| Partially oxidized hydrocarbons are important ingredients of plastics and synthetic fibers, furthermore they play a dominant role as intermediates in everyday chemical production. These molecules are prepared from natural gas and volatile fractions of petroleum by partial oxidation, using oxygen as the most economic oxidant. However, with oxygen in solution or gas or with activated oxygen on solid catalysts, achieving product selectivity is a serious challenge. The main reasons for the lack of selectivity are the often very high temperatures required, the free-radical nature of the reactions, and the tendency to cause runaway oxidation leading to carbon oxides. An alternate milder route is the use of visible light at mild temperatures to activate oxygen and small saturated or unsaturated hydrocarbons loaded into the nanocages of a zeolite, with high selectivity.The key ingredients responsible for this route are the largely unshielded alkali or alkaline-earth ions in the large zeolite cages. The positive charge of these cations balances the negative charge introduced into the framework by the aluminum centers, and the unusually high electrostatic fields in the vicinity of the cations dramatically reduce the energy needed to excite hydrocarbon-oxygen charge transfer. Related to the above, the research group Catalytic Processes and Materials has recently been active in the field of oxygenation of alkanes, a conversion possible at room temperature by co-adsorbing propane and oxygen on Ca-modified zeolite Y. The main problem of this approach is the fact that the products cannot desorb from the catalyst without applying a significant temperature cycle. Attempts to operate at steady state in a continuous operated reactor have failed so far; desorption is possible only at high temperatures, leading to carbon oxides. Because of the contradictory requirements for activation (requires high electrical fields) and desorption (enhanced by low electrical fields), the desorption-problem cannot be resolved under conditions close to the reaction temperature. For this reason, we propose to investigate the effect of a tuneable and switchable electrostatic field generated in a micro-reactor as a new approach to selectively oxygenate alkanes into higher value products. This will be done in such a way that alkane is oxygenated with the field on, whereas products desorb and leave the micro reactor with field off. The basic configuration of the proposed micro-reactor consists of a micro-channel with integrated electrodes embedded in alumina or silica. In-situ analysis of the processes in the microreactor will be done with infrared techniques, and exhaust gases will be analyzed with GC |
