Study On Preparation And Property Of Ammonia Adsorbent Based On Calcium Sulfate

Gaseous ammonia?NH₃?is an important precursor of atmospheric haze and photochemical smog,and its harmfulness and control have paid more and more attention.Its agricultural source emissions can be controlled by intensive farming and deep application of fertilizer.In addition,there are so many the gaseous ammoina treatment technologies for non-agricultural sources.Among them,the adsorption method has many advantages such as simple operation,high flexbility,low energy consumption,etc..However,the ordinary adsorbents usually have poor selectivity and a high requirement of temperature for NH₃ desorption.The reactions of ammonia with metal inorganic salts lead to formation of ammonia complexes,which can be used to prepare and modify adsorbents with better ammonia adsorption performance.Calcium sulfate,a kind of common metal inorganic salt,is very cheap and easy to obtain,and has a certain adsorption potential for purifying pollutants.But there are still some challenges to be resolved,such as low affinity to pollutant and small specific surface area.So,it is necessary to systematically optimize the preparation of calcium sulfate-based material with multi-layer structure and improve its ammonia adsorption performance from the perspective of the improvement of material phase structure and surface activity,which is of great practical significance to the innovation of ammonia-containing waste gas purification technology and the resource utilization of gypsum.Firstly,we studied the preparation of calcium sulfate by alcohol-thermal method using the anhydrous calcium chloride and ammonium sulfate as raw materials in the presence of ATMP,discussed the effects of factors such as the volume ratio of ethylene glycol to water?G/W?,reaction time,raw material concentration,and ATMP concentration on the morphology of products,screened out product with abundant pore structure and large specific surface area as the carrier,and analyzed the formation mechanism of the product.The results show that the G/W,raw materials and ATMP concentration have significant effects on the morphology and structure of the products.Under the condition of reaction time of 60min,G/W of 5.0,raw material concentration of 40mM,and ATMP concentration of 10mM,the achieved products with embroidered-ball shape has a BET specific surface area of 179.641m²/g and a pore volume of 0.576cm³/g.A combination of XRD and FT-IR analysis reveals that the prepared product is a compound of calcium sulfate and ATMP.When the concentration of ATMP is too high,most of the products are Ca?SO₄??HPO₄?·4H₂O and Ca?H₂PO₄?₂.ATMP can aggregate and fix Ca²⁺in solution and constantly chelate newly generated calcium sulfate microcrystals,regulate the shape and size of primitives,and the primitives stack each other to generate products whose the morphology and structure differ from the original mineral.Secondly,CaSO₄-ATMP was modified by impregnation method for loading calcium chloride,and the effects of impregnation time,impregnation liquid concentration,calcination temperature,and calcination time on the ammonia adsorption performance of the composite were discussed.The results show that the ammonia adsorption efficiency of composite rises first and then decreases with the increase of calcination temperature,impregnation time and liquid concentration.The calcination time has no significant effect on the ammonia absorption.Under the conditions of impregnation time of 60min,impregnation liquid concentration of0.25M,calcination temperature of 350?and calcination time of 60min,the ammonia adsorption capacity of the product is 50.26mg/g.In addition,except for the calcination temperature,the other factors have no obvious influence on the composite morphology.Characterization analysis shows that the crystallinity of calcium sulfate is up first and then down with the increasing of the impregnation liquid concentration and calcination temperature.Besides,the impregnation solution concentration and calcination temperature affect the weight loss ratio of the product,while the impregnation time and calcination time have no significant effect on the phase composition and thermal decomposition of the product.Finally,the modification conditions of the composite were optimized by the BBD experiment,and a quadratic model was obtained for ammonia adsorption capacity of the composite.The response surface analysis of two factors interaction on the ammonia adsorption performance of the composite shows that the ammonia adsorption capacity first increases and then decreases with the increase of the impregnation time and liquid concentration.As the increasing the calcination temperature,the adsorption capacity is up first and then down.The optimum conditions are:impregnation time of 91 min,impregnation liquid concentration of0.33M,calcination temperature of 360?,calcination time of 60min,ammonia concentration of 150ppm?1.0 L/min Air?.Under these conditions,the predicted ammonia adsorption capacity is 52.14mg/g,and the factual value is 51.09mg/g.Under the condition of low ammonia concentration,the adsorption capacity of the composite is the same as the modified activated carbon.