JPS6320878B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lubricating oil composition for high-pressure gas compressors, and particularly to a lubricating oil composition suitable for use in reciprocating high-pressure gas compressors for producing polyethylene. The production of high-pressure polyethylene usually starts at 400 atmospheres.
The reaction is carried out at a reaction pressure of 3,500 atmospheres, during which ethylene is compressed to approximately 300 to 500 atmospheres by primary compression and to approximately 3,000 to 3,500 atmospheres by secondary compression. A technical problem with the reciprocating high-pressure gas compressor used for this is gas leakage due to wear of the metal packing surrounding the plunger. Generally, a bearing alloy such as lead bronze is used for the metal packing, and tungsten carbide is used for the plunger, and the surface is given an ultra-precision finish, and lubricating oil is supplied to the gap between the two to remove the oil film. It also maintains lubrication and gas sealing of friction surfaces. As the above-mentioned lubricating oil, polybuten alone or a mixture of it and white oil is generally used. The reason for using these non-polar hydrocarbon oils is that if they contain polar substances, they may get mixed into the ethylene circulation system, inhibiting the ethylene polymerization reaction, and reducing the quality of the polyethylene product. be. Polybutene is a polymer of previously purified butene gas and is a substantially pure aliphatic hydrocarbon oil. In addition, white oil is produced by extremely refining petroleum lubricating oil fractions using sulfuric acid to remove the sulfur content in the distillate.
Since aromatic hydrocarbons as well as chlorine and nitrogen are removed, if these are used, the above concerns will be resolved. However, under actual operating conditions, the metal packing wears out in a relatively short period of time, and gas leakage becomes significant, forcing the operation to be shut down or requiring inspection and maintenance. Since all of the lubricating oils are aggregates of nonpolar hydrocarbon molecules, their adsorption power to metal surfaces is weak, and the oil film breaks down as the metal packing and plunger slide, resulting in a so-called dry friction condition. In order to improve this defect, the inventor considered adding an extreme pressure additive consisting of a soluble polar substance to polybutene. This kind of polar substance must have properties such as not inhibiting the polymerization reaction of ethylene, not degrading the quality of polyethylene, and not decomposing its molecules under high temperature and high pressure. Nitrogen, phosphorus, sulfur, and chlorine compounds used in lubricating oils are unsuitable. As a result of examining compounds consisting of the three elements carbon, hydrogen, and oxygen, the inventor recognized the effectiveness of carboxyl and hydroxyl groups, and developed alkenylsuccinic acid and its half ester with a specific chemical structure. It was found to be effective as an extreme pressure additive when used in actual equipment. That is, the present invention uses at least one hydrocarbon oil selected from the group consisting of polybutene, white oil, and α-olefin oligomer as a base oil, and has the following general formula (1). (In the formula, n represents an integer of 12 to 30.) Straight chain alkenyl succinic acid represented by the following general formula (2) or (3) (In the formula, n represents an integer from 12 to 30, and R ³ is -
(CH ₂ ) ₂ -, - (CH ₂ ) ₃ - or - (CH ₂ ) ₂ -O-
Indicates a group represented by (CH ₂ ) ₂ --. The present invention relates to a lubricating oil composition for a high-pressure gas compressor, characterized in that it contains 0.05 to 5% by weight of at least one hydroxyl group-containing half ester represented by the following formula, or a mixture of the succinic acid and the half ester. Carbon number of alkenyl group, which is an extreme pressure additive, is 12-30
The linear alkenylsuccinic acid has the following structural formula and can be easily produced by a conventional method by reacting a linear α-olefin with maleic anhydride. Further, the hydroxyl group-containing half ester of succinic acid is represented by the following general formula (2) or (3). (In the formula, n represents an integer from 12 to 30, and R ³ is -
(CH ₂ ) ₂ -, - (CH ₂ ) ₃ - or - (CH ₂ ) ₂ -O-
Indicates a group represented by (CH ₂ ) ₂ --. ) This half ester is produced by reacting the alkenylsuccinic acid with at least one glycol selected from the group consisting of ethylene glycol, propylene glycol and diethylene glycol, or by reacting the alkenylsuccinic anhydride with alkylene oxide or polyethylene glycol. It can be obtained in a conventional manner by reaction with alkylene oxide. This extreme pressure additive strongly adsorbs to metal surfaces because the two carboxyl groups in formula (1) and the carbocasyl group and hydroxyl group in formulas (2) and (3) are located close to each other in the molecule. Its adsorption power is stronger than that of compounds with one polar group such as monohydric carboxylic acids or monohydric alcohols, so it exhibits excellent extreme pressure properties. Further, compounds in which two carboxyl groups of succinic acid are esterified or compounds having only two hydroxyl groups have poor adsorption power to metal surfaces and are unsuitable as extreme pressure additives. Even if a compound has two carboxyl groups, those in which they are not adjacent, such as dimer acid, have poor adsorption power to metal surfaces and are unsuitable as extreme pressure additives. Note that the half ester has the advantage of lowering the acid value of the extreme pressure additive and maintaining adsorption power to the metal surface. Since alkenyl groups have unsaturated bonds in their molecules, they have excellent affinity with hydrocarbon base oils such as polybutene, and are superior to alkyl groups in forming stable oil films. The number of carbon atoms in the alkenyl group is 12-30, preferably 12
-18. Extreme pressure properties are poor when the carbon number is less than 12, and 30
If it exceeds , it has poor oil solubility. When the number of carbon atoms is 18 or less, the oil solubility is particularly good. Because the alkenyl group is linear and the polar group is present at the end, extreme pressure additives stand on the metal surface.
Coupled with the above-mentioned affinity with hydrocarbon oils such as polybutene due to the limited number of carbon atoms in the alkenyl group, a stable oil film is formed. Branched alkenyl groups have poor compatibility with hydrocarbon oils, and the steric hindrance of the branched chains reduces the density of the extreme pressure additive on the metal surface, reducing its effectiveness. The oil film formed from the extreme pressure additive and hydrocarbon oil serves as a lubrication and gas seal between the metal packing and the plunger. In this case, unlike branched carbon atom chains such as propylene tetramer and polybutenyl groups, linear carbon atom chains have excellent lubricity, are resistant to mechanical action, and have extremely low molecular chain scission, so they can be used for long periods under high pressure. Can withstand continuous operation for a period of time. Also, linear carbon atom chains are less susceptible to degradation by heat and oxygen. The extreme pressure additive used in the present invention has extremely limited structural characteristics as described above, which makes it possible to achieve extreme pressure properties in lubricating oils used under harsh conditions, such as lubricating oils for reciprocating high-pressure gas compressors. It has clearly different effects from polybutenyl succinic acid derivatives, which are conventionally known as rust inhibitors or detergents and dispersants. The hydrocarbon oil used as the lubricating oil base oil is at least one type of hydrocarbon oil selected from the group consisting of polybutene, white oil, and α-olefin oligomer. These base oils have excellent lubricating oil properties, do not inhibit ethylene polymerization, and are harmless from a sanitary standpoint even if they are mixed into polyethylene products. Polybutene is obtained by polymerizing isobutylene obtained by naphtha decomposition etc. and a C ₄ hydrocarbon fraction containing 1-butene, 2-butene, etc. in the presence of a Friedel-Crafts type catalyst such as aluminum chloride. It is a liquid polymer and has an average molecular weight (Staudinger method) in the range of 470-2350, more preferably 470-1260. Polybutene in which the double bonds are substantially hydrogenated can also be used. White oil is a petroleum lubricating oil fraction that is extremely refined using sulfuric acid to remove sulfur, chlorine, nitrogen, and aromatic hydrocarbons, and its main components are isoparaffin and cycloparaffin. The kinematic viscosity at 100° C. (37.8° C.) is preferably 12 to 120 centistokes, more preferably 30 to 90 centistokes. The purity level of the white oil must be JISK2231 liquid paraffin grade or higher, and it is particularly preferable that the white oil meets the requirements of the Japanese Pharmacopoeia. When using a mixture of polybdenum and white oil, the standard viscosity of the mixed oil is 250-300 centistokes (37.8°C), and it is preferable that the white oil be 200-350% by weight relative to 100% by weight of polybdenum. The amount of the extreme pressure additive of the present invention added to hydrocarbon oil is 0.05 to 5% by weight, preferably 0.05 to 1% by weight.
It is. Excellent properties as a lubricating oil for reciprocating high-pressure gas compressors, particularly for the production of polyethylene, are exhibited only when the extreme pressure additive and hydrocarbon oil are used in combination. In other words, the wear of the metallic packing is significantly reduced, allowing long-term continuous operation, and it has good thermal stability, does not decompose even under high pressure, does not inhibit the ethylene polymerization reaction, and is not mixed into the polyethylene product. However, it is harmless from a sanitary standpoint. The lubricating oil composition of the present invention may optionally contain an antioxidant such as BHT and other known additives. Below, a method for testing lubricating oil using the extreme pressure additive of the present invention will be described. [Test method] The effects observed in actual machine operation were also observed in laboratory wear tests. Although various methods such as the four-ball test are used as laboratory evaluation methods, the inventor has recognized that the ASTM D 2670 Farex test method is appropriate for reproducing the effects of actual machine operation. To give an overview of this test method, a cylindrical pin is held between two blocks with a V-shaped cross section, lubricant for the test is supplied, and the blocks are rotated while applying pressure to reduce the weight of the pin. Measure it to determine the amount of wear. The inventor added the following innovations to the test method in order to reproduce the results of the actual machine in the Farex test. (1) The pin is made of lead bronze alloy (PB12.6%, Ni0.33%, Zn1.14%, Fe0.03%,
The block was diamond-polished using the same tungsten carbide as the plunger. (2) Considering that the gap between the packing and plunger in the actual machine is an ethylene gas atmosphere, which means no oxygen, the pin and block were sealed in a nitrogen gas atmosphere. (3) The pressure applied to the block is 350 Ib (24.6Kg/cm ² )
The oil temperature is 70℃, the rotation time is 20 minutes, and the rotation speed is
The rate was set at 290 times/min. [Manufacturing Example] Next, a method for synthesizing alkenyl succinic acid and its ester will be shown as a manufacturing example, and evaluation results of lubricating oils to which the obtained synthetic substances have been added will be shown in Examples. Production Example 1 A four-necked flask equipped with a thermometer, stirrer, nitrogen gas blowing capillary tube, and backflow condenser is placed on a mantle heater. This was added to α-olefin (Mitsubishi Kasei Dialene 168, n-hexadecene).
Add 0.1 mol of maleic anhydride (a mixture of 57% n-octadecene and 43% n-octadecene), heat it to 180°C, and stir for 15 hours to stop the reaction. Next, the reactants were heated to 200℃ and 5mmHg for 3
Unreacted α-olefin and maleic anhydride are distilled and separated by distillation under reduced pressure for a period of time. 1/5 weight ratio of water was added to the residue and the mixture was stirred at 80° C. for 1 hour for hydration, and the water was further evaporated to obtain alkenylsuccinic acid of formula (1). Samples were taken at any time during the reaction, and the progress of the reaction was confirmed by IR analysis and GPC analysis. Production Example 2 Alkenyl ( _{C 12 ′} , C ₁₄ ′) Succinic acid was obtained. Production Example 3 Alkenyl ₍ C _{28 ′} ,
C ₃₀ ′) Succinic acid was obtained. Production Example 4 0.1 mol of alkenylsuccinic anhydride and 0.1 propylene glycol, which are intermediate products in Production Example 1.
mol was put into the same reaction vessel, 0.1 mol of polybutene was added thereto, and the mixture was stirred at 120°C for 15 hours to complete the esterification reaction. What you get is the following formula
(4) and (5) were half ester mixtures of hexadecenylsuccinic acid and octadecenylsuccinic acid. [Examples and Comparative Examples] Nisseki Polybutene LV-100 (Nippon Petrochemicals,
Average molecular weight 570, kinematic viscosity 240 centistokes at 37.8°C, pour point -25°C) in blank test 1, a mixed oil consisting of 100% by weight of this polybutene and 270% by weight white oil (High White 350 manufactured by Matsumura Oil Co., Ltd.) was tested in blank test 1. Test 2: Blank test 3 using α-olefin (PAOL 60 manufactured by BRAY OIL CO), which has a kinematic viscosity of 33.04 centistokes at 100°C (37.8°C).
Examples 1 to 12 are lubricating oil compositions obtained by adding the extreme pressure additives obtained in Production Examples 1 to 4 to these base oils. In Examples 5 and 12, BHT (2.6-di, tert. butyl-p-cresol) was added as an antioxidant. Examples 1 to 12 used the base oil of Blank Test 1, Examples 13 to 16 used the base oil of Blank Test 2, and Examples 17 to 18 used the base oil of Blank Test 3. In Comparative Examples 1 to 7, similar compounds having chemical structural characteristics different from conventional additives and the extreme pressure additive of the present invention were added to the above base oil. In each comparative example, the base oil of Blank Test 1 was used. In addition, the dimer acid of Comparative Example 4 was Empol 1010, Dimer Acid, manufactured by Emily Co., Ltd., USA, and had an acid value of 191~.
197. The amount of each additive added is shown in Table 1 in weight % based on 100 weight % of the base oil. The blank test, the sample oils of Examples 1 to 12, and Comparative Examples 1 to 7 were evaluated by the Farex test method, and the results are shown in Table 1 in terms of wear amount and wear marks. The wear marks indicate the surface condition of the pin after the completion of the Farex test, and are indicated by ◎, 〇, and × symbols in the table. ◎ indicates that fine scratches are aligned and there is no disorder; ○ indicates that thin scratches are aligned but disorder is observed; × indicates that the scratches have disappeared and many spots are observed. Regarding the surface condition, ◎ is the best, and × is the worst. The following is clear from Table 1. The lubricating oil composition of the present invention causes less wear on metal packing and improves the condition of wear marks. On the other hand, the monocarboxylic acids of Comparative Examples 1 to 3, the dicarboxylic acid of Comparative Example 4 and a dimer acid in which two carboxyl groups are separated, the alcohol of Comparative Example 5 with one hydroxyl group, the comparative example 6 and All of the succinic acids having a branched alkenyl group of No. 7 were inferior to Examples 1 to 12 in both the amount of wear and the wear marks. That is, the extreme pressure performance of the lubricating oil is significantly improved due to the specific structure of the extreme pressure additive of the present invention. 【table】

Claims (1)

[Claims] 1. At least one hydrocarbon oil selected from the group consisting of polybutene, white oil, and α-olefin oligomer is used as a base oil, and the following general formula (1) is used. (In the formula, n represents an integer of 12 to 30.) Straight chain alkenyl succinic acid represented by the following general formula (2) or (3) (In the formula, n represents an integer from 12 to 30, and R ³ is -
(CH ₂ ) ₂ -, - (CH ₂ ) ₃ - or - (CH ₂ ) ₂ -O-
Indicates a group represented by (CH ₂ ) ₂ --. 1. A lubricating oil composition for a high-pressure gas compressor, characterized in that it contains 0.05 to 5% by weight of at least one hydroxyl group-containing half ester represented by the following formula, or a mixture of the succinic acid and the half ester. 2. The lubricating oil composition according to claim 1, wherein the alkenyl group has 12 to 18 carbon atoms. 3. The lubricating oil composition according to claim 1, wherein the polybutene has an average molecular weight of 470 to 2350. 4. The lubricating oil composition according to claim 1, wherein the white oil has a kinematic viscosity of 12 to 120 centistokes (37.8°C). 5. The lubricating oil composition according to claim 1, wherein the base oil is a mixture of polybutene and white oil in an amount of 200 to 350% by weight of white oil based on 100% by weight of polybutene.