Electrodialysis processes using an organic solvent for separating dissolved species

Provided are water treatment systems and methods of treating water that include separating dissolved salts from a feed stream using an organic solvent brine stream. For example, described are water treatment systems comprising: an electrodialysis device comprising an inlet feed stream, an inlet brine stream, an outlet product stream, and an outlet brine stream; and a precipitation tank comprising an inlet stream and an outlet stream, wherein the inlet stream of the precipitation tank comprises the outlet brine stream of the electrodialysis device, and the inlet brine stream of the electrodialysis device comprises the outlet stream of the precipitation tank, and wherein inlet brine stream and outlet brine stream comprises an organic solvent.

FIELD OF THE DISCLOSURE

This disclosure relates to electrochemical processes for separating charged chemical species using an organic solvent brine stream.

BACKGROUND OF THE DISCLOSURE

Electrochemical methods were developed to reduce the energy requirements of desalination processes by avoiding energy intensive phase changes. Generally, electrochemical methods include two electrodes having ion exchange membranes placed in between. The ion exchange membranes allow the passage of positively or negatively charged ions depending on the nature of the functional groups of the charged ions. Alternating these membrane types creates compartments that allow the removal of ions from one stream and the addition of ions to an adjacent stream when an electric field is applied between the electrodes that encapsulate the membranes.

The electrochemical desalination method provides an energy efficient desalination process. To increase the process capacity of this method, pairs of ion exchange membranes are stacked on top of each other to form stacks. These stacks can range from 1 pair to over 1000 pairs.

Electrochemical desalination methods and even physical separation methods such as reverse osmosis produce a concentrated brine. Disposal of brines can be difficult due effects on salinity of surface water, ground water, and aquatic life. Brine producers are interested in developing zero liquid discharge or minimum liquid discharge to reduce the environmental impact of their concentrated brines and to recover more water from their processes.

In many cases, the brine contains desirable chemicals from compounds of boron, bromine, calcium, iodine, lithium, magnesium, potassium and sodium. These compounds are traditionally recovered using evaporation technologies such as evaporation ponds or thermal crystallizers. The former requires large land (0.5 acres/gpm evaporation) and the latter requires large energy (>140 kW*hr/m3).

Conventional electrochemical methods are not used to precipitate chemicals from solutions due to the potential for forming scale in the electrochemical cells. Chemical species present in aqueous brines have a range of solubilities, which can limit the ability to concentrate other species present in the brine. Another limitation in electrochemical technologies results from the practical limits on concentration using the state-of-the-art ion exchange membranes. As gradients in the electrochemical cell increase, the rate of diffusion in the reverse and forward directions become similar. This results in no further concentrating capability. In order to achieve minimum liquid discharge or recover the chemical in the brine, the brines must be sent through thermal evaporation technologies such as mechanical vapor recompression, multi-effect distillation, or multi-effect flash distillation prior to crystallization in thermal crystallizers or evaporation ponds.

SUMMARY OF THE DISCLOSURE

Provided are electrochemical processes for separating charged chemical species from an aqueous feed stream using an organic solvent as a brine stream. Processes provided herein are capable of achieving a super saturated solution while requiring a relatively low amount of energy. Further, by using organic solvent in the brine stream, which has a relatively low solubility compared to an aqueous brine stream, a positive chemical gradient is produced between the aqueous feed stream and the organic solvent brine stream. A positive chemical gradient reduces the resistance of charged ions from moving to the organic brine stream form the aqueous feed stream. Dissolved salts in the resulting brine stream may be precipitated out of solution and the supernatant of the brine stream may be collected and returned to the electrochemical process for further concentration.

In some embodiments, the pH of the feed stream may be controlled to further enable charged ion separation. For example, a common dissolved salt, boron, generally exists in aqueous solutions as boric acid (H3BO3). Boric acid can dissociate into ions at a pKa of 9.23. Thus, to keep boron in non-ionic form (i.e., boric acid), the pH of the feed stream can be controlled to 9.23 or lower. As the pH value is decreased, so too is the number of borate ions in solution.

In some embodiments, electrochemical processes may include flash evaporation to promote salt crystallization and/or a solvent recovery stream to help replenish the inlet organic solvent brine stream of the electrodialysis unit should it be diluted via osmosis or electro-osmosis.

In some embodiments, provided are water treatment systems, the water treatment system comprising: an electrodialysis unit comprising an inlet feed stream, an inlet brine stream, an outlet product stream, and an outlet brine stream; and a precipitation tank comprising an inlet stream and an outlet supernatant stream, wherein the inlet stream of the precipitation tank comprises the outlet brine stream of the electrodialysis unit, and the inlet brine stream of the electrodialysis device comprises the outlet supernatant stream of the precipitation tank, and wherein the inlet brine stream and the outlet brine stream of the electrodialysis unit comprise an organic solvent.

In some embodiments of the water treatment system, a salt concentration of the outlet product stream is greater than a salt concentration of the outlet brine stream of the electrodialysis unit.

In some embodiments of the water treatment system, the inlet brine stream and the outlet brine stream of the electrodialysis unit comprise a water and organic solvent composition.

In some embodiments of the water treatment system, the water and organic solvent composition of the inlet brine stream comprises 2-20 wt. % water.

In some embodiments of the water treatment system, the organic solvent comprises at least one of ethanol or isopropanol.

In some embodiments of the water treatment system, the salt concentration of the outlet product stream is less than that of the inlet feed stream.

In some embodiments of the water treatment system, the salt concentration of the outlet product stream is 50-80 wt. % that of the inlet feed stream.

In some embodiments of the water treatment system, the salt concentration of the inlet brine stream is less than that of the outlet brine stream.

In some embodiments of the water treatment system, the salt concentration of the inlet brine stream is 30-60 wt. % that of the outlet brine stream.

In some embodiments of the water treatment system, the salt concentration of the outlet brine stream is less than that of the outlet product stream.

In some embodiments of the water treatment system, the salt concentration of the outlet brine stream is 30-70 wt. % that of the outlet product stream.

In some embodiments of the water treatment system, the outlet supernatant stream of the precipitation tank comprises a supernatant.

In some embodiments of the water treatment system, the water treatment system comprises a screw conveyor configured to remove precipitated salts from the precipitation tank.

In some embodiments of the water treatment system, the precipitation tank comprises a flash valve configured to flash off a fraction of the solution of outlet brine stream as vapor to accelerate salt precipitation.

In some embodiments of the water treatment system, the water treatment system comprises a solvent recovery step configured to replenish organic solvent in the inlet brine stream.

In some embodiments of the water treatment system, the inlet feed stream is controlled to a pH of 9 or less.

In some embodiments of the water treatment system, the inlet feed stream is controlled to a pH of 7 or less.

In some embodiments of the water treatment system, the dissolved salts comprise one or more of sodium chloride, lithium carbonate, boric acid, sodium sulfate, lithium hydroxide, sodium bicarbonate, or potassium chloride.

In some embodiments, a method of separating dissolved salts from a feed stream is provided, the method comprising: passing water through an electrodialysis unit configured to separate dissolved salts from a feed stream, wherein the electrodialysis unit comprises an inlet feed stream, an inlet brine stream, an outlet product stream, and an outlet brine stream; routing the outlet brine stream of the electrodialysis unit to a precipitation tank to allow the dissolved salts to precipitate from solution, wherein the precipitation tank comprises an inlet stream and an outlet supernatant stream; and routing the outlet supernatant stream from the precipitation tank to the electrodialysis unit, wherein the inlet brine stream of the electrodialysis unit comprises the outlet supernatant stream of the precipitation tank, wherein the inlet brine stream and the outlet brine stream of the electrodialysis unit comprise an organic solvent.

In some embodiments of the method, a salt concentration of the outlet product stream is greater than a salt concentration of the outlet brine stream of the electrodialysis unit.

In some embodiments of the method, the inlet brine stream and the outlet brine stream of the electrodialysis unit comprise a water and organic solvent composition.

In some embodiments of the method, the water and organic solvent composition of inlet brine stream comprises 2-20 wt. % water.

In some embodiments of the method, the organic solvent comprises at least one of ethanol or isopropanol.

In some embodiments of the method, the salt concentration of the outlet product stream is less than that of the inlet feed stream.

In some embodiments of the method, the salt concentration of the outlet product stream is 50-80 wt. % that of the inlet feed stream.

In some embodiments of the method, the salt concentration of inlet brine stream is less than that of outlet brine stream.

In some embodiments of the method, the salt concentration of the inlet brine stream is wt. % that of the outlet brine stream.

In some embodiments of the method, the salt concentration of the outlet brine stream is less than that of the outlet product stream.

In some embodiments of the method, the salt concentration of outlet brine stream is wt. % that of the outlet product stream.

In some embodiments of the method, the outlet supernatant stream of the precipitation tank comprises a supernatant.

In some embodiments of the method, the method comprises removing precipitated salts from the precipitation tank using a screw conveyor.

In some embodiments of the method, the method comprise flashing off a fraction of the solution of the outlet brine stream as vapor to accelerate salt precipitation.

In some embodiments of the method, the method comprises recovering the organic solvent with a solvent recovery step configured to replenish organic solvent in the inlet brine stream.

In some embodiments of the method, the solvent recovery step comprises a distillation column and a condenser.

In some embodiments of the method, the inlet feed stream is controlled to a pH of 9 or less.

In some embodiments of the method, the inlet feed stream is controlled to a pH of 7 or less.

In some embodiments of the method, the dissolved salts comprise one or more of sodium chloride, lithium carbonate, boric acid, sodium sulfate, lithium hydroxide, sodium bicarbonate, or potassium chloride.

DETAILED DESCRIPTION OF THE DISCLOSURE

Provided are electrochemical processes for separating charged chemical species from an aqueous feed stream using an organic solvent in a brine stream. Processes provided herein are capable of achieving a super saturated solution while requiring a relatively low amount of energy. Organic solvents, such as those that may be used as the brine stream in electrochemical processes provided herein, typically have a low solubility for charged ions. Thus, electrochemical processes provided can have a positive chemical gradient between the aqueous feed stream and the organic solvent brine stream. This is in contrast to electrochemical processes having an aqueous brine stream. Because aqueous brine streams have a much greater solubility, they become more highly concentrated during the electrodialysis process. Conversely, an organic solvent brine stream having a lower solubility will likely be less concentrated than the feed stream. This will produce a positive chemical gradient. A positive chemical gradient reduces the resistance of charged ions from moving to the organic brine stream from the aqueous feed stream. Dissolved salts in the resulting brine stream may be precipitated out of solution and the supernatant of the brine stream may be collected and returned to the electrochemical process for further concentration. Example dissolved salts can include, but are not limited to, sodium chloride, lithium carbonate, boric acid, sodium sulfate, lithium hydroxide, sodium bicarbonate, and potassium chloride.

As described above, the organic solvent brine stream has a low solubility for dissolved ions as compared to water. For example, suitable organic solvents that may be used as brine streams in electrodialysis processes provided herein include ethanol, isopropanol, and other alkyl alcohols, as well as ketones, such as acetone, methyl ethyl ketone (MEK), etc. One common dissolved species, sodium chloride, has a solubility of ˜0.360,000 mg/L in water, but a solubility of only 650 mg/L in pure ethanol, 30 mg/L in isopropanol, and 0.42 mg/L in acetone. Additionally, the organic solvent also has a high vapor pressure as compared to water, meaning that the solvent will more readily evaporate relative to water.

Using an organic solvent brine stream having a relatively low salt solubility can allow for an electrodialysis process to produce a super saturated solution with greatly reduced energy requirement. The amount of current applied to the process can be two to three orders of magnitude less than what would otherwise be necessary to achieve the same relative levels of saturation in a system using an aqueous brine stream.

In some embodiments, the brine stream may comprise some water in addition to an organic solvent. The presence of water in the brine stream, even in electrodialysis systems provided herein that are characterized with brine streams comprising predominantly of organic solvent, can reduce the amount of water osmosis across the ion-exchange membranes of electrodialysis devices. Although the presence of water in the brine stream will increase the solubility of dissolved ions, it will also help prevent loss of water in the feed stream.

Once the ions are transferred into the brine stream, the brine stream is separated from the electrodialysis cell. It is introduced to a tank that provides residence time for the separation to occur (i.e., salting out). Once the precipitation occurs, the supernatant may be collected and returned to the electrochemical cell for further concentration. The salts collected may be dried or removed using methods such as centrifugation and filter pressing.

In some embodiments, it may be beneficial to concentrate the brine to just below the saturation point. The solution may then be super saturated by flashing off the organic solvent of the supernatant. Due to the high vapor pressure of the organic solvent relative to water, the energy required for flash evaporation and/or distillation is less than that which would be required for an aqueous solution. Using flash evaporation may be used when multiple species are present in the brine stream, particularly in cases in which it is desirable to perform multi-stage distillation to remove dissolved species in separate steps.

If water osmotes across the ion exchange membrane into the brine stream, a solvent recovery step may be performed to ensure that the concentration of organic solvent remains at levels that allow for precipitation. The solvent recovery step may be composed of a stripping column or fractional distillation to separate the water from organic solvent. Molecular sieves may be used to further purify the solvent if such a step is desirable.

Provided below is a discussion of the basic operation of an individual electrodialysis device according to some embodiments and with respect toFIG.1. Electrodialysis systems and methods for separating ions using an organic solvent brine stream provided herein may include one or more individual electrodialysis devices.

An individual electrodialysis device (i.e., an ion-exchange device) can include at least one pair of electrodes and at least one pair of ion-exchange membranes placed there between. The at least one pair of ion-exchange membranes can include a cation-exchange membrane (“CEM”) and an anion-exchange membrane (“AEM”). In addition, at least one of the ion-exchange membranes (i.e., CEMs and/or AEMs) has a spacer on the surface of the ion-exchange membrane facing the other ion-exchange membrane in an electrodialysis device. In some embodiments, both the CEMs and the AEMs have a spacer on at least one surface facing the other ion-exchange membrane. The spacer can include a spacer border and a spacer mesh.

FIG.1shows a schematic side view of electrodialysis device100according to some embodiments disclosed herein. Electrodialysis device100can include CEMs104and AEMs106sandwiched between two electrodes102. In some embodiments, one or more CEM104and one or more AEM106may alternate throughout a length of the electrodialysis device100.

An electrode102is shown on opposing ends of electrodialysis device100. One electrode102can be a cathode and another electrode102can be an anode. In some embodiments, one or more electrodes102can encompass one or more fluid channels for electrolyte stream112. Electrolyte stream112may comprise raw influent, a separately-managed electrolyte fluid, a sodium chloride solution, sodium sulfate, iron chloride, or another suitable conductive fluid. For example, a fluid channel for electrolyte stream112of electrode102can be located between one or more CEM104and an electrode102, or between one or more AEM106and an electrode102. Electrodialysis device100may also include one or more fluid channels for influent streams136aand136b. Influent streams136aand136bmay be located between a CEM104and an AEM106. Influent streams136aand136bcan comprise water. In some embodiments, water of influent streams136aand136bmay be purified by flowing through one or more intermembrane chambers located between two or more alternating CEM104and AEM106. In particular, influent stream136amay flow through electrodialysis device100and exit electrodialysis device100as brine stream108. Influent stream136bmay flow through electrodialysis device100and exit electrodialysis device100as product stream110. Thus, influent stream136ais a brine inlet stream for electrodialysis device100, and influent stream136bis a product inlet stream for electrodialysis device100ofFIG.1. Of course, the ionic composition of the streams within each channel may change when an electric current is applied to the device, allowing ions to migrate from one channel to an adjacent channel.

AEM106can allow passage of negatively charged ions and can substantially block the passage of positively charged ions. Conversely, CEM104can allow the passage of positively charged ions and can substantially block the passage of negatively charged ions.

Electrolyte stream112may be in direct contact with one or more electrodes102. In some embodiments, electrolyte stream112may comprise the same fluid as the fluid of influent streams136aand136b. In some embodiments, electrolyte stream112may comprise a fluid different from the fluid of influent streams136aand136b. For example, electrolyte stream112can be any one or more of a variety of conductive fluids including, but not limited to, raw influent, a separately managed electrolyte fluid, sodium chloride solution, sodium sulfate solution, or iron chloride solution.

In some embodiments, electrodialysis device100can include one or more spacers on at least one surface of a CEM104or an AEM106. In some embodiments, one or more spacer may be located on two opposing surfaces of a CEM104and/or an AEM106. Further, electrodialysis device100may include one or more spacers between any two adjacent ion-exchange membranes (i.e., between an AEM106and a CEM104). The region formed between any two adjacent ion-exchange membranes by one or more spacers forms an intermembrane chamber.

When an electric charge is applied to one or more electrodes102of electrodialysis device100, the ions of influent streams136aand136bflowing through an intermembrane chamber between any two ion-exchange membranes (i.e., one or more CEM104and one or more AEM106) can migrate towards the electrode of opposite charge. Specifically, ion-exchange membranes can comprise ionically conductive pores having either a positive or a negative charge. These pores can be permselective, meaning that they selectively permeate ions of an opposite charge. Thus, the alternating arrangement of the ion-exchange membranes can generate alternating intermembrane chambers comprising decreasing ionic concentration and comprising increasing ionic concentration as the ions migrate towards the oppositely-charged electrode102.

An intermembrane chamber can be formed from a spacer border and a spacer mesh and can create a path for fluids to flow. The number of intermembrane chambers may be increased by introducing additional alternating pairs of ion-exchange membranes. Introducing additional alternating pairs of CEMs104and AEMs106(and the intermembrane chambers formed between each pair of ion-exchange membranes) can also increase the capacity of electrodialysis device100. In addition, the functioning ability of an individual ion-exchange cell (i.e., a single CEM104paired with a single AEM106to form a single intermembrane chamber) can be greatly augmented by configuring ion-exchange cells into ion-exchange stacks (i.e., a series of multiple ion-exchange cells.)

As described above, ions of influent streams136aand136bflowing through an intermembrane chamber can migrate towards electrode102of opposite charge when an electric current is applied to electrodialysis device100. The ion-exchange membranes have a fixed charge (CEMs have a negative charge, AEMs have a positive charge). Thus, as a counter-ion approaches an ion-exchange membrane (e.g., as a cation approaches a CEM), the counter-ion is freely exchanged through the membrane. The removal of this counter-ion from the stream makes the stream a product stream. On the other hand, when a co-ion approaches the ion-exchange membrane (e.g., as an anion approaches a CEM), it is electrostatically repelled from the CEM. This separation mechanism can separate influent streams136aand136binto two different streams of opposite ionic charge. For example, when used for desalination, influent stream136amay flow to brine stream108, and influent stream136bmay flow to product stream110. Brine stream108is generally a waste stream. In some embodiments, product stream110may have a lower ionic concentration than brine stream108.

In some embodiments, product stream110may have a predetermined treatment level. For example, ion-exchange system100may be configured to remove several types of ions (e.g., monovalent ions, divalent ions, etc.) or it may be configured to remove a specific type of ion (e.g., arsenic, fluoride, perchlorate, lithium, gold, silver, etc.). Further, ion-exchange system100can be held together using a compression system that comprises using two compression plates on opposite ends of the device. In some embodiments, a single pair of compression plates may be used (i.e., one on either end of the outside of the stack) to achieve a working, reliable seal.

FIG.2shows the basic operation of an electrodialysis device200using an organic solvent brine stream. Electrodialysis device200can include a pair of electrodes202, an electrolyte stream212, a plurality of CEMs204, a plurality of AEMs206, influent stream236, inlet brine stream238, output product stream210, and output brine stream208.

As explained with reference toFIG.1, above, when a potential is applied across the electrodes202of the electrodialysis device200, ions within the streams begin to migrate across the ion exchange membranes. The dissolved, salt ions that are transferred from influent stream236to organic solvent brine stream238may become saturated within brine stream238and precipitate from the brine stream as a solid crystal. In some embodiments, this precipitation may occur in a precipitation tank after the dissolved ions have been transferred by electrodialysis device200. Particularly if the induction time for precipitation is known, a system can be designed such that the precipitation occurs outside of electrodialysis device200. This concept (i.e., a precipitation tank) is explained further with respect toFIGS.4-6.

In some embodiments, inlet brine stream (i.e., organic solvent brine stream)238may comprise entirely of an organic solvent. In some embodiments, inlet brine stream238may include a mixture of water and an organic solvent. While the organic solvent has a low salt solubility and high vapor pressure with respect to water, which may allow for a positive concentration gradient between influent stream236and inlet brine stream238, including some water in inlet brine stream238comes with benefits as well. In particular, anhydrous alcohols tend to quickly hydrate themselves, so a purely organic solvent as inlet brine stream238is impractical. If this were the case, water from influent stream236would osmote or transfer across the ion-exchange membranes of electrodialysis device200and into inlet brine stream238. Further, the presence of water in inlet brine stream238reduces the osmotic pressure observed by the ion-exchange membranes. A high osmotic pressure will exist when there is a great difference in water concentrations between influent stream236and inlet brine stream238. By including some water in inlet brine stream238, the difference in water concentration between influent stream236and inlet brine stream238is decreased as well as the osmotic pressure in the ion-exchange membranes located between influent stream236and inlet brine stream238.

FIG.3shows electrodialysis device300for separating dissolved ions from an influent/feed stream using an organic solvent brine stream. The pH of the influent feed stream of electrodialysis device300is controlled. In some embodiments, pH control can help control the transfer of specific dissolved species. Electrodialysis device300can include a pair of electrodes302, an electrolyte stream312, a plurality of CEMs304, a plurality of AEMs306, influent stream336, inlet brine stream338, output product stream310, and output brine stream308.

In some embodiments, the presence of boron in influent stream336and in the solids produced by precipitation may be undesirable. In particular, this can be the case in the treatment of lithium brines mined for producing lithium carbonate for lithium ion batteries. By lowering the pH of influent stream336, most of the boron will remain in boric acid form, which is unaffected by the ionic current in electrodialysis device300. While other methods of lithium recovery require boron concentration and separation in at least two separate steps, electrodialysis device300can concentrate and separate boron in a single step. In some embodiments, electrodialysis device300is designed to remove dissolved species such as lithium carbonate, lithium hydroxide, and co-precipitates from electrodialysis device300prior to precipitation or crystal formation.

In some embodiments, influent stream336may comprise boron and/or boric acid. In aqueous solution, boron typically exists as boric acid (H3BO3). However, boric acid readily dissociates into ions according to the equation below, having a pKa of 9.23:
H3BO3↔H++BO2−+H2O;pKa=9.23

Thus, if the pH of the aqueous solution is controlled to a level below 9.23, boric acid less readily dissociates. As the pH of aqueous solution decreases, so too does the number of dissociated ions. Accordingly, influent stream336of electrodialysis device300may be controlled to a pH lower than 9.23 to limit the rate of boric acid dissociation.

When the pH of influent stream336is controlled to a level below 9.23, boron has a tendency to remain in boric acid form. At a higher pH (i.e., 9.23 or higher), boric acid has a tendency to dissociate into ions according to the equation provided above. Because the pKa of the equation is 9.23, boric acid tends to resist dissociation more as the pH decreases. Acids such as sulfuric acid, hydrochloric acid, or citric acid may be used to control the pH. In some embodiments, influent stream336may be controlled to a pH of less than 9, less than 8.5, less than 8, less than 7.5, or less than 7.

As shown in the Figure, influent stream336comprises dissolved species such as sodium ions, lithium ions, boric acid, sulfate, and chlorine ions. So long as the pH of influent stream336remains below 9.23, the boron should remain in boric acid form. However, the lower the pH, generally the better. Because boric acid is non-ionic, it will not migrate across a membrane, and will instead stay within the channel between the CEM304and the AEM306that it is routed to. Thus, the boric acid of influent stream336will pass through electrodialysis device300without migration across any membranes, and will exit electrodialysis device300with output product stream310. Conversely, the dissolved ions in influent stream336—sodium ions, lithium ions, sulfate, and chlorine ions—will migrate across at least one membrane and towards the electrode of opposite charge. Thus, the sulfate and chlorine ions, both of which are negatively-charged, will migrate across the adjacent anion-exchange membrane306and towards electrode302having a positive charge. Similarly, the lithium and sodium ions, both of which are positively-charged, will migrate across the adjacent cation-exchange membrane304and towards electrode302of negative charge. Only boric acid (and any other non-ionic species) will remain in the influent stream336and exit electrodialysis device300with product stream310. The ionic species that have migrated across an ion-exchange membrane will exit electrodialysis device in output brine stream308.

FIG.4shows a process flow diagram for separating and precipitating dissolved salts from a feed stream using an organic solvent brine stream. As shown,FIG.4includes electrodialysis device400, precipitation tank450, and screw conveyer460. The stream in the process include influent stream436, inlet brine stream438, outlet product stream410, and outlet brine stream408.

As shown, the process ofFIG.4includes a single electrodialysis device400. However, electrodialysis processes according to embodiments provided herein may comprise any number of electrodialysis devices from one to ten. Additionally, a single precipitation tank450is shown inFIG.4. However, the number of precipitation tanks in electrodialysis processes according to embodiments provided herein may increase as the number of electrodialysis devices increases.

Influent stream436comprises an amount of dissolved salts that are to be separated from influent stream436and into inlet brine stream438as the two streams pass through electrodialysis device400. The salt concentration of outlet product stream410is less than that of influent stream436. In some embodiments, the salt concentration of outlet product stream410is wt. %, 20-70 wt. %, 30-60 wt. %, or 50-80 wt. % of the salt concentration of influent stream436. In some embodiments, the salt concentration of outlet product stream410is 50-80 wt. % of the salt concentration of influent stream436. In some embodiments, the salt concentration of outlet product stream410is less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, less than 30 wt. %, or less than 20 wt. % of the salt concentration of influent stream436. In some embodiments, the salt concentration of outlet product stream410is greater than 10 wt. %, greater than 20 wt. %, greater than 30 wt. %, greater than 40 wt. %, greater than 50 wt. %, greater than 60 wt. %, or greater than 70 wt. %.

Outlet brine stream408comprises a greater concentration of dissolved salts than that of inlet brine stream438. Specifically, outlet brine stream408comprises dissolved salts that have been transferred from influent stream436to the brine stream as the streams pass through electrodialysis device400. In some embodiments, the salt concentration of inlet brine stream is less than that of outlet brine stream408. In some embodiments, the salt concentration of inlet brine stream438may be 20-80 wt. %, 30-70 wt. %, 30-60 wt. %, or 40-50 wt. % that of outlet brine stream408. In some embodiments, the salt concentration of inlet brine stream may be less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, or less than 30 wt. % that of outlet brine stream408. In some embodiments, the salt concentration of inlet brine stream may be more than 20 wt. %, more than 30 wt. %, more than 40 wt. %, more than 50 wt. %, more than 60 wt. %, or more than 70 wt. % that of outlet brine stream408.

In some embodiments, the salt concentration of outlet brine stream408is less than that of product stream410. In some embodiments, outlet brine stream408may be super saturated with dissolved salts. In some embodiments, the salt concentration of outlet brine stream408is 20-80 wt. %, 30-70 wt. %, or 40-60 wt. % that of product stream410. In some embodiments, the salt concentration of outlet brine stream408is less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, or less than 30 wt. % that of product stream410. In some embodiments, the salt concentration of outlet brine stream is more than 20 wt. %, more than 30 wt. %, more than 40 wt. %, more than 50 wt. %, more than 60 wt. %, or more than 70 wt. % that of product stream410.

The separation process ofFIG.4includes precipitation tank450and screw conveyor460. Outlet brine stream408is fed to precipitation tank450, where the dissolved salts of brine stream408are allowed to precipitate out of solution. In some embodiments, inlet brine stream438(i.e., inlet brine stream for electrodialysis device400) may comprise supernatant454, which is generated in precipitation tank450when the dissolved salts are separated from solution and form solid crystals456. Solid crystals456may be removed from precipitation tank450using screw conveyor460.

In some embodiments, outlet brine stream408may be introduced to precipitation tank450at a location that is vertically at or below the top surface of solid crystals456. By depositing outlet brine stream408at or below the top surface of solid crystals456, the stream is exposed to a high surface area (i.e., the high surface area generated by solid crystals456). A high surface area can promote nucleation of crystals, thus increasing the efficiency of precipitation. Additionally, the density of the saturated solution will cause a gradient to form within precipitation tank450, with the most dilute solution near the top of the fluid column. In some embodiments, baffles or packing may be included to help with the settling of the crystals they form throughout the height of the column.

FIG.5also shows a process flow diagram for separating and precipitating dissolved salts from a feed stream using an organic solvent brine stream. As shown,FIG.5includes electrodialysis device500, precipitation tank550, screw conveyer560, and valve558. The streams in the process include influent stream536, inlet brine stream538, outlet product stream510, and outlet brine stream508.

As shown, the process ofFIG.5includes a single electrodialysis device500. However, electrodialysis processes according to embodiments provided herein may comprise any number of electrodialysis devices from one to ten. Additionally, a single precipitation tank550is shown inFIG.5. However, the number of precipitation tanks in electrodialysis processes according to embodiments provided herein may increase as the number of electrodialysis devices increases.

Influent stream536comprises an amount of dissolved salts that are to be separated from influent stream536and into inlet brine stream538as the two streams pass through electrodialysis device500. The salt concentration of outlet product stream510is less than that of influent stream536. In some embodiments, the salt concentration of outlet product stream510is wt. %, 20-70 wt. %, 30-60 wt. %, or 50-80 wt. % of the salt concentration of influent stream536. In some embodiments, the salt concentration of outlet product stream510is 50-80 wt. % of the salt concentration of influent stream536. In some embodiments, the salt concentration of outlet product stream510is less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, less than 30 wt. %, or less than 20 wt. % of the salt concentration of influent stream536. In some embodiments, the salt concentration of outlet product stream510is greater than 10 wt. %, greater than 20 wt. %, greater than 30 wt. %, greater than 40 wt. %, greater than 50 wt. %, greater than 60 wt. %, or greater than 70 wt. %.

Outlet brine stream508comprises a greater concentration of dissolved salts than that of inlet brine stream538. Specifically, outlet brine stream508comprises dissolved salts that have been transferred from influent stream536to the brine stream as the streams pass through electrodialysis device500. In some embodiments, the salt concentration of inlet brine stream is less than that of outlet brine stream508. In some embodiments, the salt concentration of inlet brine stream538may be 20-80 wt. %, 30-70 wt. %, 30-60 wt. %, or 40-50 wt. % that of outlet brine stream508. In some embodiments, the salt concentration of inlet brine stream may be less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, or less than 30 wt. % that of outlet brine stream508. In some embodiments, the salt concentration of inlet brine stream may be more than 20 wt. %, more than 30 wt. %, more than 40 wt. %, more than 50 wt. %, more than 60 wt. %, or more than 70 wt. % that of outlet brine stream508.

In some embodiments, the salt concentration of outlet brine stream508is less than that of product stream510. In some embodiments, outlet brine stream508may be super saturated with dissolved salts. In some embodiments, the salt concentration of outlet brine stream508is 20-80 wt. %, 30-70 wt. %, or 40-60 wt. % that of product stream510. In some embodiments, the salt concentration of outlet brine stream508is less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, or less than 30 wt. % that of product stream510. In some embodiments, the salt concentration of outlet brine stream is more than 20 wt. %, more than 30 wt. %, more than 40 wt. %, more than 50 wt. %, more than 60 wt. %, or more than 70 wt. % that of product stream510.

The separation process ofFIG.5includes precipitation tank550, screw conveyor560, and valve558. Outlet brine stream508is fed to precipitation tank550, where the dissolved salts of brine stream508are allowed to precipitate out of solution. In some embodiments, inlet brine stream538(i.e., inlet brine stream for electrodialysis device500) may comprise supernatant554, which is generated in precipitation tank550when the dissolved salts are separated from solution and form solid crystals556. Solid crystals556may be removed from precipitation tank550using screw conveyor560.

In some embodiments, the super saturated solution of outlet brine stream508is flashed by valve558above the fluid line of supernatant554in the headspace of precipitation tank550. Flashing off at least a portion of the solution as vapor in this way can increase the salt concentration in the liquid phase of the solution by reducing the amount of organic solvent in the solution (i.e., outlet brine stream508). This flashing process will further saturate the solution and can accelerate crystallization/precipitation of salts. The majority of liquid in precipitation tank550may remain at saturation concentration after the super saturated salt precipitates.

Once flashed off, the vapor phase may be condensed by a coil or heat exchanger in the headspace of precipitation tank550to form condensed solvent stream512. In some embodiments, the effluent of electrodialysis device500may be preheated by the condensation of the vapor on the coil prior to passing through valve558. Condensed solvent stream512may be substantially free of dissolved salts, allowing it to be used to dilute inlet brine stream538of electrodialysis device500. Thus, in some embodiments, inlet brine stream538comprises condensed solvent stream512. This dilution of condensed solvent stream512can also help ensure a minimum salt concentration in inlet brine stream538. The amount of dilution of condensed solvent stream512depends on the fraction of vapor partitioned by flash valve558.

In some embodiments, outlet brine stream508may be heated and/or pumped prior to reaching flash valve558. Heating and/or pumping may increase the amount of vapor formed during the flash evaporation step.

FIG.6also shows a process flow diagram for separating and precipitating dissolved salts from a feed stream using an organic solvent brine stream. Specifically, the process ofFIG.6includes a solvent recovery step that can help replenish solvent that may become diluted over time. For example, dilution of the solvent (e.g., the composition of inlet brine stream638), can occur by osmosis and electro-osmosis across the membranes of electrodialysis device600. (Osmosis in electrodialysis device600may occur due to a gradient in water concentrations and, and electro-osmosis may occur due to solvation shells that accompany transferred ions.) This is described in more detail below. As shown,FIG.6includes electrodialysis device600, precipitation tank650, screw conveyer660, and valve658. The streams in the process include influent stream636, inlet brine stream638, outlet product stream610, and outlet brine stream608, as well as outlet supernatant stream640, flash condensate stream612, high boiling point solvent680, vapor stream672, and condensed solvent recovery stream678.

As shown, the process ofFIG.6includes a single electrodialysis device600. However, electrodialysis processes according to embodiments provided herein may comprise any number of electrodialysis devices from one to ten. Additionally, a single precipitation tank650is shown inFIG.6. However, the number of precipitation tanks in electrodialysis processes according to embodiments provided herein may increase as the number of electrodialysis devices increases.

Influent stream636comprises an amount of dissolved salts that are to be separated from influent stream636and into inlet brine stream638as the two streams pass through electrodialysis device600. The salt concentration of outlet product stream610is less than that of influent stream636. In some embodiments, the salt concentration of outlet product stream610is wt. %, 20-70 wt. %, 30-60 wt. %, or 50-80 wt. % of the salt concentration of influent stream636. In some embodiments, the salt concentration of outlet product stream610is 50-80 wt. % of the salt concentration of influent stream636. In some embodiments, the salt concentration of outlet product stream610is less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, less than 30 wt. %, or less than 20 wt. % of the salt concentration of influent stream636. In some embodiments, the salt concentration of outlet product stream610is greater than 10 wt. %, greater than 20 wt. %, greater than 30 wt. %, greater than 40 wt. %, greater than 50 wt. %, greater than 60 wt. %, or greater than 70 wt. %.

Outlet brine stream608comprises a greater concentration of dissolved salts than that of inlet brine stream638. Specifically, outlet brine stream608comprises dissolved salts that have been transferred from influent stream636to the brine stream as the streams pass through electrodialysis device600. In some embodiments, the salt concentration of inlet brine stream is less than that of outlet brine stream608. In some embodiments, the salt concentration of inlet brine stream638may be 20-80 wt. %, 30-70 wt. %, 30-60 wt. %, or 40-50 wt. % that of outlet brine stream608. In some embodiments, the salt concentration of inlet brine stream may be less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, or less than 30 wt. % that of outlet brine stream608. In some embodiments, the salt concentration of inlet brine stream may be more than 20 wt. %, more than 30 wt. %, more than 40 wt. %, more than 50 wt. %, more than 60 wt. %, or more than 70 wt. % that of outlet brine stream608.

In some embodiments, the salt concentration of outlet brine stream608is less than that of product stream610. In some embodiments, outlet brine stream608may be super saturated with dissolved salts. In some embodiments, the salt concentration of outlet brine stream508is 20-80 wt. %, 30-70 wt. %, or 40-60 wt. % that of product stream610. In some embodiments, the salt concentration of outlet brine stream508is less than 80 wt. %, less than 70 wt. %, less than 60 wt. %, less than 50 wt. %, less than 40 wt. %, or less than 30 wt. % that of product stream610. In some embodiments, the salt concentration of outlet brine stream is more than 20 wt. %, more than 30 wt. %, more than 40 wt. %, more than 50 wt. %, more than 60 wt. %, or more than 70 wt. % that of product stream610.

As explained above, dilution of the organic solvent may occur over time due to osmosis and electro-osmosis. Dilution of the organic solvent can increase the solubility of salts in solution. In some embodiments, an increase in salt solubility in the organic solvent may be undesirable. Thus, to maintain a relatively lower solubility in the organic solvent composition, it may be necessary to recover the solvent using a thermal process, for example. As shown inFIG.6, the solvent is recovered using a forced recirculation process. Flash condensate stream612is fed from the headspace of precipitation tank650to distillation column670of the forced recirculation process. Distillation column670generates vapor stream672that comprises a higher concentration of low boiling point organic solvent than does flash condensate stream612. Vapor stream672may be condensed via condenser676to generate condensed solvent recovery stream678, which may then be returned to electrodialysis device600to enrich the organic solvent brine stream and dilute the dissolved salt in the brine stream. In some embodiments, inlet brine stream638may comprised condensed solvent recovery stream678.

The bottoms, or high boiling point solvent680, produced by distillation column670, may be further processed to recover water. This recovery process may be conducted using additional distillation methods known to those skilled in the art. The recovered water may also be used as fuel for thermal processes.

The preceding description sets forth exemplary methods, parameters and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is instead provided as a description of exemplary embodiments. The illustrative embodiments described above are not meant to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described to best explain the principles of the disclosed techniques and their practical applications. Others skilled in the art are thereby enabled to best utilize the techniques, and various embodiments with various modifications as are suited to the particular use contemplated.

Although the disclosure and examples have been thoroughly described with reference to the accompanying figures, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosure and examples as defined by the claims. In the preceding description of the disclosure and embodiments, reference is made to the accompanying drawings, in which are shown, by way of illustration, specific embodiments that can be practiced. It is to be understood that other embodiments and examples can be practiced, and changes can be made without departing from the scope of the present disclosure.

Although the preceding description uses terms first, second, etc. to describe various elements, these elements should not be limited by the terms. These terms are only used to distinguish one element from another.

The term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in response to detecting,” depending on the context.