Technology And Mechanism Of QI Removal From Coal Tar Targeting For Making High Value-added Pitch

As the traditional coal tar pitch market becomes saturated, it is necessary to separate QI from coal tar to develop high value-added pitch to meet different market demands. Impurities such as QI in coal tar, their contents, compositions and size scale have important effects on the properties of the high value-added pitch and their applications. Therefore, separation technology was developed based on raw coal tar, its current production process and application.QI removal technology from coal tar by adding solvents such as non-aromatic hydrocarbon, wash oil and dephenolized oil was investigated together with the interaction mechanism between the solvents and coal tar QI. Coal tar and the solvents were characterized,which showed that both coal tar and solvents contained aromatic hydrocarbons, aliphatic hydrocarbons and some polar side chains, the content of aliphatic hydrocarbons is highest in non-aromatics and the polar groups are the most in the de-phenol oil. The QI particles were released from the QI colloidal system by adding low proportion nonaromatic and wash oil or dephenolized oil solvent mixture to coal tar via destroying the colloidal environment of QI surface in coal tar, and reducing the viscosity of the system, by which the coking value and pitch yield after the QI removal were ensured.The rheological properties of modified coal tar with solvents at 50?150? were investigated after a single solvent or a solvent mixture were added to coal tar. A viscosity model based on Dutt model was established to provide accurate solvent parameters for forecasting the QI removal efficiency and reducing the test. With increasing temperature, coal tar viscosity was gradually reduced when different kinds of solvents or their mixtures were added at the same percentage of solvents.QI removal efficiency from coal tar by the gravity sedimentation method was investigated by adding non-aromatic hydrocarbon, wash oil and dephenolized oil to coal tar under solvent amounts of 20 % and 30 % and the weight ratios of nonaromatic to aromatic hydrocarbons of 4: 6 and 3: 7 at different settling times (5, 10, 24 and 36 h). The results show that the addition of 20% or 30% of the solvents can realize QI separation from coal tar by the gravity sedimentation method. The more the solvent added, the less the liquid yield, the longer time, the better the removal efficiency at the same proportion of the same solvent system with the ratio of nonaromatic to aromatic hydrocarbons of 3: 7 or 4: 6, but the QI removal efficiency is no longer increased with the further increase of time. In order to ensure the yield of pitch and the recovery rate of solvents, the amount of solvents is chosen to be 20%, the ratio of non-aromatic hydrocarbon to de-phenol oil is 3: 7, the yield is 65%, and the QI removal rate is 98 %.QI removal by centrifugal sedimentation was investigated using coal tar as raw material,nonaromatic hydrocarbon and aromatics as solvents. The effect of centrifugal parameters on QI removal efficiency was investigated under the centrifugal speed of 3500, 4000 and 4500r /min, the centrifugal time of 0.5, 1 and 2 min, using single solvent or solvent mixture to save energy and to meet the requirement of process. The more amount of solvent, the longer the centrifugal time, the better the removal efficiency. As optimized by the orthogonal tests,non-aromatic hydrocarbon and dephenolized oil are the best, QI removal rate is 96.1%.Refined pitch can be obtained by laboratory distillation of the purified coal tar. Its yield is 65%, QI content is 0.37%, softening point is 89.5? and the coking value is 50.63% when the mixture of non-aromatic hydrocarbon and de-phenol oil was employed with a solvent content of 20 wt% and a gravity sedimentation time of 24 h at 80?.