JP2007332134A - Production method of ester for lubricating oil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of an ester for lubricating oil of which, even when the ester product is stored for a long term, the acid value rises little and the ester is hardly degraded. <P>SOLUTION: The production method comprises an esterification process of reacting a polyhydric alcohol with a carboxylic acid and a deacidification process of removing unreacted carboxylic acid. The deacidification process comprises a separation step of catching and separating at least the unreacted carboxylic acid by using an inorganic acid scavenger and a salt elimination step of eliminating a carboxylic acid salt remaining in the ester after the separation step. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for producing an ester for lubricating oil including a deoxidation step for removing unreacted carboxylic acid after the reaction, and particularly relates to a method for producing an ester for lubricating oil that is suitably used as a lubricating oil for refrigerator 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 severe usage conditions, increased energy-saving equipment, and more advanced performance requirements for lubricating oils, such as reduced impact when diffused into the environment. Performances such as oxidation stability, low temperature fluidity, and biodegradability have become insufficient.

  Therefore, as a substitute for mineral oil, hinders such as neopentyl glycol, trimethylolpropane, pentaerythritol, etc., called POE (polyol ester) with excellent lubricity, heat resistance, oxidation stability, low temperature fluidity, and biodegradability Esters of alcohols 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 lubrication for hydrogen-containing chlorofluorocarbon refrigerants whose main component is an ester obtained by using a polyhydric alcohol having 15 or less carbon atoms and having 3 or more valences and a monovalent fatty acid having 2 to 18 carbon atoms as a raw material. Oil 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.

  For example, Patent Document 2 proposes a production 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 coloring degree. At that time, after deoxidizing from a reaction product containing an ester obtained by reacting pentaerythritol and carboxylic acid under reduced pressure, an adsorbent for decolorization and an adsorbent for deoxidation are added together. , Decolorization, deoxidation.

  Patent Document 3 discloses an aliphatic polyhydric alcohol and a saturated aliphatic monocarboxylic acid as 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. From the reaction product obtained by reacting with the acid, a first deoxidation step for removing unreacted acid, a step for decolorizing the deoxidized reaction product, and a step again from the decolorized reaction product. A method for producing an ester for a lubricating oil having a second deoxidation step for removing an acid has been proposed. Moreover, regarding the second deoxidation step, a process is disclosed in which a filter aid is added together with an acid adsorbent, and unreacted acid is filtered and separated by a filtration operation.

Japanese Patent Laid-Open No. 3-127992 JP 2001-107067 A JP 2005-170998 A

  However, as in the prior art described above, it is possible to obtain only when the carbon number of the saturated aliphatic monocarboxylic acid, which is a raw material, is increased only by the process of filtering and separating the unreacted acid after adsorption using an acid adsorbent. After long-term storage of the ester, it was found that the acid value increased and the ester deteriorated (the mechanism for increasing the acid value has not been known so far).

  Accordingly, an object of the present invention is to provide a method for producing an ester for a lubricating oil, in which even if the obtained ester is stored for a long period of time, the increase in acid value is small and the deterioration of the ester does not easily occur.

  In particular, the inventors of the present invention produced a saturated aliphatic monocarboxylic acid having a large number of carbon atoms because the temperature at the time of filtration and separation needs to be increased and the affinity with the ester may be increased. It was considered that the solubility of the salt in the filtrate increased, and after the obtained ester was stored for a long time, the acid was liberated from the remaining salt and the acid value increased. For this reason, when an attempt was made to adsorb and remove unreacted carboxylate contained in the filtrate of the separation step, it was found that even when stored for a long period of time, a product with little increase in acid value was obtained. The invention has been completed.

  That is, the method for producing an ester for lubricating oil according to the present invention comprises an esterification step for reacting a polyhydric alcohol and a carboxylic acid and a deoxidation step for removing unreacted carboxylic acid. The deoxidation step is a separation step in which at least unreacted carboxylic acid is captured by an inorganic acid scavenger and separated, and a salt removal in which the carboxylate remaining in the ester that has undergone the separation step is removed. Process.

  According to the production method of the present invention, unreacted carboxylic acid can be captured and separated / removed by an inorganic acid scavenger in the separation step, and further the carboxylate remaining in the ester that has undergone this step is removed. Therefore, even when the obtained ester is stored for a long period of time, an increase in the acid value due to the liberation of the acid is reduced, and the deterioration of the ester is less likely to occur.

  Hereinafter, embodiments of the present invention will be described in detail.

  The method for producing an ester for lubricating oil according to the present invention comprises an esterification step of reacting a polyhydric alcohol [hereinafter referred to as component (A)] with a carboxylic acid [hereinafter referred to as component (B)], and an unreacted carboxylic acid. And a deoxidation step for removing the.

  In the esterification step, an aliphatic polyhydric alcohol is preferably used as the component (A), and a saturated aliphatic monocarboxylic acid is preferably used as the component (B). It is a process to obtain and can be performed according to the conventional method.

  Specific examples of the aliphatic polyhydric alcohol include 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, Hindered polyhydric alcohols such as pentaerythritol, ditrimethylolethane, ditrimethylolpropane, dipentaerythritol, and tripentaerythritol, or ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, propylene glycol Le, dipropylene glycol, tripropylene glycol, 1,3-propanediol, 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 15 and more preferably 2 to 10 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. From this viewpoint, it is preferable that the molecule contains 2 to 8 hydroxy groups.

  Furthermore, from the viewpoint of heat resistance, hindered polyhydric alcohols are excellent, and neopentyl glycol, trimethylolpropane, pentaerythritol, and dipentaerythritol are particularly preferable.

  As the other component (A), alicyclic polyhydric alcohols, aromatic polyhydric alcohols and the like can be used. Two or more kinds of the above component (A) can be used in combination.

  Moreover, as a saturated aliphatic monocarboxylic acid which is a preferable component (B), a saturated aliphatic monocarboxylic acid having 5 to 24 carbon atoms can be used. Particularly, in a refrigerator oil application, when mixed with a refrigerant, From the viewpoint of ensuring high lubricity such as maintaining the viscosity at a suitable level, a saturated aliphatic monocarboxylic acid having 10 to 24 carbon atoms is preferred. When such higher fatty acids are used, as described above, the conventional method increases the solubility of the separation target in the ester, and the acid value tends to increase after long-term storage of the obtained ester. The production method of the present invention is particularly effective.

  Specific examples of the saturated aliphatic monocarboxylic acid having 10 to 24 carbon atoms include capric acid, isodecanoic acid, lauric acid, palmitic acid, stearic acid, isostearic acid, behenic acid, coconut oil fatty acid, palm oil fatty acid, and beef tallow fatty acid. One or more of these can be used, and a normal temperature (25 ° C.) liquid fatty acid (isodecanoic acid, isostearic acid, coconut oil fatty acid) is preferable for handling.

  Examples of saturated aliphatic monocarboxylic acids having a smaller carbon number include linear saturated aliphatic monocarboxylic acids such as butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, and pelargonic acid, isobutyric acid, isovaleric acid, and pivalic acid. 2-ethylpentanoic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 3-ethylhexanoic acid, 2-methylheptanoic acid, cyclohexylacetic acid, 3,5,5-trimethylhexanoic acid, 2-methyloctanoic acid, etc. And branched chain saturated aliphatic monocarboxylic acids.

  Moreover, it is also possible to use an unsaturated aliphatic monocarboxylic acid as the component (B), and in particular for refrigerating machine oils, high lubricity is ensured, such as keeping the viscosity moderate when mixed with a refrigerant. From the viewpoint, an unsaturated aliphatic monocarboxylic acid having 10 to 24 carbon atoms is preferable. As such an unsaturated aliphatic monocarboxylic acid, caproleic acid, undecenoic acid, lauroleic acid, tridecenoic acid, myristoleic acid, pentadecenoic acid, palmitoleic acid, heptadecenoic acid, oleic acid, basenic acid, gondoic acid and the like are preferable.

  As the other component (B), alicyclic monocarboxylic acid, aromatic monocarboxylic acid and the like can be used. Two or more kinds of the above component (B) can be used in combination.

  In the esterification step, the reaction between the component (A) and the component (B) is preferably performed under the condition that the component (B) is excessive from the viewpoint of increasing the reaction rate of the esterification. ) And (B) are preferably reacted at an equivalent ratio of (B) / (A) = 1.05 to 1.5, more preferably at an equivalent ratio of 1.1 to 1.3. .

  In addition, this equivalence ratio is the number of the carboxyl groups of the (B) component [all the (B) component in plural]] per one hydroxyl group of the (A) component [when plural, all (A) component]. .

  Thus, by using the (B) component excessively, as will be described later, it becomes advantageous when the (B) component removed by the deoxidation step is recycled as the (B) component in the esterification step.

  If an example of reaction of (A) component and (B) component in an esterification process is given, when the equivalent ratio of (A) component and (B) component is the said range, reaction temperature 200-260 degreeC, reaction The reaction pressure is 13 to 101 kPa for 5 to 12 hours.

  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. The hydroxyl value in the present invention is a value measured based on JIS K0070 7.2.

  Completion of the esterification reaction in the esterification step can be based on the hydroxyl value in the reaction product, preferably the hydroxyl value of the reaction product is 5 mg KOH / g or less, more preferably the hydroxyl value of the reaction product is The reaction is performed until 4 mgKOH / g or less.

  In the deoxidation step, the unreacted component (B) is removed from the reaction product obtained in the esterification step. As the treatment to be performed in the deoxidation step, at least an unreacted carboxylic acid is captured by an inorganic acid scavenger and separated, and a salt removal treatment to remove the carboxylate remaining in the ester that has undergone the separation step And, if necessary, a depressurizing process by depressurizing distillation, an azeotropic removing process by blowing water vapor, an evaporating process by heating, an adsorbing and removing process by an adsorbent, a precipitation removing process by salt formation and the like. These deoxidation treatments can be performed in any order, and a plurality of deoxidation treatments can be used in combination.

  Moreover, in this invention, in addition to a deoxidation process, the decoloring process using a decoloring agent etc. can be added as needed.

  In the present invention, preferably, first, the reaction product is subjected to a decompression treatment to remove the component (B) from the reaction product. The reduced pressure treatment can be performed by exposing the reaction product to a reduced pressure atmosphere. The removed component (B) can be recovered and reused as a reaction raw material in the esterification step, that is, the component (B).

  The removal of the unreacted component (B) from the reaction product in the reduced pressure treatment can be carried out based on the acid value in the reaction product, but the removal by the reduced pressure treatment increases as the carbon number of the (B) component increases. It becomes difficult. Therefore, when a C10-24 saturated aliphatic monocarboxylic acid is used as the component (B), the acid value in the reduced pressure treatment is used as a guideline, taking into account the relationship between the time required for the reduced pressure treatment and the subsequent treatment. The reduced pressure treatment is preferably performed until the acid value of the reaction product is 0.5 to 2 mgKOH / g, more preferably 0.7 to 1.5 mgKOH / g. At this time, for the purpose of improving the deoxidation efficiency, an azeotropic removal treatment by blowing water vapor may be used at the time of the decompression treatment.

  When a saturated aliphatic monocarboxylic acid having less than 10 carbon atoms is used, the acid value of the reaction product is preferably set to a value of 0.5 mgKOH / g or less as a guide for the reduced pressure treatment. The acid value in the present invention is a value measured based on JIS K0070 3.1.

  The pressure in the decompression treatment is preferably 0.05 to 3 kPa, more preferably 0.1 to 1 kPa, from the viewpoint of the treatment speed and ease of decompression operation.

  The production method of the present invention includes a separation step of capturing and separating unreacted carboxylic acid with an inorganic acid scavenger. Although this separation step can be performed on a reaction product that has not been subjected to reduced pressure treatment, performing the separation step on the reaction product that has been subjected to reduced pressure treatment increases the removal efficiency of the separation step. preferable. Moreover, it is more preferable to carry out this separation step while performing a decompression treatment from the viewpoint of increasing the removal efficiency by the combined treatment of both.

  In the separation step, the unreacted carboxylic acid can be separated by bringing an inorganic acid scavenger capable of capturing unreacted carboxylic acid into contact with the reaction product. The contact with the reaction product is possible by a method of passing the reaction product through the packed bed of the inorganic acid scavenger, but preferably after adding and mixing the inorganic acid scavenger to the reaction product, Solid-liquid separation is performed by filtration, centrifugation, sedimentation, etc.

  In the present invention, it is more preferable to perform solid-liquid separation by filtration operation from the viewpoint of motive energy and processing speed. During the filtration operation, a filter aid can be used to increase the separation efficiency. Moreover, the temperature of filtration operation is 60-100 degreeC from viewpoints, such as a processing rate and decomposition | disassembly suppression of an inorganic type acid capture agent, when C10-C24 saturated aliphatic monocarboxylic acid is used as (B) component. Is preferable, and 75-85 degreeC is more preferable.

  The inorganic acid scavenger generally contains a metal component, and captures unreacted carboxylic acid as a metal salt (including a complex), as an anion by intercalation, or by ion exchange. The carboxylic acid can be captured (including adsorption) by various mechanisms. In either case, a metal salt of a carboxylic acid may be generated, and the salt-formed product is dissolved in an ester although it is a trace amount and needs to be removed.

  Examples of such inorganic acid scavengers include hydrotalcites, activated alumina, activated clay, aluminum hydroxide, synthetic zeolite having anion exchange ability, and metal oxide ion adsorbents. Of these, hydrotalcites are preferable from the viewpoint of capturing ability of fatty acids, capturing capacity, and removability by filtration.

As hydrotalcite, general formula:
[(M ²⁺ ) _1−x (M ³⁺ ) _x (OH) ₂ ] ^{x +} [(A ⁿ⁻ ) _{x / n} · mH ₂ O] ^{x−
[M 2+} is a divalent ^{metal, M 3+} represents an anion of trivalent ^{metal, A n-n-valent} (n is an integer of 1 or more), x is in the range of 0 <x ≦ 0.33, m Is a positive number. The thing shown to] is mentioned.

In this general formula, examples of M ²⁺ include Mg ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ^2+, etc., and examples of M ³⁺ include Al ³⁺ , Fe ³⁺ , Cr ³⁺ , Co ³⁺ , In ^{3+ and the} like. Examples of ^{A n-} is ^{also, OH -, F -, Cl} -, Br -, NO 3 -, CO 3 -, SO 4 -, Fe (CN) 6 3-, CH 3 COO -, oxalic acid ion, Examples include salicylic acid ions, and particularly preferable examples include CO ₃ ⁻ and OH ⁻ .

Specific examples of hydrotalcites include natural hydrotalcite represented by Mg _0.75 Al _0.25 (OH) ₂ (CO ₃ ) _0.125 · 0.5H ₂ O, Mg _4.5 Al ₂ ( Synthetic hydrotalcite represented by OH) ₁₃ CO ₃ .3.5H ₂ O, Mg _4.3 Al ₂ (OH) _12.6 CO ₃ or the like.

  The metal oxide ion adsorbent is at least two selected from at least one selected from alkali metal and alkaline earth metal oxides and at least one selected from trivalent and tetravalent oxides. And an ion adsorbent containing as a main component an oxide.

Here, examples of the alkali metal oxide include Na ₂ O and K ₂ O, examples of the alkaline earth metal oxide include MgO and CaO, and examples of trivalent and tetravalent element oxides. , Al ₂ O ₃ , SiO ₂ , TiO _{2 and the} like.

As ion adsorbents mainly composed of at least two kinds of oxides selected from these oxides, specifically, 2.5 MgO.Al ₂ O ₃ .nH ₂ O, 2MgO.6SiO ₂ .nH ₂ O, Al ₂ O ₃ · 9SiO ₂ · nH ₂ O, Al ₂ O ₃ · Na ₂ O · 2CO ₃ · nH ₂ O, Mg _0.7 Al _0.3 O _1.15 , Mg _0.75 Al _0.25 O _{1. 125} etc. are mentioned.

  The inorganic acid scavenger is used in a proportion of 0.2 to 2% by weight, particularly 0.5 to 1% by weight, based on the reaction product, from the viewpoint of sufficiently capturing unreacted carboxylic acid. It is preferable.

  From the viewpoint of reducing the acid value of the product ester, the acid value of the separated product after the separation step is preferably 0.02 mgKOH / g or less, and more preferably 0.01 mgKOH / g or less.

  The production method of the present invention includes a salt removal step of removing a carboxylate remaining in the ester subjected to the separation step. When the unreacted carboxylic acid is captured and separated by an inorganic acid scavenger as in the present invention, the generated salt is not a little dissolved in the ester and remains without separation. This tendency is considered to increase as the carbon number of the aliphatic monocarboxylic acid increases. For this reason, it is considered that by carrying out the salt removal step after the separation step, the amount of carboxylate that easily liberates acid when stored for a long time is reduced in the ester, and an increase in acid value after long-term storage can be prevented.

  Carboxylate can be removed by adsorption using an adsorbent, extraction using water, removal using an ion exchange resin, etc., but adsorbing carboxylate using an adsorbent. Then, a salt removal step of removing this by solid-liquid separation is preferable.

  Solid-liquid separation can be performed by filtration operation, centrifugation, sedimentation separation, or the like. During the filtration operation, a filter aid can be used to increase the separation efficiency. Moreover, when using C10-24 saturated aliphatic monocarboxylic acid as a component (B), the temperature of the filtration operation is preferably 60 to 100 ° C, more preferably 75 to 85 ° C, from the viewpoint of processing speed. .

  Examples of the adsorbent capable of adsorbing a carboxylate include activated carbon and synthetic zeolite, and activated carbon is preferred from the viewpoint of selectivity of adsorption from an ester.

  Activated carbon is mostly carbonaceous charcoal and has high adsorptivity. Examples of the activated carbon include those obtained by treating with wood chloride, lignite, peat or the like with zinc chloride or phosphoric acid as an activator to dry distillation, or activating charcoal with steam. These are usually powdery or granular, and any of them can be used. As a result of the production process of activated carbon, chemically activated charcoal shows acidity, and inherently steam activated charcoal shows basicity.

  The adsorbent is added in an amount of 0.2 to 2% by weight, particularly 0.5 to 1% by weight, based on the reaction product after the separation step, from the viewpoint of sufficiently capturing the carboxylate in the ester. It is preferable to be used at a ratio of

  In the production method of the present invention, the acid value of the resulting ester for lubricating oil is preferably 0.02 mgKOH / g or less, more preferably 0.01 mgKOH / g or less. The acid value after storage for 2 months at room temperature (25 ° C.) is preferably 0.02 mgKOH / g or less, more preferably 0.01 mgKOH / g or less.

  The ester obtained by the production method of the present invention has a low 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. Particularly, it is suitable as a refrigerating machine oil for a carbon dioxide refrigerant, and when used together with a carbon dioxide refrigerant, lubricity, refrigerant compatibility, stability, electrical insulation and the like tend to be good. In addition, lubricating oil, especially refrigerating machine oil can be manufactured by mix | blending additives, such as antioxidant and a rust preventive agent, with this ester as base oil suitably.

  Examples and the like specifically showing the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.

(1) Acid value The acid value was measured based on JIS K0070 3.1.

(2) Hydroxyl value The acid value was measured based on JIS K0070 7.2.

Example 1
First, a stirrer, a thermometer, a nitrogen gas blowing tube, and a dehydrating tube with a condenser were attached to a 5 L four-necked flask. Next, 380 g of raw materials pentaerythritol and 3800 g of isostearic acid (1.15 equivalents of carboxyl groups with respect to 1 equivalent of hydroxyl groups of pentaerythritol) are put into the four-necked flask, and 0.3 NL / m / kg nitrogen gas is added. The temperature was raised to 250 ° C. under blowing, and the esterification reaction was performed until the hydroxyl value reached 3 mgKOH / g while removing the water in the four-necked flask out of the system.

  Next, the dehydration tube with a cooler is replaced with a deoxidation tube and a receiver, and unreacted isostearic acid is removed under reduced pressure until the acid value becomes 2.0 mgKOH / g under a reduced pressure of 0.1 kPa. Pentaerythritol ester was obtained by blowing 50 g per hour and performing azeotropic removal of isostearic acid until the acid value reached 1.0 mgKOH / g.

  Subsequently, the ester was cooled to 80 ° C., and 1.0% by weight of an inorganic acid scavenger (manufactured by Kyowa Chemical Industry Co., Ltd., hydrotalcite, trade name: KYOWARD 500SH) was added, and 0.7 kPa. The mixture was stirred for 1 hour under reduced pressure of No. 2 filter paper manufactured by Toyo Roshi and Radiolight # 900 manufactured by Showa Chemical Engineering, and the pentaerythritol ester having an acid value reduced to 0.01 mgKOH / g was obtained. Obtained (separation step).

  To this, 1.0% by weight of activated carbon (Carborafine manufactured by Takeda Pharmaceutical Co., Ltd.) was added, stirred for 1 hour under a reduced pressure of 0.7 kPa, and then No. 2 filter paper manufactured by Toyo Filter Paper and Radiolight # 900 manufactured by Showa Chemical Industry. And filtered at 80 ° C. to obtain a pentaerythritol ester from which the residual salt was removed (salt removal step). When this pentaerythritol ester was stored at room temperature for 2 months and the acid value was measured, it was 0.01 mg KOH / g, and no increase was observed.

Comparative Example 1
First, a stirrer, a thermometer, a nitrogen gas blowing tube, and a dehydrating tube with a condenser were attached to a 5 L four-necked flask. Next, 380 g of raw materials pentaerythritol and 3800 g of isostearic acid (1.15 equivalents of carboxyl groups with respect to 1 equivalent of hydroxyl groups of pentaerythritol) are put into the four-necked flask, and 0.3 NL / m / kg nitrogen gas is added. The temperature was raised to 250 ° C. under blowing, and the esterification reaction was performed until the hydroxyl value reached 3 mgKOH / g while removing the water in the four-necked flask out of the system. Next, the dehydrating tube with a cooler is replaced with a deoxidizing tube and a receiver, and unreacted isostearic acid is removed under reduced pressure until the acid value becomes 2.0 mgKOH / g under a reduced pressure of 0.1 kPa. Pentaerythritol ester was obtained by blowing 50 g per hour and performing azeotropic removal of isostearic acid until the acid value reached 1.0 mgKOH / g.

  Subsequently, the ester was cooled to 80 ° C., and 1.0% by weight of an inorganic acid scavenger (manufactured by Kyowa Chemical Industry Co., Ltd., hydrotalcite, trade name: KYOWARD 500SH) was added, and 0.7 kPa. The mixture was stirred for 1 hour under reduced pressure of No. 2 filter paper manufactured by Toyo Roshi and Radiolight # 900 manufactured by Showa Chemical Engineering, and the pentaerythritol ester having an acid value reduced to 0.01 mgKOH / g was obtained. Obtained (separation step). When this pentaerythritol ester was stored at room temperature for 2 months and the acid value was measured, it was 0.50 mg KOH / g, and a marked increase in the acid value was observed.

Example 2
In Example 1, except that isostearic acid was used instead of isostearic acid and esterification was carried out under the charging conditions shown in Table 1 (equivalent ratio 1.20), and the pressure under reduced pressure deoxidation conditions was 0.7 kPa, Pentaerythritol ester was obtained under exactly the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Comparative Example 2
In Comparative Example 1, except that isostearic acid was used instead of isostearic acid, the esterification reaction was carried out under the charging conditions shown in Table 1 (equivalent ratio 1.20), and the pressure under reduced pressure deoxidation conditions was 0.7 kPa, Pentaerythritol ester was obtained under exactly the same conditions as in Comparative Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Example 3
In Example 1, pentaerythritol ester was obtained under exactly the same conditions as in Example 1 except that the salt removal step was performed using zeolite (Mizusawa Chemical Co., Ltd., Y-520, pore size 5 mm) instead of activated carbon. . The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Comparative Example 3
In Example 3, pentaerythritol ester was obtained under exactly the same conditions as in Example 3 except that the salt removal step was not performed. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Example 4
In Example 1, instead of using Kyoward 500SH as an inorganic acid scavenger, Kyoward 2000W (manufactured by Kyowa Chemical Industry Co., Ltd., solid solution of MgO and Al ₂ O ₃ ) was used in an amount of 0.5% by weight. A pentaerythritol ester was obtained under exactly the same conditions as in Example 1 except that the removing step was performed. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Comparative Example 4
In Comparative Example 1, instead of using Kyoward 500SH as an inorganic acid scavenger, 0.5% by weight of Kyoward 2000W (Kyowa Chemical Industry Co., Ltd., solid solution of MgO and Al ₂ O ₃ ) was used. A pentaerythritol ester was obtained under exactly the same conditions as in Comparative Example 1 except that the removing step was performed. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Example 5
In Example 1, neopentyl glycol was used under exactly the same conditions as in Example 1 except that neopentyl glycol was used instead of pentaerythritol and the esterification reaction was carried out under the charging conditions shown in Table 1 (equivalent ratio 1.15). An ester was obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Comparative Example 5
In Comparative Example 1, neopentyl glycol was used under exactly the same conditions as Comparative Example 1, except that neopentyl glycol was used instead of pentaerythritol and the esterification reaction was carried out under the charging conditions shown in Table 1 (equivalent ratio 1.15). An ester was obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Example 6
In Example 1, trimethylolpropane was used under exactly the same conditions as in Example 1 except that trimethylolpropane was used instead of pentaerythritol and the esterification reaction was performed under the charging conditions shown in Table 1 (equivalent ratio 1.15). An ester was obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Comparative Example 6
In Comparative Example 1, trimethylolpropane was used under exactly the same conditions as in Comparative Example 1, except that trimethylolpropane was used instead of pentaerythritol and the esterification reaction was carried out under the charging conditions shown in Table 1 (equivalent ratio 1.15). An ester was obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Example 7
In Example 1, dipentaerythritol was used under exactly the same conditions as in Example 1, except that dipentaerythritol was used instead of pentaerythritol and the esterification reaction was carried out under the charging conditions shown in Table 1 (equivalent ratio 1.15). An ester was obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Comparative Example 7
In Comparative Example 1, dipentaerythritol was used under exactly the same conditions as in Comparative Example 1, except that dipentaerythritol was used instead of pentaerythritol and the esterification reaction was carried out under the charging conditions shown in Table 1 (equivalent ratio 1.15). An ester was obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 1 together with various conditions.

Example 8
In Example 1, pentaerythritol ester was prepared under exactly the same conditions as in Example 1 except that oleic acid was used instead of isostearic acid and the esterification reaction was performed under the charging conditions shown in Table 2 (equivalent ratio 1.15). Obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Comparative Example 8
In Comparative Example 1, pentaerythritol ester was prepared under exactly the same conditions as in Comparative Example 1, except that oleic acid was used instead of isostearic acid and the esterification reaction was carried out under the charging conditions shown in Table 2 (equivalent ratio 1.15). Obtained. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Example 9
In Example 1, except that oleic acid was used instead of isostearic acid, and trimethylolpropane was used instead of pentaerythritol, the esterification reaction was carried out under the charging conditions shown in Table 2 (equivalent ratio 1.15). Trimethylolpropane ester was obtained under exactly the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Comparative Example 9
In Comparative Example 1, except that oleic acid was used instead of isostearic acid and trimethylolpropane was used instead of pentaerythritol, the esterification reaction was performed under the charging conditions shown in Table 2 (equivalent ratio 1.15). Trimethylolpropane ester was obtained under exactly the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Example 10
In Example 1, except that oleic acid was used instead of isostearic acid and neopentyl glycol was used instead of pentaerythritol, the esterification reaction was carried out under the charging conditions shown in Table 2 (equivalent ratio 1.15). Neopentyl glycol ester was obtained under exactly the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Comparative Example 10
In Comparative Example 1, except that oleic acid was used instead of isostearic acid and neopentyl glycol was used instead of pentaerythritol, the esterification reaction was performed under the charging conditions shown in Table 2 (equivalent ratio 1.15). Neopentyl glycol ester was obtained under exactly the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Example 11
In Example 1, esterification was performed at 230 ° C. under the charging conditions shown in Table 2 (equivalent ratio 1.15) using capric acid instead of isostearic acid and neopentyl glycol instead of pentaerythritol. Except for the above, neopentyl glycol ester was obtained under the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Comparative Example 11
In Comparative Example 1, capric acid was used instead of isostearic acid, and neopentyl glycol was used instead of pentaerythritol, and the esterification reaction was performed at 230 ° C. under the charging conditions shown in Table 2 (equivalent ratio 1.15). Except for the above, neopentyl glycol ester was obtained under the same conditions as in Comparative Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Example 12
In Example 1, esterification was performed at 230 ° C. under the charging conditions shown in Table 2 (equivalent ratio: 1.15) using capric acid instead of isostearic acid and trimethylolpropane instead of pentaerythritol. A trimethylolpropane ester was obtained under exactly the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Comparative Example 12
In Comparative Example 1, capric acid was used instead of isostearic acid, and trimethylolpropane was used instead of pentaerythritol, and the esterification reaction was performed at 230 ° C. under the charging conditions shown in Table 2 (equivalent ratio 1.15). Except that trimethylolpropane ester was obtained under the same conditions as in Comparative Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Example 13
In Example 1, esterification was carried out at 240 ° C. under the charging conditions shown in Table 2 (equivalent ratio 1.15) using lauric acid instead of isostearic acid and neopentyl glycol instead of pentaerythritol. Except for the above, neopentyl glycol ester was obtained under the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Comparative Example 13
In Comparative Example 1, the esterification reaction was performed at 240 ° C. under the charging conditions shown in Table 2 (equivalent ratio 1.15) using lauric acid instead of isostearic acid and neopentyl glycol instead of pentaerythritol. Except for the above, neopentyl glycol ester was obtained under the same conditions as in Comparative Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Example 14
In Example 1, esterification reaction was performed at 240 ° C. under the charging conditions shown in Table 2 (equivalent ratio 1.15) using lauric acid instead of isostearic acid and trimethylolpropane instead of pentaerythritol. A trimethylolpropane ester was obtained under exactly the same conditions as in Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

Comparative Example 14
In Comparative Example 1, an esterification reaction was performed at 240 ° C. under the charging conditions shown in Table 2 (equivalent ratio 1.15) using lauric acid instead of isostearic acid and trimethylolpropane instead of pentaerythritol. Except that trimethylolpropane ester was obtained under the same conditions as in Comparative Example 1. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.
Comparative Example 15
In Comparative Example 1, instead of adding 1.0% by weight of the inorganic acid scavenger, 1.0% by weight of the same inorganic acid scavenger and 1.0% by weight of activated carbon (Takeda Kaburafin) are simultaneously added. Then, a pentaerythritol ester was obtained under exactly the same conditions as in Comparative Example 1 except that the acid removal step was performed. The final acid value and the acid value after being stored at room temperature for 2 months are shown in Table 2 together with various conditions.

  As shown in the results of Tables 1 and 2, according to the production methods of Examples 1 to 14, even when the obtained esters are stored for a long period of time, it is possible to produce an ester for a lubricating oil with little increase in acid value. it can. On the other hand, in the production methods of Comparative Examples 1 to 14 in which the salt removal step was not performed, when the obtained ester was stored for a long time, the increase in the acid value was remarkable. In addition, even in the production method of Comparative Example 15 in which the acid removal step was performed using an inorganic acid scavenger and activated carbon in combination, the removal of carboxylate was insufficient, and thus the obtained ester was stored for a long time. Like the other comparative examples, the increase in acid value was remarkable.

Claims (6)

A method for producing an ester for lubricating oil, comprising an esterification step of reacting a polyhydric alcohol and a carboxylic acid, and a deoxidation step of removing unreacted carboxylic acid,
A separation step in which the deoxidation step captures and separates at least unreacted carboxylic acid with an inorganic acid scavenger;
A method for producing an ester for lubricating oil, comprising: a salt removal step of removing a carboxylate remaining in the ester that has undergone the separation step.   The manufacturing method according to claim 1, wherein the salt removing step adsorbs the carboxylate using an adsorbent and then removes it by solid-liquid separation.   The method according to claim 1 or 2, wherein the polyhydric alcohol is an aliphatic polyhydric alcohol having 2 to 15 carbon atoms.   The method according to any one of claims 1 to 3, wherein the carboxylic acid is a saturated aliphatic monocarboxylic acid having 10 to 24 carbon atoms.   The production method according to claim 1, wherein the polyhydric alcohol and the carboxylic acid are reacted at an equivalent ratio of 1.05 to 1.5 (polyhydric alcohol / carboxylic acid).   The production method according to any one of claims 1 to 5, wherein an acid value of the obtained ester for lubricating oil is 0.02 mgKOH / g or less.