Field of the invention

The present invention relates to new methods for production of deuterium oxide (heavy water) and deuterium gas. The invention further relates to deuterium oxide and deuterium gas produced according to the present methods. More specifically, the processes enhance the isotope purity of deuterium oxide and produce deuterium gas is a fast, efficient and cost-effective way. The method is characterized by use of silicon particles, preferably in an aqueous medium.

Background

Deuterium oxide (D2O, Heavy water) is a form of water that comprises deuterium (D) rather than hydrogen (H). Deuterium is a non-radioactive isotope of hydrogen. The atom comprises a neutron in addition to the proton in the atomic core. The atomic weight of deuterium is therefore appr. 2 compared to the hydrogen atom with atomic weight 1. This results in that D2O has a molecular weight of 20 Dalton which is 2 more than for H2O.

The physical properties of heavy water are very similar to water, however, there are some minor differences.

Heavy water is naturally present in water in small quantities. About 0.016% of the hydrogens in natural water molecules are naturally in the form of heavy hydrogen (deuterium).

There are several applications of deuterium oxide. These include applications as neutron moderators in nuclear reactors and use as a solvent in research, typically as a solvent for nuclear magnetic resonance studies and for labelling of organic compounds in chemistry and pharmacology.

For many of these applications there is a need for heavy water with very high isotope purity. This means deuterium oxide comprising almost 100% deuterium atoms and almost no hydrogen atoms in the heavy water molecule.

Processes for the production of deuterium oxide are described in several patents and scientific publications. Some of the US patent documents are in ascending order after priority date: US2134249, US2156851, US2469869, US2999795, US3036891, US3206365, US3256163, US3399967, US3431080, US3437567, US3514382, US3681021, US3685966, US3789113, US3789112, US4124502, US4125598, US4446012, US2002141916, US2011027166, US2011027165 and US9670064.

A commercial process for the production of D2O is a process called Girdler sulfide process which is a dual temperature exchange sulfide process. Other processes are ammoniahydrogen isotopic exchange processes and processes based on electrolysis of water, distillation processes, use of lasers and use of various catalysts.

Deuterium gas (D2) is the deuterium version of hydrogen gas (H2). The gas has several applications within industry, production of nuclear weapons and in research.

There are several methods for the production of deuterium gas described in the literature. Most of these utilize deuterium oxide as a starting material. Recently an interesting process for the preparation of deuterium gas was published (A. Enomoto et al. : Convenient Method for the Production of Deuterium Gas Catalyzed by an Iridium Complex and Its Application to the Deuteration of Organic Compounds in Chem. Lett. 2019, 48, 106-109). The authors describe this as follows: “The reaction of deuterated methanol and deuterium oxide in the presence of an iridium catalyst bearing a functional bipyridonate ligand and sodium hydroxide under reflux for 48 hours gave deuterium gas in 63% yield.”

The present method for production of deuterium gas from deuterium oxide using silicon particles does not include any organic solvents nor catalyst, and seems to be a safe, fast and efficient method for production of deuterium gas within a few hours or less.

The present inventors have unexpectedly found that elemental silicon particles can be used for isotopical enhancement of deuterium oxide and production of deuterium gas by careful selection of the reaction conditions.

Summary of the invention

In a first aspect, the invention provides a new method for isotope enhancement of deuterium oxide by use of silicon particles, preferably in an aqueous medium comprising deuterium oxide. In a second aspect, the invention provides a new method for production of deuterium gas by use of silicon particles in deuterium oxide.

In a further aspect, the invention provides deuterium oxide produced by a process characterized by use of silicon particles, preferably in an aqueous medium comprising deuterium oxide.

Another aspect of the present invention provides deuterium gas produced by a process characterized by use of silicon particles in deuterium oxide.

In another aspect, the invention provides a method for production of deuterium oxide by use of silicon particles in the aqueous medium where said aqueous medium has pH of at least 7.0.

In another aspect, the invention provides a method for production of deuterium gas by use of silicon particles in deuterium oxide where said deuterium oxide has pH of at least 8.0.

Definitions

The term “porous” particles refer to particles with pores and not a smooth surface. Porous particles can be prepared by etching process typically using hydrofluoric acid or by a process where smaller particles form aggregates with pores.

The term “mesoporous” particles refer to particles containing pores with diameters between 2 and 50 nm.

The term “microporous” particles refer to particles having pores smaller than 2 nm in diameter.

The term “macroporous” particles refer to particles having pores larger than 2 nm in diameter.

The term “CVD” silicon particles refer to a process where the particles have been prepared by a chemical vapor deposition preferably using silane gas. The term “non-CVD” silicon particles refer to a process where the particles have not been prepared directly by a chemical vapor deposition. Such particles are typically prepared by grinding of larger silicon materials.

The term cCVD-SP is used to denote “centrifuge Chemical Vapor Deposition Silicon Particles” and refers to silicon particles which have been prepared by a centrifuge method. In particular, this term refers to silicon particles which have been prepared by a CVD method in a reactor wherein the reactor comprises a reactor body and a rotation device operatively arranged to the reactor, wherein the rotation device is configured to rotate the reactor around an axis during production of said silicon comprising particles.

The term PcCVD-SP is used to denote “Porous centrifuge Chemical Vapor Deposition Silicon Particles” and refers to silicon particles which have been prepared by a centrifuge method, optionally followed by a process to prepare the porosity of the particles.

The term “deuterium oxide” used without any isotope purity indication means any deuterium oxide.

Detailed Description

The present invention relates to new methods for production of deuterium oxide (heavy water) and deuterium gas. The invention further relates to enhancement of isotope purity of deuterium oxide and production of deuterium gas according to the present methods. The methods are characterized by use of silicon particles, preferably in an aqueous medium. Thus, ideally, the methods involve mixing silicon particles with an aqueous medium, wherein said aqueous medium preferably comprises water and deuterium oxide.

In one preferred embodiment of the invention, deuterium oxide is prepared from natural water comprising smaller amounts of deuterium oxide by use of silicon particles.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide in water is above 50% by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation of deuterium oxide, from the present method or from a mixture of methods. Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide is above 90% by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation of deuterium oxide, from the present method or from a mixture of methods.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide is above 95% by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation of deuterium oxide, from the present method or from a mixture of methods.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide is above 98% by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation of deuterium oxide, from the present method or from a mixture of methods.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide is above 99% by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation deuterium oxide, from the present method or from a mixture of methods.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide is above 99.5% by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation deuterium oxide, from the present method or from a mixture of methods.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide is above 99.8% by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation deuterium oxide, from the present method or from a mixture of methods.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the concentration of deuterium oxide is above 99.9 % by weight by use of silicon particles. The starting mixture comprising water and heavy water can be prepared from any state of the art method for preparation deuterium oxide, from the present method or from a mixture of methods.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide by use of silicon particles where pH of the aqueous solution is 7 or above 7.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide by use of silicon particles where pH of the aqueous solution is above 7.5.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide by use of silicon particles where pH of the aqueous solution is above 8.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide by use of silicon particles where pH of the aqueous solution is below 13.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide by use of silicon particles where said solution comprise a basic substance or a buffer.

Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide by use of silicon particles where the temperature is above 10 degrees centigrade. Another preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide by use of silicon particles where the temperature is above 20 degrees centigrade.

An even more preferred embodiment of the invention, the deuterium oxide is prepared from a mixture of water and deuterium oxide where the pH is between 7 and 9 and the temperature is between 20 degrees centigrade and 50 degrees centigrade.

In another preferred embodiment of the invention, deuterium gas (D2) is prepared from deuterium oxide using silicon particles. The isotope purity of the starting deuterium oxide should be as high as possible to secure high isotope purity of the deuterium gas. Typical isotope purity of the starting deuterium oxide could be about 99% or preferably higher.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where pH of the aqueous solution is above 8.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where pH of the aqueous solution is above 9.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where pH of the aqueous solution is above 10.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where pH of the aqueous solution is above 11.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where the temperature is 20 degrees centigrade or higher.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where the temperature is 40 degrees centigrade or higher.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where the temperature is 60 degrees centigrade or higher. Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where the temperature between 20 and 100 degrees centigrade at a pH between 8 and 14.

Another preferred embodiment of the invention, the deuterium gas is prepared from deuterium oxide by use of silicon particles where said solution comprise a basic substance or a buffer.

In another preferred embodiment of the invention, both deuterium oxide and deuterium gas (D2) are prepared from deuterium oxide using silicon particles. The isotope purity of the starting deuterium oxide should be as high as possible to secure high isotope purity of the deuterium gas. Typical isotope purity of the starting deuterium oxide could be about 99% or preferably higher.

In another preferred embodiment of the invention, the deuterium oxide and/or the deuterium gas are prepared according to the present process using silicon particles prepared from a non-CVD process. Such particles can typically be produced from grinding and/or milling processes.

In another preferred embodiment of the invention, the silicon particles used in the above processes are prepared by a CVD method which does not comprises a grinding and/or milling step.

In a particularly preferred embodiment of the present invention, the silicon particles used in the present invention are porous centrifuge Chemical Vapor Deposition Silicon Particles (PcCVD-SP). A particularly preferred method for the preparation of the silicon particles is disclosed in WO 2013/048258 and is briefly described below.

In this preferred process, chemical vapor deposition is carried out in a reactor comprising a reactor body that can rotate around an axis with the help of a rotation device operatively arranged to the reactor, at least one sidewall that surrounds the reactor body, at least one inlet for reaction gas, at least one outlet for residual gas and at least one heat appliance operatively arranged to the reactor, characterized in that during operation for the manufacture of silicon particles by CVD, the reactor comprises a layer of particles on the inside of, at least, one side wall.

Thus, the CVD process is preferably characterized by:

- producing a particle layer from the silicon containing reaction gas in the reactor or importing particles for the formation of an inner particle layer on the inner wall surface of the reactor,

- importing reaction gas for chemical vapor deposition,

- producing silicon by chemical vapor deposition on the particle layer,

- loosening the produced silicon from the particle layer and taking it out and carrying out any preparation of the inner surface of the reactor before the production of the silicon is continued by repeating the steps of the method.

Depending on the application the particles may be coated inert or exposed to air to form a thin native oxide layer on the particles. Further processing may include etching of the particles in HF with or without subsequent coating depending on the application. However, preferably, the particles are not subject to an etching process.

In a particle formed from milling of electronic grade silicon wafers the average crystal size of the material will be many orders of magnitude larger than the particle size. For CVD formed particles the average crystal size is tunable. It is possible to have one or few crystallites within each particle, to have a number of nano-crystallites within each particle or to have a completely un-ordered amorphous structure. This is tunable by the process and it is therefore both possible to choose a particular crystallinity or average crystallite size for the specific application or according to further processing. For instance the etching speed will depend on the crystallite size and orientation as well as the defect distribution and frequency within each crystal.

The particle degradation time will to some degree depend on the number of crystal interfaces reaching the surface, in other words how many oxidation channels the oxidation may propagate along down into the material as well as how imperfect the individual crystals are. The more imperfections and interfaces the easier it is both to reach the individual silicon atoms and to oxidize them. Since these are tunable properties in a CVD produced material it is thus possible to tune the material to any specific application in a completely different way than for a crushed large crystals material where these properties are given. Especially for applications where rapid bio-degradation is desirable the CVD particles will have a substantial advantage over the classical crushed crystalline silicon.

In a further preferred aspect of the present invention, the silicon particles used in the above processes are porous particles.

In a further preferred aspect of the present invention, the silicon particles used in the above processes are non-porous particles.

As discussed previously, the silicon particles of the invention are capable of generating hydrogen.

The silicon particles have the capability of reacting with water but have been found to be much less reactive towards deuterium oxide, however, if the pH is sufficient high especially in combination with higher temperature, the silicon particles react with deuterium oxide and form deuterium gas.

Silicon

The silicon in the silicon particles used in the present process (typically cCVD-SP) is present in at least 50 wt% as elemental silicon (silicon with oxidation number 0), relative to the total weight of silicon. More preferred form of silicon in the present silicon particles is at least 70 wt% as elemental silicon, even more preferred at least 80 wt% as elemental silicon, relative to the total weight of silicon. Another preferred aspect related to the form of silicon in the present particles is that the amount of elemental silicon and silicon dioxide is more than 80%, more preferably more than 90% most preferably more than 95%, relative to the total weight of silicon.

The elemental silicon in the particles used in the present process may be in amorphous or crystalline form. The elemental silicon in particles produced by the CVD process is mainly in the form of amorphous elemental silicon at ambient temperature, however, particles comprising crystalline silicon can directly be prepared by CVD at high temperature (e.g. 600 °C and above) and longer reaction times. The particles comprising crystalline silicon prepared from a CVD method typically are in the form of poly crystalline material (crystal size around 1.5 nm) while crystalline milled particles typically consist of one crystal of silicon.

The crystalline versus amorphous form of silicon can routinely be determined by X-ray diffraction analysis (XRD analysis). The amorphous form of silicon can be transformed to crystalline form of silicon by heating to relative high temperatures (e.g. above 500 °C).

Silicon particles produced by the CVD method typically comprise some material comprising one or more silicon-hydrogen bond. This hydrogen might be available for formation of some hydrogen gas in a reaction with water.

In certain embodiments, the elemental silicon is present in a crystalline form, in some embodiments typically more than 50 wt % in the crystalline form and in some embodiments more than 70 wt % in a crystalline form and finally in some embodiments more than 90 wt % in a crystalline form, relative to the total weight of elemental silicon.

In other embodiments, the silicon particles comprise elemental silicon in amorphous form, in some embodiments more than 50 wt %, in some embodiments more than 70 wt %, in some embodiments more than 90 wt % and finally in some embodiments more than 95 wt% in amorphous form, relative to the total weight of elemental silicon.

One preferred embodiment of this aspect of the invention is wherein the silicon particles are cCVD-SP or PcCVD-SP.

One of the most preferred embodiments of this aspect of the invention is wherein the silicon particles are cCVD-SP comprising silicon in amorphous form, such as in the wt% ranges defined above.

Another of the most preferred embodiment of this aspect of the invention is wherein the silicon particles are cCVD-SP that are not produced by an etching process; especially not by a hydrofluoric acid (HF) etching process, i.e. the silicon particles are non-etched.

The ultimate form of the most preferred embodiment of this aspect of the invention is wherein the silicon particles comprise amorphous silicon, such as in the wt % ranges defined above, and are non-etched. Particle size

The silicon particles may have “tailor made” particle sizes. Typical median diameter for the silicon particles of the invention may be less than 500 nm, such as 30 to 300 nm, using the technique of Dynamic Light Scattering (DLS), for example using instruments like Zetasizer.

The poly dispersity index can also vary from almost monodisperse particles to particles with very broad particle size distribution.

In one embodiment, the silicon particles preferably have an average diameter of less than 1 pm, more preferably less than 0.8 pm, even more preferably less than 0.6 pm, such as less than 0.5 pm.

Porosity

The silicon particles of the invention can be non-porous (cCVD-SP) or porous (PcCVD- SP). One aspect of the present invention relates to use of porous particles. In all embodiments, it is preferred if the particles are prepared by a non-etching process. Porous particles can be prepared by forming stable aggregates of smaller particles; so-called stable particle clusters.

The porosity of the PcCVD-SP can vary over a large range. The porosity is a measure on the volume of the pores. A PcCVD-SP with porosity of 50 % has a porosity volume that is 50% of the total PcCVD-SP volume. The porosity of PcCVD-SP may typically be from 20% to 90%. In certain embodiments, the porosity is more than 40%, typically more than 50%, more than 60%, more than 70%, more than 80% such as 90%. In other embodiments the porosity is preferably around 50% or lower.

The pore size of PcCVD-SP can vary from microporous particles through mesoporous particles to macroporous particles. Typical average pore size of PcCVD-SP is from 1 nm to 200 nm. In one embodiment of the present invention, the average pore size is 1-10 nm, in another embodiment the typical pore size is 5-20 nm, in still another embodiment, the typical pore size is 10-50 nm and finally, in still another embodiment, the typical pore size is 2-50 nm.

In one embodiment, the particles are microporous. In this embodiment, preferably at least 2 vol% of the pores are micropores, more preferably at least 5 vol%, even more preferably at least 10 vol%, especially at least 20 vol%, such as at least 50vol%, relative to the total pore volume.

In another embodiment, the particles are mesoporous. In this embodiment, preferably at least 2 vol% of the pores are mesopores, more preferably at least 5 vol%, even more preferably at least 10 vol%, especially at least 20 vol%, such as at least 50vol%, relative to the total pore volume.

In a further embodiment, the particles are macroporous. In this embodiment, preferably at least 2 vol% of the pores are macropores, more preferably at least 5 vol%, even more preferably at least 10 vol%, especially at least 20 vol%, such as at least 50vol%, relative to the total pore volume.

The invention will now be described with reference to the following, non-limiting, examples.

Examples

All CVD silicon particles were produced in a reactor where the reactor comprises a reactor body and a rotation device operatively arranged to the reactor, wherein the rotation device is configured to rotate the reactor around an axis during production according to WO2013048258.

Part 1 : Hydrogen release

Example 1: Formation of hydrogen gas and deuterium gas at pH 8.5 at 37 degrees centigrade

Silicon particles (labelled H18, amorphous silicon, hydrodynamic size 210 nm with poly dispersity index of 0.180) (50 mg) were suspended in deuterium oxide (Cambridge Isotope Laboratories, 99.9%) (25 ml) comprising sodium bicarbonate (Sigma- Aldrich, 99.7%) (210 mg) in a round bottle equipped with a tubing with a needle for hydrogen outlet in an inverted metered vial comprising water. The inverted vial is placed in a water bath (standard laboratory upset for collection of gas). The suspension was stirred at 37 degrees centigrade. The gas volume was observed over time.

A parallel experiment using water instead of deuterium oxide was performed as a control.

Results:

A similar experiment at room temperature did not generate hydrogen gas from water nor deuterium gas from deuterium oxide.

The cleavage of water was appr.5 times faster than the cleavage of deuterium oxide at pH 8.5 and 30 degrees centigrade. Examples 2 - 4. Production of deuterium gas from deuterium oxide at different temperatures and pH values

Sodium bicarbonate (Sigma- Aldrich, 99.7%) (42 mg) was dissolved in deuterium oxide (Cambridge Isotope Laboratories, 99.9%) (5 ml) generating solutions with pH 8.5 for use in Example 2 and Example 3.

Potassium carbonate (Sigma- Aldrich, 99.0%) (61 mg) was dissolved in deuterium oxide (Cambridge Isotope Laboratories, 99.9%) (5 ml) generating solutions with pH 11 for use in Example 4.

Silicon particles (Hl 8, amorphous silicon, hydrodynamic size 210 nm with poly dispersity index of 0.180) (50 mg) were suspended in each of the three solutions. The same type of equipment as described in example 1 was used in each example. The suspensions were headed and stirred using magnetic stirring. The gas volume was observed over time.

Results:

Deuterium gas (appr. 50 ml) was produced from deuterium oxide at room temperature at pH 11 and at 70 degrees centigrade at pH 8.5 during about 2 hours. At pH 8.5 the production of deuterium gas was much lower at 50 degrees centigrade versus the higher temperature.

Example 5. Production of hydrogen gas and deuterium gas from deuterium oxide at pH above 7

Tris(hydroxymethyl)aminomethane (TRIS) (Merck, 99.5%) (42 mg) was dissolved in deuterium oxide (Cambridge Isotope Laboratories, 99.9%) (5 ml) generating solution with pH above 7.

This example was performed as Example 2 with tris(hydroxymethyl)aminomethane and not sodium bicarbonate as base.

A parallel experiment using water with TRIS and not deuterium oxide was performed as control.

Results:

Silicon particles react much faster with water than deuterium oxide at pH above 7.

Example 6 Production of hydrogen gas and deuterium gas at pH 11

Triethyl amine (Sigma, 99.5%) (3 drops) was dissolved in deuterium oxide (Cambridge Isotope Laboratories, 99.9%) (5 ml) generating solution with pH 11.

This example was performed as Example 5 with triethyl amine as base and not TRIS as base.

A parallel experiment using water with triethyl amine and not deuterium oxide was performed as control.

Results: n.a.: not available

Example 7 Formation of deuterium oxide with high isotope purity

Silicon particles (Hl 8, amorphous silicon, hydrodynamic size 210 nm with poly dispersity index of 0.180) (200 mg) were suspended in deuterium oxide (Cambridge Isotope Laboratories, isotope purity 99.5%) (5 ml) comprising sodium bicarbonate (Sigma- Aldrich, 99.7%) (50 mg) in a round bottle equipped with a tubing with a needle for hydrogen outlet in an inverted metered vial comprising water. The inverted vial is placed in a water bath (standard laboratory setup for collection of gas). The suspension was stirred at 50 degrees centigrade for 3 hours.

The mixture was cooled and centrifugated at high speed (15 000 rpm.) for 15 minutes. The deuterium oxide product and the deuterium oxide starting material are analyzed by proton NMR to quantify isotope purity.