Polyol esters

The boric and sulfuric acids are recycled to a HBF solution by reaction with CaF2. As a strong acid, fluoroboric acid is frequently used as an acid catalyst, eg, in synthesizing mixed polyol esters (29). This process provides an inexpensive route to confectioner s hard-butter compositions which are substitutes for cocoa butter in chocolate candies (see Chocolate and cocoa). Epichlorohydrin is polymerized in the presence of HBF for eventual conversion to polyglycidyl ethers (30) (see Chlorohydrins). A more concentrated solution, 61—71% HBF, catalyzes the addition of CO and water to olefins under pressure to form neo acids (31) (see Carboxylic acids). 

Other Fire-Resistant Hydraulic Fluids. Phosphate and more recently polyol esters are marketed as fire-resistant compounds. They are formulated with additives to control wear, oxidation, corrosion, and misting. Seal compatibdity and solvency characteristics of these fluids may be quite different from those of mineral ods. 

Polyol Esters. Polyol esters are formed by the reaction of an alcohol having two or more hydroxyl groups, eg, a polyhydric alcohol and a monobasic acid. In contrast to the diesters, the polyol in the polyol esters forms the backbone of the stmcture and the acid radicals are attached to it. The physical properties maybe varied by using different polyols or acids. Trimethylolpropane [77-99-6] C H O, and pentaerythritol [115-77-5] are... 

Dibasic acid esters and polyol esters are used as the bases in all aircraft jet-engine lubricants. They also are employed in aircraft greases that are subjected to wide temperature ranges. 

Synthetic oils have been classified by ASTM into synthetic hydrocarbons, organic esters, others, and blends. Synthetic oils may contain the following compounds diaLkylben2enes, poly(a-olefins) polyisobutylene, cycloaUphatics, dibasic acid esters, polyol esters, phosphate esters, siUcate esters, polyglycols, polyphenyl ethers, siUcones, chlorofluorocarbon polymers, and perfluoroalkyl polyethers. 

Polyol ester turbine oils currendy achieve greater than 10,000 hours of no-drain service in commercial jet aircraft with sump temperatures ranging to over 185°C. Polyol esters are made by reacting a polyhydric alcohol such as neopentyl glycol, trimethylol propane, or pentaerythritol with a monobasic acid. The prominent esters for automotive appfications are diesters of adipic and a2elaic acids, and polyol esters of trimethylolpropane and pentaerythritol (34). 

The newer HFC refrigerants are not soluble in or miscible with mineral oils or alkylbenzenes. The leading candidates for use with HFC refrigerants are polyol ester lubricants. These lubricants are derived from a reaction between an alcohol and a normal or branched carboxyflc acid. The most common alcohols used are pentaerythritol, trimethylolpropane, neopentjlglycol, and glycerol. The acids are usually selected to give the correct viscosity and fluidity at low temperatures. 

Ammonia has low miscibility in mineral oils, alkylbenzenes, and polyol ester lubricants, particularly at low temperatures. A typical ammonia system uses a coalescing separator that removes all oil in droplet or aerosol form and drains it back to the compressor. Sometimes separators are equipped with some means of cooling the discharge gas to condense any oil that is discharged as a vapor. 

Fuels, Lubricants, and Transmission Fluids. Polyol esters of neopentanoic acid have been used as high vacuum pumping hquids that are stable in chemically aggressive environments (70). Esters such as 6- -ani1inophenoxy)hexy1 pivalate are used as antioxidants for synthetic ester lubricants (71). PivaUc anhydride [1538-75-6] has been claimed as an antiknock additive for gasoline (72). 

Miscellaneous Commercial Applications. Dimer acids are components of "downweU" corrosion inhibitors for oil-drilling equipment (see Petroleum Corrosion and corrosion inhibitors). This may account for 10% of current dimer acid use (71). The acids, alkyl esters, and polyoxyalkylene dimer esters are used commercially as components of metal-working lubricants (see Lubrication). Dimer esters have achieved some use in specialty lubricant appHcations such as gear oils and compressor lubricants. The dimer esters, compared to dibasic acid esters, polyol esters and poly(a-olefin)s, are higher in cost and of higher viscosity. The higher viscosity, however, is an advantage in some specialties, and the dimer esters are very stable thermally and can be made quite oxidatively stable by choice of proper additives. 

R-401B (22/152a/124) MP66 AlliedSignal DuPont CFC-12 R-500 Blend (moderate glide) Alkylbenzene or polyol ester Alkylbenzene or polyol ester or in some cases mineral oiF Transport Refrigeration retrofits Retrofits including air conditioners dehumidifiers Close to CFC-12. Use where evap. temperature below -10 F. 

R-416A (124/134a/600) FRIGC FR-12 Intercool Energy CFC-12 Blend (small glide) Polyol ester Retrofits Lower pressure tha 134a at high ambiei... 

ICI HCFC-22 Pure fluid Polyol ester New equipment Lower capacity than HCFC-22,... 

Esters for lubricant applications are divided into five groups monocarboxylic acid esters (monoesters), dicarboxylic acid esters (diesters), glycerol esters, polyol esters, and complex esters. 

It has long been recognized that boron is required by higher plants [61, 62], and recent research indicates the involvement of boron in three main aspects of plant physiology cell wall structure, membrane function, and reproduction. In vascular plants, boron in solution moves in the transpiration stream from the roots and accumulates in the stems and leaves. Once in the leaves, the translocation of boron is limited and requires a phloem transport mechanism. The nature of this mechanism was only recently elucidated with the isolation of a number of borate polyol compounds from various plants [63-65]. These include sorbitol-borate ester complexes isolated from the floral nectar of peaches and mannitol-borate ester complexes from the phloem sap of celery. The implication is that the movement of boron in plants depends on borate-polyol ester formation with the particular sugar polyol compounds used as transport molecules in specific plants. 

Over a number of years, the early polyol esters, the formulas of some of which are shown below, appeared to he adequate lor coping with the increasing rigorous properties required for increasingly difficult lubrication problems. They continue to be used, but some professionals in the field have developed a number of proprietary formulations that are claimed to be superior to the polyuleslers. 

Neopemrl Polyol Esters. These polyesters are prepared by the esterification of. -carbon polyfunclional alcohols with mono-lunctional acids. Because the beta carbon of the starting alcohol does not contain hydrogen, these esters are superior in thermal stability to the diesters. Most of the oilier characteristics arc similar to those of the dicsters. As a result of their superior stability, the neopentyl esters are finding increasing use as the luhricuni for aircraft turbine engines. 

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