Travertine ($3M to sequester CO2 through mineral carbonation while producing useful products)

Travertine, an American cleantech company founded in 2022, develops integrated carbon removal technology that sequesters carbon dioxide (CO₂) through mineral carbonation while producing useful by-products like sulfuric acid, green hydrogen, phosphoric acid, and lithium. The company works with fertilizer producers to turn phosphogypsum waste into phosphoric acid, hydrogen, oxygen, and carbonate minerals. The company also partners with mining companies to produce carbon-negative sulfuric acid, which is used to extract critical elements such as lithium, nickel, and cobalt.

Challenges: carbon emissions and carbon removal

Carbon emissions

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.

This warming effect has caused the global average temperature to rise by about 1.1 ºC since the pre-industrial period. This has led to rising in the frequency and intensity of extreme weather events, melting of polar ice caps and glaciers and rising sea levels, shifts in species ranges and increased risk of species extinction, agriculture and food security,  and ocean acidification.

To mitigate these impacts, the Paris Agreement aims to limit global warming to well below 2 ºC above pre-industrial levels. 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.

Carbon removal technologies

Negative emissions technologies (NET) can help companies, sectors, or countries remove more CO₂ from the atmosphere than they emit. Examples of NETs include Direct Air Capture (DAC),  enhanced weathering, and Ocean Alkalinity Enhancement. According to climate models, a significant deployment of NETs will be needed to prevent catastrophic ocean acidification and global warming beyond 1.5 ºC.

Enhanced weathering of gypsum (CaSO₄·2H₂O) has been proposed for large-scale permanent mineral carbonation sequestration. Gypsum feedstocks are abundant in natural evaporite deposits and industrial phosphoric acid production byproducts. There are an estimated 700Mt of natural gypsum reserves in the United States. The global fertilizer industry produces between 100 and 280Mt phosphogypsum (PG) powder annually.

However, the lack of a sufficiently large and cost-effective source of alkalinity has prevented the mineral carbonation of gypsum on a large scale.The dissolution of gypsum releases calcium ions into solution, but the production of carbonate minerals still requires an alkalinity source. For industrial acid and base production, electrolysis methods have been developed, but they consume too much energy to be cost-competitive with conventional methods.

Travertine Technology

Travertine develops carbon removal technology that integrates an electrolyzer stack with mineral carbonization and mineral leaching to sequester CO₂ while producing valuable byproducts, such as phosphoric acid, hydrogen (H₂), and lithium.

In the cathode chamber, the water electrolyzer produces alkaline solution and hydrogen, and in the anode chamber, acid solution and oxygen. The alkaline solution acts as absorbent to capture CO₂ by forming carbonate ions (CO₃²⁻). By reacting with carbonate ions, calcium sulfate (CaSO₄) is converted to CaCO₃ precipitation, which can be disposed of underground for carbon sequestration.

The sulfate ions (SO₄²⁻) in the cathode chamber traverse the  anion exchange membrane (AEM) to reach the anode chamber, where they combine with protons to form sulfuric acid (H₂SO₄). Sulfuric acid can be used to leach fluorapatite or lithium claystone to produce valuable products of phosphoric acid for phosphate fertilizer or lithium for Li-ion batteries.

Travertine carbon removal system

The diagram depicts the Travertine carbon removal system, which sequesters CO₂ while producing sulfuric acid.