General Mixing Considerations

When it is snspected that a reacting system is subject to mixing effects, scale-up can be particnlarly critical since most organic reactions have multiple byproducts. Success or failure on scale-up could be determined not only by the selectivity of the desired product, as it affects costs, but also by the abihty to maintain the ratio of other by-products constant to minimize effects on product quality and downstream processing. Increases in by-products as little as 0.1% can be a significant problem. 

These values were combined into a mixing Damkoehler number as the ratio of mixing time constant to reaction time constant  

The mixing Damkoehler numbers obtained were 0.050, 0.032, and 0.023, respectively. These are reasonably close for such radically different experimental conditions vessel size, impeller rotation rate, feed location, and concentration. 

Generally, it is recommended that bench and pilot data for mixing sensitive reactions be obtained at the same concentrations as are to be used in the commercial plant. That eliminates concentration as a concern in scale-up. 

2 Concentration Effects in Parallel Reactions Product Degradation Due to High pH. The effect of concentration may be very significant in the case of the use of a strong acid or base in pH adjustment. These pH 

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The specific heat of mixtures of liquids can rarely be calculated additively from the specific heats of the components. There is generally a considerable deviation from the law of mixtures, and the calculated value is always larger than one would expect. Mixtures of hquids which are closely related chemically, such as ethyl and methyl alcohol, chloroform and carbon disulphide, behave normally mixtures of water with alcohol, or of alcohol with other organic hquids, show large deviations. It is noteworthy that heat is evolved on mixing these hquids, an indication that chemical combination also is taking place. This is probably the reason for the alteration in the heat capacity, since the specific heat of liquid chemical compounds cannot be calculated additively from the specific heats of the components. The regularities shown by sohd bodies do not hold even approximately for hquids. 

In general, mixed ligand stability constants are larger, and often considerably larger, than predictions based on single ligand type stability constants, ( 1, 6). A simple example of this occurs... 

It follows from general thermodynamic considerations that at one and the same product compositions the column with several feed flows of different composition should require less energy for separation than the column with one feed flow formed by mixing all the feed flows. It follows from the fact that summary entropy of all feed flows should be smaller than that of the mixed flow because the mixing of flows of different composition increases the entropy and the separation of flows decreases it. Therefore, the minimum reflux number for the column with several feed inputs should be smaller than that for the column with one mixed feed flow (i.e., it is unprofitable to mix flows before their separation). 

Oldshue [57] reviewed the basic principles of fluid mixing of cosmetic formulations, presenting the General Mixing Theory, the applications to liquid-liquid, liquid-solid, and gas-liquid systems, scale-up, and pilot planting considerations. 

In addition to the use of a melting point determination as a criterion of purity, an equally valuable application is for the identification of oiganic compounds. If the melting point is known within one degree, the major proportion of possible substances is immediately eliminated from consideration. The study of the general chemical properties of the compound and a mixed melting point determination (Section 1,17) will largely establish the identity of the compound. 

If the ether is a simple one (R — R ), the identification of the resulting alkyl iodide presents no difficulties. If, however, it is a mixed aliphatic ether, the separation of the two alkyl iodides by fractional distillation is generally difficult unless R and R differ considerably in molecular weight and sufficient material is available. 

The constant may depend on process variables such as temperature, rate of agitation or circulation, presence of impurities, and other variables. If sufficient data are available, such quantities may be separated from the constant by adding more terms ia a power-law correlation. The term is specific to the Operating equipment and generally is not transferrable from one equipment scale to another. The system-specific constants i and j are obtainable from experimental data and may be used ia scaleup, although j may vary considerably with mixing conditions. Illustration of the use of data from a commercial crystallizer to obtain the kinetic parameters i, andy is available (61). 

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