ELECTROCHEMICAL PRODUCTION OF HYDROGEN FROM SEA WATER

Abstract

The invention relates to an apparatus for the electrochemical production of hydrogen gas from salt water, the apparatus comprising at least one cathode; at least one anode spaced apart from the cathode by a defined distance and connectors for electrically connecting the electrodes to a pulsating DC power supply; wherein the cathode comprises a paramagnetic material and the anode comprises a diamagnetic material. The invention also relates to an environmentally-friendly method for the production of hydrogen gas from sea water.

Claims

1. An apparatus for the electrochemical production of hydrogen gas from salt water, the apparatus comprising: a plurality of cathodes; at least one anode spaced apart from the plurality of cathodes by a defined distance; a cathode end connector for electrically connecting the cathode to a negative terminal of an electrical power supply unit; an anode end connector for electrically connecting the anode to a positive terminal of an electrical power supply unit; an electrical power supply unit comprising an AC power supply and at least one rectifier, wherein the electrical power supply unit is configured to convert the AC power supply to a pulsating DC supply; wherein the cathode comprises a paramagnetic material and the anode comprises a diamagnetic material; and wherein the distance between anode and the cathode is equal to the radius of the anode x 3.0 to 3.7.

2. An apparatus as claimed in claim 1, wherein the electrical power supply unit comprises a single-phase or three-phase full-wave rectifier.

3. An apparatus as claimed in claim 1, wherein the anode is configured to be central to an array of cathodes.

4. An apparatus as claimed in claim 1, wherein the cathodes are spaced apart at equal distances from the anode.

5. An apparatus as claimed in claim 3, wherein the distance between each cathode in the array is equal to the diameter of the cathode x 3.0 to 3.7.

6. An apparatus as claimed in claim 1, wherein the at least one anode and the plurality of cathodes are provided in a tetrahedral configuration.

7. An apparatus as claimed in claim 1, wherein the distance between the anode and each cathode is equal to the radius of the anode x 3.2 to 3.6.

8. An apparatus as claimed in claim 3, wherein the distance between the cathodes in the array is equal to the diameter of the cathode x 3.2 to 3.6.

9. An apparatus as claimed in claim 1, wherein the paramagnetic material is selected from 316-904 L stainless steel, 317 L stainless steel, 317 LM stainless steel, 317 LMN stainless steel, molybdenum, tungsten, aluminium, scandium, vanadium, manganese, yttrium, zirconium, niobium, rhodium, palladium, lanthanum, hafnium, tantalum, rhenium, osmium, iridium and iron pyrite, preferably wherein the paramagnetic material is 316 L stainless steel.

10. An apparatus as claimed in claim 1, wherein the diamagnetic material is Zn64, Zn66, Zn67, Zn68 or Zn70.

11. A method of producing hydrogen gas from salt water, the method comprising providing an apparatus as in claim 1, providing a pulsating DC current to the at least one anode and the at least one cathode, and collecting hydrogen gas produced thereby.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings where like parts are provided with corresponding reference numerals and in which:

[0049] FIG. 1 illustrates types of electric current, namely (i) pulsating, (ii) direct, (iii) variable and (iv) alternating.

[0050] FIG. 2 provides a schematic of an electrical power supply unit according to an embodiment of the invention.

[0051] FIG. 3 provides a schematic of an apparatus according to an embodiment of the invention.

[0052] FIG. 4 is a schematic illustration of an electrode configuration according to an embodiment of the invention.

[0053] FIG. 5 comprises waveforms from mains power supply (i), from the secondary winding (ii) and from the second stage bridge rectifier (iii) for each of examples 8a to 8c.

DETAILED DESCRIPTION

[0054] As described above, FIG. 1 shows for comparative purposes the different types of electric current, with a pulsating DC identified by (i). A pulsating DC is formed by rectification of an AC power supply resulting in a pulsating signal which varies periodically in magnitude, but which does not change in polarity.

[0055] FIG. 2 shows the configuration of an electrical supply unit according to an embodiment of the invention. In detail, the primary winding (01) of the stray-field transformer is connected to an AC power input source providing the desired AC voltage to the coiled secondary winding (03). Through the magnetic shunt (02), a variable AC voltage signal is applied to the secondary coiled winding (03). The secondary coiled winding outputs are applied to the input ends of the first bridge rectifier (06) through AC output (04) and (05). A DC rectified signal from the first bridge rectifier output terminals (06) is provided to the input terminals of the second bridge rectifier (09) through terminal connections (07), (08). To support the current demand and back EMF of the reactor, further directional diodes are placed at (11), (12) and (13) and a capacitor is placed at (10) exiting the second-stage bridge rectifier output terminals (09), with the pulsating DC wave signal input directly to the apparatus of the invention via terminal end connectors (14) and (15).

[0056] An embodiment of the invention is depicted in FIG. 3. Referring to FIG. 3, the apparatus comprises a housing (01) which in this embodiment is formed of Pyrex™. The housing comprises a sea water inlet (02) and an outlet (03) for the collection of hydrogen gas and water. The housing comprises two anodes (04), in the form of cylindrical rods of Zn64. Each anode is surrounded by a plurality of stainless steel 316 L cylindrical cathode rods (05) spaced equally apart from the anodes. The anodes and cathodes are connected to a positive DC power input and a negative DC power input, respectively, via positive input (06) and negative input (07).

[0057] The anodes and cathodes are arranged in a tetrahedral configuration, which is shown schematically in FIG. 4. In FIG. 4, each anode (08) is surrounded by a plurality of cathodes (09). Each cathode is spaced apart from the anode, and from each other cathode, at a predetermined distance. It is considered that in operation, this configuration means that the whole area is not conductive—simply the area around the rods, leading to a lower amp draw and therefore increased efficiency.

[0058] The invention will now be described by reference to the following examples, which are illustrative only, and are not intended to limit the invention which is defined by the appended claims.

EXAMPLES

[0059] Materials and Methodology

[0060] Experiments were conducted in a purpose-built system connected to a Hoffman apparatus, and filled with 2 litres of sea water. The system comprised a Pyrex™ housing comprising an inlet for the introduction of sea water, and outlet pipe comprising a 100 ml standard syringe with inline tap for the collection of the gaseous reaction products. Voltage and current readings were measured using a Siglent™ Oscilloscope (Siglent™ SDS 1202 DL). A Sniffer BC gas detector (methane calibrated) was used.

[0061] Gas analysis was carried out by an independent ISO 17025 accredited facility, which is UKAS accredited for many analyses. Certified gas mixtures were used (Supplier CK Gases (now Buse gases)), with the exception of Hydrogen, supplied by Air Products (Certified at >99.95% vol). To this end, sample traces were compared to calibrations, run at the time of the analysis.

Example 1

Analysis of Sea Water

[0062] Sea water used in the experiments was independently analysed and the results are shown in Table 1 below:

TABLE-US-00001 TABLE 1 Sea water composition Analysis Sea Water Total Dissolved Solids mg/l 12,100 Total iron μg/l 49,100 Total magnesium μg/l <1.0 Alkalinity mg/l 112 Total molybdate μg/l 1,210 Total chlorine mg/l 0.06 Dissolved iron mg/l 49.6 Chlorides mg/l 23,600 Conductivity μS/cm 52,300 Nitrites mg/l <10 pH 7.65 Total Cadmium μg/l 5.00

Example 2

Initial Testing of Apparatus and Contaminant Removal

[0063] 2.1

[0064] Initial tests were conducted by taking an initial weight measurement of a metallic sample using a scientific scale. The sample was then connected to a S/S 316 L cathode in the apparatus and subjected to a positive charge of 3 volts @ 0.64 Amps=1.92 Watts for a period of 1 hour. The sample was then allowed to dry at atmospheric pressure and temperature for 24 hours, before being re-weighed. The results of this experiment are shown in Table 2.1 below:

TABLE-US-00002 TABLE 2.1 Initial cleaning and testing with S/S cathode Initial Weight End Weight Material (g) (g) % difference S/S 316L 5.68 5.68 0 Molybdenum 42.22 42.12 0.99 Tungsten 3.19 3.19 0 Aluminium 4.72 4.42 0.97 Titanium 1.19 0 100 (electrode dissolved) Iron Pyrite 31.34 31.34 0.99 Zinc (64) 14.65 14.54 0.99

[0065] 2.2

[0066] The same methodology as for Example 1.1 was repeated, with samples being connected to a zinc anode (negative charge). The results of this experiment are shown in Table 2.2 below:

TABLE-US-00003 TABLE 2.2 Initial cleaning and testing with Zn64 anode Initial Weight End Weight Material (g) (g) % difference S/S 316 L 5.68 5.68 0 Molybdenum 42.12 42.12 0 Tungsten 3.19 3.19 0 Aluminium 4.42 4.42 0 Titanium 1.17 1.17 0 Iron Pyrite 31.34 31.34 0 Zinc (64) 14.54 14.54 0

Example 3

[0067] The same materials as tested in Example 2 were connected to a paramagnetic anode—in this case stainless steel (S/S 316 L). Samples were subject to a positive charge of 3 Volts @0.64 amps for 1 hour. Resistance was measured throughout the reaction with an analogue probe. The results of this experiment are shown in Table 3.1 below.

TABLE-US-00004 TABLE 3.1 Paramagnetic anode connection Start Finish (Visual (Visual Material observation) Ohms observation) Ohms S/S 316 L Clear 5 Brown 5 Molybdenum Clear 5 Brown 5 Tungsten Clear 5 Brown 5 Aluminium Clear 5 Brown 5 Titanium Clear 5 Brown 5 Iron pyrite Clear 5 Brown 5 Zinc (64) Clear 5 Brown 5

[0068] Visual observation of the output liquid showed a brown colour, indicating the generation of Cl.sub.2.

[0069] The testing was repeated with connection to a diamagnetic anode, Zn64. The results of this testing are shown in Table 3.2 below.

TABLE-US-00005 TABLE 3.2 Diamagnetic anode connection Start Finish (Visual (Visual Material observation) Ohms observation) Ohms S/S 316 L Clear 5 Clear 5 Molybdenum Clear 5 Clear 5 Tungsten Clear 5 Clear 5 Aluminium Clear 5 Clear 5 Titanium Clear 5 Clear 5 Iron pyrite Clear 5 Clear 5

[0070] Visual observation of the liquid removed after completion of the experiment showed a clear colour, suggesting that no chlorine was evolved.

Example 4

Hydrogen Production

[0071] The 100 ml syringe was pre-weighed, and then attached to the apparatus set up with a S/S 316 L cathode and Zn64 anode. A voltage of 3v @0.64 amp was applied, and the gas produced collected in the syringe. The syringe was re-weighed. The results showed that the syringe at the end of the reaction weighed 50.33 g, versus 50.425 at the start of the reaction, suggesting the presence of hydrogen gas.

[0072] Gas was produced at a rate of 4.6 ml/min (276 ml/hr).

[0073] The gas evolved was collected in a test tube over the output of the Hoffman apparatus and ignited with wooden splints. The gas gave a popping sound when ignited, again indicating the presence of hydrogen gas. Further gas detection was carried out with a sniffer and cross-checked against a density chart. Again, the presence of hydrogen gas was confirmed. A syringe of the gas produced was sent for independent GC-TCD testing, under the following conditions: ̊ ̊

TABLE-US-00006 TABLE 4.1 GC-TCD conditions Column Carboxen 1010, 30 m × 0.32 mm Injector Split/splitless, 150° C. Carrier gas Helium, 1.8 ml/min, 0.7:1 split Column Temperature 80° C. for 12 mins/25° C./min Program to 240° C. held for 3 mins Detector (TCD) 150° C. Temperature

[0074] The results indicated that the composition of the gas was as follows:

TABLE-US-00007 TABLE 4.2 Composition of gas Hydrogen Nitrogen* Carbon dioxide 44.28% 54.49% 1.22% *The lab has indicated a possible minor error in the abundance of nitrogen due to saturation of the detector by the nitrogen contained in the sample.

Example 5

Effect of Electrode Distance

[0075] The effect of the distance between an anode positioned central to an array of cathodes on the amps drawn by the apparatus was investigated. A schematic of the array system is shown in FIG. 4. The distance, D.sub.1, is measured from the centre of the anode to the centre of the cathode. The flow rate was 4.6 ml/min.

TABLE-US-00008 TABLE 5.1 Effect of distance on amps drawn Radius Volt- Temp Distance Dis- of age Ohms at range ratio tance, anode in start/ (° C.) (radius D (mm) (mm) (V) Watts finish Amps (over 1 hr) anode:X) 10 5 3 4.92 5/5 1.64  0-11.3 2 15.7 5 3 1.92 5/5 0.64 0-8.4 3.14 20 5 3 1.92 5/5 0.64 0-8.4 4 30 5 3 1.92 5/5 0.64 0-8.4 6 50 5 3 1.92 5/5 0.64 0-8.4 10

[0076] These results demonstrate that when the distance between the anode and the arrayed cathodes was controlled between approximately 3 and 3.2 times the radius of the anode at an input voltage of 3 V, the amps drawn remains stable and low. This indicates that the overall design of the electrode array plays a key role in maintaining a stable and efficient method for producing hydrogen gas from sea water while mitigating some of the problems associated with standard plate configurations for electrolysis.

[0077] While temperatures increased slightly over time, the temperature can be controlled by the simple flow design structure of the housing.

Example 6

[0078] The experiment of example 4 was reproduced with a DC power input of 10 v @9 amp, and gas collection in a 1 L cylinder. A filtration step was added after gas collection, and the gas was forced through a three-stage filter composed of 12 inches/30.48 cm each of 1) polymer filter (polymer beads pre-soaked in water); 2) carbon filter and 3) zeolite filter (38 inches/91.44 cm of filter in total). The three stage filtration serves to 1) absorb salt residue from the reaction process; 2) absorb the carbon monoxide/carbon dioxide and 3) absorb any remaining moisture. The gas was then compressed to 3 bar, before being sent for independent analysis. The results of the analysis are shown in Table 6.1 below:

TABLE-US-00009 TABLE 6.1 composition of evolved gas Test Method Units Results Hydrogen content ASTM D2504 mod* % v/v 38.3 Carbon monoxide ASTM D2504 mod* ppm v/v <20 content Carbon dioxide ASTM D2504 mod* ppm v/v 213 content Oxygen content ASTM D2504 mod* % v/v Greater than 10 Nitrogen content ASTM D2504 mod* % v/v Greater than 30 Methane IP 405 mod* % v/v Less than 0.0005 C2-C6 Hydrocarbons IP 405 mod* % v/v Less than 0.01 ASTM D2504: Standard Test Method for Non Condensable Gases in C.sub.2 and Lighter Hydrocarbon products by Gas Chromatography. mod* indicates that modifications to the standard method were made, as detailed below:

[0079] ASTM D2504: Standard Test Method for Non Condensable Gases in C.sub.2 and Lighter Hydrocarbon products by Gas Chromatography. mod* indicates that modifications to the standard method were made, as detailed below:

[0080] Section 9.2—Calibration

[0081] Prepare at least 3 synthetic standard samples containing the compounds to be determined over the range of concentration desired in the products to be analysed, using pure gases or certified blend. *mod: two or one point calibrations were used depending on the individual component concentrations in the sample.

[0082] Section 10.1—Procedure

[0083] Connect the sample cylinder containing a gaseous sample to the gas sample valve with a metal tube and allow the sample to flow for about ½ min. at a rate of 70 to 100 mls/min. *mod: the flow rate is not measured but is run according to experience with this particular GC configuration, and the repeatability of successive runs. This will vary from system to system.

[0084] Section 12 —Precision and Bias

[0085] Data relating to repeatability and reproducibility. *mod: There is no precision data for this particular application.

[0086] IP 405. Commercial Propane and Butane-analysis by GC mod* indicates that modifications to the standard method were made, as detailed below:

[0087] Section 3—Principle

[0088] Physical separation by Gas Chromatography. Identification of components by passing a standard reference mixture or pure hydrocarbons through the column, or by comparison with relative retention volumes of typical chromatograms. Calculation of concentrations of components by measuring peak areas and applying correction factors. Method excludes levels below 0.1%. *mod: All standard methodology applies except gas standards were used to calculate concentrations by relative areas, and the reporting limit reduced on discovery that the samples contained little or no hydrocarbons. ppm gas standards were used and a signal to noise ratio of 3:1 used to calculate the reporting limits.

[0089] Section 5.2 —Materials

[0090] Pure gases or a mixture of gases with certified compositions. *mod: used as stated above.

[0091] Section 6—Apparatus

[0092] 6.3 Column

[0093] The types of column described in this clause have been found suitable and are recommended. Other columns may be used provided that the resolution performance quoted in 6.3.3 is achieved and provided that the relative retention of other hydrocarbons are well known. *mod: The standard method allows for ‘other’ columns so long as they match resolution and correct identification by retention times. Capillary columns have now exceeded, in the main, packed column performances, as is the case in this analysis.

[0094] 6.3.3 Resolution

[0095] R.sub.ab must be >1.5 where R.sub.ab is the resolution between peaks A and B where A and B are either propane and propene, or propene and isobutane. *mod: The resolution R.sub.ab set at >1.5 is easily exceeded by the column used where C3 elutes at 3.28″, propene at 5.70″ and isobutane at 8.11″.

[0096] Section 8 —Quantitation

[0097] 8.2.2.2. Flame Ionisation Detector

[0098] Peak area corrections factors are only employed if standard blends are not used according to a formula based on carbon atoms, hydrogen atoms and a mass factor for the component. *mod: peak area correction factors are not used, but certified standards are.

[0099] Section 10—Precision

[0100] Data relating to repeatability and reproducibility. *mod: There is no precision data for this particular application.

Example 7

[0101] The experiment of example 6 was reproduced with the exception that the filter length was increased to 12 inches/30.48 cm of polymer, 24 inches/60.96 cm of zeolite and 24 inches/60.96 cm of carbon (i.e. 60 inches/152.4 cm of filter in total). The results are shown in Table 7.1 below:

TABLE-US-00010 TABLE 7.1 composition of evolved gas Test Method Units Results Hydrogen content ASTM D2504 mod* % v/v 29.86 Carbon monoxide content ASTM D2504 mod* ppm v/v 0.0082 Carbon dioxide content ASTM D2504 mod* ppm v/v 0.0255 Oxygen content ASTM D2504 mod* % v/v 14.10 Nitrogen content ASTM D2504 mod* % v/v 56.00

Example 8

[0102] The experiment of example 7 was reproduced with a number of modifications. The filter lengths were 12 inches/30.48 cm of polymer, 12 inches/30.48 cm of zeolite and 12 inches/30.48 cm of carbon (i.e. 36 inches/91.44 cm of in-line filter in total). A second-stage carbon filter (36 inches/91 cm) was positioned prior to the gas collection chamber and a copper mesh filter was connected to the gas bottle. The electrode distance was at a ratio of 3.5, and a pulsating DC input was generated through the electrical power supply unit configured as described with respect to FIG. 2, and with an initial AC voltage of 151 V AC, 167 V AC and 185 V AC (Examples 8a, 8b and 8c, respectively). The AC voltage input to primary winding, output from secondary winding, and DC output from second-stage bridge rectification to the terminal input of the apparatus were measured and are shown in Table 8.1 below:

TABLE-US-00011 TABLE 8.1 AC voltage inputs and DC output to apparatus Example 8a 8b 8c AC Voltage input (to 151 V ac 167 V ac 185 V ac primary winding) @5.1 A = @ 7.1 A = @ 8.7 A = 770 Watts 1185.7 Watts 1609.5 Watts AC output (from 18 V ac 20 V ac 23 V ac secondary winding) @ 31.8 A = @ 36.6 A = @ 42.9 A = 572.4 Watts 732 Watts 986.7 Watts DC output to 14.2 V dc 16.3 V dc 18.9 V dc terminal input (from @ 13.3 A = @ 16.8 A = @ 20.5 A = second stage 188.86 Watts 273.84 Watts 387.45 Watts rectification)

[0103] The resultant AC output waveform from the mains power supply (i), from the secondary winding (ii), and from the second-stage bridge rectifier (iii) are shown in FIG. 5 for each of examples 8a, 8b and 8c. FIG. 5A shows results from Example 8a from mains power supply (151 V AC); from transformer (18V AC); from second stage bridge rectifier (14.2 V DC). FIG. 5B shows results from Example 8b from mains power supply (167 V AC); from transformer (20V AC); from second stage bridge rectifier (16.3 V DC). FIG. 5C shows results from Example 8c from mains power supply (185 V AC); from transformer (23V AC); from second stage bridge rectifier (18.9 V DC).

[0104] Further results suggested that a positive waveform is produced from the second stage bridge rectifier up to 20 V dc, at which point a reverse in polarity was noted with the cathode becoming positively charged and the anode negatively charged. To accommodate the voltage increase, the distance between the electrodes was increased to a ratio of 3.5 (i.e. distance between the anode and the arrayed cathodes was 3.5 times the radius of the anode). This greater distance appeared to prevent interaction of the filed lines and no reversal of polarity was noted at this distance.

[0105] Thus, the pulsating DC output from the second stage rectification (shown in 8a to 8c above) was applied to the apparatus as in Example 7, with the exception that the electrode distance was at a ratio of 3.5 (and with the filter modifications noted above).

[0106] The composition of the evolved gas for each of these examples is shown in Table 8.2 below.

TABLE-US-00012 TABLE 8.2 composition of evolved gas Test Method Units 8a 8b 8c Methane IP 405 % v/v Less Less Less mod* than 0.0005 than 5 than 5 C2-C6 IP 405 % v/v Less Less Less Hydrocarbons mod* than 0.01 than 50 than 10 Hydrogen ASTM % v/v   38.3 55.83 79.9 content D2504 mod* Carbon ASTM ppm <20 190 55 monoxide D2504 v/v content mod* Carbon ASTM ppm 213 850 190 dioxide D2504 v/v content mod* Oxygen & ASTM % v/v >10 oxygen 44.06 20.08 nitrogen D2504 >30 nitrogen content mod*

[0107] These results therefore highlight the efficiency of the process, with a hydrogen content of 79.9% being obtained.

[0108] The compiled data demonstrates that an increase in hydrogen gas results with increasing voltage, and suggest that a final voltage of 21.4 V dc would lead to 99.98% hydrogen production.

[0109] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0110] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0111] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations).

[0112] It will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope being indicated by the following claims.