Study On Preparation And Improvement Of Cold Flow Properties Of Biodiesel

Biodiesel is a kind of environmentally friendly biofuels.However,cold flow properties of that is poor.Biodiesel used low temperature separates out waxy crystals easily,and blocks fuel pipe and filter of diesel engine,which affects normal startup of the engine.In this paper,biodiesel was prepared with six vegetable oils,such as rice oil,rapeseed oil,and so on,as raw material.Further,the effect factors of cold flow properties of biodiesel was researched to find the way to improve its cold flow properties.The main contents and conclusions are as follows:(1)Taking the rice oil biodiesel as an example,the effect of petroleum ether on the alkali catalysis transesterification was researched.It was found that the yield of biodiesel increased significantly after adding petroleum ether,and optimum Concentration of petroleum ether was determined.Simultaneously,effect of the molar ratio of methanol to oil,catalyst concentration,reaction temperature,and reaction time on the yield of biodiesel was integrated.A maximum biodiesel yield of 96.3 wt.%was achieved with a 7:1 molar ratio of methanol to oil,10 vol.%petroleum ether,and 1.2 wt.%NaOH at 50 ℃ for 1 h.Concurrently,we also optimized experimental conditions of other five biodiesel such as rapeseed oil biodiesel(RB),peanut oil biodiesel(PB),and so on.Besides,we tested main physical and chemical properties of six biodiesel,which were compared with the standard.Other than poor cold flow properties of PB,other five biodiesel all meet standard of no.0 petroleum diesel fuel.In addition,such as acid value,viscosity,flash point,density,copper corrosion,and water content all complied with the standard of EN 14214 and ASTM D6751.(2)Composition and content of six biodiesel was analyzed by GC-MS.Varieties and content of fatty acid methyl esters(FAME)were different in biodiesel from various raw materials.The relationship of content of FAME and cold flow properties was investigated.The results prove that cold flow properties for biodiesel mainly depend on saturated FAME.Long-straight chain saturated FAME tend to have relatively poor cold flow properties.Long alcohol chain and high degree of branched chain fatty acid esters tend to have relatively good cold flow properties.Saturated branched esters are more than unsaturated branched chain esters can help reduce cold flow properties for biodiesel.The results might be useful in improving cold flow properties for biodiesel with the method of isomerization in the future.Saturated and unsaturated fatty acids might be separated from vegetable oil,then branched chain esters were obtained from esterification of saturated fatty acids with branched chain alcohol,and FAME were obtained from esterification of unsaturated fatty acids with methanol.(3)Cold flow properties for biodiesel were improved by changing composition with three methods,such as mix oil of rice oil and rapeseed oil,mix alcohols of methanol and branched chain alcohols,and mix fuels of rice oil and petroleum diesel.The above three methods all can improve effectively cold flow properties for biodiesel.Relevant conclusions were as follows:fatty acids composition was changed in biodiesel from mix oil of rice oil and rapeseed oil,content of saturated FAME lowed and methyl linolenate content of unsaturated FAME increased,which improved cold flow properties for biodiesel.Especially,cold flow properties were the best for biodiesel from mix oil(volume content of rapeseed oil was 30%).Methyl palmitate content lowed a lot and branched chain esters was seldom,which improved cold flow properties for biodiesel.However,transesterification of palmitic acid esters and methanol was incomplete,which reduced the yield of biodiesel and was a waste of resources.After adding petroleum diesel into rice oil,yield of blend fuels lowed and cold flow properties were improved.Cold filter plugging points of blend fuels lowed to-19℃ when 70vol.%diesel from direct coal liquefaction was added into rice oil.