CBET Award #1336385
Direct-In-Liquid Electrical Discharge for the Production of Hydrogen-Rich Gas
Manufacturing of hydrogen from hydrocarbons is needed for a variety of applications, especially for the production of hydrogen-rich gas for fuel cell powered vehicles and plasma treatment of exhaust gas. Compared to other reforming technologies, electrical discharge plasmas provide several advantages including fast response time, durability, compactness, low weight, and high conversion efficiencies. However, to maximize the conversion of hydrocarbons and increase the byproduct selectivity, it is important to elucidate chemical reaction mechanisms and develop complete reaction schemes.
This project investigates the fundamental chemical process occurring during plasma-assisted reforming of liquid hydrocarbons and alcohols using direct-in-liquid pulsed streamer-like electrical discharges. Due to the relatively unexplored field of plasma-chemical reactions in liquid plasmas, and especially in organic liquids, the focus is on elucidating chemical pathways responsible for the formation of hydrogen, short-chained hydrocarbons and syngas during direct reforming of liquid fuels, reforming in the presence of water (termed water-assisted reforming), and reforming in the presence of air (oxidative reforming). It is expected that the unique combination of the experimental approach coupled to mathematical modeling and plasma imaging will lead to new insights and novel means of analyzing liquid plasmas.
The experimental approach will use radical scavenging techniques, plasma spectroscopy, as well as deuterated and isotopically labeled solvents to elucidate chemical reactions responsible for the formation of stable gaseous and liquid byproducts. The major hypothesis underlying the research is that in the absence of oxidants, the main decomposition byproducts of <C8 hydrocarbons and aromatic compounds will be short-chained hydrocarbons (<C4) and hydrogen. Hydrocarbons with >C8 will also produce alkanes with five or more carbon atoms. The presence of water and air will scavenge carbon atoms in plasma, lower the concentrations of light hydrocarbons, and increase the yield of CO (and possibly CO2). Experiments will first be conducted in simple fuel surrogates (e.g. parrafins, toluene, cyclohexane, etc.) followed by electrical discharges in real fuels (diesel, gasoline and kerosene).
Chemical kinetic models for fuels are a critical part of engine models. Unfortunately, increases in engine efficiency and decreases in engine emissions are being inhibited by an inadequate ability to simulate in-cylinder combustion and emission formation processes. To address this need and predict experimentally measured concentrations of stable byproducts, kinetic models for an electrical discharge in ethanol and in iso-octane will also be developed.
Imaging studies will be performed in order to characterize the discharge and its growth as a function of several parameters and, in particular, electrode polarity and molecular structure of the starting liquid. The mentioned techniques include fast optical imaging of the discharge, schlieren and shadowgraphic imaging of the discharge, and interferometry. The results of these measurements will yield valuable information about the streamer velocity, shock velocity branching, pressure in front of and behind the shock, plasma volume and possible electron density, all of which will be used to advance the understanding of the chemistry behind the discharge interaction with the fuel.
Membrane liquid phase plasma reactor
The main objective of this study is to engineer, develop and demonstrate an innovative water treatment technology that could potentially replace conventional water treatment unit processes for small water treatment systems. To this end, the PIs propose to integrate membrane technology (i.e., ceramic NF, UF or MF) with electrical discharge plasma generated via a novel reticulated vitreous carbon (RVC) electrode material. The reasons for the integration of these two processes are four-fold: (1) the novel RVC electrode material will significantly improve the efficiency and longevity of the electrical discharge; (2) the membrane process protects the porous electrode material from clogging and removes constituents targeted in conventional water treatment processes and that reduce the effectiveness of the AOP; (3) both the membrane and electrical discharge remove pathogens; and (4) electrical discharge is effective for the destruction of a wide variety of organic contaminants and contaminant precursors.
A tiered approach will be undertaken to achieve the overall project goal of demonstrating the integrated membrane/plasma process as an innovative, affordable, sustainable and effective treatment technology for small treatment systems. The team will first use a regimented approach to carefully select contaminants to investigate and evaluate the plasma process. Fundamental bench-scale studies will then be undertaken to investigate and optimize the plasma and membrane systems as individual and integrated processes. Findings from fundamental studies will be used to develop a scalable engineered membrane/plasma process that will be tested under carefully controlled conditions. Finally, long-term testing will be conducted with the developed system at small treatment systems to fully demonstrate the scalable membrane/plasma system.
The successful development of this process will result in a technology that is scalable, robust, requires minimal chemical input, has a small foot-print, and achieves a finished water quality better than treatment systems that require multiple technologies. The developed process will have unique treatment capabilities (i.e., targets both suspended and dissolved constituents) enabling the production of high-quality water from impaired sources, which will foster water recycling, a decreased reliance on imported water, and more efficient management of water supplies.
BRIGE Award #1125592
Production of biodiesel using liquid-phase electrical discharge plasmas
Over the past ten years, the PI has studied the fundamental phenomena that occur during electrical discharges in water and strived to expand the applications of liquid-phase plasmas to mediums other than water. She has demonstrated that an electrical discharge in dimethyl sulfoxide yields diamondlike carbon and that discharges in methanol and sucrose solutions yield hydrogen gas and ethanol, respectively. More recently, she discovered that within thirty minutes of plasma treatment, the viscosity of vegetable oil is reduced by about sixty percent. Because this later result could be important in the area of biodiesel (alkyl ester) production, the PI believes it must be explored further. Thus, the main goal of this proposal is to investigate and assess electrical discharges as a novel technology for the production of biodiesel and to study the fundamental chemistry of plasmas in oils. The first objective will be achieved by conducting electrical discharges in different vegetable oils (sunflower oil, palm oil and coconut oil) with or without additives (methanol, glycerol and sucrose), identifying reaction by-products and characterizing physical properties of the liquids after the discharge. In order to elucidate and categorize chemical processes inside the plasma and thus achieve the second objective, it is critical to examine the nature of chemical reactions. There has always been a suspicion that chemical reactions in plasmas are not driven purely by the electron impact dissociation but also, because of the high plasma temperatures, the pyrolysis. Thus, the development of a mathematical model to predict the plasma temperature will assist in answering fundamental questions regarding the types of chemical reactions in plasma and facilitate the understanding of the reaction pathways for the conversion of vegetable oil into biodiesel.