03-24 Sublime Systems lime

[Image above] Carbon-neutral lime created using a new process developed by Massachusetts Institute of Technology researchers. The MIT researchers launched a company called Sublime Systems to commercialize the process. Credit: Sublime Systems


By Laurel Sheppard

It has been just over one year since the U.S. National Science Foundation announced the establishment of the Directorate for Technology, Innovation, and Partnerships (TIP).

The TIP directorate embodies the push in recent years for the federal government to take a larger role in supporting use-inspired research and its transition from the lab to the marketplace. It has already started to spin up smaller-scale initiatives alongside its flagship initiative, the Regional Innovation Engines program, and this work is expected to continue (albeit with lower-than-desired funding) based on the recently passed fiscal year 2023 budget.

Green technologies are a main area into which this use-inspired research funding is being channeled. If the U.S. is to uphold its commitment to the Paris Climate Agreement, industrial operations need to be decarbonized, be that through capturing emissions, implementing new processing methods, or using alternative fuels. (See the April 2023 Bulletin for articles on hydrogen fuel markets and industrial uses.)

Cement manufacturing accounts for a significant portion of industrial emissions. To create ordinary Portland cement, calcium carbonate (CaCO3, generally limestone) is ground and then cooked with sand and clay at high heat, produced by burning coal. The cooking process breaks CaCO3 down into calcium oxide (CaO) and CO2. The CaO is then reacted with silica (SiO2) to produce alite, the major mineral phase in Portland cement.

While the coal for heating could be replaced with other fuels, the CO2 emitted from breaking down CaCO3 cannot be overcome due to the fundamental nature of the material. However, there are different ways for processing CaCO3 that result in purer CO2, which makes it easier to reuse in other applications.

Researchers at the Massachusetts Institute of Technology (MIT), led by ACerS Fellow and Kyocera Professor of Materials Science and Engineering Yet-Ming Chiang and postdoctoral fellow Leah Ellis, are working on one such process.

The process, which we originally reported on CTT in 2019, is called ambient temperature electrochemical calcination. It uses electrolysis to reduce the CaCO3.

Not only is the need for fossil fuels removed, as calcium is extracted using low-cost electricity rather than heat, CO2 is released in a pure stream of O2/CO2 gas. The CO2 can be easily extracted from this stream, in contrast to the impure flue gas from traditional cement kilns that must undergo an expensive amine scrubbing process for usable CO2 to be secured.

Additionally, the researchers say that the process is naturally purifying, so impure inputs can be used, including low-grade limestones or noncarbonate calcium minerals that do not have embedded CO2.

“We can separate the calcium from common impurities such as silica, magnesium, iron, and aluminum since these components either don’t dissolve in acid or don’t precipitate at the same pH as calcium. … [So] Sublime’s process of making lime results in a pure lime almost no matter what the starting material, and other higher-value minerals, such as magnesium, can be isolated too,” they say in a Medium blog post.

In 2020, the MIT researchers established a start-up company called Sublime Systems to commercialize the process. Since then, they made several improvements to the process, including

  • More energy efficient,
  • Eliminated net production of H₂,
  • Allowed separation of CO₂ and O₂ gas streams,
  • Enabled continuous extraction of calcium oxide from the reactor, and
  • Used commercial off-the-shelf electrolyzer hardware.

In January 2023, Sublime Systems announced that it had closed a $40 million Series A funding round. The funding round was led by climate-tech focused fund Lowercarbon Capital with participation from existing investors, including The Engine, Energy Impact Partners, and others. Siam Cement Group, the largest cement producer in Southeast Asia, also plans to join as a strategic investor.

The new capital will be used to ramp up production at a pilot plant, build the company’s team, conduct product testing, and advance offtake commitments from new customers and partners. Beyond that, Sublime Systems plans to construct and operate a commercial demonstration plant by 2025 and then construct a full-scale, million-tonne-per-year cement plant by 2026/2027, with operations by 2028.

If the process is successfully commercialized, Sublime Systems may be able to take advantage of the Biden–Harris Administration’s Buy Clean initiative, which prioritizes the federal government’s purchase of steel, concrete, asphalt, and glass with lower emissions. On the state level, New Jersey recently signed a bill that incentivizes the implementation of concrete in construction projects with lower carbon emissions than traditional concrete.

With the ramp-up of use-inspired research funding and programs at the TIP directorate, ideally more university researchers will be able to transition their research to market, just as Chiang and Ellis are doing with Sublime Systems.

Share/Print