WO2007126207A1

WO2007126207A1 - Vegetable-based electric insulation oil and preparation thereof

Info

Publication number: WO2007126207A1
Application number: PCT/KR2007/001142
Authority: WO
Inventors: Jai-Kwy Ro; Chung-Souk Ro; Hyo-Suk Ro; Yeung-Ho Park
Original assignee: Dong Nam Petroleum Ind. Co., Ltd.
Priority date: 2006-05-03
Filing date: 2007-03-08
Publication date: 2007-11-08
Also published as: KR100705296B1; CN101438356A; JP5047271B2; CN101438356B; HK1130559A1; JP2009535763A

Abstract

Disclosed herein are vegetable-based electrical insulating oil capable of being readily biodegraded in ecosystems and preparation thereof. The preparation is carried out by esterifying a vegetable-oil mixture of 40 to 50 parts by weight of soybean oil and 50 to 60 parts by weight of rapeseed oil, with ethyl alcohol under the presence of an aluminosilicate catalyst.

Description

[DESCRIPTION] [Invention Title]

VEGETABLE-BASED ELECTRIC INSULATION OIL AND PREPARATION THEREOF

[Technical Field]

The present invention relates to electrical insulating oil. More specifically, the present invention relates to vegetable-based electrical insulating oil which exhibits superior antioxidability and is readily biodegradable in ecosystems after use via characteristics of vegetable oil.

[Background Art] The mechanical development originated with the industrial revolution brought about rapidly increased demand for oil. In particular, with strict regulations associated with the requirements for lubricants, there was a need for oils that satisfy more improved properties. Mineral-based oils are being widely used in a variety of industries. However, mineral-based oils have low biodegradability, thus involving an environmental problem resulting from leakage or waste disposal.

With recent trends toward high-voltage and high- capacitance electrical appliances, there has been increased demand for electrical insulating oils that satisfy requirements corresponding to the trends. In an attempt to satisfy such a demand, electrical insulating oils, in which mineral oil as a main component is mixed with other additives, have been developed.

For example, Korean Patent Publication No. 1994- 0003803 discloses electrical insulating oil with superior voltage characteristics which comprises mineral-based electrical insulating oil and one material selected from linear hydrocarbon compounds, rapeseed oils and ester compounds. Japanese Patent Publication No. 63-4286 discloses electrical insulating oil with improved dielectric breakdown voltage which comprises a mixture of mineral-based electrical insulating oil and a fluorine-based organic compound. Japanese Patent Application Publication No. 69-84714 discloses mixing mineral oil with phosphate ester as a surfactant .

Theses methods utilizing mixing mineral oil as a main component with various additives enables considerable improvement in the electrical properties of mineral-based electrical insulating oils, thus contributing to prolonged lifetime of the electrical insulating oils. However, waste electrical insulating oils are reused in conjunction with fresh oils, but otherwise are discarded. The reuse of the insulating oils is accomplished by collecting the deteriorated electrical insulating oils from electrical appliances, e.g., transformers, and subjecting the oils to purification and recycling.

Unrecyclable waste electrical insulating oils cannot be readily burned due to an antioxidant used as an additive.

Although burned, the waste electrical insulating oils create toxic contaminants, e.g., dioxin, thus causing environmental pollution.

Accordingly, there has been a demand to develop environmentally friendly electrical insulating oils. In an attempt to meet such a demand, US Patent No. 5,958,851 discloses electrical insulating oil for transformer which is prepared by subjecting oleic acid-containing soybean oil as a base component to hydrogenation or methyl-esterification, and adding an antioxidant to the base component.

As can be seen from the disclosure of this prior-art, there is a limitation to put soybean oils to practical use due to their disadvantages of crystallization at a low temperature, solidification at a high temperature, and low antioxidability . The prior-art exhibits that vegetable oil such as soybean oil may be substituted for electrical insulating oil.

Meanwhile, US Patent No. 5,949,017 discloses electrical insulating oil for transformer via combination of mineral oil, etc., and vegetable oil comprising oleic acid triglyceride of 75% or higher, C₁₆-C2₂ unsaturated fatty acid, C16-C₂2 saturated fatty acid, and an antioxidant. Sunflower oil, olive oil and safflower oil are exemplified as the vegetable oil having the content of the oleic acid. Since the electrical insulating oil disclosed in this prior-art comprises an ester compound such as oleic acid triglyceride, it is disadvantageously susceptible to hydrolysis upon coming in contact with water at high temperature and involves high costs. The electrical insulating oil is effective in improving biodegradability via combination of vegetable oil and mineral oil, etc.

However, vegetable oil only has not yet been practically available as high-voltage electrical insulating oil. Accordingly, electrical insulating oil needs to ensure the requirements of superior antioxidablity and low pour point so that it can endure high voltage.

[Technical Problem]

It is one object of the present invention to provide environmentally friendly vegetable-based electrical insulating oil with superior antioxidablity, high dielectric breakdown voltage and low pour point due to a desired composition and chemical reactions of vegetable oil.

[Technical Solution] In accordance with an aspect of the present invention for achieving the above object, there is provided a method for preparing vegetable-based electrical insulating oil comprising esterifying a vegetable-oil mixture with ethyl alcohol under the presence of an aluminosilicate catalyst wherein the vegetable-oil mixture consists of 40 to 50 parts by weight of soybean oil, and 50 to 60 parts by weight of rapeseed oil.

[Best Mode]

The present invention will now be described in greater detail.

The present invention provides a method for preparing vegetable-based electrical insulating oil comprising esterifying a vegetable-oil mixture of 40 to 50 parts by weight of soybean oil, and 50 to 60 parts by weight of rapeseed oil, with ethyl alcohol under the presence of an aluminosilicate catalyst.

Soybean oil has the disadvantages in that it undergoes crystallization at a low temperature and solidification at a high temperature, and has low antioxidability. Accordingly, mixing soybean oil with rapeseed oil advantageously ensures low iodine number, low total acid number (TAN) , low pour point, superior compatibility with metal, and reduction in viscosity variation depending upon temperature variation. For this reason, the method of the present invention utilizes the mixture of soybean oil and rapeseed oil. In a case where the rapeseed oil is used in an amount exceeding 60 parts by weight, the vegetable-oil mixture may be readily hydrolyzed and oxidized due to a deterioration in stability, thus causing corrosion of a nonferrous metal. Meanwhile, in a case where the rapeseed oil is used in an amount less than 50 parts by weight, the vegetable-oil mixture is unsuitable for use in winter due to an increase in the pour point thereof. When a pour point depressant is used to reduce the pour point, deterioration of biodegradability occurs. Thus, soybean oil and rapeseed oil are preferably used in an amount of 40 to 50 parts by weight and 50 to 60 parts by weight, respectively. The catalyst suitable for use in the esterification may be an alkaline-based and aluminosilicate-based catalyst. Preferred is use of a zeolite catalyst.

Preferably, the esterification is carried out at 140 to 170^°C for 3 to 5 hours. When the esterification of the vegetable oil with ethyl alcohol is carried out at a temperature of 140^°C or below, it is incompletely accomplished, thus leaving vegetable oil mixed with the remaining solvent. Meanwhile, when the esterification is carried out at a high temperature exceeding 170 ^°C, there occurs deterioration in color and properties of final products. Thus, the esterification temperature is preferably within the range as defined above.

The esterification under the temperature condition within 3 hours involves incomplete reaction, thus making it impossible to obtain the desired pour point and antioxidability. The esterification for 5 hours above causes a deterioration in color and properties of final products and an increase in production cost due to high-temperature reaction for long time. Thus, the esterification time is preferably within the range as defined above.

Acid catalysts (e.g., sulfuric acid, and hydrochloric acid) and alkaline catalysts (e.g., sodium hydroxide, sodium methoxide, and potassium hydroxide) are generally used as catalysts for esterification. The acid catalysts result in phase separation and reaction on the interface, thus involving low reaction rate, strong stirring required to facilitate the reaction, and inconvenience caused by removal of water from the interface. The alkaline catalysts have the advantages of relatively high yield and superior reaction stability. But, the alkaline catalysts involve a risk of deterioration in the yield due to saponification of the vegetable oil caused by alkalinization thereof.

However, the aluminosilicate-based catalyst used in the present invention phase involves no separation and saponification, thus advantageously obtaining high-yield products and being readily removed from the product after the reaction. Zeolite and bentonite, etc., may be used as the aluminosilicate-based catalyst.

A variety of alcohols may be used to form ester together with vegetable oil. When taking into consideration the properties such as viscosity, pour point and total acid number, it is preferable to use ethyl alcohol.

[Mode for Invention]

The present invention will be better understood from the following examples. These examples are not to be construed as limiting the scope of the invention.

EXAMPLES

Example 1

Each mixture of soybean oil and rapeseed oil was prepared depending upon variation of the mixed ratio shown in Table 1 below. The viscosity (KS M 2014), pour point (KS M 2016), and flash point (KS M 2010) of the oil mixture were measured. The results were shown in Table 1. TABLE 1

As could be seen from the data shown in Table 1, as the amount of the rapeseed oil increases, the viscosity thereof increases, but the pour point and the flash point thereof decrease. On the other hand, as the amount of the rapeseed oil decreases, the viscosity thereof decreases, but the pour point and the flash point thereof increase.

The increase in pour point of the oil mixture accelerates after esterification, thus causing disadvantages of unsuitability for use in winter, inconvenience associated with addition of a pour point depressant to reduce the pour point, and deterioration of biodegradability caused by the depressant addition. In addition, when taking into consideration the flash point of the oil mixture, the mixed ratio (parts by weight) of soybean oil (X) and rapeseed oil (Y) is preferably X : Y = 40 - 50 : 60 - 50.

Example 2

It could be confirmed from the data obtained in Example 1 that the oil mixture consisting of 40 parts by weight soybean oil and 60 parts by weight of rapeseed oil brought about the best results. Accordingly, 100 parts by weight of the oil mixture, 0.4 parts by weight of a zeolite catalyst, and alcohol are put into a reaction vessel. At this time, the alcohol is varied in accordance with the kind and the content shown in Table 2. The mixture was subjected to esterification at 170 ^°C for 5 hours with stirring at 400 rpm to prepare electrical insulating oil. The viscosity and the pour point of the electrical insulating oil were measured in the same manner as Example 1. The total acid number of the electrical insulating oil was measured in accordance with KS M 2004. The results were shown in Table 2. TABLE 2

As could be seen from the data in Table 2, in a case where ethyl alcohol is used for the esterification, the electrical insulating oil prepared thus exhibited the lowest viscosity, the lowest pour point, and the lowest total acid number. In addition, the use of ethyl alcohol enabled stable results throughout the content range in view of viscosity, pour point, and total acid number.

Example 3

Based on the results in Examples 1 and 2, the mixed ratio of soybean oil to rapeseed oil, and the content of catalyst were varied as shown in Table 3 below. Accordingly, 100 parts by weight of the oil mixture, a predetermined amount of a zeolite catalyst, and 10 parts by weight of ethyl alcohol were put into a reaction vessel. The mixture was subjected to esterification at 170 ^°C for 5 hours with stirring at 400 rpm to prepare electrical insulating oil. Then, the viscosity, the pour point, and total acid number of the electrical insulating oil were measured in the same manner as Examples 1 and 2. The results were shown in Table 3. TABLE 3

As could be seen from the data in Table 3, as the amount of the catalyst increased, the flash point thereof increased, but the pour point and total acid number thereof decreased. As a result, it could be confirmed that the addition of the catalyst considerably affects the esterification. In a case where no catalyst was added, the total acid number was a considerably high value as 0.102 mg KOH/g, 0.110 mg KOH/g, and 0.115 mg KOH/g. The high total acid number causes formation of sludge in an early stage upon introduction of the electrical insulating oil into a transformer, thus disadvantageously involving a reduction in specific resistance of the electrical insulating oil, damage to the transformer, and a deterioration in insulating performance as a major function of the electrical insulating oil. Thus, it could be confirmed that the esterification is preferably carried out under the presence of a catalyst.

Example 4

The vegetable oil mixture consisting of 40 parts by weight of soybean oil and 60 parts by weight of rapeseed oil,

0.4 parts by weight of a zeolite catalyst, and ethyl alcohol were put into a reaction vessel. At this time, the amount of the ethyl alcohol added was varied as shown in Table 4. The mixture was subjected to esterification at 170 ^°C for 5 hours with stirring to prepare electrical insulating oil. The flash point, the pour point and total acid number of the electrical insulating oil were measured in the same manner as Examples 1 and 2. The results were shown in Table 4. TABLE 4

As could be seen from the data in Table 4, in a case where ethyl alcohol is used in an amount of 3 parts by weight, the electrical insulating oil thus prepared has no problem in view of flash point, but the high pour point thereof involves use of excessive additives and deterioration of biodegradability, and the high total acid number thereof involves a deterioration in insulating performance as a major function of the electrical insulating oil. Thus, the content of ethyl alcohol is preferably equal to or larger than 5 parts by weight. However, although the content of ethyl alcohol is larger than 15 parts by weight, there is no large variation in the flash point, the pour point and total acid number of the electrical insulating oil. Accordingly, addition of excessive ethyl alcohol is unnecessary and involves inconvenience, e.g., removal of the remaining ethyl alcohol. Example 5

The vegetable oil mixture consisting of 45 parts by weight of soybean oil and 55 parts by weight of rapeseed oil, 0.4 parts by weight of a zeolite catalyst, and ethyl alcohol are put into a reaction vessel. At this time, the amount of the ethyl alcohol added and reaction temperature are varied as shown in Table 5. The mixture was subjected to esterification at 170 ^°C for 5 hours with stirring to prepare electrical insulating oil. The flash point, the pour point and total acid number of the electrical insulating oil were measured in the same manner as Examples 1 and 2. The results were shown in Table 5. TABLE 5

As could be seen from the data in Table 5, in a case where the reaction temperature was at 130 ^°C, the flash point of electrical insulating oil thereof was significantly low, and the pour point and total acid number thereof were high. As a result, it could be confirmed that the reaction was insufficiently accomplished. On the other hand, in a case where the reaction temperature was at 180 ^°C, the total acid number of electrical insulating oil was considerably increased values as 0.083 mg KOH/g, and 0.089 mg KOH/g. The increase in total acid number considerably affects deterioration in insulating performance. Thus, the range of the reaction temperature is preferably adjusted to 140 to 170 ^°C, which is utilized in the present invention. As apparent from the results obtained in Examples 1 to

5, the mixed ratio (parts by weight) of soybean oil (X) to rapeseed oil (Y) is preferably X : Y = 40 - 45 : 60 - 55. The alcohol for the esterification thereof with the vegetable oil mixture is preferably used in an amount of 5 to 20 parts by weight, based on 100 parts by weight of the vegetable oil mixture. An aluminosilicate-based zeolite is preferably used as a catalyst for the esterification. The catalyst is preferably used in an amount of 0.2 to 0.6 parts by weight, based on 100 parts by weight of the vegetable oil mixture. The reaction temperature is preferably within 140 to 170 ^°C

The electrical insulating oil of the present invention is prepared from esterification of vegetable oil. Since the electrical insulating oil maintains a high flash point, low total acid number, and the desired viscosity, it can be effectively used for electrical appliances, e.g., transformers. However, general vegetable oils are more vulnerable to oxidation, as compared to mineral oils. When an antioxidant, e.g., buthylated hydroxytoluene (BHT) and tertiary buthyl hydroquinone (TBHQ) , is added in a desired amount to electrical insulating oil in order to reinforce antioxidabllity, the electrical insulating oil can be utilized for a longer period.

Experimental examples <Dielectric breakdown voltage test>

There was prepared electrical insulating oil by esterifying a vegetable-oil mixture of 40 parts by weight of soybean oil and 60 parts by weight of rapeseed oil with 10 parts by weight of ethyl alcohol under the presence of 0.4 parts by weight of a zeolite catalyst. At this time, the esterification is carried out for 5 hours while the reaction temperature was varied from 140^°C to 170^°C. The dielectric breakdown voltage of the electrical insulating oil thus prepared was measured in accordance with KS C ISO 60156. The results were shown in Table 6 below. TABLE 6

As could be seen from the data shown in Table 6, the dielectric breakdown voltage of the electrical insulating oil thus prepared was 73 to 80 KV, which is far larger than those of Class I. No. 2 and Class I. No. 4 (i.e., 30 KV and 40 KV, respectively) of electrical insulating oil standards in accordance with the Korean Industrial Standards (KS) .

The biodegradation test was performed using the apparatuses and the methods in accordance with the U.S. EPA OPPTS Test Guideline No. 835.3100. First, 900 mL of deionized water containing each 1 mL of a test reagent 1, a test reagent 2 and a test reagent 3, and 100 mL of inoculum were put into a flask to prepare 1 L of a culture solution. After the culture solution was stood for 14 days, a test sample was added thereto. The test sample used herein was vegetable-based electrical insulating oil based on the results obtained in Example 5. More specifically, the vegetable-based electrical insulating oil was prepared by esterifying a vegetable-oil mixture of 40 parts by weight of soybean oil and 60 parts by weight of rapeseed oil with 10 parts by weight of ethyl alcohol under the presence of 0.4 parts by weight of a zeolite catalyst at 170^°C for 5 hours.

The flask used herein was an Erlenmeyer flask equipped with a medium vessel containing 10 cc of 0.2 N Ba (OH) 2 solution. The culture solution was put into each of three flasks to prepare an experimental group, a control group, and a normal group, respectively. The experimental group was where 153 uL of the vegetable-based electrical insulating oil is added. The control group was where 35.8 mg of sodium citrate is added. The normal group was where no addition is carried out.

Each flask was purged by using CO₂-free air, followed by sealing. The biodegradation was performed for 30 to 45 days with stirring on a stirrer at 125 rpm. After 10 mL of 0.2 N Ba(OH)₂ solution was collected from the medium vessel of each flask at regular intervals during the biodegradation, 10 mL of deionized water and 0.2 mL of phenolphthalein were added thereto. The mixture was titrated with 0.1 N HCl. The CO₂ amount generated in the titrate was calculated by the following equation 1. The results were shown in Table 7. Equation 1

wherein TF is an amount (mL) of 0.1 N HCl used for Ba(OH)₂ titration of the experimental and control groups; and

CF is an amount (mL) of 0.1 N HCl used for Ba(OH)₂ titration of the normal group.

TABLE 7

I Type 1 Amount of CO₂ generated |

As could be seen from the data shown in Table 7, CO₂ gradually increased with the process of the time, and the theoretical amount of CO₂ then reached 96.4 % after 30 days. This value was far larger than that CO₂ amount (64.8%) generated from sodium citrate as standard sample. It could be confirmed from this fact that the vegetable-based electrical insulating oil exhibited superior biodegradability.

Other solutions herein used were prepared in accordance with the following process.

25 mL of activated sludge obtained from a sewage disposal plant were homogeneously mixed with soil respectively collected from a hill which stands in Yeoju-si, Kyonggi-do; a hill which stands Pyeongtaek-si, Kangwon-do; and Ban-Wall Industrial Complex, Ansan-si. The soil was colleted around 20 cm under the Earth's surface. The mixture was passed through a sieve with diameter of 5 mm. 1 g of the resulting mixture was mixed with 1 L of deionized water, followed by filtering. The filtrate was put into an Erlenmeyer flask. After an adaptation period of 14 days at 25^°C with sealing a top inlet, the final product was used.

<Preparation of test reagent> Test reagent 1

35 g of NH₄Cl, 15 g of KNO₃, 75 g of K₂HPO₄3H₂O, and 25 g of NaH₂PO₄H₂O are mixed with distilled water to adjust the amount of the solution to 1 L.

Test reagent 2 10 g of KCl, 20 g of MgSO₄, and 1 g of FeSO₄7H₂O are mixed with distilled water to adjust the amount of the solution to 1 L.

Test reagent 3

5 g of CaCl₂, 0.05 g of ZnCl₂, 0.5 g of MnCl₂4H₂O, 0.05 g of CuCl₂, 0.001 g of CoCl₂, 0.001 g of H₃BO₃, and 0.004 g of

MoO₃ are mixed with distilled water to adjust the amount of the solution to 1 L.

[Industrial Applicability]

As apparent from the foregoing, the electrical insulating oil prepared by the method according to the present invention can be readily degraded by microorganisms present in the natural world. Accordingly, the electrical insulating oil exhibits superior biodegradability upon leakage or waste-treatment, high dielectric breakdown voltage, low flash point, excellent antioxidability, and superior tolerance to electrical deterioration, thus being greatly effective in use for transformers.

Claims

WHAT IS CLAIMED IS:

1. A method for preparing vegetable-based electrical insulating oil comprising: esterifying a vegetable-oil mixture with ethyl alcohol under the presence of an aluminosilicate catalyst, wherein the vegetable-oil mixture consists of 40 to 45 parts by weight of soybean oil, and 55 to 60 parts by weight of rapeseed oil.

2. The method according to claim 1, wherein the aluminosilicate catalyst is a zeolite catalyst, and the aluminosilicate catalyst is used in an amount of 0.2 to 0.6 parts by weight, based on 100 parts by weight of the vegetable-oil mixture.

3. The method according to claim 1 or 2, wherein the esterification is carried out at 140 to 170 ^°C .

4. The method according to claim 3, wherein the esterification is carried out for 3 to 5 hours.

5. Vegetable-based electrical insulating oil prepared by esterifying a vegetable-oil mixture with ethyl alcohol under the presence of an aluminosilicate catalyst, wherein the vegetable-oil mixture consists of 40 to 45 parts by weight of soybean oil, and 55 to 60 parts by weight of rapeseed oil.

6. The vegetable-based electrical insulating oil according to claim 5, further comprising an antioxidant.

INTERNATIONAL SEARCH REPORT

PCT/KR2007/001142

A. CLASSIFICATION OF SUBJECT MATTER

HOlB 3/20(2006.01)i

According to International Patent Classification (IPC) or to both national classification and IPC

B. FIELDS SEARCHED

Minimum documentation searched (classification system followed by classification symbols) IPC8 H01B

Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched

Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) eKIPASS

C. DOCUMENTS CONSIDERED TO BE RELEVANT

Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No

WO 2005/022558 Al (TAKEI MITSUHIKO et al ) 10 MARCH 2005 1-6 claims, best mode for carrying out the invention

JP 09259638 A (UZAWA HISAJI et al ) 03 OCTOBER 1997 1-6 claims, examples

US 06613250 B2 (C PATRICK MCSHANE et al ) 02 SEPTEMBER 2003 1-6 claims 14-16, column 8, line 37-49

Further documents are listed in the continuation of Box C See patent family annex

* Special categories of cited documents "T" later document published after the international filing date or priority

"A" document defining the general state of the art which is not considered date and not in conflict with the application but cited to understand to be of particular relevance the principle or theory underlying the invention "E" earlier application or patent but published on or after the international "X" document of particular relevance, the claimed invention cannot be filing date considered novel or cannot be considered to involve an inventive "L" document which may throw doubts on priority claim(s) or which is step when the document is taken alone cited to establish the publication date of citation or other "Y" document of particular relevance, the claimed invention cannot be special reason (as specified) considered to involve an inventive step when the document is "O" document referring to an oral disclosure, use, exhibition or other combined with one or more other such documents, such combination means being obvious to a person skilled in the art "P" document published prior to the international filing date but later "&" document member of the same patent family than the priority date claimed

Date of the actual completion of the international search Date of mailing of the international search report 25 JUNE 2007 (25 06 2007) 26 JUNE 2007 (26.06.2007)

Name and mailing address of the ISA/KR Authorized officer

Korean Intellectual Property Office

920 Dunsan-dong, Seo-gu, Daejeon 302-701, LEE, Young Wan

Republic of Korea

Facsimile No 82-42-472-7140 Telephone No 82-42-481-5560

Form PCT/ISA/210 (second sheet) (April 2007) INTERNATIONAL SEARCH REPORT International application No

Information on patent family members PCT/KR2007/001142

Patent document Publication Patent family Publication cited in search report date member(s) date

W02005022558A 1 10.03.2005 CN1856843A 01.11.2006

EP1662513A1 31.05.2006

EP1662513A4 06.09.2006

JPW02005/022558 10.03.2005

KR1020070015103 01.02.2007

US2007069188A1 29.03.2007

JP09259638A 03.10.1997 JP3145301B2 12.03.2001

US06613250B2 02.09.2003 US2002109128A1 15.08.2002 US2004069975A1 15.04.2004 US2005040375A1 24.02.2005 US6905638B2 14.06.2005

Form PCT/ISA/210 (patent family annex) (April 2007)