Sustainable development meets the needs of present generations
without compromising the possibility of future generation
to attend their needs and aspirations.
Green chemistry or sustainable chemistry or environmentally benign chemistry is the frontiers of science with the utilisation of set of principles that attempts to reduce or eliminates the use or generation of hazardous substances in the design and manufacture of environmentally and economically sustainable products. The growing attention to sustainable development includes the reduction of environmental impact and the effective utilization of renewable resources. It can help to solve large global problems such as climate change, energy consumption of effective utilization of natural resources, especially renewable resources.
The terms ‘green chemistry’ and ‘sustainable chemistry’ have been often used in several areas to introduce the efforts of academics, scientists and industrialists towards the development of new efficient chemical processes accounting for their environmental impact. Green chemistry may be considered as a modern scientific platform where the common efforts of academia, industry and government converge to develop a sustainable civilization, and in this context, it is certainly clear that fundamental chemistry has an important role to play.
Probably one of the most important steps in the evolution of green chemistry is closely related to U.S. Environmental Protection Agency (USEPA). In the 1980s, a significant change began in the execution of environmental regulations, and pollution became the priority instead of end-of-pipeline control. In 1990, the pollution Prevention Act, approved by the American Congress in the United States, initiated to create a modus operandi for dealing with pollution in an innovative and sustainable way and paved the way to green chemistry concept. Green chemistry takes advantage for technological advancement chemical processing to achieve environmental efficiency.
Paul Anastas and John Warner of the U.S. Environmental Protection Agency coined the two-letter word “green chemistry” and formulated 12 principles of green chemistry. They are as follows:
Green chemistry addresses many challenges by opening a wide and multifaceted research scope and allowing the invention of novel reacting chemicals that can maximise the desired products and minimise the waste products, as well as the design of new synthetic schemes that are inherently, environmentally and ecologically benign.
The following are the importance of green synthesis:
Over the past decades, green chemistry has convincingly demonstrated how fundamental scientific methodologies can be devised and applied to protect human health and the environment in an eco-friendly and economically beneficial manner.
Example: Production of dimethyl carbonate (DMC)
Dimethyl carbonate is a versatile and environmentally friendly material for chemical industry. Due to high oxygen content and blending properties, it is used as a good component of fuel.
Traditional Method
In this method, phosgene (COCl2) and methanol (CH3OH) are used to produce DMC.
Here phosgene (reactant) and hydrochloride acid (by-product) are environmentally harmful.
Greener Method (Alternative Method)
This method makes use of copper chloride, methanol, oxygen and carbon monoxide.
Here copper chloride further comes as a by-product, and usage of CO in this method is cheap and indirectly decreases the pollution.
Bioleaching is the extraction of specific metals from their ores by using microorganisms such as bacteria.
Example: Extraction of gold
Traditional Method
Heap leaching method is the traditional method employed for the extraction of gold using cyanide. Here, cyanide is hazardous to health and environment.
Greener Method
In this method, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans bacteria are used to oxidise ferrous and sulphur. The gold will be easily separated from the ore and solution. This method is much cleaner than the traditional heap leaching method.
Catalytic methods are superior than stoichiometric methods.
Example: Synthesis of adipic acid
Adipic acid is a monomer for nylon and starting material for cathode.
Traditional Method
In the past, for the production of adipic acid, benzene is used as a starting material. However, it is highly carcinogenic and causes leukaemia. Afterwards, the starting material became cyclohexanone or a mixture of cyclohexanone and cyclohexanol. In oxidation with nitric acid, it produces toxic fumes of nitric oxides, which are contributors to the greenhouse effect, acid rain and the destruction of ozone layer.
In this method, cyclohexane is oxidised by 30 per cent of hydrogen peroxide in the presence of a catalyst. The catalyst used is a salt of the metal wolfram and dissolved in an organic solvent such as aliquot 336.
Oxidation with H2O2 is very effective and environmentally benign. Scientists improved the reaction with other metal catalysts such as tungsten and molybdenum. The process also promoted towards biocatalytic method by using genetically transgenic bacteria like Klebsiella pneumoniae, a non-toxic strain of E. coli. Dr Karen M. Draths and Professor John W. Frost were awarded the “Presidential Green Chemistry Challenge Award” in 1998 in the USA for this achievement.
Green synthesis has wide applications in many fields. Few of them are as follows:
A greenhouse is also known as a glasshouse. In the greenhouse, plants are grown in a building or other complexes. Building of the greenhouse is made up of either glass or plastic material. In a greenhouse, the incoming UV light is absorbed consequently the temperature of air inside the greenhouse increases and retained in the building by the roof and wall, and air is warmed near the ground and flowing within the complex.
A greenhouse is divided into two types:
In both types of greenhouses, the plastics used are polyethylene, polycarbonate or PMMA glass.
In greenhouse effect, UV radiations from sun of short wavelength are absorbed through a transparent medium, but IR radiations of longer wavelength are unable to pass back from that medium. As a result, inside temperature increases. Such effect is called the greenhouse effect. This effect is shown due to absorption of excess heat by carbon dioxide present in it.
The greenhouse effect is a natural process that produces a relatively warm environment near the earth’s surface conducive to life on earth; this is broadly of two types: natural and enhanced greenhouse effects.
The natural greenhouse effect occurs naturally by greenhouse gases present in the earth’s atmosphere; the main natural greenhouse gases are carbon dioxide, methane, nitrous oxide and water vapour.
The enhanced greenhouse effect occurs by human activities which release greenhouse gases into the atmosphere. The main anthropogenic or human-induced greenhouse gases are carbon dioxide, nitrous oxide, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), methane and sulphur hexafluoride. The enhanced greenhouse effect is responsible for the increase in global temperature, that is, global warming.
Sources of greenhouse gases, properties and their impacts are shown in Table 21.1.
Table 21.1 Greenhouse gases their sources, properties and impacts
Greenhouse gases in the earth’s atmosphere absorb infrared radiation from the ground. This radiation is re-emitted in all directions and radiated back towards the earth’s surface, thereby leading to the warming of the earth’s surface. Scientists have been able to determine carbon dioxide concentrations on earth over time and the temperature variation by using data from ice cores and other sources.
Since middle of 20th century, temperature variations and climate changes have been observed due to manmade sources of greenhouse gases but not on the basis of the presence of natural greenhouse gases.
During the 21st century, the earth is likely to experience the following greenhouse effects:
Finding alternatives to these greenhouse gases in chemical and industrial processes have led to the development of a new branch of chemistry called green chemistry.
Green synthesis methods have a good impact on the environment.
In these processes, there is less exposure to pollutants, waste reduction and less energy consumption. In research, green synthesis methods include the use of microwave reactors to minimize energy needs and use of microfluidic reactors to minimize solvent waste.
Main aim of Green chemistry the design of chemical products and processes that reduce or minimize the hazardous effects to living beings and the environment.
Carbon sequestration is the process of carbon capture from burning fossil fuels and the long term storage of CO2 safely before releasing into the atmosphere.
Terrestrial or biologic sequestration is the storage of carbon via agricultural and forestry practices. Geologic sequestration involves injecting carbon dioxide to deep underground where it stays permanently.
Carbon dioxide capture and sequestration (CCS) is a set of three step processes that can greatly reduce CO2 emissions from new and existing coal- and gas-fired power plants and large industrial sources. The processes are as follows:
Carbon dioxide (CO2) capture and sequestration (CCS) can significantly reduce emissions from large stationary sources of CO2, which include power plants using coal and natural gas, as well as industries such as ethanol processing plants, natural gas processing plants and cement industries.
Carbon dioxide capture and sequestration play an important role in reducing greenhouse gas emissions dramatically and enabling low-carbon electricity generation from power plants and industries that burn fossil fuels. With this process, about 80–90% CO2 emission may reduce from the power plants and is equal to:
In pre-industrial age, every million molecules of air contained about 280 molecules of carbon dioxide, and now, that proportion exceeds 380 molecules per million and it continues to increase. Evidence is mounting that carbon dioxide’s heat-trapping power has already started to boost average global temperatures. If carbon dioxide levels continue to increase, then further atmospheric warming occurs and its consequences result in rising of sea levels, agriculture disruptions, stronger storms (e.g., hurricanes) striking more often, etc.
However, reducing carbon dioxide emission does not have a simple solution. Fossil fuels, which provide about 85 per cent of the world’s energy, are made of hydrocarbons, and burning them releases huge quantities of carbon dioxide. Fossil-fuel burning will remain substantial, even renewable energy sources emerge. In fossil fuels, coal is the worst carbon dioxide emitter per unit of energy produced. A grand challenge for the 21st century’s engineers will be developing systems for capturing the carbon dioxide produced by burning fossil fuels and sequestering it safely away from the atmosphere.
[Ans.: American congress]
[Ans.: Paul Anastas and John Warner]
[Ans.: prevention]
[Ans.: renewable]
[Ans.: enhanced greenhouse effect]
[Ans.: Greenhouse effect]
[Ans.: d]
[Ans.: d]
Ans.: Green chemistry is the frontier of science with the utilization of set of principles that attempts to reduce or eliminate the use or generation of hazardous substances in the design and manufacture of environmentally and economically sustainable products.
Ans.: Bioleaching is the extraction of specific metals from their ores by using microorganisms such as bacteria.
Example: Extraction of gold
Traditional method: Heap leaching method by using cyanide.
Greener method: Acidithiobacillus ferocious and Acidithiobacillus thiooxidans bacteria are used.
Ans.: In greener route, cyclohexane is oxidized by 30 per cent of hydrogen peroxide in presence of catalyst.
Q.1 Give brief note on Carbon sequestration and its importance.
Q.2 Explain Greenhouse effects and its impacts.
Q.3 Give brief note on types of greenhouses.
Q.4 Discuss the use of solar energy for space heating, water heating and production of electricity.
Q.5 Discuss the use of indirect solar energy for generation of electrical power.
Q.6 Write short notes on the following:
Q.7 Explain the solar desalination process and solar cooking process.
Q.8 Write informative note on wind power with its merits and limitations.
Q.9 Define green chemistry and explain 12 principles of green chemistry.
Q.10 Explain any two greener methods with examples.
Q.11 Give a brief note on greenhouse concept.
Q.12 What is the importance of green synthesis?
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