NL2032487B1

NL2032487B1 - Membrane stack, stack assembly and system for ammonia recovery and method therefor

Info

Publication number: NL2032487B1
Application number: NL2032487A
Authority: NL
Inventors: Cornelis Scheepers Franciscus; Daniël Molenaar Sam
Original assignee: W&F Tech B V
Priority date: 2022-05-17
Filing date: 2022-07-14
Publication date: 2023-11-24

Abstract

The invention relates to a membrane stack having at least one stack cell comprising a ﬁrst bipolar membrane and a second bipolar membrane that extends substantially parallel to the ﬁrst bipolar 5 membrane, and comprising a cation exchange membrane extending between and parallel to the bipolar membranes, a compartment extending between the ﬁrst bipolar membrane and the cation exchange membrane, and a compartment extending between the cation exchange membrane and the second bipolar membrane, 10 or comprising an anion exchange membrane extending between and substantially parallel to the ﬁrst and the second bipolar membranes, a compartment extending between the ﬁrst bipolar membrane and the anion exchange membrane and a compartment extending between the anion exchange membrane and the second bipolar membrane, and wherein at least one compartment is provided with an ion exchange resin. 15 The invention also relates to a stack assembly, a system and a method for recovering ammonia.

Description

MEMBRANE STACK, STACK ASSEMBLY AND SYSTEM FOR AMMONIA RECOVERY

AND METHOD THEREFOR

The present invention relates to a membrane stack for ammonia recovery, a stack assembly comprising such membrane stack and a system comprising such a stack assembly. The present invention further relates to a method for ammonia recovery from low conductivity condensates and gas scrubber concentrates.

The removal of ammonia from gases. such as air, biogas, is known in practice and is often required by law. This is often performed using gas scrubbing. In addition, process condensates in the (process) industry often contain ammonia, in addition to other condensables. This is for example due to a sequence of an evaporation step and a heat recovery step. Such condensates often contain low concentrations of ammonia (in absolute terms). These concentrations often exceed concentration allowed for (direct) disposal. while simultaneously being too low for valuable recovery and application. As a result, both gas scrubbers and condensers provide wastewater that require secondary treatment and/or recovery for re-use.

However, a disadvantage of removal of ammonia using air and/or gas scrubbers is that the removal 1s predominantly performed using sulphuric acid, which leads to significant costs due to the high price of sulphuric acid. Suitable alternatives for sulphuric acid also have high prices. In addition, the scrubbers produce sulphate salts, which are difficult to dispose of. Even agriculture, which is known to use sulphate, requires only limited amount thereof. Therefore, scrubbers do not provide a satisfactory solution for ammonia removal.

In an alternative approach, ammonia can be removed using a combination of aeration for nitrification/denitrification plus input of some electron donor. This particular approach is often used for condensates that have a low concentration of ammonia, which however still do not comply with the present effluent norms. A disadvantage of this approach is that it, in part due to the aeration required for nitrification/denitrification, represents a very expensive way of removing ammonia.

The present invention aims at obviating or at least reducing the aforementioned problems and to enable efficient and effective removal of ammonia from wastewater flows, especially gas scrubber condensates and/or low conductivity condensates.

This objective is achieved with a membrane stack according to the invention, the membrane stack comprising at least one stack cell, wherein the at least one stack cell comprises: — a first bipolar membrane (BPM); — a second bipolar membrane that extends substantially parallel to the the first bipolar membrane;

further comprising: — acation exchange membrane (CEM) extending between and substantially parallel to the first and the second bipolar membranes; — a feed flow compartment that extends between the first bipolar membrane and the cation exchange membrane and is delineated thereby; and — a concentrate compartment that extends between the cation exchange membrane and the second bipolar membrane and is delineated thereby; and wherein at least one compartment is provided with an ion exchange resin; or further comprising: — an anion exchange membrane (AEM) extending between and substantially parallel to the first and the second bipolar membranes; — an acid compartment that extends between the first bipolar membrane and the anion exchange membrane and is delineated thereby; and — a feed flow compartment that extends between the anion exchange membrane and the second bipolar membrane and is delineated thereby; wherein at least one compartment is provided with an ion exchange resin.

The membrane stack according to the invention provides several advantages over the known devices and methods for removal of ammonia. It is noted that the membrane stack according to the invention may comprise a single stack cell. In practice, the membrane stack according to the invention will often comprise a plurality of cells that are positioned adjacent to and m direct contact with each other. In fact, in case of a plurality of stack cells, adjacent cells will share a common membrane, in that the second bipolar membrane of a first stack cell will also be the first bipolar membrane of the second stack cell. Although technically possible, it is generally not necessary to have two membranes being placed adjacent to and in contact with each other.

An advantage of the membrane stack according to the invention is that it provides a cost- effective and efficient device for extracting ammonia from wastewater flows, and especially condensates, effluent flows, and condensates from gas scrubbers.

Another advantage is that the ammonia extracted from the flow is substantially recovered and thus forms a useful commodity for other uses.

It is noted that the membrane stack is especially useful in recovering ammonia from gas scrubber condensates and low conductivity condensates, because these flows have a limited amount of solids and a low hardness (in terms of calcium/magnesium content) and/or often also do not contain other cations than ammonium.

A further effect is that the energy consumption of the ammonia removal is relatively low compared to the existing devices and methods for ammonia removal. This is mainly due to the fact that the ion exchange resin provides a significantly larger recombination area for recombination of ammonium and hydroxide, which in turn leads to a reduction of concentration polarisation and a lower required cell potential.

Another advantage is that, due to the fact that the ion exchange resin in the concentration compartment provides a significantly larger recombination area, the back diffusion of ammonium to the feed flow is significantly reduced. This leads to a higher coulombic efficiency in the membrane stack.

It is noted that the membrane stack according to the invention is configured to be used in conjunction with an acid and an alkaline, which respectively form the basis for an anionic flow and a cationic flow. It is noted that in the abovementioned membrane stack according to the invention, the feed is an acid or acidic solution, whereas the concentrate compartment contains the alkaline. It has been found that both strong acids and alkalines and weak acids and alkalines can be used.

Combinations thereof may also be possible.

It is noted that in the membrane stack according to the invention, the cation exchange membrane, when viewed in a first direction, is positioned at a distance from the first bipolar membrane. Similarly, it is noted that in the membrane stack according to the invention, the second bipolar membrane, when viewed in a first direction, is positioned at a distance from the cation exchange membrane.

The distance between the respective membranes defines the thickness, which is the distance viewed in the first direction, of the flow compartments in the stack cells. The thickness may for example be in the range of 0.05 mm — 15 mm, preferably in the range of 0.1 mm - 10 mm, and more preferably in the range of 0.5 mm — 5 mm.

In an embodiment of the membrane stack according to the invention, the feed flow compartment may be provided with an ion exchange resin.

An advantage of providing an ion exchange resin in the feed flow compartment is that the depletion of ammonium ions at the membrane interface between the feed compartment and the associated adjacent compartment is limited, especially in situations in which the (starting) concentration of ammonium is low, such as often is the case for condensates from (industrial) processes.

In an embodiment of the membrane stack according to the invention, the acid compartment may be provided with an ion exchange resin.

An advantage is that the conductance towards ions in the acid compartment is increased, therewith further increasing the effectiveness of the membrane stack according to the invention.

This is mainly due to the fact that concentration polarisation is reduced and the recombination area for the ions is increased.

In an embodiment of the membrane stack according to the invention, the concentrate compartment may be provided with an ion exchange resin.

An advantage of this embodiment is that the energy consumption of the ammonia removal is relatively low compared to the existing devices and methods for ammonia removal. This is mainly due to the fact that the ion exchange resin provides a significantly larger recombination area for recombination of ammonium and hydroxide, which in turn leads to a reduction of concentration polarisation and a lower required cell potential.

In an embodiment of the membrane stack according to the invention in which the membrane stack comprises the cation exchange membrane (CEM), the at least one stack cell may additionally comprise an anion exchange membrane (AEM) that extends between the first bipolar membrane and the cation exchange membrane and extends substantially parallel to the first bipolar membrane and the cation exchange membrane. Further it may comprise an acid compartment that extends between the first bipolar membrane and the anion exchange membrane. The feed flow compartment may be positioned between the anion exchange membrane and the cation exchange membrane.

As mentioned above, the membrane stack according to the invention can be used with both a strong acid and a strong alkaline as well as with a weak acid and a weak alkaline. An advantage of providing an additional compartment in each stack cell is that an improved Coulombic efficiency with respect to extraction of ammonia is achieved due to the reduction of proton and/or hydroxide cycling. This is especially true for situations in which a strong acid and a strong alkaline are used.

The membrane stack according to this embodiment essentially comprises three adjacent compartments, which sequentially are: - an acid compartment containing a strong acid, or preferably comprising a flow of a strong acid; - afeed compartment containing an ammonia containing solution or comprising a feed flow containing ammonia; and - a concentrate compartment containing a strong alkaline or comprising a flow of a strong alkaline.

In use, the ammonia, in the form of ammonium ions are collected in the concentrate compartment. The extracted protons, in the form of hydrogen ions, and the extracted anions are collected in the acid compartment.

In an embodiment of the membrane stack according to the invention, the membrane stack 5 may be an Electro-Delonization-by-Bipolar-Membranes (EDIBM) stack.

It was found that an EDIBM provides an efficient and effective device for extracting ammonia from wastewater flows, and especially condensates, effluent flows, and condensates from gas scrubbers for aforementioned reasons.

Furthermore, the EDIBM enables that the ammonia extracted from the flow is substantially recovered and thus forms a useful commodity for other uses.

In an embodiment of the membrane stack according to the invention, multiple or all of the compartments may be provided with an ion exchange resin.

In an embodiment of the membrane stack according to the invention, the packing density of the ion exchange resin in at least one compartment. may be in the range of 10% — 98%, may preferably be in the range of 25% — 95%, and more preferably may be in the range of 50% — 92.5%.

The ionic resistance in the membrane stack during ion transport is to a large extent determined by the presence of ion exchange resins in the flow compartment(s). This is especially the case when treating low conductivity feed flows, because the charge density in the resin in these cases is often orders of magnitude higher than in the liquid phase. It has been found that with the abovementioned ranges there is sufficient direct contact within the resin to obtain an overall low stack resistance.

It is noted that the term packing density, or the equivalent term packing fraction, is defined as the amount of space filled by the ion exchange resin.

In an embodiment of the membrane stack according to the invention, the ion exchange resin or 10n exchange resins is formed as packed bed particles or as a 3D porous structure.

An advantage of a packed bed is that the packing density may be varied, for example by varying the number of particles and/or the shape of particles. An advantage of a 3D porous structure is that it may simultaneously function as a spacer.

In an embodiment of the membrane stack according to the invention, the ion exchange resin is an anion exchange resin.

In an embodiment of the membrane stack according to the invention, the anion exchange resin may comprise polystyrene, preferably crosslinked polystyrene, as backbone, wherein said anion exchange resin is functionalized by strong base functionalized groups such as quaternary amines. For example, Dowex Marathon A and/or Amberlite Type I may be used

An advantage of the abovementioned ion exchange resins is that these resins provide a good balance between costs and efficiency in terms of ion transport resistance in the compartment.

In an embodiment of the membrane stack according to the invention, the ion exchange resin is a cation exchange resin.

In an embodiment of the membrane stack according to the invention, the cation exchange resin may comprise polystyrene, preferably crosslinked polystyrene, as backbone, wherein said cation exchange resin is functionalized by strong acid functionalized groups such as sulfonic acid.

For example, Dowex 650C and/or Dowex Marathon C may be used.

In an embodiment of the membrane stack according to the invention, the ion exchange resin in at least one compartment may comprise a mixture of, preferably different, ion exchange resins.

An advantage of providing a mixture of ion exchange resins is that the beneficial aspects of different resins can be combined in a single compartment. This approach allows the characteristics of the mixture to be optimized to achieve a desired result that may not be achievable with a single resin,

In an embodiment of the membrane stack according to the invention, the ion exchange resin mixture in at least one compartment may comprise an anion exchange resin and a cation exchange resin.

An advantage of providing a mixture of both an anion and a cation exchange resin is that the recombination of ammonium and hydroxide ions to ammonia takes place in the compartment at an increased distance from the membrane surface. This is due to the larger mobility of both ammonium and hydroxide ions through the mixed resin. As a result, the back-diffusion of ammonia through the membrane to the feed is (significantly) reduced. Another result is that the potential difference that is to be applied over the membrane stack may be lower, therewith leading to a reduced energy consumption of the membrane stack (and thus the process). It is preferred that the mixture is (at least) provided in the concentrate compartment.

In an embodiment of the membrane stack according to the invention, the ion exchange resin may be provided in the feed flow compartment, and the ion exchange resin may comprise a cation exchange resin.

An advantage of providing a cation exchange resin in the feed flow compartment is that it even further increases the mobility of the ions throughout the compartment and, therewith, decreases the specific energy consumption of the membrane stack.

It is noted that the application of the cation exchange resin in the feed flow compartment is especially effective if the feed flow comprises (low conductivity) condensates.

In an embodiment of the membrane stack according to the invention, the ion exchange resin may be provided in the feed flow compartment, and the 10n exchange resin may comprise an anion exchange resin.

An advantage of providing an anion exchange resin in the feed flow compartment is that it even further increases the mobility of the ions throughout the compartment and, therewith, decreases the specific energy consumption of the membrane stack.

In an embodiment of the membrane stack according to the invention, the mixture may be provided in a predetermined mixture pattem.

An advantage of providing a mixture of resins in a predetermined pattern or configuration is that the diffusion properties of the mixture can be optimized. This is especially interesting when a mixture of an anion exchange resin and a cation exchange resin is used.

The predetermined mixture pattern may be provided in different ways. The configuration may be built up during insertion of the resin in the compartments, yet may also be a preformed resin, for example a resin based structure or module, which can be inserted as an insert into the compartment.

In an embodiment of the membrane stack according to the invention, the ion exchange resin in at least one compartment may be beads or pearls.

An advantage of beads or pearls is that these shapes provide a high packing density.

Another advantage of these shapes is that, even with the high packing density, it does not result in a significant pressure drop over the compartment. This is mainly due to the fact that the flow of fluid between the beads or pearls is relatively unobstructed.

In an embodiment of the membrane stack according to the invention, the ion exchange resin in at least one compartment may be manufactured by sintering, extrusion, or printing.

An advantage of the abovementioned manufacturing methods for the ion exchange resin is that the methods provide a good balance between costs and efficiency. Another advantage, especially with for example printing, is that the resin can be formed with high accuracy on a layer by layer basis. This is for example interesting in case a (predetermined) mixture of ion exchange resins is to be provided in a specific configuration.

The invention also relates to a stack assembly, the stack assembly comprising: — a membrane stack according to the invention; and — an anode; and — acathode wherein the anode and the cathode are positioned to opposite sides of the membrane stack and that extend substantially parallel to the membranes in the membrane stack.

The stack assembly according to the invention provides similar effects and advantages as the membrane stack according to the invention. In addition, it is noted that the various embodiment and/or combinations thereof as disclosed for the membrane stack can also be used and/or applied with the stack assembly according to the invention. It is noted that the wording ‘stack assembly’ for the purpose of this application also encompasses the wording ‘membrane stack assembly”.

These wordings or phrases are used interchangeably throughout the application.

An advantage of the stack assembly according to the invention is that the energy consumption of the ammonia removal using the stack assembly is lower than compared to the ammonia removal using existing devices and methods. This is mainly due to the fact that the ion exchange resin in the concentration compartment provides a significantly larger recombination area for recombination of ammonium and hydroxide, which in turn leads to a reduction of concentration polarisation. As a result, the potential applied over the cathode and anode can be reduced, while maintaining (and even increasing) the ammonia removal rate and efficiency.

It is noted that, with reference to the membrane stack, the anode may be positioned adjacent to or near the feed compartment, or alternatively, near or adjacent to the acid compartment, and the cathode may be positioned near or adjacent to the feed compartment, or alternatively, near or adjacent to the concentrate compartment.

This configuration means that the anode faces the negative side of the bipolar membranes and the cathode faces the positive side of the bipolar membranes, which provides an efficient functioning of the stack assembly.

In an embodiment of the stack assembly according to the invention, the membrane stack further comprises electrolyte compartments that are respectively positioned between the anode and the adjacent compartment and between the cathode and the adjacent compartment.

An advantage of providing electrolyte compartments is that the anode and/or cathode due to the presence of the electrode rinse solution are, during operation, less exposed to impurities from the feed water. This results in an increase of the operational up-time and the life-time of the stack assembly.

Another advantage is that the (ionic) composition of the electrolyte rinse solution can be independently controlled.

In an embodiment of the stack assembly according to the invention, the membrane stack may comprise a shielding membrane that is positioned between the anode and the adjacent compartment and/or a shielding membrane that is positioned between the cathode and the adjacent compartment.

An advantage of shielding membranes is that the products related to the anode and/or cathode, such as oxidative products from the anode, are prevented from entering the membrane stack. This increases life-time and operational up-time of the membrane stack.

Preferably, the membrane stack comprises two shielding membranes, that is one on each end of the membrane stack, and the electrolyte compartments are positioned between one of the respectively shielding membranes on the one hand and the anode or the cathode on the other hand.

An advantage of the combination of shielding membranes and electrolyte compartments is that the cleaning or rinsing of the electrodes (i.e. the anode and the cathode) can be achieved without mixing of the rinsing solution/electrolyte into the compartments of the membrane stack.

In an embodiment of the stack assembly according to the invention, the shielding membrane or membranes may comprise a fluor-carbonfiber backing.

An advantage of the mentioned backing is that these are resistant to the oxidative compounds that are formed or may be formed at the anode.

In an embodiment of the stack assembly according to the invention, the anode may be manufactured from one or more selected from the group of: titanium, platinum, platinumoxide, iridium, ruthenium or mixtures thereof.

An advantage of the abovementioned materials is that these materials have a high dimensional stability combined with catalytic properties towards water splitting.

In an embodiment of the stack assembly according to the invention, the cathode may be manufactured from one or more selected from the group of: titanium, platinum, platinumoxide, iridium, ruthenium, stainless steel, for example Hastelloy C. or carbon black or mixtures thereof.

An advantage of the abovementioned materials is that most of these materials have a high dimensional stability. An advantage of some other materials, such as carbon black and stainless steel is that these are relatively cheap and therewith reduce the (manufacturing) costs of the cathode.

The invention also relates to a system for ammonia recovery from low conductivity condensates and gas scrubber concentrates, the system comprising: — a stack assembly according to the invention; — a Membrane Vacuum Distillation (MVD) unit comprising:

— a concentrate compartment that is connected to the one or more concentrate compartments of the membrane stack and configured to accommodate a flow through the compartment; and — a vacuum compartment that is separated from the concentrate compartment by at least one gas permeable hydrophobic membrane; — a condenser unit that connected to an outlet of the vacuum compartment and that is configured to provide a liquid ammonia solution.

The system according to the invention provides similar effects and advantages as the membrane stack and the stack assembly according to the invention. In addition, it is noted that the various embodiment and/or combinations thereof as disclosed for the membrane stack and/or the stack assembly can also be used and/or applied with the system according to the invention.

An advantage of the system according to the invention is that it provides a high yield and requires less energy than the known systems for recovering ammonia from (low conductivity) condensates. This is mainly due to the application of ion exchange resin in one or more of the compartments of the membrane stack. This increases the ammonia in the flow leading to the MVD unit, which subsequently can extract a larger amount of ammonia.

In addition, the application of ion exchange resin in one or more of the compartments of the membrane stack leads to a lower energy use of the membrane stack (compared to existing systems), which decreases the specific energy use per unit of ammonia extracted.

In an embodiment of the system according to the invention, the system may comprise a heat exchanger or heat source that is between the membrane stack and the MVD unit. and that is configured to supply heat to the concentrate flow to the MVD unit.

An advantage is that the heat exchanger allows the MVD unit to be operated at elevated temperatures relative to the membrane stack. This increases the efficiency of the MVD unit.

The invention further also relates to a method for recovering ammonia from low conductivity condensates and gas scrubber concentrates, the method comprising the steps of: — providing a membrane stack according to the invention, providing a stack assembly according to the invention or a system according to the invention; — feeding an ammonia-containing feed flow to the one or more feed compartments of the membrane stack: — extracting, using the membrane stack, ammonia; and — outputting a concentrate flow containing ammonia.

The method according to the invention provides similar effects and advantages as the membrane stack, the stack assembly and the system according to the invention. In addition. it is noted that the various embodiment and/or combinations thereof as disclosed for the membrane stack and/or the stack assembly and/or the system can also be used and/or applied with the method according to the invention.

An advantage of the method according to the invention is that, compared to the known methods, the vield of extracted ammonia is higher and the specific energy use per unit of extracted ammonia is lower. Therewith, the method according to the invention 1s more cost-effective, more efficient and widely applicable.

In an embodiment of the method according to the invention, the membrane stack comprises a cation exchange membrane (CEM) and the steps of extracting ammonia and outputting ammonia respectively comprise the steps of extracting the ammonia from the feed flow in the feed flow compartment and outputting the ammonia containing concentrate flow from the concentrate compartment.

In an embodiment of the method according to the invention, the membrane stack comprises an anion exchange membrane (AEM) and the steps of extracting ammonia and outputting ammonia respectively comprise the steps of extracting the ammonia from the flow in the acid compartment and outputting the ammonia containing concentrate flow from the feed flow compartment.

In an embodiment of the method according to the invention, the method may additionally comprise the step of discharging residual flows, wherein the residual flows have been substantially stripped from ammonia, wherein the discharging preferably comprises re-using or recycling the residual flows.

In an embodiment of the method according to the invention, the step of extracting further may comprise applying a potential difference over the stack assembly, preferably a potential difference between the anode and the cathode.

An advantage of this embodiment is that the potential applied over the anode and the cathode can be significantly lower than the potential applied to existing devices. This is mainly due to the fact that the membrane stack according to the invention comprises a larger recombination area for ammonium and hydroxide ions, thus resulting in a lower energy consumption (expressed in the required electric energy). This reduces the specific energy consumption per unit of ammonia extracted from the feed.

In an embodiment of the method according to the invention, the method may further comprise the steps of: — recirculating the ammonia containing concentrate from the concentrate compartment of the membrane stack through a membrane vacuum distillation (MVD) unit; — inthe MVD, extracting ammonia from the alkaline solution; and — condensing, preferably in a condenser, the extracted ammonia to a liquid ammonia solution.

An advantage of providing the abovementioned steps is that the ammonia can be extracted from the feed flow in an efficient manner, while providing ammonia with a relatively high purity.

This increases the market value of the ammonia as a resource.

An advantage of the method that combines the membrane stack and the MVD is that the concentration of recovered ammonia with respect to the amount of water can be increased even further (compared to the use of only the membrane stack or stack assembly according to the invention).

It has been found that the amount of ammonia that can be recovered from a feed flow is increased compared to the known methods. due to the presence of an ion exchange resin in the concentration compartment (and the resulting higher recombination surface and lower back diffusion of ammonia).

It has further been found that, compared to methods that provide a high ammonia vield, the recovery costs per unit of ammonia are significantly lower with the method according to the invention.

In other words, the method according to the invention, especially when used with an MVD, provides a cost-effective, high-yield ammonia recovery method compared to the known methods.

In an embodiment of the method according to the invention, the extracting may be performed using a vacuum and/or the extracted ammonia may be gaseous (wet) ammonia.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which: — Figure | shows a schematic overview of an example of a membrane stack comprising a number of adjacent stack cells; — Figure 2 shows a schematic overview of a second example of a membrane stack comprising a number of adjacent stack cells; — Figure 3 shows a schematic overview of a third example of a membrane stack comprising a number of adjacent stack cells; — Figures da, 4b shows a schematic cross-section of an example of a concentration compartment of a membrane stack according to the invention; — Figure 5 shows a schematic overview of an example of a system according to the invention; — Figure 6 shows a schematic overview of a second example of a system according to the invention; — Figure 7 shows a schematic overview of a third example of a system according to the invention; and

— Figure 8 shows a schematic overview of an example of the method according to the invention.

In an example of membrane stack 2 according to the invention (see figure 1), membrane stack 2 comprises two stack cells 4, 6 which are positioned adjacent to each other. Each stack cell 4, 6 comprises feed compartment 8. 10 and alkaline compartment 12, 14 and each compartment 8, is delineated by a membrane. In the example shown in figure 1, each feed compartment 8, 10 is delineated by bipolar membrane BPM and cation exchange membrane CEM, and each alkaline compartment 12, 14 is delineated by cation exchange membrane CEM and bipolar membrane

BPM. In principle, each stack cell 4, 6 of membrane stack 2 includes two bipolar membrane BPM 10 and cation exchange membrane CEM, which is positioned in the middle between bipolar membranes BPM. It is noted however that, when stacking stack cells 4, 6 of membrane stack 2, only one bipolar membrane BPM is provided between alkaline compartment 12 of stack cell 4 and feed compartment 10 of stack cell 6.

In another example of membrane stack 402 according to the invention (see figure 2), membrane stack 402 comprises two stack cells 404, 406 which are positioned adjacent to each other. Each stack cell 404, 406 comprises feed compartment 408, 410 and acid compartment 412, 414 and each compartment 408, 410 is delineated by a membrane. In the example shown in figure 2, each feed compartment 408, 410 is delineated by anion exchange membrane AEM and bipolar membrane BPM, and each acid compartment 412, 414 is delineated by bipolar membrane BPM and anion exchange membrane AEM. In principle, each stack cell 404, 406 of membrane stack 402 includes two bipolar membranes BPM and an anion exchange membrane AEM, which is positioned in the middle between bipolar membranes BPM. It is noted however that, when stacking stack cells 404, 406 of membrane stack 402, only one bipolar membrane BPM is provided between acid compartment 412 of stack cell 404 and feed compartment 410 of stack cell 406.

In a further example (see figure 3), membrane stack 102 according to the invention comprises two stack cells 104, 106 which are positioned adjacent to each other. Each stack cell 104, 106 comprises feed compartment 108, 110, alkaline compartment 112, 114 and acid compartment 116, 118. Each compartment 108, 110 is delineated by a membrane. In the example shown in figure 2, each feed compartment 108, 110 is delineated by anion exchange membrane

AEM and cation exchange membrane CEM. Each alkaline compartment 112, 114 is delineated by cation exchange membrane CEM and bipolar membrane BPM. Each acid compartment 116, 118 1s delineated by bipolar membrane BPM and anion exchange membrane AEM. In principle, each stack cell 104, 106 of membrane stack 102 includes two bipolar membranes BPM, cation exchange membrane CEM and anion exchange membrane AEM. Both bipolar membranes are positioned at the outer sides. It is noted however that, when stacking stack cells 104, 106 of membrane stack

102, only one bipolar membrane BPM is provided between alkaline compartment 112 of stack cell 104 and acid compartment 118 of stack cell 106. In the present example of figure 2, this means that, when viewed from left to right, membrane stack 102 subsequently comprises bipolar membrane BPM, anion exchange membrane AEM, cation exchange membrane CEM, bipolar membrane BPM, anion exchange membrane AEM, cation exchange membrane CEM and bipolar membrane BPM.

In this particular example of membrane stack 2, 102, the flows through the feed and alkaline compartments are based counterflow. In membrane stack 102, the flow through acid compartment 116, 118 is in co-flow with the flow in feed compartments 108, 110 and in counterflow direction with the flow in alkaline compartments 112, 114. It is noted that this example is not limiting, as other types of flow, such as cross-flow or co-flow are also possible.

In a more detailed schematic view of an example of alkaline compartment 212, 214 (figures 4a, 4b), alkaline compartment 212, 214 can be seen to comprises anion exchange resin 220 and cation exchange resin 222, which are positioned in alkaline compartment 212, 214. In a first example (see figure 4a). anion exchange resin 220 and cation exchange resin 222 are solid structures that are positioned between the cation exchange membrane CEM and bipolar membrane

BPM in alkaline compartment 212, 214.

In a second example (see figure 4b), anion exchange resin 220 and cation exchange resin 222 are formed as anion exchange beads 220 and cation exchange beads 222, which are provided in a mixed configuration between the cation exchange membrane CEM and bipolar membrane

BPM in alkaline compartment 212, 214.

In a schematic example of system 300 according to the invention (sce figure 5). system 300 comprises membrane stack 302, which in this example comprises two stack cells 304, 306 which are positioned adjacent to each other. Each stack cell 304, 306 comprises feed compartment 308, 310, alkaline compartment 312, 314 and acid compartment 316, 318. Each compartment 308, 310 is delineated by a membrane. In the example shown in figure 4, each feed compartment 308, 310 is delineated by anion exchange membrane AEM and cation exchange membrane CEM. Each alkaline compartment 312, 314 is delineated by cation exchange membrane CEM and bipolar membrane BPM. Each acid compartment 316, 318 is delineated by bipolar membrane BPM and anion exchange membrane AEM. In principle, each stack cell 304, 306 of membrane stack 102 includes two bipolar membranes BPM, cation exchange membrane CEM and anion exchange membrane AEM. Both bipolar membranes are positioned at the outer sides. It is noted however that, when stacking stack cells 304, 306 of membrane stack 302, only one bipolar membrane BPM is provided between alkaline compartment 312 of stack cell 304 and acid compartment 318 of stack cell 306.

Membrane stack 302 in this example forms part of stack assembly 301, which, aside from membrane stack 302, further comprises anode compartment 324 that in this example is positioned adjacent bipolar membrane BPM of acid compartment 316 and that is delineated by said bipolar membrane BPM on one side and by anode 326 on the other side. Anode compartment 324 is configured to contain an anolyte. Stack assembly 301 also comprises cathode compartment 328 that in this example is positioned adjacent bipolar membrane BPM of alkaline compartment 314 and that is delineated by said bipolar membrane BPM on one side and by cathode 330 on the other side. Cathode compartment 328 is configured to contain a catholyte.

System 300 further comprises membrane vacuum distillation (MVD) unit 332, which comprises concentrate compartment 334 and vacuum compartment 336 that are in this example fluidly connected to each other by means of gas permeable hydrophobic membrane 338. It is noted that other types of membranes 338 may be used and/or that multiple membranes 338 may be used.

Inlet 340 of MVD unit 332 is connected to outlets of alkaline compartments 312, 314, whereas outlet 342 of MVD unit 332 is connected to inlets of alkaline compartments 312, 314 to form a recirculation loop 344 that includes alkaline compartments 312, 314 and concentrate compartment 334 of MVD unit 332.

Vacuum compartment 336 of MVD unit 332 is connected to condenser unit 346, which liquifies the outflow of vacuum compartment 336 of MVD unit 332 to provide liquid ammonia solution. In this example system 300 further comprises vacuum pump 348 that is configured to discharge the liquid ammonia solution from MVD unit 332 to condenser unit 346.

In use of system 300, a feed flow containing ammonium-ions is provided to feed compartments 308, 310 and, optionally, to acid compartments 316, 318. In the present example (see figure 5), the feed flow in this example comprises an ammonium containing condensate.

Under influence of the electric potential difference provided between anode 326 and cathode 330, the ammonium ions migrate across cation exchange membrane CEM towards concentrate compartment 312, 314. Due to the presence of ion exchange resin 320, 322, which may comprise anion exchange resin 320, cation exchange resin 318 or both, the ammonium ions migrate towards the centre of concentrate compartment 312, 314. Concentrate compartment 312, 314 further receives hydroxide ions from respectively acid compartment 318 or catholyte compartment 328. In concentrate compartments 312, 314, mostly near a centre thereof, the ammonium ions and the hydroxide ions form ammonia, which is subsequently discharged to MVD unit 332, in which the (gaseous) ammonia is extracted from concentrate compartment 334 to vacuum compartment 336 for further processing in condenser unit 346, after which it is discharged as liquid ammonia solution as product.

The influence of the electric charge provided by anode 326 and cathode 330, also result in the migration of anions, which in this example is sulphate, across anion exchange membrane AEM to acid compartment 316, 318, in which acid compartment 316, 318 it recombines with hydrogen ions (also called protons) that are received from respectively the membrane that is positioned between anode compartment 324 and acid compartment 316, 318 or between alkaline compartment 312 and acid compartment 316, 318. The feed flow from feed compartments 308, 310 and the flow from acid compartments 316, 318 are discharged through a common discharge.

In a schematic example of system 500 according to the invention (see figure 6), system 500 comprises membrane stack 502, which in this example comprises two stack cells 504, 506 which are positioned adjacent to each other. Each stack cell 504, 506 comprises feed compartment 508, 510, and acid compartment 516, 518. Each compartment 508, 510, 516, 518 is delineated by a membrane. In the example shown in figure 6, each feed compartment 508, 510 is delineated by anion exchange membrane AEM and bipolar membrane BPM. Each acid compartment 516, 518 is delineated by bipolar membrane BPM and anion exchange membrane AEM. In principle, each stack cell 504, 506 of membrane stack 502 includes two bipolar membranes BPM and one anion exchange membrane AEM. Both bipolar membranes are positioned at the outer sides of stack cell 504, 506. It is noted however that, when stacking stack cells 504. 506 of membrane stack 502, only one bipolar membrane BPM is provided between alkaline compartment 512 of stack cell 504 and acid compartment 518 of stack cell 506.

Membrane stack 502 in this example forms part of stack assembly 501, which, aside from membrane stack 502, further comprises anode compartment 524 that in this example is positioned adjacent bipolar membrane BPM of acid compartment 516. Between bipolar membrane BPM of acid compartment 516 and anode compartment 524 shielding membrane SM is provided. Anode compartment 524 is thus delineated by shielding membrane SM on one side and by anode 526 on the other side. Anode compartment 524 is configured to contain an anolyte.

Stack assembly 501 also comprises cathode compartment 528 that in this example is positioned adjacent bipolar membrane BPM of feed compartment 510. Between bipolar membrane

BPM of feed compartment 510 and cathode compartment 528 shielding membrane SM is provided.

Thus, cathode compartment 528 is delineated by shielding membrane SM on one side and by cathode 530 on the other side. Cathode compartment 528 is configured to contain a catholyte.

System 500 further comprises membrane vacuum distillation (MVD) unit 532, which comprises concentrate compartment 534 and vacuum compartment 536 that are in this example fluidly connected to each other by means of gas permeable hydrophobic membrane 538. It is noted that other types of membranes 538 may be used and/or that multiple membranes 538 may be used.

Inlet 540 of MVD unit 532 is connected to outlets of feed compartments 508, 510, whereas outlet 542 of MVD unit 532 is connected to inlet 552 of water supply 550. Similarly, outlets 554 of acid compartments S16, 518 are connected to inlet 552 of water supply 550. In this example, water supply 550 is provided with ammonia from air scrubber 556 to which it is connected.

Electrode compartments 524, 528 (formed by anode compartment 524 and cathode compartment 528) are connected to each other as well as to electrode rinse unit 558. In this example, outlet 562 of electrode rinse unit 558 is connected to an inlet of anode compartment 524.

The outlet of anode compartment 524 is connected to an inlet of cathode compartment 528. An outlet of cathode compartment 528 is connected to inlet 560 of electrode rinse unit 558. As such, a closed electrolyte loop is formed.

Vacuum compartment 536 of MVD unit 532 is connected to condenser unit 546, which liquifies the outflow of vacuum compartment 336 of MVD unit 532 to provide liquid ammonia solution. In this example system 500 further comprises vacuum pump 548 that is configured to discharge the liquid ammonia solution from MVD unit 532 to condenser unit 546.

In a schematic example of system 600 according to the invention (see figure 7), system 600 comprises membrane stack 602, which in this example comprises a single stack cell 604. Stack cell 604 comprises feed compartment 608 and alkaline compartment 612. Each compartment 608, 612 is delineated by a membrane. In the example shown in figure 7, feed compartment 608 is delineated by bipolar membrane BPM and cation exchange membrane CEM. Alkaline compartment 612 is delineated by cation exchange membrane CEM and bipolar membrane BPM.

Stack cell 604 of membrane stack 602 thus includes two bipolar membranes BPM and one cation exchange membrane CEM. It is noted that, in an similar alternative, cation exchange membrane

AEM may be replaced with anion exchange membrane AEM to provide similar results.

Membrane stack 602 in this example forms part of stack assembly 601, which, aside from membrane stack 602, further comprises anode compartment 624 that in this example is positioned adjacent bipolar membrane BPM of feed compartment 608. Between bipolar membrane BPM of feed compartment 608 and anode compartment 624 shielding membrane SM is provided. Anode compartment 624 is thus delineated by shielding membrane SM on one side and by anode 626 on the other side. Anode compartment 624 is configured to contain an anolyte.

Stack assembly 601 also comprises cathode compartment 628 that in this example is positioned adjacent bipolar membrane BPM of alkaline compartment 612. Between bipolar membrane BPM of alkaline compartment 612 and cathode compartment 628 shielding membrane

SM is provided. Thus, cathode compartment 628 is delineated by shielding membrane SM on one side and by cathode 630 on the other side. Cathode compartment 628 is configured to contain a catholyte.

The outlet of feed compartment 608 is connected to inlet 652 of water supply 650, and the outlet of water supply 650. In this example, water supply 650 is provided with ammonia from air scrubber 656 to which it is connected.

Electrode compartments 624, 628 (formed by anode compartment 624 and cathode compartment 628) are connected to each other as well as to electrode rinse unit 658. In this example, outlet 662 of electrode rinse unit 658 is connected to an inlet of anode compartment 624.

The outlet of anode compartment 624 is connected to an inlet of cathode compartment 628. An outlet of cathode compartment 628 is connected to inlet 660 of electrode rinse unit 658. As such, a closed electrolyte loop is formed.

Alkaline compartment 612 is fed with a feed flow through inlet 611. The feed flow may for example comprise MilliQ or scrubber fluid. Outlet 613 provides a flow comprising a large amount of ammonia, which can subsequently (directly) be used or sold.

In an example of a method 1000 according to the invention (see figure 8), method 1000 may comprise the steps of: — providing 1002 a membrane stack, a stack assembly or a system according to the invention; — feeding 1004 an ammonia-containing feed flow to the one or more feed compartments of the membrane stack: — extracting 1006, using the membrane stack, ammonia from the feed flow; and — outputting 1008, from the concentrate compartments, a concentrate flow containing ammonia.

The step of extracting 1006 may further comprise the step of applying 1010 a potential difference over the stack assembly, which preferably comprises applying 1010 a potential difference over the anode and cathode of the stack assembly.

Method 1000 may additionally comprise other (optional) steps. such as the step of recirculating 1012 the ammonia containing concentrate from the concentrate compartment of the membrane stack through a membrane vacuum distillation (MVD) unit and the step of, in the MVD, extracting 1014 ammonia from the alkaline solution. Method 1000 may further also comprise the optional step of condensing 1016, preferably in a condenser, the extracted ammonia to a liquid ammonia solution. Further optionally, the method may comprise the step of providing 1018 heat, for example from a heat exchanger, to the concentrate flow containing ammonia.

It is noted that the step of extracting 1006 may be performed under a vacuum and that the extracted ammonia may be gaseous (wet) ammonia.

The present invention is by no means limited to the above described preferred embodiments and/or experiments thereof.

The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.

CLAUSES

I. Membrane stack comprising at least one stack cell, wherein the at least one stack cell comprises: — a first bipolar membrane (BPM); — a second bipolar membrane that extends substantially parallel to the first bipolar membrane; further comprising: — a cation exchange membrane (CEM) extending between and substantially parallel to the first and the second bipolar membranes; — a feed flow compartment that extends between the first bipolar membrane and the cation exchange membrane and is delineated thereby; and — a concentrate compartment that extends between the cation exchange membrane and the second bipolar membrane and is delineated thereby; wherein at least one compartment is provided with an ion exchange resin; or further comprising: — an anion exchange membrane (AEM) extending between and substantially parallel to the first and the second bipolar membranes; — an acid compartment that extends between the first bipolar membrane and the anion exchange membrane and is delineated thereby; and — a feed flow compartment that extends between the anion exchange membrane and the second bipolar membrane and is delineated thereby; wherein at least one compartment is provided with an ion exchange resin. 2. Membrane stack according to clause 1 comprising the cation exchange membrane (CEM), wherein the at least one stack cell additionally comprises: — an anion exchange membrane (AEM) that extends between the first bipolar membrane and the cation exchange membrane and extends substantially parallel to the first bipolar membrane and the cation exchange membrane; and — an acid compartment that extends between the first bipolar membrane and the anion exchange membrane; and wherein the feed flow compartment is positioned between the anion exchange membrane and the cation exchange membrane.

3. Membrane stack according to clause 1 or 2, wherein the membrane stack is an Electro-

Deionization-by-Bipolar-Membranes (EDIBM) stack. 4. Membrane stack according to any one of the preceding clauses, wherein multiple or all compartments are provided with an ion exchange resin. 5. Membrane stack according to any one of the preceding clauses, wherein a packing density of the ion exchange resin in at least one compartment, is in the range of 10% — 98%. preferably in the range of 25% — 95%, and more preferably in the range of 50% — 92 5%. 6. Membrane stack according to any one of the preceding clauses, wherein the ion exchange resin is an anion exchange resin. 7. Membrane stack according to clause 6, wherein the anion exchange resin comprises polystyrene, preferably crosslinked polystyrene. as backbone, and wherein said anion exchange resin is functionalized by strong base functionalized groups such as quaternary amines. 8. Membrane stack according to any one of the preceding clauses, wherein the ion exchange resin is a cation exchange resin. 9. Membrane stack according to clause 8, wherein the cation exchange resin comprises polystyrene, preferably crosslinked polystyrene, as backbone, wherein said cation exchange resin is functionalized by strong acid functionalized groups such as sulfonic acid. 10. Membrane stack according to any one of the preceding clauses, wherein the ion exchange resin in at least one compartment comprises a mixture of different ion exchange resins. 11. Membrane stack according to clause 10, wherein the mixture of different ion exchange resins comprises an anion exchange resin and a cation exchange resin. 12. Membrane stack according to any one of the preceding claims, wherein the ion exchange resin is provided in the feed flow compartment and wherein the ion exchange resin comprises a cation exchange resin.

13. Membrane stack according to clause 10 or 11, wherein the mixture is provided in a predetermined mixture pattern. 14. Membrane stack according to any one of the preceding clauses, wherein the ion exchange resin at least one compartment comprises beads or pearls. 15. Membrane stack according to any one of the preceding clauses, wherein the ion exchange resin in at least one compartment is manufactured by sintering, extrusion, or printing. 16. Stack assembly, comprising: — a membrane stack according to any one of the preceding clauses; — an anode that is positioned adjacent to the feed compartment, or alternatively, adjacent to the acid compartment; and — a cathode that is positioned adjacent to the feed compartment, or alternatively, adjacent to the concentrate compartment. 17. System for ammonia recovery from condensates and low conductivity gas scrubber concentrates, the system comprising: — a stack assembly according to clause 16; — a membrane vacuum distillation (MVD) unit comprising:

— a concentrate compartment that is connected to the one or more concentrate compartments of the membrane stack and configured to accommodate a flow through the compartment; and

— a vacuum compartment that is separated from the concentrate compartment by at least one gas permeable hydrophobic membrane; and — a condenser unit that connected to an outlet of the vacuum compartment and that is configured to provide a liquid ammonia solution. 18. Method for recovering ammonia from condensates and low conductivity gas scrubber concentrates, the method comprising the steps of: — providing a membrane stack according to any one of the clauses 1 to 15, providing a stack assembly according to clause 16, or a system according to clause 17;

— feeding an ammonia-containing feed flow to the one or more feed compartments of the membrane stack; — extracting, using the membrane stack, ammonia; and

— outputting a concentrate flow containing ammonia. 19. Method according to clause 18, wherein the step of extracting further comprises the step of applying a potential difference over the stack assembly, preferably a potential difference between the anode and the cathode. 20. Method according to clause 18 or 19, wherein the method further mprises the steps of: — recirculating the ammonia containing concentrate from the concentrate compartment of the membrane stack through a membrane vacuum distillation (MVD) unit; — in the MVD, extracting ammonia from the alkaline solution; and — condensing, preferably in a condenser, the extracted ammonia to a liquid ammonia solution. 21. Method according to clause 20, wherein: — the extracting is performed using a vacuum; and/or — the extracted ammonia is gaseous (wet) ammonia.

Claims

CONCLUSIONS

1. Membrane stack comprising at least one stacking cell, wherein the at least one stacking cell comprises: - a first bipolar membrane (BPM); — a second bipolar membrane (BPM) extending essentially parallel to the first bipolar membrane (BPM); further comprising: - a first cation exchange membrane (CEM) extending between and substantially parallel to the first and second bipolar membranes: - a supply compartment extending between the first bipolar membrane and the cation exchange membrane and being bounded thereby; and — a concentrate compartment extending between and bounded by the cation exchange membrane and the second bipolar membrane; wherein at least one compartment is provided with an ion exchange membrane; or further comprising: - an anion exchange membrane (AEM) extending between and substantially parallel to the first and second bipolar membranes; — an acid compartment extending between and bounded by the first bipolar membrane and the anion exchange membrane, — a supply compartment extending between the anion exchange membrane and the second bipolar membrane and bounded by it: wherein at least one compartment is provided with an ion exchange membrane.

A membrane stack according to claim 1, comprising the cation exchange membrane, wherein the at least one stack cell further comprises: - an anion exchange membrane extending between and substantially parallel to the first bipolar membrane and the cation exchange membrane; and - an acid compartment extending between the first bipolar membrane and the anion exchange membrane; and wherein the supply compartment is positioned between the anion exchange membrane and the anion exchange membrane.

A membrane stack according to claim 1 or 2, wherein the membrane stack is an Electro-Deionization with Bipolar Membranes (EDIBM) stack.

4. Membrane stack according to any one of the preceding claims, wherein several or all compartments are provided with an ion exchange resin.

A membrane stack according to any one of the preceding claims, wherein a packing density of the ion exchange resin in at least one compartment is in the range of 10% - 98%. preferably in the range of 25% - 95%, and preferably in the range of 50% - 92.5%.

A membrane stack according to any one of the preceding claims, wherein the ion exchange resin is an anion exchange resin.

7. Membrane stack according to claim 6, wherein the anion exchange resin comprises polystyrene, preferably networked polystyrene, as support, and wherein the anion exchange resin functionalized by a strong base functionalized groups such as quaternary amines.

A membrane stack according to any one of the preceding claims, wherein the ion exchange resin is a cation exchange resin.

9. Membrane stack according to claim 8, wherein the cation exchange resin comprises polystyrene, preferably networked polystyrene, as support, and wherein the cation exchange resin is functionalized by a strong acid functionalized groups such as sulfonic acid.

10. Membrane stack according to any one of the preceding claims, wherein the ion exchange resin comprises a mixture of different ion exchange resins in at least one compartment.

The membrane stack of claim 10, wherein the mixture of different ion exchange resins comprises an anion exchange resin and cation exchange resin.

12. Membrane stack according to any one of the preceding claims, wherein the ion exchange resin is arranged in the supply compartment and wherein the ion exchange resin comprises a cation exchange resin.

A membrane stack according to claim 10 or 11, wherein the mixture is applied in a predetermined pattern.

A membrane stack according to any one of the preceding claims, wherein the ion exchange resin comprises spheres or beads in at least one compartment.

15. Membrane stack according to any one of the preceding claims, wherein the ion exchange resin in at least one compartment is manufactured by means of sintering, extrusion or printing.

16. Stack assembly, comprising: - a membrane stack according to any one of the preceding claims: - an anode arranged next to or adjacent to the supply compartment, or alternatively next to or adjacent to the acid compartment; and — a cathode arranged adjacent to or adjacent to the supply compartment, or alternatively adjacent to or adjacent to the concentrate compartment 1s.

17. System for recovering ammonia from condensates and low-conductivity gas scrubber concentrates, the system comprising: - a stack assembly according to claim 16; — a membrane vacuum distillation (MVD) unit. comprising: - a concentrate compartment connected to the one or more concentrate compartments of the membrane stack and adapted to accommodate flow through the compartment; and — a vacuum compartment separated from the concentrate compartment by at least one gas-permeable hydrophobic membrane; and — a condenser unit connected to an outlet of the vacuum compartment and adapted to provide a liquid ammonia solution.

18. Method for recovering ammonia from condensates and low-conductivity gas scrubber concentrates, the method comprising: - providing a membrane stack according to any one of claims 1 to 15, providing a stack assembly according to claim 16 or a system according to claim 17: - supplying an ammonia-containing supply stream to the one or more supply compartments of the membrane stack; - extracting the ammonia using the membrane stack; and - running a concentrate stream containing ammonia.

A method according to claim 18, wherein the step of extracting further comprises the step of applying a potential difference across the stack assembly, preferably a potential difference between the anode and the cathode.

A method according to claim 18 or 19, wherein the method further comprises the steps of: - recirculating the ammonia-containing concentrate through the concentrate compartment of the membrane stack and a membrane vacuum distillation (MVD) unit: - extracting ammonia from the ammonia in the MVD basic solution: ne — condensing, preferably in a condenser unit, the extracted ammonia into liquid ammonia solution.

Method according to claim 20, wherein: - the extraction is carried out under vacuum; and/or — the extracted ammonia is gaseous wet ammonia.