以粉煤灰为铝源纳米级ZSM-5分子筛的合成调控

发布时间：2019-05-22 21:41

【摘要】：粉煤灰是煤炭在燃烧与转化过程中产生的固体废弃物,粉煤灰的大量排放与堆积不仅占用土地面积、污染环境而且危害人体健康。粉煤灰中有70%以上为SiO_2与Al2O_3,与分子筛的主要成分相似,故以粉煤灰为原料合成分子筛不仅能提高其资源利用价值、降低分子筛的合成成本,而且在一定程度上减少了环境污染,符合我国循环经济发展的战略需求。本论文以固体废弃物粉煤灰为原料,经过焙烧、活化、除杂等步骤提取其中Al(OH)_3作为合成ZSM-5分子筛的铝源,以正硅酸乙酯(TEOS)为硅源,以四丙基氢氧化铵(TPAOH)为模板剂,通过水热合成法制备纳米级ZSM-5分子筛。优化了ZSM-5分子筛水热合成体系的工艺参数(硅铝比、晶化温度、晶化时间、水硅比),考察了有机空间位阻剂对ZSM-5分子筛合成过程的影响,利用对Ni~(2+)的吸附能力评价分子筛的离子吸附性能与再生,初步探究了分子筛的吸附机理。并考察了不同晶化温度、水硅比、有机添加剂条件下ZSM-5分子筛晶体生长动力学规律,建立分子筛晶化生长动力学模型。从宏观和微观的角度对ZSM-5分子筛的合成进行调控,采用XRD、SEM、FT-IR、TGA、BET和PSD对ZSM-5分子筛产品进行表征分析,研究结果如下:(1)粉煤灰中加入活化助剂(Na_2SiO_3),高温焙烧后可以打破粉煤灰中较为稳定的玻璃相和莫来石结构,转化为易溶于酸的霞石,进而提高了粉煤灰的化学活性,提高了粉煤灰的转化利用率。粉煤灰经焙烧后在盐酸中浸渍,可成功提取其中的铝元素,调解溶液pH值,可去除溶液中的Fe~(2+)、Ca~(2+)、Mg~(2+),得到较为纯净的Al(OH)_3,其提取率为80.89%。(2)以从粉煤灰中提取的Al(OH)_3作为铝源,以TEOS为硅源,以TPAOH为模板剂,水热合成法合成纳米级ZSM-5分子筛的最佳工艺参数为:原料摩尔质量比为n(H2O):n(SiO_2):n(TPAOH):n(Al(OH)_3)=2400:40:12:1,晶化温度为140°C,晶化时间为6 h。(3)适量有机添加剂的添加可以有效调控分子筛晶粒大小、提高分子筛的产量,还可以增加分子筛比表面积,其中PVP的加入效果最好。(4)ZSM-5分子筛的生长动力学曲线为典型的“S”型曲线。其晶化过程有四个阶段:诱导期、成核期、快速生长期、缓慢生长期。温度是分子筛晶化动力学的主要动力学因素,随着温度的升高,分子筛成核期缩短,晶体的成核及生长速度增加。ZSM-5分子筛的成核表观活化能En=24.18 kJ·mol-1及生长表观活化能Eg=10.19 kJ·mol-1。;水硅比是影响水热反应体系碱性的主要因素,过高过低的水硅比均不利于分子筛的晶化,其中适宜的摩尔质量比为:n(H2O):n(SiO_2)=60;有机添加剂尤其是PVP的加入可以提高分子筛的晶化生长速度,缩短成核期,使分子筛分散度有所提高,晶型更加完整。(5)有机添加剂可以提高分子筛的吸附性能,其中添加PVP制备的ZSM-5分子筛吸附性能最好,30°C、60 min时Ni~(2+)的最大去除率可达到92.8%。0.01 mol/L的EDTA-2Na作为再生助剂时,在40°C再生30 min时ZSM-5分子筛再生吸附能力最好,可达90.9%。ZSM-5分子筛对Ni~(2+)的吸附过程更符合Lagergren准二级动力学方程,且PVP的加入,使ZSM-5分子筛吸附Ni~(2+)的能力提高。
[Abstract]:The fly ash is the solid waste produced in the process of combustion and conversion of the coal, and a great deal of discharge and accumulation of the fly ash not only occupy the area of the land, pollute the environment but also endanger the health of the human body. The fly ash has more than 70% of SiO2 and Al2O _ 3, and is similar to the main component of the molecular sieve, so that the molecular sieve is synthesized by using the fly ash as a raw material, not only can the resource utilization value of the molecular sieve be improved, the synthesis cost of the molecular sieve is reduced, and the environmental pollution is reduced to a certain extent, It is in accordance with the strategic demand of China's circular economy development. In this paper, Al (OH) _ 3 is taken as an aluminum source for synthesis of ZSM-5 molecular sieve, and tetrapropyl hydroxide (TPAOH) is used as a template agent by using solid waste fly ash as a raw material, and the Al (OH) _ 3 is used as an aluminum source for synthesizing a ZSM-5 molecular sieve through the steps of roasting, activation, impurity removal and the like, And the nano-scale ZSM-5 molecular sieve is prepared by a hydrothermal synthesis method. The process parameters (silicon-to-aluminum ratio, crystallization temperature, crystallization time and water-to-silicon ratio) of the ZSM-5 molecular sieve hydrothermal synthesis system were optimized, and the influence of the organic space-resistance agent on the synthesis process of the ZSM-5 molecular sieve was studied. The adsorption capacity of Ni ~ (2 +) was used to evaluate the ion adsorption performance and regeneration of the molecular sieve. The adsorption mechanism of molecular sieve was studied. The growth kinetics of ZSM-5 molecular sieve under different crystallization temperature, water-to-silicon ratio and organic additive were investigated. The synthesis of ZSM-5 molecular sieve was controlled by the macro and micro angle. The results of XRD, SEM, FT-IR, TGA, BET and PSD were used to characterize the ZSM-5 molecular sieve. The results were as follows: (1) The activation aid (Na _ 2SiO _ 3) was added to the fly ash. The stable glass phase and the mullite structure in the fly ash can be broken after the high-temperature roasting, so that the nepheline which is easily soluble in the acid is converted, so that the chemical activity of the fly ash is improved, and the conversion utilization rate of the fly ash is improved. After the fly ash is roasted in hydrochloric acid, the aluminum element can be extracted successfully, the pH value of the solution can be adjusted, and the Fe ~ (2 +), Ca ~ (2 +) and Mg ~ (2 +) in the solution can be removed to obtain the pure Al (OH) _ 3, and the extraction rate is 80.89%. (2) Al (OH) _ 3 extracted from fly ash is used as an aluminum source, TEOS is used as a silicon source, and TPAOH is used as a template agent, and the hydrothermal synthesis method is used for synthesizing the nano-scale ZSM-5 molecular sieve with the best technological parameters as follows: the molar mass ratio of the raw materials is n (H2O): n (SiO2): n (TPAOH): n (Al (OH)3) = 2400:40:12:1, and the crystallization temperature is 140 DEG C, The crystallization time is 6 h. (3) the addition of the appropriate amount of organic additive can effectively control the size of the crystal grain of the molecular sieve, improve the yield of the molecular sieve, and also increase the specific surface area of the molecular sieve, wherein the addition effect of the PVP is the best. (4) The growth kinetics curve of the ZSM-5 molecular sieve is a typical "S"-type curve. The crystallization process has four stages: the induction period, the nucleation period, the rapid growth phase and the slow growing period. The temperature is the main dynamic factor of the crystallization kinetics of the molecular sieve, and with the increase of the temperature, the nucleation period of the molecular sieve is shortened, and the nucleation and growth rate of the crystal are increased. The apparent activation energy (En = 24.18 kJ 路 mol-1) and the apparent activation energy (Eg = 10.19 kJ 路 mol-1) of the ZSM-5 molecular sieve. and the water-to-silicon ratio is the main factor which influences the alkalinity of the hydrothermal reaction system, and the water-to-silicon ratio is not good for the crystallization of the molecular sieve, wherein the appropriate molar mass ratio is: n (H2O): n (SiO2) = 60; the addition of the organic additive, in particular the PVP, can improve the crystallization and growth speed of the molecular sieve and shorten the nuclear phase, The dispersity of the molecular sieve is improved, and the crystal form is more complete. and (5) the organic additive can improve the adsorption performance of the molecular sieve, wherein the adsorption performance of the ZSM-5 molecular sieve prepared by the addition of the PVP is the best, the maximum removal rate of the Ni-(2 +) can reach 92.8% and the EDTA-2Na of 0.01 mol/ L can be used as the regeneration assistant when the adsorption performance of the ZSM-5 molecular sieve prepared by adding the PVP is the best; The adsorption capacity of the ZSM-5 molecular sieve can reach 90.9% at 40 掳 C for 30min. The adsorption process of the ZSM-5 molecular sieve to Ni ~ (2 +) is more in line with the Lagergren's quasi-second-order kinetic equation, and the addition of PVP increases the ability of the ZSM-5 molecular sieve to adsorb Ni ~ (2 +).
【学位授予单位】：东北石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ424.25;TB383.1

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