保护性脱硅构建高介孔度ZSM-5分子筛催化剂及其甲醇制烃反应性能研究

发布时间：2018-02-27 03:30

本文关键词： ZSM-5 甲醇制烃碱处理介孔　出处：《太原理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：石油在能源和化工产业中扮演重要角色,是汽油、烯烃和芳烃生产的重要原料来源。随着全球石油储量的不断降低和世界原油价格的频繁波动,寻找高效、绿色的上述液烃燃料和基础化工产品的技术路线十分迫切,也是优化我国能源结构,降低对石油资源依赖的重要选择。甲醇制烃反应(MTH)是甲醇经过酸性分子筛催化剂作用定向转化成烷烃、烯烃和芳烃等烃类化合物的反应。ZSM-5分子筛催化剂,硅铝比范围大,酸性可控性高,其择型效应和水热稳定性使其成为目前MTH反应广泛使用的催化剂。但是ZSM-5分子筛的扩散限制是催化剂失活的重要原因:甲醇在ZSM-5微孔的酸性位点转化成芳烃等积炭前驱物,难以从微孔孔道扩散,堵塞扩散孔道出口,并继续反应形成积炭,覆盖微孔上的酸活性位点,导致催化剂积炭失活。因此,提高ZSM-5分子筛的孔道扩散性能是解决催化剂积炭失活的关键所在。介孔构建能够有效改善ZSM-5分子筛的扩散性能,碱处理是目前介孔构建的简单高效方法,但传统碱处理过程中硅的脱除受铝分布显著影响,构建的介孔分布不均匀,且容易形成大孔,分子筛介孔度低。为了提高碱处理后ZSM-5分子筛建的介孔度,本论文对微米和纳米ZSM-5进行保护性碱处理脱硅,控制脱硅过程,以提高介孔度,延长其催化MTH反应寿命,并明确介孔度与催化寿命的构效关系。本文的主要结论如下:(1)对比研究碱溶液中TPA~+(四丙基氢氧根离子)/Na~+(钠离子)比对微米ZSM-5分子筛介孔度的影响发现,TPA~+离子的引入促进了体相均匀分布介孔的形成,增加了介孔数量,介孔孔径更为集中。随着溶液中TPA~+/Na~+比增加,ZSM-5分子筛的外比表面积先增加后降低,高浓度TPA~+不利于高介孔ZSM-5催化剂的制备。当TPA~+/Na~+比为0.5时,ZSM-5分子筛的外比表面积最大,达210 m2·g-1。通过ICP-AES、XPS和29Si NMR表征手段,发现了TPA~+的吸附位点在ZSM-5分子筛的Si(4Si,0Al)位,并明确了混合碱处理高介孔度ZSM-5分子筛构建机理,TPA~+离子的保护性脱硅和Na~+离子的选择性脱硅的协同作用共同促进了高介孔微米ZSM-5分子筛的形成。结合MTH反应评价,ZSM-5催化剂的催化寿命与其外比表面积成正相关关系:ZSM-5分子筛的外表面积越大,MTH反应催化寿命越长。在400 oC,1 MPa,9.4h-1反应条件下,具有最大外比表面积的ZSM-5的MTH反应寿命达到102 h,约为传统NaOH碱处理样品催化寿命的2倍。(2)在碱处理具有高扩散性能纳米ZSM-5分子筛催化剂时,发现引入硝酸铝能够抑制空心纳米ZSM-5分子筛的形成,促进ZSM-5分子筛体相介孔的形成,有利于提高介孔度。相较于传统NaOH碱处理,低浓度Al~(3+)混合碱碱处理的纳米ZSM-5分子筛的外比表面积进一步提升至144 m2·g-1。而随着碱溶液中Al~(3+)浓度的增加,ZSM-5分子筛的外比表面积开始降低。同时结合ICP-AES和NH3-TPD表征,发现加入硝酸铝的碱处理的ZSM-5分子筛的酸量随着溶液中Al~(3+)浓度的增加而增加,但是其酸量仍然低于传统NaOH碱处理的ZSM-5分子筛,而且其酸强度也随碱溶液中Al~(3+)浓度的增加而增强。通过对比碱处理前后ZSM-5的织构性质和TEM图,ZSM-5分子筛的外比表面积的利用程度直接影响了MTH反应的催化寿命。ZSM-5催化剂的酸性和扩散性能影响MTH反应产物分布,高酸量和强酸性促进氢转移反应,有利于芳烃和烷烃的选择性;而外表面高酸量分布的ZSM-5催化剂不利于低碳产物进行二级反应生成高碳芳烃等产物,具有高的烷烃选择性和低的芳烃选择性。
[Abstract]:The oil in the energy and chemical industry plays an important role, is an important raw material of gasoline, olefin and aromatics production. With the global oil reserves continue to reduce the frequent fluctuations, and the world crude oil price for an efficient and technical route of the liquid hydrocarbon fuel and basic chemical products green is very urgent, but also optimize the energy structure of our country. A major choice of reducing dependence on oil resources. The reaction of methanol to hydrocarbons (MTH) methanol after acidic zeolite catalyst directed into alkanes, olefins and aromatics reaction of.ZSM-5 molecular sieve catalyst such as hydrocarbons, silicon aluminum ratio, acid high controllability, the selection effect and thermal stability of the water the catalyst is widely used in MTH reaction. But the diffusion limitation of ZSM-5 molecular sieve is an important reason for the deactivation of the catalyst in methanol: ZSM-5 microporous acidic sites into aromatic hydrocarbon product Carbon precursor, difficult to diffuse from the pore pore diffusion, pore blockage and exports continue to react to form coke acid active sites on the pore cover, resulting in catalyst deactivation. Therefore, to improve the performance of ZSM-5 molecular sieve pore diffusion is the key to solve the coking of the catalyst deactivation. The mesoporous construction can effectively improve the performance of ZSM-5 diffusion molecular sieve, alkali treatment is simple and effective method at present mesoporous construct, but the traditional alkali treatment process of silicon removal by aluminum distribution significantly affects the construction of the mesoporous distribution is not uniform, and easy to form a large hole, the mesoporous molecular sieve is low. In order to improve the alkali treated ZSM-5 zeolite mesoporous degree construction in this paper, the protection of the alkali treatment desilication of micron and nanometer ZSM-5, control of the desilication process, in order to improve the mesoporous degree, prolong the life of catalyst for the MTH reaction, and clear the mesoporous degree and catalytic life of structure-activity relationship. In this paper, the main Conclusions are as follows: (1) a comparative study on TPA~+ in alkaline solution (four propyl hydroxyl ions) /Na~+ (sodium) than the micron of ZSM-5 molecular sieve mesoporous degree that TPA~+ ions promote the body to form uniform mesoporous distribution, increase the number of mesoporous, mesoporous pore size is more concentrated with the increase of TPA~+/Na~+ ratio. In the solution, ZSM-5 molecular sieve to increase the specific surface area decreased, the high concentration of TPA~+ is not conducive to high mesoporous ZSM-5 catalyst preparation. When the TPA~+/Na~+ is 0.5, ZSM-5 molecular sieve the largest specific surface area of 210 M2 - g-1. by ICP-AES, XPS and 29Si methods the characterization of NMR, found the TPA~+ adsorption sites in ZSM-5 zeolite Si (4Si, 0Al), and the mixture of alkali and high processing degree of mesoporous ZSM-5 molecular sieve structure mechanism, synergistic effect of selective protection of TPA~+ ion and Na~+ ion of the desilication of desilication promoted high mesoporous micron The formation of ZSM-5 molecular sieve. Combined with MTH reaction, catalytic lifetime of ZSM-5 catalyst and its specific surface area is a positive correlation between the ZSM-5 molecular sieve surface area is larger, longer catalyst life MTH reaction. In 400 oC, 1 MPa, 9.4h-1 reaction conditions, with the maximum reaction surface area than MTH life ZSM-5 up to 102 h, about 2 times as much as the traditional NaOH alkali treatment samples by catalytic life. (2) in alkali treatment with high diffusion properties of nano ZSM-5 molecular sieve catalyst, found that the introduction of aluminum nitrate inhibits the formation of nanometer ZSM-5 molecular sieve hollow, promote the formation of ZSM-5 molecular sieve mesoporous phase, is conducive to improve the degree. Compared with the traditional mesoporous NaOH alkali treatment, low concentration of Al~ (3+) ZSM-5 nano molecular sieve mixed alkali treatment to further enhance the external surface area of 144 m2 / g-1. with alkali solution Al~ (3+) concentration increased, ZSM-5 molecular sieve external surface area At the same time began to decrease. The combination of ICP-AES and NH3-TPD were found with aluminum nitrate alkali treatment of ZSM-5 molecular sieve with acid solution Al~ (3+) concentration increased, but the amount is still lower than the traditional NaOH ZSM-5 molecular sieve and alkali treatment, the acid strength with alkali solution concentration of Al~ (3+) the increase. The texture and TEM map contrast before and after alkali treatment of ZSM-5, ZSM-5 molecular sieve ratio surface area utilization degree directly affect the acidity and diffusion properties of MTH reaction product distribution of catalytic life of.ZSM-5 catalyst for MTH reaction, high acid and strong acid to promote the hydrogen transfer reaction, selective for aromatic hydrocarbons the surface of the ZSM-5 catalyst and alkanes; high acidity distribution outside is not conducive to low carbon products were two grade reaction of high carbon hydrocarbon products with high selectivity and low alkane compounds.

【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ211

【参考文献】