JP4545422B2 - Method for producing ester for lubricating oil - Google Patents

Description

  The present invention relates to a method for producing an ester used as a base oil for lubricating oil.

  Conventionally, mineral oil, which is easily available, has been used as a base oil for lubricating oil. However, in recent years, mineral oils have improved lubricity and heat resistance in response to increasingly demanding conditions for lubricants, such as severer use conditions, increased energy-saving equipment, and reduced impact when diffused into the environment.・ Performance such as oxidation stability, low-temperature fluidity and biodegradability has become insufficient. Therefore, as a substitute for mineral oil, hindered materials such as neopentyl glycol, trimethylolpropane, pentaerythritol, etc., called POE (polyol ester) with excellent lubricity, heat resistance, oxidation stability, low-temperature fluidity, and biodegradability Alcohol esters have been used in lubricating base oils.

  Among these, the lubricating oil for refrigeration oil is required to be compatible with such a refrigerant as the refrigerant in the refrigeration machine has shifted to a hydrogen-containing chlorofluorocarbon refrigerant that does not contain chlorine. For example, Patent Document 1 discloses a hydrogen-containing fluorocarbon refrigerant lubricating oil mainly composed of an ester obtained from a raw material of a polyhydric alcohol having 15 or less carbon atoms, a trihydric or higher polyhydric acid and a monovalent fatty acid having 2 to 18 carbon atoms. Is disclosed.

On the other hand, hindered alcohol esters usually obtained by reacting industrial grade polyhydric alcohols with carboxylic acids are colored and the acid used in the reaction remains, so decolorization and deoxidation treatment Is given. Conventionally, from a reaction product containing an ester obtained by reacting a polyhydric alcohol and a carboxylic acid, deoxidization is performed under reduced pressure or the like, and then an adsorbent for decolorization and an adsorbent for deoxidation are collectively It is added to decolorize and deoxidize. Patent Document 2 proposes a method using pentaerythritol having a high monopentaerythritol content as a raw material in order to obtain a base oil for refrigerating machine oil having a low degree of coloring.
Japanese Patent Laid-Open No. 3-1278992 JP 2001-107067 A

  However, in the conventional method, if the adsorbent is reduced for cost reduction, the decoloring effect and the deoxidation effect are remarkably lowered, so that it is difficult to reduce the cost. Although the method of Patent Document 2 satisfies the requirement for decolorization to some extent, no specific mention is made regarding deoxidation or acid value reduction.

  An object of the present invention is to provide a simple method for producing an ester for lubricating oil that can achieve sufficient deoxidation and decolorization even if the amount of adsorbent used is reduced.

The present invention
(1) A step of obtaining a reaction product containing an ester by reacting an aliphatic polyhydric alcohol (A) and a saturated aliphatic monocarboxylic acid (B) [hereinafter referred to as step (1)],
(2) a first deoxidation step (hereinafter referred to as step (2)) for removing unreacted saturated aliphatic monocarboxylic acid from the reaction product obtained in step (1);
(3) A step of decolorizing the reaction product deoxidized in step (2) [hereinafter referred to as step (3)],
(4) Second deoxidation step for removing unreacted saturated aliphatic monocarboxylic acid from the reaction product decolorized in step (3) [hereinafter referred to as step (4)]
The present invention relates to a method for producing an ester for a lubricating oil.

  In the production method of the present invention, decolorization and deoxidation are sufficiently achieved, and the adsorbent, particularly the adsorbent for deoxidation, can be significantly reduced, thereby improving yield.

<Step (1)>
Step (1) comprises reacting aliphatic polyhydric alcohol (A) [hereinafter referred to as component (A)] and saturated aliphatic monocarboxylic acid (B) [hereinafter referred to as component (B)] to contain an ester. This is a step of obtaining a reaction product, which can be carried out according to a conventional method.

  As the component (A), specifically, neopentyl glycol, 2-ethyl-2-methyl-1,3-propanediol, 2-isopropyl-2-methyl-1,3-propanediol, 2,2- Diethyl-1,3-propanediol, 2-n-butyl-2-ethyl-1,3-propanediol, di (3-hydroxy-2,2-dimethylpropyl) ether, trimethylolethane, trimethylolpropane, penta Hindered polyhydric alcohols such as erythritol, ditrimethylolethane, ditrimethylolpropane, dipentaerythritol, or ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanedioe , 1,4-butanediol, 1,6-hexanediol, glycerin, diglycerin, and polyhydric alcohols and triglycerin. The number of carbon atoms of these aliphatic polyhydric alcohols is preferably 2 to 12 and more preferably 2 to 7 from the viewpoint of the viscosity of the produced ester. Moreover, the viscosity of the produced ester can be adjusted also by the hydroxy group in the molecule, and it is preferable from this point of view to contain 2 to 6 hydroxy groups in the molecule. Further, from the viewpoint of heat resistance, hindered polyhydric alcohols are excellent, and neopentyl glycol, trimethylolpropane, and pentaerythritol are particularly preferable. (A) 2 or more types can also be used together for a component.

  Specific examples of the component (B) include butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, and other straight-chain saturated aliphatic monocarboxylic acids, and isobutyric acid. , Isovaleric acid, pivalic acid, 2-ethylpentanoic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 3-ethylhexanoic acid, 2-methylheptanoic acid, cyclohexylacetic acid, 3,5,5-trimethylhexanoic acid, Examples include branched chain saturated aliphatic monocarboxylic acids such as 2-methyloctanoic acid. From the viewpoint of the low temperature fluidity of the resulting ester and the corrosiveness to metals, the number of carbon atoms is preferably 4 to 12, and more preferably 5 to 10. From the viewpoint of hydrolysis resistance, a carboxylic acid having a branched chain at the α-position of the carbonyl group such as 2-ethylhexanoic acid is preferable. (B) 2 or more types can also be used together.

  In the step (1), the reaction between the component (A) and the component (B) is preferably carried out under the condition that the component (B) becomes excessive. Specifically, (A) and (B) are B) / (A) = 1.05 to 1.4, more preferably 1.1 to 1.3 is preferably reacted from the viewpoint of increasing the reaction rate of esterification. In addition, this equivalence ratio is the number of carboxyl groups of (B) component [all (B) component in plural]] per one hydroxyl group of (A) component [when plural, all (A) component]. . Thus, by using the component (B) excessively, as will be described later, it becomes advantageous when the component (B) removed in the step (2) is recycled as (B) in the step (1). .

  If an example of reaction of (A) component and (B) component in a process (1) is given, when the equivalent ratio of (A) component and (B) component is the said range, reaction temperature 200-260 degreeC, The reaction time is 5 to 12 hours, and the reaction pressure is 13 to 101 kPa. For example, when the component (A) is pentaerythritol, the reaction is performed at 230 to 260 ° C. for 5 to 12 hours under a nitrogen stream, and the reaction is performed until the hydroxyl value becomes 5 mgKOH / g or less.

  Completion of the esterification reaction in the step (1) can be performed based on the hydroxyl value in the reaction product, and preferably the reaction is carried out until the hydroxyl value of the reaction product is 5 mgKOH / g or less.

<Step (2)>
In step (2), the unreacted component (B) is removed from the reaction product obtained in step (1). Specifically, the reaction product is treated under reduced pressure to remove the component (B) from the reaction product. The removed component (B) can be recovered and reused as a reaction raw material in step (1). In addition, although (B) component may be removed with the adsorbent which can adsorb | suck (B) component, the decompression process is more preferable at the point of removal efficiency and reuse of (B) component.

  The removal of the unreacted component (B) from the reaction product in the step (2) can be carried out based on the acid value in the reaction product, preferably the reaction product has an acid value of 0.3 mgKOH / g. In the following, it is preferable to perform deoxidation, preferably reduced pressure treatment, until it becomes 0.2 mgKOH / g or less, more preferably 0.1 mgKOH / g or less.

<Step (3)>
In step (3), the reaction product deoxidized in step (2) is decolorized. The decolorization is preferably performed by bringing an adsorbent having an ability to adsorb a dye (hereinafter referred to as a decolorizing adsorbent) into contact with the reaction product.

  Examples of the decolorizing adsorbent include activated carbon and activated clay. These decolorizing adsorbents are preferably used in an amount of 0.1 to 1.5% by weight based on the reaction product, depending on the degree of coloration of the reaction product.

  Moreover, it is preferable to carry out until the coloring degree of a reaction product becomes APHA100 or less. This APHA can be measured based on JIS K-0071-1 (the same applies hereinafter).

<Process (4)>
In step (4), a second deoxidation step is performed to remove unreacted component (B) from the reaction product decolorized in step (3). In the second deoxidation step, it is preferable to remove the component (B) by bringing an adsorbent capable of adsorbing the component (B) (hereinafter referred to as an acid adsorbent) into contact with the reaction product. Although it is possible to remove the component (B) from the reaction product by the reduced pressure treatment, the concentration of the component (B) in the reaction product is considerably reduced by the time the process (4) is reached. Use of an acid adsorbent is preferable to treatment in terms of removal efficiency.

  Examples of the acid adsorbent include activated alumina, activated clay, aluminum hydroxide, synthetic zeolite having anion exchange adsorption ability, ion exchange resin, and hydrotalcite. The acid adsorbent is preferably used in a proportion of 0.1 to 0.6% by weight with respect to the reaction product. When an acid adsorbent and a decolorizing adsorbent are added together as in a normal production method, the acid adsorbent is used at a ratio of 0.6 to 2.0% by weight with respect to the reaction product. According to the present invention, the amount of acid adsorbent used can be greatly reduced. Thereby, the amount of adsorption of the reaction product to the acid adsorbent is also reduced, and it is expected that the yield will be improved. In particular, industrially, the economic effect brought about by the improvement in the yield of the final ester is large, and the method of the present invention is extremely useful also in this respect.

  Through the second deoxidation step of step (4), an ester for lubricating oil is obtained. The acid value of the ester is preferably 0.02 mgKOH / g or less, and more preferably 0.01 mgKOH / g or less.

  The ester obtained by the production method of the present invention has a low degree of coloring and an acid value, and can be suitably used as a base oil for lubricating oil. For example, it can be used as a base oil for lubricating oil such as refrigeration oil, grease oil, hydraulic oil, and engine oil, and is particularly suitable for refrigeration oil. Lubricating oils, in particular, refrigerating machine oils can be produced by appropriately blending additives such as antioxidants and rust inhibitors with the esters as base oils.

Example 1
Into a 2 liter four-necked flask equipped with a stir bar, a nitrogen gas blowing tube, a thermometer and a water separator with a condenser, 272 g (2.0 mol) of pentaerythritol and 1382.4 g of 2-ethylhexanoic acid (9. 6 mol) (the carboxyl group of 2-ethylhexanoic acid is 1.20 equivalents per equivalent of hydroxyl group of pentaerythritol).

Next, the reaction was carried out at 250 ° C. for 10 hours while blowing nitrogen gas into the flask under stirring [Step (1)] to remove the distilled water. After completion of the reaction, the pressure was gradually reduced, and finally excess carboxylic acid was distilled off at 0.2 kPa for 1 hour, and further steaming was performed for 1 hour under a reduced pressure of 1 kPa [step (2)]. The amount of 2-ethylhexanoic acid recovered by distillation was 223 g, the acid value of the resulting ester mixture after distillation of the fatty acid was 0.06 mgKOH / g, and the hue was APHA300. Next, 6 g of activated carbon (Carborafine manufactured by Takeda Pharmaceutical Co., Ltd.) and 2 g of filter aid (Radiolite # 900 manufactured by Showa Chemical Co., Ltd.) are added to the resulting ester mixture and stirred at 1.3 kPa and 80 ° C. for 1 hour [step ( 3)] Subsequently, activated carbon and filter aid were removed using Toyo filter paper No2 filter paper. The acid value of the ester mixture as the filtrate was 0.06 mgKOH / g, and the hue was APHA15. Next, the filtrate was put into a 2 liter four-necked flask equipped with a stirring bar, a nitrogen gas blowing tube and a thermometer, and 6 g of an acid adsorbent (manufactured by Kyowa Chemical Industry Co., Ltd., trade name: KYOWARD 500SH). ) And 2 g of filter aid (same as above) were added, and the mixture was stirred at 1.3 kPa and 80 ° C. for 1 hour [Step (4)], followed by filtration in the same manner as described above. The acid value of the obtained ester was 0.004 mgKOH / g, the hue was APHA15, and the kinematic viscosity was 44.34 mm ² / s (40 ° C.).

Example 2
Into a 2 liter four-necked flask equipped with a stir bar, a nitrogen gas blowing tube, a thermometer and a water separator with a condenser, 272 g (2.0 mol) of pentaerythritol and 691.2 g of 2-ethylhexanoic acid (4. 8 mol), 3,5,5-trimethylhexanoic acid 758.4 g (4.8 mol) (total of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid per 1 equivalent of hydroxyl group of pentaerythritol To 1.20 equivalents).

Next, while stirring, nitrogen gas was blown into the flask while reacting at 250 ° C. for 10 hours [Step (1)] to remove the distilled water. After completion of the reaction, the pressure was gradually reduced, and finally excess carboxylic acid was distilled off at 0.2 kPa for 1 hour, and further steaming was performed for 1 hour under a reduced pressure of 1 kPa [step (2)]. The total amount of 2-ethylhexanoic acid and 3,5,5-trimethylhexanoic acid recovered by distillation was 230 g. The acid value of the resulting ester mixture after the carboxylic acid was distilled off was 0.10 mg KOH / g, and the hue was APHA200. Met. Next, 6 g of activated carbon (same as in Example 1) and 2 g of filter aid (same as in Example 1) were added to the resulting ester mixture and stirred at 1.3 kPa and 80 ° C. for 1 hour [step ( 3)] Subsequently, activated carbon and filter aid were removed using Toyo filter paper No2 filter paper. The acid value of the ester mixture as the filtrate was 0.10 mg KOH / g, and the hue was APHA25. Next, the filtrate was put into a 2 liter four-necked flask equipped with a stirring bar, a nitrogen gas blowing tube and a thermometer, and 6 g of an acid adsorbent (same as in Example 1) and a filter aid (Example 1). 2 g was added and stirred at 1.3 kPa and 80 ° C. for 1 hour [Step (4)], followed by filtration in the same manner as described above. The acid value of the obtained ester was 0.007 mgKOH / g, the hue was APHA15, and the kinematic viscosity was 67.36 mm ² / s (40 ° C.).

Comparative Example 1
In the same manner as in Example 1, a reaction product was synthesized, and then excess carboxylic acid was distilled off. The acid value of the resulting ester mixture after the carboxylic acid was distilled off was 0.06 mgKOH / g, and the hue was APHA250.

Next, 6 g of activated carbon (same as in Example 1), 11 g of acid adsorbent (same as in Example 1), and 2 g of filter aid (same as in Example 1) are added to the resulting ester mixture. The mixture was stirred at 3 kPa and 80 ° C. for 1 hour. Subsequently, adsorbent activated carbon, acid adsorbent, and filter aid were removed using Toyo No. 2 filter paper. The acid value of the ester mixture as the filtrate was 0.01 mg KOH / g, the hue was APHA 20, and the kinematic viscosity was 44.51 mm ² / s (40 ° C.).

Comparative Example 2
The reaction product of Example 1 was synthesized in the same manner, and then excess carboxylic acid was distilled off. The acid value of the resulting ester mixture after the carboxylic acid was distilled off was 0.06 mgKOH / g, and the hue was APHA350.

Next, 10 g of acid adsorbent (same as in Example 1) and 2 g of filter aid (same as in Example 1) were added to the resulting ester mixture, and stirred at 1.3 kPa and 80 ° C. for 1 hour. Subsequently, the acid adsorbent and the filter aid were removed using No. 2 filter paper manufactured by Toyo Filter Paper. The acid value of the ester mixture as the filtrate was 0.02 mg KOH / g, and the hue was APHA200. Next, 6 g of activated carbon (same as in Example 1) and 2 g of filter aid (same as in Example 1) were added to the filtrate and stirred at 1.3 kPa and 80 ° C. for 1 hour. Filtration was performed in the same manner. The acid value of the obtained ester was 0.018 mgKOH / g, the hue was APHA80, and the kinematic viscosity was 44.53 mm ² / s (40 ° C.). In this example, the steps (3) and (4) in Example 1 are reversed (that is, the step (4) is performed first and then the step (3)).

Example 3
Except for using 272 g (2.0 mol) of pentaerythritol, 1152 g (8.0 mol) of 2-ethylhexanoic acid and 223 g (1.5 mol) of 2-ethylhexanoic acid recovered in Example 1, In the same manner as in Example 1, an esterification reaction was performed, excess fatty acid was distilled off, and decolorization and deoxidation processes were sequentially performed to obtain an ester. The acid value of the resulting ester mixture after the deoxidation step of step (2) was 0.08 mgKOH / g, and the hue was APHA300. Further, the acid value of the final ester after the step (4) is 0.005 mg KOH / g, the hue is APHA 10, and the kinematic viscosity is 44.28 mm ² / s (40 ° C.), which is equivalent to the case of using a new raw material. An ester was obtained.

Claims (9)

(1) A step of obtaining a reaction product containing an ester by reacting an aliphatic polyhydric alcohol (A) and a saturated aliphatic monocarboxylic acid (B) [hereinafter referred to as step (1)],
(2) A first deoxidation step of removing unreacted saturated aliphatic monocarboxylic acid from the reaction product by exposing the reaction product obtained in step (1) to a reduced-pressure atmosphere [hereinafter, step (2)],
(3) A step of bringing the reaction product deoxidized in step (2) into contact with activated carbon to decolorize (hereinafter referred to as step (3)),
(4) The reaction product decolorized in step (3) is activated alumina, activated clay, aluminum hydroxide, synthetic zeolite having anion exchange adsorption ability, ion exchange resin having anion exchange adsorption ability, and anion exchange adsorption ability. A second deoxidation step (hereinafter referred to as step (4)) for removing unreacted saturated aliphatic monocarboxylic acid from the reaction product by contacting with an adsorbent selected from hydrotalcites having
The manufacturing method of ester for lubricating oil which has these.   The process according to claim 1, wherein the acid value of the reaction product deoxidized in step (2) is 0.3 mgKOH / g.   The method according to claim 1 or 2, wherein (A) and (B) are reacted at an equivalent ratio of (B) / (A) = 1.05 to 1.4.   The manufacturing method according to any one of claims 1 to 3, wherein an acid value of the ester for lubricating oil is 0.02 mgKOH / g or less.   The production method according to any one of claims 1 to 4, wherein a saturated aliphatic monocarboxylic acid is recovered in step (2) and reused as (B) in step (1). The manufacturing method according to any one of claims 1 to 5, wherein in the step (3), the activated carbon is used at a ratio of 0.1 to 1.5% by weight with respect to the reaction product.   The production method according to any one of claims 1 to 6, wherein in the step (4), the adsorbent is used at a ratio of 0.1 to 0.6% by weight with respect to the reaction product.   The process according to any one of claims 1 to 7, wherein in the step (2), the reduced pressure treatment is performed until the acid value of the reaction product becomes 0.3 mgKOH / g or less.   The production method according to any one of claims 1 to 8, wherein in step (3), decolorization is performed until the coloring degree of the reaction product becomes APHA 100 or less.