Equatic is a Los Angeles-based startup that has developed an electrolytic process for atmospheric carbon dioxide (CO₂) removal that leverages the size and scale of the oceans. The process stabilizes CO₂ permanently in the form of dissolved bicarbonate ions (CO₃²⁻) in seawater, and in the form of solid mineral carbonates (CaCO₃ and MgCO₃). Equatic’s technology has the potential to combat climate change commercially and power the green economy by coupling carbon dioxide removal from the atmosphere with the generation of green hydrogen at the lowest costs.
Challenges: climate change and carbon removal
Since the early 1900s, carbon dioxide (CO₂) levels in the atmosphere have increased by 50% due to human activities. When fossil fuels (such as coal, oil, and natural gas) are burned for energy production, transportation, and industrial processes, CO₂ is released into the atmosphere. This excess CO₂ acts as a greenhouse gas, trapping heat and causing the air and ocean temperatures to rise. CO₂ emissions play a crucial role in driving climate change.
The Paris Agreement aims to limit global warming to well below 2 ºC above pre-industrial levels. The average global temperature has already risen by between 0.8 ºC and 1.2 ºC. The Intergovernmental Panel on Climate Change (IPCC) estimates that a “carbon budget” of about 500 GtCO₂, which corresponds to about ten years at current emission rates, provides a 66% chance of limiting global warming to 1.5 ºC.
Ocean carbon sequestration
The oceans cover more than 70% of the earth’s surface. They store a lot of CO₂. At its current average pH of 8.1, seawater contains 150 times more CO₂ than an equal volume of the air. The seawater captures atmospheric CO₂ and lock it in the form of ions (HCO₃⁻ and CO₃²⁻) and solid precipitates (CaCO₃ and MgCO₃) according to the following reversible chemical reactions:
CO₂ + H₂O ⇆ H₂CO₃
H₂CO₃ ⇆ H⁺ + HCO₃⁻
HCO₃⁻ ⇆ H⁺ + CO₃²⁻
CO₃²⁻ + Ca²⁺ ⇆ CaCO₃↓
CO₃²⁻ + Mg²⁺ ⇆ MgCO₃↓
The ocean is the largest carbon sink on the planet, absorbing about 40% of the CO₂ emitted by human activities. The oceans are an important buffer in climate change.
As the atmospheric CO₂ concentration rises, the ocean absorbs more CO₂. As the oceans absorb more CO₂ than they can handle, it could lead to several potential consequences, such as ocean acidification and its negative impacts on marine life and ecosystems.
Ocean Alkalinity Enhancement is one of the important Negative emissions technologies (NETs) to accelerate this natural ocean carbon capture process. NETs are important because they can help companies, sectors, or countries remove more CO₂ from the atmosphere than they emit. According to climate models, a significant deployment of NETs will be needed to prevent catastrophic ocean acidification and global warming beyond 1.5 ºC.
Ocean Alkalinity Enhancement involves the addition of alkaline substances, such as NaOH, to seawater to enhance the ocean’s natural carbon sink and helps to deacidify the ocean. The process transforms dissolved CO₂ into bicarbonate ions (HCO₃⁻) at a high pH according to the chemical reaction:
CO₂ + OH⁻ → HCO₃⁻
Ebb Carbon company has developed an Ocean Alkalinity Enhancement system that uses renewable energy and an electrodialysis stack to produce NaOH base solution. The base solution is safely added to the seawater and increases the local pH to create a natural chemical reaction that removes CO₂ from the air.
Equatic has developed a transformative electrolytic method for CO₂ removal that leverages the high concentration of CO₂ in seawater and the enormous abundance of Ca²⁺ and Mg²⁺ cations. The in-situ alkalization of seawater in electrolytic flow reactors forces CO₂ mineralization via reactions between dissolved CO₂ and Ca²⁺ and Mg²⁺ to permanently lock CO₂ as stable carbonate solids and/or as aqueous bicarbonates. The process also produces green hydrogen (H₂) that can be used to fuel the process during intermittency or sold to generate revenue.
Equatic carbon removal system
The diagram below depicts the carbon removal system with the electrolytic flow reactor.
The system comprises a rotary vacuum membrane drum, a vacuum pump, an electrolyzer, a heating element, and carbon disposal tank. The system is powered by renewable energy sources, such as wind turbines and solar panels.
The membrane drum comprises a metallic mesh membrane as a filtration medium surrounding a central rod. The metallic mesh membrane and central rod function as the cathode and anode of the electrolyzer, respectively, to electrochemically produce sodium hydroxide (NaOH) base and hydrogen gas from seawater. The hydroxide ions (OH⁻) precipitate carbonates from seawater, while hydrogen is used as a green fuel.
The mesh cathode is a hybrid of metallic and carbon-based materials. The metallic material is low-cost 316L stainless steel mesh or perforated sheet with a topical sintered-titanium film (Magneli-phase sintered Ti₄O₇ materials). The stainless steel mesh and sintered plates have pore sizes of 37 μm (400 mesh) and 1 μm, respectively. The carbon nanotube-based membrane is formed by air-brushing a percolating network of carbon nanotubes onto a porous polymeric support and then cross-linking with polyvinyl alcohol (PVA).
The hybrid cathode has a high conductivity and stability in seawater, particularly under anodic conditions that may be periodically needed to clean the mesh which can corrode Fe-based materials.
The anode rod is a MnO₂-coated titanium (Ti) rod.
The membrane drum rotates in the CO₂-rich and Ca-/Mg-containing seawater within a tank. A vacuum pump connected to the central duct draws the liquid onto and through the membrane surface, where the OH⁻ ions are produced and Ca²⁺ and Mg²⁺ precipitate with CO₃²⁻ as carbonates at a high pH. The heating of the seawater via a heating element assists the precipitation of carbonates. The Ca-/Mg-poor filtrate flows to the interior of the membrane drum and returns to the ocean. H₂ is generated during the CO₂ mineralization process. Each ton of CO₂ that is mineralized would generate 45 kg of low-pressure H₂, which can be used as a green fuel.
The carbonate solids adhere to the outside of the membrane drum, which then passes a knife. The knife removes the solids from the membrane, thereby regenerating the membrane surface for subsequent carbonation as the drum rotates back into the liquid. The carbonates can be thrown back into the ocean, where they can settle on the seafloor and remain in solid form for tens of thousands of years.
How does Equatic technology work?
The diagram below depicts the working mechanism of the electrolytic flow reactor.
Seawater flows through a rotary vacuum membrane drum as described above. The electrode reactions occur as follows:
- Oxygen evolution reaction (OER) at the anode:
2H₂O → O₂↑ + 4H⁺ + 4e⁻
The evolution of chloride gas (Cl₂) at the anode caused by electrolysis of seawater can be inhibited by coating the Ti rod with MnO₂, an oxygen-selective material with 95-100% efficiency of OER.
- Oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) at the cathode:
O₂ + 2H₂O + 4e⁻ → 4OH⁻
2H₂O +2e⁻ → H₂↑ + 2OH⁻
A significant advantage of mineralization using electroactive membranes for the localized generation of alkalinity is that it enhances the kinetics of precipitation as a result of the elevated pH > 10 and supersaturation, as well as the rise in membrane surface temperature. The CO₂ mineralization occurs according to the chemical reactions:
Ca²⁺ + CO₂ + 2OH⁻ → CaCO₃↓ + H₂O
Mg²⁺ + CO₂ + 2OH⁻ → MgCO₃↓ + H₂O
Energy requirement of Equatic carbon removal system
The energy requirements of Equatic carbon removal system are primarily associated with water electrolysis. Modern electrolyzers operating at 79% efficiency consume 50 kWh of electricity to produce 1 kg of H₂ and 1,000 moles of OH⁻ ions, which can mineralize 22 kg of CO₂. This results in an energy intensity of 2.3 MWh per ton CO₂. If the produced low-pressure hydrogen is converted into electricity using a hydrogen fuel cell (HFC) with a conversion efficiency of about 80% for the process during intermittency, this results in an overall energy intensity of 0.84 MWh per tonne of CO₂ mineralized.
The cost of Equatic carbon removal
It is estimated that Equatic’s system yields $145 per ton of CO₂ mineralized (i.e., including CapEx and OpEx, while applying a capital recovery factor to the CapEx component), assuming no cost offset from the sale of H₂(g). However, if the produced green hydrogen was sold in commercial markets in its low-cost low-pressure form, this results in $55 per tonne of CO₂ mineralized (H₂ = $2 per kg) or $10 per tonne of CO₂ mineralized (H₂ = $3 per kg).
Advantages of Equatic carbon removal
In addition to the low energy requirement and low cost of carbon removal, Equatic’s carbon removal system have several other benefits:
- It is more efficient than the vast majority of other Direct Air Capture (DAC) methods;
- It allows straightforward use of low-carbon/zero electricity;
- It ensures end-to-end CO₂ abatement;
- The electrolytic reactor can be simply modularly integrated with existing desalination facilities, thereby allowing CO₂-removal and sequestration while producing potable water; and
- Hydrogen is a useful byproduct and can be used as a green fuel.
- US11413578B2 Alkaline cation enrichment and water electrolysis to provide CO2 mineralization and global-scale carbon management
Carbon offset credit market
The market value of carbon offset credits varies widely. In current carbon markets, the price of one carbon credit can range from a few cents per metric ton of CO₂ emissions to $15/mtCO₂e (metric tons of CO₂ equivalent) or even $20/mtCO₂e. However, the voluntary carbon offset market, which was worth about $2 billion in 2021, is projected to grow to $10-40 billion by 2030, transacting 0.5-1.5 billion tons of CO₂ equivalent, as opposed to the current 500 million tons. The total value of carbon credits produced and sold to help companies and individuals meet their de-carbonization goals could approach $1 trillion as soon as 2037.
Equatic can generate revenue by selling carbon offset credits to corporate buyers. The company operates a small pilot facility in Los Angeles to prove their technology, as shown in the picture below.
This pilot facility can remove 100 kg of CO₂ and produce a few kilograms of H₂ daily. In 2024, a larger test plant will be integrated into a desalination facility in Singapore. This large plant will remove at least 3,500 tons of CO₂ per year, or 10 tons per day.
By the late 2020s, Equatic aims to operate large commercial-scale plants capable of removing 1 million metric tons of CO₂ and making 35,000 metric tons of hydrogen annually.
Equatic has raised a total of $1M in funding over one round. This was a Grant round raised on Apr 12, 2023.
Equatic is funded by ARPA-E.
Gaurav N. Sant is Founder.
Gaurav N. Sant is CEO.