Catalytic conversion of high S-lignin to a sustainable tri-epoxide polymer precursor

More than 40 million tons of thermosetting plastics are produced annually and 70% of those are epoxy polymers. The synthesis of bio-based epoxide provides a pathway for making renewable thermoset plastics. We describe in this study the use of a genetically modified high-S poplar lignin to produce 4-propyl-2,6-dimethoxyphenol (DMPP), which is converted to the tri-functional compound propylpyrogallol (DMPPO) by a reaction catalysed by N2O5 in the green solvent water. The resulting DMPPO can be converted to a novel tri-epoxide by reaction with epichlorohydrin. Native high-S lignin as well as several organosolv lignins extracted from this poplar biomass were investigated as feedstocks. Notably, direct reductive catalytic fractionation (RCF) of the high-S poplar wood over Pd-Zn/C catalyst with Pd : Zn ratio 1 : 10 at 225 degrees C under 35 bar H-2 in methanol gave the highest yield of biophenol monomers from the lignin present, the major product being DMPP. Under optimized conditions, conversion of DMPP to DMPPO over the Nb2O5 was nearly quantitative (96% yield), and this conversion could be made without extensive prior purification of the DMPP. The Nb2O5 catalyst could be recycled several times before significant deactivation. This sequence of two catalytic reactions demonstrates that the production of epoxides from lignin-derived DMPPO is a realistic strategy for making renewable polymer building blocks from biomass.

Automated summary

In this study, a genetically modified high-S poplar lignin was used to produce renewable thermoset plastics. A series of catalytic reactions were employed to extract 4-propyl-2,6-dimethoxyphenol (DMPP) from high-S poplar lignin, convert it to propylpyrogallol (DMPPO), and then react with epichlorohydrin to yield a novel tri-epoxide. Direct reductive catalytic fractionation of the high-S poplar wood gave the highest yield of biophenol monomers, mainly DMPP, using Pd-Zn/C catalyst. Nb2O5 catalyst could efficiently convert DMPP to DMPPO without extensive prior purification. This study demonstrates a feasible strategy for producing renewable polymer building blocks from lignin-derived DMPPO.