Preparation of crude fish oil Take the fresh fish liver that has removed the gallbladder, washed and chopped, put it in a pot, add water, pass steam to 80 ° C, flow out the oil, filter, cool the filtrate to 0 ° C, precipitate solid fat, and filter under pressure , the filtrate is crude fish oil. Fish oil[water]→[80℃]oil quality[filtration]→crude fish oil or minced fish as raw material, minced and mixed with starch at 7-10℃, extracted with hexane for 15min, filtered to obtain filtrate. The filtrate was washed with sodium chloride solution, dehydrated by adding anhydrous sodium sulfate, and hexane was recovered to obtain crude fish oil. Minced fish [starch, hexane]→[7-10℃, 15min] filtrate [NaCl]→[anhydrous sodium sulfate] crude fish oil Preparation of refined fish oil Take crude fish oil, add sodium hydroxide ethanol solution to saponify, filter, The filtrate was acidified with acid, extracted with an organic solvent insoluble in water, the extract was washed with water, and the organic layer was removed. The aqueous layer was a light red or reddish-brown clear liquid, which was placed at 10°C for 30 minutes without solid precipitation to obtain refined fish oil. Crude fish oil [alkaline ethanol solution] → filtrate [organic solvent] → [HCl] extract [water washing] → refined fish oil pre-concentration, alcoholysis and ethyl esterification of refined fish oil, and urea inclusion crystallization method to saturate the fish oil The fatty acid with less degree is removed to obtain fish oil fatty acid ethyl ester. Refined fish oil [ethanol, urea inclusion crystal] → preparation of fish oil fatty acid ethyl ester DHA Put the fish oil fatty acid ethyl ester into the extraction tank, open the steel cylinder, after the CO2 is condensed, pressurize it to the set pressure by the high-pressure metering pump, and then preheat it. After heating to the working temperature, enter the extraction tank. SC-CO2 carries fish oil fatty acid ethyl ester into the rectification column, the components come out from the top of the column according to the solubility, and enter the separator to receive after decompression. Experimental conditions: the extraction pressure is 11-15MPa, and the extraction temperature is 35°C; the rectification pressure is 11-15MPa, and the rectification temperature is 40-85°C. Collect the EPA-rich fraction of 12-13.5MPa and the DHA-rich fraction of 14-15MPa, and measure by gas chromatography, EPA+DHA is purified to 90%. The EPA-rich fraction and the DHA-rich fraction are subjected to secondary extraction at 11.5-13MPa and 13.5-15MPa respectively, EPA is purified to 67%, and DHA is purified to more than 90%. Fish oil fatty acid ethyl ester [supercritical CO2 extraction] → [separation] DHA