Development of a micro reactor for the isobutane oxidation as a multiphase process

The partial oxidation of liquid isobutane to tertiary butyl hydroperoxide (TBHP) is currently conducted on an industrial scale with bubble columns at a selectivity of 60% and a maximum conversion of 25%. In this process, liquid isobutane is converted with oxygen at high temperatures (130 to 140°C) and pressures (25 to 37 Bar) at high residence times of 10 to 12 hours. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“ a micro reactor has been built and used to investigate this reaction for the first time as a continuous two-phase process in a broad range of flow rates, temperatures (120 to 150°C) and pressures (25 to 100 bar). For the improvement of the selectivity of the industrial process the influence of the residence time, hydrodynamics, initiator, additives and pressure on the reaction is studied. To realize a large range of residence times, flow rates in the range of 15 µl/min to 188 µl/min for isobutane and in the range of 0.1 up to 1.5 ml/min for oxygen were realized, using different capillary lengths which lie between 20 and 100 m. To charac¬terize the isobutane flow, preliminary measurements of the system isobutane – nitrogen were performed in a glass capillary. As the target product and initiator TBHP is sensitive to most metals, the micro reactor and further parts of the lab facility have been coated. To assure reasonable results of the hydrodynamic and kinetic studies, it was also important to realize a flow without pulsation by large pressure fluctuations. Therefore, the pressure is controlled by a gas pressure valve after a gas-liquid separation. The oxidation is followed by taking samples and analysis of the liquid reaction mixture by means of a GC-MS-System. In the frame of the presentation the challenges of the reactor construction and their solutions are discussed.