Temperature and pressure effects on the product distribution of PTFE pyrolysis by means of qualitative, in-line FTIR analysis

Abstract

The results of the depolymerisation of PTFE under steady operating conditions in a semi-automated, continuous depolymerisation system are presented. The influence of temperature and pressure on the selectivity of the three main products of depolymerisation (tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and octafluorocyclobutane (OFCB)) was investigated via qualitative in-line FTIR analysis. No carrier gas was used, with the PTFE feed rate and experimental run time kept constant. The temperature and pressure ranges investigated were: 650 °C-750 °C and <10 kPa-40 kPa. The optimum operating conditions to maximise the three main products were determined using response surface methodology following a three-level face centered composite design. A TFE mole fraction of 0.95 and higher was achieved at operating conditions of ± 675 °C and < 10 kPa. HFP mole fractions of 0.19 and higher were achieved within the operating range of 744 °C to 750 °C and 32 kPa up to 40 kPa. At operating conditions of 750 °C and 40 kPa, OFCB fractions of 0.5-0.55 were achieved. The OFCB and HFP mole fractions achieved differed from those previously mentioned in the literature. Analysis of the determined product specific kinetics indicates that the predominant HFP production pathway at low residence times (< 3 s) is via the reaction of TFE with difluorocarbenes. At higher residence times the dominant reaction pathway is the dissociation OFCB.

Polytetrafluoroethylene: Synthesis and Characterization of the Original Extreme Polymer

“…This option has already been pursued to a great extent in the Fluoro-Materials Group at the University of Pretoria and in the research group at the University of Ottawa. The literature on the pyrolysis of PTFE has already been reviewed. ,− PTFE may be pyrolyzed under vacuum of ∼1 Pa and at 600 °C to yield nearly pure (99.5%) TFE, with minor amounts of HFP, octafluorocyclobutane (OFCB), and the perfluorobutene isomers. The pyrolysis reactions are summarized in Schemes and .…”

“…Extreme care must be taken with the pyrolysis of PTFE because improper pyrolysis conditions will lead to the production of large quantities of perfluorobutene compounds . The effects of temperature and pressure on the composition of the pyrolysis stream have been documented in detail by Bezuidenhoudt et al…”

Dynamic Modeling of a Sub‐zero, Fed‐Batch, Packed Distillation Column to Produce Tetrafluoroethylene

“…This waste is not biodegradable and the incineration of PTFE in the presence of oxygen produces toxic gases. Therefore, numerous works have been published that deal with the depolymerization of PTFE through pyrolysis to produce its monomer, tetrafluoroethylene (TFE), as the first step in a chemical recycling process [1][2][3][4].…”

“…During the pyrolysis process, TFE undergoes secondary reactions to produce hexafluoropropylene (HFP) and octafluorocyclobutane (OFCB) at temperatures higher than 948.15 K and pressures above 40 kPa, in the absence of a carrier gas [1]. The next step in the recycling process is to separate TFE from the ternary mixture, to serve as feedstock to a polymerization reactor.…”

Perfluorocyclobutane (PFC-318, &lt;i&gt;c&lt;/i&gt;-C&lt;sub&gt;4&lt;/sub&gt;F&lt;sub&gt;8&lt;/sub&gt;) in the global atmosphere

“…One potentially major source of c-C 4 F 8 that seems to have received too little attention is the production of TFE and HFP monomers, the building blocks for PTFE, fluorinated ethylene propylene (FEP, TFE/HFP copolymer), and other fluoropolymers, which involves pyrolysis of hydrochlorofluorocarbon 22 (HCFC-22, CHClF 2 ) as c-C 4 F 8 , the dimer of TFE, is a by-product/intermediate of this process (Chinoy and Sunavala, 1987;Broyer et al, 1988;Gangal and Brothers, 2015). This reaction can be steered towards HFP or c-C 4 F 8 by controlling the dimerization of TFE to c-C 4 F 8 and the co-pyrolysis of c-C 4 F 8 with TFE to HFP (Jianming, 2006).…”