Study On The Alkali-free Extraction Of Phenolic Compounds From Low Temperature Coal Tar

Nowadays,China,Vietnam,Indonesia and other countries have huge lignite storage;the production of low-temperature coal tar by coking lignite is becoming a huge industry.Low-temperature coal tar contains a large amount of phenolic compounds,and they are significant raw materials in the chemical industry.Meanwhile,the presence of unsaturated bonds in the phenolic compound leads to excessive hydrogen consumption in the subsequent hydrogenation process,so it is economically advantageous to extract the phenolic compounds in the coal tar.At present,the phenol extraction method is caustic washing method,which has a high extraction rate.However,it usually produces a large amount of alkali residue and wastewater containing-phenol,causing serious environmental pollution.In order to solve the environmental pollution problem,this paper explored several environmentally friendly phenol extraction processes.First,ethanolamine was used as an extractant to study the extraction of phenolic compounds from low temperature coal tar.After obtaining the phenol oil fraction at170-240? and extracting,the composition and content of the phenol oil fraction extracted by the caustic washing method and the ethanolamine method were analyzed by GC/MS.During the study,the effects of extraction time,extraction temperature and amount of extractant on the extraction were investigated.The maximum extraction rate was 95%at a reaction temperature of 55?,a reaction time of 25 min and a ratio of 1:2.5,which was close to the caustic washing method.The reaction mechanism of the extractant and the phenolic compound was studied by FT-IR and ~1H NMR.The results of the spectrogram showed that when the ethanolamine reacted with the phenolic compound,the FT-IR of the complex formed was compared with the spectrum of the reactant.The nuclear magnetic resonance spectrum has undergone a certain movement,and it has been proved by analysis that hydrogen bond and acid-base coordination occur in the reaction.The interaction energy of the reaction and the electron energy are calculated by quantum chemistry to provide theoretical support for the experimental results.The results of economic accounting show that ethanolamine extracts phenolic compounds more efficiently than caustic washing.It is also confirmed by experiments that ethanolamine and phenolic compounds have a lot of relative volatility,which can be rectified and separated,and the conceptual design of industrial processes is carried out accordingly.Then,diethanolamine was used as extractant to extract phenolic compounds from low temperature coal tar,the optimal conditions were investigated.The results showed that the reaction time was 20 min,the reaction temperature was 55?,and the ratio was 1:3.Under the conditions,the maximum extraction rate can reach 95%,which shows that diethanolamine can also achieve the extraction efficiency equivalent to the caustic washing method.The reaction mechanism between the extractant and the phenolic compound was studied by FT-IR and ~1H NMR.The results of the spectrum showed that when the diethanolamine reacted with the phenolic compound,it was compared with the spectrum of the reactant to form a complex.Both infrared and nuclear magnetic resonance spectra have undergone some movement,and it has been proved by analysis that hydrogen bonding and acid-base coordination occur in the reaction.Moreover,the interaction energy and electron energy of the reaction are calculated by quantum chemistry,which provides theoretical support for the experimental results.Finally,it was considered that the boiling point of diethanolamine is too high and it is not suitable to use rectification separation,the solvent recovery process of diethyl ether stripping method is studied,and the process flow is conceptualized.The results of the process simulation also demonstrate that the process is feasible.Finally,the designed daul-basic ionic liquid was used as an extractant to extract phenolic compounds from low-temperature coal tar.The phenol was used as the probe molecule for nuclear magnetic analysis and combined with quantum chemistry to determine the basicity of ionic liquids.The reaction time,the reaction temperature and the amount of the extractant have an effect on the extraction rate of the phenolic compound,and the reaction time is 35 min,the reaction temperature is 30?,and the extraction ratio of the ionic liquid and the model oil is 1.1 g/4 mL.The optimal extraction rate of phenolic compounds in ionic liquids can reach 98.2%;the reaction mechanism of ionic liquids and phenols is studied by UV-vis and FT-IR.The results show that hydrogen bonding and acid-base coordination are formed between the ionic liquid and the phenolic compound,and the interaction energy and electron energy of the reaction are calculated by quantum chemistry.Theoretical support was provided for the experimental results.Finally,diethyl ether was used as the back-extraction extractant to recover the phenolic compounds.The experimental results show that diethyl ether can well separates the phenolic compounds and ionic liquids,and realize the recovery and reuse of ionic liquids.The phenol extraction process using ethanolamine,diethanolamine and designed double basic ionic liquid as extractant has high phenol extraction efficiency and avoids secondary pollution problems,and has good environmental friendliness.The relevant research in this paper provides a theoretical basis for the industrial application of these processes instead of the caustic washing method.