Refrigeration oil and compositions with carbon dioxide refrigerant
View Patent ↗Lubricant compositions comprising certain mixtures of esters of pentaerythritol, di-pentaerythritol, tri-pentaerythritol and higher pentaerythritol oligomers are ideally suited for use with CO 2 as refrigerant in heat transfer devices provided that at least 30% by weight of the esters are esters of pentaerythritol oligomers containing 4 or more pentaerythritol monomer units and wherein a majority of the alkylcarboxylate groups are straight chain C 3-6 alkanoyl groups, such as n-pentanoyl. Said mixture of alkylcarboxylate esters are shown to not only have higher than expected viscosity and exceptional CO 2 miscibility, but also possess excellent lubricity, film building properties and load bearing properties even as part of a lubricant/CO 2 solution.
1. A working fluid for a heat transfer device comprising
i) CO 2 as a refrigerant, and
ii) a polyol ester lubricant composition having a viscosity index of 130 or higher comprising a mixture of esters of formula I
wherein n is an integer of from 1 to 20,
each R is independently an alkyl carbonyl of from 5 to 10 carbon atoms,
each R 1 is independently selected and is either a group R or a substituent of formula II:
and wherein from 70% to 100% of all R groups in the mixture of compounds of formula I are selected from isomers of alkyl carbonyl groups of 5 carbon atoms, at least 50% of all groups R in the compounds of formula I present in the working fluid are n-pentanoyl, and wherein the polyol ester lubricant composition ii) comprises:
a) from 20 to 45 wt % compounds of formula I wherein n is 1 and each R 1 is independently selected and is a group R,
b) from 15 to 20 wt % compounds of formula I wherein n is 2 and each R 1 is independently selected and is a group R,
c) from 10 to 15 wt % compounds of formula I wherein n is 3 and each R 1 is independently selected and is a group R, and
d) from 30 to 55 wt % compounds of formula I which are pentaerythritol oligomers of 4 or more pentaerythritol monomer groups.
2. The working fluid according to claim 1 wherein at least 70% of all R groups in the mixture of compounds of formula I are n-pentanoyl.
3. The working fluid according to claim 1 further comprising in addition to components i) and ii), a hydrocarbon refrigerant, halocarbon refrigerant, ammonia, mineral oil, poly-α-olefin, alkylbenzenes, carboxylic acid ester other than a compound of formula I, polyether, polyvinyl ether, perfluoropolyether, phosphoric acid ester or mixture thereof.
4. The working fluid according to claim 1 comprising a halocarbon refrigerant selected from the group consisting of carbon tetrafluoride (R-14), difluoromethane (R-32), 1,1,1,2-tetrafluoroethane (R-134A), 1,1,2,2-tetrafluoroethane (R-134), pentafluoroethane (R-125), 1,1,1-trifluoroethane (R-143A) and tetrafluoropropene (R-1234YF).
5. The working fluid according to claim 1 further comprising one or more antioxidant, extreme-pressure additive, antiwear additive, friction reducing additive, defoaming agent, profoaming agent, metal deactivator, acid scavenger or mixture thereof.