Reductive Catalytic Fractionation of C-Lignin

Abstract

Lignin composed solely of caffeyl alcohol units, or C-lignin, was recently discovered in the seed coats of a number of vanilla orchid and cactus species. The caffeyl alcohol monomer polymerizes into a highly uniform benzodioxane backbone, making C-lignin a promising substrate for lignin valorization, where heterogeneity is a key challenge. In this study, we used reductive catalytic fractionation (RCF) on vanilla seeds to investigate the depolymerization of naturally grown C-lignin. To overcome challenges associated with the high extractive content and poor sugar retention in vanilla seeds, the ratio of monomer yield to total lignin yield was used to isolate the depolymerization efficiency of C-lignin from the extraction efficiency of lignin from seeds. This approach allowed us to compare extents of depolymerization across lignin types and biomass feedstocks. C-Lignin RCF generated extents of depolymerization akin to those of hardwoods, despite observing incomplete benzodioxane cleavage due to catalyst deactivation caused by the seed extractives. In addition, depolymerization of C-lignin produced a favorable monomeric product distribution consisting of only propyl and propenyl catechol. These promising results suggest that genetic modification of other plant species to incorporate C-lignin has the potential to yield a single, valuable catechol product via RCF.

Enzymatic basis for C‐lignin monomer biosynthesis in the seed coat of Cleome hassleriana

“…Requirements for engineering C-lignin in plants C-lignin possesses several properties that make it potentially a much higher value molecule than classical lignin in the processing of lignocellulosic biomass. Its linear, non-crosslinked nature favors spinning of carbon fibers (Nar et al, 2016), and its homopolymeric nature favors chemical or biological deconstruction to simple mixtures of aromatics for funneling to high value chemicals (Berstis et al, 2016;Li et al, 2018;Stone et al, 2018). It is therefore unfortunate that, to date, C-lignin has not been discovered in any high biomass, agricultural species.…”

Reductive catalytic fractionation of pine wood: elucidating and quantifying the molecular structures in the lignin oil

“…[54][55][56] Although RCF is now being developed as a biorening strategy, its use as powerful tool for the structural analysis of native lignin is gradually revisited. 31,[57][58][59][60] Current characterization efforts of the RCF lignin oil are mainly focusing on the quan-tication of the lignin derived monomers, as well as on the identication of some phenolic dimers. 31,[33][34][35] However, the chemical structure of the RCF lignin oligomers, at least 40% of the lignin oil content, remains largely unexplored.…”

Evaluating lignin valorization via pyrolysis and vapor-phase hydrodeoxygenation for production of aromatics and alkenes

“…Lignin valorization is commonly suggested as producing value-added oxygenated chemicals such as aromatic aldehydes (e.g. vanillin, syringaldehyde, and p-hydroxybenzaldehyde), [4][5][6] organic acids, 7 alkyl-catechols, 8 phenolic monomers, [9][10][11] and occasionally fuel-like mixtures comprised of fully hydrogenated hydrocarbons. 12 While there is value in investigating possible routes for producing specialty oxygenated chemicals, there are limited market sizes for such compounds.…”