Preliminary analysis of the causes of swelling in galvanized steel drums containing monoethanolamine
Preliminary analysis of the causes of swelling in galvanized steel drums containing monoethanolamine
Qingjiang Metal Container Factory Wang Shoushan Xia Meiran
Is there a chemical reaction in the galvanized steel drum filled with ethanolamine? The author took this question and made a visit and investigation.
During the visit and investigation, we learned that the reason why steel drum users have caused galvanized barrel expansion during filling has not yet been clarified. Wenggong, an authority of the Chemical Industry Research Institute of the city, said: "It is a complicated problem to solve the chemical reaction between monoethanolamine and galvanized barrels. In short, there is a certain category of expansion and selection of barrels for loading ethanolamine steel drums. The relationship between us. With the assistance of the Institute of Chemical Research, we have reviewed some of the information at home and abroad. The preliminary analysis of the reasons for the expansion of the ethanol-zinc galvanized barrel is as follows:
From the physicochemical properties of ethanolamine, the product is a colorless viscous liquid, hygroscopic and ammoniaous, strong alkaline, miscible with water and ethanol in any ratio, soluble in carbon tetrachloride and chloroform. Slightly soluble in toluene, insoluble in ether. The hydrogen atom in the amino group may be substituted with an acid halide, an alkyl halide or the like. It can absorb CO 2 in the air. Under the influence of light, it gradually promotes the deterioration of oxygen and carbon dioxide in the air, so the product is a photo-degradable reagent.
In short, to fill the barrel of ethanolamine, the barrel should be determined according to the standard of the ethanolamine product of the Ministry of Chemical Industry. From the perspective of foreign materials, tin-plated barrels or plastic-coated barrels are generally used. This phenomenon has not occurred in domestically sprayed plastic (lined plastic) barrels. From this point of analysis: zinc is an amphoteric metal, easy to react with monoethanolamine, is one of the causes of gas expansion; monoethanolamine in the presence of water, carbon dioxide and at a certain temperature, with a metal such as zinc to form carbamate, and The bicarbonate b is slowly formed. It also reacts with a metal such as zinc in the presence of a gas such as carbon, oxygen, or hydrogen sulfide, and at a predetermined temperature, and generates a gas. Containing carbon dioxide, hydrogen oxysulfide (mainly CO 2 ) and the higher the amount of water, the more complete the reaction, the greater the pressure of the gas. This phenomenon does not occur because there is no reaction between the amphoteric metal and monoethanolamine in the plastic bucket filling.
The carbon dioxide gas in the barrel is mainly adsorbed during the ethanolamine filling process, and the maximum content is 0.45-0.5 mol/mol monoethanolamine. Therefore, in the production process, the moisture content must be strictly controlled. During the filling process, minimize the contact surface of carbon dioxide with monoethanolamine to reduce the amount of carbon dioxide absorbed. Monoethanolamine absorbs carbon dioxide to form a carbamate. The carbamate is used as an intermediate to form bicarbonate slowly. Metastable isobaric pressure when carbamate is produced. It can be calculated by the following formula:
P1=mka2(1-2a2)
Where: m is the metastable isobaric constant of the CO2-H2O system. k is the reaction to produce an isobaric constant of the carbamate. a is the degree of carbonation.
When a=0.5, the metastable isobaric pressure exceeds the final isostatic pressure P. When the concentration of monoethanolamine is 2000 mol/m2, 50 °C, a=0.48, the pressure ratio P1/P>10, and the monoethanolamine should be filled according to the standard. Fill and store in a cool place away from light, which can reduce or even prevent the gas expansion of the barrel.
In short, there is a certain problem in the filling of galvanized barrels with an alcoholamine. However, the author believes that the use of units should focus on selecting the type of barrels. Secondly, pay attention to the filling conditions and storage conditions. The superiority of the barrel to replace the galvanized barrel with one ethanolamine.
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