Harvesting Heat from Safer, Energy-Dense Slow Pyrolant Mixtures for Future Space Missions

Energy sources powering space missions range from highly energetic nuclear reactions to short-lifetime and low-output batteries. The proper selection of a power system is dependent on the mission duration and destination and oftentimes energy sources that may be optimal for the former may be unsuitable for the latter. Various limitations of these power sources hinder the capacity for regular and frequent space exploration. However, the ability to harvest heat for electrical power generation would allow for long-distance and long-duration missions at a reduced cost. By employing a regulated, self-propagating, exothermic chemical reaction between solid fuel and oxidizer, we hope to devise a slow-burning reactant system capable of generating heat at a harvestable rate. Eighteen energy-dense fuel and oxidizer combinations were selected to assess for their slow-propagating potential. One ceramic and one graphite propagation cell were designed to monitor combustion along a linear length of pyrolant powder and to measure reaction temperatures. Each reaction was ignited through heating of a nichrome wire placed at one end of the pyrolant mixture and four thermocouples were placed at 1 cm intervals along the length of powder following the wire. In addition to the propagation cell, a multi-step selection process was devised to evaluate each pyrolant. By this process, the pyrolant mixture between lithium peroxide and boron was selected, and the best propagation rate achieved by this system was measured to be 1.49 cm/s

Synthesis and Assessment of Sustainable Fuels for Transportation and Space Exploration

As global energy sources transition towards renewable energy, the demand for sustainable fuels has never been greater. The sheer scale of this transition will require numerous solutions to accommodate for the diverse and complex situations worldwide. This dissertation will discuss 3 studies: the utilization of CO2 waste gas to produce fuels sustainably, characterizing biofuels for efficient use in automobiles, and developing a solid, emissonless fuel intended for spaceflight but also applicable on Earth. The hydrogenation of CO2 into value-added molecules could reduce greenhouse gas emissions if waste stream CO2 were captured for conversion. We found that atomic vacancies induced in defect-laden hexagonal boron nitride (dh-BN) can activate the CO2 molecule for hydrogenation. Subsequent hydrogenation to formic acid (HCOOH) and methanol (CH3OH) occur through vacancy-facilitated co-adsorption of hydrogen and CO2. Boron and nitrogen are abundant elements, making h-BN an attractive catalyst in the synthesis of value-added molecules, facilitating efforts to reduce GHG emissions. Biofuels could be vital in a sustainable fuel future. However, their implementation into existing engines requires an understanding of their interactions with engine components at temperature. The formation of carbon deposits on hot metal components can reduce engine performance. Using a novel test rig and gasoline and diesel analog compounds, the degree of fuel degradation to form carbon can be measured on various metal surfaces. Thus, we can screen for low soot-forming biofuels as promising candidates surface on the market. Historically, innovations in space exploration have led to immensely beneficial applications on Earth. Currently, various limitations of power sources hinder the capacity for regular and frequent space exploration. The ability to harvest heat for electrical power would reduce the cost of long-distance and long-duration missions. Employing a regulated, self-propagating, exothermic chemical reaction, we have devised a slow-burning reactant system capable of generating heat at a harvestable rate

Methanol carbonylation to acetaldehyde on Au particles supported by single-layer MoS2 grown on silica

Homogenous single-layer MoS2 films coated with sub-single layer amounts of gold are found to isolate the reaction of methanol with carbon monoxide, the fundamental step toward higher alcohols, from an array of possible surface reactions. Active surfaces were prepared from homogenous single-layer MoS2 films coated with sub-single layer amounts of gold. These gold atoms formed clusters on the MoS2 surface. A gas mixture of carbon monoxide (CO) and methanol (CH3OH) was partially converted to acetaldehyde (CH3CHO) under mild process conditions (308 kPa and 393 K). This carbonylation of methanol to a C2 species is a critical step toward the formation of higher alcohols. Density functional theory modeling of critical steps of the catalytic process identify a viable reaction pathway. Imaging and spectroscopic methods revealed that the single layer of MoS2 facilitated formation of nanoscale gold islands, which appear to sinter through Ostwald ripening. The formation of acetaldehyde by the catalytic carbonylation of methanol over supported gold clusters is an important step toward realizing controlled production of useful molecules from low carbon-count precursors

The Scalability In The Mechanochemical Syntheses Of Edge Functionalized Graphene Materials And Biomass-Derived Chemicals

Mechanochemical approaches to chemical synthesis offer the promise of improved yields, new reaction pathways and greener syntheses. Scaling these syntheses is a crucial step toward realizing a commercially viable process. Although much work has been performed on laboratory-scale investigations little has been done to move these approaches toward industrially relevant scales. Moving reactions from shaker-type mills and planetary-type mills to scalable solutions can present a challenge. We have investigated scalability through discrete element models, thermal monitoring and reactor design. We have found that impact forces and macroscopic mixing are important factors in implementing a truly scalable process. These observations have allowed us to scale reactions from a few grams to several hundred grams and we have successfully implemented scalable solutions for the mechanocatalytic conversion of cellulose to value-added compounds and the synthesis of edge functionalized graphene

Towards Higher Alcohol Formation using a single-layer MoS2 activated Au on Silica: Methanol Carbonylation to Acetaldehyde

We demonstrate that a fused silica substrate can be rendered active for acetaldehyde (CH3CHO) synthesis from a gas mixture of carbon monoxide (CO) and methanol (CH3OH) under mild process conditions (308 kPa and 393 K) by deposition first of a homogenous single-layer MoS2 film and subsequently of a sub-mnonolayer (1 Angstrom) loading of gold. In operando monitoring of the catalyst performance in a flow reactor reveals uncompromised activity even after 2 hours on stream. The carbonylation of methanol to a C2 species represents a crucial step toward the formation of higher alcohols from syngas derived from methane or biomass. Characterization of the film by imaging and spectroscopy reveals that the single-layer MoS2 film disperses the gold loading into nanoscale islands; density functional theory (DFT) calculations identify low-coordinated edge sites on these islands as active centers for the carbon-carbon coupling at barriers significantly below 1 eV. </p