Homogeneous catalysts of redox reactions based on heteropoly acid solutions. II. Synthesis of catalyst for pilot industrial production of methylethylketone

Abstract

The homogeneous catalyst used in the 2005–2006 scale-up of the oxidation of n-butylenes into methylethylketone to the industrial level is a chloride-free aqueous solution of palladium complexes in a modified 0.25 M solution of Mo-V-P heteropoly acid with the molecular formula H₁₂P₃Mo₁₈V₇O₈₅ (HPA-7′). Its advantages are increased oxidative capacity in the primary oxidation of n-C₄H₈ and increased thermal stability, which allows quick catalyst regeneration with atmospheric oxygen at 160–170°C. The paper describes the preparation of a pilot lot of the catalyst with a total volume of 50 L; the starting substances were V₂O₅, MoO₃, and H₃PO₄. The key point of the synthesis was dissolving V₂O₅ while stirring in a dilute and cooled H₂O₂ solution. This formed V(V) peroxide complexes, which decompose at elevated temperature to give a 0.0175 M H₆V₁₀O₂₈ solution. This solution was stabilized by adding a calculated amount of H₃PO₄ to give a more stable 0.0125 M H₉PV₁₄O₄₂ solution. Since the H₉PV₁₄O₄₂ solution occupied a large volume, its synthesis was performed three times in a 300-L reactor. In the main 500-L reactor, MoO₃ was dissolved in water with stirring, while adding the remaining portion of H₃PO₄. The resulting mixture was evaporated, gradually introducing all of the previously obtained portions of the dilute H₉PV₁₄O₄₂ solution. The resulting HPA-7′ solution was evaporated to ∼100 L and filtered twice, separating the insignificant amount of the precipitate. The filtered solution was again evaporated to 50 L, and a calculated amount of PdCl₂ was added to it while stirring at 70–80°C. A total of 27 lots of the (Pd + 0.25 M HPA-7′) catalyst with a total volume of 1350 L were obtained. All apparatuses of the pilot industrial unit for MEK synthesis were filled with this catalyst.