| Waste cooking oil is one of the main components of food waste.The content of waste cooking oil is 20-30%in food waste,which has high economic value.Waste cooking oil mainly distributes in solid and liquid phases of food waste,the separation of oil in solid phase of food waste is more difficult than that in liquid phases.The content of oil in solid phase of food waste is high(about 10-30%of the dry weight of food waste),but the studies on the separation and extraction of oil in solid phase of food waste are few.Ii order to make full use of resources and reduce the waste of resources,waste cooking oil in solid phase of food waste was extracted by using the microwave-assisted ionic liquid extraction method in this work,and the process of preparing biodiesel from waste cooking oi1 was studied.Firstly,the contents of oil,protein and starch in food waste were determined by the method of Soxhlet extraction,Kjeldahl and acid Hydrolysis respectively.The content of oil,protein,starch were 18.46%,14.35%,60.95%separately,and the cellulose and inorganic salts were 6.24%.The waste cooking oi was extracted by the method of organic solvent reflux,and the effects of solvent,temperature,time and liquid-solid ratio on the extraction were investigated.When the extraction time,liquid-solid ratio and extraction temperature were 60 min,10:1 mL/g and 80“C separately,extract waste cooking oil with n-hexane,the yeild of waste cooking oil was 5.99 wt%.Seven kinds of fatty acids were found in the waste cooking oil by gas chromatography-mass spectrometry analysis,and the total content of fatty aeids was 99.48%.The content of fatty acids such as hexadecanoic acid(20.96%),octadecadienoic acid(32.83%),octadecanoic acid(37.44%)and octadecanoic acid(7.07%)were high,which is conducive to the preparation of biodiesel.Secondly,the mixture of ionic liquids and organic solvents was used to extract waste cooking oil with microwave heating.The effects of ionic liquids,extraction temperature,extraction time,particle size of food waste sample and microwave power on the extraction of waste cooking oil were investigated.When the extractant was the mixture of ethanol-[EMIM]DEP(l-ethyl-3-methylimidazole diethyl phosphate),the ratio of mixture,diameter of sample particles,ratio of solvent to sample,extraction time,extraction temperature and microwave power were 1:1(g/g),0.53 mm,5:1(mL/g),10 min,70“C and 600 W separately,the yeild of waste cooking oil was 9.25%.The results showed that microwave-assisted ionic liquid extraction could improve the yield of waste cooking oil,and shorten the extraction time.Sixteen kinds of fatty acids were found in the waste cooking oil by gas chromatography-mass spectrometry analysis,and the total content fatty acids was 95.96%.The content of fatty acids such as hexadecanoic acid(7.09%),heptadecanoic acid(7.74%),octadecanoic acid(17.44%),octadecadienoic acid(17.00%)and octadecatrienoic acid(7.78%)were high.Thirdly,the mechanism of microwave heating promoting extraction was analyzed by Fick9 law,and the relationship between extraction rate constant and temperature,particle size,microwave power were investigated.The results showed that the relationship between extraction rate constant and temperature was in accordance with Arrhenius equation.The extraction rate constant was proportional to the reciprocal of the square of particle size of food waste sample.The extraction rate constant was proportional to the power of microwave power.And the activation energy of extraction was 16.40 kJ/mol,the rate control step of extraction process was internal diffusion.The experimental data were in good agreement with the theoretical model of extraction,so the macro dynamic model of microwave-assisted ionic liquid extraction of waste cooking oil was obtained.At the same time,the extraction of cooking waste oil using microwave heating and water bath heating showed that the microwave influence factor was proportional to the natural logarithm of temperature.Finally,biodiesel was prepared using one-step method coupled with oil extraction and transesterification reaction steps by strong acidic ionic liquids as catalyst.When the sample of food waste,reaction time,reaction temperature,the dosage of ionic liquid[BS03HMIM][HSO4](1-butylsulfonate-3-methylimidazole bisulfate),the dosage of methanol and microwave power were 3.0 g,20min,60℃,1.5 g,30 mL and 700 W separately,the yield of biodiesel was 69.32%.The preparation process of biodiesel accords with the pseudo-first-order kinetics,and the activation energy of the reaction is about 26.05 kJ/mol.Nine kinds of fatty acid methyl ester were found in the waste cooking oil by gas chromatography-mass spectrometry analysis,the total content of fatty acid methyl ester was 89.78%.The content of fatty acid methyl ester such as heptanoic acid methyl ester(14.82%),octadecanoic acid methyl ester(15.34%),octadecadienoic acid methyl ester(22.74%)and octadecadienoic acid methyl ester(7.58%)were high.It was feasible to prepare biodiesel from food waste directly,which can effectively reduce production time and energy consumption. |
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