Novel methods for landfill gas and biogas clean-up

In this study a novel catalytic oxidation technology appropriate for landfill gas (LFG) clean-up based on the flow-through catalytic membrane reactor (FTCMR) concept has been studied. For the experiments, a model LFG stream has been used with a volatile organic compound (VOC) composition which was shown previously by the authors to simulate well the behavior of real LFG in field-scale investigations. Asymmetric tubular alumina membranes were used in the research and were rendered catalytic by wet impregnation. Their pore-structure characteristics were measured with single-gas permeation tests, as they are important in determining the transport mechanisms of the VOC through the catalytically active membrane layer. When comparing the FTCMR with the more conventional reactors the "yardstick" of success is the ability of the FTCMR to operate under lower temperature for a given level of conversion, and/or attain higher conversion under the same conditions and catalyst loading. For the LFG application, light-off temperature experiments showed promising results when compared to the monolith reactor. Also, no catalyst deactivation was observed during the time-on-stream experiments, proving that the FTCMR is robust towards corrosive by-products (e.g., HCl) produced during the oxidation reactions.;Siloxanes are another major class of compounds detected in LFG. This Thesis is also a study on the impact of siloxanes on various types of equipment using LFG which is not treated for siloxanes. Specifically, in this study an internal combustion engine and a residential furnace operating on natural gas (NG) spiked with siloxanes have been studied experimentally with the goal of understanding the impact of siloxane impurities on their performance. These impurities are shown to completely decompose during NG combustion in the engine to form silica microparticulates. These coat the internal metal surfaces in the equipment and severely reduce their efficiency and damage important components, such as furnace flame sensors and engine oxygen sensors. A method to remove these siloxane impurities has also been studied in this thesis based on UV Photodecomposition. Specifically, this Thesis also describes efforts to evaluate the technical feasibility and environmental implications of a novel technology for the treatment of biogas and LFG which involves the in situ conversion of the siloxanes, typically found in the gas, into inert silicon dioxide via a photochemical conversion process. The approach involves using high energy UV light to convert the siloxanes into SiO2 powder, which can be conveniently removed from the biogas via a downstream filter. The technique is shown to be very effective with high siloxane conversions attained in the laboratory.