TECHNICAL FIELD

[001] The present invention relates to a decarbonisation system and process.

BACKGROUND

[002] Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.

[003] The world face challenges in the areas of air pollution, public health, economic growth, energy security and national security due to overdependence on fossil fuels. While the world targets complete decarbonisation by 2050, energy is still required for continuous development and economic growth.

[004] Many technological processes are being considered to achieve low-carbon pathways to achieve targets in line with the Paris Agreement and limit the rise in the global average temperature below 2°C.

[005]The separation of carbon dioxide from other light gases such as nitrogen is important for achieving carbon dioxide sequestration. For example, the flue gases of a conventional power station typically contain from about 4% (by volume) to about 14% carbon dioxide (CO2). It is commonly believed that this CO2 represents a significant factor in increasing the greenhouse effect and global warming. Therefore, there is a clear need for efficient methods of capturing CO2 from flue gases so as to produce a concentrated stream of CO2 that can readily be transported to a safe storage site or to a further application. [006] The use of Hydrogen as an alternative fuel is well known. Hydrogen is known to have many applications ranging from synthesis of chemicals such as ammonia, petroleum refining in producing high octane gasoline and aviation jet fuel and in removal of sulfur, hydrogenation in various industrial processes, to propellant fuels in combination with oxygen or fluorine for rockets and spacecraft. Pure hydrogen usually takes a form of a colorless, odorless, and tasteless gas composed of diatomic molecules, H2, under ordinary conditions. Alternatively, pure hydrogen may also be stored in the liquid phase under a certain pressure. Pure hydrogen is usually produced by producing the hydrogen gas.

[007]At present, there are no means of decarbonisation and as well commercial hydrogen production that are commercially viable and H+ production relies mainly on the steam reformation of methane (natural gas). Over three quarters of the global production of hydrogen occurs using steam-methane reformation or via the gasification of coal. In this process, steam and methane at high temperatures (about 1 ,000° C.) react to yield synthesis gas or syngas (a mixture of carbon monoxide and hydrogen).

[008]Coal gasification is the oldest method of hydrogen production in both Europe and the USA. Small amounts of pure hydrogen are produced from the electrolysis of water. In this process, water is decomposed into hydrogen and oxygen using an electric current passed between two electrodes that are immersed in the water. Hydrogen is collected at the cathode and oxygen is collected at the anode. The process is still in its infancy and electrolysis is not considered as a commercially viable technology for deployment on a large scale.

[009]The decomposition of water into hydrogen and oxygen by electrolysis at standard temperature and pressure is not favourable thermodynamically. Energy in the form of electricity or heat must be supplied. The reaction occurring at the anode can be represented by:

Anode (oxidation) 2H20 02+4H++4e-E=-1.23V The reaction occurring at the cathode can be represented by:

Cathode (reduction) 4H++4e- 2H2E=0.00V [0010] Pure water conducts electricity poorly. If an appropriate electrolyte at an appropriate concentration is added to water, the electrical conductivity of water increases considerably. However, care must be exercised in the choosing of electrolytes so that competition does not occur between the electrolyte and water to gain electrons at the cathode (reduction of cation) and to give up electrons at the anode (oxidation of anion).

[0011] Hydrogen can be used as a fuel directly in an internal combustion engine. Some automobile companies produce automobiles that can combust either hydrogen or gasoline. Because of its relative purity, the hydrogen produced by the electrolysis of water can be utilised also in hydrogen fuel cells. In a hydrogen fuel cell, as with hydrogen combustion, water is the final product. Vehicles in cities that operate utilising either hydrogen fuel cells or hydrogen combustion produce negligible pollutants compared with vehicles combusting gasoline or methane or other fossil fuels. The largescale use of hydrogen, produced by electrolysis, either in fuel cells or in internal combustion engines of vehicles would diminish city air pollution very significantly.

[0012] Hydrogen also is an essential component in the production of ammonia and a range of other compounds. The most important use of ammonia is as an agricultural fertiliser. Its importance arises also from its conversion into a wide range of nitrogen containing compounds. A source of uncontaminated hydrogen and ammonia is vital for a clean chemical and food industry.

[0013] At present, the cost of producing hydrogen from the electrolysis of water is many times the cost of producing hydrogen from methane. This high cost occurs because electrolysis in practice does not meet efficiencies that are possible in theory. Overpotentials are needed to overcome interactions at the electrode surface. Competing side reactions at the electrodes result in various products and pollutants and are produced at less than ideal Faradaic efficiency. In addition, much energy is lost as heat because of the difficulty in finding suitable electrodes — particularly anodes. The cost of hydrogen production from electrolysis is a linear function of the cost of electricity.

[0014] While the focus is on zero emissions, the mining, steel, oil and gas and the other rest of industries are necessary and focusing on power or fossil fuels reduction do not resolve the issue. While the renewables energy industry has taken a huge step forward, the decarbonisation need to cover the renewable plant and equipment manufacturing and as well the decommissioning stage which in many cases is overlooked and the circular economy is stopped.

SUMMARY OF INVENTION

[0015] In an aspect, the invention provides a process for generating hydrogen and simultaneously capturing carbon dioxide, the process comprising the steps of: directing a gas stream rich in carbon dioxide into a collection tank and pressurizing the carbon dioxide rich gas collected in the collection tank; contacting the pressurized carbon dioxide rich gas with an aqueous liquid to promote dissolution of carbon dioxide in the aqueous solution and saturate the aqueous solution with carbon dioxide; electrolyzing the saturated aqueous solution using one or more electrolysis units, the electrolysis units comprising an anode module and a cathode module being electrochemically connected to the saturated aqueous solution, to generate hydrogen.

[0016] In an embodiment, the process further comprises the step of directing undissolved carbon dioxide back to the collection tank.

[0017] In an embodiment, the anode module is adapted for generation of oxygen in the anode module and protons separated from the cathode module to generate the hydrogen and hydroxide ions.

[0018] In an embodiment, the hydroxide ions generated at the cathode module are in contact with the saturated solution to sequester the dissolved carbon dioxide as bicarbonate or carbonate or a mixture.

[0019] In an embodiment, the oxygen produced at the anode is purified and/or utilized for combustion.

[0020] In an embodiment, the step of mixing the pressurized carbondioxide rich gas with the aqueous solution in a mixing tank and transferring the saturated solution to the electrolyzing unit step for electrolyzing the saturated solution. [0021] In an embodiment, the process further comprises the step of collecting the generated hydrogen and purifying the generated hydrogen for further use.

[0022] In an embodiment, the gas stream rich in carbon dioxide is a waste gas from an industrial process.

[0023] In an embodiment, partial pressure of the carbon dioxide in the collection tank is greater than 1 atmosphere.

[0024] In an embodiment, partial pressure of the carbon dioxide in the collection tank is in the range of 1 to 1000 atmosphere.

[0025] In an embodiment, the electrolyzing units apply a current in the range of 0.1 to 50V and more preferably less than 1.3V and still more preferably less than 1V.

[0026] In an embodiment, the process further comprises the step of heating the aqueous solution and/or controlling the temperature of the solution in a range between 0-100° C.

[0027] In an embodiment, the gas stream comprises 95% or greater carbondioxide on a volume basis.

[0028] In an embodiment, the aqueous liquid comprises a pH in the range of 0 to 7.

[0029] In an embodiment, the aqueous liquid is obtained from, potable water, non- potable water, waste-water, storm water, reclaimed water, recycled water, sea water, ocean water, brackish water, saline water, brine, fresh water, stored water, surface water ground water or rain., or any combination of two or more of these. [0030] In an embodiment, the hydrogen generated at the cathode is reacted with carbon dioxide from the gas stream to produce methane.

[0031] In an embodiment, each electrolyzer unit comprises a proton exchange membrane or a polymer electrolyte membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way. The Detailed Description will make reference to a number of drawings as follows:

Figure 1 is a simplified flow diagram of a decarbonisation system 100 in accordance with a preferred embodiment.

Figure 2 is a box diagram to show detailed views of the buffer tank/collection tank 110.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS [0033] Figure 1 provides a flow diagram for a decarbonisation system and process 100. The process comprises an initial step of a directing a gas stream rich in carbon dioxide (such as but not limited to a flue gas stream which can contain up to 14% or more carbon dioxide by volume) into a buffer tank 110 or a collection tank 110. The carbon dioxide containing gas in the buffer tank 110 may be pressurised to pressures that are preferably at least greater than 1 atmosphere. Pressures of up to 1000 atmospheres may be used by coupling a compressor 115 to compress the carbon dioxide rich gas in the buffer tank 110.

[0034] Once the carbon dioxide containing gas stream has been collected and pressurised in the buffer tank 110, the pressurised carbon dioxide containing gas may be directed via a flow directing means into mixing tanks 120 to undertake a mixing step with an aqueous liquid solution. The aqueous liquid solution which may comprise an electrolyte. It may comprise an electrolyte which is obtained from, potable water, non-potable water, waste-water, storm water, reclaimed water, recycled water, sea water, ocean water, brackish water, saline water, brine, fresh water, stored water, surface water ground water or rain., or any combination of two or more of these.

[0035] As shown in Figure 1, the aqueous solution may be pumped into the mixing tank by using one or more pumps (denoted by 130) from an aqueous liquid storage facility (not shown in Figure 1). In at least some embodiments, heat exchangers 140 may be utilised for controlling or maintaining the temperature of the aqueous solution flowing into the mixing tank 120. Mixing of the pressurised CO2 rich gas and the aqueous solution is undertaken in the mixing tank 120 to achieve an aqueous solution that is saturated with CO2. Any CO2 that does not dissolve in the aqueous solution is redirected back into the collection tank via the CO2 flow circuit. The provision of a continuous flow of pressurised CO2 allows high levels of dissolved CO2 concentration to be maintained in the aqueous solution over prolonged periods of time. The importance of saturating the aqueous electrolyte solution with CO2 and maintaining the saturation has been explained in detail in the foregoing sections. [0036] The saturated aqueous solution flows from the mixing tank 120 to one or more electrolysing units 150. Each electrolysis unit 150 units comprises an anode module and a cathode module that are electrochemically connected to the saturated aqueous solution. At the cathode module of each electrolysis unit, hydrogen is produced as a result of electrolysis. The anode module is adapted for generation of oxygen in the anode module. The oxygen produced in this way may be used in the plant for combustion activity or alternatively capture and sold as a bi product or released into atmosphere. The combustion activity may involve combustion of methane, coal or petroleum or of some other substance. Thus, the oxygen may be combined with, or exposed to, a fuel and said fuel may then be combusted using Oxyfuel combustion. Protons are separated from the cathode module to generate the hydrogen and hydroxide ions. It is important to note that the cathode module is to be specifically designed to contact the saturated aqueous solution to sequester the dissolved carbon dioxide as bicarbonate or carbonate or a mixture.

[0037] Carbon dioxide dissolves to some extent in water at normal atmospheric pressure. At a gas pressure of one atmosphere (Standard Temperature and Pressure Dry — STPD) approximately 1.5 litres of carbon dioxide gas dissolves in 1 litre of cold water at 5° C. and 0.5 litres of carbon dioxide gas dissolves in 1 litre of warm water at 30° C. Accordingly, the concentration of carbon dioxide (optionally of carbon dioxide plus bicarbonate ion plus carbonate ion) during step b) of the present process may be at least about 0.1 litres (equivalent of carbon dioxide for carbonate and bicarbonate) per litre of water, or at least about 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.25 or 1.5 litres per litre of water, or about 0.1 to about 1.5, 0.1 to 1, 0.1 to 0.5, 0.5 to 1.5, 1 to 1.5 or 0.5 to 1 litres per litre of water, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.75, 1, 1.25 or 1.5 litres per litre of water, depending on the temperature of the water. It is evident that under increasing pressure, the concentration of carbon dioxide increases in the aqueous solution. [0038] Water is a polar molecule with a dipole moment of 1.85 Debyes. Carbon dioxide does not possess a dipole moment but has a polarizability of 2.63 x 10-24 cm3. Carbon dioxide can be seen to have a linear resonance structure. When carbon dioxide is dissolved in water, the slight negative charge on the oxygen atom of the water molecule attracts the slight positive charge on the carbon atom of carbon dioxide. It is understood by the inventor that the product of this interaction is a proton (H+) and a bicarbonate ion (HCC>3 ).

[0039] It has been found that under increasing pressure and/or increasing carbon dioxide concentration in the aqueous solution results in increased concentrations of protons and bicarbonate ions whilst electrolysis is taking place. It is possible to achieve a proton and bicarbonate ion concentration of more than 10 ^_1 moles per litre by further increasing the contact between carbon dioxide molecules and water molecules either by further increasing pressure of the gas stream or by utilising appropriate mixing and mechanical baffles in the mixing tank 120 and reach a pH value less than pH=1. In biological processes, the enzyme carbonic anhydrase produces sufficient proton concentrations from carbon dioxide and water to achieve pH values between pH 2 and pH 4 in various body organs and cell organelles (for example, the stomach and intracellular lysosomes). Commercial carbonation of drinks utilising pressure can obtain pH values of pH=2 to pH=3. The carbon dioxide dissolved in rain-water results in a pH value of pH=5 to pH=6 depending on temperature.

Cathode (reduction) 4H ⁺ + 4e ® 2H2

Anode (oxidation) 40H 02 + 2H ₂ 0 + 4e- 4HC03 40H + 4C0 ₂ ;

2H ₂ 0 0 ₂ + 4H ⁺ + 4e- [0040] As shown above, hydrogen gas is produced at the cathode and oxygen gas is produced at the anode. Carbon dioxide gas may also released from bicarbonate ions at the anode.

[0041] In this scheme, hydrogen gas is produced at the cathode and oxygen gas is produced at the anode. Carbon dioxide gas is released from bicarbonate ions at the anode. However, in the presently described system, by maintaining excessive amounts of dissolved carbon dioxide, the electrolytic conditions are controlled to prevent breakdown of the bicarbonate ions into carbon dioxide at the anode. Specifically, using an aqueous solution that is saturated with carbon dioxide not only results in the CO2 being dissolved in the aqueous solution but also results in formation of carbonic acid. (Equation 1). Carbonic acid rapidly dissociates (splits apart) to produce bicarbonate ions (HCO3 , Eq. 2). In turn, bicarbonate ions can also dissociate into carbonate ions (CO3 ² , Eq. 3). Both of these reactions (Eqs. 2, 3) result in the production of additional protons (H+) and therefore lower the pH of the aqueous electrolytic solution (i.e. , the water is now more acidic). Maintaining high levels (excess) of dissolved carbon dioxide in the electrolytic solution results in the carbon dioxide being effectively neutralised by its reaction with carbonate ions (CO3 ² ) to form an aqueous solution with dissolved bicarbonate ions as shown in the reaction below.

C02(aq) + CO3 ² + H2O 2HCG3

[0042] In other words, constant buffering of the electrolytic solution with carbon dioxide by providing the buffer tank to collect the carbon dioxide and pressurise the carbon dioxide prior to carrying out the electrolysis step prevents the dissociation of the bicarbonate ion into carbon dioxide which would not be desirable since carbon dioxide would be released which would be contrary to the intended outcome of carrying out de-carbonisation.

[0043] The h produced at the cathode can be harvested and used as chemical feed stock or as an energy source/carrier, the value of which could help offset the cost of the simultaneous hydroxide solution production and CO2 mitigation. Conversely, the process can also be viewed primarily as a source of renewable, electrolytic H2 with the added benefit of a CO2 sink formed by the bicarbonate ion rich solution which can then be utilised for other industrial processes. The bicarbonate ion rich solution may be pumped out from the electrolysis unit and the electrolysis units 150 may be recharged with more saturated aqueous solution.

[0044] The carbon dioxide used in the process may be derived from the combustion of a fossil fuel (coal, oil, natural gas, waste) or anaerobic process for the organics where ChU is utilised in the industry and CO2 capture or from the fertiliser, industrial process where CO2 is a biproduct of induced reactions (as an example CO2 is aby product in the ammonia plants which convert ChU in H2 as the main product with the following as process bi products CO, CO2, H2O and others.

[0045] The hydrogen evolved in the process may be at least partially purified. The process may comprise the step of at least partially purifying the hydrogen generated in the process. The at least partially purifying may comprise passing the hydrogen through a gas separation membrane. The process may additionally comprise reacting the hydrogen with carbon dioxide so as to produce methane and water. [0046] The hydrogen evolved in the process may be at least partially purified. This may for example be accomplished by passing through a gas separation membrane. Suitable membranes include dense polymer membranes, ceramic membranes, dense metallic membranes (e.g. Pd-Cu membranes) and porous carbon membranes.

[0047] The current that may be applied for carrying out the electrolysis may be under a voltage of about 0.1 to about 50V, or about 0.1 to 20, 0.1 to 10, 0.1 to 5, 0.1 to 2, 0.1 to 1.3, 0.1 to 1, 0.1 to 0.5, 0.5 to 1, 0.5 to 1.3, 0.5 to 2, 0.5 to 5, 0.5 to 10, 0.5 to 20, 0.4 to 4, 1 to 4, 2 to 4, 1 to 10, 1 to 5, 1 to 2 or 1 to 1.3V, e.g. about 0.1, 0.2, 0.3,

0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1,3, 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45 or 50V. The applied voltage may be less than about 50V, or less than about 40, 30, 20, 10, 5, 4, 3, 2, 1.3, 1.23, 1 or 0.5V.

[0048] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term “comprises” and its variations, such as “comprising” and “comprised of” is used throughout in an inclusive sense and not to the exclusion of any additional features.

[0049] It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect.

[0050] Without being bound by theory, the inventors hypothesize that embodiments of the present invention provides a process for decarbonization and industrial application with the chemical reaction being undertaken in the process being similar to processes when carbon dioxide molecules are transported in the blood from body tissues to the lungs by: dissolution directly into the blood or, binding to hemoglobin, or carried as a bicarbonate ion.

[0051] Several properties of carbon dioxide in the blood affect its transport. First, carbon dioxide is more soluble in blood than oxygen. About 5 to 7 percent of all carbon dioxide is dissolved in the plasma. Second, carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin. This form transports about 10 percent of the carbon dioxide. When carbon dioxide binds to hemoglobin, a molecule called carbaminohemoglobin is formed. Binding of carbon dioxide to hemoglobin is reversible. Therefore, when it reaches the lungs, the carbon dioxide can freely dissociate from the hemoglobin and be expelled from the body. Third, the majority of carbon dioxide molecules (85 percent) are carried as part of the bicarbonate buffer system. In this buffer system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H2CO3).

[0052] Carbonic acid is an unstable intermediate molecule that immediately dissociates into bicarbonate ions (HCO ^-3 ) and hydrogen (H ⁺ ) ions. Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood down its concentration gradient. It also results in the production of H ⁺ ions. If too much H ⁺ is produced, it can alter blood pH. However, haemoglobin binds to the free H ⁺ ions and thus limits shifts in pH. The newly synthesized bicarbonate ion is transported out of the red blood cell into the liquid component of the blood in exchange for a chloride ion (Cl ); this is called the chloride shift. When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion. The H ⁺ ion dissociates from the hemoglobin and binds to the bicarbonate ion.

[0053] The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.