A: The molecular formula of nitrous oxide is N2O, also known as nitrous oxide, commonly known as laughing gas.The concentration of nitrous oxide in the atmosphere is about 3 times 10-9.With the deterioration of ecological environment, its content increases by 0.2% ~ 0.3% per year.
The amount of nitrous oxide generated by soil microorganisms during their oxidation and denitrification activities in soil and ocean accounts for one-third of the atmospheric nitrous oxide content, and another two-thirds is generated artificially.For example, the combustion of fossil fuels, organisms, wastes, sewage treatment, fermentation sources, automobile exhaust, etc. all lead to the generation of N2O.In the vicinity of the N2O generating source, the N2O content in the atmosphere can be more than 3 times 10-6.Although N2O is chemically inert and neither corrodes nor explodes, its physical properties are hazardous to air separation.The critical temperature is 309.7k, the critical pressure is 7.27mpa, and the three phase points are 182.3k and 0.088mpa.It has sublimation property under the pressure and temperature of air separation device.At atmospheric pressure, the boiling point is 185K, higher than that of N2, O2 and Ar. Therefore, in the separation process of oxygen and nitrogen, it will be concentrated in liquid oxygen.
The solubility of N2O in water is very small. After the processed air passes through air filters, compressors, coolers and water separator, N2O cannot be separated and removed.Most N2O will be brought into the molecular sieve purifier. The adsorption capacity of the molecular sieve to N2O is lower than that to CO2.N2O enters the distillation column through the adsorption bed layer, and in the co-adsorption process of H2O, CO2, C2H2 and other hydrocarbons by the molecular sieve, CO2 can replace the N2O molecules already absorbed by the molecular sieve.Therefore, the molecular sieve cannot clear N2O.In the main heat exchanger, the processed air is cooled to near the liquefaction temperature, and N2O first condenses into a solid, causing the air passage to block.When the air pressure of processing is 0.6mpa and the N2O content is 1 x 10-6, the setting temperature of N2O is 113K.
In the distillation column, because N2O is divided into high boiling point components relative to N2, O2 and Ar groups, it will be dissolved in liquid oxygen, making it impossible to obtain high purity liquid oxygen and gas oxygen products at the bottom of the upper column.When the purity of oxygen products was 99.5%, the average N2O content was 1.4x10-5.In addition, when the discharge of liquid oxygen is insufficient, N2O accumulates continuously in the liquid oxygen. When the N2O content in the liquid oxygen is greater than 50 x 10-6, it will precipitate out in a solid state and block the main condensation evaporator channel.
In the production of rare gas krypton and xenon, with the concentration of krypton and xenon, N2O is also concentrated.The content of N2O can reach 100 x 10-6 ~ 150 x 10-6.N2O itself does not burn, but it can be thermally decomposed.This will affect the elimination of catalytic combustion of crude krypton, CH4 in xenon and the adsorption of water and carbon dioxide generated by using molecular sieves.
Due to environmental problems, the concentration of N2O in the air keeps increasing.Moreover, industries such as electronics require higher and higher levels of oxygen product purity (99.99% ~ 99.9999%), so the removal of N2O from processed air is more important than in the past.A better cleaning method is to find the appropriate molecular sieve. In the molecular sieve purifier, H2O, CO2, C2H2 and N2O in the processed air are absorbed and removed.