Synthesis Of Deep Eutectic Solvents And Their Application In Extractive Desulfurization Of Oil

SOx emitted by fuel combustion is one of the important factors for the formation of acid rain and air pollution.For this reason,many countries of the world have successively issued strict fuel sulfur standards.Developed countries have successively implemented“sulfur-free fuel oil”of 5 to 10?g/g(European V)standard.In the face of increasingly strict environmental protection requirements,China has also promulgated the same National V Standard as Euro V.In order to meet the domestic market's large demand for the National V standard fuel,it is imperative to develop a new method for deep desulfurization of fuel.In this paper,three types of desulfurizers,namely aromatic eutectic eutectic extraction desulfurizer,aromatic alcohol eutectic extraction desulfurizer,and three-component eutectic extraction desulfurization agent,were synthesized and applied to the extraction and desulfurization of fuel oil.All have achieved a good effect of extractive desulfurization.In this study,three types of extractive desulfurization systems were designed,including-aromatic acid,aromatic aicohol and three component-based deep eutectic solvents.Excellent extractive desulfurization effects were obtained in extractive desulfurization performed using these three types of deep eutectic solvents.The aromatic acid-based-deep eutectic solvents were synthesizedusing[TEA][BA]as a precursor and proton nuclear magnetic resonance(~1H-NMR)spectroscopy,Fourier-transform infrared(FT-IR)spectroscopy,and thermogravimetry/differential thermogravimetry(TG-DTG).The aromatic solvents were used inextractive desulfurization and the effects of hydrogen bond accepter(HBA)and hydrogen bond doner(HBD)on extractive desulfurization were also investigated.Benzothiophenes(BT)at 500 ppm were reduced to less than 10 ppm under the optimal conditions ofmDES:mOil=1.5:1,t=10 min,T=25°C,and the sulfur concentration Csulfur=500 ppm.[TEA][OHBA]was reused more than 10 times under these optimal conditions and the change in the rate of extractive desulfurizationwas negligible.The extractive selectivity followed the order dibenzothiophene(DBT)>BT>(thiophene)TH>4,6-dimethyldibenzothiophene(4,6-DMDBT).The binding energies of[TEA][BA]···TH,[TEA][BA]···BT and[TEA][BA]···DBT were calculated by quantum chemistry calculations to investigate the selectivity of extractive desulfurization by the aromatic acid-based-deep eutectic solvents.Wander Walls were identified as the main driving forces for extractive desulfurization byreduced-density gradient(RDG)and electrostatic potential(ESP)analyses.Aromatic alcohol-based-deep eutectic solvents were synthesizedfrom the[tetrabutylammonium bromide][benzyl alcohol]([TBAB][PA])as a precursor and were analyzed similarly.Extractive desulfurization efficiencies of 81%and 89%were achievevd in this work by[tetrapropylammonium bromide][o-bromobenzyl alcohol]([TPAB][OBBA])and[tetrabutylphosphoniumbromide][o-bromobenzyl alcohol]([TBPB][OBBA])under the optimal conditions of T=30°C,t=20 min,r=880r/min and Csulfur=500 ppm.The extractive selectivity obeyed the order DBT>BT>TH>4,6-DMDBT,as did that using aromatic acid-based-deep eutectic solvents.The binding energies of[TPAB][PA]···TH,[TPAB][PA]···BT,and[TPAB][PA]···DBT were calculated by quantum chemistry calculations to investigate the selectivity of extractive desulfurization by the aromatic alcohol-based-deep eutectic solvents.The binding energy of[TPAB][PA]with BT was much lower than that of[TEA][BA]···BT,consistent with the experimentally observed extractive desulfurization efficiencies.The vander Waalsinteractions wereidentified as the main driving force for extractive desulfurization by RDG and ESP analysis.The?-?interactionswere ruled out as the main driving force for extractive desulfurization by aromatic alcohol-baseddeep eutectic solvents through the experiments and quantum chemistry calculations.Finally,three-componentdeep eutectic solvents were synthesized and applied to extractive desulfurization.The relationship between the structures of the deep eutectic solvents and mutual solubilities were also investigated.[Tetramethylammonium bromide][HCl][n-buty alcohol]([TEAB][HCl][NBA])and[[Tetramethylammonium bromide][HCl][n-hexyl alcohol]]([TBAB][HCl][BA])were analyzed by ~1H-NMR,FT-IR,and TG-DTG;their viscosities,densities,and conductivities were also investigated.The rate of extractive desulfurization reached 75%under the optimal conditions of T=30°C,t=5 min,r=880 r/min,Csulfur=500 ppmand mDES:mOil=1:2.The selectivity of extractive desulfurization obeyed the order TH>2-Methylthiophene(2-MT)>DBT>BT>4,6-DMDBT.In this paper,a new type of one stype extractive desulfurization by deep eutectic solvent was constructed.Combined with quantum chemical calculations,the formation of deep eutectic solvent and the mechanism of extractive desulfurization were revealed.A one-step extraction and separation of fuel desulfurization was achieved,and difficult-to-remove thiophenes were removed from the fuel,and the desulfurization agent was recycled to provide a new approach and theoretical basis for fuel desulfurization.