Study On The Performance Mechanism Of Biodiesel Under Low Temperature

Biodiesel is a kind of oxygenic clean fuel, which is made by using renewable resources as raw material. However, because its carbon number distributes mainly from14to18, its low temperature fluidity is bad. It is easy to crystallize and gel when the temperature is low, which limits the application of Biodiesel. In this topic, firstly, the simulate biodiesel will be adopted to study the structure-activity relationship between the different components of biodiesel, which are made from different sources and have different compositions, and the low temperature fluidity of the biodiesel. A study on the crystal structure at low temperature, morphology and the thermodynamic phase change mechanism will be proceeded.Secondly, cryo-SEM microscopy and in-situ X-ray technology will be used to investigate the low temperature performance of biodiesel low temperature flow improver in itself. Finally, the representative flow improver will be chosen to research the interaction mechanism between the low temperature flow improver and biodiesel at low temperature, and the interaction theory model and molecular simulation for biodiesel and the flow improver at low temperature will be set up from the angle of computational chemistry, which will provide theoretical basis for the development of new biodiesel low temperature flow improvers. This research has important application significance for the generalization of biodiesel marketing. And it can help to alleviate the present situation of our country’s energy nervous, guarantee energy security and protect the ecological environment.Conclusions:(1)When the number of carbon atom in the carbon chain is more than16, it is not necessary that the methylates will gear up the SP of the system. As the double bond grows in number, the effectiveness of lowing SP becomes more obvious. With the content of C18rises, in the system, the spherical-like wax crystals and acicular crystals which are smaller in size are formed, and there can gather more easily, thus make the SP of the system increase. The condensation procedures follow a quite similar characteristic, but when the temperature is near SP, the amount of orthogonal crystal peaks in C18three (40%) is bigger, indicating the condensation is more intense.(2)When the content of methyl linolenate rises, the shape and size of the wax crystals is changed, thus changes the crystallization behavior and weakens the development of larger bulk-like crystals. Finally, the growing of wax is restrained.(3) The PPDs which are in common use have a certain effective on biodiesel, but the effect is essentially unobvious, so it is very necessary to research and develop new high efficient PPDs of biodiesel or design excellent compound PPDs.(4) It can be seen from the calculated results, the optimal technological condition is PMA-2 and PPD-6(mass ratio,1:8),lowering the SP and CFPP of biodiesel by5℃and3℃respectively.(5)DSC analysis shows that the compound pour point depressant (CPPD) makes the temperature at which the crystals emerge lower. But it has essentially no effect on the slope of the peak, and the CFPP has not changed the rate of precipitation of wax crystals. The dispersion is more stable when the CP is added in biodiesel. The amount of crystals is smaller. And all of the factors lead to the drop of the SP and CFPP of the biodiesel.(6)Low-temperature XRD analysis shows that, the compound pour point depressant essentially prevents the aggregation of crystals when the temperature is lowering, changes the construction way of the crystals, decreases the amount of orthorhombic crystals, monishes the size of crystals and resists the construction of bigger crystals. So the overall result is that CFPP and SP of biodiesel are lowered.(7) Polarizing optical microscope shows that, when the compound pour point depressant (CPPD) is added; the polar groups of the CPPD insert the cores of the crystals in biodiesel, which results in eutectic effect. The no polar-groups of the CPPD distribute on the surface of the crystals and change the interfacial characteristic of the crystals, which alters the shape and disperse of the crystals, thus improves the flow ability of biodiesel in low temperature.(8) The impact of methylacrylate PPD10-320on cold flow properties of biodiesel blends was investigated, The results show that adding1%additive in B60produced a cold filter plugging point of-10℃.(9) DSC analysis shows that, in B60with PPD, the crystallization rate of the wax crystals slowed down, and the content of crystal decreased, solid-liquid phase change energy lessened in system, was0.579Jg-1, the system was more stable, so the CFPP was the lowest.(10) Polarizing optical microscope shows that, there were lots of smaller spherical-like wax crystalline in B60, particle size<20μm. They went through the filter easily, so the CFPP was depressed. This is because in B60, on the one hand PPD changed the process of the crystal growth by co-crystallization, on the other hand the composition of diesel and biodiesel are quite different. It produced certain exclusion between the diesel and biodiesel, which inhibited the aggregation and growth. The crystals remained in smaller size.(11) Low-temperature XRD analysis shows that, the content of crystal in B60was less, in which the ratio of orthorhombic and monoclinic peak area was0.086. The content of orthorhombic crystal precipitated was relatively less, the content of monoclinic crystal precipitated was relatively more, and the monoclinic crystal was easier to go through the filter, so the CFPP of B60was the lowest.