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Increasingly challenging international engine emissions reductions have resulted in some advances in engine emissions technologies that may motivate a change from the customary ethylene glycol and/or propylene glycol bases that have been the mainstay of engine antifreeze formulations for almost a century. The new engines' components, especially exhaust gas recirculation (EGR) devices, generate much greater thermal stress on the engine coolant. The oxidation of ethylene glycol and propylene glycol may be accelerated dramatically, resulting in coolant unsuitable for continued use in as little as a few months. The industry has been working towards extended engine coolant service intervals1,2,3,4, with some recommendations for service extended to as long as five years. It follows, therefore, that a requirement for coolant change at four to six month intervals (due to accelerated oxidation & aging) would be unacceptable to vehicle owners.

Reverse Osmosis (R/O) is reported by Huff' to offer a high volume engine coolant recycling process with very significant purification capabilities. The higher productivity per investment dollar, in spite of the initial capital cost of the equipment, may present the best opportunity for a practicable commercial recycling method capable of producing coolant that compares favorably with new (virgin) coolant. A system described by Huff has, since its introduction in 1990, been re-invented and re-engineered to optimize both the quality and cost effectiveness of the process. This paper describes many of the technical obstacles in the evolution that had to be overcome, and reports the state-of-the-art in commercial reverse osmosis coolant recycling technology. Process improvements that affected coolant quality and productivity are recorded.

In the late 1980s engine coolant recycling technologies were developed in response to a temporary but significant increase in the cost of ethylene glycol. Among these technologies was the adaptation of reverse osmosis water desalination processes by Stanadyne Automotive Corp.1 The technical paper describing the reverse osmosis (R/O) technology reports that the process efficiently recovers ethylene glycol and water in a sufficiently pure state to allow its use as a base fluid to reblend into engine coolant. Data generated in standard ASTM bench tests has demonstrated the capability of properly reinhibited R/O recycled engine coolant (ROREC) to comply with the performance requirements of accepted SAE, TMC, ASTM and OEM specifications. The technology has been applied commercially and this paper reports the operating experience of 15 users in Texas and California with diverse service applications. The experience has been very good.