Reactive fractionation of biomass to give lignin carbonates

To realize a biorefinery, all components of biomass should be valorized: including lignin. In current biorefineries such as pulp mills the lignin fraction is compromised in favor of the cellulose fraction.

The resulting technical lignins are highly condensed giving a more rigid structure with less functional groups than native lignin and this limits its applications.Herein, we propose to apply a reactive fractionation of biomass using carbon dioxide as sustainable protecting group to generate a lignin carbonate in concert to fractionation.

The chemistry is noteworthy as an oxygen on carbon dioxide will act as nucleophile and attack a generated carbocation on the lignin polymer.

The fractionation will lead to a lipophilic lignin carbonate with few disruptions, an intact cellulose-rich pulp and aqueous hemicellulose: thus, a holistic valorization of biomass is realized. The lignin carbonate itself will be unique and a great advantage is that the lignin backbone is intact. This protected lignin will open up new avenues to study the structure of lignin, that is still under discourse.

Using 13C labelled carbon dioxide will enable quantitative determination of beta-ether bond content without disruption of the lignin for the very first time.

We intend to further transform the lignin carbonate by reaction with, for instance, polyols to promote crosslinking and give thermoset materials. As the formed chemical bond is labile, the novel thermoset will be recyclable.