基于富里酸的载银碳基吸附剂脱除元素态汞的研究 -

汞是煤中有害微量元素之一,具有很强的挥发性,几乎所有的汞在煤燃烧过程中都会释放进入大气,对环境和人体健康造成影响。焦炉煤气甲烷化制取液化天然气过程中,为降低元素态汞的污染,通常在液化前将Hg~0脱除。本文针对工艺要求,利用富里酸廉价、储量丰富、碳含量≥40%、具有亲水性和弱酸性、可与金属离子发生离子交换反应生成络合物等优点,选取富里酸为模板剂和碳源,利用其分子结构中丰富的表面官能团易与银离子螯合的特性,采用冷冻干燥、高温碳化等手段原位合成了纳米银负载的碳基吸附材料Ag/FA,用于低温脱除还原性气体中的元素态汞(Hg~0)。对合成的材料进行分析表征,重点考察了操作温度、空速、H_2S等因素对吸附剂脱汞性能和寿命的影响。XRD表征结果表明,单质银出现了4个尖锐的衍射峰,分别对应单质银的不同立方晶面,这说明纳米级单质银粒子以高分散形态成功负载到碳材料中,并计算出银颗粒的平均粒径约为12 nm。吸附剂评价结果表明,在反应温度30～60℃,空速小于60 000 h~(-1)时,吸附剂具有良好的脱汞性能,脱汞效率可保持在99%以上,并具有一定抗H_2S毒化能力。当穿透率为5%时,吸附剂的汞吸附量可达到650μg/g。Ag/FA吸附剂在经过4次再生后,仍保持95%以上的脱汞效率,且吸附50 h后的Hg~0吸附量为552μg/g。Hg-TPD表征结果表明,吸附剂表面负载的纳米银粒子是汞吸附的活性位,气态汞首先扩散到吸附剂表面,然后与吸附剂上负载的银粒子反应生成Ag-Hg合金。本文利用腐植酸可以螯合银离子的特性,制备的基于腐植酸的Ag/FA新型气态汞吸附材料,可有效脱除焦炉煤气甲烷化气体中的单质汞,具有优良的吸附效率和吸附容量。 Abstract:Mercury is one of the harmful trace elements in coal,and it has strong volatility.Almost all mercury is released into the atmosphere during coal combustion,which has an impact on the environment and human health.In the process of methanation of coke oven gas to produce liquefied natural gas,in order to reduce the pollution of elemental mercury,Hg0 is usually removed before liquefaction.In view of the process requirements,this paper taked advantage of the advantages of low-cost fulvic acid,abundant reserves,carbon content not less than 40%,hydrophilicity and weak acidity,and ion exchange reaction with metal ions to form complexes.The fulvic acid was selected as a template and a carbon source,and the rich surface functional groups in the molecular structure were easily chelated with silver ions.The nano-silver-loaded carbon-based adsorbent Ag/FA was synthesized in situ by freeze-drying and high-temperature carbonization to remove elemental mercury (Hg0) in the reducing gas at a low temperature.The synthesized material was analyzed and characterized,and the effects of operating temperature,space velocity and H2S on the performance and life of the adsorbent were investigated.XRD characterization results show that there are four sharp diffraction peaks in elemental silver corresponding to different cubic crystal planes of elemental silver,which indicates that nano-sized elemental silver particles are successfully loaded into carbon materials in a highly dispersed form,and silver particles are calculated.The average particle size is about 12 nm.The evaluation results of the adsorbent show that the adsorbent has good mercury removal performance when the reaction temperature is 30-60 ℃ and the space velocity is less than 60 000 h-1.The mercury removal efficiency can be maintained above 99% and has anti-H2S poisoning performance.When the penetration