粉煤灰为原料ZSM-5分子筛的制备及应用

Preparation and application of ZSM-5 zeolite derived from fly ash

利用低成本的原料生产高催化剂性能的分子筛一直是业界关注的焦点。将工业废物资源化利用与分子筛制备相结合,可达到一举两得的效果。以NaOH处理宁东能源化工基地粉煤灰,得到的硅铝凝胶作为ZSM-5分子筛合成原料的铝源和部分硅源。通过对NaOH用量考察,发现ZSM-5分子筛合成时不再需要额外添加NaOH。在硅铝凝胶中补充硅溶胶,并按比例加入模板剂(TPABr)和水即可合成ZSM-5分子筛。采用4水平9因素的均匀设计,考察晶化温度、晶化时间、模板剂及水用量等因素的影响。二次回归优化后,得出最佳合成条件。在晶化时间60 h、晶化温度190℃、TPABr用量5.4 g和水用量18 mL最佳条件下,对再次合成的ZSM-5分子筛进行表征,产品为长度(35~40)μm长条形纯净无杂晶的ZSM-5分子筛。并将制得的ZSM-5分子筛催化剂用于制备乙酸乙酯,在反应温度130℃、反应时间90 min、酸醇比1∶3和催化剂用量5%条件下,转化率最高为62%,产率为55%。

The production of zeolite with excellent catalytic performance using low-cost feedstock has been a focus of academic and industrial attention.Synthesis of zeolite using industrial waste residue not only makes resource utilization of waste residue,but also alleviates the environmental problems caused by waste residue dumping.Here,ZSM-5 zeolite are successfully prepared by hydrothermal method using NaOH pretreated fly ash as aluminum source and part of the silicon sources.ZSM-5 zeolite synthesis did not require the introduction of NaOH to modulate the alkalinity,but required the introduction of an appropriate amount of silica sol as silicon source and tetrapropylammonium bromide(TPABr)as template agent.The effect of temperature,time,template and water were studied using orthogonal experiments of 9 factors 4 levels.ZSM-5 zeolite with long strips of(35-40)μm in length was synthesized under the optimized condition of crystallization time of 60 h,crystallization temperature of 190℃,TPABr dosage of 4.5 g,and water dosage of 18 mL.In ethanol and acetic acid esterification to ethyl acetate,a conversion of up to 62%and a yield of 55%over the as-synthesize catalyst were obtained at 130℃,90 min,acid to alcohol ratio of 1∶3,and catalyst dosage of 5%.