Patent Publication Number: US-2023141446-A1

Title: System and method for separating a reaction product from a fluid

Description:
TECHNICAL FIELD 
     This disclosure relates generally to systems and methods for removing a reaction product from a fluid in a redox flow electrochemical separation device. 
     BACKGROUND 
     Condensation reactions are reactions in which two molecules, or two parts of the same molecule, combine to form a larger molecule with the elimination of a smaller molecule. Similarly, polycondensation reactions involve the covalent connection of monomer molecules, leading to high molecular weight polymers with the release of multiple small molecules. Examples of condensation and polycondensation reactions include industrially significant processes such as polyester synthesis (via polycondensation) and biodiesel production (via esterification or transesterification). 
     The reactions are in equilibrium with the formation of the larger molecule product and the smaller molecule product; therefore, to drive the reaction to completion and collect the desired product (e.g., the larger molecule), the smaller molecule is separated from the reaction fluid. As current techniques for removing the smaller molecule product involve thermal energy, expensive procedures, and/or wasteful amounts of reactant materials, described herein are systems and methods for in-situ separation of the smaller molecule product using a redox flow electrochemical separation device. 
     SUMMARY 
     Embodiments described herein are directed to an electrochemical system for separating a reaction product from a first fluid stream. The system includes a first reservoir that comprises the first fluid stream input to the first reservoir and a catalyst input to the first reservoir, wherein the first fluid stream comprises a reaction mixture that reacts to form a first product and a second product in the first reservoir. A second reservoir comprises a second fluid stream input to the second reservoir. A first electrode contacts a first solution of a first redox-active electrolyte material and is configured to have a reversible redox reaction with the first redox-active electrolyte material, and to accept at least one ion from the catalyst in the first reservoir. A second electrode contacts a second solution of a second redox-active electrolyte material and is configured to have a reversible redox reaction with the second redox-active electrolyte material, and to drive at least one ion into the second fluid in the second reservoir. The system also includes an energy source configured to supply electrical potential to the first and second electrodes. A first type of inert ion exchange membrane is disposed between the first and second reservoirs, and a second type of inert ion exchange membrane, different from the first type, is disposed between the first electrode and the first reservoir and is disposed between the second electrode and the second reservoir. A waste effluent stream comprising the second product and the catalyst is output from the second reservoir, wherein the second product is removed from the first reservoir via electroosmosis, and a product effluent stream comprising the first product is output from the first reservoir. 
     Other embodiments are directed to a method for separating a reaction product from a first fluid steam. The method includes inputting a first fluid stream comprising a reaction mixture to a first reservoir defined by a first ion exchange membrane and a second ion exchange membrane of an electrochemical cell, wherein the second ion exchange membrane is a different type of membrane from the first ion exchange membrane. A catalyst is also input to the first reservoir. A second fluid stream is input to a second reservoir of the electrochemical cell, wherein the second reservoir is defined by the first ion exchange membrane and a third ion exchange membrane, wherein the third ion exchange membrane and the second ion exchange membrane are of the same type. A first component and a second component of the reaction mixture undergo a condensation reaction in the first reservoir to form a first product and a second product. An external voltage is applied to first and second electrodes of the electrochemical cell, and a solution comprising 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 the reduction and oxidation of the redox-active electrolyte material, ions are transported across each of the ion exchange membranes to remove the catalyst and the second product from the first reservoir. A waste effluent stream comprising the second product and the catalyst is outputted from the second reservoir, and a product effluent stream comprising the first product is output from the first reservoir. 
     Further embodiments are directed to a method for separating a reaction product from a first fluid steam. The method includes inputting a first fluid stream comprising a reaction mixture to a first channel of a forward osmosis membrane contactor and inputting a catalyst to the first channel. A draw solution comprising a concentrated solution of ionic species is input to a second channel of the forward osmosis membrane contactor, wherein the second channel is separated from the first channel by a forward osmosis membrane. The first component and the second component of the reaction mixture react in a condensation reaction in the first channel to form a first product and a second product. In response to formation of the second product, the second product is transported across the forward osmosis membrane to remove the second product from the first channel. A draw solution effluent stream comprising the draw solution and the second product is output from the second channel, and a product effluent stream comprising the first product and the catalyst is output from the first channel. 
     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 schematic diagram of fluid flow in a redox flow electrochemical separation system in accordance with certain embodiments; 
         FIG.  2    is a schematic diagram of fluid flow in a forward osmosis membrane contactor in accordance with certain embodiments; 
         FIG.  3 A  is a block diagram of a relationship between the separation system of  FIG.  1    and the forward osmosis membrane contactor of  FIG.  2    in accordance with certain embodiments; 
         FIG.  3 B  is a block diagram of a relationship between the separation system of  FIG.  1    and the forward osmosis membrane contactor of  FIG.  2    in accordance with certain embodiments; and 
         FIGS.  4 - 5    are flow diagrams of methods in accordance with certain embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to redox flow electrochemical salt separation systems. In certain embodiments, a redox flow electrochemical separation system may be part of a dehumidification system as a liquid desiccant system used in, among other things, heating, ventilation, and air-conditioning (HVAC). A redox-assisted dehumidification system utilizes a liquid desiccant (commonly an aqueous solution of an inorganic salt such as lithium chloride) that is fed through an air contactor where it absorbs humidity from input humid air and becomes diluted, or weakened. The weak desiccant is then fed into an electrochemical regenerator (e.g., cell or stack) that uses a redox shuttle to move salt from one liquid stream to another. In other embodiments, redox flow electrochemical separation systems may be used in dewatering applications. 
     As set forth above, condensation and polycondensation reactions (hereinafter referred to collectively as “condensation reactions”) produce a larger molecule first product and a smaller molecule second product. The smaller molecule second product may be water or a low carbon number alcohol such as methanol. Systems and methods described herein remove the smaller molecule second product, such as water, that is produced in a condensation or polycondensation reaction, in-situ, thereby driving the reaction forward to completion. This allows for continuous removal of the smaller molecule second product from a reaction mixture without any heat or phase changes. The avoidance of heat and/or phase changes is useful when a reactant or solvent in the reaction mixture is volatile, e.g., more volatile than water and because it can lower the rate of the reverse (unwanted, e.g., hydrolysis) reaction of the larger molecule first product with the smaller molecule second product. 
     The smaller molecule produced by a condensation reaction can limit, or determine, how the reaction is driven to completion to obtain the desired product (e.g., the larger molecule). Typical condensation reactions involve an organic acid reacting with an alcohol to form an ester and a molecule of water, or in other typical condensation reactions, an organic acid reacts with an amine to form an amide and a molecule of water. To drive the reactions to completion, the smaller molecule second product (e.g., water) is removed to perturb the equilibrium state of the reaction. When the eliminated smaller molecule second product is more volatile than either of the reactants, heat can be supplied to boil off, in certain circumstances continuously, the volatile elimination product. While this may work when the smaller molecule second product is volatile, using thermal energy is not an option when one of the reactants is more volatile than the smaller molecule second product such as an alcohol (e.g., in the case of ethanol reacting with acetic acid to form ethyl acetate and water) or an amine such as methylamine. 
     When thermal energy is not advisable or available due to the volatility of the reactants, other techniques are used to drive the condensation reaction to completion. For example, a large excess of one of the reactants can be used to drive the reaction. However, this is wasteful, can be expensive, and the volatile reactant still needs to be condensed, recovered, and re-separated from water, or the smaller molecule second product. A catalyst with a high affinity for water, or the smaller molecule, such as concentrated sulfuric acid may be added to the reaction mixture to drive the reaction, but sulfuric acid is corrosive and must be neutralized after the reaction is complete. Another technique is to mix in a water-absorbing material such as a zeolite or molecular sieve, but the absorbent material is usually a solid and has limited chemical compatibility, especially with acidic catalysts. Pre-activating one of the reactants, e.g., by converting carboxylic acid to an acyl chloride, can drive the reaction. However, this requires stoichiometric amounts of reagent and is expensive. Further, fractional distillation of the recovered water and volatile reactant can be used and the reconcentrated reactant can be returned to the reaction mixture. Each of these techniques is costly (e.g., in time, money, and/or energy), and in certain circumstances, can lower the reaction rate. Instead, the in-situ techniques, and systems therefor, described herein utilize a redox shuttle to drive ion motion to remove the smaller molecule second product from a condensation reaction mixture. 
     The in-situ removal of the smaller molecules, e.g., water, formed through a condensation reaction, occurs when a reaction mixture is fed into a device containing multiple ion exchange membranes in an electrochemical cell. The electrochemical cell utilizes a solution phase redox shuttle circulating between two electrodes, between which lie the ion exchange membranes—alternating cation exchange membranes and anion exchange membranes. When an electrical potential is applied between the two electrodes, the redox shuttle is simultaneously reduced at one electrode and re-oxidized at the opposite electrode. Between the two electrodes, cations and anions are transported selectively through the intervening ion exchange membranes, such that ions present in the reaction mixture are removed to a waste stream. The removed ions may come from a catalyst, an added supporting electrolyte, or both. In addition, the smaller molecule (e.g., water) is removed from the reaction stream through electroosmosis. When the waste stream has a higher affinity for the smaller molecule than the reaction mixture, the smaller molecule may also move to the waste stream due to forward osmosis. This device is further described below. 
       FIG.  1    is a diagram of an electrochemical system  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. Each electrode  116 ,  118  is in contact with a redox shuttle solution comprising a redox-active electrolyte material. Examples of 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 (Attorney docket number 20210171US01/0600.382US01), which is hereby incorporated by reference in its entirety. 
     The redox shuttle 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 reduced at a first electrode (e.g.,  116 ) and oxidized 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 circulates between the electrodes, the portions of the shuttle 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 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 periodically reverses 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 . The first membrane  110 , in combination with a third membrane  114 , also defines a second reservoir  108 . The membranes are ion-selective as well as water-permeable, are insoluble in organic solvents, and are inert (i.e., 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. 
     Within the first reservoir  106  is a reaction mixture  104 . The reaction mixture may be fed into the first reservoir  106  as a feed stream. The reaction mixture comprises at least two components (e.g., an organic acid and an alcohol) that undergo a condensation reaction to form a first, larger molecule product, and a second, smaller molecule product. The reaction mixture may also include a catalyst (e.g., sulfuric acid, or Lewis acidic salt such as scandium triflouromethanesulfonate, or indium (III) chloride) and/or a supporting electrolyte. The catalyst and/or supporting electrolyte may be present in the reaction mixture  102  before the reaction mixture enters the electrochemical device  150 , or it may be added to the first reservoir to mix with the reaction mixture  104 . In the first reservoir  106 , the first and second components (e.g., reagents) of the reaction mixture undergo a condensation reaction to form the first and second products in the first reservoir  106 . As discussed above, to collect or obtain the desired product (e.g., the first, larger molecule product), other components are removed from the first reservoir  106 . When an electrical potential is applied to the electrodes  116 ,  118 , the oxidation and reduction of the shuttle solution drives ions across the membranes  110 ,  112 ,  114 . As shown, ions of the catalyst and/or supporting electrolyte material (e.g., M + , X − ), are transported  132 ,  134  across the respective cation and anion exchange membranes  110 ,  112  defining the first reservoir  106  toward the oppositely charged electrodes  116 ,  118 . 
     The same ion transport occurs for catalyst and/or supporting electrolyte material ions  136  throughout the electrochemical device  150 . Thus, the catalyst is removed from the first reservoir  106  and concentrated in the second reservoir  108  where the ions reform the catalyst in a fluid operating as a waste fluid stream. The fluid in the second reservoir may comprise water, methanol, acetonitrile, brines, process wastewater from a different system, etc. The fluid in the second reservoir may further comprise one or more dissolved solutes such as buffers, sugars, amino acids, salts, more or a different type of catalyst, glycerol, ethylene glycol, etc. The movement of the ions  132 ,  134 ,  136  across the ion exchange membranes  110 ,  112 ,  114 , also drags  138 ,  140 ,  142  the smaller molecules of the second product of the condensation reaction across the membranes due to electroosmosis. In certain embodiments where the fluid in the second reservoir  108  has a higher affinity for the smaller molecules than the reaction mixture, the smaller molecules may also move to the second reservoir  108  due to forward osmosis. Thus, both the catalyst and the second product are removed from the first reservoir  106  leaving a concentrated product stream  144  that may be collected, or further processed, upon output from the electrochemical device  150 . The concentrated product stream may also still contain residual amounts (i.e., lower than the starting reaction mixture  102 ) of the reactants, second product, and catalyst. 
     As indicated by brackets  120 , the two membranes  110 ,  114  and the corresponding first and second reservoirs  106 ,  108 , can be considered a single cell pair that repeats within the electrochemical device  150 . For example, a plurality of these cell pairs may result in a stack of up to 10, up to 20, up to 50, up to 100, up to 200, up to 500, or more, membranes, alternating in ion exchange type, between the electrodes  116 ,  118 , where the total number of membranes is an odd number. A final membrane (e.g.,  112 ) couples to the stack to define the n th  first reservoir. Increasing the number of cell pairs in the electrochemical device  150  increases the overall membrane area in the device and allows for smaller footprints overall to be achieved. In addition, the rate of water removal would be further enhanced if the second reservoirs  108  contain fluid that has a higher affinity for the small molecules than the affinity of the shuttle solution for the small molecules because the 1 st  to the (n−1) th  first reservoirs  106  will be in contact with two kinds of second reservoir  108 , rather than one kind of second reservoir  108  and a shuttle solution. When a plurality of cell pairs is combined into a stack the condensed product effluent streams  144  are combined into an output and the waste effluent streams of the respective second reservoirs  122  are combined and output from the electrochemical device  150 . 
     While the fluid in the second reservoir takes up catalyst, it also takes up the second product. When the second product is water, or an alcohol, the fluid in the second reservoir may be diluted depending on the amount of second product taken up with respect to the amount of catalyst, or other ions, taken up. Using just the catalyst and second product as an example, if the fluid in the second reservoir takes up more of the second product than catalyst compared to the starting second product:catalyst ratio, the fluid in the second reservoir will be diluted with respect to the initial second fluid composition. If the fluid in the second reservoir takes up more catalyst than second product compared to the starting second product:catalyst ratio, the fluid in the second reservoir will be more concentrated in catalyst than the initial second fluid composition. Further, if the fluid in the second reservoir takes up a proportional amount of both catalyst and second product compared to the starting second product:catalyst ratio, the composition of the waste effluent stream  122  may be substantially equal to that of the initial second fluid. 
     The waste effluent stream from the second reservoir  122  is circulated to a regeneration system  124  to remove the unwanted smaller molecule second product as a discharge stream  126  and concentrate the fluid supplied to the second reservoir  108  as output stream  128 . A portion  130  of the output stream  128  may also be diverted to the first reservoir  106  to supply catalyst to the reaction mixture  102 . The regeneration system  124  may be a conventional regenerator (e.g., thermal regeneration, electrodialysis, reverse osmosis, forward osmosis, membrane pervaporation, falling-film evaporation, etc.) or a redox-assisted regenerator. 
     A redox-assisted regenerator has a similar configuration to the electrochemical device  150 . When the regeneration system  124  utilizes a redox-assisted regenerator, the regenerator has two outer ion exchange membranes separating outer redox shuttle channels proximate respective electrodes from an inner concentrate stream and an inner dilute stream (e.g., waste effluent stream  122  from the second reservoir  108 ). The outer ion exchange membranes are of a first type of ion exchange membrane (e.g., anion exchange membranes (AEM)), and the concentrate and dilute streams are separated by a central ion exchange membrane of an opposing ion exchange type (e.g., cation exchange membrane (CEM)). In other configurations, the central ion exchange membrane may be an AEM and the outer membranes may be CEMs. 
     When an external voltage induces oxidation or reduction in the redox-active shuttle molecules (see redox shuttle solution examples above) at the respective electrodes, ions (e.g., of a liquid desiccant, a draw solution, or the ionic catalyst) from the waste effluent stream  122  are driven across the membranes without splitting water or producing other gaseous by products (e.g. chlorine, oxygen, hydrogen). The ion movement creates two streams: re-concentrated catalyst stream  128  (formerly the waste effluent stream  122 ) and a discharge stream  126  of the second product (e.g., water). The regeneration can also be achieved over multiple stages or with a membrane stack similar to the stack described above. Moving parts of the system may include low pressure pumps for liquid circulation and fans for air circulation. The regeneration system  124  may share power supply  152  or have a dedicated power supply. Additional details of this type of four-channel, electrodialytic, stack with redox shuttle assist can be found in commonly-owned U.S. Pat. No. 10,821,395, which is hereby incorporated by reference in its entirety. 
     In other embodiments, an alternative separation system  200  is configured to remove the smaller molecule, second product from the reaction mixture.  FIG.  2    illustrates fluid flow in a forward osmosis membrane contactor  250 . A forward osmosis membrane contactor  250  includes at least one forward osmosis membrane. When a contactor  250  comprises a single forward osmosis membrane, the membrane divides the contactor  250  into to two channels, or reservoirs, where a first reservoir contains a reaction mixture and the second reservoir contains a draw solution of a concentrated ionic species. While a forward osmosis membrane contactor  250  may contain a single forward osmosis membrane, it may also include a plurality of two or more forward osmosis membranes. The example shown in  FIG.  2    includes three forward osmosis membranes,  210 ,  212 ,  214 , and the following description of a three-membrane forward osmosis contactor  250  similarly applies to a contactor  250  comprising one, two, or more than three membranes as well. 
     The forward osmosis membranes  210 ,  212 ,  214  are selected to have high permeability for the smaller molecule, second product of the condensation reaction (e.g., water). In the three-membrane configuration shown, the first membrane  210  and a second membrane  212  define a first channel, or reservoir,  206 , and the first membrane  210  and a third membrane  214  define a second channel, or reservoir  208 . Each of the membranes  210 ,  212 ,  214  may be the same or they may differ in materials, size, shape, etc. 
     Within the first reservoir  206  is a reaction mixture  204 . The reaction mixture may be fed into the first reservoir  206  as a feed stream  202 . The reaction mixture comprises at least two components (e.g., an organic acid and an alcohol) that undergo a condensation reaction to form a first, larger molecule product, and a second, smaller molecule product. The reaction mixture may also include a catalyst (e.g., sulfuric acid, scandium trifluoromethanesulfonate, indium(III) chloride, etc.) and/or a supporting electrolyte. The catalyst and/or supporting electrolyte may be present in the reaction mixture  202  before the reaction mixture enters the forward osmosis contactor  250 , or it may be added to the first reservoir  206  to mix with the reaction mixture  204 . In the first reservoir  206 , the first and second components (e.g., reagents) of the reaction mixture undergo a condensation reaction to form the first and second products in the first reservoir  206 . As discussed above, to collect or obtain the desired product (e.g., the first, larger molecule product), the second product is removed from the first reservoir  206 . 
     Within the second reservoir  208  is a draw solution of a concentrated ionic species. The dissolved species in the draw solution can be identical to a supporting electrolyte in the reaction mixture (e.g., sodium chloride) or identical to the catalyst (e.g., sulfuric acid, scandium trifluoromethanesulfonate, indium(III) chloride, etc.), or include both. The smaller molecule, second product is moved  238 ,  242  to the draw solution in the second reservoir  208 , or out  240  of the first reservoir  206 , by forward osmosis. The dehydrated, or concentrated reaction stream in the first reservoir, where the condensation reaction has been driven to, at least substantial, completion, is output as an effluent stream  244  comprising the first product, the catalyst, and possibly residual traces of the second product. In certain embodiments, the first reaction product may be further separated from the catalyst using a redox-assisted regenerator as discussed above in connection with regeneration system  124 , or a conventional separation process such as filtration, distillation, crystallization, precipitation, chromatography, electrodialysis, etc. 
     As discussed above and indicated by brackets  220 , the forward osmosis membrane contactor  250  may include a plurality (n) of forward osmosis membranes in addition to forward osmosis membrane  212 . As shown by the location of the brackets  220 , in total, there are 2n+1 forward osmosis membranes disposed in a container that divide the container into 2n+2 channels, or reservoirs. When n=0, a single membrane defines two channels as discussed above. The channels are configured to accept and flow reactant streams and draw solution streams in an alternating configuration thereby outputting dehydrated (e.g., concentrated) reaction streams  244  and effluent streams  222 . The total forward osmosis membranes may form a stack of up to 10, up to 20, up to 50, up to 100, up to 200, up to 500, or more, membranes. The membrane e.g., 212 couples to the stack to define the n th  first reservoir. Increasing the number of cells in the forward osmosis membrane contactor  250  increases the overall membrane area in the device and allows for smaller device footprints overall to be achieved. When a plurality of membranes is combined into a stack to define a plurality of first and second channels, the condensed first product effluent streams  244  are combined into an output and the effluent streams of the respective second reservoirs  222  are combined and output from the forward osmosis membrane contactor  250 . 
     Due to the influx transport of the second product into the second reservoir(s)  208 , the fluid in the second reservoir(s)  208  is diluted. The diluted effluent stream from the second reservoir  222  is circulated to a regeneration system  224  to remove the unwanted smaller molecule second product as a discharge stream  226  and reconcentrate the fluid supplied to the second reservoir  208  as output stream  228 . A portion  230  of the output stream  228  may also be diverted to the first reservoir  206  to supply catalyst to the reaction mixture  202 . As discussed above, the regeneration system  224  may be a conventional regenerator (e.g., thermal regeneration, electrodialysis, reverse osmosis, forward osmosis, membrane pervaporation, falling-film evaporation, etc.) or a redox-assisted regenerator. 
     In certain embodiments as shown in  FIG.  3 A , the separation system  200  is coupled to the output of the electrochemical system  100  to form a removal system  300 A for the smaller molecule, second product of a condensation reaction. Thus, the output  144  would be the input  244  to the forward osmosis membrane contactor  250 . While the separation system  100  removes most of the second product from the reaction mixture, any remainder may be removed by forward osmosis in the forward osmosis membrane contactor-based separation system  200 . The overall system  300 A utilizes a redox shuttle to drive water, or other small molecules, from a reaction mixture without thermal energy. 
     In certain other embodiments as shown in  FIG.  3 B , the separation system  200  is coupled to the input of the electrochemical system  100  to form a removal system  300 B for the smaller molecule, second product of a condensation reaction. Thus, the output  244  would be the input  144  to the electrochemical device  150 . While the separation system  200  removes most of the second product from the reaction mixture, any remainder may be removed by electroosmosis with the catalyst in the electrochemical system  100 . The overall system  100 ,  300 A, and/or  300 B utilizes a redox shuttle to drive water, or other small molecules, from a reaction mixture without thermal energy. Thus, the respective systems may be used with condensation reactions with volatile reactants but without costly redistillation of those reactants from the liberated second product (e.g., water). The system  300 A,  300 B, electrochemical system  100  alone, or forward osmosis-based separation system  200  alone also avoid the need to use excess stoichiometric amounts of volatile reactants which can be costly and lower the reaction rate. 
     A separation process for removing the smaller molecule product from a condensation reaction mixture is further illustrated in  FIG.  4   . A reaction mixture is input to a first reservoir of an electrochemical cell, such as described above in connection with  FIG.  1   , where a first and second component of the reaction mixture undergo a reaction to form a first, larger molecule product and a second, smaller molecule product  402 . In certain embodiments, the first and second components are an organic acid and an alcohol, which undergo a condensation reaction. In other embodiments, the first and second components are an organic amine and an organic acid, which undergo a condensation reaction. Another fluid stream is input to an adjacent, second reservoir of the electrochemical cell  404 . When an external voltage is applied to first and second electrodes of the electrochemical cell and a redox shuttle is circulated between the electrodes, it drives ion movement in the electrochemical cell across membranes toward oppositely charged electrodes  406 . Specifically, ions of a catalyst in the reaction mixture are driven out of the first reservoir, taking the smaller molecules of the second product with them due to electroosmosis  408 . A waste effluent stream comprising the second product and the catalyst is output from the second reservoir  410 , and a product effluent stream comprising the first product is output from the first reservoir  412 . Although the first and second products are separated, they may each be further processed, or if undesired (e.g., the second product), discarded as waste. 
     Another separation process for removing the smaller molecule product from a condensation reaction mixture is illustrated in  FIG.  5   . A reaction mixture is input to a first channel of a forward osmosis membrane contractor, such as described above in connection with  FIG.  2   , where a first and second component of the reaction mixture undergo a reaction to form a first, larger molecule product and a second, smaller molecule product  502 . In certain embodiments, the first and second components are an organic acid and an alcohol, which undergo a condensation reaction. In other embodiments, the first and second components are an organic amine and an organic acid, which undergo a condensation reaction. A draw solution stream is input to an adjacent, second channel of the forward osmosis membrane contactor  504 . Because the draw solution has a salt concentration with a high affinity for the smaller molecule second product, the second product is transported across the forward osmosis membranes and out of the first channel to the second channel via forward osmosis  506 . A waste effluent stream comprising the second product is output from the second channel  508 , and a product effluent stream comprising the first product is output from the first channel  510 . The waste effluent stream is optionally regenerated, as described above, and recirculated to be input to the second channel  512 . Although the first and second products are separated, they may each be further processed, or if undesired (e.g., the second product), discarded as waste. 
     As set forth above, various embodiments directed to separating a smaller molecule product (e.g., water) of a condensation reaction from a reaction mixture may utilize a redox-assisted shuttle separation system and/or a forward osmosis membrane contactor to drive the reaction to completion and recover a desired reaction product. An electrochemical cell contains a solution phase stream of a redox shuttle that is circulated from one electrode to the other and back again. Between the electrodes lies a series of substantially parallel, alternating cation and anion exchange membranes. A first stream of fluid comprising a reaction mixture present in a first reservoir of the electrochemical cell does not mix with a second fluid stream in an adjacent reservoir of the electrochemical cell but the two fluid streams contact each other through opposite sides of a membrane separating the two channels. Application of an external voltage to the electrodes of the cell initiates selective transport of ionic species and small molecules (i.e., a second product of the reaction mixture) from the first fluid stream to the second fluid stream across the membrane. The ionic transport in the electrochemical cell and/or the forward osmosis of the contactor separates a first reaction product from a second reaction product without the use of thermal energy or costly materials and/or processes. 
     In all embodiments described above, the small molecule second product is directly (through forward osmosis), or indirectly (through electroosmosis), transported from one fluid stream to another at some point in the system or process. This should be understood to also encompass other molecules identical to the small molecule second product that were in the reaction mixture before the second product is introduced to the system or process. For example, a reaction mixture of organic acid and alcohol may also include water at the beginning together with a sulfuric acid catalyst, and further molecules of water are created during the reaction between the organic acid and alcohol to form an ester. The systems and processes described above are intended to remove not just the water that is created in the reaction, but also water that was present at the beginning, if so desired. 
     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.