Study on Electrostatic Separation of Quinoline Insolubles from Coal Tar Pitch

Abstract

The feasibility of electrical separation in the removal of quinoline insoluble (QI) particles from coal tar pitch (CTP) was experimentally investigated. QI particle involvement prohibits the effective fabrication of high-quality value-added products, such as carbon fibers, from CTP. A substantial and sustainable CTP market exists around the world; therefore, a strong incentive exists to develop a viable technical approach to effectively and economically remove QI particles from CTP. The electrical separation method shows promise to achieve this technical goal (Cao et al., 2012).Even with the given setup (wire- cylinder adapted), critical issues remain to be addressed for this method to be applicable to the CTP: (1) identifying the wash oil used in the original QI separation, (2) understanding the mechanism of QI separation, (3) characterizing the deposit, and (4) identifying the QI.This study integrated a set of experimental and analysis techniques into the electrical separation tests to address the aforementioned issues.Key findings are as follows:1.Electric current responses•The electric current level of the CTP–wash oil solution reported by Cao et al. (2012) can be attained by using a mixture of 25% quinoline and 75% toluene for the CTPs examined in this study under the same electrical load condition.•The electric current tends to decrease during the test period because of the decreasing number of charged particles.•The reversed field corresponded to the configuration of electrostatic precipitation for positive corona discharge. The high electric field can result in dielectric breakdown and lead to an abrupt current surge.2.Deposit response and solvent candidates•Deposit of particles in CTP mixture can be effectively implemented in a wire-cylinder configuration as proposed and examined in this study.•Deposit depends on the solvents. Among the solvents tested, two- and three-part solvents that included quinoline and ethanol (i.e., 25% quinoline and 75% toluene; 50% quinoline and 50% toluene; and 33% wash oil, 33% BTX, and 34% ethanol) produced the highest deposit weight•The deposit process examined in this study is derived from the charged particles. An appreciable relation exists between deposit weight and electric charge.3.QI removal efficiency (RE)•The RE of the electrostatic separation can reach as high as 76.2% for Carbores, and 61.6% for Koppers. •The RE can be further enhanced if the field level increases from 0.16 kV/mm that was used in the current study to 0.23 kV/mm, according to the relation established between the RE and the electric field.4.Testing of the modeling system•The motion of particles is originally driven by the charge-based electric force in the cases tested. The solid particle separation mechanism is similar to that of QI deposition in CTP.•The mechanical movement of solid particles can be strongly affected by the gravitational and viscous forces in the electric field. 5.EDS analysis and chemical compositions•The main chemical composition of deposit QI matches that of as-prepared CTP QI. The deposit QI is derived from the same group of the CTP QI.•In addition to carbon, the QI contains oxygen, sodium, aluminum, silicon, iron, and sulfur.The work for the near future is also discussed.