Method for the Control of NO_x Emissions in Long-Range Space Travel

Abstract

The wheat straw, an inedible biomass that can be continuously produced in a space vehicle has been used to produce activated carbon for effective control of NOx emissions from the incineration of wastes. The optimal carbonization temperature of wheat straw was found to be around 600 degrees C when a burnoff of 67% was observed. The BET surface area of the activated carbon produced from the wheat straw reached as high as 300 m2/g. The presence of oxygen in flue gas is essential for effective adsorption of NO by activated carbon. On the contrary, water vapor inhibits the adsorption efficiency of NO. Consequently, water vapor in flue gas should be removed by drying agents before adsorption to ensure high NO adsorption efficiency. All of the NO in the flue gas was removed for more than 2 h by the activated carbons when 10% oxygen was present and the ratio of carbon weight to the flue gas flow rate (W/F) was 30 g min/L, with a contact time of 10.2 s. All of NO was reduced to N2 by the activated carbon at 450 degrees C with a W/F ratio of 15 g min/L and a contact time of 5.1 s. Reduction of the adsorbed NO also regenerated the activated carbon, and the regenerated activated carbon exhibited an improved NO adsorption efficiency. However, the reduction of the adsorbed NO resulted in a loss of carbon which was determined to be about 0.99% of the activated carbon per cycle of regeneration. The sufficiency of the amount of wheat straw in providing the activated carbon based on a six-person crew, such as the mission planned for Mars, has been determined. This novel approach for the control of NOx emissions is sustainable in a closed system such as the case in space travel. It is simple to operate and is functional under microgravity environment.

Simultaneous removal of SO2 and NOx from flue gas by low-temperature adsorption over activated carbon

“…As shown in Table 4 , the presence of oxygen can significantly increase the breakthrough time and specific capacity of NO. With presence of oxygen, NO can be oxidized to NO 2 which is a much more adsorbable species over activated carbon 26 , 27 . The oxidation rate η (NO 2 ) is calculated by the following equation: where C out (NO 2 ) is the concentration of NO 2 when it reaches steady state.…”

“…The mechanism of NO oxidation over activated carbon is complicated, involving both surface reactions and gaseous reactions. The oxidation of gaseous NO by adsorbed oxygen over the activate surface site is believed to be the dominant pathway 26 . where C( ) represents the activated carbon with active surface site.…”

Simultaneous Removal of SO2 and NOx From Flue Gas by Low-temperature Adsorption Over Activated Carbon

“…The presence of oxygen can significantly increase the adsorbability of NO because of the catalytic oxidation of NO to NO2 which is a much more adsorbable species over activated carbon [24,25]. The oxidation conversion rate η(NO2) is given in Fig.8 and Tab.1.…”

“…The mechanism of NO oxidation over activated carbon is complicated, involving both surface reactions and gaseous reactions. The oxidation of gaseous NO by adsorbed oxygen over the activate surface site is believed to be the dominant pathway [24].…”

Waste-derived activated carbons for control of nitrogen oxides

“…The kinetics of NO x removal by carbon of commercial origin has been studied by many researchers (Claudino et al, 2004;Klose and Rincón, 2007;Mochida et al, 1994;Shirahama et al, 2002;Teng and Suuberg, 1993;Zhang et al, 2008) and it has been concluded that the origin, the natural impurities in the feedstock, surface chemistry and the conditions used to prepare activated carbon are the main factors that can control its efficiency for NO x reduction (Xu et al, 2003). Although there has been much research into NO x control using activated carbons, the factors controlling the NO x adsorption process are still not clear.…”