Despite the rapid advances in lignin depolymerisation, two issues remain. First, lignin is composed of three types of substituted phenols connected by a number of C–O and C–C bonds, forming a three-dimensional amorphous, irregular polymer. Second, lignin polymers may undergo non-selective fragmentation and rearrangement during depolymerisation, further complicating the product stream. One solution to the problem is to produce lignin with a simpler structure via generic engineering. For instance, overexpression of the ferulate 5-hydroxylase gene in poplar (Populus spp.) affords lignin with almost pure syringyl units and close to 90% β-O-4 linkages. Nevertheless, this technique is currently not widely applied and its economic viability remains to be seen. Another solution is to develop strategies that are able to converge complex monomers derived from lignin into a single stream. An elegant biological funnelling strategy was proposed and developed, in which a lignin liquor stream was converted to polyhydroxyl acid, forming the foundation of various end uses. As far as we are aware, one-step chemical transformation that convert, or conceptually that are able to convert, lignin derived monomer mixtures such as 2-methoxy-4-propylphenol and 2,6-dimethoxy-4-propylphenol into a single value-added product is rare. In this presentation, we communicate two recent approaches developed in our lab to produce aromatic compounds from lignin derived mixtures. Despite the complexity of decomposed lignin, the structures of the products are not without patterns. A common feature for the monomers obtained from lignin under neutral or reductive conditions is that they are substituted phenols bearing zero to two methoxyl groups in the ortho-position and an alkyl group in the para-position. In the first route, we developed selective de-methoxyl and de-alkyl chemistry to convert a mixture of substituted phenols to be converted into a single-compound phenol. In the second route, a mixture of lignin derived oil is upgraded into terephthalic acid via sequential demethoxylation, carbonylation, and oxidation steps.

Chemical funneling of lignin derived monomers into aromatic chemicals

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.