Study On The Effect And Mechanism For Treatment Of Methanol-to-Olefin Quench Water By Electrocoagulation

The reactor of Methanol-to-Olefin is fluidized bed reactor,so the product will carry catalyst powder,which needs to be washed by quench water.While the cyclone separator has a limited ability to separate small particles,filter is connected to achieve further separation,but the oil and wax substances in the quench water will combine with the catalyst powder,causing the filter to be easily blocked and difficult to backwash.The electrocoagulation is used to pretreat the quench water to coagulate the fine catalyst powder to be larger particles,which will be convenient for cyclone separation.The effects of electrode material,current density,plate spacing,conductivity and initial p H on the removal rate of solid content were studied.The results show that:Using Fe anode will get the highest value;higher current density can obtain higher solid removal rate in the first 25 minutes of the reaction,during this period,the best range of current density is 80～120A/m²;far or close electrodes distance will not conducive to the reduction of solid and the best range is 2～4 cm;a high conductivity corresponds to a higher solid removal rate in the first 25minutes,however,the effect of conductivity is not obvious at 35 min;the initial p H has a very obvious effect on electrocoagulation,and the best p H is 8,followed by p H 7 or 6,and the effect is very bad when the p H is 3 or 11.Based on the single factor experiments,the current density,electrodes spacing and electrolysis time were selected as the influencing factors.The solid removal rate was used as the response value to carry out the response surface optimization experiments.The ternary quadratic regression model between the response value and the influencing factors was obtained.Variance and residual analysis of this regression model verified the high reliability.The optimal reaction canditation was obtained by the regression model:the current density is102.2 A/m²,the distance between electrodes is 2.9 cm,and the electrolysis time is 23.8 min.It is found that the relative error between the solid removal rate and the predicted value is less than 1%.Scanning electron microscope,energy dispersive spectrometer,X-ray photoelectron spectroscopy,X-ray diffraction and Fourier transform infrared spectroscopy were used to study the micro morphology,elements composition,elements valence and crystal structure of the flocculation.The result show that:the floc was formed by the inclusion of molecular sieve particles in the substances like cotton,which contains a lot of filaments;there are small substances adhering to the molecular sieve particles;O,Al and Fe are the main elements of flocculation;the exciting form of O is Al₂O₃ and–OH;Al is Al₂O₃,Al₂O₃-n H₂O;and the form of Fe is Fe₂O₃,γ-Fe OOH and Fe（OH）₃.Finally,the formation of iron-containing flocculant and the kinetic model of combination between flocculant with catalyst particles are analyzed.The effects of flocculant kinds,stirring rate and the amount of flocculant on the removal rate of solid in quench water were studied.It was found that cationic polyacrylamide had the best effect compared with alum and PAC.When the stirring rate is too fast,the floc would be broken and its size will reduce.In a certain range,increasing the amount of flocculant could improve the removal rate of solid,but if the amount exceeds,it will not change the removal rate of solid.The characteristics of electrocoagulation and chemical flocculation are compared and analyzed,and it is believed that electrocoagulation is more suitable for the treatment of MTO quench water.Finally,the phenomenon of surface passivation and prevention methods are introduced.