| Biomass pyrolysis liquefaction technology is a method of thermochemical conversion,which converts biomass feedstock into three different products of liquid,gas and solid,wherein the liquid product as the main target product is called bio-oil.As a renewable liquid fuel,bio-oil is an ideal alternative to fossil liquid fuels.Therefore,pyrolysis liquefaction technology is one of the most promising biomass energy utilization technologies.After decades of rapid development,the laboratory-scale biomass pyrolysis liquefaction technology has been quite mature,basically meeting the technical requirements for large-scale production of bio-oil,but so far it has not really realized commercial application.The main reason is that bio-oil has defects such as high oxygen content,poor ignition characteristics,high acidity,poor stability and complex chemical composition.As a direct application of fuel,there are not only technical difficulties,but also lack of market competitiveness in the economy.Therefore,before application,bio-oil needs to be upgraded,refined,separated and purified.Microemulsification is a simple and effective method for upgrading.It can blend bio-oil into fossil liquid fuels or other commercially used liquid fuels such as biodiesel,which can effectively improve the fuel grade of bio-oil.If used as a thermal equipment fuel,it can also reduce the cost of burner reform.Based on the above background,this study has carried out systematic and in-depth research on the preparation of bio-oil/diesel micro-emulsified fuel.First,the basic physicochemical properties and chemical composition of the original bio-oil were studied,and a new bio-oil model compound was tried to better simulate the properties of the bio-oil.The water content,calorific value,element,viscosity,surface tension and chemical composition of bio-oil were measured and analyzed.The storage characteristics of bio-oil were investigated,and the physical and chemical properties of bio-oil before and after storage were compared.According to GC/MS analysis results,several components that best reflected the characteristics of bio-oil were selected,and GC/FID was used for quantitative analysis to select new bio-oil model compounds.The experimental results show that the bio-oil has a water content of 23.9%and a high calorific value of 18.39 MJ/kg.Compared with fossil fuels such as diesel,the calorific value of bio-oil is lower,the water content and oxygen content are higher,and the fuel quality is poor.The bio-oil is prone to esterification,oxidation,polycondensation and other aging reactions during storage.Small molecules of organic acids such as acids,aldehydes,ketones,and furans decrease with increasing storage time,and macromolecular polycondensates increase with storage time,leading to organisms.The water content of the bio-oil rises,the viscosity increases,the viscosity-temperature characteristics deteriorate,the acidity decreases,and the calorific value decreases.Twelve substances such as acetic acid and guaiacol were selected as the characteristic components of bio-oil,and quantitative analysis was carried out.Among the selected characteristic compounds,the acetic acid content is up to 4.126 wt.%,the total content of phenolic substances is higher,and the content of benzene,2,5-dimethoxytetrahydrofuran and methylcyclopentenolone is lower.Considering the addition of methanol as a spray medium in the first stage of condensation,the proportion of small molecule alcohol is increased in the bio-oil characteristic model compound.In this study,water,ethanol,acetic acid,m-cresol and guaiacol were selected as the characteristic components of bio-oil model compounds,and their mass contents were 28.8%,23.2%,9.8%,26.1%and 12.1%,respectively.The emulsification test was carried out using a bio-oil model compound.Two-factor and five-level full-factor experimental analysis was carried out with the emulsifier content and the model compound/diesel volume ratio(B/D ratio)as variables.The experimental results show that the stable bio-oil model compound/diesel microemulsion can be successfully prepared by using the blended Span80 and Tween80 as emulsifiers under the condition of hydrophilic-lipophilic balance(HLB)value of 5.By fitting the solubilization characteristics of each component,a fitting equation with higher accuracy can be obtained,and the predicted result is very close to the actual measured value,so that the solubilization result of the bio-oil model compound under different conditions can be effectively predicted.It can be seen from the experimental results and the fitting equation that increasing the content of the emulsifier is beneficial to increase the solubilizing ability and the percentage of solubilization of the bio-oil model compound,but is not conducive to improving the solubilizing efficiency of the emulsifier.An increase in the B/D ratio can increase the solubilizing ability of the model compound,but is not conducive to increasing the percentage of solubilization of the model compound.Considering the amount of solubilization and solubilization efficiency,the emulsifier content is 0.3 to 0.45 mol/L,and the B/D ratio is 4:12,which is the best preparation method.In this context,the model compound/diesel microemulsion is W/O type.The volume of the barrier zone of the reverse micelle is larger than that of the hydrophilic core,and the guaiacol dissolved in the barrier zone is significantly higher in solubilization and solubilization efficiency than water and acetic acid in the hydrophilic core.The fuel properties of the microemulsion are closer to that of diesel.However,due to the influence of the emulsifier and the model compound,the microemulsion is slightly inferior to diesel in terms of calorific value and viscosity.In order to enhance the emulsification effect,it is attempted to add n-octanol as a co-emulsifier in the microemulsification process.Using the central composite design method,the experimental design and analysis were carried out with the emulsifier HLB value,emulsifier and co-emulsifier content as the main factors.The quantitative analysis of the layered aqueous phase revealed the presence of n-octanol in the aqueous phase,indicating that some of the co-emulsifier entered the aqueous phase during the preparation of the microemulsion?The layered aqueous phase is not only an un-solubilized bio-oil.If the solubilization is characterized by a stratified volume at this time,there is a certain error.According to the GC/FID quantitative results,the solubilization of each characteristic component is fitted,and the fitting equation with higher accuracy can also be obtained.The predicted results are very close to the actual measured values,which can effectively predict the solubilization of bio-oil model compounds.The addition of a co-emulsifier can significantly increase the solubilization of the model compound in the microemulsion and the solubilizing efficiency of the emulsifier.According to the fitting formula,there is an interaction between the emulsifier HLB value,the emulsifier content and the co-emulsifier content.The interactions between emulsifier content and co-emulsifier content have a significant effect on the solubilization of the model compound.Using walnut shell pyrolysis oil and commercially 0#diesel as raw materials,the experiment was designed by using the central composite design method with the emulsifier HLB value,emulsifier content and co-emulsifier content as the influencing factors.The solubilization of bio-oil in the microemulsion,the fuel properties of the microemulsion,and the thermogravimetric properties of the microemulsion were analyzed.The experimental results show that a stable bio-oil/diesel microemulsion can be obtained by adding an emulsifier and a co-emulsifier.The fuel quality of microemulsion is slightly inferior to that of diesel oil,but it is far superior to bio-oil and has good practical value.The evaporation of microemulsified fuel in N2 and 02 atmospheres is mainly divided into three stages:the first stage is from room temperature to 280?,which is the evaporation stage of light components.The second stage in the N2 atmosphere is 280-500?,and the mass loss is mainly caused by the cleavage of macromolecules in the emulsifier and bio-oil components.The third stage is 500-650?,which is the stage of pyrolysis coke production.The second stage of the O2 atmosphere is 280-450?,and the thermal mass loss is due to the cracking and oxidation of macromolecular substances.The third stage is 450-650?,and the thermal weight loss is mainly from the combustion of pyrolysis coke.The activation energy of the evaporation or combustion process of the microemulsified fuel under nitrogen and oxygen atmospheres was calculated by KAS and FWO methods,respectively.The results show that the activation energy of microemulsion in N2 atmosphere is in the range of 30.899-40.167 kJ/mol,and the activation energy of emulsion fuel in O2 atmosphere is in the range of 53.849-61.621 kJ/mol.The correlation coefficient is higher when thermal weight losses in N2 atmosphere are fitted by KAS method and FWO method,which is more suitable for the kinetic analysis of emulsion fuel in N2 atmosphere. |
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