【作者】 杨光成；

【导师】 潘仁明； 权恒道；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2010， 博士

【摘要】 CF3I具有较低的GWP值和ODP值,在哈龙替代灭火剂和制冷剂方面具有潜在的应用意义,本文针对CF3I目前合成方法得率低、间歇操作等缺陷,研究了气相CF3I合成反应的机理、工艺条件和催化剂技术。通过对气相合成CF3I的四条路线的吉布斯自由能计算,选择CHF3、碘和氧气为原料合成CF3I,设计了装置线路在550℃条件下进行反应,采用GC-MS、FTIR和分子量测定确认产物为CF3I,表明该反应能够合成CF3I。采用捕捉剂H2、2-甲基-2-丁烯对反应中间体进行捕捉,不同条件下分析产物组分变化；对吸附了中间体的载体进行氢化和热解实验,分析产物结构。空管热解CHF3能够产生CF₂卡宾中间体,与H2得到CH2F2,当有载体活性炭（AC）存在时,CHF3受热脱HF得到中间体CF2卡宾,CF2卡宾吸附在活性炭表面形成稳定结合,捕捉剂检测不到CF2卡宾,且CF2卡宾不能二聚形成四氟乙烯。结合在AC表面的CF2卡宾受热发生岐化反应得到CF3自由基,CF3自由基与碘自由基结合生成产物CF₃I, CF₃自由基与CF2卡宾结合形成CF₃CF₂自由基,CF₃CF₂自由基与H自由基结合形成CF₃CHF₂,与Ⅰ自由基结合生成CF₃CF₂I,CF₃自身结合生成CF₃CF3_。采用CHF₂C1和六氟环氧丙烷（HFPO）在AC或多孔氟化铝（PAF）表面进行类似的实验,发现生成类似的产物,表明实验条件下得到CF3自由基只与中间体CF2卡宾相关,CF2卡宾在AC或PAF上发生岐化反应生成CF3自由基。通过实验得到了气相催化合成CF3I的机理为CF2卡宾岐化机理。为验证CF2卡宾岐化机理成立,采用Material Studio的DMol3模块对CF2卡宾在AC表面吸附和岐化进行模拟计算,并依据机理设计了HFPO低温催化反应合成CF3I以验证反应机理成立。计算结果表明CF2卡宾能在AC表面形成较强的结合,与AC表面的共轭π键反应形成偕二氟环丙烷化合物。两个相邻CF2卡宾在AC表面吸附后,其中一个CF2卡宾上的F原子逐渐靠近另外一个CF2卡宾上的C原子形成CF3基团。CF2卡宾在AC表面的吸附能-36.32 kcal/mol,岐化反应第一步的活化能为36.4kcal/mol,岐化反应第二步的活化能为42.1kcal/mol。CF₂能够在AC表面能够形成稳定结合并发生岐化反应,与实验结果吻合。HFPO在较低温度下能够热解产生CF₂卡宾,在KF/AC催化剂作用下170℃与碘能够产生CF₃I,210℃时反应2h可使HFPO的转化率达到99%以上。理论计算和HFPO合成CF3I的实验证明CHF3与碘合成CF3I的CF2卡宾岐化机理成立。利用机理研究结果对反应工艺条件进行优化研究,研究了温度、空速、投料比对反应的影响规律。适宜的反应温度为550℃时；适宜的空速为300h-1；最佳投料量为CHF3为36ml/min; I₂: 8.2g/h; O₂:3ml/min（对应的催化剂的体积为16ml）。为提高反应的转化率和催化剂的使用寿命,研究了气相催化合成CF3I的催化剂活性物和载体对反应的影响。结果发现碱金属盐作为催化活性组分具较高的活性；AC作为载体时,CHF3的转化率较高,多孔金属氟化物氟化铝和氟化镁作为载体时转化率偏低,但金属氟化物对氧气和HF惰性,作为载体具有工业应用潜力。在优化条件下,RbNO₃-KF/AC催化剂使用寿命得到提高,达到120h。更多还原

【Abstract】 CF₃I has potential applications in replacement of Halon extinguishing agents and refrigerants due to its low GWP value and low ODP value. Current methods do not seem likely candidates for large-scale production of CF₃I due to the low yield and batch processes. In this dissertation, a continuous vapor-phase catalytic process for preparation of CF3I was studied, especially in the reaction mechanism, process conditions and catalytic technique.According to the Gibbs free energy, the reaction between CHF₃ with I₂ in the presence of O₂ is an appropriate synthetic route. Over an experimental line system, CHF₃,I₂ vapor and O₂ were mixed and fed into the reactor at 550℃, then the producted was collected and analyze by GC-MS, GC and FTIR. It was found that CF₃I can be synthesis by this method.H₂ or 2-methyl-2-butene, as capture agent, was fed into reactor with CHF₃ over catalysts or non-catalyst. And the intermediate absorbed on the surface was conducted pyrolysis reaction and hydrogenation reaction. It was found that in pyrolysis of CHF₃ through empty reactor in the presence of H₂, CH₂F₂ was obtained via the reaction of CF₂ carbene with H2. But over AC, the formed CF₂ carbene was adsorbed on the surface of AC. the CF₂ carbene intermediate can not be trapped by H₂,2-methyl-2-butene and CF₂ carbene itself. CF₂ carbene takes plcae disproportionation reaction takes place to generate CF3 radical. CF₃ radical reacts with I₂ to form CF₃I, whereas with H radical to form CHF₃. CF₃ radical reacts with CF2 carbene to form CF₃CF₂ radical, which generates CF₃CF₂I and CF₃CHF₂. When CHF₂Cl and hexafluoropropylene oxide （HFPO）, as other CF₂ carbene sources, were conducted the same reactions over AC or porous AlF₃ （PAF）, the similar products were detected. It was indicated that under experimental conditions, CF₃ radical generation associated only with the intermediate CF₂ carbene. CF₂ carbene disproportionation took palce over AC or PAF. It was verified that the reaction mechanism was CF₂ carbene disproportionation by experimental means.To check the above mechanism, the software of Material Studio was used to simulate the reaction process and a low temperature catalytic reaction for CF₃I synthesis was conducted. Calculation results showed that CF₂ carbene was strongly combined with AC and reacted with conjugatedπbond to form difluoro-cyclopropane compound. Between two closed CF₂ carbene, one F atom of one CF₂ carbene will close to the C atom of the other CF₂ carbene to form CF₃ group. The adsorption energy of CF₂ carbene with AC was-36.32 kcal/mol and activated energy of two steps of disproportionation reaction were 36.4kcal/mol and 42.1kcal/mol, respectively. Through the simulation, it is indicated that CF2 carbene can adsorb on the surface of AC and take palce disproportionation reaction to generate CF3 group. It was in accordance with experimental results. When HFPO reacted with I₂ over KF/AC catalyst at 170℃, CF3I was generated. When reaction temperature was increased to 200℃and hold for 2h, the conversion of HFPO reached 99%,. Calculation results and CF₃I synthesis via HFPO showed that the reaction mechanism is positive.Based on mechanism above, the reaction conditions were optimized. The appropriate reation temperature was 550℃.and the appropriate space velocity was 300h^-1. The optimized amount of raw materials was CHF3:36ml/min, I₂:8.2g/h and O₂:3ml/min （catalyst volume was 16ml）To increase the conversion of CHF3 and prolong catalyst life, the catalytic technique of this catalytic reaction for CF3I synthesis was investigated, including activated substances supporters. It was found that alkali metal salts showed a higher catalytic activity than the alkaline earth metal salts. AC, as the catalytic supporter, showed higher activity due to its high surface area. Porous metal fluoride, such as porous aluminum fluoride and porous magnesium fluoride, as carriers showed medium activity and stable properties in the presence of O₂ and HF. So, Porous metal fluoride processed industrial potential application as carrier for this reaction. Under optimized conditions, the catalyst life of RbNO₃-KF/AC increased and reached 120h.更多还原