Sublime Cement says it is ready to start producing the "cleanest cement in the world" that meets industry performance standards, relying on room-temperature electrolyzers instead of cement kilns, using a variety of zero-carbon raw materials.
Conventional manufacturing processes produce one ton of carbon dioxide for every ton of cement produced. In 2022, global carbon emissions will be about 4.1 billion tons, and cement is a huge contributor to climate change, accounting for about 8% of global carbon emissions.
But there is also a huge opportunity: as the decarbonisation mandate and carbon tax come into force, companies that pioneer a cost-competitive, completely zero-carbon alternative to cement around the world will make a lot of money.
There is no shortage of low-carbon and carbon-capturing cement products, but Sublime Systems, a spin-out of MIT, is unique because it uses a novel electrochemical method to make cement. This is "true zero carbon" rather than "net zero carbon" or "carbon sequestration" – because it can completely eliminate two key points of carbon emissions that occur during traditional cement production.
Sublime's zero or ultra-low carbon cement production technology
heats limestone to around 1400 ° C in conventional cement production by burning fossil fuels, the first major source of emissions, to produce clinker . Limestone contains about 50% carbon dioxide by weight, and the carbon dioxide released by calcination is mixed with flue gas and is difficult to capture.
Sublime's method is completely different and is based on electrolysis. Company co-founders Leah Ellis, PhD, and Yet-Ming Jiang, PhD, explain this in detail in the Medium post, and the gist of the process is as follows:
Water decomposes at a near-neutral pH to produce hydrogen and oxygen, while also creating a pH gradient between the two electrodes. The calcium-containing mineral reacts with the acid formed at the anode to form dissolved calcium ions, which then migrate to the cathode. When they reach a pH of at least 12.5, they react with the alkali produced by the cathode to precipitate out as solid calcium hydroxide — also known as building lime or slaked lime.
Sublime's process uses room-temperature electrolysis to separate the necessary calcium
from a range of different input materials. The lime is a drop-in substitute for clinker that can be fed into conventional cement production. The founders say Sublime has improved the technology by making it more energy efficient, eliminating hydrogen production, separating oxygen and carbon dioxide streams, continuously extracting lime from the reactor, and producing it with off-the-shelf electrolysis equipment.
The process is very flexible and suitable for a variety of different raw materials. Even low-grade limestone can still be used effectively. While the process cannot completely avoid the production of carbon dioxide, it does at least ensure that the carbon dioxide comes out in a pure, cold state, making it easier to capture and store, and using much less energy and emitting much less than conventional cement production.
For true zero-carbon cement, the process can extract pure calcium from impurities in silica, magnesium, iron, or aluminum, for example, refining them into higher-grade materials in the process. Crucially, this all happens at room temperature, with no need for calcination or electrical heating.
Sublime claims it is "the only fossil-fuel-free, scalable, direct replacement for conventional concrete cement.".
Progress, Commercialization, Timeline and Pricing
When will Sublime begin to bring the "world's cleanest cement" to market, and how long will it take to scale up to a size that can actually make a difference to global carbon emissions?
"It may take another eight to ten years for the process to scale up and the technology to mature to a level comparable to traditional cement manufacturing," said Dr. Jesse Benck, vice president of research and development at Sublime. "To promote this technology, we need to achieve a cost comparable to the current cement production process. "We know the cement industry is very cost sensitive, so reducing costs to make the most impact is our goal."
"In the short term," he continued, "we are using a completely new approach and new technology that can compete with cement production that has been around for more than 100 years, and it is a large, global, mature industry. The reality is that in the short term, the cost of this new process is a little bit high, but at least for our first full-scale manufacturing plant, we expect the cost to be lower than cost of traditional cement production plus carbon capture.
The Sublime process produces zero-carbon lime
that currently costs about $130 per ton of cement, and the Harvard Belfer Center 2022 Policy Brief prices carbon capture in cement production at $19 to $205 per ton of CO2. As a result, Sublime's first clean cement product is likely to sell for 15-158% more than its competitors.
"Our plant can now produce 100 tons of cement per year," Benck said.
"We are now working to build a new demonstration plant with an annual capacity of about 25000 tons," he continued. "We aim to be operational by the end of 2025. After that, we plan to build our first full-scale, commercial-scale cement production facility with an annual output of approximately 1 million tons. Of course, the details are still being worked out, and the expected realization time is 2027-28. In addition, we hope to promote it globally after 2030.
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