The Design Of Ionic Liquids And Deep Eutectic Solvents And Their Applications In Separation Of Phenolic Compounds And Aromatics Compounds From Coal-converted Oils

Phenolic and aromatic compounds are two kinds of chemical raw materials with high added values,and they can be used to produce pharmaceutical,pesticide,synthetic fiber,dye and other chemical products.The demand for these two substances increase rapidly with the development of the modem industry,and a part of them even needs an import to fill the domestic demand.As a large producer of coal,China has a considerable production amount of coal-converted oils including coal tar,and coal liquefied oil.It is found that these oils are rich in phenolic and aromatic compounds,so the efficient separation of these two substances from the oils is important for the economic improvement of the coal conversion process.At present,the traditional method to separate phenolic compounds from oils is alkaline washing,which uses large amounts of strong alkaline aqueous solutions and mineral acids,and also produces large quantities of toxic phenols-containing wastewater.It not only causes environmental pollution but also greatly increases the cost of production and environmental treatment.Therefore,it is urgent to develop new separation methods to avoid the above problems.Currently,the most widely used method in the industry to separate aromatics is liquid-liquid extraction(LLE).This method uses a large amount of toxic and volatile organic solvents,which is also harmful to the environment,so the development of new solvents with environmental friendliness and good extraction ability has attracted the attention of the researchers.Due to their excellent properties,ionic liquids(ILs)and deep eutectic solvents(DESs)have become a research hotspot in the separation of phenolic and aromatic compounds from oils.The purpose of this paper is to design and synthesize new and efficient extractants to separate phenolic and aromatic compounds from oils and provide guidance for the application of extractants by analyzing the present extractants.The main contents and results are shown as follows.1.Separation of phenolic compounds from oils using carboxylate based zwitterions via forming deep eutectic solvents.According to the problems of extractants reported previously,such as the existence of halogen ions and the poor reusability,we analyzed the feasibility of carboxylate based zwitterions to separate phenolic compounds from oils.The experimental results showed that the carboxylate based zwitterions could separate phenolic compounds from oils via forming DESs.The highest phenol extraction efficiency is 94.6%at an L-carnitine:phenol mole ratio of 0.4-and a temperature of 25?.The extractants could be regenerated and reused for 4 cycles without an obvious decrease in extraction efficiency and extractants mass,showing that they had good reusability.The extraction mechanism was studied by FT-IR characterization,which indicated that-COO-on carboxylate based zwitterions could form hydrogen bonds with-OH on phenolic compounds.2.Separation of phenolic compounds from oils using sulfonate based zwitterions via forming DESs.The previous researches showed that phenolic compounds could form DESs with zwitterions,which played the role of hydrogen bond acceptors(HBAs).According to the analyses above,we designed and synthesized eight sulfonate based zwitterions as HBAs to separate phenolic compounds from oils.The study showed that the extraction capacity of the eight sulfonate based zwitterions were much higher than that of the carboxylate based zwitterions,and they could well balance the relationship between extraction and regeneration ability.Moreover,the structure of zwitterions had effects on the phenol extraction efficiencies and the minimum phenol content in oils and the maximum extraction efficiency at 25? could reach 4.8 g·dm-3 and 98.6%,respectively,by using TPA-BS.Compared with the extractants reported in the literature,the dosages of the extractants of this work were reduced,while the extractants had good reusability.3.Phase equilibrium and removal of neutral oil using the deep eutectic solvent method.The extraction process was analyzed from the perspective of phase diagram,and the effects of temperature and amount of extractant on the ternary phase diagrams,distribution coefficient and selectivity of phenol were studied.The results indicated that the separation of phenol from oil mixtures via forming DESs could only oeeur at the liquid-liquid and liquid-liquid-solid phase regions when the initial phenol contents were in a specific range.A high temperature was not beneficial to the extraction process,and with increasing temperature,the phenol content in oils increased,but the distribution coefficient and selectivity of phenol decreased.Due to the existence of the ?-?bond between toluene and phenol,the extraction of phenolic compounds by DESs inevitably led to the entrainment of neutral oil such as toluene.We found that the use of nitrogen stripping at a packed tower could effectively removal neutral oil from DESs,which could improve the quality of phenolic compound products.4.Selective separation of aromatics from aliphatics using imidazolium-based dication ionic liquids(DILs).According to the results of previous extractants reported in the literature for separating aromatics from aliphatics,the selectivity coefficients(S)and distribution coefficients(D)were opposite,i.e.a high S usually was accompanied with a relatively low Di or in reverse,and the dissolution of some extractants in oils happened.To solve the above problems,we designed and synthesized imidazolium-based DILs and used the DILs to separate aromatics from aliphatics.The results indicated that a high selectivity coefficient(5)and a high distribution coefficient(D)could be satisfied at the same time.At 30?,the highest values of selectivity and distribution coefficient for toluene/n-heptane,benzene/n-hexane and benzene/cyclohexane systems were 50.4,64.8,24.9 and 1.44,2.44,2.25,respectively.Moreover,the longer chain of aliphatics in oil mixtures,the higher selectivity for aromatics could be obtained.Especially,the selectivity could reach 61.4 when the aliphatic compound was n-nonane.Importantly,the solubility of the DILs in the oil phase was extremely low,which could be negligible.The DILs could be regenerated by simple distillation.As an example,the aromatic compounds in naphtha could be enriched efficiently using the DILs.5.Separation aromatics from aliphatics using DIL-organic solvent composite extractants.In order to decrease the viscosity of extractants and enhance the mass transfer in the extraction process,we designed a series of composite extractants.When a certain amount of organic solvent was added,the viscosity of the DIL could be greatly reduced,which suggested that the mass transfer during extraction was improved and the energy consumption was reduced in the application.Tetraethylene glycol(TTEG)was chosen as the best solvent to form composite extractants with DIL,and DIL-TTEG(mDIL:mTTEG=10:1)showed proper viscosity,density and best extraction performance.At this condition,the viscosity decreased 43.0%and the highest S and Dtol were 38.7 and 1.05,respectively,at 30?.Notably,the S and Dtol were 1.89 and 2.56 times,respectively,of pure TTEG.At the same time,the best performance for benzene/n-hexane and benzene/cyclohexane systems were S:44.6 and 23.6,D:1.91 and 1.78,respectively.When the oil mixtures contained cycloalkanes,the composite extractant could maintain the similar level of selectivity to DIL.Besides,after extraction,DIL-TTEG could also be regenerated by simple distillation.6.Separation of aromatics from aliphatics using hydrophobic DIL-water composite extractants.As we all know,water is a green and cheap solvent.It has been found that the so-called hydrophobic ionic liquids are not completely miscible with water,and the existence of water in DILs may influence the physicochemical properties of DIL.In order to solve the problem of large viscosity of the DIL,we proposed DIL-water composite extractants to separate aromatics from aliphatics.The results showed that the solubility of water in the DIL was 2.24 wt%at 303.15 K.When the water contents of the DIL were 1.10 wt%and 1.59 wt%,the viscosity of the DIL was reduced by 56.3%and 65.0%,respectively.At this time,the highest selectivity and distribution coefficient for toluene were 45.7,41.5 and 0.86,0.75,respectively.The results indicated that a small amount of water in the DIL not only made the DIL have a high D and a high S simultaneously,but also enhanced the extraction process.More importantly,the use of water let the extraction process accord with the concept of green chemistry.