Vanillin from Kraft Lignin

Siegfried Waldvogel and a team of researchers at the University of Mainz, Germany have developed a green method for recovering the flavouring agent vanillin from a by-product in the papermaking processes.

Around 20,000 tons of vanillin are used every year so it’s in high demand for not only vanilla flavouring but also in chocolates, perfumes and as a precursor material for pharmaceuticals. As the vanilla plant alone cannot keep up with this demand, researchers have now discovered a method for producing vanillin from Kraft lignin — the results have been reported in the journal Angewandte Chemie.

Lignin and cellulose are essential components of wood. The molecular structure of lignin contains the structure of vanillin, the main flavouring substance from the vanilla plant, meaning that vanillin can be produced from lignin, although the process is laborious.

In order to make paper from wood fibres, all lignin has to be removed, otherwise the paper will take on the brown colour of the lignin.

At present, lignosulfonate, a substance that also forms in some papermaking methods, is used for the industrial production of vanillin. However, the waste product in the most commonly used pulping method for industrial papermaking, the Kraft method, is not lignosulfonate but rather a technical lignin referred to as Kraft lignin.

Kraft lignin is much harder to oxidise and depolymerise than other lignins and so at present cannot be used as a raw material. Instead, it is usually simply burnt as fuel for papermaking processes.

The researchers’ method for producing vanillin from Kraft lignin is claimed to be environmentally friendly as it doesn’t use any harmful chemicals, and it is convenient as it uses the raw materials present in pulp production. A key step in this new method is the production of the oxidiser by electrolysis of sodium carbonate.

The team reported that, when freshly produced, the peroxodicarbonate depolymerises and oxidises Kraft lignin with similar effectiveness to traditional methods. However, in a departure from these conventional methods, no harmful chemicals are used or produced in the process.

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