Premium air compressor oils require good thermal oxidation stability, superior deposit control, corrosion resistance, low foam, fast air release property and so on. Good oxidation stability means long oil service lifetime. Deposit (including varnish, sludge, coking, etc.) is a very common challenge for lubricant and a big enemy of air compressor reliability. Foaming can lead to high lubricant carry over as there is massive agitation in the sump of the air compressor. Rapid air release means reduced risk of cavitation, lower rates of fluid oxidation, improved efficiency of air compression and heat transfer. Rapid air release without excessive foaming also ensure reliable start-up and trouble free operation. The market for air compressor lubricants continues to demand longer lifetime and reduced coking and varnishing.
Current conventional air compressor oil technology includes mineral oils, synthetic hydrocarbons, esters, silicone oil and polyalkylene glycols (PAG). Mineral oils have the lowest cost but also the shortest life time and heavy deposit issues. Synthetic hydrocarbons and esters have much longer lifetime than mineral oils but still form varnish after long time operation. Silicone oil has the longest lifetime but also the highest cost. For decades, lubricant formulators have preferred PAGs for their high viscosity index, excellent deposit control and cooling efficiency among many other advantages. However, formulating with conventional PAGs face some limitations, as they are not miscible with mineral oil and synthetic hydrocarbons. Recently developed oil soluble PAGs (OSP) derived from butylene oxide provide compatibility with mineral oil and synthetic hydrocarbons while retaining the advantages of conventional PAGs. Formulators can use revolutionary OSP technology as an additive or cobase stock in other base oils to meet the high performance requirements of premium air compressor oils.
Compare to propylene oxide, the butylene oxide building block will bring positive performance impact to molecules in terms of pour point, hygroscopicity, elastomer compatibility, air release property and lubricity. The pour point improvement is due to the heterogeneous conformation of butylene oxide, which may lead to better low temperature performance. Hygroscopicity is correlated with carbon to oxide ratio and linked to the performance of corrosion protection, demulsibility and so on. Rapid air release property means reduced risk of cavitation, lower rates of fluid oxidation, improved efficiency of air compression and heat transfer. The butylene oxide derivative also exhibited a superior tribology profile than the tested corresponding propylene oxide homopolymer in the explored test condition. Significant better oil miscibility and elastomer compatibility should also be related to the carbon to oxide ratio.
Both lab data and field trial results of the OSP based RSAC oils are discussed. The field trials were conducted in several conventional air compressors to evaluate this new technology. All field trial samples show long lifetime and significantly less sludge weight in comparison to the benchmark samples. This new technology provides formulators an alternative solution to formulate premium air compressor oils.
Dr. Yaokun Han is Associate Research Scientist of Performance Lubricants at Dow Chemical China. He is responsible for Research and Development and also Technical Service of Performance Lubricants for Asia Pacific. He joined Dow Chemical in 2010. He built up the alkoxylation research capability at Dow China, developed three new industry lubricants and published more than 27 internal and external publications. He graduated at Nankai University with a Ph.D. in polymer in 2010. During his Ph.D. research, he published two patents and contributed articles at more than six international publications, including Macromolecules, Macromolecular Chemistry and Physics, Chemistry European Journal, Polymer, Langmuir, etc.
Oil soluble PAG, air compressor oil, deposit control
