粉煤灰微波-水热合成法制备分子筛的研究进展

煤炭燃烧与转化过程产生大量的固体废弃物粉煤灰,其大量排放与堆积造成的环境污染已引起人们的广泛重视,以粉煤灰为原料制备分子筛是粉煤灰资源化利用的重要途径。传统水热合成加热方式所需合成时间较长,能量消耗量大;微波加热可极大地缩短反应时间,并对产物晶粒大小、纯度和分子筛产品性能有明显改善。本文介绍了微波-水热合成法将粉煤灰转化为不同类型分子筛的反应机理及其所制备的分子筛产品的应用,分析了粉煤灰制备分子筛过程中阴离子和阳离子、前驱液的碱度、晶种、加热方式等关键因素的影响,讨论了粉煤灰经过分级处理和除杂后,用微波-水热相结合替代传统加热对分子筛产品纯度、晶粒尺寸、孔径分布的调控和优化规律,为粉煤灰合成不同种类分子筛提供了重要的理论指导与发展方向。同时提出了将煤粉炉粉煤灰经除杂和分级处理获取其中的硅铝组分、通过调控硅铝比以微波-水热合成制备方沸石的新工艺,为粉煤灰资源化利用开辟了新途径。

Research development of zeolites preparation from coal fly ash by microwave-hydrothermal synthesis

Coal fly ash(CFA), a solid waste formed in the process of coal combustion and conversion has caused serious environmental pollution by large-scale emission and accumulation, and has attracted extensive attention. Preparation of zeolite from CFA is an important way for resource utilization of CFA. It takes longer crystallization time and more energy in the hydrothermal synthesis process by traditional heating method than by the microwave heating method. Moreover, it is easier to obtain zeolite with fine grain size and high performance by the microwave-hydrothermal synthesis method. The mechanism and application of different types of zeolite from CFA by the microwave hydrothermal synthesis method were introduced. The effects of cations and anions, alkalinity of liquid precursor, seeding and heating manner were analyzed, and improvement and optimization for the purity, grain size and pore size distribution of the zeolite product produced from CFA by the microwave-hydrothermal synthesis method after removal of impurity were also discussed, which provided theoretical direction and development orientation for synthesizing zeolites. A new process, analcite synthesized by the microwave-hydrothermal synthesis method using silicon and aluminum components extracted from the purified CFA, was proposed, which opened up a new way for resource utilization of CFA.