SK271992A3 - High-pressure lubricant used preferably for high-pressure compressors - Google Patents

Abstract

A lubricant is a mixture comprising 40-60 percent by weight of white oil and/or 60-40 percent by weight of polybutene and/or polyisobutene, at least two usable lubricating power-improving additives being composed of by esters saturated fat acids and high-molecular-weight alcohol groups, whereof the overall content of the said additives is 0.1-3.0 percent by weight. At least one of the additives is composed of such ester with at least one free alcohol group. Unsaturated castor oil is a possible additive as well. The lubricant contains 0.05-0.1 percent by weight of at least one antioxidant agent, i.e. usable anisole derivative and/or usable derivative of a pentaerythritol ester and fat acid ester in an overall amount ranging from 0.05 to 0.1 percent by weight. The lubricant further contains a metal-binding deactivator, e.g. a succinimide derivative or amino acid derivative, e.g. N-acyl-sarcosan, in an overall content ranging from 0.005 to 0.5 percent by weight.

Description

Technical field

The invention relates to an edible lubricant which can be used in particular for high-pressure compressors. As is known, such an edible or edible and thus virtually non-toxic lubricant is required for the lubrication of machine parts, of which certain proportions, mostly only trace amounts, of lubricants can directly or indirectly enter the foodstuffs and foods. However, such practically non-toxic lubricants have the advantage that they are only slightly harmful to the environment, in comparison with the known lubricants, which often contain poisonous substances. Edible substances are either

(a) non - toxic and digestible, such as vegetable and animal fats and oils; or

(b) non-toxic since they are insoluble and chemically inert, such as liquid paraffin, and leave the organism in undigested form.

The invention relates to a lubricant consisting of a mixture consisting predominantly of a component of group b) in the form of a base lubricant mixture (base or base of a lubricant), as well as of edible substances of group a) in the form of additives.

This lubricant is particularly suitable for high-pressure compressors which are used to produce polyolefin (high-pressure polyethylene and high-pressure polypropylene) from corresponding gaseous monomers, these high-pressure compressors operating at pressures from 150 to 350 MPa. The films obtained from the high pressure polyethylene or high pressure polypropylene thus produced are also used for food packaging. The trace amounts of lubricant that may be present in these films may then partially enter these foods upon contact with the food that is packaged in such films. It is therefore essential that the lubricants used are edible.

BACKGROUND OF THE INVENTION

Edible lubricants of this type and for this purpose are known. DE-PS 2137590 discloses such a lubricant. It consists of white mineral oil and from 5 to 50%, preferably 20 to 40%, polybutene and 0.1 to 1.0%, preferably 0.1 to 0.5%, fatty acid with 16 to 18 carbon atoms and / or lower alkyl ester such as fatty acids as well as from 0.01 to 2% of an antioxidant (tert-alkyl-substituted phenol). The fatty acids or their lower alkyl esters, which are used in the lubricant described in DE-PS 2137590 as an additive for lubricity, consist of saturated or unsaturated aliphatic monocarboxylic fatty acids having 8 to 22 carbon atoms, as well as numerous lower alkyl esters; these alkyl esters contain up to about 5 carbon atoms and are, for example, methyl oleate, n-butyl stearate and the like esters.

SUMMARY OF THE INVENTION

In particular, the lubricant according to the invention is novel with respect to the ingredients contained and differs substantially from the lubricant described in the aforementioned DE-PS 2137590.

The nature and the amounts of additives contained are crucial to the quality of the lubricant. Even small deviations from the lubricant formulation can lead to a significant deterioration in its quality. For this reason, the inventive height of the present invention lies in particular in the fact that it has been necessary to investigate a very large number of different additives, in numerous combinations, mixing ratios and concentrations.

The lubricant of the invention differs substantially from that described in DE-PS 2137590 in that it does not contain any free fatty acids which, as is known, can lead to corrosion of the compressor components; the lubricant of the invention also contains no lower alkyl esters of fatty acids. The lubricant is also not composed of unsaturated fatty acids or their lower alkyl esters, for example oleic acid, linoleic acid or linolenic acid, and their lower alkyl esters whose chemical and thermal stability has not been shown to be optimal.

The lubricant according to the invention, on the other hand, contains, as an additive for lubricity, only saturated fatty acid derivatives in which there is, on the one hand, no free acid group (carboxyl group COOH) and, on the other hand, no unprotected double or multiple bond; moreover, the lubricants according to the invention are not esters of monohydric alcohols but only esters of higher edible alcohols. These higher edible alcohols include, for example

propylene glycol glycerin erythrit (2 alcohol hydroxy groups), (3 alcohol hydroxy groups), (4 alcohol hydroxy groups, 4 carbon atoms) pentaerythritol (4 alcohol hydroxy groups, 5 carbon atoms), hexitol (6 alcohol hydroxy groups),

mannitol, sorbitol and arabite.

An exception is castor oil (triglyceride), which contains ricinoleic acid (hydroxyoleic acid); this acid is not readily oxidizable and does not tend to be thermally, unstable as oleic acid, since it is protected by a (clonene) hydroxyl group it contains. In contrast to oleic acid and its ester, castor oil is chemically and thermally stable.

It goes without saying that the chemical and thermal stability of the additives used is crucial for the quality of the lubricant.

The lubricant according to the invention preferably contains more than one additive in the form of edible esters, in particular at least one additive in the form of a saturated fatty acid ester with 2-, 3-, 4- and 6-saturated alcohol, preferably castor oil being one component each.

The content of total lubricity enhancing additives is 0.1 to 3.0% by weight, based on the total weight of the finished lubricant.

Castor oil contains the following fatty acids:

up to 91%

up to 2% to 3% to 5% acid of ricinoleic acid, stearic acid and palmitic acid, dihydroxystearic acid, but also oleic and linoleic acid.

Since the latter two components are unsaturated acids, the addition of an antioxidant or antioxidants to the castor oil-containing lubricant is also contemplated to protect the hydroxyl group. Hardened (hydrogenated) castor oil is a hardened fat having similar properties to wax and melting in the temperature range of 84 to 86 ° C. Also in this form, castor oil can be used as a lubricity enhancing additive to the lubricant of the invention.

Said additives are better dissolved in the mineral lubricant base when the mixture of the lubricant base and the additives is heated, in particular to a temperature that is higher than the melting point of the highest melting additive. Thus, the practical limitation of the applicability of the additive to the lubricant of the present invention is too high a melting point of such an additive, since heating the mixture of lubricant base and additives to temperatures higher than, for example, 100 ° C is lengthy and unfavorable.

As an example of the lubricant enhancement formulation, the following mixture consisting of five such various additives:

Additive Ester z Content in finished (name) alcohol: grease fatty acids (% by weight)

Castor oil glycerin ricinoleic acid

0.05 - 0.5

Table (continued)

Pentaerythrit ester pentaerythritol stearic acid and palmitic acid 0,06 - 0.6 Ethyhexylpalmitát ethylhexyl palmitic acid 0,03 - 0.3 ethyl hexyl ethylhexyl stearic acid 0,03 - 0.3 Sorbitantrist. sorbitol stearic acid 0,03 - 0.3

The base lubricant oil blend (lubricant base) always consists of about 40 to 60% white oil and about 60 to 40% polybutene and / or polyisobutene. As an antioxidant (anti-aging agent), the lubricant of the present invention comprises 0.05 to 0.1% of a pentaerythritite compound or 0.05 to 0.1% of anisole compound or 0.05 to 0.1% of a mixture of the two compounds in a ratio of about 1 1, preferably a solidified 0.01 to 0.1% organic phosphite compound.

The lubricant according to the invention with ester-based additives has the following advantages:

1) the choice of edible saturated fatty acids in the acid residue of the ester achieves optimum thermal and chemical stability as well as improved lubricity and reduced wear of the lubricated components;

2) the same is achieved by selecting edible higher alcohols with 2 to 6 alcohol groups (hydroxyl groups) for the alcohol residue ester.

3) The preferred choice of more, but at least two components, one of which should preferably always be castor oil or hardened castor oil, achieves optimum lubricant performance over a wide range of temperatures, pressure and residence time in the lubricated compressor as well as optimum mechanical properties. parameters (including relative velocity of driven parts to lubricated parts, their material service, friction coefficients and other properties).

4) The lubricant additive content amounts to a total of 0.1 to 3.0% by weight irrespective of the number of lubricant additive components, so increasing the number of these components will not significantly increase the price of the lubricant.

5) Appropriate targeted choice of ester in the function of lubricant additives can achieve the desired physical and chemical properties, such as low melting point (freezing point), high boiling point and high flash point and low vapor pressure, lubricants according to the invention; polyhydric alcohols allow ester formation. with 1 to 2 6-saturated alcols with up to 6 alcohol groups, the free non-esterified alcohol groups providing some desirable properties such as low melting point, good solubility in the mineral oil base of the lubricant and high viscosity at elevated temperature.

6) The free acids which are possibly formed as additive degradation products (only in trace amounts), for example by oxidation of the alcohol hydroxyl group, can lead to the formation of neutral reacting edible esters with the other free alcohol groups; this ester formation is promoted by the fact that the esterification water produced is removed from the lubricant by evaporation due to the high temperature prevailing in the lubricant, thereby favorably shifting the chemical equilibrium in favor of ester formation (equilibrium constants, active mass act). Thus, free, non-esterified alcohol hydroxyl groups can provide aging protection to the lubricant by acid binding.

7) Chemically significant stable esters of higher saturated fatty acids undergo partial oxidation at higher temperatures and longer delays in the compressors, degrading at the carbon atom in the beta position, so that the oxidation product is always the closest lower fatty acid; for example, the stearate produces the same lubricant-active palmitate and the like. These fatty acid esters therefore constitute an intrinsic, built-in anti-aging protection and act in a manner similar to an antioxidant medium.

8) Due to the fact that the lubricant additives according to the invention may contain free alcohol groups in the ester, it is thus possible to eliminate the addition of alcohol, for example fatty alcohols, which do not always have the desired properties and which are often inedible.

9) Compared to the known alternative formation of polyesters esters, such as adipic acid and fruit acids, the lubricant additives according to the invention have the advantage that neutral ester groups remain after partial esterification, while free acid acids remain after partial esterification of polybasic acids. groups that are undesirable due to the risk of corrosion.

The lubricant further comprises a metal-binding deactivator in an amount of 0.005 to 0.5% by weight, based on the weight of the finished lubricant mixture, in the form of a succinimide derivative or an amino acid derivative, for example N-acyl sarcosan.

As a second example, this time concerning a mixture consisting of only two lubricity enhancing ingredients, the following recipe can be mentioned:

Ingredient Ester z Content in finished (name) alcohol: fatty acids: grease (% by weight)

Castor oil glycerin castor oil 0.12 - 1.25

Sorbitantrist. sorbit stearic acid 0.08 - 0.75

total

0.2

The lubricant according to the invention may optionally additionally contain, as a solvent for the additives and / or as a substance for dissolving the additives, any of the edible higher alcohols.

Claims (7)

1. Edible high-pressure lubricant, in particular usable for high-pressure compressors, consisting, on the one hand, of a lubricant base consisting of 40 to 60% polybutene and / or polyisobutene, and 60 to 40% of white oil, and on the other hand at least two lubricity enhancing additives as well as at least one antioxidant and at least one metal-binding deactivator, characterized in that the lubricity enhancing additives consist of at least two edible alcohol esters with at least two alcohol groups which are each esterified with at least one higher saturated fatty acid, the total content of lubricity enhancing additives being 0.1 to 3.0% by weight, based on the total weight of the finished lubricant. The edible high-pressure lubricant according to claim 1, characterized in that the at least one lubricity enhancing additive is formed by such an ester with at least one free alcohol (hydroxyl) group. The edible high-pressure lubricant according to claims 1 and 2, characterized in that the edible fatty acid residues in such esters are saturated and that additionally unsaturated castor oil, ricinoleic acid triglyceria and unsaturated hydroxyoleic acid may also be used as such an additive. The edible high-pressure lubricant according to claims 1 to 3, characterized in that the edible alcohols of such edible lubricating esters are preferably propylene glycol, glycerin, erythrit, pentaerythrit, arabite and hexites (mannitol, sorbitol), and their edible alcohol derivatives. 5th The edible high-pressure lubricant of claim 1 comprising 0.05 to 2.0% by weight, based on the total weight of the finished lubricant composition, of at least one known antioxidant composition consisting of an edible anisole derivative and / or an edible ester derivative. pentaerythrite and a fatty acid having a radical-binding amino and hydroxyl group and / or 0.01 to 1.0% by weight of the organic phosphite compound. The edible high-pressure lubricant according to claim 1, characterized in that it contains as additive from 0.005 to 0.5%, based on the finished lubricant mixture, of at least one known per se contact-acceptable metal-binding deactivator, in particular in the form of a succinimide derivative. or an amino acid derivative, preferably N-acyl-sarcosan. The edible high-pressure lubricant according to claims 1 to 6, characterized in that, if desired, it contains at least one known, edible, thermally and chemically stable higher mono- or polyhydric alcohol as an agent for dissolving the additives.