| The oxidation reaction of N-Phosphonomethyl iminodiacetic acid(PMIDA) is the final step in the production of glyphosate(PMG), PMIDA is used as raw material, gas containing oxygen is used as the oxidant, activated carbon is used as the catalyst. Existing process is operated in the batch stirred tank, and the large number of solid-liquid materials have to be separated outside the tank in a short time. filtering operation requires highly, the end point of reaction is controled difficultly,and yied is difficult to guarantee. Therefore, research and development of continuous production process for Pmida oxidation is very important.The three-phase fluidized bed with an inner filter is probably to make the reaction and liquid-solid separation continuous at the same time. In order to develop this continuous oxidation process, the kinetics of PMIDA oxidation, the separation of liquid-solid and the characteristics of flow in the three-phase fluided bed with an inner filter were studied.1. In a5L autoclave, the effect of the catalyst’s concentration, temperature, and pressure on the reaction rate were investigated for PMIDA oxidation with oxygen as the oxidant, activated carbon as the catalyst. According to the principle of PMIDA oxidation under activated carbon, the mechanism of PMIDA oxidation was proposed, and the intrinsic kinetics model was established as following: -dCA/dt=K·CAThe results showed that the PMIDA oxidation on activated carbon was a surface control reaction, and the adsorption of PMIDA and PMG was weak, The rate of reaction is proportional to the concentration of catalyst and0.5power of pressure of oxygen, the kinetic parameters on the0.5Mpa were obtained by fitting the experimental data: k·PO21/2＝7.53×1010exp(-7.34×104/RT) k·PO21/2＝7.53×1010exp(-7.34×104/RT)In the range of experimental conditions, the calculated values by kinetic equation was high agreement with experimental data.2. A Φ100three-phase fluidized bed with an inner filter having a stainless steel screen (800mesh) as the filter material was designed for the cold model research, the three-phase materials is water, air and sand. The results showed that the critical fluidization velocity of liquid umf in the three-phase system was smaller than in the two-phase system, and decreased with the increasing gas velocity ug. Gas bubbles had a significant self-cleaning effect on the surface of filter, and the filtration flux0of the filter increased rapidly with increasing gas velocity at low gas velocity, and gradually became flat. The filtration flux could be improved obviously by the compressed air cleaning. The cleaning interval tf increased rapidly with increasing gas velocity at low gas velocity, but gradually became flat at higher gas velocity, even decreased slightly at high liquid gas velocity. The fluided bed was disturbed severely by gas, which caused the obvious smearing of RTD curve. The liquid backmixing was more serious with increasing gas velocity, especially at low gas velocity.3. A microfiltration membrane was used as the filter material to explore the capability of filtering simulating the system of reaction with PMIDA catalyzed and oxidated by activated carbon, respectively in upstream and downstream of gas and liquid. The experiments showed that the membrane had good effect on the separation of liquid and activated carbon,so the membrane could be used to separate micro-particle catalyst continuously in the three-phase reaction system. The membrane flux of liquid was larger in liquid downstream operation than in liquid upstream operation, but declined continuously with no reverse cleaning gas.Based on the above results and some factory production data, a pilot reactor of three-phase fluidized bed with an inner filter was calculated and designed for PMIDA oxidation. |
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