Spruce Scrubbers

Spruce cone scales were burned and the resulting residue ground into carbon particles capable of absorbing CO2. Image courtesy of Xiao Guo.

Trapping carbon dioxide before it exits power plants, vehicle exhaust pipes, and industrial smokestacks is believed by many experts to be a key step in fighting climate change. The most effective technology now in use for absorbing carbon dioxide is an ammonia-based liquid compound, but this chemical “scrubber” – as it’s called – degrades quickly and is too expensive to be used for large-scale applications.

A research team at University College London has investigated a renewable, abundant, and inexpensive alternative. Chemistry professor Zheng Xiao Guo sought a solid material – rather than a liquid – that contains numerous tiny pores that could capture carbon. He followed the lead of other scientists, who attempted to make a porous material from biowaste like palm shells and leaves, and he eventually identified spruce cones as a surprisingly effective material without the downsides of chemicals.

“Spruce cones are biomass waste, rich in carbon-based lignocellulosic compounds, intrinsically porous, abundant in nature, but are not being effectively utilized at the moment,” he said. “They can be collected from urban areas and forests, and thus they are a low-cost raw material to generate effective porous carbons for CO2 capture.”

After peeling and washing the cone scales, Guo burned them in a furnace at elevated temperatures in a process called controlled pyrolysis, which causes the organic material to decompose and change its chemical composition. The resulting residue was then ground into tiny, extremely porous carbon particles. The particles were then tested under conditions similar to those of an industrial flue’s gas stream, which is 15 percent CO2 by weight. The results were similar to those of chemical scrubbers and among the best when compared to other renewable carbon-absorbing materials.

One significant advantage of spruce cones over chemicals is their reusability.

“They act like gas sponges, absorbing lots of CO2 from carbon emission sources and then dumping the CO2 into a collecting chamber. Then they go back into action again and again,” Guo said. “There are no carbon-filled cones to worry about disposing. The captured CO2 can then be turned into a fuel using solar energy, which is yet another important topic we are working on.”

Although the concept is effective in small-scale tests, Guo is seeking industrial collaborators to commercialize the process. He said that porous carbons from synthetic and natural materials have been created in laboratories for decades, so it is already a mature technology. What was missing was a low-cost and abundant raw material for mass production, and he believes spruce cones meet the requirements.

But spruce cones are probably not the only answer. Guo believes that other biomass wastes, such as leaves and husks, can have a second life as carbon-absorbing materials rather than being sent to landfills. Moreover, he concluded, such materials “can also be integrated with liquid scrubbers to produce a hybrid sorbent material that can combine the best of both types of materials, making industrial carbon capture much more energy efficient and cost effective.”

 
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