HYDROGEN CARRIER COMPOUNDS

Abstract

The present invention relates to novel branched hydrogen carrier compounds and so to a method for producing hydrogen from said branched hydrogen carrier compounds. The present invention also relates to a process for producing and for regenerating said branched hydrogen carrier compounds.

Claims

1. Hydrogen carrier compound selected amongst TABLE-US-00004 R.sub.nSiA.sup.1.sub.4?n Si.sub.2A.sup.1.sub.6 A.sup.1CH.sub.2SiA.sup.1.sub.3 R.sub.nSiA.sup.2.sub.4?n Si.sub.2A.sup.2.sub.6 A.sup.2CH.sub.2SiA.sup.2.sub.3 R.sub.nSiA.sup.3.sub.4?n Si.sub.2A.sup.3.sub.6 A.sup.3CH.sub.2SiA.sup.3.sub.3 CH.sub.2(SiA.sup.1.sub.3).sub.2 Si(SiA.sup.1.sub.3).sub.4 A.sup.1H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.1 CH.sub.2(SiA.sup.2.sub.3).sub.2 Si(SiA.sup.2.sub.3).sub.4 A.sup.2H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.2 CH.sub.2(SiA.sup.3.sub.3).sub.2 Si(SiA.sup.3.sub.3).sub.4 A.sup.3H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.3 wherein R can be any of hydrogen or a radical having up to 50 carbon atoms chosen amongst alkyl, aryl and aralkyl, n can be any of 0, 1,2 or 3, m is any integer comprised between 1 and 100, wherein A.sup.1 is selected from ##STR00028## wherein A.sup.2 is selected from ##STR00029## wherein X in A.sup.1 or A.sup.2 can be any halide, wherein A.sup.3 is selected from ##STR00030## and wherein m in A.sup.1, A.sup.2 or A.sup.3 is any integer comprised between 1 and 100, or a mixture of two or more of these compounds, with the proviso that the hydrogen carrier compound is not 2,2,4,4-tetrasilylpentasilane or 2,2-disilyltrisilane.

2. Hydrogen carrier compound according to claim 1 and selected amongst H.sub.nSiA.sup.1.sub.4-n; H.sub.nSiA.sup.2.sub.4-n; H.sub.nSiA.sup.3.sub.4-n; (CH.sub.3).sub.nSiA.sup.1.sub.4-n; (CH.sub.3).sub.nSiA.sup.2.sub.4-n; (CH.sub.3).sub.nSiA.sup.3.sub.4-n; CH.sub.2(SiA.sup.1.sub.3).sub.2; CH.sub.2(SiA.sup.2.sub.3).sub.2; CH.sub.2(SiA.sup.3.sub.3).sub.2; Si.sub.2A.sup.1.sub.6; Si.sub.2A.sup.2.sub.6; Si.sub.2A.sup.3.sub.6; Si(SiA.sup.1.sub.3).sub.4; Si(SiA.sup.1.sub.3).sub.4; Si(SiA.sup.1.sub.3).sub.4; or a mixture of two or more of these compounds, with A.sup.1, A.sup.2 and A.sup.3 selected from TABLE-US-00005 A.sup.1 A.sup.2 A.sup.3 wherein n can be any of 0, 1, 2 or 3, and X can be any halide.

3. Hydrogen carrier compound according to claim 1 and selected amongst ##STR00038## ##STR00039##

4. Hydrogen carrier compound according to claim 1 and selected amongst ##STR00040## ##STR00041## or a mixture of two or more of these compounds.

5. Hydrogen carrier compound according to claim 1 and selected amongst ##STR00042## ##STR00043## or a mixture of two or more of these compounds.

6. Hydrogen carrier compound according to claim 1 and selected amongst ##STR00044## or a mixture of two or more of these compounds.

7. Hydrogen carrier compound according to claim 1 and selected amongst ##STR00045## or a mixture of two or more of these compounds.

8. Hydrogen carrier compound according to claim 1 and selected amongst ##STR00046## wherein m is any integer comprised between 1 and 100, or a mixture of two or more of these compounds.

9. Hydrogen carrier compounds according to claim 1, characterised by a molecular weight ranging from 152 to 10 212 g/mol.

10. Method for the production of hydrogen by hydrolytic oxidation of 2,2,4,4-tetrasilylpentasilane or 2,2,4,4,6,6-hexasilylheptasilane or 2,2-disilyltrisilane or any of the hydrogen carrier compounds of claim 1 or a mixture of two or more of these compounds in the presence of a proton source.

11. Method according to claim 10 wherein the proton source is water.

12. Method for the production of hydrogen according to claim 10 wherein the proton source/[(SiH) plus (SiSi) bonds] molar ratio is comprised between 1 and 10, or between 1 and 3.

13. Method for the production of hydrogen according to claim 10 in a reaction mixture which is characterised in that the branched hydrogen carrier compound, corresponding silicate-type by-products, the hydrogen, the proton source, an optional hydrogen release initiator which favours the hydrolytic oxidation of the branched hydrogen carrier compound, an optional catalyst which increases the kinetic of the hydrolytic oxidation of the branched hydrogen carrier compound, and optional solvents represent at least 90 percent by weight of the said reaction mixture.

14. Method for the production of hydrogen by hydrolytic oxidation of any of the hydrogen carrier compounds of claim 1 characterised in the use of UV light irradiation.

15. Use of a hydrogen carrier compound according to claim 1 or 2,2,4,4-tetrasilylpentasilane or 2,2,4,4,6,6-hexasilylheptasilane or 2,2-disilyltrisilane or a mixture of two or more of these compounds for the storage and transport of hydrogen and/or energy.

Description

[0138] FIG. 1

[0139] In an embodiment of the present invention, which is illustrated in with 3?x?36

[0140] FIG. 1, the process for the production or regeneration of the branched hydrogen carrier compound(s) comprises the following consecutive steps: [0141] either subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(a) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0142] mixing the silica compound and/or silicate compound with Si in step 1(b) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0143] subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(c) to produce silicon, [0144] Then [0145] Subjecting silicon to a halogenation step (2a) to produce R.sub.nSiX.sub.4-n [0146] Then [0147] Subjecting R.sub.nSiX.sub.4-n to a branching step (3) to produce R.sub.nSiA.sup.1.sub.4-n [0148] Optionally subjecting R.sub.nSiA.sup.1.sub.4-n to a halogenation step (4) to produce R.sub.nSiA.sup.2.sub.4-n [0149] Optionally subjecting R.sub.nSiA.sup.2.sub.4-n to a branching step (5) with x A.sup.- to produce R.sub.nSiA.sup.3.sub.4-n [0150] Optionally repeating the halogenation step (4) and/or branching step (5).

[0151] FIG. 2

[0152] In an embodiment of the present invention, which is illustrated in FIG. 2, the process for the production or regeneration of the branched hydrogen carrier compound(s) comprises the following consecutive steps: [0153] either subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(a) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0154] mixing the silica compound and/or silicate compound with Si in step 1(b) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0155] subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(c) to produce silicon, [0156] Then [0157] Subjecting silicon to a hydrochlorination step 2(c) to produce SiCl.sub.4 and mixing SiCl.sub.4 with Si to produce hexachlorodisilane Si.sub.2Cl.sub.6 [0158] Then [0159] Subjecting Si.sub.2C1.sub.6 to a branching step (3) to produce Si.sub.2A.sup.1.sub.6 [0160] Optionally subjecting Si.sub.2A.sup.1.sub.6 to a halogenation step (4) to produce Si.sub.2A.sup.2.sub.6 [0161] Optionally subjecting Si.sub.2A.sup.2.sub.6 to a branching step (5) to produce Si.sub.2A.sup.3.sub.6 [0162] Optionally repeating the halogenation step (4) and/or branching step (5).

[0163] FIG. 3

[0164] In an embodiment of the present invention, which is illustrated in FIG. 3, the process for the production or regeneration of the branched hydrogen carrier compound(s) comprises the following consecutive steps: [0165] either subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(a) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0166] mixing the silica compound and/or silicate compound with Si in step 1(b) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0167] subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(c) to produce silicon, [0168] Then [0169] Subjecting silicon to a methylhalogenation step 2(b) to produce MeSiX.sub.3 [0170] Then [0171] Subjecting MeSiX.sub.3 to a halogenation step 2(d) to produce XCH.sub.2SiX.sub.3 [0172] Then [0173] Subjecting XCH.sub.2SiX.sub.3 to a branching step (3) with to produce A.sup.1CH.sub.2SiA.sup.1.sub.3 [0174] Optionally subjecting A.sup.1CH.sub.2SiA.sup.1.sub.3 to a halogenation step (4) to produce A.sup.2CH.sub.2SiA.sup.2.sub.3 [0175] Optionally subjecting A.sup.2CH.sub.2SiA.sup.2.sub.4-n to a branching step (5) to produce A.sup.3CH.sub.2SiA.sup.3.sub.3 [0176] Optionally repeating the halogenation step (4) and/or branching step (5).

[0177] FIG. 4

[0178] In an embodiment of the present invention, which is illustrated in FIG. 4, the process for the production or regeneration of the branched hydrogen carrier compound(s) comprises the following consecutive steps: [0179] either subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(a) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0180] mixing the silica compound and/or silicate compound with Si in step 1(b) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0181] subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(c) to produce silicon, [0182] Then [0183] Subjecting silicon to a hydrohalogenation step 2(a) to produce HSiX.sub.3 [0184] Then [0185] Subjecting HSiX.sub.3 to a alkylhalogenation step 2(e) for the production of CH.sub.2(SiX.sub.3).sub.2 [0186] Then [0187] Subjecting CH.sub.2(SiX.sub.3).sub.2 to a branching step 3 to produce CH.sub.2(SiA.sup.13).sub.2 [0188] Optionally subjecting CH.sub.2(SiA.sub.3).sub.2 to a halogenation step 4 to produce CH.sub.2(SiA.sup.2.sub.3).sub.2 [0189] Optionally subjecting CH.sub.2(SiA.sup.2.sub.3).sub.2 to a branching step 5 to produce CH.sub.2(SiA.sup.3.sub.3).sub.2 [0190] Optionally repeating the halogenation step (4) and/or branching step (5).

[0191] FIG. 5

[0192] In an embodiment of the present invention, which is illustrated in With 36?108

[0193] FIG. 5, the process for the production or regeneration of the branched hydrogen carrier compound(s) comprises the following consecutive steps: [0194] either subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(a) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0195] mixing the silica compound and/or silicate compound with Si in step 1(b) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0196] subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(c) to produce silicon, [0197] Then [0198] Subjecting silicon to a hydrochlorination step 2(c) to produce SiCl.sub.4 and mixing SiCl.sub.4 with Si to produce hexachlorodisilane Si.sub.2Cl.sub.6 [0199] Then [0200] Subjecting hexachlorodisilane Si.sub.2Cl.sub.6 to a disproportionation step 2(f) to produce Si(SiCl.sub.3).sub.4 [0201] Then [0202] Subjecting Si(SiCl.sub.3).sub.4 to a branching step 3 to produce Si(SiA.sup.13).sub.4 [0203] Optionally subjecting Si(SiA.sup.13).sub.4 to a halogenation step 4 to produce Si(SiA.sup.2.sub.3).sub.4 [0204] Optionally subjecting Si(SiA.sup.2.sub.3).sub.4 to a branching step 5 to produce Si(SiA.sup.3.sub.3).sub.4 [0205] Optionally repeating the halogenation step (4) and/or branching step (5).

[0206] FIG. 6

[0207] In an embodiment of the present invention, which is illustrated in FIG. 6, the process for the production or regeneration of the branched hydrogen carrier compound(s) comprises the following consecutive steps: [0208] either subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(a) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0209] mixing the silica compound and/or silicate compound with Si in step 1(b) to produce SiO and subjecting SiO to a hydrogenation step to produce silicon, or [0210] subjecting the silica compound and/or silicate compound to a hydrogen-assisted reduction step 1(c) to produce silicon, [0211] Then [0212] Subjecting silicon to a hydrochlorination step 2(g) to produce H.sub.2SiX.sub.2 [0213] Then [0214] Subjecting H.sub.2SiX.sub.2 to a controlled hydrolysis step 2(h) to produce XH.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2X [0215] Then [0216] Subjecting XH.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2X to a branching step 3 to produce A.sup.1H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.1 [0217] Optionally subjecting A.sup.1H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.1 to a halogenation step 4 to produce A.sup.2H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.2 [0218] Optionally subjecting A.sup.2H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.2 to a branching step 5 to produce A.sup.3H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.3 [0219] Optionally repeating the halogenation step (4) and/or branching step (5).

Step 1(a)Reduction of Silica/Silicate Type Products to Form Silicon Monoxide (SiO)

[0220] Any appropriate method can be used for the reduction of silica/silicate type products to form silicon monoxide (SiO). In an embodiment according to the present invention, said reduction is performed in one stage. In an embodiment according to the present invention, said reduction is performed at high temperatures, for example above 1500? C.

[0221] For example, in an embodiment according to the present invention, the silica/silicate compound is reduced in the presence of hydrogen gas for the production of SiO as exemplified by the following equation: SiO.sub.2+H.sub.2->SiO+H.sub.2O Other gas(es) can optionally be employed in addition to hydrogen, e.g. an inert gas such as argon or nitrogen. The reaction can be performed either with both reactants in the gas phase, in a plasma jet for example, or in a heterogeneous manner by reacting the solid silica/silicate compound with hydrogen gas, in a fluidised bed reactor for example.

[0222] Reaction in the gas phase is preferred. The H.sub.2/SiO.sub.2 molar ratio is preferably comprised between 0.1 and 1000, for example between 1 and 50. A heat source is preferably used; any source of heat can be selected, e.g. hot oil, steam, electric arc technology, induction heating, microwave, hot filament, plasma technology. In an embodiment, a cooling source may be used too to trap desired species; any appropriate cooling source can be selected e.g. water cooler, oil cooler, brine cooler, special heat exchanger . . . . Heat may advantageously be recovered to heat up reactors from other steps, and/or to heat up plant facilities, and/or to produce electricity etc. . . . . In addition to the main reaction according to this step 2(a) which leads to compound SiO, other compounds may also be produced, e.g. H.sub.2SiO, and/or HSi(O)(OH), and/or H.sub.2Si(OH).sub.2, and/or SiH.sub.4, and/or Si; the production of Si is considered as a side reaction, i.e. represented by the full reduction reaction leading to elemental silicon, as exemplified by the following equation: SiO.sub.2+2 H.sub.2->Si+2H.sub.2O. Said Si, when produced, can advantageously be used in the following disproportionation step 2(b).

Step 1(b)Elemental Silicon Mediated Disproportionation of Silica/Silicate Type Products to Form Silicon Monoxide (SiO)

[0223] Any appropriate method can be used for the disproportionation step 1(b) to produce SiO. For example, in an embodiment according to the present invention, the step 1(b) consists in the reduction of the silica/silicate compound in the presence of elemental silicon for the production of SiO as exemplified by the following equation: SiO.sub.2+Si->2 SiO. The Si/SiO.sub.2 molar ratio is preferably comprised between 0.5 and 1.5, for example between 0.9 and 1.1. Any source of elemental silicon can be used, e.g. metallurgical, photovoltaic or electronic grade silicon. In an embodiment according to the present invention, elemental silicon is preferably produced by full reduction of the silica/silicate compound by hydrogen as exemplified by the following equation: SiO.sub.2+2 H.sub.2->Si.

[0224] In an embodiment according to the present invention, a catalyst may be added to the SiO.sub.2/Si mixture in order to facilitate the said disproportionation. Any appropriate catalyst can be used to facilitate the said disproportionation, for example a metal, an ore or an organic compound.

[0225] In an embodiment according to the present invention, an additive may be added to the SiO.sub.2/Si mixture in order to facilitate the said disproportionation. For example, organic binders, fillers etc. . . . can be used. In an embodiment according to the present invention, said disproportionation is performed at high temperatures, for example above 1500? C.

[0226] In an embodiment according to the present invention, said disproportionation is performed under reducing atmosphere, for example in the presence of hydrogen gas.

[0227] Other gas(es) can optionally be employed, e.g. an inert gas such as argon or nitrogen. Since this reaction is endothermic, a heat source is preferably used; any source of heat can be selected, e.g. hot oil, steam, electric arc technology, induction heating, microwave, hot filament, plasma technology.

Step 1(c)Reduction of Silica/Silicate Type Products to Form Si

[0228] In an embodiment according to the present invention, there is provided a method for the reduction of the silica/silicate compound in the presence of hydrogen gas for the production of elemental silicon. The elemental silicon produced can be either metallurgical or photovoltaic grade. Other gas(es) can optionally be employed in addition to hydrogen, e.g. an inert gas such as argon or nitrogen. Since the reaction of reduction of silica/silicate compounds by hydrogen is endothermic, a heat source is required; any source of heat can be selected, e.g. electric arc technology, induction heating, microwave, hot filament, plasma technology. Plasma is particularly preferred; for example, a corresponding plasma technology can advantageously comprise a plasma torch allowing to create a plasma jet. The plasma jet is preferably made from hydrogen gas, with or without additional gas(es) (such as, for example, argon), going through electrodes. Silica can be introduced into the hydrogen plasma jet under vacuum prior to react in the gas phase with hydrogen at a temperature comprised between 2000 and 20 000? K to form silicon and water. Silicon is then condensed and recovered as a solid.

[0229] The reduction reaction of silica/silicate compounds by hydrogen gas produces water as by-product. The formed water can advantageously be used as chemical reactant, and/or as heating source for other utilities and/or can be transformed in an electrolyser to reform hydrogen gas and/or can be used to run a steam turbine to produce electricity.

Step 2(a): RnSiX4-n Formation

[0230] In an embodiment according to the present invention, there is provided a method for R.sub.nSiX.sub.4-n formation. The hydrohalogenation or the alkyhalogenation of the elemental silicon are preferred. In an embodiment according to the present invention, there is provided a method for the hydrohalogenation of the elemental silicon for the production of halosilanes, e.g. monohalosilane (H.sub.3SiX), dihalosilane (H.sub.2SiX.sub.2), trihalosilane (HSiX.sub.3) and/or tetrahalosilane (SiX.sub.4), or a mixture of these compounds (X being a halide). Elemental silicon used in the hydrohalogenation step is preferably originating from the previous step of the process. Hydrogen chloride (HCl) is a preferred hydrogen halide source for the said hydrohalogenation of the elemental silicon into monochlorosilane (H.sub.3SiCl), dichlorosilane (H.sub.2SiCl.sub.2) and/or trichlorosilane (HSiCl.sub.3) and/or tetrachlorosilane (SiCl.sub.4); said hydrogen chloride can advantageously be an aqueous solution or a gas. In the case where hydrogen chloride is used, a process can be designed in order to redistribute HSiCl.sub.3, which is the main product of the silicon hydrochlorination reaction, through a catalysed dismutation reaction into a mixture of H.sub.3SiCl, H.sub.2SiCl.sub.2, HSiCl.sub.3 and SiCl.sub.4. SiCl.sub.4 can advantageously be recycled via reduction by hydrogen gas in the presence of elemental silicon into a mixture of H.sub.2SiCl.sub.2, HSiCl.sub.3 and SiCl.sub.4. Elemental silicon used in the SiCl.sub.4 reduction step is preferably originating from the previous step of the process. Hydrogen gas used in the SiCl.sub.4 reduction step can advantageously be a by-product of another step of the process, for e.g. from the elemental silicon hydrohalogenation step mentioned above.

[0231] In an embodiment according to the present invention, there is provided a method for the formation of alkylhalide silane from the elemental silicon e.g. MeSiX.sub.3, Me.sub.2SiX.sub.2, Me.sub.3SiX, SiX.sub.4. Methylchloride (MeCl) is a preferred alkyl halide source for the said alkylhalogenation of the elemental silicon. When MeCl is used as alkylhalide source MeSiCl.sub.3, Me.sub.2SiCl.sub.2, Me.sub.3SiCl, SiMe.sub.4 compounds are obtained. In an embodiment according to the present invention, a catalyst may be used to enhance the performances of the said alkylhalogenation, for example a metal, a metal immobilized on a support, an ore or an organic compound. Copper (Cu) is a preferred catalyst for the said reaction. The catalyst may optimally contain promoter metals to facilitate the reaction e.g. zinc, Tin magnesium, calcium, arsenic, bismuth, cadmium.

Step 2(c): Silicon Chlorosilylation Step

[0232] In an embodiment according to the present invention, there is provided a method for the chlorosilylation of silicon for the production of hexachlorodisilane. Elemental silicon used is preferably originating from the previous step of the process. Tetrachlorosilane used in the silicon chlorosilylation step is preferably originating from the previous step 2(a) of FIGS. 1 or 4. In an embodiment according to the present invention, a catalyst may be used to enhance the performances of the said chlorosilylation. Amines are preferred catalyst for the said reaction, more preferably tertiary amines e.g. trimethylamine, triethylamine, tri-n-butylamine.

Step 2(d): Methyltrihalosilane Halogenation Step

[0233] In an embodiment according to the present invention, there is provided a method for the halogenation of methyltrihalosilane. Gaseous chlorine (Cl.sub.2) is preferred halide source for the production of chloromethyltrichlorosilane. Free-radical halogens may be generated to enhance the performance of the said halogenation. UV irradiation, visible irradiation, or high temperature (300-400? C.) are preferred for free-radical halogens generation.

Step 2(e): Hydrohalosilylation of Halomethyl

[0234] In an embodiment according to the present invention, there is provided a method for the hydrohalosilylation of halomethyl for the production of bis(trihalosilyl)methane. Chloromethyl is a preferred halomethyl source and trichlorosilane is a preferred halosilane source for the production of bis(trichlorosilyl)methane. In an embodiment according to the present invention, a catalyst may be used to enhance the performances of the said hydrochlorosilylation. Amines are preferred catalyst for the said reaction, more preferably tertiary amines e.g. triethylamine, tri-n-butylamine.

Step 2(f): Disproportionation of Hexachlorodisilane

[0235] In an embodiment according to the present invention, there is provided a method for the disproportionation of hexachlorodisilane in the presence of amine to produce dodecachloroneopentasilane (neo-Si.sub.5Cl.sub.12). Hexachlorodisilane used is preferably originating from the step 2(e) of the process of FIG. 4. Tertiary amines are preferred for the disproportionation reaction, more preferably trimethylamine (NMe3).

Step 2(g): Hydrohalogenation of Elemental Silicon

[0236] In an embodiment according to the present invention, there is provided a method for the hydrohalogenation of the elemental silicon for the production of dihalosilane (H.sub.2SiX.sub.2). Elemental silicon used in the hydrohalogenation step is originating from the previous step of the process. Hydrogen chloride (HCl) is a preferred hydrogen halide source for the said hydrohalogenation of the elemental silicon into dichlorosilane (H.sub.2SiCl.sub.2); said hydrogen chloride can advantageously be an aqueous solution or a gas. In the case where hydrogen chloride is used, a process can be designed in order to redistribute HSiCl.sub.3, which is the main product of the silicon hydrochlorination reaction, through a catalysed dismutation reaction into a mixture of H.sub.3SiCl, H.sub.2SiCl.sub.2, HSiCl.sub.3 and SiCl.sub.4. Several subsequent separation and purification steps may allow to isolate pure H.sub.2SiCl.sub.2 (or generically H.sub.2SiX.sub.2 with X being a halogen) which can be directly consumed in the next step 2(h) of the process.

Step 2(h): Controlled Hydrolysis of Halosilanes

[0237] In an embodiment according to the present invention, there is provided a method for the controlled hydrolysis of halosilanes by water to produce/regenerate the siloxane hydrogen carrier compounds. In the case where H.sub.2SiCl.sub.2 is used as halosilane source for the said controlled hydrolysis, HCl is formed as by-product. The formed HCl can advantageously be reinjected in the step 4 of the process. In the case where H.sub.2SiF.sub.2 is used as halosilane source for the said controlled hydrolysis, HF is formed as by-product. Said hydrolysis can advantageously be performed under operating conditions characterised in that the molar ratio [H.sub.2O/H.sub.2SiX.sub.2] is inferior to 0.99, preferably inferior to 0.98; in an embodiment of the present invention, this ratio is superior to 0.2, preferably superior to 0.25, for example higher than 0.3. Said hydrolysis can advantageously be performed under controlled atmosphere, for example atmosphere of argon, nitrogen . . . Said hydrolysis can advantageously be performed in the presence of a solvent. Any solvent can be used, e.g. diethylether, tetrahydrofuran, methyltetrahydrofuran, cyclohexane, methylcyclohexane, dichloromethane, pentane, heptane, toluene, decahydronaphtalene; pentane and dichloromethane being particularly preferred. Said hydrolysis can advantageously be performed under operating conditions characterised in that the volume of solvent per weight of H.sub.2SiX.sub.2 is inferior to 10, preferably inferior to 8. Said hydrolysis can advantageously be performed under operating conditions characterised in that the speed of addition of water into the reacting medium is higher than 0.05 mL/min, preferably higher than 0,075 mL/min. Said hydrolysis can advantageously be performed under operating conditions characterised in that the volume of solvent per weight of water is lower than 50 mL/g, preferably lower than 45 mL/g. Said hydrolysis is exothermic, the temperature of the reacting medium is thus preferably maintained during the reaction between ?50 and +100? C., for example between ?50 and +50? C., more preferably between ?40 and 30? C.

[0238] An illustrative example of an equation showing the chemical equilibrium occurring during the step 2(h) of the present invention is depicted hereafter

[0239] y?(m+1) H.sub.2SiCl.sub.2+(y?m) H.sub.2O.fwdarw.y Cl(H.sub.2SiO).sub.mSiH.sub.2Cl+2?(y?m) HCl wherein y and m are integers, y?(m+1) being the number of H.sub.2SiCl.sub.2 molecules in the reacting medium, (y?m) the number of water molecules in the reacting mixture, y the number of polymer chain of composition Cl(H.sub.2SiO).sub.mSiH.sub.2Cl with m being the number of (H.sub.2SiO) repeating units and 2?(y?m) the number of HCl molecules produced.

Step 3: Branching Step:

[0240] In an embodiment according to the present invention, there is provided a method for branching R.sub.nSiX.sub.4-n, Si.sub.2Cl.sub.6, XCH.sub.2SiX.sub.3, CH.sub.2(SiX.sub.3).sub.2, Si(SiCl.sub.3).sub.4, XH.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2X, with a silyl anion to form, respectively, R.sub.nSiA.sub.4-n, Si.sub.2A.sup.1.sub.6, A.sup.1CH.sub.2SiA.sup.1.sub.3, CH.sub.2(SiA.sup.1.sub.3).sub.2, Si(SiA.sup.1.sub.3).sub.4, A.sup.1H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.1. The silyl anion can be generated with the help a chemical base, for example, by SiH.sub.3 abstraction from neopentasilane (Si.sub.5H.sub.12), 2,2,4,4-tetrasilylpentasilane (Si.sub.9H.sub.20), 2,2,5,5-tetrasilylhexasilane (Si.sub.10H.sub.22) or by SiCl.sub.3 abstraction from dodecachloroneopentasilane Si(SiCl.sub.3).sub.4 or by Si(OEt) abstraction from dodecamethoxyneopentasilane (Si.sub.5(OEt).sub.12), or by chloride abstraction from Cl(H.sub.2SiO).sub.mSiH.sub.2Cl. In the cases where SiH.sub.3 is abstracted from neopentasilane (Si.sub.5H.sub.12), 2,2,4,4-tetrasilylpentasilane (Si.sub.9H.sub.20), 2,2,5,5-tetrasilylhexasilane (Si.sub.10H.sub.22), the silyl anions (SiH.sub.3).sub.3Si, (SiH.sub.3).sub.3SiSi(H.sub.2)(SiH.sub.3).sub.2Si, (SiH.sub.3).sub.3SiSiH.sub.2SiH.sub.2 (SiH.sub.3).sub.2Si are preferably obtained, respectively. In the case where SiCl.sub.3 is abstracted from dodecachloroneopentasilane Si(SiCl.sub.3).sub.4 the silyl anion Si(SiCl.sub.3).sub.3 is preferably obtained. In the case where Si(OEt) is abstracted from dodecamethoxyneopentasilane (Si.sub.5(OEt).sub.12), the silyl anion Si(Si(OEt).sub.3).sub.3 is preferably obtained. Methyl lithium (MeLi), potassium ter-butoxide(tBuOK), sodium ter-butoxide or lithium ter-butoxide are preferred bases for generation of silyl anions. In the case where Cl is abstracted from Cl(H.sub.2SiO).sub.mSiH.sub.2Cl, the silyl radical Cl(H.sub.2SiO).sub.mSiH.sub.2* is formed. Any appropriate chloride abstraction agent can be used. For example elemental sodium can be used as chloride abstraction agent.

Step 4: Haloaenation Step (Optional)

[0241] In an embodiment according to the present invention, there is provided a method for the halogenation of R.sub.nSiA.sup.1.sub.4-n, Si.sub.2A.sup.1.sub.6, A.sup.1CH.sub.2SiA.sup.1.sub.3, CH.sub.2(SiA.sup.1.sub.3).sub.2, Si(SiA.sup.1.sub.3).sub.4, AlH.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.1. Hydrogen chloride (HCl) or tin tetrachloride (SnCl.sub.4) are preferred halide sources for the said halogenation. In the case where tin tetrachloride is used, hydrogen chloride is formed and can advantageously be recycled for step 2(a) or 2(c). In the case where hydrogen chloride is used, 1,2,3-trichloroneopentasilane is formed as a by-product and can be used to form branched polysilane.

Step 5: Branchinl Step (Optional)

[0242] In an embodiment according to the present invention, there is provided a method for branching of R.sub.nSiA.sup.2.sub.4-n, Si.sub.2A.sup.2.sub.6, A.sup.2CH.sub.2SiA.sup.2.sub.3, CH.sub.2(SiA.sup.2).sub.2, Si(SiA.sup.2).sub.4, A.sup.2H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.2 with a silyl anion to form R.sub.nSiA.sup.3.sub.4-n, Si.sub.2A.sup.3.sub.6, A.sup.3CH.sub.2SiA.sup.3.sub.3, CH.sub.2(SiA.sup.3.sub.3).sub.2, Si(SiA.sup.3).sub.4, Si(SiA.sup.3.sub.3).sub.4, A.sup.3H.sub.2SiO(H.sub.2SiO).sub.mSiH.sub.2A.sup.3. The silyl anion can be generated with the help a chemical base, for example, by SiH.sub.3 abstraction from neopentasilane (Si.sub.5H.sub.12), 2,2,4,4-tetrasilylpentasilane (Si.sub.9H.sub.20), 2,2,5,5-tetrasilylhexasilane (Si.sub.10H.sub.22) or by SiCl.sub.3 abstraction from dodecachloroneopentasilane Si(SiCl.sub.3).sub.4 or by Si(OEt) abstraction from dodecamethoxyneopentasilane (Sis(OEt).sub.12), or by chloride abstraction from Cl(H.sub.2SiO).sub.mSiH.sub.2Cl. In the cases where SiH.sub.3 is abstracted from neopentasilane (Si.sub.5H.sub.12), 2,2,4,4-tetrasilylpentasilane (Si.sub.9H.sub.20), 2,2,5,5-tetrasilylhexasilane (Si.sub.10H.sub.22), the silyl anions (SiH.sub.3).sub.3Si, (SiH.sub.3).sub.3SiSi(H.sub.2)(SiH.sub.3).sub.2Si, (SiH.sub.3).sub.3SiSiH.sub.2SiH.sub.2 (SiH.sub.3).sub.2Si are preferably obtained, respectively. In the case where SiCl.sub.3 is abstracted from dodecachloroneopentasilane Si(SiCl.sub.3).sub.4 the silyl anion Si(SiCl.sub.3).sub.3 is preferably obtained. In the case where Si(OEt) is abstracted from dodecamethoxyneopentasilane (Si.sub.5(OEt).sub.12), the silyl anion Si(Si(OEt).sub.3).sub.3.sup.- is preferably obtained. Methyl lithium (MeLi), potassium ter-butoxide(tBuOK), sodium ter-butoxide or lithium ter-butoxide are preferred bases for generation of silyl anions. In the case where Cl is abstracted from Cl(H.sub.2SiO).sub.mSiH.sub.2Cl, the silyl radical Cl(H.sub.2SiO).sub.mSiH.sub.2* is formed. Any appropriate chloride abstraction agent can be used. For example, elemental sodium can be used as chloride abstraction agent.