| As the byproduct of FCC process,FCC slurry oil is considered to be the potential feedstock to produce high-value-added petrochemical products such as needle coke as a result of abundant 2-to 4-ring aromatics with short side chains.However,there are three key challenges in the production of superior needle coke using FCC slurry oil as feedstock:separation of micro and sub micro solids in slurry oil,adjustment of the composition of slurry oil,and selection of the carbonization route.Pretreatment of slurry oil is an essential prerequisite for its high-value-added utilization.Therefore,this dissertation studies the separation of micro and sub micro solids in slurry oil,adjustment of the composition of slurry oil,and the subsequent carbonization process systematically,with the pretreatment of slurry oil and its carbonization as the mainline.This dissertation is aimed at the tentative exploration of the key scientific challenges in the production of superior needle coke using FCC slurry oil as feedstock,so as to providing theoretical basis and data support for the developing of production technology of superior needle coke in future.Firstly,the solids in slurry oil were characterized elaborately in terms of the content,morphology and composition,and the effect of thermal treatment on the separation of solids from slurry oil by distillation was also investigated.Study shows that the solid content of slurry oil determined by filtration method can basically reflect the contents of coke powder and catalysts,and is not affected by the resin and asphaltene contents of slurry oil.The filtration method has both high accuracy and precision,and should better use filter membrane with bore diameter of 0.22 ?m as filter material and use toluene as diluting agent.The solids in slurry oil used in this study mainly contain plenty of small particles with diameter of around 1 ?m and a small number of large particles with diameter of 5-20 ?m.The spherical main bodies of large particles are catalyst fines,while the smaller irregular particles coated on the spherical main bodies or existing alone are coke powders.Thermal treatment of slurry oil can promote the separation of solids from slurry oil by distillation greatly.Thermal treatment can decrease the solid contents of the middle fractions remarkably,and the solid content below 100 ?g/g can be achieved for the middle fraction under optimum thermal treating conditions.The solid contents of the middle fractions have a close relationship with the thermal treating severities.The solid contents of the middle fractions have a negative linear correlation with the asphaltene contents of thermally treated slurry oil under different thermal treating severities,and the higher the asphaltene contents,the lower the solid contents of the middle fractions.After thermal treatment,the solids flocculate and become larger in apparent particle sizes,and the mechanism of flocculation of the solids upon heating was therefore proposed.Asphaltenes and solids can form solid-asphaltene flocs under the effect of thermal treatment,making their removal by distillation easier.Secondly,the effect of thermal treatment on the thermal stability of the middle fraction of slurry oil and the effect of the thermal stability of the middle fraction on the characteristics of carbonized cokes were studied.Study shows that thermal treatment of slurry oil can decrease the yield of the middle fraction and increase the yield of the distillation bottoms as well as their condensation degree.Thermal treatment can increase the aromatic and hydroaromatic nature,and decrease the paraffinic nature of the middle fraction.Moreover,thermal treatment can decrease the content of 4-ring aromatics,and increase the contents of 3-and 5-ring aromatics.A method to evaluate the thermal stability of the carbonization feedstock by using thermal excitation experiment and spot test was proposed.The evaluation results show that thermal treatment can improve the thermal stability of the middle fraction,which is attributed to the conversion of thermal sensitive components in the middle fraction into distillation bottoms.Carbonization feedstock with higher thermal stability has better characteristics of carbonized cokes.The thermal stability of carbonization feedstock can be viewed as a simple indicator to predict the characteristics of the carbonized cokes.Thirdly,the effect of thermal treatment under hydrogen on the hydrogen transfer ability of the middle fraction of slurry oil and the effect of the hydrogen transfer ability of the middle fraction on the characteristics of carbonized cokes were studied.Study shows that thermal treatment under hydrogen can decrease the loss of the middle fraction yield on the basis of pure thermal treatment,but at the same time will decrease the solid removal efficiency.The middle fraction yield and the solid content cannot reach the best result at the same time.Thermal treatment under hydrogen can increase the contents of hydroaromatics and donatable hydrogens in the middle fraction,and decrease the number of the condensation rings of aromatics.The calculation method of hydrogen-donating ability was modified and the calculation method of hydrogen-accepting ability was hereby proposed.It is found that the inherent anthracenes and 9,10-dihydroanthracenes can affect the calculated values of hydrogen-donating ability and hydrogen-accepting ability greatly.Thermal treatment under hydrogen can improve the hydrogen transfer ability of the middle fraction.The value of hydrogen-donating ability depends on the content and type of hydroaromatics.The hydrogen-donating activity of hydroaromatics increases as the aromatic ring number increases.From the viewpoint of hydrogen transfer ability,the carbonization performance of slurry oil fraction neither depends on the hydrogen-donating ability of the fraction alone,nor depends on the hydrogen-accepting ability of the fraction alone,but is the result of joint influence of both hydrogen-donating ability and hydrogen-accepting ability.That is,carbonization feedstock with higher hydrogen transfer ability has better characteristics of carbonized cokes.The hydrogen transfer ability of carbonization feedstock can be viewed as a simple indicator to predict the characteristics of the carbonized cokes.Lastly,the carbonization of combined fractions of slurry oil was studied.There exists synergistic effect in the hydrogen transfer ability of combined fractions of slurry oil,leading to the synergistic effect in the characteristics of the carbonized cokes.The characteristics of the carbonized cokes derived from slow carbonization are better than those derived from rapid carbonization.The carbonization feedstock releases transferable hydrogens gradually during every stage of slow carbonization of combined fractions.Moreover,the combined fractions can release more transferable hydrogens to stabilize the carbonization system,therefore the combined fractions can show better characteristics of the carbonized cokes during every stage of carbonization. |
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