Research On The Properties And Component Of Waste Edible Oil And Its Transformation Process To Biodiesel

In recent years,with the rapid development of the catering industry,the consumption of edible oil has gradually increased.Thus,the disposal of waste edible oils(WEOs)has also attracted widespread attention from the society.WEOs would cause environmental risks due to its high organic matter content.As well,its high physical properties similar to fresh edible oils,used by some unscrupulous businessmen,has caused a quantity of food safety problems.Resource utilization of WEOs would reduce its environmental damage,and provide cheap and renewable raw materials for a series of industrial industries,with high economic benefits.Resource utilization of WEOs includes the preparation of free fatty acids,soaps,surfactants,and single-cell proteins.While,these methods all have certain deficiencies in the cost control of raw materials,product quality and process principle.Because biodiesel has better combustion performance and lower environmental impact,refining biodiesel from WEOs has become a hot research topic.In this study,the physicochemical properties and fatty acid composition characteristics of WEOs in Shanghai,as well as their potential for biodiesel production,were investigated by means of literature survey,sampling,and simulated cooking.Triglyceride oleate was selected as the model compound and converted into biodiesel by base-catalyzed transesterification.The effects of reaction temperature,reaction time,alcohol-oil molar ratio and catalyst content on transesterification were systematically investigated.When the reaction temperature was 60 °C,the reaction time was 30 min,the molar ratio of alcohol to oil was 6:1,and the catalyst concentration was1.0%,the methyl ester content in the biodiesel reached the maximum value.The transesterification reaction can be regarded as a pseudo-first-order reaction,and the transition state equation is used to solve it: when the model compound is used as the raw material,the activation energy,enthalpy,entropy and Gibbs free energy of the transesterification reaction are 27 536 J·mol-1、26.27 k J·mol-1、-0.227 J·(mol·K)-1和 101.67 k J·mol-1(at T = 60℃).A positive value of ΔH indicates that the reaction is endothermic,and ΔS < 0 indicates that triglyceride oleate exhibits a better arrangement of reactants in the transition state than in the ground state.As a result,before the reaction equilibrium shifts to the left,as the reaction time increases,the reaction rate would accelerated.A positive value of ΔG indicates that the reaction is endothermic and cannot proceed spontaneously.In order to further explore the influence of the properties and components of WEOs on the yield of biodiesel conversion,six kinds of fresh vegetable oils were selected and subjected to alkali-catalyzed transesterification.The effects of concentration and fatty acid composition on the transesterification reaction were calculated kinetically and thermodynamically.The transesterification reaction was carried out with the samples after simulated cooking according to Shanghai cooking habits as raw materials.According to the experimental results and with reference to Shanghai edible oil consumption habits,the yield of waste edible oil into biodiesel should be between 64.54% and 91.96%.between.The infrared spectra of different oil samples were measured,the relative percentages of four typical functional groups were obtained by area normalization,and a partial least squares structural model was established to judge the effects of different factors.Among the four characteristic functional groups selected(acid hydroxyl,carbonyl,alkenyl and-CH2-groups with a length greater than 4),the alkenyl content has a positive effect on the yield,that is,oils with high unsaturation are more likely to obtain higher FAME yields.The content of the other three characteristic functional groups had no positive effect on the preparation of fatty acid methyl esters.Among them,the acid hydroxyl group has obvious negative effect on the yield,indicating that The acid value is the limiting factor of the reaction conditions.Even if the acid value of the oil and fat raw material is within the required range of the catalyzed transesterification with the base,different reaction conditions should be used for the raw oil and fat with different acid values to maximize the yield.Under the same reaction conditions,the carbon chain length also had a negative effect on the transesterification yield.In actual production,the dosage of methanol should be increased or the reaction temperature should appropriately increase for oils with high long carbon chain content.The base-catalyzed transesterification was carried out for the simulated cooking oil of Shanghai cooking method,and the life cycle analysis of its preparation process was carried out according to the obtained results.The results of the life cycle assessment show that the transesterification stage has a high environmental impact due to the input of methanol materials.In terms of pollution emissions,the process of refining biodiesel from WEOs has no positive environmental benefits.However,because biodiesel is renewable energy,the energy consumption of its production and consumption process is greatly reduced.When the yield of fatty acid methyl ester is used as the benchmark,the change of the yield directly affects the energy consumption of the raw material collection and transportation stages,and the energy consumption change of the raw material collection and transportation process also plays a crucial role in the total energy consumption of the entire production process.In the case of the production rate of91.96%,the energy consumption of the production process is-23 846 MJ,and in the case of the production rate of 64.54%,the energy consumption of the production process is 3005 MJ,which also loses positive benefits in terms of energy consumption.