Journal of Analytical and Applied Pyrolysis, 11 (1987) 25-38 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands 25 zyxwvutsrqpo TECHNIQUES IN GAS-PHASE THERMOLYSES PART 8 *. THE FATE OF MOLECULES IN LOW-PRESSURE PYROLYSIS REACTORS. A THEORETICAL STUDY HELGE EGSGAARD and LARS CARLSEN * Chemistry Department, Ris0 National Laboratory, DK-4000 Roskilde (Denmark) ABSTRACT The fate of molecules in low-pressure pyrolysis reactors has been studied theoretically based on a “random walk” approach of single molecules. The study has been used to elucidate average collision numbers, mean residence times and energy transfer in surface-molecule interactions for different types of cylindrical reactors including those for Curie-point pyrolysis. The results are discussed taking the original studies on molecular flow under low-pressure conditions by Knudsen and Clausing into account. The possible applica- tion of the computer program in simulating low-pressure pyrolytic reactions, with special emphasis of low-pressure gas kinetics, is discussed. Collision number; Curie-point pyrolysis; pyrolysis reactor; reaction kinetics; residence time. INTRODUCTION In order to design the optimal configuration of low-pressure pyrolysis reactors, for a given type of experiment, a knowledge of the fate of the gaseous molecules is of importance. Several factors are determining in this context, such as collision number, mean residence time and energy transfer from the surface to the molecule. With a Curie-point pyrolysis reactor, the problem becomes even more complicated, as the molecule-surface interac- tions are divided into collisions between the molecules and the hot filament surface and those with the reactor surface, the latter typically exhibiting ambient temperature. Hence, both thermal activation and deactivation must be considered. This paper describes a theoretical approach to studies of the fate of molecules in low-pressure pyrolysis reactors based on a “random walk” of * For Part 7, see H. Egsgaard and L. Carlsen, J. Anal. Appl. Pyrolysis, 10 (1986) 83. 0165-2370/87/$03.50 0 1987 Elsevier Science Publishers B.V.