Kinetics of anaerobic degradation of glycol-based aircraft deicing fluids
The kinetics of anaerobic degradation of glycol-based Type I aircraft deicing fluids (ADFs) were characterized using suspended-growth fill-and-draw reactors. First-order degradation rate constants of 3.5 d–1 for propylene glycol-based Type I ADF and 5.2 d–1 for ethylene glycol-based Type I ADF were obtained. Similar reactors were used to determine activation energies using Arrhenius temperature dependence relationships. Temperature had a significant effect on degradability below 25°C. High substrate concentrations substantially reduced anaerobic degradability in both Pd-based and EG-based Type I ADF fill-and-draw reactors.
Anaerobic fill-and-draw reactors were tested in batch mode to determine first-order intrinsic kinetics constants. Values of 1.9 d–1 and 3.5 d–1 were obtained for PG-based and EG-based Type I ADF, respectively. Shock organic loadings resulted in substantially lower first-order batch kinetics constants. Batch first-order kinetics constants of cultures accustomed to mesophilic temperatures were substantially reduced when introduced to immediately lower temperatures.
Serum bottle tests showed that specific ADF additives used for corrosion control can be inhibitory to anaerobic glycol degradation. 5-methyt- 1H-benzotriazole was shown to be more severely inhibitory than benzotriazole. Inhibition of anaerobic Type IV ADF degradation, caused most likely by thickeners, might be overcome by adaptation. The rate of methane production from PG-based Type IV ADF approached that from pure PG upon repeated exposure. A similar conclusion was not obtained for EG-based Type IV ADF. Different types and/or amounts of thickeners may have been used between the two Type IV ADFs tested.
Anaerobic degradation of 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol was successfully demonstrated by acclimating anaerobic PG-based Type I ADF-degrading cultures. First-order intrinsic degradation rates of 0.55 d–1 , 0.83 d–1, and 0.73 d–1 were obtained for 1,2-, 1,3-, and 1,4-butanediol, respectively. Specific metabolic processes previously demonstrated during anaerobic degradation of ethylene glycol (1,2-ethanediol) and propylene glycol (1,2-propanediol) were not demonstrated for anaerobic 1,2-butanediol. degradation.
The compound isopropanol is suspected to have formed during fill-and-draw kinetics and temperature dependence testing of PG-based Type I ADF, as well as temperature shock batch testing of the same. This has potential implications for reactors operating under kinetic stress because isopropanol is difficult to degrade anaerobically.
0542: Chemical engineering