SYSTEM AND METHOD FOR CARBON CAPTURE AND UTILIZATION

Abstract

A system and a method for converting captured carbon dioxide (CO.sub.2) into hydrogen (H.sub.2) by using metallic iron or metallic magnesium in anaerobic process are described. In a first step, the CO.sub.2 can be absorbed in an alkaline solution such as NaOH and a soluble bicarbonate is formed. In a second step, the soluble bicarbonate HCO.sub.3 is converted into H.sub.2 by reacting it with zero valent metal, like metallic Fe (powder) or scrap Fe or Magnesium ribbon in anaerobic ambient conditions. Metal carbonate, like siderite, is created on the outer surface of Fe(.sup.0) and can be separated by the alkaline solution, which is recycled in the first reaction to be used for CO.sub.2 absorption. Exposing the separated siderite to weak acid, either citric acid or oxalic acid, zero valent metal is obtained, which is recycled in the second reaction. Alternatively, the siderite can be used as a raw material in the steel industry or cement industry or commercialized as an iron scrap. The generated H.sub.2 can be directly used for energy purposes or can be directed to another reactor comprising also bicarbonate solution and mix hydrogenotrophic methanogens to be converted into methane (CH.sub.4) or to a bioreactor comprising homoacetogenic bacteria to be converted into carboxylic acids, like acetic acid (CH.sub.3COOH). Alternatively, the reaction with Fe(.sup.0) or Mg(.sup.0), bicarbonate solution, CO.sub.2 and hydrogenotrophic methanogens for the production of CH.sub.4 can take place in one and same bioreactor.

Claims

1. A process for capturing and converting carbon dioxide (CO.sub.2), the process comprising: absorbing a flux of gaseous carbon dioxide (CO.sub.2) in an aqueous alkaline solution comprising an alkali metal hydroxide, wherein the carbon dioxide (CO.sub.2) reacts with the alkali metal hydroxide to form a bicarbonate, obtaining a bicarbonate solution, converting the bicarbonate solution into hydrogen (H.sub.2), wherein said bicarbonate in the bicarbonate solution reacts with a zero valent metal species under anaerobic conditions to produce said hydrogen gas (H.sub.2) and an exhaust alkaline solution, wherein a solid metal carbonate is produced on the surface of the zero valent metal species as by-product, and separating said metal carbonate and obtaining an aqueous alkaline solution, said aqueous alkaline solution being recycled in the absorbing of the flux of gaseous carbon dioxide in the aqueous alkaline solution.

2. (canceled)

3. The process of claim 1, wherein said aqueous alkaline solution is an alkaline solution containing NaOH with a concentration in a range between 0.1M to 1.3M, preferably with a concentration of 0.9M.

4. The process of claim 1, wherein said bicarbonate solution has a pH in a range between 7 and 8.

5. The process of claim 1, wherein said zero valent metal species is selected from a group comprising metallic Fe, scrap Fe, metallic Mg, Mg ribbon.

6. The process of claim 1, wherein said solid metal carbonate is Fe carbonate or Mg carbonate.

7. (canceled)

8. The process of claim 1, wherein converting the bicarbonate solution into hydrogen (H.sub.2) further comprises treating said separated metal carbonate with either citric acid or oxalic acid to obtain zero valent metal, wherein said zero valent metal is recycled.

9. The process of claim 1, further comprising directing said hydrogen gas H.sub.2 to a second reactor comprising a bicarbonate solution with Hydrogenotrophic methanogens to produce methane (CH.sub.4).

10. The process of claim 1, further comprising directing said hydrogen gas H.sub.2 to a second reactor comprising a bicarbonate solution with Homoacetogenic bacteria to produce acetic acid (CH.sub.3COOH).

11. The process of claim 1, wherein said converting the bicarbonate solution into hydrogen (H.sub.2) occurs in one and same reactor comprising a bicarbonate solution including zero valent metal species and Hydrogenotrophic methanogens to produce methane (CH.sub.4).

12. An apparatus for capturing and converting carbon dioxide (CO.sub.2), the apparatus comprising: a first reactor comprising a first inlet module for gaseous carbon dioxide, a second inlet module for an aqueous alkaline solution comprising an alkali metal hydroxide, at least one outlet module configured to dissolve the gaseous carbon dioxide in the aqueous alkaline solution comprising an alkali metal hydroxide such that the carbon dioxide reacts with the alkali-metal hydroxide to form a bicarbonate, a second reactor comprising an inlet module for the bicarbonate solution and at least one outlet module, wherein said second reactor is operatively connected to said first reactor and is configured to bring in contact the bicarbonate solution with a zero valent metal species under anaerobic condition to form a reaction mixture of H.sub.2, solid metal carbonate and aqueous alkaline solution, wherein said second reactor comprises a liquid/solid separation module configured to separate the reaction mixture into a regenerated aqueous alkaline solution and a solid metal carbonate, wherein said regenerated aqueous alkaline solution is recycled in the first reactor.

13. (canceled)

14. The apparatus of claim 12, further comprising a third reactor having an inlet module and at least one outlet module, said third reactor being configured to receive Fe carbonate from the second reactor, and bring in contact said Fe carbonate with either citric acid or oxalic acid to form zero valent Fe, wherein said zero valent Fe is recycled in the second reactor.

15. (canceled)

16. (canceled)

17. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] For a better understanding of the present invention, preferred embodiments, which are intended purely by way of example and are not to be construed as limiting, will now be described with reference to the attached drawings, where:

[0032] FIG. 1 is a diagram representing a first embodiment of the method of capturing carbon dioxide according to an aspect of the present invention.

[0033] FIG. 2 is a diagram representing a second embodiment of the method of capturing carbon dioxide according to another aspect of the present invention.

[0034] FIG. 3 is a diagram representing a third embodiment of the method of capturing carbon dioxide according to an aspect of the present invention.

[0035] FIG. 4. Production of H.sub.2 (mmol)/Fe(kg) from Fe.sup.(0) (50 gr/L) in solution (a) flushed with N.sub.2, (b) flushed with CO.sub.2 and (c) with 10 gr NaHCO.sub.3/L flushed with CO.sub.2.

[0036] FIG. 5a. Production of H.sub.2 (mmol)/Fe(kg) from Fe.sup.(0) (25 g/L) in solution (a) flushed with N.sub.2, (b) flushed with CO.sub.2, (c) with 25 gr NaHCO.sub.3/L flushed with CO.sub.2 and (d) with 50 gr NaHCO.sub.3/L flushed with CO.sub.2. Initial pH=7.3.

[0037] FIG. 5b. Production of H.sub.2 (%) from Fe.sup.(0) (25 g/L) in solution (a) flushed with N.sub.2, (b) flushed with CO.sub.2, (c) with 25 gr NaHCO.sub.3/L flushed with CO.sub.2 and (d) with 50 gr NaHCO.sub.3/L flushed with CO.sub.2. Initial pH=7.3.

[0038] FIG. 6. Production of H.sub.2 (%) in solution with 10 gr NaHCO.sub.3/L, flushed with CO.sub.2 and with Fe.sup.(0) concentration of 5 gr.sup./L, 10 gr/L, 25 gr/L, 50 gr/L.

[0039] FIG. 7. Production of H.sub.2 (%) from Mg.sup.(0) (2 gr/L) in solution (a) exposed to air, (b) flushed with CO.sub.2, (c) with 10 gr NaHCO.sub.3/L flushed with CO.sub.2. Initial pH=6.

[0040] FIG. 8. Production of H.sub.2 (%) over time from Mg.sup.(0) (2 gr/L) in solution (a) flushed with CO.sub.2, (b) with 10 gr NaHCO.sub.3/L flushed with CO.sub.2, (c) with 20 gr NaHCO.sub.3/L flushed with CO.sub.2 and (d) 40 gr NaHCO.sub.3/L flushed with CO.sub.2. Initial pH=7.3.

[0041] FIG. 9. Production of H.sub.2 (%) over time from Fe.sup.(0) (50 gr/L) in solution of NaHCO.sub.3 previously formed from 0.35M NaOH and CO.sub.2. Initial pH=7.3.

[0042] FIG. 10. Gibbs free energy change ?G (KJ/mol) for metallic iron reaction with H.sub.2O and N.sub.2 at headspace and Gibbs free energy change ?G (KJ/mol) for metallic iron reaction with H.sub.2O, bicarbonate and CO.sub.2 at headspace.

DETAILED DESCRIPTION

[0043] The following discussion is presented to enable a person skilled in the art to make and use the invention. Various modifications to the embodiments will be readily apparent to those skilled in the art, without departing from the scope of the present invention as claimed. Thus, the present invention is not intended to be limited to the embodiments described therein, but it has to be accorded the widest scope consistent with the principles and features disclosed herein and defined in the appended claims.

[0044] According to FIG. 1, a process (100) of capturing and converting carbon dioxide (CO.sub.2) is described comprising a first step (101) by which carbon dioxide, CO.sub.2 (111) is absorbed in an alkaline solution (112), typically an aqueous solution comprising, for example, sodium hydroxide (NaOH), with a concentration comprised between 0.1M to 1.3M, preferably with a concentration of 0.9M, having an initial pH>10, and as a result soluble bicarbonate, NaHCO.sub.3 (113), having pH between 7-8, is formed, according for example to the following reaction formula (1):

NaOH (aq)+CO.sub.2.fwdarw.NaHCO.sub.3 (aq) 1)

[0045] Bicarbonate (NaHCO.sub.3), as reaction product, is stable and is hardly decarbonized. To overcome this problem, a second step (102) is used, wherein bicarbonate (113) is reacted with zero valent metal, for example commercial powder Fe, to produce hydrogen gas, H.sub.2 (114), according for example to the reaction formula (2):

Fe.sup.(0) (s)+HCO.sub.3 (aq)+H.sub.2O.fwdarw.FeCO.sub.3 (s)+H.sub.2 (g)+OH (aq). 2)

As shown in FIG. 1, in step (102) the bicarbonate solution reacts with metallic Fe.sup.(0) and H.sub.2 (114) is generated in the headspace. Also, the initial CO.sub.2 in the headspace is moved to the liquid solution and reacts with metallic Fe.sup.(0) therefore the headspace contains final >98% H.sub.2. As shown by the reaction formula (2), the second reaction step (102) comprises the production of solid metal carbonate, for example FeCO.sub.3, as by-product increasing alkalinity (OH.sup.?).

[0046] Instead of commercial powder Fe, a scrap-Fe can be used, which will significantly reduce the process cost; however, the reaction rate is 4-5 times slower but the final H.sub.2 concentration is still more than 98% Furthermore, Magnesium (Mg.sup.(0)) ribbon can be used instead of Fe.sup.(0) at a lower concentration than Fe, according to the reaction formula (3):

Mg.sup.(0) (s)+HCO.sub.3 (aq)+H.sub.2O.fwdarw.MgCO.sub.3 (s)+H.sub.2 (g)+OH (aq). 3)

[0047] Both the reactions (2) and (3) occur in anaerobic carbonate ambient conditions using metallic Fe (powder) or scrap Fe or Magnesium (Mg) ribbon.

[0048] According to an aspect of the present invention, the reaction become faster (higher reaction rate) in the production of H.sub.2 in the presence of high concentration of bicarbonate, for example (10-100 gr NaHCO.sub.3/L). Final gas composition comprises a Hydrogen (H.sub.2) concentration>98% after a reaction time ranging from 1 to 96 hours.

[0049] The rate and the yield of reaction depend on several conditions, comprising: [0050] Fe or Mg concentration, [0051] surface area of Fe or Mg, [0052] bicarbonate concentration, [0053] temperature, [0054] initial pH, [0055] initial headspace gas, [0056] agitation, [0057] initial pressure, [0058] headspace volume.

[0059] According to an embodiment of the present method, the reaction is more thermodynamically favorable (compared to the same conditions with oxygen or with low bicarbonate) and increases the reaction rate. Specifically using Fe.sup.(0) powder, the reaction rate (H.sub.2 mmol/Fe(kg).Math.(h)) of H.sub.2 is 1.5-2.5 higher at higher bicarbonate concentration compared to the condition without bicarbonate or to the use of only CO.sub.2. On the other hand, the reaction rate (H.sub.2 mmol/Fe(kg).Math.(h)) of high bicarbonate is 250-350 higher compared with the Fe.sup.(0) powder exposed to water and nitrogen (N.sub.2). For example, the reaction (2) is very slow when N.sub.2 is used instead of CO.sub.2. However, bicarbonate solution and CO.sub.2 in the gas phase (at initial conditions) result in a significantly higher H.sub.2 production rate than using water and CO.sub.2 in the gas phase. In this process according to reaction (2), no external energy is needed for the reaction to occur.

[0060] At the end of the reactions (2) or (3), pH is alkaline (pH 8.5-9.5), therefore once the alkaline solution is separated from Fe or Mg, it can be recycled to be used again for more CO.sub.2 absorption as in reaction (1) and then the final pH will be drop to 7.0-8.

[0061] According to a first aspect of the present invention, the hydrogen gas, H.sub.2 (114) generated according to the reaction formula (2) can be directly utilized for energy purpose.

[0062] According to an embodiment of the present method the metal carbonate (115b) obtained in the reaction step (102) is separated obtaining an aqueous alkaline solution, comprising for example NaOH (115a), wherein said aqueous alkaline solution is recycled in the reaction step (101). According to an embodiment of the present method, a solid metal carbonate (115b), for example the siderite (FeCO.sub.3), is created in the outer surface of Fe.sup.0.

[0063] The solid metal carbonate (115b) can be removed, by a further a step (103), by which weak acid (116), comprising citric acid or oxalic acid, is used with concentration in the range 0.1M-0.5M, so that the remaining zero valent metal (117) can be recycled in the reaction step (102) and the reaction according to the formula (2) can be initiated again. The generation of carbonate (115) on the surface of Fe or Mg is indicated by the reduction of the concentration of H.sub.2 from the gas phase to lower than 95% (after several batch cycles). According to a preferred embodiment, after removal of carbonate the remaining solid (FeCO.sub.3 or MgCO.sub.3) is exposed to citric acid or weak acid for several hours so the external FeCO.sub.3 is removed and the inner Fe can react again in step (102).

[0064] According to another embodiment of the present method, the solid FeCO.sub.3 (s) or MgCO.sub.3 (s) instead of being directed to step (103) to be removed from the outer surface, it is used as a raw material in steel industry or cement industry or they are commercialized as iron scrap.

[0065] According to a further embodiment of the present method, the siderite is used in other applications, such as Phosphate absorption or heavy metals adsorption from wastewater.

[0066] According to a second aspect of the present invention, the hydrogen gas (H.sub.2) generated according to the reaction formula (2) or (3), instead to be used for energy purposes, is directed to a bioreactor comprising Hydrogenotrophic methanogens for methane (CH.sub.4) production or Homoacetogenic bacteria for acetic acid (CH.sub.3COOH) production. The bioreactor should also contain sodium bicarbonate (NaHCO.sub.3) solution from reaction (1).

[0067] The microbial inoculum can be a mixed culture such as anaerobic granular sludge or anaerobic sludge from the digester. The inoculum can be pre-exposed to favorable conditions to enrich the hydrogenotrophic methanogens or homoacetogens, depending on the final product.

[0068] According to an embodiment of the present method (200a), the hydrogen gas (H.sub.2) generated according to the reaction formula (2) or (3), is directed to a bioreactor (104a) comprising hydrogenotrophic methanogens, as shown in FIG. 2a, wherein the reagents H.sub.2 and soluble CO.sub.2 are converted to CH.sub.4, according to a reaction formula (4):

3H.sub.2+HCO.sub.3.fwdarw.CH.sub.4+3H.sub.2O 4)

[0069] Methane (CH.sub.4) has more potential final uses than H.sub.2, said uses comprising energy, fuel vehicle, storage in natural gas grid.

[0070] Conventionally, in the process of using hydrogenotrophic methanogens to convert CO.sub.2 to CH.sub.4, the external H.sub.2 gas is added from a separate electrochemical process unit (electrolysis), which splits water into H.sub.2 gas and O.sub.2 by utilizing surplus renewable electric power. One of the current drawbacks to use this process is the relatively high cost of electrolysis and the integration of various systems such as electrolysis process and the H.sub.2 addition to anaerobic digester/bioreactor. In other studies, microbial electrosynthesis has been used for biogas upgrading; however, the main challenges in this case are the cost reduction and the absence of pilot-scale and full-scale demonstration for the process.

[0071] According to the present invention, in the process of using hydrogenotrophic methanogens to convert CO.sub.2 to CH.sub.4, the use of H.sub.2 as generated from the reaction (2) and/or (3) is proposed. By experimental results, it has been shown that in 4 days higher than 98% of CH.sub.4 can be obtained starting by a system comprising CO.sub.2 and Fe.sup.(o).

[0072] Alternatively, according to another embodiment of the present method (200b) the gaseous hydrogen (H.sub.2) can be directed to a bioreactor (104b, FIG. 2b) comprising homoacetogenic bacteria to convert H.sub.2 and CO.sub.2 to carboxylic acids, for example acetic acid (CH.sub.3COOH) according to a reaction formula (5):

2HCO.sub.3+4.5H.sub.2.fwdarw.CH.sub.3COO+4H.sub.2O 5)

[0073] At the end of reaction (4) or reaction (5) pH is alkaline and the solution can be recycled for CO.sub.2 absorption (as previously descripted).

[0074] According to another embodiment (300) of the present method, the reactions (2) or (3) can take place in-situ with the reaction (4) in one and the same reactor (105, FIG. 3), reacting them with hydrogenotrophic methanogens in the same reactor, in such a way to produce a final gas with CH.sub.4>97%, according to the reaction formula (6) or (7):

4Fe.sup.(0)+4HCO.sub.3+4H.sup.++CO.sub.2.fwdarw.4FeCO.sub.3+CH.sub.4+2H.sub.2O; 6)

Mg.sup.(0)+4HCO.sub.3+4H.sup.++CO.sub.2.fwdarw.4MgCO.sub.3+CH.sub.4+2H.sub.2O. 7)

[0075] The limitation of using this in-situ process is the inhibition of sodium to the microorganisms; therefore, the sodium bicarbonate should be less than 30 gr NaHCO.sub.3/L. For higher concentrations of sodium bicarbonate, halophilic microorganisms has to be used.

[0076] The FeCO.sub.3 formation can be removed with citric acid as already shown in the foregoing. The reaction (6) or (7) will require about 3-6 days to be completed (CH4>97%).

[0077] Referring to FIG. 1b, an apparatus (10) for carrying out the method of capturing and converting carbon dioxide (CO.sub.2) as described in the foregoing comprises at least a first reactor (11) and a second reactor (21). The first reactor (11) comprises a first inlet module (12) for the gaseous carbon dioxide (CO.sub.2), a second inlet module (13) for an aqueous alkaline solution comprising an alkali metal hydroxide, at least one outlet module (14), and is configured to absorb the gaseous carbon dioxide in the aqueous alkaline solution comprising an alkali metal hydroxide such that the carbon dioxide reacts with the alkali-metal hydroxide to form a bicarbonate. The second reactor (21) comprises an inlet module (22) for the bicarbonate solution, at least one outlet module (23), and is operatively connected to said first reactor (11) and is configured to bring in contact the bicarbonate solution with a zero valent metal species to form a reaction mixture of H.sub.2, solid metal carbonate and aqueous alkaline solution.

[0078] According to a preferred embodiment of said apparatus (10), said second reactor (21) comprises a liquid/solid separation module (24) configured to separate the reaction mixture into a regenerated aqueous alkaline solution and a solid metal carbonate, wherein said regenerated aqueous alkaline solution is recycled in the first reactor (11).

[0079] According to an embodiment, said apparatus comprises a third reactor (31), having an inlet module (32) and at least one outlet module (33), and is configured to receive Fe carbonate from the second reactor (21), bring in contact said Fe carbonate with either citric acid or oxalic acid to form zero valent Fe, wherein said zero valent Fe is recycled in the second reactor (21).

Experimental Results

[0080] 1) Examined parameters: N.sub.2, CO.sub.2 and 10 gr NaHCO.sub.3/L. with CO.sub.2 at 50 gr Fe.sup.(0)/L. [0081] Experimental condition: Fe.sup.(0) (50 g/L), serum bottles (165 ml), working volume 65 ml of water, headspace 100 ml, temperature 33? C., initial pH 6, agitation 100 rpm. [0082] As can be seen from the chart in FIG. 4, representing the H.sub.2 mol generation Vs time, when the system was flushed with N.sub.2 (for 2 min), it resulted in negligible H.sub.2 production after 75 hours. On the contrary, when the system was a) flushed with CO.sub.2 or b) with CO.sub.2 plus 10 gr NaHCO.sub.3/L in the solution, it resulted in a dramatically higher H.sub.2 (mmol) generated over time. The presence of 10 gr NaHCO.sub.3/L in addition to being flushed with CO.sub.2 resulted in double H.sub.2 mmol/Fe(kg) than in the samples flushed with CO.sub.2 without extra 10 gr NaHCO.sub.3/L. [0083] 2) Examined parameters: N.sub.2, CO.sub.2, 25 gr NaHCO.sub.3/L with CO.sub.2 and 50 gr NaHCO.sub.3/L with CO2 at 25 gr Fe.sup.(0)/L. [0084] Experimental condition: Fe.sup.(0) (25 gr/L), serum bottles (165 ml), working volume 50 ml of water, headspace 115 ml, temperature 33? C., initial pH 7.3, agitation 100 rpm. [0085] 3) The chart in FIG. 5a shows that the higher the bicarbonate concentration, the higher the H.sub.2(mmol)/Fe(kg) generated over time. Again, the use of N.sub.2 instead of CO.sub.2 results in negligible H.sub.2 production FIG. 5a and FIG. 5b. The samples with bicarbonate solution (25 and 50 gr NaHCO.sub.3/L) produced higher than 94% H.sub.2 in 48 hours, whereas the samples flushed with CO.sub.2 without the addition of NaHCO.sub.3 generated 78% H.sub.2. [0086] Examined parameters: N.sub.2, CO.sub.2, 25 gr NaHCO.sub.3/L with CO.sub.2 and 50 gr NaHCO.sub.3/L with CO.sub.2, 75 gr NaHCO.sub.3/L with CO.sub.2, 100 gr NaHCO.sub.3/L with CO.sub.2 at 25 gFe.sup.(0)/L. [0087] Experimental conditions: Fe.sup.(0) (25 g/L), serum bottles (165 ml), working volume 50 ml of water, headspace 115 ml, temperature 33? C., initial pH 7.5-7.7, agitation 100 rpm. [0088] Table 1 shows the production of H.sub.2 (mmol)/Fe(kg).Math.h from Fe.sup.(0) (25 gr/L) under various NaHCO.sub.3 concentrations with a) flushed with N.sub.2 without NaHCO.sub.3 b) flushed with CO.sub.2 without NaHCO.sub.3 c) 25 gr NaHCO.sub.3/L and flushed with CO.sub.2 d) 50 gr NaHCO.sub.3/L and flushed with CO.sub.2.

TABLE-US-00001 Rate of the reaction after 24 h H2 (mmol)/Fe(kg) .Math. h Fe(0) exposed to N.sub.2 0.22 Fe(0) exposed to CO.sub.2 101.7 Fe(0) exposed to 25 g NaHCO.sub.3/L + CO.sub.2 151.5 Fe(0) exposed to 50 g NaHCO.sub.3/L + CO.sub.2 160.8 Fe(0) exposed to 75 g NaHCO.sub.3/L + CO.sub.2 173.1 Fe(0) exposed to 100 g NaHCO.sub.3/L + CO.sub.2 198.8 [0089] The rate H.sub.2 (mmol)/Fe(kg).Math.h of the reaction for Eq 2a for Fe.sup.(0) was measured after 24 h. The higher the bicarbonate concentration, the higher the rate for higher production, as shown in Table 1. In the samples flushed with CO.sub.2, the presence of 100 gr NaHCO.sub.3/L almost double the reaction rate compared with no extra NaHCO.sub.3 added in the solution. [0090] 4) Examined parameters: Concentrations of Fe.sup.(0) (5, 10, 25, 50 gr/L) under 10 gr NaHCO.sub.3 and CO.sub.2. [0091] Experimental conditions: Fe.sup.(0) (50 g/L), serum bottles (165 ml), working volume 65 ml of water, headspace 100 ml, temperature 33? C., initial pH 6, agitation 100 rpm. [0092] Results from section FIG. 6 show that the higher concentrations of powder Fe resulted in higher production of H.sub.2. At 50 gr Fe/L with 10 gr NaHCO.sub.3/L, the H.sub.2 is higher than 97% after 81 hours, whereas at this time point for 25 gr Fe/L, the H.sub.2 concentration was 84%. However, as shown in FIG. 5b, the samples with 25 gr Fe/L and 25 gr NaHCO.sub.3/L generated higher than 94% H.sub.2 in 48 h. With 50 g/L Fe.sup.(0) and 75 gr/L NaHCO.sub.3 higher than 92% and 99% H.sub.2 in 24 and 48 hours, are respectively produced. Therefore, both the Fe.sup.(0) and NaHCO.sub.3 positively contribute to H.sub.2 production in the reaction, although NaHCO.sub.3 concentrations had a more profound positive effect than Fe. [0093] 5) Examined parameters: exposure to Magnesium ribbon in air, in CO.sub.2 ambient and CO.sub.2+NaHCO.sub.3 ambient. [0094] Experimental conditions: Mg.sup.(0) ribbon (2 gr/L), serum bottles (125 ml), working volume 70 ml of water, headspace 55 ml, temperature 33? C., initial pH 6, agitation 100 rpm. [0095] As shown in FIG. 7, after 2 hours, the presence of bicarbonate and CO.sub.2 resulted in a higher rate of H.sub.2 production (around 90% H.sub.2), whereas the exposure of the samples to CO.sub.2 resulted in 43% H.sub.2 in 24 hours. [0096] 6) Examined parameters: exposure to Magnesium ribbon to CO.sub.2, CO.sub.2+10 g NaHCO.sub.3/L, CO.sub.2+20 g NaHCO.sub.3/L and CO.sub.2+40 gNaHCO.sub.3/L. [0097] Experimental conditions: Mg.sup.(0) ribbon (2 gr/L), serum bottles (125 ml), working volume 70 ml of water, headspace 55 ml, temperature 33? C., initial pH 7.2, agitation 100 rpm. [0098] As shown in FIG. 8, the higher the amount of bicarbonate, the higher the H.sub.2 production over time. After 24 hours a crystal was formed on the metal surface. The crystal was identified to be a carbonate called Nesquehonite (MgCO.sub.3.Math.3H.sub.2O). [0099] 7) Examined parameters: temperature (T)=4? C., 20? C., 33? C. [0100] Experimental conditions: same as experiment n.6 with 10 gr NaHCO.sub.3/L. [0101] The reaction rate was: [0102] 2856.4 H.sub.2 mmol/Fe(Kg).Math.hours at T=4? C., [0103] 4314.4 H.sub.2 mmol/Fe(Kg).Math.hours at T=20? C., [0104] 4746.9 H.sub.2 mmol/Fe(Kg).Math.hours at T=33? C. [0105] At 4? C. the reaction rate is decreased however a substantial amount of H.sub.2 can be generated. [0106] 8) Examined parameters: Concentrations of Fe.sup.(0) (50 gr/L), NaHCO.sub.3 formed from initial 0.35 M NaOH continuously flushed with CO.sub.2. [0107] Experimental conditions: Fe.sup.(0) (50 g/L), serum bottles (125 ml), working volume 80 ml of water, headspace 45 ml, temperature 33? C., initial pH 7.3, agitation 100 rpm. [0108] Results from section FIG. 9 show that the H.sub.2 is higher than 98% in 48 hours. At higher initial NaOH and higher initial Fe.sup.(0) concentration the reaction occurs at a higher rate. [0109] Examined parameters: metallic iron reaction with H.sub.2O and N.sub.2 at headspace by varied pH 0-14 conditions (temperature 25? C., all concentrations 1 M and all partial pressures 1 atm). Gibbs free energy change, .Math.G (KJ/mol) is shown in FIG. 10. The reaction (formula 8)

Fe.sup.(0)+2H.sub.2O.fwdarw.Fe.sup.2++H.sub.2+2OH.sup.?8) [0110] becomes unfavorable at pH higher than 7. [0111] In FIG. 10, the Gibbs free energy change ?G (KJ/mol) for metallic iron reaction (formula 2) with H.sub.2O, bicarbonate and CO.sub.2 at varied pH 0-14 (temperature 25? C., all concentrations 1 M and all partial pressures 1 atm) is also shown. In the presence of bicarbonate the reaction (formula 2) takes place even at alkaline pH.

[0112] Finally, it is clear that numerous modifications and variants can be made to the present invention, all falling within the scope of the invention, as defined in the appended claims.