The Research Of Sulfonated Multi-Walled Carbon Nanotubes For Catalyzing Triglycerides Transesterification In The Ethanol System

With the rapid development of society,environmental issues are increasingly becoming the focus of attention,the use of mineral energy has had some negative effects on the environment such as air pollution and so on.At the same time,the demand of human’s society life and production for energy is increasingly high.At present,the global transportation required energy comes mainly from the mineral energy which has annual growth rate of 2%.As an non-renewable resource,mineral resources are getting reduced and have emissions of quantities of greenhouse gases.Thus,biomass energy takes the place of mineral energy drawing the worldwide attention.Biodiesel is a new type of renewable energy,which has broad application prospects.It is a kind of long chain fatty acid ester which made by physical and chemical methods of raw materials of oil such as animal and vegetable oil,cooking oil with low carbon alcohols.It has a wide source of raw materials.Besides,it has some advantages such as renewable clean degradable and nontoxic.Transesterification reaction is one of the simplest and most economical method of producing high quality biodiesel.In this paper,we studied the triglycerides transesterification in ethanol system by the use of sulfonated multi-walled carbon nanotube（S-MWCNTs）as an effective solid acid catalyst.The main results and conclusions are as follows:（1）The present work describes a facile technique for the synthesis of a high-performing sulfonated multi-walled carbon nanotube solid acid catalyst.The results indicated that S-MWCNTs possessed high acidity due to their polycyclic textural matrix.An overall conversion of 97.8%is achieved for triglycerides at 1 h,150℃ using 3.7 wt%of catalyst in ethanol,outperforming its counterpart catalysts,such as hydrothermal carbonization synthesized sulfonated carbon and metal oxide catalyst WO₃/ZrO₂.（2）The catalyst was fully characterized by BET,FT-IR,XPS and TEM measurements to understand and evaluate their physical and structural properties.Aware of this catalyst has a large surface area,pore width,structure stability,and the advantages of high catalytic activity,suitable for the transesterification of triglycerides.（3）The exploration of the effect of the catalyst loading,the pressure of CO₂,dwell time and reaction temperature for triglycerides transesterification.First,the ethyl ester yield increased with the increase of the catalyst loading,dwell time and reaction temperature and then kept stable.The pressure of CO₂ has no effect on ethyl ester yield.Comparison experiments of using sulfonated multi-walled carbon nanotube and dilute sulphuric acid,such as that of sulfonated multi-walled carbon nanotube by dilute sulphuric acid effectively sulfonated and functionalization.The recycling of catalyst proved its high stability.（4）A kinetic modeling was also proposed to describe triglycerides transesterification,which gives the activation energy（Ea）72.1±4.1 kJ/mol and the frequency factor 17.38±1.16.（5）Combining activity and characterization data enables the postulation of the following reaction mechanisms for triglyceride transesterification based on S-MWCNTs:SO₃H groups first absorb triglycerides and ethanol through the interaction between the acid sites and the atomic oxygen.The carbonyl carbon was then attacked by the nucleophilic ethanol to produce fatty acid ethyl ester（CH₃CH₂COOR）,the final product.Findings from this work provide useful insights on designing effective solid acid catalysts via facile synthesis and regeneration protocol for the transesterification of triglyceride to produce biodiesels.