Study On New Technology Of Waste Catalyst Microwave Oxidation Roasting Decarburization

Platinum group metal catalysts are widely used in petroleum refining and chemical industry,in the modern chemical production process,about 80%of the reactions can not leave the relevant catalyst.Globally,70%of rhodium,40%50%of platinum and palladium is applied in the preparation of catalysts.It is necessary to recycle platinum group metals from secondary resources.Because of the carbon deposit in the carrier channel after the catalyst lost their activity,the recovery of platinum group metals will be inefficient.Therefore,in order to improve the recovery efficiency of platinum group metals,the spent catalyst need to roast to decarburize before leaching.At present,conventional roasting is employed to pretreat the spent catalyst.The method has many shortcomings such as high energy consumption,long production cycle etc.,therefore,a new fast,low energy consumption roasting process need to be found.Based on the problems of the conventional roasting decarburization process and combining the characteristics of the selective heating of microwave,this paper provides a new technology of microwave roasting to decarburize the spent catalysts.Dielectric properties and the temperature rising behavior of the spent catalyst in the microwave field,also the microwave roasting decarburization process were studied,and the results provided the theoretical basis for the industrial application.1.Dielectric characteristics of spent catalystsDielectric constant ?'? of the spent catalyst increased with the increase of temperature,the value of dielectric constant changed from 2.27 to 2.85 with temperature changing from room temperature to 800?;and dielectric constant ?'? had a positive linear relationship with the apparent density,it changed from 1.92 to 2.66 with the changing of relative density from 0.7 g/cm3 to 1.25 g/cm.The penetration depth decreased exponentially with the increasing of relative density;Critical temperature Tcrit occurred at 450? during the dielectric constant measurement of spent catalysts with changing temperature;When temperature is above 450 ?,dielectric loss increased significantly and the temperature rising behavior of spent catalysts would be better;Dielectric loss increased from 0.012 to 0.05 when the temperature changing from 450? to 800?.2.Microwave heating behavior of spent catalystsThe thickness of the material and the microwave power had a great influence on the temperature rising process of the spent catalyst.The thicker the material,the lower the rate of the temperature rising process was;The bigger the microwave power,the faster the rate of the temperature rising process was.Under different thicknesses,temperature rose to 800? need 21min(2 cm)?23min(3cm)?25min(4cm)?42min(5cm)respectively;When the thickness of the material was 4 cm,rising the power from 1 kW to 2.5 kW,would cut the heating time in half.3.Decarburization reaction mechanism of spent catalystsTG/DTG analysis technique was used to study the spent spent catalysts oxidation roasting decarburization process,since the structure of the deposit carbon in spent catalysts is complex,four kinds of solid phase reaction activation energy calculation methods(Coat-Redfern integral method,Ozawa integral method,Achar and Kissinger differential methods)were discussed;Both the application of Coat-Redfern integral method and Ozawa integral method need the decarburization reaction mechanism function which was difficult to acquire at the beginning for the complex structure of spent catalysts,and for the Kissinger differential method,the peak temperatures of the spent catalysts under different heating rates were too close to use;Thermogravimetric analysis data of the spent catalysts meets liner fitting condition of Ozawa integral method,through Ozawa integral method,the decarburization reaction kinetics process was studied in detail,and the apparent activation energy Ea changing with reaction conversion and temperature was calculated.Decarburization process dynamics analysis of the chemical industry spent catalysts showed that,an exponential type critical point temperature occurred at 540?,and the value of the apparent activation energy dropped quickly after the critical point.This phenomenon indicated temperature had a significant effect on apparent activation energy.4.Decarburization process of spent catalystsThe conventional decarburization and microwave decarburization of the spent catalyst research shows that when the thickness of material was 2 cm,the temperature was 600 ?,the decarburization time was 40 min,only 96.7%decarburization percent could be reached during conventional heating process,while it was 99.5%during microwave process.When the reaction time prolonged to 120 min,conventional decarburization percent could reach(99.5%).The optimum parameters of microwave heating process were 2 cm of material thickness,600? of temperature,40 min of decarburization time,and on which conditions decarburization percent was 99.5%which satisfied the follow-up process(leaching).