(27d) Catalytic Selective Oxidations in Microchannel Reactors

Catalytic selective oxidations pose a number of processing challenges, such as uniform heat removal and adequate oxygen mixing. The salient consequences of these challenges are shorter catalyst life, and poor conversion and selectivity. The decreased catalyst life is due to hot spots that form in the reactor where the heat generated from the selective oxidation reaction can not be sufficiently dissipated to the heat exchange medium. Low conversion and selectivity arise from a combination of unreacted reagents and fully combusted products. Dilution is the tactic commonly used to overcome both of these challenges, but this solution comes at the price of higher capital and operating costs from increasing the size of the reactor and other equipment, and the large volume of gas that must be recycled in the process.

Microchannel reactors offer a number of key features for improving catalytic selective oxidation processes and overcoming the challenges described above. These include: 1) Tailored mixing of reactants to prevent inappropriate oxygen concentrations that limit both conversion and selectivity to the desired product, 2) Enhanced heat transfer to eliminate hot spots in the reactor; thereby prolonging catalyst life, 3) Rapid quenching after the reaction takes place to limit side reactions and improve overall selectivity, 4) High surface area to volume ratio that intensifies the reaction, decreasing the size and cost of the reactor, 5) Capability to work with otherwise explosive or flammable mixtures by mixing them internally, and 6) Potential for higher pressure partial oxidation, which would further intensify the process.

This presentation will describe the development efforts by Velocys, and its partnering organizations (Dow Chemical, Pacific Northwest National Laboratory and others) regarding the viability of the microchannel approach to catalytic selective oxidation. Early laboratory experiments with microchannel reactors have shown very encouraging results. Per pass conversions of for one selective oxidation process could be increased to more than double that of state-of-the-art plant, while selectivity was comparable to that seen in the commercial process. It should also be noted, in microchannel devices the chemistry and flow dynamics inside the reactor do not change during scale-up, so results similar to those observed in the laboratory are also expected for industrial scale selective oxidation processes.