Highly selective vapor phase nitration of toluene to 4-nitro toluene using modified and unmodified H3PO4/ZSM-5

摘要

The nitration of toluene has been studied in the vapor phase at various temperatures over a series of surface modified and unmodified ZSM-5(Si/Al=170)loaded with H3PO4,differing in the external surface treatment of the zeolites.All samples were characterized by X-ray diffraction,BET and FT-IR.The nature of acid sites of the supports,i.e.,H3PO4/ZSlVT-5-surf-l 70 and H3PO4/ZSM-5-l 70 was determined using FT-IR-pyridine adsorption study.2,4,6-Trimethyl pyridine adsorption was used for calculating the external surface acidity of the H3PO4/ZSM-5-surf-170 and H3PO4/ZSM-5-170.The superior performance of the externally blocked catalysts(modified)relevant to the H3PO4/ZSM-5-l 70 catalyst shows that by blocking the external surface area of the ZSM-5 support,it exhibits a superior catalytic selectivity than the unmodified catalyst.Catalysts containing 0-4.9 wt.% P were prepared using ZSM-5-surf-l70 and ZSM-5-170,and their catalytic performance was determined for the vapor phase nitration of toluene to 4-nitrotoluene(4-NT),2-nitrotoluene(2-NT)and oxidation products.The effect of reaction temperature,H3PO4 content,feed ratio of toluene to HN03,WHSV,TOS and carrier gas flow rate was also investigated.