Association Structure Analysis And Component Separation Of Aromatic Compounds In Liquid Products From Direct Coal Conversion

Phenolic compound and anthracene are two kinds of chemical organic raw materials with high added value.High purity phenolic compound and anthracene can be used in the production of fine chemical products such as medicine,pesticide,dye,pigment and other chemical products.The content of phenolic compound in coal-to-liquid?coal tar and coal liquefaction oil?is more than 10%and the content of anthracene is 1.2¹.8%.If coal-to-liquid is directly hydrogenated to produce gasoline and diesel oil,not only precious phenols and anthracene resources are wasted,but also hydrogen consumption is increased.At the same time,water produced by the hydrogenation reaction will affect the conversion efficiency of effective elements in coal,reduce product value,impact on production efficiency,and increase the cost of ecological environment treatment.Therefore,according to the research idea of the project,phenolic compound and anthracene are first separated from coal-to-liquid,and then the technical route of hydrogenation conversion is carried out.The focus is the basic research of how to separate phenolic compound and anthracene from coal-to-liquid.At present,the traditional method of phenolic compound extraction in industry is caustic washing,which not only needs strong acid and alkali,but also produces large amounts of phenol containing wastewater.These will increase the environmental pressure and pollution control cost.The traditional method of anthracene extraction in industry is the combination of solvent crystallization and distillation,which has low purity of anthracene product and high energy consumption.These industrial separation methods have gradually failed to meet the requirements of green production,so the development of separation agents with large separation capacity,high selectivity and large distribution coefficient has attracted extensive attention.Due to the excellent properties,although deep eutectic solvents?DESs?has not been used in the purification of anthracene,it has become a research hotspot in the separation of phenolic compound.Through the investigation of the existing separation methods,DESs are used as the extractant or additive for the separation and purification of phenolic compound and anthracene,in order to develop a green and efficient separation method and provide theoretical guidance and technical support for the industrial application of the separation of high value-added chemicals from coal-to-liquid.The main research contents and results are as follows:1.Molecular association structure of aromatic compounds in coal-to-liquid.At first,FG-DVC model and NLP theory were combined to analyze the products of coal pyrolysis and the composition of coal tar was predicted.Then,in view of the complex components and unclear molecular association forms of coal-to-liquid,the association structure of phenols,aromatics,nitrogen-containing compounds and sulfur-containing compounds were explored by combining spectral experiment and quantitative calculation.The results show that the combination of FG-DVC and NLP theory can realize the composition prediction from coal to pyrolysis products,and the high oxygen content of raw coal will produce high phenol content tar.Aromatics and phenols,nitrogen-containing compounds and phenols,sulfur-containing compounds and phenols,nitrogen compounds and aromatics,sulfur-containing compounds and aromatics are associated by two or more interactions among O-H...?,C-H...?,?-?,and O-H…N.The hydrogen bond of O-H…N between nitrogen-containing compounds and phenols is the dominant in the association of phenols,aromatics,and basic nitrogen-containing compounds.The three compounds of phenols,aromatics,and non-basic nitrogen-containing compounds form a ring association structure by interactions of O-H...?,C-H...?,and?-?.The three compounds of phenols,aromatics,and sulfur-containing compounds also form a ring association structure by interactions of O-H...?and?-?.2.Design of extractant.Based on the molecular association structure of aromatic compounds,the extractant for phenols extraction and anthracene purification were designed.The results show that there are two O-H...O hydrogen bonds between phenols and DESs,and the interaction energy between phenols and DESs?-77.7 kJ/mol?is obviously stronger than that between phenols and other components in coal-to-liquid?-32.6^-24.5 kJ/mol?,and also stronger than that between DESs and aromatics in coal-to-liquid?-41.9 kJ/mol?,which lays a foundation for the extraction of phenol by DESs.There is a N-H...Cl hydrogen bond between carbazole and DESs,and the interaction energy?-88.3 kJ/mol?is stronger than that between carbazole and anthracene?-40.3 kJ/mol?,and stronger than that between DESs and anthracene?-58.0 kJ/mol?,which provides the possibility of high selective separation of anthracene and carbazole by DESs.3.Separation of phenolic compounds from coal-to-liquid using DESs.In view of the discharge of wastewater containing phenols or not easy to be used in real coal-to-liquid of the existing separation method,DESs were applied to separate phenols from model oil and real coal-to-liquid.The results show that the?G of phenols phase transfer is 69²24 times of that of aromatics.Under the optimal separation condition,the phenol removal efficiency of model oil,real coal tar,and coal liquefaction oil by choline chloride-glycerol DESs is over 96%,and the neutral oil entrainment is 2²1%.The separation performance is better than the literature value.After DESs recycling for four times,the phenol separation efficiency remains the same and the structure of DESs does not change significantly.There are hydrogen bonds between DESs and phenols,which is the main driving force for the extraction of phenolic compounds from coal-to-liquid by DESs.4.The entrainment behavior of neutral oil during the separation of phenols by DESs.In view of the fact that neutral oil will be entrained in the separation of phenols by solvent extraction,which will seriously affect the purity of phenol product and cause problems for the further separation of mixed phenols,the essential reason of neutral oil entrainment is analyzed by spectral experiments and quantum chemical calculation,so as to“reduce the neutral oil entrainment during separation”.The results show that there are O-H...?,C-H...?,C-H...O,and van der Waals interactions between neutral oil and phenols or DESs,which cannot be completely eliminated by physical means,therefore,making the neutral oil entrainment inevitable.However,it can be reduced by the design of DESs or the selection of separation objects.Among the investigated DESs composed of different hydrogen bond donors and hydrogen bond acceptors,the neutral oil entrainment of choline chloride-glycerol DESs without H₂O is the lowest?66.1 mg/g?.At the same time,reducing the high temperature of phenol oil used for phenols extraction from 230 ^o C to 220 ^o C can reduce the neutral oil entrainment from 283.2 mg/g to 113.5 mg/g,and avoid the entrainment of alkanes and indenes.The compounds with specific structure are easy to be entrained in the extraction of phenolic compounds by DESs.5.Purification of anthracene from crude anthracene oil by mixed solvent of DESs and traditional organic solvent.In view of large energy consumption of industrial separation method,the repeated experiments of traditional organic solvent to purify anthracene,the mixture of DESs and traditional organic solvent was first used for the separation of anthracene and carbazole,and the separation mechanism was also studied.The results show that the separation efficiency is low by DESs alone,while it can be significantly improved using the mixed solvent of DESs and traditional organic solvent.The single separation purity of anthracene can reach 97.5%by using the mixed solvent of tetraethyl ammonium chloride-glycerol DESs and N,N-dimethyl formamide with the molar ratio of 1:9,which is superior to the literature value.There is hydrogen bond of N-H...Cl and C-H…?interaction between DESs and carbazole,these interactions are stronger than the interactions of C-H…O and C-H…?between DESs and anthracene.Adding DESs to traditional organic solvent can significantly improve the interaction between extractant and carbazole,but there is no obvious influence on the interaction between extractant and anthracene,the separation of anthracene and carbazole is therefore improved.