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Industrial production method of 1. ethylene glycol
At present, the main industrial production method of ethylene glycol at home and abroad is the direct hydration of ethylene oxide. Although mature, it has high water content, high energy consumption and high production cost. Therefore, people have developed various new production methods, such as ethylene oxide catalytic hydration, ethylene carbonate method and synthesis of ethylene glycol from syngas. Among them, ethylene oxide catalytic hydration method and ethylene carbonate method are considered to be the most promising industrial production methods of ethylene glycol in the future, and they are the hot spots of research and development at home and abroad.
2. Research progress of industrial production methods of ethylene glycol.
Direct hydration of (1) ethylene oxide
Direct hydration of ethylene oxide is the main method for industrial production of ethylene glycol at home and abroad. In this process, ethylene oxide (E0) and water were mixed in a molar ratio of 1: 20-22, and reacted in a tubular reactor at 190-220℃ and 1.0-2.5MPa, and all ethylene oxide was converted into mixed alcohol. The content of the generated ethylene glycol aqueous solution is about 10% (mass fraction), and then ethylene glycol and its by-products diethylene glycol (DEG) and triethylene glycol (TEG) are obtained by dehydration and concentration in a multi-effect evaporator and vacuum distillation separation. The molar ratio of ethylene glycol, diethylene glycol and triethylene glycol in the mixed alcohol is about 100: 10: 1, and the total yield of the product is 88%. The disadvantages are long production process, many equipments and high energy consumption, which directly affect the production cost of ethylene glycol.
At present, the direct hydration technology of ethylene oxide is basically monopolized by three companies: British and Dutch Shell, American Halcon-SD and American United Carbon. Their process technology and process flow are basically similar, that is, using ethylene and oxygen as raw materials, in the presence of silver catalyst, methane or nitrogen stabilizer and chloride inhibitor, ethylene is directly oxidized to generate ethylene oxide, which is further hydrated with water in a tubular reactor to generate ethylene glycol, and the ethylene glycol solution is evaporated, concentrated, dehydrated and fractionated to obtain ethylene glycol and other by-products. In addition, the whole process is also equipped with an air separation unit, carbonate treatment and waste gas and waste liquid treatment system matching its production capacity. The patented technologies of the three companies are mainly different in catalysts, reaction and absorption processes and some technical details.
⑵ Catalytic hydration of ethylene oxide.
In view of the shortcomings of direct hydration of ethylene oxide to ethylene glycol, in order to improve selectivity, reduce water consumption, reduce reaction temperature and energy consumption, many companies in the world have developed the technology of catalytic hydration of ethylene oxide to ethylene glycol. Among them, there are mainly Shell Company, United Carbon Company, Moscow Mendeleev Institute of Chemical Technology, Shanghai Institute of Petrochemical Technology, Nanjing University of Technology, etc. The key technology is the production of catalyst, and the production methods can be divided into homogeneous catalytic hydration and heterogeneous catalytic hydration, among which the most representative production methods are heterogeneous catalytic hydration of Shell Company and homogeneous catalytic hydration of UCC Company.
(3) Ethylene carbonate method
Ethylene glycol is synthesized by vinyl carbonate method. Carbon dioxide and ethylene oxide react under the action of catalyst to produce ethylene carbonate (EC), and then ethylene carbonate is hydrolyzed to produce ethylene glycol. This method can be divided into two production methods: co-production of ethylene glycol and dimethyl carbonate (DMC) and hydrolysis of ethylene carbonate.
① Co-production of ethylene glycol and dimethyl carbonate
The main process of this method is divided into two steps. Firstly, ethylene carbonate was synthesized from carbon dioxide and ethylene oxide under the action of catalyst. Secondly, dimethyl carbonate and ethylene glycol are formed by the reaction of vinyl carbonate and methanol (MA). Both reactions belong to the reaction with atomic utilization rate of 65,438+0,000%.
② Hydrolysis and synthesis of vinyl carbonate
Halcon-SD, United Carbon, Japan Catalyst and other companies in the United States have successively developed the technology of synthesizing ethylene glycol by hydrolyzing ethylene carbonate since 1970s. Halcon-SD company's process first generates ethylene oxide through the reaction of ethylene and oxygen. After passing through the first absorption tower and the stripping tower, the ethylene oxide vapor is washed in the second absorption tower with a solution containing ethylene carbonate, ethylene glycol and carbonation catalyst to form a rich solution of ethylene carbonate reaction. Then enter the carbonation reactor and introduce carbon dioxide, so that ethylene oxide and carbon dioxide react with the catalyst at 90℃ and 6. 18MPa to generate vinyl carbonate. The ethylene carbonate is stripped from the reaction solution and layered, and the upper layer is returned to the second absorption tower as washing liquid. Water is added to the lower layer of ethylene carbonate, which is hydrolyzed under the same catalyst to produce ethylene glycol. Halcon-SD process is characterized by the development of a new catalyst suitable for both carbonation and hydrolysis, and the yield of ethylene glycol is as high as 99%. In addition, Halcon-SD found that even though ethylene oxide contains a small amount of water, it can still ensure the efficient center of ethylene carbonate, so that the purification operation conditions of ethylene oxide are not too harsh, and the addition reaction and hydrolysis reaction can use the same catalyst, thus avoiding the problem of catalyst recovery in homogeneous reaction. However, the hydrolysis of ethylene carbonate to ethylene glycol requires a large-scale high-pressure reactor, and the production cost is still high, so far it has not been industrialized.
Diethylene glycol 3
Diethylene glycol, diethylene glycol, is made by the reaction of ethylene oxide and ethylene glycol. Diethylene glycol mainly comes from the by-product of ethylene oxide (EO) hydration to produce ethylene glycol (EG). Among the by-products, diethylene glycol (diethylene glycol) accounts for about 8-9%, triethylene glycol (triethylene glycol) accounts for 0- 1%, and the rest is higher molecular weight polyethylene glycol. The amount of by-products varies with the ratio of ethylene oxide to water. In recent years, with the completion and commissioning of large-scale ethylene glycol production facilities in China, China's ethylene glycol production capacity has reached104 ~105000 tons/year, so the diethylene glycol production has increased rapidly, and it is expected to reach105000 tons/year. With the completion of 320,000 tons/year ethylene glycol plant in Nanhai Petrochemical Company and 380,000 tons/year ethylene glycol plant in Shanghai Petrochemical Company, the production of diethylene glycol in China and Shanghai will further increase. Therefore, it is a project with great economic value and market potential to develop the downstream products of diethylene glycol and comprehensively utilize diethylene glycol.