The effect of solvent on acidic depolymerization of lignin
Woody biomass can be a very useful source of a plethora of platform chemicals but it needs to first be separated into cellulose, lignin and hemicellulose. Classical procedures are mostly focused on the preservation of cellulose structure while degrading lignin rendering it useless for further utilization. For the future utilization lignin needs to be separated without major degradation.
Our work was focused on kinetic description of the acidolysis of benzyl phenyl ether, which is an aromatic dimer used as lignin model compound and can be cleaved to two monomers. We have shown that the with the use of acid as a catalyst benzyl phenyl ether splits to benzyl carbocation and phenol. Benzyl carbocation is an unstable structure and thus further stabilizes via the reaction with either solvent or phenol. Its reaction with phenol should however be discouraged due to the formation of the recalcitrant C-C bonds which have shown troublesome for future upgrading of lignin.
In our work we have described the effects of temperature, solvent and the acid concentration on the selectivity and the kinetics of transformation. The results show that the choice of the solvent which has the ability to form nucleophiles essential to the production of the high quality lignin using the organosolv process. In addition we have shown that the rate of the acidolysis is in most solvents linearly dependent on the acid concentration, while the selectivity is independent of it. The effect of temperature was described with the use of with regression calculated activation energies.
Link: https://doi.org/10.1016/j.cej.2022.140912
Contact person: matej.zula(at)ki.si