A by‑product of the pulp and paper industry could become one of the most promising materials for capturing carbon dioxide from industrial emissions and even from the atmosphere. This is stated in a study by researchers from Tampere University in Finland and the National University of Malaysia, who summarized the results of recent research in the field of creating carbon sorbents from lignin, a natural polymer that makes up to 30% of wood and is mostly used as low‑grade fuel.
Today, the atmospheric CO₂ concentration has already exceeded 420 ppm, while existing materials for its capture are far from ideal. Many of them are expensive to produce, sensitive to moisture, quickly lose efficiency, and require high energy inputs for regeneration. Therefore, scientists are looking for affordable and sustainable alternatives that could be produced on an industrial scale. Lignin – a by‑product of paper, cardboard, and biofuel production, generated annually in huge volumes – turned out to be one of such materials.
To convert lignin into a sorbent, it is heated in the absence of oxygen to obtain a porous carbon material. It is then additionally treated with chemical reagents or steam to form a network of tiny pores. The most effective are so‑called ultra micropores with a size of less than 0.7 nanometers. It is in these pores that carbon dioxide molecules are held particularly strongly. Additionally, atoms of nitrogen, sulfur, phosphorus, and other elements are introduced into the material, creating active sites on the surface that enhance CO₂ attraction even at its low concentration in flue gases.
According to research data, the best samples of such materials are capable of absorbing nearly 7 millimoles of CO₂ per gram of sorbent and can operate rapidly in cyclic mode. Some sorbents reached up to 90% of their maximum capacity within just one minute. Since carbon dioxide is retained primarily through physical interactions, relatively little energy is required for regeneration: it is enough to heat the material or reduce pressure, after which the sorbent is ready for use again.
However, the scientists emphasize that laboratory results do not yet guarantee successful industrial application. Real flue gases contain water vapor, oxygen, sulfur oxides, and nitrogen oxides, which can reduce the efficiency of sorbents. Furthermore, the isolation of pure lignin from wood itself requires chemical reagents and additional energy, which currently significantly increases the cost of the technology. Another open question is the full environmental footprint of producing such materials: the researchers consider it necessary to assess emissions at all stages of their manufacture to ensure that the new technology indeed contributes to reducing CO₂ emissions.
