Study On Complexation Separation Of Normal Alkanes From Fischer-tropsch Oil Products

Fischer-Tropsch Synthesis(FTS)downstream products mainly include gasoline,diesel and aviation kerosene,which usually contain some n-paraffins.The existing n-paraffins will reduce the products quality.Therefore,it is beneficial to separate n-paraffins from gasoline and diesel oil by inclusion method for raising gasoline octane number and decreasing pour point of diesel.For the Fischer-Tropsch diesels,including straight-run diesel and heterogeneous diesel,normal hydrocarbon were separated by urea/thiourea inclusion method and urea-thiourea inclusion method respectively.By optimizing experimental conditions,highly pure wax and low condensation point diesel were obtained.(1)After separation from heavy straight-run diesel,the n-alkane content in complex phase product can reach 97.0wt% by primary urea separation and rise to 98.0wt% by secondary urea separation at the optimum experimental conditions: urea:activators:raw oil=1:8:1,reaction temperature,30℃ and reaction time,4hrs.The yield of wax can reach 59%.(2)By separating n-alkane from the light straight-run diesel,light wax,in which n-alkane content above 98.0wt%,was obtained by urea inclusion method and urea-thiourea inclusion method.The yield of light paraffin was 37.5%.(3)In separation heterogeneous diesel by urea inclusion method,by adding urea 25g/50g/100 g reapectively,the condensation point of heterogeneous diesel can be lowered to-25 ℃ /-35 ℃ /-41.The condensation point of heterogeneous diesel will decrease more with more urea dosage.For boosting octane rating of FCC gasoline,n-alkane was mainly separated by urea-thiourea inclusion method.By optimizing dewaxing process conditions including urea to thiourea ratio,reaction temperature,complex dosage,activator dosage,activator type and reaction time,the optimum experimental conditions were obtained as: absolute ethanol as activator,urea to thiourea ratio,1:1,reaction temperature,-10℃,reaction time,4h and complex to activator mass ratio,0.65.Octane number of FCC gasoline was added up by 14 units under optimum experimental conditions.To investigate separation mechanism of inclusion methods,structure and stability of urea inclusion crystal(UIC)and urea-thiourea inclusion crystal(U-TIC)were analyzed by MD simulation,XRD,DSC and IR.It can be concluded from MD simulation that inclusion compounds with higher carbon number n-alkane are more stable,and that low temperature is beneficial to the stability of inclusion compounds.It can also be seen from XRD,DSC and IR analysis that thiourea,in dewaxing process by urea-thiourea method,will improve inclusion efficiency between urea and n-paraffins.