From industrial waste to renewable resource: Lignin, an organic polymer, may soon have new life in the chemical industry

Lignin, a product that is commonly classified as industrial waste, may one day become an alternative to crude oil thanks largely to the Sun and photocatalysts. Lignin is a black, oily substance that emits a foul odor. Previous attempts at converting the toxic waste into a potentially important renewable source have been futile in the past, but a team of international researchers at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS), the Warsaw University of Technology in Warsaw, Poland, and the University of Cordoba in Spain has developed new photocatalysts designed to do just that.

“From the chemical point of view lignin is a natural polymer with a very complex three-dimensional structure, constructed of, among others, many derivative aromatic compounds including those from various phenyl alcohols. This chemical richness makes lignin a potentially very interesting raw material for the chemical industry. Unfortunately, at the same time, this is its curse, because it is very difficult to develop chemical reactions that would efficiently transform lignin into a specific, single chemical compound, readily suitable for further processing,” researcher Prof. Juan Carlos Colmenares tells EurekAlert online.

The photocatalysts are made of titanium dioxide that are deposited on a specialized carrier. One of the photocatalyst cases contain nanocomposites with iron oxide, while the other contained zeolites with a small amount of iron. The scientists then tested the materials’ efficacy by incorporating them into the toxic substance and having them exposed to ultraviolet light, which meant to resemble sunlight.

New photocatalysts show promising results

The results show that both catalysts are significantly effective in converting the benzyl alcohol in lignin into a benzaldehyde, a substance that is commonly used in manufacturing dyes and perfumes. According to the research team, up to 50 percent of the original benzyl alcohol content of lignin underwent conversion within only four hours of exposure. The findings also reveal that up to 90 percent of lignin reacted to the photocatalysts, which means that the converted byproduct is less polluted. (Related: Papermaking waste could provide safer alternative to BPA.)

“In the presence of our photocatalysts, illuminated by light imitating solar radiation, the reactions took place spontaneously in lignin-based model compounds, at ordinary atmospheric pressure and at a temperature of approx. 30 degrees Centigrade, thus in conditions naturally occurring in direct sunlight. This is the exact opposite of traditional refineries, which require very complicated and expensive to maintain technical infrastructure,” Prof. Colmenares explains.

The research team also stressed on the relatively low cost of producing the photocatalysts. The experts noted that the new materials were inexpensive as their carriers were made from common materials, and that they did not require expensive precious metals such as palladium during the production phase. Moreover, the researchers noted that one of the photocatalysts possessed magnetic properties that made it easy to recover and reuse once the conversion had taken place.

DOE doles out funding for another lignin research

The Department of Energy (DOE) recently awarded the Washington University in St. Louis a $3.9 million grant for a development project designed to study certain bacterial species that manufacture renewable biofuels from plants and microbes. The research team is examining the potential of Rhodococcus opacus bacteria in biofuel production. According to the scientists, these bacteria are originally discovered on toxic compounds outside a chemical plant. The experts note that the bacteria uses the hazardous substance as a food source in order to produce biofuels.

“These compounds are related closely to lignin, complex polymers that make up roughly 30 percent of plant matter. Our team is using a combination of chemistry, systems biology and synthetic biology to try to process lignin plant matter into biofuels that can be added directly to current petroleum-based engines,” co-investigator Gautam Dantas explains in a university press release.

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