Catalytic Decomposition of Gaseous Byproducts from Primary Solid Waste Treatment Technologies

Several solid waste management (SWM) systems currently under development for spacecraft deployment result in the production of a variety of toxic gaseous contaminants. Examples include the Plastic Melt Waste Compactor (PMWC) at NASA - Ames Research Center¹, the Oxidation/Pyrolysis system at Advanced Fuel Research², and the Microwave Powered Solid Waste Stabilization and Water Recovery (MWSWS&WR) System at UMPQUA Research Company (URC). The current International Space Station (ISS) airborne contaminant removal system, the Trace Contaminant Control Subassembly (TCCS), is designed to efficiently process nominal airborne contaminants in spacecraft cabin air. However, the TCCS has no capability to periodically process the highly concentrated toxic vapors of variable composition, which are generated during solid waste processing, without significant modifications. To overcome this limitation, a gas-phase catalytic oxidation system, based on a high activity platinum - ruthenium bimetallic catalyst, is under development at URC to rapidly oxidize these contaminants and eliminate the release of toxic gases from solid waste treatment systems. The proof of concept catalytic oxidation reactor was challenged with four contaminants: carbon monoxide, benzene, naphthalene, and diethylphthalate. These contaminants represent typical solid waste processing byproducts and include a highly toxic inorganic gas, a typical volatile aromatic, a polycyclic aromatic hydrocarbon (PAH), and a plasticizer, respectively. The catalytic oxidation of each contaminant was evaluated over a range of concentrations, flow rates, and reaction temperatures. The experimental results summarized in this paper demonstrate very high rates of conversion of these toxic vapors to innocuous gases, primarily CO₂ and H₂O, at low temperatures, and indicate superior performance to that of current state-of-the-art catalysts.