Research On The Interaction Mechanism During Medium-and-Low Temperature Coal Tar DMSO Extraction Process

Separating coal tar by the group composition of alkanes,aromatics and phenolic compounds,is an important process to realize the efficient coal tar utilization.In this thesis,dimethyl sulfoxide（DMSO）,which performs well on the extraction separation of middle-and-low temperature coal tar,was selected as the extractant.The extraction separation laws of different alkane-aromatic model oil systems and the interaction mechanism between the molecules were investigated firstly.Meanwhile,the interaction discrepancy between the extractant and the typical composition of medium-and-low temperature coal tar（including alkanes,aromatics and phenolic compounds）were manifested.Taking these research results as the theoretical basis,customized scheme of coal tar sequential separation by group composition was designed.The structure and main research conclusions of of this thesis are as follows:（1）The third chapter is dedicated to the liquid-liquid equilibria（LLE）determination and the thermodynamic model accuracy evaluation.The LLE of 13 groups of typical alkanes-aromatics model oil and DMSO ternary system were measured firstly.Subsequently,the accuracy of the experimental data was confirmed by the methods of linear regression,Aspen Plus thermodynamic regression verification and Gibbs minor common tangent test.Finally,by comparison with the experimental data,the accuracy of NRTL,UNIQUAC,UNIFAC and COSMO-RS model LLE prediction was investigated.The most widely used UNIFAC model,also with the minimal deviation,was applied to predict the LLE of another 14 aromatic-alkane-DMSO systems.These LLE simulation results were utilized as the verification and supplement of the experimental systems.（2）In the fourth and fifth chapters of this thesis,the experimental and simulated LLE data were comprehensively discussed.The influence of the aromatic and alkane molecular structure characteristics on the extraction separation laws was obtained.Among them,with the increase or extension of aromatic side chains（the increase of the relative molecular weight）,the spread of side chain positions,and the addition of another benzene rings（naphthalenes）,the aromatics distribution coefficient of the corresponding aromatic-alkane system will decrease.Meanwhile,the entrainment of alkanes also declines.With the extension of the carbon chain of linear alkanes（the increase of carbon number of cycloalkanes）,the formation of linear alkanes（instead of cycloalkanes）,and the reduction of carbon branch chains,the entrainment of alkanes in the system decreases,and the selectivity of aromatics increases.By means of computational chemistry and visual analysis of the intermolecular non-covalent interaction（including ESP analysis,molecular polarity index,interaction energy,AIM topological analysis,IGMH analysis and SAPT energy decomposition,etc.）The position,type（van der Waals interaction and hydrogen bonding）,intensity and physical origin（dispersion,electrostatic and induction contribution）of the intermolecular interactions among the above system are shown in the form of numerical results and images.Correlating the computational chemistry results with the molecular structural features of the model compounds,it is elaborated that the intermolecular interaction propensity of these molecules and the underlying reasons for the differences in extraction results between different systems are macroscopic manifestations of the strength of these intermolecular interactions.（3）In the sixth chapter of the thesis,the computational chemistry analyses were also employed to investigate the nature of the interaction between the extractant and the typical composition of coal tar.Aromatics bridge the poorly mutually dissolved non-（weak）polar alkanes and the more polarized phenol compounds.The interaction between extractant and phenolic compounds is much intensifier than that of extractant-alkanes（or aromatics）.Medium hydrogen bonds appear,and the E_elst and E_ind contributions increase significantly.The electrostatic contribution gradually becomes dominant among the intermolecular attractive interaction.By shedding light on the strength and nature of the interaction between the extractant and the typical components of coal tar,the grail of separating coal tar by group composition can be achieved.DMSO is the optimal extractant considering both selectivity and solubility.（4）In the seventh chapter of the thesis,taking these interaction discrepancy between the extractant and the typical composition of medium-and-low temperature coal tar as the theoretical basis,the sequential extraction separation experiments of Xinjiang medium-and-low temperature pyrolysis coal tar by group composition were carried out.Vacuum distillation was performed at first to enrich phenolic compounds.Customized separation schemes were designed according to the specific composition of different fractions.The0-230°C fraction is mainly composed of naphtha and phenolic oil,and the content of phenolic compounds reaches 62.64%.When the solvent-tar ratio is 1:1 and the extractant is compounded with 30%water,after two consecutive extractions,almost all phenolic compounds are extracted.Meanwhile,aromatics and alkanes are both enriched in the raffinate.The percentages reached 51.60%and 39.43%,respectively.Only 0.95%of phenol and o-cresol are detected in the raffinate phase.The content of alkane compounds reaches 41.19%in the 230-300°C fraction.The non-（weak）polarity alkanes can be separated firstly by increasing the solvent-tar ratio or by performing a multistage extraction.Subsequently,the separation of aromatics and phenol components can be accompolished by compounding water in the extraction phase of the previous section.When the amount of water compounded in the extractant reaches 30%,there are no aromatic compounds detected in the water phase,and the percentage of phenolic compounds reaches 91.06%.Under the condition of water-extractant ratio of 3:1,the purity of DMSO reaches 96.69%,and only 0.11%DMSO residue is found in the oil phase.The recovery of DMSO can be achieved by means of water re-extraction.