Recycling Strategies

The application of AB materials as hydrogen source materials requires a cost effective production or at least an economical regeneration procedure for spent material. As pointed out, the type of spent material depends very much on the dehydrogenation procedure. Decomposition of AB in the solid state and in inert solvents leads, depending on the conditions, to products of various B N H rations, divers degree of polymerization, and of very different reactivity. 

Unless procedures are developed that generate a singular type of waste product, a generic recycling procedure that can process all, or at least most, of different types of spent materials is desirable. 

Most of the tested BNH systems are considerably exothermic in respect to hydrogen release (see Table 8.6) and, therefore, cannot be recycled simply by exposure to high-pressure hydrogen gas at practically obtainable pressures. Some 

Besides the ability to cope with the very inhomogenous nature of the spent materials, an energy efficient procedure for the regeneration of BH3NH3 must be developed. 

Ideally, typical production considerations, such as cost of the chemicals and the technological issues (temperature level, reaction rates etc.) should also be taken into account. Especially, any use of costly auxiliary agents that cannot be recycled or production of by-products that require their disposal needs to be avoided. In this respect, the most favorable recycling procedure would be self-contained, that is, the regeneration is only carried out with molecular hydrogen and the BNH waste. To date, none of the proposed recycling schemes fulfill all of these requirements. 

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The objective of this case study is to determine the target for minimizing the total load (flowrate x composition) of CE discharged in terminal wastewater of the plant using segregation, mixing, and recycle strategies. 

It is interesting to compare the optimal configuration shown in Fig. 7.16 to end-of-pipe solutions. Suppose we retain the identified segregation, mixing, and direct recycle strategies shown in Fig. 7.14, but intercept the wrong stream. For instance, if the CE content of the terminal wastewater stream is to be reduced from 6.5 ppmw... 

Scheme 10.2 The basic recycling strategy for the monoaza-substituted crown ethers. (Reproduced by permission of the American Chemical Society from Luo, H. M., Dai, S., and Bonnesen, R V., Anal. Chem., 76, 2773-2779, 2004.)...

Although not all of the factors that influence homogeneous hydrogenation and hydroboration in sc C02 are fully understood, it is clear that the use of sc C02 can lead to an increase in selectivity for some reactions. Additional work is needed to understand the opportunities for further selectivity enhancements and catalyst separation/recycle strategies. Even sc C02 systems that exhibit similar selectivities to those obtained in organic solvents could offer a practical, environmentally responsible method for the production of many important chiral building blocks. 

Figure 3.29. Quasi-steady State Off-cut Recycle Strategy in Binary...

Mujtaba (1989) suggested an alternative strategy to collect and store the off-cuts separately and recycle each of them to the reboiler in sequential order (Figure 3.31). Quintero-Marmol and Luyben (1990) discussed a similar recycling strategy. They also considered other alternative off-cuts handling strategies for multicomponent mixtures. 

Mujtaba (1989) considered the off-cut recycling strategy shown in Figure 8.11 and formulated an optimisation problem with an objective to minimise the overall batch distillation time. The problem can be stated as ... 

Figure 8.11. General Sequential Off-cut Recycle Strategy in Multicomponent...

Binary to multi-component off-cut recovery and optimal recycling strategies. 

From a chemical point of view, the AB decomposition in solution may allow one to adjust the type of decomposition product obtained after dehydrogenation and thus may influence the recycling strategy to be applied. Furthermore, benefits from improved kinetics can also be expected. Of course, the fundamental prerequisite is a high solubility and the stability of ammonia borane in the solvent in question. Corresponding data are given in Section 8.2. 

Select packing (irregular vs. spherical) based on lifetime, feed purity and operating pressure Evaluate and design solvent recycling strategy Economics of scale... 

On the other hand, complementary systems provide recovery backup that can be exploited by considering the consequences of various recycle strategies within the WTF under conditions of malopera-tion. 

Modify Preloninary Flow Diagrams. On the busis of the results of the single-module process, it may be found that target product compositions and recoverias cannot be achieved without recycle strategies. 

Management of these processes can reduce the emission of these Cl2-com-pounds,whilst the fate of CI2 which is incorporated into products such as PVC depends on recycling strategies, by the production of new composite materials, or the use as fuel or technical products (Campbell et al. 2001, Cavalieri and Padella 2002, Tuncan etal. 2003). The capacity of certain bacteria, for example, strains of Pseudomonas sp. to decompose chlorinated compounds may, in the future, provide a powerful means by which these residues may be handled (e.g., PVC Wischnak etal. 1998). 

The cost and benefit analysis for different plastics recycling strategies in Germany are presented in Table 16.4 [Bauermeister et al, 1994]. The... 

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