First, what is green chemistry?
Green chemistry is also called environment-friendly chemistry, and the corresponding technologies are called green technology and environment-friendly technology. The ideal green technology should adopt highly selective chemical reaction, generate the target product with a certain conversion rate, produce no or little by-products or waste, and realize or approach the "zero emission" process of waste. Non-toxic and harmless raw materials, solvents and catalysts are used in chemical processes.
Green consciousness is an advanced expression of human pursuit of natural perfection. It does not regard man as the master of nature, but as an ordinary member of nature, and pursues man's respect for nature and the harmonious relationship between man and nature.
Green consciousness is different from environmental protection. They belong to two different concepts. The so-called "environmental awareness" is obviously passive and has a strong utilitarian purpose. We often talk about how many diseases and economic losses environmental pollution has brought to human beings. In fact, we still put people in a position opposite to nature. Under the guidance of this idea, people can control and solve some imminent pollution problems, but they are not so active in the problems that do not harm human beings but only harm nature at present. Only by talking about environmental awareness with green awareness as the core can there be correct and sustainable products.
The product of the development of green consciousness is green science and technology, and the scope of green science and technology is much wider than that of green chemistry. The so-called green science and technology refers to the study of green science and engineering technology that adapts to the environment, does not destroy the ecological balance, and saves resources and energy under the guidance of green consciousness. Its goal is to study the source strategy of sustainable development.
Because most of the major environmental problems in the world today are directly related to chemical reactions, chemical production processes and their products, green chemistry naturally becomes an important part of green science and technology.
Because of the above point of view, green chemistry can be defined as a chemical and chemical production process that has as little negative impact on the environment as possible under the guidance of green consciousness and is technically and economically feasible.
The biggest feature of green chemistry is that it uses scientific means to prevent pollution from the beginning, so the process and terminal are zero emissions or zero pollution. Obviously, green chemical technology is not to control or deal with pollution in the terminal or production process. Therefore, there is an essential difference between green chemical technology and "three wastes treatment", which is terminal pollution control rather than initial pollution prevention.
Second, the main research problems of green chemistry
Of course, the study of green chemistry should focus on both the present and the future. At present, the main research topic is 12 (also known as 12 principle).
(1) Stop pollution at the source, not at the end.
(2) The synthetic method should have the principle of "atomic economy", that is, try to make all the atoms involved in the reaction process enter the final product.
(3) Try not to use or produce substances that are toxic and harmful to human health and the environment in the synthesis method.
(4) Design chemical products with high efficiency and low environmental toxicity.
(5) Try not to use auxiliary substances such as solvents, which must be harmless when used.
(6) The production process should be carried out under mild temperature and pressure, with the lowest energy consumption.
(7) Try to use renewable raw materials, especially replacing mineral raw materials such as oil and coal with biomass.
(8) Minimize by-products.
(9) Use a highly selective catalyst.
(10) Chemical products can be degraded into harmless substances after use, and can enter the natural ecological cycle.
(1 1) Develop timely analytical techniques to monitor the formation of harmful substances.
(12) Select the substances involved in the chemical process to minimize the accident risk.
Third, the task of green chemistry.
1. Design safe and effective target molecules
To eliminate pollution from the source, we must first ensure that the substance molecule we need-the target molecule is completely effective. Therefore, a key task of green chemistry is to design safe and effective target molecules.
The design of safety chemicals is to use the relationship between molecular structure and performance and molecular control methods to obtain the molecules with the best required functions and the lowest toxicity. This can be solved from two aspects: one is to design new safe and effective target molecules. Second, redesign the existing effective but unsafe molecules, so that these molecules retain their existing efficacy, eliminate unsafe properties, and get improved safe and effective molecules.
2, looking for safe and effective reaction raw materials.
At present, phosgene, formaldehyde, hydrocyanic acid and acrylonitrile are often used as raw materials in chemical production, which is very toxic. Take phosgene as an example, it is a kind of military poison gas, but it can react with many organic compounds to produce many products. Since the emergence of green chemistry, the production of polyurethane from phosgene is a famous example.
Polyurethane foam accounts for the largest proportion in foam, with large consumption and wide application. It is also used in coatings, adhesives, synthetic fibers and synthetic rubber.
The traditional process of producing polyurethane is to synthesize isocyanate from amine and phosgene;
RNH2+COCl2-→RNCO+2HCl
Then, RNCO reacts with R'OH to produce polyurethane;
RNCO+R′OH-→rnh CO2 R′
This process not only uses highly toxic phosgene as raw material, but also produces harmful by-product hydrogen chloride.
The new process of Monsanto company in the United States uses carbon dioxide instead of phosgene. The difference between CO2 and CoCl _ 2 is that CO2 replaces chlorine atoms in CoCl _ 2 with oxygen atoms, but retains the components containing CO in the molecule. Therefore, when CO2 reacts with amines, isocyanates can also be formed:
RNH2+CO2-→RNCO+H2O
In addition, polyurethane can also be prepared:
RNCO+R′OH-→rnh CO2 R′
As we all know, carbon dioxide is a non-toxic gas, and its harm to the environment is the greenhouse effect. However, in the process of producing polyurethane, carbon dioxide is a consumed raw material, which will not produce greenhouse effect, and has also made great contributions to reducing the consumption of carbon dioxide on the earth. At the same time, after CO in CO2 is consumed, the remaining oxygen combines with hydrogen to generate water, which is a pollution-free by-product.
Therefore, the new process designed by Monsanto for polyurethane is very clever, and the guiding ideology of the design is green chemistry. Therefore, from 65438 to 0996, the US government awarded Monsanto the US President Green Chemistry Challenge Award.
A more advanced method than using nontoxic and harmless raw materials is to use biological resources as raw materials.
/kloc-in the middle of the 0/9th century, most industrial organic chemicals came from biomass provided by plants, and a few came from animal biomass. The industrial revolution began to use coal as a chemical raw material. After inventing a cheap method to extract oil from underground, oil became the main chemical raw material. At present, more than 95% of organic chemicals are processed from petroleum.
Oil and coal are non-renewable resources. Therefore, considering the long-term interests of mankind, we should consider replacing non-renewable resources with renewable biological resources.
Biological resources mainly refer to biomass, which can be divided into two categories, namely starch and lignocellulose. Corn, wheat and potatoes are the representatives of starch. Agricultural wastes (such as jade stalks and wheat stalks). ), forest waste and grass are the representatives of lignocellulose. Lignocellulose is the most abundant biomass on the earth, and it is constantly regenerated around the world at the rate of16.4 billion tons every year, but so far, only 1.5% is used by human beings.
Starch and lignocellulose both contain carbohydrate polymers, from which sucrose and glucose can be extracted as chemical raw materials to produce the chemicals we need under the catalysis of enzymes or bacteria. The improvement of adipic acid production process can see the prospect of utilizing biomass resources.
Adipic acid is the raw material for producing nylon 66, and also used as plasticizer and lubricant. The traditional production process of adipic acid is: benzene is hydrogenated to cyclohexane, cyclohexane is oxidized to cyclohexanone and cyclohexanol, and then cyclohexanone and cyclohexanol are oxidized to adipic acid with nitric acid. The disadvantage of this traditional process is that the starting material benzene is a known carcinogen and nitrogen oxides are contained in by-products.
The improved green synthesis of adipic acid adopts direct oxidation of cyclohexene and hydrogen peroxide: benzene is no longer used in this process, hydrogen peroxide is also a non-toxic oxidant, and the reaction does not produce toxic by-products. This reaction meets the requirements of green chemistry, but the fly in the ointment is that cyclohexene is used as raw material.
A safer and cleaner method for producing adipic acid is designed, that is, a green process for producing adipic acid from biomass glucose: obviously, this new process is the most ideal.