Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
  • B01D61/44—Ion-selective electrodialysis
  • B01D61/46—Apparatus therefor
  • B01D61/468—Apparatus therefor comprising more than two electrodes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
  • B01D61/44—Ion-selective electrodialysis
  • B01D61/46—Apparatus therefor
  • B01D61/50—Stacks of the plate-and-frame type
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
  • B01D63/08—Flat membrane modules
  • B01D63/082—Flat membrane modules comprising a stack of flat membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
  • B01D65/08—Prevention of membrane fouling or of concentration polarisation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2313/00—Details relating to membrane modules or apparatus
  • B01D2313/14—Specific spacers

Definitions

• the invention pertains to a clogging-resistant membrane spacer body and to a membrane unit containing such bodies, as well as to a process for the treatment of liquids containing particles.
• Membrane processes are interesting processes for the removal or concentration of compounds from aqueous streams. Membrane processes include pervaporation, microfiltration, ultrafiltration, nanofiltration, reversed osmosis, electromembrane processes, and other membrane processes known by people skilled in the art.
• Electromembrane processes include electrochemical processes (e.g. electrodialysis, membrane electrolysis, and diffusion dialysis), bio-electrochemical systems (e.g., microbial fuel cells, microbial electrolysis cells and microbial electro- synthesis), and other processes known by people skilled in the art. Electromembrane processes make use of ion exchange membranes, such as cation exchange membranes, anion exchange membranes, and bipolar membranes. Under the influence of a concentration or voltage gradient, ionic compounds, such as salt ions and dissociated organic acids, can move across ion exchange membranes thus changing the ionic composition and/or pH on either side of the ion exchange membrane.
• electrochemical processes e.g. electrodialysis, membrane electrolysis, and diffusion dialysis
• bio-electrochemical systems e.g., microbial fuel cells, microbial electrolysis cells and microbial electro- synthesis
• Electromembrane processes make use of ion exchange membranes, such as
• WO 2010/050815 describes a method for the prevention of membrane fouling in tubular membrane modules.
• the tubular membranes are arranged in such a way that the liquid flow through the tubular membranes is downwards and that at the same time there is a downward flow of gas through the tubular membranes.
• the gas shears the membrane and in this way mitigates membrane fouling.
• the simultaneous downward flow of liquid and gas results in a self-regulating distribution of liquid and gas across multiple membrane tubes and results in effective membrane fouling reduction at low energy use. Due to the self-regulating distribution principle, the simultaneous downward flow of liquid and gas achieves better fouling reduction at lower energy use compared to prior art systems that use simultaneous upward flow of liquid and gas.
• WO 2008/048103 discloses a process for separating cations from an aqueous salt stream using an electrode cell comprising three or more cation-selective membranes. It does not provide a solution for the problem of clogging of the electrode cell by suspended solids which may be present in the aqueous salt stream.
• WO 2009/082205 discloses a process for removing sulfide from an alkaline sulfidic liquid using an electrodialysis cell comprising one or more ion- selective membranes. Like WO 2008/048103, WO2009/082205 does not provide a solution to the problem of clogging of the electrodialysis cell by suspended solids which may be present in the aqueous sulfidic liquid.
• waste water containing suspended solids of particle sizes up to several mm can be effectively treated in a membrane unit, when the membranes are separated from each other or from a wall or an electrode by a spacer body which provides multiple parallel passages preferably having a maximum width or diameter of between 2 and 20 mm.
• the invention pertains to a process of treating, i.e. changing the composition and/or the pH of, a raw liquid containing suspended solids through a membrane module comprising a first membrane and at least one further body arranged in parallel with a clogging-resistant spacer between the two.
• the use of the clogging-resistant spacer allows the changing of the composition and/or the pH, without being hindered by coarse solids suspended in the liquid.
• Changing the composition and/or the pH herein means changing the solutes composition of the liquid, i.e. changing the concentration of dissolved or finely dispersed molecules and ions, including protons, capable of passing selectively permeable membranes. It is not intended to change the level of the coarse particles contained in the raw liquid having particle size of, say, 1 ⁇ or more, in particular 10 ⁇ or more, up to e.g. 5 mm ore even up to 10 mm.
• the invention also pertains to a membrane module comprising one or more membranes and/or walls arranged in parallel having a clogging-resistant spacer between membranes and other membranes or walls.
• a clogging-resistant spacer between membranes and other membranes or walls.
• one or more, usually two, electrodes may also be arranged in parallel.
• the clogging-resistant spacer is positioned between at least two of said membranes and/or between a membrane and a wall or electrode.
• Inlet means for introducing liquid and preferably also for gas are provided at the top end of the spacer and outlet means for carrying off liquid and preferably gas are provided at the bottom end of the spacer.
• the spacer ensures a predetermined distance between two membranes or between a membrane and an electrode or a wall, and provides a flow-through area comprising multiple parallel passages connecting said top end and said bottom end of the parallel membranes.
• the passages also referred to below as channels, preferably have a (maximum) width between 2 and 20 mm, preferably 3- 12, most preferably 4-8 mm. For cylindrical passages, the maximum width is the diameter of the cylinders.
• the spacer occupies an area of no more than 50% of the total area between the two parallel bodies (membranes and/or wall or electrode), referred to below as “inter-body area” or “inter-membrane area”, which is equal to the width of the membrane times the distance between membrane and the further flat body.
• the area available for the passage of liquid is at least 50% of the total area of the cross-section.
• the spacer occupies an area of between 10 and 40 % of the inter-body area, i.e. the resulting flow-through area is between 60 and 90% of the inter-body area.
• inter-body area this is a surface unity, defining the cross-sectional surface between two bodies perpendicular to the flow direction of the liquid passing the unit. Since these two bodies are essentially parallel, the "inter-body area” is equivalent and proportional to an “inter-body volume”, which is obtained by the multiplying the area by the height under consideration.
• the distance between the membranes or between a membrane and another flat body depends on the particular lay-out of the module.
• the pre-determined distance between a membrane and a further flat body is the same as the cross-sectional width of the passage, i.e. 2-20 mm, preferably 3- 12, most preferably most preferably between 4 and 8 mm.
• the passages can be rectangular, cylindrical, or of any other geometrical shape, as long as the maximum channel width/diameter is within in the ranges defined above.
• the channels are cylindrical.
• the channels are rectangular.
• a “spacer” or “spacer body” means the physical body ensuring a predetermined distance between two essentially parallel bodies and ensuing passage of solid particles. It is referred to as “clogging-resistant" spacer, to emphasise its function in preventing the solid particles from clogging the membrane module.
• the spacer preferably directly contacts the adjacent bodies, or still have a certain distance. Such residual distance, however, is small, i.e. less than 20%, in particular less than 10% of the total distance to be kept between the two parallel bodies excluding the spacer.
• the spacer body is essentially rectangular and flat. Two opposite sides of the rectangular shape are referred to as “one end” and “other end” or as “top end” and “bottom end”, respectively, where “top” and “bottom” refer to the preferred, downward direction of the liquid flow.
• the membrane and the other parallel body can also be a flat body.
• the term "flat” or “substantially flat” as used herein is not meant to be an absolute term, but a primarily relative term.
• the membranes and other "flat" bodies such as electrodes, while being in parallel position to each other, are curved vertically, for example in a cylindrical or spiral arrangement.
• the spacer typically, and preferably, is a rigid (flat) body, the rigidity may be moderated to an extent which allows bending or curving of the spacer.
• the spacer can have various shapes, provided it is effective in keeping the membranes at a predetermined and essentially constant distance and in providing the vertical passages.
• the spacer may comprise a plurality of inter- connected strips positioned perpendicular to the membranes, for example with a free space between two consecutive strips which is comparable to the width of the passages, for example between 2 and 20 mm, or more advantageously between 3 and 12 mm.
• the repetitive distance between strip may be between 2 and 30 mm, preferably between 3 and 15 mm.
• the strips are preferably interconnected by crosspieces so as to give the spacer solidity and strength, for example every 2 to 30 cm over the height of the spacer.
• the crosspieces may be placed at alternating sides of the spacer, so as to provide maximum rigidity and flatness of the spacer.
• the crosspieces may be present at one side of the spacer only, thus allowing some flexibility of the spacer so as to accommodate vertically curved arrangements of the membranes and other bodies.
• the spacer may comprise a plurality of strips longitudinally connected to each other with alternating angles of e.g. between 60° and 90° to provide a staircase (or zigzag) type arrangement; the strips then contact the membrane at angles of e.g. between 60° and 45°.
• a staircase or zigzag
• Such an arrangement allows some curving, and the degree of allowable curving can be determined by the rigidity of the spacer material and the thickness of the strips.
• Further alternatives are equally feasible, as long as vertical channels are secured and the spacer occupies no more than 50% of the inter-body (inter-membrane) space.
• the spacer should ensure that liquid which is present in the spacer passages has access to the membrane or membranes separated by the spacer, over at least part of the height of the spacer; where necessary, this can be achieved by providing perforations in the vertical walls defining the passages.
• the inlet means for liquid, and preferably also for gas is a liquid (and gas) distributor comprising multiple openings in a sheet or plate defining the top end of the module.
• the openings are preferably in line with the passages formed by the spacer channels.
• the spacer is constructed in such a way that the principle of simultaneous downward flow of liquid and gas for membrane fouling reduction can be utilised.
• This clogging-resistant spacer consists of vertical channels. The tops of the channels are connected to a liquid/gas distributor. The bottoms of the channels are connected to a liquid/gas collector.
• the liquid/gas distributor consists of two compartments on top of each other.
• the top compartment of the liquid/gas distributor is separated from the bottom compartment of the liquid/gas distributor by a liquid distributor.
• this liquid distributor has holes that are aligned above the channels of the spacer. These holes have a similar diameter as the width/diameter of the spacer channels.
• the bottom compartment of the liquid/gas distributor is in direct connection with the spacer channels.
• the bottom compartment of the liquid/gas distributor is fed with gas.
• the gas is fed using a pump, compressor or blower.
• the gas may also be provided through natural convection.
• the gas may comprise nitrogen, air, oxygen, natural gas, biogas, carbon dioxide, methane, helium, or other gases known to the skilled person. This gas pushes and distributes the liquid from the top compartment of the liquid/gas distributor inside the channels of the spacer.
• the means for feeding the gas such as a compressor should have a capacity which allows to provide a gas to liquid ratio in the range of 1 : 1 to 1 : 1000, preferably in the range 1 :3 to 1 :200, more preferably in the range 1 :4 to 1 :20.
• the gas holdup in the liquid downward flow through the spacer is in the range 0.1-50%, preferably in the range 0.5-25%, more preferably in the range of 5-20% (by volume).
• the liquid and gas are fed in such a way that the downward liquid flow has a superficial liquid flow velocity in the range of 0.01-5 m/s, preferably 0. 1-4 m/s, more preferably 0.2-1.5 m/s.
• the simultaneous downward flow of liquid and gas results in a self-regulating distribution of liquid and gas across the spacer channels and results in effective membrane fouling reduction at low energy use.
• the module is provided with means for switching the gas flow on and off, for an intermittent gas flow so as to optimise the passage of liquid through the module.
• the spacer can be made of any material which is relatively inert to wastewater and, in case of an electromembrane process, indifferent to electrical fields, and which can provide rigidity to the spacer. These include metals (particularly in non- electromembrane processes), ceramics and organic polymers. Preferred materials are selected from thermoplastic or thermosetting resins or polymers. Preferred polymers include propylene and polyethylene, as well as mixtures or copolymers thereof or mixtures or copolymers with other polymers, especially polyolefins.
• the spacer and the gas-liquid distributors are produced through methods known by people skilled in the art and include but are not limited to milling, injection moulding, extrusion, 3D printing, welding, laser cutting. The invention also concerns the spacer as such.
• the height of the membrane module and the membrane unit can be any feasible height e.g. from 0. 1 m up to 10 m.
• the height is preferably between 0.25 and 5 m, more preferably between 0.5 and 4 m, most preferably between 1 and 3.5 m.
• the width of the module and the unit is not limiting. Practical widths are e.g. between 0.1 and 5 m, in particular between 0.4 and 2 m.
• the membrane unit is an electromembrane unit
• the membrane unit according to the invention comprises one or more membrane modules as described above positioned between two or more electrodes.
• the one or more membrane modules with electrodes are positioned within a container.
• the side walls of the membrane modules, which are in contact with the vertical sides of the membranes, may advantageously be part of the side walls of the container.
• the gas and liquid distributors can be placed within the container, at the top side, or directly on top of it.
• the outlet means may be placed within the container or outside, at the bottom.
• the unit comprises sets of more than two, e.g. three or four, membranes separated by spacers, e.g. for a stepwise separation of ions or other species.
• the unit comprises a plurality of membrane units and electrodes in alternate arrangement, i.e. in the order: electrode - space - membrane - spacer - membrane - space - electrode - space - membrane - spacer - membrane - space - electrode etc.
• space may be a space as such (without a body in it) or a space maintained by a spacer (the same as between membranes or different).
• the raw liquid and a gas are passed through the module in a downward flow.
• the membranes may be semi-permeable membranes, which are permeable to certain molecules, but less or not permeable to other molecules.
• the membranes may be semi-permeable for small molecules, and not for larger molecules, or they may be permeable for hydrophilic or polar molecules and not for hydrophobic or apolar molecules.
• An example is the separation of alcohols from an alcohol-containing fermentation broth using hydrophobised silica membranes, as described e.g. in WO 201 1/145933.
• the membranes may be selectively permeable to cations or anions, i.e. cation-exchange membranes or anion-exchange membranes.
• the membranes may also be bipolar membranes comprising a combination of a cation-selective and an anion-selective membrane.
• suitable cation exchange membranes include polymers containing carboxylic or sulfonic groups, e.g. polyether sulfone (PES), polysulfone (PSf), polyether-ether- ketone (PEEK), polystyrene (PS), polyethylene (PE), polytetrafluoroethylene (PTFE, e.g. Nafion), cation exchange membranes based on resins (e.g. polymer-clay composite materials) or other materials which have a selectivity for ions and a selectivity of cations over anions.
• PES polyether sulfone
• PSf polysulfone
• PEEK polyether-ether- ketone
• PS polystyrene
• PE polyethylene
• PTFE polytetrafluoroethylene
• Scaling of multivalent ions in the membrane can be avoided by using membranes which exhibit selectivity for monovalent ions over multivalent ions.
• Membranes with selectivity for monovalent ions are described in the art (e.g. Strathmann, Ion-Exchange Membrane Separation Processes, Membrane Science and Technology series, 9 (2004) Elsevier, Amsterdam, NL p. 105). Such selectivity can be achieved for example by the introduction of a small amount of anion exchange groups in the membrane.
• Suitable anion exchange membranes typically comprise polymer backbones to which quaternary ammonium groups are attached, such as styrene- divinylbenzene copolymers or vinylpyridine polymers carrying trimethylammonio- methyl substituents.
• anion exchange membranes include Aciplex A201 (Asahi Chemical Industry Co., JP), Selemion ASV (Asahi Glass Co. Ltd, JP), FAS (Fuma-tech, GmbH, DE), AR204szra (Ionics, Inc, USA) and Neosepta AM-I (Tokuyama Co., JP) or other materials which have a selectivity for ions and a selectivity of anions over cations.
• the invention also pertains to a process for separating components from a raw liquid containing suspended solids, i.e. for selectively changing the composition and/or pH of the raw liquid by passing the raw liquid through the membrane module or the membrane unit described above, preferably in a liquid downward flow using gas for forwarding the liquid with its suspended solids through the membrane module.
• the liquid downward flow can have a superficial liquid flow velocity in the range of 0.01-5 m/s, preferably in the range of 0. 1-4 m/s, more preferably in the range of 0.2- 1.5 m/s.
• the resulting liquid having a changed composition and/or a changed pH, and containing the suspended solids is collected from the spaced flow-through area at the bottom of the membrane unit.
• a second liquid containing components separated from the raw liquid can be collected from a parallel area between the first membrane and a further parallel body at the bottom, or alternatively at the top or elsewhere at the membrane module.
• Changing the ionic composition of a raw liquid may comprise the removal of cations such as alkali metal or alkaline earth metal cations or, in particular, ammonium anions, from a raw liquid which may be a wastewater such as manure. It may also be removal of anions such as halogen ions or organic acid anions from a wastewater or fermentation broth.
• cations such as alkali metal or alkaline earth metal cations or, in particular, ammonium anions
• the electro-membrane unit of the present invention can be used for separating cations from an aqueous stream and/or controlling the pH of an aqueous stream as disclosed in WO 2008/048103.
• the unit then comprises an anode chamber, an electrolysis chamber, an intermediate chamber and a cathode chamber, wherein the anode chamber, electrolysis chamber, intermediate chamber, and cathode chamber are each separated by a selectively permeable membrane for cations, and the membranes are separated by a spacer according to the present invention.
• the aqueous stream is then introduced, preferably from the top in a downward flow, into the electrolysis chamber, an acidified stream issues from the electrolysis chamber, an alkaline aqueous stream issues from the cathode chamber, and a further stream containing monovalent and/or multivalent ions issues from the intermediate chamber, while an electric potential difference is applied between the anode and the cathode.
• the stream containing monovalent and/or multivalent ions may be processed to separate off monovalent ions, and the stream containing multivalent ions may be returned to the intermediate chamber.
• the anode chamber and the electrolysis chamber may be combined to a single chamber which serves both for receiving the influent water to be treated, and for electrolysis in the presence of the anode.
• the electro-membrane unit of the present invention can also be used for a process for treating sulfidic spent caustics by a combination of membrane electro- dialysis and biological oxidation as disclosed in WO2009/082205. This process results in the removal of sulfides from the sulfidic spent caustics stream and the production of a reusable alkaline solution and a reusable elemental sulfur stream.
• the sulfidic liquid is subjected to electrodialysis using an anion exchange membrane to produce a sulfide-enriched stream (concentrate), which is subjected to biological oxidation, where sulfide-depleted stream (diluate) of the electrodialysis can be reused as an alkaline liquid for scrubbing sulfide.
• the wastewater containing suspended solids is pre-treated prior to entering the electro-membrane unit using a coarse pre-treating means, such as a screw press, centrifuge, belt press, filter press, or another coarse pre-treating means known by a person skilled in the art.
• a coarse pre-treating means such as a screw press, centrifuge, belt press, filter press, or another coarse pre-treating means known by a person skilled in the art. This reduces the particle size of the suspended solids entering the electro-membrane unit to 0 to 10 mm, preferably to 0 to 6 mm, more preferably to less than 2 mm.
• Figures l a,b,c depict a spacer according to the invention.
• spacer 1 1 comprises a spacer plate 1 , a liquid supply 2 with liquid inlet 21 gas, a gas supply 3 with gas inlet 3 1 and a liquid and gas collector 4 with outlet 41.
• Passages 12 with connecting strips 13 are provided in spacer plate 1 1.
• Circle Ic refers to the part shown in Figure l c in more detail.
• Figure lb shows the membrane in a side- view, showing the same parts as in figure l a, and connecting passages 33 from the gas and liquid inlet to the main passages.
• Figure l c shows details of the vertical passages: vertical strips 15 provide passages 12 between the strips, and these are interconnected with connections 13.
• Arrows II refer to the view shown in detail in Figure 2.
• Figure 2 provides a schematic view from above on a spacer as depicted in Figure 1.
• Vertical strips 15 define channels 12.
• Connections 13 and 14 are provided only at certain heights of the strips as shown in Fig l c.
• Figures 3a,b provide cross-sectional views of the liquid supply 2 and gas supply 3.
• Figure 3a provides a view from above, showing liquid tube 22 and passages 23 toward the gas tube. Arrows IIB point to the vie shown in Figure 3b.
• Figure 3b is a side view showing liquid tube 22 and gas tube 32 with inlets 21 , 31 , and passages 23.
• Figure 4 provides a side view cross-section of an inlet means for liquid 2 and gas 3 with liquid tube 22 and gas tube 32 and passages 23 from liquid to gas supply and 33 from gas supply to the membrane.
• Figure 5-9 not drawn to scale, schematically show different forms of an electromembrane unit of the invention. These are further explained in the Examples.
• Figure 5 shows an electromembrane unit 5 with three chambers 51 , 52 and 59, anode 60, cathode 61 , and power supply 62, two cation- selective membranes 64, 65, liquid inlet 21 , gas inlet 3 1 and outlet 41, as well as a spacer body 1 1.
• Figure 6 similarly shows a unit 5 with four chambers 51 , 52, 53 and 59, three cation-selective membranes 64, 65, 66, and a spacer body 1 1.
• Figure 7 shows a unit 5 with three chambers 51 , 52 and 59, oppositely charged membranes 63, 64, spacer 1 1 , as well as biological sulfide oxidation reactor 8 and caustic scrubber 9 with connecting lines 21 , 41 , 72, 73, and inlets and outlets, 81, 82, 91 and 92.
• Figure 8 shows a multi-chamber (51-59) electromembrane unit 5, with anode 60, cathode 61 and power supply 62, alternating membranes 67, 68, inlets 21 and outlets 41 for liquid containing particles with spacer bodies 1 1 in between, and inlets 70 and outlets 71 for clear liquids carrying off ionic species. Air may be introduced through liquid inlets 21 , or though separate inlets (not shown)
• Figure 9 shows a unit 5 with three chambers 51 , 52 and 59, two anion- selective membranes 6, anode 60, cathode 61 , and a spacer body 1 1 , as well as a fermentor 100, with inlets and outlets 21 , 41, 101, 102.
• Liquid manure is first filtered using a suitable filtering means.
• This filtering means such as a screw press, separates the manure into a thick and thin fraction.
• the thick fraction is a solid fraction that can be applied to land as an organic fertilizer.
• the thin fraction is an aqueous fraction, but still contains a large amount of suspended solids.
• anaerobic digestion i.e. to produce biogas
• magnesium to precipitate phosphate in the form of magnesium ammonium phosphate i.e., MAP or struvite
• this thin fraction is treated in an electromembrane unit 5 as depicted in Figure 5.
• compartment 52 is occupied by the clogging resistant spacer 1 1 as described herein, and air or biogas is used as the gas feed fed to the spacer through gas inlet 3 1 , which may be combined with liquid inlet 21.
• Cation-selective membranes 64 and 65 separate compartment 52 from anode compartment 51 and cathode compartment 59. The membranes may be placed at some distance of the spaces 1 1 , as shown in Figure 5, but in practice, they will be in direct contact with the spacer.
• Anode 60, cathode 61 and power supply 62 provide the required potential. The anode reaction produces protons (and for example oxygen) and the cathode produces hydroxyl ions (and hydrogen for example).
• the liquids in anode and cathode compartments 51 and 59 may be exchanged though inlets and outlets (not shown).
• This electromembrane unit transports cations, such as potassium, sodium, ammonium, calcium, and magnesium, from the manure to the cathode and replaces those cations by protons coming from the anode compartment. These protons react with bicarbonate in the manure under formation of carbon dioxide (H + + HC0 3 " H 2 CO 3 H 2 0 + C0 2 ). By doing so, the conductivity of the manure is effectively reduced and important nutrients, such as ammonium and potassium are recovered in the cathode compartment for reuse. The partly desalinated manure leaves the unit through exit 41.
• Example 2 Simultaneous production of acid and base from an aqueous stream
• a waste water stream is treated in an apparatus as depicted in Figure 6.
• the apparatus is a membrane electrolysis stack 5 consisting of 4 chambers (51 , 52, 53, 59) separated by cation exchange membranes (64, 65, 66; selective for cations).
• Outer chamber 51 contains an anode 60 and outer chamber 59 contains a cathode 61.
• An electrical potential is applied between the electrodes by power supply 62.
• H + is formed by an electrode reaction
• in the cathode chamber 59 OH " is formed by an electrode reaction.
• the electrical potential causes the protons to migrate to chamber 52 adjacent to the anode by passing the cation exchange membrane 64.
• the aqueous influent stream 21 enters chamber 52, which is provided with a clogging resistant spacer 1 1 as described herein between membranes 64 and 65.
• An air or biogas supply 3 1 is used as a gas feed for propelling the feed through the spacer.
• Liquid (and gas) leave chamber 52 through exit 41.
• the pH of this stream is lowered because of the replacement of cations (e.g. Na + , NH 4 + ) by H + .
• the cations permeate to chamber 53 adjacent to the cathode, where a salt (e.g. NaCl) solution recycles.
• Divalent cations e.g. Ca 2+ and Mg 2+
• that have the tendency to form crystals e.g.
• a spent caustic liquor e.g. originating from a gas scrubber for scrubbing H 2 S-containing gas is treated in a unit as depicted in Figure 7.
• the unit comprises an electrodialysis cell 5, which comprises an anode 60 and a cathode 61 connected by an electrical circuit containing a power supply 62.
• the membrane electrodialysis cell can be divided into three compartments 51 , 52 and 59 by a cation exchange membrane 64 and an anion exchange membrane 63.
• the anode compartment 51 contains an electrolyte suitable for the anode reaction
• the second compartment 52 is occupied by a clogging- resistant spacer 1 1 as described herein between membranes 64 and 65, and may be in direct contact with the membranes. Air is used as the gas feed in this spacer (not shown).
• the compartment is fed with a biological reactor medium through 21.
• Compartment 59 is fed with the sulfidic spent caustics from a caustic scrubber 9, having gas inlet 91 and gas outlet 92. This electromembrane unit transports protons from anode compartment 51 into second compartment 52.
• this electromembrane unit transports anions, such as sulfide, hydroxyl ions, and carbonate from compartment 59 into second compartment 52.
• anions such as sulfide, hydroxyl ions, and carbonate from compartment 59 into second compartment 52.
• a coupling can be made between the caustic scrubber 9, the electrodialysis cell 5, and a biological sulfide oxidation reactor 8.
• the effluent from the middle compartment 52 is fed to the biological sulfide oxidation reactor 8 and the treated medium thereof is returned through 21 to compartment 52 of the dialysis cell 5.
• Air can be fed to the bioreactor though inlet 81 and sludge and/or elemental sulfur produces by biological oxidation of the sulfide can be carried off through exit 82 and further separated and/or treated.
• the effluent of the cathode compartment 59 is directed towards the caustic scrubber 9.
• membranes 67 are bipolar membranes and membranes 68 are anion exchange membranes. Inlets and outlets for the intermediate compartments are numbered as 70 and 71, respectively.
• Example 4 Separation of organics acids from fermentation broths
• the unit 5 comprises an anode compartment 51 with an anode 60, a process compartment 52 and a cathode compartment 59 with cathode 61 connected to a power supply 62, with cation-selective membranes 63 between the compartments.
• An anti-clogging spacer 11 is placed in compartment 52 between the membranes 63.
• Fermentation broth from a fermentor 100 optionally after pre-treatment (e.g. sieving), enters compartment 52 through inlet 21 and is driven by a biogas feed (not shown).
• the anode reaction produces protons (and for example oxygen) and the cathode produces hydroxyl ions (and for example hydrogen).
• This electromembrane unit removes carboxylates (i.e., dissociated organic acids represented by RC0 2 " ), such as formate, acetate, propionate, butyrate, caproate, caprylate, oxalate, succinate, lactate, citrate, etc., from the fermentation broth and replaces these carboxylate anions with hydroxyl ions (OH " ) entering from the cathode compartment.
• carboxylates are combined with protons from the anode, effectively converting them into carboxylic acids. These carboxylic acids and can be collected at the anode as a product stream (not shown).
• the de-acidified broth may be returned to the fermentor 100 through 41.
• the fermentor is fed and unloaded through inlet 102 and outlet 101, respectively.

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• 2013
  • 2013-02-21 WO PCT/NL2013/050110 patent/WO2013125954A1/fr not_active Ceased

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