Sublime Systems ($40M to produce sustainable cements using renewable energy and electrolyzer)

Sublime Systems, an American cleantech company founded in 2020, uses electrolyzers to produce acid and base solutions to generate reactants of the pozzolanic reaction for the formation of Portland cement with significantly reduced CO₂ emission. The electrolyzers are powered by renewable electricity and operate near ambient temperature.

Challenges: cement emissions

The production of cement is a major source of carbon dioxide (CO₂) emissions, accounting for around 8% of global CO₂ emissions. This is because the production of cement involves a chemical reaction called calcination, in which limestone (CaCO₃) is heated to over 1400 ºC in a kiln to produce lime (CaO). This process releases carbon dioxide according to the following reaction:

CaCO₃ + heat → CaO + CO₂

Additionally, the cement production also requires large amounts of energy to heat the kiln and grind the raw materials into the fine powder that is used to make cement. The energy required for cement production comes mainly from burning fossil fuels such as coal, oil, and natural gas, which also releases CO₂ into the atmosphere.

It is estimated that 75% of the infrastructure that will exist in 2050 has not yet been built, which will lead to a massive increase in demand for cement, which necessitates new approaches to producing low-carbon cement.

Efforts are being made to reduce its environmental impact, including using alternative fuels, such as hydrogen (H₂), biomass, and waste materials, to replace fossil fuels, using low-carbon raw materials, such as industrial byproducts and recycled materials, in cement production, and developing new technologies to capture and store CO₂ emissions from cement plants.

Sublime Systems Technology

Sublime Systems develops a new approach to producing Portland cement with lower CO₂ emission. The approach uses electrolyzers, which are powered by renewable electricity and operate near ambient temperature, to produce acid and base solutions. The produced acid and base solutions can process various raw materials to generate reactants of the pozzolanic reaction for the formation of the Portland cement.

The pozzolanic reaction is a slow reaction that involves calcium hydroxide or slaked lime (Ca(OH)₂, also known as portlandite) and silicic acid (H₄SiO₄ or Si(OH)₄) or silica (SiO₂) to form a strong cementation matrix according to the following reaction:

Ca(OH)₂ + H₄SiO₄ → CaH₂SiO₄∙2H₂O

The pozzolanic reaction can also be written in an ancient industrial silicate notations as:

Ca(OH)₂ + SiO₂ → CaSiO₃∙H₂O

How Sublime Systems reduces CO2 for cement production

The diagram below depicts the structure and working mechanism of the Sublime Systems’s decarbonization reactor.

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