Extraction Of Phenolic Compounds From Oils Using Ionic Liquids

Separation of phenolic compounds from coal tar and coal liquefactionoil has important economic, environmental and social benefits. Alkaliextraction is used commercially as a method to separate phenols from coalliquefaction oil with large consumption of inorganic acid and base, and atthe same time, a considerable quantity of waste water containing phenols isproduced. In this work, green solvents, ionic liquids, were investigated asextractants to separate phenolic compounds from coal liquefied oil or coaltar. Some kinds of ionic liquids were selected to have a large dissolvingcapacity with phenols and immiscibility with oil species. After extraction,ionic liquids can be easily recovered by reduced distillation or nitrogenstripping for next use. The ionic liquids can be reused for several timeswithout any loss. We are dedicated to finding out the extraction mechanismbetween phenols and ionic liquids for better designation of extractants forthis separation process. The contents of this work are shown as follows:(1) Imidazolium based ionic liquids were selected to extract phenolsfrom model oil. The effects of temperature, phase ratio, and structure ofionic liquids were investigated. The temperature has an influence on the extraction efficiency of phenols, and an increase of temperature willdecrease the extraction efficiency. However, the extraction efficiency byhalogen based ionic liquids, such as [bmim]Cl, is not sensitive to thetemperature. The anions of the selected ionic liquids influence greatly onthe extraction. Extraction efficiency for the [bmim] based ionic liquids isshown as follows, Cl^-> Br^-> BF₄^-> PF₆^-.(2) Determination of the phase equilibrium of a ternary system oftoluene (1)-phenol (2)-[bmim][PF₆](3) has been performed at303.15Kand1atm. A trace fraction of [bmim][PF₆] can be found in the toluenephase,105g/g in weight fraction. With the increase of phenol content intoluene, the solubility of ionic liquids in toluene can be expanded due tothat the phenol acts as a cosolvent. The ionic liquid phase also has a smallamount of oil, which will result in difficulty in separation.(3) Recovery of ionic liquids is important for the separation process.Two ways, back extraction with ether and nitrogen stripping, have beeninvestigated to recover the ionic liquids after extraction. Ionic liquid[bmim][PF₆] can be recovered easily by back extraction with ether, while[bmim]Cl is difficult to be recovered by back extraction with ether.Nitrogen stripping can recover [bmim]Cl and phenols is obtained bycooling nitrogen stream. In this process, most of phenols in ionic liquidphase can be stripped by nitrogen. Experimentally, temperature has a greatinfluence on the recovery efficiency, and an increase of temperature decreases the recovery time. The recovered ionic liquids can be reused for4times without any loss in both of mass and extract efficiency.(4) Selected ionic liquids have been used to extract phenols from coaltar and coal liquefaction oil. The extraction performance for separation ofcoal tar and coal liquefaction oil is similar to that for separation of tolueneand phenol mixture. Temperature does not influence significantly on theextraction of coal tar and coal liquefaction oil by the ionic liquids. With asame cation of [bmim],[bmim]Cl is better than [bmim]Br in extractionefficiency. With a same anion of Cl^-, the extraction efficiency decreaceswith an increace of the chain length of alkyl on the imidazolium of theionic liquids.