Two-step crystallization

This shows the possibilities to save energy and time by a good introduction of the sweating procedure and the co-ordination of the two steps crystallization and sweating. 

Lonza S.p.A. Furmaric acid Maleic anhydride Liquid-phase isomerization, two-step crystallization process 6 1991... 

Huang F, Zhang H, Banfield IF (in prep.) Two-step crystal-growth kinetics observed in hydrothermal coarsening of nanocrystalline ZnS. 

The liquid product from the lOO C reactor is countercurrently stripped with 90 C air to remove nitrogen oxide gases. The more volatile oxidation by-products such as valeric and butyric acids are removed by steam distillation and the liquors concentrated for adipic acid recovery. Adipic acid is crystallised from the liquors at about 40-50 C and is recovered by centrifugal separation. Mother liquor is then recycled to the process. Two-step crystallization may be used to improve recovery and reduce the proportion of succinic acid impurity in the recycle. 

Experiments performed on poly(vinylidene fluoride) show a development of large-scale structure before a small-scale structure could be observed (149). The authors concluded that this was in agreement with earlier findings where in a nonquiescent sample, crystallization was initiated via spinodal decomposition. The final structure was reached via a two-step crystallization mechanism and resulted in a shish-kebab-hke structure where it could be noted that there was... 

CRYSTAF was developed by Monrabal [50] as an alternative to TREF. Both techniques basically provide comparable results but TREF is the more time consuming process involving two steps, crystallization and elution, while CRYSTAF has (Mily a crystallization step. CRYSTAF is based on the continuous crystallization of polymer chains from a dilute polymer solution. The concentration of the polymer in solution as a function of temperature is measured with a suitable detector like IR. As a result a COTicentraticMi profile of the polymer in solution as a function of... 

When both blocks are crystalline, the morphology formation is more complicated because two kinds of crystallization, as well as microphase separation, intervene during morphology formation. It is useful to summarize this morphology formation in terms of a difference in the crystallizable temperature 7), of both blocks (Fig. 10.8). When of one block is considerably higher than that of the other block, two crystallizations occur almost independently (two-step crystallization). That is, the crystallization of higher 7), blocks... 

Figure 10.8 Schematic illustration showing the possible morphology formation in crystaUine-crystaUine diblock copolymers by two kinds of crystallization. The upper route represents two-step crystallization, whereas the lower route shows simultaneous crystallization, where an interactive crystallization is usually observed, a-d indicate driving factors for the morphology formation.

The crystalline morphology formed in crystalline-crystalline diblock copolymers is more complicated as compared with that in crystalline-amorphous diblock copolymers, because two kinds of crystallization start from some microdomain structure existing in the melt. It is useful to classify this crystallization into two cases in terms of the crystallizable temperature of both blocks (Fig. 10.8) two-step crystallization when of one block is significantly higher than that of the other, and simultaneous crystallization when both values are sufficiently close. 

The two-step crystallization has been examined using several crystalline-crystalline diblock copolymers [111-124]. Essential points of this crystallization are summarized in the upper route of Figure 10.8 first, the crystallization of higher 7). blocks forms the lamellar morphology (Fig. 10.2c)... 

Inaba, A. Andersson, O. (2007) Multiple glass transitions and two step crystallization for the binary system of water and glycerol, Thermochim. Acta Vol. 461 44-49. 

Semictystallme polymers can be fractionated by means of TREE, which is based on chain crystallizabilities. It consists of two steps crystallization and elution. The method can be operated in an analytical (A-TREF) or in a preparative mode (P-TREF). Hie principle of the experimental setup is the same and shown in Figure 17. The main differences of the two modes are the elution step and sample size as well as the used column dimensions. 

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