Study On Chemical Chain Oxidative Desulfurization Of High Sulfur Petroleum Coke

High-sulfur petroleum coke is widely used in the electrolytic aluminum industry as the raw material for preparing anode production.During the electrolysis process,the sulfur in the petroleum coke is decomposed and released as SO₂,causing serious air pollution.Therefore,high-efficiency removal of sulfur from high-sulfur petroleum coke before the production of prebaked anodes is an important way to control SO₂emissions from the aluminum electrolysis process.The development of economical,efficient and environmentally friendly desulfurization methods is currently a hot research direction for the application of high-sulfur coke.This paper takes the lead in proposing a new idea of chemical chain oxidative desulfurization,synthesizes a magnetic iron-based oxygen carrier that can be used for catalytic desulfurization of high-sulfur coke,and systematically conducts chemical chain oxidative desulfurization experiments to achieve selective oxidative removal of sulfur.The specific results are as follows:（1）The speciation distribution of sulfur in high-sulfur coke was analyzed by XPS,thermogravimetric-infrared combined method,etc.,and the release behavior of sulfur during heat treatment was revealed.The sulfur in high-sulfur petroleum coke mainly exists in the form of mercaptan,thioether and thiophene,and the sulfur content of thiophene is as high as 94.49%.The weight loss process of high-sulfur petroleum coke in the pyrolysis process can be divided into three stages,and CO₂,H₂O,CH₄ and other gases are generated.The release of CO₂ and H₂O accompanies the entire pyrolysis reaction process;when the temperature rises to 550～700°C,CH₄ gas begins to be released;the release of sulfur occurs in the second and third stages,and the initial temperature is 400℃and 400℃respectively.At 700℃,the main form of sulfur released is SO₂.During the pyrolysis process of N₂ and CO₂ atmosphere,the sulfur volatilization rate of high-sulfur coke increased with the increase of temperature,but the highest sulfur release ratio was only 18.33%,and the CO₂atmosphere pyrolysis would lead to a significant increase in the loss rate of petroleum coke.（2）The iron-aluminum oxygen carrier was prepared by the sol-gel method.Adding iron-aluminum oxygen carrier can significantly improve the desulfurization rate of petroleum coke.The effect of desulfurization efficiency.When the reaction temperature is 800℃,adding an oxygen carrier with a particle size of 0.08 mm can remove 63.35%of sulfur in only 1 hour of catalytic reaction.The sulfur content of petroleum coke after desulfurization is 2.32%,which is lower than the 3%required for use.,which can be directly used in the production of prebaked anodes.After the reaction,the magnetic saturation intensity of the iron-aluminum oxygen carrier is 24.64 emu/g,which has strong magnetic properties and can be recovered and regenerated by magnetic separation.The desulfurization rate of iron-aluminum oxygen carrier after regeneration is49.92%,and it has good cycle performance.Further impregnating K₂CO₃and Na₂CO₃ on the surface of the iron-aluminum oxygen carrier,it was found that compared with the undoped iron-aluminum oxygen carrier,the desulfurization efficiency of the oxygen carrier doped with alkali metal K₂CO₃ was slightly improved,from 52.92%to 53.4%.（3）Combined with SEM,XRD,FT-IR,XPS and other methods,the changes of the morphology,structure and surface groups of petroleum coke before and after desulfurization were studied,and the reaction mechanism of thiophene sulfur oxidative desulfurization was revealed.After the high-temperature desulfurization reaction,the petroleum coke undergoes a certain graphitization.The FT-IR analysis results show that the C-S and thiophene characteristic absorption peaks of the petroleum coke are significantly weakened.The XPS analysis results show that the2p photoelectron spectrum intensity of sulfur is significantly reduced,indicating that the oxygen carrier during the reaction process.Catalytic oxidation can remove most of the organic sulfur on the surface of petroleum coke.Quantum chemical calculation method was used to reveal the mechanism of thiophene sulfur oxidation reaction from the molecular level.Thiophene sulfur oxidation can be divided into two steps.In the first step,because the C-S bond in the thiophene structure is the weakest,it is first oxidized by oxygen atoms in the reaction process to form a C-S-O structure;The O atom replaces the thiophene S atom to obtain dissociated S=O,and the second is that the O atom attacks the remaining C-S bond to form SO₂.The reaction path 1 is the main path of the thiophene sulfur oxidation reaction.