The Influence Of Inorganic Salts And Surfactants On Oxygen Mass Transfer In An Airlift Reactor

With the rapid development of economy,living standard is improving gradually,which leads to the increasing use of detergent.The main components of detergent are surfactants and cleaner,and the main component of the cleaner is inorganic salt which acts as softening agent.In view of this kind of sewage,it is necessary to study the influence of inorganic salts and surfactants on oxygen mass transfer.However,the effects of inorganic salts and surfactants on gas-liquid oxygen mass transfer processes and the reasons for their effects are not very clear currently,let alone the effects of their synergistic effects on the gas-liquid oxygen mass transfer.Research into the gas-liquid oxygen mass transfer performance was done in the internal-loop airlift reactor(ILAR),the volumetric mass transfer coefficient KLa was regarded as referential characteristic.That inorganic salts and surfactants were both in presence and were separated were thorough researched to study the effects of gas-liquid oxygen mass transfer rules and mechanisms about inorganic salts and surfactants were both in presence and were separated.The main research work and results are as follows:(1)The effects of surfactants on the gas-liquid oxygen mass transfer was the result of two factors,on the one hand,the surfactants hindered the gas-liquid oxygen mass transfer by reducing the liquid film mass transfer coefficient kL;on the other hand,the surfactants promoted the gas-liquid oxygen mass transfer by incresing the gas-liquid specific surface area a.The experimental results showed that the total effect was to suppress the gas-liquid mass transfer process,which indicated that the influence of surfactants on kL was greater than that of a.The correlation formula between KLa,surface tension and gas hold-up was obtained.The t value of surface tension was 8.840,while the t value of gas hold-up was only 0.710,which quantitatively illustrated the impact of surfactants on surface tension was more significant than gas holdup.In addition,the Sardeing model for predicting the liquid film mass transfer coefficient of surfactants was improved,and the relevant parameters were fitted again.The new correlation formula could predict the experimental value better,and the errors were within ±10%.(2)Inorganic salts could increase the gas holdup and decrease the average diameter of the bubbles,which leaded to the increase of the gas-liquid specific surface area,thus enhancing the gas-liquid oxygen mass transfer.The correlation formula between KLa and ionic strength of inorganic salts solution was obtained,and the result of the fitting was good,which indicated that the effect of inorganic salts on KLa can be related to the ionic strength of the solution.In addition,the transition concentration on KLa of inorganic salts has been theoretically analyzed,and the theoretical calculation transition concentration of the CaCl2 solution was 5.883 g·L-1,lower than about 7 g·L-1 of the experimental transition concentration.(3)Inorganic salts would increase the accumulation of ionic surfactants on gas-liquid interface,which reduced the surface tension,and then suppressed the gas-liquid oxygen mass transfer.However,the effect of inorganic salt on gas-liquid oxygen mass transfer of nonionic surfactant is slight,equivalent to stacking of effects of inorganic salt and surfactant solution when they are not in presence at the same time.