SE2350105A1

SE2350105A1 - Continuous production of ammonia by electrolysis of a lithium salt with changing polarity

Info

Publication number: SE2350105A1
Application number: SE2350105A
Authority: SE
Inventors: Göran Bolin; Ray Olssson
Original assignee: Superstate AB
Priority date: 2023-02-03
Filing date: 2023-02-03
Publication date: 2024-03-26
Also published as: SE545957C2; EP4433628B1; EP4433628C0; EP4433628A1; WO2024160570A1

Abstract

There is provided continuous production method for ammonia by electrolysis of a lithium salt with changing polarity. The method is performed in an electrolytic cell comprising a first and a second compartment, wherein the first and second compartments are separated by an ion-membrane, the method comprising the steps:• heating the lithium salt above its melting point, • applying a voltage over the electrodes and adding nitrogen gas to the cathode so that lithium is formed at the cathode, 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,• cooling the lithium salt below its melting point, • adding water or steam to the cathode so that it reacts with the lithium nitride formed in step d) and forms ammonia and lithium hydroxide,• changing polarity and repeating the process.

Description

Continuous production of ammonia by electrolysis of a lithium salt with changing polarity Field of the invention The present invention relates to manufacture of ammonia. More in detail it relates to manufacture of ammonia by electrolysis of a lithium salt, where the polarity changes.

Background 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 There is for instance the so called which studied and described. Haber-Bosch process described in US 1,202,995, 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 1% of the global energy and about 3-5% 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.

WO 2021/176041 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.

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

Summary 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, comprising an electrolytic cell (l) comprising a first (2) and a second (3) compartment, wherein the first and second compartments are separated by wherein the first a membrane (4) permeable to ions, compartment (2) comprises a first electrode (5) and wherein the second compartment (3) comprises a second (6), compartments comprise at least one lithium salt and the second (3) (7), electrode wherein the first (2) the method comprising the steps of: a.connecting the first electrode (5) as a cathode (C) and the second electrode (6) as an anode (Ä), km an initial step of adding lithium hydroxide to the anode, c.heating the at least one lithium salt above its melting point, d.applying a voltage (V) over the first (5) and second (6) electrodes and adding nitrogen gas to the cathode (C) so that lithium is formed at the (C), added nitrogen gas to form lithium nitride at cathode and which lithium reacts with the the cathode, and so that the lithium hydroxide at the anode reacts to form water and oxygen, e. cooling the at least one lithium salt 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 (5) is the anode (A) and the second electrode (C) , process from step c). (6) is the cathode and repeating the In a second aspect there is provided an electrolytic cell (l) comprising a first (2) and a second (3) compartment, wherein the first (2) and second (3) compartments are separated by a membrane (4) permeable to ions, wherein the first compartment (2) comprises a first electrode (5) and wherein the second compartment (3) comprises a second (6), electrodes are adapted to change polarity so that the electrode wherein the first (5) and second (6) first electrode (5) is adapted to change between being a cathode (C) and an anode (A), whereas the second electrode (6) is adapted to change between an anode (A) and a (C) , heater and a cooler so that a content cathode wherein the electrolytic cell (l) comprises a (7) in the first and second compartment can be heated or cooled, wherein the comprises a tube for addition of (C) , electrolytic cell (l) nitrogen to the cathode and wherein the electrolytic cell (l) comprises a tube for addition of water or steam to the cathode (C).

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.

Brief description of the drawings Aspects and embodiments will be described with reference to the following drawings in which: Figure la shows the electrolytic cell (l) comprising a first (2) and a second (3) compartment separated by a membrane (4), a first electrode (5), a second electrode (6), as well as the content (7) in the first and second compartments, i.e. at least one lithium salt. Also shown are a cathode (C) an anode (A) applied (5), and a voltage (V) over the first a second (6) electrode.

Detailed description 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 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 a xternal source of (D Q» n electrical energy to force a chemical re ction that woul otherwise not occur. The external energy source is a voltage applied between the cell's two electrodes; an and a cathode anode (positively cnarged electrode) 1 narged electrode), which are immersed in an t..J ( ive fe [IS (D LO, D) F? | .t x O !...l (D O ( 1 H (D m O H f: ( 1 kJ , 'on. "n the electrolytic cell, a current |...J w f* \J pa 'ID ses through the cell by an external voltage, causing a non~spontaneous chemical reaction to proceed.

The electrolytic cell has three main components: an |\ |\ (i.e. a cathode nd n anode). The electr lyte comprises at least one lithium I . salt, which ia molten during the e .ctrolyeis. When driven e 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 Only with an external elñctric potential (i.e., voltage) of correct polarity and sufficient magnitude can the reaction take place. The electrical energy providee can produce a chemical reaction that would i In the first aspect there is provided a method for manufacturing ammonia, comprising an electrolytic cell (l) comprising a first (2) and a second (3) compartment, wherein the first and second compartments are separated by wherein the first a membrane (4) permeable to ions, compartment (2) comprises a first electrode (5) and wherein the second compartment (3) (6), compartments comprise at least one lithium salt comprises a second electrode wherein the first (2) and the second (3) (7), the method comprising the steps of: and a. connecting the first electrode (5) as a cathode (C) the second electrode (6) as an anode (A), b. an initial step of adding lithium hydroxide to the anode, c. heating the at least one lithium salt (7) below its melting point, over the first (5) d. applying a voltage (V) and second (6) electrodes and adding nitrogen gas to the cathode (C), which lithium reacts with the added nitrogen gas to (C) so that lithium is formed at the cathode and form lithium nitride at the cathode, and so that the lO lithium hydroxide at the anode reacts to form water and oxygen, e. cooling the at least one lithium salt (7) 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 (5) is the anode (A) is the (C), and the second electrode (6) cathode and repeating the process from step c). 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. 6Li+ Ng ä 2Li§N 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 In one embodiment, is carried out by the reaction. step d) 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.

Li3N + 3H2O ä NH3 + 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 at least one lithium salt (7) is in an eutectic mixture comprising at least one lithium salt. A eutectic mixture is a homogenous mixture that has a meltihg point lower than those of the constituents. The lewest possible melting point over all of the mixing ratios of the constituents is caliüd the eutectic temperature. In one embodiment, the mixing ratio of the f* O+'¿*'-11f:>ﬁ~"-O "l fﬂﬁ... C>1...^*+"rfl\"1"... IC' C* k" t1>^^t 'ftkfä 1/*r1QC'*'" t,Ol"1._>cic-a.t.uc._> ifl cmC eiCL-ciuii/ríl lo» .JUCL end.. bli... iuvveec possible melting temperature occurs, i.e. at the eutectic temperature.

In one embodiment, the at least one lithium salt (7) is an eutectic mixture of lithium chloride and potassium chloride, and wherein the at least one lithium salt (7) is heated above 354 °C in step c). 354 °C 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 at least one lithium salt can also be heated a bit above its an eutectic melting temperature. In one embodiment, mixture of lithium chloride and potassium chloride is heated to 100 °C 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. the at least one lithium salt is cooled to In step e) below its melting point. In one embodiment, it is cooled to below the boiling point of water to facilitate the the at least one addition of water. In one embodiment, lithium salt (7) is cooled below 80 °C 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 In one the hydroxy ions, but not the chlorine ions react. embodiment, the voltage (V) is adjusted so that essentially no chlorine gas is formed at the anode (A). ll In the second aspect there is provided an electrolytic cell (l) comprising a first (2) and a second (3) compartment, wherein the first (2) and second (3) compartments are separated by a membrane (4) permeable to ions, wherein the first compartment (2) comprises a first electrode (5) and wherein the second compartment (3) (6), electrodes are adapted to change polarity comprises a second electrode wherein the first (5) and second (6) so that the first electrode (5) is adapted to change (A), whereas the between being a cathode (C) and an anode second electrode (6) (C) , comprises a heater and a cooler so that a content (7) in is adapted to change between an anode (A) and a cathode wherein the electrolytic cell (l) the first and second compartment can be heated or cooled, wherein the electrolytic cell (l) comprises a tube for (C) , comprises a tube for addition of addition of nitrogen to the cathode and wherein the electrolytic cell (l) water or steam to the cathode (C).

In one embodiment of the second aspect, the first (5) and second (6) 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 (4) is a porous magnesia diaphragm.

In one embodiment of the second aspect, cell (l) the electrolytic 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 (5) and second (6) electrodes, and iv) the polarity of the voltage applied l2 over the first (5) and second (6) and wherein the programmable controller is communicatively connected electrodes, to at least one selected from the group consisting of i) (2) a voltage sensor for the (6) and a polarity sensor for the polarity of the voltage (5) (6) temperature sensor for the temperature in the first and second (3) compartments, ii) voltage between the first (5) and second electrodes, applied over the first and second electrodes. The programmable controller has the advantage that the different functions can be programmed so that the system is easier to operate and/or so that it can operate autonomously. Further there is the possibility to use an artificial intelligence to optimize and control the process.

Claims

1. Claims A method for manufacturing ammonia, comprising an electrolytic cell (l) comprising a first (2) and a second (3) compartment, wherein the first and second compartments are separated by a membrane (4) permeable to ions, wherein the first compartment (2) comprises a first electrode (5) and wherein the second compartment (3) comprises a second electrode (6), wherein the first (2) and the second (3) compartments comprise at least one lithium salt (7), the method comprising the steps of: a.connecting the first electrode (5) as a cathode (C) and the second electrode (6) as an anode (A) , km an initial step of adding lithium hydroxide to the anode, c.heating the at least one lithium salt (7) below its melting point, d.applying a voltage (V) over the first (5) and second (6) 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 at least one lithium salt (7) 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 (5) is the anode (A) and the second electrode (6) is the cathode (C), and repeating the process from step c)..The method according to claim 1, wherein step d) is carried out until the lithium hydroxide added in step b) is consumed. .The method according to any one of claims 1-2, wherein the at least one lithium salt (7) is an eutectic mixture comprising at least one lithium salt. .The method according to any one of claims 1-3, wherein the at least one lithium salt (7) is an eutectic mixture of lithium chloride and potassium chloride, and wherein the at least one lithium salt (7) is heated above 354 °C in step c). .The method according to any one of claims 1-4, wherein the at least one lithium salt (7) is cooled below 80 °C in step e). .The method according to any one of claims 1-5, wherein the voltage (V) is adjusted so that essentially no chlorine gas is formed at the anode (A). .An electrolytic cell (1) comprising a first (2) and a second (3) compartment, wherein the first (2) and second (3) compartments are separated by a membrane (4) permeable to ions, wherein the first compartment (2) comprises a first electrode (5) and wherein the second compartment (3) comprises a second electrode (6), wherein the first (5) and second (6) electrodes are adapted to change polarity so that the first electrode (5) is adapted to change between being a cathode (C) and an anode (A), whereas the second .The electrolytic cell (1) .The electrolytic cell (1) electrode (6) is adapted to change between an anode (A) and a cathode (C), wherein the electrolytic cell (1) comprises a heater and a cooler so that a content (7) in the first and second compartment can be heated or cooled, wherein the electrolytic cell (1) comprises a tube for addition of nitrogen to the (C) , comprises a tube for addition of water or steam to cathode and wherein the electrolytic cell (1) the cathode (C). according to claim 7, wherein the first (5) and second (6) electrodes comprise at least one selected from the group consisting of graphite, platinum, and platinum coated metal. according to any one of claims 7-8, wherein the membrane (4) is a porous magnesia diaphragm. The electrolytic cell (1) according to any one of claims 7-9, wherein the electrolytic cell (1) 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 (5) and second (6) electrodes, and iv) the polarity of the voltage applied over the first (5) and second (6) 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 (2) and second (3) compartments, ii) a voltage sensor for the voltage between the first (5) and second (6) electrodes, andiii) a polarity sensor for the polarity of the voltage applied over the first (5) and second (6) electrodes.