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Catalytic Oxidation Of Benzothiophenes For Deep Desulfurization Under Water-free Condition

Posted on:2009-02-23Degree:DoctorType:Dissertation
Country:ChinaCandidate:X R ZhouFull Text:PDF
GTID:1101360272470440Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
The effective oxidation of benzothiophenes and dibenzothiophenes,which are the most stable sulfur-containing compounds in the distillates of petroleum,is the base for developing a deep oxidative desulfurization(ODS) of fuels.This thesis presents the study on the catalytic oxidations of benzothiophene and dibenzothiophenes using alkyl peroxides and molecular oxygen as oxidants in the simulated and industrial diesel fuels under water-free conditions.The catalytic oxidation of dibenzothiophene(DBT) in decahydronaphthalene(decalin) as stimulated fuel was first performed using oil-soluble oxidant,cyclohexanone peroxide (CYHPO),under various conditions to screen adapted catalyst and optimize reaction conditions.The catalyst with high activity for this oxidation is molybdenum oxide(MoO3), and its catalytic activity may increased remarkably by attaching on the macroporous polyacrylic cationic exchange resin D113,weak acidic chelating resin D751 and Al2O3,where D113 display the highest performance among the three supporters.The addition of Co and Ni onto the MoO3/Al2O3 led to a significant decrease of its catalytic activity in the oxidation of DBT.Analyses with weight calculation and Inductively Coupled Plasma Spectrum demonstrated that the losses of MoO3/D113 and MoO3/D751 were less than MoO3/Al2O3 during 10 consecutive batch reactions,where the catalyst was recycled and reused,meanwhile the catalyst activity was not decreased.When oxidations of DBT using TBHP and TAHP were performed in the same way as using CYHPO,activity of alkyl oil-soluble peroxides showed the decreases in the order:CYHPO>TAHP>TBHP.The oxidations of model sulfur-containing compounds,4,6-dimethyl dibenzothiophene(DMDBT) and benzothiophene (BT),were also carried out.The results indicated that the oxidation activities of these sulfur compounds decreased in the order of DMDBT>DBT>BT.The effect of the model unsaturated compounds and nitrogen-containing compounds found in the middle distillates on the oxidation of DBT were also investigated.The results demonstrated that the DBT oxidation was not influenced by 1-tetradecylene,4,6,8-trimethyl-2-nonylene,and 2-methylnaphthalene; whereas influenced differently by carbazole depending on the different oxidants,i.e. conversion of DBT in the oxidation using TBHP was decreased greatly with adding of carbazole,using TAHP was decreased slightly,but using CYHPO was not changed.The reaction kinetics of model sulfur compounds was further investigated.The results suggested that the oxidative reaction of each sulfur compound could be treated as a first-order reaction. Finally,the coordinate mechanism of oxidation of DBT using CYHPO in the presence of MoO3 was presumed.Next,Oxidation of dibenzothiophene(DBT) using molecular oxygen was performed in an unpolar hydrocarbon solvent under water-free condition.To stimulate the activity of molecular oxygen,iron phthalocyanines(FePc) substituted were employed as catalyst.Three kinds of catalysts with different substituents,FePc(NO2)4,FePc(NO2)3NH2 and FePc(NH2)4, were synthesized to investigate the effect of substituent on activity and stability of iron phthalocyanines.The results indicated that the catalytic activity of these phthalocyanines decreased in the order of FePc(NO2)4>FePc(NO2)3NH2>FePc(NH2)4,reversing the order of electronic density of Pc resonance ring.FePc(NO2)4 not only has the highest activity but also best stability.The decreased activity of FePc(NH2)4 may decomposed during the first run of oxidation according to the typical Pc peaks(1405 cm-1 and 1605 cm-1) of IR;whereas the catalytic activity and structure of FePc(NO2)4 was kept during 5 runs of oxidations.At a temperature of 100℃and an initial pressure of 0.3 MPa,conversion of DBT in decalin reached to 98.7%in presence of 1%of FePc(NO2)4 as catalyst.The sulfoxide was detected by LC-MS in this oxidation using molecular oxygen in the presence of FePc(NO2)4.Finally,The oxidative desulfurization of industrial diesel fuels was examined in a fixed bed stainless single steel flow reactor and an adsorption column.More than 94%of sulfur of fuels was removed with more than 99%recovery of fuels.The sulfur content of oxidized diesel fuel with an initial sulfur content of 200μg/g was reduced to 5.1μ/g,which is under the ultra sulfur content restriction(<10μg/g);with an initial sulfur content of 400μg/g and 600μg/g were reduced respectively to 14.8μg/g and 36.0μg/g,which are under the level of sulfur content of diesel fuel for some special cities such as Beijing and Shanghai etc taking the lead in performing low sulfur regulation of diesel fuels(<50μg/g).
Keywords/Search Tags:Benzothiophene, Oxidative Desulfurization, Cyclohexanone Peroxide, Molecular Oxygen
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