Article 9 (2) of the “Implementation Measures for the Safety Production License for Hazardous Chemicals Production Enterprises†(Decree No. 41 of the State Administration of Work Safety), which was implemented on December 1, 2011, stipulates that the first domestically adopted process must pass the province. The relevant departments of the people's government organize the safety and reliability argumentation. As a grassroots worker responsible for the safety permit work of dangerous chemicals construction projects, the author talks a little about the impact of some chemical processes on production safety.
First, the impact of the process route
Different process routes must have different reaction equations, reaction processes, operating conditions and reaction equipment. For example, the synthesis of vinyl chloride can be carried out by adding water to acetylene by calcium carbide, then by acetylene and hydrogen chloride, or by oxychlorination of ethylene; the synthesis of methyl chloride can be obtained by chlorination of methane (natural gas), or It is synthesized by methanol and HCl; ethanol production can be produced by fermentation of starchy materials or by hydrophilic treatment of ethylene.
The process routes listed above have industrial applications. If the source of the raw materials, technical economy and other issues are left out, the safety and reliability of each of the above three substances are fundamentally different.
In the vinyl chloride synthesis process, if acetylene and hydrogen chloride addition are used, the principle is as follows: CaC2 + 2H2O→Ca(OH)2 + C2H2, C2H2+HCl→CH2CHCl, two-step reaction, and no dangerous process, but acetylene and ethylene phase More lively than. Production of vinyl chloride by diethylene oxychlorination, including three-step reaction: (1) ethylene direct chlorination CH2=CH2 + Cl2→CH2ClCH2Cl, (2) dichloroethane cleavage 2CH2ClCH2Cl→2CH2=CHCl + 2HCl, (3) ethylene Oxychlorination CH2=CH2 +2HCl +O2→CH2ClCH2Cl+H2O, total reaction formula 2CH2=CH2 + Cl2+O2→ 2CH2=CHCl+H2O, the process flow is long, the side reaction may be large, and it involves chlorination, Three dangerous processes of cracking and oxidation.
The synthesis process of methyl chloride, if the methane chlorination method is adopted, involves a dangerous process of chlorination, and may cause side reactions to form dichloromethane, chloroform, and tetrachloromethane; if synthesized with methanol and HCl, it is generally The liquid phase reaction has fewer side reactions, shortening the process of product refining.
The production process of ethanol is made by ethylene hydro-formation. Ethylene is a flammable gas with active properties. It has been industrialized in the gas phase process, the reaction temperature is about 250 ° C, the reaction pressure is about 7 MPa, and the diatom phosphate is used as a catalyst. Lower, there are side reactions that produce diethyl ether and acetaldehyde. The fermentation method produces ethanol, as long as the fermented bacteria are pure, the starch can be converted into ethanol under relatively mild conditions, and then refined to obtain the product, the whole process involves only a dangerous chemical of the product ethanol, relative to the former A route with less risk.
If it is specific to a kind of fine chemical products such as pharmaceutical intermediates, because the process is more verbose and complicated, involving the arrangement and combination of various process routes, the impact of the process route on production safety is also ever-changing.
Second, the impact of raw material selection
Raw materials are the material basis for the production of chemical products. Even the same process route, raw materials and auxiliary materials such as catalysts can not only directly affect the yield and technical level of the products, but also have an important impact on the intrinsic safety conditions of the process. For example, in the permanent violet production process, the alkylation of carbazole can be carried out with ethyl bromide or ethyl chloride. The properties of the two are similar, but the reaction conditions are completely different.
First, the impact of the nature of the raw materials. The ignition temperature, flash point and explosion limit of the raw materials determine the possibility of fire and explosion of the material; the stability of the raw material determines the safety of the material storage, and determines whether the reaction conditions are harsh or not; the semi-lethal concentration of the raw materials is determined. Its toxicity; the purity of raw materials determines the method of refining or pretreatment. The more operating steps, the lower the intrinsic safety conditions; the physical properties such as color, state and taste of raw materials also have an impact on safe production conditions: if solid materials are used, The possibility of dust generation is that dust is easily caused by electrostatic hazard, and secondly, improper dust protection can cause occupational diseases such as pneumoconiosis; if gas raw materials and liquid raw materials are used, the gas will spread faster if it leaks. The danger of explosion or poisoning is greater. For example, carbon monoxide (hazard number 21005) and hydrogen sulfide (hazard code 21006), both of which are flammable gases, can cause fire, explosion, and poisoning accidents, but the former is odorless, and the latter has a smell of rotten eggs at low concentrations. The latter is more likely to cause vigilance. Therefore, the choice of raw materials has an important impact on the intrinsic safety level of the chemical production process. Raw materials that are non-toxic, harmless and chemically stable should be selected as much as possible.
Second, the catalyst not only determines the rate of chemical reaction, but also affects the safety of the chemical reaction. The instability of the catalyst property tends to cause the chemical reaction rate to be unstable. The too fast reaction is likely to cause the danger of over-temperature and over-pressure. The too slow reaction causes a large amount of reaction raw materials to accumulate, and when a certain condition is met, a violent reaction occurs. In addition, the catalyst can also affect the selectivity of the chemical reaction. If a large amount of side reactions occur, not only the expected main product is not obtained, the yield is lowered, and a large amount of by-products are generated, and an accident is caused by by-products. For example, in the nitrification process, once the nitric acid undergoes a redox reaction to form nitrogen oxides, there is a possibility that a poisoning accident may occur due to the generation of nitrogen oxides. For example, the synthesis of bisphenol-A from phenol and acetone, the use of sulfuric acid as a catalyst is generally a batch production, and the use of hydrogen chloride as a catalyst can be continuously produced. The safety risks of the two completely different operation methods are completely different.
In view of the development and development of chemical products, it is actually a rather complicated process. The research and development of the process also involves process amplification, equipment selection, etc. Here I will briefly explain the impact of chemical process route selection on production safety, with a view to causing Engaged in the attention of chemical product research and development personnel, use non-toxic and harmless raw materials as much as possible in the process route selection, simplify the process flow as much as possible, use advanced technology to reduce the occurrence of side reactions, and make comprehensive use and closed loop as much as possible to achieve The intrinsic safety of chemical production.
(Yang Jie, Haimen City, Jiangsu Province)
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