New Type Lube Oil for HFC-134a Compressor System

In order to find proper lubricants for HFC-134a compressor system, many polar compounds have been synthesized and evaluated. Among such compounds, polyalkylene glycol (PAG) derivatives and carboxylates (esters) have been identified as candidates for car air· conditioners and for refrigerators respectively.',.') However, it is dear that these amdidates have weaknesses: PAGs • demonstrate poor miscibility of high viscosity types and high water absorption. Esters • cause corrosion due to the generation of carboxylic: acid upon degradation. Our research has resulted in a new chemistry based on carbonates which overcome the shortcomings of the current candidate lube oils for both refrigerator and car air-conditioner compressors. INTRODUCTION The industrialized countries of the world have agreed to phase out production of chlorofiourocarbon (CFC) which aredepleting the Earth's ~none layer, by the year 2000. Due to the worRning conditions recorded this past year, President Bush recently decided to accelerate the ban by eliminating production in, and importation into the United States by December 31,1995. ·Among the possible CFC replacements, HFC-134a (hydrofluorocarbons) is the most likely candidate for replacing CFC-12 in car air conditioners and a good candidate for refrigerators. Conventional lubricants, mineral oils, which have been traditionally used in these applications with CFC-12, are not compatible with HFC-134a. In order to find an appropriQte lubricant for · HFC-134a compressor systems, many polar compounds have been synthesized and evaluated such as polyalkylene glycols (PAG's) derivatives and t::lrboxylates (esters). However, both PAG's and esters have some shortcomings. Specifically, esters cause corrosion problems due to their tendency to degrade to calboxylic acids and PAG's are not miscible enough with HFC-134a at high temperatures. In designing a new molecular structure for refrigerator and car air conditioner oil services, carbonates were considered because they have high polarity and do not degrade to acids. In introducing arbonates groups into molecules, we utilized dimethyl carbonate (DMC) " and alcohols as raw materials. Typical properties and characteristics of the products based on this new carbonate chemistry are described below. MOLECULAR STRUCTURE AND DIPOLE MOMENT Comparing the dipole moments of the arbonate, ester, ether, HFC-l34a and CFC-12, table 1 shows that the dipole moments of HFC-134a is higher than CFC-12. This means that the new base oils are to have high dipole moments to be miscible with HFC-134a. In order to increase the dipole moments of a base oil, it is necessary to bring polar groups into the molecular strncture. Since the polarity of carbonate group is large in comparison to the ester group and ethe.group (table I), the introduction of carbonllte group into the molecule is very effective way to obtain excellent miscibility with HFC-134a. Although it is possible to introduce other hetero atoms into the molecule, only oxygen was selected to avoid probleJJIIItic complications of side-reactions.