Hi everyone, I know you guys enjoy the technical details so I’ve added a short rundown:

Heimdal is opening its first pilot facility in Kohala, HI in partnership with a solar powered desalination facility, Terraformation. Utilizing spent brine from active desalination plants allows us to synergistically leverage existing infrastructure, however our technology is equally viable in an independent setting. In our process, brine undergoes bipolar membrane electrodialysis (BPMED) to produce NaOH (aq), H2(g), O2(g), and HCl (aq). The hydroxide is distributed into the ocean for alkalinity. Byproducts can be sold as carbon neutral or negative commodities. Our process is filed with the US PTO and the UK Patent Office.

The Heimdal system runs entirely on renewable energy so there are next to no carbon costs of power. We expect our pilot facility in Kohala, HI to generate 100kg/day of sodium hydroxide (8% NaOH, 1250 L/day).
Bipolar Membrane Electrodialysis (BPMED) produces an acid and base from a neutral salt feed stream using an electric potential and selective ion membranes. Equation 1 shows the overall reaction of BPMED using purified seawater.

𝐍𝐚𝐂𝐥+𝐇𝟐𝐎 →𝐇𝐂𝐥+𝐍𝐚𝐎𝐇 Equation 1

In our system, negatively charged membranes (Cation Exchange Membrane (CEM)) facilitate the flow of sodium ions and positively charged Anion Exchange Membranes (AEM) allow for chloride transport. Bipolar membranes (BPM) contain a catalyst sandwiched between a CEM and AEM. Water splitting occurs at the BPM junction where a catalyst assists in the reaction and ions are transported through the AEM or CEM. Ion flow through the system is also facilitated by an applied voltage which accelerates hydroxide flow toward the positively charged anode and proton flow towards negatively charged cathodes.

In the acid channel, H+ generated from BPM and Cl- transported across the AEM combine to form HCl. In the base channel, OH- ions and Na+ ions combine to form NaOH. The acid or base is recirculated through the system to maintain a steady pH and increase efficiency. Flow of NaOH around the anode and cathode aid in the production of H2 and O2 gas at the cathode and anode sites. The half reaction at the anode and cathode are displayed in Equation 2 and Equation 3.

𝟒 𝐎𝐇−→ 𝐎𝟐(𝐠)+𝟐𝐇𝟐𝐎+𝟒𝒆− Equation 2

𝟐 𝐇𝟐𝐎+𝟐 𝒆−→ 𝟐𝐇𝟐+𝟐 𝐎𝐇− Equation 3

The input of alkalinity will be monitored by pH and conductivity of the base feed as it enters the ocean. As the feed reacts with the ocean carbonate system, quantification of NaOH will be intangible. Based on Equation 1, HCl and NaOH are produced in a 1:1 fashion so the HCl produced and bottled on site can physically verify the amount of NaOH added to the ocean for alkalinity. We propose a mechanism for verification of alkalinity enhancement whereby a third party can physically verify the quantity of HCl produced and, by extension, the amount of atmospheric CO2 that must have been captured with the corresponding hydroxide.
Sodium hydroxide and magnesium hydroxide will be readily dissolved in surface seawater, but mineral carbonates will likely be stored in the deep ocean since dissolution is unfavorable in surface waters. Ultimately these minerals will uptake CO2, but this proposal focuses on hydroxide as a catalyst for direct air capture of carbon dioxide. The stoichiometry of CO2 uptake is described by:

𝐍𝐚𝐎𝐇+𝐂𝐎𝟐 ⇋𝐍𝐚++𝐇𝐂𝐎𝟑− Equation 4

𝐌𝐠(𝐎𝐇)𝟐+𝟐𝐂𝐎𝟐 ⇋𝐌𝐠𝟐++𝟐𝐇𝐂𝐎𝟑− Equation 5

𝐂𝐚𝐂𝐎𝟑+𝐂𝐎𝟐+𝐇𝟐𝐎 ⇋𝐂𝐚𝟐++𝟐𝐇𝐂𝐎𝟑− Equation 6

If we produce 100 kg/day (0.1 t/day) NaOH, we will have 2.5 kmol/day.

𝟏𝟎𝟎 𝐤𝐠 𝐍𝐚𝐎𝐇𝐝𝐚𝐲≈𝟐.𝟓𝐤𝐦𝐨𝐥 𝐍𝐚𝐎𝐇𝐝𝐚𝐲 Equation 7

Assuming a 1:1 reaction with CO2:OH- estimates a maximum of 110 kg/day (~0.11 t/day) CO2 uptake.

𝟐.𝟓𝐤𝐦𝐨𝐥 𝐂𝐎𝟐𝐝𝐚𝐲𝐂𝐎𝟐≈𝟏𝟏𝟎𝐤𝐠 𝐂𝐎𝟐𝐝𝐚𝐲 Equation 8

Hydroxide in seawater will ultimately result in a decrease in free protons and uptake in CO2 since it is a strong base. Nevertheless, it is unlikely that system occurs at 100% efficiency, so these numbers are the upper limit for CO2 capture in the current proposal. We assume a modest 90% efficiency to account for natural ocean-mixing effects.

𝟎.𝟗∗𝟐.𝟓𝐤𝐦𝐨𝐥 𝐎𝐇−𝐝𝐚𝐲=𝟐.𝟐𝟓 𝐤𝐦𝐨𝐥 𝐂𝐎𝟐𝐝𝐚𝐲≈ 𝟗𝟗𝐤𝐠 𝐂𝐎𝟐𝐝𝐚𝐲 Equation 9

Based on 365 operating days per year and 90% CO2 draw-down efficiency, we expect to capture 37 tCO2 in the first year. Although this is a fractional percentage of global emissions, it is a great start and expanding production can be done quicker than other DAC companies because we do not have to transport or store captured CO2.