Study On Reaction Process Of Catalytic Oxidation Of PMIDA By Pt/C

As an organophosphorus herbicide with functional properties of high performance,low toxicity,broad spectrum and low residue,glyphosate has been developed as the most competitive herbicide with the biggest output in the world.A more advanced technology for glyphosate production is the iminodiacetic acid process(IDA),of which the critical step is the catalytic oxidation of PMIDA into glyphosate.However,formaldehyde was observed during the synthesis process,leading to more side reactions and lowered glyphosate yield.By applying Pt/C catalyst,formaldehyde can be oxidized into formic acid catalytically same as the catalytic oxidation of PMIDA,and into carbon dioxide and water further on,which results in improved glyphosate yield,decreased wastewater discharge.First,liquid phase impregnation reduction technique is adopted to prepare the Pt/C catalyst and the influence of different factors on the catalyst activity were investigated.By physical characterization such as BET,TEM and XRD as well as evaluation through oxidation reaction,the optimum preparation conditions for catalyst preparation were established:formaldehyde used as the reducing agent,reducing temperature of 363.15K,pH value of 12.4,ration of HCHO to(PtCl6)2-of 200:1 and capacity of Pt of 3%.Under above conditions,higher activity of Pt/C for oxidizing formaldehyde and removal rate of 85%for formaldehyde are observed.After eliminating the influence of internal and external diffusion,with reaction pressure of 0.6MPa,stirring speed of 800rpm,oxygen flow rate of 120ml/min and reaction temperature of 323.15-353.15K,oxidization kinetic experiments were conducted.Combining experiment data in fitting calculation,the kinetic parameters were obtained following the building of intrinsic kinetic model.Activation energies of formaldehyde's oxidization into formic acid and oxidizing reaction of formic acid are 36.04kJ/mol and 19.93kJ/mol respectively.The adsorption heats of formaldehyde and formic acid are-60.26 kJ/mol and-39.96kJ/mol respectively.Last,the effects of various factors on the catalytic oxidation of PMIDA were investigated.The optimum process conditions were a stirring speed of 500rpm,reaction temperature of 343.15K,reaction pressure of 0.6MPa and ratio of Pt/C to PMIDA of 10%,which gives yield of 95.79%for glyphosate and removal ratio of 85%for formaldehyde.