Thermochemical Conversion of Biomass to Renewable Fuels

Valorization of lignocellulosic biomass to renewable biofuels provides a promising solution to address growing concerns regarding energy security and environmental issues. Researchers are breaking the chemical & engineering barriers to efficiently convert lignocellulosic biomass to liquid fuels. The thermochemical deconstruction strategies can be classified into three categories: gasification, pyrolysis, and liquefaction. Pyrolysis and liquefaction are called selective thermal processing which generate liquid products via depolymerization and fragmentation of biomass feedstocks. This dissertation focuses on the pyrolysis and liquefaction of whole lignocellulosic biomass. The liquid products (called bio-oil) are inherently chemical complex, of high oxygen content, low heating values compared to commercial heavy fuels, thus need treatments towards the thermal process to enhance the bio-oil’s properties. This dissertation thoroughly examined thermochemical conversion strategies to generate high quality bio-oils as a fuel precursor. Two major aspects in this dissertation include 1) the biomass pyrolysis and 20 solvent liquefaction. Two strategies have been examined to promote the pyrolysis oils’ qualities, including pretreatment and ex-situ catalysis. Two different strategies have been studied during the one-pot liquefaction including the metal chloride additive and a bi-catalyst system of Pd/C and water tolerant Lewis acid. The major objectives in this dissertation are listed below: 1. Investigated the pretreatment effect on the biomass structure and the subsequent pyrolysis oil’s properties (Chapter III) 2. Optimized the auto-hydrolysis pretreatment on biomass towards the “optimal” pyrolysis oils as a fuel precursor (Chapter IV) 3. Accomplished the ex-situ upgrading of the pyrolysis oils using metal oxide catalysts (Chapter V) 4. Evaluate the structures of the ex-situ catalytic upgraded pyrolysis vapors from a bench-scale unit (Chapter VI) 5. Examined the one-step liquefaction of biomass in solvent to produce bio-oils using metal chlorides (Chapter VII) 6. Explored the bi-catalyst system performance in one-step liquefaction of biomass (Chapter VIII

Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy

The analysis of chemical structural characteristics of biorefinery product streams (such as lignin and tannin) has advanced substantially over the past decade, with traditional wet-chemical techniques being replaced or supplemented by NMR methodologies. Quantitative 31P NMR spectroscopy is a promising technique for the analysis of hydroxyl groups because of its unique characterization capability and broad potential applicability across the biorefinery research community. This protocol describes procedures for (i) the preparation/solubilization of lignin and tannin, (ii) the phosphitylation of their hydroxyl groups, (iii) NMR acquisition details, and (iv) the ensuing data analyses and means to precisely calculate the content of the different types of hydroxyl groups. Compared with traditional wet-chemical techniques, the technique of quantitative 31P NMR spectroscopy offers unique advantages in measuring hydroxyl groups in a single spectrum with high signal resolution. The method provides complete quantitative information about the hydroxyl groups with small amounts of sample (~30 mg) within a relatively short experimental time (~30-120 min)

Characteristics of Lignin Fractions from Dilute Acid Pretreated Switchgrass and Their Effect on Cellobiohydrolase from Trichoderma longibrachiatum

To investigate the interactions between acid pretreated switchgrass lignin and cellobiohydrolase (CBH), three different lignin fractions were isolated from dilute acid pretreated switchgrass by (i) ethanol extraction, followed by (ii) dioxane/H2O extraction, and (iii) cellulase treatment, respectively. Structural properties of each lignin fraction were elucidated by GPC, 13C-NMR, and 2D-HSQC NMR analyses. The adsorptions of CBH to the isolated lignin fractions were also studied by Langmuir adsorption isotherms. Ethanol-extractable lignin fraction, mainly composed of syringyl (S) and guaiacyl (G) units, had the lowest molecular weight, while dioxane/H2O-extracted lignin fraction had the lowest S/G ratio with higher content of p-coumaric acid (pCA) unit. The residual lignin fraction after enzymatic treatment had the highest S/G ratio without hydroxyphenyl (H) unit. Strong associations were found between lignin properties such as lignin composition and S/G ratio and its non-productive enzyme adsorption factors including the maximum adsorption capacity and binding strength