FeMnK@SAPO-34核壳结构催化剂的制备及其费—托反应性能

发布时间：2018-04-28 09:14

  本文选题：核壳结构 + 分子筛膜　； 参考：《浙江大学》2017年硕士论文

【摘要】：低碳烃是现代化学工业中最重要的基础原料之一,工业上主要通过石脑油蒸汽裂解过程获得。但随着石油短缺问题日益严重,开发以煤、天然气及生物质为原料的非石油生产低碳烃工艺路线已经迫在眉睫。而以煤、天然气及生物质为原料,经合成气通过费-托合成反应直接生产低碳烃是目前最具应用前景的工艺路线之一。但受费-托合成产物分布规律限制,工业上费-托合成流程主要生产汽油、柴油、润滑油等产品。为了解决费-托合成反应对低碳烃选择性低的问题,研究者分别从工艺流程及催化剂角度出发,提出了反应段-裂解段串联方法、费-托合成催化剂与分子筛物理混装方法及将费-托合成活性组分浸渍到分子筛制成双功能催化剂等方法。但上述方法存在以下问题:一、流程长、投资成本高;二、费-托合成产物并不是完全进入分子筛进行裂解;三、费-托合成活性组分与分子筛酸性位强结合,导致催化剂活性较低。而如果在费-托合成催化剂(核)外包覆一层分子筛膜(壳),形成核壳结构型催化剂。那么可以利用壳层分子筛(如SAPO-34)上的质子酸,将重质烃进一步裂解为低碳烃,从而达到提高合成气直接转化对低碳烃的产物选择性。为了实现上述要求的催化剂,本文提出构建一种新型的核壳型催化剂。首先采用共沉淀-焙烧-浸渍-焙烧法制备传统的FeMnK催化剂,然后采用喷涂法在其表面涂覆混有SAPO-34分子筛粉末的硅溶胶,经干燥焙烧后制成FeMnK@SAPO-34核壳催化剂。对所制备催化剂,采用表面积-孔隙度测试、X射线粉末衍射测试、扫描电子显微镜、H_2-TPR等表征方法进行分析,并在高压微型固定床反应器中经还原后进行费托合成反应考评。结果表明,制备得到的核壳型催化剂的比表面积及孔容有明显上升,核心FeMnK催化剂的活性不受外层分子筛的影响;新型FeMnK@SAPO-34核壳催化剂实现了费-托合成反应与烃类分子筛裂解的反应耦合,明显改善了合成气制备低碳烃的产物选择性。其中二次涂覆核壳催化剂在氢碳比为3.5、反应压力为1.0 MPa、反应温度为325 ℃和反应空速为1500h-1的较优条件下,其催化的CO转化率为74.8%,全产物组成中低碳烯烃选择性为42.4%,低碳烃(C_2~=～C_4~=和C_2～C_4)总选择性为51.5%(若不计CO_2,仅碳氢化合物中低碳烯烃选择性则达到57.0%,低碳烃选择性达到69.2%)。
[Abstract]:Low carbon hydrocarbon is one of the most important basic raw materials in modern chemical industry. But with the problem of oil shortage becoming more and more serious, it is urgent to develop non-oil production process of low carbon hydrocarbon using coal, natural gas and biomass as raw materials. Using coal, natural gas and biomass as raw materials, the direct production of low carbon hydrocarbons through the synthesis reaction of syngas is one of the most promising technological routes. However, limited by the distribution law of Fischer-Tort synthetic products, the industrial Fischer-Tort synthesis process mainly produces gasoline, diesel oil, lubricating oil and other products. In order to solve the problem of low selectivity for low carbon hydrocarbons in Fischer-Tropsch synthesis reaction, the researchers put forward a series method from the point of view of process flow and catalyst, respectively. The physical mixing method of Fischer-Tort synthesis catalyst and molecular sieve and dipping the active component of Fischer-Tropsch synthesis into molecular sieve to make bifunctional catalyst. However, the above methods have the following problems: first, the process is long and the investment cost is high; second, the products of Fischer-Tort synthesis are not completely entered into the molecular sieve for pyrolysis; third, the active components of the Fischer-Tropsch synthesis are strongly bound to the acidic sites of the molecular sieve. As a result, the activity of the catalyst is low. If a layer of molecular sieve membrane (shell) is coated on the surface of Fischer-Tropsch synthesis catalyst (nucleus), a core-shell structure catalyst is formed. The proton acid on the shell molecular sieve (such as SAPO-34) can be used to further decompose the heavy hydrocarbon into low carbon hydrocarbon so as to improve the product selectivity of direct conversion of syngas to low carbon hydrocarbon. In order to achieve the above requirements, a new type of core-shell catalyst is proposed in this paper. The traditional FeMnK catalyst was prepared by coprecipitation calcination impregnation roasting method. Then the FeMnK@SAPO-34 core-shell catalyst was prepared by spraying the silica sol mixed with SAPO-34 molecular sieve powder. The catalysts were characterized by surface area and porosity measurements by X-ray powder diffraction, scanning electron microscopy (SEM) and H _ (2-TPR), respectively. Fischer synthesis reaction was evaluated after reduction in a high-pressure micro-fixed-bed reactor. The results showed that the specific surface area and pore volume of the core-shell catalyst increased obviously, and the activity of the core FeMnK catalyst was not affected by the outer molecular sieve. The new FeMnK@SAPO-34 core-shell catalyst has realized the coupling of Fischer-Tropsch synthesis reaction with the cracking of hydrocarbon molecular sieve, which has improved the selectivity of synthesis gas for the preparation of low carbon hydrocarbons. When the ratio of hydrogen to carbon is 3.5, the reaction pressure is 1.0 MPA, the reaction temperature is 325 鈩，

本文编号：1814661