碱及载金处理改性ZSM-5在催化裂化柴油增产丙烯中的研究

发布时间：2018-03-30 05:10

  本文选题：催化裂化　切入点：ZSM-5　出处：《烟台大学》2016年硕士论文

【摘要】：ZSM-5分子筛作为流化催化裂化生产丙烯装置中最常用的催化剂组分,其较小的孔尺寸限制了较大的烃分子进入其孔道内部,致使其孔道内的活性位点难以参与反应。为消除其扩散限制并阐明限域在分子筛孔道内的纳米金粒子在轻柴油催化裂化增产丙烯反应中的催化作用,本文在不同条件下使用NaOH溶液对微米ZSM-5分子筛进行处理,并采用Au(en)_2Cl_3金前驱体对分子筛进行金元素改性,通过控制金载量,还原温度,焙烧温度等条件制备了一系列Au/ZSM-5催化剂。本文以直馏轻柴油馏程(235~337℃)为原料,考察了各分子筛样和Au/ZSM-5催化剂在催化裂化柴油增产丙烯反应中的丙烯等低碳烯烃的选择性及其微反活性指数。并结合XRD,NH3-TPD,BET,ICP-AES,UV-Vis,TEM,FE-SEM等表征所得的催化剂的物化性质进行综合分析,得到以下结果:(1)采用不同浓度的NaOH溶液对ZSM-5进行处理,结果表明:在NaOH溶液浓度不太高的情况下,可以获得晶相结构保持不变的微介孔复合ZSM-5,其介孔体积和平均孔径相对于ZSM-5原样有明显增加,但强酸量明显减少,进一步的酸处理则会使弱酸量减少。经过碱处理和碱酸连续处理的分子筛,其微反活性和丙烯等低碳烯烃的选择性相较于分子筛原样有明显的提高。而对于碱处理的分子筛样品,经过进一步的800℃高温水汽处理后,虽然分子筛晶相结构得到保留,且介孔度进一步增加,但是其酸量急剧减少。与分子筛原样相比,该系列处理的分子筛样品的轻柴油催化裂化增产丙烯反应中的微反活性及丙烯等产物的选择性并没有明显变化,但ZSM-5中介孔的引入无疑为后续孔道限域Au/ZSM-5样品的制备打下了基础。(2)以Au(en)_2Cl_3为前驱体制备得到的一系列不同金载量的Au/ZSM-5催化剂,ICP-AES的结果表明:Au的实际负载量能达到理论值的80%以上,可见Au(en)_2Cl_3中的金物种与分子筛的结合力较强,它是适宜分子筛载金的前驱体。但是载金过程中由于需要使用高浓度的NaOH溶液对pH进行调节,所以Au/ZSM-5样品的酸性受到一定程度的影响,原有的两个NH3脱附峰只剩一个,并且峰位置发生变化,同时随着载金量的提高分子筛的酸性逐渐降低。但是进一步的微反活性评价结果表明,虽然金载量不同,但是各Au/ZSM-5样品的丙烯等低碳烯烃的选择性和微反活性等指数均相差不大。这可能是由于金对烃类的催化裂化反应有一定的促进作用从而弥补了分子筛酸性下降带来的催化活性降低。(3)在不同温度下,采用H_2对载金量相同的Au/ZSM-5样品进行还原处理,BET结果表明:随着还原温度的升高,Au/ZSM-5样品的比表面积和孔体积等均减小,载金分子筛的催化活性却随之变大,这可能是由于高度分散在分子筛表面的金颗粒在高温下聚集长大并对分子筛的酸性产生了贡献,而且大的金颗粒可能覆盖了分子筛的外表面并阻塞孔道从而最终影响催化活性。(4)在不同温度下,采用空气对载金量相同的Au/ZSM-5样品进行焙烧处理,XRD结果表明:随着焙烧温度的升高,Au/ZSM-5样品的MFI特征衍射峰强度逐渐下降,但即使是1000℃的高温也未能使分子筛的骨架结构完全破坏。随着焙烧温度的升高,分子筛酸性明显下降,在1000℃高温焙烧后,分子筛酸性消失殆尽。然而,各不同温度焙烧后的分子筛样的催化活性依然没有太大差别,我们仍将其归因于分子筛表面高度分散的金颗粒在高温下聚集长大并对分子筛酸性产生了贡献,并且大的金颗粒覆盖了分子筛表面并阻塞孔道进而影响催化活性。
[Abstract]:ZSM-5 molecular sieve as catalyst was the most commonly used FCC propylene production device, the smaller pore size limits larger hydrocarbon molecules into the pores, causing the pores of the active site to take part in the reaction. In order to eliminate the catalytic effect of its diffusion limit and clarify the limit of gold nanoparticles in the domain of molecular sieve in the production of propylene catalytic cracking reaction of light diesel oil, this paper use NaOH solution processing of micron ZSM-5 molecular sieve under different conditions, and the use of Au (EN) on the molecular sieve Au modified _2Cl_3 gold precursor, through the control of gold loading, reduction temperature, a series of Au/ZSM-5 catalysts preparation the calcination temperature conditions. In this paper, straight-run diesel distillation (235~337 C) as raw material, the effects of the molecular sieve and Au/ZSM-5 catalyst in propylene catalytic cracking diesel reaction of propylene and other low carbon olefins Selectivity and micro activity index. Combined with XRD, NH3-TPD, BET, ICP-AES, UV-Vis, TEM, a comprehensive analysis of the physicochemical properties of the catalyst FE-SEM were obtained. The results are as follows: (1) treatment of ZSM-5 by using different concentrations of NaOH solution. The results showed that: in the solution of NaOH concentration is not too high under the condition, can obtain the crystal structure of micro mesoporous composite ZSM-5 remain unchanged, the pore volume and average pore diameter compared to the original ZSM-5 has increased significantly, but the strong acid significantly reduced, acid treatment will make the weak acid further reduced. Molecular after alkali treatment and alkali acid continuous processing sieve, the micro reaction selectivity the activity and propylene compared to the molecular sieve is significantly improved. The molecular sieve samples after alkali treatment, the high temperature of 800 DEG C after further processing of water vapor, although the molecular sieve crystal structure has been retained, and the mesoporous degree To further increase, but the amount decreased sharply. Compared with the original molecular sieve, micro reaction activity and selectivity of propylene and other products of FCC light diesel molecular sieve of the series of processing samples in the propylene reaction did not change significantly, but the introduction of ZSM-5 mesoporous undoubtedly for subsequent pore confinement of Au/ZSM-5 sample preparation the foundation. (2) to Au (EN) _2Cl_3 was prepared by a series of different gold loading Au/ZSM-5 ICP-AES catalyst, the results show that Au can reach the actual load above the theoretical value of 80% Au (EN), visible gold species and molecular sieves of the _2Cl_3 strong bonding force, it is suitable for molecular sieve precursor gold. But the gold loaded process due to NaOH solution with high concentration of pH was adjusted, so the sample Au/ZSM-5 acid affected to a certain extent, the original two NH3 desorption peak only one , and the peak position changes at the same time, with the increase of molecular sieve amount of gold loaded acid decreased gradually. But the further micro activity evaluation results show that although the gold load is different, but the selectivity of the Au/ZSM-5 samples propylene and micro activity index were not significant. This may be due to the catalytic the reaction of hydrocarbon cracking gold has certain stimulative effect to compensate for the molecular sieve catalytic activity of acid to bring down lower. (3) at different temperatures, using H_2 for the same amount of gold loaded Au/ZSM-5 samples BET reduction treatment, the results show that with the increase of reduction temperature, Au/ZSM-5 sample surface area and pore the volume decreases, the catalytic activity of Au molecular sieve has become larger, which may be due to high dispersion of gold particles on the surface of molecular sieve under high temperature and acid production of the aggregation and growth of molecular sieve had Gong Xian, and large gold particles may cover the outer surface of the molecular sieve and pore blocking and eventually affect the catalytic activity. (4) at different temperatures, the Au/ZSM-5 samples of the same amount of gold loaded air roasting treatment, XRD results showed that: with the increase of calcination temperature, MFI characteristic diffraction peak intensity of Au /ZSM-5 samples decreased, but even the skeleton structure of the high temperature of 1000 DEG C also failed to make the molecular sieve completely destroyed. With the increase of calcination temperature, zeolite acidity decreased significantly at 1000 degrees Celsius after calcination, acid molecular sieve disappeared. However, the catalytic activity of the molecular sieve samples after different calcination temperature is still not too the big difference, we will still be attributed to the molecular sieve surface of highly dispersed gold particles under high temperature and acidic agglomeration has a contribution to the molecular sieve, and gold particles covering the surface of molecular sieve and hole blocking The channel further affects the catalytic activity.

【学位授予单位】：烟台大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ221.212;O643.36
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本文编号：1684482