A Study On Dynamic Adsorption Of VOCs By Fixed Bed Filled With Activated Carbon And Modified Activated Carbon

Volatile organic compounds?VOCs?are an important component of atmospheric pollutants and an important source of PM2.5 and PM10.It has a wide variety and complex composition,which not only damages the ecological environment,but also endangers human health.At present,the most mature method for VOCs removal is adsorption.Recently,activated carbon as an adsorbent has achieved good results in the treatment of VOCs,and it is a research hot.Activated carbon has the characteristics of well-developed pores and rich surface oxygen-containing functional groups,which is an environmentally-friendly adsorbent capable of adsorbing and recovering most of VOCs.At present,the method of adsorbing VOCs by activated carbon is mainly static adsorption,resulted the lower adsorption capacity and the lower utilization rate of the fixed bed.Therefore,it is important to develop a new fixed bed adsorption unit and activated carbon with high adsorption performance of VOCs.In this paper,we first designed and prepared a new fixed bed device using commercial activated carbon and modified commercial activated carbon as adsorbent.And different types of VOCs and dynamic adsorption methods have been chosen to study the adsorption behavior.The main research work carried out in this paper are as follows:?1?A new type of VOCs fixed bed adsorption device was developed,and five VOCs of acetone,isopropanol,ethyl acetate,propyl acetate and butyl acetate were chosen as a target pollutant adsorped by commercial activated carbon.The results showed that the adsorption capacity of activated carbon on the above five VOCs were355.8,382.4,443.7,467.4 and 474.3 mg g^-1,respectively.The order was:acetone<isopropanol<ethyl acetate<propyl acetate<butyl acetate,and we found that the maximum adsorption capacity is positively correlated with the relative molecular mass and molecular dynamic diameter of VOCs.As the molecular weight and molecular dynamic diameter increase,the adsorption amount increases.After fitting the Boltzmann model to the breakthrough curves of five VOCs,it was found that the acetone had the lowest mass transfer resistance and the fastest adsorption rate in the activated carbon adsorption column,which was consistent with the experimental results.The Yoon-Nelson model fitting results show that the semi-transparent time???is similar to the experimental data,so the Yoon-Nelson model can be used to predict the breakthrough time of VOCs on activated carbon.In addition,the Banham adsorption rate equation fitting results found that the theoretical maximum adsorption capacity and the actual adsorption capacity have the smallest difference,which has certain reference significance.?2?After modification of activated carbon with NaOH,the specific surface area and pore volume of activated carbon were improved.With the increase of NaOH modified concentration,the adsorption capacity of formaldehyde increased gradually.It is mainly due to the increase of the basic group on the surface after modification,which is good for adsorption.However,when the concentration is too high,the adsorption amount will decrease due to the blockage of the pores and the non-polarity of the surface.In addition,after modification of activated carbon with polyethyleneimine,the specific surface area and pore volume will also increase,and the concentration of amine group on the surface of activated carbon will increase significantly.And the adsorption capacity of formaldehyde by PEI modified activated carbon is also increasing first and then decrease.Through the analysis of the intraparticle diffusion model,it is found that the adsorption of formaldehyde by the activated carbon by the two methods is mainly divided into three stages:surface-filling adsorption,internal slow adsorption and equilibrium adsorption.?3?When investigating the recycling ability of activated carbon,ethanol was used as the target VOCs.When the activated carbon was saturated with ethanol,the activated carbon was ultrasonically desorbed in water,and the desorption efficiency was found to be 94.08%.Then the second adsorption was carried out after the activated carbon was dried,the capacity of adsorption slightly decreased.At the second and third desorptions,the desorption rate can be maintained above 85%,indicating that the activated carbon has excellent cycle performance and can be reused in such recovery and concentration applications.