Transport Limitations in Zeolites and Biomass Pyrolysis

Biomass pyrolysis has been widely explored for its potential to generate a sustainable chemical source capable of producing synthetic fuels and chemicals. Lignocellulosic biomass is the carbon rich, inedible fraction of wood that is comprised of long oxygenated biopolymers, primarily cellulose, hemicellulose and the highly aromatic lignin. High temperature thermal conversion of biomass to bio-oil (pyrolysis oil) occurs on the order of milliseconds and converts long chain biopolymers to a carbon-rich liquid crude. The chemistry of biomass pyrolysis is greatly complicated by significant heat and mass transport challenges. The complex fluid dynamics of the reactive liquid intermediate are examined in situ with high temperature spatiotemporally resolved techniques (T = 450 – 1000 °C, 1 µm, 1 ms), chemical analyses and computational fluid dynamics. Discoveries include the mechanism for aerosol generation during pyrolysis, existence and control of the Leidenfrost effect, and understanding bio-oil microexplosions. Zeolites are widely utilized to catalytically upgrade fuels by cracking, hydrogenation and hydrodeoxegenation as well as having applications in separations, sorption, ion-exchange. While new hierarchical materials are synthesized with transport lengthscales that are increasingly smaller, substantial diffusional transport limitations persist in small particles, often dominating the observed rates. The presence of these transport limitations remains a significant technical challenge. In this work, a mechanistic understanding is developed to describe such limitations. The potential for surface barriers to diffusion are experimentally assessed by Zero Length Chromatography and frequency response methods, and further confirmed by dynamic Monte Carlo simulations

The aging and impacts of atmospheric soot: closing the gap between experiments and models

The main goal of this dissertation is to generate data and parameterizations to accurately represent soot aerosols in atmospheric models. Soot from incomplete combustion of fossil fuels and biomass burning is a major air pollutant and a significant contributor to climate warming. The environmental impacts of soot are strongly dependent on the particle morphology and mixing state, which evolve continuously during atmospheric transport via a process known as aging. To make predictions of soot impacts on the environment, most atmospheric models adopt simplifications of particle structure and mixing state, which lead to substantial uncertainties. Using an experimentally constrained modeling approach, this dissertation aims to improve the predictive capabilities of atmospheric models regarding the impacts of soot. Accordingly, the study objectives are to: (1) conduct experiments and simulations to investigate how soot properties evolve during aging; (2) develop physical parameterizations between soot particle properties and aging environment using established relationships; (3) incorporate the parameterizations in a particle-resolved aerosol model. Experiments to investigate morphological changes are conducted by exposing airborne aggregates of well-defined mass, size, and composition to vapors of chemicals condensable at atmospheric conditions. The underlying mechanisms that lead to structural change are then identified and applied in theoretical calculations for soot aging. Optical experiments are conducted to measure light absorption and scattering by soot and compared against literature reported values to resolve differences. Additionally, rigorous optical calculations are performed with morphological data from aging experiments to investigate the contributions of morphology and mixing state to parameters of interest in atmospheric models. This work has developed a novel analytical framework for predicting the morphological mixing state and extent of restructuring of soot aggregates during atmospheric aging. The framework is validated by experimental measurements for a wide range of condensing vapors in realistic multicomponent systems, and is based on a single dimensionless parameter χ. The χ-parameter is controlled by coating material properties of vapor supersaturation and wettability for a specified soot monomer diameter. In the course of this study, the roles of vapor condensation and coating evaporation on aggregate restructuring are also found to be influenced by coating wettability. Based on rigorous optical calculations, the differences in measured and modeled optical properties of soot are resolved by varying monomer size and introducing necking material, between monomers. Additionally, the effect of the morphological mixing state on soot optical properties is found to depend strongly on the compactness of the aggregate. A simplified representation of χ-framework is incorporated into the particle resolved aerosol model, PartMC-MOSAIC and successfully tested on soot particles in an idealized urban air parcel. This demonstrates the suitability of this approach in facilitating accurate predictions of morphology-dependent soot properties in PartMC-MOSAIC. Overall, the findings of this dissertation represent a significant advancement in understanding the processes governing the transformations and environmental impacts of soot that will benefit the atmospheric experimental and modeling research communities

Catalytic Pyrolysis of Olive Mill Wastewater Sludge

Olive mill wastewater sludge (OMWS) is the solid residue that remains in the evaporation ponds after evaporation of the majority of water in the olive mill wastewater (OMW). OMWS is a major environmental pollutant in the olive oil producing regions. Approximately 41.16 wt. % of the OMWS was soluble in hexanes (HSF). The fatty acids in this fraction consist mainly of oleic and palmitic acid. Catalytic pyrolysis of the OMWS over red mud and HZSM-5 has been demonstrated to be an effective technology for converting this waste material into fuel. Red mud-catalyzed pyrolysis gave higher organics yields than the HZSM-5 catalysis. The viscosity as well as the oxygen content of the catalytic pyrolysis oils were significantly lower than those of the non-catalytic oil. The reaction pathways of red mud and HZSM-5 were different. The catalytic pyrolysis of the HSF gave an acidic oil with low viscosity and high energy content, and was nitrogen and sulfur free, whereas the catalytic pyrolysis of the solid residue after hexanes extraction (SR) gave an oil with higher viscosity, close to neutral pH, lower energy content, and had high nitrogen content and traces of sulfur

Co-pyrolysis of Birchwood Bio-oil and Reduced Crude in a Mechanically Fluidized Reactor

Atmospheric Reduced crude (ARC) was co-pyrolyzed with 23-44 dry wt. % birchwood bio-oil at 480-530°C in a mechanically fluidized reactor (MFR) to investigate the feasibility of integrating bio-oil with heavy petroleum feedstocks into a Fluid CokerTM. The liquid products of the bio-oil and ARC were predominately segregated into two separate phases. The product yields of valuable petroleum liquid products were significantly reduced during co-pyrolysis when compared to the pyrolysis of ARC. The effects of removing the aqueous phase of bio-oil before co-pyrolysis were investigated by separating the aqueous phase from birchwood bio-oil utilizing a novel co-distillation technique with ARC. The resulting 19-29 wt. % bio-oil distillation residues were pyrolyzed in a MFR at 480-500°C. The pyrolyzed distillation residues resulted in higher valuable liquid yields with significantly lower water contents when compared to the co-pyrolysis bio-oil and ARC. Valuable liquid yields were lower when compared to the pyrolysis of ARC