Insights into Biomass Characterization, Degradation, and Utilization
Abstract
The dramatic growth of energy demand and rapid depletion of fossil sources have motivated the development of technologies for producing chemicals, fuels, and materials from sustainable energy sources. Nonfood lignocellulosic biomass is a renewable source with a high energy content. The objective of this research was to develop technologies for conversion of biomass to valuable chemicals and materials, as well as to gain a deeper understanding of the reaction processes for further improvement and optimization. 5-Hydroxymethylfurfural (HMF) and levulinic acid have been evaluated as important platform chemicals for generating value-added chemicals and liquid fuels from biomass. However, the production of HMF and levulinic acid from biomass has reached a bottleneck due to its high production and purification cost. To address this issue, catalytic conversion of glucose to these platform chemicals was explored by using earth-abundant and environmentally friendly iron catalysts. Active catalytic iron (II) species formed at the beginning of the reaction was identified for the first time by using mass spectrometry. Additional analytical techniques including UV-Vis spectroscopy and X-ray absorption spectroscopy were utilized to confirm the formation of iron (II) catalytic species. The reaction pathway of glucose conversion, the rate constant of each step, and the contributions from hydronium ion and iron (II) species were elucidated by investigating reaction kinetics. The reaction conditions for either HMF or levulinic acid production with high yield and selectivity were optimized. The approach of glucose conversion catalyzed by iron catalyst was further extended to the conversion of intact poplar and lignin-removed miscanthus to the platform chemicals. The furan and phenol products obtained from biomass catalytic conversion were selected for the preparation of thermosetting materials. The evolution of bisphenol-furan monomers to polymers was monitored by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR) and high-resolution mass spectrometry (MS). The thermo-mechanical properties of the resulting polymer materials were analyzed by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). These polymer materials exhibited competitive properties on the aspects of glassy modulus, glass transition temperature, and thermal stability, compared with commercially available thermosets generated from petroleum products. Biomass conversion by organosolv lignin methods or fast hydropyrolysis generates complex mixtures of unknown compounds. To determine the composition and delineate the pathways for the formation of these complex mixtures, high-resolution tandem mass spectrometry was employed to analyze these samples. Various parameters, including biomass feedstocks and process conditions, were evaluated based on the compositions of compounds in the product mixtures. Fast pyrolysis was coupled with mass spectrometry to facilitate the analysis of the product mixtures. To further probe the structures of the components in the mixtures, high-performance liquid chromatography coupled with high-resolution multiple-stage tandem mass spectrometry (HPLC/MSn) was employed. Different ionization methods, including atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), was used with the assistance of different dopants. Fragmentation patterns of ionized model compounds were studied via collision-activated dissociation (CAD) and in-source fragmentation experiments. The knowledge obtained in these studies was then applied to the analysis of unknown compounds in the samples. The obtained structural information of compounds in the samples is beneficial for the process optimization and downstream process development.
Degree
Ph.D.
Advisors
Kenttämaa, Purdue University.
Subject Area
Chemistry|Alternative Energy
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