Gewinnung von biomassebasierten Verbindungen durch Adsorption an Aktivkohlen, Zeolithen und porösen Polymeren

• Recovery of biomass-based compounds by adsorption on activated carbons, zeolites and porous polymers

Deischter, Jeff Gaston Jean; Palkovits, Regina (Thesis advisor); Rose, Marcus Sören (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

In this dissertation, the recovery of biobased products from aqueous phase by adsorption on commercial as well as tailored adsorbents was investigated. The understanding of structure-adsorption relationships could be extended by detailed studies of the adsorption of the products L-lysine, itaconic acid and D-glucose on activated carbons, covalent triazine-based frameworks (CTFs) and zeolites. This allows an establishment of adsorption-based separation processes for future biorefineries. In the first part of the work, a detailed insight into the liquid phase adsorption of L-lysine on activated carbons and its separation from D-glucose was given. Detailed characterization allowed the implementation of structure-adsorption relationships. By testing a variety of different commercial activated carbons, it was demonstrated that a large specific surface area in combination with a large amount of surface oxygen functionalities is required to achieve high L-lysine adsorption capacities of up to 256 mg g-1. A high amount of oxygen functionalities resulted in improved separation of L-lysine from lysine-glucose mixtures. The adsorption of L-lysine in a continuous fixed bed adsorber, a setup essential for an industrial application, was evaluated. In addition, up to 95 % of the adsorbed L-lysine could be desorbed by a suitable desorption strategy using water, ethanol or sulfuric acid. In the next chapter, CTFs, a material class that can be prepared via a variety of nitrile-based monomers, were investigated for itaconic acid, L-lysine and D-glucose adsorption applications. A number of different monomers were used to synthesize CTFs using ZnCl2 as solvent and catalyst. For itaconic acid/glucose mixtures, hydrophobic materials with a high C/N ratio showed the best adsorption performance, with itaconic acid capacities up to 400 mg g-1 and high separation efficiencies. For the lysine-glucose mixtures, high hydrophilicity proved to be beneficial to facilitate L-lysine separation. Overall, CTFs appear to combine the best of both worlds - polymer and carbonaceous material - and can serve as model systems for understanding N-based carbonaceous feedstocks. In the third chapter of this thesis, the selective adsorption of L-lysine from lysine-glucose mixtures was evaluated on various zeolites with different structural properties and Si/Al ratios. Zeolites can act as a molecular sieve and thus selectively adsorb or exclude compounds with specific molecular sizes. In the competitive adsorption of L-lysine and D-glucose, the effect of zeolites as a molecular sieve was highlighted. High separation factors could be achieved, due to the fact that D-glucose cannot enter the pore system of the zeolites because of its molecular size. In the last part of the work, the adsorption process was coupled with a bio-technological itaconic acid production process to investigate its suitability for in situ product re-covery. The in situ separation of itaconic acid prevented product inhibition, resulting in an in-crease of 11 % in the space-time yield of the bioprocess. In combination with highly selective product recovery, a promising downstream technology for future biorefinery processes can be achieved.

Institutions

• Department of Chemistry [150000]
• Chair of Heterogeneous Catalysis and Technical Chemistry [155310]