Polyalkylene glycol lubricant base oils with narrow molar mass distribution

Abstract

The present invention provides a process for preparing polyalkylene glycols by reacting a mixture of a mono- or polyhydric alcohol and a polyalkylene glycol prepolymer with a C2- to C4-alkylene oxide or a mixture of such alkylene oxides in the presence of a catalyst which comprises Zn3[Co(CN)6]2, the mono- or polyhydric alcohol having a molecular weight of up to 500 g/mol and containing from 1 to 20 carbon atoms and from 1 to 10 hydroxyl groups, and the polyalkylene glycol prepolymer being the addition product of a C2- to C4-alkylene oxide or of a mixture of such alkylene oxides in an amount of at least 500 g/mol to a mono- or polyhydric alcohol having from 1 to 20 carbon atoms and from 1 to 10 hydroxyl groups.

Description

Claims

1. A process for preparing polyalkylene glycols by reacting in an alkoxylation reaction a mixture of a mono- or polyhydric alcohol and a polyalkylene glycol prepolymer with a C2- to C4-alkylene oxide or a mixture of such alkylene oxides in the presence of a DMC catalyst which comprises Zn3[Co(CN)6]2, the mono- or polyhydric alcohol having a molecular weight of up to 500 g/mol and containing from 1 to 20 carbon atoms and from 1 to 10 hydroxyl groups, and the polyalkylene glycol prepolymer being the addition product of a C2- to C4-alkylene oxide or of a mixture of such alkylene oxides in an amount of at least 500 g/mol to a mono- or polyhydric alcohol having from 1 to 20 carbon atoms and from 1 to 10 hydroxyl groups.

2. The process as claimed in claim 1, in which a weight ratio of the mixture of polyalkylene glycol prepolymer and mono- or polyhydric alcohol before the alkoxylation reaction is between 99:1 and 60:40.

3. The process as claimed in claim 1, wherein the DMC catalyst is present in a concentration of 100-600 ppm.

4. The process of claim 1, in which the polyalkylene glycol prepolymer is an addition product of C2- to C4-alkylene oxide or a mixture of such alkylene oxides to an alcohol having from 2 to 12 carbon atoms and from 1 to 6 hydroxyl groups.

5. The process of claim 1, in which the polyalkylene glycol prepolymer of the formula 2 R5—O-(A-O)a—R4   (2)in whicha is from 5 to 70,(A-O) is a C2- to C4-alkoxy group, andR4 and R5 are each independently hydrogen or a C1- to C6-alkyl group, but at least one of the R4 or R5 radicals is hydrogen andcontains propylene oxide in a proportion of at least 20% by weight as a monomer.

6. The process of claim 1, in which the starter alcohol contains from 2 to 12 carbon atoms and from 1 to 6 hydroxyl groups.

7. The process of claim 1, in which the starter alcohol R′—OH is selected from monoalcohols of the formula R′—OH where R′═C1-C20-alkyl or R′═C1-C20-alkyl-(O—(C2-C4)-alkylene)n- where n=1, 2, or 3, diols of the formula HO—R2—OH where R2═C2-C6-alkylene, —(C2-C4)-alkylene-O—(C2-C4)-alkylene- or —(C2-C4)-alkylene-O—(C2-C4)-alkylene-O—(C2-C4)-alkylene-, glycerol, trimethylolpropane or pentaerythritol.

8. The process of claim 1, in which the C2-C4-alkylene oxide or mixture thereof is selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide, and mixtures thereof.

9. The process of claim 1, in which the alkoxylation reaction is effected at a temperature of 90-170° C.

10. A polyalkylene glycol prepared by a process comprising: reacting in an alkoxylation reaction a mixture of a mono- or polyhydric alcohol and a polyalkylene glycol prepolymer with a C2— to C4-alkylene oxide or a mixture of such alkylene oxides in the presence of a DMC catalyst which comprises Zn3[Co(CN)6]2, the mono- or polyhydric alcohol having a molecular weight of up to 500 g/mol and containing from 1 to 20 carbon atoms and from 1 to 10 hydroxyl groups, and the polyalkylene glycol prepolymer being the addition product of a C2— to C4-alkylene oxide or of a mixture of such alkylene oxides in an amount of at least 500 g/mol to a mono- or polyhydric alcohol having from 1 to 20 carbon atoms and from 1 to 10 hydroxyl groups.

11. The polyalkylene glycol as claimed in claim 10 which has a mean molar mass of from 700 to 50 000 g/mol and a kinematic viscosity at 40° C. of between 20 and 40 000 mm2/s.

12. The polyalkylene glycol as claimed in claim 10 which has a polydispersity D=Mw/Mn by GPC analysis of less than 1.25.

13. The polyalkylene glycol of claim 10, in which the volatile fractions determined to DIN 55649 are less than 1200 ppm.

14. A lubricant base oil comprising the polyalkylene glycol of claim 10.

15. An aqueous hydraulic fluid comprising the polyalkylene glycol of claim 10.

16. A lubricant base oil consisting of the polyalkylene glycol of claim 10, customary lubricant additives, antioxidants, and corrosion inhibitors.