Tech

A FILTER made from natural crystals may help dirty, carbon-emitting fossil fuels green up.

Zeolite crystals are a popular industrial "sieve" because their tiny pore spaces allow only certain molecules to slip through. Now a group of researchers led by Steven Kuznicki at the University of Alberta in Edmonton, Canada, and Anthony Ku at General Electric think they can be used to screen out the carbon dioxide produced when processing or burning fossil fuels.

The vast oil-sand deposits of Alberta are estimated to hold up to 170 billion barrels of recoverable oil, second only to Saudi Arabia. But extracting the oil accounts for millions of tonnes of carbon emissions each year, and the industry is growing rapidly. Much of the emissions are generated when superheated steam is pumped into the deposits. The steam pushes oil to the surface, but also picks up carbon from the oil and surrounding bedrock, which is then released into the atmosphere.

The team found that passing such dirty steam through a zeolite crystal, such as the mineral clinoptilolite, traps everything but water, hydrogen, helium and ammonia. Carbon captured by the crystals could then be buried underground or utilised.

This technique could cut emissions related to oil sands by a quarter, the researchers say. The sieves could also work in coal gasification plants, which currently use solvents to scrub CO₂.

Long-term stability and creating reliable, leak-free seals between crystals are still challenges, however. "We must prove we can go from a rock to a piece of equipment that really works," says Ku. He hopes to have a pilot plant running in Alberta in two years.

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