Analysis and comparison of properties of air-blown and of thermally treated pitches

Abstract

The work reports results of investigations in how methods for modification of coal-tar pitches by means of air-blowing and of thermal treatment influence properties of producible air-blown pitches and microstructure of cokes based thereupon. Conditions under which air-blown pitches (ABP) were obtained: temperature varied from 300 to 370°C, 3 h duration of the process, the air flow rate about 100 L/kg h. Conditions of thermal treatment: temperature varied from 300 to 450°C, 3 h duration of the process. A sort of coal-tar pitch served as initial raw material. The ABP had the following parameters: softening point values from 117 to 190.2°C, content of toluene insolubles from 39.4 to 57.1%, content of quinoline insolubles from 10 to 48%. The thermally treated pitches (TTP) had the following parameters: softening point values from 86.2 to 264°C, content of toluene insolubles from 32.6 to 76%, content of quinoline insolubles from 6.2 to 70.7%. Comparison of two modification methods for pitches had evinced the air-blowing process to change properties of pitches at the same temperature to a larger extent as compared with thermal preparation. If temperature of thermal preparation exceeds temperature of air-blowing by 80–100°C, the softening point value for TTP samples is as near the same as that for the ABP samples. Samples of ABP have more high values of aromaticity index and of ortho-substitution index. Cokes based on ABP are capable of forming isotropic microstructure; at this point, their mean microstructure scores decrease from 3.8 to 2.7, as processing temperature rises. Cokes based on the TTP do not change their microstructure, as processing temperature varies; their mean microstructure score equals 4.2. This fact permits to classify the above mentioned cokes as regular cokes.