Microreactor studies for efficient organic oxidation processes

Abstract

Abstract Industrially important partial oxidations of hydrocarbons are frequently characterized by low conversions and yields, which are mostly related to mass and heat transfer problems. Due to the reaction conditions, such processes include also important safety risks and are still not sufficiently understood. To study the influence of the process parameters on the product selectivity, a lab facility including a silicon-coated micro reactor of stainless steel has been developed and constructed. Due to its modular construction (e.g. replaceable capillary), it permits for the first time to perform catalysed and non-catalysed oxidations of hydrocarbons with oxygen as a two-phase process in a capillary reactor in wide ranges of residence times (some minutes to 24 h), temperatures and pressures. As an example, the oxidation of isobutane to tertiary butyl hydroperoxide (TBHP) has been studied. The reaction has been investigated for the first time as a Taylor-Flow process in a micro reactor at different reaction conditions as a prerequisite to enhance the space-time yield of the process. The advantages of micro reactors are the high surface-to-volume ratio ensuring efficient heat transfer and the improved, nearly inherent, safety. These permit investigating yet unexplored process windows, for instance within the explosive region of a reaction mixture. The reaction has been studied for varying flow rates, temperature, pressure and the molar ratio of the starting products using two different initiators, namely TBHP and di-t-butyl peroxide (DTBP). For all experiments, the selectivity of the reaction products and the conversion of the reaction have been studied by sampling and analysing the reaction by GC/ MS. The use of TBHP as initiator increased the selectivity of the reaction for the target product TBHP. TBHP as initiator yields a better selectivity since at high temperatures, which are common for DTBP, the formation of propanone already becomes important and favours the decomposition of TBHP. The replacement of the initiator diluent water by decane resulted in a faster reaction and the highest autocatalytic isobutane conversion (˜18%) obtained ever for this reaction in a micro reactor.