Ultrapyrolysis of chlorodifluoromethane

Abstract

Pyrolysis of chlorodifluoromethane ($CHClF_2$;R22) has been used for the commercial preparation of tetrafluoroethylene ($C_2F_4$; TFE) as the monomer of polytetrafluoroethylene, known as Teflon^？. To date, the tubular type reactor has been used for the pyrolysis of chlorodifluoromethane ($CHClF_2$; R22). Main features of the conventional tubular pyrolysis are that TFE yield is lower than 30~40 %, and that TFE yield more than 80 % and faster kinetics are obtainable if R22 is diluted by an inert gas or a heating medium such as superheated steam. However, the factor that controls the output of R22 pyrolysis is still not clearly understood. In this dissertation, the material and energy balance are set up following previously known the reaction steps and kinetic parameters, the behavior of a tubular reactor being numerically investigated. This study describes quantitatively that R22 pyrolysis is a typical example of ultrapyrolysis (or fast pyrolysis) where supplying heat is a critical factor. Thus, it turns out to be the deficient supply of heat is the reason why the tubular pyrolysis without dilution of R22 suffers from the poor TFE yield with 30~40 %. A possible solution against its limitation in the heat supply is feeding reactant (R22) into reactor with a heating medium such as superheated steam. The numerical estimation also reveals that, in the conventional tubular pyrolysis, the reaction with the superheated steam proceeds under an adiabatic condition due to short reaction time. Since the behavior of adiabatic operation is determined by a starting temperature ($T_0$), TFE yield depends on the temperature and the amount of the superheated steam by which $T_0$ is determined. The our results obtained by the numerical estimation show that higher $T_0$ is desirable for better TFE yield. Therefore, the more and hotter superheated steam reveals better TFE yield. The adiabatic condition leads to being non-isothermal operation. Besides variety of diluent used, its...