The effect of oxygenate additives on the performance of Pt–Sn/γ - Al2O3 catalyst in the propane dehydrogenation process

The effect of oxygenate modifiers on the performance of Pt–Sn/γ–Al2O3 catalyst in dehydrogenation of propane was studied. Dehydrogenation reaction was carried out in a fixed-bed quartz reactor in the temperature range of 575–620 °C. Two types of oxygenate modifiers, namely water and methanol, were added to the feed. The optimum amounts of water for reaction temperatures of 575, 600 and 620 °C were 84, 120 and 140 ppm, respectively. The optimum amounts of methanol for the same reaction temperatures were 9.9, 25 and 50 ppm, respectively. Any further addition of water or methanol beyond these optimum levels resulted in a loss in activity. The addition of water or methanol led to the formation of COx at the expense of selectivity loss of propylene. The propylene yields, however, passed a maximum at the optimum amounts of added oxygenates. The addition of water and methanol in the optimum amounts resulted in a substantial reduction of coke formation as well. The improved propane conversions in the presence of optimum amounts of added water or methanol could be explained in terms of enhanced ββ H-elimination step in propane dehydrogenation mechanism in the presence of hydroxyl groups.