Study On Efficient Catalysis For Microalgae Biodiesel Synthesis

Biodiesel is one of important new energies that has industrialization prospects due to it's environmentally friendly,renewable and excellent safety performance.For the biodiesel synthesis,extraction of oil and selection of catalyst play important roles.In the traditional synthesis process,the expensive raw material price and high cost of extraction limit the extension production of biodiesel.Therefore,it's important for biodiesel marketization to find a cheap raw material and develop a low cost extraction method.Microalgae,a material with high oil content and large output,interests widely eyelight of researchers based on its potential value as a new generation material of biodiesel synthesis.Solid acid catalyst is one of the catalysts commonly used to synthesize biodiesel.Contrast to homogeneous acid catalyst,it has the advantages of easy separation,small corrosion,recyclability and so on.Compared with the alkali catalyst,it also eliminates the consideration of the reactant acid value and thus has wider applicability.Nevertheless,the current solid acid catalyst is not very active and requires high reaction temperature.In the research process of preparing catalysts with higher catalytic activity,we found that the use of microalgae as a raw material to synthesize biodiesel in one step is the most promising reaction route among many synthetic methods.So the work of this article includes the following steps:First of all,we measured the fat content of microalgae,about 18.3%by dry weight as desired,which can be used as raw material of biodiesel.In the next step,two kinds of catalysts,sulfonated carbon nanosheets and nanosheet SO₄^2-/ZrO₂ solid acid were prepared by the framework method in this article.The effect of different sulfonation conditions and calcination time on the catalytic activity was investigated:1)When the carbon nanosheets obtained by boric acid and gelatin sulfonate for 1 h at 500°C,have an acid amount of 6.0 mmol·g^-1.The yield of biodiesel from soybean oil was 48.1%catalyzed by the sulfonated carbon nanosheets.2)Using Zr?NO₃?₄·5H₂O as a precursor,glucose and urea as templates,calcining at 700°C for 3 h after sulfonation,the acidity of obtained nanosheet SO₄^2-/ZrO₂ solid acid is 0.054 between the pH=-2⁺3.The yield of biodiesel from soybean oil reached 40.3%catalyzed by the nanosheet SO₄^2-/ZrO₂ solid acid.Based on this situation,summarize the effect of sulfonated amount on the catalytic activity of the catalysts:1)When the catalyst is sulfonated carbon nanosheets,the amount of acid is positively correlated to the yield of biodiesel,the higher the amount of acid,the better the catalytic activity;2)When SO₄^2-/ZrO₂ solid acid is used as the catalyst,the acidity of the catalyst calcined at 300⁷00°C for 3 h is the same,but the yield off biodiesel is different,the catalyst with better nanosheet structure has better catalytic activity;3)sulfonated carbon nanosheets contain two acidic functional groups?-SO₃H and-OH?,and-SO₃H occupies the main part.In addition,the influence of reaction conditions on the catalytic activity of the catalyst was also investigated.The optimal reaction temperature of sulfonated carbon nanosheets was 90°C.The optimal molar ratio of alcohol to oil was 12:1;and the optimal reaction temperature of SO₄^2-/ZrO₂ solid acid was 120°C.The optimal molar ratio of alcohol to oil is 12:1.Simultaneously,the sulfonated carbon nanosheets and SO₄^2-/ZrO₂ solid acid with best activity were compared with the homogeneous acid catalyst H₂SO₄.When the catalyst mass were the same,the catalytic activity of the sulfonated carbon nanosheets was close to the catalytic activity of sulfuric acid,and SO₄^2-/ZrO₂ solid acid had better catalytic stability.Trying a microwave-assisted transesterification reaction,the SO₄^2-/ZrO₂ solid acid catalyst prepared by calcining at700°C was used to synthesize biodiesel from microalgae.When the reaction time was40 min under microwave irradiation,the yield was 21.5%.