C 6 oxygenates from n-hexane in a single-gauze reactor

Abstract

Partial oxidation of n-hexane in an autothermal single-gauze reactor can produce 70% selectivity to oxygenated hydrocarbons, including >50% selectivity to C 6 oxygenates with ∼35% selectivity to 2,5-dimethyltetrahydrofuran at ∼20% n-hexane conversion and 100% oxygen conversion. Experiments are performed with 40-mesh Pt–10%Rh single gauzes ( ∼100 μm wire diameter and ∼630 μm spacing) at n-hexane–oxygen molar ratios (C 6H 14/O 2) of 0.5–5.0, preheat temperatures of 100–300° C, N 2 dilution of 10–75%, and flow rates of 1.0–3.5 standard liters per minute. Oxygenates are optimized at C 6H 14/O 2≈2.5 and are favored by low preheat temperature, some dilution, and intermediate flow rate (catalyst contact time). Catalytically assisted gas-phase reaction pathways are proposed for partial oxidation of n-hexane and compared to similar experiments for cyclohexane and methylcyclohexane. The differences in product distributions can be qualitatively explained by the number of unique primary, secondary, and tertiary carbon sites in cyclohexane, n-hexane, and methylcyclohexane because the abundance of possible products grows quickly as the number of distinct sites increases. Results suggest that initial H-atom abstraction rates for these alkanes increase in the order 1<2<3°, while the overall reactivities increase in the order methylcyclohexane <cyclohexane< n-hexane. The low reactivity of methylcyclohexane, despite its high initial rate of abstraction, is likely a result of the stability of the tertiary radical.