TECHNICAL FIELD

This disclosure relates to a method for producing hydrogen, although the method is not limited to the production of hydrogen. More specifically, a method for producing a precursor compound from seawater is disclosed. A solution comprising the precursor compound may be electrolysed to produce, inter alia, hydrogen.

BACKGROUND ART

Seawater comprises a multitude of indigenous microorganisms such as bacteria, viruses, protists and other single-celled microorganisms, such as Archaea. For example, it is understood that seawater may comprise many thousands of microbes (i.e. more than 20,000 species) although with many present only in small numbers.

Bacteria and Archaea are single-celled organisms without cell nuclei (prokaryotes). They can be found throughout the seawater column, as well as at the surface of and within ocean sediment. Bacteria and Archaea each possess several metabolic pathways.

Some of the microorganisms in seawater are aerobic (requiring oxygen), whereas others are anaerobic (not requiring oxygen).

It is to be understood that a reference to the background and prior art does not constitute an admission that the background and prior art forms a part of the common general knowledge in the art, in Australia or any other country.

SUMMARY OF THE DISCLOSURE

Disclosed herein is a method for producing from seawater a precursor compound, in the form of a carboxylic acid. A solution comprising the precursor compound may be electrolysed to produce hydrogen. In other words, it has been surprisingly discovered that hydrogen can readily be produced from seawater. As is known, hydrogen can form a renewable fuel, such as when it is employed in fuel cells, etc. Additionally, it has been found that a secondary gas, namely chlorine, can also be produced. Chlorine gas also has commercial value. Other compounds may be produced by the method, as well as at least partially desalinated water.

The method comprises mixing a predetermined amount of a sugar with the seawater. The mixing of the resultant mixture can be maintained for a sufficient period of time such that catabolysis of the sugar is able to occur. When catabolysis of the sugar occurs a carboxylic acid compound can be produced. The carboxylic acid can form a precursor compound which can optionally be electrolysed to produce hydrogen. It has been surprisingly discovered that the indigenous bacteria and Archaea that are found in seawater can be availed so as to convert the sugar via a metabolic pathway (e.g. anaerobically) into a carboxylic acid, etc. The carboxylic acid that is produced can be pyruvic acid or a similar alpha-keto acid, or beta- or gamma-keto acids. As set forth hereafter, additional acids can be produced if the metabolic pathway is promoted.

In this regard, it has been discovered that if the catabolysis of the sugar is further promoted, additional compounds can be produced, including compounds such as ethanoic (acetic) acid and methanoic (formic) acid. These compounds may also be electrolysed to produce further hydrogen. Additionally, the residual solution from electrolysis can comprise ions in solution such as the ethanoate and methanoate anions, which can be reduced to recover e.g. ethanol and methanol.

Advantageously, the various ions that are produced by catabolysis (pyruvates, acetates, etc.) are highly soluble in water and thus function as electrolytes during electrolysis. These various ions therefore function to replace the sodium chloride, etc. electrolytes (i.e. the seawater salts) that facilitate and are thus consumed during the electrolysis stage.

The method may comprise optimising the pH levels to enhance hydrogen extraction by electrolysis. For example, acid concentrations can be maximised which can increase the efficiency of hydrogen extraction by electrolysis (e.g. it may be more efficient to extract hydrogen at a pH of ~ 3 rather than ~ 5).

In one embodiment, the predetermined amount of the sugar may be less than about 50g of sugar per litre of seawater. For example, the predetermined amount of the sugar may optimally be about 25g/L of seawater. Whilst greater than about 50g/L of sugar can be added, it has been observed that no additional carboxylic acid compound is produced. This is attributed to a limiting capacity of the indigenous bacteria to catabolyse (metabolyse) this sugar.

Typically, an ideal ratio of sugar to (seawater) salt is sought to be achieved, taking into account factors such as (but not limited to) salinity, temperature, pressure, microbial species and the concentrations thereof. Where an optimal concentration of sugar to salt is achieved, this may result in the removal of sufficient sodium and chlorine during electrolysis such as to render the seawater desalinated.

In one embodiment, the sufficient period of time may be greater than about 50 hrs. This is assuming no externally applied catalysis of the catabolysis. For example, the incubation of the indigenous bacteria in the seawater may be accelerated by heating; and/or by increasing the concentration of the catabolysing microbes, with a corresponding increase in the concentration and consumption of sugars; and/or by selective "breeding" of the catabolysing microbes; etc. The microbes may be concentrated, for example, by first subjecting the seawater to a concentration stage

(e.g. evaporation; reverse osmosis or another membrane process, to remove e.g. a salt water fraction therefrom; etc.).

In one embodiment, (e.g. in the absence of any externally applied catalysis of the catabolysis) the sufficient period of time may be in the range of about 70-90 hrs. More specifically and optimally, the sufficient period of time may be in the range of about 72-84 hrs. In one embodiment, the sugar may comprise a monosaccharide or a disaccharide. Other carbohydrates may be contemplated. For example, the sugar may comprise one or more of glucose, fructose, galactose, lactose, sucrose, maltose, etc.

In one embodiment, the catabolysis may comprise glycolysis, fructolysis or a similar metabolic pathway. The type of catabolysis that is induced or encouraged is such as to produce a carboxylic acid such as pyruvic acid, a similar alpha-keto acid, or beta- or gamma-keto acids, or possibly even more simple carboxylic acids such as carbonic acid, formic acid, acetic acid, etc.

In one embodiment, the catabolysis may be controlled so as to end once the pH of the mixture is less than about 5. In this regard, the catabolysis may be controlled to end once the pH of the mixture is in the range of about 3-5. For example, the introduction of bacillus or similar bacteria to the catabolysing solution can lead to the formation of acids such as acetic (ethanoic) acid and result in a lower pH approaching approximately pH 3 (and hydrogen extraction by electrolysis may then be conducted on the solution at this lowered pH of ~ 3).

Again, this pH range assumes there is no other externally applied catalysis of the catabolysis (e.g. heating; increased concentration of catabolysing microbes and sugars; selective "breeding" of microbes; etc.). With such externally applied catalysis, an even lower pH range may be reached (e.g. pH 2-4). The method may further comprise subjecting the catabolysed mixture to electrolysis so as to produce hydrogen. The electrolysis may employ e.g. renewable electricity such as may be generated via various sources (e.g. solar energy such as photovoltaic and/or solar thermal; geo-thermal; wind; wave; tidal; etc.).

Also disclosed herein is a method for producing hydrogen from seawater. The method comprises mixing a predetermined amount of a sugar with the seawater for a sufficient period of time such that catabolysis of the sugar is able to occur, and whereby a carboxylic acid compound is produced. The method also comprises subjecting the catabolysed mixture comprising the carboxylic acid compound to electrolysis so as to produce hydrogen. The method may be otherwise as set forth above.

The hydrogen that is produced by the method (e.g. produced at the cathode of the electrolysis stage) can be captured and sold as a product. Chlorine gas can also be produced at the anode of the electrolysis stage. This can also be captured and sold as a product.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments will now be described, by way of example only, with reference to the accompanying drawing in which: Figure 1 is a schematic flowsheet illustrating various embodiments of the method as disclosed herein.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

In the following detailed description, reference is made to accompanying drawing which forms a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawing and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawing can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

Referring firstly to Figure 1, a method 10 for producing hydrogen from seawater 12 is shown as a schematic flowsheet. As explained below, the method 10 can be adapted to the local conditions from which the seawater is sourced, such that optional stages (e.g. 14 & 22) can selectively be added. A first stage 18 of the method 10 produces an acidic solution 20 that comprises a precursor compound, in the form of a carboxylic acid (typically pyruvic acid). The equilibrium equation for pyruvic acid is as follows:

CH ₃ COCOOH _(aq) <→ H ⁺ _(aq) + CH ₃ COCOO ^" _(aq ) A second stage of the method 10 electrolyses the acidic solution comprising the carboxylic acid compound in an electrolysis stage 24 to produce hydrogen gas at the cathode and chlorine gas at the anode. The half reactions are:

2H ⁺ ₍ aq) + 2e → H _2(g )

The remaining "discard" solution 26 (i.e. post electrolysis) comprises the pyruvate CH3COCOO ^" (aq) anion in conjunction with the sodium Na ⁺ ( _aq ) cation. The discard stream 26 also includes the by-products of seawater metabolysis. Because sodium and pyruvate ions are now present in solution, the method has effectively manufactured sodium pyruvate (i.e. by removing the hydrogen and chlorine ions). This sodium pyruvate can be separately recovered. Similarly, where the metabolic process is allowed to continue and/or is promoted, various sodium compounds for each of the metabolysing acid species phases can be produced and recovered, including sodium acetate, sodium formate, etc.

The method 10 ascertains and recognises that hydrogen can be produced from seawater (i.e. from the simple combination of seawater with a sugar). As is known, hydrogen is a renewable fuel, and can be employed in fuel cells, etc.

In a simple case, the method 10 involves mixing a predetermined amount of a sugar 16 with a source of seawater 12 in a continuously stirred tank reactor 18 that is operated at atmospheric temperature and pressure. It is also noted that variations in temperature and pressure can act as a catalyst in this process step.

The resultant mixture is stirred for a sufficient period of time such that catabolysis (i.e. metabolysis) of the sugar is able to occur due to the sugar being ingested by indigenous bacteria and Archaea that are found in the seawater. As a result of the particular metabolic pathway (e.g. glycolysis) that is undergone by the sugar added into the reactor 18, a precursor carboxylic acid compound is ultimately produced (typically pyruvic acid, although other alpha-keto acids and/or beta- or gamma-keto acids may be produced). This means that the resultant solution 20 is acidic, typically approximately pH 5 and in the range of pH 4-5.

In the simple case, the solution 20 comprising the carboxylic acid compound is then passed directly to the electrolysis stage 24, where the solution is electrolysed in one or more cells. Because of the acidity of solution 20 hydrogen gas is produced at the cathode and chlorine gas is produced at the anode. Each of the hydrogen gas and chlorine gas that is produced can be captured and each sold individually as a product. Electricity for the electrolysis stage can be from renewable sources such as solar energy (photovoltaic and/or solar thermal), geo-thermal, wind, wave, tidal, etc.

The method 10 recognises and makes use of indigenous bacteria and Archaea that are found in seawater to convert the sugar via an anaerobic metabolic pathway into the carboxylic acid compound. Typically the metabolic pathway is glycolysis or similar, and typically the carboxylic acid that is produced is pyruvic acid although, as above, other alpha-keto acids and/or beta- or gamma-keto acids may be produced. The method 10 can be deployed with a range of sugars such as monosaccharides (e.g. glucose, galactose and fructose) and disaccharides (e.g. lactose, maltose and sucrose). The method 10 can make use of waste forms of these sugars from other industries. Use of other carbohydrates may be possible, providing that the resultant metabolic pathway produces in the solution an acid that is suitable for electrolytic treatment and hydrogen production.

In the simple case, it has been discovered that the amount of sugar 16 that is added to the mixing stage 18 to be induced by the indigenous bacteria and Archaea to produce carboxylic acid can be less than about 50g of sugar per litre of seawater. Optimally it can be at or around 25g/L of seawater. Whilst greater than about 50g/L of sugar can be added to mixing stage 18, it is observed that no additional carboxylic acid is produced. This is attributed to a limiting capacity of the indigenous bacteria to metabolise this sugar. It is further noted that this level of consumption may vary with the seawater source. In the simple case, the seawater and sugar are mixed in the mixing stage 18 for a period of time that is greater than about 50 hrs. A typical mixing period is in the range of about 70-90 hrs and, optimally, in the range of about 72-84 hrs. It is noted that, beyond this time, little to no additional carboxylic acid is produced.

In the simple case, the metabolysis taking place in mixing stage 18 can be controlled (i.e. ended) once the pH of the mixture is about 5; more typically in the range of about 4-5.

In a variation of the simple scenario of the method as described above, prior to being mixed with the sugar, the seawater can be pre-treated (indicated by optional stage 14). Such pre-treatment can include one of more of: - filtering of the seawater to remove impurities therefrom (e.g. by micro- or membrane- filtration, etc.);

- heating of the seawater (e.g. by heat exchange, such as from a solar- or geo- thermal plant), either prior to feeding it to, or within the mixing stage 18; concentration of the solution, including especially of the indigenous bacteria and Archaea in the seawater (e.g. by evaporation, microbial stimulation, selective "breeding" such as by feeding of the microbes, reverse osmosis to remove a water fraction thereof, etc.).

In a further variation of the simple scenario of the method as described above, and after mixing stage 18, the solution can be post-treated prior to electrolysis (indicated by optional stage 22). Such post-treatment can produce a discard stream 26A, and can again include one of more of filtration (e.g. to separate off and remove the waste products of metabolysis); heating; concentration; etc. In yet another variation of the simple scenario of the method as described above, and after post-treatment stage 22, a portion or all of the solution can be subjected to additional metabo lysis prior to electrolysis (indicated by optional stage 30). Such additional metabolysis 30 can include the addition of further bacteria (e.g. bacillus) and/or longer residence time to extend the metabolic breakdown of the intermediate compounds produced, such as pyruvic acid, lactic acid, etc. through to simple carboxylic acids. Such additional metabolysis 30 can take place in a series of holding tanks, each of which can be further catalysed, such as by one or more of: heating; increased concentration of catabolysing microbes and sugars; selective "breeding" of microbes; etc.

The additional metabolysis 30 can produce a final acid (e.g. simple acids, such as ethanoic acid). The solution containing such acids can then be passed to electrolysis 24, where it can be electrolysed to produce hydrogen gas, chlorine gas, etc. Rather than discard the electrolysed solution, it can be passed to a compound recovery stage, where e.g. the simple acid anions (e.g. the ethanoate ion) can be separated (e.g. by membrane separating), reduced and then recovered - e.g. as ethanol.

Such treatment stages can be employed individually or collectively in the method 10. Each such treatment stage can be considered as an externally applied catalysis of the metabolic process of the mixing stage 18, in comparison to the simple case set forth above. In turn, electrolysis and hydrogen, etc. production can be enhanced.

Increasing the concentration of the indigenous bacteria and Archaea, and addition of other bacteria, can allow for a corresponding increase in the concentration and consumption of sugars. This can result in greater carboxylic, etc. acid production, a lowering of the solution pH range (e.g. to pH 2-4), and ideally - greater hydrogen production (e.g. in volume and/or rate).

The catabolic (metabolic) pathway undergone by the sugar may comprise glycolysis, fructolysis or a similar metabolic pathway. As above, the type of sugar and catabolic pathway is such as to produce an alpha-keto carboxylic acid such as pyruvic acid or similar, and optionally may produce beta- or gamma-keto acids, or if allowed to progress, can produce simple carboxylic and other acids such as carbonic acid, formic (methanoic) acid, acetic (ethanoic) acid, etc.

Examples

A number of experimental procedures were conducted in Carnarvon, Western Australia, with seawater samples being obtained from the Fascine Inlet. The samples were also tested by an independent testing laboratory to confirm the results of the experimental procedures.

During the experimental procedures it was noted that the concentration of the reactive bacteria varied, as did the reaction times, pH, volumes of fluid flow, and production of hydrogen and chlorine gases.

The experimental procedures were conducted with simple, raw table sugar - sucrose C12H22O11, being a disaccharide molecule consisting of glucose and fructose. It was noted that all forms of sugar could be substituted for the sucrose, including various monosaccharides and disaccharides. Example 1

Sucrose was mixed with seawater in a continuously stirred mixing tank at an approximate ratio of 25g/Litre, and was observed to completely dissolve in solution. Multiple concentrations of the sucrose were tested, with ~ 25g/Litre being found to be optimal for the level of microbes in the seawater of that region. The seawater had an initial pH in the range of between 8-9, with the resultant mixed solution being measured to have an initial pH of approximately 8-9.

It was noted that the indigenous micro-organisms in the seawater anaerobically processed the sucrose for energy, as a normal function of cell respiration. The particular metabolic pathway that the micro-organisms used to break down the sucrose molecules was glycolysis, with the molecules eventually being broken down to form a carboxylic acid of general chemical formula: RCOOH (R being the remainder of the molecule). In the case of sucrose, by glycolysis, it was noted to form pyruvic acid CH ₃ COCOOH _(aq) , with a decrease in the pH of the solution being to approximately 5, and typically in the range ~ 4 to 5.

The experimental procedures were conducted at ambient temperatures and pressures, and revealed that, at such temperatures and pressures, glycolysis took greater than 50 hours, and typically took approximately 72 - 84 hours to produce a pH of 5 or less. Some residual reaction was observed to still take place, but was observed to be much slower, with the pH not being reduced below 4 under the ambient temperature and pressure conditions (i.e. in the absence of any externally applied catalysis). The resultant solution was passed to an electrolysis cell, where it was subjected to electrolysis under normal (ambient temperature and pressure) conditions. The cell produced hydrogen gas at the cathode (-ve) and chlorine gas at the anode (+ve).

The approximate ratio of gas production was found to be approximately 7 parts of hydrogen gas to approximately 0.8 parts of chlorine gas. The testing also indicated that no chlorine liquid (Cl( _aq) ) was produced and no sodium hydroxide (NaOH _(aq) ) or sodium chloride (NaCl( _aq) ) was evident in the discard solution

It was understood that the remaining ions left in the solution post-electrolysis were the pyruvate CH3COCOO ^" _(aq) anion in conjunction with the sodium Na ⁺ _(aq) cation. Such as solution was noted to be suitable for re-release into the ocean, subject to regulatory approval. Alternatively, the solution was further treated to break down the acids into simple acids such as ethanoic and methanoic acids, which were able to be further electrolysed. The resultant anions were able to be separated to recover the corresponding alcohol.

Example 2 A sample of untreated seawater was supplied to the independent testing laboratory. The laboratory was instructed to analyse the conductivity, salinity, pH and pyruvic acid content of the sample as follows: before it was subjected to metabolysis; after metabolysis; and after electrolysis. The laboratory was also instructed to subject the seawater to metabolysis (as set forth above).

In this regard, 25 gm of raw cane sugar was added to a 1 L sample of the untreated seawater and the metabolysis was allowed to occur over a 4 day period. The conductivity, salinity and pH were tested by the laboratory using an

"iPHlWASE pH in water by pH meter". Pyruvic acid content was tested using a "K-PYRUV Megazyme Pyruvic Acid test kit". The metabolysed solution was then subjected to electrolysis in a Hoffman apparatus wherein it was electrolysed using a 12 V battery. The results are summarised in the following table:

Observations

The pH of the sample dropped from its initial value and during each of metabolysis and electrolysis. It was noted that the pH continued to lower, indicating further metabolysis of the sugars and acids in solution. As such, an additional amount of hydrogen ions became available for recovery by electrolysis as hydrogen gas. Thus, it was noted that the method provided for multiple hydrogen extraction phases at each of the acid phases, thereby producing a number of different intermediary compounds. These phases progressed until extraction of ethanol was achieved. It was further noted that each of these products (e.g. hydrogen, desalinated water, chlorine, ethanol, various sodium compounds, etc.) were able to be achieved through the processing of the original sugar and seawater feed stock. It was further noted that, as the processing conditions varied (e.g. with variations in seawater parameters), the optimum process variables were adjusted accordingly (e.g. metabolysing and electrolysing conditions and additives, etc.).

The conductivity of the sample only dropped marginally from its initial value and during each of metabo lysis and electrolysis. Thus, continuing metabolysis did not affect the ability of the solution to be electrolysed. However, it was also noted that the salinity of the sample dropped, which indicated that the method was also able to assist with desalination (e.g. as part of a desalination process). In this regard, it was noted that the method could be used in conjunction with a conventional desalination process, whereby the electrolysis discard solution 26, 26A and/or the solution from stage 35 could form a feed solution to a conventional desalination process.

The pyruvic acid produced by metabolysis was measured to rise by a factor of greater than 3. It will be seen that the amount of pyruvic acid that was measured prior to and after electrolysis increased slightly, from 0.025 g/L to 0.029 g/L. It was noted that, as hydrogen was being extracted from the solution (i.e. as hydrogen gas), it is postulated that hydrolysis occurred between the remaining sodium pyruvate in solution and water, whereby the sodium pyruvate and/or water molecules donated a hydrogen ion (i.e. which showed/detected as an increase in pyruvic acid). It was also noted that other process variables that may have contributed to the slight increase of pyruvic acid included temperature fluctuations and/or loss of water volume. It was further noted that sodium can act as a hydrogen pump in some metabolic pathways which can also influence the H+ concentration and thus the pyruvic acid reading.

The laboratory testing thus confirmed the production of a precursor carboxylic acid (pyruvic acid). The laboratory testing also confirmed that this solution was able to be electrolysed to yield hydrogen gas.

Example 3 A further sample of untreated seawater was supplied to the independent testing laboratory, with the laboratory being instructed to subject the seawater to metabolysis (i.e. as set forth above). The laboratory was also instructed to measure for hydrogen gas produced by the electrolysis. In this regard, 25 gm of raw cane sugar was added to a 1 L sample of the untreated seawater and the metabolysis was allowed to occur over a 4 day period. During this time, the pH was measured and was observed to drop from 8.07 to 4.36, indicating that metabolysis had proceeded.

The metabolysed solution was then subjected to electrolysis in a Hoffman apparatus in which it was electrolysed using a 12 V battery. Hydrogen gas produced at the cathode was captured and measured by the laboratory using an "ORG512 by Gas Chromatography/ Thermal Conductivity Detection/Flame Ionisation Detection (GC/TCD/FID)" methodology. The results are summarised in the following table:

Observations

The results indicated that hydrogen with a high level of purity (> 95%) was being produced by electrolysis of the metabolysed seawater. Example 4

A further sample of untreated seawater was supplied to the independent testing laboratory, with the laboratory being instructed to subject the seawater to metabolysis (as set forth above). The laboratory was also instructed to measure for each of hydrogen gas and chlorine gas produced by electrolysis. In this regard, 25 gm of raw cane sugar was added to a 1 L sample of the untreated seawater and the metabolysis was allowed to occur over a 4 day period. During this time, the pH was measured and was observed to drop from ~ 8 to less than 5, again indicating that metabolysis had proceeded. The metabolysed solution was again subjected to electrolysis in a Hoffman apparatus in which it was electrolysed using a 12 V battery. Hydrogen gas produced at the cathode was captured and measured by the laboratory using an "ORG512 by Gas Chromatography/ Thermal Conductivity Detection/Flame lonisation Detection (GC/TCD/FID)" methodology. Chlorine gas produced at the cathode was captured and measured by the laboratory using an "ORG 173 analysis of gas by VRAE monitor" methodology. The results are summarised in the following tables:

Observations The results confirmed that hydrogen with a very high level of purity (> 99%) was being produced by electrolysis of the metabolysed seawater, and at significant rates (45.4 mL after 2 hours). In addition, chlorine was being produced, albeit at a much lower rate than hydrogen, due to the relatively lower amounts of chlorine present in the seawater. The results thus confirmed that hydrogen and chlorine could each be produced commercially from seawater.

Example 5 Subsequent testing was performed to further lower the pH of the solution produced by metabolysis. In this testing the solution pH was lowered by the introduction of additional microbial species, using added bacillus or similar. This resulted in a solution pH of around 3 or less prior to electrolysis. It was noted that several species of bacteria could be employed, with a number of such bacteria able to metabolise pyruvate to lactate and eventually to ethanoate (i.e. allowing the production of ethanol).

All increases in hydrogen ions greatly improved the efficiency of the method over more conventional methods such as splitting the water molecule. Further, a low pH environment was observed to be more favourable to hydrogen production. Because the method did not make use of fermentation, it favoured the production of carboxylic acids (such as pyruvic acid, etc.) and not e.g. lactic and similar acids.

In the experiments it was thus confirmed that a number of techniques were able to be deployed to both accelerate metabolysis of the sugar, as well as to increase hydrogen production (volume and rate). As described above, various other products were also produced including desalinated water, chlorine, ethanol, various sodium compounds (sodium pyruvate, sodium ethanoate), etc.

Variations and modifications may be made to the embodiments previously described without departing from the spirit or ambit of the disclosure. In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments.