Homogeneous separation freeze concentration

In this chapter we consider the separation of species contained in a homogeneous phase, such as a liquid or gas. The separation is based on exploiting a fundamental difference that exists between the species. Section 4.0 gives some overall guidelines. Methods that exploit differences in vapor pressures are evaporation, in Section 4.1 and distillation, in Section 4.2. Methods that exploit differences in freezing temperature and solubility are freeze concentration. Section 4.3, melt crystallization. Section 4.4 and zone refining. Section 4.5. Methods exploiting solubility are solution crystallization. Section 4.6 precipitation. Section 4.7 absorption, Section 4.8, and desorption. Section 4.9. Solvent extraction. Section 4.10, exploits differences in partition coefficient. 

Add 101 g. (55 ml.) of concentrated sulphuric acid cautiously to 75 ml. of water contained in a 1 htre beaker, and introduce 35 g. of finely-powdered wi-nitroaniline (Section IV,44). Add 100-150 g. of finely-crushed ice and stir until the m-nitroaniUne has been converted into the sulphate and a homogeneous paste results. Cool to 0-5° by immersion of the beaker in a freezing mixture, stir mechanically, and add a cold solution of 18 g. of sodium nitrite in 40 ml. of water over a period of 10 minutes until a permanent colour is immediately given to potassium iodide - starch paper do not allow the temperature to rise above 5-7° during the diazotisation. Continue the stirring for 5-10 minutes and allow to stand for 5 minutes some m-nitrophenjddiazonium sulphate may separate. Decant the supernatant Uquid from the solid as far as possible. 

In a 1-1. flask fitted with a reflux condenser are placed 106 g. (0.6 mole) of 1-chloromethylnaphthalene 1 (Note 1), 168 g. (1.2 moles) of hexamethylenetetramine, 250 ml. of glacial acetic acid, and 250 ml. of water. This mixture is heated under reflux for 2 hours. In about 15 minutes the solution becomes homogeneous, and then an oil starts to separate. After the reflux period, 200 ml. of concentrated hydrochloric acid is added and refluxing is continued for an additional 15 minutes (Note 2). After cooling, the mixture is extracted with 300 ml. of ether the ether layer is washed three times with 100-ml. portions of water, then with 100 ml. of 10% sodium carbonate solution (Note 3), and again with 100 ml. of water. The ether extract is dried with about 15 g. of anhydrous sodium sulfate and filtered, and the ether is removed by distillation. The residual liquid is distilled under reduced pressure, the distillate being collected at 105-107°/0.2 mm. or 160-162°/18 mm. (Note 4). The yield of colorless 1-naphthalde-hyde freezing between 0.0° and 2.5° (Note 5) is 70-77 g. (75-82%). 

Downstream processing Intracellular products have to be extracted from the cells (by sonication, freeze thawing, and/or homogenization), and separated from the cells (centrifugation or filtration). Extracellular products require concentration and separation from the bulk supernatant. 

PVA-AgX membranes exhibited large selectivities and benzene permeation rates for the separation of benzene and cyclohexane over a wide range of feed concentrations. Much lower selectivites were observed for styrene/ethylbenzene and o-xylene/p-xylene separations. Long term transport depends on the membranes remaining hydrated. A freeze-drying procedure was developed that provided homogeneous distribution of silver in the PVA membranes. Absorption/extraction experiments indicated that the membranes had low absorption and diffusion selectivities for benzene/cyclohexane. 

---