New olefin production method in sight
30 mei 2002
promotie L. Leveles, Faculteit Chemiche Technologie:
‘Oxidative conversion of lower alkanes to olefins’
Olefins are the most important building blocks in the modern petrochemical industry. Propene and ethene are the raw materials for polypropylene and polyethylene and their demand continuously increases. While the current processes for ethylene and propylene production (steam-cracking and fluid catalytic cracking [FCC]) are well developed, increasing their capacity is limited. Propylene is produced as byproduct in both steam-cracking and FCC, thus the strongly increasing propylene demand can only be satisfied by dedicated processes. One such process, catalytic dehydrogenation of propane shows major disadvantages: thermodynamic limitation that causes high cost separations and recycling due to low conversions and coking of catalyst that causes feedstock loss and need for catalyst regeneration. Conceptually, dehydrogenation in the presence of oxygen can help to overcome these limitations. Oxidative dehydrogenation has been recognized as new alternative olefin production method and it has been studied extensively. However, commercial application has not been realized to date, mainly due to low yields of olefins (max. achieved so far: 30%) over transition metal oxide catalysts with pronounced redox character.
In this thesis, alkali promoted magnesia catalysts were studied for the oxidative conversion of lower alkanes to olefins. Yields of olefins above 50% could be obtained with a product spectrum similar to that of steam-cracking from dehydrogenation and cracking reactions. Additionally, there are major advantages compared to steam cracking: the share of propylene is higher in the olefin yield, the temperature is lower, and the heat is generated internally. The kinetics of the reaction implied a reaction mechanism that involves radical initiation reactions on the catalyst surface and radical chain propagation reactions in the gas-phase. The active sites for radical generation are active oxygen ions in the defects of the magnesia surface. The catalyst controls the concentration of gas-phase radicals as it not only generates but also quenches radicals.
promotor prof. dr. ir. L. Lefferts
co-promotor prof. dr. J. A. Lercher
assistent-promotor dr. K. Seshan
informatie drs. B. Meijering, telefoon (053) 489 43 85