Study On Synthesis Of Schiff Base Metal Complexes And Oxidative Desulfurization Of Sulfide In Oil

Sulfur and its compounds are present in petroleum widely.Sulfides can corrode equipments in different degrees and cause serious environmental affects in processing,transportation,or burning petroleum and its distillate oils.Therefore,pre-desulfurization of crude oil is very important for maintaining producted equipment and protecting environment.The purpose of the study is to synthesize a kind of Schiff base metal complex,to study the oxidative desulfurization performance of sulfides in oil and investigate the relationship between their structures and properties.Meanwhile,study the desulfurization performance for pre-desulfurization of crude oil.In this paper,six kinds of Schiff base ligands L1-L6 were synthesized by Salicylaldehyde and its derivatives and Ethylenediamine and o-phenylenediamine.Then synthesized seven kinds of Schiff base metal complexes with ligands L1-L6 and cobalt nitrate hexahydrate,nickel nitrate hexahydrate as raw materials.The effect of the ratio of Salicylaldehyde and Ethylenediamine,the amount of solvent,the reaction temperature,the reaction time on the yield of Schiff base ligand and the effect of the ratio of the Schiff base ligand and metal salt,the amount of solvent,the reaction temperature,and the reaction time on the yield of Schiff base metal complex were examined.The experiment shows that the best ratio of the Salicylaldehyde to Ethylenediamine is 2:1,the best solvent dosage is 40.0mL,the best reaction temperature is 40°C,and the best reaction time is 2h.The Schiff base metal complex C1 has the highest yield of 89.6%under the reaction conditions.The best ratio of the ligand L1 to cobalt nitrate is 1.5:1,the best solvent dosage is 60.0mL,the best reaction temperature is 80°C,and the best reaction time is 3h.The Schiff base metal complex C1 has the highest yield of 89.6%under the reaction conditions.Ligands and metal complexes were characterized by ¹H NMR,IR and UV spectroscopy.Put 1-hexanethiol,dibutyl sulfide,2-methylthiophene,and benzothiophene into n-octane for formulating the sulfur-containing simulated oil.Using schiff base metal complexes C1-C7made in laboratory as desulfurizers,catalytic oxidation of desulfurization for simulated oil in aqueous alkaline system was studied.The results showed that the total sulfur removal rates by C1-C7 were 31.9%,18.6%,18.2%,26.3%,28.6%,28.2%,and 31.3%,respectively;the removal rate of 1-hexanethiol by C1-C7 was 42.4%,18.2%,21.2%,13.9%,64.7%,74.2%,and 55.9%,respectively;the removal rates for 2-methylthiophene were 26.8%,9.1%,11.3%,22.8%,19.6%,22.7%,and 24.4%,respectively.the removal rates for dibutyl sulfide were26.7%,7.1%,12.5%,10.0%,62.1%,65.1%,and 37.8%,respectively.However,the removal rates for benzothiophene was still poor.The structure-property relationships of desulfurizers and possible oxidation reactions were further discussed.The oxygen carrying of the desulfurizers C1-C7 in DMF was measured,then the structure-property relationship between the oxygen-carrying performance and the desulfurization performance of the desulfurizers were investigated in aspect of the central atoms,the substituents of Salicylaldehyde and Ethylenediamine.It showed that the main factors affecting the oxygen carrying capacity of metal complexes are electronic effects and steric hindrance.The better oxygen carrying capacity on the grounds of the greater density of electronic cloud of central atom,the smaller steric hindrance of the substituents,The desulfurization performance is affected by both oxygen carrying capacity and the solubility of complexes in oil.The higher the oxygen uptaking and solubility,the better the desulfurization performance.desulfurizers C1-C7 are used for oxidative desulfurization of single model sulfide respectively,which containing 1-thiohexane,dibutyl sulfide and 2-methylthiophene.Infrared spectroscopy analysis of the oil layer before and after oxidation was taken.It showed that three sulfides are oxidized,and corresponding sulfones and sulfoxides are generated after the oxidation.Ion chromatographic analysis of the oxidized aqueous layer revealed that1-hexanthiol and dibutyl sulfide were further oxidized to SO₄^2-,while the SO₄^2-was not found in model oil containing 2-methylthiophene,so 2-methylthiophene was only oxidized to sulfones or sulfoxides.Finally,the desulfurization performance of desulfurizers on Iranian heavy crude oil was discussed,and the sulfur content of crude oil before and after desulfurization was measured by tube furnace according to the method of determining the sulfur content of dark petroleum products（GB/T 387-90）.The removal rates of C1-C7 for Iranian heavy crude oils were calculated.they were 18.0%,11.5%,15.8%,13.7%,29.5%,48.6%,and 50.8%,respectively.In aspects of pre-desulfurization of crude oil.Schiff alkali metal desulfurizers are promising for the future.