JP2012201833A - Ester synthetic oil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ester synthetic oil having high purity, high flash point, and excellent thermal stability and oxidation stability.
SOLUTION: A transesterification reaction between a fatty acid alkyl ester and neopentyl polyol is selected, and the reaction is continued until the full ester selectivity becomes 97.0% or more under the condition where the fatty acid alkyl ester is excessive. An ester synthetic oil comprising a polyol fatty acid ester obtained by topping removal until the residual ratio of fatty acid alkyl ester is 0.5% or less.

[Selection figure] None

Description

  The present invention relates to a synthetic oil comprising a polyol fatty acid ester synthesized from neopentyl polyol and a fatty acid alkyl ester.

  In recent years, due to increasing environmental awareness, attention has been focused on materials that use environmentally friendly plant-derived materials or that are easily biodegradable even when released into the environment. Above all, synthetic oils consisting of hindered polyol fatty acid esters with ester structures of fatty acid moieties and neopentyl polyol moieties such as neopentyl glycol, trimethylolpropane, and pentaerythritol are biodegradable compared to mineral oils made from petroleum. It is expected to be used because of its excellent properties, low viscosity, low pour point, and high flash point.

  These polyol fatty acid esters are usually produced by an esterification reaction of neopentyl polyol and a fatty acid, but it is difficult to remove unreacted fatty acids in the synthesis step, and the reaction rate remains at about 95%, There was a problem that unreacted neopentyl polyol and fatty acid remained and the purity could not be increased. In addition, the remaining unreacted fatty acid has a problem in that the flash point is lowered and the thermal stability and oxidation stability are deteriorated.

  An object of the present invention is to provide a synthetic oil composed of a polyol fatty acid ester that solves the conventional problems and has high purity, high flash point, and excellent thermal stability and oxidation stability.

  As a result of intensive research on the synthesis method and properties of hindered polyol fatty acid esters, the present inventors have selected a transesterification reaction between a fatty acid alkyl ester and neopentyl polyol, and under conditions where the fatty acid alkyl ester is excessive. React until the ester of fatty acid group bonded to all hydroxyl groups of neopentyl polyol, that is, the selectivity of full ester is 97.0% or more, and the remaining amount of unreacted fatty acid alkyl ester is 0.5% or less. It has been found that an ester synthetic oil characterized by containing a polyol fatty acid ester obtained by topping up to the above level solves the above problems.

  ADVANTAGE OF THE INVENTION According to this invention, the said various problems in the past can be solved, and the ester synthetic oil excellent in thermal stability and oxidation stability with high purity and a high flash point can be provided.

The present invention uses fatty acid alkyl esters and neopentyl polyol as synthetic raw materials. The fatty acid alkyl ester is one or two selected from alkyl esters of linear or branched saturated or unsaturated fatty acids having 6 to 22 carbon atoms and linear or branched lower alcohols having 1 to 4 carbon atoms. It consists of more than seeds.
Examples of the fatty acid alkyl esters include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, isostearic acid, oleic acid, linoleic acid, linolenic acid, erucic acid Methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, and isobutyl ester.
More specifically, methyl caproate, ethyl caproate, methyl caprylate, ethyl caprylate, propyl caprylate, isopropyl caprylate, butyl caprylate, methyl caprate, ethyl caprate, propyl caprate, isopropyl caprate, Butyl caprate, methyl laurate, ethyl laurate, propyl laurate, isopropyl laurate, butyl laurate, isobutyl laurate, methyl myristate, ethyl myristate, isopropyl myristate, butyl myristate, isobutyl myristate, myristic acid tert butyl, methyl palmitate, ethyl palmitate, isopropyl palmitate, methyl stearate, ethyl stearate, methyl isostearate, methyl oleate, ethyl oleate , Methyl behenate, methyl linoleate, methyl linolenate, methyl arachidate, methyl erucate and the like.
Of these, methyl ester of caprylic acid, capric acid, and lauric acid medium-chain saturated fatty acid is preferable in terms of excellent thermal stability and oxidation stability.

  Examples of the neopentyl polyol include neopentyl glycol, trimethylol ethane, trimethylol propane, and pentaerythritol. Among these, trimethylolpropane is preferable in that low temperature fluidity can be secured when the polyol fatty acid ester is synthesized.

The hindered polyol fatty acid ester obtained in the present invention has a full ester structure in which fatty acid groups are bonded to all the hydroxyl groups of neopentyl polyol. A structure in which a part of the hydroxyl group remains is called a partial ester. In the peak area obtained by analysis of the synthesized product by gas chromatography, the area ratio of the full ester is defined as the selectivity among the total amount of the synthesized full ester and partial ester, and this selectivity is 97.0% or more. It is required to be. Preferably, it is 98.0% or more. When the selectivity is less than 97.0%, the partial ester having a hydroxyl group that becomes a reaction site remains, so that the thermal stability and oxidation stability deteriorate.
Regarding the residual ratio of fatty acid alkyl ester, the fatty acid alkyl ester is the sum of the full ester content, partial ester content, and unreacted fatty acid alkyl ester content in the peak area obtained by analyzing the product by gas chromatography. The area ratio of minutes is defined as the fatty acid alkyl ester residual rate. This residual ratio is required to be 0.5% or less. Preferably, it is 0.4% or less, more preferably 0.3% or less. When it is more than 0.5%, the flash point is lowered, and the thermal stability and oxidation stability are further deteriorated.

The reaction between the fatty acid alkyl ester and neopentyl polyol is carried out by transesterification. The fatty acid alkyl ester and neopentyl polyol are charged into the reaction vessel so that the amount of fatty acid alkyl ester is excessive, and the fatty acid alkyl ester is charged under a predetermined temperature and pressure conditions in the presence of an alkali catalyst in a nitrogen atmosphere. While refluxing, while distilling off the alcohol produced as a byproduct, the polyol fatty acid ester is synthesized until the full ester selectivity is 97.0% or more. Thereafter, unreacted fatty acid alkyl ester is removed out of the system by topping under reduced pressure until it becomes 0.5% or less. When a solid catalyst is used, the catalyst is removed by filtration or a homogeneous catalyst is appropriately removed. When used, the desired polyol fatty acid ester is obtained by neutralization. As the reaction vessel, a reaction vessel made of glass, glass lining, or stainless steel equipped with a reflux tube can be used.
The charging ratio of fatty acid alkyl ester and neopentyl polyol is 1.05-1.30 times equivalent of the required molar amount of fatty acid alkyl ester for full ester production relative to the number of moles of hydroxyl group of neopentyl polyol. It is preferable. If it is less than 1.05, the reaction does not proceed sufficiently, and if it is more than 1.30, the amount of fatty acid alkyl ester that must be removed by the topping operation becomes large and inefficient.

  As the alkali catalyst, a catalyst used in a normal transesterification reaction may be used. For a solid catalyst, for example, potassium carbonate, sodium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium catalyst for a homogeneous catalyst. Methylate is mentioned. A solid catalyst is preferable because it can be easily removed after the reaction, and sodium hydrogen carbonate is particularly preferable. The addition amount of the catalyst is preferably 0.05 to 5.0% by mass with respect to the total weight of the fatty acid alkyl ester and neopentyl polyol. If the amount is less than 0.05% by mass, the reaction may not proceed sufficiently. If the amount is more than 5.0% by mass, the amount of catalyst to be removed or neutralized increases, and the load on the production process increases.

The reaction is carried out in a nitrogen atmosphere, but may be carried out under reduced pressure or under normal pressure nitrogen gas flow. Conditions under which the by-produced alkyl alcohol can be efficiently distilled off are preferred. Under reduced pressure, 133 Pa (1 torr) to 53320 Pa (400 torr) is preferable, and 133 Pa to 33325 Pa (250 torr) is more preferable. The degree of decompression may be under a certain condition within these ranges, or may be a condition in which the degree of decompression is increased step by step. If it is under nitrogen gas flow, the gas flow rate is preferably about 0.1 to 50 L / min.
The reaction temperature may be a temperature at which a normal transesterification reaction proceeds, preferably 50 to 250 ° C, more preferably 100 to 230 ° C. When the temperature is lower than 50 ° C, the reaction may not proceed. When the temperature is higher than 250 ° C, the color tone of the reaction product may deteriorate or the odor may deteriorate.
The reaction time is the time until the amount of full ester produced reaches a predetermined amount due to the progress of the transesterification reaction, but is usually 1 to 20 hours.

  A topping operation is performed in order to remove the fatty acid alkyl ester charged excessively after the reaction, but the degree of vacuum during the topping is preferably 1330 Pa (10 torr) or less. The higher the degree of vacuum, the shorter the time for removing the fatty acid alkyl ester. The topping time is preferably 0.5 to 6 hours.

After the reaction and topping operation, it is preferable to remove or deactivate the catalyst. When a solid catalyst is used, the catalyst is preferably removed by filtration using a leaf filter or a filter press. At this time, in order to perform filtration efficiently, an aggregation accelerator or a precoat treatment may be performed.
When a homogeneous catalyst is used, an adsorption treatment by neutralization or ion exchange of the catalyst is preferable. In neutralization, the alkaline catalyst is neutralized by adding an acidic compound. Examples of the acidic compound include hydrochloric acid, sulfuric acid, acetic acid, citric acid, p-toluenesulfonic acid, methanesulfonic acid and the like. Moreover, as an adsorption treatment agent by ion exchange, the Kyoward series manufactured by Kyowa Chemical Industry is listed.

  The same hindered polyol can be synthesized in the esterification reaction of a fatty acid and neopentyl polyol, but the fatty acid has a higher boiling point than that of the fatty acid methyl ester, so that the fatty acid cannot be sufficiently removed in the topping process. % Or more will remain. If the fatty acid remains, the acid value of the ester oil increases and the thermal stability deteriorates. In order to reduce the residual amount of fatty acid, it is conceivable to react the fatty acid and neopentyl polyol in an equivalent amount, but in this method, the selectivity of the full ester after the reaction can only be increased to about 93%, Thermal stability and oxidation stability deteriorate.

  Since the polyol fatty acid ester of the present invention has high purity, high flash point, and excellent oxidation stability and thermal stability, it can be used as a single product or mixed with other lubricating oils. It can be used as oil, hydraulic fluid, refrigeration oil, refrigerant and heat medium. Further, for the purpose of enhancing durability, it can be used by mixing with any antioxidant or lubricating oil additive as necessary. Antioxidants include phenolic antioxidants such as dibutylhydroxytoluene (BHT) and butylhydroxyanisole (BHA), amine antioxidants such as dioctyldiphenylamine and phenyl-α-naphthylamine, ascorbic acid (vitamin C), Tocopherol (vitamin E) and the like can be mentioned, among which phenolic antioxidants and tocopherol are preferable, and BHT, BHA, and tocopherol are more preferable. Lubricating oil additives include extreme pressure agents, cleaning dispersants, pour point depressants, rust inhibitors, and antifoaming agents.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these.

In the examples and comparative examples of the present invention, the following raw materials were used.
<Raw material>
Trimethylolpropane: Mitsubishi Gas Chemical Co., Ltd. Pentaerythritol: Kanto Chemical Co., Ltd. Methyl caprylate: Lion Chemical Co., Ltd. Pastel M-08
-Methyl caprate: Pastel M-10 manufactured by Lion Chemical Co., Ltd.
-Sodium bicarbonate: Asahi Glass Co., Ltd.-Caprylic acid: Tokyo Chemical Industry Co., Ltd.-Tin oxide: Junsei Chemical Co., Ltd.

Example 1
In a 5 L four-necked round bottom flask equipped with a stirrer, a condenser, and a thermometer, 2889 g of methyl caprylate (Lion Chemical Co., Ltd., Pastel M-08, molecular weight 158.24), trimethylolpropane (Mitsubishi Gas Chemical Co., Ltd.) 682 g of a company-made molecular weight 134.18) and 7.1 g of sodium hydrogen carbonate (Asahi Glass Co., Ltd., molecular weight 84.01) were added as a catalyst. At this time, the molar ratio of methyl caprylate to trimethylolpropane is 3.6 / 1. Moreover, the catalyst preparation amount is 0.2 mass% with respect to the raw material. After replacing the system with nitrogen gas, the temperature was raised to 230 ° C. at normal pressure under a nitrogen gas flow condition and reacted for 12 hours. Thereafter, an excessive amount of methyl caprylate was distilled off at a temperature of 230 ° C. under a reduced pressure of full vacuum (133 Pa) for 4 hours. After cooling, the catalyst was removed using a pressure filter to obtain the product trimethylolpropane tricaprylate.

The product trimethylolpropane tricaprylate was analyzed by gas chromatography under the following conditions.
<Gas chromatography conditions>
Column: J & W DB-1HT
Oven temperature: 80-390 ° C, 10 ° C / min
Vaporization chamber temperature: 390 ° C
Detector temperature: 390 ° C (FID)
Carrier gas: Helium linear velocity: 30 cm / min
Split ratio: 50: 1
Sample solution: 20 μL of sample, 500 μL of acetic anhydride, and 500 μL of pyridine are mixed and heat-treated at 80 ° C. for 20 minutes.

From the analysis results of gas chromatography, the selectivity of full ester and the residual rate of fatty acid alkyl ester were calculated using the following formulas (1) and (2).
(Formula 1)

Selectivity of full ester [%] = F / (F + P) × 100
F: Area for full ester P: Area for partial ester

(Formula 2)
Residual rate of fatty acid alkyl ester [%] = A / (A + N + F + P) × 100
A: Area of fatty acid alkyl ester N: Areas F and P of neopentyl polyol are the same as in formula (1)

As a result, the full ester selectivity was 99.1%, and the fatty acid alkyl ester residual rate was 0.2%. The results are shown in Table 1.

  Next, physical properties of the product trimethylolpropane tricaprylate were measured. The flash point was measured by JIS-K2265 Cleveland open method, and the acid value was measured according to JIS-K2501. The results are shown together in Table 1, and the flash point was as high as 258 ° C., and the acid value was as low as 0.01 mgKOH / g.

The following items were evaluated for evaluating the thermal stability and oxidation stability of the product.
In the hot tube test, a sample was poured little by little into a glass tube at a test temperature of 300 ° C. for 16 hours, and the evaluation was performed in 11 levels of 0 to 10 points according to the amount of gum produced. The air flow rate was 10 ± 0.5 cc / hr, and the sample flow rate was 0.31 ± 0.01 cc / hr. The higher the score, the better the heat resistance and cleanliness, and the less sludge is produced.
In the differential thermal analysis (5% weight loss temperature), the temperature was increased in air at a rate of 10 ° C./min using a differential thermal analyzer, and the temperature decreased by 5% from the initial mass was measured. The higher the 5% weight loss temperature, the better the evaporation resistance and heat resistance.
In the oxidation stability test, an oxidative degradation test was performed by a method based on the JIS-K2514-4 lubricating oil oxidation stability test for internal combustion engines, and the kinematic viscosity and total acid value of the oxidized oil were measured. Compared to them, the increase in viscosity ratio and total acid value was determined. The oxidation deterioration condition is a temperature of 165.5 ° C. and a time of 24 hours.
The results are shown in Table 1. The results of the hot tube test are as good as 10 points, the results of differential thermal analysis (5% weight loss temperature) are as high as 248 ° C., and the oxidation stability is evaluated in the evaluation of oxidation stability. The results are 8.9 and a viscosity ratio of 1.3, which can be said to be excellent in thermal stability and oxidation stability.

(Example 2)
In the same manner as in Example 1, 2940 g of methyl caprate (manufactured by Lion Chemical Co., Ltd., pastel M-10, molecular weight 186.29), 588 g of trimethylolpropane, and 14.1 g of sodium hydrogen carbonate were charged, reacted, and produced. A trimethylolpropane tricaplate was obtained.
The product was subjected to gas chromatography analysis, physical property measurement, and stability evaluation in the same manner as in Example 1, and the results are also shown in Table 1.

(Example 3)
In the same manner as in Example 1, 1994 g of methyl caprylate, 997 g of methyl caprate (weight ratio of methyl caprylate to methyl caprate is 2 to 1), 669 g of trimethylolpropane, and 14.6 g of sodium hydrogen carbonate were charged and reacted. The product trimethylolpropane caprylic acid / capric acid triester was obtained.
The product was subjected to gas chromatography analysis, physical property measurement, and stability evaluation in the same manner as in Example 1, and the results are also shown in Table 1.

Example 4
In the same manner as in Example 1, 2848 g of methyl caprylate, 511 g of pentaerythritol (manufactured by Kanto Chemical Co., Inc., molecular weight 136.15) and 20.2 g of sodium hydrogen carbonate were charged and reacted. The reaction time was 18 hours, the topping time was 5 hours, and other conditions were in accordance with Example 1.
The product pentaerythritol pentacaprylate was subjected to gas chromatography analysis, physical property measurement, and stability evaluation in the same manner as in Example 1. The results are also shown in Table 1.

(Comparative Example 1)
The reaction was carried out using the same raw materials, blending ratios and methods as in Example 1, but when the full ester selectivity reached 95%, the reaction was stopped and topping was performed. The topping time was shortened, and a sample having a full ester selectivity of 95.9% and a fatty acid alkyl ester residual ratio of 0.7% was obtained. This sample was measured for physical properties and evaluated for stability in the same manner as in Example 1. The results are also shown in Table 1.

(Comparative Example 2)
A 5 L four-necked round bottom flask equipped with a stirrer, a condenser, and a thermometer was charged with 2596 g caprylic acid (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 144.21), 732 g trimethylolpropane, and tin oxide as a catalyst (Pure Chemical Co., Ltd.) 3.3g of molecular weight 134.71) manufactured by company was added. At this time, the molar ratio of caprylic acid to trimethylolpropane is 3.3 / 1. The amount of catalyst charged is 0.1% by mass with respect to the raw material. After replacing the system with nitrogen gas, the temperature was raised to 230 ° C. at normal pressure under a nitrogen gas flow condition and reacted for 12 hours. Thereafter, an excessive amount of caprylic acid was distilled off from the topping at a temperature of 230 ° C. under a reduced pressure of full vacuum (133 Pa) for 4 hours. After cooling, the catalyst was removed using a pressure filter to obtain the product trimethylolpropane tricaprylate.
The product was subjected to gas chromatography analysis, physical property measurement, and stability evaluation in the same manner as in Example 1, and the results are also shown in Table 1. However, in the case of this comparative example, fatty acid was used in place of the fatty acid alkyl ester, so the fatty acid residual rate was calculated by the formula (3).
(Formula 3)
Fatty acid residual rate [%] = B / (B + N + F + P) × 100
B: Areas N, F and P of fatty acid are the same as in formula (1)

As shown in Table 1, the polyol fatty acid esters of Examples 1 to 4 had a high flash point, a low acid value, and good thermal stability and oxidation stability. In Comparative Example 1 where the full ester selectivity does not reach 97.0% and the fatty acid alkyl ester residual rate is more than 0.5%, the flash point is lower and the acid value is higher than in Example 1. Thermal stability and oxidation stability deteriorated. Moreover, in the comparative example 2 synthesize | combined from the fatty acid, the fatty acid residual rate was as high as 1.8%, the flash point became low, and the value of the acid value also became high. Furthermore, the thermal stability and oxidation stability deteriorated.
From the above results, the polyol fatty acid ester of the present invention has a high full ester selectivity of 97.0% or more and a fatty acid alkyl ester residual ratio of 0.5% or less, so the acid value is extremely low at a high flash point. It has good thermal stability and oxidation stability, and it can be used as a single product or mixed with other lubricating oils to produce metalworking oil, engine oil, gear oil, hydraulic fluid, refrigerator oil, refrigerant, heat It can be suitably used as a medium.

Claims (2)

In the transesterification reaction between the fatty acid alkyl ester and neopentyl polyol, the reaction proceeds until the full ester selectivity becomes 97.0% or more under the condition of excess fatty acid alkyl ester, and then the residual rate of the unreacted raw material fatty acid alkyl ester An ester synthetic oil comprising a polyol fatty acid ester obtained by topping removal until the water content becomes 0.5% or less. The ester synthetic oil according to claim 1, wherein the fatty acid alkyl ester is methyl caprate, methyl caprylate, or a mixture thereof, and the neopentyl polyol is trimethylolpropane.