Unit operations, liquid systems purification

The dominant mechanism of purification for column crystallization of solid-solution systems is recrystallization. The rate of mass transfer resulting from recrystallization is related to the concentrations of the solid phase and free liquid which are in intimate contact. A model based on height-of-transfer-unit (HTU) concepts representing the composition profile in the purification section for the high-melting component of a binary solid-solution system has been reported by Powers et al. (in Zief and Wilcox, op. cit., p. 363) for total-reflux operation. Typical data for the purification of a solid-solution system, azobenzene-stilbene, are shown in Fig. 20-10. The column crystallizer was operated at total reflux. The solid line through the data was com-putecfby Powers et al. (op. cit., p. 364) by using an experimental HTU value of 3.3 cm. 

The last talk in this session, by Andrew Lyddiatt (University of Birmingham, United Kingdom), showed how liquid-liquid extraction can address some of the problems associated with the purification of nanoparticulates (e.g., viral and nonviral gene delivery vehicles). Nanoparticles (particle size range 20-150 nm) with low diffusivity and low molalities in culture feedstocks pose unique process engineering problems in the design and implementation of selective recovery and formulation operations. This paper demonstrated how aqueous two-phase partition systems (polymer-polymer and polymer-salt) can circumvent the process bottlenecks posed by the use of... 

Solid-liquid separations are important operations in chemical engineering ranging from upstream raw material purification, to downstream product separation and waste managements. They are usually low cost, and low energy consumption. A successful operation of a SLS system upstream a major chemical engineering unit such as a catalyst bed will help to improve the efficiency the catalyst, and decrease overall cost of the whole process. 

Figure 6.29. Conversion of substrate in the liquid phase (Cs,l) measure of purification effect in waste water treatment versus mass loading rate per unit mass in case of CSTR and CPFR operation Compared are systems operating with one common sedimentation tank (SED), exhibiting only a small difference in conversion, and systems with separated SED, called contact stabilization or sludge-reaeration, in which case the CPFR is superior to the CSTR. (Adapted from F. Moser, 1977.)...

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