Study of n-butanol conversion to butenes : effect of Si/Al ratio on activity, selectivity and kinetics

As bio-butanol is gaining more and more interest as a commercially available bioresource, the dehydration of this alcohol towards butenes and higher carbons gains more of interest. In general HZSM-5 has shown to be the most promising catalyst for this conversion. The role of the zeolite’s Si/Al ratio in the butanol dehydration reaction is still not fully understood. Experimental data obtained for a series of HZSM-5 with decreasing Si/Al ratio revealed an increase in activity of the catalyst per active site without affecting the selectivity profile. To understand the underlying effects, a microkinetic model was constructed for H-ZSM-5 with a Si/Al ratio of 25, based on literature DFT calculations, and the model was further modified by fitting the key parameters to the measured data at the four different temperatures studied in this work. This resulted in an adequate model for the dehydration of butanol across the evaluated temperature range of 503K to 533K. Investigation of the occurring mechanisms indicated a inhibiting effect due to the strong adsorption of di-n-butylether. This ‘poisoning’ of the catalyst surface resulted in a peculiar S-like curve for the conversion site time relation, which was also experimentally observed. This newly fitted base model was used to obtain more insight in the effect of the Si/Al ratio by implementing an additional H parameter, which is related to the adsorption strength of n-butanol in the base model. H varies between -4.8 to +11.3 kJ/mol and provides a good fit for Si/Al ratios ranging from 15 to 140. The higher dehydration rates observed with decreasing Si/Al can be traced back to an increase in adsorption strength resulting in an overall increase in surface coverage. The constant selectivity-conversion profile can be explained by a similar dependency of all elementary steps on the adsorption strength. The model developed in this study enables to simulate and understand the experimentally observed effects of temperature and Si/Al ratio on the n-butanol dehydration

Typisierung von Bezirken der Agenturen für Arbeit (Classification of employment office areas)

In a project group of the Federal Employment Service, two classification systems were developed for categorizing employment office areas, one with five and the other with twelve types. The former is intended for the development of strategies of labour market policy; the latter serves to facilitate comparison of the areas themselves. Both are consistent, as the more precise division can be converted into the more approximate one by means of combination. Causal analyses of the exogenous determinants of the success of labour market policy form the basis of the classification. An innovative methodical approach is based on the linking of regression and cluster analyses. The types are now used in the Federal Employment Service for practical tasks of labour market policy, decentralised management and controlling purposes. The classification is also of scientific interest. The empirical diversity of regional disparities is reduced to just a few types which are, however, meaningful. (IAB2) ((en))Arbeitsagenturbezirke - Typologie, Benchmarking - Indikatoren, regionaler Vergleich, Westdeutschland, Ostdeutschland, Bundesrepublik Deutschland

Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz

We present radio observations of the Moon between 35 and 80 MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, we show that (i) the Moon appears as a negative-flux source at frequencies 35 z >12) and the Epoch of Reionization (12 > z>5)

Bio-butanol conversion over zeolites : experimental approach supported by microkinetic modelling

De zoektocht naar alternatieven voor petrochemische producten kent een sterke groei zowel op industrieel als fundamenteel vlak. De dehydratatie, ofwel het chemisch verwijderen van water uit een molecule heeft het potentieel om een aantal grondstofstromen in de klassieke petrochemie te vervangen. Butanol, het grotere broertje van ethanol, heeft vele voordelen ten opzichte van ethanol en groeit dus in populariteit binnen de chemische industrie. Het gebruik van katalysatoren is één van de hoekstenen in de klassieke chemie om processen te optimaliseren. Specifiek in de petrochemie zijn zeolieten onmisbaar als stabiele, actieve en selectieve katalysatoren. Deze hebben dan ook reeds hun potentieel voor dehydratatie reacties bewezen. Om industrialisatie van dit proces te realiseren is het nodig om op fundamenteel vlak deze processen te begrijpen. In dit onderzoek werd de klassieke, experimentele aanpak gecombineerd met microkinetisch modelleren. Diverse parameters van de dehydratatie reactie werden gevarieerd om vervolgens de bekomen resultaten te verifiëren en verklaren via microkinetisch modeleren. Industrieel parameters zoals type voeding, type zeoliet en de zuursterkte binnen een specifiek type werden bestudeerd en geëvalueerd. Het begrijpen van de onderliggende kinetische paden en effecten van de parameters hierop hebben geleid tot inzichten die kunnen helpen voor de industrialisatie van deze type processen

Propofol-infusion syndrome in traumatic brain injury: consider the ECMO option

status: publishe