【作者】 王毅；

【导师】 赵迎宪； 张胜建；

【作者基本信息】 浙江大学 ， 化学工程， 2014， 硕士

【摘要】 本文主要研究了在丙酮氨肟化合成丙酮肟中,催化剂空心钛硅分子筛(HTS)的失活机理和副产物的形成机理。HTS催化丙酮氨肟化合成丙酮肟结果显示：以水作为溶剂的间歇反应中,催化剂经8次循环反应,丙酮的转化率一直维持在73-80%,丙酮肟选择性大于95%,稳定性较好。催化剂循环使用9次后丙酮转化率出现明显降低,降至65%；10次循环反应后丙酮转化率降至55%。以水作为溶剂的连续反应中,连续运转32h内,丙酮转化率一直维持在78-84%。继续延长反应时间,丙酮转化率出现明显降低,运转33h,丙酮转化率降至73%；运转34h,降至65%。通过气相-质谱(GC-MS)、液相-质谱(LC-MS)和核磁共振(NMR)对反应过程中的各种副产物进行了鉴别,结果显示它们主要包括若干种有机碱化合物和多硝基化合物2,3-二甲基-2,3-二硝基丁烷(DMNB)。有机碱的生成主要经历一个碱自催化反应过程,而DMNB的生成则主要经历自由基的加成与偶联反应过程。HTS分子筛经历32h连续反应后丙酮转化率出现显著降低,在间歇反应中经循环使用8次后,丙酮转化率也出现明显降低。采用X射线衍射(XRD)、紫外-可见吸收光谱(UV-vis)元素分析(ICP-MS)、吡啶吸附红外(Py-IR)氨程序升温脱附(NH3-TPD、N2物理吸附、热重-差热分析(TG-DTA)等表征手段对新鲜和失活催化剂进行了表征分析。结果显示：失活催化剂的晶型结构、酸类型及酸强度、骨架钛配位情况均未发生明显变化,但硅、钛元素出现明显流失、酸点数目减少、催化剂比表面积和孔容大幅减少。由此判断HTS分子筛失活主要包含两个阶段：一是有机碱副产物吸附或沉积占据催化活性中心,导致催化剂活性缓慢下降；二是有机碱副产物在催化剂孔道的积累和反应后期大量生成的副产物DMNB堵塞催化剂孔道,导致催化剂活性迅速降低。硝酸-氯仿溶剂浸洗可除去部分使失活HTS分子筛活性降低的物质,使丙酮转化率恢复到新鲜催化剂水平,但再生后催化剂寿命明显缩短。更多还原

【Abstract】 In this work, the new process of catalytic synthesis of acetone oxime by acetone ammoximation on hollow titanium silicalite (HTS) was investigated, and the mechanisms of catalyst deactivation and by-product formation were discussed in detail.The investigation on catalytic synthesis of acetone oxime by HTS showed water was the best solvent for keeping activity of catalyst. For batch reaction where water was used as solvent, the catalyst was reused for10times. For the first8times, the conversion of acetone was maintained within the range of73～80%, while the selectivity of acetone oxime was above95%. After that, the catalyst started to deactivate remarkably. When the catalyst was reused for9and10times, the conversion of acetone was decreased to65%and55%respectively. For continuous reaction, water was also used as solvent. The conversion of acetone was kept in the range of78～84%during32hours reaction. As the reaction went on, the catalyst began to deactivate rapidly. The conversion of acetone was dropped to73%after33hours reaction, and65%after34hours reaction.Two kinds of by-products were obtained in this ammoximation reaction, organic base like amines and a polynitro-compound2,3-dimethyl-2,3-dinitrobutane (DMNB). It should be noted that, polynitro-compound was found in the reaction of ketone ammoximation for the first time. Organic base by-products were formed by alkaline autocatalytic reaction system, including condensation reaction, nucleophilic substitution reaction, ammoximation reaction and oxidation reaction. Polynitro-compound by-product DMNB was formulated via a free radical addition and coupling reaction. The by-products were analyzed by GC-MS. LC-MS and NMR.Fresh and deactivated catalysts were characterized by XRD. UV-Vis, ICP-MS, Py-IR, NH3-TPD, N2adsorption-desorption and TG-DTA. The results demonstrated that deactivation of HTS zeolite could be divided into two stages:(1) slow deactivation due to by-product organic base adsorbed and deposited on the active sites of catalyst surface;(2) rapid deactivation in the late period due to by-products, DMNB and accumulated organic base, filling and blocking the catalyst pores.The deactivated HTS catalysts could be regenerated by HNO3and CHCl3 washing, which helped recover the activity of the catalytic. However, the lifetime of regenerated catalysts was shortened.更多还原