| As the quality of global crude oil supply tends to be inferior,the production of high sulfur crude oil is increasing.In the future,the problem of sulfur corrosion will become more and more prominent in the process of exploitation,storage,transportation and processing of sulfur-containing crude oil.The oxidation and spontaneous combustion of sulfur corrosion products in tanks will lead to a series of environmental and safety problems which cause great economic losses and seriously affect the normal production of petrochemical enterprises.In order to effectively prevent the occurrence of spontaneous combustion of sulfur corrosion products in sulfur storage tanks,it is necessary to fully understand the spontaneous combustion characteristics of sulfur corrosion products.Therefore,it is necessary to carry out experimental research on the spontaneous combustion characteristics of the tank by quantitative structure of sulfur corrosion products.In view of the fact that there are many types of sulfur corrosion in the actual production process of petrochemical industry,there are many kinds of patterns of sulfur corrosion in the storage tank.The formation of sulfur corrosion products is very different under different environment conditions.Moreover,the amount of sulfur corrosion products and rust in the inner wall of the crude oil storage tank is very limited and difficult to collect.In this thesis,sulfur corrosion products of model compounds were used as the research object by means of X-ray diffractometer,low temperature nitrogen adsorption instrument,electron microscopy scanner,synchronous thermaland analyzer,electrochemical workstation and other modern characterization techniques,the system reveals the relationship between quantitative structure storage of spontaneous combustion of sulfur corrosion products,the main research contents are as follows:(1)The oxidation characteristics of the compound system of sulfur corrosion products of different models under different environmental conditions,temperature and relative humidity were studied systematically.The oxidation weight gain rate was used as the criterion of oxidation spontaneous combustion tendency.It was deduced that the oxidation of model compounds the greater the weight,the higher the spontaneous combustion tendency.The effects of multiple factors and their interactions on the oxidation of sulfur compounds in tank samples were investigated by orthogonal test.The results show that the influence of each factor on the oxidation of the model compound is from large to small is that the composition of the corrosion products(A),water content(B),ambient temperature(C)and relative humidity(D).The influence degree is from A×C>B×D>C×D>A×D>A>×B>B×C.Then,the four factors are respectively studied by single factor experiment.Through the influence factors of oxidation and within 30 days the weight gain rate curve can be found,the oxidation weight gain rate increases with the increase of the mass fraction of FeS in the sulfur corrosion product model.The higher the water content is,the higher the oxidation weight gain is,and the ambient temperature and relative humidity and the same trend is observed.In addition,new materials such as FeSO4 ·7H2O and FeSO4 were formed by X-ray diffractometer.(2)The pore structure and fractal characteristics of the model compounds of sulfur corrosion products were determined by low temperature nitrogen adsorption.The experimental results show that the low temperature nitrogen adsorption-analytic curves of the six samples are slightly different in morphology,but belong to type IV.The gas adsorption of the model compounds is mainly concentrated on the mesopores of 2?8nm.With the increase of the mass fraction of FeS in the sulfur corrosion product model,the BET specific surface area and BJH total pore volume of the model compound increased with the increase of the average pore size.The pore volume contribution rate of the six samples is similar.Microporous and mesoporous are the main sites for sulfur corrosion product model compound to adsorb storage air.With the increase of the mass fraction of FeS in the sulfur corrosion product model compound,the fractal dimension of the sulfur corrosion product model compound increases gradually.The maximum fractal dimension of sample a is 2.5899,followed by sample B is 2.5871.Fractal dimension reflects the variation characteristics of the pore structure of the six samples,which is negatively correlated with the average pore size and positively correlated with the specific surface area,the total pore volume and the adsorption capacity.(3)The thermal analysis kinetics parameters and reaction mechanism of FeS,FeS2 and FeS-FeS2 compounds,which are the main components of sulfur corrosion products,were studied by using modsrn synchronous thermal analysis technique.The results showed that the chemical properties of FeS2 are more stable than FeS,the TG curves of different FeS-FeS2 compounds were similar.There were two mass loss peaks in DTG curves and the two peaks corresponded to the two inflection points of TG curve.The first peak appeares at 500?550?,the second peak appeared at 600?650?,the second peak appears at 600?650?,the ignition temperature of different FeS-FeS2 compounds decreases from 508.80? to 479.78?,the burnout temperature decreased from 926.74? to 885.95?.During FeS-FeS2 compounds in oxidation spontaneous combustion process,FeS and FeS2 is not a simple isolated reaction,but both interaction in the reaction process.The activation energy curve calculated by FWO method is similar to the activation energy curve of Kissinger method,but the apparent activation energy of Kissinger method is generally smaller than that of FWO method.When the mass fraction of FeS was 80%,the average apparent activation energy is the largest,and the average apparent activation energies calculated by FWO and Kissinger were 304.31 and 301.30kJ/mol,respectively.When the mass fraction of FeS was 80%,the average apparent activation energy is the lowest,and the average apparent activation energies calculated by FWO and Kissinger were 172.95 and 164.56 kJ/mol,respectively,so The spontaneous combustion tendency of sample 2 is largest,.(4)The electrochemical characteristics of the sulfur corrosion products of the storage tank was studied by linear sweep voltammetry and AC impedance method.The electrical resistance of FeS-FeS2 compounds powder electrode was measured by electrochemical workstation.It is found that with the increase of FeS mass fraction in FeS-FeS2 compounds,the resistance of FeS-FeS2 compounds powder electrode is smaller,the better the conductivity,the higher the electrochemical reactivity.According to the principle of thermal effect of current,the lower the current resistance value,the higher the heat released by the electrochemical corrosion of the sulfur corrosion product of the storage tank,which is more likely to lead to the occurrence of spontaneous combustion accident.The electrochemical characteristics of FeS-FeS2 compounds are studied from the point of view of electrochemical impedance,which provide the theoretical basis and guidance for the effective prevention of spontaneous combustion of sulfur-containing oil tank. |
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