A green method for obtaining vanillin from technical lignin produced from pulp
Huge amounts of technical or Kraft lignin are formed during pulp
production. This lignin is difficult to process and so is usually just
incinerated for heat production. A team of researchers, reporting in the
journal Angewandte Chemie, have now succeeded in developing a
green method for recovering the flavoring agent vanillin from this raw
material. The materials used in this method are all recycled from
papermaking processes, and only power and heat need to be added.
© Wiley-VCH, re-use with credit to 'Angewandte Chemie' and a link to the original article.
Lignin and cellulose are essential components of wood. The molecular
structure of lignin contains the structure of vanillin, the main
flavoring substance from the vanilla plant, meaning that vanillin can be
produced from lignin, although the process is laborious. At present,
lignosulfonate, a substance also formed in some papermaking methods, is
used for the industrial production of vanillin.
In order to make paper from wood fibers, all lignin has to be
removed, otherwise the paper will take on the brown color of the lignin.
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 oxidize and depolymerize than other lignins and so at
present cannot be used as a raw material. Instead, it is simply burnt as
fuel for papermaking processes.
Siegfried Waldvogel and a team of researchers at the University of
Mainz, Germany, have now discovered a method for producing vanillin from
Kraft lignin. They say the method is environmentally friendly as it
does not 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 oxidizer by electrolysis of sodium carbonate.
"The idea started many years ago when playing around with innovative
electrode materials that make it possible to take simple carbonates and
make an oxidizer from them," explains Waldvogel. One of these electrode
materials was boron-doped diamond, and the researchers observed that,
when carrying out electrolysis using this electrode material, the sodium
carbonate was readily oxidized to peroxodicarbonate. The team then
found out that this oxidizer was strong enough to degrade stubborn Kraft
lignin.
The team report that, when freshly produced, the peroxodicarbonate
depolymerizes and oxidizes Kraft lignin with similar effectiveness to
traditional methods. However, in a departure from these conventional
methods, no environmentally harmful chemicals are used or produced in
the process.
The need for vanillin is high: "Most people only know of it from
vanilla flavoring, but it is present in most chocolates and perfumes as
well," explains Waldvogel. Vanillin is also a precursor material for
pharmaceuticals. All these uses mean that around twenty thousand tons of
vanillin are needed every year, and the vanilla plant alone cannot keep
up with this demand. Until now it wasn’t possible to utilize Kraft
lignin to meet demand, but the first steps are being made. Waldvogel and
the team are already working on a pilot plant to test scaling up.
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About the Author
Prof. Dr. Siegfried
Waldvogel is a Professor at the Department of Chemistry of the
University of Mainz, Germany. The research interests of his research
group are new electrochemical conversions of biobased raw materials,
among others, with the goal to use electric current as a "reagent" to
make previously difficult conversions sustainable and to upcycle
chemicals.
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