Experimental Study On Coke Content Distribution Measurement Of MTO Catalyst

Methanol to olefin is an important step in the coal-to-chemical process.In this technology,the catalyst is deactivated in the reactor and burned and regenerated in the regenerator.The reactor and regenerator are typical gas-solid fluidized bed with continuous production and high mass and heat transfer efficiency.In industrial MTO production,olefins selectivity is generally 6～10 percentage points lower than that of laboratory evaluation device,and coke yield is significantly higher than that of laboratory evaluation device.This gap probably reflects the difference in gas-solid contact and catalyst utilization efficiency between industrial fluidized bed reactor and laboratory small-scale evaluation device.The ideal catalyst carbon content required for MTO reaction ranges from 2 to 8w%.Due to the difference in the distribution of catalyst particles in fluidization quality and residence time in fluidized bed,the catalyst carbon content distribution may be very different from that of the laboratory small-scale evaluation device,and may exceed the above ideal range.This is reflected in the presence of various colors from white to black in industrial MTO units,while the colors of catalysts in laboratory small-scale evaluation units are relatively uniform.Therefore,accurate quantitative measurement of carbon distribution of industrial MTO catalyst can be used as an index to evaluate the efficiency of industrial MTO reactor,to evaluate the efficiency of different industrial MTO devices and to guide the development of strengthening technology for different reaction processes.The purpose of this study is to develop a laboratory evaluation method that can quantitatively measure the distribution of carbon deposition on MTO catalysts.In this study,an experimental method was proposed to determine the distribution of catalyst coke content by using the difference of catalyst float and sink density.The method mainly includes the following contents: first of all,the organic and inorganic heavy liquids were used for the preliminary attempt of heavy liquid separation method,the preliminary attempt includes the following steps,select a reasonable heavy liquid,the pretreatment of catalyst,check the separation effect of coke catalyst in the heavy liquid,check the effectiveness of centrifuge to accelerate the separation process.TG method to measure the coke content of the separated catalyst,check whether the coke content of float and sink catalyst is obviously different,and do the conservation calculation of catalyst mass and coke mass.To further improve the separation accuracy,the separation of catalysts with smaller coke content difference was attempted,and the relationship between coke content and float density was established.Finally,the coke content distribution of the catalyst was calculated according to the floating and settling density distribution,and the coke content distribution was verified by model calculation.Through the above studies,the following conclusions are drawn: :(1)inorganic heavy liquid is not suitable for the separation process due to the influence of ion exchange on the framework of molecular sieve catalyst,while organic heavy liquid of halogenated hydrocarbon is easy to be suitable for the separation process due to the insoluble coke and low boiling point post-treatment.(2)It is generally recognized that the skeleton density of catalyst particles will decrease due to the presence of coke and float more easily in heavy liquid.However,it was found in the organic heavy liquid separation experiment that it was difficult for the heavy liquid to enter into the molecular sieve,and the catalyst with carbon is more likely to settle than the catalyst without carbon because the internal cavity is partially filled with coke.(3)The heavy liquid separation method was applied to the separation process of binary simulated samples,and the effectiveness of the method was preliminarily verified by the obvious difference in coke content of float and sink catalysts.(4)The floating and settling of catalyst particles in heavy liquid cannot be determined simply by skeleton density.There are three main factors that determine the catalyst float density,namely particle density,coke content and heavy liquid adsorption capacity,among which coke content is positively correlated with float density.(5)due to the wide industrial catalyst particle density distribution in itself,to a certain extent coke content on the density of fugitive dust cover,with the method of model calculation can eliminate its influence on coke content distribution measurement,to calculate the standard deviation of 2.2%,the coke content determination of specific distribution form to further improve the separation accuracy of heavy liquid separation.