摘要
随着环境保护意识的增强,世界各国将实施更加严格限制燃料油中硫含量的新规定,为此进一步发展低硫汽油生产技术具有重要意义。吸附脱硫技术操作简单、方便、快速,成为目前较为关注的脱硫技术。与工业化的加氢脱硫相比,其投资成本及操作费用可降低一半以上,且不会降低汽油的辛烷值。但是其工业化面临的主要问题在于吸附剂的硫容量不高以及选择性差,因此目前最迫切的问题是制备高性能的吸附剂。复合分子筛材料同时具备介孔材料的孔道优势和微孔材料的选择性优势,在石油化工、吸附分离、大分子择形催化等领域具有广泛的应用前景。因此,本文尝试采用复合分子筛作为吸附脱硫剂以及作为吸附剂的载体进行汽油吸附脱硫,得到了较好的结果。
采用碱处理ZSM-5的浆液作为硅铝源合成新型微孔-介孔复合分子筛MCM-41 -ZSM-5,采用XRD、BET等分析手段对其进行了表征,以模拟汽油吸附脱硫对分子筛进行性能评价。XRD和BET结果显示:产物为微孔、介孔双孔分布的复合分子筛,具有类MCM-41的典型六方介孔结构,长程有序性较好,孔分布集中,比表面积较高。通过制备过程的单因素考察,实验范围内找到了复合材料的最优制备条件。正交实验结果表明,pH值对分子筛的吸附性能影响最大,其次是碱浓度,影响较小的是晶化时间和碱处理时间,并得出了优化合成条件。
以合成的复合分子筛为载体,采用浸渍法制备了两类高效吸附剂: Fe/ MCM-41 -ZSM-5和Ni-Co/MCM-41-ZSM-5。其活性组分分别为Fe2O3,Co3O4和NiO。通过对两种吸附剂的制备条件、吸附条件的考察,确定了适宜的制备条件和吸附工艺条件。Fe型吸附剂的适宜制备条件:浸渍液浓度0.20mol/L,浸渍时间10h,干燥温度100℃,550℃焙烧4h。最佳吸附条件:常温、常压,吸附时间1h,剂油比1:60,在该条件下吸附剂的饱和吸附量为36.46mgS/g吸附剂。Ni-Co型吸附剂的适宜制备条件为:负载量10%,浸渍时间12h,干燥温度100℃,450℃焙烧4h。最佳吸附条件与上述Fe型吸附剂相同,其饱和吸附量为36.84mgS/g吸附剂。当有芳烃存在时两种吸附剂的硫容量都有明显下降,说明芳烃对硫化物存在竞争吸附作用。当用总硫含量为250.7μg/g的真实汽油为研究对象时吸附剂的吸附量降低,分别为10.21、10.5mgS/g吸附剂,考察两种吸附剂的动态吸附效果,硫容量分别为8.6和9.6mgS/g吸附剂。分析吸附机理,π-络合可能是本论文中制备的两种吸附剂能够有效吸附噻吩类硫化物的主要因素。
With the enhanced awareness of environmental protection, countries around the world will implement more stringent restrictions on sulfur content in fuel oil in the new requirement, for the further development of low sulfur gasoline production technology is of great significance. The technology of adsorptive desulfurization is operated easily, expediently, quickly and become an important desulfurization technology. Compared to the others technology, adsorption desulfurization has several potential advantages: reduce the investment and operating cost markedly, no or quite less reduction of octane number. Key issue for the commercialization of adsorption desulfurization is developing new adsorbents with higher sulfur capacity and selectivity. The composite molecular sieves possess the pore advantage of the mesoporous material and the high selectivity of the microporous material has comprehensively applicational prospects in the fields such as petrochemical industry, adsorption, macromolecule shape selective catalysis, and so on.
In this paper, the composite molecular sieve materials MCM-41-ZSM-5 were employed as adsorbents for adsorption desulfurization on model gasoline,the better result was obtained.
A series of micro-mesoporous composite molecular sieves were synthesized by the assembly behaviors of alkali-treated ZSM-5 zeolite, and characterized by XRD, BET techniques. Adsorption properties for sulfur removal from model gasoline on the composite molecular sieves were studied. The results indicate the composite materials with microporous and mesoporous double pores-size distribution possess ordered hexagonal structure of MCM-41-type and high surface areas. The factors were studied one by one, got the optimum synthesis condition. Analysis of orthogonal experiments gives the orders of the importance of each factor in the synthesis of composite materials: pH value is the most important; it is more important to control the pH value than the concentration of NaOH; less important influential factors are crystallization time and time of alkali-treatment.
The composite molecular sieve material as the support, two kinds of adsorbents were prepared using impregnation method: Fe/MCM-41-ZSM-5 and Ni-Co/MCM-41-ZSM-5. Active components within the adsorbents were Fe2O3, and Co3O4,NiO respectively. The effects of preparation and adsorption conditions on performance of the adsorbents were investigated and the suitable conditions were determined.
The suitable preparation conditions of Fe/MCM-41-ZSM-5 are iron nitrate concentration 0.20 mol/L, impregnation time 10h, drying temperature 100℃, calcinating 550℃for 4h. The suitable adsorption conditions are: ambient temperature and pressure, the adsorbent-oil ratio 1:60, adsorption time 1h. The saturated adsorption quality is 36.46mgS/g adsorbent. The suitable preparation conditions of Ni-Co/MCM-41-ZSM-5 are : nickel and cobalt loaded quality 10%, impregnation time 12h, drying temperature 100℃, calcinating 450℃for 4h. The suitable adsorption conditions are the same as the first adsorbent. The saturated adsorption quality is 36.84 mgS/g adsorbent.
Aromatic hydrocarbon compound have strong competence with sulfide. Therefore, it is necessary that how to enhance selectivity of sorbent, when use the real gasoline, the sulfur capacities of the adsorbents are 10.21、10.5mgS/g adsorbent respectively. Reviewed by dynamic adsorption experiments, the sulfur capacities are 8.6 and 9.6 mg S/g.π-complexation will be the mainly mechanism of the adsorption.
引文
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