文档介绍：中文摘要
乙烯是重要的化工基础原料,工业上乙烯的生产来自于石油路线,由于石油资源的紧缺和原油价格的上涨,乙醇脱水制乙烯越来越具有竞争优势而受到研究者的关注。在众多报道的乙醇脱水催化剂中 HZSM-5 最具有工业应用价值的潜力。然而它的水热稳定性和抗积碳能力不太理想而限制了其工业化应用。本文通过对 HZSM-5 分子筛改性来提高其催化性能。
采用离子交换法分别引入 Fe3+、Co2+、Ni2+对 HZSM-5 分子筛进行改性,通
过改变离子交换次数,制备了一系列具有不同金属含量的 HZSM-5 分子筛催化剂。在连续流动固定床微型反应装置上考察了催化剂的活性,结果表明 Ni-Z-%分子筛的活性最好。采用 X-射线衍射(XRD)、吡啶程序升温脱附(Py-TPD)、N2-吸附脱附、吡啶红外(Py-IR)、热重(TG)和程序升温氧化(TPO) 等手段对改性前后的催化剂进行了表征。表征结果表明,催化剂的乙醇脱水性能与其微孔结构和表面酸性质有关,其中表面酸性质对催化剂的活性影响较为显著。适当的减少催化剂表面的强酸量,降低酸强度,增加弱酸量,保持一定的总酸量,并控制强酸量和弱酸量的比例为 1,有利于乙醇转化率和乙烯选择性的提高。
影响离子交换的因素除了离子交换次数外,主要还有交换液的浓度、温度等。本研究采用正交实验考察了镍改性 HZSM-5 分子筛制备中***镍溶液浓度、交换温度和交换次数对催化剂催化性能的影响,得到催化剂的最佳制备条件为:***镍浓度 ,交换温度 80℃,交换次数 2 次。
以最佳条件下制备的镍改性 HZSM-5 分子筛为催化剂,考察了反应温度,质
量空速和乙醇浓度对乙醇脱水制乙烯反应的影响,得到最佳工艺条件为:温度
260℃,质量空速 2h-1,乙醇浓度 50% (V)。稳定性实验表明在最佳工艺条件下
15 小时以内乙醇转化率和乙烯选择性保持大于 95%。
关键词:HZSM-5,乙醇脱水,乙烯,离子交换
ABSTRACT
Ethylene is one of the major feedstocks in the petrochemical industry Conventionally it was produced from the nonrenewable petroleum resources. Recently due to the shortage of natural resources and the rise of crude oil prices, catalytic dehydration of ethanol to ethylene has e an petitive and promising route, and therefore has been drawing much attention. This paper is trying to modify the HZSM-5 zeolite in order to improve its catalytic performance.
A series of modified HZSM-5 zeolite catalysts with different metal contents were prepared through changing the ion-exchange times. The reaction of dehydration of ethanol to ethylene was carried out in a continuous flow fixed-bed reactor. Results showed that Ni-Z-% exhibited the best activity. The catalysts were characterized by X-ray diffraction (XRD), pyridine temperature programmed desorption (Py-TPD),
infrared spectra after adsorption of Pyridine(Py-IR),N2 adsorption-desorption and
temperature programmed oxidation (TPO). Characterization revealed that catalytic performance was related to the micropore structure and surface acidity, especially the latter one. It was found that m