WO2018002524A1

WO2018002524A1 - Solid product, the composition of which contains borazane, preparation thereof and use of same for generating hydrogen

Info

Publication number: WO2018002524A1
Application number: PCT/FR2017/051732
Authority: WO
Inventors: Jean-Philippe Goudon; Benoit Richard; Jean-Jacques FOURNIER; Nicolas VANDECANDELAERE
Original assignee: Arianegroup Sas
Priority date: 2016-06-29
Filing date: 2017-06-28
Publication date: 2018-01-04
Also published as: FR3053324A1; FR3053324B1

Abstract

The main subject of the present invention is a solid product, containing borazane in the composition thereof, capable of generating hydrogen by thermal decomposition of said borazane. The composition of said solid product essentially consists of said borazane, present in the form of grains and of at least 10% by weight of silica, present in the form of grains, the median diameter (D₅₀) of which is less than a micron. The presence of said silica is particularly opportune for solving the technical problem of the expansion of the reaction volume during the thermal decomposition of the borazane.

Description

SOLID PRODUCT INCLUDING THE COMPOSITION CONTAINING BORAZANE, ITS PREPARATION AND USE FOR

The present invention relates to the generation of hydrogen by thermal decomposition (or thermolysis) of borazane (or "ammonia borane"). More specifically, it relates to a solid product whose composition contains borazane, the preparation of said solid product and the use of said solid product for hydrogen generation (by thermal decomposition of borazane that its composition contains). The thermal decomposition of borazane present in the composition of said solid product (with a formulation adjuvant) is improved over that of Persian borazane.

Borazane (or "ammonia borane"), a chemical compound with the formula NH3BH3, has been identified as an excellent candidate for hydrogen storage. Indeed, its mass content in hydrogen of 19.6% makes it a raw material of choice for the hydrogen generation. Said borazane can be obtained according to different synthetic routes. The most common and most mature of these synthetic routes is the metathesis of salts, borohydride salt on the one hand (NaBH ₄ , for example) and ammonium salt on the other hand ((NH ₄ ) ₂ CO ₃ , for example), implemented in an organic solvent.

The use of borazane as a hydrogen generator has been described in two variants.

According to a variant, in particular described by the Applicant in the patent application WO 2009/138629, borazane is used after formulation with at least one inorganic oxidant. It then releases hydrogen in a self-sustaining (exothermic) combustion reaction. According to another variant, in which the present invention is inscribed, borazane is directly (without prior formulation with an oxidant) heat-treated (by raising the temperature), in the absence of oxygen. Borazane then rapidly releases hydrogen, by thermal decomposition, according to the following three successive stages:

1) nNH ₃ BH ₃ → (NH ₂ BH ₂ ) _n + nH ₂ (90-120 ° C)

2) (NH ₂ BH ₂ ) n → (NHBH) n + nH ₂ (150 - 400 ° C)

3) (NHBH) n → BN + nH ₂ (> 1000 ° C).

In fact, the rise in temperature is generally limited and only the first two steps above are implemented (for a possible theoretical recovery of the 12.9% by mass of the hydrogen initially present in the decomposed borazane). Incidentally, it is noted here that the temperature values indicated above for the said first two steps are indicative. Those skilled in the art are aware that these temperature values depend on the purity of the decomposed borazane and the exact mode of implementation of the rise in temperature.

Borazane (solid: S), subjected to the temperature rise (so generally 400 ° C) to be thermally decomposed with hydrogen liberation (according to steps 1) and 2) above) actually begins ( in view of its melting temperature) by melting. It passes from the solid state (S) to the liquid state (L): S → L. It is therefore within a liquid phase (L) that the hydrogen (gas: G) is released, with parallel formation of polyaminoborane (of formula (NH ₂ BH ₂ ) _n ) solid. There is then ineluctably strong expansion of the reaction volume (by more than 200%) with generation of a foam that solidifies. Solid polyamine foam (NH ₂ BH ₂ ) _n is formed, a solid foam which decomposes, as the temperature continues to rise, of solid polyiminoborane foam (of formula (NHBH) _n ). This strong expansion of the reaction volume with generation of a solid foam is likely to be very damaging for the gas generator in the structure of which the borazane is decomposed (by raising the temperature): the filtration system of the released hydrogen and the tubes provided for the release of said released hydrogen are likely to to be reached by the expanding foam then blocked by it, solidified. It is particularly with this technical problem, the expansion of the reaction volume during the thermal decomposition of borazane to generate hydrogen (= technical problem of foaming explained above), that the present invention provides an interesting solution .

According to the prior art, alternative embodiments of the thermal decomposition of borazane (for the purposes of generating and recovering hydrogen) have already been described.

In the patent application CN 102030313, particular mention has been made of solid hydrogen storage materials whose composition essentially comprises borazane and an organic compound (formulation adjuvant) chosen from phthalic anhydride and polyethylene oxide. , dextrose, mannitol and mannitol hexaacetate. The presence of said organic compound is appropriate, with reference to the thermal decomposition rate of said solid materials (higher than that of borazane alone), their decomposition temperature (lower than that of borazane alone) and the generation of toxic gases. (less important than during the decomposition of borazane alone) ... The said solid materials are obtained by wet process, with the intervention of an organic solvent (the handling of which increases the process and whose residual traces are always likely to pollute the materials obtained) and their composition contains a significant amount of said organic compound (which is hardly conducive to obtaining a good yield of hydrogen). It has also been described in the patent application US 2014/0178292, solid materials for storing hydrogen, the composition of which essentially comprises borazane and polyethylene oxide (formulation adjuvant), said polyethylene oxide having a mass average molecular weight preferably greater than or equal to 1 MDa. Said solid materials, with reference to the technical problem of the expansion of the reaction volume during the thermal decomposition of borazane to generate hydrogen (= technical problem of foaming) mentioned above, contain at least 30% by weight of said polyoxide ethylene. It is conceivable that the said technical problem is solved by trapping borazane (in decomposition) in the polymer matrix of poly (ethylene oxide) (more or less softened).

It was also described in 2005 - in Angew. Chem. Int. Ed. 2005, 44, 3578-3582 - a hybrid solid material for storing original hydrogen: mesoporous silica, the inner channels of which are coated (with a film) of borazane.

In such a context, with reference to the technical problem of the expansion of the reaction volume during the thermal decomposition of borazane to generate hydrogen (= technical problem of foaming), the inventors propose an innovative solution, particularly powerful. Said solution is based on the effective original action of a formulation adjuvant specific to borazane. It is the merit of the inventors to have identified such an adjuvant formulation specific borazane and to have determined the conditions (particle size and quantities) in which it is effective. Said adjuvant of specific formulation is capable of retaining at source the liquid resulting from the melting of borazane, hence the non-expansion of the reaction volume, hence the non-generation of foam, and hence also, in a particularly timely manner , the retention at the source of the products of formed solid reaction (reaction residues). It is a mineral compound, totally chemically inert with respect to borazane (it does not react (at all) with said borazane: thus, it does not degrade the stability over time of said borazane; does not influence the thermal decomposition of said borazane (thermal decomposition responsible for the hydrogen release targeted)) and hydrogen, and stable at the temperatures involved (chemical decomposition temperatures of borazane up to about 400 ° C). It is silica, small particle size, intervening in an adequate amount. Said silica, according to a posteriori explanation of the inventors, acts in an original way to retain at source the liquid resulting from the melting of borazane: it acts as a thickening filler of said liquid.

According to its first object, the present invention therefore relates to a solid product which contains borazane in its composition. Said solid product is capable of generating hydrogen by thermal decomposition of said borazane. Said solid product therefore constitutes a solid (original) material for storing hydrogen. Said solid product is likely to exist in different solid forms (see below). Conventionally, borazane is present in the form of grains, in the form of a powder, in the said various solid forms (see below). Typically, the composition of said solid product consists essentially of borazane and at least 10% by weight of silica (= the specific formulation adjunct, in powder form, in the form of grains) whose median diameter (D ₅₀ ) (constituent grains) is less than one micron. The 10% by weight are obviously part of the mass composition of said product. The median diameter indicated here as well as all the median diameters considered in the present text are median diameters in mass. The borazane-specific formulation adjuvant retained by the inventors is therefore characterized by its chemical nature, its particle size and its intervention rate.

It is silica (SiO ₂ ), of small particle size (D ₅₀ <1 mm), and has at least 10% by weight.

Said silica is therefore (in the form of a powder) in the form of grains whose median diameter (D ₅₀ ) is less than one micron. Such a small particle size is required for the desired (non-foaming) result (see Table 1 below) and it certainly allows a homogeneous dispersion of the silica in the borazane.

The particle size of the silica present as formulation adjuvant in the composition of the products of the invention is advantageously the lowest possible. Thus the median diameter less than one micron is conveniently less than or equal to 700 nm, very conveniently less than or equal to 500 nm. It can even be much lower than the values indicated above. Those skilled in the art are aware of the existence of pyrogenic silicas having median diameters (D ₅₀ ) of the order of 10-50 nm. He is aware, however, that such fine silicas are likely to exist agglomerated, agglomerates involved having higher median diameters, especially 10 times higher (100-500 nm).

It has been indicated that the composition of the products of the invention consists "essentially" in said borazane and in said silica (present at least 10% by weight). It would indeed be totally exclude the presence, in very small quantities, of at least one other component, additive type, for example manufacturing aid. However, the person skilled in the art understands that the products of the invention (hydrogen storage materials), intended to be thermally decomposed to produce hydrogen, must be as pure as possible, in order to produce said hydrogen on more pure possible. Hence the choice, as adjuvant of formulation, a chemically inert mineral and the possible presence, only in very small quantities, of another component. In general, the mass composition of the products of the invention is such that:

borazane + silica≥ 99% (this quantifies the "essentially");

in fact, it is often (preferably) such that:

borazane + silica = 100%.

The silica is at least 10% by weight to be effective (see Table 1 below). It is not advantageous, with reference to the hydrogen yield, to use it in large quantities. It advantageously intervenes at most at 30% by weight, very advantageously at less than 30% by weight, preferably at most at 15% by weight. It is particularly appropriate to have found an effective borazane formulation adjuvant at such low levels.

According to an advantageous variant, the composition of the products of the invention, expressed in percentages by weight, essentially consists of or even consists of:

70 to 90% borazane (of borazane grains), and

10 to 30% silica, the median diameter (D ₅₀ ) of grains is less than one micron.

According to a preferred variant, the composition of the products of the invention, expressed in percentages by weight, consists essentially of or even consists of:

85 to 90% borazane (of borazane grains), and

10 to 15% of silica, the median diameter (D ₅₀ ) of the grains is less than one micron.

This variant is preferred insofar as the silica content is minimized. The impact on the hydrogen yield is also minimized. It has been understood, as indicated above, that the borazane present in the composition of the solid products of the invention is in the form of powder (of grains), mixed with the silica (also in the state powder, grains (very fine powder, grains whose D ₅₀ is less than one micron (see above))). Said borazane also advantageously has the smallest possible particle size (with reference to its thermal decomposition and its intimate mixture with silica). The borazane present in the composition of the solid products of the invention generally has a median diameter (D ₅₀ ) of 1 μm to 1 mm (Ιμηι ≤ D ₅ ≤ 1 mm). It generally has a median diameter of a few tens to a few hundred microns. It will be understood that the values indicated above correspond more exactly to the median diameters (D ₅₀ ) of the grains of said borazane.

The solid products of the invention are, as indicated above, likely to exist in several forms and more particularly:

in powder form, ie in the form of powders, more specifically mixtures of powders (of borazane powder (with grains) (with a D ₅ o generally between 1 m and 1 mm (see above) and a silica powder (with grains) (with a D ₅₀ <1 Mm, advantageously ≤ 700 nm, very advantageously ≤ 500 nm)) One can speak of the primary form (of existence of the solid products of the invention );

- in the form of granules. We can speak of a secondary form (likely to be obtained by transformation of the primary form). Such granules generally have a median diameter (D ₅₀ ) of 1 to 5 mm (1 mm ≤ D ₅₀ ≤ 5 mm) and a mass of a few milligrams;

- in the form of discs or pellets. We can also speak here of secondary forms (likely to be obtained, directly or indirectly, by transformation, from the primary form). Such discs or pellets generally have a thickness (constant or not) and a median diameter (D ₅₀ ) of a few millimeters to 30 mm and a mass of a few grams. The concepts of discs and pellets are relative, they are obviously associated with the thickness

(epastille> edisque)

- in the form of blocks. It is also a secondary form (likely to be obtained, directly or indirectly (it proceeds rather indirectly on an industrial scale)), by transformation, from the primary form). Such blocks generally have a thickness and a median diameter (D ₅₀ ) of more than 30 mm and a mass of a few tens of grams to a few hundred grams.

Said secondary forms - compacted forms - are conventionally obtained from the primary form (see below). They contain borazane and silica in the form of grains.

The inventors verified that the transformations of the primary form did not affect the thermal decomposition of the borazane present (see in particular point III.l.B.a and b below).

The shape of the solid products of the invention is opportunely optimized according to the exact mode of use of said products (especially the geometry of the decomposition chamber in which they are to be thermally decomposed to generate hydrogen ).

According to its second object, the present invention relates to a process for preparing the solid products of the invention (as described above). Said method comprises:

- The mixture of a borazane powder, and a silica powder, whose median diameter (D ₅₀ ) grains (silica, therefore) is less than one micron, said silica powder representing at least 10% by weight. mass of the powder mixture, for obtaining, by the dry route, the solid product (of the invention) in the form of a powder,

- optionally followed by a granulation step of said solid product obtained in powder form, for obtaining the solid product (of the invention) in the form of granules;

said solid product in powder form or said solid product in the form of granules being optionally compressed to obtain the solid product (of the invention) in the form of at least one disc or at least one lozenge , or

- Said solid product in powder form or in the form of granules being optionally compressed to obtain the solid product (of the invention) in the form of at least one block.

This is a process by analogy of the technical field of powders, implemented, typically, with adequate powders, in adequate proportions (see above).

It can be summed up in a simple mixture of powders (a mixture that is as intimate as possible). From such a mixture of powders it is possible to prepare granules, discs, pellets and blocks directly. From such a mixture of powders, it is possible to prepare indirectly, via the preparation of granules, disks, pellets and blocks.

The processes in question are therefore conventional methods. Because of the nature of the powders (due to the presence of the borazane powder), the compression steps do not require the presence of a manufacturing aid (see above).

The mixture of the powders (borazane powder, on the one hand, and silica powder, on the other hand) is used by the dry route. This way is familiar to the skilled person. Dry, two pre-existing powders are mixed. It is understood that neither obtaining suitable powder mixtures within the meaning of the invention (borazane + specific adjuvant of the invention, in an effective amount and at the appropriate particle size), nor the possible shaping of these powder mixtures do not raise particular difficulties for the person skilled in the art. However, this does not in any way make obvious the solution thus brought by the inventors to the technical problem identified above (that of the foaming of borazane during its thermal decomposition). It is the merit of the inventors to have demonstrated the timely use of silica (in an effective amount and at the appropriate particle size), as formulation adjuvant borazane, with reference to said technical problem.

According to another of its objects, the present invention relates to the use of the solid products of the invention (described above) and / or solid products prepared by the process of the invention (described above) for the generation hydrogen. In other words, it relates to a method of generating hydrogen by thermal decomposition of borazane, said method comprising thermal decomposition of a solid product of the invention (as described above) and / or a product prepared according to the process of the invention (as described above). The inventors have demonstrated that the presence of the specific formulation adjuvant of the invention, which is appropriate with reference to the technical problem of foaming, does not have a substantially negative impact on the production of hydrogen (see in particular the points III.lAb2 "and III.lBb below).

The method of the invention, based on the thermal decomposition of borazane, in the presence of silica, is conveniently implemented to supply a hydrogen fuel cell membrane proton exchange. The invention is now illustrated by the example section below. Said example portion presents the results of the prior art (see point II below), the results of the invention (see point III below) and comparative test results (see Table 1 of this point). III). His interest is reflected in the consideration of these results. Said example is to be considered with the appended figures:

- Figure (photo) 1 shows the expansion of borazane after its thermal decomposition test tube (see point II.2.a. below); this figure illustrates the prior art;

- Figure 2 schematizes the decomposition chamber of a test bench (used with borazane alone (see point II.2 b) below) and then with borazane formulated according to the invention (see point III). .lAb2 "below);

FIGS. (photos) 3A (before thermal decomposition) and 3B (after thermal decomposition) show the non-expansion of a powder containing borazane formulated according to the invention (see point III.l.A.b2 ', hereinafter);

FIGS. (photos) 4A (before thermal decomposition) and 4B (after thermal decomposition) show a tablet of the invention (see III.l.B.b. below).

Said figures are commented on in the example section below.

I. Raw materials

1. Borazane

The borazanes used were synthesized by the Applicant (by metathesis) and crystallized according to two different methods (hence their different particle size). at. Powder: purity measured by boron and proton NMR of 98.9% (by mass); median diameter (D ₅₀ ) of 50 Mm; DSC (see below);

b. powder (sieved at 500 μm): purity measured by boron and proton NMR of 98.9% (by mass); median diameter (D ₅₀ ) of 340 Mm.

2. Formulation adjuvants

at. Pyrogenerated silicas, distributed by CABOT Corp., under the names CAB-O-SIL® M5 (hydrophilic silica) and CAB-O-SIL® TG-3130 (hydrophobic), both having a median diameter (D ₅₀ ) of 20 nm and a surface area of 200 m ² / g It should be noted that these silicas of very small particle size are most often in the form of agglomerates whose median diameter (D ₅₀ ) is 200 nm. These two silicas are hereinafter referred to as type A silica and type B silica;

b. mesoporous silica, distributed by the company SIGMA ALDRICH having a median diameter (D ₅₀ ) of 500 nm and a specific surface area of 100 m ² / g. This silica is hereinafter called type C silica;

vs. silica having a median diameter (D ₅ o) of 35 Mm, sold by SIGMA ALDRICH (under the particle size 200 - 425 mesh); d. alumina having a median diameter (D ₅ o) of 450 nm, sold by the company Goodfellow.

II. PRIOR ART: borazane

1. DSC

DSC ("Differential Scanning Calorimetry") was performed on a sample (powder) of borazane (see item I. l.a. above, D ₅₀ = 50 Mm), sample of 1.4705 mg. Said powder sample was placed in an aluminum crucible, kept under an argon sweep (100 ml / min), and raised from 30 to 300 ° C. at a rate of 5 ° C./min.

The curve obtained showed a first endotherm at 114.99 ° C (corresponding to the melting of borazane) followed by a first exotherm which began at 116.78 ° C (corresponding to the beginning of the decomposition of borazane with release of the first mole of hydrogen). Said first exotherm was itself followed by a second exotherm (corresponding to the release of the second mole of hydrogen). Said curve was completely in accordance with the general knowledge of the person skilled in the art.

2. Thermal decomposition with foam formation a. Test tube experiment (see attached figure (photo) 1)

100 mg (powder) of borazane (see point I.l.a. above;

D ₅₀ = 50 μm) were introduced by means of a spatula into a test tube. The powder introduced was slightly compressed by means of a spatula and the level reached by the upper surface of the compacted powder was raised: it represented a height of 1 cm in the tube (see the line on the tube of the figure 1).

Said glass tube, containing the packed powder, was then introduced into an oil bath heated to 100 ° C. and left in said bath for 3 hours.

At the end of these 3 hours, the tube was taken out of the bath and the level of the powder within it was again measured. It was then 5 cm (even a little more on the edges), well above the 1 cm starting (see the line). There was therefore 400% expansion (see Table 1 below). The formation of foam is visualized in Figure 1 attached: photograph of the tube out of the bath, with the line indicating the level before heating. b. Test bench experience

. Device used (see appended FIG. 2): on the test bench, there is essentially a reaction chamber (= decomposition chamber) 1, a control valve (not shown in the figure) and a storage chamber of the hydrogen generated (not shown in the figure). Said reaction chamber 1 has a tubular shape; it is equipped with ignition means 3 arranged upstream of its part la (see below). The ignition means 3 consist of a Chromel film (alloy: Ni 90%, Cr 10%), of diameter 0.57 mm, shaped as a spiral with 14 turns of 6 mm in diameter; its extended length is equal to 30 cm; its resistance is about 2 Ω (at room temperature). The loading 2 of powder is very schematically represented.

Said reaction chamber 1 is made of a transparent material, to allow visualization of the reaction during the test.

Said chamber 1 comprises two parts:

a first part la (upstream part) which contain the load 2 (presently borazane (powder)) and the ignition means 3 of said load 2; and

a second part lb (downstream part) called filtration (hydrogen reservoir);

said first and second portions being separated by a first filter element 4a and its support grid 5a. At the distal end (downstream) of said second portion 1b of the chamber 1, there is a second filter element 4b supported by another support grid 5b.

There are provided, associated with said chamber 1, means (not shown) for measuring the (upstream) pressure PI in said first portion 1a of the chamber 1 and for measuring the (downstream) pressure P2 in said second portion 1b of the chamber 1 downstream of said second filter element 4b. The clogging of the filter element 4a inexorably results in a pressure P1> P2.

. Experiment carried out: 10.3 g of borazane (see point IIb above, D ₅₀ = 340 mm) were introduced into chamber 1a. The decomposition of said borazane was initiated by the heated wire 3. The operating time of the hot wire was 40 s. The hot gases released by the thermal decomposition of the first lit layers of the load 2 traveled through said load 2. Their path and the exothermicity of the decomposition favored the propagation of the decomposition in the entire mass of the load 2.

It has been observed the appearance of a liquid phase.

The pressures recorded (during the first 100 seconds

(100 seconds of operation, after, the borazane being consumed, the pressure and the temperature decrease)) showed a significant difference: PI (pressure (in the first part of the chamber 1) maximum of 50 bars> P2 (pressure ( in the second part 1b of the chamber 1 downstream of the second filter element 4b) maximum of 10 bars), attesting to the clogging of the filter element 4a, this clogging has been confirmed at dismantling, a large amount of residues (in the form one block) was glued to said filter element 4a. III. Invention (and Comparative Trials): Borazane Blends / Formulation Adiuvant

Dry route preparation (in solid / solid phase) and tests

A. Mixtures of powders

at. Preparation of powder mixtures al. In a 100 ml flask equipped with a screw cap, were introduced 4.43 g of (powder) borazane (see point Ila above, D ₅₀ = 50 mm), then 0.785 g of silica powder type A.

The flask is closed and introduced into a Turbulat powder mixer (planetary stirrer). The powders were stirred for 10 min at maximum power. The mixture (intimate of said powders) obtained is thus a mixture 85/15 (% by weight) of borazane (50 Mm) / silica (hydrophilic, 200 nm). a2. The procedure was the same (in III.lAal above) to prepare different powder mixtures, varying the level and / or the nature of the formulation adjuvant: see Table 1 below. after. a3. The procedure was the same with 6.7 g of sieved borazane (at 500 μm, see point Ilb above, D ₅₀ = 340 mm) and 1.18 g of type A silica. powders) obtained is a mixture 85/15 (% by weight) of borazane (340 Mm) / silica (hydrophilic, 200 nm). b. Tests bl. DSC

DSC ("Differential Scanning Calorimetry") was performed on a sample of the mixture prepared in III. 1. A. al. above (borazane / silica), under the conditions indicated above (in II.1.) for borazane alone (sample of 1.4705 mg, placed in an aluminum crucible, kept under argon sweep ( 100 ml / min), and raised from 30 to 300 ° C at 5 ° C / min).

The curve obtained showed a first endotherm at 112.20 ° C.

(corresponding to the melting of borazane) followed by a first exotherm which began at 115.12 ° C (corresponding to the beginning of the decomposition of borazane with release of the first mole of hydrogen). Said first exotherm was itself followed by a second exotherm (corresponding to the release of the second mole of hydrogen).

The DSC curve of the mixture "borazane + formulation adjuvant of the invention" does not show a significant difference with that of borazane alone. It is thus demonstrated that the presence of said formulation adjuvant of the invention does not modify the thermal stability of borazane. b2. Thermal decomposition b2 ^f : Experiments in test tube

. 100 mg of the mixture prepared in III. A. al. above was taken and introduced by means of a spatula into a test tube. These 100 mg were slightly packed with a spatula and the level reached by the upper surface of the packed powder was raised: it represented a height of 1 cm in the tube (see the reference line in the figures 3A and 3B). The glass tube, containing the packed powder mixture, was then introduced into an oil bath heated to 100 ° C and left in said bath for 3 hours.

The tube was then removed from the bath and the level of the powder was again measured.

This was always 1 cm (= 0% expansion): there was therefore no foaming in the tube, as visualized in the photographs (Figures 3A and 3B). Of course, the photograph of FIG. 3B is considered more particularly in parallel with that of FIG.

. The same procedure was followed with the mixtures prepared in III. 1. A. a2. above. For mixtures that are not mixtures of the invention, a strong expansion (expressed in%) was observed.

. The results obtained are shown in Table 1 below.

TABLE 1

* see point I.2.a. above

2 * see point I.2.b. above

3 * see point I.2.c. above

4 * see point I.2.d. above. b2 ": Test bench experience

The mixture prepared in III.lAa3. was (completely) introduced into the reaction chamber 1 which was placed on the test bench. The operation was the same as that described in II.2. b. above.

The decomposition of the mixture (= the decomposition of the borazane contained in said mixture, according to the first two stages of hydrogen liberation) was total, with a gas yield equal to 60.9 mol / kg of borazane for a theoretical yield of 64.5 mol / kg (or equal to 51.7 mol / kg of borazane + silica mixture for a theoretical yield of 54.8 mol / kg).

The observation made during the decomposition in the first part of the chamber 1 has not shown passage of the load 2 in liquid form.

The decomposition products of the borazane / silica mixture were in the form of a fine powder and were also found on the first filter element 4a. However, they did not clog it.

The decomposition was maintained over the first 100 seconds with a pressure (in the first part of the chamber 1) PI maximum of 10 bar, then a slow decrease in temperature and pressure within said first part la of said chamber 1.

During the first 100 seconds of operation, there has been no pressure difference (of hydrogen generated) between the first portion 1a of the chamber 1 and the second portion 1b thereof (P2 = P1), which shows that the filter element 4a placed between the parts 1a and 1b of the chamber 1 had not clogged.

B. Pastilles

at. Preparation of pellets

5 g of powder mixture remaining (from the 5.215 g prepared in III.lAal above, from which samples were taken) were used. the sample for the implementation of the DSC and the 100 mg for implementing the thermal decomposition test tube) to make pellets. It should be verified that when it is pelletized, the powder mixture behaves as before it has been pelletized (ie to verify that the pelletizing operation (borazane + formulation adjuvant) does not modify the decomposition of borazane).

Ten pellets of 500 mg were obtained as follows: 500 mg of the powder mixture was introduced into a mold with a diameter of 13 mm. These 500 mg of powder were then subjected to a compression of 800 kg / cm ² . The operation was repeated 10 times.

The pellets obtained had, for a diameter of 13 mm, a thickness of 10 mm. b. Test (see figures (photos) 4A and 4B appended)

A pellet (see the photograph of Figure 4A) was introduced into a 50 mL stainless steel reactor. Said reactor was then closed and then subjected to an argon sweep to remove the air contained therein.

At the end of said sweep, the argon inlet was closed and the reactor, completely closed, was left under 1 bar of argon.

The reactor was then heated for 3 hours at 150 ° C and then cooled to 25 ° C. The pressure was controlled: after 3 hours, it reached 12.3 bars (which reflected the formation of hydrogen).

The quantity of hydrogen recovered corresponded entirely to the theoretical calculation. It has thus been confirmed that the formulation adjuvant of the invention in no way disturbs the decomposition of borazane (co-formulated with said adjuvant in the form of pellets).

After cooling, the reactor was opened to check the state of the pellet having undergone the temperature cycle (having delivered the expected hydrogen by decomposition of the borazane it contained). Figures 4A and 4B show, respectively, the pellet before and after its thermal decomposition. They show that said pellet (borazane + formulation adjuvant of the invention) retained its shape during the decomposition of the borazane it contained ... that there was therefore no spreading of liquid borazane (in the bottom of the reactor) during the decomposition thereof (in the presence of said formulation adjuvant). Said pellet, after thermal decomposition, was very friable.

Claims

1. A solid product, containing borazane in its composition, capable of generating hydrogen by thermal decomposition of said borazane, characterized in that its composition consists essentially of said borazane, present in the form of grains, and at least 10% mass of silica, present in the form of grains whose median diameter (D ₅₀ ) is less than one micron.

2. Solid product according to claim 1, characterized in that the grains said silica have a median diameter (D ₅ o) less than or equal to 700 nm, preferably a median diameter (D ₅₀ ) less than or equal to 500 nm.

3. Solid product according to claim 1 or 2, the composition, expressed in percentages by weight, consists essentially of:

70 to 90% borazane, and

4. Solid product according to any one of claims 1 to 3, the composition, expressed in percentages by weight, consists essentially of:

85 to 90% borazane, and

A solid product according to any one of claims 1 to

4, characterized in that the grains of said borazane have a median diameter (D ₅₀ ) of 1 mm to 1 mm.

A solid product according to any one of claims 1 to

5, characterized in that it is in the form:

- a powder,

- a granule,

- a tablet, a disc, or

- a block.

7. Process for the preparation of a solid product according to any one of claims 1 to 6, characterized in that it comprises:

the mixture of a borazane powder and a silica powder whose median diameter (D ₅ o) of the grains is less than one micron, said silica powder representing at least 10% by weight of the mixture of the powders, for obtaining, by the dry route, the solid product in powder form,

- Followed, optionally, a granulation step of said solid product obtained in powder form, for obtaining the solid product in the form of granules;

said solid product in the form of a powder or said solid product in the form of granules being optionally compressed to obtain the solid product in the form of at least one disc or at least one tablet, or

said solid product in the form of a powder or said solid product in the form of granules being optionally compressed to obtain the solid product in the form of at least one block.

8. Process for generating hydrogen by thermal decomposition of borazane, characterized in that it comprises the thermal decomposition of a solid product according to any one of claims 1 to 6 and / or a solid product prepared according to claim 7.

9. A method according to claim 8, characterized in that it is implemented to supply a hydrogen fuel cell proton exchange membrane.