Studies On The Regeneration Of Long-Chain Paraffine Dehydrogenation Catalyst

Pt-Sn/Al₂O₃ catalyst has been widely used in dehydrogenation industry for its high activity. However, the catalyst is easily deactivated by coking and need to be regenerated frequently, which is usually accomplished by burning off the coke with an air or oxygen-containing mixtures and the following catalyst modificationIn this study, the nature and distribution of the coke deposited on Pt-Sn/Al₂O₃ catalysts have been studied by thermogravimetry(TG) and temperature-programmed oxidation(TPO). The coke burning behavior as well as the burning kinetics was also investigated. Three types of carbon were found on the catalyst and the kinetic behavior for each type of carbon was discussed individually. The noble metal platinum on the catalyst increases the burning rate of part of coke, which is a main cause of temperature runaway. According to the kinetic analysis, both temperature and oxygen concentration are the most sensitive factors on the burning rate. So, enhancing the oxygen concentration gradually during the coke burning process may greatly reduce the risk of temperature runaway. In addition, the hydrogen chemsorption results indicate that air treatment between 500-520℃ may increase the metal dispersion.The reaction results of regenerated catalyst show that coke burning and catalyst modification could affect the activity,stability and selectivity. The high activity was obtained by oxygenation at 520℃, but the selectivity decreased with the burning temperature. Platinum modification after coke burning enhanced the activity, and maintained high selectivity and stability as the fresh catalyst.