(274b) Reaction Vs Separations in Oxidative Dehydrogenation

The oxidative dehydrogenation reaction comprises subjecting feedstock ethane and oxygen to oxidative dehydrogenation to produce an ethylene and water stream. After drying, the ethylene stream is passed through a separations unit; conventional distillation, vapor recompression or membranes, to separate the ethylene from unreacted ethane in the ethylene rich stream. A mixed metal oxide catalyst capable of producing an alkene, such as ethylene, from an alkane, such as ethane is assessed versus separations in terms of efficacy and economic performance. This technology comprises contacting ethane and oxygen in the presence of a mixed metal oxide catalyst, such as an M1 catalyst, in a reactor of packed tubes to produce a stream comprising unreacted ethane as well as, ethylene and water. Since the ethylene is refractory and will not undergo secondary reactions, the effluent of the first reactor may be cooled and then fed directly in to another tubular reactor to convert additional quantities of ethane. After the reaction section, the ethylene rich stream is dried, then passed through a membrane separation unit or distillation to separate the ethylene from unreacted ethane in the ethylene stream. The ethylene is recovered as permeate from the membrane separation unit or overhead in the distillation column. Ethylene having purity of at least 90 % will be recovered from the stream entering the membrane system. As in conventional recovery, polymer grade ethylene may be produced in a super fractionator. Therefore, the overall system comprises at least one ODH reactor configured to convert ethane to ethylene. Multiple reactors in series can be used to reduce the size of the separation system. In the techno-economic analysis, an economic assessment is made as to whether the additional reactors are cost effective relative to less reaction and more separation. A heat management unit is coupled to each ODH reactor and configured to reduce the temperature of the ethylene product stream while simultaneously generating steam from the heat of reaction. The techno-economic analysis indicates that using traditional assumptions regarding CAPEX and OPEX, two reactors in series is the most cost effective case and will reduce the overall risk assessment. It is suggested that the reactors be piped for operation in series or parallel to further reduce any risk and provide some operational flexibility.