Analysis and processing optimization of products from medium temperature Fischer-Tropsch synthesis in industrial slurry bed reactor

The medium temperature Fischer-Tropsch (MTFT:260-275 ℃ ) synthesis process was first in a large-scale industrial application in China,and an industrial demonstration plant with a capacity of 4 million tons per year has been built. The core unit of the industrial demonstration plant is characterized by many series of synthesis reactors,a large scale and complex configuration,which causes many problems,such as the difficulty in the operation of the unit,the interaction between the reactors,and the interference between the reactors and downstream units,reducing the op- eration stability of the system. The industrial operation results show that the composition of the MTFT intermediates ap- pears a significant change. Compared with the design value,the wax decreased by 1 058 800 t / a,while heavy oil and light oil increased by 531 600 t / a and 278 200 t / a,respectively. The MTFT products have the advantages of a higher α-olefin content and a higher C+ yield in comparison with the products from the low temperature Fischer-Tropsch (LT- FT) synthesis. The yield of C+ with the main components of α-olefin and n-alkane is 92. 82% . The content of α-olefin in the light oil is 66. 34% . The 1-hexene account is 62. 47% in the total content of C6 ,and the 1-octene account is 70. 43% in the total content of C8 . The composition of α-olefin and n-alkane is about 89. 63% in the MTFT heavy oil, in which the content of α-olefin decreases with the increase of carbon number. The temperature at which 90% of the material is distilled from the synthesized wax is 700 ℃ . The selectivity of C2+2 synthesized from the MTFT process is 59. 79% ,which is equivalent to that of the LTFT wax,but the olefin content is higher. After a hydrotreating and hydro- cracking process for the MTFT intermediates,the MTFT diesel oil is mainly composed of alkanes,with high cetane number (≥60). It is a high-quality clean fuel,but its density is low with the highest value of 780 kg / m3 ,which does not meet the standard of vehicle diesel oil (GB 19147—2013). The octane number of the MTFT naphtha without cy- cloalkanes and aromatics is very low (less than 50). It cannot be used as a blending component to producing gasoline, but it is a high-quality raw material for the production of ethylene and propylene by a steam cracking process. The yield of ethylene can reach 37. 56% ,the yield of propylene is 20. 16% ,and the total yield of ethylene,propylene and 1,3-butadiene is more than 61. 82% . In terms of the limitation of the single product structure of the project,a techni- cal route of CO-production of the diesel oil as a main product and high value-added chemicals such as α-olefin,liquid paraffin,F-T wax,lubricating oil base oil and so on is proposed and gradually implemented in practice. The significant economic benefits have been achieved.