Field of the Invention

The present invention relates to the generation of hydrogen from water using a photocatalyst in a continuous reactor. In particular, the invention makes use of a pipe-based reactor that has a surface within the pipe that is coated with photocatalyst.

Background of the Invention

The energy supply for future generations depends on innovative breakthroughs regarding the design of low-cost, durable and efficient systems for clean energy conversion and storage. The global demand for clean energy and for ways to reduce C0 ₂ emissions is increasing.

The amount of energy in the sunlight that falls on the earth is around 3 x 10 ²⁴ joules per year. This is about 10,000 times the world’s current energy usage. Large scale conversion of solar energy to a usable form on earth is therefore a potential solution to global energy needs.

Photocatalytic hydrogen generation via water splitting has been identified as a route to provide useable energy from the sun. Photocatalysts utilise charge separation to drive a catalytic reaction. Charge separation is achieved through the transfer of energy from a photon to an electron in the valence band (VB), promoting the electron to the conduction band (CB) of the catalyst. This is known as the Becquerel, or photovoltaic, effect.

The current technology for photocatalytic water splitting relies on noble metal-based catalysts such as Pt, Ru, and Ir. These noble metals are expensive and can be environmentally harmful to obtain via mining. It would therefore be desirable to reduce the need for such noble metals.

Energy Environ. Sci., 2015, 8, 2668-2676 describes EL production from water using semiconductor nanorods integrated with crystalline Ni ₂ P co-catalysts. This provided a turnover number (TON) of around 3,270,000 in 90 hours, a turnover frequency (TOF) of 36,400, and an apparent quantum yield of around 41% at 450 nm.

Scientific Reports, 2017, 7, 8670 describes nano-hybrid plasmonic photocatalysts for hydrogen production which achieve solar -to-fuel efficiencies of up to 20%. The catalytic system comprised a light absorber and oxidation catalyst (Ag NPs), a molecular wire linker (pABA), a semiconductor (Ti0 ₂ ), a co-catalyst (Ru NPs) and regenerators (Bts).

Known systems for photocatalytic hydrogen generation via water splitting have tended to be based on a sheet or plate type reactor. For example, the thesis of Stuart James Bell, Queensland University of Technology, June 201 1, entitled“The effect of light intensity and temperature on photocatalytic water splitting” utilised P25 Ti0 ₂ films deposited on conducting glass as photocatalyst electrodes; these were coupled with platinum electrodes which were also deposited on conducting glass. These films were used to form a photocatalysis cell and were tested at temperatures between 20°C and l00°C.

Despite some progress, overall obtaining robust, efficient and commercially viable hydrogen production systems that are driven by light, e.g. sunlight, remains a significant challenge.

An efficient and commercially viable system for hydrogen generation will depend significantly upon the efficiency and viability of the reactor itself. Challenges in this area remain unresolved.

A photocatalytic reactor for the conversion of water to hydrogen and oxygen gases is disclosed by WO 2017/221 136. In this regard, a device includes a housing having an inlet and an outlet; a channel formed in the housing in fluid communication with the inlet and the outlet, wherein the channel is configured to allow fluid passage between the inlet and the outlet; a membrane disposed within the channel, the membrane configured to allow fluid flowing through the channel to pass through the membrane; and a photocatalyst disposed adjacent the membrane. The membrane includes a porous frit, and the fluid flowing through the channel passes through the porous frit of the membrane, thereby engaging the photocatalyst and initiating a reaction to generate hydrogen and oxygen gases.

A photocatalytic reactor system that is capable of being viably used in a commercial setting is still desired. In particular, there is a need for a new photocatalytic reactor system that is efficient, economical and robust, and which can be utilised on an industrial-scale.

Summary of the Invention

The present inventor has identified that known methods and apparatuses for the photocatalytic generation of hydrogen are not suitable for use at elevated temperatures and pressures, such as above l00°C and/or above !50kPa. For example, the photocatalytic reactor of WO 2017/221 136 is not suitable for withstanding elevated pressures and/or temperatures. Thus, the apparatus of this document may not operate under conditions for optimal efficiency for many photocatalysts, and may not be commercially viable in many instances.

In particular, when operating above temperatures of H 0°C and/or above pressures of l 50kPa, failure of reactor systems can occur due to cracking of glass and/or the development of leaks.

The present inventor has sought a solution to such problems.

According to a first aspect, the present invention provides a method for the continuous generation of hydrogen from water, the method comprising:

i) providing a photocatalytic reactor that comprises :

a) a light focussing device that is able to focus light along a focal path; b) a reactor pipe, which may be elongate; and

c) a photocatalyst;

wherein the photocatalyst is provided on a surface located within the reactor pipe, and wherein the light focussing device is arranged relative to the reactor pipe such that the photocatalyst lies in the focal path of the light focussing device; ii) directing water into the reactor pipe and to the photocatalyst, and directing light into the reactor pipe and to the photocatalyst using the light focussing device;

iii) generating hydrogen in the reactor pipe by the reaction of the photocatalyst, the water and the light.

The present invention also provides, in a second aspect, a photocatalytic reactor for the continuous generation of hydrogen from water, the reactor comprising:

a) a light focussing device that is able to focus light along a focal path; b) a reactor pipe, which may be elongate; and

c) a photocatalyst;

wherein the photocatalyst is provided on a surface located within the pipe,

and wherein the light focussing device is arranged relative to the reactor pipe such that the photocatalyst lies in the focal path of the light focussing device . It has been determined that a pipe-based continuous reactor system according to the invention is more resistant to temperature and pressure than traditional reactors. This allows for a greater photochemical yield and/or yield of hydrogen.

The present invention provides methods of generating hydrogen, and apparatuses for generating hydrogen, that are capable of operating at temperatures of over l25°C and/or at pressures of over 200kPa.

The present invention enables photocatalysts to be used in large scale commercial systems, under optimal temperature and pressure conditions.

The methods and apparatuses of the present invention are efficient, economical and robust. For example efficiencies of 40-50% may be achieved, or more, as compared to 10% efficiencies in previous systems.

In particular, the present invention provides a novel system for the photocatalytic generation of hydrogen, which makes use of pipes, which may suitably be elongate, rather than glass sheets. These pipe-based methods and systems are of the present invention have been found to achieve advantageous robustness and in particular are able to withstand high temperatures (e.g. of l25°C or more) and high pressures (e.g. of 200kPa or more). Advantageously, the uniform nature of the internal surface of the pipe means that pressures and temperatures are more equally distributed around that surface, leading to higher resilience.

The present invention also provides, in a third aspect, a system for the industrial-scale generation of hydrogen from water, the system comprising the photocatalytic reactor according to the second aspect.

In one embodiment, the system is modular. The system may comprise a plurality, such as two or more, or ten or more, or preferably 100 or more photocatalytic reactors according to the second aspect.

It is beneficial for the system to be modular so that modules can be operated immediately once constructed. In other words, the entire system does not need to be constructed in order for operation to occur. This reduces the construction risk with the construction of such systems as, among many other benefits, it allows for demand to be met and for more rapid return on investment. All subsequent discussions of the invention referring to optional features will be understood to be non-limiting. In particular, it will be understood that open wording, such as“in one embodiment”,“for example”,“may be”,“in one preferred embodiment” and“preferable” or “preferably”, used in relation to a feature indicates that the claimed invention is not limited to the feature. The term“comprises” means“includes but is not limited to”.

When considering the method of the first aspect, it will be appreciated that the reaction of the photocatalyst, the water and the light may generate heat. Further, the light as provided to the reactor pipe may cause an increase in temperature. In addition to this, heat may be provided to the reactor pipe, e.g. by pre-heating the water before it is directed into the reactor pipe and/or by the use of a heating device to heat the reactor pipe or to heat the water in the reactor pipe. In one embodiment, temperatures of H0°C or more, such as l20°C or more and especially l25°C or more, are generated within the reactor pipe.

It will also be appreciated that elevated pressures may be desired, e.g. to ensure that the water remains liquid. In one embodiment, elevated pressures are achieved by directing water into the reactor pipe at pressure, e.g. through use of a pump. In one embodiment, pressures of l50kPa or more, such as l75kPa or more and especially 200kPa or more, are generated within the reactor pipe. In one embodiment, elevated pressures may be desired when also carrying out reactions at elevated temperatures.

The present inventor has recognised that significant increases in quantum yield may be obtained by performing photocatalytic reactions at higher temperatures and/or higher pressures.

It is important to note that an increase in quantum yield may be independent from any increase in rate. Whilst an increase in rate might be expected with increased temperature and/or pressure, an increase in quantum yield under these conditions is surprising. The present invention permits this to be effected in practice.

In one embodiment of the method of the invention, some or all of the heat that is generated in the reaction vessel is subsequently utilised in a down-stream process. In one embodiment of the method of the invention, oxygen that is generated in the photocatalytic process is separated from water. The oxygen as separated may then be subsequently utilised in a downstream process.

In one embodiment, the method may use a gas separation system that is able to separate gas from liquid. In one embodiment the photocatalytic reactor used in the method of the first aspect and/or the photocatalytic reactor of the second aspect includes a gas separation system that is able to separate gas from liquid. The gas separation system may be used in the method of the first aspect to separate the hydrogen as generated in step iii) from the water. Thus in one embodiment the method of the first aspect includes the further step iv), after step iii):

iv) separating the hydrogen from the water using the gas separation system.

In one embodiment, the method may use a liquid controller that is able to control the flow of liquid. In one the photocatalytic reactor used in the method of the first aspect and/or the photocatalytic reactor of the second aspect includes a liquid controller that is able to control the flow of liquid. The liquid controller may be arranged relative to the reactor pipe such that the liquid controller can direct a flow of water into the reactor pipe. The liquid controller may be used in the method of the first aspect to direct water into the reactor pipe and to the photocatalyst. Thus in one embodiment, step ii) in the method of the first aspect is as follows:

ii) directing water into the reactor pipe and to the photocatalyst using the liquid controller and directing light into the reactor pipe and to the photocatalyst using the light focussing device.

In one embodiment, the method of the first aspect uses both the liquid controller and the gas separation system. In one preferred embodiment, the photocatalytic reactor used in the method of the first aspect and/or the photocatalytic reactor of the second aspect includes both the liquid controller and the gas separation system.

In one preferred embodiment of the method of the first aspect, liquid water is directed into the reactor pipe such that water in the liquid phase (rather than in the form of steam) contacts the photocatalyst. Without being bound by theory, it is thought that this allows for a faster reaction rate, because the collisions between the water molecules and the photocatalyst are more frequent when the water is in the liquid phase. The skilled reader will appreciate that liquid water can be directed such that it reaches and directly contacts the photocatalyst in the liquid phase by use of conventional equipment and process control. For example, due account can be taken of the temperature of the liquid water at its source as well as the temperature and pressure inside the reactor pipe.

In particular, in one preferred embodiment the liquid water at its source is provided at a temperature of from 1 to 90°C, e.g. from 1 to 75°C or from 2 to 50°C, or from 5 to 40°C or from 10 to 30°C, to ensure that the water remains liquid when it reaches the photocatalyst. Higher temperatures may also be used, however.

Alternatively or additionally, in one preferred embodiment elevated pressures may be used to ensure that the water remains liquid, even at an elevated temperature, when it reaches the photocatalyst. In one embodiment, elevated pressures are achieved by directing water into the reactor pipe at pressure, e.g. through use of a pump. In one embodiment, pressures of l50kPa or more, such as l75kPa or more and especially 200kPa or more, are generated within the reactor pipe. It will be appreciated that if elevated pressures are used then higher temperatures can be used for the liquid water at its source whilst still ensuring that the water remains liquid when it reaches the photocatalyst.

In one embodiment it can also be desirable to pre-set the direction of flow of liquid water towards the photocatalyst as it leaves its source, e.g. via the use of a directional nozzle or the like, to assist the liquid water reaching the photocatalyst. Alternatively or additionally, it can also be desirable to direct the flow of liquid water as it travels between its source and the photocatalyst, e.g. via the use of a channel or the like, assist the liquid water reaching the photocatalyst.

In the method of the first aspect, oxygen may be generated in substantially the same step that the hydrogen is generated. In one embodiment oxygen that is generated in the photocatalytic process is separated from the water. For example, the gas separation system may be used to separate the oxygen from the water. It may then be subsequently utilised in a down-stream process.

In one embodiment of the first aspect, the present invention provides a method for the continuous generation of hydrogen from water, the method comprising:

i) providing a photocatalytic reactor that comprises:

a) a light focussing device that is able to focus light along a focal path; b) an elongate reactor pipe; c) a photocatalyst;

d) a liquid controller that is able to control the flow of liquid; and

e) a gas separation system that is able to separate gas from liquid;

wherein the photocatalyst is provided on a surface located within the elongate pipe, and wherein the light focussing device is arranged relative to the reactor pipe such that the photocatalyst lies in the focal path of the light focussing device, and wherein the liquid controller is arranged relative to the reactor pipe such that the liquid controller can direct a flow of water into the reactor pipe; ii) directing water into the reactor pipe and to the photocatalyst using the liquid controller and directing light into the reactor pipe and to the photocatalyst using the light focussing device;

iii) generating hydrogen in the reactor pipe by the reaction of the photocatalyst, the water and the light; and

iv) separating the hydrogen from the water using the gas separation system.

When considering the method and/or the photocatalytic reactor of the invention, the reactor pipe that is utilised may suitably be elongate. However, the shape of the reactor pipe is not particularly limited, for example it may comprise one or more straight sections and/or one or more bent (curved) sections along its length. The reactor pipe may be continuous or may be formed of smaller sections of pipe. The reactor pipe may be a pipe bundle. The reactor pipe may comprise a plurality of smaller rods or components in close proximity

In one embodiment of the method and the photocatalytic reactor of the invention, the surface on which the photocatalyst is provided runs substantially parallel to the elongate axis of the reactor pipe. In one such embodiment, the photocatalyst may be provided on the inner surface of the reactor pipe itself. In another such embodiment, a support is provided within the reactor pipe, whereby the support has a support surface on which photocatalyst can be provided, and the support is positioned relative to the reactor pipe such that the support surface runs substantially parallel to the elongate axis of the reactor pipe.

When a support is utilised, the support may, for example, be a plate or an elongate member such as a bar or rod or pipe. The support may be made, at least in part, from a metal, ceramic or alloy, such as aluminium, brass, copper, steel, iron, nickel or titanium. The support may be made, at least in part, from carbon, glass or other crystalline substances, or from organic matter, or any combination of the aforesaid. In one embodiment some, most or all of the support is made from a metal or alloy, such as aluminium, brass, copper, steel, iron, nickel or titanium. Without being bound by theory, it is thought that supporting the photocatalyst on a metal or alloy may provide the benefit of increased hydrogen yield and/or increased rate of hydrogen production because the metal/alloy support can facilitate charge transfer of the photocatalyst. The metal/alloy support can conduct both charge and heat to/away from the photocatalyst, to facilitate the function of the photocatalyst. In one preferred embodiment the support is made from or comprises aluminium. Aluminium is particularly preferred because it has a high activation barrier towards hydrogen absorption and dissociation.

The embodiments where the surface on which the photocatalyst is provided runs substantially parallel to the elongate axis of the reactor pipe are beneficial, because water can flow through the pipe with the flow being substantially aligned with the surface on which the photocatalyst is provided. This means that there is a reduced impediment to the flow of water caused by the surface on which the photocatalyst is provided, as compared to embodiments where the flow is not aligned. This permits the use of higher pressures without adversely affecting the robustness and resilience of the photocatalytic reactor.

It may be that the photocatalytic reactor is configured such that at any point along the length of the reactor pipe, liquid can flow through the reactor pipe over 1% or more, or 10% or more, or 25% or more, e.g. 50% or more, or 90% or more, of the cross sectional area of the reactor pipe. In other words, to the extent that there are any physical objects located within the reactor pipe, they do not block all of the cross sectional flow area in the pipe. For example, in the embodiment where liquid can flow through the reactor pipe over 50% or more of the cross sectional area of the reactor pipe, this means that to the extent that there are any physical objects located within the reactor pipe, they block no more than 50% of the cross sectional flow area in the pipe. Hence any such physical objects do not impede liquid flow to an extent that additional pressure could build up against those objects. This permits the use of higher pressures without adversely affecting the robustness and resilience of the photocatalytic reactor.

In one such embodiment, the photocatalyst may be provided on the inner surface of the reactor pipe itself and preferably in this embodiment there are no physical objects located within the reactor pipe. In another such embodiment, a support is provided within the reactor pipe, whereby the support has a support surface on which photocatalyst can be provided, and the support is positioned relative to the reactor pipe such that the support surface runs substantially parallel to the elongate axis of the reactor pipe, and the support has a cross sectional area that is less than 99% (e.g. less than 75%, or less than 50%, or less than 40%, or less than 30%, or less than 10%) of the cross sectional area of the reactor pipe. The support may, for example, be a plate or an elongate member such as a bar or a rod or a pipe or may comprise a combination of the aforesaid.

In one embodiment of the second aspect, the present invention provides a photocatalytic reactor for the continuous generation of hydrogen from water, the reactor comprising:

a) a light focussing device that is able to focus light along a focal path; b) an elongate reactor pipe;

c) a photocatalyst;

d) a liquid controller that is able to control the flow of liquid; and

e) a gas separation system that is able to separate gas from liquid;

wherein the photocatalyst is provided on a surface located within the elongate pipe, and wherein the light focussing device is arranged relative to the reactor pipe such that the photocatalyst lies in the focal path of the light focussing device,

and wherein the liquid controller is arranged relative to the reactor pipe such that the liquid controller can direct a flow of water into the reactor pipe.

Detailed Description of the Invention

The present invention provides a method for the continuous generation of hydrogen from water. The invention also provides a photocatalytic reactor for the continuous generation of hydrogen from water. In addition, the present invention provides a system for the industrial- scale generation of hydrogen from water.

Light focussing device

The present invention uses a light focussing device to focus some or all of the light from a source of light along a focal path. The light focussing device is arranged relative to the photocatalyst such that the photocatalyst lies in the focal path. Therefore, in use, light is focused onto the photocatalyst.

In one embodiment, the source of the light is the sun. Therefore, the light may be sunlight. As such, it is preferable that the reactor is located in an area that has a high amount of sunshine per year. For example, the reactor may be located in a desert area, such as the Middle East.

In one embodiment the light focussing device comprises a parabola-shaped reflector, such as a parabolic mirror. The parabolic reflector, e.g. parabolic mirror, may be single-faceted, where one reflector is formed into the parabolic contour, or multi-faceted, where a number of parabolic reflectors are mounted together, for example to form a trough. A plurality of mirror troughs may be mounted together.

In one embodiment the light focussing device of the present invention comprises a heliostat. Heliostats are devices that include a mirror that turns over a period of time, with the turning movement compensating for the sun's apparent motion in the sky, such that the mirror continues to direct sunlight at a target. Heliostats can be used for extended periods of time, such as one or more years. Heliostats are presently used in, for example, solar enhanced oil recovery. In such an application, heliostats are used to generate steam to be pumped into an oil well.

It will be appreciated that a system according to the invention may comprise more than one photocatalytic reactor, and that each photocatalytic reactor may individually track the position of the sun.

Heliostat mirrors may be made from conventional materials such as metal/alloy (e.g. steel or aluminum) and/or glass, and/or may be made from a plastic to reduce weight and cost. In one embodiment, the light focusing device of the present invention comprises a heliostat and the heliostat is adapted to have a single axis of rotation, relative to the ground, to track the position of the sun.

It will be appreciated that the photocatalytic reactor of the invention and/or a heliostat may be positioned within a glass building (such as a glasshouse or a greenhouse) to conserve heat, to protect the photocatalytic reactor from weather, such as wind and sands, and for ease of cleaning.

The photocatalytic reactor, such as the light focusing device and/or the reaction pipe of the photocatalytic reactor, may be suspended from wires descending from the roof of a glass building. The wires may move throughout the day to position the light focusing device and/or the reaction pipe relative to the sun.

In one embodiment the light focussing device focuses all of the light from the source of light along the focal path. In another embodiment, the light focussing device focuses only some of the light from the source of light along the focal path.

In one such embodiment the light focussing device comprises a separating device that separates the light into two or more portions, with at least one portion being focused along the focal path, or with two or more separate focal planes. This light separation may also be achieved via any other optics device which can create refraction or a similar effect.

In one such embodiment the separating device comprises a prism. It will be appreciated that a prism acts to separate light. At least one portion of the separated light is then focused along the focal path, and in use reaches the photocatalyst. The skilled reader will know that photocatalysts can selectively absorb certain regions of the light spectrum and therefore it will be understood that a prism may be used to separate the light into at least one portion that is selectively absorbed by the photocatalyst and said portion can then be focused along the focal path.

The portions of the light that are not focussed along the focal path may be used for other purposes, such as in another photocatalytic system, e.g. a photoelectrocatalytic (PEC) system, photocatalyst system, or to heat water into steam, which may be used for other useful applications, e.g. to drive a turbine.

For example, in one embodiment a prism may be used to separate light (e.g. sunlight) into two or more portions, e.g. a UV light portion and a visible light portion, or a visible light portion and an infrared light portion. A prism may in particular be used to separate light (e.g. sunlight) into (i) a UV light portion and (ii) a visible light portion and (iii) an infrared light portion.

A UV light portion may be focused along a focal path and directed to a UV photocatalyst. A visible light portion may be focused along a focal path and directed to a visible light photocatalyst. An infrared portion may be used for heating.

In one embodiment, an infrared portion is directed towards water, causing the water to be heated to obtain hot water or steam, or is directed towards an object to be heated. The skilled reader will be aware of many useful applications for hot water and steam, but as examples hot water may be used in a photocatalytic reaction and steam may be used to drive a turbine. Heat reflector

The photocatalytic reactor used in the method of the first aspect and/or the photocatalytic reactor of the second aspect of the present invention may include a heat reflector to reflect heat that has been emitted from the reactor pipe back into the reactor pipe.

In one embodiment the heat reflector in use has its reflective surface directed towards the reactor pipe. In one embodiment the heat reflector is positioned substantially above the reactor pipe. In one embodiment the heat reflector comprises a mirror.

The heat reflector can reflect infrared radiation emitted by the reactor pipe (and/or the contents thereof) back into the reactor pipe. This is beneficial because it may help maintain an elevated temperature within the reactor pipe. This may be used to keep the photocatalyst at, or close to, its optimum temperature for hydrogen production.

It will be appreciated that the heat reflector may block some sunlight from reaching the photocatalyst. This may be tolerated, but to minimize the blocking of sunlight by the heat reflector, the heat reflector may, in one embodiment, have a width (e.g. as measured in the horizontal plane, in use) of no more than three times, e.g. no more than two times, the internal or external diameter of the reactor pipe. There may be some instances where there is a desire to have the reflector wider than this, however.

In one embodiment the width of the heat reflector may be substantially the same as the internal diameter of the reactor pipe. The skilled reader will be able to readily appreciate that a heat reflector, e.g. mirror, that is in the form of a relatively thin strip may suitably be used.

In one embodiment the heat reflector comprises a parabola-shaped reflector, such as a parabolic mirror. The parabolic reflector, e.g. parabolic mirror, may be single-faceted, i.e. where one reflector is formed into the parabolic contour, or multi-faceted, i.e. where a number of parabolic reflectors are mounted together, for example to form a trough. A plurality of mirror troughs may be mounted together. However, it may be sufficient for the heat reflector have a substantially flat surface pointing towards the reactor pipe. It will be appreciated by the skilled reader that in some embodiments the heat reflector does not necessarily extend around the reactor pipe as much as the light focusing device. In one embodiment the heat reflector comprises a heliostat-like arrangement, which is configured to compensate for the sun's apparent motion in the sky.

The heat reflector may be configured to be moved, for example tilted, either manually or automatically, to adjust the temperature within the reactor pipe. As such, at the beginning and end of the day, when the atmospheric temperature is typically lowest, the heat reflector may be configured in a first position that is directly above the reactor pipe and such that the heat reflector points directly towards the reactor pipe; and in the middle of the day, when the atmospheric temperature is typically highest, the heat reflector may be moved to a second position that is not directly above the reactor pipe and/or such that the heat reflector does not point directly towards the reactor pipe.

The heat reflector may extend over some or all of the length of the reactor pipe. In one embodiment the heat reflector may extend over the entire length of the reactor pipe. In another embodiment, the heat reflector may extend over 10% or more, or 25% or more, or 50% or more, e.g. 75% or more or 85% or more, of the length of the reactor pipe.

The heat reflector may suitably be positioned apart from, but relatively close to, the reactor pipe. For example, the heat reflector may be positioned at a distance from the reactor pipe of lOcm or less, such as 5cm or less, or 1 cm or less. This will maximise the insulating ability of the heat reflector whilst maintaining smallest footprint of the heat reflector, and thus minimising the area of the sun’s shadow cast by the heat reflector onto the reactor pipe. In one embodiment the heat reflector is positioned at a distance from the reactor pipe of from 0.5cm to lOcm or from lcm to lOcm, such as from l .5cm to 5cm or from 2cm to 5cm.

Provision of water/ liquid controller

In one embodiment, the photocatalytic reactor used in the method of the first aspect and/or the photocatalytic reactor of the second aspect includes a liquid controller that is able to control the flow of liquid. The liquid controller may be arranged relative to the reactor pipe such that the liquid controller can direct a flow of water into the reactor pipe. The liquid controller may be used to direct water into the reactor pipe and to the photocatalyst.

In general, in use, water is provided from a source of water to the photocatalyst in the present invention. The water may be provided from any source. It may be that the water is provided as fresh water or tap water or river water or sea water or spring water or brackish water or collected rainwater, e.g. from a reservoir. It may be that the water is deionised water or desalinated water. Combinations of different water types and/or water sources are also envisaged.

The skilled reader will appreciate that the water should ideally be from a cost-effective and reliable source. The water may be generated industrially. The water may, additionally or alternatively, be recirculated.

It may be that certain sources of water are more appropriate for certain applications, for example applications located near the sea may utilise sea water and applications located near a river or lake or a reservoir may utilise water from these sources. Certain catalyst systems may necessitate that the water meets certain requirements, e.g. in terms of the levels of dissolved salts.

In one embodiment, the water used is from a natural source. In one embodiment, the water used is river water, spring water, sea water or collected rainwater. It may be that the water is processed, or processed in part, before use. Alternatively, the water may be used in a form where it has not been processed.

The water may be provided directly to the reactor pipe or to the liquid controller (from which it then passes to the reactor pipe) from its source, e.g. from the sea or from a river or from a reservoir. Alternatively, the water may be provided to the reactor pipe or the liquid controller (from which it then passes to the reactor pipe) from a container, with the container having been provided with water from the source, e.g. from the sea, from a river, from a reservoir, and/or from wastewater. For example, such wastewater may be from industrial processing, sewage, drainage water, and/or agriculture.

In one embodiment, the water is untreated. In another embodiment, it is treated before use, e.g. it may be filtered, purified and / or desalinated. In one preferred embodiment, deionised water is used. In one preferred embodiment deionised sea water is used.

The liquid controller may use pressure to direct the water inside the reactor pipe and to the location of the photocatalyst. In other embodiments, the liquid controller does not use pressure to direct the water. In one embodiment gravity may be used to help direct the water to the reactor pipe. The liquid controller may optionally have a nozzle to assist with directing the water in the direction of the photocatalyst.

In one embodiment water, which may be liquid or gas, is directed into the reactor pipe and to the photocatalyst, such that water directly contacts the photocatalyst.

In one preferred embodiment liquid water is directed into the reactor pipe and to the photocatalyst, such that liquid water (water in the liquid phase) directly contacts the photocatalyst. Without being bound by theory, it is thought that this allows for a faster reaction rate as the collisions between the water molecules and the photocatalyst are more frequent when the water is in the liquid phase.

The liquid controller may comprise one or more pump, or other means of generating pressure, to direct the water inside the reactor pipe and to the location of the photocatalyst. It may be that mechanical or thermal means of generating pressure are used. In one embodiment the liquid controller comprises a heat pump. It is envisaged that there could be a heat exchanger used, and that there may be heat recovery.

The liquid controller may pump the water into the reactor pipe at elevated pressure. In one embodiment a mechanical pump is used to pump the water into the reactor pipe at elevated pressure. For example, a reciprocating plunger pump such as the Ruhrpumpen RDP 100 may be used. However, a heat-driven pump may be used to pump the water into the reactor pipe at elevated pressure. The skilled reader will also be aware of alternative means to pump the water into the reactor pipe at elevated pressure, and such means may be applied to the present invention.

The liquid controller may pump the water into the reactor pipe such that the pressure within the pipe is l50kPa or more, such as l75kPa or more and especially 200kPa or more, e.g. 250kPa or more. In one embodiment the pressure within the pipe is from 150 to 500kPa, such as from 175 to 450kPa, or from 200 to 400kPa, e.g. from 250 to 350kPa or from 200 to 300kPa. In one embodiment the pressure within the pipe is 500kPa or more, such as lOOOkPa or more, and especially 2500kPa or more, or 3500kPa or more, such as 4000kPa or more. In a particularly preferred embodiment the pressure within the pipe is 5000kPa or more, or 10,000 kPa or more. In one embodiment the pressure within the pipe is froml50kPa to l0,000kPa, such as from lOOOkPa to 9000kPa, or particularly from 5000kPa to 7000kPa. In one preferred embodiment the pressure within the pipe is from 3000kPa to 5000 kPa.

The pressure in the reactor pipe may be measured, for example, by a general use pressure gauge (manometer), such as the tecsis P 1420 gauge. For example the pressure in the reactor pipe may be measured on entry to and/or exit from the reactor pipe. It will be preferable to use a pressure measuring device that also allows for in-line flow monitoring. The pressure measuring device may have one or more controller. The pressure measuring device may optionally be remote monitored and may be controlled remotely. The pressure measuring device may be automated. The pressure measuring device may be mechanical, electrical or both. The pressure measuring device may involve one or more computer devices, which may be pre-programed.

In one embodiment the flow rate of the water is controlled by the liquid controller. For example, the flow rate of the water may be altered according to the intensity of the (solar) irradiation upon the reactor tube. It may be that the flow rate of the water is increased when the (solar) irradiation upon the reactor tube increases, and/or that the flow rate of the water is decreased when the (solar) irradiation upon the reactor tube decreases or vice versa. For example the flow rate of the water may be controlled to be 10 cm ³ /s or more, or 100 cm ³ /s or more. For example the flow rate of the water may be controlled to be from 10 cm ³ /s to 10000 cm ³ /s, such as from 100 cm ³ /s to 1000 cm ³ /s.

The water may circulate around in a closed loop.

The water may be heated before it is provided into the pipe and/or when it is within the pipe. For example, the water may have been heated by an industrial process, and therefore the water may have been used to remove waste heat from an industrial process. However, in other embodiments there may be enough heat from the light source and from the exothermic nature of the reaction. In general, there may be heat provided to the water from any source of heat, which may include heat generated from and / or recovered from, the system, and/or heat from any other co-located source.

It is envisaged that the water could be heated by the use of heating devices, e.g. electric heaters, and/or that heat exchangers could be used. These may, for example, be counter-flow heat exchangers where the heat released from a process, e.g. from cooling gases obtained as products of the reaction, provides energy to heat the water, either before it is provided into the pipe and/or when it is within the pipe.

The water within the pipe may be at a temperature of l °C or more, such as l 0°C or more; e.g. 50°C or more, or 80°C or more, or l 00°C or more; preferably H 0°C or more, such as l20°C or more; and especially l25°C or more, e.g. l 50°C or more. In one embodiment the temperature of the water within the pipe is from l °C to 500°C, such as from 50°C to 500°C, or from 80°C to 500°C or from l 00°C to 500°C; especially from 1 10 to 500°C, such as from 120 to 400°C or from 125 to 350°C, e.g. from 150 to 300°C or from 150 to 250°C. In one embodiment, the temperature of the water within the pipe may be from l °C to 2 l O°C, such as from 5°C to 200°C, especially from 50°C to 200°C or from 80°C to l 80°C, e.g. from 1 10 to l 80°C. In another embodiment the temperature of the water within the pipe is 200°C or more, such as 250°C or more, or 300°C or more. In one embodiment the temperature of the water within the pipe is up to the autoignition point of molecular hydrogen (about 500°C), for example up to 400°C or up to 350°C or up to 300°C. In one embodiment the temperature of the water within the pipe is from l 50°C to 350°C, preferably from 200°C to 250°C.

The temperature of the water in the reactor pipe may be measured, for example, using a thermocouple, such as a high pressure thermocouple. The WIKA Alexander Wiegand SE & Co. KG TC90 High-pressure thermocouple may be used. For example the temperature of the water may be measured when it enters and/or when it exits the reactor pipe and may be maintained, monitored and controlled.

In one preferred embodiment, the pressure within the pipe is 3000kPa or more, such as 3500kPa or more, such as from 4000kPa to 6000kPa, and the temperature of the water within the pipe is 2 l O°C or less, such as 200°C or less, e.g. from 50°C to 200°C or from 80°C to l 80°C.

In another preferred embodiment, the pressure within the pipe is from l OOOkPa to 9000kPa, such as from 4000kPa to 6000kPa, and the temperature of the water within the pipe is from l 50°C to 350°C, such as from 200°C to 250°C.

In one preferred embodiment the water is recirculated through the system such that unreacted water leaving the gas separation system will re-enter the reactor pipe and be directed to the photocatalyst again. It will be appreciated that, as the photocatalytic reaction proceeds, water within the reactor will be converted into hydrogen. Thus, the amount of water in the reactor will decrease. Further water may need to be provided to the photocatalytic reactor to maintain optimum hydrogen generation.

Reactor pipe

The present invention has determined that performing a photocatalytic reaction to generate hydrogen within a reactor pipe is significantly more reliable, and less susceptible to damage, than the sheet-based systems known in the prior art for generating hydrogen. The reactor pipe may be elongate.

The reactor pipe may be lOcm in its greatest dimension or more, such as lm or more, or lOm or more, or 50m or more or 1 km or more. In one embodiment the reactor pipe may be from lm to 200m in its greatest dimension, such as 50m to l50m. It will be appreciated that a system according to the invention may comprise two or more, or 10 or more, or preferably 100 or more or 1000 or more such reactor pipes. The reactor pipe may be continuous or may be formed of smaller sections of pipe which may be joined together. It will be appreciated that different reactor pipes may act together or separately. A plurality of reactor pipes may be joined together to form a system.

In one embodiment the focal path of the light passes through a section of the wall of the reactor pipe. In such an embodiment it will be appreciated that this section of wall must be able to transmit light. In one embodiment, some, most or all of the reactor pipe walls are able to transmit light.

Suitable pipes for the present invention include those made of a plastic, such as acrylic (e.g. poly(methyl methacrylate)) or PVC (polyvinyl chloride), or glass, such as borosilicate glass. Materials such as quartz or other crystalline substances or composites, including graphene, can also be considered. It will be appreciated that a range of materials can be used, provided that they allow light to permeate. Combinations of materials can also be used. In one preferred embodiment the pipes of the present invention are made of borosilicate glass. Pressure-resistant borosilicate glass pipes are available from SCHOTT.

Suitable pipe wall thicknesses for the present invention may range from 0.5 mm to 50mm or more, such as from 1 mm to 30 mm or more, or from 1.5 mm to 15 mm or more, or from 2.5mm to 10 mm or more. It will be appreciated that the higher the pressure used, the thicker the walls that will be required. A much larger pipe could also be used, with much thicker walls, if higher pressures were desired or if it was viable to do so.

Glass pipes with walls according to the above size ranges are capable of withstanding pressures of at least 600 psi (4.14 MPa) at l50°F (66°C) and 340 psi (2.34 MPa) at 425°F (2 l 8°C), which makes them particularly suitable for use in the present invention.

The shape of the reactor pipe is not particularly limited. In one embodiment the reactor pipe is elongate. In one embodiment the reactor pipe has a consistent cross-sectional size and shape but in other embodiments the shape and/or the size can change along its length. In one embodiment, the reactor pipe has a substantially circular cross-section. In one embodiment, the reactor pipe may comprise one or more straight sections and/or one or more bent (curved) sections along its length. The reactor pipe may, additionally or alternatively, include one or more bulges and/or other features, such as connectors or protrusions for mounting, along its length.

In one embodiment, in use, a first end of the reactor pipe is in a higher position relative to a second end of the reactor pipe. The reactor pipe may, for example, be placed on a gradient to achieve this. The gradient may be measured with reference to the ratio of a) the height difference between the first end and the second end of the reactor pipe, to b) the length of the reactor pipe from the first end to the second end. This ratio a):b) may be from 1 : 100 to 100: 1, for example from 1 :75 to 75 : 1, or from 1 :75 to 1 :25, or from 1 :75 to 1 :50, or from 25 : 1 to 75 : 1, but could be modified outside of these bounds, depending on the length of the pipe section.

The photocatalyst is provided on a surface within the reactor pipe. The photocatalyst may be provided in a fritted glass membrane, or the like.

The photocatalyst may be described as being supported within the reactor pipe or immobilised within the reactor pipe. This is therefore different to the use of a fluidised bed for providing the photocatalyst. This has the benefit that the photocatalyst remains on the surface within the reactor pipe. It is secured (immobilised) within the reactor pipe. No additional filtration or other separation is likely to be required. The configuration of the present invention has benefits over alternative configurations, such as a fluidised bed of photocatalyst, in that the separation of the water and hydrogen from the photocatalyst under the present invention is far simpler. The photocatalyst may be supported within the pipe in a number of different ways.

In one embodiment, the photocatalyst may be provided on the inner surface of the reactor pipe itself. The photocatalyst may be provided as a continuous or discontinuous coating and may be provided over some or all of the inner surface of the reactor pipe.

In one such embodiment the photocatalyst may be coated onto a section of the inner surface of the pipe so as to form one or more band of photocatalyst, wherein each band extends around some or all of an inner circumference of the pipe. The or each photocatalyst band may, for example, extend over a distance of from 5% to 100% of the inner circumference of the pipe, e.g. from 10% to 100% or from 50% to 95% of the inner circumference of the pipe. In another such embodiment, the photocatalyst may be coated onto a section of the inner surface of the pipe so as to form one or more stripe of photocatalyst, wherein each stripe extends along some or all of the inner length of the pipe. The or each photocatalyst stripe may, for example, extend over a distance of from 1% to 100% of the inner length of the pipe, e.g. from 5% to 90% or from 10% to 75% of the inner length of the pipe. The bands and/or stripes of photocatalyst may be continuous or discontinuous.

In another embodiment, a support is, in use, provided within the reactor pipe, whereby the support has a support surface on which photocatalyst can be provided. The support may, for example, be a plate or may be an elongate member such as a bar or a rod or a pipe. The elongate member may have any suitable cross sectional shape, e.g. it may be triangular or rectangular or square or pentagonal or hexagonal or circular. The elongate member may be hollow, i.e. it has an inner elongate surface and an outer elongate surface, or it may be solid, i.e. it only has an outer elongate surface.

If the support is a plate, it is preferred that the photocatalyst is provided on one or both of the planar faces of the plate. Photocatalyst may optionally also be provided on the edge surfaces and/or end surfaces, but this is not required.

The photocatalyst may, for example, extend over an area of from 1% to 100%, such as from 5% to 100%, of the surface area of the planar faces of the plate, e.g. from 15% to 90% or from 25% to 75% of the planar faces of the plate. The photocatalyst may be provided on the plate in a continuous or discontinuous manner. It may be provided as one or more stripes. If the support is an elongate member, it is preferred that the photocatalyst is provided on one or more of the elongate surfaces of the elongate member. It will be appreciated that the number of elongate surfaces will depend on the cross sectional shape and also on whether the elongate member is hollow or solid. For example, a solid elongate member with a circular cross sectional shape only has one (curved) elongate surface whereas a hollow elongate member with a square cross sectional shape has eight (planar) elongate surfaces. Photocatalyst may optionally also be provided on the end surfaces, but this is not required.

The photocatalyst may, for example, extend over an area of from 5% to 100% of the surface area of the elongate surfaces of the elongate member, e.g. from 15% to 90% or from 25% to 75% of the elongate surfaces of the elongate member. The photocatalyst may be provided on the elongate member in a continuous or discontinuous manner. It may be provided as one or more stripes.

In one preferred embodiment, the photocatalyst is provided on a surface of a support that, in use, is located within the reactor pipe. Thus the photocatalyst is immobilised on a support that is located within the reactor pipe during the photocatalytic generation of hydrogen. The support may be permanently secured within the reactor pipe but in one embodiment the support is removable from the reactor pipe.

Thus it can be appreciated that the photocatalytic reactor may be provided in a‘ready to use’ form, with the support temporarily or permanently secured within the reactor pipe. Alternatively, the photocatalytic reactor may be provided with the support separate from the reactor pipe, and the support can subsequently be inserted into the reactor pipe.

A benefit of using a support that can be removed from and inserted into the reactor pipe is that the photocatalyst can readily be changed, if required, by removing a support having a first photocatalyst and replacing it with a support having a second photocatalyst. This could provide benefits, for example, when cleaning, servicing and/or upgrading the reactor.

The support may be mounted inside the reactor pipe in a desired location. The mounting may be temporary or permanent. The support may, in one embodiment, be separated from the inner surface of the reactor pipe by spacers or the like.

The support may be made of any suitable material. It may be made from the same material as the pipe or from different material. It may, for example, be made of plastic, such as poly(methyl methacrylate), ceramic, metal, wood or glass, such as borosilicate glass, or a combination of two or more of these materials.

The support may be made from a metal or alloy, such as aluminium, brass, copper, steel, iron, nickel or titanium. Without being bound by theory, it is thought that supporting the photocatalyst on the metal/alloy may provide the benefit of increased hydrogen yield and/or increased rate of hydrogen production because the metal/alloy support can facilitate charge transfer of the photocatalyst. The metal/alloy support can conduct both charge and heat to/away from the photocatalyst, to facilitate the function of the photocatalyst. In one preferred embodiment the support is made from or comprises aluminium. Aluminium is particularly preferred because it has a high activation barrier towards hydrogen absorption and dissociation.

As noted above, in one embodiment it is preferred that the photocatalyst is provided on a surface that runs substantially parallel to the elongate axis of the reactor pipe. In such embodiments, water can flow through the pipe with the flow being substantially aligned with the surface on which the photocatalyst is provided. In other words, the surface on which the photocatalyst is provided does not significantly impede the flow of water. This permits the use of higher pressures without adversely affecting the robustness and resilience of the photocatalytic reactor.

In one preferred embodiment, the photocatalytic reactor is arranged such that at any point along the length of the reactor pipe, liquid can flow through the reactor pipe over 1 % or more, such as 10%, 50% or 90 % or more, of the cross-sectional area of the reactor pipe at that point. In other words, if there are any physical objects located within the reactor pipe, these do not impede liquid flow to an extent that additional pressure could build up against those objects. This permits the use of higher pressures without adversely affecting the robustness and resilience of the photocatalytic reactor. This proportion through which liquid can flow may vary along the length of the pipe, or may be consistent along the length of the pipe.

It may be that a support is used and that this is positioned relative to the reactor pipe such that the support surface runs substantially parallel to the elongate axis of the reactor pipe, and the support has a cross sectional area that is less than 1%, such as less than 10%, or less than 50%, or 90% or 99%, of the cross sectional area of the reactor pipe. This proportion of the cross sectional area taken up by the support may vary along the length of the pipe, or may be consistent along the length of the pipe.

In one such embodiment, the support is a plate and the planar faces of the plate run substantially parallel to the elongate axis of the reactor pipe. An edge surface of the plate that lies in the plane of the cross sectional surface area of the reactor pipe, i.e. perpendicular to the flow of water, has a cross sectional area that is less than 99% of the cross sectional area of the reactor pipe, such as from 1 to 99%, or from 30 to 50%, or from 50 to 99%; e.g. it may have a cross sectional area that is less than 50% of the cross sectional area of the reactor pipe, such as from 1 to 30%, or from 2 to 25%, or from 5 to 15%. This proportion of the cross sectional area taken up by the edge surface of the plate may vary along the length of the pipe, or may be consistent along the length of the pipe.

In another such embodiment, the support is an elongate member and the elongate face or faces of the member run substantially parallel to the elongate axis of the reactor pipe. An end surface of the elongate member that lies in the plane of the cross sectional surface area of the reactor pipe, i.e. perpendicular to the flow of water, has a cross sectional area that is less than 99% of the cross sectional area of the reactor pipe, such as from 1 to 99%, or from 30 to 50%, or from 50 to 99%; e.g. it may have a cross sectional area that is less than 50% of the cross sectional area of the reactor pipe, such as from 1 to 45%, or from 2 to 35%, or from 5 to 25%. It will be appreciated that if the reactor pipe is hollow, the end surface area does not include the surface area of the opening to the inner bore. Only the cross sectional areas of the solid portions of the end surface are to be considered, because that is what impacts on the flow of the liquid along the reactor pipe.

Gas separation system

In one embodiment, the photocatalytic reactor used in the method of the first aspect and/or the photocatalytic reactor of the second aspect includes a gas separation system that is able to separate gas from liquid. The gas separation system may be used to separate the hydrogen generated in step (iii) from the water.

The gas separation system is suitable for separating gas from liquid. Specifically, the gas separation system is suitable for separating the produced hydrogen from the pressurised liquid within the reactor pipe. The gas separation system may comprise mechanical components to achieve this separation, by the depressurisation of an amount of the liquid, removal of gases therefrom, and re- pressurisation of the liquid. Such mechanical systems may include pneumatic and/or hydraulic apparatus to achieve this.

The gas produced by the photocatalyst may comprise more than one gas. For example, both hydrogen and oxygen may be generated. The gas separation system may therefore further comprise one or more component suitable for separating hydrogen from other gases.

In one embodiment, one or more gas-permeable membrane may be used for separating the produced gases from the water. In this regard, one or more selectively gas-permeable membrane may be used for separating the produced hydrogen from other gases (e.g. oxygen) produced by the photocatalyst; for example vanadium-based or palladium-based membranes or ceramic membranes may be used. There may, additionally or alternatively, be a graphene- based membrane; such a membrane may comprise a layer of graphene or a derivative thereof on a support. Thus one or more selectively gas-permeable membrane may be included in the gas separation system. Such membranes are known in the art.

In one embodiment, a pneumatic control device is adapted to control the flow of gas through the one or more gas-permeable membrane.

The gas-permeable membrane may comprise doped vanadium, for example vanadium doped with a metal such as chromium, nickel, iron, cobalt and/or aluminium. Such membranes are disclosed in JP 2008-055295A. Doped vanadium membranes, i.e. membranes made from a doped vanadium material, have the benefit of being less brittle and less expensive than palladium membranes.

The gas-permeable membrane may comprise graphene. Such membranes are described in ACS Appl. Mater. Interfaces, 2018, 10, 13, 1 1242-1 1250 and in Nature Communications, volume 9, Article number: 2632 (2018). Graphene membranes coated with platinum nanoparticles are known to be permeable to protons and may be used.

As the skilled person will appreciate, graphene is a one-layer or few-layers thick sheet of crystalline graphite. Graphite oxide is an oxidized product of graphite with 8 or more layers. Graphene oxide is an oxidized product of graphite with fewer than 8 layers. Reduced graphene oxide is a reduced product of graphene oxide. Reduced graphene oxide is prepared from the reduction of graphene oxide by thermal, chemical or electrical treatments.

In the context of the present invention, a graphene membrane includes membranes made from graphene, graphene oxide, reduced graphene oxide and/or graphite oxide. Membranes made from graphene may be preferred.

In one embodiment, the one or more gas-permeable membrane comprises a doped vanadium membrane and/or a graphene membrane. The, or each, membrane may optionally be coated, e.g. with platinum and/or gold nanoparticles or the like.

The gas-permeable membrane may extend through the inner volume of the reactor pipe. In one embodiment, the gas-permeable membrane extends along substantially all of the length of the reactor pipe, through the inner volume of the reactor pipe. In one embodiment the gas- permeable membrane is housed by a unit through which the gas-containing water is pumped after exiting the reactor pipe.

In one embodiment, the gas separation system is adapted to form a headspace of gas above the water and below the gas-permeable membrane, and from the headspace the gas may be isolated.

The elongate axis of the reactor pipe may, in use, be positioned horizontally. However, to allow gases to travel through the reactor pipe, it may be preferable to have the elongate axis of the pipe positioned, in use, non-horizontally. In one embodiment the elongate axis of the reactor pipe is positioned at an angle of 5° or more from horizontal, such as 15° or more from horizontal, or 25° or more from horizontal, or 45° or more from horizontal. In one embodiment, the elongate axis of the pipe is positioned at an angle of from 5° to 90° from horizontal, such as from 15° to 60° from horizontal.

Separation of produced gases may additionally or alternatively be achieved using temperature and/or pressure swing adsorption. This technology exploits the differing molecular characteristics and differing affinities for an adsorbent material of mixed gaseous components to separate gaseous components, and is well known in the art. Thus a temperature and/or pressure swing adsorption system may be included in the gas separation system. Photocatalvst

The photocatalyst used in the present invention preferably produces hydrogen from water when it is exposed to light of a wavelength that passes through the earth’s atmosphere. In one preferred embodiment, the photocatalyst used in the present invention is effective at producing hydrogen from water when exposed to light in the visible part of the spectrum.

Therefore in one embodiment the present invention uses a photocatalyst capable of generating hydrogen from water upon exposure to sunlight, and specifically upon exposure to the visible wavelengths of sunlight.

In one preferred embodiment the photocatalyst used in the present invention is a plasmonic photocatalyst based on nanoparticles. In one preferred embodiment the photocatalyst used in the present invention comprises a linker unit. In one preferred embodiment the photocatalyst used in the present invention comprises a titanium dioxide tail, or a tail of CdS, or WSe ₂ , or bismuth vanadate, or the like. In general, a tail of any known common photocatalyst could be contemplated.

In one preferred embodiment the photocatalyst used in the present invention comprises graphene. For example, the photocatalyst used in the present invention may include a graphene based support and/or a graphene based linker unit. Without being bound by theory, it is considered that a graphene based support and/or linker unit can increase hydrogen production by increasing the charge transfer between units of a photocatalyst.

As the skilled person will appreciate, graphene is a one-layer or few-layers thick sheet of crystalline graphite. Graphite oxide is an oxidized product of graphite with 8 or more layers. Graphene oxide is an oxidized product of graphite with fewer than 8 layers. Reduced graphene oxide is a reduced product of graphene oxide. Reduced graphene oxide is prepared from the reduction of graphene oxide by thermal, chemical or electrical treatments.

In the context of the present invention, a graphene photocatalyst includes photocatalysts that comprise graphene, graphene oxide, reduced graphene oxide and/or graphite oxide. Photocatalysts that comprise graphene may be preferred.

Photocatalysts for the production of hydrogen from water are known to the skilled reader. The photocatalyst may, for example, be: • a Ga/Zn-based photocatalyst (which may optionally be used with a co-catalyst, e.g. a Rh/Cr-based co-catalyst or a Pt-based co-catalyst);

• a CdS-based photocatalyst (which may optionally be used with a co-catalyst, e.g. a WS ₂ /graphene hybrid (WG) co-catalyst, or a MoSx co-catalyst, or a reduced graphene oxide (RGO) co-catalyst);

• a plasmonic photocatalyst (e.g. an Au nanoparticle-based photocatalyst or an Ag nanoparticle-based photocatalyst; with a co-catalyst such as a graphene co-catalyst or a Ru-nanoparticle based co-catalyst; and optionally further comprising Ti0 ₂ );

• a semiconductor nanorod photocatalyst (e.g. CdS nanorods, which may be optionally used with a Pt- or Ni-based co-catalyst, such as Ni ₂ P);

or combinations thereof.

Non-limiting examples of photocatalysts that can be used in the present invention are described in the following documents:

• Maeda et al, Journal of Catalysis, 254, (2008), 198-204, which describes a photocatalyst of formula (Gai _x Zn _x )(Ni _x O _x ), where x = 0.18, loaded with Rh _{2 y} Cr _y 0 ₃ co-catalyst (2.5 wt% Rh, 2 wt% Cr) and post-calcined at 823 K which exhibits an apparent quantum efficiency of ca. 5.9% at 420-440 nm.

• Xiang et al, ChemSusChem 2016, 9, 996 - 1002, which describes a graphene-based ternary composite consisting of CdS nanorods grown on hierarchical layered WS ₂ /graphene hybrid (WG) as a high-performance photocatalyst for hydrogen evolution under visible light irradiation. The optimal content of layered WG as a co catalyst in the ternary CdS/WS ₂ /graphene composites was found to be 4.2 wt%, giving a visible light photocatalytic H ₂ -production rate of 1842 pmol h ¹ g ¹ with an apparent quantum efficiency of 21.2% at 420 nm.

• Energy Environ. Sci., 2015, 8, 2668-2676, which describes semiconductor CdS nanorods integrated with crystalline Ni ₂ P co-catalysts that provided a turnover number (TON) of around 3,270,000 in 90 hours, a turnover frequency (TOF) of 36,400, and an apparent quantum yield of around 41% at 450 nm.

• Singh et al, Nanotechnology, 25, (2014), 265701, which describes plasmonic Au/graphene/Ti0 ₂ photocatalysts that display enhanced photocatalytic H ₂ evolution for water splitting in the presence of methanol as a sacrificial reagent, compared to a pure graphene catalysts. The optimal graphene content was found to be 1.0 wt %, giving a H ₂ evolution of 1.34 mmol (i.e. 26 pmollT ¹ ). The plasmonic Au and the graphene as co-catalyst were described as effectively prolonging the recombination of the photogenerated charges.

• Scientific Reports, 2017, 7, 8670, which describes nano-hybrid plasmonic photocatalysts for hydrogen production which achieve solar-to-fuel efficiencies of up to 20%. In this example, the catalytic system comprised a light absorber and oxidation catalyst (Ag NPs), a molecular wire linker (pABA), a semiconductor (Ti0 ₂ ), a co-catalyst (Ru NPs) and regenerators (Bts).

It will be appreciated that the photocatalyst should be immobilised within the reactor so that filtration of the photocatalyst is not required. This may be achieved by immobilising the photocatalyst on a surface, such as a glass surface. This may be an inner surface of the reactor pipe or may be a surface of a support that, in use, is located within the reactor pipe.

To immobilise a photocatalyst on a surface, e.g. on glass, known techniques may be used. It is known, for example, to immobilise a hematite photocatalyst on glass and such techniques may be likewise used for the photocatalysts contemplated herein.

For example, the procedures described in AU2006317512 (B2) may be followed.

A solution of iron nitrate in methanol or water may be provided and poly(methyl methacrylate) (PMMA) spheres are added. The resulting PMMA/Fe(N0 ₃ ) ₃ solution is then spread on the surface of a FTO coated glass substrate. This may be by using one of a number of methods: doctor blading (Nazeeruddin et al, JACS, 1 15(14), 6382-6390), or spray coating (Li et al, Surface and Coatings Technology, 167(2-3), 278-283) or spray pyrolysis (Acosta et al, Journal of Molecular Catalysis A: Chemical, 228(1-2), 183-188). It is preferable that calcination of the coated surface is performed, for example for from 2 to 6 hours, such as 4 hours, at from 300°C to 600°C, such as at 450°C. Ti0 ₂ -containing photocatalyst may naturally adhere to a glass substrate.

The skilled reader will readily understand that known processes can be readily adapted to coat a variety of surfaces with a wide variety of different photocatalysts.

Reaction conditions The present invention has recognised that significant increases in quantum yield can be obtained by utilizing higher temperatures and/or higher pressures. It is important to note that the increase in quantum yield may be independent from any increase in rate. Whilst an increase in rate might be expected with increased temperature and/or pressure, an increase in quantum yield under these conditions is surprising. The methods and systems described herein permit this to be effected in practice.

In addition, an increased rate of hydrogen production and an increased rate of recombination/reaction can be achieved.

In one embodiment, the photocatalytic reactor is capable of withstanding temperatures of H0°C or more, such as l20°C or more and especially l25°C or more. In one embodiment, the photocatalytic reactor is capable of withstanding temperatures of l50°C or more, such as 200°C or more, or 250°C or more, for example 300°C or more, or 350°C or more, or 400°C or more. The methods of the present invention may, therefore, be performed at temperatures of l°C or more or l0°C or more, or 50°C or more; especially H0°C or more, such as l20°C or more and more especially l25°C or more; in particular they may be at l50°C or more, such as 200°C or more, or 250°C or more, for example 300°C or more, or 350°C or more, or 400°C or more. In one embodiment, the methods of the present invention may be performed at temperatures of from l°C to 2 l O°C, such as from l0°C to 200°C, or from 50°C to l 80°C, or from 80°C to l 80°C. In another embodiment, the methods of the present invention may be performed at temperatures of from H0°C to 500°C, such as from l20°C to 450°C, or from l25°C to 350°C, or from l50°C to 350°C.

In one embodiment, the photocatalytic reactor is capable of withstanding temperatures of up to 500°C, such as up to 450°C, or up to 350°C. The methods of the present invention may, therefore, be performed at temperatures of up to 500°C, such as up to 450°C, or up to 350°C.

In one embodiment, the photocatalytic reactor is capable of withstanding pressures of l50kPa or more, such as l75kPa or more and especially 200kPa or more. In one embodiment, the photocatalytic reactor is capable of withstanding pressures of 250kPa or more, such as 350kPa or more, or 500kPa or more, or lMPa or more, for example 2MPa or more. The methods of the present invention may, therefore, be performed at pressures of l50kPa or more, such as l75kPa or more and especially 200kPa or more; in particular they may be at 250kPa or more, such as 350kPa or more, or 500kPa or more, or lMPa or more, for example 2MPa or more, or 3MPa or more, or 3.5MPa or more. The generation of hydrogen may be performed under conditions where both temperature and pressure are elevated above standard atmospheric conditions. Alternatively, the generation of hydrogen may be performed under conditions where just one out of temperature and pressure is elevated above standard atmospheric conditions.

Hole scavenger

It is known that recombination of reaction products and recombination of photo-generated charge carriers can occur, decreasing hydrogen production and, therefore, the efficiency of the water splitting process.

In many catalytic systems, the recombination of electrons and holes generated by the photo irradiation of the semiconductor catalyst takes place to at least some extent. In order to overcome these issues, one option is to add sacrificial agents to consume the oxygen-derived species produced, avoiding further dioxygen gas evolution and its recombination with H _2. Moreover, these sacrificial agents act as hole scavengers, diminishing the recombination of electrons and holes.

In one embodiment of the present invention, therefore, a sacrificial reagent, such as a hole scavenger can be used. In one embodiment, the sacrificial reagent is an alcohol, preferably selected from: glycerol, methanol, ethanol, cellulose, sugars (such as glucose), and combinations thereof. Cobalt oxide is another example of a hole scavenger.

A. Caravaca et al , Proc. R. Soc. A 472: 20160054 describes that hydrogen can be produced by photo-reforming cellulose/water mixtures over Ti0 ₂ catalysts loaded with metal nanoparticles.

It will be understood that catalytic systems can work efficiently without a hole scavenger. Therefore, in one embodiment, a hole scavenger is not used.

In another embodiment, a hole scavenger is used and the hole scavenger is glycerol. Glycerol is a waste product from the production of fatty acid methyl ester, and is therefore abundantly available. Glycerol currently finds large-scale application in the production of biodiesel. Thus this is an economically viable option. Adding a hole scavenger, such as methanol or glycerol, can considerably boost the quantum yield of the photocatalytic generation of hydrogen from water in some catalytic systems.

In general, it will be understood that a hole scavenger is not necessary. The skilled reader will appreciate that due consideration can be given to the benefits of including a hole scavenger versus the disadvantages, in some systems, of including a hole scavenger, especially if it might reduce the efficiency of the water splitting process due to the build-up of by-products.

Down-stream processes

The system of the present invention will generate heat. The system may also convert waste heat or under-utilised heat into a useful form. To further increase the economy of the overall process, in one embodiment, this heat is used in a down-stream process.

In one embodiment, the heat is used for the purification of water, such as the desalination of salty water, such as seawater or brackish water. For example, the heat may be used to drive a flash distillation process and/or any other process requiring heat. The resulting desalinated water may find applications in industrial and/or domestic environments, for example for agriculture, recreation, consumption by humans and/or animals, and/or for the safe dissipation of excess energy.

It will be understood that the heat may be beneficial for many down-stream processes. Such processes may benefit from co-location in proximity to the photocatalytic reactor. The heat may, for example, be used for agriculture and/or to heat buildings (such as domestic or industrial premises). The heat may be stored, such as for a period of up to one week, or up to a month, or up to a year, or more, for example as hot water in a reservoir.

In one embodiment, the heat is used for the generation of steam and this can be used to generate electricity.

In one embodiment, the heat is used for the generation of electricity, for example by driving one or more turbine, which may comprise a low-temperature turbine and which may operate at around 200°C-250°C. In one embodiment, water that is not converted into hydrogen and/or the heat and/or energy generated may be used to drive a turbine, which may be via a heat exchanger, such as a low-temperature turbine adapted to operate at around 200°C- 250°C, to generate electricity. This embodiment is particularly economic, since the electricity produced may in turn be used to drive the apparatus required in the present invention. Of course, the electricity produced may alternatively be sold, or some may be used and some may be sold.

One or more turbine could be used, at least in part, to drive one or more aspects of the plant, for example, a mechanical drive system and, additionally or alternatively, a pumping system. One or more turbine could, alternatively or additionally, be used, at least in part, to drive one or more aspects of a co-located plant. Therefore, a plant employing this apparatus may not need any other source of power. For example, it may not need any other source of power at least during daylight hours and optionally during night time hours. Said one or more turbine may be connected to an energy storage device, an electrical grid, and/or other domestic and/or industrial equipment. Furthermore, exhaust heat from the turbine may be used for the purification of water, as described above, which may drive desalination.

In another embodiment, the heat generated may be used in a reaction such as the reverse water gas shift reaction or the like. As the skilled reader will appreciate, this reaction converts carbon dioxide and hydrogen into carbon monoxide and water, and vice versa. As the skilled reader will be aware, such carbon dioxide may be sourced from an industry source, such as a gas, coal or incineration-fuelled power station. As such, the present invention provides a useful alternative to conventional carbon capture schemes where carbon dioxide is stored underground. This reaction is important to the production of widely-used chemicals such as ammonia and methanol, as well as the Fischer-Tropsch reaction.

The Fischer-Tropsch reaction in one embodiment converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons. For example, this reaction could be used to produce (and/or produce feedstocks for) fuels, lubricants, plastics and/or pharmaceuticals. The Fischer-Tropsch reaction is known to be exothermic and, therefore, the heat generated from this reaction can be used to benefit other processes as described above. The skilled reader will be aware that reactions similar to the Fischer-Tropsch reaction are known and could be used. These processes could be performed industrially, and may be co-located with the reactor or system of the present invention, or may be connected to the reactor or system of the present invention via a grid or distribution network.

It may be preferable that the reactor is located in an area that has a high amount of sunshine per year. For example, reactor may be located in a desert area, such as the Middle East. In areas such as the Middle East there is an abundance of naturally occurring methane that could be used as a co-feedstock along with the heat, hydrogen and/or oxygen generated by the present invention, or derivatives from the present invention such as liquid hydrocarbons.

The heat and/or hydrogen generated by the present invention may be employed in the Sabatier reaction. The skilled reader will appreciate that this reaction converts carbon dioxide and hydrogen into methane and water. The reaction may optimally be performed at an elevated temperature, such as 300-400°C, at an elevated pressure and in the presence of a catalyst, such as a nickel, ruthenium or rhodium catalyst.

The hydrogen and/or oxygen produced by the present invention may be used in industrial, domestic and/or consumer applications. The hydrogen and/or oxygen produced by the present invention may be stored, for example underground, such as in one or more former oil and/or gas well(s). As such, proximity of the reactor to a former oil and/or gas well may be beneficial. The hydrogen and/or oxygen produced by the present invention may be transported worldwide for use. For example, the hydrogen and/or oxygen may be transported by a pipeline, or by ship.

It is noted that the oxygen produced by the present invention may be high in purity, such as 95% pure by weight or more or 99% pure by weight or more, or 99.9% pure by weight or more. Such high-purity oxygen will typically be more valuable than oxygen of lower purity.

In one embodiment, the oxygen output of the reactor is used to produce synthesis gas (also known as“syngas”, a mixture of hydrogen, carbon monoxide and carbon dioxide) by its reaction with methane. This process may require a catalyst, such as a nickel catalyst. The production of synthesis gas may be part of a gas-to-liquid, coal-to-liquid and/or biomass-to- liquids process, which may further produce compounds for use in industries such as aviation fuel and/or chemical production (such as plastic synthesis or pharmaceutical synthesis).

In one embodiment, the oxygen output of the reactor is used in a chimney. The chimney may be a chimney with one or more chemical and/or process. For example it may be a chimney of an industrial process, such as a power station and/or a blast furnace for scrubbing, flaring, or the like. Accordingly, the present invention may be co-located or performed in conjunction with a power station and/or a blast furnace, and/or any other process, to boost efficiency. Such operations are more efficient when increased amounts and/or concentrations of oxygen are used. In one embodiment, the oxygen output of the reactor is used in an oil refinery. Accordingly, the present invention may be co-located or performed in conjunction with an oil refinery. For example, the oxygen may be used to facilitate cleaner burning of a fuel or to clean equipment. Such uses, and more, are known in the art.

In another embodiment, the oxygen output of the reactor is reacted with methane to produce methanol. This reaction may be catalysed by a catalyst, such as a transition metal catalyst. Methanol is particularly useful as a feedstock for synthesis of other chemicals, as a solvent, and as a fuel, and as such has a high economic value.

Methanol or methane may be converted by bacteria, filamentous fungi and/or yeast (such as Komagataella pastoris) into protein (single cell protein), optionally in the presence of further oxygen. Such protein may be used as a feedstock, for example as a feedstock for swine, crustaceans such as prawns, and/or fish. Such protein, or the swine, crustaceans and/or fish fed on the protein, may be produced for human consumption. The protein produced could also be sold or distributed for human consumption, in a product similar to tofu or Quorn® or the like.

Aerobic methanotrophic bacteria known to the skilled reader may be used to metabolise methane with the oxygen output of the reactor to produce products such as formaldehyde and/or methanol or protein, to be used and/or sold in a similar way to that discussed above.

In one particularly useful embodiment, the hydrogen output of the reactor and/or the hydrogen of the synthesis gas may be used with carbon dioxide (such as carbon dioxide from a power station and/or a blast furnace) in a reverse water gas shift reaction, to generate carbon monoxide, followed by the Fischer-Tropsch reaction. Fischer-Tropsch reactions may be performed in the presence of metal catalysts, typically at temperatures of l50-300°C and at pressures of one to several tens of atmospheres. The water-gas shift reaction is known to be particularly important to the Fischer-Tropsch reaction to ensure that the ratio of hydrogen to carbon monoxide is balanced carefully.

The hydrogen may be used to power a hydrogen fuel cell and/or may be sold, e.g. for use as a fuel. In this way, the hydrogen may be used to power an automobile, such as a car, a lorry and/or a ship. The hydrogen may be used to power a home. The hydrogen may be used in the production of ammonia, for example under the Haber process. As such, the resulting ammonia may be converted into a fertiliser, such as ammonium nitrate and/or urea. The hydrogen may be used in the production of explosives, for example through the synthesis of ammonium nitrate, as described above, which can be used as an oxidant.

The plant/system of the invention could, alternatively or additionally, be used for degradation reactions of soluble material, potentially with the same photocatalyst or with another (similar) photocatalyst. This would permit the breakdown of waste products or effluent from human and/or industrial/agricultural production.

Detailed Description of the Drawings

An embodiment of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a photocatalytic reactor comprising an elongate pipe that may be used to implement the methods of the present invention;

Figure 2a is a cross-section view of the elongate pipe shown in Figure 1, in an embodiment where the pipe contains a plate, wherein one or more surfaces of the plate are coated with a photocatalyst;

Figure 2b is a cross-section view of the elongate pipe shown in Figure 1, in an embodiment where the pipe contains an inner cylindrical member which has a surface that is coated with a photocatalyst;

Figure 2c is a cross-section view of the elongate pipe shown in Figure 1, in an embodiment where the inner surface of the elongate pipe is coated with a photocatalyst; and

Figure 3 is a schematic view of a system comprising a plurality of photocatalytic reactors according to the present invention.

Referring firstly to Figure 1 of the accompanying drawings, there is shown a photocatalytic reactor 10 that can be used to implement the methods of the present invention. The photocatalytic reactor 10 comprises a light focussing device 20 that is able to focus light L into a focal region. In this illustrated embodiment, the light focussing device 20 is a parabolic mirror, but other devices may suitably be used to focus the light.

The photocatalytic reactor 10 also comprises an elongate pipe 30. The elongate pipe 30 has a surface 34 provided within its interior and at least a section of this surface 34 is coated with photocatalyst.

In use the elongate pipe 30 is positioned such that the section of the surface 34 coated with a photocatalyst is aligned with the focal region of the light focussing device 20. Therefore light that has been focussed by the light focussing device 20 is directed to and reaches the section of the surface 34 that is coated with a photocatalyst.

The photocatalytic reactor 10 must of course be configured such that light that has been focussed by the light focussing device 20 can reach the photocatalyst. In other words, there must not be any element located on the path of the focussed light that would block it from reaching the photocatalyst.

Suitably, therefore, the elongate pipe 30 is formed at least in part from transparent material, such as glass, so that light can pass through the transparent material and reach the photocatalyst. The elongate pipe 30 may suitably be made of glass, e.g. borosilicate glass.

It will be appreciated that the elongate pipe need not be fully formed from transparent material, provided that the elongate pipe and light focussing device can be arranged relative to one another such that there is transparent material located at any portion of the elongate pipe that lies in the path of the light that has been focussed by the light focussing device towards the photocatalyst.

Referring now to Figures 2a-c of the accompanying drawings, three different embodiments for the elongate pipe 30 are shown in cross-section, each one including a surface 34 coated with a photocatalyst.

Figure 2a shows an elongate pipe 30a containing a plate 33, wherein the plate has two surfaces 34a that are coated with a photocatalyst. In the illustrated embodiment both of the outer planar surfaces 34a of the plate are shown as coated with photocatalyst but it will be appreciated that in another embodiment just one of the outer planar surfaces of the plate 33 could be coated with photocatalyst. The coating may fully or partially coat the or each surface.

The plate 33 is contained within the outer wall 32 of the pipe 30a. It may extend across part or all of the internal diameter of the pipe. In the illustrated embodiment the plate 33 extends across the diameter of the pipe 30a, i.e. both of the opposing end faces of the plate 33 contact the pipe 30a, and is secured to the pipe at these end faces. However, the plate 33 may be permanently or temporarily fixed within the pipe 30a by any means, including the use of spacers.

The plate 33 may suitably be made of glass, e.g. borosilicate glass, but other materials may be contemplated.

It can be seen that the edge surface of the plate that lies in the plane of the cross sectional surface area of the elongate reactor pipe, i.e. perpendicular to the flow of water, has a cross sectional area that is considerably less than 50% of the cross sectional area of the elongate reactor pipe. By using a plate that has a relatively small cross sectional area perpendicular to the flow of water, the flow of water is not significantly impeded by the presence of the plate.

Figure 2b shows an elongate pipe 30b comprising an elongate member 35 which has a surface 34b that is coated with a photocatalyst. The elongate member 35 is shown as hollow (i.e. with an elongate central bore) but in an alternative embodiment it may be solid (i.e. without an elongate central bore).

The elongate member 35 is contained within the outer wall 32 of the elongate pipe 30b, and is supported therein by spacers 36. However, the elongate member 35 may be permanently or temporarily fixed within the pipe 30b by any means.

The elongate cylindrical member 35 may suitably be made of glass, e.g. borosilicate glass, but other materials may be contemplated.

The spacers 36 may suitably be made of glass, e.g. borosilicate glass, but other materials may be contemplated.

The elongate member 35 is shown as cylindrical in shape. However, although this embodiment is illustrated by showing an elongated member 35 that is cylindrical, it will be appreciated that the elongate member could have alternate cross sectional shapes instead of circular. For example, the cross section could be triangular or square or rectangular or pentagonal or hexagonal.

In embodiments where the elongate member 35 has multiple elongate surfaces, e.g. due to having a cross sectional shape that has more than one side and/or due to being hollow and therefore having both internal and external elongate surfaces, one or more of said elongate surfaces may be coated with photocatalyst.

In the illustrated embodiment the outer surface 34b of the cylindrical elongate member 35 is coated with photocatalyst.

It can be seen that the solid end surface of the hollow elongate member that lies in the plane of the cross sectional surface area of the elongate reactor pipe, i.e. perpendicular to the flow of water, has a cross sectional area that is considerably less than 50% of the cross sectional area of the elongate reactor pipe. By using an elongate member that has a relatively small cross sectional area of solid material perpendicular to the flow of water, the flow of water is not significantly impeded by the presence of the elongate member.

Figure 2c shows an elongate pipe 30c which has an inner surface 34c that is coated with a photocatalyst. In other words, in this embodiment it is the inner surface 34c of the pipe’s outer wall 32 that is coated with photocatalyst.

In the illustrated embodiment the photocatalyst is provided as a band that extends around the whole circumference of the pipe 30c. However, a band that only extends around part of the circumference of the pipe 30c and/or stripes that extend along the length of the pipe 30c can also be contemplated.

It can be seen that in this embodiment there are no physical objects within the pipe 30c. Thus the flow of water along the pipe is not impeded by the presence of any physical objects.

Referring back to Figure 1, the elongate pipe 30 is provided with water W by liquid controller 50. In this regard, the liquid controller 50 pumps liquid along the elongate pipe 30. The flow of water W within the elongate pipe 30 is depicted by dotted lines and arrows. In use, water W reaches the surface 34 coated with a photocatalyst. The liquid controller 50 provides the water W under pressure within the system. The water W may be preheated before being pumped into the elongate pipe 30.

Light L is provided to the light focussing device 20. In one preferred embodiment, the light L is sunlight. The light focussing device 20 in turn focuses the light L into the focal region and thereby onto the elongate pipe 30 and specifically the section of the surface 34 coated with a photocatalyst.

The light L as focussed onto the elongate pipe 30 may lead to the water W being heated.

In the presence of both water W and light L, the photocatalyst produces hydrogen. The generated hydrogen may be transported in a gaseous state or dissolved in the liquid depending on the composition of the liquid and/or pressure of the liquid.

The generated hydrogen H ₂ is separated from the water W using the gas separation system 60. The water W that is separated from the hydrogen is returned to the liquid controller 50.

Water W is continuously circulated under pressure through the elongate pipe 30, as controlled by the liquid controller 50, such that hydrogen H ₂ is continuously generated from water provided that light L is provided via the light focussing device 20.

Referring now to Figure 3 of the accompanying drawings, a system 70 comprises a plurality of photocatalytic reactors 10 that can be used to implement the methods of the present invention. Each reactor 10 is fed by water W. Each reactor 10 generates hydrogen H ₂ that may be collected and/or used as described previously. Each reactor 10 may also generate oxygen 0 ₂ that may be collected and/or used as described previously. Each reactor 10 may also produce heat (not shown) that may be that may be collected and/or used as described previously.

The reactors 10 are controlled by a central control unit 80. For example, the central control unit 80 may comprise: a temperature control unit that controls the temperature of the water within the elongate reactor pipe of each reactor; a pressure control unit that controls the pressure within the elongate reactor pipe of each reactor; and/or an orientation control unit that controls (optimises) the orientation of the light focussing device and/or the elongate reactor pipe. By controlling these parameters, the central control unit can maximise photocatalysis, and therefore the generation of hydrogen, within the elongate reactor pipe of each reactor.

It will be envisaged that the system shown in Figure 3 may be in proximity to an oil refinery, a desalination plant, a chemical or pharmaceutical synthesis plant, a power station, and/or a blast furnace for convenience of use of the hydrogen, oxygen and/or heat generated from the present invention. Alternatively or additionally, the system shown in Figure 3 may be in proximity to a port and/or pipeline for convenience of transportation of the hydrogen and optionally oxygen generated from the present invention.

Further information relating to the invention

Design for photocatalysis reactor primarily for splitting water

The reactor consists of a vessel, with one or more openings, whereby liquid and gas can pass through the opening. The vessel may be, but is not limited to being, glass and, additionally or alternatively, plastic - or additionally or alternatively any other substance. Ideally, yet not limited to, the vessel would have two or more openings, to allow liquid to flow. This may be, but not limited to, be structured as a pipe, which may be straight, but also may be bent or curved, and additionally or alternatively, further attachments, which may include, but are not limited to, pneumatics and further pipe work which may have, yet is not limited to having, further attachments such as a pump and additionally or alternatively, a circulator and may comprise in the system, one or more heat exchangers.

The vessel, which may be, but is not limited to being, a pipe, may contain photocatalyst which may be on the inside of the pipe wall, or may be, additionally or alternatively, on a structure within the pipe, such as, yet not limited to, a rod. There may be, yet not limited to, spacers, to keep the rod, or any other structure, from the inner walls of the pipe. The pipe may be layered, and one pipe may be in another pipe, and so on.

Water, which may be between the temperatures or 1 and 500 degrees C, may be, yet is not limited to be, held under pressure, and flows into the vessel, either by its own accord or by action, of a component, such as, yet not limited to, a circulator and additionally or alternative a circulator, and additionally or alternatively, any other devise known in the art, or any other devise. The vessel may, yet is not limited to, be at an angle or gradient, such as, yet not limited to, allow a 1 in 50 fall. It may be horizontal, or up to 90 degrees in orientation.

There may be a focussing device, which may be, yet is not limited to being, a mirror trough, which may be, yet not limited to being, a heliostat, in that it tracks the sun in one or more axis.

As gases are formed in the vessel, there may be a separation devise at one or more end/opening. This may consist of some gas, such as those being produced, but not limited to, forming a headspace, whereby pneumatics, or some other device in the art, then allows gas and, additionally or alternatively, water, out of the opening. This vessel may be held under constant pressure, or may vary in pressure. It may be held at ambient pressure, and up to higher pressure, such as 10, 20, 50 or 100 bar or more. These vessels, and additionally or alternatively focussing devices, may form a unit which may, yet is not limited to, repeat, i.e., it may be modular. They may, yet are not limited to, connect together, and additionally or alternatively, may connect to a connecting network, such as, yet not limited to, a pipe infrastructure or other grid.

The gases and focused, useful heat outputs, it is envisaged, would be used, yet not limited to being used, in further down-stream processes. There are many useful and economic used for correctly priced hydrogen, oxygen and heat, along with any other products.

There may be, yet not limited to being, a membrane to separate the hydrogen and oxygen from one or more gas streams coming from the vessel. Any other separation method could also be used, such as are known in the art or being developed. A membrane is likely to be optimum due to cost, yet is not limited to being just a membrane that can be used in the gas separation.

The water, heat and products may also be allowed to be recycled/recirculated around the system by known means, such as, yet not limited to, pipework, which may then allow some of the products and, additionally or alternately, heat and water to also exit the system if necessary, for reasons such as, yet not limited to, being economic, safety, servicing, or any other reason. One or more heat exchangers may be used in the system, and the water running through the vessel, may be, yet is not limited to, being recirculated. As the reaction progresses, more reactants can be added to the system, either in continuous production, or in batch process, or not at all, or any combination of the aforesaid. The reaction vessel may contain sub units or reaction vessels, and may be enclosed, or the entire unit may be, yet not limited to being, enclosed. This could be, yet is not limited to being, for collection of products, safety, or any other reason as to why this would be enclosed, such as reduced cost of cleaning, aesthetics, etc.

Down-stream processes

Some possible down-stream reactions to utilise the products from the hydrogen generation apparatus, which may include utilising the oxygen and useful heat generated as well.

Some possible down-stream reactions and processes for the products and additionally or alternatively, outputs of the reactor, or any cheap source of one or more of the products/outputs would be, yet not limited to, using the useful heat output to drive desalination/water purification, additionally or alternatively, using the useful heat to drive one or more turbines, which may be, yet not limited to being, in a system, which may be, yet not limited to being, configured for optimum at the relative heat output of the system, such that it is possibly, yet not limited to being, economic, and possibly, yet not limited to being, most economic. This may include, yet not limited to including, one or more low temperature turbine, such as those known in the art. Exhaust heat from this turbine may be used to drive the desalination. Heat may be, yet is not limited to being, recycled throughout all parts of the generation apparatus and all parts of the down-stream processes, independent of which down-stream processes are being utilized. Heat could also be exported and, additionally or alternatively, be sold to other users, and, additionally or alternatively, used for agriculture, warming living quarters for habitation, heating a medium for safe discharge, stored, or any other non-listed down-stream process which would benefit from colocation or any additional use where it is economic to do so, or even if it is uneconomic to do so, or any combination of the aforesaid.

A non-limiting use for the oxygen would be to insert into combustion and, additionally or alternatively, any industrial process to make the process run more efficiently and, additionally or alternatively, economically and, additionally or alternatively, where oxygen is a required and, additionally or alternatively, preferred feedstock. There are many such uses known in the art. Oxygen generated could also be used in the Fischer-Tropsch type pathway to generate liquid fuels, lubricants, feedstocks for plastics, and any other use for these well-known compounds, or any combination of the aforesaid. This would involve methane, yet not limited to, as an additional feed stock. Due to the likely location, yet not limited to being, areas with large amounts of sunshine, such as, yet not limited to, desert areas, to include, yet not limited to being, in the Middle East, whereby there is an abundance of naturally occurring methane, as just one example of a co-feedstock, and its likely beneficial location for optimum, yet not limited to, operation of the proposed system. In such a desert region, as an example, yet not limited to, there is also a requirement for clean drinking water for many uses, such as, yet not limited to, agriculture, human consumption and enjoyment, or any combination of the aforesaid. There are also many other uses for the oxygen known in the art, of which this covers; this is simply to outline the likely, yet not limited to, main and possibly most economic uses, simply as examples. Another example use, and lesser-known than the above, which is covered by the present invention, would be for the production of protein for use in animal feed, fish/prawn feed or for human consumption, which may, yet is not limited to, undergo further processing before being consumed by humans. The reaction of methane and oxygen by, yet not limited to, methanotrophs, is well known in the art, as an example, but the invention is not limited to this, and there are also many other pathways to use the products generated from the apparatus, at least in part, either initially or after further processing, or both, to create food.

The hydrogen has many uses, either in its raw form or for further processing or both. Many reactions are known in the art, but some to highlight as examples, yet not being only limited to these examples, would be the reverse water gas shift and Sabatier reaction. These, as just a minor example, would show how to convert C0 ₂ into more useful products, thus at least giving another, possibly more, yet not limited to, economic use for the C0 ₂ than burying it in the ground. Much more interesting is to use it as a feedstock to create CO and methane, as examples, yet not limited to, of which CO and hydrogen is syngas, with many uses known, yet not limited to, in the art, and so on. Co-location of industry, near the proposed, is likely, yet not limited to, yield positive impact on economics, and additionally or alternatively, C0 ₂ emissions from otherwise polluting industries.

The products generated from the proposed system can be added with other components to make many things, not just limited to those mentioned above. These are just some example down-stream processes for the proposed system, yet the invention is not limited in scope to just those mentioned.

Another economic pathway, as an example, is to use the proposed system, at least in part, or not at all, to generate methanol from one or more of its products. This is also a useful feedstock for other chemicals, and has economic value. Such methods are known in the art. There are many possible reactions and production systems that become economic and useful when the hydrogen and oxygen and heat become cheap enough, of which this reactor and method will allow these processes to be possible and additionally or alternatively, economic whereby, they were not before.

Further, for economic storage of the produced gases and additionally or alternatively, products, such as yet not limited to, hydrogen, underground storage, such as that in a disused oil well, and, additionally or alternatively, gas well, is likely, yet not limited to, be desirable. This is due to other means of storage, such as, yet not limited to, tankers and, additionally or alternatively, bullets, or any other device being likely, yet not limited to, being more expensive. Close proximity, in terms of a global infrastructure, to natural and possibly, yet not limited to, one or more depleted oil/gas well, is likely, yet not limited to, being desirable. As an example, yet not limited to, this could be in the Middle East.

There are many other possibilities to use the discussed apparatus and method, those mentioned herein are just some examples to show the range and give some ideas as to scope. The apparatus and method and down-stream process from one or more of its products and, additionally or alternatively, outputs, to include heat, are also included. There are many uses for these listed in the art or known by a professional person in the chemical industries.

Further down-stream processes

The hydrogen generation apparatus and method may also be used, yet not limited to, in a system involving the Haber process, and, additionally or alternatively, any similar process, as well as many other reactions, known in the art, for the production of fertilizer, or additionally or alternatively, explosives, and, additionally or alternatively, anything involving ammonia and, additionally or alternatively, any similar product. Such products are known in the art, and, additionally or alternatively, by a skilled reader in the art.

In addition, heat, and mechanical drive, which may be, yet is not limited to being useful, and, additionally or alternatively, pressure, and, additionally or alternatively, any other product from the initial reaction with economic value, at that time or other, and, additionally or alternatively, product from any other down-stream reactions, and, additionally or alternatively, co-located plants, may be recycled and moved around the plant, or system described, and may be exchanged with other reactions running within a similar vicinity to the plant and, additionally or alternatively, connected in some way, known in the art as part of, yet not limited to, a global distribution system.

The hydrogen, and, additionally or alternatively, other products, are not limited to being used in this way - it is simply an example of a likely economic use case, of which there are many others, for the purposes of illustration.