Depolymerization of clean unfilled PTFE waste in a continuous process

Abstract

A continuous process is described whereby waste PTFE was converted into tetrafluoroethylene (C2F4, TFE), hexafluoroethane (C2F6, HFE), hexafluoropropylene (C3F6, HFP), and octafluorocyclobutane (c‐C4F8, OFCB). The waste PTFE was depolymerized inside a reactor that was heated by a radiofrequency induction generator. The reactor was capable of operating at various temperatures (600–900°C) as well as various reduced pressures (5–80 kPa). The depolymerization reaction conditions could be changed while the reactor was in operation in order to manipulate the reaction product composition. Under certain conditions, high yields of TFE (> 94%) and low concentrations of by‐products were formed. The PTFE was fed vertically downward from the hopper, with the screw feeder, into the reactor where the depolymerization process took place. The hot intermediate products were continuously evacuated through a self‐cleaning quench probe, where it was quenched to form the final products. The depolymerized products were analyzed with a gas chromatograph. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2752–2759, 2006

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

“…The most important of all of the industrial fluoropolymers is polytetrafluoroethylene (PTFE) due to its wide range of unique and extraordinary characteristics. Due to the nonmelt-processability of PTFE resin, a large amount of waste is generated annually, most of which is either incinerated, landfilled or ground up and ram extruded to produce lower quality tubes and profiles [1] [2]. These destructive or re-use methods pose economic and environmental issues, particularly when considering the evolution of extremely toxic gases (eg perfluoroisobutylene (PFIB)) during the incineration of PTFE.…”

“…Even though the overall effects of these two variables seem to stay the same, experimental results achieved at the University of Pretoria indicate that the exact distribution of the three main products (TFE, HFP, and OFCB) appear to be system specific. Meissner [6] and van der Walt [2]performed indepth studies into the temperature and pressure effects on the product distribution and recommended the optimum operating conditions to optimise the three main products (TFE, HFP, and OFCB).…”

The continuous depolymerization of filled polytetrafluoroethylene with a continuous process

“…A possible reason for this could be an increased residence time of the intermediate products inside the paddle reactor with respect to the reactor used in previous work. 10,16 The formation of each product will be discussed separately below.…”

A kinetic expression for the pyrolytic decomposition of polytetrafluoroethylene

“…For industrial cases such as ours [2], where coarse granules are used for depolymerisation and where contact with hot surface areas is expected to be poor, radiative heating is anticipated to contribute significantly to energy transfer. In light of this, and some apparent lack of congruence in the literature, the decision was made to re-evaluate the thermal depolymerisation kinetics of PTFE, of granule size typical of what would be used for commercial depolymerisation.…”

“…The product ratios can be tailored by manipulating the working temperature, the pressure, the residence time of the gaseous product stream in the hot zone, and the quench rate [2,3]. PTFE is non-melt-processible, hence one of the recycling methods is via pyrolysis of the solid waste and subsequent recovery of the monomer for re-use.…”