By: Teun Schröders The American Sublime Systems, a spin-off from MIT (Massachusetts Institute of Technology), has developed a technology that allows it to make cement without releasing CO2 emissions. All processes are done at room temperature using electrolysis. The start-up has plans to scale up quickly. The production of cement, a main component of concrete, has a major impact on global CO2 emissions. More than 4 billion tons of the building material were produced in 2022, accounting for about 8 percent of the planet's total greenhouse gas emissions that year. These enormous emissions also make making production more sustainable an enormous opportunity. If we can make emission-free cement, the world will instantly become a lot greener. 'Cleanest cement' MIT also saw this opportunity. Scientists developed a technology that became part of the spin-off Sublime Systems. And that company now claims to be able to make 'the cleanest cement in the world'. This is possible because the company uses electrochemical processes that operate at room temperature, instead of ovens that operate on fossil fuels. In regular cement production, limestone is heated to approximately 1,400 °C by burning fossil fuels to produce pure lime. But limestone is about 50 percent carbon dioxide by weight. And when the furnace emits that CO2, it is difficult to capture because it is mixed with other flue gases. Electrolyser Sublime Systems takes a very different approach to this. The company uses a variant of the electrolyser; a technique with two electrodes (plus and minus) that can separate water into hydrogen and oxygen. Sublime's electrolyser also has two electrodes: one produces a solution that removes calcium from minerals, leaving behind a reactive silicate. The second electrode produces alkalinity, leaving reactive pure calcium (also known as lime). The reactive calcium and silicate are mixed together at low temperatures to make the final product: cement. Capturing CO2 According to Sublime Systems, this process can produce pure lime from very low-quality limestone; a raw material that is abundantly available in the world. CO2 remains a residual product in this process, but at least it comes out in a pure, cold state, compressed to 10 bar. This makes capture and storage relatively simple. Certificates have arrived Earlier this month, Sublime announced that their cement has received the correct certificates that support the quality of things such as strength, resistance and drying time. These certificates pave the way for actual application in American buildings. Scale up quickly The biggest challenge now is to make Sublime's cement price competitive with the current standard. The company expects this point to be reached in about 10 years. Sublime Systems is already able to produce 100 tons of their cement annually. By 2025, there should be a demonstration factory that can produce 25,000 tons. In the run-up to 2030, Sublime wants to be active worldwide and be able to produce one million tons of cement annually.