at Google ScholarTitle data
Mierdel, Konstantin ; Gerdes, Thorsten ; Jess, Andreas ; Schmidt, Achim ; Hintzer, Klaus:
Energy- and ressource efficent production of fluoralkens in high temperature microreactors.
2018
Event: IsFC: 22th International Symposium on Fluorine Chemistry
, 22.-27.07.2018
, Oxford, UK.
(Conference item: Conference
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Speech
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Abstract in another language
Tetrafluoroethylene (TFE) is the most common monomer for the synthesis of fluoropolymers at industrial scale. TFE is produced via multistep pyrolysis of chlorodifluoromethane (R22) at temperatures between 700 °C and 800 °C resulting in high values of waste acids containing HCl and HF.
In this work, a new chlorine-free process for producing the monomers tetrafluorethene (TFE) and hexafluorpropene (HFP) in a plug flow microreactor will be presented, starting from partially fluorinated alkanes obtained from electrochemical fluorination (ECF). Depending on the feedstock of the ECF up to 70% of partially fluorinated alkanes can be obtained in the product spectrum. Actually, no industrial process exists for utilizing these by-products besides incineration. Therefore, great attempts are made to achieve a material- instead of thermal utilization.
The first step in the synthesis of TFE and HFP is the decomposition of partially fluorinated substances yielding difluorocarbene (CF2), which is a highly endothermic reaction. For this reason, a microreactor is used (3M), offering high thermal conductivity and thereby enabling isothermal operation mode. The reaction channel has a cross section of 1 mm x 1 mm. The advantage of such small channels is the determination of kinetic parameters without the limitations in terms of heat- and mass transfer of a labscale-reactor.
The crucial process parameters of fluoromonomer synthesis in the microreactor are short residence time, 0.1 s to 2.5 s, at a sufficiently high temperature, 750 °C to 900 °C, and a fast quenching of the product gas to suppress the formation of oligomers and hazardous by-products. It will be shown that at high temperatures the conversion rate of partially fluorinated alkanes reaches 65-90% with monomer yields up to 90%. In this contribution, the influence of the dwell time and process temperature on different partially fluorinated feed gases will be discussed.
In addition, a comparative life cycle assessment (LCA) shows the benefit of using partially fluorinated alkanes for fluoromonomer-production instead of thermal recovery.