Preparation Of A Novel Lewis Carbon Nanotube Solid Acid And Its Application In Catalytic Synthesis Of Biodiesel

The biodiesel was produced by chemical catalysis and the solid acid as catalyst,which has the following advantages: low requirement for raw material quality,catalyze esterification and transesterification reaction simultaneous,overcomes the disadvantages that the complex process and generates a large number of containing salt waste water of the traditional acid and alkali complex catalysis method.A carrier with flexible spatial structure has a significant effect on the catalytic performance of solid acid.Carbon nanotubes is a kind of closed ends one-dimensional quantum structure materials,space constraints strictly advantageous to display space choice catalysis,have a strong guiding in the spatial direction of the reactant molecules and the intermediate states of the reaction.Therefore,the carbon nanotubes as a support and was modified by metal or nonmetal and sulfonation in this study.The catalyst was applied to synthesis biodiesel and has a good effect.First,the multi-walled carbon nanotubes is modified by sulfonation method at high temperature,because F element has strong nonmetallic,the Al metal has metal properties and the rare earth element Ce has special spatial structure.We prepared the solid acid catalysts F^--SO₄^2-/MWCNTs,Al³⁺-SO₄^2-/MWCNTs and Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs.The characterization results showed that the specific ions were introduced into the sulfonated carbon nanotubes system,which enhanced the stability of the catalyst,reduced the loss of the sulfate,changed the SO₄^2-chemical state on surface of carbon nanotubes and improved the system charge imbalance of SO₄^2-/MWCNTs catalyst.As a result,the trend of exhibition of an excess of positive charge was increased.Hence,the acid activity sites of the catalyst comprised Lewis acid type mainly.It will be favorable for the avoiding of the acid activity sites of a catalyst was mainly comprised by Br???nsted when it was prepared from the sulfonation treatment alone,so the occurrence of hydration to decrease,and when existed in a reaction medium with large amounts of water can be used to keep the catalytic activity.Second,the effects of different temperatures,molar ratio of methanol to oil and the amount of catalyst on the conversion were investigated.When F^--SO₄^2-/MWCNTs was used as catalyst,the experimental results showed that the conversion of oleic acid reached 93.4% after 5 hours when the reaction temperature was 65?,the amount of catalyst was 1% and the molar ratio of methanol/oleic acid was 14:1.WhenAl³⁺-SO₄^2-/MWCNTs was used as catalyst,the conversion ratio of oleic acid reached95% after 7 hours when the reaction temperature was 65?,the amount of catalyst was0.9% and the molar ratio of methanol/oleic acid was 12:1.The Ce³⁺-Ti⁴⁺-SO₄^2-/MWCNTs was used as catalyst,the conversion ratio of oleic acid reached 93.4% after 5 hours when the reaction temperature was 65?,the amount of catalyst was 1% and the molar ratio of methanol/oleic acid was 14:1.Third,using F^--SO₄^2-/MWCNTs as catalyst,the kinetics of esterification reaction of oleic acid with methanol was simulated and calculated.The factors influence the esterification reaction were discussed from the aspects of reaction temperature,the ratio of alcohol to oil and the amount of catalyst.Assuming that the reaction is a quasi homogeneous reversible second-order reaction,the results showed that the experimental data and the model has good consistency,so got the positive and negative reaction activation energy was 31.46 kJ·mol-1 and-16.1 kJ·mol-1,respectively.The above results indicated that the sulfonated carbon nanotubes is modified by some specific elements,changed the acidic properties of sulfonated carbon nanotubes,further improved the catalytic performance of sulfonated carbon nanotubes,and reduced the loss of acid active sites.Carbon nanotubes will become a new catalytic material for the production of biodiesel.