Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Tertiary butyl hydroperoxide (TBHP), as an intermediate for the production of propylene oxide according to the Oxirane process, is currently produced at industrial scale by the partial oxidation of liquid isobutane using bubble columns or bubble tray reactors. In this process, liquid isobutane reacts with oxygen under two phase conditions at temperatures of 120 to 140 °C and pressures of 25 to 37 bars at high residence times of up to 12 hours. The conversion is limited to 35 to 50 % in order to obtain a TBHP selectivity of 50 to 60 % minimizing the formation of by-products, which are caused by the decomposition of the TBHP due to the complex reaction mechanism. Besides safety aspects, the high reaction enthalpy of the oxidation as well as heat and mass transport problems are further issues of this process. In the frame of the Helmholtz-Energy-Alliance project “Energy efficient chemical multiphase processes“, this reaction is investigated for the first time at supercritical conditions in a broad range of flow rates, temperatures and pressures in a micro reactor with the aim to enhance the space-time yield of the process. The advantage of micro reactors are the high surface – volume ratio for an efficient heat transfer, the related, improved – nearly inherent – safety and the resulting possibility to investigate yet unexplored process windows for instance within the explosive region of a reaction mixture. A number of levers for the process intensification have been identified (e.g. initiator type, oxygen concentration, additives and high pressures). Supercritical conditions i.e. pressures above 40 bars and temperatures above 140°C are especially interesting because of the higher reaction rate and lacking mass transfer limitations. In addition to the parameter ranges studied in the past, e.g. oxygen concen¬trations (50 to 100%) and high pressures of up to 100 bars have been applied. Furthermore, the influence of process parameters on the start-up time is investigated. For all experiments, the selectivity and conversion of the reaction have been studied. Therefor, the reaction course is followed by sampling and analyzing the reaction by GC/MS and GC–TCD where analytical methods have been developed to detect a maximum of by-products and intermediates. The results of the first supercri-tical experiments are given and discussed with respect to the reaction characteristics.