Research Project – Emiel Hensen/Xianhong Ouyang
Lignin, cellulose and hemicellulose are the major components of lignocellulosic biomass. For decades, biomass research has focused on utilization of the polysaccharides cellulose and hemicellulose for the production of renewable platform chemicals, such as ethanol and levulinic acid.1 Therefore, nowadays, lignin is mainly considered to be waste and remains underexploited in most biorefinery schemes. Due to its polyaromatic nature, however, lignin has the potential to serve as resource for renewable aromatic monomers.2 Hence, efficient methods turning lignin into valuable aromatic compounds are highly desired.
In this project, a two-step lignin valorization approach is investigated, consisting of a biomass delignification and a lignin depolymerization step. In the first step, homogeneous Brønsted acids and Lewis acids are applied to cleave ester and ether linkages, separating lignin fragments from the lignocellulose matrix. Small lignin fragments (monomers, dimers and oligomers) dissolve, while a cellulose-rich pulp is obtained as solid residue. Unfortunately, the soluble fragments are very reactive and can easily form recalcitrant C-C bonds via undesired side reactions, like the aldol condensation.3 In the second step, the dissolved lignin fragments are subjected to further depolymerization by a heterogeneous hydrogenolysis catalyst (Pd/C). However, the C-C bonds cannot be cleaved anymore.
Biomass delignification and lignin depolymerization is a complex yet challenging catalytic process. Solvent, dissolved carbohydrates, side reactions and the acid and hydrogenolysis catalyst have a significant impact on the aromatic monomer yield. In order to explain observations and understand the reaction mechanism of native wood experiments, you will use proper lignin model compounds to simplify the system and investigate the time course of the reaction. Ultimately, these insights will help you directing the reaction to the desired products.
During this master project, you will get familiar with many important analysis techniques. You will apply GC-MS and GC-FID for determining the aromatic monomer yield, NMR for studying structural changes after depolymerization and GPC for measuring the average molecular weight. Furthermore, the purity, crystallinity and morphology of the solid residue can be analyzed by XRD and SEM in order to assess the quality of this cellulose-rich pulp. Eventually, the (spent) catalyst is characterized by TEM, ICP and XRD.
Zhou, C.-H.; Xia, X.; Lin, C.-X.; Tong, D.-S.; Beltramini, J. Chem. Soc. Rev. 2011, 40 (11), 5588–5617.
Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckhuysen, B. M. Chem. Rev. 2010, 110 (6), 3552–3599.
Shuai, L.; Amiri, M. T.; Questell-Santiago, Y. M.; Héroguel, F.; Li, Y.; Kim, H.; Meilan, R.; Chapple, C.; Ralph, J.; Luterbacher, J. S. Science (80-. ). 2016, 354 (6310), 329–333.
For further information:
Emiel Hensen (Helix, STW 3.35), Tel 5178, firstname.lastname@example.org
Xianhong Ouyang (Helix, STW 3.29), Tel 4001, email@example.com