Utilization of Solid Waste for Activated Carbon Production in Space

Activated carbons have a unique capability of strongly absorbing a great variety of species, ranging from SO₂ and NO_x, to trace organics, mercury, and other heavy metals. Activated carbons can also be used for gas storage and gas separations, including systems of practical interest to NASA (e.g., CO₂/N₂/O₂), and even for the purification of liquids. No single activated carbon is suitable for all applications, but appreciable control over sorbent properties can be exercised in the process of carbon preparation. Since activated carbons can be produced from a wide range of organic materials, including waste streams, the preparation of activated carbons on board spacecraft should involve a limited amount of additional resources, help manage on-board waste, and reduce the weight of materials to be launched from earth. The feasibility of producing waste-derived activated carbons suitable for SO₂ and NO control was the subject of the current study. The conclusions from this work are as follows: 1) high levels of NO and SO₂ removal (up to 95%) were obtained with biomass-derived sorbents; 2) at low temperatures, the biomass sorbent performance was even better than that obtained with a commercial activated carbon which had a much higher nominal BET surface area (793 m²/g versus 292 m²/g); 3) in general, catalyst impregnation of wheat straw chars was successful, despite the microporous nature of these materials, and resulted in improved sorbent performance (higher removal efficiencies); 4) activation of the biomass (wheat straw) derived char with CO₂ resulted in relatively high surface areas (∼300 m²/g) compared to most literature results for similar materials.