Combustion of coke on dehydrogenation catalysts

Abstract

The kinetic parameters and characteristic of coke burning on Pt/Al2O3 dehydrogenation catalyst were investigated by Temperature-Programmed Oxidation (TPO) and constant temperature oxidation techniques. Coked catalysts were prepared by dehydrogenation reaction of propane to propylene. TPO and constant temperature oxidation reveal that coke can deposit on dehydrogenation catalyst in three forms: 1)on metal sites but does not completely cover the sites which can be eleminated at a temperature around 110 ℃, 2)on metal sites and completely cover the sites which can be burnt at a temperature around 450 ℃ and 3)on support that can be removed at the temperature around 550 ℃. Additionally, experimental evidences suggest that changing temperature of dehydrogenation reaction in the range of 550 – 650 ℃ and variation of hydrogen/hydrocarbon mole ratio between 0 and 3, though can significantly affect area of TPO curve, only affects the amount of coke. Characteristic of coke burning emerge from this research is that the combustion should be in series, i.e.coke1, coke 2 followed by coke 3.The calculation gave values of activation energy/gas constant (Ea/R); for coke 2 about 11100 K. and for coke3 about 4560 K.respectively. The values of the coke precursor (coke1) can not be measured because this coke rapidly burn off at low temperature and its amount is very small. Good agreement was obtained between experimental results and simulation. The results shown that both peak heights and peak locations obtained from simulation agree very well with experimental data. The reaction order with respect to the concentration of coke was 0.5. The kinetic parameters result from this research work can be used in developing mathematical models for catalyst regenerator design and control.