Study On The Production Of Biodiesel And Fermentable Sugar Using Microalgae(Chlorella Vulgaris) Assisted By Radio Frequency

The limitation of fossil fuel has become a threat of energy security worldwide.Rapid growth,fixation of carbon dioxide,and little competition with food plus some species possessing high lipid content make microalgae a suitable feedstock to produce biodiesel.However,high cost related to dehydration,lipid extraction and conversion to biodiesel hampers industrialization of biodiesel production from microalgae.In order to make microalgae biodiesel production economically feasible,the comprehensive utilization of microalgae has become a research hotspot in recent years.In short,the concept requires mild cell disruption,extraction and separation technologies on microalgae to reduce production cost meanwhile encourage utilization of all compounds in microalgae.At present,there are few reports about the comprehensive utilization of microalgae lipids and starch at home and abroad,that is,the use of microalgae lipids and starch components to reduce the cost of raw materials.Therefore,the purpose of this study is to use radiofrequency heating technology to assist the production of biodiesel and fermentable sugar from microalgae,so as to make comprehensive use of lipids and carbohydrates in microalgae.The main results are as follows:1 Direct biodiesel production from wet microalgae assisted by radio frequency heatingThe objective of this study was to develop a biodiesel production procedure directly from wet microalgae.The system was operated under atmospheric pressure without requiring any specific apparatus.Wet microalgae(Chlorella vulgaris)was pretreated by radio frequency(RF)heating to disrupt cell walls first,followed by esterification and transesterification with relatively small amount of methanol and catalyst(either HCL or Na OH)assisted by RF heating at 55℃ for only 20 min.The fatty acid methyl esters(FAME)yield reached as high as 79.5±3.0%.The two major factors impacting biodiesel yield are catalyst and methanol.The SEM images visually verified the significant effect of cell disruption by the pretreatment.2 Application of response surface method for optimization of biodiesel production directly from wet microalgae assisted by radio frequencyThen,the procedure for biodiesel production was optimized using response surface methodology(RSM).A three-variable,five-level central composite design(CCD)was employed to evaluate the effects of three key parameters,i.e.,HCl to Me OH ratio(v/v),Me OH volume and RF heating time.An optimized point was successfully found.The best predicted FAME yield of 93.1% was obtained at HCl to Me OH ratio of 4.27(v/v),Me OH volume of 28.5 m L and RF heating time of 19.2 min.Experiments carried out at the optimized point resulted in 92.7±0.1% yield,which validated the reliability of the prediction model.All processing steps,including cell destruction,esterification and transesterification,were carried out under temperatures below 100℃ and atmospheric pressure.Therefore,no pressure-proof nor high-temperature apparatus was required.The procedure shows great potential for industrial application because of its high FAME yield,simple operation,low chemical consumption and short processing time.3 Fermentable sugar production from wet microalgae residual after biodiesel production assisted by radio frequency heatingBesides lipid,there was also high content of carbohydrate in Chlorella vulgaris.In this study,the feasibility of comprehensive recovery of lipid and carbohydrate in wet microalgae Chlorella vulgaris was explored.First,four sets of enzyme combinations ofα-Amylase,Amyloglucosidase and CTec2 were evaluated for hydrolysis efficiency on microalgae disrupted with radio frequency heating.Then,the most suitable combination was applied to raw microalgae and microalgae residual after biodiesel production,respectively,for saccharification.Adsorption kinetics of the optimized enzyme combination on the aforementioned three samples were determined and adsorption isotherm was analyzed by Freundlich equation.Morphology of microalgae was also investigated by scanning electron microscopy.A yield of reducing sugars in microalgae residual at 54.5% was obtained after 72 h saccharification.The results from enzyme adsorption kinetics,isotherm and SEM images were consistent with each other.This study demonstrated that the microalgae residual after biodiesel production could be used as carbohydrate feedstock for fermentable sugar production through simple enzymatic hydrolysis.