Increasing the electrical resistivity of ester lubricants, especially for use with hydrofluorocarbon refrigerants

A process for increasing the electrical resistivity of a first liquid mixture consisting essentially of esters of hindered polyole with organic carboxylic acids, which is used with chlorine-free hydrofluorocarbon refrigerants, said process comprising the steps of:

• (1) pretreating the first liquid mixture by alkali refining in order to reduce the acid value of the mixture;
• (2) mixing the pretreated liquid mixture with solid activated alumina so as to form a solid-liquid mixture and maintaining mutual contact between the liquid and the alumina in said solid-liquid mixture at a temperature of at least 30.degree. C. for a period of time;
• (3) separating the solid material from the liquid in the solid-liquid mixture formed at the end of step (2) to produce a second liquid mixture consisting essentially of esters of hindered polyols with organic carboxylic acids;
• (4) mixing the second liquid mixture with solid activated alumina so as to form a solid-liquid mixture and maintaining mutual contact between the liquid and the alumina in said solid-liquid mixture at a temperature of at least 30.degree. C. for a period of time;
• and
• (5) separating the solid material from the liquid in the solid-liquid mixture formed at the end of step (4) to produce a third liquid mixture consisting essentially of esters of hindered polyols with organic carboxylic acids and having an electrical resistivity that is higher than that of the first liquid mixture wherein the esters of said first liquid mixture include:
• (A) an ester made by reacting one or more of NPG, TMP, and PE with 2-ethylhexanoic acid;
• (B) a mixture of polyol ester molecules in which (1) at least about 45% of the alcohol moieties are those of TMP and a total of at least about 75% of the remainder of the alcohol moieties are selected from those of the group consisting of NPG, TMP and PE and (2) at least 70% of the acyl groups are straight-chain pentanoyl groups and at least about 75% of the balance of the acyl groups are those selected from the group consisting of butanol, 2-methylpropanoyl, 2-methylbutanoyl, and 3-methylbutanoyl;
• (C) a mixture of polyol ester molecules in which at least about 92% of the alcohol moieties are selected from the group consisting of the alcohol moieties derived from TMP, DTMP, PE and DPE and at least about 92% of the acyl groups are selected from the group consisting of the acyl groups of all the straight and branched chain monobasic and dibasic carboxylic acids with from four to twelve carbon atoms each, said alcohol moieties and acyl groups being further selected subject to the constraints that (a) a total of at least about 3% of the acyl groups in the mixture are acyl groups of i-C.sub.5 acid;
• (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than about 81;
• (c) not more than about 2% of the acyl groups in the ester mixture are part of acid molecules with more than two carboxyl groups each;
• and either (d) (1) a total of at least about 20% of the acid molecules in the mixture are one of the trimethylhexanoic acids at least about 90% of the alcohol moieties in the esters are those of PE;
• and not more than about 7.5% of the acyl groups in the ester mixture are dibasic;
• or (d) (2) at least about 2.0%, but not more than about 13%, of the acyl groups in the ester mixture are dibasic;
• and a total of at least about 82% of the monobasic acyl groups in the acid mixture have either five or six carbon atoms each;
• (D) a mixture of polyol ester molecules in which at least about 92% of the alcohol moieties are selected form the group consisting of the alcohol moieties derived from TMP, DTMP, PE, DPE, TPE and TTMP and at least about 92% of the acyl groups are selected subject to the constraints that (a) a total of at least about 5% of the acyl groups in the mixture are acyl groups of i-C.sub.5 acid;
• (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than about 1.56;
• (c) the % of the acyl groups in the mixture that contain at least nine carbon atoms, whether branched or not, is not greater than about 81;
• and (d) not more than about 2% of the acyl groups in the ester mixture are part of acid molecules with more than two carboxyl groups each;
• and either (d) (1) a total of at least, about 20% of the acid molecules in the mixture are one of the trimethylhexanoic acids;
• at least about 90% of the alcohol moieties in the ester are those of PE;
• and not more than about 7.5% of the acyl groups in the ester mixture are dibasic;
• or (d) (2) at least about 5.5%, but not more than 13.5% of the acyl groups in the ester mixture are dibasic;
• and a total of at least about 82% of the monobasic acyl groups in the acid mixture have either five or six carbon atoms each;
• (E) a mixture of polyol ester molecules in which at least about 92% of the alcohol moieties are selected from the group consisting of the alcohol moieties derived from TMP, DTMP, PE, DPE, TPE and TTMP and at least about 92% of the acyl groups are selected from the group consisting of the acyl groups of all the straight and branched chain monobasic and dibasic carboxylic acids with from four to twelve carbon atoms each, said alcohol moieties and acyl groups being further selected subject to the constraints that (a) a total of at least about 5% of the acyl group in the mixture are acyl groups of i-C.sub.5 acid;
• (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the % of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than about 1.56;
• (c) the % of acyl groups in the mixture that contain at least nine carbon atoms whether branched or not, is not greater than about 81;
• (d) not more than about 2% of the acyl groups in the ester mixture contain more than two carboxyl groups each ;
• and (e) at least about 13.8% of the acyl groups in the ester mixture are dibasic;
• and a total of at least about 82% of the monobasic acyl groups in the acid mixture have either five or six carbon atoms each;
• or
• (F) a mixture of polyol ester molecules in which at least about 85% of the alcohol moieties are selected from the group consisting of the alcohol moieties derived from PE, DPE and TPE, at least about 20% of the alcohol moieties are selected from the group consisting of the alcohol moieties derived from DPE and TPE, and at least about 92% of the acyl groups are selected from the group consisting of the acyl groups of all the straight and branched chain monobasic and dibasic carboxylic acids with from four to twelve carbon atoms each, said alcohol moieties and acyl groups being further selected subject to the constraints that (a) a total of at least about 3% of the acyl groups in the mixture are acyl groups of i-C.sub.5 acid;
• (b) the ratio of the % of acyl groups in the mixture that contain 8 or more carbon atoms and are unbranched to the e of acyl groups in the mixture that are both branched and contain not more than six carbon atoms is not greater than 1.56;
• (c) the % of acyl groups in the mixture that contain at least nine carbon atoms, whether branched or not, is not greater than about 81;
• (d) not more than about 2% of the acyl groups in the ester mixture are part of acid molecules with more than two carboxyl groups each;
• and (e) a total of at least about 20% of the acyl groups in the mixture are selected from the group consisting of the trimethylhexanoyl acyl groups and not more than about 7.5% of the acyl groups in the ester mixture are dibasic.