Separation Of Linolenic Acid Methyl Ester By Complexing With Silver Nitrate

Linolenic acid has important physiological functions to human body,and it can be used in medicine,cosmetics and dietary supplement industry.Thus,it is meaningful to enrich linolenic acid.Owing to the complex composition of vegetable oil,moreover,linolenic acid and its homologues have similar molecular structure,it is difficult to separate linolenic acid from vegetable oil.This paper studied the extraction separation of linolenic acid methyl ester from tallow seed oil methyl ester by the method of silver nitrate complexation.The study focused on three parts.Firstly,the influence factors in the extraction of linolenic acid methyl ester by silver nitrate complexation were investigated,and the extraction conditions were optimized.Secondly,the packed extraction column for separation linolenic acid methyl ester was established,and the structure parameters of the column and the mass transfer were investigated.Thirdly,the bulk liquid membrane extraction device was established.When tallow seed oil methyl esters was used as raw material and silver nitrate-methanol-water as extractant,the influences of extraction temperature,the concentration of silver ion and methanol on the extraction partition coefficient and selectivity of linolenic acid methyl ester(C18:3)were investigated.The partition coefficient of C18:3 was between 0.151 and 1.272,the selectivity was more than 9 when 1 mol/L AgNO3-60% methanol-40% water used as extractant at 0℃-20℃.The work further investigated the effects of extraction stages,the liquid volume ratio and the initial concentration on the extraction yield of C18:3,and the effects of stripping temperature and stages on the recovery of C18:3 when petroleum used as stripping agent.The purity of C18:3 was over 86%,and the yield was 72.1% after four steps extraction and three steps stripping when the volume ratio of the extractant to the oil was 3,the extraction temperature was 10℃,the volume ratio of the stripping agent to the extractant was 1,and the stripping temperature was 50℃.The residuals of silver ions in the raffinate and the product were determined by titration.The residual of silver ion in the raffinate was 5.4 mg/g oil,and silver ion wasn’t found in the product.The further study found that the extractant after stripping could be recycled.In this paper,the extraction column was constructed.When the aqueous phase was the dispersed phase,and the oil phase was the continuous phase,the glass-spring packed column had a good mass transfer performance.The total mass transfer coefficient increased with the increase of the superficial velocity,the relationship between the two ones was Kxa=0.0459e1.166 u.But the flooding would happen when the superficial velocity of the continuous phase and the dispersed phase was 0.00261 m/s and 0.00782 m/s respectively.Furthermore,the device of bulk liquid membrane extraction was constructed,where tallow seed oil methyl esters as raw materials,AgNO3-methanol-water as liquid membrane and petroleum as stripping agent.The effects of the concentration of AgNO3 and methanol,the stirring speed and the stages on extraction were investigated.The results showed that the high concentration of silver nitrate and methanol and the high stirring speed and the small liquid membrane thickness could improve the mass transfer,which was helpful to increase of extraction rate and yield.The increasing number of extraction stages could also increase the yield of the product.When the liquid membrane was composed of 1.8 mol/L silver nitrate,30% methanol and 70% water,the stirring speed was 300 r/min,the extraction temperature was 20 ℃,the purity of linolenic acid methyl ester could be 93% and the yield could be 37.6%.