<br/>The lignin first approach in which an organosolv pulping is combined with a transition metal catalyzed hydrogenolysis or transfer hydrogenolysis has emerged as a future pulping technology where not only the cellulose part of the wood is valorized but also the lignin and sometimes the hemicellulose. The current examples, all performed in a batch process, fractionate the lignocellulose to the main components by delignification in which the reactive monomeric lignin fragments are reductively transformed into less reactive species by the transition metal catalyst to prevent condensation and re-polymerizations. Disadvantages with current processes are that fractionation and (transfer) hydrogenolysis reactions are performed in the same batch where: 1) optimization of each process cannot be performed separately; 2) the heterogeneous catalyst and cellulose end up in the same phase which leads to tedious purification problems and lower the ability of catalyst recovery; 3) the fractionation and transition metal catalyzed reactions are not feasible to study separately.<br/>We have developed a hydrogen-free lignin first approach in which the hemicellulose operates as an internal hydrogen donor that delivers hydrogen equivalents in the reductive process of the lignin transformation. In this talk, a novel lignin first approach in which the fractionation and transfer hydrogenolysis are separated in time and space by a continuous flow system is presented. By separating the pulping from the transition metal catalysis, both processes can be optimized and studied separately. It was found that the processes have different optimal reaction temperatures and that pulping alone generates a substantial amount of lignin derived monomers by a peeling process where terminal monomer, linked by the beta-O-4’ bond, are cleaved in a fast step. In the transfer hydrogenolysis reaction, also internal beta-O-4’ bond are cleaved and a theoretical maximum of lignin derived monomers are formed. Interestingly, this occurs in a slow step. The generated pulp is highly delignified and susceptible for enzymatic transformations without prior purifications. We believe that this is an important step that enables fundamental studies of the processes involved and also for a future commercialization.<br/>

Lignin first approach using a continious flow system

255th National Meeting (2018)

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