European oil majors Shell and Eni have led an early stage funding round for climate technology start-up Mantel Capture, which aims to use molten salts to capture carbon dioxide emissions at refineries, factories and other industrial sites.

Capturing carbon where it is produced, or "point source" capture, allows polluters to reduce emissions and retain existing, expensive infrastructure, although it has been criticized by some environmentalists for perpetuating emissions.

Boston-based Mantel aims to pull 95% of the carbon out of smokestack emissions using the molten salts, a process that it says is unusually cost-effective because it takes advantage of the extremely hot environments inside industrial furnaces and boilers, requiring much less additional energy than rival capture methods.

"This is a technology that could radically change the energy industry, but there is still risk to what we're doing," Mantel CEO Cameron Halliday said in an interview.

The $30 million raised in the Series A round will allow Mantel to build a demonstration project at a paper mill that can capture 1,800 metric tons of emissions a year, around 10 times more than the half a ton a day captured in a laboratory setting. 

At a scale of hundreds of thousands to millions of tons, Mantel could theoretically capture carbon at about $30 to $50 a ton, making it economically viable in many countries offering either incentives for carbon capture or taxing emissions, and far below competing systems, Halliday said.

"I feel very confident that those numbers are going to win that market, and that means that's going to be lowest cost provision of abatement in a number of heavy industrial sectors," said Michael Kearney of Engine Ventures, an early investor that is also part of this funding round.

Co-led by the innovation units of the two oil companies, Series A investors also include BP's bp Ventures, New Climate Ventures, Hartree, Arosa Ventures, Vale Ventures, and MCJ Collective.

The investment by Shell follows its decision to row back on its near-term climate targets amid uncertainty about the pace of the energy transition and pressure from investors to improve returns.

Shell will watch pilot efforts before going too far down the road on potential uses for itself, said Hector MacQuarrie, principal at Shell Ventures, but he added the technology could make carbon capture much more achievable for hard-to-abate industries. 

"If it's successful, if they're able to deploy in the field, this has the potential to generate a step change" in carbon capture costs, he said.