Selectively combusting CO in the presence of propylene

Acrylic acid plant capacity can be increased by 30% by substituting propane for nitrogen (in air) thereby increasing the overall gas heat capacity. To minimize propane purge rates, the effluent is recycled but the CO in the recycle stream must be oxidized to avoid poisoning the catalyst. We studied the kinetics of CO combustion in a micro-fluidized bed with a catalyst inventory of 1 g and a 4 cm ID reactor charged with 5 g of catalyst – Pd/zeolite – and 145 g of inert. Experiments were run at temperatures between 90 and 240 °C and at 1 and 3.2 bara. At temperatures below 140 °C propylene conversion was less than 30% while CO conversion approached 90% at gas hourly space velocities near 10,000 h−1. A first order kinetic model characterized the data over the whole range of conditions in which conversion was varied between 2% and 99+%. The rate constant for CO conversion was equal to 0.75 s−1 whereas it equaled 0.04 s−1 for propylene oxidation; the activation energy for CO oxidation was 95 kJ mol−1 K−1 whereas it was 140 kJ mol−1 K−1 for propylene.