Study of the substrate-related factors affecting sustainable production and utilization of high recalcitrant food-waste aromatics in reductive catalytic fractionation process

Abstract

Aromatic compounds are essential fuels and key chemical precursors for organic chemical synthesis; however, their production predominantly relies on fossil resources, leading to carbon emissions. Lignin, a complex polymer abundant in biomass, has gained recognition as a promising alternative to conventional aromatics. To advance research, development, and economic viability of the lignin valorization process, this thesis focuses on in-depth investigations of substrate-related factors and explores sustainable methodologies for the production and utilization of highly recalcitrant food waste, with the specific objective of enhancing monomer production. Particular emphasis is on unexplored lignin structures and their potential functions, highlighting the breakthroughs in lignin­ first pretreatment, catalytic lignin depolymerization, and the production of high-value products benchmarked against modern aromatics. Given that, the reductive catalytic fractionation (Anderson, #118) process is highlighted as a favorable strategy and has been adopted to generate lignin oil and transform the lignin-rich biomass into high-value products. In the realm of biomass resources, the inedible components of nuts and stone fruits emerge as an economically viable and lignin-rich feedstock for the sustainable production of aromatic chemicals, surpassing the potential of agricultural and forestry residues. However, the depolymerization performances on food-related biomass remain unclear, owing to the broad physicochemical variations from the edible parts of the fruits and plant species. The monomer production potentials of ten major fruit and nutshell biomass were investigated with comprehensive numerical information derived from instrumental analysis, such as plant cell wall chemical compositions, syringyl/guaiacyl (S/G ratios, and contents of lignin substructure linkages (β−O−4, β−β, β−5). A standardized one-pot RCF process was applied to benchmark the monomer yields, and the results were statistically analyzed. Among all the tested biomass, mango endocarp provided the highest monolignol yields of 37.1% per dry substrate. Positive S-lignin (70-84%) resulted in higher monomer yield mainly due to more cleavable β–O–4 linkages and less condensed C–C linkages. Strong positive relationships were identified between β–O–4 and S-lignin and between β–5 and G-lignin. The analytical, numerical, and experimental results shed light on the process design of lignin-first biorefinery in food-processing industries and waste management works. Next, we investigated the influence of process design and control on biomass pre-treatment and RCF in relation to the quality and yield of lignin. We compared different pre-treatment methods (organosolv, biphasic, and staged organosolv) with the one-pot RCF process to enhance lignin accessibility and reactivity. The results revealed that direct RCF yielded more lignin monomers, while biphasic and staged pre-treatments preserved crucial β–O–4 linkages, enhancing lignin reactivity. The insights gained from this work are of critical importance for optimizing the process parameters in a lignin-first biorefinery. Consequently, these findings establish a connection between the earlier chapters and the subsequent discussions on techno-economic evaluation. Furthermore, the potential retrofitting of conventional petroleum refineries for lignin-based products is discussed as a means to progressively transition the industry towards carbon neutrality. The application of obtained lignin is also explored, particularly in the field of wastewater treatment. Woody waste-derived organosolv lignin nanoparticles (LNPs) with uniform colloidal spherical morphology and optimized particle size are synthesized via a simple and facile anti-solvent nanoprecipitation technique. These LNPs are then used to fabricate ultrafiltration nanocomposite membranes with enhanced properties. The lignin-enabled membranes exhibit high permeation flux and excellent removal efficiencies for cationic and anionic dyes, making them suitable for real-world wastewater treatment applications. To guide research efforts towards commercialization, the thesis concludes with a techno-economic evaluation of lignin-first biorefineries utilizing RCF. The economic feasibility and sustainability of the concepts discussed throughout the study are assessed, providing a comprehensive view of the lignin-first biorefinery concept. This evaluation facilitates the transition towards a more sustainable and value-driven biorefinery industry. Overall, this thesis contributes to the development and utilization of lignin as a renewable resource, promoting a more environmentally friendly and economically viable approach to aromatic compound production.