Cool evaporator

Add 1 ml. of the alcohol-free ether to 0-1-0-15 g. of finely-powdered anhydrous zinc chloride and 0 5 g. of pure 3 5-dinitrobenzoyl chloride (Section 111,27,1) contained in a test-tube attach a small water condenser and reflux gently for 1 hour. Treat the reaction product with 10 ml. of 1-5N sodium carbonate solution, heat and stir the mixture for 1 minute upon a boiling water bath, allow to cool, and filter at the pump. Wash the precipitate with 5 ml. of 1 5N sodium carbonate solution and twice with 6 ml. of ether. Dry on a porous tile or upon a pad of filter paper. Transfer the crude ester to a test-tube and boil it with 10 ml. of chloroform or carbon tetrachloride filter the hot solution, if necessary. If the ester does not separate on cooling, evaporate to dryness on a water bath, and recrystallise the residue from 2-3 ml. of either of the above solvents. Determine the melting point of the resulting 3 5 dinitro benzoate (Section 111,27). 

Amides. TVeat the acid chloride cautiously with about 20 parts of concentrated ammonia solution (sp. gr. 0 - 88) and warm for a few moments. If no solid separates on cooling, evaporate to dryness on a water bath. Recrystallise the crude amide from water or dilute alcohol. 

Better product characteristics are obtained through control of the rate at which supersaturation (cooling, evaporation, and addition of a nonsolvent or precipitant) is generated. An objective of the operation may be to maintain the supersaturation at some constant prescribed value, usually below the metastable limit associated with primary nucleation. For example, the batch may be cooled slowly at the beginning of the cycle and more rapidly at the end. 

Crystallization-based separation of multi-component mixtures has widespread application. The technique consists of sequences of heating, cooling, evaporation, dilution, diluent addition and solid-liquid separation. Berry and Ng (1996, 1997), Cisternas and Rudd (1993), Dye and Ng (1995), Ng (1991) and Oyander etal. (1997) proposed various schemes based on the phase diagram. Cisternas (1999) presented an alternate network flow model for synthesizing crystallization-based separations for multi-component systems. The construction... 

Air cooling evaporators for coldrooms, blast freezers, air-conditioning. 

Figure 7.2 A r cooling evaporators, (a) Floor mounted, (b) Ceiling mounted (Courtesy of Searle Manufacturing Co.)...

Air cooling evaporators working below 0°C will accumulate frost which must be removed periodically, since it will obstruct heat transfer. 

Prevent frost forming on an air cooling evaporator, where this is close to freezing point, or where a temporary malfunction cannot be permitted to interrupt operation. 

Choong KL and Smith R (2004) Novel Strategies for Optimization of Batch, Semi-batch and Heating/Cooling Evaporative Crystallization, Chem Eng Sci, 59 329. 

Batch crystallization. Crystallization is extremely common in the production of fine and specialty chemicals. Many chemical products are in the form of solid crystals. Also, crystallization has the advantage that it can produce a product with a high purity and can be more effective than distillation from the separation of heat-sensitive materials. Crystallization has already been discussed in Chapter 10 and has two main steps. Firstly the solute to be crystallized is dissolved in a suitable solvent, unless it is already dissolved, for example, solute dissolved in a solvent from a previous a reaction step. Secondly, the solid is then deposited in the form of crystals from the solution by cooling, evaporation and so on. 

Solution crystallisers are usually classified according to the method by which supersaturation is achieved, that is by cooling, evaporation, vacuum, reaction and salting out. The term controlled denotes supersaturation control whilst classifying refers to classification of product size. 

Antarctic Bottomwater, which is formed by sinking in the Weddell Sea, is defined by a single salinity and temperature (-0.4°C, 34.66%o). This is referred to as a water type, whereas water parcels of common original that exhibit a range of temperature and salinity values are said to constitute a water mass. The variability in temperature and salinity within a particular water mass is due to spatial and temperature variations in the processes responsible for their formation, i.e., cooling, evaporation, sea ice formation, etc. In general, the deeper water masses exhibit less variabiUty than the shallower water masses. The most common are listed in Table 4.1. The deepest and, hence, the densest... 

Crystallization is generally preceded by two types of nucleation. The primary nucleation occurs with the formation of clusters of molecules at the submicron level. When the concentration exceeds saturation to afford supersaturation, the clusters become nuclei. The secondary nucleation is caused by particles due to primary nucleation or seeds. There are many strategies to achieve supersaturation to initiate crystallization such as cooling, evaporation, and antisolvent addition. 

Tryptamine from Tryptophan. Prepare a suspension of 1 g tryptophan (preferably L-tryptophan) in 40 g of warm diphenylmethane. In a stream of nitrogen (nitrogen atmosphere) gently reflux the suspension until the CO2 stops evolving (10 to 30 min). Cool, evaporate in a vacuum, treat the resulting residue with about 80 ml of benzene, saturate with dry HCl and filter off the precipitate. Wash the precipitate with hexane and dry to get the tryptamine in about 60% yield. 

The term supersaturate was coined in 1788 and was deLned as to add to a solution beyond saturation. The state of supersaturation may be obtained through cooling, evaporation, oras a result of a chemical reaction between two homogeneous phases. In addition, in the case of drug solutions, supersaturation may be reached through dissolution of... 

---