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EP-4452869-B1 - METHOD FOR ELECTROCHEMICAL OCEAN ALKALINITY ENHANCEMENT

EP4452869B1EP 4452869 B1EP4452869 B1EP 4452869B1EP-4452869-B1

Inventors

  • EISAMAN, Matthew

Dates

Publication Date
20260513
Application Date
20221222

Claims (15)

  1. A method for enhancing alkalinity comprising: (i) providing a bipolar membrane electrodialysis device (BPMED) which comprises electrodes and at least one unit comprised of a brine compartment, an acid compartment, and a base compartment; (ii) flowing an aqueous brine solution through the base compartment at a first volumetric flow rate (fba) and through the brine compartment at a second volumetric flow rate (fbr), the aqueous brine solution comprising at least one divalent cation that precipitates out of the aqueous brine solution to form a solid precipitate when the aqueous brine solution is at or above a precipitating pH; (iii) applying a voltage between the electrodes at a current density to the BPMED device to form, in the base compartment, an enhanced alkaline brine product that has a pH higher than the pH of the brine but below the precipitating pH; (iv) maintaining, at the current density, the first volumetric flow rate through the base compartment at a rate sufficiently greater than the second volumetric flow rate through the brine compartment so as to keep the pH of the enhanced alkaline brine product formed in the base compartment below the precipitating pH; and (v) outputting the enhanced alkaline brine product from the base compartment.
  2. The method of Claim 1 wherein the aqueous brine solution flowing to the base compartment and flowing to the brine compartment is from a brine source, which brine source is the same or a different source for each of base compartment and the brine compartment individually.
  3. The method of Claim 2 wherein the aqueous brine solution is flowed directly from the brine source to the base compartment, flowed directly to the brine compartment, or flowed directly to both.
  4. The method of Claim 1 wherein the aqueous brine solution comprises seawater, reverse osmosis concentrate brine, or both.
  5. The method of Claim 2 wherein the brine source is a natural body of seawater or a mined salt dissolved to make an aqueous brine solution.
  6. The method of Claim 1 wherein the divalent cation is selected from the divalent cation of calcium (Ca), magnesium (Mg), or both; and the precipitate is selected from CaCO 3 , or Mg(OH) 2 , or both.
  7. The method of Claim 1 wherein the pH of the brine is about 6 to about 8.5; the precipitating pH is about 8.9 or above; and the pH of the enhanced alkaline brine product is about 8.5 to about 8.9.
  8. The method of Claim 1 wherein the first volumetric flow rate is greater than 1 to about 10 times greater than the second volumetric flow rate.
  9. The method of Claim 1 wherein least a portion of the enhanced alkaline brine product outputted from the base compartment is flowed into a body of seawater.
  10. The method of Claim 1 wherein a partially desalinated brine product is formed in and outputted from the brine compartment, and at least a portion of the desalinated brine product outputted from the brine compartment is combined with at least a portion of the enhanced alkaline brine product outputted from the base compartment.
  11. The method of Claim 1 wherein a partially desalinated brine product is formed in and outputted from the brine compartment, and at least a portion of the desalinated brine product outputted from the brine compartment is inputted to the base compartment.
  12. The method of Claim 10 wherein the combination of the partially desalinated brine product and the enhanced alkaline brine product are flowed into a body of seawater.
  13. The method of Claim 10 wherein the desalinated brine product outputted from the brine compartment has a pH of about 8.5 or lower; and the pH of the combined desalinated brine product and the enhanced alkaline brine product is about 8.1 to about 8.9.
  14. The method of Claim 1 wherein the brine compartment, the acid compartment, and the base compartment are included in a cell triplet and the BPMED comprises a plurality of cell triplets in series, and wherein the voltage applied across the electrodes is about 1V to about 4V per cell triplet, and the current density is about 5 mA/cm 2 to about 120 mA/cm 2 .
  15. The method of Claim 1 wherein an aqueous stream comprising a first concentration of HCl is flowed into the acid compartment, and an acidified product having a second concentration of HCl greater than the first concentration is formed in and outputted from the acid compartment, wherein the aqueous stream comprises a combination of at least a portion of the acidified product outputted from the acid compartment and a water feed, wherein the water feed comprises deionized water or brine, and wherein a first portion of the aqueous stream is recovered as an HCl product having an HCl concentration of about 0.1M to about 1M and a second portion of the aqueous stream is flowed into the acid compartment.

Description

FIELD The disclosure pertains to a method for alkalinity enhancement of a fluid such as brine, e.g. seawater, the result of which can be utilized for negative emission carbon removal, including returning the alkaline-enhanced brine to the ocean to enhance the ability of the ocean to remove carbon dioxide from the air and store it in dissolved ionic form (bicarbonate and carbonate) in the ocean. BACKGROUND Alkaline enhancement of fluids such as brine include electrochemical ocean alkalinity enhancement (OAE), which relates to the use of electrochemistry to generate alkalinity, which alkalinity, in this instance, is added to the ocean, resulting in the mitigation of ocean acidification and the safe continued absorption of atmospheric CO2 into the ocean as bicarbonate. Using the ocean to capture atmospheric CO2 is commonly referred to as ocean carbon dioxide removal, or ocean CDR. Typically, these electrochemical systems take in electricity and some brine stream (seawater, reverse osmosis concentrate, etc.) as input, the output being the constituent acid and base of the incoming salt, e.g., the NaCl in seawater is converted into HCl acid and NaOH base. Bipolar membrane electrodialysis (BPMED) is an electrochemical process that uses ion selective membranes between two end electrodes to generate HCl and NaOH from incoming NaCl-containing brine. If the resultant NaOH and seawater is returned to the ocean, this enhances the alkalinity of the ocean, mitigating ocean acidification and the increasing the ability of the ocean to remove CO2 from the atmosphere and store it safely in dissolved ionic form (bicarbonate and carbonate) in the ocean; the resulting HCl can be kept on land for other purposes, such as commercial sale or improving the reaction rate and storage capacity of CO2 mineralization reactors. Normally, the incoming brine streams to the BPMED, e.g., seawater or reverse osmosis concentrate, contain divalent cations of calcium (Ca++) and/or magnesium (Mg++). These divalent cations can form solid calcium and/or magnesium precipitates, such as CaCO3 and/or Mg(OH)2, as the pH increases. These precipitates can cause scaling on the BPMED membranes which in turn leads to higher energy consumption, shorter membrane lifetime, and often disruption of BPMED operation. Heretofore, the problem of scaling was addressed by removing these divalent cations prior to the BPMED, typically by pretreatments such as water softening treatment. However, these pretreatments are expensive and add to the complexity of operations. There is thus a need for method and system to enhance the alkalinity of fluids such as brine without necessitating the removal of these divalent cations from the input stream to a BPMED. A known method for protecting electrodialysis membranes and improving the efficiency/productivity of electrodialysis cells and stacks is disclosed in US 7,632,387 B1. The US patent application 2013/008792 A1 discloses a process for the separation of CO2 gas from seawater using bipolar membrane electrodialysis (BPMED). SUMMARY In one aspect, the disclosure is directed to a method for enhancing alkalinity comprising (i) providing a bipolar membrane electrodialysis device (BPMED) which comprises electrodes and at least one unit comprised of a brine compartment, an acid compartment, and a base compartment; (ii) flowing an aqueous brine solution through the base compartment at a first volumetric flow rate (fba) and through the brine compartment at a second volumetric flow rate (fbr), the aqueous brine solution comprising at least one divalent cation that precipitates out of the aqueous brine solution to form a solid precipitate when the aqueous brine solution is at or above a precipitating pH; (iii) applying a voltage between the electrodes at a current density to the BPMED device to form, in the base compartment, an enhanced alkaline brine product that has a pH higher than the pH of the brine but below the precipitating pH; (iv) maintaining, at the current density, the first volumetric flow rate through the base compartment at a rate sufficiently greater than the second volumetric flow rate through the brine compartment so as to keep the pH of the enhanced alkaline brine product formed in the base compartment below the precipitating pH; and (v) outputting the enhanced alkaline brine product from the base compartment. In another aspect, the method of the disclosure provide for electrochemical ocean alkalinity enhancement which produces "negative emission" carbon removal of very high quality at a reduced cost due to the avoidance of pretreatment to remove precipitating divalent cations. In one practice, the flow-through design of the method permits the ability to feed seawater, or other aqueous brine solutions such as reverse osmosis concentrate, directly into the brine and base compartments without the need for pretreatment and removal of divalent cations such as Ca++ and Mg++. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schema