PYROLYSIS OF PITCH

Kinetics of thermal pyrolysis of pitches from two heavy oil upgrading processes have been studied using thermogravimetric analysis. Experime nts were carried out at atmospheric pressure with heating rates of 25- 150 degrees C min(-1) to a final temperature of 800 degrees C. At temp eratures below 150 degrees C, there is little devolatilization of eith er pitch. At higher temperatures, the pyrolysis takes place in two sta ges. Heating rate had a minor effect on the weight loss at a given tem perature. Single-stage, first-order reaction methods, including models which incorporate a Gaussian distribution of activation energies, wer e found to be inadequate to interpret the thermogravimetric analysis r esults. A two-stage model which reflects changes in the chemical const itution or structure as conversion proceeds was necessary to describe the dependence of devolatilization rates on remaining volatile content . The transition between these two stages is a sharp one, occurring at about 450 degrees C for both pitches. The magnitudes of the activatio n energies suggest that both stages are kinetically controlled. (C) 19 98 Published by Elsevier Science Ltd. All Rights reserved.