Synthesis Of Phosphomolybdenum Tungsten Heteropoly Acids For Catalytic Oxidation Of NMST

2-nitro-4-methylsulfonylbenzoic acid(NMSBA)is an important raw material for the synthesis of highly effective herbicide mesotrione.In industry,NMSBA is prepared from oxidation of 2-nitro-4-methylsulfonyltoluene(NMST)with nitric acid,which has serious problems of low yield and environmental pollution.In this paper,phosphomolybdenum tungsten heteropoly acids(H3PMoxW12-xO40·nH2O,HPMoW)were synthesized by ether extraction,and the structure of heteropoly acids were confirmed to be Keggin type structure by ICP-AES,FT-IR,TG.The Co-Mn-Br-HPMoW homogeneous system was constructed to prepare NMSBA by liquid phase oxidation.The optimum experimental conditions were as follows:H3PM02.9W9.1O40·12.17H2O:1162.8 ppm;Co:247.5 ppm;Mn:453.5 ppm;Br:1075.2 ppm;water content:2.5(wt)%;oxygen content:30%,gas flow:700 mL/min,pressure:2.0 MPa,stirring speed:200 rpm,reaction temperature:215℃.The best results showed that the conversion of NMST was 94.93%,the selectivity of NMSBA was 99.84%,and the yield of NMSBA was 94.78%.On the basis of the homogeneous system,solid catalysts(HPMoW/AC)were prepared by using activated carbon supported H3PMo2.9W9.1O40·12.17H2O,and the Co-Mn-Br-HPMoW/AC heterogeneous system was constructed to catalyze the oxidation of NMST to prepare NMSBA.The optimal preparation conditions for solid catalysts were as follows:load rate:7.5%,activation temperature:280℃,activation time:4 h;the optimum concentration of catalyst components was 2.5×10-3 Kg/L for HPMoW/AC,220.0 ppm for Co,417.0 ppm for Mn,1075.2 ppm for Br;the best process conditions were as follows:water content:0%,gas flow:1000 mL/min,oxygen content:100%,pressure:2.0 MPa,stirring speed:200 rpm,reaction temperature:215℃.The best results determined that the conversion of NMST was 94.36%,the selectivity of NMSBA was 98.07%,and the yield of NMSBA was 92.54%.Compared with the homogeneous system,the NMSBA yield of the heterogeneous system was slightly decreased,but the usage of catalyst was significantly reduced,especially the amount of phosphomolybdenum tungsten heteropoly acid was only 15%.It is conducive to reducing production costs and improving economic benefits.