How Green Chemistry reduces the utilization and evolution of hazardous substances?

Green Chemistry is a field of chemistry and chemical engineering that stresses majorly upon the design of products and processes which reduces the utilization and evolution of hazardous substances. It is different from environmental chemistry in a way that it focuses on the effects of polluting chemicals on nature while green chemistry focuses on technological approaches to prevent pollution and decreasing consumption of non-renewable resources.

During 1998, Paul Anastas (Green Chemistry Program at US EPA) and John C. Warner (Polaroid Corporation) published a set of 12 principles to suggest various ways to reduce the environmental and health impacts of chemicals on nature, and also suggest research priorities for the development of green chemistry technologies. The principles include the following concepts:

• Designing of processes to increase the quantity of raw material that makes the product
• Utilization of renewable material feedstock and energy sources
• Utilization of safe, environmentally benign substances, including solvents
• Designing of energy efficient processes
• Avoiding the production of waste that is considered as the ideal form of waste management

Principles of green chemistry

• One should try to prevent the waste rather than to destroy or clean up waste once it is produced.
• Artificial methods must be designed to increase the inclusion of all materials used in the process into the finished product.
• Wherever possible, synthetic methods must be designed to use and produce substances that have negligible toxicity to human health and also the environment.
• Chemical products must be designed to secure efficacy of function as well as reducing toxicity.
• The use of supplementary substances (such as solvents, etc.) should be avoided wherever possible and harmless when used.
• Energy requirements must be identified for their environmental and financial impacts and should be reduced.
• All raw materials or feedstock must be renewable wherever technically and financially feasible.
• Where derivatization (blocking group, protection or deprotection, temporary modification) is not necessary, it should be avoided.
• Catalytic reagents must be selected as these are superior to stoichiometric reagents.
• Chemical products must be designed in such a way that at the end of their function, they do not retain in the environment and break down into harmless degradation products.
• Analytical methodologies should be more developed to permit for real-time, in-process control and monitoring before the formation of harmless substances.
• Substances and their various forms used in a chemical process must be selected to reduce the possibility for chemical accidents, such as evolution, explosions, and fires.

Green solvents: These are the solvents consumed in large amounts in various chemical syntheses, cleaning and degreasing. These are different from traditional solvents that are usually toxic or chlorinated. Green solvents are derived from renewable resources that can biodegrade to harmless, naturally occurring product.

Synthetic techniques: Innovative synthetic techniques can provide improved environmental performance, thereby enabling better consistency to the green chemistry principles. In 2005, the Nobel Prize for Chemistry was given for the development of the metathesis method in organic synthesis. Three key developments in green chemistry were identified in the area of organic synthesis:

1. Utilization of supercritical carbon dioxide as green solvent.
2. Utilization of aqueous hydrogen peroxide for clean oxidation.
3. Utilization of hydrogen in asymmetric synthesis.

Carbon dioxide used as blowing agent: In 1996, the Greener Reaction Conditions Award was won by Dow Chemical for their cent percent carbon dioxide blowing agent for polystyrene foam production. They discovered that supercritical carbon dioxide works as good as a blowing agent, without indulging any hazardous substances, permitting the polystyrene to get easily recycled. The carbon dioxide involved in this process is reused from other industries in order to reduce the net carbon production from the process to zero. 

Image Courtesy: www. greenchemistry.yale.edu