Study On Stochastic Dynamic Model And Low Temperature Fluidity Evaluation Of Biodiesel Prepared By Two - Step Method

With the fast development of biodiesel preparation technology in the past decade, countries around the globe are becoming more and more proficient in preparing biodiesel. However, it is affected by the material problems and theoretical problems of the preparation process, and its industrialization is going slowly. At present, China has a small supply of raw oil and complicated oil types, which can not meet the demand of market and national energy reserves. Therefore, this paper proposes an optimal preparation method of biodiesel. And it is very necessary to investigate the random preparation process of biodiesel.This paper illustrates the method of biodiesel preparation and research of process parameters. The respond surface method (RSM) is adopted to explore the optimization of technical parameters in two-step biodiesel preparation method (sub-critical hydrolysis and super-critical esterification) and experiments testify the effectiveness of RSM. Macro and microscopic perspectives are used to control the working mechanism in the reactions of two-step method. Microscopic rules of the generation of fatty acid are investigated and to a certain extent, rules of the generation of methyl oleate can be understood. DEA is adopted to analyze the physical properties of biodiesel. Meanwhile, an approach to improve the low-temperature fluidity of biodiesel based on DEA is introduced. The main results can be summarized as follows. 1. The study on the technical parameter optimization of two-step biodiesel preparation method. The testing device in this paper is self-made. Technical parameters of biodiesel preparation are investigated. The optimal reaction conditions are respectively:subcritical hydrolysis of 290℃,30min and 25.6MPa; supercritical methanol esterification of 270℃, 40min and 24.8MPa. On this basis, an approach combined with tests and data analysis is adopted to optimize the above parameters, which in details are:the reaction temperature of hydrolysis is 293.1℃, reaction time 32.64 min, the ratio of water-oil is 4.04:1 and reaction pressure 26.1 Mpa; the reaction temperature of esterification is 278.01℃, reaction time 39.21 min, the ratio of alcohol-acid is 2.39:1 and reaction pressure 25.2 Mpa. 2. Study on the stochastic dynamic model of two-step biodiesel preparation method. Macroscopic rate equation is used to investigate parameters of hydrolysis and esterification reactions. The reaction order of hydrolysis is n=0.7766, activation energy Ea=61.499kJ/mol, frequency factor A=7261 and its dynamic model is -dc/dt=7261e-61.9/RTCA0.7766;while the reaction order of esterification is n=1.8, v Ea=20.14, frequency factor A=62.98 and its dynamic model is -dcA/dt=62.98e-20.14/RTCA1.8. Meanwhile, based on stochastic dynamical system and basic theories of stochastic dynamics, it constructs a stochastic dynamic model of hydrolysis and esterification from the model of conversion rate and time φ(x,t)=f(x,t)+(2Dx) dH(t), which offers an microscopic perspective to analyze the detailed process of hydrolysis and esterification of rapeseed oil. The stochastic dynamic model is verified with the parameter Adj.R2 that is determined by mean square error D, the reaction rate constant K, order of reaction n and modification of the random system, which provides a reference for quality control and process control of biodiesel industrialization.3. Study on the improvement of the low-temperature fluidity of biodiesel made from rapeseed oil. The low-temperature fluidity of biodiesel is essential for its market and future development. There is a variety of low-temperature modifiers and depressants in the market. We randomly select 10 kinds of modifiers and depressants. By univariate test and orthogonal test, the improved outcomes of different modifiers and depressants are analyzed. Considering the cost, combination of different modifiers and depressants are tested and assessed by means of data envelopment analysis (DEA). DEA is introduced into the assessment of low-temperature fluidity of biodiesel, which is helpful for enterprises to make different combinations of modifiers and depressants in accordance with the market demand.