Patent Description:
Ammonia is a very important chemical, which is produced in many millions of tonnes every year.

Manufacture of ammonia in an industrial scale is well studied and described. There is for instance the so called Haber-Bosch process described in <CIT>, which discloses that ammonia can be obtained by passing a mixture of nitrogen and hydrogen over a catalytic agent at a high temperature and removing at a lower temperature the ammonia contained in the gases leaving the catalyst. A disadvantage of the Haber-Bosch process is its large emission of greenhouse gases. The Haber-Bosch process consumes a lot of energy and it has been estimated that it consumes more than <NUM>% of the global energy and about <NUM>-<NUM>% of the fossil gas in the world for production of the hydrogen to the process. The Haber-Bosch process operates at a high pressure, which makes the equipment more expensive.

Ammonia can also be made using electrolysis. Then electricity from renewable sources can be used as energy source to manufacture ammonia from for instance water and nitrogen.

<CIT> discloses electro-chemical processes for reduction of carbon dioxide, for example converting carbon dioxide to formate salts or formic acid. In selected embodiments, operation of a continuous reactor with a three dimensional cathode and a two-phase (gas/liquid) catholyte flow provides advantageous conditions for electro-reduction of carbon dioxide. In these embodiments, the continuous two-phase flow of catholyte solvent and carbon dioxide containing gas, in selected gas/liquid phase volume flow ratios, provides dynamic conditions that favour the electro-reduction of CO<NUM> at relatively high effective superficial current densities and gas space velocities, with relatively low reactor (cell) voltages (<<NUM> Volts). In some embodiments, relatively high internal gas hold-up in the cathode chamber (evident in an internal gas to liquid phase volume ratio ><NUM>) may provide greater than equilibrium CO<NUM> concentrations in the liquid phase, also facilitating relatively high effective superficial current densities.

<CIT> discloses a method for manufacturing of ammonia using electrolysis. Lithium ions are reduced to lithium and reacted with nitrogen on the cathode. Lithium nitride reacts with water to form ammonia and lithium ions. The cathode potential is pulsed between the lithium reduction potential and a less negative cathode potential.

<CIT> describes a method of electrolytically producing ammonia with a step of switching the polarity of the electrodes after production of ammonia.

There is a need to improve the manufacture of ammonia with a lower carbon footprint, lower energy consumption and a simpler process.

One object of the present invention is to obviate at least some of the disadvantages in the prior art and provide an improved method and device for the manufacture of ammonia.

In a first aspect there is provided a method for manufacturing ammonia, by means of an electrolytic cell <NUM> comprising a first <NUM> and a second <NUM> compartment, wherein the first and second compartments are separated by a membrane <NUM> permeable to ions, wherein the first compartment <NUM> comprises a first electrode <NUM> and wherein the second compartment <NUM> comprises a second electrode <NUM> , wherein the first <NUM> and the second <NUM> compartments an electrolyte comprising comprise at least one lithium salt <NUM> , the method comprising the steps of:.

In a second aspect there is provided an electrolytic cell <NUM> comprising a first <NUM> and a second <NUM> compartment, wherein the first <NUM> and second <NUM> compartments are separated by a membrane <NUM> permeable to ions, wherein the first compartment <NUM> comprises a first electrode <NUM> and wherein the second compartment <NUM> comprises a second electrode <NUM>, wherein the first <NUM> and second <NUM> electrodes are adapted to change polarity so that the first electrode <NUM> is adapted to change between being a cathode C and an anode A, whereas the second electrode <NUM> is adapted to change between an anode A and a cathode C, wherein the electrolytic cell <NUM> comprises a heater and a cooler so that a content <NUM> in the first and second compartment can be heated or cooled, wherein the electrolytic cell <NUM> comprises a tube for addition of nitrogen to the cathode C, and wherein the electrolytic cell <NUM> comprises a tube for addition of water or steam to the cathode C, wherein the electrolytic cell <NUM> is communicatively connected to a programmable controller, wherein the programmable controller is configured to control at least one selected from the group consisting of i) the heater, ii) the cooler, iii) a voltage V applied over the first <NUM> and second <NUM> electrodes, and iv) the polarity of the voltage applied over the first <NUM> and second <NUM> electrodes, and wherein the programmable controller is communicatively connected to at least one selected from the group consisting of i) a temperature sensor for the temperature in the first <NUM> and second <NUM> compartments, ii) a voltage sensor for the voltage between the first <NUM> and second <NUM> electrodes, and iii) a polarity sensor for the polarity of the voltage applied over the first <NUM> and second <NUM> electrodes.

Further embodiments of the present invention are defined in the appended dependent claims, which are explicitly incorporated herein.

One advantage is that the method can be run virtually continuously since the polarity of the electrode changes, thereby regenerating the electrodes.

The method is energy efficient and only requires addition of water and nitrogen when the process is up and running.

It is possible to perform the method under lower pressure compared to the prior art which gives a more cost effective process.

The technology makes it possible to manufacture ammonia locally, which minimizes distribution costs.

Aspects and embodiments will be described with reference to the following drawings in which:
<FIG> shows the electrolytic cell <NUM> comprising a first <NUM> and a second <NUM> compartment separated by a membrane <NUM> , a first electrode <NUM> , a second electrode <NUM> , as well as the content <NUM> in the first and second compartments, i.e. at least one lithium salt. Also shown are a cathode C an anode A and a voltage V applied over the first <NUM> , a second <NUM> electrode.

Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular configurations, process steps and materials disclosed herein as such configurations, process steps and materials may vary somewhat.

It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise.

The following terms are used throughout the description and the claims.

Continuous as used herein refers to the production of ammonia, but is not truly continuous in a strict sense since the process requires an interruption for cooling and so on. The ammonia is produced alternatingly at both electrodes, which is close to a truly continuous process and no interruption is required for regeneration of the electrodes. In this sense the process is continuous and is thus denoted as continuous.

Electrolytic cell as used herein denotes an electrochemical cell that utilizes an external source of electrical energy to force a chemical reaction that would otherwise not occur. The external energy source is a voltage applied between the cell's two electrodes; an anode (positively charged electrode) and a cathode (negatively charged electrode), which are immersed in an electrolyte solution. In the electrolytic cell, a current passes through the cell by an external voltage, causing a non-spontaneous chemical reaction to proceed.

The electrolytic cell has three main components: an electrolyte and two electrodes (i.e. a cathode and an anode). The electrolyte comprises at least one lithium salt, which is molten during the electrolysis. When driven by an external voltage applied to the electrodes, the ions in the electrolyte are attracted to an electrode with the opposite charge, where charge-transferring reactions can take place. Only with an external electric potential (i.e., voltage) of correct polarity and sufficient magnitude can the reaction take place. The electrical energy provided can produce a chemical reaction that would otherwise not occur spontaneously.

In the first aspect there is provided a method for manufacturing ammonia, by means of an electrolytic cell <NUM> comprising a first <NUM> and a second <NUM> compartment, wherein the first and second compartments are separated by a membrane <NUM> permeable to ions, wherein the first compartment <NUM> comprises a first electrode <NUM> and wherein the second compartment <NUM> comprises a second electrode <NUM> , wherein the first <NUM> and the second <NUM> compartments an electrolyte comprising comprise at least one lithium salt <NUM> , the method comprising the steps of:.

The electrolyte comprises at least one lithium salt and is present in the first and second compartments. The electrolyte is a molten salt.

When the reaction starts, one polarity is chosen, such as the first electrode as cathode and the second electrode as anode. This polarity is reversed in step g.

When the reaction is started an amount of lithium hydroxide is added to the anode. This is normally done only when the reaction starts. The lithium hydroxide is regenerated during the reaction.

When the electrolysis is to begin the electrolyte, i.e. a salt is heated so that it melts. It is suitable to select a salt with relatively low melting point for better process economy. One option is to mix the lithium salt with another salt so that a mixture with lower melting point is obtained. One example is an eutectic mixture comprising a lithium salt.

Water should not be present in the electrolyte during the electrolysis (step d) since any formed lithium will react with the water.

During the electrolysis a voltage V is applied over the electrodes. At the same time nitrogen gas is added to the cathode. Elemental lithium forms at the cathode. The elemental lithium reacts with the nitrogen gas to form lithium nitride.

At the anode lithium hydroxide reacts so that water and oxygen is formed. Lithium ions are transferred to the cathode.

When the reaction has proceeded for some time, the electrolysis is stopped and the electrolyte (i.e. the at least one lithium salt) is cooled. This can suitably be made when the lithium hydroxide at the anode is consumed by the reaction. In one embodiment, step d) is carried out until the lithium hydroxide added in step b) is consumed.

After the cooling of the electrolyte, i.e. the at least one lithium salt, water is added to the cathode. The water is added as steam and/or liquid water. The lithium nitride formed at the cathode then reacts with the water to form ammonia and lithium hydroxide.

Li<NUM>N + <NUM><NUM>O → NH<NUM> + 3LiOH.

When the lithium nitride has reacted, the lithium hydroxide is regenerated. The polarity is then changed so that the reaction can be carried out again.

The polarity change makes it possible to run the process continuously with a shorter interruption for cooling to generate the ammonia. The reaction can be repeated as many times as desired. Steps c)-g) are then repeated as desired. Normally no additional salts have to be added to the system. Only nitrogen gas and water has to be added during operation when the device is up and running. It is an advantage of the process that the system can regenerate so that the polarity can be switched.

Lithium hydroxide should be present at the anode. If for instance lithium chloride is the lithium salt, then chlorine gas may form at the anode if the hydroxy ions were not present. The hydroxy ions have a lower ionization potential compared to the chlorine ions. If the voltage is not too high, then no chlorine gas or essentially no chlorine gas will be formed at the anode.

In one embodiment, the electrolyte comprising the at least one lithium salt <NUM> is in an eutectic mixture comprising at least one lithium salt. A eutectic mixture is a homogenous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the eutectic temperature. In one embodiment, the mixing ratio of the constituents in the electrolyte is such that the lowest possible melting temperature occurs, i.e. at the eutectic temperature.

In one embodiment, the electrolyte comprising the at least one lithium salt <NUM> is an eutectic mixture of lithium chloride and potassium chloride, and wherein the electrolyte comprising the at least one lithium salt <NUM> is heated above <NUM> in step c). <NUM> is roughly the eutectic temperature of a mixture consisting of lithium chloride and potassium chloride. Hence, the composition of lithium chloride and potassium chloride with the lowest melting point is chosen in one embodiment. The electrolyte comprising the at least one lithium salt can also be heated a bit above its melting temperature. In one embodiment, an eutectic mixture of lithium chloride and potassium chloride is heated to <NUM> above its melting temperature. An advantage of selecting an eutectic mixture is that the melting point is lower.

Many different mixtures comprising at least one lithium salt can be used. It is suitable that the melting temperature is not too high and thus a mixture of a lithium salt with another salt or another compound which reduces the melting point is suitable.

In step e) the electrolyte comprising the at least one lithium salt is cooled to below its melting point. In one embodiment, it is cooled to below the boiling point of water to facilitate the addition of water. In one embodiment, the electrolyte comprising the at least one lithium salt <NUM> is cooled below <NUM> in step e).

If the voltage is too high, then chlorine ions may form chlorine gas at the anode. However since hydroxy ions are present they will react easier than the chlorine ions and thus it is possible to choose a suitable voltage so that the hydroxy ions, but not the chlorine ions react. In one embodiment, the voltage V is adjusted so that essentially no chlorine gas is formed at the anode A.

In the second aspect there is provided an electrolytic cell <NUM> comprising a first <NUM> and a second <NUM> compartment, wherein the first <NUM> and second <NUM> compartments are separated by a membrane <NUM> permeable to ions, wherein the first compartment <NUM> comprises a first electrode <NUM> and wherein the second compartment <NUM> comprises a second electrode <NUM>, wherein the first <NUM> and second <NUM> electrodes are adapted to change polarity so that the first electrode <NUM> is adapted to change between being a cathode C and an anode A, whereas the second electrode <NUM> is adapted to change between an anode A and a cathode C, wherein the electrolytic cell <NUM> comprises a heater and a cooler so that a content <NUM> in the first and second compartment can be heated or cooled, wherein the electrolytic cell <NUM> comprises a tube for addition of nitrogen to the cathode C, and wherein the electrolytic cell <NUM> comprises a tube for addition of water or steam to the cathode C, wherein the electrolytic cell <NUM> further comprises a programmable controller, wherein the programmable controller is configured to control at least one selected from the group consisting of i) the heater, ii) the cooler, iii) a voltage V applied over the first <NUM> and second <NUM> electrodes, and iv) the polarity of the voltage applied over the first <NUM> and second <NUM> electrodes, and wherein the programmable controller is communicatively connected to at least one selected from the group consisting of i) a temperature sensor for the temperature in the first <NUM> and second <NUM> compartments, ii) a voltage sensor for the voltage between the first <NUM> and second <NUM> electrodes, and iii) a polarity sensor for the polarity of the voltage applied over the first <NUM> and second <NUM> electrodes.

In one embodiment of the second aspect, the first <NUM> and second <NUM> electrodes comprise at least one selected from the group consisting of graphite, platinum, and platinum coated metal.

In one embodiment of the second aspect, the membrane <NUM> is a porous magnesia diaphragm.

Claim 1:
A method for manufacturing ammonia, by means of an electrolytic cell (<NUM>) comprising a first (<NUM>) and a second (<NUM>) compartment, wherein the first and second compartments are separated by a membrane (<NUM>) permeable to ions, wherein the first compartment (<NUM>) comprises a first electrode (<NUM>) and wherein the second compartment (<NUM>) comprises a second electrode (<NUM>), wherein the first (<NUM>) and the second (<NUM>) compartments an electrolyte comprising comprise at least one lithium salt (<NUM>), the method comprising the steps of:
a. connecting the first electrode (<NUM>) as a cathode (C) and the second electrode (<NUM>) as an anode (A),
b. an initial step of adding lithium hydroxide to the anode,
c. heating the electrolyte comprising the at least one lithium salt (<NUM>) above its melting point,
d. applying a voltage (V) over the first (<NUM>) and second (<NUM>) electrodes and adding nitrogen gas to the cathode (C) so that lithium is formed at the cathode (C), and which lithium reacts with the added nitrogen gas to form lithium nitride at the cathode, and so that the lithium hydroxide at the anode reacts to form water and oxygen,
e. cooling the electrolyte comprising the at least one lithium salt (<NUM>) below its melting point,
f. adding water or steam to the cathode (C) so that it reacts with the lithium nitride formed in step d) and forms ammonia and lithium hydroxide,
g. changing polarity so that the first electrode (<NUM>) is changed between being the cathode (C) and the anode (A), whereas the second electrode (<NUM>) is changed between being the anode (A) and the cathode (C), and repeating the process from step c).