α-olefin selectivity of Fe–Cu–K catalysts in Fischer–Tropsch synthesis: Effects of catalyst composition and process conditions

Fischer–Tropsch (FT) synthesis has been studied over a series of precipitated Fe catalysts promoted to investigate the effect of K and Cu promoters on the carbon number distribution of FT product. The main intention is to maximize the α-olefin selectivity by controlling the secondary reactions of α-olefin as a function of potassium and copper loadings. The results showed that impregnation of different loadings of Cu and K promoters to precipitated iron-based catalyst was found to have significant influences on the crystallographic structure, morphological and physical properties of iron-based catalysts, as well as catalytic activity, stability and selectivity performances during FT synthesis. 100Fe7Cu3K sample exhibited the highest catalytic activity and stability in TOS tests. The catalyst is capable of working under a variety of temperatures and space velocities at a same activity level with no significant activity loss. Proper control of Cu and K contents is essential to obtain maximum C5+ yield since the changes in the relative loadings of both Cu and K promoters affect hydrocarbon product distribution. 100Fe7Cu3K sample has high secondary α-olefin hydrogenation activity as olefin/paraffin ratio decreases with increasing carbon number while C19+ selectivity is relatively low compared to other samples. The effects of space velocity and temperature on α-olefin selectivity are strongly dependent on the amounts of Cu and K promoters and chain length. The maximum α-olefin/n-paraffin ratio has been obtained over 100Fe3Cu1K sample at 543 K with a space velocity of 3 NL/h/g-cat.

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► 100Fe7Cu3K sample exhibited the highest FT catalytic activity and stability.
► Changes in loadings of both Cu and K promoters affect hydrocarbon product distribution.
► α-olefin selectivity is dependent on the amounts of Cu and K and chain length.