Waste reduction reactors

The care for the purity of waste streams requires a similar sort of quality control. Since many pollutants originate from chemical reactors, waste reduction starts with reactor design. 

Reactor Wastes. The same fimdamental approach of immobilization and disposal is being taken for reactor wastes. Work has been underway in AECL for several years on immobilization techniques (21). These include volume reduction processes of incineration for combustible materials and reverse osmosis for concentrating solids from aqueous streams. The concentrates from these processes will be immobilized in bitumen. The deep underground disposal facility developed for fuel wastes will most likely also be used for the iinnobilized reactor wastes. 

In order to perform waste reduction and pollution prevention in reactor design, studying the effects of reaction... 

A.G. Dixon, W.R. Moser and Y.H. Ma, Waste reduction and recovery using 02-perme-able membrane reactors. Ind. Eng. Chem. Res., 33 (1994) 3015-3024. 

A second level of analysis for waste reduction in chemical reactors considers the fact that hazards associated with many wastes are due to trace contaminants. For example, if a reactor produces a by-product stream that is considered a waste only because it contains a trace of a chlorinated dibenzodioxin, then eliminating the trace level of dioxin may allow the by-product stream to be used productively. Eliminating the production of very hazardous trace-level components may involve far different reactor designs than those used for maximizing selectivity. These types of improvements are still in their infancy and will require significant fundamental research to become practical. They are discussed in more detail in Section IV. 

A fourth method for waste reduction in reactors focuses on spent catalyst wastes where recycling, controlling attrition, and limiting deactivation may reduce wastes. Consider the case of hydroprocessing catalyst wastes, which are extensively recycled to recover cobalt, molybdenum, nickel, vanadium, and alumina (Chemical and Engineering News, October 26, 1992, p. 20). More than a third of the domestic demand for vanadium is met via these recovery processes (Chemical and Engineering News, November 23, 1992,... 

Finally, integrating chemical reaction and separation in a single vessel offers opportunities for waste reduction. As an example of this strategy, consider the synthesis of methyl-tert-butyl ether (MTBE). Two processes are in common industrial use in the synthesis of MTBE from methanol and isobutylene. In one process, a series of fixed-bed catalytic reactors send a mix of product, unreacted methanol, and unreacted isobutylene to a series of separation devices. In an alternative process configuration, the feed materials are sent to a distillation column that contains a series of catalytic beds. The processes are contrasted in Fig. 17. There are several advantages to the catalytic distillation configuration ... 

Ni(II) and Co(II) both produce reduction waves ( — 0.8 and —1.2 V versus SCE, respectively, in ammoniacal solution) and have been determined in chromites, reactor waste, and natural waters. Interferences such as Zn can be minimized by the addition of complexing reagents (e.g., crown ethers), which selectively complex with Ni and Co producing a greater cathodic potential shift compared to the Zn reduction potential. Detection limits using this approach would amount to lO moll . ... 

Wille, H., Sato, Y. Field experience of chemical decontamination and waste reduction with the Cord process. Paper presented at the Intemat. Conf. Chemistry in Water Reactors — Operating Experience and New Developments. Nice, France, 1994... 

Expand partnerships and information exchange and facilitate collaborative research and development for beneficial uses of nuclear energy — including evolutionary and innovative technological developments for improved competitiveness, safety, proliferation resistance and waste reduction — particularly for developing countries in the areas of small and medium size reactors and non-electricity applications such as desalination, heat production and hydrogen production. ... 

Both continuous and batch methods may be used in methanolysis. The batch mediod requires an autoclave, crystallizer, and centrifuge and a system for the melting and distillation of the DMT obtained. In the two-stage Hoechst continuous process, waste PET is melted and fed to a reactor. Preheated methanol is added to the autoclave, which is equipped with a mixer. The conversion reaches 70-90% in the first reactor, after which the reaction stream is introduced into a second autoclave at a lower temperature near the bottom, where it rises slowly and die higher density impurities settle at the bottom. The reaction stream leaves the second autoclave and its pressure is reduced to 0.3 MPa. On further reduction of the pressure and cooling, DMT precipitates and is subsequently purified.12... 

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