Optimization of the polyelectrolyte dosage for dewatering sewage sludge suspensions by means of a new centrifugation analyser with an optoelectronic sensor

The flocculation of sewage sludge with poly(diallyldimethylammonium chloride) (PDADMAC) as well as cationic, poly[acrylamide-co-(N,N,N-trimethylammoniumethylacrylate chloride)] (PTAC), and anionic acrylamide copolymers, poly(acrylamide-co-acrylate) (PAAM/AA), was investigated by using a new method to evaluate the velocity of centrifugal separation and the packing behaviour of the sediments. By means of a centrifugation analyser with an optoelectronic measuring system the position of the centrate/sediment interface of the conditioned suspensions can be determined as a function of the separation time, which allows the polyelectrolyte dosage to be optimized for various rotational speeds. At high centrifugal accelerations it was found that using the anionic polyelectrolyte PAAM/AA does not result in better dewatering performance, whereas both polycations recorded high degrees of separation. Furthermore, the measurements with the high-molar-mass PTAC indicate a high resistance to centrifugation which correlates with floc stability. In contrast, addition of the low-molar-mass PDADMAC gives more fragile flocs, leading to faster collapse of the sludge cake in the compression zone of the centrifuge at lower gravitational forces. These experimental findings agree well with the much higher filtration capacity of sludges conditioned with PTAC which was measured by means of a pressure filtration device. Comparisons of the optimum polyelectrolyte concentrations obtained by pressure filtration or centrifugation at low gravitational forces with the zeta potential of the flocculated particles appear to be consistent with bridge formation for PTAC and with the charge patch mechanism for PDADMAC. The centrifugation experiments at high centrifugal accelerations show an optimum separation efficiency at relatively low degrees of coverage and a high level of agreement with the large-scale process. Received: 24 November 1998 Accepted in revised form: 12 February 1999     

Eco-conception of Highly Salt-Tolerant Alkyl Ether Carboxylate Hydrotropes with a Glyceryl Spacer

New alkyl ether carboxylates with a glyceryl spacer instead of ethylene glycol units have been synthesised using environmentally friendly methodology. A cascade synthesis of acetalisation and hydrogenolysis was developed to obtain products containing an alkyl chain linked to a glycerol unit bearing a polar carboxylate head. These products were methylated by using trimethyl phosphate to observe the influence of a free or methoxylated alcohol on the physicochemical properties. Finally, saponification gave the carboxylate anionic group of the new hydrotropes. Studying the amphiphilicity, the tolerance to sodium and calcium ions, and the solubilising power of these bio-based ionic/nonionic hydrotropes has shown that they exhibit significantly improved application properties compared to similar petro-based hydrotropes.     

First syntheses of model long-chain trichloro[ω-(trimethylsilyl)alkynyl]silanes suitable for self-assembled monolayers on silicon surfaces

The preparation of the title compounds involves the introduction of the required Me₃SiCC and trichlorosilyl groups at the termini of the alkyl chain via derivatization of easily accessible and inexpensive materials/reagents. Trichloro[ω-(trimethylsilyl)alkynyl]silanes are useful for the linkage to a hydroxylated silicon surface for multilayer formation and for further chemical modification of the tail group of the monolayer.     

Ritter-type amidation of alkylboron derivatives with nitriles

A mild and facile synthesis of amides from alkylboron compounds and nitriles promoted by copper acetate and BF₃·OEt₂ at room temperature is disclosed.     

A simple O-sulfated thiohydroximate molecule to be the first micromolar range myrosinase inhibitor

New non-hydrolyzable analogues of glucosinolates have been prepared. Myrosinase inhibition was observed with modified aglycon moieties, even bulky phenothiazine analogue 6 gave reasonable inhibition. The simplest structure 8 derived from dimethylaminoethanethiol has shown to be the most potent inhibitor with an IC₅₀ of 3.32 μM.     

Michael Addition Initiated Carbocyclization Sequences with Nitroolefins for the Stereoselective Synthesis of Functionalized Heterocyclic and Carbocyclic Systems

The synthesis of various heterocycles and carbocycles (tetrahydrofurans, pyrrolidines, cyclopentanes) has been achieved by using new and efficient ionic addition/cyclization sequences. Nitroolefins play an important role in the Michael addition induced ring‐closing reactions (MIRC) reported in the present article, with various substituted alcohols, amines, Grignard reactants, or malonate derivatives acting as the nucleophile partner. The optimized cascade reactions were high yielding in most cases and highly stereoselective, creating up to three stereogenic centers starting from achiral substrates.     

Chemically and Electrochemically Triggered Assembly of Viologen Radicals: Towards Multiaddressable Molecular Switches

We have established that bipyridinium radicals can be reversibly π‐dimerized under the combined effects of chemical (proton transfer) and electrochemical (electron transfer) stimuli. Our investigations also led to the discovery that a bis‐pyridinyl appended calixarene intermediate is involved in a fully reversible redox‐triggered σ‐dimerization process. The structure of the most stable intramolecular σ‐dimer was provided by computational chemistry and its complete conversion into a noncovalent π‐dimer could be triggered chemically by addition of protons, leading to the formation of protonated cation radicals. Theoretical data collected with the N‐methylated and N‐protonated π‐dimers also support the existence of multivariant orientations in π‐bonded dimers of viologen cation‐radicals.