Selective hydrogenation of olefins with mass transfer control in a structured packed bed reactor

Mass-transfer-controlled hydrogenation of butadiene in the presence of 1-butene and benzene using two differently-structured catalytic packings was studied. Kinetic expressions were developed in a continuous stirred-tank reactor (CSTR) using a PdNiCe/SiAl-SS-316 catalyst with two packing structures. The two packing methods were also tested in a trickle bed down-flow isothermal reactor at similar gas and liquid flow rates. To model the effects of mass transfer on reactor efficiency a simulation was developed using this reaction kinetics and published data regarding gas and liquid hold ups and mass transfer correlations. The results confirmed that the apparent kinetics follow a heterogeneous-type expression, which is first order for the hydrogenation of butadiene and butene and is of order 0.3 with respect to hydrogen isomerization and dimerization reactions followed respectively a first- and second-order with respect to hydrocarbon. Simulations showed that the rate of mass transfer of hydrocarbon in liquid and liquid–solid interface controls butadiene hydrogenation at low conversion rates because its reaction rate is 10 times faster than that of 1-butene or benzene hydrogenation. The benzene/olefin ratio and the temperature were the main parameters governing the selectivity, and there was an important difference in mass transfer behavior between the two catalytic packings used.