Spruce Cone Material Could Scrub CO₂ Emissions

Spruce cones could yield a material for capturing and storing carbon dioxide emissions that outperforms other solid sorbents, says a new study (ACS Sustainable Chem. Eng., DOI: 10.1021/acssuschemeng.5b01113).

Carbon capture and storage—plucking CO₂ molecules out of smokestacks and injecting them underground—is necessary to tame climate change, experts say. But the prohibitive cost of the standard capture process, which uses aqueous amines, has scientists investigating less costly methods.

Porous, carbon-based sorbents derived from metal organic frameworks (MOFs) have a high capacity for CO₂, but MOFs are costly to synthesize and are made from petrochemicals, an unsustainable resource. So Zhengxiao Guo at University College London and colleagues wondered if they could turn biowastes into a CO₂ sorbent. Other researchers have used cones to produce activated carbon for water cleanup, so the team tried cones from a Norway spruce (Picea abies). They carbonized spruce cone scales in a furnace, ground them into particles, and activated them with potassium hydroxide. The KOH treatment helped generate nanosized pores that increase the particles’ surface area. The scientists exposed the sorbent to the same CO₂ concentration found in flue gas—15% CO₂ by weight—and found that the sorbent had adsorbed 21% CO₂ by weight. “This capacity to adsorb CO₂ is similar to that of MOFs, but MOFs are not as selective for CO₂ and are more expensive to produce than the pinecone adsorbent,” Guo says. X-ray photoelectron spectrometry revealed that nitrogen and calcium naturally present in the cones remains in the nanoporous material, boosting CO₂ uptake by introducing active sites on the sorbent surface.

Pine and spruce cones are cheap, renewable and abundant, Guo notes. He figures that enough could be collected from forests to make a significant contribution to CO₂ capture on an industrial scale.