Accumulation of the reactant supplied to a cooled semibatch reactor (SBR) will occur if the mass transfer rate across the interface is insufficient to keep pace with the supply rate. Then, due to a low starting temperature or supercooling, the reaction temperature does not rise fast enough to the desired value. This accumulation may eventually lead to a temperature runaway. We investigated the possibility of such an event for reactions of the type "chemically enhanced mass transfer" or "fast" and found that only low distribution coefficients, i.e. or lower, can lead to accumulation. At higher distribution coefficients, the mass transfer rate across the interface of a well-mixed dispersion is generally sufficient to prevent accumulation. A thermal runaway in the fast regime exerts a moderate effect, because the effective activation energy is halved. Calculations for the "instantaneous" reaction regime, regarded as a special case of fast reactions, show that there is no runaway possible.* Dr. ir. M. Steensma,

Accumulation of the reactant supplied to a cooled semibatch reactor (SBR) will occur if the mass transfer rate across the interface is insufficient to keep pace with the supply rate. Then, due to a low starting temperature or supercooling, the reaction temperature does not rise fast enough to the desired value. This accumulation may eventually lead to a temperature runaway. We investigated the possibility of such an event for reactions of the type "chemically enhanced mass transfer" or "fast" and found that only low distribution coefficients, i.e. or lower, can lead to accumulation. At higher distribution coefficients, the mass transfer rate across the interface of a well-mixed dispersion is generally sufficient to prevent accumulation. A thermal runaway in the fast regime exerts a moderate effect, because the effective activation energy is halved. Calculations for the "instantaneous" reaction regime, regarded as a special case of fast reactions, show that there is no runaway possible.

The major obstacle for the introduction of fractional reactive extraction as a chiral separation method in the chemical and pharmaceutical industries is the lack of versatile enantioselective extractants. Therefore, a rational approach is developed to transfer the extensive knowledge of chiral selectors reported in the literature on chiral recognition and other chiral separation techniques to extraction. Based on a similarity in separation mechanisms, it was expected that chiral selectors originating from a technique in which chiral recognition takes place in the liquid phase are most likely to function as enantioselective extractant. Using this approach, a selection of promising extractants was made from the literature and experimentally evaluated for the enantioseparation of aminoalcohols and amines. As a result, four enantioselective extractant systems, namely, dibutyl-L-tartrate with boric acid, N-(2-hydroxydodecyl)-L-hydroxyproline Cu(II) complex, N-dodecyl-L-hydroxyproline Cu(II) complex, and azophenolic crown ether, have been identified. The azophenolic crown ether system performed the best and demonstrated an enantioselectivity between 1.3-5.0 for five out of six test compounds. Identification of the enantioselective extractant systems was highly facilitated by the developed rational transfer approach that, although partially qualitative, appeared capable of reducing more than 50 encountered candidates to only three promising systems for further experimental evaluation. Therefore, it is expected that this approach can be successfully applied to identify enantioselective extractants for other classes of enantiomers as well.

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Thermally safe operation of a semi

Reactive extraction is studied as a promising chiral separation technique for commercial production scale. For chiral separation of amines and amino alcohols, a chiral crown ether was identified as a versatile enantioselective extractant. In this paper, the influence of various process conditions on the extraction performance is studied experimentally, and a predictive model is constructed based on the chemical and physical equilibria. It was found that the operational selectivity in one extraction step is mainly determined by the complexation constants between crown ether and enantiomers (which are dependent on solvent and temperature) and by the extractant concentration, whereas the distribution ratio is also strongly influenced by the pH. The model gives an excellent prediction of the operational selectivity and a good explanation for the system's responses to changes in process conditions. The model can be used as a basis for a multistage equilibrium extractor model and for conceptual process design. Under optimal process conditions, an operational selectivity >1.5 was obtained for five out of seven model compounds, with satisfying distribution ratios (D ∼ 1-10).

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The influence of moisture content in the environment during manufacture of a novel cobalt-free UP matrix reinforced with flax fibres, on the fibre-matrix adhesion was studied. Flax surface energy was experimentally determined by measuring contact angles on technical fibres, using the Wilhelmy technique and the acid-base theory. The mechanical strength of the interface under different humidity conditions was characterized by the critical local value of interfacial shear stress, τ d , at the moment of crack initiation, which was assessed by single-fibre pull-out tests. Differential scanning calorimetry and x-ray photoelectron spectroscopy analysis gave further insight into the topic. The results suggest that the effect of humidity during manufacturing on the composite interface might be limited. However, longitudinal composite strength decreased somewhat for composites produced in humid conditions, showing that there is some detrimental effect of high levels of moisture during cure on the fibre mechanical performance, likely caused by some fibre degradation.