Benign waste streams

The key intermediate chloromethyloxadiazole 18 was prepared in two steps from inexpensive, commercially available materials as shown in Scheme 5.10. Bishydrazide 19 was prepared in a one-pot procedure by reaction of 35% aqueous hydrazine with ethyl trifluoroacetate in acetonitrile and subsequent addition of chloroacetyl chloride and base. This procedure affords the unsymmetrical bis(hydrazide) 19 in higher than 95% assay yield. While a number of dehydrating agents were found to be effective in the dehydration to prepare 18, phosphorus oxychloride was chosen because of its low cost and relatively benign waste stream. Sub-stoichiometric (0.3 equiv.) amounts were found to be as effective as full equivalents in the reachon when used in conjunction with catalyhc amounts of DMAP as a nucleophilic catalyst. The entire sequence was transformed into a one-pot through process in order to improve efficiency. Following the cyclization, an aqueous work-up was performed and the organic extracts carried directly into the next step. 

RECYCLING OF BENIGN WASTE STREAMS IN CBPC VALUE-ADDED PRODUCTS... 

Recycling of Benign Waste Streams in CBPC Value-Added Products 159... 

This report will describe the realization of these goals by proper selection of the catalyst and operating conditions, which ultimately led to a process with exceptional turnover numbers (TON>10,000) and exceptional reactor productivities (product concentrations >25 wt% in 3 hrs). Further, the process ultimately requires little or no solvent while generating a benign NaCl waste stream. 

Because water can be considered as one of the most benign solvents available, together with its solvation powers at high temperature, its applicability for a variety of wastes is tremendous. However, based on the current developments of the process, its applicability remains limited to pumpable waste streams. In addition, it is generally understood that the waste streams with organic content in the 1-20 wt.% range is most suitable for this technology. Waste streams with 100 wt.% can be treated with appropriate dilution. However, the cost for the dilution may add prohibitively to the total cost. 

Over the past decade, carbon dioxide has become an attractive alternate solvent for a variety of polymer synthesis and processing applications due to its environmentally benign nature and chemical inertness I T Properties of CO2, such as dielectric constant and density are sensitive to the temperature and pressure of the system. The fluid density and dielectric constant, can be fine tuned using temperature and pressure profiling. In addition, CO2 offers an environmentally sound medium with the potential to eliminate organic and aqueous waste streams in manufacturing facilities. 

As stated previously and in Chapter 24. this section should be eliminated or minimized through pollution prevention and green engineering. However, especially if the contaminant has little or no value if concentrated, there will be relatively dilute waste streams generated and sent to the environmental control section. Here, they are concentrated (by the separation techniques discussed earlier) and then disposed of (by incineration, neutralization, oxidation, burial, or other means). The keys are to concentrate the waste and to make it benign. 

Alternatively, a hazardous waste stream may be produced. In such cases additional cosdy treatment steps (either on-site or off-site) would be required in order to render the material benign to the environment. The economic penalties for these treatment steps—incineration, neutralization, and so on—are often great and may severely impact the overall economic picture for the process, hi addition to the economic penalties that the production of waste streams cause, there are political ramifications that may overshadow the economic considerations. For many conpanies, the production of hazardous wastes is no longer an acceptable process choice, and alternative reaction routes, which eliminate such waste streams, are aggressively pursued. 

Ecologically benign destruction of Lewisite and Mustard has been achieved by electrochemical pretreatment of their neutralization products followed by biological oxidation of the waste stream. 

The reductive amination of carbonyl compounds can be carried out using sodium cyanoborohydride, sodium triacetoxyborohydride or NaBH coupled with sulfuric acid. These reagents involve the use of corrosive acids and/or produce waste stream. The environmentally benign methods using wet montmorillonite KIO clay supported sodium borohydride facilitated by microwave irradiation has been developed by Varma and Dahiya (1998). Clay montmorillonite KIO not only behaves as a Lewis acid but it also provides water from its interlayers that enhance the reducing ability ofNaBH.. 

Water is cheap, relatively abundant in many part of the world, safe, and, when pure, environmentally benign [40]. It is also true that some reactions show unusual selectivity and/or rate enhancements when run in, or more accurately, on water [41]. However, a closer examination of many reactions in water reveals that in fact one or more liquid reagents have been used in large excess, so they are in fact biphasic reactions. There is also a misguided perception that water, after use as a reaction medium, can be poured down the drain [42]. On an industrial scale, there can be a considerable cost and environmental burden associated with remediation of waste water streams contaminated with solvents and organic and metal residues-see Chapters 2 and 3. 

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