苯和丙烯液相烷基化合成异丙苯β沸石催化剂的失活

【作者】 卞俊杰；

【导师】 王祥生；

【作者基本信息】 大连理工大学 ， 工业催化， 2003， 博士

【摘要】 异丙苯是重要的化工原料，有90％以上的异丙苯用来生产苯酚和丙酮，其余的用来生产苯乙酮及合成橡胶和树脂的单体α-甲基苯乙烯。目前，全球异丙苯的产量已超过千万吨／年，并将继续以3.8％的年增长率递增。工业上生产异丙苯主要以苯与丙烯为原料，在催化剂的作用下，经烷基化反应制备。传统工业中使用的AlCl₃和固体磷酸催化剂都存在不同程度的难以彻底解决的腐蚀和污染问题，在环保要求日益严格的形势下，从20世纪60年代开始，世界各大公司逐步转向开发无腐蚀、无污染的新型固体酸催化生产异丙苯的新技术，其中使用沸石催化剂的固定床工艺和催化精馏工艺，如使用脱铝丝光沸石的Dow／Kellog工艺、使用MCM-22的Mobile／Badge工艺、使用β沸石的UOP的Q-MAX工艺及Enichem工艺、和使用Ω沸石和Y沸石的CDTech工艺，都已投入工业化生产。 本课题组研制开发的改性β沸石催化剂BPA，用于苯和丙烯液相烷基化合成异丙苯反应，已经完成了催化剂装填量100kg的中试，催化剂表现出很好的活性、选择性和稳定性。第一运转周期（the first circle）连续运转8000小时催化剂失活。经程序升温烧炭再生后，又进行第二周期（the second circle）运转，已连续反应7000小时催化剂无失活迹象。 本论文首先在小型固定床中考察了反应条件对BPA催化剂积炭行为的影响。 然后对催化剂装填量为1.5g的固定床催速积炭催化剂、催化剂装填量为20.0g小试运转1000小时积炭催化剂、催化剂装填量100kg中试第一周期运转8000小时积炭催化剂、和中试第二周期运转7000小时积炭催化剂上积炭的性质进行了研究。 采用核磁共振¹³C NMR、傅立叶变换红外光谱FT-IR、紫外可见吸收光谱UV-Vis、气相色谱-质谱联用GC-MS、热重分析TG和程序升温烧炭TPO法研究催化剂上积炭的组成、性质。 应用扫描电子显微镜SEM、N₂物理吸附、正己烷／环己烷动态吸附、结合N-甲基吡咯烷酮作溶剂，在密封釜中高温萃取沸石外表面积炭的方法，确定了沸石外表面积炭的组成，进而与HF溶沸石骨架后CCl₄萃取内外积炭的结果相比较，确定了积炭的沉积部位是在沸石孔道内、外表面，还是晶间孔。 由于BPA催化剂的中试反应器挂在现有UOP工业烃化反应器的侧线，因此中试BPA催化剂的积炭行为与工业生产中BPA催化剂的积炭性质非常接近。通过比较BPA催化剂在实验室和中试反应中积炭的组成、性质、积炭沉积部位、积炭生成方式，探明不同反应规模下BPA催化剂积炭的共性和差异。结合采用NH₃-TPD、三甲基膦吸附³¹P NMR、和作者改进的吡啶、2，6-2-甲基吡啶吸附UV-Vis光谱法，对中试β沸石催化剂的酸性质的考察，并采用X射线衍射XRD、X射线荧光分析XRF对催化剂结晶度、硅铝比的测定，推测出BPA催化剂的积炭失活机理。 在此基础上，论证用实验室催速积炭反应模拟中试、乃至工业反应中BPA催化剂积炭反应的可行性。并提出了工业烧炭过程的改进方法。 最后，采用不同方法对Na β沸石原粉进行后处理，研制出一种制备高活性合成异丙苯β沸石催化剂的新方法。 结果表明：（1）实验室条件下，反应温度影响BPA催化剂上积炭的性质，150℃～195℃范围内，温度升高，积炭稠环化程度增加；增加丙烯进料量使苯烯摩尔比由1.5：1降至1.2：1，积炭中多异丙基苯和烷基萘的量增加，苯烯比继续降至0.9：1，积炭中烷基苯和丙烯液相烷基化合成异丙苯已沸石催化剂的失活蔡的量减少;当温度和苯烯比一定，丙烯的质量空速分别为1.oZh‘1、2.03n-l和4.o6h一l时，积炭的性质和生成量变化不大;反应时间延长，积炭的生成速率减小。 （2）积炭的组成:无论是在实验室固定床催速反应20小时失活的BPA催化剂，还是中试第一周期8000小时失活、和第二周期7000小时积炭的催化剂，其上的积炭均是由多异丙基苯（包括二异丙基苯、三异丙基苯、四异丙基苯）、烷基蔡、及少量的重质量“焦”三类物质组成。但反应规模不同，BPA催化剂上积炭各组分的含量略有差别。与实验室催速失活的B队催化剂上的沉积物相比，中试失活的催化剂上的沉积物中重质量“焦”的量增加，即C舰比较小的难烧除的炭的量增加。 （3）积炭在催化剂上的分布:无论是在实验室催速反应中，还是在小试、中试反应中，B队催化剂上的积炭均是在p沸石孔道内生成，在沸石孔道内沉积，而并非沉积在沸石晶粒的外表面。 （4）积炭的生成方式及积炭失活的机理:B队催化剂的积炭失活机理相同，在p沸石上B酸中心的作用下产物异丙苯深度烷基化生成多异丙基苯;同时，在强B酸中心和L酸中心的共同作用下，多异丙苯或异丙苯发生侧链烷基化的产物、进一步发生缩合、氢转移、芳构化等反应生成大体积、重质量、高C从比的烷基稠环芳烃。由于沸石的孔道位阻作用，在沸石孔道内生成的三、四异丙基苯和烷基稠环芳烃无法扩散到沸石外表面，从而在孔道内沉积，造成孔道阻塞，导致催化剂失活。即BPA催化剂的积炭失活机理符合积炭生成反应与主反应串行的连贯失活（consecutive deactivation）机理。 （5）可通过小型固定床催速积炭反应模拟中试反应中催化剂的积炭行为，确定实更多还原

【Abstract】 Cumene, one of the largest commercial volume derivatives of benzene, is an important intermediate in the production of phenol and acetone (>90%), acetophenone, and a-methylstyrene. The worldwide capacity for cumene topped 10 million metric tons per year, and the growth rate is expected to be 3.8% per year in the next decade. Conventional cumene plants use alumimium chloride and solid phosphoric acid catalysts. However, these catalysts caused corrosion and disposal problems, creating an opportunity for commercialization of cumene processes based on zeolites. Novel zeolite-based cumene processes have been commercialized by Dow/Kellog (dealiminated mordenite), Mobile/Badge (MCM-22), UOP(Q-MAX process used zeolite p) , Enichem(zeolite (3), and CDTech (zeolite Q for alkylation, zeolite Y for transalkylation).BPA, the modified zeolite P catalyst, explored by our group, used for benzene alkylation to synthesize cumene, has been tested in pilot plant where the 1 00kg catalyst loaded , and the BPA showed high activity, high selectivity and long life. The BPA catalyst deactivated after 8000 hours time on stream in the first circle. The deactivated catalyst underwent temperature programmed oxidation to refresh, and the refreshed BPA performed well in 7000 hours time on stream of the second circle.In this dissertation, the effect of reaction conditions on the coking behavior of BPA in a small fixed-bed scale was estimated, followed by the coking deactivation study concerning or the BPA catalysts coked in the small fixed-bed scale both in the accelerated decay where 1.5g catalyst loaded, and in 1000 hours time on stream activity evaluation where 20.0g catalyst loaded, and concerning on BPA catalyst coked in pilot first circle 8000 hours’ run and second circle 7000 hours’ operation where 100kg catalyst loaded.The coking deactivation study of BPA catalyst was divided into (1) nature of coke, (2) coke distribution on catalyst (in pores of zeolite, on surface of zeolite particles, and in secondary pores of zeolite particles), and (3) coking mechanism and mode of coke formation.13C NMR, FT-IR, UV-Vis, GC-MS, Thermal Gravity and Temperature Programmed Oxidation were applied to detect the coke nature. SEM, N2 physical adsorption, n-hexane/c-hexane adsorption, and coke extraction by N-methyl pyrrodine above 200 ℃ in an autoclave were employed to determine the nature of the coke on zeolite particle surface. XRD, XRF, NH3-TPD, 31P NMR, pyridine/2,6-dimethyl-pyridine adsorption UV-Vis (modified by author), and pyridine adsorption FT-IR were used to explore the change of crystallinity, and acidity between fresh BPA and the coked ones.For the reactor of pilot was installed bypass of the industrial UOP device, the coking behavior of BPA in pilot is similar to that in industry. The commonness and the difference ofBPA coking in lab and in polit can be deduced, and the coking mechanism of BPA can be inferred. Then, accelerated decay was designed for simulating the BPA coking process in pilot, even for predicting the BPA coking way in industry. The ameliorations of TPO regeneration conditions were proposed.Lastly, A new post-synthesis method to prepare Hp from Nap was developed, and the HP made in this way showed a high activity for benzene alkylation to cumene.It can be concluded: (1) In lab, reaction temperature effects the nature of coke, 150℃ ~ 195 ℃, coke shows more character of polyaromatics as temperature higher; The amount of multi-alkylbenzene and polyaromatics increases when benzene to propene mole ratio decreases from 1.5:1 to 1.2:1 as additional propene added, while the amount of polyaromatics decreases when benzene to propene mole ratio decreases from 1.2:1 to 0.9:1, for more multi-alkylbenzene created; The nature and the amount of coke change little when temperature and ratio of benzene to propene fixed, WHSV of propne is 1.02h"1, 2.03h~’, and 4.06h-1; and the coke formation speed decreases as time on stream increases.(2) Coke composition: Whether in lab or in pilot, the coke deposited on decayedBP更多还原