Linear driving force (LDF) model is widely used in a diffusion process. However thismodel has inherent weakness. When the dimensionless time is less than 0.1, its relativeerror is up to 95%. In this paper a new concen...Linear driving force (LDF) model is widely used in a diffusion process. However thismodel has inherent weakness. When the dimensionless time is less than 0.1, its relativeerror is up to 95%. In this paper a new concentration profile is proposed, and then a newmodified LDF model (MLDF) is deduced. Compared with the exact solution ofintraparticle diffusion equation, the transient volume-average amount adsorbedcalculated from the MLDF is more accurate than that calculaled from the LDF modeL .Ifone takes ±10% relative error for the limit of validity of approximation, the new model isvalid when the dimensionless time is just larger than 0. 0002, while the LDF model is notvalid until the dimension time is large than 0.05. The new model is superior to the LDFmodel. The new concentration profiles corresponding to the MLDF model are much closeto the exact concentration profiles within a particle than the parabolic propescorresponding to the LDF model.展开更多
A bidisperse model for transient diffusion and adsorption processes in porous materials is presented in this paper.The mathematical model is solved by numerical methods based on finite elements combined with the linea...A bidisperse model for transient diffusion and adsorption processes in porous materials is presented in this paper.The mathematical model is solved by numerical methods based on finite elements combined with the linear driving force approximation.A criterion based on the model to identify the diffusion controlling mechanism(macropore diffusion,micropore diffusion,or both)is proposed.The effects of different adsorption isotherms(linear,Freundlich,or Langmuir)on the concentration profiles and on curves of fractional uptake versus time are investigated.In addition,the influences of model parameters concerning the pore networks on the fractional uptake are studied as well.展开更多
As a potential adsorption material,it is still a challenge for activated carbon fiber(ACF)in efficient adsorption of ethanol due to its nonpolar surface,which is mainly emitted from the grain drying industry.This stud...As a potential adsorption material,it is still a challenge for activated carbon fiber(ACF)in efficient adsorption of ethanol due to its nonpolar surface,which is mainly emitted from the grain drying industry.This study prepared surface polarity-modified ACF using the heteroatom doping method.The modified ACF possessed a richer array of strongly polar oxygen/nitrogen-containing functional groups(primarily phenolic hydroxyl and lactone groups),a larger specific surface are1,and a more developed micropore structure.The adsorption capacities of ethanol for O-ACF and N-ACF were 4.110 mmol/g and 1.698 mmol/g,respectively,which were 11.3 times and 4.7 times those of unmodified ACF.This was a significant improvement over our previous work(0.363 mmol/g).The improvement of adsorption capacity for the N-ACF was mainly due to the higher specific surface are1,greater number of micropores(more adsorption sites)and abundant existence of defects,whereas,for O-ACF,the improvement mainly relied on the abundant presence of oxygen-containing functional groups on the surface.However,water had a negative effect on the adsorption of ethanol for the modified ACF due to competitive adsorption and the disappearance of capillary condensation.It was further revealed that the adsorption process of ethanol and water was quite different.It obeyed the linear driving force(LDF)model for ethanol adsorption,however,the intraparticle diffusion(IPD)model for water adsorption.展开更多
Trichloroethylene(TCE)is largely used in industries as a cleaning and degreasing solvent.TCE is a potential carcinogen and is known to cause organ damage when exposed to prolonged higher concentrations.Numerical simul...Trichloroethylene(TCE)is largely used in industries as a cleaning and degreasing solvent.TCE is a potential carcinogen and is known to cause organ damage when exposed to prolonged higher concentrations.Numerical simulation of fixed and fluidized bed adsorption of TCE can help in the development of efficient adsorption processes to prevent industrial workers in the vicinity from acute TCE exposure.In the present work,a parametric optimization based numerical experimentation algorithm is implemented by open-source computational solvers to model fixed and fluidized bed adsorption of trichloroethylene vapors on activated carbon.The algorithm optimizes four parameters pertaining to linear driving force(LDF)formulation of surface barrier and microporous diffusion.The optimized parameters were utilized to evaluateζ,a dimensionless number defined as the temporal and spatial average ratio of surface barrier diffusion resistance to microporous diffusion resistance.The average value ofζis 0.139 for fixed bed operation(u/u_(mf)=0.7),1.130 for fluidized bed operation(u/u_(mf)=1),4.436 for fluidized bed operation(u/u_(mf)=1.5)and 6.317 for fluidized bed operation(u/u_(mf)=2).Therefore,the dimensionless numberζmay serve to predict the extent of change in amount adsorbed per unit adsorbent mass with change in fluidization velocity.展开更多
文摘Linear driving force (LDF) model is widely used in a diffusion process. However thismodel has inherent weakness. When the dimensionless time is less than 0.1, its relativeerror is up to 95%. In this paper a new concentration profile is proposed, and then a newmodified LDF model (MLDF) is deduced. Compared with the exact solution ofintraparticle diffusion equation, the transient volume-average amount adsorbedcalculated from the MLDF is more accurate than that calculaled from the LDF modeL .Ifone takes ±10% relative error for the limit of validity of approximation, the new model isvalid when the dimensionless time is just larger than 0. 0002, while the LDF model is notvalid until the dimension time is large than 0.05. The new model is superior to the LDFmodel. The new concentration profiles corresponding to the MLDF model are much closeto the exact concentration profiles within a particle than the parabolic propescorresponding to the LDF model.
基金financial support by the National Natural Science Foundation of China(Grant No.91534120)China National Petroleum Company under the contract number DQZX-KY-17-019
文摘A bidisperse model for transient diffusion and adsorption processes in porous materials is presented in this paper.The mathematical model is solved by numerical methods based on finite elements combined with the linear driving force approximation.A criterion based on the model to identify the diffusion controlling mechanism(macropore diffusion,micropore diffusion,or both)is proposed.The effects of different adsorption isotherms(linear,Freundlich,or Langmuir)on the concentration profiles and on curves of fractional uptake versus time are investigated.In addition,the influences of model parameters concerning the pore networks on the fractional uptake are studied as well.
基金supported by the National Key R&D Program of China(Nos.2022YFB4101500 and 2022YFE0209500)the National Natural Science Foundation of China(Nos.22276191 and 21976177)the Qinghai Province Air Pollution Assessment and Fine Management Support Project,and the University of Chinese Academy of Science.
文摘As a potential adsorption material,it is still a challenge for activated carbon fiber(ACF)in efficient adsorption of ethanol due to its nonpolar surface,which is mainly emitted from the grain drying industry.This study prepared surface polarity-modified ACF using the heteroatom doping method.The modified ACF possessed a richer array of strongly polar oxygen/nitrogen-containing functional groups(primarily phenolic hydroxyl and lactone groups),a larger specific surface are1,and a more developed micropore structure.The adsorption capacities of ethanol for O-ACF and N-ACF were 4.110 mmol/g and 1.698 mmol/g,respectively,which were 11.3 times and 4.7 times those of unmodified ACF.This was a significant improvement over our previous work(0.363 mmol/g).The improvement of adsorption capacity for the N-ACF was mainly due to the higher specific surface are1,greater number of micropores(more adsorption sites)and abundant existence of defects,whereas,for O-ACF,the improvement mainly relied on the abundant presence of oxygen-containing functional groups on the surface.However,water had a negative effect on the adsorption of ethanol for the modified ACF due to competitive adsorption and the disappearance of capillary condensation.It was further revealed that the adsorption process of ethanol and water was quite different.It obeyed the linear driving force(LDF)model for ethanol adsorption,however,the intraparticle diffusion(IPD)model for water adsorption.
基金The authors are thankful to Shri.B.K.Chougule,Shri.M.C.Jadeja,Shri.CA.Shinde,Shri.V.D.Likhar,Shri.S.Sarang,Shri.R.Rathod,and Shri.D.Avhad for their constant supervision and assistance during the experimental studies.The authors are also thankful to Shri.S.Satre and Shri.N.Ghuge for constantly monitoring the safety aspects of the experiments.
文摘Trichloroethylene(TCE)is largely used in industries as a cleaning and degreasing solvent.TCE is a potential carcinogen and is known to cause organ damage when exposed to prolonged higher concentrations.Numerical simulation of fixed and fluidized bed adsorption of TCE can help in the development of efficient adsorption processes to prevent industrial workers in the vicinity from acute TCE exposure.In the present work,a parametric optimization based numerical experimentation algorithm is implemented by open-source computational solvers to model fixed and fluidized bed adsorption of trichloroethylene vapors on activated carbon.The algorithm optimizes four parameters pertaining to linear driving force(LDF)formulation of surface barrier and microporous diffusion.The optimized parameters were utilized to evaluateζ,a dimensionless number defined as the temporal and spatial average ratio of surface barrier diffusion resistance to microporous diffusion resistance.The average value ofζis 0.139 for fixed bed operation(u/u_(mf)=0.7),1.130 for fluidized bed operation(u/u_(mf)=1),4.436 for fluidized bed operation(u/u_(mf)=1.5)and 6.317 for fluidized bed operation(u/u_(mf)=2).Therefore,the dimensionless numberζmay serve to predict the extent of change in amount adsorbed per unit adsorbent mass with change in fluidization velocity.
