Alternative recycling concepts

A different concept is the idea of manufacturing at point of use rather than transporting materials. A simple and familiar example is the office water cooler. The majority that you see around use large bottles of water. These need to be transported and stored and the empty bottles recycled. More than 600 kT of bottled water were imported into the UK in 1999, creating a significant transport impact. The alternative is to chill and filter mains water on-site. The water needs to be filtered and purified to meet consumer perceptions and expectations. These systems use a mixture of purification techniques including advanced filters, UV-disinfection and silver-treated surfaces to give users the confidence they require. 

Recent developments to the hydrothermal process include improvements in yield and reaction rate and in overcoming the difficulty associated with the coproduct salt. One method of overcoming the co-product problem is to use magnesium nitrate instead of chloride, with the ammonium nitrate being utiHsed for fertiliser production [102-104]. At least one plant based on this concept is now in commercial production. While a considerable advance on the initial chloride process, the nitrate route does require close integration with a fertiliser process and thus lacks flexibility. An alternative approach being developed is to recycle the ammonium salt co-product (nitrate or chloride) and use it to leach magnesium oxide, a potentially inexpensive raw material [103]. 

A further alternative is the totally deintegrated sequential process, where the reactor is followed by an SMB separation and the glucose is recycled to the reactor. Figure 8.14 shows the three continuous concepts considered here. 

The concept of immobilized ionic liquids entrapped, for instance, on the surface and pores of various porous solid materials (supported ionic liquid phase, SILP) is rapidly become an attractive alternative. In addition, the SILPs can also answer other important issues, such as the difficult procedures for product purification or IL recycling, some toxicity concerns and the problems for application in fixed-bed reactors, which should be addressed for future industrial scale-up. This new class of advanced materials shares the properties of true ILs and the advantages of a solid support, in some cases with an enhanced performance for the solid material. Nevertheless, a central question for the further development of this class of materials is to understand how much the microenvironment provided by the functional surfaces is similar or not to that imparted by ILs. Recent studies carried out using the fluorescence of pyrene to evaluate the polarities of a series of SILPs based on polymeric polystyrene networks reveal an increase in polarity of polymers, whereas the polymer functional surfaces essentially maintain the same polarity as the bulk ILs. However, this is surely not a simple task, in particular if we consider that the basic knowledge of pure ILs is still in its infancy, and we are just starting to understand the fundamentals of pure ILs when used as solvents. 

An important alternative is the successive reaction and product extraction procedure shown in Figure 5. First the reaction of A and B is carried out in a single polar homogeneous phase containing the catalyst. Downstream, the products are extracted with a nonpolar solvent or solvent mixture. In the third unit, the distillation, the low boiling extractant is distilled off and recycled to the extraction unit. Two examples will demonstrate the practicability of this concept. 

Alternative Approaches / 5.62 Basic Concepts of the Capacity-Based Method / 5.6.3 Reactor-Column-Recycle Example... 

Peroxyarsonic acids. While the perbenzoic acid species described above were extremely attractive alternatives to the homogeneous species, the need to recycle polymer still required a reagent preparation step. The concept of using the polymer as a catalyst was an... 

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