What are Phosphate Esters?
WHAT ARE PHOSPHATE ESTERS?
There are many types of ester based fluids and
several are widely as used as lubricants, as hydraulic fluids and/or as lubricant additives. Examples include phosphate esters, diesters and polyol esters. These are used because they have performance and/or safety advantages over just mineral oil based fluids.
More details later but first, esters themselves have been described as compounds formed by replacing the hydrogen of an acid by a hydrocarbon radical of the ethyl type. The name was coined by the German chemist Gmelin and was some time ago because he died in 1853. Without getting to much into the chemistry, esters can be produced by the reaction of an organic or inorganic acid with an alcohol or with another organic compound
containing the hydroxyl (-OH) radical.
Chemically, phosphate esters can be called organic salts of orthophosphoric acid O=P(OH)3. They are also organophosphorous compounds, of which there are thousands. However, only one relatively small
group has found significant use as basestocks for synthetic fluids. These are the trisubstituted, or tertiary (t), phosphate esters with the general structure as follows;
O 4 P 4 OR”
Typically all three R groups are organic groups
containing four or more carbon atoms. Consequently, the important phosphate esters are either triaryl, trialkyl or aryl alkyl phosphates. The triaryl phosphates are the most significant which can have all three organic groups the same as in tricresyl or trixylenyl phosphate or they might be different as in isopropylphenyl diphenyl phosphate.
Originally the raw materials used included cresylic acids derived from coal tar and coking operations. While still
synthetic fluids, they have become known as “natural” phosphate esters. Examples include tricresyl or trixylenyl phosphate and GLCC (was FMC) fluids
such as Reolube Turbofluid 32XGT and 46XC. Those made from phenolics derived from other processes are known as “synthetic phosphate esters. Examples of
these are isopropylphenyl diphenyl phosphate and tertiary butylphenyl phenyl phosphate. The corresponding FMC fluids are Reolube Turbofluid 46 and Hyd 701 and 32B GT and 46B. The products with GT are for gas turbine driven equipment while the others are for hydraulic and/or electrohydraulic control applications. The different fluids are required because the various fluids have
pros and cons. However, they all share the characteristics of being fire
resistant and having high flash and fire points as well as high autoignition
temperatures and low heats of combustion. Plus, having good oxidative stability
and EP wear characteristics.
TYPES OF PHOSPHATE ESTER CONTROL FLUIDS
EHC-N (Stauffer EHC3)
Trixylenyl Phosphate Ester (TXP)
Lowest air release times, best hydrolytic stability and good
Turbofluid 46B (Durad EHB)
Butylated Phenol Phosphate Ester (TBPP)
Best bulk oxidation resistance.
Isopropyl Phenol Phosphate Ester (IPPP)
Beterr hydrolytic stability than butylated synthetics
Blend of Butylated Phenol and Trixylenyl Phosphate Ester
A compromise of the natural and the synthetic.
ICL Select Products, then
Fyrquel EHC or the product of interest.
This information is provided as a
service and makes no specific recommendations. For specifics contact us.
Limitorque is a trademark of Limitorque Corp., Selexsorb a trademark of Alcoa,
Turbofluid a trademark of GLCC, and VSG, MOV Long Life and MOV Extra are
trademarks of FluidCenter.
1. Fluids were originally from both
FMC and Ciba-Geigy but became FMC later Great Lakes Chemical Company and now
2. Fyrquel fluids were originally
from Stauffer, later Chesborough, Chesborough Ponds, Akzo and Akzo Nobel
Chemicals Inc. and then Supresta owned by a holding company but is now owned by
ICL (Israel Chemical Ltd.).
3. EHC stands for electrohydraulic
control systems that have servo-valves and HYD for control systems not having
servo-valves. Typically EHC fluids can be used in HYD systems but the converse
is seldom recommended. Also the listed fluids are not necessarily approved for
use so check with the turbine manufacturer.
4. Fyrquel EHC was a 100% TXP until
about the mid 80’s.
Additional Fluids: Castrol Anvol PE
46 XC is a TXP as appears to be Mobil Pyrogard 53T while Castrol Anvol PE 46
and Mobil Pyrogard 53 are synthetics or blends.