Crystallization kinetics analysis

Crystallization kinetics have been studied by differential thermal analysis (92,94,95). The heat of fusion of the crystalline phase is approximately 96 kj/kg (23 kcal/mol), and the activation energy for crystallization is 104 kj/mol (25 kcal/mol). The extent of crystallinity may be calculated from the density of amorphous polymer (d = 1.23), and the crystalline density (d = 1.35). Using this method, polymer prepared at —40° C melts at 73°C and is 38% crystalline. Polymer made at +40° C melts at 45°C and is about 12% crystalline. 

The CSD from the continuous MSMPR may thus be predicted by a combination of crystallization kinetics and crystallizer residence time (see Figure 3.5). This fact has been widely used in reverse as a means to determine crystallization kinetics - by analysis of the CSD from a well-mixed vessel of known mean residence time. Whether used for performance prediction or kinetics determination, these three quantities, (CSD, kinetics and residence time), are linked by the population balance. 

Dehydration reactions. In early studies of dehydration reactions (e.g. of CuS04 5 H20 [400]), the surfaces of large crystals of reactant were activated through the incorporation of product into surfaces by abrasion with dehydrated material. An advantage of this pretreatment was the elimination of the problems of kinetic analysis of the then little understood relationship between a and time during the acceleratory process. Such surface modification resulted in the effective initiation of reaction at all boundary surfaces and rate studies were exclusively directed towards measurement of the rate of interface advance into the bulk. 

Phosphate ester crystal structures have been determined of zinc 1,5,9-triazacyclononane including an interesting structure containing an oligophosphate bridged zinc unit.450 The zinc complex of 1,5,9-triazacyclododecane was studied as a hydrolysis catalyst for substituted phenyl acetates.451 Kinetic analysis suggested that hydrolysis occurs by a mechanism involving hydroxide attack of a metal-bound carbonyl. 

Crystals of [Tc(tu)6]Cl3 or [TcCl(tu)5]Cl2 are often employed for the synthesis of technetium(III) complexes. However, since the direct reduction of pertechnetate with excess thiourea in a hydrochloric acid solution yields [Tc(tu)6]3+ in high yield [37], direct use of the aqueous solution of the thiourea complex would be preferable for the synthesis of the technetium(III) complex without isolation of the crystals of the thiourea complex. In fact, technetium could be extracted from the aqueous solution of the Tc-thiourea complex with acetylacetone-benzene solution in two steps [38]. More than 95% extraction of technetium was attained using the following procedure [39] First a pertechnetate solution was added to a 0.5 M thiourea solution in 1 M hydrochloric acid. The solution turned red-orange as the Tc(III)-thiourea complex formed. Next, a benzene solution containing a suitable concentration of acetylacetone was added. After the mixture was shaken for a sufficient time (preliminary extraction), the pH of the aqueous phase was adjusted to 4.3 and the aqueous solution was shaken with a freshly prepared acetylacetonebenzene solution (main extraction). The extraction behavior of the technetium complex is shown in Fig. 6. The chemical species extracted into the organic phase seemed to differ from tris(acetylacetonato)technetium(III). Kinetic analysis of the two step extraction mechanism showed that the formation of 4,6-dimethylpyrimidine-... 

StoU VS, Manohar AV, Gillon W, Mac Farlane EL, Hynes RC, et al. 1998. A thioredoxin fusion protein of VanH, a d-lactate dehydrogenase from Enterococcus Faecium cloning, expression, purification, kinetic analysis, and crystallization. Protein Sci 7 1147-1155. 

From the literature only a few examples of an enzyme-catalyzed kinetic racemic resolution via C-C bond-cleavage are known [64]. The broad substrate range of BAL in combination with the high extent of stereoselectivity observed for BAL-catalyzed resolutions impressively demonstrates the high potential of this strategy. Very recently, it has become possible to determine the three-dimensional structure of BAL via X-ray crystal structure analysis, which will enable a structure-based discussion of the observed stereocontrol [65]. 

The above /(-hydroxo /(-peroxo complex represents an important class of complexes, and a series of L4Co(0H)(02)CoL43+ complexes has been prepared with other amines such as NH3, tn, tren, and trien (108, 231-244) the structures of these have been established by X-ray crystal-structure analysis (108,109,242,243). The kinetics of formation and the chemical properties of these dinuclear species have been studied in detail, as discussed in a recent review by Fallab and Mitchell (119). 

In the oxidation of secondary alcohols by DADH, the coenzyme is the leading substrate, the release of NADH from the enzyme-NADH complex is the rate-limiting step, and the maximum velocity vmax is independent of the chemical nature of the alcohol. In the case of primary alcohols, as vmax is much lower and depends on the nature of the alcohol, Theorell-Chance kinetics (Figure 9.9) are not observed and the rate-limiting step is the chemical interconversion from alcohol to aldehyde. With all this biochemical information it is possible to delineate a catalytic reaction mechanism that is in agreement with the crystal structures and the steps of alcohol oxidation observed in the kinetic analysis of the DADH reaction. 

A detailed two-dimensional numerical analysis of nonisothermal spinning of viscoelastic liquid with phase transition was carried out recently by Joo et al. (15). They used a mixed FEM developed for viscoelastic flows (16) with a nonisothermal version of the Giesekus constitutive equation (17), the Nakamura et al. (18) crystallization kinetics... 

D. W. Henderson, Thermal Analysis of Non-Isothermal Crystallization Kinetics in Glass Forming Liquids , Journal of Non-Crystalline Solids, 30 301-315 (1979). 

Equation (5), respectively, during the main parts of the crystallization processes (autocatalytic stage) indicates that Equation (1) is equivalent to Equation (5) and that both kinetic forms are suitable for the kinetic analysis of the autocatalytic stage of zeolite crystallization. 

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