Development Of High Efficiency And Low Energy Consumption Separation Process For Fischer-tropsch Synthetic Oil

Fischer-Tropsch（F-T）synthetic oil contains a lot of high added value component,such asα-olefins.However,there is no mature separation and utilization process for F-T synthetic oil in China for now.Therefore,if an appropriate separation and utilization technology for F-T synthetic oil can be developed,not only the fine value-added utilization of F-T synthetic oil could be realized,but also the market would be influenced tremendously.In this paper,the preliminary separation of Fischer-Tropsch synthetic oil was carried out by batch distillation,and the products,i.e.C₅-C₉ narrow fractions,were obtained which were analyzed by gas chromatography.The main products,i.e.the C₆ and C₈ narrow fractions,were enriched by repeated batch distillation,thus the products with high purity were obtained by fine separation.On one hand,the C₆ and C₈ narrow fraction products could provide the information of the key components for thermodynamic study,on the other hand,they could be used as feedstock in the n-hydrocarbon separation process.To verify the accuracy of the simulation process,continuous distillation was conducted to obtain the C₆ narrow fraction,which was selected as representative.Next the main impurities in C₆ and C₈ narrow fraction products obtained after fine separation were analyzed respectively by gas chromatography-mass spectrometry,then the thermodynamic data of the key components were measured.In this paper,the isobaric vapor-liquid equilibria data of five binary systems,i.e.1-hexene+2-hexene,1-hexene+2-methylpentane,1-hexene+3-methylpentane,1-octene+2-octene and1+octane+3-methylheptane,were measured by a double circulating vapor-liquid equilibrium glass still at 101.3 k Pa.The optimal thermodynamic model and the corresponding thermodynamic interaction parameters were obtained after the experimental dada were fitted and regressed by the activity models such as Wilson,NRTL,and UNIQUAC.What’s more,the thermodynamic interaction parameters were introduced to the property database of the process simulation software to improve the simulation accuracy.The accuracy of simulation model was verified by the continuous distillation experimental data.The preliminary separation process of F-T synthetic oil were simulated and the energy consumption of different separation sequences is analyzed in order to select the optimal separation process.New energy-saving separation technologies,such as dividing wall column（DWC）was introduced in the F-T synthesis oil preliminary separation process.Compared with the traditional process,the energy consumption and TAC of the DWC processes were reduced by 11.7% and 10.1%respectively.As for theα-olefins separation process pressure-swing thermally coupled distillation technology（PSTC）was introduced.In the PSTC process since no extra reboiler duty was needed due to the reboiler dury of the low-pressure column could be totally offset by the high-pressure column so that the TAC could be cut down about 45% compared with the traditional one.Moreover,the high efficiency separation method for n-hydrocarbons and iso-hydrocarbons in C₆ and C₈ narrow fractions has been studied.The urea inclusion reaction was apply in this section.Three kinds of materials,such as the pure substance of the C₆ and C₈ hydrocarbons,the simple mixture of C₈ hydrocarbons and the C₈ narrow fraction obtained from the F-T synthesis oil,was studied.The effect of cooling time,urea mass,ethanol content,water content and washing method on the urea inclusion seperation effect were investigated.The mass content of n-hydrocarbon in the C₈ narrow fraction could reach above 98 wt% after urea inclusion reaction.