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Solid - Liquid Equilibria

Measurement of Solid - Liquid Equilibria of Organic Compounds

The knowledge of solid-liquid-equilibria (SLE) is important in many fields of industrial chemistry (e.g. design of crystallization processes, safe operation of pipelines,...). For the development of thermodynamic models SLE data of eutectic mixtures deliver information at low temperatures in order to ensure reliable temperature dependent model parameters. With the help of the group contribution method modified UNIFAC (Dortmund) it is possible to estimate (besides VLE, hE, LLE and ) also SLE data of eutectic mixtures with a high accuracy. This means that the model can be used for interesting problems like the design of crystallization processes and the selection of suitable solvents for extractive crystallization processes.

Measurement of SLE

Different methods of SLE-measurement are established. For most of the problems the synthetic visual method (Fig. 1) is used.

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Fig.1 Static Apparatus for SLE Measurement
(
Specifications: temperature range 180-373 K, probe volume 160 cm3,
accuracy: temperature: ± 0.1 K, composition: 0.01 mole-%)

Take a look at the static apparatus

Measurements at lower temperatures (minimum 70 K) can be performed using a Tian-Calvet microcalorimeter. Systems of high viscosity are measured analytically. Fig. 2 shows typical experimental results and the predicted behavior using mod. UNIFAC (Dortmund).

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Fig. 2 Typical results

 

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