Carbon–carbon bond cleavage for a lignin refinery

Abstract

Carbon–carbon bonds, ubiquitous in lignin, limit monomer yields from current depolymerization strategies, which mainly target C–O bonds. Selective cleavage of the inherently inert σ-type C–C bonds without pre-functionalization remains challenging. Here we report the breaking of C–C bonds in lignin obtained upon initial disruption of labile C–O bonds, achieving monocyclic hydrocarbon yields up to an order of magnitude higher than previously reported. The use of a Pt (de)hydrogenation function leads to olefinic groups close to recalcitrant C–C bonds, which can undergo β-scission over zeolitic Brønsted acid sites. After confirming that this approach can selectively cleave common C–C linkages (5–5′, β–1′, β–5′ and β–β′) in lignin skeletons, we demonstrate its utility in the valorization of various representative lignins. A techno-economic analysis shows the promise of our method for producing gasoline- and jet-range cycloalkanes and aromatics, while a life-cycle assessment confirms its potential for CO2-neutral fuel production. Carbon–carbon bonds are ubiquitous in lignin, limiting monomer yields from current depolymerization strategies mainly targeting C–O bonds. Now, a bifunctional hydrocracking approach uses a Pt/zeolite catalyst to break C–C bonds in lignin waste, achieving monocyclic hydrocarbon yields up to 54 C%.