As a result of the high biological oxygen demand (BOD) and high chemical oxygen demand (COD) of urea and propylene glycol (PG), as well as the high ecotoxicity of urea, the DoD and commercial airports have switched to organic salts, such as potassium acetate and sodium or potassium formate, to be used as runway deicers and anti-icers. The acetate and formate deicers have a much lower BOD and COD than urea or PG and are significantly cheaper, but are unacceptably corrosive to aircraft components. Furthermore, based on recent testing by the Air Force Research Laboratory (AFRL), their compatibility with advanced DoD aircraft is questionable.
The objective of the project was to develop and evaluate novel chemistries to formulate runway deicing fluids (RDF) from low-cost bio-based raw materials, while simultaneously improving the environmental, materials compatibility, and performance properties without increasing lifecycle deicer costs.
Battelle Memorial Institute partnered with the Department of Energy’s Pacific Northwest National Laboratory (PNNL), the Air Force Research Laboratory (AFRL), and the Air Force Aeronautical Systems Center (ASC) to develop an advanced RDF. The team completed the testing to determine how to alter the tail end of the well established process for transesterification of fats and oils, now also used for biodiesel manufacture, to make feedstocks for RDFs that have improved properties. With application of appropriate additives, several RDFs that are less corrosive, less toxic, and less expensive than commercial runway deicers, and that meet strict environmental and deicing performance requirements, were formulated. These first generation RDFs were evaluated through physical property and performance testing. Next, crude, biobased feedstocks were purified to prepare second generation RDFs. Again, physical property and performance testing was performed and two preferred RDF formulations were selected from the group. Ultimately, Military Test Method Standard (MTMS) testing was performed and cost-benefit analyses were completed on these two RDF formulations to evaluate performance and life cycle costs relative to current RDF formulations.
The acute ecotoxicity of the biobased Battelle-RDFs, based on LC50 values for Daphnia magna and fathead minnows, was less than half of the ecotoxicity of the currently used RDFs due to the elimination of toxic corrosion inhibitors. Similarly, the chronic toxicity of the two preferred Battelle-RDFs were two to ten times lower than that of commercial RDFs.
The Michigan Technological University (MTU) performed deicing performance testing that covered ice melting, ice undercutting, and ice penetration. The Battelle-RDFs were comparable to the commercial RDFs.
Runway friction tests confirmed that Battelle-RDFs are as good as, and in some cases better, than commercial RDFs. In fact, the Federal Aviation Administration (FAA) issued a letter to all US airports approving the use of all the Battelle-RDFs it tested.
A key concern with potassium acetate and other organic-salt RDFs is their aggressive attack on carbon brakes, cadmium-plated parts, and some other materials included in the MTMS protocol. The Battelle-RDFs performed dramatically better than commercial RDFs with respect to compatibility with carbon brakes, cadmium-plated parts, and cast magnesium alloys. The preferred Battelle-RDFs were typically 75% less reactive to carbon, and are thus projected to improve brake life by one to four years. The financial impact of this improvement is dramatic and would accommodate significant RDF-cost increases.
Battelle-RDFs can reduce the environmental burden caused by the discharge of hundreds of thousands of pounds of mildly toxic and corrosive RDF waste each year and also eliminate the need for toxic corrosion control measures to be implemented and discharged as hazardous waste. Application of these bio-based RDFs will help address the requirements of Executive Order 13423, Strengthening Federal Environmental, Energy, and Transportation Management, and can yield a reduction of ecotoxicity by one-third compared to commercial RDFs.
A cost-benefit analysis of the two preferred Battelle-RDFs showed that the Battelle-RDFs were not only cheaper than commercial RDFs, but also reduced aircraft/airport maintenance costs. The combined annual savings for application in the U.S. alone was projected to be $20M to $55M. These two Battelle-RDFs are now being field-tested at Wright-Patterson Air Force Base under ESTCP project WP-200924: Demonstration of an Environmentally Benign and Reduced Corrosion Runway Deicing Fluid.