Study On The Inclusion Separation Processes Of Normal-Alkanes In Fischer-Tropsch Synthetic Oil

Fischer-Tropsch synthesis is one of the important methods for indirect coal liquefaction to produce oil.Its low-temperature route products are mainly light oils such as diesel,which contain a large number of normal alkanes.Separating n-alkanes from oil products can not only produce low pour point diesel oil,but also produce Fischer-Tropsch synthetic liquid paraffin products with high added value.Therefore,in this study,the urea inclusion method was used to separate n-alkanes from Fischer-Tropsch synthetic oil.Used Orthogonal experiments and controlled variable methods to study the optimal inclusion reaction conditions.Studied the reaction characteristics of urea inclusion with n-alkanes by POM（polarizing microscope）.Used thermogravimetric analysis and other methods to study the non-isothermal thermal decomposition kinetics of urea inclusion compounds.Firstly,used the orthogonal experiment and the controlled variable method to study the optimal inclusion conditions.The mass ratio of dewaxing solution（urea isopropanol aqueous solution）to raw oil was 10:1.The mass ratio of urea to isopropanol and water was 38:40:22.The temperature of the reaction system decreased from 45 ℃ to 25 ℃ at a rate of 1 ℃/min.The urea inclusion compounds were washed twice with petroleum ether at 25 ℃.The content of n-alkanes in liquid paraffin was about 93%.The recovery of n-alkanes in urea inclusion product with gradient cooling was higher than that with traditional cooling.Secondly,the reaction characteristics of n-alkanes in urea were studied by polarizing microscope and infrared microspectroscopy.The results showed that as the reaction proceeded,the rate of the inclusion reaction was slow first,then rapid and finally slow.The growth rate of urea inclusion reaction in the channel direction was much higher than that in the vertical channel direction.The growth rate of urea inclusion compound crystals were the same as the overall reaction rate.As the carbon chain length of n-alkanes increased,the separation efficiency of n-alkanes increased.Thirdly,used thermogravimetric analysis and other methods to study the non-isothermal thermal decomposition kinetics of urea inclusion compounds（UIC）.In a nitrogen atmosphere,the solid-phase thermal decomposition reaction of urea inclusion compound was a first-order reaction.Moreover,the mechanism was the random nucleation and subsequent growth of Avrami-Erofeev.Used Coats-Redfern method and Doyle method to analyze the thermal decomposition process,The activation energy of thermal decomposition of urea compounds in Fischer-Tropsch synthesis was 104.56 k J/mol by the Doyle method with better correlation.The enthalpy change of the thermodynamic parameters was 101.50 k J/mol,the entropy change was –73.95 J/（mol·K）,and the molar free energy was 128.75 k J/mol.Analyze the thermal decomposition temperature of guest urea inclusion compounds with different chain lengths.We can know that urea inclusion compounds formed with high carbon n-alkaneswas more stable.