Elemental mercury removal from coal gas by CeMnTi sorbents and their regeneration performance

Abstract

Ce and Mn modified TiO 2 sorbents (CeMnTi) were prepared by a co-precipitation method, and their ability to remove elemental mercury from coal gas in a fixed bed reactor was studied. Based on results of Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) studies, the modification mechanisms of the CeMnTi sorbents are discussed. Mn doping improved the specific surface area and dispersion of cerium oxides on the sorbent surface, while Ce doping increased the proportion of Mn 4+ in manganese oxides by a synergetic effect between manganese oxides and cerium oxides. The effects of the active component, temperature, and coal gas components on the mercury removal performance of the sorbents were investigated. The results showed that the CeMnTi sorbents exhibited high mercury removal efficiency. Ce 0.2 Mn 0.1 Ti adsorbed 91.55% elemental mercury from coal gas at 160 °C. H 2 S and O 2 significantly improved the ability of sorbents to remove mercury. Part of the H 2 S formed stable sulfates or sulfites through a series of oxidation reaction chains on the sorbent surface. HCl also improved the mercury removal performance, but reduced the promotion effect of H 2 S for mercury removal when coexisting with H 2 S. CO and H 2 had a minor inhibitory effect on mercury adsorption. The recycling performance of the sorbents was investigated by thermal regeneration. The thermal decomposition of the used sorbents indicated that mercury compounds were present mainly in the form of HgO and HgS, and higher temperature was beneficial for regeneration. The formation of sulfates and sulfites in the presence of H 2 S led to a decrease in mercury removal efficiency. 目的 探明复合金属氧化物吸附剂协同改性机理,研究温度、活性组分负载量和煤气组分等因素对吸附剂脱汞的影响和机理,并进一步通过热脱附再生对吸附剂的再生性能和机理进行探索,为提高该类吸附剂的脱汞效率以及实际工业应用提供理论基础。 创新点 1.利用多种表征方法,推导出了Ce-Mn金属氧化物吸附剂的协同改性机制;2.通过硫化氢存在下的脱汞和再生实验,得出了吸附剂再生后脱汞效率下降的机理:金属硫酸盐和亚硫酸盐的形成使得活性组分出现不可逆损失。 方法 1.通过共沉淀法制备CeMnTi吸附剂;2.在固定床反应器上进行煤气脱汞实验,控制变量为反应温度、活性组分负载量和煤气成分,结合表征方法对脱汞机理进行探究;3.在固定床反应器上通过热脱附再生的方法考察吸附剂再生性能。 结论 Ce 0.2 Mn 0.1 Ti吸附剂相对CeTi和MnTi吸附剂具有更高的脱汞效率和热稳定性。其脱汞效率在160°C时达到91.55%,而在200°C时仍保持在83%以上。2. Mn掺杂可改善吸附剂表面积和铈氧化物在吸附剂表面的分散性,而Ce掺杂可通过与锰氧化物的相互作用提高Mn4+的比例。3. H 2 S可通过在吸附剂表面生成活性硫显著促进汞的吸附,但是H 2 S也会与活性成分形成硫酸盐和亚硫酸盐,因此很难进行吸附剂的再生。CO和H 2 的存在会抑制汞的脱除。HCl可提高脱汞性能,而HCl与H 2 S共存时则会由于竞争吸附使得脱汞效率下降。4. 吸附剂上的汞化合物主要以HgO和HgS的形式存在,且大部分可以在500°C下脱附分解。再生后脱除效率降低的主要原因可能是在H 2 S存在时形成了硫酸盐和亚硫酸盐。