Study On The Preparation Of Aviation Hydrocarbon Fuel Via Thermochemical Conversion Of Triglycerides

Biomass is the only renewable resource that can be directly converted into liquid fuel.Compared with other biomass,the molecular structure of triglycerides is closer to that of petroleum,which is suitable to be transformed into high quality aviation biofuel.The main components of jet fuel are alkanes,cycloalkanes and aromatic hydrocarbons distributed in C₈^C₁₅.To prepare high quality aviation biofuel,catalytic cracking can be performed to obtain the mixture of chain-alkanes and olefins,which is similar to the composition of fossil fuel.Meanwhile,the molecular weight of the pyrolytic oil can be regulated by changing the pyrolysis-distillation conditions.Then,the compositions of the pyrolytic oil can be modified to realize the transformation of the bio oils into the key components of jet fuel including alkane,aromatics and cycloalkanes.Finally,the whole-component substitution of aviation fuel is expected to be realized.Now,the main contents and results of the study are summarized as follows:1.The conversion process of triglycerides to chain hydrocarbons was studied.The mechanism of catalytic cracking process and the effect of pyrolysis-distillation conditions on liquid products were studied.Other pyrolytic products were also analyzed.TG analysis of potassium stearate,sodium stearate and calcium stearate was performed,combining with the dissolution process of catalyst in oil,to explore the mechanism of base catalytic cracking.The results show that the key step of base catalytic cracking is to form carboxylic acid salts via neutralization reaction.When the reaction temperature reached 350?,the catalyst was dissolved in the oil completely,carboxylic salts started to be decomposed and liquid products were produced.The effects of various kinds of base catalysts and various distillation column temperature on the catalytic cracking were studied.When 5 wt%Na₂CO₃ was used as catalyst,the total yield of liquid was 75%,the light oil yield reached 49%,and the acid value was 40.3 mg KOH·g^-1.When the dosage of catalyst was increased to 10 wt%,the yield of liquid products changed little and the acid value of light oil could be decreased to 13.1mg KOH·g^-1.The effect of base catalytic cracking on rubber seed oil,waste cooking oil and acidified oil were studied.The results show that base catalytic cracking has good applicability to various raw materials,and alkanes and olefins are the main components of pyrolytic oil.The pyrolysis gas was collected and thermal calculation of it was performed.The results show that the heat of the pyrolysis gas is sufficient to support the cracking reaction.Based on the analysis of the coke from catalytic cracking,the free radical mechanism of coke formation in the process of base catalytic cracking was proposed.The high temperature graphitization treatment of the coke was carried out,and the conductivity of coke treated under high temperature of 1400? was up to 50 S·cm^-1.2.The method of transforming chain-hydrocarbons into cycloalkanes and aromatics was studied.The mixture of alkanes,cycloalkanes and aromatics can obtained by aromatization and hydrogenation of aviation fuel fraction,respectively.The diesel fraction was treated with hydrogenation,and after regulation of molecular structure,the content of olefins can be decreased The results show that aromatization can effectively reduce the olefin content in aviation fuel fraction and realize the regulation of aromatic hydrocarbons content ranging from 20% to 78%.With further hydrogenation experiment,a mixture of alkanes,aromatics and cycloalkanes is obtained,which is similar to the composition of jet fuel.The preparation of aviation biofuel without no acid,whose density,viscosity,calorific values,freezing point are808 kg·m^-3,2.11 mm²·s^-1,44.4 MJ·kg^-1 and-48?,respectively,meeting the requirements of RP-3 jet fuel.The engine can start successfully at different temperatures,when testing the aviation biofuel on the engine bench.Comparing the flow characteristics of aviation biofuel and RP-3 jet fuel,the fluidity of the two are very close.