Alkali sulfation during combustion of coal in a pilot scale facility using additives to alter the global sulfur to potassium and chlorine to potassium ratios

Due to the urgent needs to reduce anthropogenic carbon dioxide emissions there is an increasing interest in the use of alternative fuels. For this reason, there is a need for new knowledge on how to design and adapt existing heat and power plants to biogenic and waste-derived fuels. This work relates to co-firing of biomass and coal and the sulfation of alkali chlorides in coal-fired flames doped with chemical additives. We aim to examine the global time scales of alkali sulfation and chlorination based on combustion experiments that were conducted in a 30-kW coal flame. Temperature, gas and particle composition measurements were conducted. Both experiments and modelling support that the apparent alkali sulfation kinetics are fast in a coal-fired flame and that it is dominated entirely by the presence of SO₂. The availability of oxygen and carbon monoxide, or hydrocarbons, is also critical to sustain the sulfation reaction cycle; low concentrations are sufficient. For industrial boilers this implies that sulfur addition, in combination with reburning, should constitute an efficient strategy to mitigate alkali-chlorination and the related high temperature corrosion.     

New Tungsten Cluster Based Contrast Agents for X-ray Computed Tomography

In recognition of the seminal contributions of F. A. Cotton and A. Bino to the field of aqueous chemistry of organometallic, trinuclear cluster compounds of tungsten, we describe their modifications and use as contrast agents for X-ray computed tomography. To enable their fundamental work for an advantageous diagnostic application in medicine a new generation of polydentate W₃O₂ complexes with improved hydrolytical stability has been synthesized and characterized. The applicability as new metal based contrast agent has been demonstrated in a computed tomography angiography animal study with increased signal intensity. Especially the bis tridentate W₃O₂ complexes with their reduced stereochemical complexity represent a promising new class in the field of X-ray contrast agents.     

Effects of caffeine on stereoselectivities of high cell density biotransformations of cyclic beta-keto esters with Saccharomyces cerevisiae

Caffeine affects the stereoselectivity of microbial high cell density reductions with commercial grade Saccharomyces cerevisiae (Baker's yeast). Cyclic beta-keto esters ethyl 2-oxocyclopentanoate (1) and ethyl 2-oxocyclohexanoate (3) were shown to be reduced with increased diastereoselectivity (1: 90.1 --> 92.1% de, 3: 75.0 --> 90.0% de) after addition of caffeine. Effects on enantioselectivity were less pronounced (1: 97.3 --> 98.5% ee, 3: 90.1 --> 92.1% ee). The observations are ascribed to the action of caffeine on cellular calcium homeostasis. These effects are accompanied by caffeine-induced cell-death, which preferably takes effect on pre-stressed cells which were found to decrease diastereoselectivity.     

Mechanistic models for pool nucleate boiling heat transfer: input and validation

Correlations for nucleate boiling heat transfer should be improved, or in the long term possibly be replaced, by the development of mechanistic simulations that include the non-uniform spacing and variable characteristics of the nucleation sites and non-linear interactions between the sites. This paper discusses the interactions that should be included in simulations and some lessons from a first attempt to validate a particular simulation against experimental spatio-temporal data for wall temperature. Input data for nucleation site positions and characteristics are a particular problem and the prospects for obtaining this data from measurements that are independent of boiling are discussed.     

1,2,3-Triazolidine durch Cycloaddition von Aziminen an Olefine

1,2,3-Triazolidines by Cycloaddition of Azimines to Olefines Azimines A can undergo [3+2]-cycloadditions with olefines B to give 1,2,3-triazolidines C , a class of hitherto unknown heterocycles. The three examples of this reaction realized here involved the azimine 1 with electron-withdrawing substituents and the olefines 2, 3 and 4 with an electron-donating substituent, yielding the cycloadducts 5,6 and 7 . The triazolidine structure of 5 was established by an X-ray diffraction analysis. Characteristic for 5 are also: (a) that the three N-atoms are pyramidal (and thus centers of chirality), (b) that the five-membered heterocycle takes on a twist (half-chair) form, and (c) that the regioselectivity of the cycloaddition places the (E)-substituent of the olefine 2 vicinal to the terminal (Z)-substituent of the azimine 1 . On this basis the constitutions of 6 and 7 are assigned. The spectral properties of the triazolidines 5, 6 and 7 , including the ¹⁵N-NMR signals of one example, are compared with those of the related triazane 12 .