Method for Electrochemical Ocean Alkalinity Enhancement

Background

As companies work to meet their net zero goals, the need for additional carbon offsets is presented. Ocean carbon dioxide (CO2) capture is a general technique used for decreasing CO2 levels in the atmosphere by using the ocean to capture atmospheric CO2. In order for this to occur, the ocean’s acidity must be mitigated through a process called electrochemical ocean alkalinity enhancement. This describes the use of electrochemistry to generate alkalinity to be added to the ocean, decreasing its pH and allowing for the safe absorption of CO2 into the ocean as bicarbonate. These electrochemical systems often take in electricity and brine streams as inputs and output the constituent acid and base of the incoming salt (e.g. NaCl in seawater is converted to HCl acid and NaOH base).

One way of doing this is with bipolar membrane electrodialysis, which 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 HCl is kept on land and the NaOH and seawater are returned to the ocean, the alkalinity of the ocean is enhanced, thus inducing the absorption of CO2 from the atmosphere.

A problem is presented in which the incoming brine streams often contain unwanted divalent cations like calcium or magnesium. They are typically removed via water softening pretreatment to avoid scaling of solid calcium and magnesium precipitate on the membranes, which leads to higher energy consumption and shorter membrane lifetime. However, this pretreatment is expensive.

Technology

Researchers at Stony Brook University (SBU) propose a technology that enables electrochemical ocean alkalinity enhancement without the need for pretreatment of incoming seawater. This system produces “negative emission” carbon offsets of very high quality at a highly reduced cost due to the avoidance of pretreatment.

Advantages

• Cheaper
• More energy efficient
• No need for expensive water-softening pretreatment

Application

• High quality carbon offsets
• Ocean acidification mitigation