| Soybean oil is the most consumed edible vegetable oil in China,and it is a nutritious and healthy oil.Waste cooking soybean oil can replace animal and vegetable oils to produce biodiesel,which can turn waste into treasure.Before either producing edible soybean oil or using waste cooking soybean oil to prepare biodiesel,the oil needs to be deacidified.Extractive deacidification techniques include traditional organic solvent extraction and deep eutectic solvent extraction.Traditional organic solvent extraction and deacidification is a common method in industry today,which can avoid the problems of waste water and low yield of neutral oil produced by alkali refining method;Deep eutectic solvent（DES）is a new type of solvent with the advantages of non-volatility,low melting point and environmental friendliness,but it is currently less used in extractive deacidification.Therefore,the search for extractants for the efficient removal of free fatty acids（FFA）from soybean oil is of obvious practical importance for extractive deacidification technology.In this paper,soybean oil was extracted and deacidified using traditional organic solvents and deep eutectic solvents,and soybean oil and waste cooking soybean oil were used for the study,to study the effect of extraction and deacidification techniques on FFA removal rate,neutral oil yield and decolorization rate.First,traditional organic solvents were used as extractants and applied to remove FFA from degummed soybean oil.The effects of solvent type,solvent volume fraction and extraction method,oil solubility ratio,extraction time,extraction temperature,stirring speed and extraction frequency on the FFA removal rate,neutral oil yield and decolorization rate of soybean oil were systematically investigated by using 90%ethanol as the extractant and stirring-assisted extraction method.The optimal extraction conditions were:oil-solution ratio of 1:2（g/m L）,extraction time of 15 min,extraction temperature of 30℃,stirring speed of600 r/min,and three times of extraction.Under these conditions,the FFA removal rate was87.6%,the neutral oil yield was 93.0%,the decolorization rate was 56.2%,and the acid value of oil and grease was reduced from 3.46 mg/g to 0.43 mg/g,meeting the acid value requirement of the national standard first grade soybean oil.Then 1%mass fraction of Ca Cl2was added to the aqueous solution of 90%ethanol and extracted twice under the conditions of oil-soluble ratio of 1:2（g/m L）,extraction time of 15 min,extraction temperature of 30°C and stirring speed of 600 r/min.The FFA removal rate was increased by about 5%compared with that without salt extractant,while the addition of salt helped the rapid stratification of solvent extraction after deacidification and oil,which was beneficial to the neutral retention of the oil.After that,the ethanol was recycled and finally the quality of soybean oil before and after deacidification was compared and analyzed.Next,the deep eutectic solvent was used as extractant and applied to remove FFA from degummed soybean oil.A green non-toxic DES composed of betaine monohydrate and polyethylene glycol 600（PEG600）was selected as the extractant for liquid-liquid extraction and deacidification.The effects of DES type,molar ratio,extraction temperature,stirring speed,extraction time and extractant dosage on the FFA removal rate,neutral oil yield and decolorization rate in soybean oil were systematically investigated.The optimal extraction conditions were:betaine monohydrate:PEG600 of 1:16（mol/mol）,extraction temperature of60°C,stirring speed of 1000 r/min,extraction time of 2 h,and DES:oil of 2:1（w/w）.Under these conditions,the FFA removal rate was 75.7%,the neutral oil yield was 90.6%,the decolorization rate was 60.8%,and the acid value of oil and grease was reduced from 3.46mg/g to 0.84 mg/g.After that,after the DES was washed and dried by the hexane,the soybean oil that had been extracted once was extracted once,and the FFA removal rate was90.6%,an increase of 15.0%over the first extraction.Finally,the quality of soybean oil before and after deacidification was analyzed for comparison.Finally,quaternary ammonium salts were used as extractants and applied to remove FFA from waste cooking soybean oil.Tetrabutylammonium chloride（TBAC）was selected as the extractant for solid-liquid extraction and deacidification.The effects of quaternary ammonium salt type,extraction temperature,extraction time,stirring speed and extractant dosage on the removal rate of FFA from soybean oil and the yield of neutral oil were systematically investigated.The optimal extraction conditions were:extraction temperature of 55°C,extraction time of 10 min,stirring speed of 1000 r/min and TBAC:oil of0.4:1（w/w）;Under these conditions,the acid value of waste cooking soybean oil was reduced from 8.36 mg/g to 0.82 mg/g,and the FFA removal rate was 90.2%,and the yield of neutral oil was 89.1%.By comparing the color of waste oil before and after extraction and deacidification,it was found that TBAC also had an auxiliary decolorization effect in the process of deacidification,and the red value of waste oil decreased from 12.2 to 5.9,with a decolorization rate of 56.4%.Finally,TBAC was recycled,and under optimal recycling conditions,TBAC can be used up to five times,and the FFA content in soybean oil can still be reduced to less than 1%at the fifth use. |
