Identification of catalysts for the beneficiation of ptfe pyrolysates

Abstract

This dissertation relates the results of the preliminary investigation into the catalytic interaction of PTFE with various inorganic materials, with the primary goal of find catalysts that will greatly increase the yield of the high value pyrolysis products, most notably hexafluoropropylene and octafluorocyclobutane. This dissertation is divided into three parts, viz.: A review on the literature concerning PTFE pyrolysis; a brief description of facilities built for this research; and the results of the experimental work. The experimental work was conducted with a hyphenated TGA-FTIR system in which samples of commercial PTFE mixed with catalyst were pyrolysed. Some sulfates, fluorides and common oxides of the fourth period- and group 13 metals were used as catalysts. It was found that the fluorides of the fourth period metals Zn, Cu, Ni, Co, Fe and Mn are generally inert with respect to reformation of the gas phase. The sulfates of these metals produced mixed results with NiSO4 increasing the yield of hexafluoropropylene whilst CuSO4 and CoSO4 produced unidentified side products and the rest being inert. The oxides also produced mixed results with CuO readily oxidising PTFE to CO2. Among the group 13 metals, the fluoride, sulphate, and common oxide of aluminium gave the best results, converting the PTFE pyrolysates almost completely to hexafluoropropylene and hexafluoroethane. Reaction mechanisms for the conversion of the pyrolysates on Al2O3 are proposed. No impact was noticed on the yield of octafluorocyclobutane or the yield of the octafluorobutene isomers. Research recommendations include: Metal oxides examined here should be tested further by examination of the metals in their 3+ and 2+ oxidation states, where the applicable oxide has not been covered; the phosphates of the metals examined here should also be studied to determine if the presence of a phosphorous atom will affect the reactivity; and ab initio work should be conducted to gain insight as to which crystal surfaces are responsible for the catalytic effects of the relevant materials. The work detailed here was limited to a qualitative investigation of the PTFE/catalyst system and does not include deep theoretical treatment of such topics as pyrolysate mass transfer and catalyst surface conditions.