Efficient Separation Of Low Temperature Coal Pyrolysis Oil And System Integration

Low temperature coal pyrolysis, as a new method for high efficient and clean utilization of coal, has attracted more and more attention. As the important products of pyrolysis, there are great differences between low temperature and high temperature pyrolysis oil. It would be of great significance to develop an efficient utilization way of low temperature pyrolysis oil. The studies of structure-physical property, thermodynamics, new separation method and system integration were systematically carried out for coal pyrolysis oil system. The structure-physical property correlation model was established, the green separation method of higher-value products (phenol) was formed, the separation process was structured, and the whole system was integrated and optimized. The main research work is listed as follows:(1) The new group contribution method (benzene-chain group contribution method/BC-C) that takes benzene ring as fundamental group was developed on the basis of the composition character of abundant multi-benzene substances in coal pyrolysis oil system. And the benzene chain groups and substituent groups were added as the new groups of BC-C method. The reliability of BC-C method was verified through the average absolute relative deviation(AARD) comparison between the literature and calculated value of boiling point and critical properties using BC-C method and traditional J-R method. On the basis of the calculated properties above, the density value could be obtained through the calculation using Riedel and Yamada-Gunn equations. The calculated values were agreed well with literature values, and the AARD was within 10%. Based on the estimated data and literature data, the coal pyrolysis oil physical property database was established which included single-components, azeotrope components properties data and relevant properties analysis and characterization methods.(2) Two kinds of new extraction agents with amido groups were developed. They were imidazole compounds and amide compounds, respectively. Above compounds could form deep eutectic solvents (DESs) with phenolic compounds due to the hydrogen-bond interaction. Phenolic compounds could be separated because of the insolubility of formed DESs in oil. And the phenols removal efficiencies were higher than 90%. The physical properties of the DESs were systematically measured, such as melting point, density, and viscosity. Their change regularities with composition and temperature were explored as well. The influence of extraction agent structure was investigated, the effect laws of key influence factors, such as reaction temperature, reaction time, mole-ratio were studied, finally the optimized reaction conditions were obtained. The hydrogen-bonded theory and stereo-hindrance effect of substituent groups were verified through FT-IR characterization and molecular simulation. Above developed extraction agents were applied in two kinds of actual oils with phenols removal efficiencies around 85%. At last, nicotinamide was chosen as the amplification extraction agents to use in kilo-scale separation process successfully.(3) The thermodynamic study was carried out for the new separation systems that the extracts and extraction agents formed DESs. The concept ternary phase diagram of those processes was proposed, and the relevant separation theory was established. The phase equilibrium experiment data of o-cresol, p-cresol, and m-cresol-hexane-imidazole were systematically measured, and they were correlated and regressed using NRTL and UNIQUAC models. NRTL model was selected to optimize the technological process through the comparison between estimation value and experimental value. And the relevant binary interaction parameters were obtained. The simulation and optimization of above separation processes were processed using Aspen Plus, and optimized extraction stages and addition of extraction agent were obtained eventually. Based on the experiments and simulations, the specific processes for the separation of phenolic compounds from coal pyrolysis oil using the two new extraction agents were designed.(4) The hydrogen-bonded design theory for the phenolic compounds extraction agents was applied in the separation of indole from wash oil. Halogenoid ionic liquids were developed as a new kind of extraction agent with excellent extraction ability of indole. Among them, indole extraction efficiency of [Bmim]BF4 reached more than 90%, and with rather high selectivity. The influence of indole initial concentration, extraction time, volume ratio, extraction temperature on extraction process were investigated to get corresponding change rules. The separation mechanism was explored through FT-IR spectra, molecular simulation, and the study of ionic liquid polarity, the results suggested that hydrogen bond and polarity both affected this process. [Bmim]BF4 could be recycled by reextraction, with the recovery efficiency more than 90% and high extraction efficiency. Finally, the specific process of separating indole from wash oil using ionic liquid was designed on the basis of both experiment and process simulation.