Green Technology Subject Code – PCE7J004 Chemical Engineering Department 7th Semester Mrs. Laxmi Sethi IGIT Sarang Email ID: - [email protected] PCE7J004 Green Technology 3-0-0 Module I: Principles of green technology and engineering, Principles of atom and mass economy, E-factor. Module II: Design of greener and safer chemicals, Solvent-free methods: Microwave, Ultraviolet, and Solar. Green catalysts: ionic liquids, zeolites, photocatalyst, PEG, nanocatalyst, and biocatalyst. Green solvents: Supercritical fluids, fluorous phase, and non-aqueous solvents. Module III: Scale-up effect, reactors, separators, Process intensification. Bio-conversion of renewables. Reference Books: 1. Handbook of Green Chemistry, Vol. 1 to 9 by P T Anastas, Wiley VCH. 2. Green Chemistry and Engineering: A Practical Design Approach by C J González and D J C Constable, Wiley. 3. Green Chemistry and Engineering: A Pathway to Sustainability by A E Marteel- Parrish and M A Abraham, Wiley. 4. Green Chemistry for Environmental Sustainability by S K Sharma and AMudhoo, CRC Press. 5. Green Engineering: Environmentally Conscious Design of Chemical Processes by D T Allen and D R Shonnard, PHI. Module I Contents Introduction Principles of Green Chemistry Green Metrices – Percentage Yield Atom Economy Reaction Mass Efficiency Effective Mass Yield E – Factor Introduction Chemical industries play important role in our day to day life as well in supporting the nation’s economy. Chemical Engineering deals with the conversion of raw materials into commercially important products. This conversion is done in a number of steps starting from raw material beneficiation followed by the chemical reactions for the conversion of raw materials into product and finally recovery of product. After the product recovery, some waste effluents or gases may be discharged from the system. During the reactions also some waste and toxic materials or gases may be discharged. These wastes and toxic materials may be detrimental for the reaction vessel as well as the environment, human being and animals. Chemical industries also result into running out of petrochemical feedstocks. The total cost will also be higher if a significant amount of waste is released. So, it is desirable to introduce some novel methods to reduce waste and design an ideal process or ideal product. Green Chemistry Definition Green Chemistry is the reduction or elimination of the use of or generation of hazardous substances in a chemical process. It also deals with replacing the traditional chemical processes with environmentally friendly alternate synthesis pathways for the reduction of wastes generated during chemical processes. The U.S. Presidential Green Chemistry Challenge, March 1995 defines Green Chemistry as, the use of chemistry for source reduction or pollution prevention. [3] One more aspect which is to be taken care of is sustainable development. It means fulfilling the needs of present generation without compromising with the needs of the future generation. It can only be achieved by applying green chemistry wherever possible. For designing an ideal process or ideal product some guidelines should be followed or the efficiency of the reaction should be evaluated and shortcomings should be noted to take proper actions. The set of guidelines were given by Paul Anastas and John Warner which are called 12 Principles of Green Chemistry. For the evaluation of the reactions, Green Metrices were introduced. THE TWELVE PRINCIPLES OF GREEN CHEMISTRY [4] Paul Anastas and John Warner gave a set of guidelines for the design of environmentally benign process as “The Twelve Principles of Green Chemistry”. The Twelve Principles are: 1. Prevention. It is better to prevent waste than to treat or clean it up after it has been generated in a process. This is based on the concept of “stop the pollutant at the source.” Explanation: According to this principle the synthesis process should be designed in such a way that the waste generation will be minimum or nil as waste generation results in less efficient chemical processes which may increase the cost of production. This can be carried out by adopting grinding chemistry i.e. the reactants can be mixed by grinding without using any solvent. Some other methods for waste reduction may be use of microwave or solvent less chemistry. 2. Atom Economy. Synthetic steps or reactions should be designed to maximize the incorporation of all raw materials used in the process into the final product, instead of generating unwanted side or wasteful products. Explanation: According to this principle all the atoms present in the reactants should be converted into products as those atoms that are not used end up as waste. Atom economy is the efficiency of a reaction to convert reactant into desired product. 3. Less hazardous chemical use. Synthetic methods should be designed to use and generate substance that possess little or no toxicity to the environment and public at large. Explanation: This principle aims to use less hazardous reactants or use less hazardous synthesis pathways. Example: Styrene is traditionally produced from benzene which is carcinogenic in nature. This traditional route can be replaced by greener route i.e. instead of benzene, xylene can be used as the starting material. 4. Design for safer chemicals. Chemical products should be designed so that they not only perform their designed function but are less toxic in the short and long terms. Explanation: This principle is focussed on designing less hazardous chemicals. The molecules can be designed large enough such that they will not penetrate inside lungs. Example: Detergents are sodium salt of alkyl benzene sulphonic acids with branched alkyl groups. These are not degraded naturally. So, now these compounds are replaced by sodium salts of linear alkyl benzene sulphonic acid which are readily degraded. 5. Safer solvents and auxiliaries. The use of auxiliary substances such as solvents or separation agents should not be used whenever possible. If their use cannot be avoided, they should be used as mildly or innocuously as possible. Explanation: Traditionally organic solvents are used in chemical synthesis, which are highly dangerous. This principle aims to replace the organic solvents with greener solvents such as water, supercritical carbon dioxide etc. which are less hazardous. 6. Design for energy efficiency. Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. If possible, all reactions should be conducted at mild temperature and pressure. Explanation: This principle can be fulfilled by using catalysts in the chemical reactions. 7. Use of renewable of feedstock. A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable. Explanation: This principle basically deals with shifting our dependence on petroleum to renewable feedstocks. Examples: Biodiesel obtained from biomass and polylactic acid (Biodiesel plastic) made from renewable feedstocks such as corn and potato waste. 8. Reduction of derivatives. Use of blocking groups, protection/deprotection, and temporary modification of physical/chemical processes is known as derivatization. Unnecessary derivatization should be avoided or minimized. Such steps require additional reagents and energy and can generate waste. 9. Catalysis. Catalytic reagents are superior to stoichiometric reagents. Explanation: Catalysts are used to decrease energy requirements and to make reaction take place more efficiently. Green Technology deals with using green catalysts instead of traditional chemical catalysts. 10. Design for degradation. 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. Explanation: Chemicals such as pharmaceutical drugs, plastics etc. should be designed in such a way that they will breakdown once their useful life is over. Example: Polythene and polypropylene can be replaced by biodegradable polymers which can be degraded by enzymatic action. 11. Real time Analysis for Pollution Prevention. Analytical methodologies need to be improved to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances. Explanation: If in-process monitoring can be done than it will be easier to control the reaction as per the desired requirement. Example: Micro fabricated micro fluidic analytical devices have been developed which are referred as lab-on-chip devices. All the steps in a chemical reaction can be carried out on a single microchip platform. 12. Inherently safer chemistry for accident prevention. Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, storage of toxic chemicals, explosions and fires. Explanation: This principle aims on the safety of workers and surrounding community of the industry. According to this principle chemical reactions, substances or materials having least potential for chemical accidents should be used in the industry. Green Metrices Green metrices quantify the efficiency or environmental performance of chemical processes and allow changes in performance to be measured. A single metric cannot be used to explain the greenness of a complete chemical process. So, it is very important to choose an appropriate metric to identify and describe all features of