Adsorption And Desorption Behaviors Of Methanol-Ethyl Acetate Mixture On Silica Gel

Methanol and ethyl acetate are two typical oxygen-containing volatile organic compounds（OVOCs）,which are widely used in pharmaceutical,coal chemical,fine chemical,and so forth.Due to its strong polarity and low boiling point,the efficiency of adsorption and desorption treatment using traditional activated carbon is low.Therefore,a temperature swing-pressure swing combined process is proposed to desorb the adsorbed methanol-ethyl acetate mixture using micro-mesoporous silica gel,so as to achieve the purpose of recovering methanol and ethyl acetate.First,this article systematically studied the adsorption characteristics of methanol and ethyl acetate on silica gel from the perspective of adsorption.Results show that the adsorption performance of silica gel on these two oxygen-containing organics was significantly better than that of activated carbon（>85%）.In addition,the adsorption capacity of silica gel to ethyl acetate is stronger than that of methanol,indicating that the affinity of Si-OH for ethyl acetate is stronger than that for methanol.Secondly,through the methanol-ethyl acetate binary component adsorption experiments,it is found that the breakthrough curves show a“roll up”phenomenon,indicating that ethyl acetate can replace the methanol that has been adsorbed on the silica gel,that is,the methanol and ethyl acetate have competitive adsorption on silica gel.Linear driving force model and ideal adsorption solution theory has been applied to simulate the adsorption behavior of methanol-ethyl acetate on silica gel（error<7%）.Under the same feed flow rate（or feed concentration）,the k _LDF of ethyl acetate on silica gel is larger than that of methanol,so its mass transfer rate is faster.Therefore,appropriately increasing the feed concentration and feed flow rate can strengthen the adsorption kinetics,facilitate the competitive adsorption behavior of methanol-ethyl acetate binary components,and improve the adsorption selectivity of binary VOCs on silica gel.The adsorption mechanism of binary components shows that the kinetic adsorption process can divide the bed into three zones:free adsorption zone,competitive adsorption zone and equilibrium zone.These three regions successively undergo the processes of generation,expansion,migration and disappearance in the adsorption column.The analysis and simulation results summarized the maximum adsorption concentration distribution of the two VOCs in the entire bed.The maximum adsorption concentration of ethyl acetate on the adsorption bed increases with the increase of adsorption time,and remains constant after reaching the equilibrium concentration.However,the maximum adsorption concentration of methanol on the adsorbent showed a tendency to increase first,then decrease with the increase of adsorption time,and then remain constant after falling to the equilibrium concentration.This paper adopts TSA-PSA process to optimize process parameters.Under the same desorption pressure and gas flow rate,the desorption amount,the desorption rate and the maximum enrichment concentration all increase with the increasing temperature.Considering the recovery and utilization of adsorbent and adsorbate,the optimal process conditions after optimization are:normal temperature and normal pressure adsorption,desorption temperature 35℃,desorption pressure 7 k Pa,and gas flow rate 0.9 Ndm³/min.