Green Chemistry
Chemists and chemical engineers applying green chemistry look at the entire life cycle of a product or process, from the origins of the materials used for manufacturing to the ultimate fate of the materials after they have finished their useful life. By using such an approach, scientists have been able to reduce the impacts of harmful chemicals in the environment.
Research and development in the field of green chemistry are occurring in several different areas.
Alternative feedstocks
Historically, many of the materials used to make products often were toxic or depleted limited resources such as petroleum, but green chemistry research is developing ways to make products from renewable and nonhazardous substances, such as plants and agricultural wastes. For example, cellulose and hemicellulose, which constitute up to eighty percent of biomass, can be broken down to sugars, then fermented to chemical commodities such as ethanol, organic acids, glycols, and aldehydes. Converting biomass to ethanol has become economically and technically viable due to a new class of genetically modified bacteria capable of breaking down the different sugars in hemicellulose.
Historically, many of the materials used to make products often were toxic or depleted limited resources such as petroleum, but green chemistry research is developing ways to make products from renewable and nonhazardous substances, such as plants and agricultural wastes. For example, cellulose and hemicellulose, which constitute up to eighty percent of biomass, can be broken down to sugars, then fermented to chemical commodities such as ethanol, organic acids, glycols, and aldehydes. Converting biomass to ethanol has become economically and technically viable due to a new class of genetically modified bacteria capable of breaking down the different sugars in hemicellulose.
Benign manufacturing
The methods used to make chemical materials, called synthetic methods, have often employed toxic chemicals such as cyanide or chlorine. In addition, these methods have at times generated large quantities of hazardous wastes. Green chemistry research is developing new ways to make these synthetic methods more efficient and to minimize wastes while also ensuring that the chemicals used and generated by these methods are as nonhazardous as possible. For example, a number of industries, such as the pulp and paper industry, use chlorine compounds in processes that generate toxic chlorinated organic waste. Green chemists have developed a new technology that converts wood pulp into paper using oxygen, water and polyoxometalate salts, while producing only water and carbon dioxide as by-products.
The methods used to make chemical materials, called synthetic methods, have often employed toxic chemicals such as cyanide or chlorine. In addition, these methods have at times generated large quantities of hazardous wastes. Green chemistry research is developing new ways to make these synthetic methods more efficient and to minimize wastes while also ensuring that the chemicals used and generated by these methods are as nonhazardous as possible. For example, a number of industries, such as the pulp and paper industry, use chlorine compounds in processes that generate toxic chlorinated organic waste. Green chemists have developed a new technology that converts wood pulp into paper using oxygen, water and polyoxometalate salts, while producing only water and carbon dioxide as by-products.
Designing safer chemicals
Once it is certain that the feedstocks and methods needed to make a substance are environmentally benign, it is important to ensure that the end product is as nontoxic as possible. By understanding what makes something harmful (the field of molecular toxicology), scientists are able to design the molecular structure so that it is not dangerous.
Once it is certain that the feedstocks and methods needed to make a substance are environmentally benign, it is important to ensure that the end product is as nontoxic as possible. By understanding what makes something harmful (the field of molecular toxicology), scientists are able to design the molecular structure so that it is not dangerous.
Green analytical chemistry
The detection, measurement, and monitoring of chemicals in the environment through analytical chemistry have long been a tool for environmental protection. Instead of measuring environmental problems after they occur, however, green chemistry seeks to prevent the formation of toxic substances and thus prevent such problems. By making sensors and other instruments part of industrial manufacturing processes, green analytical chemistry is able to detect even tiny amounts of a toxic substance and to adjust process controls to minimize or stop its formation altogether. In addition, although traditional methods of analytical chemistry employ substances such as hazardous solvents, green analytical methods are being developed to minimize the use and generation of these substances while conducting analysis.
The detection, measurement, and monitoring of chemicals in the environment through analytical chemistry have long been a tool for environmental protection. Instead of measuring environmental problems after they occur, however, green chemistry seeks to prevent the formation of toxic substances and thus prevent such problems. By making sensors and other instruments part of industrial manufacturing processes, green analytical chemistry is able to detect even tiny amounts of a toxic substance and to adjust process controls to minimize or stop its formation altogether. In addition, although traditional methods of analytical chemistry employ substances such as hazardous solvents, green analytical methods are being developed to minimize the use and generation of these substances while conducting analysis.
Principles
Paul Anastas, then of the United States Environmental Protection Agency, and John C. Warner developed 12 principles of green chemistry, which help to explain what the definition means in practice. The principles cover such concepts as:
- the design of processes to maximize the amount of raw material that ends up in the product;
- the use of safe, environment-benign substances, including solvents, whenever possible;
- the design of energy efficient processes;
- the best form of waste disposal: not to create it in the first place.
The 12 principles are:
1. It is better to prevent waste than to treat or clean up waste after it is formed.
2. Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
3. Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
4. Chemical products should be designed to preserve efficacy of function while reducing toxicity.
5. The use of auxiliary substances (e.g. solvents, separation agents, etc.) should be made unnecessary wherever possible and, innocuous when used.
6. Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.
7. A raw material or feedstock should be renewable rather than depleting wherever technically and economically practicable.
8. Reduce derivatives - Unnecessary derivatization (blocking group, protection/ deprotection, temporary modification) should be avoided whenever possible.
9. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
10. Chemical products should be designed so that at the end of their function they do not persist in the environment and break down into innocuous degradation products.
11. Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
12. Substances and the form of a substance used in a chemical process should be chosen to minimize potential for chemical accidents, including releases, explosions, and fires.
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