Effects of temperature and oxygen content on Hg0 oxidation and adsorption by rice husk char impregnated with NH4Br

doi:10.11949/j.issn.0438-1157.20151368

Abstract

Abstract:

The mercury sorbent was prepared from raw rice husk char impregnated with 10 g·L^-1 NH₄Br solution. The physical-chemical characteristics of sorbents before and after modification were analyzed by surface area and porosity analyzer, scanning electron microscopy and X-ray energy dispersive spectroscope. The mercury oxidation and adsorption performance of the modified sorbents were investigated by analyzing mercury speciation (Hg⁰ and Hg²⁺) in the outlet of a fixed bed reactor system in N₂ and N₂+6.4%(vol)O₂ atmosphere at different temperatures. No obvious Hg²⁺ was detected in N₂, N₂+6.4%(vol)O₂ atmosphere at 50℃ and N₂ atmosphere at 150℃. Modified rice husk char exhibited a mercury removal efficiency of 90% at 50℃ and 150℃. Total mercury (Hg^T) removal efficiency of 98.2% was obtained in N₂+6.4%(vol)O₂ atmosphere at 150℃, 82.2% Hg⁰ was bound to the sorbent surface, the remaining was removed in the form of Hg²⁺ which was generated from heterogeneous oxidation by O₂ at the surface of sorbent. The heterogeneous reaction between O₂ and gaseous Hg⁰ at relatively elevated adsorption temperature promotes the Hg⁰ oxidation efficiency of modified sorbents. Desorption performance of adsorbed mercury was identified by analyzing Hg^T at the outlet of temperature programmed tube furnace. Peak mercury desorption temperature of 300℃ manifested that mercury was bound to sorbent surface in the form of Hg-Br compound most likely. Mercury desorption temperature between 220℃ and 350℃ suggested high thermal stability of adsorbed mercury. Mercury balance ratio of 100.14%—118.62% verified the accuracy of experimental results in this study.

Key words: modified rice husk char, mercury removal, mercury speciation, oxidation, adsorption, desorption

摘要：

采用10 g·L^-1 NH₄Br溶液对原始稻壳焦进行浸渍改性制备了脱汞吸附剂。利用比表面积及孔隙度分析仪、扫描电子显微镜/X射线能谱分析仪对改性前后稻壳焦吸附剂物理化学性质进行表征。在固定床汞吸附实验台上对吸附剂床层出口元素汞(Hg⁰)和二价汞(Hg²⁺)进行同步检测,研究了不同温度下N₂气氛和N₂+6.4 %(体积)O₂气氛中改性稻壳焦的汞氧化吸附特性。50℃下N₂气氛、N₂+6.4%(体积)O₂气氛以及150℃下N₂气氛中固定床出口均未明显检测到Hg²⁺,50℃和150℃时脱汞率均可达90%。温度为150℃时,在N₂+6.4%(体积)O₂气氛中吸附剂的总汞(Hg^T)脱除效率为98.2%,其中82.2%的Hg⁰被吸附脱除,其余则被O₂非均相氧化为Hg²⁺而氧化脱除。通过对程序升温管式炉出口Hg^T进行检测研究了吸附剂表面吸附态汞的脱附特性。汞脱附峰值温度300℃表明吸附态汞可能以Hg-Br化合物的形式赋存于改性稻壳焦表面,220~350℃的脱附温度说明吸附态汞有较高的热稳定性。100.14%~118.62%的汞平衡率验证了实验结果的准确性。

关键词: 改性稻壳焦, 脱汞, 汞形态, 氧化, 吸附, 脱附

CLC Number:

TQ534.9

YAO Ting, DUAN Yufeng, ZHU Chun, ZHOU Qiang, SHE Min, CHEN Yanan. Effects of temperature and oxygen content on Hg⁰ oxidation and adsorption by rice husk char impregnated with NH₄Br[J]. CIESC Journal, 2016, 67(4): 1467-1474.

姚婷, 段钰锋, 朱纯, 周强, 佘敏, 陈亚南. 温度和氧含量对NH₄Br改性稻壳焦汞氧化吸附特性的影响[J]. 化工学报, 2016, 67(4): 1467-1474.

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Effects of temperature and oxygen content on Hg⁰ oxidation and adsorption by rice husk char impregnated with NH₄Br

温度和氧含量对NH₄Br改性稻壳焦汞氧化吸附特性的影响

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