The present work aims to develop a new vegetable insulating fluid for power transformers based on Jatropha curcas oil. Besides its technical benefits, Jatropha curcas oil has a socio-economic role by promoting income to rural families, contributing to the countryside development and avoiding rural exodus. Thus, the entire transformer oil production (extraction, processing, characterization and accelerated aging) was covered and a new process was developed. For oil extraction, the most suitable process was the solvent extraction (5 mL of hexane per gram of crushed non-peeled seeds during 30 minutes) with an oil yield of 32%. In raw oil processing stage, the degumming, with 0.4 g of phosphoric acid per 100 g of oil, at 70 °C, was used to remove phosphatides. Then, free fatty acids were 96% neutralized with a sodium hydroxide solution (0.5% w/w) at room temperature. For the oil clarification, the combination of 5% w/w oil of activated carbon and 1% w/w oil of MgO resulted in a bright, odorless and clear oil with an acid number of 0.04 mg KOH·g ﹣ 1. The oil drying in a vacuum rotary evaporator, at 70 °C, for 2 hours reduced the water content to 177 ppm. The processed oil was characterized following ASTM D6871 methods. This oil presented higher dielectric breakdown voltage (55 kV) than commercial transformer fluids (BIOTEMP®, EnvirotempFR3®, and Bivolt®), which increases transformer safety, capacity and lifetime. In addition, the processed oil has a lower viscosity than BIOTEMP® fluid, which can enhance the heat dissipation efficiency in the transformer. Moreover, the processed oil flash and fire points of 310 °C and >340 °C, respectively, confirm the great security of vegetable insulating fluids. The analyzed properties of the processed oil fulfill all the ASTM D6871, ABNT NBR 15422 and IEC 62770 specifications. Therefore, Jatropha curcas oil is a potential substitute formineral insulating fluids.
Nowadays, the constant search for sustainable economic development demands the rational use of resources and energy, including investment on renewable materials and greener processes [
Mineral oils have been used for over a hundred years in power transformers to ensure electrical insulation and cooling. However, these oils are mainly obtained from petroleum products, a non-renewable resource that involves various political and socio-economic issues. In the last half of the last century, synthetic hydrocarbon fluids, silicone, and ester fluids were introduced, but, at that time, their use was limited [
In this context, the development of alternative fluids has received great attention, especially vegetable insulating oils, produced from renewable sources. Comparing to mineral oils, bio-based oils are considered eco-friendly, since they are completely biodegradable, non-toxic and free of PCB (polychlorinated biphenyl), which simplifies the leaking protection and the further disposal. In addition, the higher flash and fire points (both greater than 300°C), compared to mineral oils, make the vegetable oils extremely safe, being classified as a Less-Flammable Dielectric Liquid, which requires no fire mitigation system and prevents the costly replacements caused by fires. Therefore, vegetable insulating fluids are not considered dangerous by international authorities such as Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA) [
Vegetable oils present higher dielectric breakdown compared to mineral oils, providing better insulation characteristics. In addition, these oils are not corrosive to copper and increase the insulation life of Kraft paper, since they present ability to absorb moisture of the paper and protect cellulose from thermal aging. Considering all these properties, vegetable oils can increase the transformer overloading capability, its performance, its useful life (about 40% higher), and can decrease its rates of failure. Its use requires no or just minor modifications and it is compatible with the existing electric power infrastructure [
Considering the reasons discussed above, in the recent years, the use of insulating vegetable oils, in electrical transformers, is growing extensively. Currently, over 300,000 distribution transformers using vegetable oil are in service. Moreover, there are, globally, approximately 200 power transformers up to 200 MVA and 242 kV being energized and operating with bio-based fluids [
Nevertheless, vegetable oils have some disadvantages, like higher viscosity and lower oxidative stability, when compared to mineral oils. Additionally, their price is subject to significant oscillation caused by the food market, since, generally, the feedstock is also used in edible oils [
Jatropha curcasis an arboreal plant of rapid growth, which belongs to the Euphorbiaceae family, with height ranging from 3 to 5 m. Studies suggest its origins in tropical America where it was taken by Portuguese navigators to other tropical parts of the world [
Jatropha curcas oil price does not compete on the food market, since the plant is non-edible and is not used for food and animal feeding [
Despite this potential, few works [
In this context, the objective of this work was to develop a new bio-based insulating fluid based on Jatropha curcasoil, for power transformers use, since the oil obtained after its processing presents a lower viscosity than commercial vegetable fluids available associated to a low acid number and a high dielectric breakdown value, besides the advantages already cited. Therefore, the whole production route (extraction and processing) was developed aiming an industrial production. In addition, the processed oil and a commercial fluid, BIOTEMP®, were characterized and compared according to the American Society for Testing and Materials (ASTM) standard (ASTM D6871) requirements for new insulating vegetable oils.
Jatropha curcasseeds were obtained from a local Brazilian producer. Initially, they were separated into two groups: non-peeled seeds and peeled seeds. Both of these materials were dried in an oven, at temperatures between 60˚C and 80˚C, until the obtainment of constant mass. Then, the extraction step was carried out (mechanical extraction, Sohxlet extraction or solvent extraction by direct contact). The extracted oils were processed in four steps: degumming, neutralization, clarification and drying. The oils were characterized before and after processing.
The peeled seeds were subjected to mechanical extraction and the resulting press cakes were subjected to chemical extraction by using a Soxhlet or by direct contact with hexane, as shown in
To evaluate the efficiency of the extraction processes, the percent yield was calculated as the ratio of the mass of oil obtained to the mass of seeds (non- peeled or peeled) used for the extraction, multiplied by 100.
The Jatropha curcas non-peeled and peeled seeds, as well as its seeds shells and crushed non-peeled seeds are shown in
The oils from dried Jatropha curcas non-peeled seeds and peeled seeds were extracted using a 15 t manual hydraulic press SIWA model CHARLOTT and the produced oils were filtered under vacuum.
To evaluate the amount of oil remaining in the cakes (non-peeled seeds and peeled seeds) resulting from the mechanical extraction, these cakes were crushed and contacted with hexane (4 mL per gram of solid) in the Soxhlet Oil and Grazes Extractor (Marconi MA004/8/50) at 80˚C, for two hours. Then, the solvent was recovered in a rotary evaporator at 80˚C under vacuum and the obtained oils were kept in an oven at 80˚C until constant mass.
Industrial plants usually combine mechanical and solvent extraction processes to extract oil from seeds [
Extraction by direct contact with hexane was also carried out for the crushed non-peeled seeds (5 mL per gram of solid), for 30 minutes, at 25˚C ± 3˚C. These seeds were not previously subjected to mechanical extraction (
To evaluate the efficiency of the extraction processes, the percent yield was calculated as the ratio between the mass of oil obtained and the mass of seeds (non-peeled or peeled) used for the extraction, multiplied by 100.
The initial methods applied in the crude oil processing were based on the standard industrial refining of vegetable edible oils [
The crude oil obtained from the extractions is mixed with other substances such as gums, phosphatides and proteins that are oil insoluble when hydrated. In order to remove them, the crude oil obtained from non-peeled seeds by direct contact extraction with the solvent, without previous mechanical extraction, was mixed with phosphoric acid (85 wt%), in a proportion of 0.4 g of this acid to 100 g of oil, at 70˚C for 10 minutes. Then, hot water was added and mixed for 10 more minutes. Finally, the mixture was centrifuged for phase separation, the aqueous whitish bottom phase, containing part of the before mentioned substances, being discarded.
In general, vegetable oils are constituted by triacylglycerol molecules, whose hydrolysis produces free fatty acids, which are responsible for the increase of the acidity of these oils. For this reason, these acids must be neutralized and removed.
The neutralization of free fatty acids was carried out by two different ways (alkali and dry neutralizations), according to
In the first one, the oil, previously adjusted to the temperature test (90˚C), was vigorously mixed, for 30 minutes, with three different alkali solutions, NaOH, NaHCO3, and Na2CO3, with the same concentration (10% w/w), containing phenolphthalein. Afterwards, other experiments were carried out with NaOH 0.5 and 5.0% w/w, at 90˚C and NaOH 0.5% w/w, at room temperature (25˚C ± 3˚C), all containing phenolphthalein. The addition of each of these solutions to the oil was done until the mixture oil/solution turned into a pink coloration. Then, it was taken to a decanter funnel for removal of part of the alkaline solution. The material in the funnel was washed with water at 90˚C and the supernatant was centrifuged for the removal of the rest of the alkaline solution and of the soap that was formed.
Dry neutralization, by using an absorbent, was also tested. Initially, the alkali-impregnated solid was prepared. For each gram of solid, 2 g of NaOH was dissolved in methanol, as suggested by Filleti [
However, the use of activated carbon is preferable because the silica gel preparation was more complex. In addition, methanol is a reagent with a high toxicity. Thus, new experiments were carried out using water as solvent and activated carbon as absorbent solid. Different proportions of NaOH (1 and 2 g∙g−1solid) and solid (0.25 and 0.5 g∙g−1oil) were studied.
In order to deodorize and remove pigments, soap, and other impurities, the clarification is commonly applied in edible oil refining [
The insulating vegetable oils are less susceptible to moisture than mineral oils [
In this context, it was studied two oil processes: drying in an oven at 120˚C and in a rotary evaporator at 70˚C. A lower temperature was used in the second process since it was done under vacuum. In both processes, two times were evaluated: two and four hours.
The characterization of the various obtained raw and processed Jatropha curcasoils, and the commercial oil, BIOTEMP®, was carried out according to ASTM D6871, for new natural (vegetable oil) ester fluids used in electrical apparatus [
Property | Standard Test Methods | ||
---|---|---|---|
ASTM D6871 | ISO/IEC 62770 | ABNT NBR 15422 | |
Physical | |||
Color | D1500 | ISO 2211 | NBR 14483 |
Flash/Fire Points | D92 | ISO 2592 | NBR 11341 |
Pour Point | D97 | ISO 3016 | NBR 11349 |
Density | D1298 | ISO 3675 | NBR 7148 |
Viscosity | D445 | ISO 3104 | NBR 10441 |
Visual Aspect | D1524 | IEC 61099 | |
Electrical | |||
Dielectric Breakdown | D877 | IEC 60156 | NBR 6898 |
Chemical | |||
Corrosive Sulphur | D1275 | IEC 62697 | NBR 10505 |
Water Content | D1533 | IEC 60814 | NBR 10710-B |
Acid Number | D974 | IEC 62021 | NBR 14248 |
PCB Content | D4059 | NBR 13882-B |
For the flash and fire points determination, it was used the Cleveland Open Cup Tester (Hipperquímica). The kinematic viscosity was evaluated using the automatic Cannon Fenske viscometer (SCHOT CT52) and the dynamic viscosity was measured by using the rheometer AR-G2 (TA Instruments). Additionally, the dielectric breakdown measurement equipment RDT 06A (Electric Test Serta) was applied to measure this property. The water content was determined by the Karl-Fisher method, by using the apparatus Q349 (Quimis). The fatty acids content was determined by using the Gas Chromatograph HP5890 (Agilent) with the column SP-2380 (Supelco), following the ASTM standards D1983 and D2800. The coefficient of expansion and specific heat were measured following the ASTM standards D1903 and D2766, respectively. For the latter, the Differential Scanning Calorimeter DSC-60A (Shimadzu) was used.
In electric power transformers, the insulating fluids can be submitted to extreme stress conditions, as high temperatures. It is know that the thermal stress combined with oxygen degrade the triglycerides and produce free fatty acids, which increase the oil acid number [
In this context, accelerating aging tests were done in order to evaluate the stability of the processed Jatropha curcas oil without antioxidants, and with 1% and 2% w/woil of tert-butylhydroquinone (TBHQ). This antioxidant is considered, in general, more effective than butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), other commonly antioxidants used in vegetable oils [
In the accelerated aging assays, 500 mL of each oils tested (around 500 mL) were added to erlenmeyer with 16 grams of Kraft paper and two meters of copper wire (1 mm diameter) shaped as a coil of one centimeter of diameter. Next, the systems were kept at 140˚C in a silicon oil bath for 5 days. Pneumatic compressors were used to bubble air in the oils inside the erlenmeyers, with a flow rate of 2 L∙min−1. The acid number, kinematic viscosities and fatty acids profile were measured of each one of the oils tested before and after aging.
For direct solvent extraction and Soxhlet extraction, reagent grade hexane was used. In the oil processing and characterization stages, the following analytical grade reagents from Synth, Merck and Sigma-Aldrich were used: sodium hydroxide, potassium hydroxide, phosphoric acid (85% w/w), magnesium oxide, sodium carbonate, sodium bicarbonate, calcium carbonate, methanol, Karl- Fischer reagent, silica gel, tert-butylhydroquinone (TBHQ), butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). Activated carbon from coconut husks was used during the oil processing tests. The commercial vegetable insulating oil used (BIOTEMP®) was gently donated by ABB Brazil.
The seeds were peeled and 38%of the initial mass corresponded to the peels and 62% to the albumens, in accordance with literature values [
The extraction of the remaining oil in the cakes was done using the Soxhlet equipment. Thus, combining mechanical and Soxhlet extraction resulted in a yield of 29% of oil for the non-peeled seeds and 37% for the peeled ones (albumens).
The yields for the extraction, by direct contact with hexane, of the remaining oil in the cakes from the mechanical extraction of the peeled seeds, were evaluated as a function of time and hexane proportion used (
From the results, presented in
For the other conditions evaluated, the maximum extraction was obtained around 30 minutes. For the proportion of 5 mL of hexane per gram of cake, the total yield in oil, by combining mechanical (20.0%) and direct contact with solvent (36.0%), was 48.8%. For the proportion of 10 mL of hexane per gram of cake, the total yield in oil was 50.4%. These results are as expected, once the oil content in albumens of Jatropha curcas is around 50%, as mentioned before. Therefore, considering the small increase in the oil yield by using twice as much solvent, the most adequate parameters for the direct solvent extraction are 5 mL∙g−1, as the ratio hexane/mass of cake, for 30 minutes, yielding 36% of oil.
Regarding the fatty acids composition (
Oil Yield (%) | |||||
---|---|---|---|---|---|
Solvent proportion (mL per gram of cake) | Extraction time (min) | ||||
5 | 10 | 15 | 30 | 60 | |
2 | 20 | 28 | - | 27 | 27 |
5 | 26 | 26 | 28 | 36 | 32 |
10 | 27 | 28 | 33 | 38 | 37 |
Fatty Acids | Percentage (%) | |||||||
---|---|---|---|---|---|---|---|---|
Non-peeled seeds | Peeled seeds | Araújo et al. [ | Freire et al. [ | |||||
Mech. | Soxhlet | Direct Solvent | Mech. | Soxhlet | Direct Solvent | |||
Myristic (C14:0) | 0.1 | 0.1 | 0.8 | 0.1 | 0.2 | 0.1 | - | - |
Palmitic (C16:0) | 13.5 | 15.1 | 13.7 | 13.9 | 16.0 | 16.5 | 13 | 13.3 |
Palmitoleic (C16:1) | 1.2 | 0.9 | 1.2 | 0.9 | 1.2 | 0.9 | 0.5 | 0.8 |
Stearic (C18:0) | 6.0 | 7.4 | 5.2 | 6.5 | 5.5 | 5.3 | 6.0 | 6.4 |
Oleic (C18:1) | 34.4 | 37.6 | 37.9 | 37.1 | 37.8 | 38.6 | 42.5 | 41.2 |
Linoleic (C18:2) | 40.0 | 36.1 | 38.9 | 36.4 | 35.8 | 36.9 | 38 | 36.5 |
Linolenic (C18:3) | 1,9 | 1,8 | 1,4 | 2,1 | 1,8 | 0,7 | - | 0.3 |
Mech. = Mechanical extraction. *Oil extracted combining mechanical extraction and solvent extraction (Soxhlet) from non-peeled Jatropha curcas seeds.
By comparing the properties of the oils, obtained by three different extraction methods (
Concluding, the mechanical extraction in a laboratorial scale resulted in low yields of oil. In addition, the solvent extraction did not affect substantially the oil properties. The oil extraction procedure used thereafter was the direct contact with hexane of crushed seeds, for 30 minutes, in a proportion of 5 mL of hexane per gram of non-peeled seeds. Through this procedure, it was obtained 32% of oil yield, a lower value than the obtained for peeled-seeds. However, the non-peeled seeds were chosen for ease of handling and due to the need of obtaining a significant amount of oil for subsequent processing study and characterization tests.
The crude Jatropha curcas degumming was evidenced by the sedimentation of an aqueous emulsion, composed of hydrated phosphatides. The analysis of the acid number has shown that the acidity of the crude oil (6.8 mgKOH∙g−1) was reduced to 5.8 mgKOH∙g−1 with the degumming step, as expected, since part of the
Property | Unit | Non-peeled seeds | Peeled seeds (albumen) | ||||
---|---|---|---|---|---|---|---|
Mech. | Soxhlet | Direct solvent | Mech. | Soxhlet | Direct solvent | ||
Density (20˚C) | g∙cm−3 | 0.915 | 0.912 | 0.912 | 0.914 | 0.912 | 0.912 |
Acid Number | mgKOH∙g−1 | 3.15 | 5.55 | 6.11 | 3.51 | 10.89 | 11.42 |
Water content | ppm | 654 | * | 463 | 627 | * | 402 |
Viscosity (40˚C) | mm∙s−2 | 32.7 | 32.6 | 32.8 | 33.8 | 31.2 | 31.8 |
*not enough oil to make the test. Mech. = Mechanical extraction.
fatty acids is removed in the process. Consequently, the degumming facilitates the neutralization step by reducing the amount of alkali required.
It was observed a reduction in the oil acidity by the color change of phenolphthalein for the degummed oil (acid number = 5.8 mgKOH∙g−1) neutralizations performed at 90˚C with NaOH, NaHCO3, and Na2CO3 solutions, with the same concentration (10% w/w). However, an excessive formation of soap occurred for NaHCO3 and Na2CO3 solutions, which resulted in a significant loss of neutral oil and did not allow the phase separation. Thus, the acidity of the oil could only be measured for NaOH solution, as shown in
Then, other concentrations of NaOH solutions were investigated (5% and 0.5% w/w at 90˚C). In these cases, it is also observed an excessive formation of soap. In this way, it was done another experiment using NaOH 0.5% w/w at room temperature (25˚C ± 3˚C), in which 96% of the free fatty acids were neutralized and the soap, neutral oil and aqueous phase could be separated. For this reason, this condition was selected as the more adequate. The yield of this process was 83% but the resulting oil remained with acidity higher than the ASTM D6871 limit value (0.06 mgKOH∙g−1), requiring another neutralization stage.
Tests involving the dry neutralization (with the solids impregnated with NaOH) have facilitated the phase separation, reduced the neutral oil consumption and decreased the water consumption. First, it was tested methanol as solvent for the NaOH dissolution and the best result was obtained with impregnated silica. However, as mentioned, the use of activated carbon is preferable because the silica gel preparation was more complex. In addition, methanol is a reagent with a high toxicity. Then, water was used as solvent and activated carbon as absorbent solid.
As shown in
Alkali | Concentration (%w/w) | Temperature (˚C) | Acid Number (mgKOH∙g−1) | Neutralization (%) |
---|---|---|---|---|
NaOH | 10 | 90 | 0.20 | 97 |
5 | * | * | ||
0.5 | * | * | ||
0.5 | 25 ± 3 | 0.23 | 96 | |
NaHCO3 | 10 | 90 | * | * |
Na2CO3 | 10 | 90 | * | * |
*The oil and the alkali solution emulsified, which did not allow acid number measurement.
Solid | NaOH (g∙g−1 solid) | Solvent | Solid (g∙g−1oil) | Acid Number (mgKOH∙g−1) | Neutralization (%) |
---|---|---|---|---|---|
Silica gel | 2 | CH3OH | 0.25 | 0.5 | 91 |
Activated Carbon | 1.6 | 72 | |||
Activated Carbon | 1 | H20 | 0.25 | 3.0 | 48 |
0.5 | 1.9 | 67 | |||
2 | 0.25 | 2.4 | 59 | ||
0.5 | 0.5 | 91 |
In view of the foregoing, the clarification was designed to clarify and neutralize the oil. The combination of 5%w/woil of activated carbon and 1%w/woil of MgO for the oil clarification (
The clarified oil (water content = 488 ppm, acid number = 0.04 mgKOH∙g−1), when dried in the stove, had an increase in the acidity (
On the other hand, using a vacuum rotary evaporator, which reduces the oxygen pressure during the process and allows working in lower temperatures for the oil drying, it was obtained, for both two and four hours, an oil with a low water content and an acid number within the ASTM D6871 standard limits.
Solid | Solid proportion (%w/woil) | Acid number (mgKOH∙g−1) | Neutralization (%) |
---|---|---|---|
Activated carbon | 5 | 0.43 | 14 |
Silica gel | 0.48 | 4 | |
Activated carbon + NaOH | 0.43 | 14 | |
CaCO3 | 0.80 | - | |
Na2CO3 | 0.35 | 30 | |
MgO | 0.15 | 70 | |
Activated carbon + MgO | 5 + 1 | 0.04 | 92 |
Color | Absorbance | |
---|---|---|
Neutralized Oil | Clarified Oil | |
Yellow (570 nm) | 0.033 | 0.012 |
Red (650 nm) | 0.024 | 0.015 |
Equipment | Temperature (˚C) | Time (h) | Water Content (ppm) | Acid Number (mgKOH∙g−1) |
---|---|---|---|---|
Stove | 120 | 2 | 280 | 0.07 |
4 | 183 | 0.09 | ||
Rotary Evaporator | 70 | 2 | 177 | 0.04 |
4 | 163 | 0.04 |
The processed Jatropha curcas oil, obtained after the extraction and processing stages, and the commercial oil, BIOTEMP®, were characterized following the test methods described in ASTM D6871 standard for Natural (Vegetable Oil) Ester Fluids Used in Electrical Apparatus. The results, shown in
It is worth to emphasize the lower values of the kinematic viscosities found for the processed oil compared to the ones determined for the BIOTEMP® fluid. In electrical power transformers, the insulating fluid also promotes heat dissipation, usually by natural convection. Thus, oils with lower viscosities can enhance heat dissipation efficiency, which can increase the transformer capacity and lifetime, in addition to more operational safety [
Moreover, the dielectric breakdown voltage of the processed Jatropha curcas oil was significantly higher (55 kV) than the minimum ASTM6871 standard value (30 kV), and also higher than the commercial fluid tested (45 kV). This higher dielectric breakdown value can also increase the safety, lifetime and capacity of power transformers.
In
Property | ASTM Test method | Unit | ASTM D6871 | ABNT NBR 15422 | IEC 62770 | BIOTEMP® | Processed Jatropha curcas Oil |
---|---|---|---|---|---|---|---|
Physical | |||||||
Flash Point | D92 | ˚C | ≥275 | * | 314 | 310 | |
Fire Point | ≥300 | 347 | >340 | ||||
Density (20˚C) | D1298 | g∙cm−3 | ≤0.96 | ≤1.0 | 0.91 | 0.912 | |
Viscosity | D445 | mm2∙s−1 | |||||
100˚C | ≤15 | 11.77 | 8.27 | ||||
40˚C | ≤50 | 49.81 | 39.72 | ||||
0˚C | ≤500 | 283.1 | 208.3 | ||||
Electrical | |||||||
Dielectric Breakdown | D877 | kV | ≥30 | * | 45 | 55 | |
Chemical | |||||||
Corrosive Sulphur | D1275 | non-corrosive | non-corrosive | non-corrosive | |||
Water Content | D1533 | mg∙kg−1 | ≤200 | 163 | 177 | ||
Acid Number | D974 | mgKOH∙g−1 | ≤0.06 | 0.05 | 0.04 | ||
PCB Content | D4059 | not detectable | free from PCBs |
*Property measured by a different test method from the ASTM D6871 standard.
Property | Unit | Yao et al. [ | Gómez et al. [ | BIOTEMP® | Processed Jatropha curcas oil | ||
---|---|---|---|---|---|---|---|
Gemini X | Bivolt A | Bivolt HW | Envirotemp FR3® | ||||
Dielectric strength | kV | 35 | 50 | 50 | 48 | 45 | 55 |
Viscosity (40˚C) | mm2∙s−1 | <13 | 36.6 | 40.1 | 36.7 | 49.8 | 39.7 |
Flash point | ˚C | ≥135 | 308 | 308 | 314 | 314 | 310 |
Fire point | ˚C | - | 342 | 338 | 338 | 347 | >340 |
Dynamic viscosity testing is not described in ASTM D6871 standard, but it can provide useful information about the rheological behavior of the fluid under shearing and under different thermal conditions. The dried raw and processed Jatropha curcas oils and BIOTEMP® presented a Newtonian behavior at temperatures of 10˚C, 25˚C and 100˚C within a shear rate range of 0.1 to 1000 s−1. In the temperature ramp test (
In ASTM D6871 standard, there are no required values for the coefficient of expansion and for specific heat, for the vegetable insulating oils. However, this standard gives the typical values for these properties, which are expected to be found in vegetable insulating fluids (
Fatty acids profiles of the oils submitted to accelerated aging are presented in
It is known that unsaturated fats are more prone to oxidation [
Property | Test Method | Typical Value | BIOTEMP® | Processed Jatropha curcas oil |
---|---|---|---|---|
Coefficient of Expansion (C−1) | ASTM D1903 | 7 × 10−4 to 8 × 10−4 | 6.88 × 10−4 | 7 × 10−4 |
Specific Heat (cal∙g−1∙˚C −1) | ASTM D2766 | 0.45 to 0.60 | 0.47 | 0.46 |
Percentage (%) | Processed Jatropha curcas Oil | |||
---|---|---|---|---|
Before aging | After 96 h of accelerated aging | |||
Without antioxidant | Without antioxidant | 1%w/woil TBHQ | 2%w/woil TBHQ | |
Myristic (C14:0) | 0.1 | 0.4 | 0.8 | 1.0 |
Palmitic (C16:0) | 14.7 | 20.8 | 22.5 | 18.5 |
Stearic (C18:0) | 5.9 | 7.4 | 9.0 | 7.0 |
Total of saturated fatty acids | 20.7 | 28.6 | 32.3 | 26.5 |
Palmitoleic (C16:1) | 1.2 | 1.4 | 1.6 | 1.4 |
Oleic (C18:1) | 37.1 | 43.8 | 44.9 | 40.1 |
Total of monounsaturated fatty acids | 38.3 | 45.2 | 46.5 | 41.5 |
Linoleic (C18:2) | 39.2 | 22.0 | 17.8 | 29.2 |
Total of polyunsaturated fatty acids | 39.2 | 22.0 | 17.8 | 29.2 |
Percentage of oil in the sample | 100 | 69.7 | 72.4 | 94.3 |
Processed Jatropha curcas Oil | ||||
---|---|---|---|---|
Before aging | After 96 h of accelerated aging | |||
Acid Number (mgKOH∙g−1) | Viscosity at 40˚C (mm2∙s−1) | Acid Number (mgKOH∙g−1) | Viscosity at 40˚C (mm2∙s−1) | |
Without antioxidant | 0.089 | 42.7 | 1.529 | 182.8 |
1%w/woil TBHQ | 0.136 | 40.2 | 2.002 | 453.4 |
2%w/woil TBHQ | 0.152 | 39.9 | 0.779 | 82.2 |
lycerides [
In this sense, it was studied the accelerated aging of the processed Jatropha curcas oil with 1% and 2%w/woil of TBHQ, a common antioxidant used in vegetable oils. As shown in
The present work focused on the development of a new vegetable insulating fluid for power transformers based on Jatropha curcas oil. Regarding the oil extraction, the solvent extraction of crushed non-peeled seeds was chosen as the most feasible to an industrial production, with an oil yield of 32%. Further, the raw oil processing was studied. The degumming with phosphoric acid was efficient to remove phosphatides from the crude Jatropha curcas oil. With a NaOH solution (0.5%w/w) at room temperature, 96% of the free fatty acids were neutralized, while by dry neutralization, using activated carbon impregnated with NaOH, an eco-friendly alternative, 92% of the free fatty acids were neutralized. The oil clarification resulted in a bright, odorless and clear oil with an acid number of 0.04 mgKOH∙g−1. The oil drying was able to lower the water content to 177 ppm. Comparing this oil with the main commercial transformer fluids available (BIOTEMP®, Envirotemp FR3®, and Bivolt®), it presents higher dielectric breakdown voltage (55 kV). In addition, it has a lower viscosity than the BIOTEMP® fluid. Moreover, the processed oil flash and fire points of 310˚C and >340˚C, respectively, confirm the great security of vegetable insulating fluids. Preliminary accelerated aging tests showed the necessity of adding antioxidants to the processed Jatropha curcas oil to prevent its oxidation under high temperatures. Finally, it was found that the analyzed properties of the processed oil fulfill all the ASTM D6871, ABNT NBR 15422 and IEC 62770 specifications for new vegetable transformer oil. In conclusion, the Jatropha curcas oil developed in the present work is a great candidate for replacing mineral oils in power transformers.
The authors are very grateful to FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais) for the financial support and to all members of the Separation Operations and Processes group from the Department of Chemical Engineering at UFMG who made this work possible.
Evangelista Jr., J.M.G., Coelho, F.E.B., Carvalho, J.A.O., Araújo, E.M.R., Miranda, T.L.S. and Salum, A. (2017) Development of a New Bio-Based Insulating Fluid from Jatropha curcas Oil for Power Transformers. Advances in Che- mical Engineering and Science, 7, 235-255. https://doi.org/10.4236/aces.2017.72018