Preparation Of Low-freezing Point Transformer Insulating Oil By Transesterification Reaction Of Canola Oil And Isooctanol

As a new type of environmentally friendly dielectric fluid,vegetable-based insulating oil has good biodegradability and high flash point.It has replaced mineral oil in a small amount and has been used in transformers.However,the main component of vegetable oil is triglyceride,which has a relatively high degree of unsaturation.Compared with mineral oils（alkanes）,the problems of higher freezing point,higher kinematic viscosity,and poor oxidation stability are common.For this reason,in this thesis,fatty acid isooctyl esters were prepared by transesterification reaction between rapeseed oil and isooctyl alcohol（2-ethylhexanol）.The refining method was studied,and the physical and chemical properties and electrical properties were tested.The main research contents are as follows.First,based on oxidation stability and freezing point,the raw materials for the transesterification reaction are selected.The results show that canola oil with higher oleic acid content（>67%）,better oxidation stability（oxidation stability time>9 h）,and lower freezing point（-18℃）is the most suitable acyl donor.Isooctyl alcohol as a medium carbon chain branched alcohol,as an acyl acceptor,can take into account the product’s flash point and low temperature fluidity（flash point is greater than 200℃,freezing point below-40℃）.Secondly,through single factor and orthogonal experiments,the process conditions for preparing fatty acid isooctyl esters from the transesterification reaction of rapeseed oil and isooctyl alcohol and the refining process conditions of the transesterification products were studied and optimized.The results showed that the suitable reaction conditions were:alcohol-to-oil molar ratio of 5:1,reaction time of 20 minutes,reaction temperature of 50°C,and sodium methoxide addition of 0.6%.At this time,the content of fatty acid esters obtained by the transesterification reaction reached 95.13%.It is better when the vacuum degree is0.01～0.02 mbar,the scraping speed is 135 r/min,the feed rate is 1 m L/min,the feed temperature is 60℃,and the distillation temperature is 130℃.The effect of dealcoholization.Under the conditions of 3%lye concentration,0.45%alkali addition,alkali smelting temperature 60℃,alkali smelting time 40 min,and activated clay content of 2%,it has a good alkali smelting decolorization effect.When the molecular distillation vacuum is within the range of 0.01～0.03 mbar,the feed temperature is 60℃,the evaporation temperature is 186℃,the scraper speed is 137 r/min,and the feed rate is 1.5 m L/min,the purity can reach 99.3%.Finally,gas-mass spectrometry was used to analyze the product composition,test its physical and chemical properties,electrical properties and change rules,and investigate its low-temperature performance and application scenarios.The results show that the main components of the transesterification products are fatty acid methyl esters and fatty acid isooctyl esters,accounting for 13.77%and 86.23%respectively.The physicochemical and electrical properties of the purified fatty acid isooctyl ester basically meet the standards of natural ester transformer oil,with a breakdown voltage of 74 k V,a relative dielectric constant of 2.8,a volume resistivity of 14.5×10⁹Ω·m,a viscosity of 6.8 mm²s^-1,and a flash point215℃,freezing point-42℃.When compounding with vegetable oil,the addition of10%～20%of fatty acid isooctyl ester can achieve a good pour point depressing effect.Compared with other types of insulating oil,this product has a lower freezing point and viscosity,showing excellent low temperature performance,and other electrical properties can also meet general application requirements.The plant-based insulating oil prepared in this paper has stable physical and chemical properties,excellent electrical properties,and has a low freezing point.It can be used alone or in combination with vegetable oil.Both can achieve a good pour point depressing effect and meet the requirements of transformer insulation oil.