Technology For Preparing Desiccant By Regeneration And Reuse Of Waste Activated Alumina

Activated alumina has the characteristics of good thermal stability,wear resistance,high strength and large specific surface area,so it is widely used as adsorbent,desiccant,catalyst,defluorination agent and so on.After being used for a certain period of time,the pore structure of alumina in dry compressed air is blocked by adsorbate,and part of the pore structure is destroyed,thus losing its original activity.Therefore,it is necessary to activate and regenerate waste activated alumina.In this paper,the method of in-situ activation regeneration is adopted,the technology of"pretreatment-pore activation-repair regeneration"is proposed,the experimental(2kg)alumina dew point measuring device is designed and assembled,and the pilot-scale study on activation and regeneration of waste alumina is carried out.The characteristics of the regenerated products are similar to those of the products sold in the market.First of all,the effects of pretreatment and calcination on the regeneration of waste activated alumina were investigated.The effect of removing impurities on the surface of waste activated alumina by mechanical stirring cleaning is better than that of ultrasonic cleaning.The waste activated alumina was impregnated in clear water according to the solid-liquid ratio at 1:6,and under certain stirring conditions,the particles and mineral impurities attached to the surface were removed by friction on the surface of the alumina ball,and the particle integrity of the alumina ball was ensured.Calcination can significantly increase the specific surface area of alumina,but decreases with the increase of calcination temperature and time,the pore volume increases at first and then decreases with the increase of calcination temperature,and the compressive strength decreases as a whole with the increase of calcination temperature.The crystal water in alumina can be effectively removed when the calcination temperature is 500℃,and the pore distribution is more uniform.After calcination at 500℃for 2 h,the specific surface area of alumina increased from 140m~2/g to 218 m~2/g,and alumina decreased from 160 N to 126.6 N.Secondly,the process of"pretreatment-acid solution impregnation activation-aluminum sulfate solution impregnation repair-calcination regeneration"was explored.Dilute nitric acid has a better effect on dredging the pore structure of activated alumina.The specific surface area of the product first decreases and then increases with the increase of acid concentration,and then decreases with the extension of impregnation time.The pore structure of alumina ball will be destroyed when nitric acid is impregnated with higher concentration and longer time,and the strength of alumina decreases with the increase of impregnation concentration and time.Acid leaching at low temperature can increase the specific surface area of alumina without destroying the particle strength;the addition of saturated aluminum sulfate can not only increase the particle strength of alumina,but also increase the specific surface area to a small extent.The best process in the small-scale test is as follows:the waste activated alumina is immersed and activated in 0℃,4%dilute nitric acid solution according to the solid-liquid ratio at 1:1 for 1h,then the hand is impregnated and repaired in saturated aluminum sulfate solution for 2 h,and finally calcined at 500℃for 2 h.The specific surface area of regenerated activated alumina is 285 m~2/g and the strength is 185 N,which meets the standard of air separation desiccant sold in the market.Thirdly,aiming at the problems of large scale of industrial dew point measuring device,large amount of desiccant and large amount of test gas,which is not conducive to the research and development of regeneration process,this paper designs and successfully assembles the gas supply system,temperature control system,humidity control system,pressure control system,flow control system and dew point testing system,and realizes the alumina dew point stability test with movable operating table and low desiccant consumption(2 kg).Under the condition of optimal regeneration process in small-scale test,the pressure dew point of the product reached-43.4℃,which was similar to that of the products sold in the market.Finally,the pilot-scale study of 50 kg was carried out on the basis of small-scale test,and the pilot-scale study was carried out by using the optimal process of small-scale study.The specific surface area of regenerated activated alumina was about 299m~2/g,the compressive strength was about 219 N,and the pressure dew point was about-51.5℃,all of which met the index of industrial air separation desiccant,but the color of alumina particles was slightly yellow and needed to be further improved.