The Study On Regeneration Of Catalyst For N-phosphonomethylglycine Catalytic Oxidation To Glyphosate

Glyphosate（PMG）is widely used herbicide because of its good weeding effect,wideapplication range and low toxicity to humans and animals.The catalytic oxidation of n-phosphonomethylglycine（PMIDA）to produce PMG is a main stream technology for industrial production of PMG,and the catalyst is the key issue for the catalytic process.Activated carbon catalysts are widely used due to the advantages of low price,high conversion of PMIDA and high PMG selectivity.However,the disadvantage of activated carbon catalysts is that it is easy to deactivate.Direct discarding the deactivate catalyst not only leads to resources waste also caused environmental pollution.In order to realize the recycling of activated carbon catalyst,we take an industrial activated carbon catalyst of an enterprise as the research project in this work.The cause of catalyst deactivation is systematically studied,and finally an efficient catalyst regeneration technology is developed.The main results are as follows:1.The searched optimization results of the reaction process show that the optimized process conditions of the activated carbon catalyst are:the amount of PMIDA 7.5 g,the amount of catalyst 1.5 g,the amount of deionized water 150 mL,and the reaction time 70 min,the oxygen flow rate was 60 mL/min,the reaction temperature 65°C,the reaction pressure 0.5 MPa,and the stirring speed 400 rpm in the laboratory reaction scale.Under the optimatl reaction conditions,the conversion of PMIDA was 98.0%,the selectivity of PMG was 99.8%,and the yield reached 97.8%.2.BET,SEM,TG,FT-IR,CO₂-TPD,NH₃-TPD,XPS characterization results of fresh and used catalysts show that the main reason incurring catalyst deactivation is that the macromolecular acidic substances generated during the reaction are deposited on the catalyst surface.The deposition of macromolecular acidic substances not only blocks the pores of the catalyst,resulting in a poor mass transfer effect,but also leads to a decrease of basic sites and an increase in acidic sites on the catalyst surface,which in turn leads to the coverage of active sites and the reduction of active centers.The simulated deactivation experiments demonstrate that the mechanism for the formation of macromolecular acidic substances is that PMIDA,PMG and HCHO form polymers during the reaction and deposit on the surface of the catalyst.3.The combined treatment of alkali surface modification→nitrogen doping modification→inert atmosphere roasting can realize effective regeneration of the catalyst,but at the same time the regeneration effect depends on the modification process and technology.The results of the study show that:first surface modification treatment with No.1 alkali,then doping modification with No.1 nitrogen source,and finally calcination in nitrogen at 600°C can regenerate the catalyst to achieve more than 95%yield after recovering.Under the same conditions,the use of No.2 nitrogen source for doping modification requires nitrogen calcination at 650°C to regenerate the yield of the used catalyst to a PMG yield greater than 95%.The characterization results show that:alkali surface modification treatment can effectively increase the specific surface area of the used catalyst,and the subsequent nitrogen doping and nitrogen calcination treatment can effectively increase the basic sites on the catalyst surface,and the basic sites are the activity of the catalyst center,thus realizing the efficient regeneration of the used catalyst.