Removal of elemental mercury from coal combustion flue gas by bentonite-chitosan and their modifier
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摘要: 应用VM3000在线测汞仪作为检测手段,在固定床实验台架上,以改性膨润土壳聚糖为吸附剂进行脱汞(Hg0)实验研究。采用N2吸附/脱附、扫描电镜(SEM)和傅里叶变换红外光谱(FT-IR)等分析仪对吸附剂进行表征。分析发现改性后吸附剂的孔隙和比表面积降低;碘离子进入了膨润土的内部,碘、硫酸和壳聚糖中的氨基发生了化学反应。脱汞实验表明,负载壳聚糖的膨润土吸附剂表现出较膨润土差的脱汞效果,证明膨润土负载壳聚糖脱除气态中单质汞的机理和液相中二价汞的机理不同。经碘改性后,各吸附剂均可不同程度地提高其脱汞效率,且以碘改性膨润土的脱汞效果最好;碘改性吸附剂中添加适量的硫酸后,膨润土负载壳聚糖吸附剂的脱汞效率从85%提高至100%,因与膨润土负载壳聚糖不同的物理化学特性,碘和硫酸改性的膨润土的脱汞效率则降低。Abstract: Adsorption experiments of vapor-phase elemental mercury were carried out by using modified bentonite-chitosan in a laboratoryscale fixed-bed reactor. VM3000 online mercury analyzer was applied to detect the inlet and outlet mercury (Hg0) concentrations. The characterizations of the sorbents were analyzed using the method of nitrogen (N2) adsorption/desorption, scanning electron microscope (SEM) and Fourier transform infra-red spectroscopy (FT-IR), etc.. It was observed that the porosity and specific surface area decreased after modifying. The FT-IR spectra demonstrated the iodine was found in the inlayer of bentonite, and the chemical reactions of iodine and sulfuric acid with the amide of chitosan occurred. The tests in the fixedbed reactor showed that the bentonite-supported chitosan exhibited lower mercury capture than raw bentonite, which indicated that the mechanism of gas phase mercury removal was different from that of ionic state mercury in liquid. Generally, the iodine-modified sorbents demonstrated higher mercury capture efficiency than raw sorbents, and the iodine-modified bentonite showed the best one. Mercury removal efficiency of bentonite supported by chitosan sorbents could be promoted from 85% to 100% when added appropriate amount of H2SO4,while that of iodine and sulfuric acid modified bentonite exhibited opposite tendency due to their absolutely different physicochemical properties.
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Key words:
- bentonite /
- chitosan /
- sorbent /
- mercury capture /
- efficiency
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