Benign alternatives development

The development of more benign alternatives to cyanide for gold-leaching (see Section 9.17.3.1) such as thiourea, thiocyanate, or thiosulfate, which form stable complexes in water has prompted research to identify suitable solvent extractants from these media. Cyanex 301, 302, 272, Ionquest 801, LIX 26, MEHPA, DEHPA, Alamine 300 (Table 5) have been evaluated as extractants for gold or silver from acidic thiourea solutions.347 Whilst the efficacy of Cyanex 301 and 302 was unaffected by the presence of thiourea in the aqueous feed, the loading of the other extractants is severely depressed. Formation of solvated complexes of gold and of an inner-sphere complex of silver has been proposed.347... 

Enzymes offer an envuonmentally benign alternative to chemical catalysts in many commercial and industrial applications. Tire expansion of their use depends on the development of new protein catalysts. This will imply the construction or identification of enzymes that have been genetically altered to improve their performance under defined, application-specific conditions. Du ected evolution offers a fast and effective way of creating improved enzymes from relatively ineffective catalysts to commercially viable products by a variety of duected evolution techniques. 

Various software tools have been developed to identify environmentally benign alternative solvents or equipment modifications to reduce the amount of toxic and volatile solvents. Some tools have attempted to consider Ufe cycle impact in their selection methodologies, but these are the exceptions rather than the rule. This section provides a brief description... 

The development of alternative pathways for chemical reactions, such as new kinds of catalysts the use of natural processes, such as photochemical reactions and the use of less harmful and ecologically benign feedstocks (raw materials)... 

The development of alternative reaction conditions, including the use of more benign solvents and greater attention to the kinds of wastes released to the environment... 

One of the most important challenges in the modern chemical industry is represented by the development of new processes aimed at the exploitation of alternative raw materials, in replacement of technologies that make use of building blocks derived from oil (olefins and aromatics). This has led to a scientific activity devoted to the valorization of natural gas components, through catalytic, environmentally benign processes of transformation (1). Examples include the direct exoenthalpic transformation of methane to methanol, DME or formaldehyde, the oxidation of ethane to acetic acid or its oxychlorination to vinyl chloride, the oxidation of propane to acrylic acid or its ammoxidation to acrylonitrile, the oxidation of isobutane to... 

The development of analytical chemistry conhnues at a steady rate and every new discovery in chemistry, physics, molecular biology, and materials science finds a place in analytical chemistry as well. The place can either be a new tool for existing measurement challenges or a new challenge to develop stable and reliable methods. Two examples are the advent of nanostructure materials and alternative solvents, both of which saw their main development in the past decade. Nanostructural materials pose a new scale of measurement challenge in size and number. New solvents with their environmentally benign properties offer a possibility for wasteless operation. 

Benign chemistry seeks to develop and institutionalize alternative chemistries for pollution prevention. Significant challenges are available for chemists to design new products and processes that are less pollnting (Anastas and Farris, 1994). 

The implementation of the Montreal Protocol, the Clean Air Act, and the Pollution Prevention Act of 1990 has resulted in increased awareness of organic solvent use in chemical processing. The advances made in the search to find green replacements for traditional solvents have been tremendous. With reference to solvent alternatives for cleaning, coatings, and chemical reaction and separation processes, the development of solvent databases and computational methods that aid in the selection and/or design of feasible or optimal environmentally benign solvent alternatives for specific applications have been discussed (Sherman et al., 1998). 

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