(223c) Catalytic Gasification for Waste Management: Selectivity of Oxidation Reactions for Model Polymers

This research seeks to provide a characterization of catalytic gasification reaction mechanisms for different polymers and catalyst types. While catalytic gasification of waste polymers has significance in a variety of engineering applications, it is of particular relevance to in-situ resource utilization (ISRU) and waste management in space exploration beyond low earth orbit (LEO).

NASA Glenn Research Center seeks solutions to the logistical costs of transporting waste back to Earth as well as the need for propellant generation technologies that can be operated on the lunar surface, an asteroid, or on the International Space Station. Low-to-mid temperature catalytic gasification presents a potential solution to both of these challenges. The carbon content of the plastics, paper, and nylon often disposed of on the ISS can serve as the raw material for the generation of fuel (methane). Long missions beyond LEO will not be possible without technologies that can reduce the dependence on logistic resupply as well as eliminate hundreds of kilograms of trash.

Catalytic gasification permits the low-temperature conversion of polymers to a synthetic gas (syngas) which can then be used to generate energy. The catalyst lowers the activation energy of reaction and makes the process possible at lower temperatures. There are four reactions that take place in the entire process: the polymer oxidation reactions (one producing carbon dioxide and another producing carbon monoxide), the Water-Gas Shift Reaction, and the Sabatier Reaction.

The studied substrates, Polyethylene and Cellulose, are both long chain organic polymers, and make up a substantial portion of both space and municipal waste composition. Although similar in nature, these substrates exhibit marked differences as it pertains to gasification, and were therefore selected as model substrates.

Experiments were performed on model polymers in the form of batch reactions over different catalysts supported by alumina. Analysis of gaseous products using a gas chromatograph with thermal conductivity detection provided data reflecting the conjunctive performance of all reactions. Application of reaction engineering parameter definitions and experimental data enabled the development of a model for the selectivities of reaction products. Kinetic parameters for the oxidation reactions of polyethylene were retrieved to be used in cooperation with a kinetic model for the gas-phase reactions composing a methodological model for the gasification of solid waste.