Used tyres and pistachio shells clean up pollution

Activated-carbon adsorbents made from the tyres and shells work as well as, or better than, current commercial products and might even be cheaper to produce.

“Coal-fired power plants are one of the largest anthropogenic sources of mercury emissions,” said Massoud Rostam-Abadi, a chemical engineer and head of Energy and Environmental Engineering at the Illinois Survey. “With funding provided by EPRI (The Electric Power Research Institute) and the Illinois Office of Solid Waste Research, we looked for materials that could effectively remove mercury from the combustion flue gases.”

The researchers prepared adsorbents from a variety of sources, which were then evaluated for their effectiveness at removing elemental mercury and mercuric chloride from several different simulated combustion gas streams.

“We found that mercury removal was affected by both the properties of the adsorbent and the flue gas compositions,” said Rostam-Abadi. “In one flue gas, the adsorbents were equally effective in removing both forms of mercury. In another flue gas, the tyre and pistachio carbons had nearly five times larger capacity for the adsorption of mercuric chloride than their coal-derived counterpart.”

The researchers are currently examining the tailoring of adsorbents so that they are more effective in removing both forms of mercury from a variety of different power plants.

The work has also shown that activated carbons containing sulphur additives are significantly more effective at removing mercury emissions from the flue gases, though this adds extra processing steps and increases production costs.

“Tyre rubber already contains sulphur – which makes the rubber more durable – so activated carbon from tyres might prove more cost-effective than existing products,” said Professor Mark Rood of the University of Illinois. “And there is certainly a plentiful supply; each year more than 200 million tyres are disposed of in the United States alone.”

The researchers will present their latest findings at the American Chemical Society meeting in Washington on 20-24 August.