Supported-gas-membrane Process For Removal Of Ammonia From Aqueous Solution By Using Dilute Hydrochloric Acid As Absorbent

Sulfuric acid is regarded as the ideal absorber for supported-gas-membraneprocess to remove ammonia from wastewater for its strong acidic, non-oxidative andnon-volatile. It can remove the ammonia from the wastewater and produceammonium sulfate solution. But in many process, the ammonium sulfate is not theideal by-product. For example, in many fine chemical process produce ammoniumchloride by-product and wastewater containing ammonia, if using dilute hydrochloricacid recovery of ammonia to ammonium chloride which can handle with the mainby-product ammonium chloride together, to realize the recycling and reuse ofresources. What’s more, the industrial value of ammonium chloride is bigger than thatof ammonim sulfate.This paper studied the hydrochloric acid as absorbent for ammonia removal fromwastewater with supported gas membrane process, taking the hydrochloric acidvolatile into account, focused on the absorption reaction occurring in the shell side.According to the double film theory, hypothesising that there is a very thin liquid filmon the shell wall, the shell side mass transfer resisitance are all in the thin liquid film,established the shell side mass tranfer model for ammonia absorpted by hydrochloricacid. Combined with the existing lumen side ammonia mass transfer model and theexperimental data, calculating the mass transfer boundary layer thickness anddimensionless ammonia diffusion distance by the numerical method.Ammonia nitrogen removal by dilute sulfate acid experiments showed that themembrane mass transfer coefficient is only the function of membrane contactor andexperimental temperature, and independent of other operating condition when thefeed-in pH is large enough. The experiment feasibility and the critical concentrationof hydrochloric acid for different feed-in concentration of ammonia were firstlyidentified by lumen side chlorine ion leakage and shell side ammonia diffusiondistance in order to assure operation stability. The effect of operation mode, feed-inpH，feed-in flow rate, ammonia concentration in the feed solution, flow rate of theabsorbent, mass concentration of the absorbent as well as operation temperature onoverall mass transfer coefficient were investigated. The experimental results showedthat the hydrochloric acid as absorbent was feasible and can obtain high concentrationof by-product ammonium chloride solution, the cocurrent operation was more stablethan countercurrent operation, the flow rate of ammonia solution had negligible effect on the mass transfer process，while the operation temperature and feed-in pH hadsignificant effect on the mass transfer process, with the increase ofacidic-stripping-solution flow rate and hydrochloric acid concentration increased theoverall mass transfer coefficient. The stable experiment had been in operation for650h under the following experimental conditions: feed flow of30L·h-1, feed-inammonia concentration of2000mg·L-1, hydrochloric acid flow of75L h-1,hydrochloric acid mass concentration of2%，the temperature of25℃and cocurrentoperation. The overall mass transfer coefficient was4.25×10-6m·s-1and the massconcentration of ammonium chloride greater than15%by this process in which itshowed great operational stability and feasibility.