General Properties and Applications of Ester Fluids

Hydrolytic stability - Hydrolysis of esters to giye acids and alcohols is a facile reaction and can proceed at elevated temperatures in the presence of water. Hydrolysis of ester generates acid that can be very corrosive to metal components and can catalyze the base stock decomposition process. Therefore, hydrolytic stability of esters is an important issue. Much work has been carried out to improve the hydrolytic stability by varying the composition of acids and alcohols. Generally, esters made from aromatic acids or from more sterically hindered acids, such as 2-alkyl substituted acids or neo-acids, have improved hydrolytic stabilities. Proper branching of the acids protect the carbonyl ester function from the detrimental attack of water. The presence of impurity, such as trace acid or metal, can catalyze the decomposition and hydrolysis of ester. Compared to PAO or alkylaromatic base stocks, ester hydrolysis is always an issue of concern in many lubrication applications. 

Volatility - Ester fluids generally have lower volatility compared to PAO and mineral oil of comparable viscosities. A General volatility ranking for 

PE ester TMP ester dibasic ester PAO Group I or II mineral oil. 

Biodegradabilitv - By carefully choosing the molecular compositions, esters of excellent biodegradability can be produced. Generally, esters from more linear acids and alcohols have better biodegradability. 

Applications - Esters, both dibasic and polyol esters, are used as co-base stocks with PAO or other hydrocarbon base stocks in synthetic automotive engine lubricants and industrial lubricants. Polyol esters are used in aircraft tuibine oils due to their excellent thermal and oxidative stabilities, good lubricity, high VI and excellent low temperature properties ( -40°C). Esters are also used in synthetic compressor oils for ozone-ffiendly refngeration units. Because of their high biodegradability and low toxicity, esters are often the base oils of choice for many environmentally-aware 

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