Pyrolysis Behavior And Reactivity Of Carbon Anode Materials Of Aluminum Electrolysis

With large-scale,high efficiency and energy saving becomes the development trend of aluminum electrolysis technology in China,the importance of pre-baked carbon anode quality is becoming more and more significant,the demand of high quality of carbon anode is proposed.With the rapid development of domestic aluminum electrolytic industry,the sulfur content and trace elements content of petroleum coke are increase,the particle size is becoming more and more fines,the use content of high sulfur petroleum coke is inevitably increasing.In the case of raw materials quality degradation,how to adjust the existing carbon anode production,control and optimization technology,to prepared high quality of carbon anode for electrolysis has great economic benefit and social effect.This article revolves around the asphalt infiltration and pyrolysis behavior,the particle size distribution optimization of calcined coke,trace elements and sulfur content on the properties of carbon anode,as well as preparation of aluminum titanium alloy by direct reduction of TiO2-containing carbon anode,etc.Using these equipments of bulk density and SEM,TG-DTG analysis and homemade pyrolysis equipment,the static asphalt infiltration and porosity of aggregate column experiments and the asphalt infiltration SEM images of calcined coke were researched.These research results show that: less than 0.15 mm stock column porosity is small,hard infiltration;Greater than 2-3 mm particles stock column porosity is larger,easy to infiltration;Middle size parts,with the particle size increase,infiltration rate gradually increased.small particles of calcined coke is pitch invasion,larger particles is infiltrating a certain thickness of asphalt layer,the larger particles surface portion is filled or packaged with " A mixture of asphalt and fine calcined coke",inside the porous and closing hole of larger particles can not infiltrate.the asphalt pyrolysis process was test using the pyrolysis equipment which were advanced and self-made for pyrolysis kinetics model,the pyrolysis kinetics model is [{-n] 21} [ fa]--?28?---//)/21?ln?1/??1(1lnRTEEERTARTn,the reaction order is 2.3,the apparent activation energy is 108.27 KJ/mol.Combined with the BET analysis of different particle size,less than 0.5 mm part is the specific surface function area,0.5-3mm part is the porous structure function area.Using these equipments of bulk density and carbon anode reactivity in CO₂ or air,the relationship between particle size distribution and the volume density or carbon anode reactivity were tested.These research results show that: Under the CS size distribution conditions,through the control middle size coke content,reduce coarse and fine particle coke content,and increase the powder coke content,the reactivity of carbon anode still have improve space.Using these equipments of coke reactivity in CO₂ or air,carbon anode reactivity in CO₂ or air,XRD analysis and homemade pyrolysis equipment,the impact of trace element content on the calcined coke reactivity,calcined coke microstructure,pitch coke microstructure and carbon anode reactivity were quantified.For the first time carried out the impact of trace elements on "asphalt coking body" reactivity,and trace element content and powder calcined coke on the asphalt pyrolysis process.The results show that,with the Na,Ca and Mg element content increase,the CO₂ residual rate of "asphalt coking body" is gradually decreased,however the V and Ni element is gradually increased.With the trace element content increase,the air reactivity rate of "asphalt coking body" is gradually increased.Overall,the reactivity residual rate of carbon anode and calcined coke in CO₂ or air are similar,the reactivity of "asphalt coking body" is a restrictive link.With the trace element content increase,the apparent activation energy of pyrolysis process increases,the yield rate of pitch coke increased.With the powder coke addition,the apparent activation energy of pyrolysis process decreases,the yield rate of pitch coke increased.Using these equipments of sulfur analyzer,X-ray photoelectron spectroscopy,infrared spectrum analyzer,coke reactivity in CO₂ or air,carbon anode reactivity in CO₂ or air,XRD analysis and homemade pyrolysis equipment,the impact of sulfur content on the calcined coke reactivity,calcined coke microstructure and carbon anode reactivity were tested.For the first time carried out the impact of sulfur content on "asphalt coking body" reactivity,and the powder calcined coke of different sulfur content on the asphalt pyrolysis process.The results show that,from sulfur in different particle size petroleum coke distribution,Sulfur priority tendency exists in large particles,then gradually expand to the part of the small particles.Sulfur can be separated by screening from different sulfur petroleum coke.The sulfur in different petroleum coke is similar,mainly exist of organic sulfur of thiophene and mercaptan class,also exist of inorganic sulfide and sulfate type.The calcined desulfurization performance,different sulfur content and particle size of petroleum coke,has obvious difference.The CO₂ residual rate of "asphalt coking body" is only about 3/4-1/2 of calcined coke,the air reactivity rate of "asphalt coking body" is far more than the calcined coke,especially influenced by the trace elements.Overall,the different high sulfur petroleum coke performance difference is bigger,not simply to the high and low sulfur content.In actual production application should be different sources of high sulfur petroleum coke were piled up.Combined with sulfur content distribution,trace elements content,the calcined coke performance and "asphalt coking body" performance,we are to make blending utilization projects.Using these equipments of coke reactivity in CO₂ or air,carbon anode reactivity in CO₂ or air,XRD analysis,SEM-EDS analysis and homemade pyrolysis equipment,the impact of TiO2 content on the calcined coke reactivity and carbon anode reactivity were tested,and reparation of aluminum titanium alloy by direct reduction of TiO2-containing carbon anode were also tested.The results show that,with increasing Ti content,the residual rate of calcined coke in CO₂ can be improved,but the air reactivity rate is gradually decreased.The residual rate of carbon anode in CO₂ or air can be greatly improved.The apparent activation energy of pyrolysis process increases.The TiO2-containing carbon anode running stability in the electrolysis process.The electrolyte phase consists of Al and Ti element,Ti element is enriched in long rods materials.