Probing the Positions of TeO Moieties in the Channels of the MoVNbTeO M1 Catalyst: A Density Functional Theory Model Study

With hybrid DFT calculations applied to periodic models of the bulk MoVNbTeO M1 catalyst, we examined how [TeO]2+ species in the hexagonal channels of this material stabilize nearby reduced metal centers. In particular, an S2(Mo) site, with adjacent [TeO]2+ moieties at both sides, is calculated to be reduced to Mo5+. The modeling study presented offers insight into how the redox behavior of V and Mo centers, a crucial aspect of the M1 catalyst for the selective partial oxidation of small hydrocarbons, may be fine-tuned via TeO moieties at various distances from the metal centers. Graphic Abstract TeO moieties in hexagonal channels, adjacent on either side of an S2(Mo) center, stabilize a gap state at the Mo center, facilitating its reduction to Mo5+.

TECHNO-ECONOMIC COMPARISON BETWEEN CONVENTIONAL STEAM PYROLYSIS AND OXIDATIVE DEHYDROGENATION OF ETHANE FOR THE PRODUCTION OF ETHYLENE

Facilities based on both Conventional Steam Pyrolysis (CSP) and Oxidative Dehydrogenation (ODH) are methods of producing and separating an alkene, such as ethylene, from an alkane, such as ethane. The CSP system is a time honored and historic process consisting of an endothermic reaction to crack ethane into ethylene followed by a separation system to remove hydrogen and methane. Distillation is then used to purify the ethylene to polymer grade. The ODH method comprises subjecting a feedstock containing ethane to exothermic oxidative dehydrogenation using an M1 catalyst to produce an ethylene stream. The ethylene stream is distilled and/or passed through membrane separators to purify and recover the ethylene. The ODH reaction system comprises at least one tubular reactor, a heat management unit coupled to the ODH reactor, and at least one membrane separation unit comprising a facilitated membrane exchanger. The ODH reactor is configured with tubes packed with the M1 catalyst to convert ethane to ethylene. Additionally, the ethylene produced is reported to be refractory, thus avoiding secondary reactions. The heat management unit is configured to reduce the temperature of the ethylene product stream and recovering the heat of reaction. These processes and the associated economics are discussed. The economic assessment indicates that the ODH route is superior in the three key areas in the cost of production: variable costs, fixed costs and capital recovery.