A process and apparatus for the production of hydrogen

Abstract

This disclosure relates broadly to methods and apparatus for preparing hydrogen, and particularly to methods and apparatus for preparing hydrogen from silicon. The method for preparing hydrogen disclosed herein includes: providing an alkaline solution; and reacting the alkaline solution with a silicon material to prepare hydrogen. The apparatus for preparing hydrogen disclosed herein includes: a caustic dissolution vessel; one or more hydrogen reaction vessels for preparing hydrogen; a first solid-liquid separator; a precipitation vessel; and a second solid-liquid separator.

Description

Technical Field

[0001] This disclosure relates broadly to methods and apparatus for preparing hydrogen, and particularly to methods and apparatus for preparing hydrogen from silicon. Prior Technology

[0002] Any discussion of prior art in the entire specification should not be construed as an admission that such prior art is well known or constitutes part of the ordinary general knowledge in the field.

[0003] Currently, fossil fuels are the world's primary energy source. However, fossil fuels are a finite resource, and their use has significant adverse environmental impacts. With dwindling fossil fuel reserves and increasing environmental concerns, the world will gradually move towards renewable and clean energy sources. Hydrogen is expected to play a crucial role in future energy production.

[0004] Currently, most industrial hydrogen (~95%) is produced from fossil fuels through steam reforming or partial oxidation of methane and coal gasification. Small amounts of hydrogen are also produced through other methods, such as biomass gasification or water electrolysis.

[0005] The inventors in this case have developed an alternative method for preparing hydrogen from silicon materials. Summary of the Invention

[0006] The first-state sample provides a method for preparing hydrogen, the method comprising: (a) Provide alkali solution; and (b) Reacting an alkaline solution with a silicon material to prepare hydrogen.

[0007] The method may further include: (c) Separating the solid from the alkali solution.

[0008] The method may further include: (d) Separation of dissolved silicates from alkaline solution. Step (d) can be carried out by mechanical vapor recompression.

[0009] The method may further include: (d1) Precipitate dissolved silicates from alkaline solution to provide precipitated silicates; and (e) Separate the precipitated silicate from the alkaline solution.

[0010] This method may further include the collection, compression, and storage of hydrogen.

[0011] The alkaline solution in steps (a) and / or (b) may have a temperature between about 20 °C and about 80 °C.

[0012] The alkaline solution in step (a) and / or step (b) may have a temperature below 0 °C.

[0013] Step (a) may include providing an alkaline solution by mixing water and hydroxide.

[0014] Excess heat generated during the mixing of water and hydroxide can be recovered.

[0015] Excess heat generated during the mixing of water and hydroxide can be recovered and transferred to a thermoelectric generator.

[0016] Hydroxides can be water-soluble hydroxides.

[0017] Water-soluble hydroxides may be one or more of ammonium hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, or cesium hydroxide.

[0018] Step (a) may include providing an alkaline solution by mixing water with (i) one or more of ammonium hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide or cesium hydroxide, and (ii) calcium hydroxide.

[0019] Water can be tap water, distilled water, wastewater, or natural surface water.

[0020] Silicon materials can be porous. In some specific instances, silicon materials are microporous or nanoporous.

[0021] In some specific instances, silicon materials are silicon-containing alloys.

[0022] Silicon materials can be pure or substantially pure silicon.

[0023] Silicon materials can have a high surface area.

[0024] After step (b), water vapor and / or caustic vapor of hydrogen can be removed.

[0025] The solid separated in step (c) may be silicon, silicon oxide, or silicate.

[0026] Step (d1) can be carried out by adding calcium hydroxide and / or calcium chloride to the alkaline solution.

[0027] After any one or more of steps (c), (d) and (e), at least a portion of the alkali solution may be reused in step (b).

[0028] After step (e), at least part or all of the alkali solution may be concentrated to provide water and concentrated alkali solution, wherein the concentrated alkali solution is reused in step (b).

[0029] Excess heat generated during step (b) can be recovered.

[0030] Excess heat generated during step (b) can be recovered and transferred to a thermoelectric generator.

[0031] Steps (c) and / or (e) may include filtration, centrifugation, or sedimentation.

[0032] Steps (c) and / or (e) may include the use of a hydrocyclone separator.

[0033] This method can be a batch, semi-batch, continuous, or semi-continuous method.

[0034] Steps (a) and (b) can be performed in individual containers.

[0035] Steps (b) and (c) can be performed in individual containers.

[0036] Steps (c) and (d1) can be performed in individual containers.

[0037] Steps (d1) and (e) can be performed in individual containers.

[0038] The second state provides an apparatus for preparing hydrogen, the apparatus comprising: A caustic dissolving container having one or more inlets suitable for introducing water and hydroxides, and outlets for discharging the alkali solution; One or more hydrogen reaction vessels for producing hydrogen, having one or more inlets suitable for introducing silicon material and alkaline solution, outlets for discharging the produced hydrogen and outlets for discharging the alkaline solution, wherein the one or more hydrogen reaction vessels are in fluid communication with the caustic dissolution vessel; A first solid-liquid separator, which is in fluid communication with one or more hydrogen reaction vessels, is used to remove unreacted solids from an alkaline solution received from one or more hydrogen reaction vessels; A precipitation container, in fluid communication with a first solid-liquid separator, is used to precipitate dissolved silicates from the alkaline solution received from the first solid-liquid separator; and The second solid-liquid separator, which is in fluid communication with the precipitation vessel, is used to separate precipitated silicates from the alkaline solution received from the precipitation vessel.

[0039] Caustic dissolving containers and one or more hydrogen reaction containers may be made of alkali-resistant materials such as stainless steel.

[0040] Caustic dissolving containers may include cooling jackets and / or one or more cooling components such as coils within the container.

[0041] Caustic dissolving containers may contain stirrers, such as mechanical stirrers, for example.

[0042] One or more hydrogen reaction vessels may contain stirrers, such as mechanical stirrers, for example.

[0043] One or more hydrogen reactors may include condensers to condense the water vapor produced by one or more hydrogen reactors.

[0044] Settling containers may contain agitators, such as mechanical agitators, for example.

[0045] The device may further include a thermoelectric generator.

[0046] The thermoelectric generator can receive heat from one or both of the caustic dissolution vessel and one or more hydrogen reaction vessels.

[0047] The first and second solid-liquid separators may be hydrocyclones, filters, centrifuges, or settling tanks.

[0048] The device may further include a conduit between the second solid-liquid separator and the caustic dissolving container for conveying the caustic solution back to the caustic dissolving container.

[0049] The apparatus may further include one or more pumps for moving the alkali solution through the apparatus.

[0050] The third state sample provides hydrogen, obtained using the same method as the first state sample. [definition] []

[0051] The following are some definitions that may help in understanding the narrative of this disclosure. These definitions are intended as general definitions and should in no way limit the scope of this disclosure to these terms, but are proposed for a better understanding of the narrative below.

[0052] Throughout this specification, unless otherwise required, the term "comprise" or variations thereof, such as "comprises" or "comprising," shall be understood to imply the element, integer, or step, or a group of elements, integers, or steps, but not to exclude any other element, integer, or step, or a group of elements, integers, or steps.

[0053] The terms “a” and “an” are used in this text to refer to one or more (i.e., at least one) grammatical object of the article. For example, “an element” refers to one or more elements.

[0054] Throughout the instruction manual, the term "approximately" is understood to refer to a range of numbers that a person skilled in the art would consider equivalent to the values ​​described throughout the text in order to achieve the same function or result.

[0055] Any numerical range described herein is intended to include all subranges with the same numerical precision contained within the range. For example, the range 1.0 to 5.0 is intended to include all subranges between (and inclusive of) the minimum value 1.0 and the maximum value 5.0, i.e., a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 5.0, such as 2.1 to 4.5. Any maximum numerical limit described herein is intended to include all lower numerical limits contained therein, and any minimum numerical limit described herein is intended to include all higher numerical limits contained therein. Simple Explanation of the Diagram

[0056] [Figure 1]: Schematic diagram of a method and apparatus according to a specific example of this disclosure.

[0057] [Figure 2]: Comparison of hydrogen production capabilities between porous silicon and non-porous solid silicon. Implementation

[0058] This disclosure provides a method for preparing hydrogen, the method comprising: (a) Provide alkali solution; and (b) Reacting an alkaline solution with a silicon material to prepare hydrogen.

[0059] The method may further include: (c) Separating the solid from the alkali solution.

[0060] The method may further include: (d) Separation of dissolved silicates from alkaline solution.

[0061] The method may further include: (d1) Precipitate dissolved silicates from alkaline solution to provide precipitated silicates; and (e) Separate the precipitated silicate from the alkaline solution.

[0062] This method involves the reaction of an alkaline solution with a silicon material to produce hydrogen. When sodium hydroxide is used to prepare the alkaline solution, the following reaction occurs in step (b): Si + 2H₂O → SiO₂ + 2H₂ (Equation 1) SiO₂ + 2NaOH → Na₂SiO₃ + H₂O (Equation 2)

[0063] In some specific instances, step (a) may include providing an alkaline solution by mixing water with a water-soluble hydroxide, such as, for example, ammonium hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide, or cesium hydroxide. The water may be wastewater (such as, for example, greywater), natural surface water (such as, for example, seawater, lake water, or rainwater), tap water, or distilled water.

[0064] The alkali solution in steps (a) and / or (b) preferably has a temperature between about 20 °C and about 80 °C. Alternatively, the alkali solution in steps (a) and / or (b) can have a temperature below 0 °C by using a caustic aqueous solution to lower the melting point; for an alkali solution containing 20% ​​NaOH, the eutectic melting point can be as low as -33.4 °C. This avoids the need for antifreeze when performing the method in cold environments.

[0065] The heat generated during the mixing of water and hydroxide can be used to raise the temperature of the alkali solution to the desired temperature, and excess heat can be recovered. In some specific instances, excess heat can be recovered and transferred to a thermoelectric generator, a heat exchanger, or other auxiliary units that utilize the heat.

[0066] The heat generated during the reaction of the alkali solution with the silicon material can be used to raise the temperature of the alkali solution in step (b) to the desired temperature, and excess heat can be recovered. In some specific examples, the excess heat can be recovered and transferred to a thermoelectric generator, a heat exchanger, or some other auxiliary unit that utilizes the heat. In other specific examples, excess heat generated in any part of the method can be recovered via a thermoelectric generator. In some specific examples, the silicon material is in the form of a porous silicon material. In other specific examples, the silicon material is in the form of a microporous silicon material or a nanoporous silicon material. In one specific example, the silicon is in the form of micron-sized microporous particles or tiny nanoporous particles.

[0067] Silicon materials can be silicon-containing alloys, such as silicon-containing alloys having the formula SiX, where X is a transition metal or a post-transition metal. Preferably, the alloy contains at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% silicon. Impurities and / or dopants in the silicon material can advantageously enhance reactivity.

[0068] In some specific instances, the silicon material is pure or substantially pure silicon. The purity of silicon can be greater than 90%, greater than 95%, greater than 96%, greater than 97%, greater than 98%, greater than 99%, or greater than 99.5%.

[0069] The degree of reaction and kinetics of the system can be managed by controlling the pH, the amount of silicon material, the type and concentration of the caustic solution, and the reaction temperature.

[0070] In some specific instances, silicon materials possess one or more of the following properties: ● The specific surface area (SSA) determined by BET is at least 1.5 m² / g, 1.6 m² / g, 1.7 m² / g, 1.8 m² / g, 1.9 m² / g, 2.0 m² / g or 2.1 m² / g, or a surface area between about 2.0 m² / g and about 2.5 m² / g, or between about 2.0 m² / g and about 2.4 m² / g, or between about 2.0 m² / g and about 2.3 m² / g, or between about 2.0 m² / g and about 2.2 m² / g, or between about 2.1 m² / g and about 2.2 m² / g, or between about 1.9 m² / g and about 2.3 m² / g, or about 2.1 m² / g. ● It has one or more of the following polymer particle size distributions: D10 0.512 μm, D25 1.115 μm, D50 2.305 μm, D75 3.980 μm or D90 5.842 μm. ● The average pore volume is between about 0.004 mL / g and about 0.007 mL / g, or between about 0.005 mL / g and about 0.006 mL / g, or as high as about 0.01 mL / g. ● The average pore diameter (4V / A, obtained from BET) is between about 0.5 nm and about 50 nm, or between about 0.5 nm and about 25 nm, or between about 1 nm and about 20 nm, or between about 10 nm and about 15 nm, or between about 11 nm and about 15 nm, or between about 12 nm and about 15 nm, or between about 12 nm and about 14 nm, or between about 11 nm and about 13 nm, or between about 11 nm and about 12 nm. ● SSA, as determined by BET, ranges from approximately 0.85 m² / g to approximately 2.5 m² / g, and is correlated with particle sizes from 0.5 mm to 5 mm.

[0071] WO2018019266 describes a method for preparing porous silicon that can be used in the methods disclosed herein, the disclosure of which is incorporated herein by reference in its entirety.

[0072] Figure 2 shows a comparison of the hydrogen production capabilities between porous silicon (denoted as "EAT-Si") and non-porous solid silicon (denoted as Solid-Si).

[0073] EAT-Si silicon has the following characteristics: ● The SSA measured by BET is approximately 2.1 m² / g, with the following particle size distribution: D10 0.512 μm, D25 1.115 μm, D50 2.305 μm, D75 3.980 μm or D90 5.842 μm. ● The SSA content determined by BET was approximately 0.85 m² / g, with a particle size of 5 mm.

[0074] Following the reactions shown in Equations 1 and 2 above, unreacted solids, such as silica, undissolved SiO₂x, and silicates (if the concentration in the liquid exceeds the solubility limit), present in the alkaline solution are removed using suitable solid-liquid separation techniques (such as, for example, filtration, centrifugation, or sedimentation). Solid-liquid separation techniques are well known to those skilled in the art. In one specific example, a hydrocyclone is used for separation.

[0075] In step (d1), the dissolved silicate is subsequently precipitated and then separated from the alkaline solution. Precipitation can be achieved by adding one or more compounds that convert the silicate to a water-insoluble form. In some specific examples, precipitation is achieved by adding calcium hydroxide or calcium chloride according to the following equations 3 and 4: Na₂SiO₃ + 2Ca(OH)₂ → 2NaOH + Ca₂SiO₄(s) + H₂O (Equation 3) Na₂SiO₃ + 2CaCl₂ + H₂O → 2NaCl + Ca₂SiO₄(s) + 2HCl (Equation 4)

[0076] Both reactions result in the formation of solid Ca₂SiO₄, which precipitates due to its insolubility in water. Precipitation involves low cost and low energy consumption, thus contributing to the overall efficiency of the method.

[0077] After any one or more of steps (c), (d), and (e), at least a portion of the alkali solution can be reused in step (b). Alternatively, after step (e), at least a portion or all of the alkali solution can be concentrated to provide water and concentrated alkali solution, which is then reused in step (b). This reuse of the alkali solution improves process efficiency by conserving water and hydroxides and also avoids the need for further treatment.

[0078] In some specific instances, calcium hydroxide is provided in the alkaline solution of step (a). Although the hydrogen generation kinetics and efficiency are slightly higher in step (b) (due to the higher hydroxide concentration resulting from the dissolved Ca(OH)₂), a longer post-hydrogenation incubation time is required to complete the reaction in Equation 3, which is limited by the Ca(OH)₂ dissolution kinetics. The resulting Ca₂SiO₄ precipitate can be removed by simple solid-liquid separation as described in steps (c) and / or (e).

[0079] The inclusion of calcium hydroxide in the alkaline solution of step (a) has two advantages: (i) the ability to recover aqueous NaOH at or near its original concentration without further concentration (e.g., as described in

[0077] ), and (ii) operation under zero liquid addition, since all water and NaOH are recovered and recycled as shown in Equation 3. The latter is well-suited for operation under aqueous conditions. Furthermore, because water always contains dissolved NaOH, it remains liquid even at temperatures below zero (as described in

[0064] ), thus allowing the reaction to proceed under such conditions.

[0080] In an alternative specific example, the alkali solution is neutralized in step (d1). This can be achieved by dividing the alkali solution into a first solution and a second solution, adding Ca(OH)₂ to the first solution and CaCl₂ to the second solution. The first and second solutions contain equimolar amounts of NaOH (Equation 3) and HCl (Equation 4), respectively, which can combine to neutralize each other (NaOH + HCl → NaCl + H₂O).

[0081] The method may further include collecting, compressing, and storing the hydrogen produced in step (b). In some specific instances, water vapor and / or caustic vapor of the hydrogen may be removed after step (b).

[0082] Hydrogen is highly flammable and readily forms explosive mixtures with air and oxygen. Therefore, the transportation of hydrogen is problematic. The methods disclosed herein allow for the safe on-site preparation of hydrogen for a given application, eliminating the need for transportation. These methods are also environmentally friendly, as they do not produce toxic byproducts. In fact, the main byproduct of the methods (silicates) can be used in many industries, to name just a few, such as for use as absorbents, food additives, refractories, and fertilizer additives. This increases the commercial value of the methods.

[0083] This disclosure also provides an apparatus for preparing hydrogen, the apparatus comprising: A caustic dissolving container having one or more inlets suitable for introducing water and hydroxides, and outlets for discharging alkali solutions; One or more hydrogen reaction vessels for producing hydrogen, having one or more inlets suitable for introducing silicon material and alkaline solution, outlets for discharging the produced hydrogen and outlets for discharging the alkaline solution, wherein the one or more hydrogen reaction vessels are in fluid communication with a caustic dissolution vessel; A first solid-liquid separator, which is in fluid communication with one or more hydrogen reaction vessels, is used to remove unreacted solids from the alkaline solution received from one or more hydrogen reaction vessels; A precipitation container, fluidly connected to a first solid-liquid separator, is used to precipitate dissolved silicates from an alkaline solution received from the first solid-liquid separator; and The second solid-liquid separator, which is in fluid communication with the precipitation vessel, is used to separate precipitated silicates from the alkaline solution received from the precipitation vessel.

[0084] Figure 1 shows an example of a method and apparatus according to a specific example of this disclosure.

[0085] Apparatus 100 includes a caustic dissolving vessel 101 having an inlet 102 for introducing water and an inlet 103 for introducing hydroxide. The caustic dissolving vessel may be made of an alkali-resistant material such as stainless steel and may be equipped with a cooling jacket (not shown). The caustic dissolving vessel 101 further includes an outlet 104 for discharging alkali solution and a mechanical stirrer 105. The caustic dissolving vessel 101 is in fluid communication with a hydrogen reactor vessel 106 via a conduit 107. The hydrogen reactor vessel 106 may be made of an alkali-resistant material such as stainless steel and may be equipped with a cooling jacket (not shown). The hydrogen reactor vessel 106 may also include a condenser (not shown). The hydrogen reactor vessel 106 includes an inlet 108 for introducing alkali solution received from the caustic dissolving vessel 101 and an inlet 109 for introducing silica material. The hydrogen reactor vessel 106 further includes an outlet 110 for discharging hydrogen produced in the hydrogen reactor vessel 106, an outlet 112 for discharging alkali solution, and a mechanical stirrer 111. A first solid-liquid separator 113 is in fluid communication with a hydrogen reactor vessel 106 via conduit 114. A settling vessel 115 is in fluid communication with the first solid-liquid separator 113 via conduit 116 and further includes a mechanical stirrer 117. A second solid-liquid separator 118 is in fluid communication with the settling vessel 115 via conduit 119. The second solid-liquid separator 118 is in fluid communication with a caustic dissolving vessel 101 via conduit 120. The first and second solid-liquid separators may be hydrocyclones, filters, centrifuges, or settling tanks. The apparatus 100 further includes a thermoelectric generator 121. The apparatus 100 may further include a pump (not shown) located between one or more of the following components: the caustic dissolving vessel and the hydrogen reactor vessel, the hydrogen reactor vessel and the first solid-liquid separator, and the settling vessel and the second solid-liquid separator, for moving the alkali solution between these components of the apparatus.

[0086] In operation, water and hydroxide are introduced into the caustic dissolving vessel 101 via inlets 102 and 103, respectively. The resulting mixture is stirred to dissolve the hydroxide, providing alkali and heat. The heat typically maintains the alkali in the caustic dissolving vessel 101 at approximately 50 °C (although the temperature and reaction kinetics can be adjusted accordingly). Excess heat is transferred to the thermoelectric generator 121. The alkali flows out from outlet 104, through conduit 107, and through inlet 108 to the hydrogen reactor vessel 106. Silicon material is introduced into the hydrogen reactor vessel 106 via inlet 109. Reactions as described in Equations 1 and 2 then occur, forming hydrogen, silica, and silicates. The prepared hydrogen is released from the hydrogen reactor vessel 106 via outlet 110 and can then be compressed and stored. The resulting alkali, according to Equations 1 and 2, flows out from outlet 112 and through conduit 114 to the first solid-liquid separator 113. Solid-liquid separator 113 separates unreacted silica material and / or undissolved silica from the alkali solution. The alkali solution is then conveyed to precipitation vessel 115 via conduit 116. Dissolved silicates are precipitated in precipitation vessel 115, for example, by adding calcium hydroxide and / or calcium chloride to the alkali solution. The alkali solution containing the precipitated silicates is then conveyed to a second solid-liquid separator 118 via conduit 119, where the precipitated silicates are separated from the alkali solution. The resulting alkali solution is then conveyed back to the caustic dissolution vessel via conduit 120. Alternatively, in a specific embodiment, the alkali solution may be conveyed back to hydrogen reactor vessel 106.

[0087] In some specific instances, the method can be implemented using batch, semi-batch, continuous, or semi-continuous methods. [Example] []

[0088] The disclosure is further described below with reference to the following non-limiting embodiments.

[0089] The following examples describe a method for producing 150 kg of hydrogen per day using porous silicon.

[0090] Water and NaOH were mixed under vigorous stirring in a 1.41 m³ stainless steel tank equipped with a cooling jacket to obtain a hydroxide concentration of 8.9 M. The alkali solution yield was maintained at 470 L / h, with the exothermic dissolution (0.11 kWh per liter of solution) used to maintain the alkali solution at a temperature of approximately 50 °C. Excess heat of up to 51.7 kWh was transferred to a thermoelectric generator.

[0091] The caustic solution was transferred to a pair of hydrogen reaction vessels with a total capacity of 941 L. The method was operated in a semi-continuous manner according to the following procedure:

[0092] Controlled dispensing of silicon (90 kg per batch) ensures hydrogen release over a 1.5-hour reaction period. The net exothermic reaction (23.8 kWh / kg H₂) causes the reaction medium in the hydrogen reactor to self-heat and maintain optimal operating conditions at approximately 80 °C. Excess heat is transferred to a thermoelectric generator. The hydrogen reactor also includes an internal condenser in the top space to condense the saturated water vapor (up to 15 kg per batch) accompanying the hydrogen stream exiting the reactor. The system's operating temperature is largely dependent on ambient temperature.

[0093] Unreacted silicon and / or undissolved silicon dioxide were separated from the alkali solution using a hydrocyclone. The recovered alkali solution contained dissolved Na₂SiO₃ (up to a concentration of approximately 3.5 M). The Na₂SiO₃ was precipitated using calcium hydroxide, resulting in the formation of Ca₂SiO₄. To process the alkali solution, a volume ratio of saturated calcium hydroxide solution to clarified solution of 300 was required to ensure complete precipitation of Na₂SiO₃. The precipitation process was carried out at a low stirring speed to promote the formation of large Ca₂SiO₄ precipitates. The Ca₂SiO₄ precipitate was separated from the alkali solution using a hydrocyclone (1.5 m³). The resulting caustic solution (approximately 0.032 M) was further concentrated to approximately 8.9 M before being recycled back to the stainless steel tank.

[0094] Those skilled in the art will understand that the invention described herein may have variations and modifications other than those specifically described, without departing from the scope of the invention. All such variations and modifications that are obvious to those skilled in the art should be considered to fall within the scope of the technical concept of the invention as broadly described above. It should be understood that the invention includes all such variations and modifications. The invention also includes all steps and features individually or jointly referenced or pointed to in the specification, and any and all combinations of two or more of such steps or features.

Claims

1. A method for preparing hydrogen, the method comprising: (a) providing an alkaline solution; (b) reacting the alkaline solution with a silicon material to prepare hydrogen; (c) separating a solid from the alkaline solution; (d) separating dissolved silicates from the alkaline solution; (d1) precipitating the dissolved silicates from the alkaline solution to provide precipitated silicates; and (e) separating the precipitated silicates from the alkaline solution; wherein after any one or more of steps (c), (d), or (e), at least a portion of the alkaline solution is reused in step (b).

2. The method of claim 1, wherein step (d) is carried out by mechanical vapor recompression.

3. The method as described in claim 1 or 2 further includes collecting, compressing and storing hydrogen.

4. The method of claim 1 or 2, wherein the alkaline solution in step (a) and / or (b) has a temperature between about 20 °C and about 80 °C.

5. The method of claim 1 or 2, wherein the alkaline solution in step (a) and / or step (b) has a temperature below 0 °C.

6. The method of claim 1 or 2, wherein step (a) comprises providing the alkali solution by mixing water and hydroxide.

7. The method of claim 6, wherein excess heat generated during the mixing of water and hydroxide is recovered.

8. The method of claim 7, wherein excess heat is recovered and transferred to a thermoelectric generator.

9. The method of claim 6, wherein the hydroxide is a water-soluble hydroxide.

10. The method of claim 9, wherein the water-soluble hydroxide is one or more of ammonium hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide or cesium hydroxide.

11. The method of claim 1 or 2, wherein step (a) comprises providing the alkaline solution by mixing water with (i) one or more of ammonium hydroxide, lithium hydroxide, sodium hydroxide, potassium hydroxide or cesium hydroxide, and (ii) calcium hydroxide.

12. The method of claim 6, wherein the water is tap water, distilled water, wastewater or natural surface water.

13. The method of claim 1 or 2, wherein the silicon material is microporous silicon or nanoporous silicon.

14. The method of claim 13, wherein the silicon material is in the form of microporous particles with a micrometer size.

15. The method of claim 1 or 2, wherein the silicon material has one or more of the following properties: ● a specific surface area of ​​at least 1.5 m² / g as determined by BET; ● a polymer particle size distribution of one or more of the following: D10 0.512 μm, D25 1.115 μm, D50 2.305 μm, D75 3.980 μm or D90 5.842 μm; ● a specific surface area of ​​at least 0.85 m² / g as determined by BET, and a particle size of 0.5 mm to 5 mm; ● an average pore volume of up to about 0.01 mL / g; and ● an average pore diameter (4V / A, obtained by BET) between about 0.5 nm and about 50 nm.

16. The method of claim 1 or 2, wherein the silicon material is a silicon-containing alloy.

17. The method of claim 1 or 2, wherein the silicon material is pure or substantially pure silicon.

18. The method of claim 1 or 2, wherein after step (b), water vapor and / or caustic vapor of hydrogen are removed.

19. The method of claim 1 or 2, wherein the solid separated in step (c) is silicon, silicon oxide or silicate.

20. The method of claim 1 or 2, wherein step (d1) is carried out by adding calcium hydroxide and / or calcium chloride to the alkaline solution.

21. The method of claim 1 or 2, wherein after step (e), at least a portion or all of the alkali solution is concentrated to provide water and concentrated alkali solution, wherein the concentrated alkali solution is reused in step (b).

22. The method of request item 1 or 2, wherein excess heat generated during step (b) is recovered.

23. The method of claim 22, wherein excess heat is recovered and transferred to a thermoelectric generator.

24. As in request item 1 or 2, the method may be a batch, half-batch, continuous, or semi-continuous method.

25. An apparatus for producing hydrogen, the apparatus comprising: a caustic dissolving vessel having one or more inlets suitable for introducing water and hydroxide, and an outlet for discharging an alkaline solution; one or more hydrogen reaction vessels for producing hydrogen having one or more inlets suitable for introducing a silicon material and the alkaline solution, an outlet for discharging the produced hydrogen, and an outlet for discharging the alkaline solution, the one or more hydrogen reaction vessels for producing hydrogen being in fluid communication with the caustic dissolving vessel; a first solid-liquid separator in fluid communication with the one or more hydrogen reaction vessels for producing hydrogen for removing unreacted solids from the alkaline solution received by the one or more hydrogen reaction vessels for producing hydrogen; a precipitation vessel in fluid communication with the first solid-liquid separator for precipitating dissolved silicates from the alkaline solution received by the first solid-liquid separator; and a second solid-liquid separator in fluid communication with the precipitation vessel for separating precipitated silicates from the alkaline solution received by the precipitation vessel.

26. The apparatus of claim 25, wherein the caustic dissolution vessel and the one or more hydrogen reaction vessels for hydrogen production are made of alkali-resistant material.

27. The apparatus of claim 25 or 26, wherein the caustic dissolving container includes a cooling sleeve and / or one or more cooling components within the caustic dissolving container.

28. The apparatus of claim 25 or 26, wherein the caustic dissolving container includes a stirrer.

29. The apparatus of claim 25 or 26, wherein the one or more hydrogen production hydrogen reaction vessels may include a stirrer.

30. The apparatus of claim 25 or 26, wherein the one or more hydrogen production reactors include a condenser for condensing water vapor produced by the one or more hydrogen production reactors.

31. The apparatus of claim 25 or 26, wherein the sedimentation vessel includes a stirrer.

32. The apparatus of claim 25 or 26 further includes a thermoelectric generator.

33. The apparatus of claim 32, wherein the thermoelectric generator receives heat from one or both of the caustic dissolution vessel and the hydrogen reaction vessel for hydrogen production.

34. The apparatus of claim 25 or 26, wherein the first and second solid-liquid separators are hydrocyclones, filters, centrifuges or settling tanks.

35. The apparatus of claim 25 or 26 further includes a conduit between the second solid-liquid separator and the caustic dissolving container for conveying the caustic solution back to the caustic dissolving container.

36. The apparatus of claim 25 or 26 further includes one or more pumps for moving the alkali solution through the apparatus.

37. Hydrogen obtained by any one of claims 1 to 24.

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