Patent Publication Number: US-2023144024-A1

Title: System and method for separating solvent from a fluid

Description:
TECHNICAL FIELD 
     This disclosure relates generally to systems and methods for removing a solvent, such as water, from a fluid using a redox flow electrochemical separation device. 
     BACKGROUND 
     Some industries utilize processes that remove solvents (e.g., water, alcohol) from a solution. For example, the food and beverage industry may wish to remove water to create a food product that is concentrated and easier to ship, such as juice concentration, creating of powdered beverages, whey processing, etc. In these examples, the concentrated stream is of value to the producer. Waste processing plants may also wish to extract clean water from a waste stream. In this case, the solvent itself is of value to the processor, where the concentrate is not. 
     Solvent removal can be currently done in a number of ways, such as by evaporating the solvent (thermal), by filtering out only the solvent under high pressure (reverse osmosis), or by extracting the solvent, across a membrane, into a draw solution of higher osmotic potential (forward osmosis). Using thermal energy can sometimes affect the end product (e.g., heat can alter the taste of foods) and also uses significant amounts of energy. Forward and reverse osmosis does not necessarily heat the stream, but can be more expensive to implement. 
     SUMMARY 
     Embodiments described herein are directed to an electrodialysis apparatus. In one embodiment, an electrochemical system includes a first reservoir receiving a feed stream. The feed stream includes a solvent, a salt having a first salt concentration in the feed stream, and a solute different than the salt at a first solute concentration. A second reservoir receives a brine stream, the brine stream having a second salt concentration higher than the first salt concentration. A first electrode contacts a first solution of a first redox-active electrolyte material and is configured to have a first reversible redox reaction with the first redox-active electrolyte material, and accept a first ion from the salt in the first reservoir. A second electrode contacts a second solution of a second redox-active electrolyte material and is configured to have a second reversible redox reaction with the second redox-active electrolyte material, and drive a second ion into the brine stream in the second reservoir. An energy source is configured to supply electrical potential to the first and second electrodes. A first membrane having a first ion exchange type is disposed between the first and second reservoirs. A second membrane having a second ion exchange type, different from the first ion exchange type, is disposed between the first electrode and the first reservoir. A third membrane having the second ion exchange type is disposed between the second electrode and the second reservoir. An effluent stream comprising the solvent and a third salt concentration is output from the second reservoir. The solvent is removed from the first reservoir via electroosmosis and forward osmosis. A concentrate stream is output from the first reservoir. The concentrate stream has a fourth salt concentration that is less than the first, second, and third salt concentrations, and a second solute concentration greater than the first solute concentration. 
     Other embodiments are directed to a method that involves inputting a feed stream comprising a first salt concentration to a first reservoir defined by a first ion exchange membrane and a second ion exchange membrane of an electrochemical cell. The second ion exchange membrane is a different type of membrane from the first ion exchange membrane. The feed stream has a solute different than the salt at a first solute concentration. The method further involves inputting a second fluid stream comprising a second salt concentration that is higher than the first salt concentration to a second reservoir of the electrochemical cell. The second reservoir is defined by the first ion exchange membrane and a third ion exchange membrane. The third ion exchange membrane and the second ion exchange membrane are of a same type. An external voltage is applied to first and second electrodes of the electrochemical cell. A solution having a redox-active electrolyte material is circulated between the first and second electrodes. The redox-active electrolyte material reduces when in contact with the first electrode and oxidizes when in contact with the second electrode. In response to reduction and oxidation of the redox-active electrolyte material, ions are transported across the first, second, and third ion exchange membranes to remove solvent and salt from the first reservoir via electroosmosis and forward osmosis. An effluent stream is output from the second reservoir, and has a third salt concentration different from the second salt concentration. A concentrate stream is output from the first reservoir. The concentrate stream comprises a fourth salt concentration that is less than the first and third salt concentrations, and a second solute concentration greater than the first solute concentration. 
     The above summary is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The figures and the detailed description below more particularly exemplify illustrative embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The discussion below refers to the following figures, wherein the same reference number may be used to identify the similar/same component in multiple figures. However, the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. The figures are not necessarily to scale. 
         FIG.  1    is a diagram of a redox flow electrochemical solvent removal stack and system according to an example embodiment; 
         FIG.  2    is a diagram of a redox flow electrochemical solvent removal stack and system according to another example embodiment; 
         FIGS.  3  and  4    are diagrams showing connection of multiple solvent removal stacks into a processing system according to an example embodiment; and 
         FIG.  5    is a flow diagram of a method in accordance with certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Systems and methods are described for removing water from a feed stream using a combination of forward osmosis and electroosmosis, by electrochemically removing solutes (e.g., salt) from the feed stream. The feed stream can be optionally enriched in solutes, either the same as, different from, or some combination of the pre-existing solutes in the feed stream, prior to its introduction into the electrochemical salt removal system. In  FIG.  1   , a diagram shows an electrochemical liquid regenerator  100  illustrating fluid and ion movement in accordance with various embodiments. An electrochemical device  150  includes two electrodes  116 ,  118 , at least three ion exchange membranes  110 ,  112 ,  114 , an energy supply  152 , a reaction mixture, and a receiving fluid. 
     The first electrode  116  contacts a first solution of a first redox-active electrolyte material and configured to have a first reversible redox reaction with the first redox- active electrolyte material. The second electrode  118  contacts a second solution of a second redox-active electrolyte material and configured to have a second reversible redox reaction with the second redox-active electrolyte material. For purposes of simplicity, the first and second redox-active electrolyte materials are shown in the  FIG.  1    as a redox shuttle solution  117  comprising a redox-active electrolyte material. 
     Examples of a redox shuttle solution include 1,1′-bis((3-trimethylammonio)propyl)ferrocene ([BTMAP-Fc] 2+ ) and 1,1′-bis((3-trimethylammonio)propyl)ferrocenium ([BTMAP-Fc] 3+ ), or 1,1′-bis((3-dimethylethylammonio)propyl)ferrocene ([BDMEAP-Fc] 2+ ) and 1,1′-bis((3-dimethylethylammonio)propyl)ferrocenium ([BDMEAP-Fc] 3+ ), which are non-toxic, highly stable, have very rapid electrochemical kinetics and negligible membrane permeability, or ferrocyanide/ferricyanide ([Fe(CN) 6 ] 4− /[Fe(CN) 6 ] 3− ). Additional details for example redox shuttle solutions can be found in commonly-owned U.S. patent application Ser. No. 17/390,600, filed Jul. 30, 2021 (Attorney docket number 20210171US01/0600.382US01), which is hereby incorporated by reference in its entirety. 
     The redox shuttle  117  is circulated between the two electrodes  116 ,  118  as shown by loop  154 . When an electrical potential is applied to each electrode  116 ,  118  by energy supply  152 , the redox shuttle is oxidized at a first electrode (e.g.,  116 ) and reduced at the opposite electrode (e.g.,  118 ). The energy supply  152  may be any variety of direct current (DC) energy supply such as a battery, photovoltaic panel, galvanic cell, potentiostat, AC/DC power converter, etc., the polarity may be kept the same throughout or periodically reversed, and the energy supply may be contained within the electrochemical device  150  or be external and coupled to the device  150 . Thus, as the shuttle  117  circulates between the electrodes, the portions of the shuttle  117  are continuously alternating between the redox states. In certain embodiments, each electrode  116 ,  118  may contact separate redox-active solutions instead of the same redox shuttle solution  117  being flowed in a loop. The separate redox-active solutions may have the same redox-active electrolyte material or different redox-active electrolyte materials. When different redox-active solutions are used for the respective electrodes  116 ,  118 , the energy supply may periodically reverse the potential supplied to the electrodes to restore the state of charge (i.e., the proportion of redox-active electrolyte material in each solution that is in the oxidized state compared to the reduced state) of each of the redox-active electrolyte material solutions. 
     Positioned between the electrodes  116 ,  118  are three, or more, ion exchange membranes, which alternate in the type of ion exchanged. For example, among three membranes, a center membrane  110  may be a cation exchange membrane flanked by second  112  and third  114  anion exchange membranes, as is shown in  FIG.  1   . However, in other embodiments, the center, first membrane may be an anion exchange membrane and the second and third membranes may be cation exchange membranes. The membranes  110 ,  112 ,  114  define channels, or reservoirs, in the electrochemical device  150 . As may be seen, a first membrane  110  and a second membrane  112  define a first reservoir  106 , which in this example is configured as a desalinate chamber. The first membrane  110 , in combination with a third membrane  114 , also defines a second reservoir  108 , which in this example is configured as a salinate (or concentrate) channel. The membranes  110 ,  112 ,  114  are ion-selective as well as water-permeable, are insoluble in organic solvents, and are inert (e.g., do not chemically change) in the reaction mixture and/or products. In certain embodiments, the membranes are as thin as possible (e.g., 10-50 μm) to maximize the rate of forward osmosis water transport through the membranes. In certain embodiments, the membranes are reinforced with a polymer mesh integrated into the membrane itself and in other embodiments, the membranes are not reinforced. 
     A feed stream  102  is input to the first reservoir  106  of the electrochemical device  150 . The feed stream  102  includes at least a solvent (water in this example) and a salt (NaCl in this example, but also Na 2 SO 4 , CaCl 2 , KCl, and any other ionic salt in the chemistry definition of “a salt”) having a first salt concentration (about 5% by weight in this example). The feed stream  102  also includes a solute at a first solute concentration, the solute being different from the salt. In this example, the solute is sugar at about 12% concentration, and could be any type of sugar or combinations thereof (e.g., sucrose, fructose, dextrose, etc.). Other solutes may include food solutes or particles, waste matter, buffers, amino acids, salts different than the salts used in the brine stream  122 , a catalyst used to encourage a chemical reaction within the feed stream, glycerol, ethylene glycol, etc. A brine stream  122  is input into the second reservoir  108  of the electrochemical device  150 . The brine stream has a second salt concentration (about 20%) higher than the first concentration A portion  130  of the concentrated brine is optionally mixed with the feed stream  102  as the feed stream  102  enters the first reservoir  106  of the electrochemical device  150 . 
     When an electrical potential is applied to the electrodes  116 ,  118 , the redox shuttle  117  is oxidized at one electrode  116  and reduced at the other electrode  118 , thereby driving salt ions  127  from the feed stream  102  in the first reservoir  106  into the brine stream  122  in the second reservoir  108 . In particular, the redox shuttle  117  at the first electrode  116  accepts at least one ion  134  from the salt in the first reservoir  106 . The redox shuttle  117  at the second electrode  118  drives at least one ion  133  into the brine stream  122  in the second reservoir  108 , and the charge is balanced by driving at least one ion  127 , of opposite sign of charge to ions  133 ,  134 , from the feed stream  102  in the first reservoir  106  across the center membrane  110  into the brine stream  122  in the second reservoir  108 . 
     The ions  127  that move from the first to second reservoirs  106 ,  108  will also drag solvent molecules (e.g., water  125 ) with them across the center membrane  110  in a phenomenon known as electroosmosis. The water  125  also leaves the first reservoir  106  and enters the second reservoir  108  through forward osmosis because the brine solution  122  in the second reservoir  108  has a higher osmotic pressure than the feed stream  102  and therefore also behaves as a draw solution. As a result, an effluent stream  123 , which includes the water  125  and a third salt concentration is output from the second reservoir  108 . In this case, the concentration of the effluent stream  123  may be the same as or less than that of the input brine stream  122 , e.g., 15-20% for the former versus 20% for the latter. Depending on the ratio of salt and water transferred, this stream may or may not be diluted in concentration, but it will have more volume (or flow rate exiting). Note that the term “effluent” used here and elsewhere is used for purposes of illustration and not limitation. In some cases, the streams described as effluent may be reused, retained, reprocessed, etc., and may have some value of their own as part of the overall fluid processing system. In other cases, the effluent streams may be discarded as a waste product. 
     The processing of the feed stream  102  through the first reservoir  106  results in concentrate stream  144  exiting the first reservoir  106 . The concentrate stream  144  includes a fourth salt concentration (e.g., less than 0.05%) that is less than the first, second, and third salt concentrations, from the first reservoir. The concentrate stream  144  also has a higher concentration of solutes than the feed stream  102 , e.g., 70% for the former and 12% for the latter. The net result is a transport of water from the feed stream  102  into the brine solution  122 . The effluent stream  123  is regenerated (restored to its original concentration and volume) using one or more of a number of possible methods, as indicated by device  124 , also referred to herein as a liquid concentrator. The effluent stream 123  can be regenerated thermally at device  124  by evaporating the absorbed water, by reverse osmosis, or electrochemically using electrodialysis or even another electrochemical device using a redox shuttle. The output of device  124  is a discharge stream  126  comprising primarily water or the chief solvent in the feed stream  102 . 
     The effluent stream  123  may also be regenerated in the same electrochemical stack (or series of identical stacks) as where the solvent is removed from the feed stream. In  FIG.  2   , a diagram shows a redox assisted solvent removal stack  200  that includes brine regeneration features according to another example embodiment. The device  200  includes a first reservoir  106 , a feed stream  102 , a second reservoir  108 , a brine stream  122 , a first electrode  116 , a second electrode  118 , redox-active electrolyte material shuttle  117 , first reservoir  106 , second reservoir  108 , first membrane  110 , second membrane  112 , third membrane  114 , effluent stream  123 , and concentrate stream  144  similar to what is shown and described in  FIG.  1   . The stack  200  will also include other components that are not shown for clarity, such as energy supply  152 . 
     In this example, the first and second membranes  110 ,  112  have a first set of electroosmotic and osmotic transport properties. The third membrane  114  has a second set of electroosmotic and osmotic transport properties that are different from the first set of properties. The system  200  further includes a third reservoir  202  defined by the second membrane  112  and a fourth membrane  204  having the first ion exchange type (the same type as the first membrane  110 , CEM in this example). The fourth membrane  204  also has the second set of electroosmotic and osmotic transport properties. A second portion  206  of the brine stream  122  is input to the third reservoir  202 . 
     A fourth reservoir  208  is defined by the fourth membrane  204  and a fifth membrane  210  having the second ion exchange type (AEM in this example) and the second set of electroosmotic and osmotic transport properties. A third portion  212  of the brine solution  122  is input to the fourth reservoir  208 . A second effluent stream  214  that includes the solvent and a fifth salt concentration is output from the third reservoir  202 . The solvent is moved from the first and fourth reservoirs  106 ,  208  to the third reservoir  202  via electroosmosis and forward osmosis. A solvent stream  216  with a sixth salt concentration is output from the fourth reservoir  208 . 
     The stack  200  enables a brine regeneration by adding a pair of opposite type (anion vs. cation or cation vs. anion) ion exchange membranes  114 ,  204  on opposite sides of the membrane pair  110 ,  112  that bounds the feed stream  102 . The outer pair of ion exchange membranes  114 ,  204  are chosen to have a second, different set of electroosmotic and osmotic transport properties than the inner pair of ion exchange membranes  110 ,  112 . The fifth membrane  210  also has these second electroosmotic and osmotic transport properties and is included to obtain the desired ion exchanges with the redox shuttle  117  at first electrode  116 . The feed stream  102  is flowed into the reservoir/chamber  106  bounded by the inner pair of ion exchange membranes 110 ,  112 , and the brine solution  122  is flowed into the remaining reservoirs/chambers  108 ,  202 ,  208 . The membranes are arranged such that the reservoir/chamber  208  that is bounded by two membranes with low electroosmotic and osmotic transport properties forms another desalination chamber. The portion of brine solution  212  that enters this chamber is thereby desalinated with a minimum of water loss to form a solvent stream  216  (water stream) which exits the electrochemical stack  200 . The net result is a single stack that accepts a dilute feed stream and outputs two streams: a concentrated product stream  144 , and water/solvent stream  216  having a very low salt content (e.g., less than 0.05% for both). 
     The electrochemical stacks described above can be combined in various ways depending on the scale of processing and/or the amount of solvent removal desired. In  FIG.  3   , a diagram shows a parallel stack arrangement according to an example embodiment. A dilute feed reservoir  300  is coupled to a manifold  302  or other fluid distribution pathway where it is fed into two or more electrochemical stacks  304 ,  305 . If the stacks  304 ,  305  are configured as shown in  FIG.  1   , they may each have their own dedicated salt regeneration device (see device  124 ) or may share a single (commonly connected) salt regeneration device. Concentrate streams  306 ,  307  of the stacks  304 ,  305  are sent into a concentrate reservoir  308  for use or downstream processing, or may be discharged, e.g., as a waste stream. Solvent streams  310 ,  311  are discharged, however may also be held in a reservoir, holding tank, etc., for use or downstream processing. The system shown in  FIG.  3    may utilize other inputs, including electricity to drive the electrochemical reactions in the stacks  304 ,  305  and to drive fluid pumps (not shown) as known in the art. 
     In  FIG.  3   , a diagram shows a series stack arrangement according to an example embodiment. A dilute feed reservoir  400  provides a feed stream  402  to a first electrochemical stack  404 , which is connected in series to a second electrochemical stack  405 . If the stacks  404 ,  405  are configured as shown in  FIG.  1   , they may each have their own dedicated salt regeneration device (see device  124 ) or may share a single salt regeneration device. Concentrate stream  406  of the first stack  404  is fed as a feed stream to second stack  405 , which outputs its own concentrate stream  407 , which has a higher concentration of solute than the concentrate stream  406 . Solvent streams  410 ,  411  are discharged, however may also be held in a reservoir, holding tank, etc., for use of downstream processing. If the stacks  404 ,  405  are configured as shown in  FIG.  1   , they may each have their own dedicated salt regeneration device (see device  124 ) or may share a single salt regeneration device. The system shown in  FIG.  4    may utilize other inputs, including electricity to drive the electrochemical reactions in the stacks  404 ,  405  and to drive fluid pumps (not shown) as known in the art. Note that the parallel and series arrangements shown in  FIGS.  3  and  4    may be combined. 
     In  FIG.  5   , a flowchart shows a method for separating a solvent from a feed steam according to an example embodiment. The method involves inputting  500  a feed stream having a first salt concentration to a first reservoir defined by a first ion exchange membrane and a second ion exchange membrane of an electrochemical cell. The second ion exchange membrane is a different type of membrane from the first ion exchange membrane. A second fluid stream having a second salt concentration that is higher than the first salt concentration is input  501  to a second reservoir of the electrochemical cell. The second reservoir is defined by the first ion exchange membrane and a third ion exchange membrane. The third ion exchange membrane and the second ion exchange membrane are of the same type (e.g., AE or CE). 
     An external voltage is applied  502  to first and second electrodes of the electrochemical cell and a solution having a redox-active electrolyte material is circulated  503  between the first and second electrodes. The redox-active electrolyte material reduces when in contact with the first electrode and oxidizes when in contact with the second electrode. In response to the reduction and oxidation of the redox-active electrolyte material, ions are transported across the first, second, and third ion exchange membranes to remove solvent and salt from the first reservoir. An effluent stream having a third salt concentration equal to or less than the second salt concentration is output  505  from the second reservoir. A concentrate stream having a fourth salt concentration that is less than the first and third salt concentrations is output  506  from the first reservoir. 
     Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range. 
     The foregoing description has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. Any or all features of the disclosed embodiments can be applied individually or in any combination and are not meant to be limiting, but purely illustrative. It is intended that the scope of the invention be limited not with this detailed description, but rather, determined by the claims appended hereto.