Microalgae Biodiesel Production By Supercritical Extraction Coupling Transesterification Reaction

With the adjusting of the global energy structure, the strategic position of green and renewable energy sources is established. As a typital renewable energy, biodiesel has become the competition point of new energy technology in recent years. Supercritical transesterification method has great advantages such as green, purification simple, high yield and high efficiency, while the high cost limits its industrial application. Therefore, this article finds methods including equipment structure, raw material and new technology to reduce the process costs based on the supercritical method. Optimizing the continuous process from the point of view of the reactors by investigating the packing types and reaction factors, as well as the reaction kinetics and thermodynamics. By using the technology of supercritical extraction coupling with the supercritical transesterification and choosing the raw material of Chrysophytes to optimize and integrate the continuous process, and the controlling step as well as optimal process condition were determined. The reaction condition was reduced by strengthening the process based on the coupling technology. The in situ technology by coupling supercritical extraction and transesterification was developed and the response surface method was used to optimize the process by using the cheap Chlorella as raw material to reduce the cost. The main research contents were as follows:(1) The continuous process of supercritical transesterification was optimized by good design of fixed bed reactors. Three packings including glass beads, glass spring and Dixon rings were used to investigate the strengthen effect of the packing types and sizes on the process. The result showed that the highest yield and the amount of fatty acid methyl ester can be achieved, as well as the shortest stabilization time, when using Dixon rings as packings. The highest yield was 90.27% when the temperature was 350?, the pressure was 22 MPa, the molar ratio of methanol to oil was 42:1, the flow rates of methanol and oil were 0.20 mL/min and 0.109 mL/min respectively and the system could reach to stable state only need 30min. The yield had no change even the packings were reused up to 60 h.(2) The reaction kinetics and the thermodynamics behavior were investigated in order to research the formation procedure mechanism of supercritical transesterification and provide theoretical evidence for the experiment.The reaction rate constants of different temperatures were obtained and the activation energy of 54.13 kJ/mol was determined by kinetics calculation based on the experimental datas of fixed bed reactor filled by Dixon rings. The critical parameters of the mixture of the oil and methanol and the solubility parameters were confirmed by theoretical calculation of the thermodynamic behaviours.(3) In the system research of supercritical extraction coupling with transesterification, the Chrysophyta was used as raw material and the kinetics of extraction and reaction were matched to optimize the coupling process. The optimal condition was that the particle size of raw material was 40 mesh, the extraction and reaction temperature were 60? and 340? respectively, the system pressure was 18-20 MPa, the flow rates of CO2 and n-hexane were 0.5 L/min and 0.4 mL/min respectively and the molar ratio of methanol to oil was 84:1. The yield was 56.31% when the system reach to stable. The coupling process was strengthened by adding small amount of sulfuric acid and potassium phosphate as catalyst respectively. When the concentration of sulfuric acid to methanol was 0.3% and the an amount of potassium phosphate was 2 g (the volume was 6.2% to the total volum of reactor), the yield can be achieved to 61.86% and 75.44% respectively when the reaction temperature was only 250?.(4) The process of supercritical extraction coupling supercritical in situ transesterification was investigated by using cheap Chlorella sp as raw material. The response surface ethodology was used to study the influence of reaction temperature, reaction time, the ratio of methanol to algae and the interaction of factors on the yield and the process condition was optimized. The highest yield of 76% was obtained when the reaction temperature was 267.49?, reaction time was 50.72 min, the ratio of methanol to algae (v/wt) was 9.91:1.