Unit 3: Green Chemistry PDF

UNIT - 03 GREEN CHEMISTRY M.Sc. Sem-1 C-104 Analytical Chemistry Prepared By Dave Harsh Manali K. R. Meswaniya Assistant Professor- Om College Of Science & PG Center What is Green Chemistry ? ❑ Green chemistry is the...

UNIT - 03 GREEN CHEMISTRY M.Sc. Sem-1 C-104 Analytical Chemistry Prepared By Dave Harsh Manali K. R. Meswaniya Assistant Professor- Om College Of Science & PG Center What is Green Chemistry ? ❑ Green chemistry is the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances. Green chemistry applies across the life cycle of a chemical product, including its design, manufacture, use, and ultimate disposal. Green chemistry is also known as sustainable chemistry. What is Green Chemistry ? ❑The main concept of Green Chemistry is the use of chemical skills and knowledge to reduce or eliminate the use or generation of hazardous substances during the planning, manufacturing and application of chemicals in order to minimize threats to the health of operators and the environment. Thus, the concern to eliminate or minimize the generation of toxic waste has become greater than treating the waste already generated. ❑The 12 principles of Green Chemistry are based on the minimization or non-use of toxic solvents in the chemical processes and analyzes, as well as on the non-generation of residues resulting from these processes. Why Green Chemistry ? ❑ Green chemicals either degrade to innocuous products or are recovered for further use. Plants and animals suffer less harm from toxic chemicals in the environment. Lower potential for global warming, ozone depletion, and smog formation. Less chemical disruption of ecosystems. Elements of Green Chemistry ❑ Ionic liquids ❑ Green solvents ❑ Bio-catalysts (Amylase) ❑ Application of non-conventional energy sources An enzyme in our saliva which converts starch to a simple sugar Ionic liquids ? Ionic liquids (ILs) are salts comprising cations and anions, and usually liquids at or below 100°C. The salts that are liquids at room temperature are generally called as room-temperature ionic liquids (RTILs). Room-temperature ionic liquids (RTILs) consist of salts derived from 1- methylimidazole, i.e., 1-alkyl-3-methylimidazolium Ionic liquids are also employed as auxiliaries and catalysts in chemical synthesis. They are used in analytical equipment. They make up electrolytes in lithium-ion batteries, supercapacitors, and metal plating baths. They can be found as lubricants and coolants. Properties of Ionic liquids Have low melting points. Are good solvents. Have high thermal stability. Have low viscosity. Have high electrical conductivity. Have no vapor pressure. Use of Ionic liquids Applications of Ionic liquids Green solvents Green solvents are environmentally friendly solvents, or bio-solvents, which are derived from the processing of agricultural crops. The use of petrochemical solvents is the key to the majority of chemical processes but not without severe implications on the environment. Green solvents Conventional methylation reactions employ methyl halides or methyl sulphate. The toxicity of these compounds and their environmental consequences render these syntheses somewhat undesirable. Tundo1 2 developed a method to methylate active methylene compounds selectively using dimethy1carbonate (DMC) (Scheme 1) in which no inorganic salts are produced. Scheme 1 Scheme 2 Dimethy1carbonate (DMC) can also act as an organic oxidant. Cyclopentanone and cyclohexanone react with DMC and a base ~C03 to yield adipic and pimelic methyl (or ethyl) esters, respectively (Scheme 2). Values & failings of Green Chemistry ? Reduced use of energy and resources. Principles of Green Chemistry 1 Prevention It concerns the prevention of waste generation. It is better to avoid generating waste than to treat it after its generation 2 Atomic economy Synthetic methods should be planned so that the final product incorporates as much of the reagents used during the process as possible. Thus, waste generation will be minimized 3 Safer chemical synthesis Synthetic methods should be designed to use and generate substances with low or no occupational and environmental toxicity. Thus, replacement of toxic solvents with low or no toxicity solvents is highly recommended 4 Safer chemicals design Great importance should be given to the toxicity of the designed chemicals. They should obviously fulfill their functions, but should also present the lowest possible toxicity 5 Use of safer solvents and auxiliaries The use of solvents and other reagents should be avoided where possible. When it is not possible, these substances should be innocuous 6 Energy efficiency Principles of Green Chemistry 7 Use of renewable raw materials Whenever it is economically and technically feasible, renewable raw materials should be used instead of nonrenewable 8 Reduction of derivatives Unnecessary derivatization processes should be avoided or minimized, as they require the additional use of reagents and, therefore, generate waste 9 Catalysis The use of catalytic reagents (as selective as possible) is better than the use of stoichiometric reagents 10 Degradation products design Chemicals should be designed so that at the end of their function they decompose into harmless degradation products and do not persist in the environment 11 Real-time analysis for pollution prevention Analytical methods should be monitored in real time to avoid the formation of hazardous substances 12 Accidents prevention Both the substances and the way they are used in a chemical process should be chosen considering the minimization of potential accidents, such as leaks, explosions and fires, aiming at greater occupational and environmental safety 1. Prevention of waste Examples: 1. At Home–Avoiding the use of disposable utensils, napkins, and paper towels, and other disposable products. 2. Use a reusable bottle/cup for beverages on-the-go. 3. Use reusable grocery bags, and not just for groceries. 4. Purchase wisely and recycle. 5. Compost it! 6. Avoid single-use food and drink containers and utensils. 7. Buy secondhand items and donate used goods. 8. Shop local farmers markets and buy in bulk to reduce packaging 9. Curb your use of paper: mail, receipts, magazines 2. Atomic economy Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product. Atom Economy, the 2nd principle of green chemistry, comes down to preventing waste on a molecular level. It is an example of a green chemistry metric, which helps us understand the efficiency of a reaction. The equation for atom economy, shown below, essentially tells us the percentage of atoms that end up in the desired reaction product compared to how many atoms are put into the reaction. The higher the atom economy the better, since any atoms that are not incorporated into the final product are considered wasted. Examples: 3. Safer chemical synthesis ❑ Chemical products should be designed to carry out their desired function, while minimizing their toxicity. ❑ Solvent-free approaches involve grinding, ultrasonic irradiation and microwave irradiation of undiluted reactants, or catalysis by the surfaces of inexpensive and recyclable mineral supports such as alumina, silica, clay, or doped aluminosilicates. ❑ Solvent-free reactions obviously reduce pollution and bring down handling costs due to simplification of experimental procedure, work up technique and saving in labor. Examples: 4. Safer chemicals design Examples: 5. Use of safer solvents and auxiliaries Any substance that do not directly contribute to the structure of the reaction product but are still necessary for the chemical reaction or process to occur which is known as auxiliaries. Ex. Types of solvents, separation agents, drying agent and dispersing agent 6. Energy efficiency ❑ This Principle states that 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. ❑ Increased efficiency can lower greenhouse gas (GHG) emissions and other pollutants, as well as decrease water use. ❑ Energy efficiency refers to using less energy to provide an energy service. For example, energy-efficient LED light bulbs are able to produce the same amount of light as incandescent light bulbs by using 75 to 80 percent less electricity. Examples: 7. Use of renewable raw materials ❑Renewable raw materials are (nearly) inexhaustible natural resources, the supply of which can be restored in a short period of time. Biomass is an example of a renewable raw material: green resources from plants and trees as well as food waste streams, which contain many valuable components. ❑What are examples renewable raw materials? ❑Renewable resources ❖ Materials: wood, bamboo, cork, straw, linseed, linoleum, cotton, soy, wool, etc. ❖ Energy: solar, wind, geothermal, hydro, biomass, wave, etc. ❖ Water: rainwater, replenishing aquifer, treated wastewater, etc Examples: Fossil Fuel Biofuel Biodiesel Biomass Hydrogen Biorefineries Feedstocks Greenhouse Gas 8. Reduction of derivatives Examples: 9. Catalysis Catalysis offers numerous green chemistry benefits including lower energy requirements, catalytic versus stoichiometric amounts of materials, increased selectivity, and decreased use of processing and separation agents, and allows for the use of less toxic materials. A catalyst is a reagent that participates in a chemical reaction, yet remains unchanged after the reaction is complete. The way they typically work is by lowering the energy barrier of a given reaction by interacting with specific locations on the reactants Common types of catalysts include enzymes, acid-base catalysts, and heterogeneous (or surface) catalysts. Examples: Bio-catalysis Bio-catalysis is defined as the use of natural substances that include enzymes from biological sources or whole cells to speed up chemical reactions. Enzymes have pivotal role in the catalysis of hundreds of reactions that include production of alcohols from fermentation and cheese by breakdown of milk proteins. E.g.: digestive enzymes such as trypsin, pepsin etc. 10. Degradation products design Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment. Sodium dodecyl benzenesulfonate (Figure 1) is a common detergent, and is often referred to as LAS, for linear alkylbenzene sulfonates. Looking at its structure, you can see that it has a linear alkyl chain with a benzyl sulfonate attached to it. It is useful as a detergent because it has a polar headgroup (sulfonate) and a non- polar alkyl group, making it a surfactant. LAS is used in many things, especially laundry detergent. It degrades quickly in the environment under aerobic conditions, or when oxygen is present, because microbes are able to use to the linear alkyl chain as energy, via a process called β- oxidation, a process which breaks down the carbon chain. Once the long chain is degraded, the rest of the molecule can be degraded as well Examples: If you compare LAS to a branched version (Figure 2), you can immediately see that the alkyl chain looks very different. This molecule was also used as a detergent just like the linear version, but because of the location of the branches, microbes cannot perform β- oxidation since there are no good sites for that reaction to be initiated. Therefore, these branched detergents have been phased out in most developed countries because they are too persistent – they do not biodegrade 11. Real-time analysis for pollution prevention Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances. Examples: 1min 3min 6min 9min 12min 15min 18min 12. Accidents prevention 1. Avoid slips and falls 2. Be aware of electrical hazards 3. Limit manual handling and lifting 4. Keep a well-stocked first aid kit in plain sight 5. Create an emergency action plan 6. Identify staff who may need extra help in an emergency 7. Promote fire safety 8. Avoid injuries by storing items safely 9. Help reduce back pain and repetitive strain injuries 10. Protect your business against water damage Applications of non-conventional energy sources: ❑Microwave ❑Ultrasonic assisted synthesis ❑Electro-synthesis and sunlight (UV) ❑Radiation assisted synthesis. Microwave Microwaves are used in radar, radio transmission, cooking and other applications that have become essential in our modern society. Microwaves are electromagnetic waves generally defined as lying within the frequency range of 100 MHz (3 m wavelength) to 300 GHz (1 mm wavelength). A microwave is a small oven that cooks or heats food very quickly. Instead of the electric or gas heat that a regular oven uses, a microwave heats with electromagnetic radiation. Microwave assist synthesis Different heating mechanisms for conventional and MW heating Conventional Microwave 4 hrs 10 min 8-18 hrs 30 min >18 hrs 1 hour Green approach Microwave  Advantages & disadvantages Microwave Advantages Limitations ❑ Rate enhancement(from hours to minute) ❑ No direct reaction monitoring ❑ No reagent addition during the reaction(closed vessel) ❑ Increase yield ❑ Not applicable for production scale ❑ Improved purity ❑ Equipment cost. ❑ Greater reproducibility ❑ Energy efficient direct in core heating, rapid energy transfer ❑ Rapid superheating of solvent in sealed vessels ❑ Can do things that you cannot do conventionally ❑ Excellent control over reaction parameter