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Item type:Publication, Access status: without files , Dried chitosan-gels as organocatalysts for the production of biomass-derived platform chemicals(Elsevier, 2012-08-24); ; ; ; Aldol condensations between sugar-derived dehydrated aldehydes (e.g. furfural) and acetone have been proposed as a route to provide useful biomass-derived chemicals. In the quest of sustainable catalytic ways for such aldol condensations, this paper assesses the use of dried chitosan-gels as naturally-immobilized, readily available and non-hazardous amino-based organocatalysts. At room temperature chitosan dried gels are not suitable catalysts for the desired reaction. However, at higher temperatures (>90 °C) reaction proceeds efficiently either in solvent-free systems (with addition of catalytic amounts of water) or in water. The set-up of closed reactor set-ups (thermoshakers or microwave reactions) proved highly beneficial for the reaction outcome. Furthermore, chitosan dried gels were successfully re-used for a number of cycles. An efficient catalyst drying method (either lyophilization or scCO2 drying) was crucial to achieve virtually full conversions in 4 h. After pertinent further process optimization, dried chitosan-gels may become very useful catalysts for their use in biomass-based reactions in biorefineries.Publicationtype: Journal Article25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Oxidative dehydrogenation of ethane in a fluidized bed membrane reactor(2005-12-12); ; ; ; The performance of a pilot scale fluidized bed membrane reactor (FLBMR) was studied experimentally in comparison to the conventional operation as a fluidized bed reactor (FLBR) for the catalytic oxidative dehydrogenation of ethane using a γ-alumina supported vanadium oxide catalyst. For both reactor configurations, the influence of process parameters such as temperature and contact time was investigated. Further, the experimental data obtained were compared to previous experiments with a fixed-bed reactor (FBR) and a packed-bed membrane reactor (PBMR) operated with a similar catalyst. For identical overall feed rates, the distributed oxidant feeding in the FLBMR improves the selectivity to ethylene significantly. The beneficial effect of oxidant dosing over the membrane is most pronounced at high temperatures and long contact times. Under limiting oxidant supply the FLBMR and the PBMR show a similar performance, but under moderate oxygen excess the FLBMR outperforms the PBMR significantly. The maximum ethylene yield observed in the FLBMR was 37% compared to 35% for the PBMR. Beside a high productivity, for the FLBMR a broader favorable operation range with respect to the oxygen-hydrocarbon ratio was observed, what indicates a lower sensitivity against oscillations and disturbances in the reactant feed, corresponding to a higher safety of operation. Because of an excellent heat transfer characteristics, the fluidized bed membrane reactor concept is very promising for maximizing the yield of the desired intermediates also in large-scale plants, especially for strongly exothermic reactions.Publicationtype: Journal Article21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A unifying approach to the security of distributed and multi-threaded programsThe security of computation at the level of a specific programming language and the security of complex systems at a more abstract level are two major areas of current security research. With the objective to integrate the two. this article proposes an adequate translation of a timing-sensitive security property for simple multi-threaded programs into a more general security framework. Soundness and completeness of the translation guarantee that the trace-based specification of the translation of a multi-threaded program is secure if and only if the original program is secure. Finally, the translation is extended to a distributed setting, and it is demonstrated how to derive global security of the overall system from local security of each thread. The translation is presented as a two-step process where the first step is independent from the concrete programming language.Publicationtype: Journal Article18