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

As an important alternative energy source,shale oil can effectively mitigate the rising energy crisis.However,the high nitrogen(N)content of shale oil severely restricts its development and utilization in the China.The hydrodenitrogenation(HDN)technology is a traditional method to removal of nitrogen compounds from shale oil,but it requires high energy consumption and harsh operating conditions,moreover,it is difficult to achieve the deep denitrogenation.The extractive denitrogenation technology based on ionic liquids(ILs),offers a simple separation method under the mild operating conditions with good recyclibility.Therefore,the research on ILs denitrogenation technology is of great significance for deep processing of shale oil and efficient energy utilization.In this study,firstly COSMO-RS was used to calculate the solubility of typical nitrogen compounds(quinoline,pyridine and indole)present in shale oil in 960 ILs.The effects of the structural properties of ILs on solubility was studied and 90 ILs with high solubility for nitrogen compounds were screened out.Then,the selectivity of these ILs to nitrogen compounds and the mutual solubility with model shale oil were investigated.Based on which,the most suitable ILs i.e.[C4min]H2PO4,[C4py]H2PO4,[C2mim]Ac and[C2py]Ac were selected for the experimental study of shale oil denitrogenation.Finally,the experiments were conducted to investigate the denitrogenation performance of single-component ILs,as well as their mixtures for basic nitrogen compounds(quinoline,pyridine)and non-basic nitrogen compounds(indole),and the optimal conditions were determined.The obtained results show that:(1)the structure of the anion and cation in the ILs has a significant influence on the solubility of the nitrogen compounds,which is comparatively greater by anion.The non-basic nitrogen compounds has a greater solubility in the ILs than the basic nitrogen compounds.(2)The hydrogen bonding between the anion and the nitrogen compound has a significant influence on the selectivity of the ILs for denitrogenation.(3)ILs with[H2PO4]-showed better removal performance for the basic nitrogen compounds,while those containing[Ac]-as anion,delivered better performance for the non-basic nitrogen compounds.Compared with single component ILs,their mixture has better comprehensive denitrogenation effect;(4)In the mixture composed of[C4py]H2PO4 and[C2mim]Ac,the distribution coefficients of different nitrogen compounds are comparatively higher.The ILs mixture to oil mass ratio of 1:6,and[C4py]H2PO4 to[C2mim]Ac mass ratio of 6:1,temperature of 35?,extraction time of 40 min,are determined as optimal denitrogenation conditions.Under these conditions,the removal efficiency of quinoline,pyridine and indole are obtained as 98.4%,98.0%and 87.0%respectively.After recycling the ILs for 4 times,the nitrogen removal efficiency can be obtained as above 83.8%.The research results of this study provides a feasible direction for the selection and synthesis of suitable ILs for shale oil denitrogenation.