A multi-scale environmental and kinetics study on the pyrolysis of sustainable biomass feedstock.

摘要

Lignocellulosic biomass is the most abundant source of carbon. Its ubiquity makes it a potentially low-cost feedstock for many bioenergy applications. Biomass pyrolysis is a thermochemical conversion technique that breaks down plant material at high temperature, with little to no oxidizing agent present to produce bio-gas, bio-char and bio-oil that can be upgraded to produce renewable fuels and useful chemicals. Many of the roadblocks facing biomass pyrolysis are issues that require fundamental knowledge of substrate and product chemistry to understand the kinetic and mechanistic processes leading to the formation of products. This research focuses on biomass pyrolysis for the sustainable production of fuels and chemicals from herbaceous biomass feedstock. A multi-scale approach was implemented to understanding global reaction kinetics at the meso-scale, pyrolysis product distributions at the micro-scale, and molecular interactions at the nano-scale. At the macro-scale, the regional sociological impacts of energy crops and biofuels production were analyzed.;Accurate kinetic data are required for the optimization and scale-up of pyrolysis reactors. Kinetic information was calculated using thermogravimetric analysis (TGA) for alfalfa, sorghumsudangrass, switchgrass and tall fescue hay. Dynamic TGA experiments that global kinetic parameters were adequately estimated by modeling the weight loss curves of the three main structural components preset in whole biomass, cellulose, hemicellulose and lignin. The kinetic model treats the decompositon of each biomass component as a partial processes that can be summed to give the volatilization of the entire biomass substrate. This model was found to adequately reproduce experimental rate curves, and is flexible enough to describe global mass loss events for a range of biomass feedstock.;Fast pyrolysis of biomass, in which high heating rates and short residence times are implemented at moderate temperatures (400-600°C) is the preferred route to maximize bio-oil production. Quantitative fast pyrolysis experiments were performed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Analysis of this data provides insight on the dependence of particle size and temperature on the product distribution for alfalfa, switchgrass, and tall fescue. Since up to 75% of biomass is composed of carbohydrates, the thermal stability of two model compounds was explored using computational modeling methods. Results from molecular dynamics simulations of maltose and cellobiose reveal that the orientation of the glycosidic bond might influence the stability of the carbohydrate compound. At 700K, the alpha- disaccharide, maltose, was found to less stable than cellobiose, a beta-disaccharide.;The role of local farmers in a developing bioenergy industry was explored. Information was collected from two farming counties in the Upper Cumberland region of Tennessee to measure knowledge, awareness and perceptions on topics related to energy crops, biofuels, and biomass pyrolysis.