Waste Production, Problems and Prevention

In an ideal chemical factory there is, strictly speaking, no waste but only products. The better a real factory makes use of its waste, the closer it gets to its ideal, the bigger is the profit. 

von Hofmann (First President of The Royal College of Chemistry, London)1848 

Source DETR publication the environment in your pocket 2000 

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Waste production, problems and prevention Environmental performance... 

Waste Production, Problems and Prevention Table 2.3 Plastic identification codes... 

Waste problems that cannot be solved by simple procedural adjustments or improvements in housekeeping practices will require more substantial long-term changes. It is necessary to develop possible prevention options for the waste problems. Process or production changes that may increase production efficiency and reduce waste generation include ... 

The efficient removal of actinides from the Na2C03 scrub waste solution presents several problems. Acidification of the carbonate solution with excess HNO3 followed by extraction with TBP (or, preferably, DHDECMP) (3) results in the rapid build-up of acidic degradation products (HDBP and H2MBP in the case of TBP) which prevent efficient back extraction. In addition, acidification of Na2C03 scrub waste results in the precipitation of actinide-DBP and -MBP complexes which are difficult to dissolve... 

Waste products from many industrial processes contain at times significant concentrations of metals which are objectionable on environmental grounds and yet constitute an appreciable economic asset. The presence of toxic metals in such wastes constitutes an environmental hazard, particularly because the ever-decreasing pH of the rainwater makes their leachability and contamination of the ground water more likely. Careful and costly waste-disposal procedures are thus mandatory so as to prevent this from occurring. A preferred alternative is the cost-effective conversion of such waste into useful products. This provides an optimal solution to the waste-disposal problem because (a) it eliminates the need for a safe and costly disposal of the hazardous waste (b) it maximizes resource utilization and conservation through recycling, and (c) it derives an economic benefit from the sale of the obtained products. 

The toxicity of phosgene has spawned a lot of research into alternates for both MDI and TDI, as well as polycarbonates. In addition to safety, there are economic incentives for developing alternate routes. In the conventional MDI process, methylene diphenylmethane diamine (MDA) is formed by reacting aniline with formaldehyde. Separating excess aniline from crude MDA is an expensive operation. Also, by-product HCl formed in the conversion of MDA to MDI is an environmental issue. The final isocyanate product contains hydrolyzable chloride compounds that are difficult to separate and dispose of. The reactants must be kept bone dry to prevent corrosion, and the introduction of water can cause a runaway reaction. Similar concerns influence the search for nonphosgene routes for TDl. Conventional routes to polycarbonates also employ phosgene, which produces chlorine waste products, primarily sodium chloride, that present disposal problems. The elimination of chlorine from the polycarbonate process would constitute a major improvement. 

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