Pinus radiata bark sequentially processed using scCO₂ and an ionic liquid catalyst yields plentiful resin acids and alkanoic acids enriched suberin

The bark of Pinus radiata is an under-utilized forest residue that is renewable, abundant and has the potential to become a source of sustainable high-value chemicals. However, the use of this bark within a biorefinery for advanced applications is hindered by its intractable characteristics: high integrity, complex composition, and high heterogeneity. Most of the bark is burnt to provide energy and heat. The bark contains a high portion of phenolic extractives, constituting a potential source of valuable compounds. It also contains the heteropolymer suberin, a source of unique building blocks for developing innovative materials with potential broad bactericidal properties. Removal of phenolic extractives and suberin from bark simplifies down-streaming pulping processing of bark's lignocellulosic part. Herein, we describe an effective green strategy to sequentially extract the lipophilic bark constituents and suberin, exploring scCO₂ (40, 50 or 60 °C / 200, 350 or 500 bar) and a biocompatible ionic liquid catalyst. The obtained scCO₂ extracts had similar diversity of lipophilic compounds and predominantly contained resin acids. Further extraction of the scCO₂ extracted bark yielded suberin amounts of 2.25% wt. The bark's suberin structure shows archetypal chemical features yet has an idiosyncratic high abundance of alkanoic acids, which is not common in most sources. The findings of this opening bark biorefinery study deserve further development and complementary techno-economic analyses to secure new value chains for the bark's major lipophilic compounds consisting of resin acids and bark suberin.