Valorization of residual streams through catalysis

This thesis explores strategies for upgrading underutilized streams, focusing on hemp hurd, softwood bark lignin, and plastics. Catalysis plays a crucial role in overcoming challenges in upgrading and efficiently converting residual streams into valuable products. By exploring lignocellulosic biomass fractionation, this research tackles the complexities of converting biomass side streams into sustainable, marketable products. Additionally, it investigates methods for recycling polyesters, particularly PET, to integrate plastic waste into a circular economy. The valorization of different biomass feedstocks, such as hemp hurd and softwood bark, requires tailored catalytic processes due to their distinct compositions. For example, reductive catalytic fractionation (RCF) is highly effective for hemp hurd, rich in syringyl lignin, yielding monophenolic compounds and dissolving-grade pulp for textiles and nanocellulose production. Oxidative catalytic fractionation (OCF) works better for softwood bark, as it cleaves not only the predominant β–O–4 linkages but also additional lignin bonds, enhancing the yield of monophenolic products such as vanillin. This highlights the importance of selecting the appropriate catalytic methods based on feedstock characteristics. However, both OCF and RCF traditionally rely on expensive noble metal catalysts. As an alternative, an organocatalytic approach is introduced through a lignin condensation strategy that preserves cleavable β-ether units to produce high-performance bisphenols. Organocatalysis is also applied to the recycling of PET, enabling the recovery of valuable monomers and facilitating the recycling of polycotton waste into high-quality viscose fibers and chemicals. This thesis presents approaches to upgrading residual streams, demonstrating how catalysis-based strategies can be used in transforming low-value byproducts into valuable chemicals and materials.