Kinetic modeling of homogeneous methanol synthesis catalyzed by base-promoted nickel complexes

Nickel complexes promoted by alkoxide bases can affect facile conversion of synthesis gas into methanol under thermodynamically favorable temperatures. At 100°C, syngas conversion of 99% with turnover frequency of 66 h^-1 is reported. The reaction is truly catalytic in Ni as well as in base. A kinetic study of the Ni(CO)₄-KOMe catalyst system in 1,2-bis(2-methoxy ethoxy)ethane (triglyme)-MeOH solvent mixture is presented. The kinetic expression includes terms of zero-order in H₂ and first-order in CO with syngas of H₂-CO stoichiometry of ∼2:1 and less than first-order in Ni (0.03-0.10 M), ∼third-order in base (2.0-4.75 M), and an exponential dependence on methanol concentration (13.0-23.7 M at 2.0 M base; 15.8-22.6 M at 3.0 M base). The activation energy of 42.2 kJ mol^-1 was estimated from the Arrhenius plot of the data between 374 and 393 K. Gas phase IR spectrum at the end of each run showed an intense signature peak at 2060 cm^-1 for Ni(CO)₄. Process uncertainties to commercialization of this versatile homogenous catalyst system for CO hydrogenation to methanol are discussed.