Catalyst instabilities during the liquid phase partial oxidation of methane

A promising catalytic system for the low temp. oxidn. of methane to a methanol deriv. was studied under both batch and semi-continuous operation in two different reactor types. The system comprises of a bimetallic palladium and copper (II) chloride catalyst contained in a trifluoroacetic acid (TFA) and an aq. phase. Methane, oxygen and a co-reductant carbon monoxide constitute the gas phase. Typical operating conditions were a temp. of 85 Deg and a pressure of 83 bar and the yields of the Me trifluoroacetate product obsd. in this present work were less than those obtained in other batch autoclave works, which employed only 4 mL of liq. phase, compared with 50 mL in this study. Furthermore, an encouraging initial product formation rate of ca. 40 mol/m3 h, quickly decreased after the first hour, and came to an apparent end after only 2 h. This observation had not been reported previously and the work performed in a semi-continuous porous tube reactor (300 mL of re-circulating liq. phase) also showed the same reaction characteristics as in the batch reactor. Thus, the deteriorating product formation rate cannot be attributed to gaseous reactant depletion (batch operation). The results suggest problems assocd. with catalyst instabilities, e.g. with the previously elucidated Wacker chem. [on SciFinder (R)]