Recycling processing options

The surviving U.S. plants have embraced all types of waste treatment processes (see Wastes treatment, hazardous waste Wastes, industrial). The most desired poUution prevention processes are those which reduce the total amount of waste discharged. Treatment and disposal are less strongly emphasized options. Zero wastewater discharge faciHties and water recycling processes are becoming more common (55,56). 

Brighton, 20th-22nd April 1999, p. 123-31 OPTIONS FOR PVC FEEDSTOCK RECYCLING RESULTS OF THE ECVM R D PROJECT ON PVC FEEDSTOCK RECYCLING PROCESSES Buehl R... 

In examining the technical options for plastic waste management, chemical recycling appears to be the least developed and most difficult. In this paper, BP Chemicals sets out its analysis of the factors that will determine the choice of chemical recycling process technology. From this a process concept based on thermal cracking is developed and the hurdles to be overcome before such a process can be realised is discussed. 

Additives often form a problem in recycling processes. Material recycling is often not possible or only with a considerable loss of quality. Plastics recycling is notoriously difficult due to the mixed composition of the plastics waste stream. The recycled material can only be used in certain applications that do not demand a pure material. Recycling of the additives themselves is theoretically possible only for metals, but in practice this type of recycling is not feasible. The metals occur only in low concentrations. Recovery from fly ash and bottom ash is possible, but expensive in view of growing scarcity problems it may become a viable options for at least some metals. 

Table 4.2 Processing options and their influence on PET recycling requirements c, critical aspect, where requirement is not or only partially fulfilled...

Several bottle-to-bottle recycling technologies have been developed to convert washed PET flakes to food-grade PET pellets [129,130], They can be categorized by four different ways of processing. The succession of process steps has an influence on the final result. To see the implications, each process option has to be evaluated with respect to the requirements discussed before. Some of these critical aspects are indicated in Table 4.2. 

The above processes are only selected examples of a vast number of process options. In the case of carbonylation, the formation of by-products, primarily isocyanate oligomers, allophanates, and carbodiimides, is difficult to control and is found to greatly reduce the yield of the desired isocyanate. Thus a number of nonphosgene processes have been extensively evaluated in pilot-plant operations, but none have been scaled up to commercial production of diisocyanates primarily due to process economics with respect to the existing amine—phosgene route. Key factors preventing large-scale commercialization include the overall reaction rates and the problems associated with catalyst recovery and recycle. 

Furthermore, a study of the behaviour of a fluidized-bed reactor is very important as one of the options for a possible commercialization of such a pyrolysis recycle process is to co-feed plastic waste into the FCC cracker unit of an oil refinery. Studies of plastic being a fraction of the feed of a cracking process have been carried out by Ng et al. [7] and Arandes et al. [12, 27, 28]. They not only showed the applicability of the method, but discovered a synergetic effect on the cracking of the oil decreasing the amount of aromatics. 

Several researchers have experimentally demonstrated the inhibiting influence of hydrogen sulfide (H2S) on HDS. This inhibiting influence is expected from simple and kinetic and equilibrium considerations. Refiners take great care to keep H2S in commercial hydrotreaters at an optimum level. For example, hydrogen—used in excess in a hydrotreater—is recirculated after scrubbing out the H2S by-product carefully. The recycle stream needs to contain an optimum level of H2S to keep the catalyst as a sulfide and thus maintain its activity and selectivity. Sie has described other process options to minimize inhibition effects by H2S, e.g., countercurrent flow reactors and monolithic catalyst systems. ... 

A wide variety of technical options are available for the recycling of plastics and products containing plastics, although only a small number of these methods have actually been implemented in pilot and production scale. In addition to the technical suitability of the methods, econontic and political conditions are decisive for development and operation of recycling processes. In areas in which direct advantages (mainly economic in nature) are generated from the start, for example in... 

Competitive penetration of polypropylene into other applications has primarily taken place in polyethylene, polystyrene, polyvinyl chloride (PVC), thermoplastic polyester, nylon-6 or -6/6, and sometimes directly from metals or thermoset polymers like phenolic or reinforced reaction injection molded (RIM) urethane. The reasons for market penetration by PP replacement vary widely with an assortment of material design options chemical resistance, heat resistance, recycleability, processability, economics, and aesthetics. 

The supercritical-water-cooled reactor (SCWR) ( Fig. 58.21) system features two fuel cycle options the first is an open cycle with a thermal neutron spectrum reactor the second is a closed cycle with a fast-neutron spectmm reactor and full actinide recycle. Both options use a high-temperature, high-pressure, water-cooled reactor that operates above the thermodynamic critical point of water (22.1 MPa, 374°C) to achieve a thermal efficiency approaching 44%. The fuel cycle for the thermal option is a once-through uranium cycle. The fast-spectrum option uses central fuel cycle facilities based on advanced aqueous processing for actinide recycle. The fast-spectrum option depends upon the materials R D success to support a fast-spectrum reactor. 

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