line 116 to a hydrogen-producing reactor 117. Water vapor enters reactor 117 through line 118 and reacts with ferrous oxide to produce ferric oxide and hydrogen. Ferric oxide is transferred to the reducing agent 115 via a pipe 119. The wet hydrogen produced leaves the reactor 117 via a pipe 120, is cooled in a heat exchanger 121, then is transferred via a pipe 123 to a condenser 122. In the condenser 122, the water content of the hydrogen stream is lowered to less than about 1% by weight. Dry hydrogen leaves the condenser 122 via a line 124 and is transferred to the methane generator 104 through a line 106.

The partially depleted gasifier gas which has entered the reducer 115 exits therefrom via a pipe 125 in the form of a gas which is almost completely depleted. However, this gas still contains usable residual energy. This energy is preferably used by burning the gas in an oven 126 with air from a source 127. A compressor 128 raises the air inlet pressure in the oven 126 to a value between approximately 10.5 and 17.5 bar. The heat produced in the oven 126 is partially consumed in the heat exchanger 113 to raise the temperature of the partially depleted gasifier gas leaving the reactor 102. The heat which still remains in the gases leaving the oven 126 is transferred from the exchanger of heat 113 through a line 129 to a turbine 130, where the gases are expanded in order to produce electrical energy at 131. The depleted gas leaves the turbine 130, is cooled in a heat exchanger 133 and is admitted to s escape into the atmosphere through a pipe 134.

This mode of implementation has several very interesting advantages. First, a very high percentage of the calorific value, in the cold state, of the gasifier gases is actually used by conversion into high-value products; synthetic natural gas and electricity. Second, the implementation of this process does not require the use of expensive oxygen. Third, the heat released during the methanation process and the sensible heat that remains in the depleted gasifier gas are available for use at elevated temperatures. This leads to high yields in the use and conversion of this heat into electrical energy, minimizing waste.

As shown schematically in FIG. 4, desulphurized gasifier gas from a source 1 can constitute the feed stream supplied for the treatment. This gas, which may contain, for example, 50% N2.25% CO, 18% H2, 6% C02 and 1% CH4 (in the assumed dry state), may be the result of a conventional operation of gasification of coal with steam and air, gasification of coal in situ, etc. The raw gasifier gas is then desulfurized to an H2S content of less than about 10 ppm.

Desulfurized gasifier gas and, for example, oxidized iron solids such as a mixture of Fe203, Fe304 and FeO are contacted in a fast fluidized bed or in a reactor of the entrained solids riser type 2 at temperatures between about 550 and 850 ° C and under pressures between 1 and 100 atm, preferably between about 1 and 20 atm. The choice of tempe5

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temperature and pressure depends on the overall thermal balance and the desired methane concentration in the gas produced. The contact between the gas and the solids is maintained for a time of sufficient duration to cause a partial reduction, by H2 and CO contained in the gasifier gas, of the iron oxides to reduced iron compounds such as FeO, Fe and Fe3C. H2 and CO contained in the feed gas feed gas are partially but not completely consumed during the reduction of iron oxides. It is estimated that hydrogen will be used more completely than carbon monoxide during this stage of the process in question.

The entrained reduced iron solids and the partially reacted gasifier are then fed to a cyclone or similar device 3, where the reduced iron solids are separated from the partially reacted gasifier. The reduced iron solids thus separated are brought by a pipe 4 to the lower part of a second reactor 5 of the lifting tube type where they are brought into contact with steam from a source 6 at temperatures between about 500 and 800 ° C and under pressures from 1 to 100 atm. A hydrogen-rich gas is the result of the reaction of water vapor with reduced iron solids. In addition to hydrogen and unreacted water vapor, this gas also contains significant proportions of methane, carbon monoxide and carbon dioxide.

The hydrogen-rich gas and the entrained oxidized iron-based solids exit the hydrogen production reactor 5 through a line 7 and are then fed to a cyclone or other similar device 8, which separates the solids from the gases. The oxidized iron-based solids are brought back through a line 9 to the first reactor 2 of the lift tube type to complete the circulation loop of the solids between the reactors 2 and 5.

After the separation of the solids, the partially reacted gasifier gas, which can then contain, for example, 15% CO, 6% H2, 16% C02, 1% CH4 and 62% N2 (at l 'dry state), is cooled in a heat exchanger 10 which generates water vapor usable for treatments. This cooled gas is transferred via a pipe 11 to the lower part of a reactor 12 of the lift tube type used for the formation of carbon deposits, where it is brought into contact with poor solids, containing carbon, which it entrains. ; The gas and the solids are kept in contact with each other for a time of sufficient duration at temperatures between 300 and 600 ° C and under pressures of 1 to 100 atm to cause the formation of a carbon deposit on the solids low in carbon and enrich them by increasing their carbon content. The formation of a carbon deposit occurs through a disproportionation of the carbon monoxide contained in the partially reacted gasifier gas, to a lesser degree by reaction of CO and H2, or as a result of the reduction of CO by other agents. reducers present.

The carbon-rich solids entrained leaving the carbon deposition reactor 12 are separated from the gasifier gas, now depleted, in a cyclone or other similar device 13 and are brought to the bottom of a methanation reactor 14 of the type riser tube where they are entrained by the gas stream rich in hydrogen coming from the hydrogen production reactor 5 passing through a heat exchanger 8a and a cooler 8b. The carbon rich solids entrained react with hydrogen in the first stage of methanation predominantly by direct reaction of carbon and hydrogen. It is an exothermic reaction, and the solids and / or the gases must be cooled between stages if one wishes to obtain high concentrations of methane. The entrained solids and the gases are cooled in a cooler 16 arranged between stages, then they are again allowed to react in a second stage 17 of the reactor to produce additional methane. Depending on the CH4 / H2 ratio desired in the gas produced, the operating pressures in the methanation reactors can vary from approximately 1 to approximately 100 atm, but are preferably between approximately 1 and approximately 20 atm. Here again, depending on the desired product, one or more can be used

intercooling stages. Operating temperatures in the initial stages of the methanation reactor can rise to values as high as 700-750 ° C, but lower temperatures must be maintained in the final stages of methanation if a high CH4 ratio is desired / H2.

The gas produced and the entrained low-carbon solids which leave the methanation reactor 14 undergo a primary separation in a cyclone 18. The low-carbon solids are then recycled through a pipe 19 which returns them to the reactor 12 for forming carbon deposits . The crude product gas still containing a significant amount of entrained dust undergoes further dust separation in a separator 20 which can be a magnetic deduster since the major part of the dust is of ferromagnetic nature. However, other types of dust collectors can be used such as sand filters, filter bags, etc. The gas produced free of dust is cooled in a heat exchanger 21 in which water vapor usable for the treatments is generated, then it undergoes further cooling and is dried in a cooler 22 at the outlet of which we obtain the gas constituting the final product.

The hot depleted gasifier gas leaving the cyclone 13 is supplied to a dust separator 23 which removes entrained dust therefrom, not separated by the cyclone 13. The dust separator 23 can be a magnetic device, since the solids are ferromagnetic, or although it can be constituted by a more conventional system such as a sand filter or a battery of filter bags. The hot depleted gasifier gas, free of dust, still containing significant proportions of H2 and CO, is burned by adding an excess of air to result in obtaining a combustion gas at high temperature, containing N2, C02 and H20. This hot gas is expanded in a gas turbine 24 making it possible to obtain, as a by-product, mechanical work on the shaft and / or electrical energy. Finally, the depleted gasifier gas can be cooled again in order to produce new quantities of water vapor which can be used for the treatments.

Two of the main advantages of the method described above with reference to FIG. 4 are as follows: a) the separation of undesirable N2 and CO2 from the CH4 / H2 mixture constituting the gas produced is carried out following a relatively easy separation of solids and gases rather than by the much more difficult separation of N2 from 02 as is necessary in conventional technology, and b) the gasifier gas, during the implementation of this process, is more completely used by conversion into a CH4 / H2 product than during the implementation work of a conventional process based on the steam / iron reaction, because the gasifier gas is first partially used to reduce iron oxides (steam / iron process),

then is more completely used to deposit carbon intended to serve as reagent.

As shown in fig. 5, gasifier gas can be initially compressed to approximately 3 to 4 atm in a compressor 1 and brought into a reactor 2 for reducing a ferrous metal oxide, for example iron oxide, with formation of carbon deposits, where it is initially contacted with iron oxides and reduces these oxides while at the same time carbonaceous matter deposits are formed on the reduced oxides. Reactor 2 is maintained at a temperature of about 350-500 ° C and under a pressure of about 3 to 4 atm. In reactor 2, approximately 70% of the carbon monoxide and of the hydrogen contained in the gasifier gas react with the iron oxides to form reduced iron compounds and the carbonaceous material according to the invention. The depleted gasifier gas, at a temperature of about 350-500 ° C, is mixed with air and is burned in a combustion zone 3. This gas can then be directly transferred to a compressor or a generator. electricity to undergo expansion without it being allowed to pass into a steam generator of the boiler type using the waste heat. However, the gas is preferably allowed to pass through a magnetic separator in order to separate any entrained dust therefrom.

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10

The carbonaceous material, comprising mass iron, is transferred by ascending fluidization tubes to a methanation reactor 5 in a fluid bed where it is brought into contact with a gas containing essentially hydrogen at a temperature of about 480- 535 ° C and under a pressure of about 3 to 4 atm to form a gas rich in methane. This methane-rich gas is cooled in boilers 6 for recovering waste heat in order to produce water vapor which can be used for treatments. The carbon-depleted material from the methanation reactor 3 is transferred by ascending fluidization tubes to a hydrogen-generating reactor 4 in a fluidized bed and is brought into contact there with steam at a temperature of about 535-650 ° C and under a pressure of 3 to 4 atm to produce wet hydrogen. The resulting iron oxides are brought back to reactor 2 for the formation of carbon deposits. The wet hydrogen is cooled in a cooler 7 to condense the water vapor, and the dry hydrogen is transferred to the methanation reactor 5.

Sulfur compounds such as H2S, CS2, COS and SO2, if present in the gasifier gas, can be removed by contacting the gas with a portion of the carbonaceous material formed in the reactor 2 for forming carbon deposits. Alternatively, the portion of the carbonaceous material which has been hydrogenated can be removed from the methanation reactor 5 and brought into contact with the gasifier gas in order to remove the sulfur compounds therefrom.

Fig. 6 shows another usable installation in which the solids remain in the individual reactors either in the form of fixed beds or in the form of fluidized beds, and the feed gas streams to be treated are periodically switched between gasifier gas and steam mixture. water / water. The reactors may be allowed to operate in one of the two modes, the routes according to the first mode being shown in solid lines and the routes according to the second mode being shown in broken lines. According to the first mode, gasifier gas is brought into a reduction reactor 6 where it is brought into contact with iron oxides. The partially depleted gasifier gas is then transferred, passing through a boiler serving as a steam generator, to a reactor 2 where it is brought into contact with mass iron to form the carbonaceous material. Simultaneously, steam is brought into a hydrogen generator reactor 4 where it is brought into contact with reduced iron in order to form hydrogen gas. This hydrogen gas is then allowed to pass into a methanation reactor 3 where it is brought into contact with carbonaceous material, previously formed, in order to form methane. At selected time intervals, the feed gas streams supplied to reactors 2, 3, 4 and 6 are switched. As the dashed line shows, hydrogen which forms in reactor 6 is allowed to pass into reactor 2 where it causes the formation of methane as a result of the reaction between hydrogen and carbonaceous material. The depleted gasifier gas is transferred from reactor 4 to reactor 3 to form the carbonaceous material.

Fig. 7 shows an installation in which a partially depleted gasifier gas is used to produce a gas rich in methane in a single reactor schematically shown in vertical section. In this apparatus, reaction cylinders with porous walls are used, the pores of which allow the passage of gas but are too small to allow the particles of solid carbonaceous material or mass iron carrying this carbonaceous material to pass. The mass disproportionation initiators preferably affect the shape of iron spheres.

The iron spheres are initially located inside a hopper 1 having at its lower part an outlet orifice 2 through which the spheres descend under the effect of gravity into a passage 3 then in a reactor 4 of formation of carbon deposits, with porous walls, inside which is formed a cavity 5. At the upper part of the cavity 5 is arranged an inlet 6 for gas serving to admit, into the cavity 5, a partially depleted gasifier gas . This partially depleted gasifier gas passes through internal porous walls 7 and thus enters the reactor 4 where the gas comes into contact with the ferrous catalyst for a time of sufficient duration, and under a pressure and at a temperature allowing form the carbonaceous matter on the spheres. Then, the completely depleted gasifier gas is allowed to pass through the openings or pores of the external porous wall 8.

At the bottom of the reactor 4 is arranged an outlet opening 9 through which the spheres, transporting the material, pass to descend into a methanation reactor 10 which is defined by a porous outer wall 10 allowing the gases to pass and by a porous inner wall 12 allowing the gases to pass. Coaxially surrounding the outer porous wall 11 is arranged an impermeable wall 13 which, with the wall 11, defines an annular chamber 14. Hydrogen gas flows through an inlet 16 'of gas and into the cavity 15 where this hydrogen passes through openings or pores of the porous inner wall 12 and comes into contact with the carbonaceous material in the methanation reactor 10 to form a gas rich in methane. This methane-rich gas then leaves the reactor 10 through the openings or pores established in the external porous wall 11, thus reaches the cavity 14, then passes through the gas outlet 16 giving access to a tube 17 for transfer of gas which brings it into a cavity 18 arranged inside a second methanation reactor 19. The cavity 18 and the reactor 19 are separated by a porous inner wall 20 allowing the gases to pass.

The solid carbonaceous material, partially depleted in carbon, coming from the first methanation reactor 10, leaves said reactor 10 by an outlet 21 for solids and is cooled by water in a cooler 22 for solids by passing water through this cooler 22 from a water inlet 23 to produce water vapor which leaves the cooler through a steam outlet 24. The cooled solids are then allowed to enter the second methanation reactor 19 where they are again brought into contact with the gaseous mixture of methane and hydrogen passing through the porous wall 20 to react further with the carbonaceous material in order to form methane. The enriched gas containing methane leaves the second methanation reactor 19 through an external porous wall 25 and then from a gas outlet 26. Carbonaceous iron-based solids depleted in carbon are then transferred to the hopper 1 to solids by an elevator return tube 27 in order to be used again to implement the process.

Below are given various examples, intended to illustrate the preparation of the carbonaceous materials in question. Example 4 shows the methanation rates for several different catalysts based on iron group metals according to the invention. Example 5 proves the remarkable and unexpected thermal stability of the catalytic substances in question.

Example 1:

Carbon is deposited on 5 g of 0.175 mm mild steel balls by decomposition of carbon monoxide at 550 ° C from a gaseous mixture of carbon monoxide and hydrogen in a tube furnace. The flow rate of carbon monoxide is 100 cm3 / min and the flow rate of hydrogen is 20 cm3 / min. After approximately 4 h, 2.7 g of a carbonaceous material containing by weight 3.7% of iron are separated from the steel balls, and 0.27 g of the carbonaceous material thus separated is exposed to the same gaseous mixture of monoxide carbon and hydrogen at 500 ° C and under a pressure of 1 atm. It is found that the rate of formation of a carbon deposit is equal to 8.8 g of carbon per hour and per gram of iron dispersed in the carbonaceous material present. This carbonaceous material has a methanation rate equal to 0.52 mol of methane formed per hour and per mole of carbon. Carbon is again deposited on the hydrogenated material, using the same gaseous mixture of carbon monoxide and hydrogen and the material is brought into contact at 500 ° C. and under 1 atm. The rate of formation of a carbon deposit is equal to 39.4 g of carbon per hour and per gram of dispersed iron. We establish a cyclic succession as above

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between the reaction of disproportionation of carbon monoxide to deposit carbon, then a hydrogenation of the resulting carbonaceous material in order to consume most of the carbon, and this succession is continued for several cycles. The result of all the cycles is summarized in Table II. s

Table II

Cycle N °

Carbon deposition formation rate (g / h / g of dispersed iron)

Methanation rate (mol / h / mol of carbon)

1 C*

8.8

1-H **

0.52

2-C

39.4

2-H

0.53

3-C

47.8

3-H

1.12

4-C

41.5

4-H

1.33

* Refers to the formation of carbon deposition. ** Refers to hydrogenation.

The hydrogen activated material has a carbon formation rate well above 10 g of carbon deposited per hour and per gram of dispersed iron present. After this material has been

subjected to several carbon deposition and methanation formation cycles, it can be seen that its methanation rate increases until reaching a value greater than 1 mol of methane formed per hour and per mole of carbon present.

Example 2:

600 g of an iron ore from the Mesabi Range (hematite-type iron ore containing 55.3% iron, 8.1% silica, 0.8% alumina), the particle size of which corresponds to extreme sieves with square openings measuring respectively 0.250 mm and 0.100 mm on a side and whose apparent density is equal to 1.91 g / cm3, are placed in a vertical pressure-resistant tubular reactor, constructed of an alloy of the so-called stainless steel type, having an internal diameter of 38.1 mm and a height of around 2.45 m. The ore is reduced by a stream of hydrogen gas brought into contact with the iron ore at a spatial speed of 2300 volumes of gas per hour and per volume of iron ore. The reduced ore is then subjected to a series of carbon deposition / metha-nation formation cycles. Carbon deposition is carried out using nitrogen / carbon monoxide / hydrogen gas mixtures of different compositions, and methanation is carried out using pure hydrogen. The volumes of gases entering and leaving the reactor after the reactor has cooled to ordinary room temperature are measured using flow indicators and the humidity level is also measured; the composition of the gases is also determined by gas chromatography. The conditions and the results of several cycles are indicated in Table III.

Table III

Cycle

Composition of gases (%)

Average temperature (° C)

Absolute pressure (atm)

Duration of stay

(s)

Total duration (min)

Atomic report

C: Fe after carburetion n2

h2

co a

46.6

8.1

45.3

456

6.1

1.9

65

1.29

b

42.5

6.9

50.6

440

3.4

1.7

75

0.88

VS

44.2

6.9

48.9

435

3.5

1.6

90

0.80

D

44.2

7.4

48.4

416

4.7

1.8

110

1.12

Methanation

Cycle

Temperature ("C) *

Absolute pressure (atm)

Average duration of gas residence time

(s)

Total duration (min)

CH4%

in the gases produced (maximum reached)

Atomic report

C: Fe after methanation

AT

540-673

6.8

4.9

174

53.5

0.08

B

500-700

11.6

9.1

120

63.0

0.04

VS

500-672

11.6

11.0

140

62.0

0.01

D

500-635

13.6

15.0

165

70.0

0.15

* The reaction is highly exothermic and the temperature can only be controlled by adjusting the hydrogen flow rate.

Example 3:

A 2.88 g sample of an iron / nickel alloy containing by weight about 50% of each of the two metals is oxidized at 982 ° C for 10 min in a muffle furnace. The alloy thus oxidized is then carburetted at 500 ° C. using a gas mixture comprising by volume 85% carbon monoxide and 15% hydrogen, at a flow rate of 200 ml / min for 9 h and 20 min. After separation of the carbonaceous material from the mass alloy, it is found that the composition of the resulting carbonaceous material corresponds to the following elementary analysis: carbon 98.06%; iron 0.54%; nickel 0 , 53%, and hydrogen 0.16% The separated carbonaceous material is then subjected to a series of three methanation / carburetion cycles The conditions and the results of these cycles are indicated in Table IV. The data collected in this table IV prove that the rates of formation of carbon deposits as well as the stages of methanation are improved by making this material go through successive cycles of formation of carbon deposits and methanation.

(Table at the top of the next column)

Example 4:

By implementing a method according to the invention, samples of carbonaceous materials containing free carbon are prepared, by carrying out the disproportionation of carbon monoxide on

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Table IV

Cycle N °

Carbon deposition formation rate (g / h / g of dispersed iron)

Methanation rate (mol / h / mol of carbon)

1-H **

0.10

1 C*

35.2

2-H

0.12

2-C

38.8

3-H

0.20

3-C

45.3

* Refers to the formation of carbon deposition. ** Refers to hydrogenation.

plates or on buttons or grains of iron, nickel, cobalt and an alloy of iron and nickel containing about 50% iron and 50% nickel. In each sample, the fibrous carbonaceous material is separated from the bulk metal and is exposed, at 550 ° C. and under a pressure of 1 atm, to a stream of dry hydrogen flowing at a flow rate of approximately 2 mol of hydrogen per hour and per mole of carbon present. The specific rates of methane formation for each of the samples are indicated in Table V:

Table V

Specific training pace

Methane disproportionation initiator for carbon monoxide fibers separated from metal in

mass (mol / h / mol of carbon)

Iron

0.10

Nickel

0.19

Cobalt

0.34

Iron / nickel alloy

0.10

Example 5:

We place 10 g of carbon steel spheres, measuring

3.175 mm in diameter, in an alumina nacelle then suspended in the center of a tubular reactor made of ceramic material. A mixture of 100 ml / min of carbon monoxide and 20 ml / min of hydrogen is passed over the spheres at 510 ° C and under atmospheric pressure for 5 h. A total of 1.94 g of carbon is deposited there. The carbonaceous material deposited is carefully separated from the carbon steel spheres, and it is found that it contains 2.08% of iron. 0.992 g of the material thus separated is placed in a nacelle which is replaced in the reactor. A mixture of 100 ml / min of carbon monoxide and 20 ml / min of hydrogen is passed over the 0.992 g sample at 408 ° C for 2 h. An additional quantity of carbon estimated at 0.2 g of carbon, determined by measuring the concentration of carbon dioxide in the ef-fluent gas stream, is deposited. A gaseous stream of pure hydrogen (110 ml / min) is then passed over this modified sample at a temperature of 560 ° C. Methane begins to form and the hydrogenation is continued until approximately 0.2 g of carbon has been gasified, which is determined by measuring the methane concentration and the flow rate of the effluent gases. The average methanation rate 20 is equal to 0.20 mol of CH4 / h / mol of carbon. Then replacing the gaseous stream of hydrogen admitted to pass over the carbon sample with a stream of pure nitrogen (40 ml / min) and the carbonaceous material is slowly heated to 865 ° C. It is kept there for about 1 h, then cooled to 560 ° C in the nitrogen stream. At 560 ° C., the gas is again replaced by hydrogen at a flow rate of 110 ml / min to carry out methanation, which is continued until an additional 0.2 g of carbon has been gasified. The average methanation rate after exposure to high temperature is 0.26 mol of CH4 / h / gram atom of carbon. The cycle of exposure to high temperature (865 ° C) to a stream of nitrogen followed by hydrogenation at 560 ° C is repeated. The average methanation rate is again determined: it is equal to 0.26 mol of CH4 / h / gram atom of carbon. Apparently, this brief exposure of the carbonaceous material according to the invention to a high temperature does not reduce its reactivity with respect to hydrogen, nor its catalytic activity to effect the direct conversion of CO and H2 to methane. After the same thermal cycles, the remaining carbonaceous material is exposed to a mixture of 110 ml / min of hydrogen and 30 ml / min of carbon monoxide at 450 ° C. It is observed that methane is formed in the effluent gas at an average rate of 0.24 mol / h / mol of catalyst.

r

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Claims (25)

642,394 CLAIMS 1. Carbonaceous material, characterized in that it comprises a fibrous carbonaceous matrix, containing nodules rich in metal of a ferrous group, chemically incorporated in this matrix, the group of ferrous metal being chosen from a group comprising iron, cobalt, nickel and a mixture thereof, iron oxides, cobalt and nickel and a mixture thereof, iron ores, cobalt and nickel and a mixture thereof and an iron carbide, cobalt and nickel, the nodules representing 0.5 to 35% by weight of the matrix. 2. Carbonaceous material according to claim 1, characterized in that it comprises hydrogen. 3. Carbonaceous material according to claims 1 and 2, characterized in that it comprises hydrogen in an amount of 0.1 to 3% by weight of the carbonaceous material. 4. A method of manufacturing a carbonaceous material according to claim 1, characterized in that it puts gaseous carbon monoxide in contact with a group of ferrous metal initiator of dispro-portionation of carbon monoxide to form the carbonaceous material on the initiating ferrous metal group. 5. Method according to claim 4, characterized in that one carries out by catalysis chemical reactions induced by catalysts of the ferrous metal group and brought into contact with carbonaceous material with at least one gaseous reagent. 6. Method according to claim 5, characterized in that the reagent is a gas containing hydrogen in contact with the carbonaceous material at an adequate temperature, pressure and velocity to produce a gas containing methane at a rate of at least 20 % in volume. 7. Method according to claim 6, characterized in that the carbonaceous material reacts with hydrogen to form methane at the rate of at least 0.3 mol of methane per hour per mole of carbon present at a temperature of 550 ° C under pressure I atm and a hydrogen supply of at least 2 mol of hydrogen per hour per mole of carbon present. 8. Method according to claim 6, characterized in that the carbonaceous material is formed by disproportionation of carbon monoxide in the presence of carbon monoxide in contact with metal initiator of disproportionation serving as a source for the group of ferrous metal. 9. Method according to claim 5, characterized in that the gaseous reagent is a sulfur compound containing a gas stream in contact with the carbonaceous material in order to extract the sulfur compounds therefrom. 10. Method according to claim 8, characterized in that nodules rich in metal of the ferrous group are dispersed so that, during the disproportionation, the carbon deposition exceeds 10 g / h on each gram of metal of the ferrous group in contact of a gas comprising 80% by volume of carbon monoxide and 20% by volume of hydrogen at 500 ° C. under pressure of 1 atm, the gas flow rate being adjusted to more than 10 mol of carbon monoxide per hour, by gram of metal of the ferrous group present. 11. Method according to claim 6, characterized in that the carbonaceous material is subjected to at least two cycles of carbon deposition and methanation, however avoiding the total removal of the carbonaceous material during methanation. 12. Method according to claim 4, characterized in that the gas containing carbon monoxide is at a temperature between 300 and 700 ° C. 13. The method of claim 6, characterized in that the hydrogen-containing gas is at a temperature between 350 and 800DC. 14. Method according to one of claims 4 to 6, characterized in that the gas pressure is from 1 to 100 atm. 15. The method of claim 6, characterized in that the hydrogen in contact with the carbonaceous material depletes its carbon content, the carbon thus detached is then brought into contact with carbon monoxide which again enriches the carbonaceous material in carbon which is brought back into contact with hydrogen. 16. The method of claim 4, characterized in that the carbonaceous material is reacted with hydrogen to produce methane by depleting the carbon content of the carbonaceous material, part of the carbon thus detached reacting with monooxide carbon which, by disproportionation, enriches the carbonaceous matter with carbon. 17. Method according to one of claims 5 or 6, characterized in that the carbonaceous material is prepared by burning a fossil fuel with a controlled air supply so as to produce a gasifier gas which is brought into contact with the group of ferrous metal constituting a disproportionation initiator to form on the initiator a deposit of carbonaceous material. 18. The method of claim 6, characterized in that the carbonaceous material is prepared by putting gasifier gas in contact with iron oxides to reduce them and form a depleted gasifier gas and by putting the depleted gasifier gas in contact of the ferrous metal group constituting a disproportionation initiator to form the carbonaceous material, while hydrogen-containing gas is formed by bringing the reduced oxides into contact with water vapor. 19. The method of claim 18, characterized in that coal is burned with a supply of air and water vapor to produce gasifier gas. 20. The method of claim 6, characterized in that a disproportionation initiator based on ferrous metal is introduced into a first zone, so that the initiator flows through this zone, and a gas containing monoxide of carbon so as to coat the initiator with carbonaceous material, that the initiator covered with carbonaceous material is introduced into a second zone, so as to flow into the latter, that a gas containing hydrogen is introduced into this second zone to react hydrogen there with the carbonaceous matter to obtain a gas rich in methane and that the initiator of the second zone is recycled in the first. 21. The method of claim 6, characterized in that the carbonaceous material is formed by disproportionation of carbon monoxide in the presence of an initiator based on ferrous metal, in that the carbonaceous material is brought into contact with depleted gas containing hydrogen, then bringing the depleted carbonaceous material into contact with the carbon monoxide containing gas to regenerate the carbonaceous material and then bringing hydrogen containing gas into contact with the regenerated carbonaceous material to form methane. 22. Method according to claim 21, characterized in that gasifier gas is used which is depleted in contact with the initiator based on iron oxide which is reduced to recover the residual energy of the gasifier gas impoverished. 23. The method of claim 22, characterized in that the residual energy is recovered by burning the gasifier gas delivered to the air. 24. The method of claim 23, characterized in that the gaseous mixture is sent to a turbine. 25. The method of claim 4, characterized in that the disproportionation reaction is exothermic, that it reacts with part of the gas containing carbon monoxide, that it makes it possible to separate the part of the unreacted gas from the carbonaceous material and burning that unreacted part, to provide a fully consumed gas in an electric generator turbine.