Monitoring And Control Of ACFC-ESA System For VOCs Adsorption/Desorption Based On Resistance Of The Adsorbent

Volatile organic compounds(VOCs),regulated as air pollutants,are hamful to environment and human health.VOCs adsorption method has been used for abatement of fatty compounds,ketones and aromatics.Metal organic frameworks(MOFs)and activated carbon fiber cloth(ACFC)have large surface area and pore volume,which are promising adsorbents for VOCs adsorption.ACFC is able to be regenerated through electrothermal swing adsorption(ESA)due to its conductivity.Dynamic adsorption of acetone and toluene with MOFs and ACFC was investigated to compare the performance of different types of adsorbents.Influence factors of resistance and resistance slope during adsorption and desorption of isobutane,acetone and toluene with ACFC-ESA system were studied.Moving average of slope of resistance(MASR)in one minute was used as the control parameter to monitor and control adsorption/desorption cycles.MIL-100(Fe),graphene oxide(GO)/MIL-100(Fe)-1(GO,50 mg)and GO/MIL-100(Fe)-2(GO,200 mg)were prepared,which were used as adsorbents for dynamic adsorption tests with acetone and toluene by comparing with ACFC-15.GO(50 mg)improves micropore surface area of GO/MIL-100(Fe)-1,which increases adsorption capacity for acetone and tolune.However,excessive amount of GO(200 mg)weakens the crystallinity of GO/MIL-100(Fe)-2,decreases micropore surface area and increases oxygen groups,which result in different influences on adsorption capacity for acetone and toluene.Adsorption capacity for acetone and toluene with ACFC-15 is higher than that for MIL-100(Fe)and GO/MIL-100(Fe).Coefficient of determination of Yoon-Nelson and Thomas breakthrough models are ? 0.987,which shows good prediction of breakthrough time and equilibrium adsorption capacity for acetone and toluene with ACFC-15,respectively.Fitting results of Yoon-Nelson and Thomas breakthrough models for acetone adsorption with ACFC-15 are better than that for toluene.Freundlich and Langmuir isotherms shows good fitting results for acetone and toluene with ACFC-15,respectively.Linear relation fits for the adsorbed amount and adsorption time for adsorption of acetone and toluene with ACFC-15,where adsorption rate is stable and increases with increase of inlet adsorbate concentration.Adsorption rate of acetone and toluene with ACFC-15 is controlled by external diffusion as demonstrated by Boyd equation.Dynamic adsorption performance of ACFC-ESA system and influence factors of resistance of ACFC-15 were evaluated with isobutane,acetone and toluene.Adsorption capacity and capture efficiency of the selected VOCs with ACFC-ESA system increase with boiling point.Increasing of relative humidity(RH)results in more decrease of adsorption capacity of acetone that is more polar than isobutane and toluene.Resistance of ACFC-15 corresponds with adsorption of VOCs and temperature during adsorption and desorption process,respectively.At the beginning of adsorption process,interactions of O2 with dangling bands,adsorption of O2 with oxygen groups through static interactions and H-bond,and higher temperature of humid gas stream cause change of resistance.As adsorption proceeding,resistance of ACFC-15 decreases with increasing of adsorbed amount of the selected VOCs.Difference of resistance increases with boiling point of the adsorbates after adsorption.Water,isobutane,acetone or toluene adsorbed onto ACFC-15 by pore filling causes rearrangement of graphene domains to be in good order as revealed by X-ray diffraction patterns,which results in reduction of hindrance for electron transportation and decrease of resistance.Competetive adsorption of VOCs with water causes disorder to graphene domains.Slope of resistance corresponds with the occurrence of breakthrough,which increases more dramatically when breakthrough occurs for gas streams containing adsorbate with higher affinity to ACFC-15.Increasing inlet concentration of adsorbate and reducing inlet RH also result in dramatic increase of slope of resistance as breakthrough occurs.During regeneration cooling,resistance initially increases fast,then decreases with decrease of temperature.Correspondingly,slope of resistance initially deceases fast,then becomes negative and unstable.Adsorption/desorption cycles of ACFC-ESA system were successfully monitored and controlled based on resistance of the adsorbent by using MASR parameter.Adsorption capacity and capture efficiency of isobutane,acetone and toluene with ACFC-ESA system controlled with MASR increase with boiling point of the adsorbates.Breakthrough concentration of all adsorption cycles controlled with MASR is 5.1% ± 4.6%.ACFC-ESA system controlled with MASR shows good reproducibility for adsorption capacity,capture efficiency and adsorption time for all adsorption cycles.The accuracy of control of adsorption cycles increase with increase of affinity of VOCs to ACFC-15 and inlet concentration of the adsorbate.Lower RH also improves control accuracy of adsorption cycles.Surface temperature of ACFC-15 is 79.6 ± 0.8 °C at the end of desorption cycles controlled with MASR.ACFC-ESA system controlled based on resistance of the adsorbent shows very good accuracy and reproducibility for adsorption/desorption cycles for the selected VOCs under different conditions.MASR corresponds with change of adsorbed amount and can be used to predict the occurrence of breakthrough.