Lubricant base stock

Abstract

The present invention relates to a lubricant base stock, a lubricant composition, a method of lubricating an object and the use of a lubricant base stock. The lubricant base stock comprises a first ester which is the reaction product of: a first polyol comprising at least 3 hydroxyl groups; a first mono-carboxylic acid comprising from 4 to 18 carbon atoms; and a poly-carboxylic acid comprising at least 2 carboxyl groups and comprising from 20 to 60 carbon atoms. The lubricant base stock also comprises a second ester which is the reaction product of: a second polyol comprising at least 3 hydroxyl groups; and a second mono-carboxylic acid comprising from 4 to 18 carbon atoms.

Claims

1. A lubricant base stock for a food-safe lubricant composition, comprising: a. a first ester which is the reaction product of: i. a first polyol comprising at least 3 hydroxyl groups; and ii. a first mono-carboxylic acid comprising from 4 to 18 carbon atoms; and iii. a poly-carboxylic acid comprising at least 2 carboxyl groups and comprising from 32 to 60 carbon atoms, wherein the poly-carboxylic acid comprises a dimer diacid; and b. a second ester which is the reaction product of: i. a second polyol comprising at least 3 hydroxyl groups; and ii. a second mono-carboxylic acid comprising from 4 to 18 carbon atoms, wherein the first ester has a kinematic viscosity value at 40 C. which is at least 6 times greater than that of the second ester.

2. A base stock according to claim 1, wherein the weight ratio of the first ester to the second ester is from 0.25:1 to 20:1.

3. A base stock according to claim 1, wherein at least one of the first polyol and the second polyol comprises a quaternary carbon atom.

4. A base stock according to claim 1, wherein at least one of the first polyol and the second polyol comprise at least one of: trimethylol propane, pentaerythritol and di-pentaerythritol.

5. A base stock according to claim 1, wherein the kinematic viscosity of the base stock at 40 C. is from 10 cSt to 600 cSt.

6. A lubricant composition for use in an incidental food-contact environment comprising a lubricant base stock according to claim 1.

7. A lubricant composition according to claim 6, further comprising at least one antioxidant.

8. A lubricant composition according to claim further comprising an additive package.

9. A lubricant composition according to claim 6, wherein the lubricant composition is a chain oil.

10. A method of lubricating an object comprising applying a lubricant base stock according to claim 1 to the object.

11. A method according to claim 10, wherein the object is exposed to a temperature of at least 200 C. for a period of time.

12. A method according to claim 11, wherein the period of time is at least 5 minutes.

13. A method according to claim 11, wherein the object is repeatedly exposed to a temperature of at least 200 C. over more than one heating and cooling cycle.

14. A method according to claim 10, wherein the object is a chain in a food-contact environment or food processing equipment.

15. A method of lubricating an object in proximity to food, comprising applying a lubricant base stock according to claim 1 to the object, wherein the object is in proximity to food.

16. A base stock according to claim 4, wherein the first polyol and the second polyol comprise at least one of: trimethylol propane, pentaerythritol and di-pentaerythritol.

17. A method of lubricating an object comprising applying a lubricant composition according to claim 6 to the object.

18. A base stock according to claim 1, wherein the first ester, the second ester, and/or the base stock has a hydroxyl value of at most 18 mg KOH/g.

Description

EXAMPLES

(1) The present invention will now be described further, for illustrative purposes only, in the following examples. All parts and percentages are given by weight unless otherwise stated.

(2) It will be understood that all tests and physical properties listed have been determined at atmospheric pressure and room temperature (i.e. about 20 C.), unless otherwise stated herein, or unless otherwise stated in the referenced test methods and procedures.

Example 1

Preparation of First Ester

(3) A reactor is used which is equipped with a reflux column for separation of condensation water and the distillates, a nitrogen sparge, and a decantor for separating organic in the condensate from water and returning the organic back to the reactor. A mixture of caprylic/capric acid first portion (120 g), dimer diacid (a C.sub.36 dimer dicarboxylic acid available ex Croda, 191 g), and trimethylol propane (TMP, 114 g), is added to the reactor. With agitation on, start nitrogen purge and heating. Once the reaction temperature reaches 180 C. reflux the reaction mixture. Raise temperature to 220 C. while separating water and returning unreacted acids to the reactor. Hold the reaction temperature at 220 C. for 3 hours. Charge the second portion of mixture of caprylic/capric acid (175 g). Hold the reaction temperature at 220 C. for additional 2-3 hours. Add TBT catalyst and apply partial vacuum 500 torr to 100 torr over 30 minutes. Hold the reaction at 210-220 C. for 2 more hours. Apply vacuum to the reactor to remove the excess acid by increasing the vacuum slowly to 20 torr. Hold the vacuum stripping at 220 C. for 2-3 hours. Break the vacuum with nitrogen. Once the reactor is filled with nitrogen, re-apply vacuum to the reactor to 20 torr or better. Hold the vacuum for 20-30 minutes. Repeat the last step for removing the residual acid, until Acid Number<0.3. Cool the product to 80 C., and discharge the product.

Example 2

Preparation of Second Ester

(4) A reactor is used which is equipped with a reflux column for separation of condensation water and the distillates, a nitrogen sparge, and a decantor for separating organic in the condensate from water and returning the organic back to the reactor. A mixture of caprylic/capric acid (1174 g) is added into the reactor. Withhold a small amount of the acid (15-20 ml) for use to aid the charge of the catalyst. With agitation on, charge TMP (305 g) into the reactor. Start nitrogen sparge after all TMP is charged. Heat the reactor to 140 C. Once the reaction temperature reaches 140 C., condensation water starts to come off. The reaction temperature rises slowly from 140 to 215 C. over 2 to 4 hours. The condensate separates into two phases clearly, and the acid (the top phase) can be easily recovered. Hold the reaction temperature at 215 C. With the aid of a small amount of the acid (15-20 ml), charge TBT catalyst into the reactor. Hold the reaction at 210-220 C. for 3 hours. Cool the reaction to 190 C. Apply vacuum to the reactor slowly to remove the excess acid. The acid starts to come off at about 560 mm Hg. Keep stripping the acid by increasing the vacuum slowly. Hold the vacuum stripping at 190 C. for 2 hours. Break the vacuum with nitrogen. Once the reactor is filled with nitrogen, re-apply vacuum to the reactor to 720 mm Hg or better. Hold the vacuum for 20-30 minutes. Repeat the last step for removing the residual acid.

Example 3

Preparation of Lubricant Base Stocks and Lubricant Compositions

(5) The first ester from Example 1 and the second ester from Example 2 were mixed as shown in Table 1 to prepare various lubricant base stocks for testing in the following examples.

(6) TABLE-US-00001 TABLE 1 Preparation of lubricant base stocks Lubricant Base Amount of first Amount of second Stock ester (wt %) ester (wt %) A 46 54 B 60 40 C 90 10

Example 4

Thin Film Testing of First and Second Ester Compared with Lubricant Base Stocks A to C

(7) To each of the neat first ester, neat second ester and lubricant base stocks A, B and C were added the antioxidants IRGANOX L06 (at 1.5 wt % treat rate) and VANLUBE 81 (at 1.5 wt % treat rate). The total antioxidant treat rate was 3 wt %. The formulated ester and antioxidant samples were then tested for heat resistance according to the following thin film test procedure.

(8) Thin film test procedure: 2 g of each sample was placed into separate smooth walled pre-weighted aluminum dishes (7 cm diameter). The samples were placed into a forced air oven at 250 C. After 8 hours of heating, the samples were taken out of the oven, allowed to cool down and weighed. This allowed the percentage weight loss of the initial sample to be calculated. To determine the residue deposited as a percentage of the initial sample, the dishes were inverted on a metal tray and placed into 70 C. oven for 1 hour to allow all liquid material to drain. Next, the dishes were weighed and the amount of residue deposited was determined by the difference between the empty dish weight and the measured weight. The amount of residue deposited when compared with the initial sample weight gives the percentage residue.

(9) The results of the thin film test are given in Table 2.

(10) TABLE-US-00002 TABLE 2 Thin film test results after 8 hours at 250 C. Sample formulated Physical State after 8 with antioxidant Weight Loss Residue hours at 250 C. First ester 43% 57% Solid Second ester 87% 13% Solid Lubricant base stock A 75% 10% Liquid Lubricant base stock B 62% 10% Liquid Lubricant base stock C 41% 10% Liquid

(11) The results shown in Table 2 indicate that the lubricant base stocks A, B and C are able to retain their liquid form after 8 hours at high temperature (250 C.) and so provide effective lubricant compositions in applications where high temperatures are employed, for example in food processing applications.

(12) It can be seen from Table 2 that there is a beneficial interaction between the first ester and the second ester in the lubricant base stocks A, B and C which improves their resistance to thermal and/or oxidative breakdown and polymerization. Both the neat first ester and the neat second ester samples have become solid after 8 hours at 250 C. i.e. they have been polymerized, degraded, or evaporated). In contrast the lubricant base stocks A, B and C all remain liquid i.e. they have resisted thermal and/or oxidative breakdown and polymerization. In addition, lubricant base stocks A, B and C each leave a lower residue (10%) after 8 hours when compared with the first ester (57%) or the second ester (13%) separately.

(13) Without being bound by theory, it is believed that at the elevated temperature of 250 C. there may be an ongoing trans-esterification process between the first ester and the second ester. The presence of the large dimer diacid group in the first ester may slow down the rate of the trans-esterification. The combination of the ongoing trans-esterification process with the rate slowing function of the dimer diacid improves the resistance to thermal and/or oxidative breakdown and polymerization of lubricant base stocks. A, B and C.

(14) Each feature disclosed herein may be replaced by alternative features serving the same, equivalent or similar purpose. Therefore, each feature disclosed is one example only of a generic series of equivalent or similar features.