椰壳活性炭微结构修饰调控途径及对气态汞吸附机制研究

Activated carbon adsorption to remove mercury is one of the most efficient technology of flue gas treatment, especially suitable for dry areas, which is the future development trend for mercury removal of flue gas. At present, the mechanism of activated carbon removal mercury is still unclear, and adsorption to remove mercury is low efficiency, poor stability, that result in ctivated carbon has not been widely used in flue gas. We have found that the developed cell cavity of coconut shell provided a rich entrance and channel for mercury adsorption, and the large specific surface area of activated carbon can significantly promote the catalytic reaction of mercury with halogen. This project with coconut shell as raw material, through the research of cellulose / lignin reconstruction behavior and water vapor activation mechanism, reveals the formation regularities of activated carbon pore structure, acquire the directional control method of suitable porosity for gaseous mercury capture. The kinetics of activated carbon surface chemical modification and catalytic oxidation were studied to proven the mechanism of morphological transformation of elemental mercury and efficient adsorption. Through construction on-line monitoring method of gaseous mercury removal effect, we are going to study and reveal the physical - chemical occupying mechanism and adsorption - desorption mechanism of mercury in the pores of the activated carbon to obtain stable enhancement methods gaseous mercury adsorption. Then, obtain the stable enhancement methods of gaseous mercury adsorption. The research results would have important scientific significance for the atmospheric mercury pollution control and ecological protection.

活性炭吸附脱汞是最有效的烟气处理技术之一，尤其适用于缺水地区，是未来烟气除汞技术的发展趋势。目前，活性炭吸附汞的机理仍不清楚，吸附效率低、稳定性差，未能在汞污染治理中广泛应用。研究发现，椰壳细胞壁“木胶合板”状的多层交叠结构为汞的吸附提供了丰富的入口，其活化产生的超大比表面可显著促进汞与卤素的催化反应作用。本项目以椰壳为原料，通过椰壳炭化过程纤维/木质素重构建行为和水蒸气活化造孔机理研究，揭示椰壳活性炭孔结构的形成规律，掌握适于气态汞捕捉的孔结构定向调控方法。通过活性炭表面化学修饰途径和催化氧化动力学研究，探明单质汞在活性炭表面的形态转化及高效吸附机制；构建气态汞准确检测方法及活性炭除汞效果在线监测评价体系，研究揭示汞在活性炭孔隙内物理-化学占位机制和吸附-解吸规律，获得增强活性炭对气态汞稳定吸附的实施方法。研究成果对大气汞污染防治和水土生态保护具有重要的科学意义。

综合国内外的文献，目前有发展前景的燃煤烟气汞排放控制的技术主要有吸附剂喷射和湿法洗涤，但是在我国北方缺水地区，活性炭吸附的干法除汞技术更有实际意义。因此，如何提高吸附剂对于各种形态汞的吸附能力、控制成本以及增强吸附汞的稳定性，避免汞的二次析出是研究的重点和热点。.本项目围绕活性炭结构与烟气脱汞构效关系的基础科学问题，开展了活性炭孔结构调控、表面掺杂改性、活性炭脱汞机理及转化机制研究，探明了椰壳炭化过程纤维/木质素重构建行为、成炭机制以及造孔机理，并通过动力学研究，探明了活性炭比表面性质与汞吸附影响机理。研究了活性炭孔结构调控技术、表面氧化改性技术以及共掺杂技术，揭示了脱汞机制，获得了高效脱汞专用活性炭的制备工艺。研究发现，椰壳中半纤维素在炭化过程中完全分解不形成固体炭，纤维素热分解形成的碳自由基发生芳构化重排构成椰壳炭中的结晶区，木质素构成了生物炭中的无定形区。生物质原料经石墨化处理后，均可发生有效的石墨化反应，纤维素在石墨化转化中起主要作用，而且原料中纤维素结晶度越高则越有利于产物石墨化效果。水蒸气二次活化有助于形成新的微孔，使微孔率显著增加，同时平均孔径减小；化学改性对孔径分布影响较小，但显著增加活性炭表面酚羟基和羰基含量。二次活化和表面氧化改性制备得到微孔率高、表面官能团丰富的改性活性炭，显著提高了活性炭的汞吸附量。通过煅烧、浸渍在活性炭表面引入硫和卤素，实现了硫卤均质掺杂，汞在活性炭表面与其形成稳定的化合物被吸附，其汞吸附量较未改性活性炭提高了30%。活性炭对汞的吸附属于单分子层吸附，微孔是吸附汞的主要活性位，表面的酸性官能团与汞可以发生络合反应，提高化学吸附效果；活性炭吸附汞是快速吸附和慢速吸附共存的过程，该吸附过程是放热反应。研究成果为提高活性炭脱汞性能以及创制烟气高效脱汞活性炭提供了理论支撑和技术支持，对大气汞污染防治和水土生态保护具有重要的科学意义。