Selective Hydrogenation of the C8 Aromatic Fraction of Pyrolysis Gasoline over NiZn3/α-Al2O3: Experimental and Modeling Studies

A non-noble NiZn3/alpha-Al2O3 catalyst was prepared by a urea co-precipitation method, which showed good stability and high selectivity to styrene (ST) (92% selectivity at above 99% conversion of phenylacetylene (PA)). The high selectivity was mainly attributed to the electronic effect of the Ni-Zn alloy. The selective hydrogenation of the C-8 aromatic fraction on NiZn3/alpha-Al2O3 was well described by a Langmuir-Hinshelwood-type kinetic model. The estimated activation energies for the hydrogenation reactions of PA -> ST, ST -> ethylbenzene (EB), and PA -> EB were 70.31, 81.65, and 74.88 kJ/mol, respectively. A reactor model allowing for an intraparticle diffusion-reaction and external mass transfer was further developed to describe the selective hydrogenation of the C-8 aromatic fraction on larger NiZn3/alpha-Al2O3 particles in a fixed-bed reactor. The observed changes in product composition with the reaction conditions were well predicted by the model, and the results demonstrated that phenylacetylene can be completely removed without loss of styrene under certain conditions.