Mechanical wash column

Wash columns can be distinguished into gravity and forced transport columns, which can be differentiated into mechanical and hydrauHc operating modes. In Figure 15.6, for instance, a mechanical wash column is shown. 

Figure 15.6 Principle of a mechanical wash column (reproduced with permission from GEA Messo PT).

Several design variations are possible for a direct freeze-separation process. The one reported utilizes the evaporation of water directly in an evacuated freeze chamber to form ice crystals and concentrated brine. Separation of ice from brine does not use any mechanical devices, such as centrifuges, but simply a counterflow wash column of ice being moved by applied hydraulic forces. 

The equipment is made of stainless steel, those parts that hold alkaline or neutral liquids may be made of carbon steel. The washing columns are equipped at the bottom with air injectors for emulsifying the nitro compounds in water. To avoid any hazards the plant is not equipped with mechanical stirrers. 

Allyl Bromide. Introduce into a 1-litre three-necked flask 250 g. (169 ml.) of 48 per cent, hydrobromic acid and then 75 g. (40-5 ml.) of concentrated sulphuric acid in portions, with shaking Anally add 58 g. (68 ml.) of pure allyl alcohol (Section 111,140). Fit the flask with a separatory funnel, a mechanical stirrer and an efficient condenser (preferably of the double surface type) set for downward distillation connect the flask to the condenser by a wide (6-8 mm.) bent tube. Place 75 g. (40 5 ml.) of concentrated sulphuric acid in the separatory funnel, set the stirrer in motion, and allow the acid to flow slowly into the warm solution. The allyl bromide will distil over (< 30 minutes). Wash the distillate with 5 per cent, sodium carbonate solution, followed by water, dry over anhydrous calcium chloride, and distil from a Claisen flask with a fractionating side arm or through a short column. The yield of allyl bromide, b.p. 69-72°, is 112 g. There is a small high-boiling fraction containing propylene dibromide. 

Tricarballylic acid. Place 228 g. (204 ml.) of ethyl propane-1 1 2 3-tetracarboxylate and 240 ml. of 1 1 hydrochloric acid in a 1-litre threenecked flask, fitted with a mechanical stirrer and a fractionating column with condenser set for downward distillation attach a receiver with side tube to the condenser and connect the side tube to a wash bottle containing water. Boil the mixture, with continual stirring, at such a rate that the... 

Scale-up depends on the mechanical complexity of the crystal-transport system and techniques for removing heat. Vertical oscillating spiral columns are likely limited to about 0.2 m in diameter, whereas horizontal columns of several meters are possible. Scale-up is limited by design of melter and/or crystal-washing section. Vertical or horizontal columns of several meters in diameter are possible. 

B. (3-Bromo-3,3-difluoropropyl)trimethylsilane. A 1-L, four-necked flask is equipped with a mechanical stirrer, thermometer, Claisen adapter, septum inlet, reflux condenser (the top of which is connected to a calcium chloride drying tube), and a solid addition funnel. The flask is charged with (1,3-dibromo-3,3-difluoropropyl)trimethylsilane (78.3 g, 0.25 mol), and anhydrous dimethyl sulfoxide (200 mL), and the solid addition funnel is charged with sodium borohydride (11.5 g, 0.30 mol) (Notes 7 and 8). The stirred solution is warmed to 80°C, and sodium borohydride is added at a rate sufficient to maintain a reaction temperature of 80-90°C (Note 9). Toward the end of the addition, an additional portion of dimethyl sulfoxide (200 mL) is added via syringe to lower the viscosity of the reaction mixture. After the addition is complete, the mixture is cooled in an ice-water bath, diluted with 100 mL of pentane, and cautiously quenched with 12 M hydrochloric acid until no further gas evolution occurs. The mixture is transferred to a separatory funnel and washed with three, 100-mL portions of 5% brine. The pentane extract is dried over calcium chloride and the solvent removed through a 15-cm Vigreux column. Further fractionation yields 41.5 g (72%) of 3-bromo-3,3-difluoropropyltrimethylsilane, bp 139-141 °C (Note 10). 

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