EP3194739A1

EP3194739A1 - Ammonia generating system for use in a vehicle

Info

Publication number: EP3194739A1
Application number: EP15739576.5A
Authority: EP
Inventors: Beatriz MONGE-BONINI; Jules-Joseph Van Schaftingen; Pierre De Man; François Dougnier
Original assignee: Plastic Omnium Advanced Innovation and Research SA
Current assignee: Plastic Omnium Advanced Innovation and Research SA
Priority date: 2014-07-18
Filing date: 2015-07-17
Publication date: 2017-07-26
Also published as: WO2016009083A1

Abstract

A system, control module and method for use on board a vehicle, the system comprising: a decomposition tank configured to hold an initial ammonia precursor solution and an initial quantity of biological catalyst, wherein the biological catalyst is suitable for decomposing the ammonia precursor into ammonia; and a controller configured to control addition of ammonia precursor and/or biological catalyst to the decomposition tank; wherein the controller is configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank once the ammonia precursor in the initial solution in the decomposition tank has been at least partially decomposed.

Description

Ammonia generating system for use in a vehicle

Field of Invention

The invention relates to an ammonia generating system for mounting on-board a vehicle. In particular, the invention relates to an ammonia generating system which uses a biological catalyst. The present invention also relates to a control module and a method for generating ammonia.

Background

There exist prior art systems for supplying ammonia or ammonia precursor to an exhaust line of a vehicle in order to reduce the NOx emissions. A SCR (Selective Catalytic Reduction) process is used for converting nitrogen oxides of an exhaust gas coming from a vehicle engine into diatomic nitrogen and water. The SCR process enables the reduction of nitrogen oxides by injection of a reducing agent, generally ammonia, into the exhaust line. This ammonia may be obtained by using different techniques.

One known technique is based on the use of an ammonia precursor, for example an aqueous urea solution. Generally, such urea solution is stored in a tank mounted on the vehicle. A catalyst can then be used to generate ammonia from the ammonia precursor solution. A problem with the known technique is that the urea concentration in the solution is relatively low and that it cannot be increased without causing the freezing temperature of the urea solution to increase significantly.

In addition, if a biological catalyst is being used to decompose the ammonia precursor and generate ammonia from the ammonia precursor solution, this catalyst can be denatured if the concentration of the ammonia precursor in the solution becomes too high. However, the extent of the urea denaturation depends not only on the urea concentration but on the temperature of the solution as well. For example, at temperatures of approximately 50°C, the biological catalyst urease can be denatured by solutions containing more than 36 wt urea (i.e. 6M urea solutions). Once the biological catalyst has been denatured, it will then not be able to catalyse the decomposition of the ammonia precursor to ammonia.

A well known ammonia precursor solution suitable for use in vehicles is AdBlue®. Adblue® is an aqueous urea solution made with 32.5% by weight high-purity urea and 67.5% deionized water. The concentration of urea is limited to that level because it corresponds to an eutectic solution with a freezing point of -11°C. The AdBlue® remains liquid above this temperature but heating systems are required whenever temperatures are lower. Higher urea concentrations that would allow more compact storage and weight savings are not used today on vehicles, because freezing would start at even higher temperatures. In addition, in systems using a biological catalyst, a urea solution having a high concentration of urea may be unfavourable for the catalyst.

Summary

The object of embodiments of the invention is to provide an ammonia generating system which is capable of utilising a greater amount of ammonia precursor compared to prior art solutions whilst maintaining acceptable handling.

According to a first aspect of the invention there is provided vehicle system for the production of ammonia comprising:

• a decomposition tank configured to hold an initial ammonia precursor solution and an initial quantity of biological catalyst, wherein the biological catalyst is suitable for decomposing the ammonia precursor into ammonia; and

• a controller configured to control addition of ammonia precursor and/or biological catalyst to the decomposition tank;

wherein the controller is configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank once the ammonia precursor in the initial solution in the decomposition tank has been at least partially decomposed.

As soon as the decomposition reaction starts to take place in the decomposition tank, the ammonia precursor will begin to be decomposed. In adding a controlled amount of ammonia precursor and/or biological catalyst to the

decomposition tank once the decomposition reaction has at least started, the amount of urea decomposed can be maximised. Maximising the amount of urea decomposed maximises the amount of ammonia produced by the system. The decomposition tank of the system of the present invention is any form of unit, chamber or container that can hold a mixture of the ammonia precursor solution and the biological catalyst. In this decomposition tank, the ammonia precursor is decomposed by the biological catalyst. In some embodiments, the decomposition tank may optionally be provided with a heater for heating the ammonia precursor/ biological catalyst mixture to a temperature suitable for the activation of the biological catalyst. Preferably, when a decomposition reaction is taking place, the decomposition tank has a temperature between 30 and 80°C. The controller is any form of control module that can control the addition of an ammonia precursor and/or biological catalyst to the decomposition tank. For example, in some embodiments, the controller may receive input on various conditions inside or outside the decomposition tank, and be suitably configured to control the addition of an ammonia precursor and/or biological catalyst on the basis of these conditions. Examples of conditions are the time lapsed since a preceding addition into the decomposition tank, the chemical composition at an outlet of the decomposition unit and/or an inlet of a subsequent reactor, for instance a fuel cell or an exhaust gas line. One or more sensors may be present to provide such or another input to the system controller.

Furthermore, the system controller may be provided with a clock and/or with a memory.

In exemplary embodiments of the invention, the biological catalyst is an enzyme.

If the biological catalyst is urease enzyme, the temperature within the decomposition chamber is preferably between 40 and 60°C, more preferably around 50°C.

In an exemplary embodiment, the controller (also referred to as a control module) is configured to add the ammonia precursor to the decomposition tank in solid form. Preferably, controller is configured to add granules of the ammonia precursor to the tank. Granules of an ammonia precursor includes ammonia precursor in the form of grains, pellets, particles, powder etc. In other embodiments, the ammonia precursor may be provided in liquid form, for example, as a liquid that can be sprayed or pumped into the decomposition tank.

In alternative embodiments, the system may further comprise a dissolution tank. In such embodiments, the controller may be configured to add solid ammonia precursor to this dissolution tank. Once in the dissolution tank, the solid ammonia precursor may be heated to dissolve it in a liquid provided in the dissolution tank. This liquid may be a solution of the ammonia precursor or an ammonia solution, for example. Once the solid ammonia precursor has been dissolved, the control module may then also be configured to add the ammonia precursor solution to the decomposition tank. The dissolution tank is, therefore, in fluid communication with the decomposition tank. The dissolution tank may be provided with a heater for heating the liquid in the dissolution tank to a temperature suitable for dissolving the solid ammonia precursor. In embodiments in which the solid ammonia precursor is provided in the form of coated granules of urea, the dissolution tank may be heated to approximately 70°C to dissolve the coating material. In some embodiments of the invention, the controller may be configured to add ammonia precursor to the dissolution chamber every time the dissolution tank receives a solution, for example, when the dissolution tank receives liquid from the decomposition tank. The system may further comprise a transfer means configured for transferring the solid ammonia precursor (for example, in the form of granules) to the decomposition and/or dissolution tank. The controller of the invention is configured to control operation of these transfer means. The transfer means may be, for example, a pump and/or a valve. In some embodiments, the transfer means may use gravity to move the ammonia precursor granules into the tank.

In a preferred embodiment, the transfer means is a dosing device configured for dosing a number of ammonia precursor granules to be inserted into the tank. In this way, the increase of the concentration of the ammonia precursor in the solution can be controlled in an accurate manner by the control means. The dosing device may be a device as described in US 20070128054A1 in the name of the Applicant, a dosing device as described in FR2911639B or FR2911641B, a powder dosing device, such as described in EP0296632A2, EP0859944B 1, EP0973015A1, US6701944B2, US0318218A1 or US6510962B1, etc.

The system may also comprise a storage compartment for storing at least ammonia precursor granules. In such embodiments, the transfer means can transfer the granules from the storage compartment and into the decomposition and/or dissolution tank. The granules can be stored safely in the storage compartment without increasing the freezing point of the ammonia precursor solution, and it is only when the ammonia precursor is needed that granules will be added. In one embodiment, the storage compartment stores ammonia precursor granules having dimensions between 0.01 micron and 50 mm, more preferably between 100 micron and 5 mm, and e.g. between 500 microns and 5 mm.

In a preferred embodiment the storage compartment stores ammonia precursor granules containing solid urea.

In an exemplary embodiment, the storage compartment stores ammonia precursor granules having a coating, said coating being adapted to be dissolved, preferably thermally dissolved, in the ammonia precursor liquid. For instance, granules containing solid urea in a protective shell can be added to eutectic AdBlue®, and be dissolved in the decomposition or dissolution tank, for example, by heating the tank to above 60 °C, preferably, around 70°C. The use of protected urea granules will increase the ammonia concentration in the fluid produced by the system. As explained above, the protected granules release urea upon reaching targeted conditions.

In some embodiments of the invention, the coating of the ammonia precursor granules may be made of a wax material, for example, from an insect, vegetal, mineral, petroleum or synthetic wax. For example, the coating could be made from beeswax, carnauba wax, candelilla wax, Montan wax, paraffin wax. In other embodiments, the coating of the ammonia precursor granules may be made of any one or more of the following materials: polyvinylidene chloride (PVDC), linear low density polyethylene (LLDPE), certain grades of ethylene vinyl alcohol (EVOH), certain grades of polyvinyl alcohol (PVOH), bi-axially oriented polypropylene (BOPP), cyclic olefin polymer (COC), polyethylene naphthalate (PEN), liquid-crystal polymers (LCPs, a class of aromatic polyester polymers), polypropylene (PP), and polyethylene terephthalate blends (PET/PE, PET/PVDC/PE, PET/PVOH/PE, PET/EVOH/PE). Suitable examples of coating materials can be found in the packaging industry. The material(s) may be chosen such that the coating is thermally dissolved in the ammonia precursor solution when the temperature is within a certain range, e.g. above 40 degrees Celsius. The coating may be a single layer coating or a multi-layer coating.

In one embodiment, the storage compartment of the system stores the ammonia precursor granules in a liquid, where this coating is not dissolved in the liquid in the storage compartment. For example, the granules may be stored in an ammonia precursor liquid. In this way, ammonia precursor solution and granules may be added together to the storage compartment, e.g. via the same filler pipe.

In another embodiment, the system further comprises a filler pipe in connection with the storage compartment for filling the storage compartment with ammonia precursor granules (and optionally also with an ammonia precursor liquid).

In embodiments of the invention, the control means may be configured to add biological catalyst in solid or liquid form. The solid form may be a powder, granule, pellet etc. If the catalyst is a liquid, it may be provided as as a liquid that can be sprayed or pumped into the decomposition tank.

Alternatively, both solid and liquid forms of a catalyst can be provided inside a solid jacket such as a cartridge or capsule.

In embodiments of the invention, the system may further comprise a transfer means configured to transfer the biological catalyst to the decomposition tank, wherein the control module of the system is configured to control operation of these transfer means. The transfer means may be, for example, a pump and/or a valve. In some embodiments, the transfer means may use gravity to move the enzyme into the tank. In a preferred embodiment, the transfer means is a dosing device configured for dosing a number of enzyme granules to be inserted into the tank. In this way, the increase of enzyme in the decomposition tank can be controlled in an accurate manner by the control means. The system may also comprise a storage compartment for storing the biological catalyst. In such embodiments, the transfer means can transfer the enzyme from the storage compartment and into the decomposition tank.

In some embodiments of the invention, the control module may be configured to add a controlled amount of the ammonia precursor to the decomposition tank to form the initial ammonia precursor solution. In addition or alternatively, the control module may be configured to add a controlled amount of the enzyme to the decomposition tank to provide the initial quantity of biological catalyst. The system according to the present invention is adapted to be located on board a vehicle. In some embodiments of the invention, the decomposition tank and the dissolution tank (if present) may be located within a tank holding a solution of an ammonia precursor, for example, within an AdBlue® tank. Alternatively, only the dissolution tank may be located within this ammonia precursor tank and the decomposition unit located elsewhere in the vehicle (whilst still in fluid communication with the dissolution tank). In other embodiments, neither the decomposition tank nor the dissolution tank (if present) may be located within a tank of an ammonia precursor.

In some embodiments, the system may be configured to contain a biological catalyst which is immobilised on a substrate. This immobilised biological catalyst may be held within the decomposition tank. For example, the enzyme can be immobilized on a substrate and confined inside a cartridge. In such embodiments, ammonia precursor solution can be pumped into the cartridge located in the decomposition unit.

In a one embodiment, the biological catalyst can be immobilized on fibres and these fibres may be attached or held within the decomposition unit. In a further embodiment, the biological catalyst may be immobilized on and in a porous support, such as an inorganic porous material. Suitable inorganic materials are for instance zeolites, alumina, zirconia, silica, as well known to the skilled person. In addition, porous support itself could be arranged on or to a substrate, which could be made of any suitable material. In other embodiments, the biological catalyst may be immobilized in different layers of resin or on membranes. Furthermore, the enzyme can also be immobilised on polymeric granules such as granules of polyethylene, nylon granules, nylon membranes, polyvinyl alcohol beads, chitosan beads etc. Alternatively, the initial ammonia precursor solution and/or the initial quantity of enzymes may be provided in other ways. For example, the decomposition tank may be filled with ammonia precursor solution and/or enzyme when it is fitted within the vehicle. In addition, the enzyme may be provided in the form of a cartridge than sits within the decomposition unit, or is attached to or forms part of the decomposition unit.

The initial ammonia precursor solution is not limited to any particular concentration of the ammonia precursor. For example, the initial ammonia precursor solution could comprise anywhere between 20 wt and 77 wt of the ammonia precursor, for example, 55% urea.

In some embodiments, the initial ammonia precursor solution may be a commercially available solution such as AdBlue®. If the ammonia precursor is urea, a solution containing more than 32.5 wt% urea, for example, 50 wt% urea, could be prepared by boosting an AdBlue® solution with extra urea before it is added to the decomposition tank. Alternatively (or additionally), the

AdBlue® solution could be boosted with extra urea after it has been added to the decomposition tank but before the decomposition reaction has started. The same principle could also be applied when forming an initial solution from other ammonia precursors. In embodiments of the invention, the controller may be configured to add a controlled amount of ammonia precursor and/or biological catalyst in one or more stages. For example, the controller may be configured to add one amount of ammonia precursor and/or enzyme to the decomposition tank once the ammonia precursor of the initial solution in the decomposition tank has been at least partially decomposed.

In some embodiments, the control module is configured to add a controlled amount of ammonia precursor and/or biological catalyst in two or more stages and/or continuously over a given period of time. For example, the controller may be configured to add two, three, four etc controlled amounts of ammonia precursor and/or enzyme once the ammonia precursor of the initial solution in the decomposition tank has been at least partially decomposed.

Preferably, in embodiments of the system of the present invention, the ammonia precursor is urea.

If the ammonia precursor is urea, the initial urea solution preferably comprises approximately 32.5 ± 0.7 wt% urea. In alternative embodiments, the ammonia precursor may be an ammonium salt such as ammonium formate, methanamide or guanidinium formate. These ammonia precursors may be used, for example, in an SCR to generate ammonia and reduce NOx emissions. In exemplary embodiments, the biological catalyst is preferably the enzyme urease.

In some embodiments of the invention, the control module is configured to add a controlled amount of ammonia precursor to the decomposition tank so that the total concentration of the ammonia precursor in the decomposition tank is increased above the concentration of ammonia precursor in the initial solution.

In this way, the present invention can be used to boost the ammonia precursor content in a solution. The more ammonia precursor that is provided in total to the system, the more ammonia that can be generated by the system.

If the ammonia precursor is urea, the control module may be configured to increase the concentration of urea in the urea solution to any value above 32.5 ± 0.7wt . For example, the control module may be configured to increase the concentration of urea to 77 wt , In an exemplary embodiment, control module may be configured to increase the concentration to approximately 55 wt .

In other embodiments of the invention, the control module may be configured to add a controlled amount of ammonia precursor to the decomposition tank so that the total concentration of the ammonia precursor in the decomposition tank is maintained below a concentration at which significant amounts of the biological catalyst are denatured.

It is well known that temperature has an effect on the rate of enzymatic reactions. The temperature at which the rate is fastest is called the optimum temperature for that enzyme. In addition, folded proteins in water (such as enzymes) may be destabilized by increasing the concentration of ammonia precursors such as urea. At concentrations at which the ammonia precursor can denature urease, the extension of the urease denaturation depends not only on the ammonia precursor concentration but as well on the temperature of the solution. The ammonia precursor -induced urease denaturation at determined temperatures can be assessed for example by means of a quantitative real-time thermocycler, circular dichroism (CD) spectroscopy or fluorescence spectroscopy. Furthermore, the extent of the denaturation of a biological catalyst will also depend on the time for which the catalyst is left in the solution.

In some embodiments, significant amounts of the biological catalysts may be considered to be denatured if more than 1%, of the total amount of catalyst is denatured after the catalyst has been left in contact with the ammonia precursor solution for a 3 day period at the operational temperature of the decomposition unit (for example, 50°C).

Preferably, the total concentration of the ammonia precursor in the decomposition tank is maintained below a concentration at which the biological catalyst is denatured.

For example, in embodiments of the invention in which the ammonia precursor is urea, the control module may be configured to add a controlled amount of urea to the decomposition tank so that the total concentration of urea in the decomposition tank is maintained below 36 wt urea (i.e. below a urea concentration of 6M) as, at this concentration, significant amounts of the biological catalyst would be denatured. For, example significant amounts of a biological catalyst such as urease are denatured when the concentration of the urea solution is 6M and the temperature of the solution is around 50°C. Biological catalysts comprise proteins such as enzymes. Proteins are made up of polypeptide chains of individual amino acids. Within a protein, strong peptide bonds are formed between the individual amino acids. This covalent bonding within the polypeptide chains is known as the primary structure of the protein. In addition, hydrogen bonding can also take place between different groups on a polypeptide chain. This hydrogen bonding can cause a polypeptide to be twisted into an alpha-helix or folded into a beta-sheet and forms the secondary structure of a protein. The hydrogen bonds formed are much weaker than the peptide bonds within the polypeptide chain. Proteins also comprise a tertiary structure. The tertiary structure of a protein is the folding of a polypeptide chain into a three dimensional shape. The bonds that form the tertiary structure of the protein include ionic bonds, hydrogen bonds and van de waals forces. These bonds are also much weaker than the strong covalent bonds formed within the polypeptide chain. Many proteins are made up of multiple polypeptide chains, often referred to as protein subunits. These subunits may be the same (as in a homodimer) or different (as in a heterodimer). The quaternary structure refers to how these protein subunits interact with each other and arrange themselves to form a larger aggregate protein complex.

If an external stress is applied to a protein, for example, a high temperature, this can cause the secondary, tertiary and quaternary bonding within the protein to be disrupted, causing the protein to lose its shape. If the protein is an enzyme, the loss of shape will cause changes to the active site of the enzyme meaning that it can no longer act as a catalyst. The enzyme is then said to be denatured. Urea is an example of a chaotropic denaturant which can denature proteins. For example, in 1943 Janet H. Clark observed that egg albumin protein solutions will be denatured slowly with 25 wt urea solution, and will denature rapidly with a 35 wt urea solution at room temperature.

Chaotropic agents denature proteins by disrupting the tertiary structure of the protein.

In embodiments of the invention in which the ammonia precursor is urea, the control module is preferably configured to add a controlled amount of biological catalyst to the decomposition tank when the urea solution in the decomposition tank comprises more than approximately 32.5 wt urea, preferably more than 33.2 wt urea, preferably more than 40 wt , preferably more than 50 wt urea, preferably approximately 55 wt urea, preferably up to 77 wt urea.

If the system for ammonia production comprises more than 32.5 wt urea, some of the enzyme will be denatured during the process of this reaction. Therefore, further enzyme needs to be added to the decomposition tank during the process of the reaction to replace the denatured enzyme.

Although some (or all) of the first amount of enzyme has been denatured, the enzyme has acted on the ammonia precursor to decompose it to ammonia. Therefore, the ammonia precursor concentration has been reduced to some extent by the first amount of enzyme. The inventors believe that this could mean that a smaller proportion of the enzyme that is being added to the decomposition tank at the later stage may then be denatured over the same period of time.

However, this would depend on factors such as the reduced ammonia precursor concentration and the temperature of the solution.

In some embodiments, the control module is configured to add a controlled amount of ammonia precursor to the decomposition tank so that the concentration of the ammonia precursor in the decomposition tank remains substantially the same as or less than the concentration of ammonia precursor in the initial solution.

As discussed previously, the present invention can be used to boost the ammonia precursor content of a solution and increase it beyond the concentration of the ammonia precursor provided in the initial solution added to the decomposition tank. However, in alternative embodiments, the extra ammonia precursor can just be added to keep the concentration of ammonia precursor at a level that is substantially the same as the concentration of the initial solution in the decomposition tank. For example, the added ammonia precursor can keep the concentration of the ammonia precursor within ±10% of the original amount. Alternatively, the ammonia precursor concentration could be kept within ±5% or within ±2% of the original amount.

In doing this, the total amount of ammonia precursor added to the decomposition tank is increased beyond the amount found in the original solution. Therefore, the total amount of ammonia produced by the system will be greater than if no ammonia precursor boosted was added.

In some embodiments of the invention, the control module may be configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank once at least 5 wt%, preferably at least 10 wt%, preferably at least 20 wt%, preferably at least 30 wt%, more preferably at least 40 wt% of the ammonia precursor in the initial solution has been decomposed.

In embodiments in which the control module is configured to add a controlled amount of ammonia precursor to the decomposition tank, the ammonia may be added once at least 80 wt%, preferably at least 90 wt%, more preferably at least 95 wt%, most preferably 100 wt% of the ammonia precursor in the initial solution has been decomposed.

In some embodiments, the control module may comprises a timing mechanism, and the control module may configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank based on information provided by the timing mechanism.

For example, the control module may be configured to add controlled amounts of ammonia precursor and/or enzyme at specific time intervals.

Alternatively or additionally, the control module may comprise a chemical sensor. This chemical sensor may be a pH sensor or an ammonia sensor, for example. If the control module comprises a chemical sensor, the control module may be configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank based on information provided the chemical sensor.

For example, the control module may be configured to use the output of the chemical to determine how much of the ammonia precursor within the decomposition tank has been decomposed already and add a further amount of ammonia precursor or enzyme accordingly.

In an exemplary embodiment, the system may further comprise a buffer compartment for storing the ammonia solution. The buffer compartment may be integrated in the same module as the decomposition compartment (and the dissolution compartment if present).

The ammonia solution with increased or "boosted" concentration in the buffer tank is ready to be sent a downstream tank, to an exhaust pipe or to any additional system storing or consuming ammonia. In a possible embodiment the system further comprises a conversion unit for converting ammonia into hydrogen. The ammonia-hydrogen conversion unit may subsequently communicate with a hydrogen fuel cell where the hydrogen is converted into a power source. The ammonia solution could also be used in a direct ammonia fuel cell.

According to a second aspect of the invention there is a control module configured to control the addition of ammonia precursor and/or biological catalyst to a solution, wherein the control module is configured to add a controlled amount of ammonia precursor and/or biological catalyst once ammonia precursor in the solution has been at least partially decomposed.

A control module according to the second aspect of the present invention can be used in any of the embodiments of the system of the present invention described above.

According to a third aspect of the present invention there is method for producing ammonia comprising:

• adding an initial ammonia precursor solution and an initial quantity of biological catalyst to a decomposition tank, wherein the biological catalyst is suitable for decomposing the ammonia precursor into ammonia;

• waiting until the ammonia precursor in the decomposition tank has been at least partially decomposed into ammonia by the biological catalyst;

• adding further ammonia precursor and/or biological catalyst to the decomposition tank. As soon as the reaction starts to take place in the decomposition tank, the ammonia precursor will begin to be decomposed. In waiting until the decomposition reaction is underway before adding a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank, the amount of urea decomposed can be maximised. Maximising the amount of urea decomposed maximises the amount of ammonia produced by the system.

The period of time in the waiting step may be anywhere from a few fractions of a second to a few seconds, a few minutes or even a few hours. In embodiments of the method of the present invention, the ammonia precursor and/or biological catalyst may be added to the decomposition tank in one or more stages. In some embodiments, the ammonia precursor and/or the enzyme may be added in two or more stages. The ammonia precursor and/or the enzyme may also be added continuously over a given period of time. Preferably, the ammonia precursor is urea. If the ammonia precursor is urea, the biological catalyst is preferably the enzyme urease.

In some embodiments, the initial urea solution comprises approximately 32.5 ± 0.7 wt urea. In embodiments of the invention, the method involves adding ammonia precursor to the decomposition tank to increase the total concentration of the ammonia precursor in the

decomposition tank above the concentration of ammonia precursor in the initial solution. For example, if the ammonia precursor is urea, the concentration of urea in the solution within the decomposition unit may be increased to approximately 55 wt .

In exemplary embodiments, the amount of ammonia precursor added may be controlled so that the total concentration of the ammonia precursor in the decomposition tank is maintained below a concentration at which significant amounts of the biological catalyst are denatured. In embodiments where the ammonia precursor is urea and the method involves adding further biological catalyst to the decomposition tank, this may be done when the urea solution in the decomposition tank comprises more than approximately 32.5 wt urea, preferably more than 33.2 wt urea, preferably more than 40 wt , preferably more than 50 wt urea, preferably approximately 55 wt urea. In other embodiments, the amount of ammonia precursor added to the decomposition tank may be controlled so that the concentration of the ammonia precursor in the decomposition tank remains substantially the same as or less than the concentration of ammonia precursor in the initial solution. In some embodiments, the method comprises waiting until at least 5 wt , preferably at least 10 wt , preferably at least 20 wt , preferably at least 30 wt , more preferably at least 40 wt of the ammonia precursor in the initial solution has been decomposed before further ammonia precursor and/or biological catalyst is added to the decomposition tank. In one embodiment, the method comprises waiting until at least 80 wt , preferably at least 90 wt , more preferably at least 95 wt , most preferably 100 wt of the ammonia precursor in the initial solution has been decomposed before further ammonia precursor is added to the

decomposition tank. The method may also comprise adding the ammonia precursor and/or enzyme to the decomposition tank at set times or at particular time intervals. Alternatively or additionally, the ammonia precursor and/or enzyme may be added in response to feedback received from a chemical sensor.

Brief description of the figures

The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

Figure 1 is a diagram illustrating an embodiment of a system for generating ammonia according to the present invention;

Figure 2 is a diagram illustrating another embodiment of a system for generating ammonia according to the invention;

Figure 3 also shows an embodiment of a system for generating ammonia according to the invention; Figure 4 illustrates a further embodiment of a system for generating ammonia according to the invention;

Figures 5 a and 5b graphically illustrate methods of boosting the ammonia precursor solution in a system;

Figures 6a and 6b graphically illustrate methods of using a biological catalyst to decompose solutions containing high concentrations of an ammonia precursor; Figures 7a, 7b, 8a and 8b graphically illustrate methods of boosting the ammonia precursor solution whilst simultaneously increasing the available biological catalyst;

Figures 9 and 10 show graphs produced using the results obtained from the experiments detailed below.

Description of embodiments

Figures 1 to 4 illustrate examples of systems suitable for the conversion of an ammonia precursor solution 2 into an ammonia solution. In Figures 1 to 4, the illustrated systems are configured to dose and boost the at least partially converted ammonia precursor solution 2 with granules 3 of the ammonia precursor.

However, in other embodiments of the present invention, the ammonia precursor for use in boosting the at least partially decomposed ammonia precursor solution 2 may be provided in liquid form.

Preferably, the ammonia precursor solution 2 is a urea solution and the granules 3 are granules of solid urea. Most preferably, the ammonia precursor solution is the commercially available liquid reductant known as AdBlue^® and matching the ISO 22241 standard specifications. This AdBlue® fluid contains 32.5 ± 0.7 wt urea.

Figure 1 shows a first embodiment of a system 1 according to the present invention. The system 1 of Figure 1 may be used in SCR (Selective Catalytic Reduction), for example.

The system 1 has a tank 4 filled with an ammonia precursor 2, for instance, AdBlue®, where the tank 4 can be filed with this ammonia precursor solution 2 using a filler pipe 17. The tank 4 comprises an inner chamber 5 containing small ball-shaped granules 3 which comprise solid ammonia precursor such as urea. The inner chamber 5 is connected to a dissolution chamber 6. In the embodiment of Figure 1, the granules 3 are introduced at the top of the dissolution chamber 6 by a dosing device 7.

In the embodiment shown in Figure 1, the ammonia precursor granules 3 are interspersed in the ammonia precursor solution 2. However, in an alternative embodiment, the granules 3 may be held in a separate unit connected to the dissolution chamber 6.

When ammonia is required, ammonia precursor solution 2 is firstly transferred from the main chamber 8 of the tank 4 to the decomposition tank 9 by a first fluid transfer device (FTD1) 10. This fluid transfer device can be, for example, a pump and/or a valve. In addition, enzyme is transferred to the decomposition tank 9. This enzyme is supplied by pipe 18. The amount of enzyme provided can be controlled by an enzyme transfer device, for example, an enzyme dosage device (not shown).

The decomposition tank 9 is equipped with a heater 11 in order to thermally activate the enzymes. When at a suitable temperature, the enzymes can decompose the ammonia precursor, converting the ammonia precursor solution into ammonia solution. When the conversion is complete, i.e. when approximately 100% of the ammonia precursor of solution 2 within the decomposition tank 9 has been converted to ammonia, the resulting ammonia solution can then be transferred to the dissolution chamber 6 by a second fluid transfer device (FTD2) 12. The use of an ammonia solution within the dissolution chamber may be advantageous as, in some embodiments, the ammonia solution may help with dissolving the ammonia precursor granules, especially if they are coated.

The system 1 also comprises a controller (not shown) configured to control the transfer of ammonia precursor granules 3 into the dissolution chamber 6 where they can be dissolved. The dissolution chamber 6 is equipped with a heater 13 in order to thermally dissolve the ammonia precursor granules 3. When completely dissolved, the controller is configured to move the ammonia precursor/ ammonia solution to the decomposition tank 9 through a third fluid transfer device (FTD3) 14.

In an alternative embodiment, instead of two separate fluid transfer devices, the system 1 shown in Figure 1 could comprise second and third fluid transfer devices (FTD2 and FTD3) 12, 14 formed by a single pump that operates in both directions.

Once the ammonia precursor/ ammonia solution has been moved back into the decomposition tank 9, the reaction proceeds until substantially all of the remaining ammonia precursor has also been converted to ammonia by the enzyme. After conversion, the boosted ammonia solution can be transferred to a buffer tank 15 by a fourth fluid transfer device (FTD4) 16.

An alternative embodiment of a system according to the present invention is shown in Figure 2. In the system 20 of Figure 2, the controller (not shown) is configured to transfer granules 3 of the ammonia precursor directly into the decomposition tank 9.

The enzyme and the ammonia precursor solution 2 are also transferred to the decomposition tank 9. The precursor solution 2 is moved into the decomposition tank 9 using a first fluid transfer device (FTD1) 10. In the embodiment of Figure 2, the decomposition tank 9 is equipped with a heater 13 in order to thermally activate the enzyme. As the temperature remains relatively high in the decomposition tank 9, no freezing or precipitate of the added ammonia precursor occur. Once the urea is totally converted into ammonia, the boosted ammonia solution can be transferred to a buffer tank 15 by a further fluid transfer device 16.

In the embodiments illustrated by Figures 1 and 2, the system comprises a buffer tank 15 for storing the boosted ammonia solution. By storing the converted effluents in a buffer tank 15, these effluents are ready to be sent to a downstream tank, to the exhaust pipe or to any additional system that stores or consumes ammonia. The converted effluents stored in the buffer tank 15 can be moved, for example, by a fluid transfer device or using gravity.

In some embodiments of the invention, the ammonia buffer tank 15 can also communicate with a unit containing an ammonia-hydrogen conversion catalyst. This catalyst is able to decompose the ammonia to hydrogen. The unit containing the ammonia-hydrogen conversion catalyst can subsequently communicate with a hydrogen fuel cell in which the hydrogen can be converted into a power source.

In other embodiments of the invention, the ammonia solution can be used in a direct ammonia fuel cell such as a solid oxide fuel cell.

A further embodiment of a system according to the present invention is shown in Figure 3. In the system 30 of Figure 3, the enzymes are introduced in one corner of the decomposition tank 9 which is filled with a solution of the ammonia precursor. At the point of entry of the enzymes, a heater 31 is provided to warm up the ammonia precursor solution 2 to the optimal reaction temperature for the enzyme. If the enzyme is urease, the optimal temperature is typically around 50°C. The ammonia precursor solution will, therefore, be decomposed by the enzyme in this area of the decomposition tank 9.

The system 30 of Figure 3 also comprises a controller (not shown). This controller is configured to add granules of an ammonia precursor to another corner of the unit. For example, in the system 30 of Figure 3, the ammonia precursor granules are introduced to the top left of the tank 9 where there is a second heater 32 and the temperature is sufficient to insure dissolution of the additional granules. For example, a temperature of around 70°C may be provided by the second heater 32. As there is a temperature difference within the decomposition tank 9 of the system 30 of Figure 3, the fluid held within the decomposition tank 9 will move around the tank 9 as a result of natural convection. Natural convection is a mechanism, or type of heat transport, in which the fluid motion is not generated by any external source (like a pump, fan, suction device, etc.) but only by density differences in the fluid occurring due to temperature gradients. In natural convection, fluid surrounding a heat source receives heat, becomes less dense and rises. The surrounding, cooler fluid then moves to replace it. This cooler fluid is then heated and the process continues, forming a convection current. The arrow in the centre of the decomposition tank 9 illustrates the convection current.

As a result of natural convection, the partially converted solution moves along the first heater 31 towards the second heater 32, where the ammonia precursor granules 3 are added and dissolved, and then the boosted solution moves towards the first heater 31 for further conversion. Figure 4 shows another embodiment of a system 40 according to the present invention. In Figure 4, the enzymes are shown as being introduced in the top left corner of the unit, where a first heater 31 is provided. This first heater 31 is powered to reach an optimal temperature for the

decomposition reaction to occur, for example, 50°C. In the system 40 of Figure 4, the ammonia precursor granules 3 are shown as being introduced in an adjacent corner, specifically in the bottom left corner of the unit near a second heater 32. This system 40 will also comprise a controller configured to control the addition of these granules 3. The second heater 32 is powered to reach a temperature (for example, 70°C) that allows for the granules 3 to be dissolved in the required time. As with the system of Figure 3, the temperature difference within the liquid held in the decomposition tank 9 of the system 40 shown in Figure 4 results in the formation of a convection current (shown by the arrows in Figure 4).

Thanks to this convection loop, the partially converted solution moves from the first heater 31 to the second heater 32 where it is enriched in ammonia precursor provided by the dissolved granules 3, and the resulting boosted solution moves back towards the first heater 31 for further conversion.

Furthermore, the system 40 of Figure 40 further comprises a flow restriction means 41. In the illustrated system 40, these flow restriction means are a series of parallel channels inserted in the decomposition tank 9 between the first and second heaters 31, 32. The flow restriction means 41 slow down the movement of the fluid around the tank 9. This allows for a suitable contact time between the enzymes and the boosted solution to ensure that the ammonia precursor is converted to ammonia at the desired rate.

In the systems of figures 1 to 4, as well as controlling the addition of the ammonia precursor, the control means may also be configured to control the addition of further enzyme to the

decomposition unit.

The present application is also directed to various methods by which the ammonia generated by a system can be maximised. Examples of such methods are illustrated graphically in Figures 5 to 8.

A first embodiment of a method according to the present invention is illustrated by Figure 5a ("strategy 1"). In the method of Figure 5a, a solution comprising 32.5 wt urea is firstly provided in a decomposition tank together with some urease enzyme. As shown in the graph, the reaction is allowed to proceed until all of the urea has been decomposed. Then, once all of the urea has been decomposed, a further amount of urea is added to boost the solution and allow the reaction to continue. With this strategy 1, a total amount of urea corresponding to an urea solution with an initial concentration of 55 wt can be converted to ammonia. Consequently, strategy allows the ammonia concentration in the final solution to be increased. A second example method according to the present invention is illustrated by the graph of Figure 5b ("strategy 2"). As with strategy 1, in strategy 2 a solution comprising 32.5 wt urea is firstly provided in a decomposition tank together with some urease enzyme. However, unlike strategy 1 , in strategy 2 the urea granules are transferred to the decomposition chamber when the conversion is partially completed. In the method shown in Figure 5b, urea granules are added to the decomposition tank when at least 40% of the ammonia precursor is converted into ammonia solution. This strategy aims to first reduce the urea concentrations to non-denaturing values prior extra urea addition.

A further two methods are illustrated graphically in Figures 6a ("strategy 3") and 6b ("strategy 4"). In these two methods, a boosted urea solution comprising 55 wt% urea is prepared prior enzymatic conversion. In strategies 3 and 4, the enzyme is added in multiple steps to convert the boosted solution.

In Figure 6a, the method comprises two enzyme addition steps. The first addition step reduces the initial urea concentration. However, as the urea concentration is so high initially, at least some of the enzyme will be denatured. Therefore, the method also comprises a second enzyme addition step to fully convert the remaining urea. As the concentration of urea is now lower, not all of the second batch of enzyme will be denatured.

Alternatively, as shown in Figure 6b, the enzyme may be gradually added during the conversion process. With each enzyme addition, the urea concentration will be reduced. However, as enzyme is being added to a solution containing a high amount of urea, some of the enzyme will be denatured. Therefore, further enzyme must be added to replace the denatured enzyme and continue with the conversion process. In the method of Figure 6a, two large quantities of enzyme are added to the decomposition tank. In contrast, Figure 6b shows a method in which six smaller amounts of enzyme are added to the decomposition tank.

Two further methods of adding enzyme and an ammonia precursor are shown in Figures 7a and 7b. As shown in both of these figures, the methods ("strategy 5" and "strategy 6" respectively) involve continuously adding urea to the decomposition tank during the conversion process. Although not shown in the figures, there will be at least a small delay between mixing the initial ammonia precursor and enzyme and then adding the ammonia continuously whilst the reaction is proceeding. This delay allows at least some of the ammonia precursor to be decomposed before more is added.

If the ammonia precursor is urea and the urea is added to the decomposition tank using strategy 5 or 6, preferably, the urea is added in such a way that the solution within the decomposition chamber does not exceed 36 wt (6M). In addition, in strategy 6 shown in Figure 7b, the enzyme is also added to the decomposition tank gradually.

In strategies 5 and 6, the extra urea is added to the decomposition tank so that the amount of urea provided to the solution increases in a linear fashion.

However, the addition of the extra this addition can follow any type of curve. For example, nonlinear increases in the amount of urea are shown in Figures 8a and 8b ("strategies 7 and 8").

In summary, all of the above described strategies comprise:

1) Filling a decomposition tank with a urea solution and an enzyme, 2) Boosting the amount of urea and/or the enzyme in the decomposition tank by adding extra ammonia precursor/ enzyme but only when the decomposition reaction has already started,

3) Converting the urea solution into ammonia solution using the enzyme. When generating ammonia on-board a vehicle, the choice of the strategy or combination of strategies to be adopted is a compromise between the reaction conditions and the urea

concentration.

Example

Experiments were conducted to compare the amount of ammonia generated from a urea solution with a high initial concentration and from a urea solution which is boosted with urea.

A first experiment was performed using 800 units of the Jack bean urease (Sigma Aldrich catalog number U4002) per ml of urea solution. In this experiment, two different urea solutions were used: the commercially available liquid reductant Adblue® containing 32.5 ± 0.7 wt% urea, and an urea solution with 50 wt% urea. The results of this experiment are summarized in table 1 below.

In the first experiment, the reactions were carried out at 40°C.

As is shown in table 1 below, for the 32.5 wt% urea solution, the urease enzyme was able to convert 27.77 grams of urea into ammonia in the first 120 minutes.

However, when the same amount of urease enzyme was used to convert a 50 wt% urea solution, only 6.15 grams of urea were converted into ammonia in the first 120 minutes.

Furthermore, after 360 minutes, the 32.5% (5.42M) solution was fully converted, whereas the 50% (8.33M) solution had 37.91 grams (6.31M) of non-converted urea left. Incubating the reaction for longer periods up to 3 days didn't improve the urea conversion indicating the enzyme was inactive.

Table 1 : Urea conversion

Reaction Time Remaining Urea (M) Converted Total condition urea wt% urea (grams) converted urea

(grams)

Zero time 32.5 5.4 0 40°C, 800U/ml 120 minutes 4.73 0.79 27.77

urea solution 240 minutes 0.240 0.04 4.49

360minutes 0.123 0.02 0.117 32.38

Zero time 50 8.33 0

120 minutes 43.85 7.30 6.15

240 minutes 41.46 6.91 2.39

360 minutes 37.91 6.32 3.55

3 days 31.40 5.23 6.51 18.6

These results are also shown in Figure 9. The bars on the left of this graph show the conversion of a standard 32.5% urea solution, and the bars on the right of this graph show conversion of 50 wt% urea solution.

In a second experiment, the reaction was also started by adding 800U of enzyme/ml to the commercial 32.5% urea solution. However, this reaction was performed at 50°C and, after 60 minutes, an amount corresponding to 17.5% of urea was added (32.5 grams + 17.5 grams, total volume 100 ml, resulting in 50% urea). The results of this second experiment are shown in Table 2 below and Figure 10.

In the second experiment, the urea concentration increased from 27.59 grams (4.6M) to 42.75 grams (7.13M, 42.75 wt%). After 360 minutes, 39.92 grams of urea were converted into ammonia, leaving 10.08 grams of non-converted urea in the solution against the 37.91 grams left in the first example. This improvement in conversion could be explained by the urea concentration.

The same amount of urea is used in both the 50% solution used in the first experiment and the solution of the second experiment. In the first experiment, a high urea concentration of 50 wt% is used. However, in the second experiment, the urea concentration is initially only 32.5 wt%. Then, after 60 minutes, this urea concentration is boosted by adding an amount corresponding to 17.5 wt% extra urea.

As the enzyme had already started to decompose the urea in the second experiment, the maximum urea concentration to which the enzyme was exposed is 7.13M. In contrast, the enzyme was exposed to a higher concentration of 8.33M in the first experiment. Therefore, experiments 1 and 2 show that adding a further quantity of an ammonia precursor to the reaction whilst the reaction is ongoing can be used to increase the total amount of urea converted (and, therefore, increase the amount of ammonia formed).

Table 2: Urea conversion

Reaction Time Remaining Urea (M) Converted condition urea wt urea (grams)

50°C, Zero time 32.5 5.42 0

800U/ml urea 60 minutes 27.59 4.6 4.91 solution 60 minutes (immediately after urea 42.75 7.13

addition)

120 minutes 39.93 6.66 2.82

240 minutes 21.00 3.5 18.93

360 minutes 10.08 1.68 10.92

Total: 37,58

Claims

A vehicle system for the production of ammonia comprising:

The vehicle system of Claim 1 , wherein the controller is configured to add a controlled amount of the ammonia precursor to the decomposition tank to form the initial ammonia precursor solution, and/or wherein the controller is configured to add a controlled amount of the enzyme to the decomposition tank to provide the initial quantity of biological catalyst.

The vehicle system of Claim 1 or 2, wherein the controller is configured to add a controlled amount of ammonia precursor and/or biological catalyst in one or more stages.

The vehicle system of any preceding claim, wherein the controller is configured to add a controlled amount of ammonia precursor and/or biological catalyst in two or more stages and/or continuously over a given period of time.

The vehicle system of any preceding claim, wherein the ammonia precursor is urea and the initial urea solution comprises approximately 32.5 ± 0.7 wt urea.

The vehicle system of any preceding claim, wherein the controller is configured to add a controlled amount of ammonia precursor to the decomposition tank so that the total concentration of the ammonia precursor in the decomposition tank is increased above the concentration of ammonia precursor in the initial solution.

7. The vehicle system of Claim 6, wherein the ammonia precursor is urea and the controller is configured to increase the concentration of urea in the urea solution to a value above 32.5 ±0.7 wt , preferably to approximately 55 wt , more preferably to 77 wt . The vehicle system of any preceding claim, wherein the controller is configured to add a controlled amount of ammonia precursor to the decomposition tank so that the total concentration of the ammonia precursor in the decomposition tank is maintained below a concentration at which significant amounts of the biological catalyst are denatured.

The vehicle system of any preceding claim, wherein the ammonia precursor is urea, and wherein the controller is configured to add a controlled amount of biological catalyst to the decomposition tank when the urea solution in the decomposition tank comprises more than approximately 32.5 wt urea, preferably more than 33.2 wt urea, preferably more than 40 wt , preferably more than 50 wt urea, preferably approximately 55 wt urea, preferably up to 77 wt urea..

The vehicle system of any one of Claims 1 to 5, wherein the controller is configured to add a controlled amount of ammonia precursor to the decomposition tank so that the concentration of the ammonia precursor in the decomposition tank remains substantially the same as or less than the concentration of ammonia precursor in the initial solution.

The vehicle system of any preceding claim, wherein the controller is configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank once at least 5 wt , preferably at least 10 wt , preferably at least 20 wt , preferably at least 30 wt , more preferably at least 40 wt of the ammonia precursor in the initial solution has been decomposed.

The vehicle system of any preceding claim, wherein the controller is configured to add a controlled amount of ammonia precursor to the decomposition tank once at least 80 wt , preferably at least 90 wt , more preferably at least 95 wt , most preferably 100 wt of the ammonia precursor in the initial solution has been decomposed.

The vehicle system of any preceding claim, wherein the controller comprises:

• a timing mechanism, wherein the controller is configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank based on information provided by the timing mechanism, and/or

• a chemical sensor such as a pH sensor or an ammonia sensor, wherein the controller is configured to add a controlled amount of ammonia precursor and/or biological catalyst to the decomposition tank based on information provided the chemical sensor. A control module configured to control the addition of ammonia precursor and/or biological catalyst to a solution, wherein the control module is configured to add a controlled amount of ammonia precursor and/or biological catalyst once ammonia precursor in the solution has been at least partially decomposed.

A method for producing ammonia comprising:

• adding further ammonia precursor and/or biological catalyst to the decomposition tank.