FR3001399A3 - ACTIVE OXYDO REDUCTION MASS COMPRISING ENRICHED NICKEL PYROLUSITE AND A SPINEL STRUCTURE COMPOUND AND USE IN A CHEMICAL LOOP COMBUSTION PROCESS - Google Patents

Abstract

The invention relates to an oxido-reducing active mass comprising a natural manganese ore of the pyrolusite type initially comprising at least 60% by weight of MnO 2, said ore being enriched in nickel, and said mass comprising a mixed nickel-manganese metal oxide crystallized according to the invention. spinel structure. The redox active mass is in the form of particles. The invention also relates to a method of combustion of solid hydrocarbon feeds, liquid or gaseous by oxido-reduction in a chemical loop using such a redox active mass, and a method for preparing such a mass. Advantageously, the invention applies in the field of CO2 capture.

Description

Field of the Invention The field of the invention is that of the chemical-looped oxidation-reduction (CLC) combustion of hydrocarbons to produce energy, synthesis gas and / or hydrogen.

The invention relates in particular to a redox active mass for the CLC process, to a CLC process using this redox active mass, and to a method for preparing such an oxido-reducing mass. General context Process of Chemical Looping Combustion or CLC: In the rest of the text, the term "Chemical Looping Combustion" (CLC) is understood to mean a process of oxidation-reduction in loop on active mass. It should be noted that, in general, the terms oxidation and reduction are used in relation to the respectively oxidized or reduced state of the active mass. The oxidation reactor is one in which the redox mass is oxidized and the reduction reactor is the reactor in which the redox mass is reduced. In a context of increasing global energy demand, the capture of carbon dioxide for sequestration has become an unavoidable necessity in order to limit the emission of greenhouse gases that are harmful to the environment. The active-loop-based oxidation-reduction method, or Chemical Looping Combustion (CLC) in the English terminology, makes it possible to produce energy from hydrocarbon fuels while facilitating the capture of the carbon dioxide emitted during of combustion.

The CLC process consists in carrying out oxidation-reduction reactions of an active mass, typically a metal oxide, in order to decompose the combustion reaction into two successive reactions. A first oxidation reaction of the active mass, with air or a gas acting as an oxidant, makes it possible to oxidize the active mass. A second reduction reaction of the active mass thus oxidized by means of a reducing gas then makes it possible to obtain a reusable active mass and a gaseous mixture essentially comprising carbon dioxide and water, or even gas synthetic material containing hydrogen and carbon monoxide. This technique therefore makes it possible to isolate carbon dioxide or synthesis gas in a gaseous mixture that is substantially free of oxygen and nitrogen.

As the combustion is generally exothermic, it is possible to produce energy from this process, in the form of steam or electricity, by having exchange surfaces in the circulation loop of the active mass or on the gaseous effluents downstream of combustion or oxidation reactions.

No. 5,447,024 discloses a chemical loop combustion process comprising a first reduction reactor of an active mass using a reducing gas and a second oxidation reactor for restoring the active mass in its state. oxidized by an oxidation reaction with moist air. Circulating fluidized bed technology is used to allow the continuous passage of the active mass from its oxidized state to its reduced state.

The active mass, passing alternately from its oxidized form to its reduced form and vice versa, describes an oxidation-reduction cycle. Thus, in the reduction reactor, the active mass (MO) is first reduced to the MxOy-2n-m / 21 state via a C 1 H 2 hydrocarbon which is correspondingly oxidized to CO 2. and H20, according to the reaction (1), or optionally in CO + H2 mixture according to the proportions used. ## EQU1 ## (1) In the oxidation reactor, the active mass is restored to its oxidized state (Mx0y) in contact with the air according to the reaction (2), before returning to the first reactor. Mx0y-2n-m / 2 (n + m / 4) 02 -> MOy (2) In the equations above, M represents a metal. The effectiveness of the circulating fluidized bed chemical loop (CLC) combustion process relies to a large extent on the physico-chemical properties of the oxidation-reduction active mass. The reactivity of the oxidation-reduction pair (s) involved as well as the associated oxygen transfer capacity are parameters that influence the design of the reactors and the particle circulation speeds. The lifetime of the particles as for it depends on the mechanical strength of the particles as well as their chemical stability.

In order to obtain particles that can be used for this process, the particles used are generally composed of an oxido-reducing couple chosen from CuO / Cu, Cu 2 O / Cu, NiO / Ni, Fe 2 O 3 / Fe 3 O 4, FeO / Fe, Fe 3 O 4. Fe 0, MnO 2 / Mn 2 O 3, Mn 2 O 3 / Mn 3 O 4, Mn 3 O 4 / MnO, MnO / Mn, Co 3 O 4 / CoO, CoO / Co, or a combination of several of these oxidoreducing couples, and a binder providing the necessary physicochemical stability . The NiO / Ni pair is often cited as a reference active mass for the CLC process for its oxygen transport capacity and its rapid reduction kinetics, especially in the presence of methane. Since nickel oxide does not exist in the natural state in a sufficiently concentrated manner to obtain properties of interest for the CLC process, it is therefore generally used in a concentrated manner in particles of synthetic active material. The use of nickel, however, poses some problems because the nickel oxide is suspected of being carcinogenic which causes significant constraints on the smoke filtration system. It also loses its reactive capacities in the presence of sulfur compounds, which does not allow to consider for the use of fuels, such as coal, which contain it.

In a more general way, the main problem posed by the use of synthetic particles is their high manufacturing cost. Since the process requires the circulation of the solid in reactors where the gas velocities are relatively high, continuous consumption of solid by attrition can not be prevented. If the cost of active mass is relatively high, then the booster active mass can become a significant part of the operating cost. It is therefore important to find a low-cost active mass in order to reduce the impact of the cost of particles on the price of CO2 capture by CLC. As such, the possibility of using ilmenite natural ore (FeTiO3) has been disclosed by the Instituto de Catalisis y Petroleoquimica (CSIC), Madrid ("Titania-supported iron oxide as oxygen carrier for chemical-looping combustion of methane, Corbella, Beatriz M. Palacios, Jose Maria, Fuel (2006), Volume Date 2007, 86 (1-2), 113-122), however this ore has only oxygen carrying capacity very small and very weak reactivity.

In GB patent application 2,058,828, various metal oxides, including a natural manganese ore, are used as oxygen sources to gasify carbon species.

Natural manganese ores have also been tested as oxygen carriers in CLC processes by Fossdal et al. ("Study of inexpensive oxygen carriers for chemical looping combustion", A. Fossdal et al., International Journal of Greenhouse Gas Control 5, 2011, pp. 483-488).

Although the use of manganese oxides from natural ores as an active mass in a CLC process may be a cost-effective solution, it is less suitable for methane combustion than for combustion. solid or liquid charges in terms of process performance.

Mixtures of natural metal oxides from ores with nickel oxide have also been studied. Thus, a mixture of natural ilmenite and nickel oxide has been tested by Rydén et al. in the context of a CLC process, in particular for the combustion of methane (Rydén M. et al., Fuel 2010, 89, pp. 3523-3533) . It appears that important transformations of the ilmenite structure occur, including a decrease in density and an increase in the porosity of the metal oxide, which may affect the lifetime of the particles. Problems of agglomeration and sintering of the particles, causing shutdowns of the CLC installation, have also been noted. These problems seriously question the value of using such a mixture as an oxygen carrier in a CLC process. The use of a mixture of natural hematite and nickel oxide has also been tested by Chen et al. (Chen, et al., Chen, et al. et al., Journal of Fuel Chemistry and Technology 2012, 40, 267-272). However, this process is limited to the combustion of the coal, and the reactivity of the mixture differs according to the methods of preparation of the mixture, with the appearance of a blockage of the porosity in certain cases. According to this study, the mixture of natural hematite and nickel oxide is obtained either by mechanical mixing or by an impregnation method. In the case of the impregnation carried out with a solution of nickel nitrate on natural hematite, the mixture shows a low surface area suggesting that the effect on the performance of reactions can not be significant. Moreover, the impregnation on the natural hematite particles, showing an 80% Fe203 hematite content, makes it possible to form nickel oxide particles on the hematite particles, but also results in a reaction with the elements. already present to form a stable phase, such as spinel NiA1204. Another undesirable effect of the impregnation carried out is the dissolution of a fraction of the iron by the impregnating solution (the Fe / Si ratio is modified). These two effects, the appearance of a stable phase and the dissolution of the oxygen carrier, result in the decrease of the mass concentration of active sites supplying oxygen to the system. In the case of a mechanical mixture of natural hematite and nickel oxide, problems of stability and sintering under reducing conditions, particularly related to the use of natural hematite, are expected. In all cases, the mixture studied by Chen et al. poses problems of chemical interaction with the refractory materials related to the diffusion of iron at the temperatures used in the CLC processes. There is therefore a need to provide a high-performance CLC process which, in particular, enables high CO2 capture, suitable for the treatment of all types of hydrocarbon feeds, whether solid, liquid or gaseous, and which uses a material as an oxidation active mass. low cost, and meeting environmental standards in terms of toxicity and reducing emissions. OBJECTS AND SUMMARY OF THE INVENTION Applicants have revealed that an oxido-reducing mass comprising a natural manganese ore commonly called pyrolusite and usually used for metallurgical production, once enriched with small amounts of nickel Ni, and comprising a mixed nickel-manganese metal oxide in the form of spinel can, after an activation phase, be used in a redox loop combustion process, in particular for the sequestration of CO2. The use of such a reductive mass makes it possible to meet, at least in part, the needs of the prior art as described above. The invention consists in providing and using a mixture comprising natural manganese ores, containing mainly MnO2 at the origin, which are enriched in Ni and mixed nickel-manganese metal oxides crystallized according to the spinel structure, as a mass redox active agent for oxidation-reduction process in chemical loop. The redox active mass is in the form of particles whose size makes it possible to obtain easy flow and transport properties. It is activated by a rise in temperature under an oxidizing atmosphere, and is used in a chemical loop combustion plant comprising a reduction zone in which the fuel is oxidized by the oxygen supplied by reduction of the particles, and an oxidation zone. of these same particles in the presence of air, the particles circulating continuously between these two zones of reduction and oxidation.

The process makes it possible to carry out the combustion of the fuel, and in particular to produce nitrogen-free concentrated CO2 fumes that facilitate the sequestration of CO2. The mixture of natural ore enriched with Ni and a mixed nickel-manganese metal oxide crystallized according to a spinel structure according to the invention (redox mass), once activated, is particularly interesting because it has a large capacity Oxygen transport, kinetic properties allow rapid reactions, it is not sensitive to sulfur that could contain the fuel, it meets the environmental standards for toxicity and emissions, and it provides a powerful process , especially in terms of chemistry and thermomechanical resistance, for a wide range of types of hydrocarbon feeds, in particular for the combustion of gaseous feeds such as methane. The oxido-reducing active mass according to the invention is particularly well suited to the combustion of gaseous feeds, in particular because of the catalytic power of the redox mass associated with the enrichment of Ni and the presence of mixed nickel metal oxides. -manganese crystallized according to a spinel structure. This catalytic power makes it possible to decompose the gaseous hydrocarbon feeds into synthesis gas during reforming reactions of the so-called "steam" gas with H 2 O and "dry" reforming with CO2. In addition, the redox active mass according to the invention has a low tendency to agglomeration.

According to the invention, the gaseous hydrocarbon feedstocks comprise the hydrocarbon feeds in the form of gas, the liquid feeds after vaporization, and the volatile hydrocarbons of solid feedstocks.

The hydrocarbon feedstocks used as fuel in the combustion process according to the invention may be of fossil origin, come from biomass, or be synthetic fuels.

In general, the invention relates to an oxido-reducing active mass for a chemical loop-redox process (CLC) comprising: a natural pyrolusite-type manganese ore initially comprising at least 60% by mass of MnO 2, said ore being enriched nickel Ni, and a nickel-manganese mixed metal oxide crystallized according to the spinel structure, said mass being in the form of particles. Preferably, the oxido-reducing active mass comprises from 0.1% to 10% by mass of elemental Ni. Preferably, the initial MnO 2 content of the pyrolusite-type manganese ore is between 70% and 90% by weight, more preferably between 76% and 82% by weight. The mixed nickel-manganese metal oxide crystallized according to the spinel structure preferably corresponds to the formula NiMn 2 O 4 or MnNi 2 O 4, preferably to the formula NiMn 2 O 4. According to one embodiment of the invention, the redox active mass comprises a mixture of particles of natural pyrolusite-type manganese ore and NiO particles. Preferably, the oxido-reducing active mass has a particle size such that more than 90% of the particles of the active mass have a size of between 100 μm and 500 μm, preferably between 150 μm and 300 μm. The invention also relates to a process for burning solid, liquid or gaseous hydrocarbon feeds by chemical loop-redox using this oxido-reducing active mass. Preferably, the redox active mass is subjected to a heat treatment at a high temperature, preferably at a temperature of between 800 ° C. and 1200 ° C., for a duration of preferably between 0.5 hours and 10 days. According to one embodiment, the heat treatment of the redox active mass is carried out in situ in a chemical loop combustion plant in which the process is carried out. According to another embodiment, the heat treatment of the oxidoreductive active mass is carried out ex situ outside a chemical loop combustion plant 35 in which the process is implemented.

In a preferred manner, the active mass is put into the form of particles having a particle size suitable for use in a fluidized bed. Advantageously, the natural manganese ore is previously ground and sieved in order to obtain particles of particle size compatible with a fluidized bed implementation, and the nickel comes from nickel oxide NiO chosen as it is under particle size particle size also compatible with a fluidized bed implementation. According to one embodiment of the process: - in a first reaction zone operating in a dense fluidized bed, the hydrocarbon feeds are brought into contact with the particles of the oxido-reducing active mass; in a second reaction zone, a combustion of the gaseous effluents from the first reaction zone is carried out in the presence of the particles of the oxido-reducing active mass; in a first division zone operating in a fluidized bed, the particle stream of the active mass coming from the second reaction zone is divided into a first sub-flow going back into the second reaction zone and a second sub-flow going into an oxidation zone; the particles of the active mass are reoxidized in the oxidation zone before being returned to the first reaction zone; in a second division zone operating in a fluidized bed, a division of the particle stream of the active mass coming from the oxidation zone into a third sub-flow going back into the oxidation zone and a fourth sub-flow going into the first reaction zone. The particle size of the NiO particles may be different from the particle size of the natural manganese ore particles such that the size of the NiO particles is greater or smaller than that of the natural manganese ore particles. In this case, the process may comprise the following steps: - contacting, in a first reaction zone operating in a dense fluidized bed, the hydrocarbon feeds with the particles of natural ore of pyrolusite-type manganese and the NiO particles; in a second reaction zone, a combustion of the gaseous effluents from the first reaction zone is carried out in the presence of particles of pyrolusite-type natural ore of manganese and particles of NiO; separating, in a zone of separation, the particles of natural ore of pyrolusite-type manganese and the particles of NiO within a mixture resulting from the zone comprising flue gas, the particles of natural ore of manganese type pyrolusite and NiO particles; the pyrolusite-type natural manganese ore particles are re-oxidized in an oxidation zone before being returned to the first reaction zone. Preferably, the active oxidation-reduction mass is activated by a gradual rise in temperature under an oxidizing atmosphere to a temperature greater than or equal to 600 ° C., preferably greater than or equal to 800 ° C., and even more preferably higher. or equal to 900 ° C.

This progressive rise in temperature under an oxidizing atmosphere can be carried out at a speed of between 5 ° C./h and 100 ° C./h. Preferably, the oxido-reducing active mass is activated in a chemical loop combustion plant in which the process is implemented. Preferably, the oxidation-reduction active mass can be used for the combustion of gaseous hydrocarbons. Advantageously, the oxido-reducing active mass can be reduced in contact with the hydrocarbon feedstocks in a reduction zone of the chemical loop, and the flow rate of the oxido-reducing active mass measured at the inlet of said reduction zone can be between 30 and 100 kg / h per kg / h of oxygen consumed in the reduction zone. Advantageously, the reduction of the oxido-reducing active mass in contact with the hydrocarbon feeds is carried out at a temperature of between 600 ° C. and 1400 ° C. Preferably, the combustion is complete and the method according to the invention is used for the capture of CO2.

The invention also relates to a process for the preparation of an oxido-reducing active mass according to the invention, in which nickel is enriched with a pyrolusite-type natural manganese ore initially comprising at least 60% by weight of MnO 2 with oxide. NiO nickel, and said nickel-enriched ore is exposed at a temperature between 800 ° C and 1200 ° C, for a period between 0.5 hours and 10 days.

The present invention will be better understood and its advantages will appear more clearly on reading the following description and examples, which are in no way limiting, and illustrated by the appended figures. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a diagram illustrating the implementation of FIG. implementation of the CLC method according to a first embodiment of the invention.

FIG. 2 is a diagram illustrating a second embodiment of the CLC method according to the invention. Figure 3 is a diagram illustrating a third embodiment of the CLC process according to the invention. Fig. 4 is a diagram showing the normalized conversion rate Xc of methane versus the number N of oxidation reduction rings in a CLC process using pyrolusite particles alone as the redox active mass (Example 1). FIG. 5 is a diagram showing the evolution as a function of time of the measured gas concentrations (CH4, CO, CO2) at the outlet of the reactor during the reduction phase with CH4 of the tenth reduction cycle of oxidation-reduction, in the case of the use of pyrolusite particles alone as an oxido-reducing active mass (Example 1). FIGS. 6A, 6B, 6C and 6D are diffractograms obtained by X-ray diffractometry (XRD) for various preparations comprising a natural Ni-enriched pyrolusite-type ore with NiO, and nickel-manganese mixed metal oxides crystallized according to FIG. the spinel structure (Example 2).

FIG. 7 is a diffractogram obtained by XRD on a sample of a redox mass according to the invention comprising nickel-enriched pyrolusite and nickel-manganese mixed metal oxides crystallized according to the spinel structure (Example 3). FIG. 8 is a diagram representing the standardized conversion rate Xc of methane as a function of the number N of oxidation-reduction cycles in a CLC process using the oxidoreductive active mass according to the invention comprising pyrolusite enriched in nickel and mixed nickel-manganese metal oxides crystallized according to the spinel structure (Example 3). FIG. 9 is a diagram showing the evolution as a function of time of the measured gas concentrations (CH4, CO, CO2) at the outlet of the reactor during the reduction phase at CH4 of the tenth oxidation-reduction cycle, in the case of the use of an active mass according to the invention comprising nickel-enriched pyrolusite and mixed nickel-manganese metal oxides crystallized according to the spinel structure (Example 3). In the figures, the same references designate identical or similar elements.

Description of the Invention The invention relates to an oxido-reducing active mass for a chemical-loop oxidation-reduction process based on a pyrolusite-type natural ore of manganese initially comprising at least 60% by mass of MnO 2, said ore being enriched in nickel, and based on a nickel-manganese mixed metal oxide crystallized according to the spinel structure. The active mass is in the form of particles. In the present description, the term "nickel enriched" refers without distinction to the nickel enrichment of the natural pyrolusite ore or the redox active mass. Preferably, the amount of elemental nickel in the oxido-reducing active mass is between 0.1 and 10% by weight, preferably from 0.1% by mass to 5% by weight, more preferably from 0 to 10% by weight. , 5% by mass at 5% by mass, more preferably from 1% to 5% by weight, and even more preferably from 1% by mass to 2% by weight. Nickel may be present in various forms in the oxidoreductive active mass, in particular in a form stabilized with the mixed nickel-manganese metal oxide crystallized according to the spinel structure, but also in the form of NiO oxide. The nickel for enriching the natural pyrolusite-type manganese ore is preferably nickel oxide NiO. The initial amount of NiO used to prepare the active mass is such that the amount of elemental nickel in the oxido-reducing active mass is preferably from 0.1 to 10% by weight and in the preferred ranges mentioned above. By initial quantity of NiO in the redox active mass, we mean the amount of NiO used for the preparation of the redox active mass, in this case the amount of NiO used to enrich the nickel in the natural manganese ore. pyrolusite type. It is an advantage to use low initial amounts of NiO to prepare the redox active mass to reduce the costs associated with said preparation and meet environmental standards in terms of toxicity and reducing emissions. Preferably, the initial amount of nickel oxide of the active mass varies from 0.1% by weight to 10% by weight in the redox mass, preferably from 0.1% by mass to 5% by mass, more preferably preferably from 0.5 wt% to 5 wt%, even more preferably from 1 wt% to 5 wt%, and even more preferably from 1 wt% to 2 wt%.

Preferably, the initial content of MnO 2 (before introduction of the particles into the chemical loop) is between 70% and 90% by mass, and very preferably between 76% and 82% by mass, which corresponds to the metallurgical quality pyrolusite available. commercially. In the case of the conversion of gaseous hydrocarbon feedstocks in a CLC process, two steps can be distinguished. First of all, the hydrocarbon molecule is converted into a synthesis gas on the oxygen carrier according to equation (3), and the synthesis gas formed is then oxidized on the CO and H2 oxygen carrier according to equations (4) and (5). Synthesis gas conversion reactions (equations (4) and (5)) exhibit very high kinetics compared to the formation reaction of this synthesis gas (equation (3)).

## STR2 ## The presence of nickel in the oxidation active mass is shown in FIG. 3. CO + MnO 2 -> CO2 ± Mn 2 O (4) H 2 + MnOy ----> H 2 O + Mn × (5) -Réductrice, with the enrichment of the active mass with small amounts of NiO and the presence of a nickel-manganese mixed metal oxide crystallized according to the spinel structure, allows to accelerate the reaction of formation of the synthesis gas according to the equations (6) and (7) below. ## STR5 ## and activation of the oxido-reducing mass for CLC process according to the invention Natural manganese ore Manganese is naturally present in the form of ores. More than 300 ores are now known to contain manganese, but only about thirty are exploited for the manganese they contain. The table below lists the most commonly used, their chemical formula, as well as their average manganese content in%: Pyrolusite Mn02 63.2 Braunite 3 (Mn, Fe) 203.MnSiO3 48.9 - 56.1 Braunite II 7 (Mn, Fe) 203.CaSiO3 52.6 Manganite yMnOOH 62.5 Psilomelane (K, Ba) (Mn 2 + Mn 4) 8016 (OH) 4 48.6 -49.6 Cryptomelane (K, Ba) Mn 80 O x H 2 O 55.8 - 56.8 Hollandite (Ba, K) Mn8016xH2O 42.5 Todorokite (Ca, Na, K) (Mn2 + Mn4 +) 6012xH2O 49.4 - 52.2 Hausmannite (Mn, Fe) 304 64.8 Jacobsite Fe2MnO4 23.8 Bixbyite (Mn, Fe) 203 55.6 Rhodochrosite MnCO3 47.6 Pyrolusite is therefore a natural variety of manganese dioxide, MnO2, also known as manganese (IV) oxide. In general, the MnO 2 concentration of the natural pyrolusite extracted from the pyrolusite mines currently exploited is greater than or equal to a concentration of about 60% by mass of MnO 2. Several commercial grades of natural MnO2 are available: - pyrolusite (ore and concentrate) metallurgical grade (MnO2 76% to 82% - MnO2 chemical grade (MnO2 82% to 85%); - MnO2 high purity (93%) for manufacture of standard batteries According to the invention, the pyrolusite is used in combination with NiO and a nickel-manganese mixed metal oxide crystallized according to the spinel structure as an oxido-reducing active mass for a loop redox process In order to obtain properties of reactivity and sufficient oxygen transport capacity for the process, this must initially comprise at least 60% by weight of MnO 2, and preferably the initial content of MnO 2 is between 70% and 70% by weight. % and 90% by weight, and very preferably between 76% and 82% by weight.

Enrichment of the nickel active mass The enrichment of the active nickel mass can be carried out in different ways.

Preferably, the active mass comprises a mixture of particles of natural ore of pyrolusite-type manganese and NiO particles. The enrichment consists in this case in mechanically mixing pyrolusite particles and nickel oxide particles. The NiO may in this case be shaped on a solid support of alumina and / or silica, for example in the form of a NiO / NiAlO spinel. In addition to alumina, where spinel is advantageously formed which stabilizes the support with respect to the migration of NiO, it is also possible to use supports based on cerium oxide, zircon, silica, rutile, of cordierite or a structure resulting from the above-mentioned oxides with NiO. These supports advantageously have the common points of good temperature resistance and good behavior with respect to attrition. Alternatively, the active mass comprising the natural manganese ore can be enriched in nickel by forming NiO directly on the manganese oxide or by synthesizing a mixed material manganese oxide pyrolusite type / nickel oxide, according to several techniques well known to those skilled in the art. By way of non-limiting examples, mention may be made of the following techniques: dry or excess impregnation using nickel precursors. The method of dry impregnation (or "incipient wetness" according to the English terminology) can be used advantageously to maintain the initial particle size distribution, but any other type of impregnation can be used, including impregnation in excess. Binder charge forming of nickel particles and / or pyrolusite. This method consists, for example, in bringing the particles of nickel and / or pyrolusite in the presence of a suspension also containing one or more organic or inorganic species whose function is to ensure the cohesion of the building resulting from the shaping and consecutive calcination, hence the name of binder given to these species. This suspension is generally, but not exclusively, aqueous. The solvent content, in general of the water, depends on the chosen shaping: extrusion, "oil drop", atomization ("spray drying" in English).

The object resulting from the shaping usually requires cooking or calcination to have its full thermomechanical properties. The cooking conditions depend on the binder used. In general, we can use the peptized bohemite as inorganic binder. co-precipitation of nickel particles and pyrolusite. According to this synthesis route, precursors of each of the targeted phases are dissolved, for example, but not exclusively, in aqueous solution. The use of other media such as ethanol is possible. Precursors such as manganese salts and nickel salts can be selected. It is preferable that the counterions be as close as possible. It is for example advantageous to dissolve nitrate salts of each of the chosen species. These salts may be chosen from the following list given by way of examples and not limited to: chlorides, nitrates, sulphates, carbonates. Preferably, and for better dispersion of the phases formed, and therefore a better homogeneity of the material, it will be attempted to dissolve these species in the same aqueous solution. It is also possible to carry out this synthesis using separate solutions. The solution (s) comprising the salts of the dissolved precursors are gradually added in a medium whose pH and composition are adjusted so that each of the species in solution precipitates, for example in the form of hydroxide. When species rush together, there is co-precipitation. The precipitates formed can be recovered by filtration and then treated in temperature to reveal the desired phases. This synthetic route can be carried out by bringing into contact a natural pyrolusite-type manganese ore and a nickel precipitate to form a nickel-manganese compound after heat treatment. resin synthesis, called "soft chemistry". This synthetic route consists in forming organometallic resins by chelating metals with protic organic compounds. It is thus possible, for example, to dissolve a metal or a metal salt in an organic acid of citric acid type whose carboxylic oxide function (in carboxylate form after dissolution of the metal or of the salt) has the capacity to induce the chelation of a metal ion. We then speak more specifically of "citrate way". This results in the formation of a resin whose viscosity increases as the excess acid evaporates. The target phase is obtained by heat treatment in air of the resin at a temperature such that the organic component of the resin will be removed, leaving only the inorganic species, ie the metals, which will subsequently react to form the desired phase.

This synthetic route can be done by bringing into contact a natural ore of pyrolusite type manganese with a nickel resin to form a nickel-manganese compound. ceramic synthesis. According to this synthetic route, precursor oxide powders of the targeted phases, such as pyrolusite and nickel oxide according to the invention, are finely ground then intimately mixed before undergoing heat treatment under air at high temperature (typically 800 to 1200 ° C). The high temperature favors the atomic mobility of the metals in the presence, which allows the formation of mixed oxide phase.

Mixed nickel-manganese metal oxide crystallized according to the spinel structure The applicants have demonstrated that, unexpectedly, the presence of a mixed nickel-manganese metal oxide crystallized according to the spinel structure in the redox active mass allowed to improve very clearly the performances of the CLC process, and allows in particular an increase in the conversion of gaseous hydrocarbon feedstocks such as methane as a function of the oxidation-reduction cycles, as well as a rapid stabilization of this conversion from the first cycles of 'redox. The mixed nickel-manganese metal oxide crystallized according to the spinel structure preferably corresponds to the formula NiMn 2 O 4 or MnNi 2 O 4. Preferably, the redox active mass comprises oxide NiMn204, which corresponds to the so-called normal form of this oxide with the most common spinel structure to be formed, the other form MnNi204 being said inverse form. Such a nickel-manganese mixed metal oxide crystallized according to the spinel structure can be added to the natural nickel enriched manganese ore to form the redox active mass according to the invention. According to one embodiment, the active mass essentially contains a natural manganese ore of the pyrolusite type as described and a mixed nickel-manganese metal oxide crystallized according to the spinel structure. In this case, the nickel enrichment of the redox active mass consists essentially in providing a mixed nickel-manganese metal oxide crystallized according to the spinel structure to the redox active mass. Preferably, such a nickel-manganese mixed metal oxide crystallized according to the spinel structure is formed after a high temperature heat treatment, typically carried out at a temperature of between 800 ° C. and 1200 ° C., for a duration preferably of between minutes and 10 days, preferably between a few hours and a few tens of hours, for example between 4 hours and 24 hours, from a natural nickel-enriched pyrolusite-type manganese ore.

Thus, the oxido-reducing active mass according to the invention can be prepared by nickel enrichment of a pyrolusite-type natural manganese ore initially comprising at least 60% by weight of MnO 2 with nickel oxide NiO, and a exposure of said nickel-enriched ore at a temperature between 800 ° C and 1200 ° C, for a period of between 30 minutes and 10 days, preferably between a few hours and a few tens of hours, for example between 4 hours and 24 hours. hours. It is advantageous to carry out the heat treatment of the redox active mass in situ, that is to say in the chemical loop combustion plant, in order to take advantage of the thermodynamic conditions of the combustion plant and to realize the saving energy required for heat treatment for the formation of nickel-manganese spinel. The heat treatment of the oxido-reducing active mass can, however, be carried out ex situ, that is to say outside the chemical loop combustion plant in which the process is carried out. An ex-situ heat treatment has the particular advantage of avoiding the manipulation of nickel at the industrial site where the CLC process is implemented, and thus to overcome the constraints related to health risks specific to the handling of nickel. On the other hand, an ex-situ treatment makes it possible to provide an already activated redox mass and to avoid an activation phase in the combustion plant.

This phase of activation of the redox mass, which makes it possible to increase the reactive capacities of the mass, is detailed later in the description. Preferably, the heat treatment of the natural ore of Ni-enriched pyrolusite-type manganese is carried out by a gradual rise in temperature, so as to reach a temperature of between 800 ° C. and 1200 ° C. The gradual rise in temperature is preferably carried out at a rate between 5 ° C / h and 100 ° C / h, more preferably at a speed between 10 ° C / h and 50 ° C / h. The heat treatment making it possible to form the nickel-manganese mixed metal oxide of spinel type can also make it possible to carry out the activation of the redox mass in order to be able to increase the reactive capacities thereof. In this case, in addition to the conditions described above for the heat treatment, the progressive rise in temperature is preferably carried out under an oxidizing atmosphere, constituted for example by air. According to the shaping of the natural manganese ore nickel-enriched, nickel can for example be present in the heart of the natural particle of manganese ore type pyrolusite (ex: atomization shaping or ceramic synthesis of micrometric powders for example) or be present on its surface (ex: impregnation). The spinel phase is usually formed at the interface between nickel and manganese. Particle size of the active mass The extraction process of the natural manganese ore usually involves a crushing step. Advantageously, the fines produced during this initial crushing can be used for the application targeted by the invention. These fines generally have a particle size less than or equal to 10 mm. To allow optimal use in the CLC process, in particular to facilitate the transport and flow of the particles of the redox active mass, the natural manganese ore of the pyrolusite type is advantageously milled and sieved to obtain a particle size compatible with its implementation in a fluidized bed. When the active mass comprises a mixture of distinct pyrolusite and NiO particles, the nickel oxide, generally of synthetic origin, is advantageously chosen so that it is in the form of particles of particle size which is also compatible with a use in fluidized bed. In the case of a NiO shaping directly on the pyrolusite or the synthesis of a mixed manganese ore material of the pyrolusite / nickel oxide type according to the aforementioned methods, the particle size of the particles at the end of the setting in form or synthesis may not be the one sought, unless a spray drying technique, to obtain a material in the form of powder to a desired particle size, is used. In the case where the particles formed are smaller than the desired particle size, the solids formed may be pellets, then ground and sieved and / or elutriated to obtain the desired particle size. In the case where the particles have a larger size than the desired particle size, sieving and / or elutriation can improve the dispersibility. The particle size of implementation of the active mass in the chemical loop combustion process is indeed important for the proper operation of the process. As a result, it is preferable to divide the manganese ore into fine particles which can then be mixed with fine NiO particles, or which can be doped with nickel, for example by means of an impregnation technique or any other technique allowing to synthesize a mixed material MnO2 and nickel from the natural ore of manganese type pyrolusite. The division of manganese ore into fine particles can be carried out for example by grinding the ore using the ore grinding technologies well known to those skilled in the art. In the chemical loop combustion process, it is necessary to control the circulation of solid between the various oxidation and reduction chambers, to control the supply of oxygen by the active mass and the temperature gradient between the different enclosures. . The use of non-mechanical valves such as L-shaped valves, the principle of which is described in patent FR 2 948 177, makes it possible to effectively control the circulation at high temperature while minimizing the presence of internals in the flow. The use of these non-mechanical valves is preferable with relatively large particles, in order to obtain in the L-shaped valves a sufficiently large range of gas / particle slip rates to control the circulation in a relatively wide range. In addition, in the chemical loop process with solid charges, it is necessary to separate the unburnt particles from the metal oxides in the reduction reactor. It is therefore advantageous to limit the content of fine particles of metal oxides with a diameter of less than 100 micrometers in the installation in order to have optimal operation of the non-metallic valves controlling the circulation, but also to limit the entrainment of metal oxides with unburnt coal in the gaseous effluents of the reactor after separation. Large particles are more difficult to transport and require high transport speeds. To limit the transport speeds in the transfer lines and inside the reactors, and thus to limit the pressure losses in the process as well as the abrasion and erosion phenomena, it is therefore preferable to limit the size of the particles at a maximum value close to 500 micrometers.

Preferably, the particle-type oxido-reducing active mass introduced into the chemical loop combustion plant therefore has a particle size such that more than 90% of the particles have a size of between 100 micrometers and 500 micrometers.

More preferably, the particle-forming oxido-reducing active mass introduced into the plant has a particle size such that more than 90% of the particles have a particle diameter of between 150 micrometers and 300 micrometers.

Even more preferably, the particle-forming oxido-reducing active mass introduced into the plant has a particle size such that more than 95% of the particles have a diameter of between 150 micrometers and 300 micrometers. According to a preferred embodiment of the invention, the particle size of the particles of natural ore of pyrolusite-type manganese is different from the particle size of the NiO particles, so as to be able to separate the NiO particles from those of the natural manganese ore during of the CLC process. Advantageously, the NiO particles are shaped to a particle size smaller or larger than that of the particles of natural manganese ore. Thus, the particles of natural manganese ore and NiO do not follow the same circuit in the chemical loop, and only the particles of manganese ore requiring to be reoxidized are sent to the oxidation reactor, which allows optimize the utilities and energy costs of the CLC process. This specific circuit also makes it possible to lower the degree of oxidation of the nickel NiO compound, by changing from the oxidized NiO form to the reduced Ni form, and consequently to increase its catalytic power. According to another embodiment of the invention, the particle size of the particles of natural ore of pyrolusite-type manganese and that of the NiO particles is substantially identical.

The active mass according to the invention is preferably activated by a phase of gradual rise in temperature under an oxidizing atmosphere. In order to be able to increase the reactive capacities of the redox mass, and according to the invention, the solid in the form of particles advantageously undergoes an activation phase comprising a gradual rise in temperature under an oxidizing atmosphere, constituted for example by the air. The temperature reached is generally greater than or equal to 535 ° C., advantageously greater than or equal to 600 ° C., more preferably greater than or equal to 800 ° C., and very preferably greater than or equal to 900 ° C.

The activation phase is preferably carried out in the chemical loop combustion plant in the combustion reactor. Once the redox mass has been shaped, for example after mixing the NiO particles with those of natural manganese ore obtained following a possible grinding and sieving step, the non-activated solid (particles of the redox mass ) is preferably introduced into an area of the plant containing an excess of oxygen, namely the oxidation reactor, for its activation. The chemical loop combustion plant comprises an oxidation reaction zone in which the active mass is oxidized, and a reduction reaction zone in which the active mass is reduced.

At start-up, before initiating the oxidation-reduction cycles by introducing fuel into the process, the non-activated solid at room temperature can be introduced at the bottom of the oxidation zone, which is advantageously at a temperature of between 400 ° C and 550 ° C under an oxidizing atmosphere, for example air. This preferential temperature range of the oxidation zone at the time of introduction of the redox mass into the installation makes it possible, for example, to minimize the air to be introduced into the process. The redox mass then equilibrates thermally with the oxidizing atmosphere in the oxidation zone where it is introduced, almost instantaneously. The charging time of the cold solid in the oxidation zone is for example between 12h and 72h, depending on the flow rate of the solid introduced and the dimensions of the installation. The redox mass then undergoes a rise ramp under this oxidizing atmosphere to a temperature generally greater than or equal to 535 ° C, preferably greater than or equal to 600 ° C, preferably greater than or equal to 800 ° C and very preferably greater than or equal to 900 ° C. During activation of the active mass, the temperature rise in an oxidizing atmosphere can be done progressively, preferably at a speed of between 5 ° C./h and 100 ° C./h, more preferably at a speed between 10 ° C / h and 50 ° C / h. The temperature rise of the oxidation reactor can be done by introducing hot air, possibly by the use of gas burners, or a combination of both. The rise in temperature of the installation by increasing the temperature of the preheating air, by starting up gas burners, or by a combination of the two, allows the circulation of the solid between the reaction zone of reduction and that of oxidation. During this phase of starting and activating the solid, the oxygen concentration in the oxidation zone is preferably at least 5% excess of O 2.

Once the mass is activated, it is possible to initiate the oxidation-reduction cycles by introducing the fuel into the reduction zone. Preferably, the NiO of the redox mass itself undergoes an activation in order to maximize its catalytic power. The activation of the NiO consists of reducing the degree of oxidation of the nickel compound, that is to say passing from the form of NiO metal oxide to the metal form Ni, also called elemental form, which can be achieved when the particles of the active mass pass into the reduction reactor. The nickel present in the stabilized form of the mixed nickel-manganese mixed metal oxide crystallized according to the spinel structure is itself already activated. In the case where the redox mass essentially contains pyrolusite-type natural manganese ore and at least one mixed nickel-manganese mixed metal oxide crystallized according to the spinel structure, a nickel activation phase is therefore not necessary.

Preferably, the combustion reaction (reduction of the active mass) is carried out in the presence of steam. In the case of using solid or liquid charges, the injection of water vapor is inherent to the process. Indeed to promote the contact between a liquid charge and the metal oxide, it is preferable to atomize the liquid charge and this can be effected effectively in two-phase atomizers in the presence of water vapor. On the other hand, water vapor promotes the gasification of hydrocarbons, and it is preferable in the case of liquid or solid feeds to maintain in the reduction reactor a high pressure of water vapor favoring the gasification reactions. In the case of a gaseous feed, it is advantageous to inject steam with the fluidization gas in order to avoid the formation of agglomerates of the oxygen-bearing solid.

It is also possible to use carbon dioxide as a gasifier or fluidizing gas. The invention also relates to a method of combustion of solid hydrocarbon feeds, liquid or gaseous by oxidation-reduction in a chemical loop using an active mass according to the invention. Process for the combustion of hydrocarbons in a fluidized bed chemical loop The active compounds according to the invention act as oxygen carriers for the oxidation-reduction loop combustion process and can be used to treat gaseous fuels (eg natural gas, syngas, biogas), liquids (eg fuel, bitumen, diesel, gasoline etc.), or solids (eg coal, coke, petcoke, biomass, oil sands, soft waste etc. .) in a circulating fluidized bed. The general scheme of an oxidation-reduction chemical loop combustion plant according to the invention is as follows: the plant comprises an oxidation reaction zone and a reduction reaction zone. The solid particles of the active mass are oxidized, at least in part, in an oxidation zone comprising at least one fluidized bed at a temperature generally between 600 ° C. and 1400 ° C., preferably between 800 and 1000 ° C. These are then transferred to a reduction zone comprising at least one fluidized bed reactor where the active mass is brought into contact with the fuel at a temperature generally of between 600 ° C. and 1400 ° C., preferably between 800 ° C. and 1000 ° C. The contact time varies depending on the type of fuel load used. It typically varies between 1 seconds and 10 minutes, for example preferably between 1 and 5 minutes for a solid or liquid charge, and for example preferably from 1 to 20 seconds for a gaseous charge. The ratio between the amount of circulating active mass and the quantity of oxygen to be transferred between the two reaction zones is advantageously between 30 and 100, preferably between 40 and 70. The combustion can be partial or total. In the case of partial combustion, the active-to-fuel ratio is adjusted to achieve partial oxidation of the fuel, producing a synthesis gas in the form of a mixture rich in CO + H2. The process can therefore be used for the production of synthesis gas. This synthesis gas can be used as a feedstock for other chemical transformation processes, for example the Fischer Tropsch process making it possible to produce liquid hydrocarbons with long hydrocarbon chains which can subsequently be used as fuel bases from synthesis gas. In the case where the fluidization gas used is water vapor or a mixture of water vapor and other gas (s), the reaction of CO gas with water (or water gas shift in English terms) Saxons, CO + H20 CO2 + H2) can also take place, resulting in the production of a CO2 + H2 mixture at the reactor outlet. In this case, the flue gas can be used for energy production purposes given its calorific value. It is also possible to use this gas for the production of hydrogen, for example to supply hydrogenation units, hydrotreating units for refining or a hydrogen distribution network (after reaction of water gas shift). In the case of total combustion, the gas flow at the outlet of the reduction reactor is composed essentially of CO2 and water vapor. A flow of CO2 ready to be sequestered is then obtained by condensation of the water vapor. The energy production is integrated in the Chemical Looping Combustion process by heat exchange in the reaction zone and on the fumes which are cooled. The invention therefore also relates to a process for capturing CO2 by total combustion in a chemical loop in a process according to the invention. In the case of the use of sulfur-containing fuels, the sulfur oxides which could be produced during the total combustion of sulfur-containing fuels can be separated, according to the implementation of the chosen process, from the concentrated CO2 stream by a conventional method such as absorption on solvent or by the addition of a desulfurization reagent (lime or limestone). Thus, the use according to the invention of the nickel-enriched pyrolusite-based active mass and the spinel-type nickel-manganese mixed oxide makes it possible not to reject sulfur oxide in the flow leaving the oxidation reactor. Thus advantageously limiting the flow to be treated, in the case where the redox mass consists of a mixture of particles of natural manganese ore and NiO particles which can be separated so that the majority of the particles of NiO are recycled to the reduction reactor and do not circulate in the oxidation reactor. In this case, the sulfur oxides produced by the process during the use of sulfur-containing fuels are thus advantageously recovered only on the flow leaving the reduction reactor ("fuel" reactor). Depending on the use of the flue gases, the process pressure is adjusted. Thus, to achieve total combustion, it is advantageous to work at low pressure to minimize the energy cost of gas compression and thus maximize the energy efficiency of the installation. To produce synthesis gas, it is advantageously possible in certain cases to work under pressure, in order to avoid the compression of the synthesis gas upstream of the downstream synthesis process: the Fischer Tropsch process working for example at pressures between 20 bar and 40 bar, it can be interesting to produce the gas at a higher pressure. In the case where the active mass comprises a mixture of particles of natural manganese ore and NiO particles, with a particle size of NiO particles different from that of particles of natural manganese ore such that the particle size of NiO is greater than or less than that of natural manganese ore particles, the process according to the invention can be carried out as illustrated in FIGS. 1 and 2. According to these embodiments, it is possible to carry out a separation of the particles of NiO of those of manganese oxide. This separation advantageously makes it possible to send to the oxidation zone only the particles requiring reoxidation, that is to say the particles of natural ore of manganese, which constitutes a significant energy and financial gain for the whole. of the process. In addition, this configuration allows the initial dopant NiO of the redox mass to remain mainly in the active form Ni. In the case of a combustion of solid hydrocarbonaceous feeds, these embodiments can furthermore make it possible to separate the unburnt particles and the ash from the remainder of the effluents leaving the reduction zone. According to these embodiments, in a first reaction zone R 1 operating in a dense fluidized bed, the hydrocarbon feeds are contacted with the particles of natural ore of pyrolusite-type manganese and the NiO particles. In a second reaction zone R2, a combustion of the gaseous effluents from the first reaction zone R1 is carried out in the presence of the particles of natural ore of pyrolusite-type manganese and NiO particles. In a separation zone S3, the particles of natural pyrolusite-type manganese ore and the NiO particles are separated in a mixture from zone R2 comprising flue gas, the particles of natural manganese ore from Pyrolusite type and NiO particles. The majority of the NiO particles are returned to the first reaction zone R1, and the majority of the natural manganese ore particles are reoxidized in an oxidation zone R4 before returning them to the zone R1. pyrolusite type manganese and NiO particles. In order to promote total combustion, it may be envisaged to introduce a certain quantity of freshly oxidized redox mass completely oxidized by a pipe 6. It is also possible to inject oxygen directly via a pipe 7.

At the outlet of the second reaction zone R2, a mixture comprising the combustion gas, the pyrolusite-type natural ore particles and the NiO particles is extracted via a pipe 8 to be sent to an S3 separation zone. in which there is a rapid separation between the lightest particles, that is to say mainly the NiO particles of smaller size than the other particles of the mass, extracted via the conduit 10 with the gas, and the heavier particles - mostly particles of natural manganese ore - extracted in the lower part of the separation zone S3 by a conduit 13 feeding a chamber F4. This enclosure F4 serves as a buffer zone, and may be materialized by a concentric fluid bed and peripheral to the second reaction zone R2, the fluidization being obtained by injection of a gas supplied by a pipe 14. Advantageously, the latter participates in the separation in the separation zone 83 by being channeled to it by a pipe 17. In this fluidized bed of the buffer zone, it is advantageous to have heat exchange means 16 which can be tubes in wall or in the fluidized bed to recover a variable part generally representing 5 to 60% of the heat produced in the chemical loop combustion process. A conduit 15 makes it possible to extract the particles of the active mass constituted, for the most part, by the natural manganese ore from the buffer zone to an oxidation zone R4 to re-oxidize the latter, and then send them back to the reaction zone R 1 by the conduit 3. In the separation zone 83, it is also possible to introduce a gas from an external source via a conduit 9. This gas may contain oxygen or an oxidizing gas to continue the combustion reactions of CO and hydrogen in the separator 83. From the separation zone 83, a part of the heavy particles having decanted (mainly ore particles). natural manganese) is extracted through a pipe 11 to be recycled to the reaction zone R1. It is thus possible to promote the temperature homogeneity in the reaction zones R1, R2 and in the separation zone S3. At the exit of the separation zone 83, the pipe 10 conveys the gas stream containing the lighter particles - mainly NiO particles and possibly a minor fraction of particles of natural manganese ore - to at least one gas separation stage. -solid, for example two gas-solid separation stages (S5, S6), for example cyclones, as shown in FIG. 1. These devices make it possible to recover almost all the particles contained in the gas stream of the pipe 10 which are then recycled to the reaction zone R1 respectively by the lines 19 and 20.

At the outlet of the first cyclone S5, the gas stream is extracted by a pipe 17 to be sent to the second cyclone S6 and at the outlet of this cyclone S6, the substantially particle-free gas is extracted via a pipe 18, the latter no longer containing that a particle content generally between 100 mg / m3 and 1 g / m3. A dense fluidized bed is understood to mean a fluidized bed in which the gas fraction Cg is less than 0.9, preferably less than 0.8. Diluted fluidized bed means a fluidized bed in which the volume fraction of the particles of the redox active mass is less than 10% by volume. In general, the redox mass can be introduced initially into the oxidation zone R4 (not shown). A booster redox mass during operation can also be performed at this level, for example to compensate for an attrition phenomenon. According to this first embodiment, the majority of the NiO is activated once within the second reaction zone R2.

In the case of the injection of a solid fuel into the reactor R1, the flow of the solid fuel particles can be either continuous or intermittent with an injection frequency corresponding to a period equal to at least half the time average residence time of all the solid fuel particles in the reaction zone R1. The solid fuel undergoes, on contact with the particles of the active mass, a devolatilization of the volatile compounds, which generally represent from 5 to 50% by weight of the solid fuel according to its origin. The temperature in the reaction zone R1 is preferably greater than 800 ° C. and preferably between 900 ° C. and 1000 ° C., so as to minimize the time required to gasify the solid fuel. From the reaction zone R1 exits through the pipe 4, in addition to the particles of the active mass and the combustion gas, a unburned solid fuel fraction. In the separation zone S3, unburnt particles and possibly fly ash can be extracted together with the NiO particles and sent to the separators S5 and S6 via the line 10. The solid particles passing through S5 and S6 can then be recovered almost completely, after possible removal of fly ash by fluidized bed elutriation, for example.

A second embodiment illustrated in FIG. 2 is adapted to the case where the NiO particles have a size greater than that of the particles of natural manganese ore. The reaction zones R1, R2, R4 function in a manner similar to that described with reference to FIG. 1. Referring to FIG. 2, the following steps are carried out: the particle mixture brought into contact with each other is brought into contact with the pipe 205 with the combustible charge introduced via line 1 into a first reaction zone R1 operating in a dense fluidized bed; a combustion of the gaseous effluents from the first reaction zone R1 is carried out by the pipe 4 in the presence of the particles of the active mass in a second reaction zone R2; in a separation zone S3, the natural pyrolusite-type manganese ore particles and the NiO particles are separated in a mixture coming from the zone R2 by the pipe 8 and comprising combustion gas, the particles of pyrolusite-type natural manganese ore and NiO particles. Larger and heavier NiO particles are mostly returned to reaction zone R1 via line 11, and the rest of the particles - mostly natural manganese ore particles - are sent with the flue gas. by the pipe 10 in a solid-gas separation zone S5, for example a cyclone, for separating the combustion gas that escapes through a pipe 18 and a stream composed mainly of particles of manganese oxide sent by a pipe 201 to an oxidation zone R4 to be re-oxidized there; the particles of manganese oxide are re-oxidized in the oxidation zone R4 by means of an oxidizing gas such as air introduced via a pipe 22. The re-oxidized particles are then returned to the first reduction zone R1; after a solid-gas separation in a cyclone separator S6, the solid particles from the oxidation reactor R4 are sent via a pipe 203 to a solid-solid division zone R5, operating in a fluidized bed, which allows to divide the partially oxidized solid stream leaving the oxidation reactor R4, composed mainly of a major fraction of particles of natural manganese ore and a minor fraction of NiO particles, into two sub-streams. A first sub-flow returns via a pipe 204 to the oxidation reactor R4 to be further oxidized, and a second sub-flow is conveyed to the reduction reactor R1 through a pipe 205 to supply the oxygen required for the combustion of the charges. fuels introduced into R1. In addition, the solid-solid division zone R5 can also be used to recover the heat produced by the oxidation of the combustible charges, for example methane, by integrating, for example, heat exchange means. The redox mass can be introduced initially into the oxidation zone R4 (not shown). A booster redox mass during operation can also be performed at this level, for example to compensate for an attrition phenomenon. As in the first embodiment, the majority of the NiO is activated once within the second reaction zone R2. A CLC installation making it possible to implement the method according to the first and second embodiments of the invention thus comprises: at least one first reaction zone R 1 operating in a dense fluidized bed and making it possible to bring into contact the gaseous hydrocarbonaceous solid feedstock , or liquid with the particles of the redox active mass. In the case of solid fuels, this first reaction zone R1 makes it possible to gasify the solid fuel particles in the presence of particles of the redox mass; a second combustion or reduction reaction zone R2 preferably operating in a diluted fluidized bed and making it possible to carry out the combustion of the gaseous effluents from the first reaction zone R1 in the presence of the particles of the oxido-reducing active mass; a separating zone S3 effecting a separation in a gas-containing mixture, the particles of pyrolusite-type natural ore of manganese and the NiO particles, said mixture coming from the second reaction zone R2, and said zone of separation comprising an enclosure in which the admission of the mixture of particles to be separated is carried out in a dilute phase in which a gas flows at an ascending speed which is imposed; an oxidation zone R4 of the particles of the oxido-reducing active mass, in particular particles of natural manganese ore, making it possible to re-oxidize said particles before returning them to the reaction zone R1.

FIG. 3 illustrates a third embodiment for implementing the method according to the invention. This embodiment is particularly adapted to the case where the particle size of the particles of natural ore of pyrolusite-type manganese and that of the NiO particles is similar, and in the case where the active mass is not a mixture of distinct particles of NiO and of manganese ore, but comprises particles formed from the same material comprising natural nickel-pyrolusite type ore of manganese. According to this third embodiment, the hydrocarbon feedstocks coming from a pipe 1 are brought into contact with the particles of the oxidoreductant active mass arriving via a pipe 308 in an oxidized state, in a first reaction zone R 1 operating in a fluidized bed. dense. Next, combustion of the gaseous effluents from the first reaction zone R1 in the presence of the particles of the oxido-reducing active mass, is carried out in a second reaction zone R2. The gaseous effluent resulting from the combustion and containing the particles of the active mass is then sent via a pipe 8 into a first gas-solid separator S1, for example a cyclone, from which the combustion gas is extracted via a pipe 18 and a particle stream through a conduit 301. The latter is divided into a first division zone R3 operating in a fluidized bed in a first sub-flow returned by a pipe 302 to the second reaction zone R2 where it is advantageously recycled, and a second sub-flow going into an oxidation zone R4 through a pipe 303. The recycling of the first sub-flow makes it possible to increase the activated form Ni of the dopant in the reaction zone R2. The particles of the second sub-flux are reoxidized in the oxidation zone R4 and then returned to the reduction zone R1. For this, the particles of the active mass are first recovered by means of a solid-gas separator S2 of the cyclone type, which are then sent through line 306 to a second division zone R5 operating in a fluidized bed. In this zone R5, the particle flow of the active mass from the oxidation zone R4 is divided into a third sub-flow going back into the oxidation zone R4 via a pipe 307, to be further re-oxidized. , and a fourth sub-flow going into the first reaction zone R1 via a pipe 308. The redox mass can be introduced initially into the oxidation zone R4 (not shown). A booster redox mass can also be performed at this level during operation, for example to compensate for an attrition phenomenon. The first division zone R3 may have an elutriation function in the case of the combustion of solid charges, for the recovery of unburnt solids, which will preferably be returned to the reaction zone R1 (not shown). Heat exchanges are carried out in the first division zone R3 and in the second division zone R5, where the slow fluidization conditions favor the heat exchange and limit the wear of the internals. Alternatively, these heat exchanges can be carried out using external heat exchangers, or heat exchangers located at the wall of the air and / or fuel reactors (R2, R4).

According to this third embodiment, if the redox mass contains NiO, it can be activated at each passage within the second reaction zone R2 when said mass comes from the oxidation zone R4.

EXAMPLES Example I: Combustion of methane at 890 ° C. in the presence of pyrolusite particles (example given for comparison) A compound charge, by volume, of 50% methane, 33.3% of nitrogen and 16.7% of vapor of water, which corresponds to a nominal power of 0.6 kW heat, is treated in a reactor of 40 mm diameter working in batch. For chemical loop combustion, pyrolusite-based oxygen-carrying particles having the following properties are used: - density: 3250 kg / m3 - oxygen transfer capacity: 6.7% - particle diameter The utilization rate of pyrolusite, ROAx, is 2%, which means that for every 100 grams of oxide, 2 grams of oxygen are used. The temperature of the oxygen carrier in the reactor varies between 870 ° C and 900 ° C, the average temperature being 890 ° C. The apparent residence time of the gas in the reactor is 1 second. This calculated residence time does not take into account the hydrodynamics of the fluidized bed, and corresponds to the ratio between the height of the bed and the superficial gas velocity (this value is conservative). The redox mass is activated by a rise in temperature of 20 ° C./minute in air, up to a temperature of 900 ° C. FIG. 4 represents the evolution of the conversion of methane Xc (%) over the first 35 oxidation-reduction cycles of the process (Number of cycles N on the abscissa). The conversion rate of methane Xc corresponds to the ratio between the amount of CO2 formed (in moles), and the amount of CH4 injected (in moles), normalized to take account of the carbon footprint. Initially, the conversion of methane is about 40%, then decreases to about 20% for the last four cycles.

FIG. 5 illustrates the measured CH4, CO and CO2 gas profiles obtained at the outlet of the reactor during the reduction phase of the 10th oxidation-reduction cycle. The gases at the outlet are analyzed with the Rosemount NGA2000 analyzer. The CO2, the CO and the CH4 are measured with a non-dispersive infrared spectrometer (NDIR), the oxygen is measured using a paramagnetic cell, and the dihydrogen is measured with a katharometer. At the beginning of the reduction there is a peak of CO2 and then a constant decrease in the conversion of C114.

EXAMPLE 2 Preparations Ex-Situed, Comprising a Ni-enriched Nickel-enriched Pyrolusite-type Natural Mineral Ore, and Nickel-Manganese Mixed Metal Oxides Filtered According to the Spinel Structure Four 20 g samples, the composition of which is detailed in FIG. Table 1 below, were prepared in alumina crucibles. For these preparations, the source of manganese dioxide is pyrolusite with the following properties: - mass volume: 3250 kg / m3 - oxygen transfer capacity: 6.7% - particle diameter: 208 μm The nickel used is initially under the form Ni (OH) 2, and decomposes to NiO between 400 and 720K. The particle size of the Ni (OH) 2 is between 5 μm and 10 μm. The two powders are mixed. Sample 1 2 3 4 Ratio Mn / NI 1 2 3 5 M sample (g) 20 20 20 20 M Ni (OH) 2 (g) 10.3 7.0 5.2 3.5 M Mn02 (g) 9.7 13.0 14.8 16.5 M NI (OH) 2 (mol) 0.11 0.08 0.06 0.04 M MnO2 (mol) 0.11 0.15 0.17 0.19 Table 125 The four preparations were heat-treated at 1050 ° C for 4 hours in an air-muffle furnace. After cooling, the samples were analyzed by XRD. FIGS. 6A and 6B show the diffractograms resulting from this analysis for samples 1 to 4 respectively (A on the abscissa corresponding to the angle 20 (in degrees) and Cps on the ordinate representing the number of shots during the measurement). These analyzes were carried out on a Bragg-Brentano type X-ray diffraction device of the PANanytical X'Pert PRO MPD 6-8 type with a Cu-K8 source (λ = 1.5402 Å) of power 35kV x 35 mA. These difractograms show the formation of Mn-Ni mixed metal oxides, such as spinels NiMn204 and MnNi204, with a characteristic signature that can be identified with visible lines at 18 °, 30 ° and 35 °. This signature is even more clear that the samples have a high Mn / Ni ratio. In this example, the Mn / Ni ratios have been chosen so as to characterize the graphical signature of the crystalline nickel-manganese mixed metal oxides according to the spinel structure that may be present in the active mass according to the invention. Example 3: Combustion of methane at 895 ° C. in the presence of a mixture comprising nickel-enriched pyrolusite and a mixed nickel-manganese mixed metal oxide according to the spinel structure A compound charge, by volume, of 50% methane, 33, 3% of nitrogen and 16.7% of water vapor, which corresponds to a nominal power of 0.6 kW heat, is treated in a reactor of 40 mm diameter working in batch. For the chemical loop combustion, an oxido-reducing mass comprising a natural manganese ore of the pyrolusite type mixed with a mixed nickel-manganese metal oxide of spinel type formed according to the protocol described in Example 2, is used. except that the exposure time in the air muffle furnace is 24 hours. The properties of pyrolusite and NiO are those given in Example 2. The pyrolusite / spinel mixture was made in such a way that the elemental nickel of the redox active mass is between 0.1% and 10%. mass. After cooling, the solid is analyzed by XRD. This analysis was performed on a Bragg-Brentano type X-ray diffraction type PANanytical X'Pert PRO MPD e-e with a Cu-K8 source (λ = 1.5402 Å) of power 35kV x 35 mA.

FIG. 7 represents the diffractogram resulting from this analysis (A on the abscissa corresponding to the angle 20 (in degrees) and Cps on the ordinate representing the number of strokes during the measurement). FIG. 7 shows the presence, with the same characteristic lines identified in FIGS. 6A to 6D), of a NiMn 2 O 4 mixed Ni / Mn mixed oxide. Other compounds are present in the sample, identifiable by the presence of other characteristic lines. It is Bunsenite NiO, two types of manganese oxides Mn304 (centered tetragonal hausmannite and centered face cubic hausmannite), of the Mn203 bixbyite.

The pyrolusite utilization rate, ROAx, is 2%, that is to say that for each 100 grams of oxide, 2 grams of oxygen are used. The temperature of the oxygen carrier in the reactor varies between 870 ° C and 920 ° C, the average temperature being 895 ° C. The apparent residence time of the gas in the reactor is 1 second. This calculated residence time does not take into account the hydrodynamics of the fluidized bed, and corresponds to the ratio between the height of the bed and the superficial gas velocity. The redox mass is activated by a rise in temperature of 20 ° C./minute. under air, up to a temperature of 900 ° C. FIG. 8 describes the evolution of the conversion of methane Xc (%) over the first 100 oxidation-reduction cycles of the process (Number of cycles N on the abscissa). The conversion rate of methane Xc corresponds to the ratio between the amount of CO2 formed (in moles), and the amount of CH4 injected (in moles), standardized to take account of the carbon footprint. The same measuring devices as those described for the other examples are used. Initially, the conversion of methane amounts to about 50%, then increases to stabilize very rapidly to the high value of 75%, from the first oxidation-reduction cycles. The carbon conversion is thus 3.5 times higher than in Example 1, which illustrates the synergistic effects of the manganese oxide from a pyrolusite-type natural ore and nickel, with the presence of a nickel-manganese mixed oxide in the form of spinel during the oxidation (oxygen transport and catalysis of the decomposition of methane).

Figure 9 illustrates the CH4, CO and CO2 profiles obtained at the outlet of the reactor during the reduction phase of the 10th oxidation-reduction cycle. The same measuring devices as those described for the other examples are used. At this time, the conversion of methane is relatively stable, given the data presented in Figure 8. At the beginning of the reduction, a peak of CO2 is observed and then an increase in the conversion of CH4 according to the time.

Claims (23)

REVENDICATIONS1. Redox active mass for a chemical loop oxidation-reduction process comprising: a pyrolusite-type natural manganese ore initially comprising at least 60% by weight of MnO 2, said ore being enriched in nickel, and a nickel-manganese mixed metal oxide crystallized according to the spinel structure, said oxido-reducing active mass being in the form of particles. 2. Redox active mass according to claim 1, comprising from 0.1% to 10% by mass of elemental Ni. 3. Redox active mass according to one of claims 1 and 2, wherein the initial MnO 2 content of the pyrolusite-type manganese ore is between 70% and 90% by weight, preferably between 76% and 82%. mass. 4. Redox active mass according to one of the preceding claims, wherein the nickel-manganese mixed metal oxide has the formula NiMn204 or MnNi204, preferably the formula NiMn204. 5. Redox active mass according to one of the preceding claims, comprising a mixture of particles of the natural ore of pyrolusite-type manganese and NiO particles. 6. Redox active mass according to one of the preceding claims, having a particle size such that more than 90% of the particles of the active mass have a size between 100 pm and 500 pm, preferably between 150 pm and 300 pm . 7. A process for the combustion of solid hydrocarbon feeds, liquid or gaseous by chemical redox oxidation using an oxido-reducing active mass according to any one of claims 1 to 6. 8. The process as claimed in claim 7, in which the oxido-reducing active mass undergoes a heat treatment at a high temperature, preferably at a temperature between 800 ° C. and 1200 ° C., for a duration of preferably between 0.5 hours and 10 days. 9. The method of claim 8, wherein the heat treatment of the redox active mass is performed in situ in a chemical loop combustion plant in which the method is implemented. 10. The method of claim 8, wherein the heat treatment of the redox active mass is performed ex situ outside a chemical loop combustion plant in which the method is implemented. 11. Method according to one of claims 7 to 10, wherein the active mass is formed into particles having a particle size suitable for implementation in a fluidized bed. 12. The method of claim 11, wherein the natural manganese ore is previously milled and sieved to obtain particles of particle size compatible with a fluidized bed implementation, and wherein the nickel comes from nickel oxide. NiO chosen as it is in the form of particle size distribution also compatible with a fluidized bed implementation. 13. Method according to one of claims 7 to 12, wherein: in a first reaction zone (R1) operating in a dense fluidized bed, the hydrocarbon feeds are brought into contact with the particles of the oxidized active mass. reductive; in a second reaction zone (R2), combustion of the gaseous effluents from the first reaction zone (R1) in the presence of the particles of the oxido-reducing active mass; in a first division zone (R3) operating in fluidized bed, a division of the particle stream of the active mass from the second reaction zone (301) into a first sub-flow going back into the second reaction zone (R2) and a second sub-flow going into an oxidation zone (R4); - Reoxidation of the particles of the active mass in the oxidation zone (R4) before returning them to the first reaction zone (R1) - is carried out in a second division zone (R5) operating in a bed fluidized, a division of the particle flow of the active mass from the oxidation zone (R4) into a third sub-flow going back into the oxidation zone (R4) and a fourth sub-flow going into the first reaction zone (R1). The method of claim 12, wherein the particle size of the NiO particles is different from the particle size of the natural manganese ore particles such that the particle size of NiO is greater or less than that of the natural manganese ore particles. 15. The method of claim 14, wherein: in a first reaction zone (R1) operating in a dense fluidized bed, the hydrocarbon feeds are contacted with the particles of natural ore of pyrolusite-type manganese and the particles of NiO; in a second reaction zone (R2), combustion of the gaseous effluents from the first reaction zone (R1) is carried out in the presence of natural pyrolusite type ore particles and NiO particles; separating, in a separation zone (S3), the particles of natural pyrolusite-type manganese ore and the NiO particles in a mixture originating from the zone (R2) comprising flue gas, the particles of pyrolusite-type natural manganese ore and NiO particles; the pyrolusite-type natural ore particles are re-oxidized in an oxidation zone (R4) before being returned to the first reaction zone (R1). 16. Method according to one of claims 7 to 15, wherein the active redox mass is activated by a gradual rise in temperature under an oxidizing atmosphere to a temperature greater than or equal to 600 ° C, preferably greater than or equal to at 800 ° C, still more preferably greater than or equal to 900 ° C. 17. The method of claim 16, wherein the gradual rise in temperature under an oxidizing atmosphere is carried out at a speed between 5 ° C / h and 100 ° C / h.35. 18. The method as claimed in one of claims 7 to 17, wherein the oxido-reducing active mass is activated in a chemical loop combustion plant in which the process is carried out. 19. Method according to one of claims 7 to 18, wherein the active redox active mass is used for the combustion of gaseous hydrocarbons. 20. Method according to one of claims 7 to 19, wherein the oxidoreductant active mass is reduced in contact with the hydrocarbon feedstock in a reduction zone of the chemical loop, and wherein the flow rate of the redox active mass measured at the inlet of said reduction zone is between 30 and 100 kg / h per kg / h of oxygen consumed in the reduction zone. 21. Method according to one of claims 7 to 20, wherein the reduction of the oxidoreductive active mass in contact with the hydrocarbon feeds is carried out at a temperature between 600 ° C and 1400 ° C. 22. Method according to one of claims 7 to 21 for the capture of CO2, wherein the combustion is total. 20 23. A process for the preparation of an oxido-reducing active mass according to any one of claims 1 to 6, in which nickel is enriched with a natural manganese ore of the pyrolusite type initially comprising at least 60% by weight of MnO 2 with magnesium oxide. nickel oxide NiO, and said nickel-enriched ore is exposed at a temperature between 800 ° C and 1200 ° C for a period of between 0.5 hours and 10 days.