Research On Passivation Mechanism Of Pyrite Compounds

With the development of petrochemical industry, the crude oil produced by mainoilfield and imported in our country is mostly sour or high sulfur crude oil. The crudeoil was corrosive. In the process of crude oil storage, transportation, processing,serious corrosion would be caused to the equipment and formed pyrite compounds.The combustion of corrosion products could cause fire and explosion accidents. So itwas significant to study the control of pyrite compounds combustion. At present,chemical cleaning method was generally used to remove pyrite compounds in theprocess of breakdown in the refining industry. However, chemical cleaning methodhad the disadvantages of high coat, high corrosion rate, hazardous H2S product,secondary processing and so on. Therefore, the study on the passivation method ofpyrite compounds is particularly imporatant.In this paper, the device for the gas phase passivation was proposed and designedfor the first time by ourself. The device had advantages of controllable temperature,easy to remove, simple structure, good sealing, convenient operation and so on. It waseasy to realize the experiment by changing the plate, so that the interval of theexperiment was shortened and the efficiency was improved.The pyrite compounds was synthesised in the liquid and solid phase, separately.The mechanism of generation and gas passivation of ferrous sulfide was studied. Thehigh purity ferrous sulfide was prepared using the ferrous sulfate and the sodiumsulfide under ambient temperature condition. The ferrous sulfide was intermittentlypassivated at120℃by changing the total pressure and the partial pressure of watervapour and air, and was continuously passivated under the condition of120℃,0.4MPa,0.15L/min air and0.45L/min water vapor. The results showed that the presence of asmall amount of water vapor played a positive role in promoting passivation, while alarge amount of water vapor played a negative role in passivation, which would attachto the surface of the ferrous sulfide and kept it away from air. High pressure isadvantageous to the passivation reaction. The best proportion of water vapor and air at0.5MPa(A) was0.1MPa water vapor and0.4MPa air. The pyrite compounds was also prepared using H2S sulfiding Fe2O3, Fe3O4,Fe(OH)3. The sulfide product of Fe2O3was passivated at the temperature of90-100℃and the pressure of0.2MPa by changing the air rate (0.5L/min,1L/min,3L/min,5L/min). The results showed that the sulfide product of Fe2O3could self-ignite underthe condition of3L/min air; it could be completely passivated under the conditions of90-100℃,0.2MPa,0.5L/min air and5.5L/min water vapor, and the temperature couldbe controlled. There was no risk of spontaneous combustion dangerousness forcommercial ferrous sulfide, the pyrite product of Fe3O4and Fe(OH)3under conditionsof90-100℃,0.2MPa and3L/min air. The sulfuration active order at ambienttemperature and micro positive pressure was Fe3O4≈Fe2O3>Fe(OH)3, while thepassivation active order of sulfide products was Fe2O3>Fe(OH)3>Fe3O4under90-100℃,0.2MPa,3L/min air conditions.By studying spontaneous combustion tendency of various ferrous sulfide and theinhibiting effects under different conditions, the passivation mechanism was oxidizingthe pyrite compounds to generate stable compounds with a proportion oxygen andwater vapor, so that it was impossible for spontaneous combustion.