What is green chemistry?

In the early 1990s, chemists put forward the concept of "green chemistry", which is different from the traditional concept of "pollution control". It requires that any chemical-related activities (including the use of chemical raw materials, chemistry and chemical engineering and final products) should be friendly to human health and the environment. The ideal of green chemistry is to stop using toxic and harmful substances and no longer produce waste. From a scientific point of view, green chemistry is the renewal of the basic content of chemical science; From the environmental point of view, emphasize the elimination of pollution from the source; From the economic point of view, it advocates the rational utilization of resources and energy, reduces production costs, and meets the requirements of sustainable development. The basic principles of green chemistry are: ① pollution prevention is better than pollution control; (2) Atomic economy (the designed synthesis method should transform all materials used in the reaction process into the final product as far as possible); ③ As long as it is feasible, the synthetic route with low toxicity or non-toxicity to human beings and the environment should be adopted as far as possible; ④ The designed chemicals should be able to maintain efficacy and reduce toxicity; ⑤ Auxiliary substances (such as solvents and separation reagents). ) should be avoided as much as possible, and should be non-toxic when used; ⑥ The impact of energy consumption on the environment and economy should be considered, and energy should be used as little as possible (normal temperature and pressure); ⑦ As long as it is technically and economically feasible, raw materials should be renewable, not about to be exhausted; (8) Try to avoid unnecessary derivatization steps (protecting groups, protecting and deprotecting, etc.). ); Pet-name ruby catalyst (as good as possible selectivity) is better than stoichiometric reagent; Attending chemical products should be able to degrade into harmless substances after completing the mission, and should not remain in the environment; Analytical methods should be further developed in order to track and control harmful substances online immediately before they are produced; In the process of chemical transformation, the selected substances and substance forms reduce the possibility of chemical accidents (including leakage, explosion, fire, etc.). ) as much as possible. The above principle of 12 green chemistry reflects all kinds of research contents in the field of green chemistry in recent years, and also points out the direction of developing green chemistry in the future, which is gradually accepted by international academic circles. The concept of "atomic economy" of chemical reaction is one of the core contents of green chemistry, which was first put forward by Professor B.M.Trost of Stanford University. He clearly pointed out that a new standard should be used to evaluate chemical processes, namely selectivity and atomic economy. Atomic economy considers how many raw material atoms enter products in chemical reactions. The ideal atomic economic reaction is that 100% of atoms in raw material molecules are converted into products, and no by-products or wastes are produced, thus achieving "zero emission" of wastes. The concept of "atomic economy" is also generally recognized at present. B. m. trost 65438-0998 won the academic award of "Presidential Green Chemistry Challenge Award" in the United States. (2) Green Chemistry in Action As the direction and foundation of the future development of the chemical industry, green chemistry has been paid more and more attention by the government, enterprises and academic circles. For example, 1995, the United States established the "Presidential Green Chemistry Challenge Award" to reward individuals, collectives or organizations that have made outstanding achievements in the creative research, development and application of the basic principles of green chemistry. Including academic award, small and medium-sized enterprise award, new synthetic route award, new technology award and safety chemical design award. The book "Theory and Practice of Green Chemistry" published by 1998 is a classic work of green chemistry, in which the definition, principle, evaluation method and development trend of green chemistry are expounded in detail. Green Chemistry is an international magazine sponsored by the Royal Chemical Society, which was founded in 1999. Its content covers many research achievements and reviews of clean chemical production technology, and covers international academic research activities to reduce environmental impact through the application or processing of chemicals. Following the awarding track of some green chemistry prizes in the United States, we can see the main achievements and trends of green chemistry technology and technology research at present: ① Developing "atomic economy" reaction In recent years, developing atomic economy reaction has become one of the hot spots in green chemistry research. For example, propylene oxide is an important raw material for producing polyurethane plastics. Traditionally, the chlorohydrin method with two-step reaction is mainly used, which not only uses chlorine gas that may bring danger, but also produces a lot of wastewater containing calcium chloride that pollutes the environment. A new atomic economic reaction method of propylene catalytic oxidation to propylene oxide is being developed at home and abroad. Another example is that cyclohexanone, ammonia and hydrogen peroxide can be directly synthesized into cyclohexanone oxime by EniChem company under the action of titanium silicalite molecular sieve catalyst. For the atomic economic reaction that has been applied in industry, it needs to be further studied and improved from the aspects of environmental protection, technical economy and so on. In order to realize the high atomic economy of this reaction, it is necessary to develop a new reaction route and replace the stoichiometric reaction with catalytic reaction. 1997 the work of BCH company, the winner of the new synthetic route award, is a good example. The company has developed a new process to synthesize ibuprofen (ibuprofen is a widely used nonsteroidal sedative and analgesic drug). The traditional production process includes six stoichiometric reactions, and the effective utilization rate of atoms is less than 40%. The new process adopts three catalytic reactions and the effective utilization rate of atoms reaches 80%. If the recycling of by-product acetic acid is considered, the effective utilization rate of atoms can reach 99%. ② Use non-toxic and harmless raw materials. For the sake of human health and environmental safety, it is necessary to use non-toxic and harmless raw materials instead of toxic and harmful raw materials to produce the required chemical products. For example, Monsanto developed a safe process for producing sodium aminodiacetate by catalytic dehydrogenation of nontoxic diethanolamine, which changed the previous two-step synthesis route with ammonia, formaldehyde and hydrocyanic acid as raw materials, and thus won the new synthesis route award in the 1996 US Presidential Green Chemistry Challenge Award. In addition, a new synthetic route of producing methyl methacrylate from isobutylene was developed abroad, and acetone and hydrocyanic acid were used as raw materials instead of acetone cyanohydrin method. ③ Non-toxic and harmless catalyst is used. At present, liquid acid catalysts such as hydrofluoric acid, sulfuric acid and aluminum trichloride are generally used for alkylation of hydrocarbons. These catalysts all have the same shortcomings, such as serious corrosion of equipment, harm to people, waste residue and environmental pollution. At present, the solid acid catalyst for alkylation reaction is being developed from new catalytic materials such as molecular sieve, heteropoly acid and superacid. For example, alkylation of isobutane with butene is an important method to provide high octane number components in oil refining industry. At present, hydrofluoric acid or sulfuric acid is the main catalyst, and some companies have developed supported sulfonate /SiO _ 2 catalyst and a new process of isobutane/butene alkylation catalyzed by solid acid. (4) A large number of pollution problems related to chemical production are caused by the use of non-toxic and harmless solvents and additives, which not only come from raw materials and products, but also from substances used in the manufacturing process, the most common being reaction media, formulas and solvents used in separation. At present, the widely used solvents are volatile organic compounds, some of which will destroy the ozone layer and some will endanger human health. Therefore, it is necessary to limit the use of such solvents. Replacing volatile organic compounds with non-toxic and harmless solvents has become an important research direction of green chemistry. At present, the most active research project is to develop supercritical fluid, especially supercritical carbon dioxide as solvent. 1997 academic award was awarded to Professor J.M.DeSimone of the University of North Carolina, because he designed a surfactant, which is a substance that loves carbon dioxide, and can produce the amphipathic effect of carbon dioxide and solute, so that carbon dioxide can be widely used as a solvent to replace the conventional halogen-containing organic solvent. In addition to using supercritical solvent, there are also studies on the interfacial reaction between organic solvent and water phase with water or near-critical water as solvent. Organic synthesis with water as the medium is an important part of environmentally friendly synthesis. The water-phase organic reaction is simple and safe to operate, has no flammable and explosive problems of organic solvents, is rich in resources, low in cost and pollution-free. Although water is a potential environment-friendly reaction medium, it will inevitably lead to many new problems, such as the hydrophobic effect of organic substrates in water, the stability of reaction substrates and reagents in water, the influence of hydrogen bonds in water on the reaction, and the possible change of reaction mechanism. Therefore, the study of aqueous organic synthesis has become an active research field in organic synthetic chemistry. The 200 1 annual "Presidential Green Chemistry Challenge Award" was awarded to Professor Li Chaojun, a China scholar in the United States, which also shows that the research on aqueous organic reactions has been paid more and more attention. Professor Li Chaojun has made a series of remarkable innovations in the design and development of transition metal intervention and catalytic organic reactions in water and air. Aqueous catalytic reaction has broad application prospects in drug synthesis, fine chemical synthesis and polymer synthesis, which opens up a new field for organic synthesis reactions that can only be carried out in inert gases and organic solvents. ⑤ Using renewable resources to synthesize chemicals and using renewable biomass (biological raw materials) to replace non-renewable petroleum, which is widely used at present, is a long-term development direction and of great significance. The technology of converting biomass into animal feed, industrial chemicals and fuel is a very active research field. Professor M.Holtzapple of the United States has made outstanding achievements in this field, and won the "Presidential Green Chemistry Challenge Award" from 65438 to 0996. Although there is no clear conclusion whether some biocatalysts will cause pollution, in general, biotransformation meets the requirements of green chemistry and has the characteristics of high efficiency, high selectivity and clean production. The reaction product is simple, easy to separate and purify, avoids the use of precious metals and organic solvents, and has low energy consumption, and can synthesize some compounds that are difficult to synthesize by chemical methods. 1996 The academic prize in the US Presidential Green Chemistry Challenge Award was awarded to Taxus A &；; Professor M. Holt Zapple of M University has developed a series of technologies to convert waste biomass into animal feed, industrial chemicals and fuel. Chi-Huey Wong, a famous chemist, won the "Presidential Green Chemistry Challenge Award" in the United States in 2000 for his outstanding innovative achievements in enzymatic reactions. ⑥ Environment-friendly products With environmental protection becoming the knowledge of modern society, the society needs environment-friendly products more and more, and the standards formulated by governments all over the world have also continuously improved the quality requirements of products in this area. For example, with the increasingly stringent environmental protection requirements, in order to reduce the ozone damage and photochemical smog caused by carbon monoxide and hydrocarbons in automobile exhaust, the US government gradually promotes the use of new formula gasoline, requiring to limit the vapor pressure and benzene content of gasoline, and will gradually limit the contents of aromatic hydrocarbons and olefins, requiring to add oxygenates (such as methyl tert-butyl ether and methyl tert-amyl ether) to gasoline. The improvement of the quality requirements of this new formula gasoline has promoted the development of related refining technologies. For another example, from 1996, the safe chemical design award of the US President's Green Chemistry Challenge Award was awarded to Rohm &; Haas company, because it successfully developed an environmentally friendly marine biological scale inhibitor to prevent the formation of seabed dirt. The SME Award was awarded to Donlar Company because the company developed two efficient processes for producing hot polyaspartic acid, which is a biodegradable product and can replace acrylic acid. (3) Green chemistry is becoming more and more active in China. During the period of 1995, the Department of Chemistry of the Chinese Academy of Sciences organized a consultation activity for academicians on "Green Chemistry and Technology —— the way to promote the sustainable development of chemical production", conducted a lot of research on the present situation and development trend of green chemistry at home and abroad, and put forward seven suggestions on developing green chemistry and technology and eliminating and reducing environmental pollution sources in combination with the domestic situation. 65438-0997 The major basic research project of "Environmental Friendly Petrochemical Catalytic Chemistry and Chemical Reaction Engineering" co-funded by the National Natural Science Foundation of China and sinopec group was officially launched. The project involves some important processes in China's petrochemical industry, namely, guiding basic research, preliminary exploration of technical feasibility and key exploration of technical feasibility and economic rationality, and carrying out exploration and research on adopting new technologies such as non-toxic and harmless raw materials, catalysts and "atomic economy" reactions. In the same year, in order to implement the strategy of rejuvenating the country through science and education, realize the grand goal of China's economic, scientific and social development by the middle of the 20th and 2nd/Kloc-0th centuries, and ensure the continuous enhancement of scientific and technological development capacity to meet the urgent needs of the new century, the national key basic research and development plan also takes the basic research project of green chemistry as one of the important support directions. In addition, some universities have set up special green chemistry research institutions.