Effect of NiW/SAPO-11 catalyst on hydroisomerization performance of model compound eicosane for tail oil hydrogenation of coal tar

Ni-based catalysts were prepared by mechanochemical method with SAPO-11 zeolite as the carrier, and W was introduced to adjust the electronic structure, grain size and morphology of Ni particle, as well as pore structure, acidity, and acid amount of the catalyst. The effect of NiW ratios on catalyst properties and the hydro-isomerization properties of n-eicosane (n-C₂₀), which is a model compound for coal tar hydrogenation tail oil, was explored by XRD, TEM, BET, NH₃-TPD and Py-FTIR. The results show that the specific surface area of Ni/SAPO-11 increases with the addition of W, and reaches the maximum value of 149 m²/g at the W addition of 0.5%. The average particle size of Ni decreases with the addition of W, and reaches to the minimum value of 4.43 nm at the W addition of 1%, which is 36% less than that of Ni/SAPO-11. At this time, the content of Ni⁰ and the amount of surface acid are the highest. In addition, W promotes the reduction of Ni, causing the reduction peak temperature to move toward lower temperature. XPS results show that with the increase of W content, the binding energy of Ni⁰ decreases while that of W⁵⁺ increases. The isomers distribution of eicosane (n-C₂₀) shows that the conversion of n-C₂₀ and the yield of i-C₂₀ are the highest in the presence of 3Ni1W/SAPO-11, which are 88.23% and 75.72%, respectively. It is mainly the mono-i-C₂₀ with a yield of 71.65%. The on-line sampling results show that n-C₂₀ generates the mono-branched isomer under the action of metal site and acid function. With the reaction, the mono-branched isomer is transformed into the multi-branched isomer, and the unstable multi-branched isomer is cracked into small molecule alkanes.