Concentration And Purification Of The Dilute Contaminated Sulfuric Acid Containing Organic Impurities

Sulfuric acid is a fundamental raw material for many chemical processes. Large quantities of sulfuric acid are needed in organic chemical industry. However, only a small part of sulfuric acid takes part in reactions as substituents, while a large part is discharged as dilute waste. Thus, how to deal with the contaminated sulfuric acid discharged from organic chemical processes has been an urgent task not only for the waste treatment but also for environmental protection.The purpose of this research is to develop a new technology to treat the contaminated sulfuric acid containing organic impurities. This new process consists of two steps: concentration and purification, i.e. the dilute contaminated sulfuric acid is concentrated first, then the concentrated sulfuric acid is purified to get rid of the organic impurities.In the concentration process, the dilute sulfuric acid is concentrated in a spray evaporator. A systematic study on the concentration of dilute sulfuric acid is carried out experimentally and theoretically. The experimental study is focused on the effects of inlet air temperature, air flux and liquid flux on the concentration of the concentrated sulfuric acid. The experimental results show: firstly, the concentration of the concentrated sulfuric acid increases with increased inlet air flux, increased intet air temperature and decreased inlet liquid flux; secondly, the heat efficiency of the evaporator basically decreased with the increased inlet air flux and the decreased inlet liquid flux; thirdly, the overall pressure-drop of the evaporator increases with the increased inlet air flux accordingly. Additionally, a dimensionless equation for the concentration process is obtained by regressing the experimental data, which can be used to predict the concentration of the concentrated sulfuric acid with ?9% relative errors. In the mean time, a theoretical model is established based on masstransfer, heat transfer and momentum transfer between acid droplets and hot air. The model is proved correctly by experimental verification (outlet air temperature, concentration of the concentrated sulfuric acid, overall pressure-drop of the spray evaporator). Based on the mathematical model, the behavior of air and acid droplets in the evaporator, the pressure-drop in the evaporator and the effects of the experimental parameters on evaporated flow rate are numerically simulated. Moreover, the simulative results are analyzed and discussed.In the purification process, the concentrated sulfuric acid containing organic impurities is purified in a tubular reactor by oxidation reaction. The oxidant here is nitric acid. Most of the organic chemicals that have already been carbonized react with nitric acid at high temperature in the reactor, which generates carbon oxide, nitrogen and a small quantity of nitrogen oxides. The experimental results show that, compared with common purificatory devices, this pilot tubular reactor can not only remove the organic impurities from the contaminated sulfuric acid, but also reduce the nitrogen oxides content in the flue gas to a large extent.