Study On Removal Of Nitrogen Compounds From Fuel Oil By Ionic Liquids

Removal of nitrogen compounds?N-compounds?from fuel oils before being used has become a more and more important research subject in recent years,because N-compounds will increase NO_x emission during combustion and pollute environment.Moreover,the N-compounds especially for the basic N-compounds can affect the activity of the hydrogenation catalyst and reduce desulfurization efficiency.In addition,N-compounds are considered as strong inhibitors of the hydrodesulfurization process because of their preferable adsorption on the surface of the catalyst.At present,the methods of denitrogenation are mainly divided into hydrogen and non-hydrogenation.Although hydrodenitrogenation technology is the best solution,the technology is very costly due to high operating temperature,pressure,and hydrogen consumption.So the study on non-hydrogenation becomes more urgent.The non-hydrodenitrogenation methods include adsorption,solvent extraction,oxidation and complex denitrogenation.Complex denitrogenation based on Lewis acid-base theory and valence bond theory can remove effectively N-compound from diesel oil,which has many advantages such as mild reaction conditions high denitrification efficiency,low investment and simple operation.However,conventional complex denitrogenation agent is volatile and the consumption quantity is large.As a new type of environmentally friendly solvent,ionic liquids have been paid more and more attention by researchers.Three types of ionic liquids were synthesized,including[Bmim]Br/ZnCl₂ and[Hnmp]H₂PO₄and ChCl/H₂C₂O₄·2H₂O,and their denitrogenation performances was investigated using coking diesel oil and Fushun shale diesel as feedstocks.The structures of the synthesized ionic liquids were characterized by Fourier Transform Infrared Spectoscopy?FT-IR?and hydrogen nuclear magnetic resonance?¹H NMR?.The results showed that the structures of compounds were in accordance with target products.The acidity of ionic liquids was studied by infrared probe method,and the thermal stability,solubility,corrosion and fluidity of the three ionic liquids were also investigated.The results show that[Bmim]Br/ZnCl₂ shows Lewis acidity and[Hnmp]H₂PO₄ shows Bronsted acidity.Thermal stability of three kinds of ionic liquid can meet the requirements of denitrification.Under the same conditions,the viscosity of[Bmim]Br/ZnCl₂ is larger,the viscosity of[Hnmp]H₂PO₄ and ChCl/H₂C₂O₄·2H₂O is smaller.The three kinds of ionic liquids are less corrosive to the equipment.The denitrification performances of[Bmim]Br/ZnCl₂,[Hnmp]H₂PO₄and ChCl/H₂C₂O₄·2H₂O were investigated using coking diesel and Fushun shale diesel fractions as raw materials.The effects of extraction time,extraction temperature and ionic liquids/oil mass ratio on the denitrification performance of ionic liquids were investigated.The results show that the denitrification process can reach equilibrium within 30 min,and the effect of extraction temperature on denitrification is not obvious.The optimum denitrification temperature of[Bmim]Br/ZnCl₂ is 50?,and that of[Hnmp]H₂PO₄ and ChCl/H₂C₂O₄·2H₂O is 30?.At IL/oil mass ratio of 1:7,basic N-removal efficiency of[Hnmp]H₂PO₄ ionic liquid is about 93.97%,and the basic N-removal efficiency can still reach 85%during three recycles of the ionic liquid.In the denitrogenation of[Bmim]Br/ZnCl₂ from coking diesel and shale diesel oil,the basic N-removal efficiency are 68.31%and 57.66%,respectively.The low-eutectic ionic liquid ChCl/H₂C₂O₄·2H₂O shows better removal performance for quinoline than indole,and the solvent also showes good denitrogenation performance for coking diesel oil achieving 96.10%basic N-extraction efficiency at IL/oil mass ratio of 1:7.In addition,the basic N-removal efficiency can still reach 87.20%during four recycles of the ionic liquid.