Study Of Composite Adsorbents For NOx Capture

Emissions of hazardous nitrogen oxide resulting from the combustion of fossil fuels have created serious air pollution problems in many parts of the world. Chemical adsorbents are used widely and play an important role in the treatment of exhaust gases. This study is based the acid mist adsorbent(SDG) invented by Beijing University of Technology and aims to develop the capture capacity of NOx.Coal fly ash and zeolite were selected from several raw materials for farther modifying experiments. The synthesis of fly ash and calcium hydroxide would be best if calcined at 460℃but zeolite and calcium hydroxide would be best if calcined at 260℃.The coal fly ash was modified when mixed with an aqueous NaOH solution and heated by microwave. The adsorption properties of the novel adsorbent were enhanced when modified coal fly ash was used instead of original coal fly ash. The influence of modified parameters such as the NaOH concentrations, the water/solid ratios, the time and frequency of microwave irradiation was studied by orthogonal experiment. The modification mechanism was discussed by the way of BET and SEM. The BET of the modified fly-ash was 3.9 times than that of the raw fly ash. The results of the dynamic state experiments showed that the adsorption made from modified fly ash is two times of that of SDG.The activated process of improving adsorption capacity of natural zeolite was studied in this paper. It was shown that adsorption capacity of natural zeolite is greatly increased by treatment with hydrochloric acid and calcining and then dipping by metals salt solution. The best concentration of hydrochloric acid is 3%. It was shown that the activated zeolite has more tiny pore by pore size distribution curve and SEM. The other result was shown that when the composite adsorbent is made, it is no use to calcine again. The 1mol/L CaCl₂ solution is the best among the NaCl,KCl,K₂CO₃,Ce(NO₃)₃ solutions and other concentrations of CaCl₂ when they were used to steep actived zeolite..The adsorption capability of the adsorbent derived from modified zeolite / calcium hydroxide with NOx capture capacity higher than SDG and that of adsorbent synthesized from modified fly ash / calcium hydroxide.A series of NOx capture experiments were performed using a fixed bed test rig. The extent of NOx capture by the adsorbent derived from modified zeolite / calcium hydroxide varies significantly under different reaction conditions such as different space velocity, relative humidity and concentration of NOx. Related mechanisms were also discussed including physical adsorption, chemical adsorption and absorption.