Research On Synthesis Of Low Carbon Hydrocarbons By Intedrated Fischer-Tropsch Reaction Of Microreactor And Fe-based Catalyst

The reactants/products of fixed bed,slurry bed and fluidized bed reactors commonly used in Fischer-Tropsch synthesis are difficult to separate from the catalyst,and there are different degrees of mass and heat transfer problems.The micro reactor can react at near isothermal and very low pressure drop,so as to improve the reaction performance of Fischer-Tropsch synthesis and improve the activity and selectivity of the catalyst.Aiming at the target of Fischer-Tropsch synthesis of low-carbon hydrocarbons,using common steel pipe as both micro reaction channel and Fe catalyst matrix,this paper first carries out KOH alkali corrosion treatment,and then uses impregnation method to load the co active components of Mn,Co and Ce to prepare Fe catalyst.It is loaded into a conventional fixed bed to build a Fischer-Tropsch synthesis micro reactor integrated with Fe catalyst.The catalytic performance of Fischer-Tropsch synthesis is evaluated through orthogonal experimental design,Taking the selectivity of C₂～C₄hydrocarbons as the index,the optimized preparation parameters and reaction process parameters of Fe catalyst were selected,and the surface morphology and crystal structure of the catalyst were characterized by SEM,XRD.（1）The corrosion rate of molten KOH is 100～1000 times higher than that of KOH solution due to higher corrosion temperature and 100%concentration;The corrosion rate of micro reactor integrated Fe catalyst matrix steel pipe prepared with carbon 20 material and 20 g/5 molten KOH at 500℃for 3 h is up to 10.28%,and a small amount of KOH remains on its surface,showing many irregular rough pits and a large number of pores;Carbon 20 material is more easily corroded than 316L and 304 due to its carbon content.The more KOH dosage and higher corrosion temperature,the easier it is to obtain high corrosion rate.After 5 hours of corrosion,a serious passive film is formed to reduce the corrosion rate.（2）Fe-Mn,Fe-Co and Fe-Ce two-component Fischer-Tropsch synthesis catalysts were prepared by impregnation method with the best corroded steel pipe as the Fe catalyst matrix.They were filled into a conventional fixed bed to construct a Fischer-Tropsch synthesis micro reactor for catalytic performance evaluation.High temperature was conducive to improve the conversion of CO and H₂,while low temperature was conducive to reduce the selectivity of CH₄and improve the selectivity of C₂～C₄hydrocarbons.The yield of C₂～C₄hydrocarbons reached 38.84%at 300℃;The active component is the main factor affecting the selectivity of C₂～C₄,followed by the concentration and impregnation time,while the calcination temperature has the least effect.Under the process conditions of H₂/CO feed ratio 2:3,reaction temperature 300℃,pressure 0.1 MPa and space velocity 4000 h^-1,Fe-Mn two-component impregnated with 2.0 M precursor concentration for 1 h and calcined at 300℃to obtain the Fischer-Tropsch synthesis catalyst with the highest C₂～C₄hydrocarbon selectivity;After impregnation with Mn,the surface of Fe catalyst tends to be smooth,and a large number of irregular pits and pores basically disappear,which is conducive to the synergistic effect of the two active components.After the surface of the Fe-based catalyst,C1 to C3 was loaded Mn,C4 to C6 was loaded Co,C7 to C9 was loaded Ce.（3）Under the process conditions of H₂/CO feed ratio of 2:3,reaction temperature of 340℃,pressure of 0.7 MPa and space velocity of 4000 h^-1,the Fe-Mn two-component catalyst prepared with the optimal parameters obtained excellent Fischer-Tropsch reaction catalytic performance of up to 57.04%C₂⁼～C₄⁼hydrocarbon selectivity and 5.42 maximum olefin/alkane ratio,realizing the high selective synthesis of high-value low-carbon olefins.The consolidated dynamic simulation of the iron-based catalyst fees in the microreactor shows that the CO reaction rate is level-0.2134 at the H₂and the CO is 1.3191.Results are the same as the distribution trend of ASF products and the model can also better simulate the distribution of products.