METHANE COUPLING TO ACETYLENE OVER PT-COATED MONOLITHS AT MILLISECONDCONTACT TIMES

We have studied the adiabatic and autothermal oxidative coupling of me thane over Pt on alpha-Al2O3 monoliths at space velocities above 10(5) h(-1). The selectivity to Ct hydrocarbons (primarily acetylene) reach es a maximum of around 20% at low fuel to oxygen ratios, low dilution, and high space velocities. These conditions promote a large temperatu re gradient in the monolith, with an exit temperature of nearly 1500 d egrees C and an entrance temperature of less than 200 degrees C. This temperature gradient appears to be the driving force far C-2 hydrocarb on formation under these conditions. Both homogeneous and heterogeneou s reactions may be involved in producing coupling products, and a comb ustion model predicts C-2 selectivities similar to those observed.