NL2034863A

NL2034863A - Reactor for use in a bioelectrochemical process

Info

Publication number: NL2034863A
Application number: NL2034863A
Authority: NL
Inventors: Schreuder Sandra; Liu Dandan; De Rink Frederikus; Henk VAN DIJK Jan
Original assignee: Paqell B V
Priority date: 2023-05-19
Filing date: 2023-05-19
Publication date: 2024-06-04
Also published as: NL2034863B1; WO2024240617A1

Abstract

The invention is directed to a reactor vessel or basin for use in a bioelectrochemical process provided with a horizontally extending reaction zone. The reaction zone 5 comprises one or more working electrodes comprising a current distributor or current collector and multiple vertically extending membrane conduits having a closed lower end. At the interior of the vertically extending membrane conduits a counter electrode and a liquid supply conduit for a liquid counter electrolyte is present. At the exterior of the multiple vertically extending membrane conduits the one or more 10 working electrodes are present. [Fig. 1]

Description

REACTOR FOR USE IN A BIOELECTROCHEMICAL PROCESS

The invention is directed to a reactor for use in a bioelectrochemical process.

The invention is also directed to a bioelectrochemical process performed in the reactor.

WO2022/079081 describes a process to convert carbon dioxide to methane in a bioelectrochemical cell. The cathode, as a working electrode, is granular activated carbon and a graphite plate is used as current collector. An anode compartment is separated from the cathode by a cation exchange membrane. At the cathode methane is formed and at the anode oxygen is formed.

WO2018/219990 describes a process to convert sulphide to elemental sulphur in a bioelectrochemical cell. The anode, as a working electrode, consisted of a graphite rod. A cathode compartment is separated from the anode by an ion selective membrane. At the anode elemental sulphur is produced and at the cathode gaseous hydrogen is formed.

There is a desire to apply the above prior art processes on a large scale. For this a reactor is required in which such a large scale process can be performed.

This is provided by the following reactor. Reactor for use in a bioelectrochemical process provided with a horizontally extending reaction zone, wherein the reaction zone comprises one or more working electrodes comprising a current distributor or current collector, multiple vertically extending membrane conduits having a closed lower end, wherein at the interior of the vertically extending membrane conduits one or more counter electrodes and a liquid supply conduit for a liquid counter electrolyte is present, and wherein at the exterior of the multiple vertically extending membrane conduits the one or more working electrodes are present.

Applicant found that in such a reactor a bioelectrochemical process can be performed on a larger scale. Especially when the process is performed continuously wherein fresh liquid electrolytes are continuously fed to the reactor and produced electrolytes are continuously discharged from the reactor. The reactor allows that the two electrolytes can flow through the reactor in separate flow paths as separated by the membranes of the membrane conduits. Further advantages will be described when describing the invention in more detail.

In this specification terms like horizontal, vertical, upper, lower, above, below are used to describe the reactor in its normal orientation of use. The terms are not to be used to limit the reactor only to such an orientation.

In this specification the following terms will have the following meaning.

Working electrolyte refers to the liquid phase in contact with the working electrode in the reactor and to any liquid supplied to or discharged from this liquid phase.

Counter electrolyte refers to the liquid phase in contact with the counter electrode in the reactor and to any liquid supplied to or discharged from this liquid phase.

Depending on the specific bioelectrochemical process the working electrode may be a cathode or an anode of a bioelectrochemical cell. Thus the working electrolyte may be a catholyte or an anolyte and the counter electrolyte may be a anolyte or a catholyte respectively.

The liquid supply conduit as present at the interior of the vertically extending membrane conduits allows that a counter electrolyte can be fed to each vertically extending membrane conduits individually and contact the counter electrode.

Preferably the liquid supply conduit is a vertically extending liquid supply conduit having a liquid inlet opening at an upper end and a liquid outlet opening at its lower end. The liquid supply conduit thus has a dip tube like design. The liquid conduit is preferably tubular. Such a design allows that the counter electrolyte can be supplied to the lower end of the vertically extending membrane conduits after which it flow upwardly with any formed gas along the one or more counter electrodes. This achieves an optimal contacting between counter electrolyte and counter electrode and enhances the discharge of any formed gas at the counter electrode from the vertically extending membrane conduits.

The liquid inlet opening of the liquid supply conduit may be directly connected to a reactor inlet for counter electrolyte. Preferably liquid inlet opening of the liquid supply conduit is present in a horizontally extending upper manifold. The reactor inlet for counter electrolyte is positioned above this upper manifold such that in use counter electrolyte is supplied to the upper side of the upper manifold. The use of a manifold is advantageous because it allows to evenly distribute the counter electrolyte among the multiple vertically extending membrane conduits. Such an even distribution may be achieved by maintaining in use a volume of counter electrolyte on top of the upper manifold. This volume of counter electrolyte may fill the entire volume above the upper manifold. This allows one to further pressurise the counter electrolyte and in this way influence the flow rate of counter electrolyte through the reactor. The volume of counter electrolyte may also be formed by volume of counter electrolyte on top of the upper manifold having a certain height wherein also a volume of gas is present above the volume of counter electrolyte in the reactor. For this latter embodiment it is preferred that liquid level control means are present to ensure, in use, a certain set height of liquid counter electrolyte on top of the horizontally extending upper manifold.

The upper manifold is vertically spaced from the reaction zone defining a horizontally extending fluid discharge zone between the upper manifold and the reaction zone. The fluid discharge zone is suitably divided by a horizontally extending lower manifold into a lower fluid discharge zone for discharge of a working electrolyte and any formed gas and an upper fluid discharge zone for discharge of the counter electrolyte and any formed gas. The upper open end of the vertically extending membrane conduits are present in the lower manifold. In this way the interior of the multiple vertically extending membrane conduits are fluidly connected to the upper fluid discharge zone. This allows that the upwardly flowing counter electrolyte of the multiple vertically extending membrane conduits is collected in the upper fluid discharge zone before being discharged from the reactor. This is advantageous, especially when a gas is formed at the counter electrode, because this upper zone can then be used to perform a gas liquid separation or at least an initial gas liquid separation.

The space which is exterior of the multiple vertically extending membrane conduits is fluidly connected to the lower fluid discharge zone. This allows the working electrolyte as present in the space which is exterior of the multiple vertically extending membrane conduits to flow upwards, via an opening or openings, to the lower fluid discharge zone. This is advantageous, especially when a gas is formed at the working electrode, because this lower zone can then be used to perform a gas liquid separation or at least an initial gas liquid separation.

The space which is exterior of the multiple vertically extending membrane conduits may be fluidly connected to a reactor inlet for working electrolyte. This inlet may be positioned in the reactor wall at an elevation below or at the reaction zone.

The working electrolyte as supplied to the reactor may comprise the feedstock for the bioelectrochemical process. An example of a working electrolyte comprising the feedstock is when the working electrolyte is obtained as a enriched absorbent in a gas-liquid absorption process or in a liquid-liquid absorption process, for example via a membrane. The feedstock may also be supplied separately to the reactor. Liquid feedstocks optionally dissolved in water, may be separately supplied. Gaseous feedstocks, such as carbon dioxide, may be separately supplied to the reactor in a zone below the reaction zone. Preferably a gaseous feedstock is supplied to a space of the reactor which is fluidly separated, for example by a gas permeable membrane, from a space in the reactor to which the working electrolyte is supplied. In this manner gas can dissolve in the working electrolyte. This ensures that the gaseous feedstock is dissolved in the working electrolyte when supplied to the reaction zone.

These zones separated by a gas permeable membrane are suitably located below the reaction zone. Between the inlets for working electrolyte and the optional zone and the reaction zone a distribution plate is present to ensure a good distribution of the working electrolyte and the feedstock over the working electrode.

The upper and/or lower fluid discharge zones are suitably provided with liquid holding means to achieve a gas liquid separation. The upper and/or lower fluid discharge zones are then suitably provided with a liquid discharge opening and a gas discharge opening. The liquid holding means may be any means which achieve some sort of fluid level and fluid holding time such that gas may escape the fluid.

Preferably a weir as present on the lower manifold and/or extending from the reaction zone is used as such means. More preferably a weir is present on the lower manifold and a weir extends from the reaction zone.

The reaction zone of the reactor comprises multiple vertically extending 5 membrane conduits having a closed lower end. The closed lower end may extend to a position below the reaction zone but is suitably present in the reaction zone. The cross-sectional shape of the membrane conduit may be any shape. Preferably this shape is oval and more preferably circular. The preferred membrane conduit is a membrane tube. The membrane itself may be any ion selective membrane, preferably a cation exchange membrane or an anion exchange membrane. The membrane conduits may have the same membrane or different membranes. For example part of the membrane conduits may be provided with a cation exchange membrane and another part of the membrane conduits may be provided with an anion exchange membrane.

Because the membranes themselves typically do not have sufficient structural strength to form a conduit or tube for use in the reactor it is preferred to combine the membrane with a support structure having the desired shape. Further it is preferred to provide a protective screen around the membrane to avoid damage of the membrane, especially when a conductive material is part of the working electrode as described below. Such a protective screen will also protect the membrane when the membrane conduits are removed from the reaction zone, for example by lifting them upwardly, for inspection and the like,

The membrane conduits are substantially vertically arranged. In this way any gas which is formed at the counter electrode can be easily discharged in an upward direction. The membrane conduits may be positioned under a small angle with the vertical where gas may still flow upwardly. Preferably the membrane conduits are positioned vertical as this allows the membrane conduits to be easily removed from the reaction zone by for example lifting.

The membrane conduits may be arranged in many possible patterns,

Preferably in a regular pattern, such as in a rhombic lattice, a square lattice, a hexagonal lattice, or a rectangular lattice.

In the space of the reaction zone and exterior to the multiple vertically extending membrane conduits the one or more working electrodes are present.

Preferably one working electrode is present. But it may sometimes be preferred to have more than one working electrode present. Different working electrodes are defined in that they can be independently controlled by independent current circuits.

The working electrode comprises a current distributor or current collector. The current distributor or current collector is a conductive structure, suitably a metal conductive structure. The metal structure may be present in the space of the reaction zone and exterior to the multiple vertically extending membrane conduits. Such a structure is also referred to as a 3D structure. The current distributor or current collector may be vertically extending rods or pipes that are interconnected.

Preferably the current distributor or current collector are vertically extending open or closed walls that are conductively connected. More preferably the walls define one or more vertically extended channels. Within such a one or more vertically extended channel one or more of the multiple vertically extending membrane conduits are present. In addition one or more of the multiple vertically extending membrane conduits may be present at the exterior of such a channel. For example in a space between such a channel and a reactor wall. The vertical orientation of the channels allows easy removal of the vertical membrane conduits as described above.

For smaller reactors it may be envisaged that only one such channel is present and wherein one or more vertically extending membrane conduits are present within this one channel. For larger reactors more channels may be present.

The channels preferably have a cross-sectional shape which allows placement of large numbers of vertically extending membrane conduits. The channels may have different cross-sectional shapes. The cross-sectional shape of a channel may be an oval, such as an ellipse or a circle. Preferably the cross-sectional shape or shapes allows tessellation. Preferred shapes are a triangle, a square, a rectangle, a pentagon, a hexagon or an octagon. A preferred shape is wherein the horizontal cross-sectional shape of the wall of the vertically extended channel is a hexagon.

In use microorganisms of the bioelectrochemical process will be present at the working electrode and preferably in the space between the current distributor or the current collector and the vertically extending membrane conduits. The working electrode may comprise a conductive material conductively connected to the current distributor or to the current collector. Such a conductive material is preferably present in the space between the current distributor or the current collector and the vertically extending membrane conduits. The preferred channels described above are advantageous because they provide a holding space for the conductive material between the channel wall and the vertically extending membrane conduits. The presence of the conductive material advantageous because it enhances the contact surface between the working electrode and the microorganisms of the bioelectrochemical process.

The conductive material may be any conductive material such as stainless steel felt. The conductive material is preferably a carbon based material, such as for example carbon granules, graphite granules, graphite felt, carbon felt, activated carbon felt or cloth modified with carbon nanotubes, and activated carbon particles such as granules or extrudates. The graphite felt may be present as a layer sandwiched between two layers of metal mesh and wherein the metal mesh is the current distributor or the current collector as for example described in Ai-Jie

Wang,Hong-Cheng Wang,Hao-Yi Cheng,Bin Liang, Wen-Zong Liu,Jing-Long Han,Bo

Zhang,Shu-Sen Wang, Electrochemistry-stimulated environmental bioremediation:

Development of applicable modular electrode and system scale-up, Environmental

Science and Ecotechnology, Elsevier, July 2020. In this publication the sandwiched graphite felt is present as walls of a hexagonal shaped channel around a membrane tube. Such a layered product may also be wound around the vertically extending membrane conduit. Preferably the carbon based material is a packed bed of activated carbon granules or extrudates. The activated carbon granules or extrudates may have a surface area of between 500 and 3000 m2/g. Preferably this surface area is the area of the exterior of the granules or extrudates and the surface area of the mesopores and macropores because microorganisms can readily enter such pores. Combinations of the layered graphite felt and activated carbon granules may be preferred wherein the activated carbon granules are present in a, for example annular, space between the layered graphite felt and the vertically extending membrane conduit.

The dimensions of the graphite granules or activated carbon granules or extrudates are suitably such that on the one hand a mass transport of the aqueous fractions is possible in the spaces between the granules without causing a high pressure drop. This means that there will be a practical lower limit with respect to the dimensions of these particles. On the other hand the particles should not be too large because this would result in long travel distances. The volume based diameter of the granules may be between 0.5 and 10 mm and preferably between 1 and 4 mm.

The microorganisms of the bioelectrochemical process may be present in the working electrolyte as planctonic microorganisms or may be present as a biofilm.

Combination of planctonic microorganisms and a biofilm of microorganisms is also possible. A biofilm may form on the current collector or current distributor. When a conductive material is present as part of the working electrode the conductive material will comprise the biofilm. When the earlier referred to activated carbon granules or extrudates are used a biofilm may be present on the external and internal surface area of especially the macropores and the mesopores.

The one or more counter electrodes as present in the vertically extending membrane conduits are suitably present along the majority of the length of the vertically extending membrane conduit. Suitably one counter electrode is present but embodiments with two, three or more are also conceivable. The material of the counter electrode will depend on the bioelectrochemical process which is performed in the reactor. For example when the counter electrode is the anode of the bioelectrochemical process with water as electron donor, the anode may be a metal based electrode material and preferably a coated titanium mesh. A preferred coated titanium mesh is a ruthenium-iridium coated titanium mesh.

The reactor may have any design such as a basin having a rectangular basis as made from fibre reinforced plastic,, like for example glass fibre reinforced plastic, concrete, metal or plastic. A preferred reactor design is wherein the reactor is a tubular vessel having a vertical tube axis. Such a tubular vessel is advantageous because it allows easy accessibility to the various parts of the reactor as will be described below.

The tubular vessel preferably has a first flange as present in the vessel wall at the elevation of the upper manifold. This allows that a vessel wall part above the first flange may be removed from a vessel wall part below the flange. This makes the upper manifold accessible from above. This in turn allows to lift the upper manifold and the vertically extending membrane conduits connected to the upper manifold from the reactor vessel. It also allows to remove an individual vertically extending membrane conduit.

The tubular vessel preferably has a second flange as present in the vessel wall at the elevation of the lower manifold. This allows that a vessel wall part above the second flange may be removed from a vessel wall part below the second flange.

This makes the lower manifold removeable and accessible from above. By removing the lower manifold, by for example lifting, the reaction zone is accessible from above.

This is advantageous because the working electrodes can then be inspected, repaired, replaced, cleaned and the like.

The reactor may be used to perform various bioelectrochemical processes.

When used the one or more working electrodes are in contact with a working electrolyte and the counter electrode is in contact with a counter electrolyte. The reactor is especially suited to perform bioelectrochemical processes where a gas is formed at the working electrode and/or at the counter electrode. The reactor is preferably used in a continuously operated process. The working electrode may be the cathode or the anode of the bioelectrochemical process wherein the counter electrode will then be the anode or the cathode respectively. The bioelectrochemical process may generate a current between the anode and the cathode or may require to apply a current between the anode and the cathode. This current can be controlled at a fixed/set value, or by maintaining a certain cell voltage, i.e. a potential between anode and cathode, or by maintaining a certain potential between the working electrode and an internal reference electrode. Below examples will be provided of bioelectrochemical processes which may be performed using the reactor of this invention.

Preferably the reactor is used to perform a process to convert carbon dioxide to methane by contacting dissolved carbon dioxide in the aqueous solution with the halophilic microorganisms under anaerobic conditions and wherein a potential or a current is applied between the anode and the cathode. The reactor for this process has a cathode as the working electrode and an anode as the counter electrode. The process may be performed as described in WO2022/079081.

For this process it is preferred that the working electrode comprises a conductive material as described above and most preferably the afore mentioned activated carbon granules or extrudates.

The reaction zone of the reactor for use in the above process is submerged in an aqueous solution, the working electrolyte, having a pH of above 7.5 and comprising between 0.3 and 4 M sodium cations or between 0.3 and 4 M sodium and potassium cations and wherein the microorganisms are halophilic microorganisms. Preferably the aqueous solution comprises between 0.4 and 2 M sodium cations or between 0.4 and 2 M sodium and potassium cations.

Preferably the aqueous solution comprises more than 20 mM phosphate ions.

Applicants found that when the process is performed in the presence of more than 20 mM phosphate ions a more stable process is obtained wherein the energy efficiency improves to values of around 60%.

Only a small content of more than 20 mM, preferably more than 40 mM and even more preferably more than 50 mM of phosphate ions is required. It is suggested that the phosphate ions suppress microbial growth of competing microorganisms which consume electrons and form other products. For this reason only small contents are required. The upper limit may be the saturation concentration that will be determined by factors like scaling, which is suitably to be avoided.

Contents of up to and even above 0.5 M are conceivable. For practical reasons one would operate the process at low phosphate ion contents. The phosphate ions may be added to the aqueous solution as a salt and preferably as an alkaline salt like sodium phosphate or potassium phosphate. The latter are preferred because sodium and optionally potassium ions are according to the invention present in the aqueous solution.

The aqueous alkaline solution suitably further comprises nutrients for the microorganisms. Examples of suitable nutrients are nutrients such as ammonium, vitamin and mineral elements as may be present as part of a so-called Wolfe's vitamin and mineral solutions. It may be desired to add such nutrients to the aqueous alkaline solution in order to maintain active microorganisms.

The anaerobic conditions are suitably achieved by performing the process in the absence of molecular oxygen, preferably also in the absence of other oxidants such as for example nitrate. By ‘in the absence of molecular oxygen’ is meant that the concentration of molecular oxygen in the loaded aqueous solution in this process is at most 130 uM molecular oxygen and preferably at most 10 uM. . Sulfate, which may be regarded to be an oxidant, may be present at low concentrations of for example 160 uM, as part of the earlier referred to Wolfe's mineral solution. It has been found that the sulfate at these low concentrations does not negatively influence the desired conversion of carbon dioxide.

The process is performed by contacting the aqueous solution with an electron charged packed bed comprising of activated carbon granules and microorganisms under anaerobic conditions wherein carbon dioxide is converted to methane. The microorganisms may be a mixed culture of microorganisms or a monoculture. The mixed culture of microorganisms is suitably obtained from an anaerobically grown culture. Suitably the mixed culture comprises hydrogenotrophic methanogens, such as for example Methanobacterium. Further microorganisms may be present, including anaerobic or facultative anaerobic bacteria, for example Proteobacteria, such as for example Deftaproteobacteria and Betaproteobacteria.

At the high salt concentration conditions of the process of this invention halophile microorganisms will dominate the culture even when the starting culture is obtained from an anaerobically grown culture which consisted of mainly non-

halophile microorganisms. Examples of halophile microorganisms which may be present in the process are slight halophiles and moderate halophiles belonging to genus level of Bathyarchaeia, Methanobacterium, Methanosaeta, Candidatus

Methanogranum, Marinobacter, Balneolaceae , Desulfovibrionaceae,

Acetobacterium, Acidaminococcaceae, Halothiobacillus, Spirochaetaceae,

Paludibacter, Rhodobacteraceae, Desulfobacteraceae, Desulfuromonadaceae,

Geobacteraceae, Solimonadaceae, Halomonadaceae, Vibrionaceae,

Ectothiorhodospiraceae, Oceanospirillaceae, Lentimicrobiaceae and/or

Synergistaceae.

The mixed culture microorganisms is preferably obtained from an anaerobic system, such as an anaerobically grown culture. The mixed culture may therefore be obtained from sources where halophile microorganisms will dominate such as in a sludge of a salt lake. Alternatively the mixed culture may be obtained from the sludge of an anaerobic bioreactor, such as an anaerobic fermenter, for example one used for anaerobic chain elongation; an anaerobic digestion reactor, for example an upflow anaerobic sludge blanket reactor (UASB); Other suitable bioreactors for providing the sludge are expended granular sludge bed (EGSB), a sequential batch reactor (SBR), a continuously stirred tank reactor (CSTR) or an anaerobic membrane bioreactor (AnMBR). In the present context, the term sludge refers to the semi-solid flocs or granules containing a mixed culture of microorganisms.

The conductive material and especially the packed bed of activated carbon granules or extrudates may be charged in such a system by applying a potential to the bioelectrochemical system resulting in a current between anode and cathode such that electrons are donated at the anode and at the cathode electrons are supplied to the conductive material. At the anode an oxidation reaction, such as water oxidation, takes place providing the required electrons. The potential may be achieved by an external power supply generating electricity, like for example power generated by wind and/or solar. Alternatively the electrons and thus the power supply may be partially donated by a chemical reaction at the anode. An example of such a chemical reaction is the organic matter (i.e. COD) oxidation as described in

Cerrillo, M., Vifias, M. and Bonmati, A. (2017) Unravelling the active microbial community in a thermophilic anaerobic digester-microbial electrolysis cell coupled system under different conditions. Water Research 110, 192-201.

Electrons do not necessarily have to be supplied to the electron charged conductive material continuously when performing the process. When the packed bed is sufficiently charged with electrons it is found that the process performs for a prolonged period of time. For example the process may be performed for between 0.03 and 12 hours, preferably between 0.05 and 10 hours, in a situation wherein no power is supplied to the electron charged conductive material. This is advantageous because this allows the use of a non-continuous power supply generating electricity, preferably a sustainable and renewable external power supply, such as for example solar and/or wind. The capability of the process to operate when such a non- continuous power supply is temporally not available is advantageous.

The reactor may also be advantageously be used to perform a process to convert a mercaptan compound to hydrocarbons. The working electrode of such a reactor is a cathode and the counter electrode is an anode. A conductive material comprising a biofilm of mercaptan reducing microorganisms is present as part of the cathode working electrode and the carbon based material. Preferably the carbon based material is graphite felt. The process may be performed as described in

WO2019/229167. The invention is also directed to a process to convert a mercaptan compound to hydrocarbon and hydrogen sulphide in a reactor according to this invention by contacting the mercaptan compound as dissolved in an aqueous solution with the mercaptan reducing microorganisms under anaerobic conditions and wherein a potential or a current is applied between the anode and the cathode.

The reactor may also be advantageously be used to perform a process to oxidise total ammonia nitrogen. The reactor for this process has as an anode as the working electrode and a cathode as the counter electrode. A conductive material, preferably the carbon based material and more preferably the afore mentioned activated carbon granules or extrudates, is present as part of the working electrode wherein the conductive material comprises a biofilm of nitrogen-related functional microorganisms. The nitrogen-related functional microorganisms are suitably ammonium oxidizing bacteria (AOB), nitrite converting bacteria (NOB) and/or anammox bacteria. The invention is also directed to a process to oxidise total ammonia nitrogen by contacting dissolved total ammonia nitrogen and dissolved oxygen in an aqueous solution, as the working electrolyte, with the nitrogen-related functional microorganisms and wherein a potential or a current is applied between the anode and the cathode.

The reactor may also be advantageously be used in a process to convert sulphide to elemental sulphur. The reactor for this process has as an anode as the working electrode and a cathode as the counter electrode. The working anode electrode is provided with a conductive material as described above. The process may be performed as described in WO2018/219990. The process is preferably performed wherein at the anode elemental sulphur is produced and at the cathode gaseous hydrogen is formed.

The invention will be illustrated by the following non-limiting figures.

Figure 1 shows a cross-sectional view AA’ of Figure 4 of a tubular reactor vessel (1) having vertical tube axis (1a) according to this invention. The reactor vessel (1) has a horizontally extending reaction zone (2) provided with one working electrode (3) and two vertically extending membrane tubes (6). The working electrode (3) has a metal wall (4) which serves as current distributor or current collector (4a). The metal walls (4) are the walls of two parallel arranged vertical channels (5) wherein within a channel (5) one of the two shown vertically extending membrane tubes (6) is present. In a larger scale reactor 30 of such channels (5) may be present as an example. In the semi-annular space (7) as present between the wall (4) and the vertically extending membrane tube (6) a conductive material (9) is present. The vertically extending membrane tubes (6) have a closed lower end (8) and are open at their upper end where they are connected to a lower manifold (14).

At this lower manifold (14) the counter electrolyte as it is upwardly discharged from the vertically extending membrane tubes (6) is collected before it is discharged from the reactor.

At the interior of the vertically extending membrane tubes (6) a counter electrode (10) and a liquid supply tube (11) is present. The liquid supply tube (11)

supplies counter electrolyte to the lower end of the vertically extending membrane tube (6). The liquid supply tube (11) therefore has a liquid inlet opening (13) at an upper end and a liquid outlet opening (12) at its lower end. This upper liquid inlet opening (13) is present in a horizontally extending upper manifold (15). To the upper manifold (15) counter electrolyte is fed via counter electrolyte inlet (16a) present at the upper end (17) of reactor vessel (1). Counter electrolyte inlet (16a) may also be positioned in the vertical wall of reactor vessel (1) such in use counter electrolyte is supplied to the upper side of the upper manifold (15). In use a certain height of liquid counter electrolyte on top of the horizontally extending upper manifold (15) is preferred as this ensures a good distribution of the counter electrolyte over the supply tubes (11) of the various vertically extending membrane tubes (6). For this liquid level control means (16b) are present. The upper manifold (15) is vertically spaced from the reaction zone (2) defining a horizontally extending fluid discharge zone (16) between the upper manifold (15) and the reaction zone (2). This fluid discharge zone (16) will be described in more detail in Figure 2.

At the lower end (18) of the reactor vessel (1) a working electrolyte inlet (18a) is shown. To ensure a good distribution over the two channels (5) of the working electrode (3) a distribution plate (19) is present below the reaction zone (2). This distribution plate (19) may also serve as a support for the conductive material (9).

The working electrolyte inlet (18a) may also be positioned in the vertical wall of the reactor vessel (1) such that in use working electrolyte is supplied to a space below distribution plate (19). As shown the working electrolyte and the counter electrolyte flow through the reactor via fluidly disconnected flow paths. The only connection is the membrane of the membrane conduit. As this membrane is ion selective, for example only for passage of cations, such as protons (H*) and Nat, substantially no water or other compounds will be able to flow via the membrane from one flow path to the other.

Figure 2 shows a detail of reactor vessel (1) at the elevation of the fluid discharge zone (16). The fluid discharge zone (16) is divided by the horizontally extending lower manifold (14) into a lower fluid discharge zone (20) for discharge of a working electrolyte and any formed gas and an upper fluid discharge zone (21) for discharge of the counter electrolyte and any formed gas. The lower fluid discharge zone (20) is fluidly connected to the space (22) which is exterior of the multiple vertically extending membrane tubes (6).

In use working electrolyte will flow upwards from this space (22) to the lower fluid discharge zone (20). Any gas as formed at the working electrode (3) will also flow to the lower fluid discharge zone (20). The lower discharge zone (20) is preferably large enough to achieve a gas-liquid separation such that gas can be discharged from lower discharge zone (20) via gas outlet (23) and liquid working electrolyte via liquid outlet (24). To achieve optimal gas-liquid separation a weir (25) is present to achieve a liquid level of working electrolyte from which gas can more easily escape.

In use counter electrolyte will flow upwards through the vertically extending membrane tubes (6) to the upper discharge zone (21). Any gas as formed at the counter electrode (10) will also flow to the upper fluid discharge zone (21). The upper discharge zone (21) is preferably large enough to achieve a gas-liquid separation such that this gas can be discharged from zone (21) via gas outlet (26) and liquid counter electrolyte via liquid outlet (27). To achieve optimal gas-liquid separation a weir (28) is present to achieve a liquid level of counter electrolyte from which gas can more easily escape.

Figure 2 also shows a vessel wall (29) and a first flange (38) as present in the wall (29) at the elevation of the upper manifold (15). When this first flange (38) is disconnected a vessel wall part (30) above the first flange (38) may be removed from the a vessel wall part (31) below the first flange (38). This makes the upper manifold (15) accessible from above. Further a second flange (32) is shown in the vessel wall (29). When this second flange (32) is disconnected the vessel wall part (31) above the flange (32) may be removed from the a vessel wall part (34) below the second flange (32). This makes the lower manifold (14) accessible from above.

Figure 2 also shows a reference electrode (35) as present in and contacting with the conductive material (9) and cable connection (36) which connect the walls (4) of the working electrode (3) with a source or sink for electrons. Also a cable connection (37) is shown which connects the counter electrode (10) with a source or sink for electrons.

Figure 3 shows an alternative lower end of the reactor (1). A gaseous feedstock is supplied via gas inlet (18b) to a space (18d) of the reactor which is fluidly separated by a gas permeable membrane (18c) from a space (18e) in the reactor (1) to which the working electrolyte is supplied via inlet (18a). These spaces (18d, 18e) are located below the reaction zone (2). A distribution plate (19) is present to ensure a good distribution of the working electrolyte and the dissolved gaseous feedstock over the two channels (5) of the working electrode (3).

Figure 4 shows cross sectional view BB’ of Figure 2. The numbers have the same meaning as in Figures 1-3.

Figure 5 shows the same cross-section as in Figure 4 but for a variant of the reactor of Figures 1-3. Only one channel (5) is present and wherein more than one vertically extended membrane tube (6) is present in one channel (5) as may be preferably used for smaller reactors.

Figure 6 shows a reactor with one channel (5) and one vertically extended membrane (6). In the space (7) a conductive material (9) is present. In the vertically extended membrane (6) four counter electrodes (10) are present.

Figure 7 shows a reactor as in Figures 1-4 except that also vertically extending membrane tubes (6) are present which are not present in a channel (5).

Figure 8 shows a reactor of Figure 7 except that a wall (4b) is added to create a channel (5) around one vertically extending membrane tube (6). Wall (4b) has another shape as the other walls (4) such to fit the formed channel (5b) in the space between the hexagonal channels (5) and the wall of the reactor.

Figure 9 shows a reactor vessel having a rectangular base shape and having features of the reactor of Figure 7

Claims

Conclusions

1. Reactor for use in a bioelectrochemical process, wherein the reactor comprises a horizontally extending reaction zone, wherein the reaction zone comprises: e one or more working electrodes with a current divider or a current collector, e multiple vertically extending membrane conduits with a closed lower end, wherein one or more counter electrodes and a liquid supply line for a counter electrolyte are present in the interior of the vertically extending membrane lines, and e where one or more working electrodes are provided externally on the several vertically extending membrane lines.

The reactor of claim 1, wherein the liquid supply line for the counter electrolyte is a vertically extending liquid supply line having a liquid outlet at its lower end, and a liquid inlet opening at an upper end thereof, the liquid inlet opening being contained in a horizontally extending upper manifold, wherein the upper manifold is vertically spaced from the reaction zone, thereby defining a horizontally extending fluid discharge zone between the upper manifold and the reaction zone.

A reactor according to claim 2, wherein liquid level control means are provided so as to ensure, during use, a height of the liquid counter electrolyte above the horizontally extending upper manifold.

4. A reactor according to any one of claims 2 to 3, wherein the fluid discharge zone is divided by a horizontally extending lower manifold into a lower fluid discharge zone for removing a working electrolyte and any gas formed, and into an upper fluid discharge zone for removing discharging the counter electrolyte and any gas formed, the upper end of the vertically extending membrane conduits being contained in the lower counter electrolyte manifold in such a manner that the interior of the plurality of vertically extending membrane conduits is fluidly connected to the upper fluid discharge zone, and wherein the space external to the plurality of vertically extending membrane conduits is fluidly connected to the lower fluid discharge zone.

5. Reactor according to claim 4, wherein the upper and/or lower fluid discharge zones is or are provided with liquid parent means, in order to carry out a gas-fluid separation, and is or are provided with a liquid discharge opening and a gas discharge opening.

6. Reactor according to claim 5, wherein the liquid container means are formed by a spillway such as that present on the lower manifold and/or extending from the reaction zone.

7. Reactor according to any one of claims 1 to 6, wherein the current distributor or the current collector are vertically extending and open or closed walls of one or more vertically extending channels, and wherein one or more of the multiple, vertically extending membrane pipes are present.

The reactor of claim 7, wherein the horizontal cross-sectional shape of the wall of the vertically extending channel is an oval, a triangle, a square, a rectangle, a pentagon, or a hexagon.

9. Reactor according to claim 8, wherein the shape of the horizontal cross-section of the wall of the vertically extending channel is a hexagon.

10. Reactor according to any one of claims 1 to 9, wherein an inlet for working electrolyte is provided below the reaction zone.

11. Reactor according to any one of claims 1 to 10, wherein the one or more working electrodes comprise or comprise a conductive material that is conductively connected to the current distributor or to the current collector.

The reactor of claim 11, wherein the conductive material is a carbon-based material.

The reactor of claim 12, wherein the carbon-based material is graphite felt.

A reactor according to claim 13, wherein the graphite felt is present as a layer sandwiched between two layers consisting of a metal grid, and wherein the metal grid is the current divider or the current collector.

The reactor of claim 12, wherein the carbon-based material is a packed bed of activated carbon granules or extrudates.

16. Reactor according to claim 15, wherein the activated carbon granules or extrudates have a specific surface area ranging between 500 m2/g and 3000 m2/g.

17. Reactor according to any one of claims 1 to 16, wherein the one or more working electrodes are in contact with a working electrolyte, and wherein the counter electrode is in contact with a counter electrolyte.

18. Reactor according to any one of claims 11 to 17, wherein the conductive material comprises a biofilm of micro-organisms.

19. Reactor according to any one of claims 1 to 18, wherein the reactor is a concrete tank.

20. Reactor according to any one of claims 1 to 18, wherein the reactor is a tubular reservoir having a vertical tube axis.

21. The reactor of claim 20, wherein the tubular reservoir includes a reservoir wall, and a first flange is provided in the wall at the level of the upper manifold, allowing a portion of the reservoir wall above the flange can be removed from a portion of the reservoir wall located beneath the flange in such a manner as to make the upper manifold accessible from above.

A reactor according to any one of claims 20 to 21, wherein the tubular reservoir has a reservoir wall, and a second flange is present at the level of the lower manifold, allowing part of the wall located above the second flange can be removed from a portion of the wall located below the second flange in such a way that the lower manifold is made accessible from above.

A reactor according to any one of claims 1 to 22, wherein the working electrode is a cathode of the bioelectrochemical method, and wherein the counter electrode is an anode of the bioelectrochemical method.

24. Reactor according to claim 23, wherein the anode is a coated grid of titanium.

The reactor of claim 24, wherein the titanium coated grid is a ruthenium-iridium coated titanium grid.

A reactor according to any one of claims 23 to 25, wherein the reaction zone is immersed in an aqueous solution having a pH value greater than 7.5 and ranging from 0.3 M to 4. M of sodium cations, or 0.3 M to 4 M of sodium and potassium cations, and wherein the microorganisms are halophilic microorganisms.

The reactor of claim 26, wherein the aqueous solution contains more than 20 mM of phosphate ions.

A reactor according to any one of claims 26 to 27, wherein the aqueous solution comprises 0.4 M to 2 M of sodium cations, or 0.4 M to 2 M of sodium and potassium cations.

A method for converting carbon dioxide into methane, in a reactor vessel according to any one of claims 24 to 28, by bringing carbon dioxide dissolved in the aqueous solution into contact with the halophilic micro-organisms in anaerobic conditions, and wherein a applies potential or causes a current to flow between the anode and the cathode.

A reactor according to any one of claims 12 to 18, wherein the working electrode is a cathode, wherein the counter electrode is an anode, and wherein the carbon-based material comprises a biofilm of micro-organisms that reduce mercaptan.

The reactor of claim 30, wherein the carbon-based material is graphite felt.

32. Method for converting a mercaptan compound into hydrocarbon and hydrogen sulfide, in a reactor according to any one of claims to 31, by contacting the mercaptan compound dissolved in an aqueous solution with the micro-organisms that reduce mercaptan under anaerobic conditions, and a current is caused to flow between the anode and the cathode. 30

A reactor vessel according to any one of claims 12 to 18, wherein the working electrode is an anode, the counter electrode is a cathode, and the carbon-based material comprises a biofilm of nitrogen-related functional microorganisms.

34. Reactor according to claim 33, wherein the nitrogen-related functional microorganisms are ammonium oxidizing bacteria (AOB), nitrite converting bacteria (NOB), and/or anammox bacteria.

35. Reactor according to any one of claims 33 to 34, wherein the carbon-based material is a packed bed of activated carbon granules with a specific surface area ranging from 500 m2/g to 3000 m2/g.

Use of a reactor according to any one of claims 1 to 10, in a bioelectrochemical process for converting sulphide into elemental sulphur, wherein the working electrode is an anode and the counter electrode is a cathode.

Use according to claim 36, wherein elemental sulfur is produced and gaseous hydrogen is formed at the cathode.