Co/Mn/Br催化体系中CO_2协助氧化对二甲苯制对苯二甲酸

CO_2-Aided Aerial Oxidation of p-Xylene to Terephthalic Acid with Co/Mn/Br Catalyst

以对二甲苯(PX)为原料、醋酸和水为溶剂,在Co/Mn/Br催化体系作用下,用N_2/O_2/CO_2混合气氧化PX制备了对苯二甲酸(TA)。考察了混合气中CO_2含量对氧化反应速率、氧化反应中间产物含量和TA收率的影响。同时,分析了PX液相氧化条件下CO_2的作用机理。实验结果表明,CO_2加快了PX的氧化反应进程,使氧化过程的耗氧速率明显加快。在反应液中w(Co)=0.030%、w(Mn)=0.060%、w(Br)=0.075%(相当于反应液的质量)和反应温度195℃的条件下,使用V(CO_2)∶V(O_2)∶V(N_2)=40∶21∶39的混合气氧化时,CO_2的协助氧化作用最为明显,与用空气氧化PX制备TA相比,反应时间缩短了4～5min,此时固体产物TA中中间产物的含量最低。紫外可见光谱分析表明,在PX液相催化氧化体系下加入CO_2,形成了一种活性组分,它促进了金属离子价位的转换。

CO2-aided aerial oxidation of p-xylene to terephthalic acid using Co/Mn/Br catalyst in liquid media of acetic acid and water was studied. The influence of CO2 content in feed gas on reaction rate, intermediate product concentration and yield of terephthalic acid was investigated. Possible mechanism of CO2-aided oxidations was discussed. Experimental results showed that oxidation was accelerated in the presence of COz. The optimal reaction conditions were： temperature 195℃, gas mixture rate V（ CO2 ） ： V（ O2） ： V（ N2 ） 40 ： 21 ： 39, and concentration of Co/Mn/Br catalyst based on total liquid mixture ： Co mass fraction 0. 030%, Mn mass fraction 0.060% and Br mass fraction 0. 075%. In comparing with ordinary aerial oxidation of p-xylene to terephthalic acid without CO2, reaction time reduced by 4 -5 min, and impurity content in solid product terephthalic acid was the minimum. UV-Vis investigation demonstrated that a new active species formed with addition of CO2 as a co-oxidant in p-xylene oxidation, which promoted the conversion of metallic ion valence, so promoted the reaction rate.