Study On Purification Of VOCs By Modified Adsorbent Of Fly Ash

Volatile organic compounds(VOCs)is one of the common pollutants in the air,which is not only an important precursor of haze formation,but also can cause secondary and multiple reactions in the air and continue to pollute the air,causing great harm.Adsorption method has a good capture effect on VOCs and the process is simple,low cost,is an important method for the prevention and control of VOCs.Fly ash is the waste residue generated after the combustion of coal and other fossil fuels.A large amount of fly ash occupies land resources and is scattered in the wind and pollutes the air.The loose and porous structure of fly ash particles determines its large adsorption potential.After modification,it can greatly enhance its adsorption capacity and become a high quality adsorbent.In this study,it is proposed to modify fly ash into adsorbent and achieve efficient adsorption of VOCs,so as to provide a high-quality and cheap adsorbent for the collection of VOCs by adsorption method,and realize the recovery and reuse of fly ash to reduce the pressure of fly ash hoarding.The research was carried out through molecular simulation combined with experiments.Silica and mullite models were constructed to simulate the adsorption process of ethyl acetate on behalf of fly ash particles,and the adsorption site and the lowest energy adsorption conformation of ethyl acetate on behalf of fly ash particles were obtained.The adsorption energy obtained by first-principles calculation proves that fly ash particles can have strong and stable adsorption on ethyl acetate.The adsorption isothermal curves and adsorption heat of ethyl acetate at different temperatures and widths were calculated to explore the effects of temperature,pressure and pore size on the adsorption and determine the adsorption properties.The existence and movement of ethyl acetate in the crack model were investigated by calculating the density distribution and diffusion coefficient.The normal fly ash and high alumina fly ash were coupled with grinding,microwave,acid-base combination and other methods.The effects of different modification methods on fly ash were explored through adsorption experiments,and the best modification scheme was obtained.Adsorption experiments showed that the adsorption capacity of ethyl acetate on fly ash after ultra-fine grinding and microwave radiation coupled acid-base combined modification increased by four times,the adsorption efficiency increased by more than 30%,and the adsorption penetration time increased by nearly two times compared with that before modification.It is found that the adsorption capacity of modified fly ash to ethyl acetate is 76.01% and 79.53% of γ-alumina and activated carbon,respectively.SEM,BET,EDS and other characterization methods were used to compare the changes of fly ash before and after modification.After modification,the surface of fly ash particles became rough and porous,the specific surface area increased greatly,and aluminum element was purified and activated.The adsorption potential of modified fly ash is fully exploited and it becomes a kind of low cost and high quality adsorbent.A new type of cyclone adsorption device with double filter barrel is designed to make the air pressure in the adsorber uniform,reduce the occurrence of gully flow and improve the utilization rate of adsorbent.The regeneration adsorption experiment of saturated modified fly ash was carried out after high temperature desorption.With the increase of regeneration times,the adsorption performance of reclaimed ash sorbent decreases gradually.The adsorption performance of the primary regeneration adsorbent is about 80% of that of the original modified fly ash adsorbent.Compared with the primary sorbent,the adsorption performance of the secondary regenerated sorbent decreased steeply and was about 50% of that of the original modified fly ash sorbent.There is little difference between the third and fourth regenerated sorbents and the second regenerated sorbents,which is about 40% of the original modified fly ash sorbents.The adsorption effect of modified fly ash is still slightly better than that of raw fly ash after four times of regeneration,and the modified fly ash adsorbent has a good reuse function.