An Experimental Study of the Formation of Perfluoroisobutene

Abstract

This paper presents an experimental study that focuses on the formation of perfluoroisobutene (i-C₄Fg). Experiments were carried out at atmospheric pressure in a quartz flow tube reactor over the temperature range of 823 to 1273K and an initial reactant feed concentration of 2% with the balance nitrogen. Reactants studied include chlorodifluoromethane (CHF₂Cl), 1,1,1,2-tetrafluoro-2-chloroethane (CF₃CHFCl), trifluoromethane (CHF₃), perfluoropropene (C₃F₆), and mixtures of these species. Effluent gas concentrations were obtained using a water cooled gas sampling probe, and analysis of products was performed via on line gas chromatography with flame ionization detection and gas chromatography with mass selective detection. C₃F₆ pyrolysis produced more than 22% i-C.F, yield, while mixtures with CHF₂Cl and CHF₃ resulted in i-C₄F_g yields of 14% and 28%, respectively. The pyrolysis of CF3CHFCI resulted in slightly greater than 6% i-C₄F_g yield, and CHF₂Cl decomposition produced up to 6% i-C₄F_g yield, while CHF₂Cl/CF₃CHFC1 copyrolysis produced 8% yield of i-C₄F_g. These results show that the addition of a difluoromethylene (iCF₂) source increases i-C₄F_g production. This suggests that a major pathway to i-C₄F_g production may be C₃F₆ isomerization to singlet perfluorodimethylcarbene (l:C(CF₃)₂) and subsequent collisional stabilization to the triplet carbene (3:C(CF₃)₂) followed by either 1:CF₂ addition or further reaction with C₃F₆. This work focuses on an experimental study. Detailed modeling work is ongoing.