Preparation Of Bayerite/?-Al₂O₃ Microspheres By Room Temperature Liquid-phase Precipitation And Their Hydrogenation And Adsorption Properties

Sodium aluminate can be used as high quality aluminum source for the preparation of hydrated alumina microspheres because of its sources widely,cheap and preparation quickly.In recent years,the preparation of hydrated alumina microspheres under mild conditions has become a hot concern.In this paper,bayerite/?-Al₂O₃microspheres with excellent performance and controllable morphology were prepared by room temperature liquid phase precipitation method,using a variety of low carbon chain alcohols and ammonium salts as structural regulators to control the hydrolysis reaction rate of sodium aluminate solution.The main results are as follows:(1)Under the condition of standing at room temperature,the precipitation rate of NaAlO₂solution was promoted by using low carbon chain alcohol as structural regulator.Bayerite microspheres with particle size of 2.53-7.83?m were prepared by slow hydrolysis reaction.After roasting,?-Al₂O₃microspheres were obtained.The product were studied via XRD,SEM,N₂adsorption-desorption and FT-IR.The optimum formation conditions of bayerite microspheres were investigated by changing the volume ratio of water to alcohol,the addition amount of sodium aluminate and the reaction time.The effects of different alcohols on phase transformation and morphology of NaAlO₂hydrolysate were studied.The sphericity of bayerite microspheres increases with the increase of alcohol volume ratio at room temperature.When the volume ratio of water to alcohol is 1:1,the sphericity of the prepared microspheres is the best.When the volume ratio of water to alcohol was less than 3:7,the sphericity and uniformity gradually decreased until the microspheres disappeared.The addition of sodium aluminate has no significant effect on the morphology of microspheres,but only the particle size and surface roughness.When NaAlO₂content was 2.4g,the sphericity of bayerite microspheres was the best.The average particle size was 4.53?m.The results obtained by the experiments with different kinds of alcohol solvents:methanol,ethanol,n-propanol and 1,4-butanediol can prepare stable crystal phase bayerite microspheres.Both ethylene glycol and1,3-propanediol can produce a single boehmite phase with low crystallinity within 2h,and finally ethylene glycol produces a mixed phase of bayerite and boehmite,while1,3-butanediol transforms into a single phase of bayerite at 6h.But the glycerol in ternary alcohol inhibited the hydrolysis of NaAlO₂solution and could not get precipitation.In order to further implement large-scale production,the amplification experiments of typical samples were carried out.The bayerite/?-Al₂O₃microspheres obtained from the experiments were similar to the small experimental products in terms of crystallinity,texture properties,morphology,particle size and properties.The preparation method has good stability.(2)Furthermore,the average particle size distribution and pelletization of bayerite/?-Al₂O₃microspheres were successfully optimized by introducing a weakly acidic acid ammonium to rapidly double hydrolyze NaAlO₂,and the adsorption performance of the optimized typical?-Al₂O₃microspheres for Congo red(CR)was studied.The products were characterized by XRD,SEM,N₂adsorption desorption and TG-DSC.The effects of different concentrations of acid ammonium,types of acid ammonium and reaction time on morphology and particle size distribution were studied.With the addition of acid ammonium,the hydrolysis reaction rate increases rapidly,precipitation can be rapidly formed within 1min,highly dispersed sphere-like nanoparticles can be obtained within 5min,and bayerite/?-Al₂O₃microspheres with good morphology can be obtained within the fastest 30min.The particle size of bayerite/?-Al₂O₃microspheres gradually decreases with the increase of acid ammonium concentration.When acid ammonium concentration is 0.05M,the sphericity,dispersion and particle size distribution of bayerite/?-Al₂O₃microspheres are the best,and the maximum adsorption capacity for CR is 819.67mg/g.