Sublime Systems is a new startup in the cement industry, part of the family of decarbonization breakthrough technologies that are enabling the net-zero economy. The company has developed a new method that eliminates the use of fossil fuels in cement production, responsible for 90% of its total emissions.
We interviewed Dr. Leah Ellis, Founder & CEO of Sublime Systems who revealed very critical information about the company’s technology. It produces cement in a completely different and innovative way compared to other methods and it also makes an astonishing difference in cement’s carbon footprint.
This interview has been edited for clarity and length.
The first question we usually ask is what is Sublime Systems? What is the story of the company?
Sublime Systems is a company commercializing new technology to make low-carbon cement. Me and my co-founder worked on batteries. I worked on lithium-ion batteries for Tesla, as part of my PhD and my co-founder has spun out several battery companies.
We also have funding from the Canadian government to work on anything we wanted, it was very open. And we wanted to use our experience in batteries to make a bigger impact.
Cement is the number one CO2 emitter in the industry, so we thought, how can we use electric chemistry to decarbonize cement? And that was the goal. Ever since then, we’ve been refining and working backwards from that goal.
What is your personal story behind your decision to co-found Sublime?
I grew up in the 90s and I always cared a lot about sustainability, especially protecting whales, saving water, recycling and composting. I feel very strongly about the need to protect the Earth’s broader ecosystem. I found a way to do that through chemistry.
Chemistry is a way of inventing new things, of really solving problems. I worked with some very powerful and brilliant scientists and that part led me to work with my co-founder Yet-Ming Chiang.
I was drawn to him because of his track record of not only inventing new things but inventing things that are useful, as many people in university create technologies that don’t have commercial traction. I found that very attractive, having to make a business out of your technology while you’re building it.
I’m interested to know, how is cement produced now, compared to let’s say, 1,000 years ago?
In Roman times and even before, cement was made by burning limestone to make lime. When you burn limestone, it loses 50% of its weight as CO2 is 50% of the mineral itself and it becomes an oxide. The oxide is very reactive and can react with silica or alumina to form a hardened cement. That’s been the method of making cement for a very long time.
It changed in the 1800s when they discovered that if you take calcium and silica and you burn them together at very high temperature, you get a particular rock that has the right chemistry. That rock – calcium silicate – reacts with water and forms the same chemistry as if you took the calcium and the silica and reacted them together at ambient temperature. But it’s set a lot faster.
There’s been a change in the way cement has been made over the years but the final hardened chemistry of the cement has stayed the same.
Is there much change in the emissions of cement production over the years?
I want to give the industry credit. People say cement is a very old industry, that they don’t have a lot of innovation, but that isn’t true. Innovations have reduced the emissions of these fossil fuel-fired kilns, that cement has been made in for many years. About 100 years ago, electricity was very expensive, and fossil fuel was very cheap, so they used it to grind the cement wet. That reduced the energy for grinding, and then they would put the wet material in the kiln.
Over the years, it moved from wet kilns to dry kilns. So the kilns have become much more fuel efficient and economical. I think a lot of that innovation was in Japan, as it’s an island and doesn’t have fossil fuels. They invented these kilns that were more efficient, but I think they hit the limit.
Now we have to decarbonize and get away from fossil fuels. In Portland cement, it’s very difficult to get that temperature using resistive electric heating. You could also capture the CO2 but that adds to the energy use and creates complexity of what you’re going to do with the CO2.
Could you walk us through the steps of ordinary cement production that are emissions-intensive and how the solution of Sublime Systems eliminate those emissions?
The most CO2-intensive step in cement production is turning the limestone into lime. Sublime replaces that step with an electrolytic process. We use an electrolyzer – very similar to a hydrogen electrolyzer. In hydrogen electrolyzer, you take water and split it into hydrogen and oxygen.
In Sublime’s cell we split the water into acid and base. The acid is then used to react with the calcium.
You can use limestone to react with the acid but this reaction is like baking soda and vinegar or Mentos and Coca Cola where you close the cap on the bottle and you build up a lot of pressure.
If you use limestone, the CO2 involved is cold, pure and compressed and it’s already captured. You don’t have to spend more money using membranes or other means to separate the CO2.
But you can also use the acid to take calcium out of different minerals. We’ve seen startups like Brimstone using a step to extract calcium from the mineral. We pull the calcium out and now we come to the second step which is to react it with the base that’s formed with the electrolyzer. That makes lime or calcium hydroxide. The lime is then separated from the liquid.
The liquid is purified and returned to the electrolyzer where it’s again split into acid and base. And now that we have the lime, we can react it with silica just the same way the Romans did. The reaction between lime and silica is called a Pozzolanic reaction. So we make the same calcium silicate hydrate phase that Portland cement makes once it reacts with water.
And everything in Sublime Systems happens at ambient temperature so we eliminate cement kilns. There’s a little bit of water drying off but otherwise, we don’t need high temperature or fossil fuels for anything.
So you decarbonize the limestone production and you eliminate the need for kilns.
Yes, exactly. Limestone emissions are about 50% to 60% of Portland cement’s carbon footprint, and the fossil fuels are the other 40% to 50%. We don’t use fossil fuel and if we do use limestone, the CO2 is already captured. But then we also have the option not to use limestone at all.
We know some companies are using processes to decarbonize cement, like sequestering the CO2 inside the concrete. Is Sublime’s process more efficient than that?
Yes, it’s a blank slate making cement. Sequestering CO2 back into the cement often works for blocks, because you really need to push the CO2 into it to make it hardened. I’ve seen this technology being used more for pavers, or to make an aggregate. Blue Planet, for example, makes inert rocks for the cement.
And then CarbonCure adds a little bit of CO2 in the ready-mix. But it’s very hard to use that mineralization for the cast in place because you need to pour it and let it set so it’s hard to get the CO2 into it.
Those technologies are great but they don’t work very well for the ready-mix as cement. Also because you’re adding the CO2 back in and CO2 is an acid, you don’t have the alkaline pH in the cement that you need to protect the rebar from rebar corrosion. That means CO2 mineralization is not going to work for the bulk of the cement industry for structural cast in place concrete.
So you don’t see these technologies as competitive to the cement production process of Sublime Systems?
No, in fact, we could work with these companies. Those companies that mineralize the cement and add CO2 back to the calcium, need calcium. If we provide those companies with a carbon-neutral calcium, then their process becomes carbon negative.
That’s why I think it’s a really interesting synergy. And I think these technologies have a lot of potential for blocks and making carbon-negative aggregate.
Do you decarbonize all of the steps of the production pipeline of concrete?
There’s part of the carbon footprint of this segment that we can’t address, like mining, quarrying, the grinding, and transportation which is something out of our control. But 90% of the emissions come from the kilns from the limestone, so we decarbonize that 90%.
What is the cost of Sublime System’s cement?
It’s going to cost the same as Portland cement if we can get it to the same scale that Portland cement is made as of today. Of course, it’s the most massively produced material in the world.
Right now we have a pilot plant that produces up to 100 tons of cement per year if we run it all around the clock. If you’re making cement at that scale, even if it’s a tiny Portland cement kiln, it’s going to be very expensive. The costs end up being exponential as a function of scale, which is why you need to get to a very large scale before the line starts to flatten out.
We don’t think of selling the cement at this scale at a profit. It is just to validate the technology, the product, to start opening up the market and generate partnerships. Our focus is to get to as big of a scale as possible and as fast as possible, because that has the most impact.
Everything we’re doing right now, including the series A, is to get to a scale of 10s of 1,000s of tons per year. That would be our demonstration scale plant – up to 40,000 tons per year, as we don’t want to go to a million tons per year right away.
The plan is to do as much technical derisking and refinement on the process as possible. We want to figure out all of the unknowns in a very small scale before making a tremendous investment into a full-scale plant. We have plans to operate the demonstration plant by the end of 2025. And from there go to the full scale.
When we are at full scale, we do expect that we will compete on cost with Portland cement. We exclude any carbon capture credits, or fuel taxes, just apples-to-apples comparison. And then, of course, any carbon credits we can get will only improve the economics of our product. That’s how we think about it.
How do you plan to scale into million of tons of cement production?
With everything we’re doing right now with the pilot plant, the goal is to produce material to de risk the system and to generate an engineering package to get us to the next scale. We have a spreadsheet model where we take data from the pilot, we get vendor quotes, we put them in the model, and we develop the package for what the next system will look like.
We’re also looking for a site where we might build this plant. It needs to be where the energy is abundant and renewable, the minerals exist, and we have proximity to the market.
Once we obtain this site, the next stage is to set up the plant and start building it, and testing it to produce the material at an even larger volume. After that we’ll be using the data we produce in these operating conditions to raise money for a very large plant.
At what stage is the company at the moment?
We’ve just raised a $40 million Series A and we have about 40 employees. A mix of scientists is working on the system and business strategy. So we’re a pretty diverse and hard-working team. The technology is being tested at the pilot scale and that’s the stage we’re at now.
How do you plan to allocate that Series A investment of $40 million?
It’s mostly going to scaling up – that’s where our focus is. You won’t have an impact, no matter how wonderful your invention is, unless you’ve really sold it. And for cement, you have to sell it in very large volumes. So everything we do is about getting to a large volume and making sure the customers really like the product. It’s important that it fits with how they need it for work.
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Cement is a very hard industry to be in. It’s a commodity material so people are very adverse to change, there is risk. In Sublime, we’re doing this because it’s hard. My co-founder and I could be doing easier things in batteries.
But we think the problem we’re working on is important. And it’s urgent. We’re working very hard to make sure we’re doing something that can be turned into a profitable business and satisfy everybody’s needs.
Do you partner with other companies at the moment?
We speak with ready mix concrete producers almost every day. Those are our main customers. We also speak with cement companies. We are not announcing any partnerships but you may have seen that Siam Cement Group was among our Series A investors and it has its roots in cement as the oldest and largest cement producer in Thailand and Southeast Asia.
Unlike other cement companies that maybe are diversified within building materials, Siam Cement Group is diversified within fine chemicals as well. They are in the cutting edge of innovation in many ways. We met with them through MIT, through their industry liaison program, and they are sponsors of Greentown Labs.
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They co-invested with Energy Impact Partners and other investors. So many companies have a seat at the table in all the places we are at. They’ve also announced recently, I think, in December, a $3 billion investment in renewable energy to decarbonize their businesses.
Their decarbonization is not just asking for handouts from governments. It’s a real pleasure to work with them and I’m honored to have them on the team. I hope that as the company grows, we’ll have formal partnerships with others like them.
How did Greentown Labs help you in your journey?
I would say Greentown Labs is a place where it’s very easy to start a science or technology-based company. You go there, two co-founders with a PowerPoint, and they take care of everything so you can grow from 2 to 30 people easily.
The founders don’t have to worry about facilities, waste management, permitting, working with the fire department, providing training for their employees or even providing coffee for them. Everything is taken care of. It’s like a full service hotel for startups where someone does your laundry and brings you breakfast, so you can just focus on what matters the most.
It’s also a very fun place to work and I think this really helps with attracting talent. I see that so many people, so many really really smart, passionate, driven people are leaving their boring jobs in consulting, banking or oil and gas, and they want to work on something that they care about, that means a lot to them.
I’d say in my experience, it’s worth at least $20,000 to both young and more mature people to leave their jobs. They would take a pay cut to work at a startup where they feel like what they do really matters. I think Greentown Labs makes that jump easier. Also it’s a very beautiful building, they host a lot of parties, and it’s important to have that energy. Investors also come, as well as people from the community. You exchange ideas, you make friends.
If you’re a small startup and you don’t have a lot of money, you probably have to set up your lab somewhere outside of the city far away where people have to drive. And it’s probably not a very beautiful office, so that matters. Also matters if your office is a happy and energetic place to work.
It makes it very easy to recruit, especially if it is 15 minutes from both Harvard and MIT and also Northeastern and Tufts which are great universities. There are a lot of really energetic and very smart young people there willing to do internships.
Do you have any advice for climate tech co-founders who are taking off with their technology now? What’s been the key to your success and what advice can you give them in relation to building a successful startup?
Once I met a very famous CTO of a very big company that everybody knows. And he answered the same question saying – you work really hard, and you figure it out. And I think that was the best advice because it’s true. Struggle is normal, I think everybody’s born to struggle with something. And I think you can choose what you struggle with.
I chose to struggle with climate and this problem is real, the struggle is hard. But I think the harder you work, the luckier you get, and the more you learn. So that’s my advice to just work as hard as you can.
Obviously, you need to find the balance so that you don’t burn out, but just realize that the struggle is real. Also my advice is to find a community like Greentown Labs. I think it’s very important to find people who are in a similar place as you.
If you’re on a journey, you can also get advice from people who are further along. That helps you understand the problems that you will face. You can also share your experiences with folks who are not as far along in your journey – it helps you gain more confidence and makes you feel more valuable. It gives me confidence and energy to be able to help and then also have the privilege to be around really smart people who helped me.