Selective chemical extraction model predictions

TABLE VI. Comparison of Model Predictions and Selective Chemical Extraction Data... 

Assuming, in Table III, that represents exchangeable activity and S2 represents the net inventory of all other mechanisms, a comparison of these model-predicted inventories with those obtained by selective chemical extraction indicates that, while the overall mass balance trends are predicted, agreement in detail of individual extraction inventories with the model-predicted inventories is not always good. The overall mass balance is governed almost totally bv the higher concentration (early time) data. In the case of °Co, inspection of residual plots indicates that, in all cases, the DFO model shows small systematic deviations at early times that account for the mass... 

Naturally, quantum chemical approaches to molecular recognition are usually employed for selected systems since the complexity of these systems requires a system-specific analysis which makes it difficult to extract results of general validity for examples, see Refs. [13-16] for studies of molecular tweezers. Further examples are mentioned in a review article by Schatz considering ab initio calculations on calixarenes and calixarene complexes [17]. Schatz concludes that although the systems are quite big, useful contributions have been made by ab intio calculations. However, a general model is needed in order to make host-guest processes and template-assisted reactions accessible to a comparison of quantitative measurements and calculations, which may finally provide the basis for rational host design and for the prediction of template effects (compare the recent attempt by Hunter [18]). 

Partial least squares (PLS) regression, develops a biased regression model between X and Y. In the context of chemical process operations, usually X denotes the process variables and Y the quality variables. PLS selects latent variables so that variation in X which is most predictive of the product quality data Y is extracted. PLS works on the sample covariance matrix (X Y)(Y X) [86, 87, 111, 172, 188, 334, 338[. Measurements of m process variables taken at n different times are arranged into a (n x m) process data matrix X. The q quality variables are given by the corresponding... 

Nickel is extracted from alkaline ammonia solutions by LIX 64N, but its equilibrium constant is five orders of magnitude smaller than that of copper.8 Also, it forms ammonia complexes more extensively than copper, which enhances the selectivity of LIX 64N for copper over nickel. Under conditions of simultaneous extraction the parameters of the chemical-reaction model for each individual metal are able to predict the iwo-metal equilibria provided that the equilibrium distribution of species in the aqueous phase is taken into account. 

Modified UNI FAC is an ideal thermodynamic model for process development. With the help of this predictive model easily various process alternatives can be compared, suitable solvents for separation processes like azeotropic distillation, extractive distillation, extraction can be selected, the influence of solvents on chemical equilibrium conversion can be predicted, and so on. 

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