Catalytic Partial Oxidation of Cyclohexane in a Single-Gauze Reactor

Cyclohexane oxidation in a single-gauze reactor can produce ∼85% selectivity to olefins and oxygenates at 25% cyclohexane conversion and 100% oxygen conversion, with cyclohexene and 5-hexenal as the dominant products. Experiments are performed with a 90% platinum–10% rhodium single gauze (∼90-μm wire diameter) at cyclohexane/oxygen (C6H12/O2) molar ratios of 0.4 to 5.0, flow rates of 1 to 3 standard liters per minute, preheat temperatures of 100 to 300°C, N2 dilution from 5% to the air composition, and pressures of 1.2 to 2 atm. The cyclohexane/oxygen ratio is the most important variable for operation of the single-gauze reactor because temperatures, reactant conversions, and product selectivities all change significantly as C6H12/O2 is varied. Low dilution favors olefin production while high dilution suppresses the homogeneous reactions necessary for oxygenate formation. Oxygenates are also favored by high flow rates and low inlet temperatures. Higher reactor pressures (up to 2 atm) increase the yield of cyclohexene and 5-hexenal and allow complete oxygen conversion. Cyclohexanone can be produced with 5% selectivity at C6H12/O2 ≈ 4. Reaction pathways for cyclohexane partial oxidation are hypothesized, and the products are consistent with the proposed surface-assisted gas-phase sequences.