改性蒙脱土的制备及其催化低温低浓度乙醇脱水制乙烯的研究

发布时间：2019-03-12 10:01

【摘要】：乙烯是石油化工产品的基础原料和合成药物的前驱体,在全球工业快速发展的同时,对乙烯的消耗与日俱增。目前,乙烯的主要来源是石油裂解,但随着石油资源的日益枯竭和价格的不断攀升,以石油为原料的乙烯工业受到了巨大冲击。乙醇脱水制取乙烯工艺能够缓解乙烯生产的压力,其工艺流程简单、能耗低、环境友好等优势,被认为是最具有应用前景的路线。因此,如何更有效的将低浓度乙醇在较低温度下高效地用于乙烯生产,已经成为研究者关注的热点。本文利用硫酸、聚合羟基铝、杂多酸对蒙脱土进行多种方法的复合改性,修饰结构,优化性能;研究改性蒙脱土在低温下对低浓度乙醇脱水制乙烯反应的催化性能,通过XRD、BET、FT-IR、TG-DTA、NH_3-TPD等技术对改性蒙脱土的结构进行了表征,进一步优化催化剂的合理构筑,主要研究内容及结论如下:以硫酸作为处理剂,对蒙脱土进行改性,在酸化温度80℃,酸化时间7 h,硫酸浓度Φ=25%的条件下对蒙脱土进行酸化处理。研究表明酸化过程中,蒙脱土层间和孔道的杂质溶出,层状结构呈剥离状态,狭缝孔转变为堆积孔,比表面积从21 m2/g增大到357 m2/g,孔容从0.0436 cm3/g增加至0.561 cm3/g。将不同量的磷钼酸和磷钨酸负载到酸改性的蒙脱土上,不仅克服了杂多酸活性组分易流失、分布不均匀等缺点,而且获得了高的乙烯选择性和乙醇转化率。当负载10%磷钨酸时,在反应温度300℃、原料浓度ΦEthanol=30%、质量空速0.65h-1的条件下,反应进行12 h后,乙烯选择性依旧保持在93%左右,乙醇转化率为89%。以硫酸改性的蒙脱土作为基体,通过离子交换引入不同量的聚合羟基铝,可以恢复蒙脱土的层状结构,将其焙烧后,可转变为活性中心均匀地分布在孔道中,将其应用于催化反应时,表现出优异的催化性能。研究结果表明:聚合物的交换量影响催化剂的稳定性和耐受性;当引入聚合物的量为CEC的70%时,催化剂的活性较高。当反应温度300℃、原料浓度ΦEthanol=30%、质量空速0.65h-1时,乙醇转化率在97%左右,乙烯的选择性接近100%。鉴于生物发酵乙醇浓度较低,需进一步降低原料浓度。以硫酸-聚合物复合改性后的蒙脱土作为载体,通过浸渍法负载不同种类、不同量的杂多酸,研究其在ΦEthanol=20%中的催化性能。研究结果表明:当负载磷钨酸量为15%时,由于表面磷钨酸的覆盖,强弱酸含量和分布得到优化,充分利用了载体的外表面,每个PW杂多酸分子能与更多的表面OH基团相作用,使得PW与载体之间的相互作用增强,耐水性提升,活性组分不易流失,因此降低反应物浓度时,依然具有较好的催化活性。当反应温度300℃、原料浓度ΦEthanol=20%时,乙醇的转化率为98%,乙烯选择性接近100%;反应12h,乙醇转化率仍可保持在95.7%左右。
[Abstract]:Ethylene is the basic raw material of petrochemical products and precursor of synthetic drugs. With the rapid development of global industry, the consumption of ethylene is increasing day by day. At present, the main source of ethylene is oil cracking, but with the increasing depletion of petroleum resources and rising prices, the ethylene industry with petroleum as raw material has been greatly impacted. The process of producing ethylene by dehydration of ethanol can relieve the pressure of ethylene production. It has the advantages of simple process, low energy consumption and friendly environment. It is considered to be the most promising route for application. Therefore, how to use low-concentration ethanol more effectively in ethylene production at lower temperature has become the focus of researchers' attention. In this paper, sulfuric acid, poly (hydroxyaluminum) and heteropolyacid were used to modify montmorillonite, modify the structure and optimize the properties of montmorillonite. The catalytic properties of modified montmorillonite for dehydration of low concentration ethanol to ethylene at low temperature were studied. The structure of modified montmorillonite was characterized by XRD,BET,FT-IR,TG-DTA,NH_3-TPD and other techniques. The main research contents and conclusions are as follows: using sulfuric acid as the treatment agent, the montmorillonite was modified at 80 鈩，

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