Feststoffbildung durch Kristallisation und Fällung

Formation of solids by crystallization and precipitation. Formation of solids from solutions can take place by crystallization or precipitation. The principal factor is the relationship between solubility and supersaturation. In crystallization, the solubility of the crystallising substance is so high that the formation of solids occurs largely in the metastable zone in the immediate vicinity of the solubility limits. Crystal growth and nucleation are functions of supersaturation. If a high supersaturation is required at low substance-specific growth rates for an adequate crystal growth, high nucleation rates and hence small crystals will result. On this basis, the authors present information for the specific design of crystallization processes. In contrast, the solubility of the precipitated product must be very low for precipitation. Direct crystal formation is possible only for substance systems of high solubility. As a rule, however, the precipitated substance is so insoluble that solids are formed via amorphous intermediates. The results of a large number of experiments show the influence of various parameters of the precipitation process on the filtrability of the precipitated product.     

Untersuchungen zur Optimierung der Fällfraktionierung von Polymeren

The possibilities for a systematic selection of the conditions for fractional precipitation in polymer/solvent/nonsolvent-systems based on data of the turbidimetric titrations have been tested experimentally. As criticism for the fractionation efficiency the molecular weight distribution of the fractions (determined by ultra-centrifuge) and the uniformity M?_w/M?_n (calculated therefrom) was taken. The successiv- and subfractionation, the dependence of the initial concentration and particularly the influence of the solvent/nonsolvent-system on the fractionation efficiency were investigated. Therefore a simple new method was developed, which allows to arrange systematically different solvent/nonsolvent-systems with few turbidimetric titrations as to be suitable for fractionation. For three selected solvent/non-solvent-systems the correctness of the selection method could be proved experimentally.     

Eindimensionale Modellierung und Simulation von Blasensäulenreaktoren

Reactor models that feature a practical way to design bubble columns on the (semi‐)industrial scale have been published only rarely in the scientific literature. Creating a one‐dimensional model in the equation‐oriented simulation software ASPEN Custom Modeler^TM, a compromise between model precision and modeling can be reached. The model quantitatively describes the processes in a bubble column reactor with sufficient accuracy.     

Zur Konzentrationsabhängigkeit der Fällungspunkte von Polymerlösungen

The concentration dependence of the cloud points of dilute benzene solutions of polystyrenes with broad and narrow molecular distributions was determined via titration with methanol or isopropanol using visuell determination, colorimetry and light scattering. All methods gave a linear dependence of the volume fraction φFM of the non-solvent from the logarithm of the polymer concentration c_p at the cloud point for three decades of c_p if certain evaluation techniques are used. Light scattering was the most accurate, visuell observation the least accurate method. The slope coefficients k of the function φFM = f(log c_p) depend linearly on 1/M^0,6 for polystyrenes of narrow molecular weight distribution.     

Faserstruktur und Färbeeigenschaften von Cellulosefasern, 1. Zusammenhänge zwischen Veränderungen der Faserstruktur und der Farbstoffadsorption bei Baumwolle durch Mercerisation und Flüssigammoniak-Behandlungen

Changes of fiber structure and the adsorption of direct dyes in cotton subjected to different kinds of mercerisation and liquid ammonia treatment have been studied. Therefrom a new general relationship between dye adsorption and fiber structure of cellulosic fibres has been given as a result. The fiber structure in the water swollen state was characterized by measurements of specific pore volume, specific pore surface and pore size distribution. The dyeing behaviour of the different treated cotton was determined by adsorption isotherms. The results revealed that for equilibrium dye adsorption from aqueous solution a transitional pore region with pore diameters of 20–60 Å has a special importance. Changes of these pores by the different swelling treatments correlated directly with the dye uptake. This pore region is found in cotton between the elementary fibrils.     

Alkylendiamide und Alkylendiisoimide von Äthyleniminocarbonsäuren und -dicarbonsäuren

Alkylenediamides and Alkylenediisoimides from Ethyleneimino Carboxylic Acids and Ethyleneimino Dicarboxylic Acids Preparation and properties of some alkylenediamides from β-ethyleneiminopropionic acid and ethyleneiminosuccinic acid as well as of two alkylenediisoimides of ethyleneiminosuccinic acid are described.     

Fällungspolymerisation von Acrylnitril in Aliphatischen Kohlenwasserstoffen. Kinetische und mechanistische Aspekte bei Verwendung des Startersystems tert.-Butylhydroperoxid/Schwefeldioxid/Trichloressigsäure

The heterogeneous polymerization of acrylonitrile in aliphatic hydrocarbons is in its kinetic behaviour similar to the bulk polymerization. This is particularly the case at low conversions (<50%). The results obtained in single-stage continuous polymerizations with short residence times are discussed in this context. The redox initiator system employed, consisting of tert.-butylhydroperoxide, sulphur dioxide and trichloroacetic acid, leads to special characteristics in the chemical structure of the acrylonitrile polymers. Parallel with the polymerization, the redox components react with acrylonitrile to form N-tert.-butylacrylamide, which can be incorporated into the growing polymer chain. A further effect of the initiator system is that the polymers formed contain a comparatively high proportion of sulphur fixed in the polymer, mainly in form of sulphonate groups. This is due to specific initiating and terminating reactions. As a result of hydrolysis the polymers also have relatively high concentrations of carboxyl groups.